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THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 124: 3393, 1999 September1999. The American Astronomical Society. All rights reserved. Printed in U.S.A.(

THE IC 342/MAFFEI GROUP REVEALED

RONALDJ. BUTA1University of Alabama Department of Physics and Astronomy, Tuscaloosa, AL 35487-0324; buta=sarah.astr.ua.edu

AND

MARSHALLL. MCCALL1,2York University Department of Physics and Astronomy, 4700 Keele Street, Toronto, Ontario, Canada, M3J 1P3 ; mccall=yorku.ca

Received 1998 November 30; accepted 1999 April 27

ABSTRACT

Deep wide-eld CCD images in the optical and near-infrared have been acquired for 14 of the 16known or suspected members of the IC 342/Maei Group of galaxies, one of the closest groups to theMilky Way, and probably the closest group to M31. Because of their low Galactic latitude, all galaxiesare heavily extinguished, and myriads of foreground stars are superimposed. A sophisticated algorithmbuilt around DAOPHOT has been developed which successfully removes the foreground stars, makingpossible comprehensive morphological and photometric studies. The cleaned near-infrared images revealthe true morphology and extent of many of the galaxies for the rst time, three of which are among thelargest in the northern sky. Besides surface brightness proles, precise total magnitudes and colors havebeen measured. Many of the results represent substantial revisions to previous estimates. The data willmake possible new determinations of the distances and masses of the galaxies, which are crucial for

evaluating the impact the group may have had upon the dynamical evolution of the Local Group.Subject headings: galaxies: clusters: individual (IC 342/Maei) galaxies: photometry

galaxies: structure infrared: galaxies

1. INTRODUCTION

The IC 342/Maei Group is a loose grouping of morethan a dozen galaxies located behind the Milky Way nearthe northern intersection of the Galactic and supergalacticplanes. The group is thought to be one of the most impor-tant within 5 Mpc of the Milky Way and may contain thenearest normal giant elliptical. Yet, denitive estimates ofits total mass and population have never been obtained,owing to severe extinction and the superposition of myriads

of foreground stars. To date, the best available estimates forthe distance are in the range of 24 Mpc. If correct, dynami-cal studies suggest that the two dominant members, IC 342and Maei 1, may have interacted with the Local Group asrecently as eight billion years ago. Clearly, the group meritsfar more attention than it has received.

This paper provides, in some cases for the rst time, stan-dard global photometric parameters for 14 of the 16 knownor suspected members of the IC 342/Maei Group, to setthe stage for determining an accurate distance to the groupand to evaluate its possible inuence on the Local Group inthe past. The photometry we present is based on CCDimaging surveys carried out with the 0.6/0.9 m Burrell-Schmidt Telescope of Kitt Peak National Observatory in

1992 and 1995. In two previous papers (McCall & Buta1995, 1997), we presented preliminary information on threenew probable members of the group identied on oursurvey images. This paper presents our nal results for thesegalaxies and 11 others, encompassing morphologies, totalmagnitudes and color indices, surface brightness proles,

1 Visiting Astronomer, Kitt Peak National Observatory, NationalOptical Astronomy Observatories, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under cooperative agreementwith the National Science Foundation. Observations made with theBurrell Schmidt of the Warner and Swasey Observatory, Case WesternReserve University.

2 Please direct all correspondence to : Marshall McCall.

ellipse ts to isophotes, orientations, and spheroid and diskproperties. In a separate paper, we will undertake a com-prehensive analysis of foreground extinctions, which may beup to a factor of 100 in the V band for several groupmembers, and then derive distances using a variety of well-established techniques.

In 2, we present some background information to placeour observations into proper perspective. Following this, in3, we discuss the processing and calibration of the Schmidtimages. In 4, we describe how images were cleaned, includ-ing the method developed to eliminate foreground stars,which posed a formidable obstacle to photometry for mostof our sample galaxies. An atlas of the galaxies, showingmorphology before and after elimination of eld stars, ispresented in 5. Surface photometry, including the deriva-tion of global photometric parameters, is covered in 6. Adetailed discussion of each galaxy, including an analysis ofthe surface photometry, is presented in 7. Other extendedsources in the vicinity of the galaxies are described in 8.Finally, a brief summary is presented in 9.

2. BACKGROUND

2.1. Census

The IC 342/Maei Group is located near the northernintersection of the Galactic and supergalactic planes inthe Galactic coordinate range 129 l 149,[1 b16. The current census stands at 16 known orsuspected members, most of which are late-type dwarfs (seeKrismer, Tully, & Gioia 1995). Table 1 gives the dates ofdiscovery, morphologies (from this paper), heliocentricradial velocities, and positions. In this table, the galaxies arelisted in order of right ascension, but in subsequent tablesand gures they will be listed in alphabetical order to easending. Figure 1 displays the locations of the galaxies inGalactic coordinates (see also Fig. 1 of Krismer et al. 1995and of Karachentsev et al. 1997). The group extends

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34 BUTA & MCCALL Vol. 124

TABLE 1

KNOWN ANDSUSPECTEDMEMBERS OF THEIC 342/MAFFEIGROUP

v_

l b L B

Object Discovery Type (km s~1) R.A. (1950) Decl. (1950) (deg) (deg) (deg) (deg) References(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

Cassiopeia 1 . . . . . . . . . . . . . 1995 IAB(s)m ]35 02 02 05.0 ]68 46 18.0 129.57 ]7.11 6.28 ]8.48 D1,V1,C1MB 1 . . . .. . . . . . . . . . . . . . . . . 1995 IBm ]189 02 31 52.1 ]59 09 39.7 135.85 [0.85 358.98 ]1.41 D2,V2,C2Maffei 1 . . . . . .. . . . . .. . . . . . 1968 E3 [87 02 32 50.7 ]59 26 16.4 135.86 [0.55 359.29 ]1.44 D3,V3,C2

MB 2 . . . . . . . . . . . . . . . . . . . . . 1995 I ? ? 02 33 16.1 ]59 01 12.8 136.07 [0.91 358.95 ]1.19 D2,V4,C2Maffei 2 . . . . . . . . . . . . . . . . . . 1968 SAB(rs)bc [23 02 38 08.0 ]59 23 24.0 136.50 [0.33 359.58 ]0.83 D3,V5,C3Dwingeloo 2 . . . . . . . . . . . . . 1995 Im ]91 02 50 19.1 ]58 48 07.0 138.16 [0.19 359.90 [0.81 D4,V6,C4MB 3 . .. . . . . . . . . . . . . . . . . . . 1997 dSph ? 02 51 53.2 ]58 39 30.0 138.41 [0.23 359.89 [1.06 D5,V4,C4Dwingeloo 1 . . . . . . . . . . . . . 1994 SB(s)cd ]108 02 53 01.9 ]58 42 38.0 138.52 [0.11 0.02 [1.15 D6,V6,C4IC 342 . . . . . . . . . . . . . . . . . . . . 1895 SA(s)cd ]25 03 41 58.6 ]67 56 26.0 138.17 ]10.58 10.60 ]0.37 D7,V7,C3UGCA 86 . . . . . . . . . . . . . . . . 1974 SAB(s)m ]80 03 54 59.2 ]66 59 56.6 139.76 ]10.65 10.85 [1.17 D8,V8,C5Camelopardalis Aa . . . . . . 1994 I/dSph ? 04 19 26.7 ]72 41 27.0 137.25 ]16.20 16.09 ]1.87 D9,V4,C6NGC 1569 . . . . . . . . . . . . . . . 1789 I (Amorphous) [77 04 26 05.8 ]64 44 18.0 143.68 ]11.24 11.91 [4.92 D10,V9,C3NGC 1560 . . . . . . .. . . . . .. . 1885 Sd [36 04 27 08.2 ]71 46 29.0 138.37 ]16.02 16.03 ]0.79 D11,V10,C3UGCA 92 . . . . .. . . . . .. . . . . 1974 IBm [95 04 27 25.9 ]63 30 22.4 144.71 ]10.51 11.32 [6.01 D8,V8,C5Camelopardalis Ba. . . . . . 1997 I ]75 04 48 03.3 ]67 01 02.0 143.38 ]14.42 15.04 [4.21 D12,V11,C7UGCA 105 . . . . . . . . . . . . . . 1974 SAB(s)m ]113 05 09 35.2 ]62 31 19.6 148.52 ]13.66 14.99 [9.25 D8,V8,C5

NOTES.Col. (1): Name of galaxy, in order of right ascension. Col. (2): Date of publication of discovery. Col. (3): Revised Hubble type, based upon imagespresented in this paper where available. For Cam A and Cam B, types are based upon the judgment of the authors on the basis of published data (see text).

Col. (4): Heliocentric radial velocity, in km s~1. Col. (5): Right ascension, epoch 1950, in units of hours, minutes, and seconds. Col. (6): Declination, epoch1950, in units of degrees, arcminutes, and arcseconds. Col. (7): Galactic longitude. Col. (8): Galactic latitude. Col. (9) : supergalactic longitude. Col. (10):supergalactic latitude. Col. (11) : References to discovery, velocity, and coordinates.

aNot observed for this paper.REFERENCES.Discovery: (D1) Weinberger 1995 (but also note Blitz et al. 1982); (D2) McCall & Buta 1995; (D3) Maei 1968; (D4) Verheijen, Burton, &

Kraan-Korteweg 1995; (D5) McCall & Buta 1997; (D6) Kraan-Korteweg et al. 1994, and Huchtmeier et al. 1995; (D7) Dreyer 1895, based upon acommunication from W. F. Denning; (D8) Nilson 1974; (D9) Karachentsev 1994; (D10) Herschel 1789; (D11) Tempel 1885; (D12) Huchtmeier et al. 1997.Heliocentric Radial Velocity (V1) Huchtmeier et al. 1995; (V2) McCall, Buta, & Huchtmeier 1995, and Huchtmeier & van Driel 1996; (V3) McCall et al.v

_:

1999; (V4) Not measured; (V5) Hurt et al. 1996; (V6) Burton et al. 1996; (V7) Newton 1980a; (V8) Huchtmeier & Richter 1986; (V9) Reakes 1980; (V10)Broeils 1992; (V11) Huchtmeier et al. 1997. Coordinates: (C1) Huchtmeier et al. 1995; (C2) McCall & Buta 1995; (C3) de Vaucouleurs et al. 1991; (C4)McCall & Buta 1997; (C5) this paper; (C6) Karachentseva & Karachentsev 1998; (C7) Huchtmeier et al. 1997.

along the supergalactic plane from the Galactic plane,where members are most heavily obscured, toward theconcentration of galaxies around M81. It is a member ofwhat Tully (1982) refers to as the Canes Venatici Cloud.

