Astronomy & Astrophysics manuscript no. n26-fin c© ESO 2014February 6, 2014

Optical and infrared observations of the young SMC “blob” N26and its environment?

G. Testor1∗∗, M. Heydari-Malayeri1, C.-H. R. Chen2,3, J.L. Lemaire1,4??, M. Sewi lo5,6, S. Diana4

1 LERMA, UMR 8112 du CNRS, Observatoire de Paris, 92195 Meudon, France e-mail: gerard.testor@obspm.fr2 Department of Astronomy, University of Virginia , PO Box 400325, Charlottesville, VA 22904, USA3 Max-Planck-Institut fur Radioastronomie, D-53121 Bonn, Germany4 Universite de Cergy-Pontoise, 95031 Cergy Cedex, France5 The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street,

Baltimore, MD 21218, USA6 Space Science Institute, 4750 Walnut St. Suite 205, Boulder, CO 80301, USA

Received ...; accepted ...

ABSTRACT

Context. High-excitation compact H ii regions of the Magellanic Clouds are sites of recent massive star formation in lowmetallicity environments.Aims. Detailed study of these regions and their environments using high-spatial resolution observations is necessary tobetter understand massive star formation, which is still an unsolved problem. We aim at a detailed study of the SmallMagellanic Cloud compact H ii region N26, which is only ∼4′′in diameter.Methods. This study is based on high spatial resolution imaging (∼ 0′′.1-0′′.3) in JHKs and L′ bands, using the VLTequipped with the NAOS adaptive optics system. A larger region (∼ 50 × 76 pc) was also imaged at medium-spatialresolution, using the ESO 2.2m telescope in optical wavelengths. We also used the JHKs archival data from the IRSFsurvey and the Spitzer Space Telescope SAGE-SMC survey.Results. Our high-resolution JHKs data of the compact high-excitation H ii region N26 reveal a new, bright component(C) between the two already known optical components A and B. Components A and C are resolved into several stars.Component A is the main ionization source of N26 and coincides with the radio continuum source B0046-7333. Anew compact H ii region with very faint [O iii] λ5007 emission is discovered. In the mid-IR, our field resembles a shellformed by filaments and dust clumps, coinciding with the molecular cloud SMCB2. N22, located in the center of theshell, is the most excited H ii region of the complex and seems to have created a cavity in SMCB2. We derive nebularparameters from spectra, and using color-magnitude and color-color diagrams, we identify stellar sources that showsignificant near-IR excess emission, in order to identify the best YSO candidates.

Key words. galaxies: Small Magellanic Cloud – ISM: individual objects: N26 – ISM: H ii regions– ISM: dust extinction– Stars: formation – Stars: massive

1. Introduction

Although they are rare and short-lived, massive stars (>8 M�) play a key role in several fields of astrophysics.However, their formation process is still an unsolved prob-lem in spite of progress, both in theory and observation, inrecent years. The Magellanic Clouds offer valuable oppor-tunities for this study since they are seen nearly face-onand have well-determined distances (Keller & Wood 2006;Schaefer 2008). This facilitates obtaining accurate absolutemagnitudes and fluxes. Moreover, their overall extinctionis low (Westerlund 1992, Massey et al. 1995, Bonanos et al.2010). Being metal-poor (Pena-Guerrero et al. 2012), theyprovide important templates for studying star formationin distant metal-poor galaxies which cannot be observedwith comparable spatial resolution.

The youngest massive stars in the Magellanic Cloudsaccessible to infrared and optical observations are found in

? Based on observations obtained at the European SouthernObservatory, El Paranal, Chile?? Visiting astronomer at VLT Paranal

High-Excitation Blobs (HEBs, Heydari-Malayeri & Testor1982, Heydari-Malayeri et al. 2010 and references therein).This is a rare class of H ii regions in the Magellanic Clouds;so far only six members have been detected in the LMCand five in the SMC. For massive stars the accretiontime-scale is larger than the Kelvin-Helmholtz time-scale.This means that massive stars reach the main sequencewhile accretion is still going on. Moreover, they evolvevery fast. Therefore, obtaining the physical parametersof massive stars “at birth” may be an unattainable task!Consequently, HEBs offer a compromise between starsinside ultra-compact H ii regions and the exciting stars ofevolved H ii regions.

In contrast to the typical H ii regions of the MagellanicClouds, which are extended structures (sizes of several arcminutes corresponding to more than 50 pc, powered bya large number of exciting stars), HEBs are very denseand small regions (∼ 4′′ to 10′′ in diameter correspondingto ∼ 1–3 pc). They have a higher degree of excitation([O iii]/Hβ]) with respect to the typical H ii regions, andare, in general, heavily affected by local dust. In compar-

2 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

ison with Galactic regions, some of the HEBs are similarto classical H ii regions and some look like compact H iiregions (Martin-Hernandez 2005). However, HEBs shouldbe considered in the context of massive star formation inthe MCs. Compared with other compact H ii regions ofthe same sizes in the MCs, they constitute a distinctlydetached group with high excitations and luminosities(Meynadier et al. 2007).

This paper is mainly focused on N26 (LHA 115-N26,Henize 1956), a HEB situated in the SMC, the first studyof which was presented by Testor (2001). Its (J2000)coordinates are α = 0h 48m 08s.60, δ = -73◦ 14′ 54′′.69.N26 is a compact H ii region of ∼ 4′′, or 1 pc, in diametercomposed of two components, A and B. This object ishighly excited, with a ratio of [O iii] λλ4959+5007/Hβreaching 8 in component A (Fig. 6 in Testor 2001). N26 hasan ultra-compact H ii region counterpart detected at high-resolution 6 cm radio continuum observations (Indebetouwet al. 2004). From optical spectra, the exciting sourceof component A was classified to be O7-9 V (Testor2001). The extinction in N26 is relatively high, reachingan E(B − V ) of ∼ 1 mag in the direction of component B.That first study used relatively low resolution observationsand only in the optical range.

N26 is located in the south-west part of the bar ofthe SMC, where several H ii regions are visible in itsclose vicinity. Figure 1a shows N25 to the north and N22,N21, and N23 to the south of N26. The largest and themost diffuse H ii region of the group is N22 around whichthe other H ii regions are distributed. These H ii regionsare associated with embedded clusters (Bica & Dutra,2000), and also detected in the Hα survey conducted byDavies et al. (1976). N26 is the most compact and smallestH ii region of the group, which suggests it to be theyoungest among them. A giant molecular cloud labelledSMCB2 (Fig. 1b) is detected toward this area of the SMC(Rubio et al. 1993). The molecular cloud presents three12CO(1-0) peaks, one to the north and two to the south,the velocities of which range from 108 to 126 km s−1;this suggests that they are likely physically associated.Bot et al. (2010) observed SMCB2 with the LABOCAcamera on the APEX telescope at 870 µm and found adust temperature of 12 K, a mass of M870

H = 8.5 × 105

M� for the northern peak SMCB2-N and 65 ×104 M�for the southern peak SMCB2-S, respectively (Fig. 1). Farinfrared and millimeter observations of the region havebeen performed by Wilke et al. (2003) and Mizuno et al.(2001), respectively. The Spitzer data base has also beenused to study point sources in the IRAC and MIPS data(Bolatto et al. 2007, Lawton et al. 2010) of our region, aspart of the Spitzer Survey of the Small Magellanic Cloud(S3MC).

Star forming regions like the N26 area are expectedto be associated with young stellar objects (YSOs). Theuse of JHK color-magnitude and color-color diagrams areuseful tools to detect the candidates. A more suitablewavelength to determine the nature of the IR-excess isthe L-band, which increases the IR-excess and reduces thecontribution of extended emission from reflection nebulaeand H ii regions (Lada et al. 2000). However, near- andmid-IR color-magnitude and color-color diagrams obtained

Table 1. Log of VLT near-infrared CCD images of SMC N26

Filter Exposure Mode seeing FWHMt(s) × n (′′) (′′)

J 1.27 µm 20 × 30 S54 0.6-0.9 0.35H 1.66 µm 4 × 30 “ “ 0.27Ks 2.18 µm 5 × 30 “ “ 0.21Ks 2.18 µm 60 × 1 S27 0.9-1.2 0.10L′ 3.8 µm 0.18 × 30 “ 0.9-1.2 0.10

from IRAC data are still better tools for identifying theorigin of the reddening of embedded stars (Allen et al.2004, Bolatto et al. 2007). In this paper we present theresults for the whole area using BVJHKs, 3.6, 4.5, 5.8,8.0, 24, 70, and 160 µm bands in mid-spatial resolutionphotometry, as well as the JHK- and L’-band high spatialresolution observations from adaptive optics.

The paper is arranged as follows. In Section 2, wepresent the instruments employed for these observations,the reduction procedures used as well as the archival data.In Section 3 we describe the results and analysis of the ob-servations. In Section 4, we discuss the results. Concludingremarks are given in Section 5.

2. Observations and data reduction

2.1. Imaging and photometry

2.1.1. VLT/NACO

Near-infrared observations of a small area centered on theSMC compact H ii region N26 were obtained at the ESOVLT in 2004, October 9 and 10. Images and spectra weretaken using NACO on UT4, composed of the NasmythAdaptive Optics System (NAOS) and the High ResolutionIR Camera and Spectrometer (CONICA). The detectorwas a 1026 × 1024 SBRC InSb Aladdin 3 array. Thecameras S54 (Fig. 2a) and S27 (Fig. 2b) were used inthe range of 1.0-2.5 µm and the L27 camera in the range2.5-5.0 µm.

The field-of-view (FOV) of the S54 camera was 54′′ x54′′ with a pixel size of 0′′.05274, corresponding to 0.015pc at the distance modulus of m − M = 18.93 mag forthe SMC (Keller & Wood 2006). The FOV of the S27and L27 camera was 27′′.15 x 27′′.15 with a pixel size of0′′.02637, corresponding to 0.0075 pc. As adaptive optics(AO) reference source for wavefront sensing we used the2MASS star (J200004809.84-731518.5) of magnitude K= 10.370 (Cutri et al. 2003). The conditions were photo-metric, and the seeing ranged from 0′′.65 to 1′′in the visible.

Broadband JHKs images were obtained with the S54camera. Images with higher spatial resolution in the Ksand L′ bands were also obtained with the S27 camera. TheL′ photometry was extracted only for the three brightestcomponents of N26 (Fig. 4). The L′ magnitudes for allother stars are the 3.6 µm data taken from the IRACcatalog (see Sect. 2.3). The log of the NIR imaging obser-vations is given in Table 1. The AutoJitter mode was used:

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 3

Fig. 1. a) False-color composite image of SMCB2-H ii from Spitzer IRAC bands 3.6 µm (blue), 4.5 µm (green), and 8 µm (red).The various H ii regions detected by Henize (1956) in this part of the SMC are labeled, as well as the YSO candidates (Sect. 4.6).The image center is α = 0h 48m 01s.85, δ = -73◦ 16′ 03′′.75. Total field size 168′′× 251′′or 50 × 76 pc. b) The MIPS 24 µm imageof the SMCB2-HII region with the CO contours overlaid. The contours outline the molecular cloud SMCB2 (Bot et al. 2010). Thebright stars are labeled.

that is, the telescope moves at each exposure according toa random pattern in a 6′′× 6′′ box. Table 1 lists the stellarfull-width-at-half-maximum (FWHM) in final images ofdifferent observed bands. The adaptive optics image isaffected by anisoplanatism when the reference star is noton axis and leads to a degradation of the point spreadfunction (PSF) becoming more elongated as the angularoffset from the reference star increases. The data werereduced mainly with the ESO software packages MIDASand ECLIPSE. A false-color image of N26 combining theJ (blue), H (green), and Ks (red) bands is shown in Fig.2.

The high resolution of NACO allowed us to separatethe crowded components in N26. However, its distancefrom the the AO reference star, ∼ 30′′, increases theanisoplanatism effects. That is why photometry will beperformed on a small area (30′′× 25′′) around N26 . In thatarea the instrumental magnitudes of the stars were derived,using the DAOPHOT multiple-simultaneous-profile-fittingphotometry routine (NSTAR) (Stetson 1987), whichis well adapted for photometry in crowded fields. Theuncertainties of the instrumental magnitudes (me) in the

J , H and Ks bands are less than 0.03 mag for stars withKs < 16.5 mag, less than 0.06 for stars with 16.5 < Ks< 18 mag, and greater than 0.1 for stars 18 < Ks < 20mag. In this small area, the anisoplanatism effects becomenegligible but due to the me of about 0.04 mag on the faintisolated stars used as PSF, the accuracy of the photometryis slightly degraded.

