hide and seek between andromeda’s halo, disk, … · the astrophysical journal, 743:19 (25pp),...

The Astrophysical Journal 74319 (25pp) 2011 December 10 doi1010880004-637X743119Ccopy 2011 The American Astronomical Society All rights reserved Printed in the USA

HIDE AND SEEK BETWEEN ANDROMEDArsquoS HALO DISK AND GIANT STREAMlowast

Gisella Clementini1 Rodrigo Contreras Ramos12 Luciana Federici1 Giulia Macario12 Giacomo Beccari3Vincenzo Testa4 Michele Cignoni2 Marcella Marconi5 Vincenzo Ripepi5 Monica Tosi1 Michele Bellazzini1

Flavio Fusi Pecci1 Emiliano Diolaiti1 Carla Cacciari1 Bruno Marano2 Emanuele Giallongo4Roberto Ragazzoni6 Andrea Di Paola4 Stefano Gallozzi4 and Riccardo Smareglia7

1 INAF Osservatorio Astronomico di Bologna Bologna Italygisellaclementinioaboinafit2 Dipartimento di Astronomia Universita di Bologna Bologna Italy

3 European Southern Observatory 85748 Garching bei Munchen Germany4 INAF Osservatorio Astronomico di Roma Monteporzio Italy

5 INAF Osservatorio Astronomico di Capodimonte Napoli Italy6 INAF Osservatorio Astronomico di Padova Padova Italy7 INAF Osservatorio Astronomico di Trieste Trieste Italy

Received 2011 February 14 accepted 2011 September 6 published 2011 November 18

ABSTRACT

Photometry inBV (down toV sim 26 mag) is presented for two 23primetimes23prime fields of the Andromeda galaxy (M31) thatwere observed with the blue channel camera of the Large Binocular Telescope during the Science DemonstrationTime Each field covers an area of about 51times 51 kpc2 at the distance of M31 (μM31 sim 244 mag) samplingrespectively a northeast region close to the M31 giant stream (field S2) and an eastern portion of the halo in thedirection of the galaxy minor axis (field H1) The stream field spans a region that includes Andromedarsquos disk andgiant stream and this is reflected in the complexity of the colorndashmagnitude diagram of the field One corner of thehalo field also includes a portion of the giant stream Even though these demonstration time data were obtainedunder non-optimal observing conditions theB photometry which was acquired in time-series mode allowed us toidentify 274 variable stars (among which 96 are bona fide and 31 are candidate RR Lyrae stars 71 are Cepheidsand 16 are binary systems) by applying the image subtraction technique to the selected portions of the observedfields Differential flux light curves were obtained for the vast majority of these variables Our sample mainlyincludes pulsating stars that populate the instability strip from the Classical Cepheids down to the RR Lyrae starsthus tracing the different stellar generations in these regions of M31 down to the horizontal branch of the oldest(t sim 10 Gyr) component

Key words galaxies individual (M31) ndash galaxies stellar content ndash stars variables Cepheids ndash stars variablesRR Lyrae

Online-only material color figures extended figures machine-readable table

1 INTRODUCTION

The Andromeda galaxy which is our nearest giant neighboris the best place to study the structure formation and evolutionof a massive spiral and to get hints on whether the mergeraccretion or the cloud collapse is the dominant mechanismin the formation of a giant spiral Our external view of thesystem is less affected by selection and line-of-sight effects thatmake it difficult to perform a homogeneous global study of theMilky Way (MW) As a result the structures observed in M31are easier to study thus making Andromeda the best currentlaboratory for investigating faint stellar structures and mergingevents occurring around large galaxies

Van den Bergh (2000 2006) suggested that M31 originatedas an early merger of two or more relatively massive metal-rich progenitors This would account for the wide range inmetallicity (Durrell et al2001 Stephens et al2001 Bellazziniet al2003) and age (Brown et al2003) observed in the M31halo compared with the MW M31 hosts spectacular signaturesof present and past merging events such as the giant tidalstream (Ibata et al2001) that extends several degrees fromthe center of the galaxy (McConnachie et al2003) and thearc-like overdensity connecting the galaxy to its dwarf elliptical

lowast Based on data acquired using the blue channel camera of the LargeBinocular Telescope (LBTLBC-blue)

companion NGC 205 (McConnachie et al2004) Metallicityluminosity and alignment with M32 are consistent with the M31stream being tidally extracted from M32 A number of earlierpapers following the stream discovery did indeed speculate thatM32 might be the source of the stream (Ibata e al 2001 Choiet al2002 Ferguson et al2002) The low-velocity dispersion(11 km sminus1) supports the notion that the giant stream is a coherentinteraction remnant However the KeckDEep Imaging Multi-Object Spectrograph spectroscopic studies (Font et al2006)the models for the progenitor and theN-body studies of its tidaldisruption tend to argue against M32 as a stream progenitor(Fardal et al2008) The infrared photometry of the M31 diskobtained by theInfrared Astronomical Satellite (Habing et al1984) and by theSpitzer Space Telescope (Barmby et al2006)revealed two rings of star formation off-centered from the M31nucleus (Block et al2006and references therein) The two ringsseem to be density waves propagating in the disk Beccari et al(2007) unveiled the near-ultraviolet view of the M31 inner ringusing the blue channel camera of the Large Binocular Telescope(LBTLBC-blue) Numerical simulations show that both ringsmay result from a companion galaxy plunging head-on throughthe center of the M31 disk about 210 Myr ago (Block et al2006)

Ferguson et al (2002) and Ibata et al (2007) presented the firstpanoramic views of the Andromeda galaxy based on the deepIsaac Newton Telescope (INT) and the CanadandashFrancendashHawaii

1

The Astrophysical Journal 74319 (25pp) 2011 December 10 Clementini et al

Telescope (CFHT) photometric observations that cover respec-tively the galaxyrsquos inner 55 kpc and the southern quadrant outto about 150 kpc with an extension that reaches M33 at adistance of about 200 kpc Their data show the whole giantstream including its extensions and also reveal a multitude ofstreams arcs and many other large-scale structures of low sur-face brightness as well as two new M31 dwarf companions(And XV and And XVI) Twelve dwarf galaxies were known tobe M31 companions until 2004 among which only six dwarfspheroid galaxies (dSphs) and an additional seventeen new M31satellites were discovered in the last five to six years mainlybased on the INT and the CFHT data The most recent censusis reported by Richardson et al (2011) along with the discoveryof five new M31 dSph satellites And XXIIIndashXXVII as a resultfrom the second year of data from the ldquoPanAndromeda Archae-ological Surveyrdquo (PAndAS McConnachie et al2009) Startedin 2008 August the PAndAS survey is extending the global viewof M31 and that of its companion M33 by collecting data withMegaPrimeMegaCam on the 36 m CFHT for a total area of300 deg2 and out to a maximum projected radius from M31rsquoscenter of about 150 kpc This survey will likely detect severalother M31 faint satellites

The primary tool for understanding the formation historyof a galaxy over the whole Hubble time is the analysis ofcolorndashmagnitude diagrams (CMDs) deep enough to reach themain-sequence turnoff (TO) of the oldest populations The TOof the oldest stars in M31 (V sim 285 mag) is still unreachableby the largest ground-based telescopes and it requires tens oforbits of theHubble Space TelescopeAdvanced Camera forSurveys (HSTACS) time devoted to ldquotinyrdquo (3prime5times3prime7) portionsof the galaxy (Brown et al2003 2006 2007 2008 2009) tobe reached and measured The shallower survey by Richardsonet al (2008) who obtained CMDs toV sim 275 mag for 14HSTACS fields and sampled different substructures around M31covers a total area that is roughly one-third of that allowed in asingle shot by a ground-based telescope like LBT

Pulsating variable stars offer a powerful alternative tool totrace stars of different ages in a galaxy because variables ofdifferent types arise from parent populations of different agesSpecifically the RR Lyrae stars and the Population II Cepheids(often referred to as Type II Cepheids [T2Cs]) which belongto the oldest stellar population (t gt 10 Gyr) allow us to tracethe star formation history (SFH) back to the first epochs ofgalaxy formation and with their mere presence can providecrucial insight into the timescale and merging episodes that mayhave led to the assembly of a galaxy These low-mass variables(M sim 1M) burn helium in the stellar core and hydrogenin the shell surrounding the core during the horizontal branch(HB the RR Lyrae) and the post-HB (the T2Cs) evolutionaryphases They are respectively about 3 and 4 magnitude brighterand hence are much easier to observe than old (t gt 10 Gyr) TOstars The typical shape of their light variation which occurswith periodicities in the range of 02 to less than 1 day for the RRLyrae stars and from 1 to 25 days for T2Cs makes them mucheasier to recognize even when the upper HertzsprungndashRussel(H-R) diagram has overlapping contributions from a complexmix of age and metallicity The Anomalous Cepheids (ACs) areintermediate-age (t sim 1ndash2 Gyr) variables with periods in therange ofsim03 tosim20 days and with mean magnitudes spanninga 15-mag range These variables are intrinsically brighter thanthe RR Lyrae stars and when observed in an external stellarsystem where distance and projection effects can be neglectedthey locate themselves along a strip with the least luminous

ones (at periodssim030 days) being about 05 mag brighter thanthe RR Lyrae stars and the most luminous ones (at periodssim20 days) being about 20 mag brighter than the RR Lyraestars They appear significantly brighter than the T2Cs at thefixed period From an evolutionary point of view they are metal-poor ([FeH] minus17) He-burning stars in the post-turnoverportion of the zero-age horizontal branch (ZAHB see Marconiet al2004and references therein) that cross the instability strip(IS) at a higher luminosity than the RR Lyrae variables Theirmass is around 15M With an age of a few Gyr they indeedrepresent the natural extension of Classical Cepheids (CCs) tolower metallicities and masses (see eg Caputo et al2004Fiorentino et al2006and references therein) Finally CCs areintermediate-mass (typically from 3 to 12M) stars that crossthe IS during the blueward excursion in the central He-burningphase also referred to as a blue loop They have pulsationperiods in the range ofsim1 tosim100 days and an absolute visualmagnitude ofminus2 to minus7 mag With a typical age ranging froma few to a few hundred Myr they represent excellent tracers ofthe properties of young Population I stars

Short- and intermediate-period variables (ie periods shorterthan a few days) of M31 have never been adequately studieddespite their great potential to trace the stellar populations andthe star formation histories (SFHs) of nearby galaxies (Mateo1998 2000 Saha1999 Catelan2004 Clementini et al2004)So far the main limitations have been the size of the telescopesemployed in the ground-based surveys (Pritchet amp van denBergh 1987 Dolphin et al2004 Vilardell et al 2007 Joshiet al2010) the limited number of availableHST archive data(Clementini et al2001) and the rather small areas of M31covered by the space observations (Brown et al2004 Sarajediniet al2009 Jeffery et al2011) In their deepHSTACS survey ofthe M31 halo Brown et al (2004) identified 55 RR Lyrae stars(29 fundamental-modeminusRRabminus 25 first overtoneminusRRc andone double-modeminusRRdminus pulsators) in a 3prime5 times 3prime7 field alongthe southeast minor axis of the galaxy Based on their pulsationproperties Brown et al concluded that the old population inthe Andromeda halo has Oosterhoff-intermediate properties anddoes not conform to the subdivision in Oosterhoff I (Oo I) andOosterhoff II (Oo II) types (Oosterhoff1939) followed by theRR Lyrae stars in the MW field and globular clusters (GCssee Clementini2010and references therein) In this respect theM31 halo field would thus be different from the MW halo fieldand this would point to a different formationevolution historyHowever a different conclusion was reached by Sarajedini et al(2009) who identified 681 RR Lyrae variables (555 RRabrsquos and126 RRcrsquos) based on theHSTACS observations of two fieldsnear M32 at a projected distance between 4 and 6 kpc from thecenter of M31 and concluded that these M31 fields have Oo Iproperties More recently Jeffery et al (2011) have extendedBrown et alrsquos study of the M31 halo RR Lyrae stars to fiveadditional HSTACS fields that include one pointing in thestream one pointing in the disk and three pointings in the M31halo at distances of 21 kpc (hereafter referred to as halo21) and35 kpc from the galaxy center (hereafter halo35a and halo35brespectively see Figure 1 in the Jeffery et al paper) Theydetected 21 RR Lyrae stars in the ldquodiskrdquo field 24 in the ldquostreamrdquofield 3 in the ldquohalo21rdquo field 5 in the ldquohalo35brdquo field and nonein the ldquohalo35ardquo field Field ldquohalo21rdquo is of particular interestto us since it overlaps with our field H1 Jeffery et al foundaverage periods for the fundamental mode pulsators of 05830560 and 0495 days in the disk stream halo21 and halo35bfields respectively and conclude that the RR Lyrae populations