FIG. 1.Map showing the locations and names of the 16 known orsuspected members of the IC 342/Maei Group. Coordinates are Galactic.The Galactic and supergalactic equators are marked with dashed lines.

The group is displaced by only 30 from M31; consideringdistances, it is likely the nearest to M31.

InB, the apparently brightest members of the group arethe Scd spiral IC 342, the peculiar amorphous galaxy NGC

1569, and the edge-on Magellanic system NGC 1560, whichwere discovered in the 18th and 19th centuries. These threeobjects have received the most attention and are actuallyrather well studied. Three faint dwarfs in the region, UGCA86, 92, and 105, were discovered by Nilson (1974). The trueextent of the group was not really recognized until the dis-covery of Maei 1 and 2 in 1968 (Maei 1968), now recog-nized as an elliptical and Sbc spiral, respectively. The mostrecent additions are Cam A (Karachentsev 1994), Cam B(Huchtmeier, Karachentsev, & Karachentseva 1997), Cas 1(Weinberger 1995; Huchtmeier et al. 1995), Dwingeloo 1(Kraan-Korteweg et al. 1994 ; Huchtmeier et al. 1995),Dwingeloo 2 (Verheijen, Burton, & Kraan-Korteweg 1995;Burton et al. 1996), MB 1 and MB 2 (McCall & Buta 1995;McCall, Buta, & Huchtmeier 1995), and MB 3 (McCall &Buta 1997). The rst two galaxies discovered by McCall &Buta (1995) are probable dwarf companions of Maei 1(although the status of the second remains uncertainseebelow), and the third is likely to be a second dwarf compan-ion of Dwingeloo 1 (McCall & Buta 1997). Most galaxiesdiscovered in the 20th century are poorly studied, and somehave never had a meaningful total magnitude measured(including, especially, Maei 2).

Intrinsically, the most luminous galaxies in the groupappear to be IC 342, Maei 1, and Maei 2. Until recently,it was believed that IC 342 and Maei 1 were the dominantmembers, but the photometry presented here reveals that

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No. 1, 1999 IC 342/MAFFEI GROUP REVEALED 35

Maei 2 may be close in luminosity (see McCall & Buta1996). A more denitive statement concerning this issue willbe presented in a separate paper. Although Dwingeloo 1was purported to be a large galaxy at the time of its dis-covery, it is substantially less luminous than the other threegalaxies, being more akin to M33.

Additional members of the IC 342/Maei Group will nodoubt be found as the region is more intensively scrutinized.Several surveys of the area around Maei 1 and 2 have been

made recently (Weinberger, Saurer, & Seeberger 1995; Hauet al. 1995; Lercher, Kerber, & Weinberger 1996; Iwata etal. 1997; Saurer, Seeberger, & Weinberger 1997; Henning etal. 1998; Buta & McCall, in preparation). Lahav et al. (1998)have suggested that a particularly good candidate for mem-bership is the edge-on system C11J7 discovered by Hau etal. (1995). Many papers concerning other current work onidentifying and studying galaxies in the Zone ofAvoidance appear in the proceedings of the meeting, Unveiling Large-Scale Structures Behind the Milky Way(Balkowski & Kraan-Korteweg 1994).

2.2. Major Galaxies

2.2.1. IC 342

IC 342 was discovered by W. F. Denning in the 1890s(Dreyer 1895), and one of the best photographs waspublished long ago by Hubble (1936). It is a large late-typespiral close to face-on.

By measuring its tilt (25 ^ 3), Newton (1980a, 1980b)revealed that IC 342 is rotating at a rate typical of a giantspiral. However, its distance was uncertain. Until 1989, dis-tance estimates for IC 342 ranged from 1.5 to 8 Mpc, pri-marily because of uncertainty in the extinction (McCall1989). Circumstantial evidence suggested that the distancewas on the low side of this range. For example, Hodge &Kennicutt (1983) counted more H II complexes in IC 342than in any other spiral except M81, indicating some benetfrom higher spatial resolution accompanying proximity tothe Milky Way. Also, the high ux observed for manymolecular lines (e.g., Henkel, Mauersberger, & Schilke1988) hinted that the galaxy was nearby.

Spectra of constituent H IIregions by McCall, Rybski, &Shields (1985) led to the realization that IC 342 was extin-guished by 2.4 mag in V, much more than previouslythought (McCall 1986, 1989). The result was subsequentlyconrmed by Madore & Freedman (1992), who examinedthe color of the blue plume in the HR diagram of an armeld. The new estimate for the extinction forced a revisionof nearly all previous distance estimates (McCall 1989). Theresulting mean was only 1.8 Mpc (with a standard deviationof 0.3 Mpc), implying that the luminosity in B was [20.2,similar to that of the Milky Way. Given the size of thegalaxy and its proximity to M31, it was realized that IC 342(along with Maei 1) might have played a signicant role inthe evolution of the Local Group (see below).

2.2.2. Maei 1 and 2

In 1968, Maei (1968) discovered two heavily reddenedextended sources in the same general area as IC 342, whichhe suspected to be galaxies. Spinrad et al. (1971, 1973) veri-ed that both were galaxies, and identied the rst as agiant elliptical and the second as an intermediate-typespiral. These classications are conrmed in this paper.The galaxies became known as Maei 1 and Maei 2,respectively.

Spinrad et al. (1971, 1973) derived the rst estimates ofthe amount of extinction toward Maei 1 and 2 by compar-ing the nuclear spectra with spectra of the spheroid of M31and giant ellipticals like NGC 3379. In visual light, Maei 1was found to be extinguished by 5.2 mag and Maei 2 by 6.3mag.

Spinrad et al. (1971) made a rough estimate of the dis-tance to Maei 1 using a measurement of the core radius, aneyeball estimate of the central velocity dispersion, an

inferred total magnitude, and an assumed mass-to-lightratio. The result, 1 Mpc, which was evaluated to be within afactor of 2 of the true distance, prompted them to suggestthat the galaxy might be an unbound member of the LocalGroup.

The extinction toward Maei 1 was a subject of contro-versy. Various methods involving foreground stars consis-tently gave visual extinctions less than about 4 mag. Buta &McCall (1983) evaluated these methods and made two newestimates of the extinction independent of Spinrad et al.(1971). First, they measured the total column density of gasin the direction of the galaxy, which was known to correlatewell with the total visual extinction by dust (Savage &Mathis 1979). The result for was 4.9 ^ 0.4 mag. Second,A

Vthey carried out photoelectric photometry of the innerregion of the galaxy, from which they were able to deriveB[V. Comparing the measurement with the known intrin-sic colors of elliptical galaxies, was estimated to beA

V5.3 ^ 0.4 mag. Together, the results conrmed the estimateof Spinrad et al. (1971).

Based on a large extrapolation of the V-band photoelec-tric growth curve, Buta & McCall (1983) estimated the totalvisual magnitude of Maei 1 to be 11.4 mag. This led to adistance of Mpc, based upon the relationship2.1

~0.8`1.3

between luminosity and central velocity dispersionobserved for elliptical galaxies in visual light (de Vaucou-leurs & Olson 1982). The corresponding absolute magni-tude in V was [20.4, close to that of the Milky Way.Membership in the Local Group seemed to be ruled out.Instead, the galaxy appeared to be located in what wasknown at the time as the Ursa Major-CamelopardalisCloud (Bottinelli et al. 1971), of which IC 342 was also apart.

More recently, by measuring surface brightness uctua-tions in the K@ passband, Luppino & Tonry (1993) esti-mated the distance to Maei 1 to be 4.2 ^ 0.5 Mpc.Although ostensibly a better method of getting the distancethan any of the other methods so far applied (see Jacoby etal. 1992), the result may be compromised by practical prob-lems unique to the eld of Maei 1. Specically, the severecontamination of the eld by faint foreground stars andvariations in the galaxy-subtracted background introducedby the dust lanes may have seriously aected the determi-nation of the uctuation magnitude (see Jensen, Tonry, &Luppino 1998). Evidence that there may be a problem issuggested by the fact that the uctuation magnitude bright-ens by 0.46 mag going from a radius of 6A to 62A, which isopposite to what would be expected if there had been arelatively recent episode of star formation focussed on thecenter, or if there were a signicant population of globularclusters.

It is very likely that Maei 1 is the nearest normalgiantelliptical galaxy to the Local Group and may, in terms ofmass, be the dominant member of the IC 342/Maei Group.Even if Maei 1 were as distant as 4 Mpc, it would still be a

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very important object. Giant elliptical galaxies are rareamong most of the nearby groups cataloged by de Vaucou-leurs (1975). If Maei 1 is the nearest giant elliptical, then itpresents an opportunity to study the core of such a galaxyat unprecedented resolution.

In principle, a good distance for Maei 2 could have beengained through application of the Tully-Fisher relation,because 21 cm radiation has been readily detectable (e.g.,Hurt, Turner, & Ho 1996). Unfortunately, the apparent

total magnitude of the galaxy has never been measured.Thus, the distance has remained extremely uncertain. Bot-tinelli et al. (1971) obtained distance estimates ranging from2 to 6 Mpc by comparing the H I properties with those ofother galaxies of comparable type. Spinrad et al. (1973)derived a value of 5 ^ 2 Mpc on the basis of the sizes ofconstituent H II regions. It is probably best to regard thelast estimate as an upper limit, because the heavy extinctionmakes the nebulae look smaller than they would appear in agalaxy at a comparable distance but at a higher galacticlatitude.

Distances to Maei 1 and 2 remain so uncertain that aphysical connection between the two galaxies cannot beruled out. If Maei 2 and Maei 1 were at comparable

distances, it is likely that the luminosity of Maei 2 wouldapproach that of Maei 1 (McCall & Buta 1996). AlthoughMaei 2 appears fainter, it is more heavily extinguished. Acomprehensive examination of the intrinsic properties ofthe members of the IC 342/Maei Group will be presentedin a separate paper.

2.3. Relevance to L ocal Group T iming

Kahn & Woltjer (1959) and Lynden-Bell (1981) haveshown that the distances and motions of nearby galaxiesmay be used to constrain the total mass of the M31MilkyWay pair and the dynamical age of the Local Group. Thelatter has been interpreted as an independent estimate forthe age of the universe. The method, known as Local

Group timing, hinges upon the assumption that M31 andthe Milky Way separated from the Hubble ow soon afterformation and have behaved dynamically like an isolatedbinary ever since, with the consequence that the Milky Wayhas turned in its orbit and is now falling back toward M31.