In the small area centered on N26 (Fig. 2, inset), weshow for the first time the presence of six stars embeddedin the H ii region N26. These stars, shown in Fig. 3 (inset),do not have IRSF counterparts. Two IRSF stars (Kato etal. 2007) of identities 0481111-73145210, corresponding toour star #207, and IRSF 0481032-731459, our star #202,were available. As their colors are the same, we could notcalculate color correction, which adds uncertainty to theYSO SED calculation. The resulting photometry for thesesix stars in all bands has errors of 0.02 to 0.04 mag for Ks< 15.5 and 0.04 to 0.09 for Ks > 15.5 mag. These aresquare root errors derived from IRSF accuracies availableonly for star #207 (Kato et al. 2007) and our instrumentaluncertainties. More specifically, we applied the IRSFinaccuray of star #207 to the six stars of the sample. This

4 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

A

#160

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A1 A2

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Fig. 2. a) False-color image of the N26 H ii region composed of J (blue), H (green), and K (red) bands obtained with the S54camera. The very faint cluster enhanced by the DDP technique seen in the inset (top right) is located between component A and#160 (see Fig. 3). The field size is 58′′ × 53′′ or 18 × 16 pc and the small area is shown in dashed lines. Star 207 is the IRSFsource 0481111-73145210 used in the photometry calibration (Sect. 2.1.1). b) Image of N26 in the Ks band, obtained with the S27camera, also processed with the same technique. The field size is 10′′× 9′′.5 or 3.0 pc × 2.7 pc. The inset of size 1′′.6 × 1′′.6 showsan enlarged view of component C. North is up and East left.

means that since #207 is weaker than stars #170, #172,and #173, we overestimate the final uncertainties on thesestars. The other JHKs magnitudes of the whole field areextracted from the IRSF catalog (see Sect. 2.3).

Table 2 presents the data set that includes our JHKsL’NACO photometry (Sect. 2.1.1), BV data (Sect. 2.1.2), aswell as the archival data from IRSF (JHKs) and SAGE-SMC (3.6-160 µm, Sect. 2.3). This table contains onlysources brighter than J = 18.8 both for IRSF and NACOphotometry, corresponding to a S/N of > 10. Column 1gives the identifications, which are our serial numbers. Thevarious identifications in the archival data for each star canbe obtained from the corresponding coordinates. The mainstars dealt with in this study (Table 2) do not have otheridentifications. Columns 3 and 4 list the correspondingJ2000.0 coordinates. Columns 5 to 28 gives the magnitudesB, V, J,H, Ks, 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 µm withtheir uncertainties.

2.1.2. 2.2m telescope

We used B and V broad bands as well as narrow emissionline bands (Hβ, [O iii] λ5007) to observe the regions N21,N22, N23, N25 and N26. The observations were made inOctober 1987 using the 2.2m telescope at La Silla. Thedetector was a 1000 × 1000 CCD (GEC) with a pixel sizeof 0′′.26 on the sky. The seeing was ∼1′′.5 and exposuretimes ranged from 90 to 900 s.

The BV data reduction of the two overlappingframes containing our field (Fig. 3) was done usingDAOPHOT/ALLSTAR. The photometric calibration wascarried out using 8 bright and isolated stars extracted fromMassey’s (2002) catalog. They belonged to two samples sit-uated toward the regions N22 in the south and N26 in the

north. The V magnitudes ranged from 13.06 to 15.03 andthe corresponding B−V colors had a value between -0.06 to1.59 mag. The zero point and color correction relationships,derived from the linear regression method, were: V = v +0.05 (B−V ) -0.03 (s.d. ±0.04) , and B−V = 0.98 (b−v) -0.02 (s.d. ±0.03). The total square root errors on B and V(Table 2) were obtained using our instrumental errors andthe corresponding average statistical errors given in Table2 of Massey (2002).

2.2. Spectroscopy

2.2.1. NACO spectroscopy

Spectroscopy of N26 was performed (October 9, 2004) inthe S54-4-SHK mode. The spectral range was 1.30 to 2.60µm, the linear dispersion 1.94 nm/pixel, and spatial scale53 mas/pixel. The seeing varied between 0′′.6 and 0′′.9. OneEW long-slit spectrum S1 crossing the component A ofN26 was taken with NACO. The slit width was 172 masand the spectral resolution ∼ 400. For each exposure thedetector integration time (DIT) was 100s. Ten exposureswere obtained in the AutoNod on Slit mode, which allowsthe spectroscopy of moderately extended objects. In orderto remove telluric absorption features, stars with a similarairmass were observed as telluric standards. Spectroscopywas reduced with the MIDAS software package LONG.

2.2.2. Boller & Chivens Spectroscopy

The optical spectroscopic observations were performed atthe ESO 1.5m telescope (September 1987) with the Boller &Chivens spectrograph (Heydari-Malayeri et al. 1989). Thegrating #25 covered from 4300 to 6800A with a dispersionof 170A/mm or 1′′.27/pix (binned × 2). The spectra wereobtained through a 4′′ slit width oriented east-west, in thedirections a, b, c, d, and e (Fig. 7) (see sect. 4.4.1). Exposure

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 5

Fig. 3. An optical image in the V band obtained with the ESO2.2m telescope. The numbers refer to Table 2. The field size is153′′ × 264′′ or ∼ 46 pc × 80 pc. A section of the field containingthe H ii region N26 is outlined. It is 9′′.6 × 9′′.6 and shows a blow-up of the J and V images obtained with the NACO (S54 camera)and the 2.2m telescope, respectively.

times were 1800 s. The flux was calibrated using observa-tions of two spectrophotometric standard stars, LTT7987and L870-2.

2.3. Archival data and matching

The Spitzer observations of the working field were ob-tained as part of the Legacy Program “Surveying” theAgents of Galaxy Evolution in the Tidally-Disrupted, Low-Metallicity Small Magellanic Cloud (SAGE-SMC; Gordonet al. 2011). These observations include images taken withthe IRAC 3.6, 4.5, 5.8, and 8.0 µm bands and MIPS 24, 70,and 160 µm bands. The L-band photometry used in thiswork refers to the 3.6 µm band. The details of observations

and data processing are given in Gordon et al. (2011). TheIRAC and MIPS 24 µm photometry of sources in the work-ing field are adopted from the SAGE-SMC point sourcecatalog. The IRAC resolution ranged from 1′′.7 to 2′′(0.5 to0.6 pc), those for MIPS images from 6′′to 40′′(1.8 to 12 pc).

We also used the data obtained with the InfraRedSurvey Facility (IRSF) (Kato et al. 2007). The IRSF hasa pixel scale of 0′′.45, average seeing of 1′′.3, 1′′.2 and 1′′.1in the JHKs bands respectively, and limiting magnitudesof J = 18.5, H = 18.2 and Ks = 17.4 mag for the SMC.For star #169, BV and JHK data were extracted fromthe catalogs of Massey and 2MASS respectively. Table2 presents the data set that includes our BV (see Sect.2.1.2) and JHKsL’ NACO photometry and archival datafrom IRSF (JHKs) and SAGE-SMC (3.6-160 µm).

The matching of the new data with those of older datafrom different catalogs was not carried out automatically.Due to the crowding as well as low magnitudes in somewavelengths, the star labels (identification numbers)were matched manually. To do this, we used the Aladintool1 to visualize our images in different wavelengths andsuperimpose the labels of the stars. Thus, for each star weobtained a table line including several labels correspondingto the star in different wavelengths.

The transformation from the chip x,y positions to theequatorial right ascension (RA) and declination (Dec) co-ordinates, listed in Table 2, was carried out using threestars in each V frame. To calibrate the coordinates, we usedMassey’s catalog (2002), which has an astrometric accuracyof ∼ 0′′.4. Our final coordinates are accurate within ∼ 0′′.5.For stars with no counterpart in the V frame, as identifiedby eye, we adopted the coordinates given by Kato et al.(2007) and the IRAC catalog, which have an accuracy of0′′.1 and 0′′.25, respectively. In the particular case of stars#170, #172, and #173, the transformation was obtainedusing neighboring stars of the Kato catalog, leading to anaccuracy of ∼ 0′′.2.

3. Results

3.1. General morphology of N26

The high spatial resolution provided by NACO reveals N26as a compact H ii region of radius ∼2′′, that is one of themost compact HEBs so far detected. It also confirms thepresence of two bright nebular components, A and B, sep-arated by 2′′.7, as first detected by Testor (2001) in opticalwavelengths.

1 http://aladin.u-strasbg.fr

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G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 7

Table 3. Relative intensities of IR spectral lines toward N26

Component He i H2 H2 H2 Brγ HeI2.11µmBrγ

2.11 µm 2.12 µm 2.22 µm 2.24 µm(1-0) S(1) (1-0) S(0) (2-1) S(1)

A (#170) 0.081 0.037 2.47 0.033C (#172) 0.015 0.243 0.13 0.107 2.05 0.0073

Fig. 4. An underexposed image of N26 in the L′ band (3.6 µm)showing the three components A, C, and B. They correspond tostars #170, #172, and #173 respectively. The field size is 3′′.4x 3′′.4; North is up and East right.

Moreover, the NACO observations uncover a well-resolved red component located between A (#170) and B(#173), which we call C (#172) (Fig. 4). Up to now, nooptical counterpart has been detected for component C.Using a Digital Development Process (DDP)2, a very faintstar cluster of diameter ∼ 4′′ (Fig. 2a) appears betweencomponent A and the faint red star #160. On the Ksimage (Fig. 2b) this cluster is not detected and componentA seems to be formed mainly by two bright stars, A1 andA2, separated by 0′′.39. The new component C, at 1′′.48to the east of A1, seems to be surrounded by at least twofaint stars, as shown in the inset of Fig. 2b.

The east-west NACO spectrum S1 (Fig. 5) crossingcomponents A and C gives the distribution of the intensityin the Brγ 2.17µm, He i 2.05µm, and H2 lines along the slit.The large profile of A allows the assumption that it containsmore than two stars. The H2 emission is mainly centeredon the red component C and spans over 3′′.5. Fig. 6 showsthe intensity profiles of the emission lines Brγ 2.17µm, He iλ2.05 µm, and H2 λ2.12 µm for each component. These 1Dspectra are extracted by summing 8 and 4 pixels centeredon the maximum intensity of A and C along the slit of S1.The corresponding relative intensities are listed in Table 3.

2 http://www.asahi-net.or.jp/∼rt6k-okn/its98/ddp1.htm

Fig. 5. The intensity profiles of near-IR emission lines from aNACO long-slit spectrum in an east (left)-west (right) directioncrossing stars #170 (component A) and #172 (component C).Star #173 (component B) does not appear because it is notsituated on the E-W cross-cut. The red line represents the H2

2.121 µm emission line. The green line represents the He i 2.113µm and the black one the Brγ emission line. The position of theradio source B0046-7333 is indicated. The plot extension is 7′′.07(1 pix = 0′′.05273).

Fig. 6. Spectra of the component A (#170) and C (#172) ex-tracted from S1.

3.2. Ionizing source of N26

From the above-mentioned spectrum S1 a He i λ2.11/Brγλ2.17 ratio of ∼ 0.033 is derived for component A (Table3). According to Hanson et al. (2002), this ratio corre-sponds to an ionizing source of type between O7V and lateO stars. This is in agreement with the result obtained byTestor (2001), who, on the basis of optical spectroscopy,derived a spectral type O7-O9 V, from the integrated lightfor components A, B, and the newly detected componentC. Note that this integrated entity will be labeled #169on the color-magnitude and color-color diagrams presentedin the following section. It appears that the main ionizing

8 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

source should be embedded in component A and that theionization of B and C is negligible. Another piece of sup-port for this deduction comes from high-resolution radiocontinuum observations by Indebetouw et al. (2004). Theirwork reveals the presence of a compact, radio continuumsource (B0046-7333) at R.A. 0h48m8s.5, Decl. -73◦14′55′′,i.e. the position of component A. These authors estimatedan equivalent spectral type of O7.5 V for the ionizing sourceof component A.