2


Figure 1 Schematic map of the Andromeda galaxy showing the location of the fields targeted with the LBTLBC-blue (boxes) and the GCs observed with theHST(filled circles) The heavy solid line shows the approximate location of the M31 giant stream according to Ferguson et al (2002) Crosses show the centers of the M31fields studied by Brown et al (2004) and Sarajedini et al (2009) using theHSTACS time-series data Open triangles show the M31 fields studied withHSTACS byJeffery et al (2011) Diamonds mark the center positions of the M31 fields studied with the ground-based time series observations by Vilardell et al (2006 2007) andJoshi et al (2010)

in these M31 fields appear to be mostly of Oo I But howgeneral are all of these results given the small areas coveredby the Brown et al (2004) Sarajedini et al (2009) and Jefferyet al (2011) studies Another open question is whether there areany RR Lyrae stars in the M31 giant stream and if any whethertheir properties differ from the properties of the variables inthe surrounding M31 fields Jeffery et al (2011) detected 24RR Lyrae stars in their ldquostreamrdquo field These RR Lyrae starscould either belong to the merged satellite to M32 whereRR Lyrae stars are claimed to exist (Alonso-Garcia et al2004Fiorentino et al2010) or have formed during the merger inwhich case the merging event would have occurred at least10 Gyr ago In any case their pulsation properties could providehints to identify the progenitor stream stars According to theaverage periods in Jeffery et alrsquos Table 2 the ldquostreamrdquo RR Lyraestars seem to be more OoI-like than the variables in the otherfields they observed However given the small number statisticsand the rather limited field of view (FOV) ofHSTACSthis could simply be a statistical artifact Clearly sampling ofmuch larger areas is needed to draw any general conclusions onthe properties of the M31 RR Lyrae population

To address the above questions we are carrying out a long-term project to study the stellar populations of both the constantand variable stars in properly selected fields and GCs of theAndromeda galaxy as well as in recently discovered M31 dSphsatellites We have used the Wide Field Planetary Camera 2on board theHST (Cycle 15HST program GO 11081 PI GClementini) to resolve the cluster stars (see Clementini et al2009 Contreras Ramos2010) and the wide field and light-collecting capabilities of the LBT to monitor portions of the M31

giant stream and halo and four of the most extended M31 dSphsAnd XIX And XXI And XXV and And XXVII A EuropeanSouthern Observatory Large Program (ID 186D-2013 PI GClementini) is also in progress at the Gran Telescopio Canariasto study the variable stars and stellar populations of five furtherM31 dSphs Figure1 shows the location of the target fields andGCs (squares and filled circles respectively) of ourHST andLBT observations on a schematic map of the Andromeda galaxyAlso shown in the figure are the fields studied for variabilityby Brown et al (2004) Sarajedini et al (2009) and Jefferyet al (2011) using theHSTACS time-series data and the fieldsstudied for variability by Vilardell et al (2006 2007) and Joshiet al (2010) using ground-based facilities

The study of the cluster variables shows that the RR Lyraestars in the M31 GCs may have different properties than theirMW counterparts (Clementini et al2009 Contreras Ramos2010 R Contreras Ramos et al 2011 in preparation) TheLBT is an ideal tool for studying the pulsating variable starsin the M31 field and in its dSphs because it reaches the samelevel of accuracy as theHST studies but on a much larger areathus allowing us to attain a statistical significance never reachedbefore for an external galaxy because each LBT field covers anarea about 37 times larger than anHSTACS-WFC field

The identification and center coordinates of the M31 regionsthat we are observing with the LBT are provided in Table1 Thestream fields were chosen to monitor both the stream portionthat enters into the M31 disk (field S1 in Figure1) and aregion toward the northeast portion of the stream that exitsfrom the disk (field S2 in Figure1) Fields H1 H2 H3 H4and H5 were instead chosen to provide a representation of the

3


Table 1Identification and Coordinates of Our LBT Fields in M31

Name Object Type α δ ξ η DM31center NBa NV

a

(2000) (2000) (deg) (deg) (kpc)

H1 Halo field 00 48 1311 +40 19 094 104 minus094 189 48 3H2 And XXI 23 54 4771 +42 28 150 minus889 183 1218 59 56H3 And XIX 00 19 321 +35 02 371 minus478 minus611 1042 48 46H4 And XXVII 00 37 271 +45 23 13 minus093 413 569 b b

H5 And XXV 00 30 089 +46 51 07 minus216 564 811 b b

S1 Stream field 00 43 5151 +39 58 094 021 minus130 177 2 middot middot middotS2 Stream field 00 49 0831 +42 16 094 118 101 209 59 8

Notesa Each image corresponds to a 300 s exposure for fields S2 H1 and S1 and to a 420 s exposure for fields H2 H3 H4 and H5b Observations scheduled for Fall 2011

different portions of Andromedarsquos halo on the opposite sidesof the galaxy In particular fields H2 and H3 are located atabout 122 kpc northwest and 104 kpc southwest of the M31center respectively and contain two new M31 dSphs And XXI(Martin et al2009) in field H2 and And XIX (McConnachieet al 2008) in field H3 Fields H4 and H5 are located alonga filamental structure at about 57 kpc and 81 kpc northwestof the M31 center respectively and contain two of the mostrecently discovered M31 satellites And XXVII and And XXV(Richardson et al2011) Finally field H1 is at about 19 kpcfrom the center of M31 in the southeast direction

In this paper which is part of our series on the study ofvariable stars in M31 we present results from pilot observationsof fields S2 and H1 obtained during the Science DemonstrationTime (SDT) of the LBC-blue mounted at the prime focus of thefirst unit of LBT (Giallongo et al2008) Each of these fieldscovers a 23prime times 23prime area We have obtainedBV CMDs down toV sim 26 mag for both fields The large FOV along with the highsensitivity of LBTLBC-blue allowed us to bridge portions ofthe M31 disk to traces of the galaxy giant stream in a single shotof field S2 Similarly the southwest corner of the halo field H1probably includes the southeast portion of the giant stream Wepresent results of a search for variable stars in these regionsof the Andromeda galaxy A number of technical problemsand rather unfavorable weatherseeing conditions hampered ourobserving campaign Nevertheless using the image subtractiontechnique we were able to identify and obtain differential fluxlight curves for a number of CCs with periods in the range of 3 to10 days a few candidate ACs andor more likely short-periodCCs (spCCs) with periods around 1ndash2 days more than 100 RRLyrae stars and a number of binary systems in the portions offields S2 and H1 where the image subtraction technique workedout properly

Observations data reduction and the calibration of thephotometry are discussed in Section2 The CMDs of fieldsS2 and H1 are presented in Section3 Results on the variablestars and the catalog of light curves are presented in Section4Finally a summary and discussion of the results are presentedin Section5

2 OBSERVATIONS AND DATA REDUCTION

BV photometry of the M31 fields S2 and H1 (see Table1)was obtained with LBTLBC-blue during 10 hr of SDTof the Blue Channel in 2007 October 11ndash18 Given theLBTLBC-blue scale (0primeprime225 pixelminus1) and the total FOV

(23prime times 23prime) each of these fields covers an area roughly cor-responding to 51times 51 kpc2 at the distance of M31 (μM31 sim244 mag) Figure2 shows the location of fields S2 and H1over a 35 times 35 deg2 image of the Andromeda galaxy ob-tained from the combination of the 34-μ 46-μ 12-μ and 22-μfluxes measured by NASArsquosWide-field Infrared Survey Explorer(WISE) along with a schematic view of the M31 giant tidalstream

Both of our fields are contained in the area surveyed byFerguson et al (2002) with INT reaching a limiting magnitudeV sim 245 mag ie 15 mag shallower than our photometryThese areas are also planned to be observed by PAndAS withlimiting magnitudeg0 sim 255 mag however no CMDs of theregions sampled by fields S2 and H1 have been published yetField H1 contains the twoHSTACS fields of the M31 ldquoMinoraxisrdquo observed by Richardson et al (2008 see their Table 1)and the field ldquohalo21rdquo (see Figure1) observed by Jeffery et al(2011)

The RR Lyrae stars in M31 are expected to have averagemagnitudes aroundV sim 253ndash255 mag Taking into accounttheir typical intrinsic colors amplitudes and periods (B minus V sim02ndash04 AV sim 03ndash05 and 06ndash12 magP sim 02ndash1 day forfirst overtone and fundamental mode pulsators respectively)we aimed at reaching a limiting magnitude ofB sim 26 mag(corresponding to the minimum light of these variables in M31)in no longer than 15ndash20 minutes to avoid smearing the lightcurve and to have an acceptable signal-to-noise ratio (SN)even at the light curve minimum Based on the LBT exposuretime calculator we had estimated that in dark time with a15 minute exposure and seeing conditions= 1primeprime we would obtainan SN sim 6 for B = 26 mag and an SN sim 9 for V = 255 mag

This would have been perfectly adequate for our purposesUnfortunately seeing conditions varied significantly during ourobserving run ranging from 0primeprime8 to 2primeprime7 We also experiencedproblems with the focus and tracking of the telescope duringthese early phases of LBT operation which did not allow us tomake individual exposures longer than 300 s Our observationswhich were acquired in time-series mode consist of 59B and8 V frames of field S2 and 48B and 3 V frames of fieldH1 each frame corresponding to a 300 s exposure and weobtained an SN sim 2 for B sim 26 mag in our best image atFWHM sim 0primeprime8 Notwithstanding the unfavorable weather andtechnical conditions we obtained 30B and 6V images of fieldS2 and 33B and 1V images of field H1 with FWHMlt 1primeprime3which after using the image subtraction technique (ISIS Alard2000) allowed us to identify candidate variable stars as faint asV sim 255 mag in the portions of fields S2 and H1 less affected

4


Figure 2 35 times 35 deg2 image of the Andromeda galaxy obtained from the combination of the 34-μ 46-μ 12-μ and 22-μ fluxes measured by the NASArsquosWide-field Infrared Survey Explorer (WISE Image Credit NASAJPL-CaltechUCLA) It shows the location of fields S2 and H1 and a schematic view of the M31giant tidal stream (heavy dashed line)

(A color version of this figure is available in the online journal)

by optical distortions where we succeeded in running ISIS Itshould also be noted that theV images of both fields S2 and H1were accidentally trimmed during the readout of the CCDs as aconsequence the upper 500 pixels of each CCD in theV imageswere lost

Pre-reduction of the entire data set (bias-subtraction andflat-fielding) through the LBC-dedicated pipeline was providedby the LBC team8 Point-spread function (PSF) photometryof the pre-reduced images of each chip of the LBC mosaicwas then performed with DoPHOT (Schechter et al1993)on the two images obtained in the best observing conditions(1B and 1V with the FWHM sim 0primeprime8ndash1primeprime for each of the twofields) to produce the CMDs This package allowed us to modelthe stellar PSF which varies significantly along each CCD ofour LBC frames much more efficiently than DAOPHOT Onthe other hand our attempt to use DAOPHOTIIALLSTARALLFRAME (Stetson1987 1994) to process the individualtime-series data and produce light curves on a magnitude scalefor the variable stars often failed due to both the geometricdistortions and the poor FWHM of the vast majority of our