McCall (1986, 1987, 1989) noticed that the modernrevision to the extinction of IC 342 moved the galaxy into aposition only 1.3 Mpc from M31. This led to the realizationthat Maei 1 might be comparably close. Relative mass-to-light ratios indicated that the present gravitational acceler-ation of M31 by IC 342 and Maei 1 is signicant withrespect to that due to the Milky Way. Considering thepresent rate of recession of the two galaxies from M31, theirpast dynamical inuence on the Local Group must havebeen even greater. In other words, the dominant membersof the IC 342/Maei Group may be massive enough andnear enough to the Local Group to have had an inuenceon local history (McCall 1986, 1987, 1989; Valtonen et al.1993; Dunn & Laamme 1993; Peebles 1990, 1994), therebycalling into question the binary hypothesis of Local Grouptiming (see, e.g., Peebles 1995).

Valtonen et al. (1993) interpreted the high speeds of IC342 and Maei 1 relative to M31 and the current approachof M31 toward the Milky Way to indicate that an encoun-ter took place 5 to 8 billion years ago. They proposed thattwo primordial binaries encountered the progenitor of M31and that the ensuing interactions led to the ejection of one

member from each (which ultimately became IC 342 andMaei 1) and the merger of the remaining member of eachwith M31. Besides conrming that the results of conven-tional Local Group timing are unreliable, they suggestedthat timing of the enlarged system (basically the four-bodysystem of the Milky Way, M31, Maei 1, and IC 342) mightyield improved estimates for the total mass and age. Ofcourse, the primary deciency of the model is that it doesnot explicitly predict the existence of any other large gal-

axies in the same direction as IC 342 and Maei 1 (at thetime, the location and size of Maei 2 were not known, andDwingeloo 1 was not discovered yet), although it could beargued that dwarfs might have arisen from tidal disruptionof the interacting systems.

2.4. Reasons for this Study

To fully evaluate models which attempt to use themotions of neighbors of the Milky Way to arrive at the ageof the universe and the local density of dark matter(Valtonen et al. 1993; Byrd et al. 1994; Peebles 1995), and todevelop improvements, it is imperative not only to completethe census of galaxies in the IC 342/Maei Group, but tohave complete and reliable data for each constituent. Asnoted by Krismer et al. (1995), any successful model must beable to account for the current placement of all members ofthe group, not just Maei 1 and IC 342.

Total colors, magnitudes, and sizes of group members areessential to rening estimates of extinction, distance, andluminosity. In addition, surface photometry of the largermembers is needed to determine relative masses and inter-action radii forn-body simulations.

Presently, apparent photometric data for most of the gal-axies is anchored to photography (or worse). Existing aper-ture photometry is often suspect because of contaminationby foreground stars, or so limited in scope that profoundextrapolations must be made to derive integrated proper-

ties. In addition, the sizes of all galaxies in the group areextremely uncertain due to the heavy obscuration (the threelargest are at least 15@30@ across). The research presentedhere overcomes all of these problems and provides for therst time a homogeneous and reliable set of fundamentaldata, which should nally make it possible to pinpoint therole that the IC 342/Maei Group has played in our ownhistory.

3. OBSERVATIONS, REDUCTIONS, AND CALIBRATIONS

3.1. Observations and Reductions for V and I

Except for Cam A and Cam B, all of the galaxies listed inTable 1 were observed. The main observations were carriedout with the 0.6/0.9 m Burrell Schmidt telescope at KittPeak National Observatory during the period 1995November 1116 (UT). All images were acquired with aTektronix 2048] 2048 CCD camera, for which pixel sizeswere 21km square. The CCD was fed an f/3.5 beam. Usingmedium brightness stars from the Space Telescope ScienceInstitute Guide Star Catalog, we determined the exact scaleof the images to be per pixel, so the frames2A.028 ^ 0A.001covered 69@] 69@ on the sky. The readout noise was only3 e~ pixel~1, so exposures were sky-noise dominated. Thegain setting was 3.75 electrons per ADU.

Images were acquired in V (KPNO lter 1542, centralwavelength full width at half-maximumj

c\ 5436 A,

FWHM \ 1004 Cousins I (KPNO lter 1539,A), jc

\

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TABLE 2

OBSERVINGLOG

Eective Number of

Object Filter Air Mass UT Date Frames Minutes/Frame

Cassiopeia 1 ...... I 1.434 1995 Nov 12 6 5

Cassiopeia 1 ...... V 1.510 1995 Nov 14 6 5

Dwingeloo 1 .. .. .. I 1.151 1995 Nov 11 5 5

Dwingeloo 1 .. .. .. V 1.282 1995 Nov 14 6 5

Dwingeloo 1 . . . . . . Ha 1.499 1995 Nov 16 1 10IC 342 . . . . . . . . . . . . . I 1.271 1995 Nov 12 6 5

IC 342 . . . . . . . . . . . . . V 1.286 1995 Nov 14 5 5

IC 342 . . . . . . . . . . . . . B 1.237 1992 Oct 26 2 10

IC 342 . . . . .. . . . . .. . Ha 1.501 1995 Nov 16 2 10Maffei 1 . . . . . . . . . . . I (1) 1.303 1995 Nov 11 6 5

Maffei 1 . . . . . . . . . . . I (2) 1.156 1995 Nov 15 6 5

Maffei 1 . . . . . . . . . . . V 1.332 1995 Nov 14 6 5

Maffei 1 . . . . . . . . . . . B 1.146 1992 Oct 26 3 10

Maffei 1 . . . . . . . . . . . Ha 1.297 1995 Nov 16 2 10Maffei 2 . . . . . . . . . . . I 1.211 1995 Nov 11 6 5

Maffei 2 . . . . . . . . . . . V 1.186 1995 Nov 14 6 5

Maffei 2 . . . . . . . . . . . B 1.274 1992 Oct 26 2 15

Maffei 2 . . . . . . . . . . . Ha 1.487 1995 Nov 16 1 10NGC 1560 . . . . . . . . I 1.303 1995 Nov 12 6 5

NGC 1560 . . . . . . . . V 1.560 1995 Nov 14 3 5NGC 1569 . . . . . . . . I 1.306 1995 Nov 12 4 5

NGC 1569 . . . . . . . . V 1.426 1995 Nov 14 3 5

UGCA 86 . . . . . . . . . I 1.262 1995 Nov 15 5 5

UGCA 86 . . . . . . . . . V 1.320 1995 Nov 14 6 5

UGCA 92 . . . . . . . . . I 1.207 1995 Nov 15 6 5

UGCA 92 . . . . . . . . . V(1) 1.174 1995 Nov 14 6 5

UGCA 92 . . . . . . . . . V(2) 1.189 1995 Nov 14 6 5

UGCA 92 . . . . .. . . . Ha 1.498 1995 Nov 16 1 15UGCA 105 . . . . . . . I 1.323 1995 Nov 15 6 5

UGCA 105 . . . . . . . V 1.232 1995 Nov 14 6 5

M81 . . . . . . . . . . . . . . . I 1.257 1995 Nov 16 1 1

M81 . . . . . . . . . . . . . . . V 1.259 1995 Nov 16 1 1

8244 FWHM \ 1954 Ha (KPNO lter 1563,A, A), jc\6573 FWHM \ 67 and a continuum band adjacentA, A),to Ha (KPNO lter 1494, FWHM \ 84j

c\ 6658 A, A).

Through each broadband lter, sequences of ve or six 5minute exposures were taken. The shortness of the expo-sures was motivated by the need to minimize the number ofsaturated stars in the very crowded elds under study andto facilitate the removal of cosmic ray events. Because ofslight eld distortion, no dithering was done between suc-cessive images. To minimize lter positioning errors andimprove at-elding, we observed with only one broadbandlter per night. One or two Ha exposures, each of 1015minutes duration, were acquired for Dwingeloo 1, IC 342,Maei 1, Maei 2, and UGCA 92. In each case, an obser-

vation of equal duration was made through the continuumlter.3

A log of the observations is given in Table 2. In additionto the galaxies in the IC 342/Maei Group, we also madeshort (60 s) exposures of M81 in V and I to provide anexternal check on our surface photometry. Besides the usualcalibration images, jittered 10 minute exposures of ablank eld at relatively high Galactic latitude[a(1950) \ 01h42m15s, d(1950) \ 1407@41@@] were acquiredafter dark to facilitate at-elding. A total of six frames was

3 Results from the analysis of the Ha and continuum images will bepresented in detail in a separate paper.

acquired in Cousins I over two nights (November 12 and15), and three in V on one night (November 14). Scatteredmoonlight impacted some of our observations either as abackground gradient or as streaks. To minimize theproblem, we positioned the dome slit to prevent moonlightfrom directly falling on the front end of the telescope.

Reductions for each night were carried out using IRAF.4Bias corrections were made using an overscan zone 32columns wide in each image and a zero correction frame forthe night constructed from the combination of two sets of11 bias frames acquired at the beginning and end of thenight. The dark current was determined to be small andshowed no pattern, therefore no dark correction was made.

Considerable care was taken to ensure accurate at-

elding over the entire eld of the CCD. Dome at eldscould not be used because it was not possible to employexposures long enough to quench the shutter pattern whenusing the lighting system required to evenly illuminate thescreen. Instead, twilight images acquired at the beginning ofeach night (when the Moon was below the horizon) wereemployed to remove pixel-to-pixel variations in response.The individual twilight ats were combined using the IRAFtask FLATCOMBINE with the option CCDCLIP to

4 IRAF is distributed by the National Optical Astronomy Observa-tories, which is operated by the Association of Universities for Research inAstronomy, Inc., under contract to the National Science Foundation.

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remove eld stars. Although faint residuals of some of thesestars remained, their eect on the at-elded images wassmall.

All frames of the blank eld acquired through a givenlter were combined to create an illumination correctionimage relative to the twilight at suitable for removing low-frequency variations in response. In the process of checkingthe illumination correction by attening the individual darksky images, it was discovered that subtle large-scale pat-

terns were left that diered from image to image. Thesepatterns were seen in the I lter, but not in the V lter,suggesting that they were caused by spatial 0.8 km varia-tions in the airglow on scales less than For the three1.2.blank eld images obtained on 1995 November 15, theamplitude of these variations was typically 1% or less. Thecombined illumination image in I averaged out the varia-tions to an extent that our illumination correction imagewas not seriously compromised by them. Similarly, by com-bining up to ve or six images of each galaxy, variationslocal to the galaxy frames would have averaged out also,minimizing or eliminating their impact on our surfacephotometry.