3.3. Distribution of H2

The H2 emission measured toward N26, in particular com-ponent A (Fig. 5), is much weaker than that of Brγ andHe i. The H2 profile is composed of two shallow bumps cen-tered around the position of component C. At this position,the profile of H2 decreases slightly. According to Black &Van Dishoeck (1987), the flux ratios 2-1(S1)/1-0 (S1) and1-0 (S1)/1-0 (S0) for radiative excitation should range from0.5 to 0.6, and from 0.4 to 0.7, respectively. Our measuredratios are 0.44 for 2-1(S1)/1-0 (S1) and 0.53 for 1-0 (S1)/1-0 (S0) (Fig. 6), i.e. not far from the predicted values. Thissuggests that component C may be a photodissociation re-gion (PDR). These two weak peaks of H2 emission discov-ered toward N26 probably belong to a more extended flatdistribution of H2, as detected by Leroy et al. (2007). Thepresence of such an extended H2 is in line with the re-sult by Israel & Maloney (2011), who in a study of theλ158 µm C ii line emission, found PDR parameters for thewhole star forming region labeled N22+N25+N26, corre-sponding to almost the whole SMCB2-H ii. Rubio et al.(2000) show that H2 knots are associated with clumps ofmolecular clouds traced by CO (2-1) and peaks of dustemission, and suggest that massive star formation could betaking place.

3.4. The environment of N26

3.4.1. Morphology in the optical and Spitzer images

N26 is located in the northern part of the molecular cloudSMCB2-H ii complex, 50 pc x 76 pc in size, mapped inthe 12CO(1-0) line (Rubio et al. 1993). The H ii region liessouth of N25, a bright extended circular region ∼ 30′′ indiameter (Figs. 1a & 7). The central part of SMCB2-H iiis occupied by N22, the bright, circular and the most ex-tended H ii region of the field, which has a size of ∼ 50′′.N22 is centered roughly on the bright blue star #86 ofV = 14.39, B − V = -0.09 mag and fills the cavity be-tween the northern and southern molecular cloud compo-nents SMCB2-N and SMCB2-S, respectively. This cavityseems to have been created by hot stars in N22. Accordingto Rubio et al. (1993), the N22 region is comparable toOrion A as far as the 12CO(1-0) flux is concerned. Theseauthors give for SMCB-N and SMCB2-S a mean radial ve-locity of 120 km−1 and 126.7 km−1 respectively, slightlysmaller than that of N22. We remark that N26 is boxed inby the regions N25 and N22. The southern part of SMCB2-H ii is composed of N23 and N21. The H ii region N23 hasa size of ∼ 25′′and contains the faint blue stars #35, #45,and #54. N21, situated west of N23, is ∼ 15′′ in diame-ter and includes the blue stars #3 and #8. A faint andcompact H ii region of radius 2′′.6 is detected between N21and N23 in the Hβ frame (Fig. 7). This region, that we la-

Fig. 7. A mosaic of two [O iii] λ5007 images showing theSMCB2-H ii field. The numbers refer to Table 2. The delineatedarea in the lower frame does not show nebular emission in [O iii]while the same area extracted from the Hβ image and displayedon the left, shows the new object N23A ∼ 10′′ south of #28 (Fig.3). The whole [O iii] mosaic has a size of the 138′′ × 264′′ or ∼ 42pc × 80 pc, while the extracted Hβ image is 28′′ x 30′′. The H iiregions N21, N22, N23, N25, N26, and the new one N23A areindicated. Horizontal lines show the positions a, b, c, d, and e ofthe ESO B&C long-slit spectroscopic observations. The brighterstars of V < 15.5 mag and B − V ≤ 0 mag are labeled.

bel N23A, is not detected in the [O iii] λ5007 A band (Fig.7). The spectrum presented in Fig. 8(a) confirms the faint[O iii] emission compared to Hβ. This object is probably alow-excitation, compact H ii region (Meynadier & Heydari-Malayeri (2007). Since its spectral lines do not show a sig-nificant velocity shift with respect to those of neighboringH ii regions, it should be part of the SMCB2 complex.

3.4.2. Physical parameters of the H ii regions

The spectral types of the main ionizing sources of theH ii regions in the field (Fig. 7) were estimated from UBV

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 9

Table 4. Main ionizing stars of the neighboring H ii regions∗

ID V B - V U - B AV AV MV Spectral Spectral(sp) (phot) Type§ Type†

N21 #3 15.40 0.69 -4.22 O9 O8.5N22 #86 14.30 -0.09 -0.96 0.48 0.63 -5.11 O7 O5.5N22 #92 14.25 -0.19 -0.96 0.57 0.27 -5.25 O7 O5N22 #97 16.44 -0.02 0.42 -2.91 B1N22 #136 15.44 -0.10 0.57 -4.06 BO O9N22 #155 15.98 -0.19 0.42 -3.37 B0N23 #35 17.60 -0.24 BN25 #182 14.25 -0.13 -0.95 0.33 0.48 -5.01 O7 O5.5

∗ U − B values in column 4 are taken from Massey’s catalog.In col. 5, AV values are derived from the Hα/Hβ ratios (Table2). In col. (6) AV values are calculated using the Q parameter(Massey et al. 1995). In col. 7, MV values are estimated usingAV from col. 5.§ Spectral types (luminosity class V) derived from Schmidt-Kaler (1982).† Spectral types from Martins et al. (2005).

Fig. 8. Optical spectra (sky unsubtracted) crossing the H ii re-gions N21, N22, N25, N26, and the faint compact nebula N23Aat the positions a, b, c, d, and e (Fig. 7).

photometry (Table 4). We used the main sequence OBstar parameters tabulated by Schmidt-Kaler (1982) andMartins et al. (2005)’s calibration. We notice that theO stars classified with Martins et al. are 0.5 to 2 typehotter. It should be underlined that the classifications,based only on color indices, are uncertain and must beconsidered as a first attempt. Indeed the intrinsic colorindices of the O stars are degenerated, that is they hardlydiffer among themselves and are similar to the values ofthe earliest B main sequence stars (Conti et al. 1986).Moreover, (B - V) and (U - B) values belong to differentdata sets. The extended H ii region N22 contains 11 bluestars with B − V ≤ 0, of which the two brightest, #86and #92, of type O7 and O5.5 V respectively, should bethe main ionizing sources of N22. The H ii region N25 iscentered on the bright star #182 whose spectral type isO5.5 V according to Martins et al.’s calibration (Table4). However, using spectroscopy, this star was classified as

Fig. 9. Infrared photometric diagrams for sources measured to-ward the SMCB2-H ii complex. See Table 2 for uncertainties. a)J−H versus H−K. The blue line is the main sequence isochronefor stars of 1.4 Myr old, and the red line shows the loci of redgiants aged 10 Gyr. The black solid line is the reddening vectorup to AV = 5 mag. The red empty circles correspond to YSOcandidates selected using Whitney et al. (2008)’s criterion andthe blue filled triangles correspond to Bolatto et al. (2007)’s cri-terion (see Sect. 3.5.1). The stars #170, #172, and #173, whichare components of the compact H ii N26 or #169, are indicated,as well as the object #169, which is the integration of the threementioned components. b) J −H versus K−L. The colors andsymbols are the same as those used in panel a. The solid line isthe reddening vector up to AV = 15 mag. c) IRAC [8.0] versus[4.5]-[8.0]. Same colors and symbols as in a.

10 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

O9 V (Hutchings & Thompson 1988) and O8 V (Testor2001). In this particular case the spectroscopic result mustbe privileged. Moreover, the discrepancy between colorindex and spectroscopic methods point to the uncertaintyinherent in using color indices. The main ionization sourceof N21 seems to be star #3 of type O9 or O8.5 V. In N23the V magnitudes of eight detected stars (Fig. 3) rangebetween 15.93 and 18.10 mag. Among them stars #31,#35 and #59 have a B − V range from -0.23 to 0.01 mag,and star #35 may be the main ionization source of theregion.

In addition to the stellar content, we investigated thephysical properties of the H ii regions using Boller &Chivens spectroscopy. From a homogeneous set of CCDframes, one-dimensional spectra of N21, N22, N23, N23A,N25, and N26A were extracted by summing a range of pix-els along the 4′′ east-west slit. Each range corresponds tothe FWHM of the nebula along the slit of the spectra a,b, c, d and e. (Fig. 7). Table 5 gives the line ratios fromwhich we derived the physical parameters, such as electrondensity (Ne) and temperature (Te) of the H ii regions. Allthe line fluxes were corrected using the coefficient c(Hβ)derived from the Hα/Hβ ratio of each spectrum (Fig. 8).We estimate Ne using the 5-level atom program by Shaw& Dufour(1995) from the [S ii] doublet λλ6717/6731 lineratios, assuming Te = 104 K. We estimate the Te using the[O iii]λλ4363/(4959+5007) ratio. N22, with an [O iii] (λλ5007+4959)/Hβ ratio of 6, appears more excited than N21and N23 of about 2.15. The ratio Hα/Hβ ranges from 3.27to 4.30. In Table 5 several other physical parameters arealso given.

3.5. Stellar populations

The photometric data at our disposal (B, V, J, H, K; 3.6,4.5, 5.8, 8.0 and 24 µm) allow us to identify and studythe stellar populations lying toward the N26 complex. Wealso use these data to search for possible young stellar ob-ject (YSO) candidates. YSOs are enshrouded in dust thatabsorbs stellar UV and optical radiation and re-radiatesin the IR. YSOs can be distinguished from normal stars,i.e., main sequence, giant, and supergiant stars, by theirexcess of IR emission. Indeed they are positioned in red-der parts of the color-color and color-magnitude diagrams.However, the interpretation is not straightforward, sinceforeground Galactic evolved stars and background exter-nal galaxies can display colors similar to those of YSOs,and also since the distribution of circumstellar dust aroundmassive stars is not well known (Stahler et al. 2000; Gruendl& Chu 2009).

3.5.1. Photometric diagrams

On the color-color J −H versus H −K diagram (Fig. 9a)the distribution of the sample stars may be divided intothree main groups. The first one appears along the mainsequence and red giant branch stars with a concentrationat H − K ∼ 0.15 and J − H ∼ 0.65 mag. Theoreticalmodels (Lejeune & Shaerer 2001) indicate the ages of 1.4Myr and 10 Gyr for the main sequence and red giantsstars, respectively. The 10 Gyr isochrone might indicatean intervening population not physically related to the

young massive star region. The second group is a smallconcentration of faint stars to the right of the reddeningvector centered at H − K ∼ 0.2 mag. And the third oneis composed of 13 stars with an IR-excess H − K > 0.6mag. In particular, #169 includes the sources #170, #172,and #173. Among these 12 red sources, the three reddest,i.e. #19, #118, and #127, have IR excess consistent withthose of a circumstellar disk, a protostellar envelope, ora dusty H ii region. The YSO candidates, shown in redempty circles, comply with the following selection criterion:[3.6] < 6.76 + 1.10 × ([3.6]-[24]) and [3.6] < 13.86 - 0.91× ([3.6]-[24]) (Whitney et al. 2008). Also are indicatedcandidate carbon stars (Bolatto et al. (2007)’s criterion)with filled triangles.

To understand the origin of the dust emission, we in-clude the L-band photometry and compare their locationsin the J - H versus K - L color-color diagram (Fig. 9b) toknown YSO candidates (e.g., Maercker & Burton 2005),where the blue and red lines represent 3 Myr and 10 Gyrisochrones, respectively (Lejeune & Shaerer 2001). All 12red sources have large (K - L) color excess similar to YSOcandidates. Four additional sources without excess in JHKcolors are found to have (K - L) color excess: #12, #45,#55, #136; these sources could be AGB or p-AGB stars.To better assess the nature of these red sources, i.e. theorigin of dust emission, it is necessary to include mid- andfar-IR photometry.

We try now to confirm these YSO candidates usingother diagnostic tools consisting of mid- and far-IRcolor-magnitude and color-color diagrams. This methodhas already been employed in several works dealing withYSO candidates (Meixner et al. 2006, Bolatto et al. 2007,Whitney et al. 2008, Gruendl & Chu 2009, Gordon etal. 2011). Gruendl & Chu (2009) showed that evolvedstars and background galaxies can be excluded from theinitial selection of massive YSOs using two simple selectioncriteria, i.e. [4.5]-[8.0] ≥ 2 and [8.0] < 14-([4.5]-[8.0])respectively. Following these criteria, we select eight YSOcandidates (Fig. 9c).