8 httplbcoa-romainafit

frames For this reason we obtained light curves on a magnitudescale only for a very limited number of variable stars located insmall portions of the frames where DAOPHOTIIALLSTARALLFRAME ran successfully A Two Micron All Sky Surveycatalog9 was used to identify astrometric standards in the LBCFOV More than a 1000 stars were used to find an astrometricsolution for each of the LBC CCDs Accuracy of the derivedcoordinates is on the order ofsim0primeprime3ndash0primeprime4 (rms) in both theright ascension and the declination The absolute photometriccalibration of the S2 and H1 photometry was obtained using aset of 192 local secondary standard stars withBV photometryin the JohnsonndashCousins system which was extracted from theMassey et al (2006) catalog and falls in the region of fieldS2 covered by CCD 1 Aperture corrections were separatelycalculated for each of the four CCD mosaics of fields S2 and H1by performing aperture photometry in each photometric bandwith the SExtractor package (Bertin amp Arnouts1996) They areprovided in Table2 The derived calibration equations are

B = b minus 00635(b minus v) + 2778minus KbXb

9 httpirsaipaccaltechedu

5


Table 2Aperture Corrections for the Four CCD Mosaic Image of

Field S2 (Upper Part) and H1 (Lower Part)

Chip Field S2

B VCCD 1 minus0236 minus0301CCD 2 minus0251 minus0304CCD 3 minus0244 minus0254CCD 4 minus0229 minus0216

Field H1


Note Corrections correspond to aperture minus PSF magnitudes

and

V = v + 00107(b minus v) + 2812minus KvXv

whereB and V are the standard magnitudes andb v are theinstrumental magnitudes normalized to 1 s and corrected foraperture corrections using the values given in Table2 Kb

and Kv are the extinction coefficients inB and V for whichwe adopted values of 022 and 015 mag respectively asprovided on the LBC commissioning Web page (available athttplbcoa-romainafitcommissioningstandardshtml) Typ-ical internal errors of our photometry for non-variable stars atthe level of the M31 HB (V sim 255 mag) areσV = 017 magandσB = 026 mag respectively as provided by the DoPHOTreduction of individualBV images corresponding to 300-sexposures

3 COLORndashMAGNITUDE DIAGRAMS

Figures 3 and 4 show theVB minus V CMDs of the fourCCD mosaics of fields S2 and H1 respectively obtained atthe end of the reduction and calibration processes from theDoPHOT photometry of pairs ofBV images of each fieldeach corresponding to 300 s exposures obtained with FWHMof about 0primeprime8ndash1primeprime0 The photometric catalogs producing theseCMDs were cleaned from stars with photometric errors largerthan twice the mean error at each magnitude and by manuallyremoving ldquospurious starsrdquo produced by ghosts and spikes ofsaturated sources and background galaxies In each figure theCMDs are arranged according to the geometry of the four CCDscomposing the LBC-blue mosaic and each CCD was dividedinto two equal parts north and south parts for CCDs 1 2 and

Figure 3 VB minus V CMDs of field S2 from a pair ofB V images with a 300 s exposure time obtained in optimal observing conditions (FWHMsim 0primeprime8ndash1primeprime0) Eachpanel shows the number of stars displayed

6


Figure 4 VB minus V CMDs of field H1 from a pair ofB V images with a 300 s exposure time obtained in optimal observing conditions (FWHMsim 0primeprime8ndash1primeprime0)

3 and east and west parts for CCD 4 Accordingly CMDscorresponding to the four different CCDs of each field werelabeled as follows C1 N and C1 S for CCD1 the north andsouth parts respectively and similarly with CCD2 and 3 whilethe east and west parts of CCD4 were labeled as C4 E andC4 W respectively Each CCD of the LBTLBC-blue mosaiccovers about a 17times 39 kpc2 area of M31 however becauseof the trimming of theV images the CMDs corresponding tothe individual CCDs in fact cover a reduced but still remarkablearea roughly the size of 17times 34 kpc2 We have accounted forthis problem when dividing the CCDs and the correspondingCMDs in parts to ensure that each CMD in Figures3 and 4samples the same area of M31 The most striking feature inthe CMDs of field S2 is a conspicuous blue plume observed inpanels C1 N C1 S and C4 W of Figure3 atV 250 mag andB minus V 04 mag This blue plume is barely discernible in C2N and eventually disappears moving eastward from CCD2 toCCD 3 Also intriguing is a feature seen in C2 N and S C3 Nand S and C4 E atV 250 mag and 02 lt B minusV lt 04 magFinally all of the CMDs show a variably populated bright redplume and a sparse distribution of bright stars of intermediatecolors We believe that the blue plume is produced by youngstars possibly associated with an M31 spiral arm and the galaxydisk while the red plume is due to local M dwarfs

The CMDs of field H1 (see Figure4) are much less populatedthan those of field S2 and the blue plume is totally absent which

is not surprising if the blue plume in field S2 is due to the diskand spiral arm stars and if field H1 is instead representing theM31 halo population

In order to correctly interpret the features we see in theCMDs in terms of the SFH and the structure of M31 a reliableevaluation of the foreground contamination due to our Galaxyis necessary To approach this problem we have run simulationsusing a well-tested star-count code for our Galaxy (see Cignoniet al 2008 Castellani et al2002) In this code the MW isdivided into three major Galactic components namely the thindisk the thick disk and the halo For each of these threecomponents an artificial population is created by a randomchoice of mass and age from the assumed initial mass functionand star formation law interpolating on a grid of evolutionarytracks (from the zero age main sequence to the white dwarfphase) the metallicity of which is determined by the adoptedagendashmetallicity relation Reddening and photometric errors ofthe data are convolved with magnitudes of the synthetic starsproducing a realistic CMD The thin disk and the thick diskdensity laws were modeled by a double exponential with thesame scale length (3500 pc) but with a different scale height(1 kpc for the thick disk 300 pc for the thin disk) The halofollows a power-law decay with an exponent of 35 and an axisratio of 08 A local spatial density of 011 stars pcminus3 was adoptedfor the thin disk whereas the thick disk and halo normalizationswere 110 and 1500 respectively relative to the thin disk

7


Table 3Range of Expected Galactic Contaminating Stars as a

Function of Magnitude and Color

Magnitude Bin Blue Red

185 V 20 0ndash1 14ndash2420 lt V 21 0ndash1 6ndash1021 lt V 22 0ndash1 3ndash922 lt V 23 0ndash1 3ndash723 lt V 24 1ndash3 3ndash8

Notes Over an area equivalent to the area covered by each ofthe CMDs shown in the eight panels of Figures3 and 4 Blue0 lt B minus V lt 05 mag Red 05 B minus V lt 10 mag

The metallicity of each Galactic component was fixed atZ =002Z = 0006 andZ = 00002 for the thin disk thick diskand halo respectively In order to establish quantitative limitsto the Galactic star counts in field S2 all free model parameterswere let to vary In particular the thin disk scale height wasallowed to vary between 250 and 300 pc with the thick disk andhalo normalizations tested between 110 and 120 and between1500 and 1850 relative to the thin disk Table3 summarizesthe predicted star counts as a function of the magnitude and colorover an area equivalent to the area covered by each of the CMDsshown in the eight panels of Figures3 and4 Figure5 showsa typical simulated CMD for the foreground contaminationin field S2 which was obtained by assumingE(B minus V ) =008 mag and the typical internal errors of our photometry(0007 lt σB lt 0296 mag and 0008 lt σV lt 0252 mag for200 lt V lt 260) The simulation describes the contaminationby Galactic stars affecting each of the CMDs shown in the eightpanels of Figures3 and4 This simulation demonstrates that theGalactic contamination is generally negligible at any magnitudelevel forB minus V 04 mag hence the blue plume observed inthe CMDs of panels C1 N C1 S and C4 W is produced by M31stars and it is not due to contamination by the Galactic starsConversely all of the bright stars with intermediate colors arelikely MW stars (of the halo and thick disk) and most of thebright red plume stars are MW thick disk M dwarfs To makea more quantitative comparison we have counted the numberof stars (as a function of the same magnitude and color binsas in the simulation) in each of the CMDs shown in the eightpanels of Figures3 and4 These counts are provided in Tables4and5 for fields S2 and H1 respectively The comparison withTable3 shows that the MW contamination clearly dominates allthe CMDs of field S2 for magnitudes brighter thanV = 21 magboth in the blue and the red bins In the 21lt V 22 mag rangethe MW dominates in the eastern CCDs (CCD4 E and CCD3N and S) but the M31 contribution increases progressively aswe move westward and approach the M31 disk and possibly aspiral arm Similarly in the 22lt B minus V 23 mag bin there isan almost equal contribution of MW and M31 stars in the easternCCDs but M31 takes over progressively and becomes dominantin the western CCDs (CCD4 W and CCD1 N and S) FinallyM31 stars dominate all of the CMDs for magnitudes fainterthanV = 23 mag Star counts for field H1 (see Table5) have asmoother distribution which is expected for a halo populationThe M31 stars only dominate for magnitudes fainter thanV =23 mag while forV lt 23 mag MW and M31 stars contributealmost equally for 00 lt B minus V lt 05 mag and the MWgenerally dominates for 05 B minus V lt 10 mag

In Figures6and7we show aB image of field S2 and aB imageof field H1 respectively where we have overplotted in blue starswith V 250 mag andB minus V 02 mag which correspond

Figure 5 Foreground simulation for field S2 including the thin disk (blackdots) the thick disk (blue dots) and the halo (red dots) stars This CMD is onthe same scale as those in Figure3 to allow for a direct comparison


to sources populating the blue plume of the CMDs and in redstars havingV 250 mag and 02 lt B minus V 04 magwhich correspond to the intermediate-color features seen inFigures3 and4 For stars located on the upper 500 pixels ofeach CCD of the mosaic we only haveB magnitudes becauseof the unfortunate trimming of theV images This is why allof these stars are missing in the CMDs of Figures3 and4 aswell as in the images shown in Figures6 and7 Neverthelesswhile the intermediate-color sources (red crosses) are almosthomogeneously spread on all four CCDs both in field S2 andin field H1 and thus likely trace the halo component the blue-plume stars (blue boxes) appear to be mainly concentrated inthe upper right (northwest) part of CCD1 and in the right (west)portion of CCD4 of field S2 thus likely tracing the disk andpossibly a spiral arm of M31 To evaluate the significance ofthese uneven distributions we have counted the number of starsin the blue and intermediate plumes of each of the CMDs shownin the eight panels of Figures3 and4 respectively and in themagnitude binsV 240 mag and 24lt V 250 magseparately These counts are provided in Tables6 and 7 forfields S2 and H1 respectively The star counts in Table6 showthat the number of blue and intermediate-plume sources infield S2 increases dramatically but not homogeneously as wemove westward from CCD4 E to CCD4 W and from CCD3 toCCD1 and approach the M31 disk The highest concentrationof blue and intermediate-plume stars is found in CCD4 W andCCD1 N but it drops significantly in CCD1 S The counts inTable7 instead confirm the smooth stellar distribution in fieldH1 showing only a marginal increase in the number of blueand intermediate-plume stars with 24lt V 25 mag in CCD1

8


Table 4Number of Stars in the Four CCD Mosaic of Field S2 as a Function of Magnitude and Color

Magnitude Bin CCD4 E CCD4 W

Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443

CCD3 N CCD2 N CCD1 N

Blue Red Blue Red Blue Red

185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667

CCD3 S CCD2 S CCD1 S


185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554

Notes Over an area equivalent to the area covered by each of the CMDs shown in the eight panels of Figure3 Blue0 lt B minus V lt 05 mag Red 05 B minus V lt 10 mag