It is difficult to assess the nal accuracy of our at-

elding for many of our sample galaxies because some eldsshow glowing foreground material and possibly variableextinction. Based on our analysis of the blank eld images,we estimate that our at-elding is good to better than0.5% for low-frequency features and much better than thisfor high-frequency features.

After attening, we combined the galaxy images in eachobserving sequence. This was performed using the IRAFtask IMCOMBINE with a rejection option to removecosmic rays and occasional satellite or meteor streaks. First,each image was shifted to the coordinate system of oneimage chosen to be the reference image. The IRAF taskIMALIGN was used for this purpose, using a le of starpositions on the reference image. Because skies were photo-

metric, each individual shifted image was scaled accordingto its air mass relative to the reference image in thesequence. Before combining, a zero level oset was removedfrom each image to make the background levels equal.Then, the oset for the reference image was added back tothe combined image. This procedure gave us a combinedimage with a cosmic signal and background level appropri-ate to a well-dened air mass. Galaxy images then werecleaned of all stars and artifacts (see 4). All surface photo-metry was performed on the combined and cleaned images.

Some of the I-band images of NGC 1560 and NGC 1569were compromised by thin clouds (easily visible in themoonlight). Before combining, the aected images werescaled to the unobscured ones using factors determinedfrom photometry of a common set of stars.

3.2. Observations and Reductions for B

Observations of IC 342, Maei 1, and Maei 2 wereobtained in B, V, and I with the Burrell-Schmidt on 1992October 26 (UT). The log is included in Table 2. Unfor-tunately, only the B-band images could be at-elded wellenough to be used for surface photometry. Imperfect repo-sitioning of the lter wheel compromised the images in VandI (a problem identied by NOAO sta after our 1992run, and then supposedly xed, but nevertheless the reasonwhy we chose to use only one lter per night during the1995 run). The same CCD setup was used as in 1995, except

for electronic improvements that came in the later run. Thepreprocessing of the images (bias correction, twilight at-elding) was basically the same as for the 1995 data, withthe dierence that no blank sky eld was observed toimprove at-elding. Also, only two frames of 10 and 15minutes each were obtained for IC 342 and Maei 2, respec-tively, so that cosmic ray removal was less automatic forthese galaxies. The B-band images are extremely useful forevaluating reddenings, especially for Maei 1 and 2.

3.3. Calibrations

Images were calibrated using observations of severalelds from Landolt (1992). Because of the large eld of viewof the Schmidt frames, we were able to use nearly everystandard star in each Landolt eld.

The Landolt elds were chosen to include the widestrange of V[I colors possible, because of the severereddening of many of the galaxies in our sample. The besteld for our purposes was Selected Area 110, where V[Iranges from 0.353 to 2.856. This range almost extends farenough to include Maei 1 and 2, for whichV[I+3.1.

On the best three of our six nights of 1995, we imaged

four dierent Landolt elds, each at least two times withdierent exposures to balance the brighter and fainter stars.One eld was observed at both high and low air mass toobtain accurate extinction coefficients. The range of airmass observed was 1.22.3.

Except for the V band on the night of November 16,natural magnitudes were measured with the IRAF taskPHOT using an aperture 14Ain diameter, the same as usedby Landolt (1992) for most of his photoelectric obser-vations. (An aperture of 18Awas used for the November 16V-band calibration owing to a slight focus error.) Since onlyone lter was used on most of the nights, we applied thePHOTCAL package in IRAF to arrive at the followingrelations:

v \ V] v0] v1(V[I)2 ] v2 x ] v3(V[I) , (1)

i \ I ] i0] i

1(V[I)2 ] i

2x ] i

3(V[I) , (2)

where V, I, and V[I are from Landolt (1992), v and i arethe natural magnitudes scaled to 1 s exposures, x is the airmass, and and are coefficientsv

0, v

1, v

2, v

3 i

0, i

1, i

2, i

3derived by least squares (see Stetson 1990). The results arelisted in Table 3.

On our best night, the standard deviation of the I-bandcalibration was 0.038 mag. For the V-band calibration, thebest night gave a standard deviation of 0.026 mag. Thelarger scatter in I may be attributable to the brighter skybackground. On other nights, when we obtained fewer stan-dards due to partial cloudiness, we used mean color coeffi-cients from the good nights and solved for zero points (andextinction coefficients if necessary).

As a check on how much light lay outside the adoptedaperture for photometry, we remeasured stars observed on1995 November 15 with a 20A aperture. The color coeffi-cients obtained were andi

1\ [0.0143 ^ 0.0050 i

3\

0.0118 ^ 0.0142, compared with i1

\ [0.0140 ^ 0.0042and for a 14A diameter aperture. Thei

3\ 0.0105 ^ 0.0117

results for the two apertures agree within the uncertainties,but mean errors for the 20Ameasurements are larger, prob-ably due to inclusion of faint companions and more skylight. If the color and extinction coefficients are xed at thevalues in Table 3, then the zero point for the 20Acalibration

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TABLE 3

STANDARD STARCALIBRATIONS

Number

UT Date PHOTCAL Solution rms of Stars

1992 Oct 26 ...... b \ B [ (18.6928 ^ 0.0161) [ (0.04406 ^ 0.00780)(B[V)2 ] (0.2893 ^ 0.0094)x ] (0.0595 ^ 0.0184)(B[V) 0.036 116

1995 Nov 11...... i \ I [ (19.4584 ^ 0.0099)[ (0.01545 ^ 0.00442)(V[I)2 ] (0.0476 ^ 0.0042)x ] (0.0157 ^ 0.0124)(V[I) 0.038 275

1995 Nov 12...... i \ I [ (19.4715 ^ 0.0036) [ 0.0147(V[I)2 ] 0.050x ] 0.0131(V[I) 0.051 155

1995 Nov 14...... v \ V[ (19.5780 ^ 0.0074) [ (0.00696 ^ 0.00278)(V[I)2 ] (0.1288 ^ 0.0038)x [ (0.0181 ^ 0.0076)(V[I) 0.026 304

1995 Nov 14...... v \ V[ (19.5772 ^ 0.0074)[ (0.00962 ^ 0.00396)(B[V)2 ] (0.1277 ^ 0.0040)x [ (0.0193 ^ 0.0088)(B[V) 0.026 304

1995 Nov 15...... i \ I [ (19.4615 ^ 0.0104)[ (0.01398 ^ 0.00416)(V[I)2 ] (0.0531 ^ 0.0050)x ] (0.0105 ^ 0.0117)(V[I) 0.041 272

1995 Nov 16...... v \ V[ (19.5847 ^ 0.0032) [ 0.007(V[I)2 ] 0.129x [ 0.018(V[I) 0.020 64

1995 Nov 16...... i \ I [ (19.4938 ^ 0.0250) [ (0.04985 ^ 0.02041)(V[I)2 ] 0.05x ] (0.0960 ^ 0.0471)(V[I) 0.034 64

changes to 19.4948, which is only 0.033 mag larger than for14A.

The calibration of the 1992 B-band observations was per-formed in a similar manner to the 1995 observations. Fourstandard star elds were observed (three of them the sameas in 1995) covering a wide range in color and air mass. To

FIG. 2.Comparison of simulated circular aperture photometry (mcalc

)with published photoelectric values in Longo & de Vaucouleurs (1983),Buta & McCall (1983), de Vaucouleurs & Longo (1988), and H. G. Corwin(1993, private communication). Magnitude dierences are plotted againstthe aperture diameter. The symbols refer to dierent galaxies as follows:vertical open triangles, IC 342; lled circles, Maei 1; crosses, NGC 1560;open circles, NGC 1569;pluses, UGCA 105;horizontal open triangles, M81.

determine B[Vcolors, it was necessary to compute a cali-bration formula for V for the night of 1995 November 14

withB[V as an independent variable (rather than V[I).The following relations were used:

b \ B ] b0

] b1

(B[V)2 ] b2

x ] b3

(B[V) , (3)

v \ V] v0

] v1

(B[V)2 ] v2

x ] v3

(B[V) . (4)

Even though separate observing runs are involved, it isperfectly feasible to combine these formulae since the stan-dard magnitudes, rather than the natural magnitudes, arethe independent variables. The resulting coefficients arelisted in Table 3. A test was made to determine if the B-bandcalibration formula required a second-order extinction cor-rection, but the term was found not to be signicant. Thestandard deviation of the B-band calibration was 0.036

mag.

3.4. External Checks

Photoelectric multiaperture photometry is available forve group members and M81 from Longo & de Vaucou-leurs (1983), Buta & McCall (1983), de Vaucouleurs &Longo (1988), and H. G. Corwin (1993, privatecommunication). Figure 2 compares simulated aperturephotometry of the galaxies in our images with the publishedphotoelectric results. The plots show the dierencesbetween the publishedB,V andI magnitudes and the fullytransformed magnitudes calculated from our CCD images

as a function of the aperture diameterA. It should be(mcalc

)noted that our magnitudes are derived from our cleanedimages (see 4), but observers who obtained the photoelec-tric photometry could only remove specic stars. Thus,comparisons for small apertures give the best idea of thequality of our zero-point determinations.

A numerical comparison of the magnitude dierences inall three lters is given in Table 4. For A 60@@, the meandierences inB and V are less than^0.05 mag, indicatingsatisfactory agreement. InI, there are no data for aperturesless than 60A in diameter available, but the two smallestapertures give a mean dierence of only 0.067 ^ 0.048 mag.For all three lters, a larger standard deviation results if allapertures are considered, due mainly to the imperfections offoreground star removal from large-aperture photoelectric

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40 BUTA & MCCALL

TABLE 4

COMPARISON OF PHOTOELECTRIC ANDCCD APERTUREPHOTOMETRY

Filter Aperture Range SPhotoelectric[ CCDT p1

N

(1) (2) (3) (4) (5)

B. . . . . . A 60@@ [0.043 0.086 11V . . . . . . A 60@@ 0.028 0.051 20I . . . . . . A 80@@ 0.067 0.067 2B. . . . . . All A [0.030 0.271 32

V . . . . . . All A 0.046 0.200 61I . . . . . . All A 0.159 0.145 12

NOTES.Col. (1): Name of lter. Col. (2): Range of aperture diametersused in photoelectric photometry, in arcseconds. Col. (3): Mean dierencebetween aperture magnitudes derived from photoelectric photometry andcorresponding aperture magnitudes derived from CCD photometry. Col. (4):Standard deviation of magnitude dierences. Col. (5): Number of photoelec-tric measurements.

photometry. This problem is particularly severe for Maei 1inB. We conclude that zero points for all three of our ltershave been determined to an accuracy of 0.05 mag or better.