All these candidates fall in the loci of class 0 to class IIYSOs, following Bolatto et al. (2007). Note that the redobject #18 has no B, V , and JHKs data; this is why it isabsent in Figs. 9 a & b. For the same reason, it is not listedin Table 6, although the [8.0] versus [4.5]-[0.8] plot suggestsit as a possible YSO candidate (Fig. 9c). The enclosedarea shows the sample that does not include normal andasymptotic giant branch stars, neither background galax-ies. The eight YSO candidates are found in the upper rightwedge. The red dots are the YSO candidates selected us-ing the above-mentioned criterion by Whitney et al. (2008).

It should also be mentioned that we had to calcu-late the IRAC photometry of star #18, because in theSAGE catalog only 4.5 and 5.8 µm values were available.Therefore, we obtained the photometry of the 3.6 to 8.0µm bands using profiles instead of apertures, because #18is a blended source, as indicated by its FWHM whichis much larger than the IRAC PSF. Indeed the profilemethod yields more accurate sky subtraction in the wings.The method consisted of crossing several cuts through#18 along rows and integrating the fluxes in each band.

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 11

Table 5. H ii region parameters derived from optical emission lines

Spectrum H ii region [O iii] Hβ [O iii] Hα HαHβ

[O iii]Hβ

[O iii]λ4363

c(Hβ) E(B-V) log F (Hβ) FWHM λ6717λ6731

Te Ne

λ4363 λλ4959+5007 erg cm−2 s−1 (′′) (K) (cm−3)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

d N26A-B 693 8019 52616 44374 5.53 6.56 76 0.84 0.58 -12.09 2.5 0.83 12950 1216e N25 172 6597 30949 21605 3.28 4.69 180 0.16 0.11 -12.18 30 1.31 10394 110c N22 north∗ 177 3736 22241 12492 3.34 5.95 129 0.19 0.13 -12.42 37 1.27 11685 182b N22S 150 2841 15327 10190 3.59 5.40 102 0.29 0.19 -12.54 50 1.31 12658 110a N23 909 2341 3143 3.46 2.58 0.23 0.16 -13.04 30 1.25 176a N23A 1014 375 3818 3.77 0.37 0.34 0.23 -12.99 8 1.34 80a N21 990 2074 3705 3.74 2.10 0.33 0.23 -13.00 18 0.89 948

∗centered at the position of stars #125 and #155

In order to calibrate the photometry, the operation wascarried out also for star #67 (Table 2). The uncertaintiesin the 3.6 to 8 µm bands are ≤ 0.05 mag. We note thatthe 24 µm measurement of #18 might include nearby #14source as these IRAC sources are unresolved by the MIPS24 µm PSF.

The red stars #75 and #127 in Fig. 9c are slightly out-side the limits of the YSO area. However, in the [3.6]-[8.0]versus [8.0]-[24] color-color diagram (not shown), they areinside the area and may therefore be classified as YSO can-didates. Moreover, the objects #170, #172, and #173 areabsent in Fig. 9c, because they lack mid-IR data. Fig. 9cshows also that most of the stars are located along a verti-cal band with [4.5]-[8.] ranging from ∼ 0 to 0.6. Accordingto Gordon et al. (2011), most of these stars occupy the lociof O and early B stars.

3.5.2. Massive YSO candidates

We have selected 12 possible YSO candidates after apply-ing several diagnostics tools, but only 9 of them, thosewith mid-IR detection, will be further investigated withspectral energy distribution (SED) fitting. Most of theseobjects should not be low-mass protostars, but rathermassive YSOs. The absolute magnitudes in the L band forour candidates range from -8.4 to -4.5. In comparison, theL absolute magnitudes for 58 low-mass YSO candidates inthe Orion Trapezium cluster are found to be between -3.5and 4.2. These comparatively large magnitudes and thered colors that characterize massive YSOs are also notablein the color-magnitude diagrams, for example the [8.0]versus [4.5]-[8.0] (Fig. 9c). It should be underlined thatthe YSO SED fitting, and consequently the parametersobtained, are formal results, i.e. mere suggestions from thephysical point of view.

Low-mass YSOs are divided into classes based on theirobserved spectral indices (Lada 1987). In contrast, we donot yet have a well-defined classification system for massiveYSOs. Therefore, we use the commonly accepted schemeof low-mass YSOs as a starting point to look into thephysical parameters of high mass YSOs. The geometry ofdust disk and envelope applicable to low-mass YSOs hasbeen adopted in radiative transfer models of high-massYSOs, e.g., Whitney et al. (2004) and Robitaille et al.(2006).

Robitaille et al. (2006) suggested a physical classifi-cation scheme for YSOs of all masses. This classificationis analogous to the Class scheme for low-mass YSOs, butuses physical quantities, instead of the slope of the spectralenergy distribution (SED) to define the evolutionary stageof the models. This classification scheme, while physical,is model dependent, and the comparison with observationsrequires data taken with sufficient angular resolutions toseparate among individual sources and from backgrounds,which is not always the case for Magellanic Cloud objects.Chen et al. (2009) suggested an empirical classification ofthe observed SEDs of massive YSOs, and used a “Type”nomenclature for distinction from the “Classes” for low-mass YSOs and the “Stages” for model YSOs. Accordingto this empirical classification, massive YSOs are dividedinto Types I, II and III.

Type I YSOs have SEDs with a steep rise from the NIRto 24 µm, which is caused by radiation from their circum-stellar envelopes. They are visible in the K band and brightat 24-70 µm, but generally not visible in the optical or Jband. Type I YSOs are often found in, or behind, darkclouds.

Type II YSOs have SEDs with a low peak in the opticaland brighten up from J to 8µm. Type II has a high peakat 8-24 µm and then faint again at 24 µm.

Type III YSOs have bright SEDs in the optical, with amodest emission of dust in the NIR to MIR, correspondingto remnant circumstellar material. Their brightness fadesin the longer wavelengths, and they are often surroundedby H ii regions.

Following the same procedure detailed in Chen et al.(2009) to infer the physical parameters for the YSOs, wecompare the observed SEDs to model SEDs and selectbest-fit models based on minimum χ2

min. We use a largemodel grid containing 20,000 pre-calculated dust radiativetransfer models and a fitting code from Robitaille et al.(2007). The fitting requires input parameters includingthe fluxes of a YSO and uncertainties of the fluxes. Theuncertainties of the fluxes are specified in Sect. 2.1.1 and2.1.2 and listed in Table 2.

Figure 10 shows the best-fitting model (plotted inblack lines) for each source, but typically there is a rangeof models that are nearly as consistent with the data,i.e. χ2 not significantly greater. We have used a cutoff ofχ2 − χ2

min ≤ 3 per data point for these acceptable models,

12 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

Table 6. Parameters derived from SED fits to the YSO candidates

ID α δ M∗ ∆M∗ Ltot ∆Ltot Mdisk ∆Mdisk Stage ∆Stage Type Remarks(M� ) (M� ) (L� ) (L� ) (M� ) (M� )

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)

19 004752.37-731712.85 17.4 3.0 22000 8400. 5.2E-02 1.4E-01 1.0 0.0 I between N21 and N2329 004753.61-731710.22 14.0 2.7 9300 3700. 8.1E-02 1.7E-01 1.1 0.2 I ”33 004754.96-731724.72 9.6 1.0 3100 1100. 5.3E-02 1.1E-01 1.1 0.2 I ”75 004801.27-731659.22 7.1 1.1 1300 350. 6.0E-02 4.4E-02 1.0 0.0 II between N22 and N23

108 004804.39-731521.60 12.7 1.3 13000 4400. 1.3E-01 2.6E-01 1.4 0.5 I N border of N22118 004804.90-731755.92 15.4 3.4 19000 17000. 1.1E-01 2.1E-01 1.0 0.2 I S-E border of N23127 004805.68-731744.36 9.9 1.7 5800 2100. 8.9E-02 1.3E-01 1.5 0.5 II ”154 004807.61-731428.19 10.5 1.0 7300 2100. 9.3E-03 7.7E-03 2.0 0.0 II S-W border of N25169 004808.60-731454.69 24.8 1.4 80000 12000. 1.6E-01 2.8E-01 1.5 0.5 I N26, H ii region, multiple

and plot them in grey. The results of the model fits aregiven in Table 6 that lists selected physical parameters:weighted averages and standard deviations of centralstellar mass (M?), total luminosity (Ltot), and disk mass(Mdisk). These averages and standard deviations, shownwith the ∆ sign, are calculated from best-fit and acceptablemodels using the inverse square of χ2 as the weight; theyshow a possible range of the physical parameters of aYSO. For each accepted model, the evolutionary stageis determined using Menv/M? and Mdisk/M? ratios asdefined in Robitaille et al. (2006) and the range of theevolutionary stage, Stage Range, is determined from thestandard deviation of all Stages inferred for a YSO.

It turns out that seven candidates have a mass ≥ 10 M�(Table 6). The most remarkable massive YSO candidatesof the sample are #19, #29, and #118 with estimatedmasses of ∼ 17, 14, and 15 M�, respectively, and all ofType I. These are very bright objects in the IRAC bands.They are situated in the southern concentration of themolecular cloud shell. #19 and #29 are adjacent objectslying near the newly detected H ii region N23A (Figs. 3 &1). As to the object #118, it is situated east of N23. Table6 also includes the object #169 which is the integration ofthe three sources #170, #172, and #173 comprising thecompact H ii region N26. We will address this object inthe next section.

4. Discussion

The main object of this study, N26, is situated in the north-ern part of the molecular cloud surrounding the centralcavity. N26 probably represents the youngest massive starformation accessible to optical and infrared wavelengthsin this region. It belongs to a small class of compact,high-excitation blobs (HEBs) in the Magellanic Clouds ofwhich only five other examples are presently known in theSMC: N88A (Testor et al. 2010), N81 (Heydari-Malayeriet al. 1999), N66A (Heydari-Malayeri & Selier 2010), N33(Selier et al. 2011), and N77A (Selier & Heydari-Malayeri2012). N26 has the particularity of being one of the mostcompact members of this class. Several observationaldata, presented in this paper, suggest that the H ii re-gion is powered by a massive star of spectral type O7-O9 V.

In comparison with Galactic regions, some of the HEBsare similar to classical H ii regions and some look likecompact H ii regions detected in the radio continuum(Martin-Hernandez et al. 2005). However, HEBs andtheir low-excitation counterparts, called LEBs (Meynadier& Heydari-Malayeri 2007), should be considered in thecontext of massive star formation in the MCs. It wouldbe interesting to know in what physical conditions theseyounger and less populous massive star forming regionsare born adjacent to typical giant H ii regions in the MCs.Given the difficulty in observing the MC HEBs and LEBs,hence the small known sample, it would be helpful to studysimilar objects in our Galaxy for which higher resolutionobservations are possible. To our knowledge, no researchworks have been undertaken yet to find and study compactH ii regions in the vicinity of Galactic giant H ii regions,such as NGC 3603, M8, M17, and others (Damineli et al.2005). As a first step, it seems helpful to identify Galactichigh-excitation H ii regions in the peripheral zone of giantH ii regions and look into their physical characteristics.Such a study will constitute a research project on its own,to which enough time and effort should be devoted. Thisstudy may, however, face two notable handicaps: distanceuncertainties involved in Galactic H ii region studies andthe difficulty of measuring the total luminosity of Galacticobjects extending over several arcminutes on the sky. Notethat Galactic H ii regions like Orion, Sh2-156, Sh2-152,Sh2-269, and RCW34 (Heydari-Malayeri 1988; Heydari-Malayeri & Testor 1981; Simpson 1973; Heydari-Malayeriet al. 1980,1982) have the same physical size and excitationas the MC LEBs. It remains to identify their higher excita-tion counterparts in the adjacent areas of giant H ii regions.

N26 may be associated with three YSOs: #170 (com-ponent A), #173 (component B), and #172 (componentC), the latter a massive one, as suggested by SED fittingof the available data (not shown in Fig. 10). However, theproblem is that the Spitzer IRAC bands do not have thenecessary spatial resolution and moreover the SEDs lackdata in the near- and mid-IR spectral ranges. The absenceof the [4.5], [5.8], [8], [24] and [70] µm for the componentsA, B and C and also BV bands for C (Table 2) makes theconstruction of the SED incomplete and hence difficult tocompare with models.