Table 5Number of Stars in the Four CCD Mosaic of Field H1 as a Function of Magnitude and Color


Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100


N and CCD1 S where the southwest corner of the halo fieldH1 perhaps touches a southeast portion of the giant stream (seeFigure2)

4 VARIABLE STARS

As anticipated in Section2 the poor seeing conditions andtechnical problems made it rather challenging to use our data

for the original purpose of studying the variable stars in theseregions of M31 A crucial complication was the significantoptical distortions of the LBTLBC-blue camera (see Giallongoet al2008 Figure4) particularly in the initial operation phaseof LBT We had to implement a number of different proceduresand conduct several trials to detect the variable stars Thereforethe number of variables we were able to identify is very limited

9


Figure 6 Position on the four CCDs mosaic of field S2 of stars in the blue plume of the CMD (see Figure3) Blue boxes are stars withV 250 andB minusV 02 magred crosses are stars withV 250 and 02 lt B minus V 04 mag




BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544

Notes Over an area equivalent to the area covered by each of the CMDs shown in the eight panels of Figure3 Blue plume(BP)B minus V 02 mag intermediate plume (IP) 02 lt B minus V 04 mag

if compared for instance to the number one would expectby extrapolating the number densities in the Brown et al(2004) study However our fields are much more external thanBrown et alrsquos and in fact our number densities are in much

better agreement with the number of RR Lyrae stars foundby Jeffery et al (2011) in their ldquohalo21rdquo field that overlapswith our field H1 This will be reviewed in further detail inSection45

10


Figure 7 Position on the four CCDs mosaic of field H1 of stars in the CMD (see Figure4) with V 250 andB minus V 02 mag (blue boxes) and withV 250and 02 lt B minus V 04 mag (red crosses)




BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11


Table 8Number of Bona Fide Candidate Variables Identified in Fields S2 and H1 Using the image subtraction technique

and the Numbers of Candidates Recovered in the ALLFRAME and DoPHOT Catalogs

Field S2

Chip N (frames) N (candidates) N (ALLFRAME) N (DoPHOT)CCD 1 (upper half) 43 96 6 49CCD 1 (lower half) middot middot middot 2 0 2CCD 2 (total) 43 143 40 74

Field H1

Chip N (frames) N (candidates)CCD 2 (upper half) 33 33 middot middot middot 13

In the following section we briefly describe the procedureswe have implemented and the results we have obtained from thesearch for variable stars in CCD2 and the upper half of CCD1of field S2 and in the upper half of CCD2 of field H1

41 Identification of the Variable Stars and Light Curves

To identify candidate variables in ourB time series images offields S2 and H1 we used the optimal image subtraction tech-nique and the package ISIS21 (Alard2000) which is known tobe very efficient at identifying variables with amplitudes as lowasΔB lt 01 mag in crowded fields The package was run ontheB time series of CCD 1 and 2 of field S2 and CCD 2 of fieldH1 We encountered several difficulties in aligning and interpo-lating the images of our LBTLBC-blue time series data withISIS which was likely due to the significant distortions of theLBTLBC-blue camera Since the regions of the LBC mosaicless affected by optical distortions are those covered by CCD2and the best observing conditions occurred during the observa-tions of field S2 we managed to properly align and interpolatea subset of 43B images of the entire CCD2 of field S2 withISIS and then make the subsequent search for variable starsInterpolation did not succeed instead for the entire CCD1 wehad to divide it into two halves and only images correspondingto the upper half of CCD1 of field S2 were successfully alignedWe encountered even more problems with the images of fieldH1 since they were generally obtained under worse seeing con-ditions We divided the CCD in two parts and were only able toalign and interpolate a subset of 33 images corresponding to theupper half of CCD2 After aligning and interpolating the im-ages we built reference images of CCD2ndashS2 CCD1ndashS2 (upperpart) and CCD2ndashH1 (upper part) We subtracted them out fromthe respective time series and summed the differences of theimages to obtainvarfits images which according to ISIS arethe maps of variable sources in the frames under study Specif-ically we used 19 and 28 frames to build twovarfits imagesof CCD2 of field H1 17 and 28 images for CCD2 of field S2and 20 and 43 images for CCD1 of field S2 In order to pick upcandidate variables from thevarfits images that were as faintas the RR Lyrae stars which at minimum light in our frameswere expected to have an SN sim 2 we had to use a very lowdetection threshold of 033 We ended up with rather large listsof about 4000 candidate variables from eachvarfits frame Listscorresponding to the pair ofvarfits frames of each field werecross-correlated thus obtaining about 2000 common candidatesources per set of images A careful inspection of these starsreturned a final catalog of 143 bona fide variables in CCD2 offield S2 96 variables in the upper portion of CCD1 of field S2and 33 variables in the upper portion of CCD2 of field H1 Twoadditional bona fide variables were also identified in the lower

half of CCD1 of field S2 during a preliminary search with ISISon the whole CCD1 of field S2 Hence the total number ofvariable stars we were able to identify was 274

We note that many of the original candidate variables could bereal variables but we only retained those that showed periodicunquestionable and better sampled light curves A summary ofthe total number of retained candidate variables per field foundwith the above procedure is given in Table8 Identification(namely ISIS ID and DoPHOT ID when available) coordinatesand a rough estimate of the period obtained by running thePeriod Determination by Phase Dispersion Minimization (PDMStellingwerf 1978) algorithm within IRAF on the differentialB flux time series of these bona fide candidates is provided inTable9 We note that only a very small fraction of the candidatesin Tables8 and9 have a counterpart with reliable photometryin the ALLFRAME catalogs and hence have a light curve ona magnitude scale while the vast majority only haveB-banddifferential flux light curves A number of different problemscaused the ALLFRAME PSF photometry of the individualphase points of the variables to be generally unreliable Theseproblems included crowding particularly in the disk field (fieldS2) rather poor and varying seeing conditions during theobservations and technical problems with the focus and trackingof the telescope which made the FWHM vary strongly alongthe frames All of these different effects combined togetherso that the PSF photometry could be obtained only in a fewcases and often only for the pair of frames at 0primeprime8 FWHMThe faintest variables were generally detected only with theimage subtraction and no ldquoreliablerdquo PSF photometry could beobtained for most of them with ALLFRAME on the otherhand the brighter variables had poorly sampled light curvesdue to the longer periods Even in the halo field (field H1)where variables were also searched using the Stetson variabilityindex on the catalogs produced by the ALLFRAME reductionsof CCD2 visual inspection of the images of many of thecandidates showed that they often had extended PSFs causedby spikes CCD defects telescope tracking problems and inturn unreliable photometry In conclusion while the presentdata allowed us to identify variable stars follow-up photometryin better technicalseeing conditions will be needed to producelight curves on a magnitude scale and to fully characterize thesevariables However publishing the identification and differentialflux light curves obtained in the present study will help futurevariability studies in these regions of M31

The study of the light curves of a few of the bona fidecandidate variables with a light curve on a magnitude scalewas performed with the Graphical Analyzer of TIme Series(GRATIS) which is custom software developed at the BolognaObservatory by P Montegriffo (see eg Di Fabrizio1999Clementini et al2000) In Figure8 we show examples of the

12


Table 9Identification and Characteristics of Candidate Variable Stars Identified in the M31 Fields S2 and H1

CCD1minus FieldS2

ID IDa α δ P Bb Vb Type Notes(ISIS) (DoPHOT) (2000) (2000) (day) (mag) (mag)

2783 middot middot middot 00 48 450 +42 21 05 026 middot middot middot middot middot middot RR c

2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin

Notesa ID(DoPHOT) is the star identification number on theB V images with FWHMsim 0primeprime8ndash1primeprime0 that were reduced with the DoPHOT package producing all the CMDsshown in the paperb B V values are from the DoPHOT photometry of theB V images obtained with FWHMsim 0primeprime8ndash1primeprime0 They correspond to values taken at a random phase on thelight curves We list the average values for six variables that have full coverage of the light curve (see Table10) over the full light cycle Random phase values aregiven in parenthesesc This candidate variable falls in the portion of theV frame that was trimmed during the read out of the CCDsd The star is on or close to a dead column of the CCD in theB framee The star was not measured on the 0primeprime8 FWHM V frame because it was too bright and close to saturationf Variable star that has full coverage of the light curve (see Table10)g The star is close to the spike of a saturated starh The star is close to a dead column of the CCD in theV framei Candidate variable stars identified during a preliminary search with ISIS on the whole CCD1 of field S2 Stars with DoPHOT IDs 14532 and 5707 are located in thesouthern part of CCD1 of Field S2l The star is on a defect of the CCD in theB framesm The star is contaminated by a bright companionn The star is saturated in both theV andB 0primeprime8 FWHM frameso The classification as an AC is mainly based on the star luminosity but it is inconsistent with the typical metal abundance of the underlying stellar population (seediscussion in Section44)

(This table is available in its entirety in a machine-readable form in the online journal A portion is shown here for guidance regarding its form and content)

Table 10Identification and Properties of Confirmed Variable Stars in the M31 Field S2 with Light Curves on a Magnitude Scale

Name ID α δ Type P Epocha NV NB 〈B〉 c AB 〈V 〉 d

b (2000) (2000) (days) (minus2450000) (mag)

V1 5089 00 48 364 +42 14 57 RRab 0605 4386822 4 31 2575 103 2536V2 4562 00 48 382 +42 15 45 Cepheid 940 4385200 5 53 2148 088 2062V3 8948 00 48 216 +42 16 55 Cepheid 325 4387942 5 49 2274 107 2203V4 6375 00 48 318 +42 16 32 Cepheid 51 4388400 5 51 2213 084 2147V5 middot middot middot 00 48 102 +42 16 31 Cepheid 292 4383700 5 51 2258 129 2197V6 9171 00 48 210 +42 19 39 Binary 0574 4389790 3 49 2352 135 2336

Notesa Epochs correspond to the time of maximum light for the pulsating variables and to the time of the main minimum light for the binary systemb Identification numbers in Column 2 correspond to the ISIS IDs (see Table9)c 〈B〉 values are intensity-averaged mean magnitudesd The〈V〉 values were derived by scaling from theB light curves according to the procedure described at the end of Section42

B light curves of some of the variables in field S2 for whichwe have light curves on a magnitude scale and a reasonablycomplete coverage of the light cycle They include four pulsatingstars with periods of 94 51 325 and 292 days that we haveclassified as CCs on the basis of their brightness and positionin the CMD (see below) an RR Lyrae star with a period of0605 days and a binary system with a period of 0574 days Theidentification and properties of these six variables are providedin Table10 Unfortunately the PSF photometry was not goodenough to obtain light curves on a magnitude scale for any ofthe candidate ACsspCCs with a period of around 1 dayB-banddifferential flux light curves for all candidate variables that wewere able to identify are presented in Figures9 10 and11which are published in their entirety in the online journal

42 Classification of the Candidate Variables

Since we only have differential flux light curves for the vastmajority of the candidate variables in Table9 we do not haveinformation on their magnitude and on the amplitude of their

light variation This complicates the identification of the typeof variability since the only characteristic parameters we canuse to classify the variables are the preliminary period and theshape of the light curve

The candidate variables have periods in the range of 012to 94 days Thus although our observing strategy was mainlydevised to optimize the detection of RR Lyrae stars it alsoturned out to be adequate to identify longer period variablesAccording to the range in the period spanned by the candidatevariables our sample is likely to contain RR Lyrae stars (02ltP lt 1 days) Anomalous (03 lt P lt 25 days) and PopulationII (P lt 10 days) Cepheids and short- and intermediate-periodCCs (1lt P lt 10 days) For 138 candidate variables we alsohave an indication of magnitude because were measured onthe pair ofBV images of field S2 and H1 with an FWHMsim 0primeprime8 and thus haveBV magnitudes from the DoPHOTphotometry (see Table8) Although the DoPHOT magnitudesfor the variables correspond to values at the random phase onthe light curves they allow us to place the candidates on the