4. CLEANING OF IMAGES

4.1. Overview

Because of the location of our sample galaxies close to theGalactic plane, and our sensitivity to cool and highlyreddened stars, the number of foreground stars on ourimages is extremely large (almost 100,000 on a few of theimages). In order to isolate isophotes and carry out accuratesurface photometry, it was essential to remove as many ofthese stars as possible. Fortunately, most stars could besubtracted by deriving prole parameters via crowded-eldphotometry. However, bright stars and their artifacts, suchas halos, diraction spikes, or saturation overows,required special attention. As well, in many of the images axed pattern of stripes was just visible above the sky, pre-

sumably due to some instability in the electronics. Toenable surface photometry down to the faintest possibleisophotes, this pattern also had to be removed.

A detailed ow chart showing the entire procedure forcleaning images is given in Figure 3. The stream of tasks isdisplayed by the connected square boxes on the left. Namesof the software tasks employed are capitalized. Input andoutput are specied by the rounded boxes on the right.Input to particular tasks is indicated by bold black arrows.Output from tasks is indicated by the wide grey arrows.Except for KILLALL, RMPAT, and GALPHOT, all tasksare a part of IRAF or the IRAF implementation ofDAOPHOT. Further details are given below.

After evaluating several dierent methods, we decided touse DAOPHOT (Stetson 1987, 1992) to t the stellar pro-les and subtract o the stars. Even though the proles wereundersampled, experiments showed that DAOPHOT couldadeptly remove fainter stars, despite the severe crowding.Noticeable residuals remained in the cores of the brightestunsaturated stars, but they could be eradicated quickly andaccurately through noninteractive editing.

Unfortunately, the IRAF implementation of DAOPHOTwas incapable of handling more than 50,000 stars at a time,or more than 100 stars in a group at a time. AlthoughALLSTAR (but not NSTAR) could deal with the group sizelimit through dynamic grouping, to handle the total starlimit it was necessary to break images into more manage-

able pieces and then put them back together once stars wereremoved.

Also, when this project was begun, DAOPHOT couldnot t properly a crowded eld of stars on a variable back-ground, such as that presented by an unresolved galaxy. In

our elds, groups were so large in extent relative to thegalaxies that the sky changed signicantly across them.Yet, DAOPHOT tted all stars in a group using the samebackground level. In response to our concerns, L. Davis(NOAO 1993, private communication) implemented a criti-cal change which enabled the sky to be dened for individ-ual stars, thus making possible good ts on a variablebackground. In addition, after a rst run of DAOPHOT(specically, the DAOPHOT tasks DAOFIND andALLSTAR), we attened the background as much as pos-sible by subtracting from the original image a median-smoothed version of the star-free galaxy image. Then,nding, tting, and subtracting were repeated.

An IRAF script was created to handle all aspects of

stellar photometry, including subdividing the image, ndingthe stars, carrying out initial photometry, attening thebackground, tting the stars, subtracting the stars, andreassembling the star-subtracted subsections. This wascalled KILLALL. The procedure for removing stars fromany given subsection is illustrated in the ow chart inFigure 4. Tasks are identied in square boxes, and decisionsare marked by the diamonds. Input and output are speciedin rounded boxes. The ow of logic is displayed by thinblack arrows. Input to specic tasks is indicated by boldblack arrows. Output from a task is indicated by a thickgrey arrow. Everywhere, names of employed software tasksare capitalized. All tasks are a part of IRAF or the IRAFimplementation of DAOPHOT.

What follows is a brief verbal summary of the steps takento clean the images. Details regarding key aspects of theprocess are given in subsections below.

For any particular image, cleaning began with a run ofKILLALL. The image was subdivided into 512]512 sub-sections, each with a border 40 pixels wide. For each sub-section, stars were identied with DAOFIND using a 5 pdetection threshold. Next, the stars were tted withALLSTAR using a xed analytical psf (Moat25), and thensubtracted from the original image. Four passes throughDAOFIND and ALLSTAR were necessary, the rst toenable subtraction of the galaxy, and the next three to singleout as many stars as possible, especially in blends. The rst

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FIG. 3.Flow chart illustrating how images were cleaned of stars and blemishes

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FIG. 4.Flow chart illustrating in detail how stars were removed from the images

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IC 342/MAFFEI GROUP REVEALED 43

version of a star-free image of the galaxy was created byreassembling the star-subtracted subsections, and a mastercatalog of stars was created by appending catalogs for eachsubsection. A galaxy-free image of the eld was created bymedian-ltering the star-free image, and subtracting it fromthe original image. Using PSELECT, stars within a specicmagnitude range were identied as being the most suitablefor determining an improved psf. The psf stars (as many as ahundred) were isolated by using SUBSTAR to subtract o

all but the psf stars from the original image. Then, an accu-rate variable psf was derived. All stars on the galaxy-freeimage appearing in the master catalog were then rettedsubsection by subsection using the revised psf. The secondversion of a star-free image of the galaxy was created byreassembling the improved star-subtracted subsections.

The resulting star-free image retained many blemishes, sofurther processing was necessary. Besides being summarizedin Figure 3, the steps are illustrated with six images of Cas 1in Figure 5 (all displayed using linear, as against logarith-mic, units for surface brightness). Residuals for the brighterunsaturated stars, called spots, were eliminated throughnoninteractive editing. Then, a faint residual pattern ofhorizontal stripes was removed by a process involving

median ltering. The detection threshold specied for therst run of KILLALL was so high that many faint stars still peppered the image. These were removed by passing allof the cleaned subsections through KILLALL, but with thedetection threshold reduced to 3 p. Remaining blemisheswere either masked or edited by hand.

Although resolved structures generally survived thecleaning process intact, for a few galaxies, such as IC 342,unresolved components of OB associations were sometimesremoved. Sharp nuclei, such as those of Maei 1 and Maei2, also were tted and subtracted. Wherever any suchproblem was recognizable, the missing component wasadded back to the cleaned image using the parameters ofthe t listed in ALLSTARs star catalog. However, the fore-

ground star problem was so severe that it is almost certainthat some removed components could not be agged.Nevertheless, it is felt that the accuracy of global photo-metry would not be impaired signicantly, as the amount oflight lost from subtracted features would have been a tinyfraction of that from a whole galaxy.

4.2. PSF Determination

Critical to the star removal was accurate modeling of thepoint spread function (psf). We used the DAOPHOT taskPSF for this purpose, initially following the Guide toComputing a PSF in a Crowded Field provided in thehelp package for this task. The psf determination involvedtwo main steps: (1) determining an initial constant PSFfrom a few stars to be used for an initial run of cleaning; and(2) determining the nal variable psf from 40 or more starsacross the whole eld of an image.

Because of the large pixel size the psf was under-(2A.03),sampled on the Schmidt images; the FWHM of stellar pro-les averaged only about 2 pixels over most of the images.The option auto in DAOPARS was used to determinethe best analytic function to employ. After considerabletesting, we adopted the three-parameter Moat25 func-tion, which is described in detail in the help package forDAOPARS. Using IMEXAMINE, the critical psf radius(PSFRAD) was determined to be 8 pixels for the brightestunsaturated stars. The tting radius (FITRAD) was taken

to be 3 pixels and the matching radius (MATCHRAD) 2pixels. The sky annulus was adopted to have an inner radiusof 8 pixels and a width of 8 pixels.

For initial ts, a constant psf was determined from theI-band image of Maei 1 obtained on 1995 November 15.This was done in two steps using six stars concentratedaround the center of the eld. Each of the six stars was freeof contamination within the tting radius, but had faintcompanions within the psf radius. These faint companions

were not always found in an initial run of DAOFIND, sohad to be added by hand to the PSF input le. In the rststep, the six stars were used with companions to get aninitial estimate for the psf. Then, the faint companions weretted with this psf and subtracted o. In the second step, thesix cleaned stars were used to improve the psf. The resultwas called bestpsf.

Initial attempts at star removal using bestpsf revealedthat the psf varied subtly from galaxy to galaxy. Further-more, residuals were enhanced in the corners of the images,revealing that the psf varied across the CCD. Thus, toimprove star removal, it was necessary to t each imageusing a variable psf tailored to that image.

It was determined that bestpsf was suitable as an

initial psf for all of the images, including theV-band images.For a given image, KILLALL was used rst with bestpsf to compile a master catalog of foreground stars. Then, usingPSELECT, a set of bright candidate psf stars in a limitedmagnitude range was pinpointed ( natural magnituderange [12.0 to [13.5 for the uniform 300 s exposuresobtained). The output le from PSELECT was used in theDAOPHOT task SUBSTAR as an exclusionary le (exle).SUBSTAR was used to subtract all of the stars found byKILLALL except the candidate psf stars. Then, the taskPSF was applied interactively to the output image fromSUBSTAR. Each candidate star was inspected on the imageand on a grid map. The procedure usually left sufficientnumbers of stars all across the eld to map the psf to second

order (VARORDER \ 2 in DAOPARS). With theimproved psf, KILLALL was applied to the original imageagain to ret and subtract all of the stars in the mastercatalog.

4.3. De-Spotting

Using KILLALL with a variable psf left each galaxyimage largely devoid of foreground stars but with manycosmetic defects. One problem was that bright unsaturatedstars left small patches of residuals, called spots, about34 pixels in radius (see Fig. 5b). These were a consequenceof undersampling. The process of eliminating them isreferred to as de-spotting.

Noticeable spots remained only for stars brighter than aspecic magnitude and could be easily pinpointed from themaster catalog of KILLALL using PSELECT. To removethe spots in an image, we used the IRAF task IMEDITnoninteractively with an input le containing the locationsof all of the spots. Each spot was eliminated by inter-polating a plane tted to pixels in an annulus 2 pixels widearound the spot. Appropriate noise was added to the inter-polations using a measurement of the noise in the image.