Since we lack mid-IR Spitzer data for the SED fittingof each of the N26 components A, B, and C, we tried

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 13

7.4 Mo 14.0 Mo 9.6 Mo

7.1 Mo 12.7 Mo 15.4 Mo

9.9 Mo 10.5 Mo 24.8 Mo

Fig. 10. Spectral density distribution (SED) of nine YSOs obtained using the YSO models of Robitaille et al. (2006). Filled circlesare the flux values converted from magnitudes listed in Table 2. The thin black line represents the best fitting SED, and the graylines show all models that also fit the data well (defined by χ2 - χ2

best where χ2 is the value per data point). The dashed linerepresents the stellar photosphere model (corrected for the foreground extinction). The derived masses are indicated; see Table 6for other parameters.

to perform the SED fitting on the whole integratedobject #169, which contains the three components #170,#172, and #173. The whole #169 measures ∼ 4′′ x 2′′.5,corresponding to 1.2 x 0.8 pc. The mass of the associatedYSO turns out to be 24.8± 1.4 M� (Table 6), which ismuch higher than the individual masses of the three YSOcandidates in components A, B, and C. The model fittingto the SED of combined fluxes from several YSOs wouldresult in a higher inferred stellar mass than that to eachof these individual YSOs, as demonstrated in Chen etal. (2010). In addition, extra uncertainties could incur infitting to these individual YSOs due to their lack of 24 µmmeasurements, as the very young ones have SEDs peakingat 24 µm or even longer wavelengths (Chen et al. 2009,2010). Most interestingly, the inferred mass of 24.8± 1.4M� from the integrated SED is consistent with that ofthe O7-9V ionizing star determined from our NIR spectra.It appears that the MIR luminosity is dominated by thiscompact HEB ionized by the most massive star (O7-9V)

in this group of stars.

In any case, It is not surprising that N26 hosts amassive YSO in its component C, because N26 is a veryyoung massive star formation region. In similar cases,YSOs have already been reported to be associated withother HEBs, for example the LMC objects N159-5 (Chenet al. 2010) and N11A (Vaidya et al. 2009), in spite of aspatial resolution of ≥ 0.5 pc. Moreover, thanks to a highspatial resolution of ∼ 0.06 pc, YSO candidates have beenlocated in the SMC HEB N88A (Testor et al. 2010). Hence,the presence of this YSO is compatible with the fact thatHEBs are sites of ongoing massive star formation.

As far as a broader view of the environment in whichN26 lies is concerned, this area of the SMC is a veryinteresting site of massive star formation. This statementis supported by the presence of several H ii regions andnumerous OB stars associated with a giant molecularcloud, as presented in the preceding sections. Massive

14 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

star formation has probably developed from the main H iiregion N22, which, with its several OB stars, has disruptedthe molecular cloud and has created a central cavity in theSMCB2-H ii complex. This suggests that the formation ofmassive stars has probably propagated from N22 in bothnorth and south directions.

This picture is consonant with the detection of the eightYSOs candidates toward the SMCB2-H ii complex, amongwhich seven massive ones. The most massive candidateof the sample, object #19, has a mass of 17.4± 3.0 M�(Table 6) and lies in the direction of the southern molecularridge, between the H ii regions N21 and N23. This objectis situated at about 4′′.5 from #29, which is the secondmost massive candidate of the sample, with a mass of14.0± 2.7 M�. There are four other YSO candidates inthat direction: #33, #75, #118, and #127. The presenceof these massive YSOs supports the observation that thesouthern concentration of the SMCB2 molecular cloudbordering the central N22 cavity is an active site of massivestar formation.

The other YSO candidates belong to the northernconcentration of the molecular cloud, where the compactH ii region N26 is located. The most massive object of thisgroup, i.e. #108, lies about 30′′(9 pc) south of N26 and hasa mass of 12.7± 1.3 M� (Table 6). Interestingly, this objectlies at the northern border of the central cavity. Althoughgeometrical coincidence cannot be firmly excluded, and wecannot reject the possibility that N22 simply erodes theless dense part of the clump that forms YSOs, there is aprobability that the formation of this object be related tonorthward expansion of the H ii region N22. The absenceof YSOs in the direction of N22 is due to the fact thatthere is no notable concentration of molecular gas anddust there. Indeed massive stars of N22 have disrupted themolecular cloud, creating the cavity visible on the Spitzerimages (Fig. 1).

More generally, apart from the lack of data, some wordsof caution are in order as to the method used in describingthe characteristics of the YSOs. The point spread function(PSF) of the IRAC bands at the SMC distance of 61 kpc is∼ 2′′, corresponding to ∼ 0′′.6 pc. The angular resolution forthe MIPS bands is even worse, ranging from ∼ 1.8 pc to12 pc for the 24 µm and 160 µm bands respectively. Evenwith a resolution of 0.6 pc, which is the size of a wholecluster, we may be probing the combined effects of theembedded components. For comparison, the Orion core,which includes lots of various components, among whichthe Trapezium cluster and BN/IRc2 (YSO), has a size ofonly ∼ 0.5 pc. Moreover, since we are dealing with H ii re-gions, an H ii region, taken globally, should contain severalcomponents such as strong nebular emission, UV photonsacting on dust concentrations (accompanied by secondaryIR emission), radio emission, embedded clusters, etc. Morespecifically, the contribution from PAH emission to theemission at IRAC wavelengths is significant, particularlyin the 8 µm band, making the sources easy to confuse withYSOs. Therefore, we must be very cautious in interpretingthe present data.

With the above precautions in mind, we now under-line another point in favor of the presence of the YSO

candidates. The SMCB2-H ii complex is a star formingregion enclosing strong ionized hydrogen emission, dustconcentrations, and hundreds of stars. We have detectedonly eleven YSOs toward this complex. The massivecandidates are moreover associated with the most recentmassive star formation events detectable in the optical andinfrared bands. It appears that massive stars tend to formwhere massive star formation has occurred before, a trendseen in other LMC H ii regions (Chen et al. 2009, 2010).Such sites already had the conditions to form massive starsin the past and hence unsurprisingly continue to form newmassive YSOs.

5. Concluding remarks

N26 is a member of the rare category of high-excitationblobs in the SMC. We have presented high spatial reso-lution imaging of this object in the JHKsL’-bands witha FWHM of ∼ 0′′.1-0′′.35. Imaging with a lower spatialresolution is also presented in B, V , near-IR, mid-IR, 24µm, and 70 µm for both N26 and its surrounding regions,which are associated with the molecular cloud SMCB2.Component A, which is ∼ 1′′ in size, contains at least twostars, one of which, A1, with a spectral type of O7-O9,might be the main exciting source of N26. Moreover,component A coincides with the radio continuum sourceB0046-7333. On the other hand, a bright component, C,which lies between A and B and has no optical counterpart,is uncovered for the first time. In general, N26 appears tocontain at least five stars superimposed on a very smallcluster of faint hardly resolved stars between componentA and star #160 in a ∼ 4′′ area. Components A and Care also found to be associated with several stars each.Massive star formation is probably still going on in N26,if the detection of the massive YSO (#172) is confirmed.This object is the most massive member of the massiveYSOs candidates in the SMCB2.

Mid-IR images of the molecular cloud SMCB2 at alarger scale of 50 pc x 76 pc display a shell structureof gas and dust surrounding a central cavity created byN22, the main H ii region of the molecular complex. N26,which is associated with the northern concentration ofthe shell, is the most compact and excited H ii regionof the complex. To check the presence of massive YSOsin other parts of the molecular cloud, we used selectioncriteria based on color-magnitude and color-color diagramsin various bands (B, V, L, J, H, Ks, 3.6, 4.5, 8.0, 24,70, and 160 µm), and then SED fitting on the qualifiedobjects. All the YSO candidates are associated with thetwo northern and southern concentrations or shells of themolecular complex SMCB2 bordering the central cavity.The southern concentration, notably N23, harbors moremassive YSO candidates than the northern concentration.A faint and compact H ii region with weak [O iii] λ5007emission is also detected toward this part of the complex.

We are aware that the low spatial resolution at the dis-tance of the SMC, in addition to contamination by dustand gas emission, makes the detection and classification ofYSOs questionable. However, taking the necessary precau-tions, we have to push the exploitation of the data to their

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 15

limit in order to study massive star formation in metal de-ficient galaxies, the nearest example of which is the SMC.

Acknowledgements. M.S. acknowledges financial support from theNASA ADAP award NNX11AG50G.

References

Allen, L.E., et al. 2004, ApJS, 154, 363Bica, E.D., Dutra, C.M. 2000, AJ, 119, 1214Black, J.H., van Dishoeck, E.F. 1987, ApJ, 322, 412Bolatto, A.D., Simon, J.D., Stanimirovic, S., van Loon, J.Th., and 11

authors. 2007, ApJ, 655, 212Bot, C., Rubio, M., Boulanger, F., et al. 2010, A&A, 524, 52Bonanos, A.Z, Lennon, D.J., Kohlinger, F., et al. 2010, AJ, 140, 416Chen, C.H.R., Chu, Y.-H., Gruendl, R. A., Gordon, K.D., Heisch, F.

2009, ApJ, 695, 511Chen, C.H.R., Indebetouw, R., Chu, Y.-H., Gruendl, R. A., Testor,

G., Heisch, F., Seale, J., Meixner, M., Sewilo, M. 2010, ApJ, 721,1206

Conti, P. S., Garmany, C. D., Massey, P. 1986, AJ, 92, 48Cutri, R. M., et al. 2003, The IRSA 2MASS All-Sky

Point Source Catalog, NASA/IPAC Infrared ScienceArchive. http://irsa.ipac.caltech.edu/applications/Gator/,

Damineli, A., Blum, R. D., Figueredo, E., & Conti, P. S. 2005. in:R. Cesaroni et al. (eds.), Massive Star Birth: A Crossroads ofAstrophysics (Cambridge: CUP); Pros. IAU Symp. 227, 407.

Davies, R. D., Elliot, K. H., Meaburn, J. 1976, MmRAS, 81, 89Dufour, R. J. 1984 , IAU Symp. 108: Structure and Evolution of the

Magellanic Clouds, 108, 353Gordon, K. D., Meixner, M., Meade, M. R., Whitney, B., et al. 2011,

AJ, 142, 102Gruendl, R. A., Chu, Y. 2009, ApJS, 184, 172Hanson, M., Luhman, K., Rieke. 2002, ApJS, 138, 35Henize, K. G. 1956, ApJS, 2, 315Heydari-Malayeri, M., Testor, G., & Lortet, M. C. 1980, A&A, 84,

154Heydari-Malayeri, M., &Testor, G. 1981, A&A, 96, 219Heydari-Malayeri, M., & Testor, G. 1982, A&A, 111, L11Heydari-Malayeri, M., Testor, G., Baudry, A., et al. 1982, A&A, 113,

118Heydari-Malayeri, M. 1988, A&A, 202, 240Heydari-Malayeri, M., Jarvis, B., Gilliotte, A. 1989, The Boller &

Chivens Spectrographs, ESO Operating Manual 9Heydari-Malayeri, M., Rosa, M.R., Charmandaris, V., Deharveng, L.,

Zinneker, H. 1999, A&A, 352, 665Heydari-Malayeri, M., Rosa, M. R., Charmandaris, V., et al. 2010,

The Impact of HST on European Astronomy, F. D. Macchetto(ed.), Astrophys. and Space Sci. Proc., p. 31

Heydari-Malayeri, M., Selier, R. 2010, A&A, 517, 39Hutchings, J.B., Thompson, I.B. 1988, ApJ, 331, 294Indebetouw, R., Johnson, K., Conti, P. 2004, AJ, 128, 2206Israel, F.P. 1997, A&A, 328, 471Israel, F.P., Maloney, P.R. 2011 arXiv:1104.2047v1Kato, D., Nagashima, C., Nagayama, T., et al. 2007, PASJ, 59, 615Keller, S. C., Wood, P. R. 2006, ApJ, 642, 834Lada, C.J. 1987, in IAU Symp. 115: Star Forming Regions, ed. M.