13


Figure 8 Examples ofB light curves for four Cepheids an RR Lyrae star anda binary system detected in the CCD1 of field S2 Each data point correspondsto a 300 s exposure Typical error bars of the individual data points are inthe range of 001 to 002 mag for the CCs 011ndash017 mag for the candidateAnomalousshort-period Cepheids and from 013 to 038 mag for the RR Lyraestars

CMDs (see Figures12 13 and 14) and thus give us somehints about their type of variability The location on the CMDsand the periodicities of the variables atV sim 25ndash254 magconfirm that they likely are RR Lyrae stars tracing the HBof the M31 old stellar component and perhaps Population IICepheids (although the tentative periods generally below 1 daymake a P2C classification unlikely) while variables havingV 24 mag are likely short- and intermediate-period CCs Onthe other hand the classification of the candidates located morethan 1 mag above the HB atV in the range of 235 to 245 mag isnot easy since the luminosity would suggest that they are ACswhile the periods which are generally well below 1 day wouldmake them more likely to be RR Lyrae stars However theAC hypothesis does not seem consistent with the typical metalabundance of the stellar population in these M31 fields but ifthese candidates are RR Lyrae stars their brightness appears tobe inconsistent (ie too bright) with the luminosity of the stars atthe red giant branch tip unless these variables are contaminated(ie blended) by the other stars In this respect it is interestingthat no such intermediate luminosity candidates were detected

in field H1 which is definitely less crowded than field S2 Thispoint will be discussed in more detail in Section44 To classifythe candidate variable stars we have combined the informationon the period shape of the light curve and position on theCMD (when available) We also visually inspected theBVimages with the FWHMsim 0primeprime8 at the position of each candidatevariable detected by ISIS thus revealing the saturated sourcesCCD defects and other problems (see notes of Table9) as wellas objects too faint to be reliably measured with DoPHOT whichcould still be tentatively classified The shape of the light curvealso revealed several eclipsing binary systems (see Figures910 and11) among which a number of detached systems arecertainly worthy of further investigation The variability typesdeduced from this procedure are provided in Column 8 ofTable 9 where uncertain periods or type classifications havebeen flagged with a question mark Our sample includes 96bona fide and 31 candidate RR Lyraes 54 bona fide and 17candidate Cepheids (classical anomalous or short period) 14bona fide and 2 candidate binary systems For the remaining 60variables no unambiguous classification was possible Howeverthe unclassified objects are likely to include a number of main-sequence variables (see eg Baldacci et al2005) such asβCepheids (P lt 03 days) and Be stars (04lt P lt 3 days)populating the blue plume atB minus V sim 00 mag

Figures12 13 and14 show the CMDs of the upper part ofCCD1 of field S2 the whole CCD2 of field S2 and the upperpart of CCD2 of field H1 respectively The candidate variablesare plotted as large filled circles and we have used differentcolors for the different types of variability In the figures thelong-dashed lines aroundV = 252 mag show the boundaries ofthe theoretical IS for the RR Lyrae stars (Di Criscienzo et al2004) and of those aroundV = 245 mag the boundaries ofthe IS of ACs withZ = 00004 and 13 lt M lt 22M(Marconi et al2004) This is the highest metallicity allowedfor ACs17 The dotted heavy lines instead represent the firstovertone and fundamental blue edges (blue lines) and thefundamental red edge (red line) for CC models withZ =0008 Y = 025 and 325 lt MM lt 11 (Bono et al1999 2002) To plot the theoretical IS boundaries on theCMDs we have adoptedE(B minus V ) = 008 mag which wasobtained by interpolating on the Schlegel et al (1998) mapsAV = 3315 E(B minus V ) and AB = 4315 E(B minus V ) fromSchlegel et al (1998) andμ0(M31)= 2443 mag The lattervalue was obtained by correcting the distance modulus measuredby McConnachie et al (2005) from the M31 red giant branch tipfor E(B minus V ) = 006 mag andAI = 194E(B minus V ) (Schlegelet al1998) to our adopted reddening ofE(B minusV ) = 008 mag

It should be noted that these variables are plotted in theCMDs using magnitudes and colors sampling random phasesof the B andV light curves because we generally have only afew measurements of magnitude for the variables and in manycases we only have the pair ofBV magnitudes that correspondto the two best images used to build the CMDs They span avery large range in color and fall well beyond the boundaries of

17 As reviewed by Caputo (1998) for low-metal abundances (Z 00004) andrelatively young ages (4 Gyr) the effective temperature of Zero-agehorizontal branch (ZAHB) models reaches a minimum (logTe sim 376) for amass of about 10ndash12M while if the mass increases above this value boththe luminosity and the effective temperature start increasing forming theso-called ZAHB turnover from which ACs are expected to evolve For largermetallicities the more massive ZAHB structures have brighter luminosities buteffective temperatures rather close to the minimum effective temperature sothat ACs are not predicted Observationally ACs are mainly detected in thevery metal poor dSphs and rarely in GCs

14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

Figure 9 Atlas of the light curves inB-band differential flux for candidate variable stars in the CCD1 of field S2 The identification of the candidate variable starand a tentative period used to fold the time-series data are provided on top of each plot Only a portion of the catalog is shown here the full atlas of thelight curves ispublished in the online journal

(An extended version of this figure is available in the online journal)15


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

Figure 10 Same as Figure9 except for candidate variable stars in the CCD2 of field S2

(An extended version of this figure is available in the online journal)

16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

Figure 11 Same as Figures9 and10 except for candidate variable stars in the CCD2 of field H1


17


Figure 12 TheVB minus V CMD of the region of field S2 imaged on the upper portion of the CCD1 with different types of variable stars plotted by large filled dotsthey include the RR Lyrae stars (aroundV sim 25ndash254 mag blue dots) the candidate ACsspCCs (aroundV sim 24 mag orange dots) the CCs (V 23 mag magentadots) the binary systems (green dots) and the candidate variables with uncertain classification (black dots) All of these variables are plotted according to their randomphase magnitudes and colors Large open stars mark five pulsating variables (blue and magenta stars) and one binary system (green star) for which we have a goodsampling of theB light curves (see Figure8) their magnitudes and colors correspond to the average values along the full light cycle Arrows connect the random phasevalues of these six variables to the mean values over the full light cycle The long-dashed black lines show the boundaries of the theoretical ISs for the RR Lyrae starsand for the ACs withZ = 00004 and 13 lt M lt 22M (Marconi et al2004) The dotted heavy lines represent the first overtone and the fundamental blue edges(blue lines) and the fundamental red edge (red line) for the CC models withY = 025 and 325 lt MM lt 11 andZ = 0008 (Bono et al1999 2002)


the ISs because of the decoupling of theirBV magnitudes Thesix variables listed in Table10 have a better sampling of theirlight curves in magnitude scale and hence they are also plottedin Figure12using the〈V 〉 magnitudes and〈B〉minus 〈V 〉 colors weobtained by averaging over the full light cycle (large open stars)and with arrows connecting the average values to the randomphase DoPHOT magnitudes When the average values are usedthe Cepheids and RR Lyrae stars populate the rather narrowregion of the CMD that corresponds to the classical IS Thisexercise illustrates how much the candidate variables plotted atthe random phase could move in theVB minusV plane and it alsodemonstrates the detection potential and analysis capabilities ofour study which is the main purpose of the present paper

We also note that although the number ofB phase pointswould in principle be adequate to obtain a reliable estimate

of the B amplitude and average magnitude of the variablestars coverage of theV-band light curve is very sparse (only3ndash8 phase points in the best cases see Table1) To recover theaverage magnitudes in the visual band and thus be able to plotcorrectly the six variable stars on the CMDs we used the starrsquosB-band light curve as a template and we properly scaled it inamplitude to fit the few availableV data points To constrainthe scaling factor for the RR Lyrae stars we used amplituderatiosA(B)A(V ) computed using literatureBV light curvesof the RR Lyrae stars with good light-curve parameters Thesewere selected from a number of Galactic globular clusters(GGCs see Di Criscienzo et al2011 for details) and weused amplitude ratios and phase lags taken from Freedman(1988) and Wisniewski amp Johnson (1968) for the CepheidsFinally we used an amplitude ratio of 1 for the binary system

18


Figure 13 Same as Figure12 except for variable stars detected in the whole CCD2 of field S2


Figure 14 Same as Figure12 except for variable stars detected in the upper portion of the CCD2 of field H1


19


Table 11Number of Bona Fide Variables Divided by Type and Plotted in the CMDs in Figures12 13 and14

Field S2

Chip RR Lyrae Stars CCs Bin Uncertain TypeCCD 1 (upper half) 9 18 2 20CCD 1 (lower half) 1 0 0 1]CCD 2 (upper half) 10 14 1 10CCD 2 (lower half) 11 7 0 21

Field H1

Chip RR Lyrae Stars CCs Bin Uncertain TypeCCD 2 (upper half) 8 2 0 3

Total Numbers

RR Lyrae Stars CCs Bin Uncertain TypeTotal 39 41 3 55

since we do not expect to see significant chromatic effects forbinaries

Given that the RR Lyrae stars are at the faint limit ofour photometry (V sim 255 mag) where the completenessdrops off rapidly understanding the completeness of our studywould be important Our data clearly suffer from a numberof shortcomings that hamper a traditional analysis making itdifficult to estimate the fraction of variables in each classFortunately our field H1 overlaps with Jeffery et alrsquos (2011)field ldquohalo21rdquo thus allowing a direct comparison of the numberof RR Lyrae stars found by the two studies and allowing usto draw some conclusions on the completeness of our variablestar detections Jeffery et al (2011) found three RR Lyrae starsin their 3prime5 times 3prime7 HSTACS field ldquohalo21rdquo which correspondsto a number density of 023 RR Lyrae arcminminus2 Accordingto Table9 we have found 15 bona fide RR Lyrae stars in the72 times 86 arcmin2 upper portion of field H1 that we analyzedfor variability corresponding to a number density of 024 RRLyrae arcminminus2 The two numbers compare very favorably thusshowing that on the assumption that the number density of theRR Lyrae stars does not vary significantly through field H1 wehave attained a good completeness of the RR Lyrae detectionsin this field

However our field S2 is too far away from Jeffery et alrsquosldquodiskrdquo field to make a similar comparison meaningful

43 Spatial Distribution of the Variable Stars

Out of the total sample of 274 bona fide candidate variablesidentified in our study we have a magnitude estimate for 138stars They include 83 objects with firm classifications and 55objects of uncertain types Among the latter are eight variableswith typical magnitudes of ACs that will be discussed in moredetail in Section44 The subdivision in types of these 138 starsis summarized in Table11 In order to check whether the spatialdistribution of the different types of variables can provide somehints to the underlying parent stellar population we have alsosubdivided the variables into the various subfields where theyare located

Discarding the lower half of CCD1 of field S2 where theidentification of variables with the image subtraction failed andwith the caveat that our statistics can in general be incompleteit is interesting to note that the number of RR Lyrae stars remainsalmost constant in the four subfields that we have analyzed withISIS while the number of CCs decreases dramatically in fieldH1 where only two CCs were detected This is consistent withthe RR Lyrae stars tracing the M31 halo and with field H1

being a typical halo field of M31 Furthermore the number ofCCs also drops significantly as we move from north (the upperhalf of CCD1) to southeast (the lower half of CCD2) movingaway from the disk of M31 The highest concentration of CCs isfound in the upper part of CCD1 of field S2 suggesting that thisregion may be crossed by a spiral arm of M31 that also producesthe blue plume in the CMD and the candidate main-sequencevariables (namely Be andβ Cepheid stars) Finally the eightsupposed ACs are all found in field S2 while field H1 does notseem to contain any candidate variables atV sim 24 mag