The de-spotted image of Cas 1 is shown in Figure 5c.De-spotting eliminated the vast majority of spots very well.However, it occasionally created new, bigger spots, if twooriginal spots were close together or if there were somethingsubstantial in the IMEDIT annulus that contaminated the

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FIG. 5.Steps in the cleaning of Cas 1: (a) the initial image with foreground stars; (b) image arising from a full run of KILLALL with a 5 p detectionthreshold and variable psf, showing residual spots and faint stripes; (c) de-spotted image created after running IMEDIT in noninteractive mode; ( d)de-striped image created by RMPAT; (e) de-peppered image created after running KILLALL again, but with a 3 pdetection threshold; (f) nal image usedfor surface photometry created after interactive editing and masking.

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interpolation. These were later removed interactively usingIMEDIT.

4.4. De-Striping

After star removal, very faint horizontal stripes wererevealed in the I-band images, especially of the fainter gal-axies in our sample. Stripes are barely visible crossingdirectly through the image of Cas 1 in Figures 5b and 5c.The amplitude of the stripes was typically 0.1% of the sky in

I. None of the V-band images showed the stripes. Theprecise alignment with the rows and the correlation with thesignal suggests that the origin was a signal-dependent insta-bility in the CCD electronics. The process of eliminating thestripes is referred to as de-striping.

To remove the stripes from theI-band images, we createda special routine outside of IRAF, called RMPAT, whichextracted and subtracted the pattern. Each de-spottedimage was boxcar smoothed with a window large enough tomedian out the stripes. The inuence of stars was removedby rejecting deviant pixels. The resulting at image wassubtracted from the original, exposing the true amplitude ofthe stripes with respect to sky. Then, a single column vectordescribing the variations in the background signal from row

to row was created by computing the median of all of thepixels in each row. This vector was then subtracted fromevery column of the original de-spotted image.

The de-striped image of Cas 1 is shown in Figure 5d. Theprocedure was successful in reducing the amplitude of thestripes to a level below the sky noise.

4.5. De-Peppering

Although KILLALL removed most of the foregroundstars from an image, large numbers of very faint stars (noteasily seen on the uncleaned images) still peppered theeld. These stars had been missed because the ndingthreshold (in FINDPARS) had been set to 5p, wherepis anestimate of the background noise level (SIGMA in

DATAPARS). The problem can be seen in the image of Cas1 displayed in Figure 5d. The process of removing remain-ing foreground stars is referred to as de-peppering.

To eliminate the faintest stars, each cleaned image waspassed through KILLALL, with the nding thresholdreduced to 3 p. Unfortunately, this procedure sometimeseliminated features intrinsic to the galaxies, such as in thecase of Maei 2, NGC 1560, NGC 1569, and UGCA 105.Subtracted galaxy features were restored using theDAOPHOT task ADDSTAR. Images of IC 342 could notbe de-peppered, because signicant quantities of light wereremoved from the patchy spiral arms, even in the I band.For this galaxy, the pepper was left as part of the sky level.The de-peppered image of Cas 1 is shown in Figure 5e.

4.6. Editing and Masking

Although KILLALL removed most of the contaminatingforeground stars, and de-spotting removed any residuals,there were usually still hundreds of remaining features oneach processed image. These took the form of saturatedstars, halos of these stars, spikes, enlarged spots fromIMEDIT de-spotting, and foreground Galactic material.The nal cleaning phases involved both interactive andnoninteractive runs of IMEDIT in which remaining arti-facts were either replaced or masked.

Features not much larger than about 10 pixels in radiuscould be reliably replaced. This was accomplished by inter-

polating a plane. However, some extremely bright starsshowed artifacts extending from 15 to 75 pixels from theircenters. If such features were superimposed on the galaxy,interpolation would not necessarily work. Instead, theywere masked. We set VALUE in IMEDIT to a xed largenumber (greater than any of the actual intensities in theimage). Both circular and rectangular masks were used asneeded. The surface photometry package we employed (see6.2) was able to ag and ignore masked areas.

5. ATLAS OF GROUP MEMBERS

Our KPNO Burrell-Schmidt images are the deepest everobtained of the members of the IC 342/Maei Group. Also,none of the galaxies have been seen ever before withoutforeground stars superimposed. Given these facts, we felt itwas appropriate to present images for all of the galaxiesbefore and after cleaning. These are displayed in alphabeti-cal order in Figures 622. Most are in the I band. Also,most are logarithmic, having been converted to units of magarcsec~2. The exceptions are Figures 10 (left) and 12, whichshow surface brightnesses in linear units. Comments oneach galaxy are given in 7 below.

Caution must be exercised in interpreting the cleaned

images. Some features are artifacts of the cleaning process.The artifacts are sometimes obvious, as in the cleaned imageof IC 342, but sometimes are not. Also, although we tried torestore stellar associations removed by the cleaning process,some may still be missing. The best way to use the cleanedimages is to refer to the uncleaned images to establish thereliability of small details. The cleaned images are best forshowing large-scale structures.

6. SURFACE PHOTOMETRY

6.1. Overview

For each galaxy, surface photometry was performed onthe cleaned images, both V and I. First, free ellipses weretted to the observed isophotes in order to examine theradial variations in shape and orientation and to determinethe center, inclination, and photometric major axis positionangle of the galaxy. Second, xed ellipses with the center,shape, and orientation of the galaxy (as determined from theanalysis of the free ellipses) were tted to determine surfacebrightness proles, length scales, and total magnitudes andcolor indices.

6.2. Fits of Free Ellipses and the Derivation ofOrientation Parameters

6.2.1. Software

How the shape and orientation of isophotes vary withradius conveys information about the intrinsic geometry ofa galaxy. Such information is particularly important forgalaxies in the IC 342/Maei Group, because numerousauthors have expressed a view that there have been tidalinteractions among members.

For each galaxy in our sample, the shape and orientationof isophotes were derived using the GALPHOT package,which was developed within the IRAF framework byW. Freudling of the European Southern Observatory.GALPHOT provides a modied version of the ellipse-tting algorithm of Jedrzejewski (1987). Jedrzejewskismethod was originally developed for ellipticals, which havemonotonically declining brightness proles, but Freudlingsmodications make possible studies of less regular galaxytypes.

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FIG.6.

I-bandimagesofCas1:(left)original;(right)cleaned.Onthisandallrem

ainingatlasimages,northisatthetopandeastistotheleft.Imageshavebeensky-subtractedandconvertedtounitsof

magarcsec~2.Thescalebaratlowerleftintheleftpanelis1@inlength.

46

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FIG.7.I-bandimagesofDwingeloo1:(left)original;(right)cleaned.Thescalebaratlowerleftintheleftpanelis5@inlength.

47

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FIG.8.I-bandimagesofDwingeloo2:(left)original;(right)cleaned.Thescalebaratlowerleftintheleftpanelis1@inlength.

48

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FIG.9.

I-bandimagesofIC342:(left)or

iginal;(right)cleaned.Thescalebaratlowerleftintheleftpanelis3@

inlength.

49

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FIG.10.(Left)DeepnegativeprintofthecleanedI-bandimageofIC342,show

ingglowingforegroundmaterialtotheeasto

fthegalaxyandpossibleevidenceforatidal

interactiontothesouthwest.

Thecircularspotsrepresentmaskedregionsthatwerereplacedwithzerointensityby

programSPHOT,butforwhichthemeansurroundingskylevelwasdierentfromzero.Thescalebaratlowerleftis10@

inlength.(

Right)V[

Icolorindexmap

ofIC342.Colorsrangefrom0.6to2.6,withb

luerfeaturesdarkandredderfeatureslight.Thescaleofthisimageisthesameasofthosein

Fig.9.

50

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FIG.11.

I-bandimagesofMaei1:(left)original;(right)cleaned.Thescalebaratlower

leftintheleftpanelis3@inlength.

51

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FIG.12.I-bandimagesoftheinner

regionofMaei1showingtheresidualsoftheobservedlightdistributionab

outamodelconstructedfromtsoffreeellip

sestothecleanedimage.The

[email protected]]

[email protected]

dierenceimageintheleftpanelincludestheforegroundstars,whiletheoneatrightisbasedonthecleanedimage.Darkareasareregionsofnegativeresidualsandareprobably

causedbydust.

52

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FIG.13.

I-bandimagesofMaei2:(left)original;(right)cleaned.Thescalebaratlower

leftintheleftpanelis5@inlength.

53

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FIG. 14.Deep negative prints of cleaned images of Maei 1 (top two panels) and Maei 2 (bottom two panels) showing low surface brightness isophotes intwo passbands. Images inBare on the left, and images in Iare on the right. Note especially the complex foreground nebulosity to the north and east of Maei1 seen in theI band. The eld shown for Maei 1 is square, and that for Maei 2 is square. The nuclei of both galaxies are exactly centered in [email protected] [email protected], in order to highlight the apparent asymmetryin the outerI-band isophotes of Maei 1 and the symmetryof the outerI-band isophotes of Maei 2, ascompared to the inner regions. Maei 1s companion galaxy MB 1 can be seen below and right of the center in the upper right panel. A bright foreground staris seen near the top of theB-band image of Maei 2; this star has been removed from theI-band image. Some artifacts of cleaning also are visible in bothimages of Maei 1.

54

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FIG.15.

I-bandimagesofMB1:(left)original;(right)cleaned.Thescalebaratlowerleftintheleftpanelis2@

inlength.

55

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FIG.16.


inlength.

56

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FIG.17.


inlength.

57

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FIG.18.

I-bandimagesofNGC1560:(left)original;(right)cleaned.Thescalebaratlowe

rleftintheleftpanelis3@inlength.

58

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FIG.19.

I-bandimagesofNGC1569:(left)original;(right)cleaned.Thescalebaratlowe


59

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FIG.20.I-bandimagesofUGCA86:(left)

original;(right)cleaned.Thescalebaratlowe


60

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FIG.21.I-bandimagesofUGCA92:(left)

original;(right)cleaned.Thescalebaratlowe


61

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FIG.22.

I-bandimagesofUGCA105:(left)original;(right)cleaned.Thescalebaratlowerleftintheleftpanelis2@

inlength.