Peimbert & J. JugakuLada, C.J., A.A Muench, Haisch, Karl E., Jr, et al. 2000, ApJ,

120,3162Lawton, B., Gordon, K.D., et al. 2010, ApJ, 716, 453Lejeune, T., Shaerer, D. 2001, A&A, 366, 538Leroy, A., Bolatto, A., Stanimirovic, S., Mizuno, N., Israel, F., Bot,

C. 2007, ApJ658, 1027Maercker, M., Burton, G. 2005, A&A, 438, 663Martin-Hernandez, N.L., Vermeij, R., van der Hulst, J.M. 2005, A&A,

433, 205Martins, F, F., Shaerer, D., Hillier, D.J. 2005, A&A 436, 1049Massey, P., Lang, C., Degi-Eastwood, K., Garmany, C. 1995, ApJ,

438, 188Massey, P. 2002, ApJS, 141, 81Meixner, M., et al. 2006, AJ, 132, 2268Meynadier, F., Heydari-Malayeri, M. 2007, A&A 461, 565Mizuno, N., Rubio, M., Mizuno, A., Yamaguchi, R., Onishi, T., Fukui,

Y. 2001, PASJ, 53L, 45Pena-Guerrero, M. A., Peimbert, A., Peimbert, M., Ruiz, M. T. 2012,

ApJ, 746, 115

Rieke, G., et al. 2004, ApJS, 154, 25Robitaille, T., P., Whitney, B. A., Indebetouw, R., Wood, K.,

Denzmore, P. 2006 ApJS, 167, 256Robitaille, T., P., Whitney, B. A., Indebetouw, R., Wood, K. 2007

ApJS, 169, 328Rubio, M., Lequeux, J., Boulanger, F., et al. 1993, A&A, 271, 1Rubio, M., Contursi, A., Lequeux, J., Prost, R., Barba, R., Boulanger,

F., Cesarsky, D., Maoli, R. 2000, A&A, 359, 1139Schaefer, B. E. 2008, AJ 135, 112Selier, R., Heydari-Malayeri, M., Gouliermis, D. A. 2011, A&A, 529,

A40Selier, R., Heydari-Malayeri, M. 2012, A&A, 545, A29Shaw & Dufour 1995, PASP, 107, 896Schmidt-Kaler, T. 1982, Landolt-Bornstein, New Series, Group VI 2,

p. 14Simpson, J. P. 1973, PASP, 85, 479Stahler, S., W., Palla, F., HO, P. T. P. 2000, Protostars and Planets

IV, 327Stetson, P. B. 1987, PASP, 99, 191Testor, G. 2001, A&A, 372, 667Testor, G., Lemaire, J.L., Heydari-Malayeri, M., Kristensen, L.E.,

Diana, S., Field., D. 2010, A&A, 510, 95Vaidya, V., You-Hua Chu., Gruendl, R., Chen C.-H.R., Looney, L.W.

2009, ApJ, 707, 1417Westerlund, B.E. 1997, The Magellanic Clouds (Cambridge:

Cambridge Univ.Press), pp. 28-34Whitney, B. A., Indebetouw, R., Bjorkman, J.E., Wood, K. 2004,

ApJ, 617, 1177Whitney, B., Sewilo, M., Indebetouw, R., et al. 2008, AJ, 681, 1341Wilke, K, Stickel, M., Hass , M., Herbstmeier, U., Klaas, U, Lemke,

D. 2003, A&A, 401, 873

16 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMCTable

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515.8

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214.2

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310.7

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310.4

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55.8

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316

43.0

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617.3

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514.3

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214.3

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213.9

40.0

413.9

80.0

614.1

20.1

137

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55.8

9-7

316

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416.7

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515.7

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315.4

60.0

615.4

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415.3

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00.4

418.8

10.1

640

9614

047

56.9

0-7

318

12.1

516.3

60.0

316.4

10.0

316.6

70.0

216.7

50.0

516.8

20.0

842

9582

047

56.5

3-7

316

45.5

416.8

20.0

316.9

20.0

417.4

50.0

417.6

00.1

117.6

40.1

943

047

56.9

5-7

316

58.3

018.6

00.1

018.6

30.1

114.6

50.0

113.8

10.0

113.5

30.0

213.3

40.0

413.3

60.0

513.1

90.0

612.9

30.1

744

047

57.0

2-7

318

10.1

517.8

0.0

417.7

70.0

817.5

30.0

417.6

70.1

117.6

70.1

845

9636

047

57.6

1-7

317

49.7

616.6

10.0

316.4

70.0

416.4

10.0

216.3

50.0

416.3

60.0

514.4

50.0

614.4

10.1

014.1

40.1

846

9633

047

57.6

1-7

317

29.1

416.1

40.0

316.1

80.0

316.4

40.0

216.4

40.0

516.4

00.0

616.0

50.0

615.7

70.0

947

047

57.8

3-7

316

26.4

117.3

60.0

317.3

70.0

517.6

50.0

517.4

70.1

017.1

80.2

448

047

57.9

1-7

316

35.9

717.6

40.0

517.6

30.0

617.4

50.0

517.1

90.0

917.0

70.2

2

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 17

No

No

mα

(2000)

δ(2

000)

Ber

rV

err

Jer

rH

err

Ker

r3.6

mµ

err4.5

mµ

err

5.8

mµ

err

8.0

mµ

err

24m

µer

r70m

µer

r160m

µer

rT

ypeH

IIre

gio

n

49

047

58.4

0-7

317

36.0

617.7

40.0

417.7

90.0

416.0

615.7

750

047

59.1

2-7

316

19.1

318.9

60.1

217.7

90.0

715.5

70.0

214.9

20.0

214.7

70.0

214.5

90.0

314.6

30.0

514.3

40.1

151

047

59.1

4-7

316

33.9

017.6

10.0

416.8

90.0

515.6

80.0

115.3

60.0

215.2

90.0

315.1

20.0

315.1

60.0

652

047

59.1

7-7

316

41.7

118.5

50.0

917.4

30.0

515.6

20.0

115.0

40.0

214.9

10.0

214.8

10.0

314.8

60.0

753

047

59.2

2-7

316

30.2

018.4

30.0

717.2

10.0

515.2

70.0

114.6

40.0

214.5

10.0

214.3

40.0

314.3

70.0

414.1

80.0

954

047

59.2

7-7

317

48.0

617.2

90.0

416.9

20.0

416.1

80.0

316.0

20.0

315.9

20.0

455

047

59.4

9-7

317

45.5

618.2

70.0

817.5

10.0

515.2

60.0

214.4

90.0

214.2

90.0

213.9

70.0

513.9

40.0

613.8

20.1

656

047

59.6

4-7

316

54.7

017.7

20.0

417.5

20.0

417.3

40.0

317.3

60.0

917.1

20.1

257

047

59.8

2-7

315

34.3

017.9

60.0

317.8

20.0

358

9705

047

59.9

1-7

317

50.6

517.3

40.0

615.9

70.0

313.6

70.0

112.9

80.0

112.8

30.0

112.7

00.0

312.7

90.0

312.6

70.0

712.7

10.1

74.6

559

048

0.1

4-7

317

45.4

317.2

20.0

317.2

10.0

560

048

0.1

6-7

318

06.0

018.5

00.1

017.1

60.0

514.9

70.0

214.3

00.0

114.1

50.0

261

048

0.2

2-7

313

58.1

217.4

70.0

317.5

30.0

562

048

0.2

6-7

317

08.7

017.7

70.0

417.7

40.0

717.9

10.0

517.7

90.1

263

048

0.2

9-7

316

29.6

818.1

20.0

517.1

70.0

515.0

00.0

214.3

80.0

114.1

70.0

214.0

10.0

313.9

60.0

514.0

20.0

714.1

20.1

964

9710

048

0.1

6-7

316

31.7

916.7

00.0

316.6

80.0

416.6

916.7

316.7

765

048

0.2

7-7

316

30.2

015.0

00.0

214.3

80.0

114.1

70.0

214.1

366

9715

048

0.3

5-7

315

07.3

517.7

30.0

316.5

90.0

314.3

90.0

213.7

70.0

213.6

20.0

213.4

40.0

313.5

10.0

313.4

30.0

713.0

70.1

967

9729

048

0.5

5-7

317

20.5

415.3

50.0

213.5

30.0

310.7

20.0

19.9

10.0

29.7

50.0

39.5

80.0

29.7

00.0

29.5

90.0

29.5

30.0

368

048

0.6

0-7

314

34.0

419.3

40.0

818.3

60.0

716.4

30.0

315.9

40.0

315.8

30.0

469

048

0.6

6-7

314

29.8

217.7

90.0

317.5

70.0

317.0

80.0

317.0

10.0

716.9

50.1

070

9737

048

0.8

2-7

314

37.9

416.9

70.0

316.3

00.0

215.0

60.0

214.7

90.0

214.7

40.0

214.5

40.0

414.4

80.0

571

048

0.9

2-7

315

24.5

518.8

70.0

618.0

10.0

616.4

20.0

216.0

10.0

315.9

20.0

472

048

1.1

5-7

315

35.9

517.7

40.0

317.7

20.0

417.2

00.0

816.9

60.0

617.0

00.1

173

048

1.1

9-7

317

11.7

517.5

70.0

416.5

00.0

414.6

60.0

114.0

90.0

213.9

90.0

213.9

00.0

513.9

20.0

513.9

60.1

074

9762

048

1.3

2-7

315

23.5

117.0

60.0

316.9

60.0

416.2

10.0

216.0

50.0

315.8

90.0

875

048

1.2

3-7

316

59.3

017.7

40.0

717.5

80.2

616.7

30.2

214.4

30.0

714.2

50.0

411.9

50.0

410.5

30.0

86.7

90.0

1II

N22

76

048

1.6

5-7

314

31.2

218.7

217.8

60.0

516.0

60.0

115.5

30.0

215.4

50.0

377

048

1.6

5-7

316

20.6

118.9

10.1

118.6

30.1

378

048

1.7

8-7

316

05.3

419.1

00.0

718.4

30.0

417.1

40.0

316.8

00.0

616.6

40.0

779

048

2.0

5-7

316

39.3

017.6

30.0

517.6

90.0

417.8

40.0

517.6

00.0

717.5

80.0

880

9792

048

2.0

0-7

313

57.9

616.4

10.0

216.3

70.0

381

048

2.1

9-7

314

04.5

218.3

10.0

518.3

40.0

782

048

2.4

0-7

316

56.7

016.6

10.0

316.6

70.0

417.0

40.0

417.1

40.1

083

9821

048

2.4

0-7

316

59.8

116.4

80.0

215.0

00.0

312.5

10.0

111.8

60.0

111.6

80.0

111.5

00.0

311.5

30.0

311.4

40.0

411.2

20.0

684

048

2.4

8-7

315

41.8

017.5

70.0

317.5

00.0

317.3

90.0

417.3

80.0

817.2

00.1

285

048

2.4

2-7

314

42.6

018.4

40.0

817.8

50.1

317.6

70.1

886

9824

048

2.5

5-7

316

38.2

014.2

70.0

414.3

60.0

314.7

50.0

214.8

50.0

214.9

20.0

214.7

80.0

314.7

40.0

614.5

80.0

987

048

2.5

9-7

317

30.1

017.8

40.0

617.6

30.0

617.3

90.0

417.4

50.1

017.4

20.1

588

048

2.6

1-7

315

27.1

018.3

10.0

818.0

20.1

617.7

30.1

989

048

2.7

2-7

314

19.8

718.6

20.0

518.3

60.0

718.3

10.0

818.0

20.1

617.7

30.0

990

9839

048

2.8

3-7

318

13.2

216.2

50.1

316.2

60.0

417.7

50.0

917.2

10.0

917.8

10.2

591

048

2.7

8-7

315

00.5

017.6

30.0

417.0

20.0

517.0

40.1

192

9845

048

3.0

-73

16

11.9

514.2

10.0

514.4

00.0

214.9

60.0

115.0

20.0

215.1

30.0

393

048

2.9

8-7

314

28.4

118.7

20.0

417.3

40.0

317.8

00.0

917.2

90.0

817.1

80.0

813.6

20.0

413.6

40.0

413.5

60.0

994

048

2.9

4-7

314

57.6

019.1

50.2

318.2

60.1

817.7

10.1

095

048

3.1

2-7

314

23.0

618.2

40.0

517.9

10.0

417.6

80.0

917.4

60.1

196

9834

048

3.0

4-7

315

19.1

417.5

90.0

316.3

70.0

313.9

70.0

213.3

20.0

213.1

80.0

213.0

20.0

313.0

60.0

312.9

70.0

7

18 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

No

No

mα

(2000)

δ(2

000)