44 Stellar Populations of Different Ageand Chemical Composition

The differences in stellar population shown by the CMDsof fields S2 and H1 are consistent with the different types ofvariable stars found in these regions of M31 and as noted inSection43 confirm that H1 is a typical halo field The smallnumber of variables detected in CCD2 of field H1 and the lackof variables in the range ofV sim 23 to 24 mag are consistent withthe rather peripheral location and low stellar density of this field

Similarly both the appearance of the CMD and the propertiesof the variables in the various portions of field S2 sampledrespectively by the whole CCD2 and the upper part of CCD1reveal significant differences and confirm the complexity ofthe stellar population in this region of M31 With reference toFigures12and13 the portion of field S2 imaged on CCD2 notonly lacks the CMD blue plume and the main-sequence brightvariables but it also has a few candidate variables at intermediateluminosity (V sim 22ndash24 mag) Specifically in the whole CCD2of field S2 only 6 candidate variables are found in the magnituderange ofV sim 24 toV sim 22 mag while 19 such variables arepresent in the upper portion of CCD1 corresponding to onlyone-half of the area of field S2 covered by CCD2 Furthermorealmost all of the bright variables in CCD2 of field S2 haveV 215 mag A large fraction of them is found within theclassical IS while the bright candidate variables in CCD1 offield S2 fall on average outside of the strip with their randomphase magnitudes We note that the three variables marked byorange circles in Figure13 which could either be ACsspCCs orbright RR Lyrae stars are all located in the lower part of CCD2

To get hints on the age and metal abundance of the compositestellar population in field S2 we have compared the CMD of theupper part of CCD1 of field S2 (Figure12) with the isochronesof Girardi et al (2002) for ages in the range of 63 to 708 Myrand metal abundances ofZ = 0008 (Figure15) andZ = 0019(Figure 16) respectively to fit the young stellar component

20


Figure 15 Same as Figure12with the following superimposed 1) isochrones from Girardi et al (2002) for a metal content ofZ = 0008 and ages of 63 79 141 316562 and 708 Myr (blue lines) and 2) the mean ridge lines of the GGCs M15 M3 M5 NGC 2808 47 Tuc and NGC 6553 (red lines)


Figure 16 Same as Figure15 except with isochrones and boundaries of the theoretical IS for the CCs corresponding toZ = 0019


21


in the CMD To account for the various types of variables ineach figure we have also overplotted the theoretical ISs of theRR Lyrae stars (Di Criscienzo et al2004) ACs withZ = 00004and 13 lt M lt 22M and CCs respectively withZ = 0008and Z = 0019 We have then used the mean ridge lines ofthe GGCs M15 M3 M5 NGC 2808 47 Tuc and NGC 6553(drawn from theBV database of GGCs by Piotto et al2002from Ferraro et al1997for M3 and from Ortolani et al1995for NGC 6553) to account for the oldest (t gt 10 Gyr) stellarcomponent These clusters span a range in metallicity from[FeH] = minus016 for NGC 6553 to [FeH] = minus233 for M15on the Carretta et al (2009 hereafter C09) metallicity scaleThe observed GGC ridge lines were preferred to theoreticalisochrones of corresponding age and metal abundance since thelatter are known to be affected by large uncertainties in the colortransformations from the theoretical to the observational planeTo plot ISs GC ridge lines and isochrones on the observedCMDs we have assumedE(B minus V ) = 008 magAV = 3315E(BminusV ) andAB = 4315E(BminusV ) andμ0(M31)= 2443 mag

Figures15 and16 demonstrate how powerful the approachis of combining information from the isochrone and GC ridgeline fitting of the CMD with information obtained from thevariable star population present in this region of M31 In factthe presence of a stellar population as old ast 10 Gyrcannot be unquestionably proven by the comparison of theCMD with the GC ridge lines because of (a) the confusionof stars with different (younger) ages and metal content inthe red giant branch region of the CMD as well as somecontamination by Galactic red stars and (b) because the HB ofsuch an old population if any cannot be disentangled from theoverwhelming young population However the mere presence ofthe RR Lyrae variables having an average magnitude consistentwith their membership to M31 definitely proves that such anold population exists and unambiguously traces the HB of suchan old population in this region of M31 The properties of thevariables also provide hints to the metal abundance of the stars inthese regions of M31 In particular the average magnitude of theRR Lyrae star having full coverage of the light curve (blue starin Figure15) appears to be consistent with the HB of the GCsM5 ([FeH] = minus133 C09) and NGC 2808 ([FeH] = minus118C09) The red giant branches of these two clusters also fit ratherwell the upper envelope of the M31 red giant stars showing thatthe bulk of the old (t 10 Gyr) stellar population in this M31field has metallicity [FeH] minus12minus13 on the C09 scale

As for the younger populations the CMD isochrone fittingseems to favor aZ = 0019 metal abundance However theposition on the CMD of the variables of a Cepheid type and thecomparison with both the isochrones and edges of the theoreticalIS for the different metal abundances show that aZ = 0008component is also needed to explain all of the bright variablesobserved in this field In fact although the 94 day Cepheid(brightest magenta star) and the candidates withV 213 mag(magenta filled circles in Figures15and16) fall on or close tothe blue loops of the 63 and 79 Myr isochrones for both theZ =0008 andZ = 019 only for Z = 0008 do the blue loopsextend blueward enough to produce confirmed and candidateCCs with 213 V 225 mag Furthermore the positionof the four confirmed CCs with respect to the boundaries ofthe IS suggests also a lower metal abundance ofZ = 0008as for Z = 0019 they all lie close to the blue edge of theIS Particularly at this metallicity the two bluest Cepheids arelocated between the blue edge of the fundamental mode andthe blue edge of the first overtone mode This circumstance

suggests that ifZ = 0019 then the two bluest Cepheidsare first overtone pulsators whereas the other two Cepheidsare at the fundamental blue edge Cepheids at the first overtoneblue edge are expected to have low pulsation amplitudes At thesame time the brightest Cepheid is at a luminosity for whichonly the fundamental mode of pulsation is efficient so that itsproximity to the blue edge again implies a quite low pulsationamplitude (see eg Bono et al2000) These predictions arenot consistent with the observed pulsation amplitudes that rangebetween 084 and 129 mag in theB band they are in betteragreement with the values expected ifZ = 0008 when theCepheids are in the middle of the IS

Finally as anticipated in Section42 the interpretation ofthe candidates about 1ndash15 mag above the HB (the orange filledcircles in Figures12 13 and15) is not easy Taking into accountthe magnitude range spanned by these stars (V in the range from235 to 245 mag) and the periods that are generally shorter than1 day with only a couple of exceptions we have consideredthree different possibilities (1) they could be spCCs falling onthe short-period tail (P lt 2 days) of the CCs distribution (2) theycould be ACs tracing an intermediate-age population as metalpoor as [FeH] minus17 or (3) they could be overluminousRR Lyrae stars Although the uncertainty in the periods and thelack of complete light curves for these objects make discerningamong the three hypotheses rather difficult the comparison ofthe Girardi et al isochrones shows that the blue loops of theZ = 0008 isochrones do not extend blueward enough to crossthe IS (see isochrones for 316 562 and 708 Myr in Figure15) atthe low mass and luminosity of these variables thus ruling outpossibility number 1 at least for populations withZ = 0008In Figure17 we show the effect of further reducing the metalabundance toZ = 0001 andZ = 00004 respectively The blueloop of a 708-Myr isochrone withZ = 0001 can produce thesefaint variables at least in part as well as the brighter CCs andwould produce them even better withZ = 00004 On the otherhand these variables would also be thoroughly consistent withthe IS of the ACs forZ = 00004 However if the bulk of theoldest stellar population in these regions of M31 has a metalabundance of [FeH] = minus12minus13 as suggested by the RRLyrae stars and the fitting of the GC HB ridge lines it doesnot seem conceivable that the intermediate-age and youngerpopulations in the same field could have metal abundancesas low asZ = 00004 (corresponding to [FeH] = minus17) Inconclusion this seems to rule out both the case of the ACs(namely hypothesis number 2) and within hypothesis number1 the case of the CCs as metal poor asZ = 00004 It is alsoworth noting that the predicted gap in magnitude between the RRLyrae level and the faintest Cepheid pulsators at a metallicityof 0004 is about 08 mag (Caputo et al2004) which is inexcellent agreement with the difference in magnitude betweenthe RR Lyrae and the two ACspCC pulsators seen in Figures1516 and17

Finally hypothesis number 3 which states that a large fractionof these variables might be RR Lyrae stars is supported bytheir periods being generally below 1 day However since thesevariables also appear to be about 1 mag brighter than the HB ofthe old population in M31 they are either blended with othersources if they are RR Lyrae stars or they cannot belong toAndromeda but perhaps to a structure (a satellite or the stream)in the galaxy foreground located in the region covered by fieldS2

It is obviously too premature to draw any firm conclusionsbased on only a few variables and the rather incomplete light

22


Figure 17 Same as Figures15 and16 except with isochrones and boundaries of the theoretical IS for the CCs corresponding toZ = 0001 The isochrone withZ =00004 and an age of 708 Myr is shown as a red dot-dashed line


curves available to us Still these results show how much couldbe learned about the stellar populations and the structure of M31by combining the study of the galaxy CMD and the variable starproperties based on LBT data

45 Comparison with Previous Variability Studies in M31

Recent studies of variable stars in M31 include the works ofVilardell et al (2007) and Joshi et al (2010) for the Cepheidsand the studies of Brown et al (2004) Sarajedini et al (2009)and Jeffery et al (2011) for the RR Lyrae stars Both the Brownet al (2004) and Sarajedini et al (2009) fields have different sizeare rather far away from our LBT pointings and generally aremuch closer to the M31 disk These aspects along with theuncertainty of the completeness of the detection of variablestars in our LBT fields make the comparison quite difficultThis is particularly true for the RR Lyrae stars since we cannoteasily evaluate the completeness of our samples at such faintmagnitude levels and on the other hand our fields are veryperipheral compared with those of Brown et al (2004) andSarajedini et al (2009) Indeed our two fields sample regions ofM31 at the projected distances of 21 kpc (field S2) and 19 kpc(field H1) from the center of the galaxy respectively whileBrown et al (2004) observed anHSTACS field at 11 kpc andSarajedini et al (2009) observed twoHSTACS fields at 4 and6 kpc respectively

On the other hand one of the Jeffery et al (2011) fieldsfield ldquohalo21rdquo overlaps with our field H1 (see Section42) Thecomparison of the number density of the RR Lyrae stars in fieldsH1 and ldquohalo21rdquo shows that in spite of all of the shortcomings

affecting our data we seem to have reached a good completenessin the detection of these variables

The comparison is easier for bright variables such as theCepheids Vilardell et al (2006 2007) detected 416 Cepheidsin a 33prime8 times 33prime8 field located along the minor axis of M31(see Figure1) using the 25 m INT in La Palma Spain Thiscorresponds to an average density of 036 Cepheids arcminminus2The Cepheids in the Vilardell et al sample have a perioddistribution roughly peaking around 4 days (see Figure 2 intheir paper) and they span the magnitude range ofV sim 23to V sim 192 mag which overlaps well with the range inmagnitude spanned by the Cepheids in our LBT fields Of ourLBT pointings the region imaged in the upper portion of theCCD1 of field S2 is the closest to the M31 disk In this region wehave identified 18 bona fide CCs and another six variables witha more uncertain classification all having a visual magnitudein the range of 23 to 19 mag (Figure12) Accounting for thetrimming of theV frames these variables span an area of about6144 arcmin2 providing a density of 039 Cepheids arcminminus2which is in good agreement with the density findings of Vilardellet al Unfortunately we only have a very preliminary estimateof the periods of our Cepheids thus it is not possible to make asound comparison of the period distributions As for the metalabundances Vilardell et al (2007) assume the galactocentricmetallicity gradient by Zaritsky et al (1994) and an empiricalmetallicity correction of the Cepheid periodndashluminosity (PL)relation According to their resulting corrections and to thereported galactocentric distances we estimate that the Cepheidsin their sample have [OH] in the rangeminus02divide 02 Since weare exploring regions of M31 that are quite external (see Figure1