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6.2.2. Sky Subtraction

The GALPHOT task SKYSUB was used to determinethe sky level appropriate to the eld of each galaxy. InSKYSUB, a display of the image and a cursor allow speci-cation of the corners of boxes sampling the sky at locationsall over the eld. Once satisfactory sky samples were deter-mined, they were tted with a horizontal plane. AlthoughSKYSUB uses the IRAF task IMSURFIT to t the nalsky level, and in principle can t a more complicated surface

(such as a tilted plane), it proved to be impractical, and, wefeel, unnecessary, to t other than a constant sky level inmost cases. The sky boxes used were uniformly distributedaround a given galaxy in a pattern resembling its shape. Wenormally used 3050 such boxes, depending on the angularsize of the galaxy. Boxes were dispersed among maskedregions where necessary. Care was taken not to place theboxes unnecessarily far from any galaxy, because manyelds were contaminated in places with foreground nebu-losity of low surface brightness. We generally placed theboxes at about twice the radius of the very faintest isophotewe could see on the image display.

SKYSUB could be used in a practical manner for all ofthe galaxies in our sample except Maei 1. The backgroundaround Maei 1 includes obvious foreground nebulositycovering a large area. For this eld, we estimated the skylevel using the IRAF tasks FITSKYPARS and PHOT. Thesky level was estimated for both the V andI images as themode of pixel values within a circular annulus having aninner radius of 550 pixels (1115A) and a width of 100 pixels(203A).

6.2.3. Fitting of Ellipses

The tting of free ellipses required the GALPHOT tasksMARKGAL, SPHOT, and ELLIPSE. With MARKGAL,we interactively chose points on an initial ellipse to be usedas the starting guess for the main ellipse-tting task,ELLIPSE. The starting ellipse was usually selected to lie in

a zone of intermediate surface brightness, because the bestt would be used as the initial guess for zones at bothsmaller and larger radii. In the case of a spiral with a lot ofstructure, ELLIPSE failed to nd the nucleus if we startedtoo far out. For IC 342, for example, we had to start theellipse tting close to the center inside the main spiral arms.

Each isophote was tted by Fourier analyzing the devi-ations from an ellipse at a given prechosen radius and iter-atively determining the best-tting center, axis ratio, andmajor axis position angle (see Jedrzejewski 1987). The pre-chosen radii were stepped both inward and outward fromthe starting radius (dened by MARKGAL) by a uniformscale factor of 1.1.

We note that miscentering of the outer isophotes was notuncommon in our sample galaxies and was particularlyprominent for Maei 1 and IC 342. The latter galaxy showsobvious tidal distortion at large radii. We are uncertainwhether the miscentering of Maei 1s isophotes is real ordue to foreground star or glowing dust complications.

The task SPHOT allowed specication of masks, i.e.,regions which would not be used in the iterations for thebest-tting ellipses. A preliminary zero point for each imagealso was specied at this stage (the full calibration formulaein Table 3 could not be used yet, because SPHOT andELLIPSE operate on only one image at a time). It wascomputed using the known air mass for each image, a roughestimate of the V[I color index of the galaxy, the solidangle subtended by each pixel, and the exposure time.

ELLIPSE tted outward from the MARKGAL position,and then inward. Outward, it normally stopped when theisophote intensity was less than 10 ADU, i.e., once the noisebecame sufficiently high compared to the signal that tsbecame unstable. If it could not make a reliable t withinthe specied number of allowed iterations (usually 100), itwould use the parameters from the previous best-ttingellipse and compute the average surface brightness alongthat ellipse for the given radius. The GALPHOT task

PLOTELL was used to interactively examine how well thetted ellipses matched the appearance of the galaxy.

The output of SPHOT is a table of tted parameters anda clean image where any masks present have been inter-polated over using the best-tting ellipses. These clean images were used for the nal surface photometry. Toimprove the appearance of replaced masks in the periph-eries of some of the disk galaxies in our sample, we used theGALPHOT task TOTMAG, which exponentially extrapo-lated tted proles down to a specied surface brightnesslevel or specied radius using the mean position angle andellipticity of several outer isophotes. Points used to denethe extrapolations were determined interactively using theGALPHOT task MARKDISK.

6.2.4. Axis Ratios and Position Angles

Plots of the axis ratio q and the photometric major axisposition angle / as a function of the length of the semimajoraxis are displayed for each sample galaxy in Figure 23.Position angles, which are for epoch 1950, were determinedusing local positional standards. For I-band images, starsfrom the STScI Guide Star Catalog were employed. Devi-ations from the equatorial system amounted to 3 to 4.Several V -band images were analyzed in the same mannerand determined to require the same corrections as theI-band images.

Note that some points in the plots are not independent ofother points because, as noted above, if ELLIPSE failed toconverge to a t of an isophote after a specied number ofiterations, it adopted the derived center, shape, or orienta-tion of the isophote previously tted and simply solved forthe surface brightness alone or the remaining parameters.The orientation parameters which we believe to be mostreective of the true orientation of each galaxy in space arelisted in Table 5. Except for Maei 1, these were determinedby averaging the values of q and / derived for the outerisophotes. For Maei 1, the axis ratios and position angleswere averaged over all radii. For Maei 1, Maei 2,Dwingeloo 1, Dwingeloo 2, MB 1, MB 2, and MB 3, theaverages are based upon surface photometry in the I bandonly, because theVband suers serious extinction. For theremaining sample galaxies, the averages are based on ellipsets in bothV andI.

Five galaxies in the IC 342/Maei Group have beeninterferometrically mapped at 21 cm. Fits to the velocityelds have provided estimates of the kinematic inclinationand the position angle of the kinematic line of nodes. Theyare summarized in Table 6. For direct comparison, the incli-nations and position angles resulting from our photometricstudy inI are included. Photometric inclinations have beencomputed fromSqT and an adopted intrinsic axis ratio q

0(i.e., the axis ratio fori \ 90) using (Hubble 1926)

cos2 i \SqT2 [ q

02

1 [ q02

. (5)

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FIG. 23.Orientation of isophotes as a function of the length of the semimajor axis, based upon ts of free ellipses. The parameterqis the minor-to-majoraxis ratio, while / is the major axis position angle corrected to 1950. For most galaxies, lled circles refer to I, while open circles refer to V. However, forMaei 1, MB 1, and MB 2, lled circles refer to the rst I-band image (image 1) and open circles refer to the second (image 2) (see Table 2). For Maei 1,crosses refer to theV-band image, and for UGCA 92, open circles refer to the rst V-band image (image 1), and crosses refer to the second (image 2) (see Table2). Only theI-band ts are shown for Dwingeloo 1, Dwingeloo 2, Maei 2, and MB 3.

For all of the disk galaxies in the sample, the intrinsic axisratio was assumed to be 0.2. This value is often assumed instudies involving the Tully-Fisher relation (Aaronson,Mould, & Huchra 1980). The additive correction of]3advocated by Aaronson, Mould, & Huchra (1980) was notapplied because each photometric axis ratio is based on anaverage over a range of surface brightnesses in the outerparts of a galaxy, rather than on a single isophote(Schommer et al. 1993).

6.3. Fits of Fixed Ellipses and the Derivation of GlobalPhotometric Parameters

6.3.1. Software

The principal objective of our study has been to measureaccurate total magnitudes and color indices of each galaxyin the IC 342/Maei Group. One way of deriving a totalmagnitude is to use TOTMAG to extrapolate the surfacebrightness prole constructed from the free ellipses tted byGALPHOT. However, the extrapolation can be large,

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FIG. 23.Continued

because the number of degrees of freedom of tted ellipses isso great that the range of radius over which ts convergemay be signicantly less than the range over which thegalaxy is detected. A prole constructed from ts of ellipseswith a xed center, shape, and orientation, which gives whatwe will call the elliptically averagedsurface brightness as afunction of radius, is capable of being extended to largerradii. A superior total magnitude can be derived from sucha prole, because less of an extrapolation is required. It isadvantageous, too, that xed ellipses can be constrained tobe centered on the nucleus, whereas free ellipses tting outerisophotes may be signicantly miscentered.

Since the GALPHOT version of ELLIPSE was notdesigned to integrate uxes within xed ellipses, we usedour own software, NEWFOURAN, for this purpose. Foreach galaxy, NEWFOURAN, which also does Fourier

analyses of the intensity distribution, was used to computeelliptically averaged surface brightness proles from thecleaned and already sky-subtracted images by averaging theintensities within elliptical annuli having a common centerand a shape and orientation constrained by the GALPHOTresults. If a clear nucleus were present in a galaxy, it waschosen as the center of all ellipses. If not, the average of thecenters of the outer isophotes derived by ELLIPSE wasadopted. Intensity averages were carried out in annuli 4Ato10Ain width (called the STEP), depending on the size of thegalaxy. Within a given annulus, allowance was made forpartial pixels by dividing pixels near the boundaries into 25subpixels and computing a weight.

6.3.2. Surface Brightness and Color Index Proles

For each galaxy, the nal, fully transformed elliptically

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FIG. 23.Continued

averaged (i.e., xed-ellipse average) surface brightnesses kV

and and the surface color index are plottedkI

kV[ kI

against radius a in Figure 24. For IC 342, Maei 1, andMaei 2, the elliptically averaged proles inBand theB[Vcolor index prole are shown, too. The radius refers to thelength of the semimajor axis of the ellipse which divides thearea of the elliptical averaging annulus into two equal parts.Proles are listed in Tables 7 and 8. For comparison, Table9 gives the transformed proles of Maei 1 derived bytting free ellipses.

To accomplish transformations, we rst solved quadrati-cally for using the appropriate relations from Tablek

V[ k

I3. Then, surface brightnesses could be derived after allowingfor the integration time and pixel area. Note thatk

V[ k

I

was sometimes very noisy at large radii, especially for thosegalaxies suering the largest amount of extinction. In suchcases, it was deemed prudent to compute using the meank

Iof for several inner points. In the tables (specically,k

V[ k

ITables 7 and 9), adopted colors are noted by parentheses.

In each table, the surface brightness and color at thecenter of each galaxy (a \ 0@@) are provided. The estimatescan be fairly precise if a denite nucleus is present, but formost galaxies they are simply an interpolation of the inten-sity array at the adopted center.