Ber

rV

err

Jer

rH

err

Ker

r3.6

mµ

err4.5

mµ

err

5.8

mµ

err

8.0

mµ

err

24m

µer

r70m

µer

r160m

µer

rT

ypeH

IIre

gio

n

97

048

3.3

1-7

316

4.5

716.4

30.0

316.4

10.0

216.3

10.0

216.2

30.0

316.0

20.0

598

048

3.3

1-7

317

56.9

117.6

20.0

517.0

70.0

516.0

50.0

215.7

00.0

315.5

90.0

499

048

3.7

1-7

315

58.8

317.9

80.0

316.6

40.0

314.1

10.0

113.3

90.0

113.2

20.0

113.0

80.0

313.1

20.0

313.1

20.0

513.3

90.1

6100

9877

048

3.8

5-7

315

32.5

216.3

60.0

715.4

90.0

213.8

30.0

113.3

70.0

113.3

00.0

113.2

60.0

313.2

90.0

413.2

80.0

513.1

40.0

9101

048

3.8

7-7

318

10.3

918.4

00.0

718.0

00.1

0102

048

3.8

9-7

314

34.2

618.2

50.0

518.3

30.0

6103

048

3.9

1-7

314

01.0

018.4

60.0

518.2

20.0

6104

048

4.0

1-7

315

13.3

018.4

90.1

118.1

40.1

618.0

10.1

4105

048

4.1

3-7

314

04.3

818.5

80.0

417.5

00.0

5106

048

4.1

7-7

317

03.1

817.2

60.0

417.2

90.0

517.6

40.0

417.8

20.1

417.4

00.1

5107

048

4.3

0-7

315

03.2

418.3

90.0

818.3

90.0

9108

048

4.3

9-7

315

21.6

019.0

00.1

016.9

00.0

316.1

70.0

514.8

40.0

312.5

00.0

311.5

70.0

210.4

40.0

28.8

60.0

23.6

00.0

1I

N22

109

048

4.4

3-7

315

21.5

016.9

00.0

316.1

70.0

514.9

60.0

3110

048

4.5

0-7

316

11.0

816.5

20.0

316.7

10.0

217.1

80.0

417.3

20.0

917.3

30.1

5111

048

4.6

6-7

316

03.4

518.5

40.0

517.2

10.0

314.2

70.0

113.4

40.0

113.2

20.0

112.9

80.0

313.0

50.0

313.0

00.0

513.0

40.0

7112

048

4.7

6-7

317

32.8

718.3

70.0

818.2

70.0

9113

048

4.7

8-7

316

14.2

418.4

60.0

517.3

80.0

315.2

00.0

214.5

50.0

214.4

20.0

1114

048

4.7

5-7

314

52.9

018.7

40.0

918.3

50.1

917.4

40.1

0115

048

4.8

6-7

316

15.7

217.6

70.0

716.6

80.0

314.8

50.0

214.2

90.0

114.1

60.0

113.6

70.0

513.4

50.0

713.5

90.1

4116

048

4.8

6-7

314

48.8

618.6

90.1

017.8

10.1

417.5

70.1

3117

048

4.8

8-7

316

44.2

918.5

60.0

917.0

70.0

414.4

50.0

113.6

70.0

113.4

80.0

113.3

30.0

313.4

00.0

513.2

60.0

513.3

40.1

0118

048

4.9

0-7

317

55.9

217.8

70.0

816.5

10.0

615.1

40.0

612.7

60.0

311.4

10.0

210.2

70.0

29.0

00.0

23.0

60.0

1-1

.06

0.0

1I

N23

119

048

4.9

1-7

318

16.3

818.1

50.0

817.2

90.0

4120

048

4.9

5-7

316

18.0

618.1

017.8

80.0

8121

9922

048

5.1

1-7

315

53.1

215.8

30.0

215.9

20.0

216.2

20.0

216.2

20.0

316.2

10.0

5122

048

5.3

7-7

316

04.5

217.0

717.0

40.0

316.9

60.0

216.8

90.0

616.7

50.0

8123

048

5.4

0-7

315

12.3

017.6

20.0

417.2

60.0

817.0

00.1

1124

048

5.4

3-7

315

03.6

015.9

50.0

215.2

80.0

215.0

60.0

2125

9944

048

5.5

8-7

316

18.5

016.3

90.0

315.4

20.0

313.3

80.0

112.7

60.0

112.6

10.0

112.4

70.0

312.5

0.0

312.4

40.0

312.4

30.0

6126

048

5.5

8-7

317

23.6

718.2

90.0

818.3

50.1

0127

048

5.8

2-7

317

43.6

016.0

60.0

214.7

60.0

213.4

40.0

211.3

30.0

210.5

00.0

19.7

50.0

18.6

90.0

15.2

80.0

1II

128

048

5.6

6-7

314

59.7

018.1

00.0

717.6

20.1

017.3

60.1

114.9

514.9

4129

048

5.7

5-7

314

31.8

818.3

20.0

418.3

50.0

9130

048

5.7

5-7

316

24.4

817.3

20.0

416.0

10.0

313.7

90.0

113.1

00.0

112.9

50.0

212.8

30.0

312.8

20.0

312.7

60.0

412.7

70.0

6131

048

6.0

2-7

314

53.5

018.3

00.0

917.8

60.1

317.6

30.1

0132

048

6.1

4-7

316

10.3

118.2

90.0

818.3

60.0

713.7

113.5

513.4

813.2

3133

048

6.2

3-7

314

57.2

518.1

00.0

617.5

60.1

117.3

40.1

4134

048

6.2

3-7

315

18.6

219.2

718.5

10.0

916.8

90.0

216.5

40.0

516.5

60.0

7135

048

6.3

7-7

315

33.9

817.7

90.0

317.7

30.0

317.8

60.0

417.8

90.1

317.7

70.2

0136

9989

048

6.5

7-7

317

0.6

215.3

00.0

215.4

00.0

315.6

80.0

515.6

50.0

415.5

00.0

514.8

50.0

414.6

50.0

714.3

40.0

913.8

60.1

5137

048

6.4

8-7

315

14.1

0138

048

6.5

4-7

314

44.1

018.1

80.0

617.9

30.1

217.6

20.1

618.1

8139

048

6.6

1-7

315

08.4

018.5

50.0

417.6

50.0

415.9

30.0

215.4

40.0

215.3

30.0

3140

048

6.6

5-7

315

07.0

617.5

70.0

317.5

90.0

317.6

60.0

717.6

60.1

417.4

40.1

5141

048

6.8

6-7

314

45.7

217.3

40.0

317.4

20.0

417.6

90.0

517.6

10.1

013.7

9142

048

6.9

3-7

317

15.6

818.6

60.1

018.8

10.1

6143

048

6.9

5-7

314

20.2

018.3

70.0

818.3

90.0

9144

048

6.9

9-7

315

21.5

015.8

90.0

115.1

10.0

214.8

50.0

2

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 19

No

No

mα

(2000)

δ(2

000)

Ber

rV

err

Jer

rH

err

Ker

r3.6

mµ

err4.5

mµ

err

5.8

mµ

err

8.0

mµ

err

24m

µer

r70m

µer

r160m

µer

rT

ypeH

IIre

gio

n

145

048

7.1

5-7

315

11.2

617.2

60.0

317.3

30.0

317.8

10.0

5146

048

7.2

2-7

315

13.4

018.6

20.0

417.4

50.0

315.0

10.0

214.3

50.0

114.2

00.0

214.0

10.0

314.0

40.0

414.0

70.1

0147

9989

048

7.2

5-7

317

01.7

816.5

90.0

316.6

90.0

317.2

60.0

317.3

70.0

917.6

30.0

8148

048

7.2

7-7

316

43.8

218.1

90.0

718.3

10.0

8149

048

7.3

4-7

315

42.1

118.0

10.0

416.6

50.0

213.4

10.0

313.5

30.0

513.4

50.0

613.3

00.0

9150

048

7.4

6-7

315

04.0

116.6

10.0

316.4

70.0

217.2

90.0

317.1

50.0

817.2

60.1

3151

048

7.5

7-7

315

03.8

518.5

80.0

818.1

80.0

517.2

90.0

317.1

50.0

817.2

60.1

3152

048

7.5

5-7

314

44.9

018.3

20.0

418.0

10.1

517.4

60.1

0153

048

7.5

9-7

314

44.7

317.3

415.9

70.0

418.9

20.0

7154

p0

48

7.6

1-7

314

28.1

918.5

718.4

50.0

817.9

70.0

717.2

00.1

016.7

80.1

313.9

00.1

413.5

00.1

911.5

70.1

010.1

20.1

54.6

90.0

2II

N25

155

10034

048

7.6

5-7

316

21.0

515.7

50.0

615.9

40.0

416.5

10.0

216.7

20.0

616.7

00.0

7156

10036

048

7.7

3-7

317

22.0

316.6

80.0

416.9

10.0

417.4

70.0

317.5

90.1

017.7

00.2

2157

10046

048

7.9

1-7

317

37.5

716.7

30.0

316.7

60.0

416.8

30.0

316.6

20.0

716.6

70.1

1158

048

7.8

1-7

316

12.0

419.3

218.4

50.0

416.9

00.0

316.3

90.0

416.3

60.0

6159

048

8.1

8-7

314

57.3

617.3

016.9

20.0

317.2

00.0

916.7

60.1

116.1

00.1

1160

n0

48

8.1

8-7

314

57.3

617.9

70.0

717.1

50.0

916.3

30.0

9161

048

8.2

0-7

317

46.3

619.8

10.1

616.8

10.0

914.2

50.0

213.8

00.0

113.6

40.0

213.4

80.0

313.5

00.0

313.3

50.0

7162

048

8.2

1-7

314

18.9

916.4

90.0

916.0

80.0

215.2

50.0

114.8

90.0

814.8

10.0

214.7

10.0

414.5

40.0

64.6

2163

048

8.3

4-7

314

22.9

517.4

50.0

317.2

40.0

316.6

80.0

216.3

70.0

416.3

60.0

6164

048

8.3

7-7

315

32.9

919.1

90.0

718.2

00.0

516.0

70.0

215.4

30.0

215.2

90.0

3165

048

8.3

9-7

316

16.7

417.8

30.0

616.9

70.0

215.6

60.0

115.2

90.0

215.1

70.0

2166

048

8.4

4-7

314

47.0

916.7

50.0

216.7

10.0

216.7

40.0

216.7

40.0

516.8

30.0

9167

048

8.4

9-7

314

46.2

016.3

50.0

215.8

80.0

315.7

00.0

4168

048

8.4

8-7

314

46.1

018.5

00.0

917.1

60.0

414.9

714.3

014.1

5169

m210069

048

8.6

0-7

314

54.6

914.8

20.0

214.2

80.0

213.6

80.0

513.1

50.0

612.3

70.0

511.2

20.0

610.2

70.0

48.7

30.0

37.0

20.0

90.0

50.0

1-3

.51

0.0

1-5

.24

0.0

2I

N26

170

n0

48

8.5

2-7

314

54.3

115.7

60.0

415.4

50.0

414.6

70.0

214.5

40.0

313.8

60.0

411.7

8II

IN

26-A

171

048

8.7

5-7

315

26.4

018.5

90.0

817.7

50.1

317.4

80.1

0172

n0

48

8.7

4-7

314

54.5

314.5

30.0

213.8

50.0

313.0

60.0

411.4

3I

N26-C

173

n0

48

8.9

6-7

314

53.7

016.8

70.0

416.4

60.0

415.2

40.0

214.9

50.0

414.3

40.0

412.7

8II

IN

26-B

174

048

9.0

8-7

315

02.7

517.6

70.0

517.1

30.0

917.2

40.1

1176

048

9.0

4-7

315

01.3

518.1

517.2

90.0

413.9

714.0

613.8

5177

048

9.0

5-7

316

14.3

517.8

90.0

417.9

80.0

3178

048

9.1

9-7

315

21.3

418.4

40.0

417.3

70.0

315.2

70.0

114.6

20.0

214.4

90.0

214.2

90.0

514.2

70.0

6179

048

9.2

5-7

317

31.0

917.9

20.1

018.0

90.0

8180

048

9.3

4-7

314

18.5

018.3

40.0

718.1

80.0

9181

048

9.3

4-7

317

38.2

918.0

70.0

518.0

80.0

9182

10107

048

9.3

6-7

314

15.6

214.2

10.0

414.3

40.0

214.7

50.0

114.8

20.0

214.8

90.0

3183

048

9.4

0-7

314

24.0

516.9

50.0

317.0

10.0

417.4

70.0

417.1

00.0

917.0

00.1

4184

048

9.4

2-7

317

23.9

818.4

10.0

818.4

00.0

5185

048

9.4

3-7

315

39.6

316.4

10.0

216.5

10.0

216.9

50.0

317.0

40.0

316.9

10.1

0186

048

9.4

6-7

314

40.5

817.7

90.0

417.1

60.0

716.8

60.0

9187

048

9.5

5-7

315

05.7

017.7

90.0

617.3

60.0

917.2

70.1

2188

n0

48

9.5

4-7

314

57.0

917.3

70.0

417.0

20.0

816.7

90.0

9189

048

9.5

4-7

314

57.0

917.6

20.0

517.0

70.0

417.3

00.0

917.1

20.1

716.6

70.0

8190

048

9.5

5-7

315

32.7

718.1

40.0

418.4

00.0

416.7

50.0

316.4

20.0

416.4

50.0

7191

048

9.6

7-7

314

56.6

016.7

60.0

717.0

90.1

0192

048

9.6

9-7

314

07.2

418.0

20.0

517.9

40.0

3193

n0

48

9.7

8-7

314

56.0

217.2

90.0

317.2

10.0

317.4

30.0

517.0

10.0

817.0

90.0

8194

048

9.7

9-7

314

26.9

618.3

10.0

418.2

60.0

4

20 G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC

No

No

mα

(2000)