23


Table 12Distance Estimates from the CCs

Name P μPL μWes μogleHSTμPL02 μWes02

V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470

and Column 7 of Table1) we expect that the metallicity of ourCepheids is close to [OH] = minus02 which impliesZ sim 001This is consistent with the metallicitiesZ = 0019ndash0008we infer for CCs brighter thanV sim 23 mag as comparedwith the isochrones from Girardi et al (2002) discussed inSection44

As for the comparison with Joshi et al (2010) those authorsused a 1 m telescope and identified 39 short-period (P lt 15 days)CCs in a 13prime times 13prime region of the M31 disk located along thesemimajor axis on the same side of our field S2 (see Figure1)This corresponds to a density of 023 Cepheids arcminminus2 whichis about one-half of the value that we derive in the upperpart of CCD1 of field S2 On the other hand the Joshi et alsample contains Cepheids that are generally brighter and ofa longer period than those seen in our sample In fact theirperiod distribution peaks at logP sim 09 and 11 days withperiods as short as 34 days and most of their Cepheids are at〈R〉 sim 20ndash21 mag Our sample includes Cepheids of a shorterperiod but our magnitudes and periods are consistent with theirresults Particularly we find〈V 〉 = 2062 mag for the 94 dayCepheid (V2 see Table10) and in the same period range theyfind consistentR magnitudes based on a typicalV minus R color andtaking into account the uncertainties related to the reddeningcorrections

To derive a distance estimate for the four CCs listed inTable10 and to confirm that they are M31 members we haveused the theoretical PL and the Wesenheit relations forZ =0008 andZ = 002 (see Caputo et al2000) and the PL relationadopted by theHST Key Project (Freedman et al2001) whichhas the slope by Udalski et al (1999) and the zero point basedon an assumed distance modulus for the Large MagellanicCloud (LMC) of 185 mag The resulting individual (fromthe Wesenheit relations) and mean (from the PL) distancesare reported in Table12 whereμPL μWes μOGLEHST μPL02andμWes02are distance moduli derived from the theoretical PLand the Wesenheit relations forZ = 0008 the PL relation byFreedman et al (2001) and the theoretical PL and Wesenheitrelations forZ = 002 We consider an uncertainty ofplusmn01 magto the individual distance moduli from the Wesenheit relationswhile the average distance modulus obtained from the Udalskiet al (1999) PL is 2457plusmn 02 mag The errors on the estimateddistances take into account both the observational errors inB and V and the intrinsic dispersion of the adopted relationsOur value is longer but it is within the errors consistent withthe modulus of McConnachie et al (2005) transformed to ouradopted reddening ofE(B minus V ) = 008 magμ0(M31) =2443 mag

Vilardell et al (2007) estimated a distance to M31 of(m minus M)0 = 2432plusmn 012 mag based on an assumed dis-tance modulus of 184 mag for the LMC The difference inthe adopted distance modulus for the LMC combined with theadopted metallicity correction explains most of the discrepan-cies between their distance estimate and our results

5 SUMMARY AND CONCLUSIONS

We have presentedVB minus V CMDs reaching the limitingmagnitudeV sim 26 mag of two fields of the Andromedagalaxy that were observed with the LBTLBC-blue cameraduring the SDT A number of technical problems during thefirst phase of the LBTLBC operation and rather unfavorableweatherseeing conditions hampered our observing campaignthereby limiting our study of the variable star populations inthese M31 fields Nevertheless we have identified 274 variablestars using the image subtraction technique and present theirdifferential flux B light curves For 138 of these variable starswe have also obtained an estimate of theBV magnitudes thatallowed us to plot the variables on the CMDs By combiningthe information gathered on the period magnitude shape ofthe light curve and position on the CMD we were able toclassify 214 variables They include 127 RR Lyrae stars 71short- and intermediate-period Cepheids (periods shorter than94 days) and 16 binary systems We have compared the CMDand the variable star population of the M31 field closest to thegalaxy disk and the giant stream with the sets of isochronesby Girardi et al (2002) for ages in the range of 63ndash708 Myrand metal abundances ofZ = 00004 0001 0008 and 0019to fit the young stellar component as well as with the meanridge lines of GGCs spanning a range in metallicity from[FeH] = minus016 dex to [FeH] = minus233 dex (on the C09metallicity scale) to account for the oldest (t gt 10 Gyr) stellarcomponent The isochrone and GC ridge line fittings and theproperties of the variable stars show that the composite stellarpopulation present in this M31 region has a typical metalabundance larger than [FeH] = minus12minus13 dex for the oldeststellar component and for the young stellar component is inthe range of [FeH] simminus13 dex to about solar metallicity Farfrom being complete and exhaustive this study neverthelessdemonstrates the powerful approach of combining informationfrom the CMD with information obtained from the variable starpopulation

LBT is an international collaboration among institutions inthe United States Italy and Germany The LBT Corporationpartners are the University of Arizona on behalf of the Arizonauniversity system the Istituto Nazionale di Astrofisica Italythe LBT Beteiligungsgesellschaft Germany representing theMax-Planck Society the Astrophysical Institute Potsdam andthe Heidelberg University the Ohio State University and theResearch Corporation on behalf of the University of NotreDame the University of Minnesota and the University ofVirginia

This publication makes use of data products from the TwoMicron All Sky Survey which is a joint project of the Univer-sity of Massachusetts and the Infrared Processing and AnalysisCenterCalifornia Institute of Technology funded by the Na-tional Aeronautics and Space Administration and the NationalScience Foundation We thank Paolo Montegriffo for the de-velopment and maintenance of the GRATIS package This re-search was partially supported by PRIN-MIUR-2007JJC53XPI F Matteucci and by COFIS ASI-INAF I016070

REFERENCES

Alard C 2000AampAS 144 363Alonso-Garcia J Mateo M amp Worthey G 2004AJ 127 868Baldacci L Rizzi L Clementini G amp Held E V 2005AampA 431 1189Barmby P Ashby M L N Bianchi L et al 2006ApJ 650 L45Beccari G Bellazzini M Clementini G et al 2007AampA 476 193

24


Bellazzini M Cacciari C Federici L Fusi Pecci F amp Rich M 2003AampA 405 867

Bertin A amp Arnouts S 1996AampAS 117 393Block D L Bournaud F Combes F et al 2006Nature 443 832Bono G Castellani V amp Marconi M 2000ApJ 529 293Bono G Groenewegen M A T Marconi M amp Caputo F 2002ApJ 574

L33Bono G Marconi M amp Stellingwerf R F 1999ApJS 122 167Brown T M Beaton R Chiba M et al 2008ApJ 685 L121Brown T M Ferguson H C Smith E et al 2003ApJ 592 L17Brown T M Ferguson H C Smith E et al 2004AJ 127 2738Brown T M Smith E Ferguson H C et al 2006ApJ 625 323Brown T M Smith E Ferguson H C et al 2007ApJ 658 L95Brown T M Smith E Ferguson H C et al 2009ApJS 184 152Caputo F 1998AampARv 90 33Caputo F Castellani V DeglrsquoInnocenti S Fiorentino G amp Marconi M

2004AampA 424 927Caputo F Marconi M amp Musella I 2000 AampA354 610Carretta E Bragaglia A Gratton R DrsquoOrazi V amp Lucatello S 2009AampA

508 695Castellani V Cignoni M DeglrsquoInnocenti S Petroni S amp Prada Moroni

P G 2002MNRAS 334 69Catelan M 2004 in ASP Conf Ser 310 Variable Stars in the Local Group ed

D W Kurtz amp K R Pollard (San Francisco CA ASP)113Choi P I Guhathakurta P amp Johnston K V 2002AJ 124 310Cignoni M Tosi M Bragaglia A Kalirai J S amp Davis D S

2008MNRAS 386 2235Clementini G 2010 in Variable Stars the Galactic halo and Galaxy Formation

ed C Sterken N Samus amp L Szabados (Moscow Sternberg AstronomicalInstitute of Moscow Univ) 107

Clementini G Baldacci L Bragaglia A et al 2004 in ASP Conf Ser 310Variable Stars in the Local Group ed D W Kurtz amp K R Pollard (SanFrancisco CA ASP)60

Clementini G Contreras R Federici L et al 2009ApJ 704 L103Clementini G Di Tomaso S Di Fabrizio L et al 2000AJ 120 2054Clementini G Federici L Corsi C et al 2001ApJ 559 L109Contreras Ramos R 2010 PhD thesis Univ of BolognaDi Criscienzo M Greco C Ripepi V et al 2011AJ 141 81Di Criscienzo M Marconi M amp Caputo F 2004AJ 612 1092Di Fabrizio L 1999 Laurea thesis Univ BolognaDolphin A E Saha A Olszewski E W et al 2004AJ 127 875Durrell P R Harris W amp Pritchet C I 2001AJ 121 2557Fardal M A Babul A Guhathakurta P Gilbert K M amp Dodge C

2008ApJ 382 L33Ferguson A M Irwin M J Ibata R A Lewis G F amp Tanvir

N R 2002AJ 124 1452Ferraro F R Carretta E Corsi C E et al 1997 AampA320 757Fiorentino G Limongi M Caputo F amp Marconi M 2006AampA 460

155Fiorentino G Monachesi A Trager S C et al 2010ApJ 708 817

Font A S Johnston K V Guhathakurta P Majewski S R amp Rich R M2006AJ 131 1436

Freedman W 1988ApJ 326 691Freedman W Madore B F Gibson B K et al 2001ApJ 553 47Giallongo E Ragazzoni R Grazian A et al 2008AampA 482 349Girardi L Bertelli G Bressan A et al 2002AampA 391 195Habing H J Miley G Young E et al 1984ApJ 278 L59Ibata R Irwin M Lewis G Ferguson A M N amp Tanvir N 2001Nature

412 49Ibata R Martin N F Irwin M et al 2007ApJ 671 1591Jeffery E J Smith E Brown T M et al 2011AJ 141 171Joshi Y C Narasimha D Pandey A K amp Sagar R 2010AampA 512 A66Marconi M Fiorentino G amp Caputo F 2004AampA 417 1101Martin N F McConnachie A W Irwin M et al 2009ApJ 705 758Massey P Olsen K A G Hodge P W et al 2006AJ 131 2478Mateo M 1998 in Stellar Astrophysics for the Local Group ed A Aparicio

A Herrero amp F Sanchez (Cambridge Cambridge Univ Press) 407Mateo M 2000 in ASP Conf Ser 203 The Impact of Large-Scale Surveys on

Pulsating Star Research ed L Szabados amp D Kurtz (San Francisco CAASP)187

McConnachie A W Huxor A Martin N F et al 2008ApJ 688 1009McConnachie A W Irwin M J Ferguson A M N Ibata R A Lewis G

F amp Tanvir N 2005MNRAS 356 979McConnachie A W Irwin M J Ibata R A et al 2003MNRAS 343 1335McConnachie A W Irwin M J Ibata R A et al 2009Nature 461 66McConnachie A W Irwin M J Lewis G F et al 2004MNRAS 351 L94Oosterhoff P T 1939 Bull Astron Inst Neth9 11Ortolani S Renzini A Gilmozzi R et al 1995Nature 377 701Piotto G King I R Djorgovski S G et al 2002AampA 391 945Pritchet C J amp van den Bergh S 1987ApJ 316 517Richardson J C Ferguson A M N Johnson R A et al 2008AJ 135

1998Richardson J C Irwin M J McConnachie A W et al 2011ApJ 732 76Saha A 1999ApampSS 267 193Sarajedini A Mancone C L Lauer T R et al 2009AJ 138 184Schechter P L Mateo M amp Saha A 1993PASP 105 1342Schlegel D J Finkbeiner D P amp Davis M 1998ApJ 500 525Stellingwerf R F 1978ApJ 224 953Stephens A W Frogel J A Freedman W et al 2001AJ 121 2597Stetson P B 1987PASP 99 191Stetson P B 1994PASP 106 250Udalski A Szymanski M Kubiak M et al 1999 Acta Astron49 201van den Bergh S 2000 The Galaxies of the Local Group (Cambridge