6.3.3. T otal Magnitudes and Color Indices

For each galaxy except Maei 1, the total magnitude wasderived by tting an exponential to the outer points of the

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FIG. 23.Continued

elliptically averaged (i.e., xed-ellipse average) prole, andthen extrapolating the t to innity. In all of these cases, it

was possible to dene an outer zone ranging in radius fromto where and declined with radius according toa

1 a

2, k

I k

V

k \ A ] Ba . (6)

The magnitude within an ellipse with semimajorm(am

)axis was computed by outwardly inte-a

m\ a

2] STEP/2

grating the ux within the xed elliptical annuli. Integratedmagnitudes were fully transformed in the same manner asthe surface brightnesses, i.e., by computing V[I rst andthenV andI. Finally, the extrapolated total magnitude m

Twas derived by computing

mT

\ [ 2.5 log (10~0.4m(am) ] *F) , (7)

where

*F \ 2nqPam=I(a)ada \ 2nq10~0.4(A`Bam)A amCB ] 1C2B2B ,

(8)

and whereI(a) \ 10~0.4(A`Ba),qis the mean axis ratio of theouter disk from Table 5, andC \ 0.4ln10.

Maei 1 does not have an exponential prole, so a dier-ent technique had to be used to estimate the total magni-tude. We determined that the elliptically averaged prolewas a reasonable prole to use for photometry, despite thefact that the outer isophotes are not centered on thenucleus. A de Vaucouleursr1@4law, dened by

k \ A ] Ba1@4 (9)

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FIG. 24.Elliptically averaged surface brightness and color index proles. In all cases, the mean intensity around an ellipse with a xed center, axis ratio,and position angle is plotted against the length of the semimajor axis of the ellipse. The mean is expressed in units of mag arcsec~2, The orientationparameters adopted for each galaxy are listed in Table 5. For IC 342, Maei 1, and Maei 2, ve proles are shown: and For thek

B,k

V,k

I,k

B[ k

V, k

V[ k

I.

remaining galaxies, three proles are shown: and Dashed or solid lines in each case show extrapolations used to get total magnitudes.kV

,kI, k

V[ k

I.

was tted over the range to Then, the extrapolateda1

a2

.total magnitude was derived from equation (7) withm

T

*F \ 2nqPam

=I(a)ada \ 8nq

10~0.4(A`Bam1@4)(CB)8

;l/0

7 (7!)y7~l

(7 [l) ! ,

(10)

where andqandCare asy \ CBam1@4,I(a) \ 10~0.4(A`Ba1@4),

before.For some of the disk galaxies, the value of the slope B in

theVband was xed to be the same as that determined forthe I band, because the outer parts of the proles were

generally better determined in I than in V. Also, few gal-axies showed a signicant radial trend in at largek

V[ k

Iradii.

Total magnitudes and colors derived for each galaxy arecompiled in Table 5. Also included in this table are esti-mates of uncertainties. Each has been estimated by propa-gating the errors associated with the calibration (see Table3), the adopted axis ratio and position angle, the scatter ofthe surface brightnesses around the t used for extrapo-lation, photon counting statistics, and the determination ofthe sky brightness. For each lter, the eect of uncertaintyin the sky level was estimated via repeated trials of the

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FIG. 24.Continued

angles. At each radius, a surface brightness was derived viabilinear interpolation. To improve the signal-to-noise ratioat large radii, the program averaged intensities along anelliptical contour having the shape and orientation given inTable 5 and within a cone having a half angle of 5.

The extracted proles are illustrated in Figures 25through 36. For two galaxies (Maei 1 and NGC 1569), theproles have been folded to improve precision. For theunfolded proles, the dierent sections are labeled by direc-tion (NE, northeast; SW, southwest, etc.). The adoptedmajor axis position angles are those listed in Table 5, andthe minor axis position angles are displaced by 90 fromthese.

For each galaxy in our sample, we measured values of the

eective radiusand eective surface brightness of the spher-oid and/or disk along one or more axes by tting the majorand/or minor axis proles directly, or by tting the ellip-tically averaged prole and then checking the results bysuperimposing the t upon the major and minor axis pro-les. Spheroidal components were modeled with a de Vau-couleurs r1@4 law, and disks were modeled with anexponential. The eective radius or and eectivea

esph b

esph

surface brightness of the spheroid and the eectivekesph

radius or and eective surface brightness ofaedisk b

edisk k

edisk

the disk were derived simultaneously by nonlinear leastsquares. Each eective radius refers to the length of thesemimajor axis or semiminor axis of the isophote(a

e) (b

e)

encompassing half the total ux of the model (r1@4 law or

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72 BUTA & MCCALL

FIG. 24.Continued

exponential), and the eective surface brightness is the radi-ance of that isophote. Results are summarized in Tables 10,11, and 12, and discussed galaxy by galaxy in 7.

6.5. Standard Photometric Parameters in B

Because we haveB-band data for Maei 1, Maei 2, andIC 342, it is possible to measure fundamental parameters forthese galaxies which are linked to the standard isophote,namely where the surface brightness is magk

B\ 25.00

arcsec~2(see de Vaucouleurs et al. 1991). These include theisophotal diameter and the axis ratio Also, it isD

25 R

25.

possible to derive eective apertures and eective colors inthe standard system and to compare them with resultsbased upon our data in V and I. Table 13 gives the mea-surements. A brief description of each parameter is given in

a footnote to the table.The isophotal diameter and major/minor axis ratioD

25were derived from a least squares t to the standardR25isophote of an ellipse centered on the nucleus. Results forMaei 1 and Maei 2 are severely aected by extinction.Even for IC 342, the standard isophote is within that part ofthe galaxy where the arms are bright, so the parameters areuncertain.

The eective aperture, is the diameter of a circularAe,

aperture transmitting half the total ux, normally in B. InTable 13, measurements are listed for B, V , and I. Alsoincluded for each lter is a measurement of the length of themajor axis, of the elliptical aperture transmitting halfD

e,

the total ux. For all three galaxies, the eective aperturedecreases fromB to I. This indicates the presence of signi-

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TABLE 7

I ANDV[I PROFILES OF ALLSAMPLE GALAXIESDERIVED BYFITTINGFIXEDELLIPSESa

a kI

kV

[ kI

a kI

kV

[ kI

a kI

kV

[ kI

a kI

kV

[ kI

Cassiopeia 1

0.00 . . . . . . . 22.49 2.12 46.04 22.86 1.81 94.02 24.04 2.02 142.01 25.31 2.38

2.83 . . . . . . . 22.63 1.93 50.04 22.95 1.80 98.02 24.18 2.11 146.01 25.59 2.42

6.32 . . . . . . . 22.64 1.81 54.04 23.01 1.82 102.02 24.31 2.09 150.01 25.85 1.71

10.20 .. . . . . 22.59 1.84 58.03 23.12 1.86 106.02 24.39 2.13 154.01 25.95 2.2414.14 .. . . . . 22.66 1.84 62.03 23.19 1.93 110.02 24.43 2.18 158.01 26.15 2.03

18.11 .. . . . . 22.66 1.85 66.03 23.29 1.98 114.02 24.63 2.17 162.01 26.24 2.18

22.09 .. . . . . 22.66 1.84 70.03 23.42 1.97 118.02 24.69 2.23 166.01 26.25 2.60

26.08 . . . . . . 22.69 1.83 74.03 23.50 1.99 122.02 24.93 2.41 170.01 26.23 (2.24)

30.07 .. . . . . 22.68 1.89 78.03 23.62 2.05 126.02 25.02 2.23 174.01 26.91 2.35

34.06 .. . . . . 22.73 1.85 82.02 23.74 2.01 130.01 25.08 2.21 178.01 26.74 2.07

38.05 . . . . . . 22.74 1.83 86.02 23.84 1.99 134.01 25.28 2.29 . . . . . . . . .

42.05 . . . . . . 22.79 1.83 90.02 23.95 2.10 138.01 25.35 2.33 . . . . . . . . .

Dwingeloo 1

0.00 . . . . . . . 20.90 2.58 102.02 23.30 2.79 206.01 24.03 2.63 310.01 25.11 2.64

2.83 . . . . . . . 21.09 2.63 106.02 23.34 2.73 210.01 24.07 2.69 314.01 25.18 2.86

6.32 . . . . . . . 21.38 2.78 110.02 23.35 2.74 214.01 24.13 2.60 318.01 25.25 2.82

10.20 . . . . . . 21.55 2.79 114.02 23.36 2.74 218.01 24.17 2.64 322.01 25.27 (2.82)

14.14 . . . . . . 21.76 2.80 118.02 23.39 2.69 222.01 24.18 2.52 326.01 25.26 (2.82)

18.11 . . . . . . 21.99 2.84 122.02 23.42 2.60 226.01 24.21 2.68 330.01 25.38 (2.82)

22.09 . . . . . . 22.16 2.73 126.02 23.44 2.69 230.01 24.28 2.60 334.01 25.38 (2.82)

26.08 . .. . . . 22.29 2.81 130.01 23.48 2.72 234.01 24.28 2.65 338.01 25.39 (2.82)

30.07 . .. . . . 22.39 2.79 134.01 23.51 2.66 238.01 24.35 2.70 342.01 25.45 (2.82)

34.06 . .. . . . 22.44 2.80 138.01 23.52 2.67 242.01 24.37 2.80 346.01 25.57 (2.82)

38.05 . .. . . . 22.50 2.82 142.01 23.55 2.72 246.01 24.49 2.86 350.01 25.56 (2.82)

42.05 . .. . . . 22.59 2.82 146.01 23.58 2.70 250.01 24.51 2.73 354.01 25.71 (2.82)

46.04 . .. . . . 22.70 2.86 150.01 23.60 2.72 254.01 24.52 2.80 358.01 25.68 (2.82)

50.04 . .. . . . 22.77 2.95 154.01 23.58 2.66 258.01 24.56 3.05 362.01 25.69 (2.82)

54.04 . .. . . . 22.83 2.87 158.01 23.63 2.55 262.01 24.58 2.78 366.01 25.71 (2.82)

58.03 . .. . . . 22.88 2.96 162.01 23.71 2.66 266.01 24.61 2.83 370.01 25.74 (2.82)

62.03 . .. . . . 22.94 2.97 166.01 23.72 2.71 270.01 24.62 3.01 374.01 25.65 (2.82)

66.03 . .. . . . 22.98 2.87 170.01 23.79 2.60 274.01 24.72 2.91 378.01 25.68 (2.82)

70.03 . .. . . . 23.03 2.95 174.01 23.80 2.74 278.01 24.73 2.65 382.01 25.73 (2.82)

74.03 . .. . . . 23.07 2.94 178.01 23.83 2.56 282.01 24.78 2.70 386.01 25.78 (2.82)

78.03 . .. . . . 23.10 2.98 182.01 23.87 2.58 286.01 24.84 2.84 390.01 25.80 (2.82)82.02 . .. . . . 23.11 2.88 186.01 23.90 2.65 290.01 24.85 2.74 3

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