δ(2

000)

Ber

rV

err

Jer

rH

err

Ker

r3.6

mµ

err4.5

mµ

err

5.8

mµ

err

8.0

mµ

err

24m

µer

r70m

µer

r160m

µer

rT

ypeH

IIre

gio

n

195

048

9.8

4-7

314

15.9

718.0

60.0

717.7

70.0

3196

048

9.9

7-7

315

18.3

218.0

00.0

416.0

50.0

211.5

210.5

810.3

79.9

80.0

210.0

00.0

39.8

50.0

29.8

00.0

3197

048

10.1

1-7

315

46.1

417.7

90.0

416.9

30.0

215.3

90.0

114.9

30.0

214.8

20.0

214.6

60.0

314.6

90.0

6198

048

10.2

7-7

314

59.6

418.4

00.0

718.0

00.0

4199

048

10.2

8-7

315

44.3

617.4

80.0

817.5

20.0

317.9

00.0

5200

048

10.3

7-7

314

39.2

917.7

10.0

517.3

50.0

917.3

20.1

6201

048

10.5

0-7

315

08.6

0202

048

10.4

4-7

314

59.8

918.2

40.0

717.9

00.0

416.3

90.0

215.8

90.0

315.7

40.0

4203

10160

048

10.5

0-7

316

01.3

316.2

90.0

215.9

80.0

215.2

60.0

115.1

00.0

215.0

70.0

3204

048

10.8

2-7

314

43.9

017.9

40.0

617.3

60.0

617.2

00.1

1205

048

10.8

9-7

315

13.1

016.4

40.0

216.2

50.0

215.9

80.0

216.0

00.0

315.9

90.0

4206

048

11.1

3-7

315

16.7

018.5

60.1

018.3

40.2

417.6

50.2

1207

048

11.2

7-7

314

51.7

319.3

918.1

80.0

316.3

10.0

215.7

90.0

315.6

60.0

4208

048

11.4

3-7

315

35.0

718.8

80.0

618.0

00.0

3209

10196

048

11.4

8-7

314

33.0

015.1

90.0

214.9

10.0

214.2

90.0

214.2

20.0

114.1

20.0

113.9

40.0

413.9

90.0

613.5

60.1

1210

048

11.5

9-7

314

48.7

119.5

00.1

218.4

30.0

416.7

00.0

316.2

30.0

216.1

10.0

5211

048

11.9

8-7

315

08.9

318.8

70.1

318.9

619.2

0212

048

11.9

4-7

314

47.4

017.3

70.0

316.7

50.0

516.6

10.0

7213

048

12.0

4-7

315

00.6

018.4

50.0

717.9

70.1

517.7

10.1

7214

048

12.0

9-7

315

15.2

018.0

40.0

617.9

50.1

317.6

10.1

9215

048

12.1

7-7

315

11.8

017.9

00.1

517.7

10.1

217.6

30.1

8216

048

12.1

9-7

316

05.4

518.0

60.0

418.0

50.0

3217

048

12.3

7-7

315

38.3

117.8

20.0

316.7

50.0

214.0

60.0

314.1

00.0

413.7

50.0

7218

048

12.7

0-7

315

25.4

017.6

20.1

316.8

70.1

316.1

10.1

6219

048

12.8

0-7

315

58.9

017.2

80.0

316.8

90.0

516.8

40.0

916.6

30.0

816.5

70.1

2220

048

12.9

4-7

314

01.9

617.7

80.0

417.2

10.0

3221

048

12.9

7-7

313

57.1

317.6

20.0

617.7

40.0

4222

048

13.1

8-7

314

44.7

618.1

00.0

718.0

50.2

018.0

4223

048

13.2

3-7

315

21.7

017.8

50.0

517.3

10.0

717.2

80.1

4224

10260

048

12.8

5-7

315

31.8

016.5

00.0

214.9

90.0

212.4

70.0

111.7

80.0

111.5

90.0

111.4

00.0

211.5

10.0

311.4

20.0

411.2

90.1

0225

048

13.2

0-7

314

05.9

518.9

017.7

60.0

3226

048

13.2

4-7

314

44.5

418.3

30.0

418.1

70.0

2227

048

13.3

7-7

314

09.8

218.6

90.0

517.7

30.0

315.9

90.0

215.4

80.0

215.3

90.0

2228

048

13.7

8-7

316

17.9

519.2

80.0

818.4

80.0

5229

048

14.4

4-7

315

15.3

019.2

40.1

418.2

70.0

716.4

60.0

215.9

30.0

315.8

20.0

315.6

20.0

615.6

80.0

8230

048

14.6

8-7

314

57.2

318.7

40.0

418.0

60.0

416.4

20.0

215.9

30.0

315.8

30.0

415.6

40.0

515.7

00.0

8231

048

14.8

8-7

315

06.8

018.8

10.0

517.1

90.0

314.3

90.0

113.6

10.0

113.3

30.0

113.1

90.0

213.2

70.0

313.1

70.0

513.1

20.1

0232

048

14.9

3-7

316

17.3

717.9

80.0

418.0

30.0

5233

048

15.2

3-7

315

01.2

918.0

00.0

317.8

70.0

3234

048

16.3

1-7

314

38.3

318.0

00.0

417.7

90.0

3235

048

16.3

4-7

316

02.1

917.2

40.0

215.4

10.0

114.8

80.0

214.7

40.0

214.6

10.0

414.6

70.0

5236

048

16.9

9-7

315

18.5

418.4

30.0

417.1

00.0

314.8

30.0

114.1

50.0

113.9

90.0

113.8

70.0

313.9

50.0

413.8

60.0

613.0

70.1

8237

048

17.0

8-7

314

24.2

718.1

10.0

317.6

90.0

416.2

90.0

216.0

00.0

315.8

70.0

4238

048

17.5

4-7

315

34.7

418.3

60.0

418.2

90.0

5239

048

17.7

2-7

315

16.0

118.3

30.0

417.4

60.0

316.0

20.0

215.6

30.0

215.5

50.0

3240

048

17.8

5-7

315

28.5

618.0

30.0

417.1

90.0

3241

048

18.0

5-7

315

01.4

318.3

40.0

418.3

10.0

6242

048

18.0

6-7

314

03.5

318.3

10.0

417.2

70.0

5243

048

18.3

0-7

314

52.7

517.9

40.0

417.9

10.0

3

G. Testor et al.: NIR VLT/NACO observations of N26 in the SMC 21

No

No

mα

(2000)

δ(2

000)

Ber

rV

err

Jer

rH

err

Ker

r3.6

mµ

err4.5

mµ

err

5.8

mµ

err

8.0

mµ

err24m

µer

r70m

µer

r160m

µer

rT

ypeH

IIre

gio

n

244

048

18.4

5-7

315

28.5

119.2

70.1

218.3

40.0

5245

048

18.5

5-7

315

48.9

417.6

20.0

417.4

80.0

416.3

60.0

215.8

40.0

315.7

10.0

4246

048

18.7

5-7

315

24.6

418.5

30.0

418.0

60.0

4247

048

18.8

3-7

315

39.9

917.8

50.0

417.5

10.0

316.4

50.0

216.2

00.0

416.1

90.0

5248

10503

048

18.9

0-7

314

59.0

113.0

60.0

213.0

60.0

213.1

70.0

113.1

90.0

113.1

90.0

113.1

40.0

712.9

20.0

512.8

60.1

249

048

19.0

2-7

316

01.4

717.5

00.0

317.4

20.0

416.8

30.0

516.6

30.0

816.4

00.0

8250

048

19.1

6-7

314

20.5

018.1

60.0

418.2

20.0

4251

048

19.3

2-7

316

09.7

918.7

70.0

518.3

30.0

4252

10532

048

19.5

0-7

316

02.2

915.8

40.0

215.4

20.0

214.4

70.0

114.2

50.0

114.1

60.0

113.9

70.0

514.0

60.0

513.8

50.0

8253

048

19.7

9-7

314

02.1

618.2

50.0

517.2

00.0

4254

048

19.7

9-7

314

22.2

917.4

00.0

317.4

70.0

216.8

016.2

316.1

6255

048

19.9

6-7

314

50.9

918.4

50.0

418.4

50.0

4256

048

20.1

1-7

315

44.9

919.3

40.0

818.3

80.0

516.8

90.0

416.3

90.0

616.3

30.0

7257

048

20.2

9-7

316

08.8

819.0

50.0

818.2

70.0

416.8

70.0

516.6

60.0

516.6

20.0

7258

048

20.3

9-7

315

19.9

119.3

60.0

818.1

40.0

416.2

30.0

215.6

80.0

215.6

00.0

3259

048

20.7

9-7

314

09.6

317.9

20.0

418.0

00.0

3260

048

21.0

3-7

315

25.1

617.4

10.0

317.4

30.0

3261

10604

048

21.2

7-7

314

25.9

117.3

00.0

316.8

70.0

215.9

20.0

215.7

30.0

215.6

90.0

3262

048

21.3

0-7

314

15.0

118.6

50.0

517.4

10.0

4263

048

21.3

2-7

313

59.1

617.3

70.0

317.3

90.0

3264

10631

048

21.3

4-7

315

38.3

416.3

20.0

215.8

70.0

214.9

50.0

114.7

30.0

114.6

70.0

214.4

40.0

414.3

70.0

514.0

40.0

7265

048

21.5

4-7

315

40.4

318.1

10.0

418.0

90.0

4266

048

21.5

5-7

315

59.0

017.0

80.0

417.1

20.0

4267

10642

0.4

821.6

0-7

315

55.0

116.2

30.0

216.1

90.0

216.0

70.0

115.9

80.0

315.8

10.0

4268

048

21.6

3-7

314

13.7

818.6

90.0

417.7

90.0

316.0

90.0

215.6

60.0

215.5

30.0

3269

048

22.0

2-7

314

16.8

019.3

40.1

418.1

90.0

4270

048

22.2

1-7

315

31.7

216.8

50.0

317.0

20.0

3

mM

ass

eyca

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ber

.m

2B

and

Vm

agnit

ude

from

Mass

ey(2

002)

and

JH

Kfr

om

2M

ASS

(Cutr

iet

al.

2003)

for

the

unre

solv

edst

ar

#169.

nJH

KL’m

agnit

udes

ofth

eco

mponen

tsA

,B

,and

CofN

26

and

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Km

agnit

udes

ofth

ree

nei

ghbori

ng

fain

tst

ars

#160,#

188

and

#193

obta

ined

from

NA

CO

photo

met

ry.

pA

sth

ephoto

met

ryin

the

Sage

cata

log

isnot

com

ple

tew

eder

ived

the

magnit

udes

ofIR

AC

and

24µ

bands

from

the

images

usi

ng

Daophot.

ph

Inth

isca

talo

gth

ephoto

met

ryof

this

star

isnot

com

ple

teei

ther

.A

sit

sFW

HM

isla

rger

than

the

psf

(∼4′′),

we

der

ived

the

magnit

udes

from

asu

mof

the

pro

file

scr

oss

ing

the

whole

star

and

anei

ghbouri

ng

isola

ted

star

use

das

standard

.