Cambridge Univ Press)van den Bergh S 2006 in The Local Group as an Astrophysical Laboratory

ed M Livio et al (Cambridge Cambridge Univ Press)1Vilardell F Jordi C amp Ribas I 2007AampA 473 847Vilardell F Ribas I amp Jordi C 2006AampA 459 321Wisniewski W Z amp Johnson H L 1968 Commun Lunar Planet Lab7 57Zaritsky D Kennicut Jr R C amp Huchra J P 1994ApJ 420 87

25

1 INTRODUCTION



4 VARIABLE STARS




44 Stellar Populations of Different Age and Chemical Composition



REFERENCES


Telescope (CFHT) photometric observations that cover respec-tively the galaxyrsquos inner 55 kpc and the southern quadrant outto about 150 kpc with an extension that reaches M33 at adistance of about 200 kpc Their data show the whole giantstream including its extensions and also reveal a multitude ofstreams arcs and many other large-scale structures of low sur-face brightness as well as two new M31 dwarf companions(And XV and And XVI) Twelve dwarf galaxies were known tobe M31 companions until 2004 among which only six dwarfspheroid galaxies (dSphs) and an additional seventeen new M31satellites were discovered in the last five to six years mainlybased on the INT and the CFHT data The most recent censusis reported by Richardson et al (2011) along with the discoveryof five new M31 dSph satellites And XXIIIndashXXVII as a resultfrom the second year of data from the ldquoPanAndromeda Archae-ological Surveyrdquo (PAndAS McConnachie et al2009) Startedin 2008 August the PAndAS survey is extending the global viewof M31 and that of its companion M33 by collecting data withMegaPrimeMegaCam on the 36 m CFHT for a total area of300 deg2 and out to a maximum projected radius from M31rsquoscenter of about 150 kpc This survey will likely detect severalother M31 faint satellites

The primary tool for understanding the formation historyof a galaxy over the whole Hubble time is the analysis ofcolorndashmagnitude diagrams (CMDs) deep enough to reach themain-sequence turnoff (TO) of the oldest populations The TOof the oldest stars in M31 (V sim 285 mag) is still unreachableby the largest ground-based telescopes and it requires tens oforbits of theHubble Space TelescopeAdvanced Camera forSurveys (HSTACS) time devoted to ldquotinyrdquo (3prime5times3prime7) portionsof the galaxy (Brown et al2003 2006 2007 2008 2009) tobe reached and measured The shallower survey by Richardsonet al (2008) who obtained CMDs toV sim 275 mag for 14HSTACS fields and sampled different substructures around M31covers a total area that is roughly one-third of that allowed in asingle shot by a ground-based telescope like LBT

Pulsating variable stars offer a powerful alternative tool totrace stars of different ages in a galaxy because variables ofdifferent types arise from parent populations of different agesSpecifically the RR Lyrae stars and the Population II Cepheids(often referred to as Type II Cepheids [T2Cs]) which belongto the oldest stellar population (t gt 10 Gyr) allow us to tracethe star formation history (SFH) back to the first epochs ofgalaxy formation and with their mere presence can providecrucial insight into the timescale and merging episodes that mayhave led to the assembly of a galaxy These low-mass variables(M sim 1M) burn helium in the stellar core and hydrogenin the shell surrounding the core during the horizontal branch(HB the RR Lyrae) and the post-HB (the T2Cs) evolutionaryphases They are respectively about 3 and 4 magnitude brighterand hence are much easier to observe than old (t gt 10 Gyr) TOstars The typical shape of their light variation which occurswith periodicities in the range of 02 to less than 1 day for the RRLyrae stars and from 1 to 25 days for T2Cs makes them mucheasier to recognize even when the upper HertzsprungndashRussel(H-R) diagram has overlapping contributions from a complexmix of age and metallicity The Anomalous Cepheids (ACs) areintermediate-age (t sim 1ndash2 Gyr) variables with periods in therange ofsim03 tosim20 days and with mean magnitudes spanninga 15-mag range These variables are intrinsically brighter thanthe RR Lyrae stars and when observed in an external stellarsystem where distance and projection effects can be neglectedthey locate themselves along a strip with the least luminous

ones (at periodssim030 days) being about 05 mag brighter thanthe RR Lyrae stars and the most luminous ones (at periodssim20 days) being about 20 mag brighter than the RR Lyraestars They appear significantly brighter than the T2Cs at thefixed period From an evolutionary point of view they are metal-poor ([FeH] minus17) He-burning stars in the post-turnoverportion of the zero-age horizontal branch (ZAHB see Marconiet al2004and references therein) that cross the instability strip(IS) at a higher luminosity than the RR Lyrae variables Theirmass is around 15M With an age of a few Gyr they indeedrepresent the natural extension of Classical Cepheids (CCs) tolower metallicities and masses (see eg Caputo et al2004Fiorentino et al2006and references therein) Finally CCs areintermediate-mass (typically from 3 to 12M) stars that crossthe IS during the blueward excursion in the central He-burningphase also referred to as a blue loop They have pulsationperiods in the range ofsim1 tosim100 days and an absolute visualmagnitude ofminus2 to minus7 mag With a typical age ranging froma few to a few hundred Myr they represent excellent tracers ofthe properties of young Population I stars

Short- and intermediate-period variables (ie periods shorterthan a few days) of M31 have never been adequately studieddespite their great potential to trace the stellar populations andthe star formation histories (SFHs) of nearby galaxies (Mateo1998 2000 Saha1999 Catelan2004 Clementini et al2004)So far the main limitations have been the size of the telescopesemployed in the ground-based surveys (Pritchet amp van denBergh 1987 Dolphin et al2004 Vilardell et al 2007 Joshiet al2010) the limited number of availableHST archive data(Clementini et al2001) and the rather small areas of M31covered by the space observations (Brown et al2004 Sarajediniet al2009 Jeffery et al2011) In their deepHSTACS survey ofthe M31 halo Brown et al (2004) identified 55 RR Lyrae stars(29 fundamental-modeminusRRabminus 25 first overtoneminusRRc andone double-modeminusRRdminus pulsators) in a 3prime5 times 3prime7 field alongthe southeast minor axis of the galaxy Based on their pulsationproperties Brown et al concluded that the old population inthe Andromeda halo has Oosterhoff-intermediate properties anddoes not conform to the subdivision in Oosterhoff I (Oo I) andOosterhoff II (Oo II) types (Oosterhoff1939) followed by theRR Lyrae stars in the MW field and globular clusters (GCssee Clementini2010and references therein) In this respect theM31 halo field would thus be different from the MW halo fieldand this would point to a different formationevolution historyHowever a different conclusion was reached by Sarajedini et al(2009) who identified 681 RR Lyrae variables (555 RRabrsquos and126 RRcrsquos) based on theHSTACS observations of two fieldsnear M32 at a projected distance between 4 and 6 kpc from thecenter of M31 and concluded that these M31 fields have Oo Iproperties More recently Jeffery et al (2011) have extendedBrown et alrsquos study of the M31 halo RR Lyrae stars to fiveadditional HSTACS fields that include one pointing in thestream one pointing in the disk and three pointings in the M31halo at distances of 21 kpc (hereafter referred to as halo21) and35 kpc from the galaxy center (hereafter halo35a and halo35brespectively see Figure 1 in the Jeffery et al paper) Theydetected 21 RR Lyrae stars in the ldquodiskrdquo field 24 in the ldquostreamrdquofield 3 in the ldquohalo21rdquo field 5 in the ldquohalo35brdquo field and nonein the ldquohalo35ardquo field Field ldquohalo21rdquo is of particular interestto us since it overlaps with our field H1 Jeffery et al foundaverage periods for the fundamental mode pulsators of 05830560 and 0495 days in the disk stream halo21 and halo35bfields respectively and conclude that the RR Lyrae populations

2








3




a

(2000) (2000) (deg) (deg) (kpc)


H5 And XXV 00 30 089 +46 51 07 minus216 564 811 b b












4










5




Chip Field S2


Field H1



and







6







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES








3




a

(2000) (2000) (deg) (deg) (kpc)


H5 And XXV 00 30 089 +46 51 07 minus216 564 811 b b












4










5




Chip Field S2


Field H1



and







6







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES




a

(2000) (2000) (deg) (deg) (kpc)


H5 And XXV 00 30 089 +46 51 07 minus216 564 811 b b












4










5




Chip Field S2


Field H1



and







6







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES










5




Chip Field S2


Field H1



and







6







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES




Chip Field S2


Field H1



and







6







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES







7












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES












8




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES




Blue Red Blue Red

185 V 20 2 16 4 520 lt V 21 3 12 1 1121 lt V 22 2 8 10 1422 lt V 23 4 13 23 4023 lt V 24 46 148 165 443



185 V 20 1 12 0 8 0 820 lt V 21 2 7 4 17 3 821 lt V 22 1 4 2 15 15 722 lt V 23 3 13 4 23 17 3623 lt V 24 35 133 38 151 260 667



185 V 20 1 15 2 4 2 1320 lt V 21 1 7 6 10 2 821 lt V 22 2 8 3 7 7 1122 lt V 23 7 14 3 19 7 2723 lt V 24 65 166 36 136 107 554




Blue Red Blue Red

185 V 20 11 10 5 1120 lt V 21 1 13 3 621 lt V 22 4 9 1 822 lt V 23 3 9 6 1623 lt V 24 21 72 15 94



185 V 20 1 16 3 10 7 820 lt V 21 3 3 4 6 3 1321 lt V 22 4 5 4 7 0 722 lt V 23 3 10 6 16 6 1023 lt V 24 25 82 25 107 22 83



185 V 20 4 9 5 12 1 620 lt V 21 2 5 2 7 2 921 lt V 22 3 11 1 11 2 522 lt V 23 5 10 6 10 6 1223 lt V 24 14 94 31 101 33 100



4 VARIABLE STARS



9






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES






BP IP BP IP

V 24 32 19 199 6524 lt V 25 139 195 679 649


BP IP BP IP BP IP

V 24 14 18 18 27 344 8224 lt V 25 116 175 129 220 740 718


BP IP BP IP BP IP

V 24 27 32 19 22 131 3624 lt V 25 142 220 83 166 469 544




10






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES






BP IP BP IP

V 24 8 14 8 1124 lt V 25 53 87 45 93


BP IP BP IP BP IP

V 24 6 16 5 19 4 1724 lt V 25 46 82 45 93 57 109


BP IP BP IP BP IP

V 24 9 13 3 24 17 1724 lt V 25 47 81 49 116 65 124


11




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES




Field S2


Field H1








12



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES



CCD1minus FieldS2



2833 1576 00 48 446 +42 19 44 057 2364 2364 Bin





b (2000) (2000) (days) (minus2450000) (mag)








13








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES








14


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15




-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



16


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES


-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15

-05 0 05 1 15 -05 0 05 1 15 -05 0 05 1 15



17







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES







18






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES






19



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES



Field S2


Field H1


Total Numbers













20






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES






21









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES









22










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







REFERENCES










23




V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









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24


























25

1 INTRODUCTION



4 VARIABLE STARS







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V2 94 2442 2424 2452 2415 2442V3 325 2456 2442 2465 2454 2462V4 51 2454 2473 2463 2441 2492V5 292 2437 2450 2446 2438 2470









REFERENCES


24


























25

1 INTRODUCTION



4 VARIABLE STARS







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25

1 INTRODUCTION



4 VARIABLE STARS







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hide and seek between andromeda’s halo, disk, … · the astrophysical journal, 743:19 (25pp),...

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