J/ApJ/730/78 Hubble and Spitzer photometry of NGC 602 (Carlson+, 2011)
A panchromatic view of NGC 602: time-resolved star formation with the Hubble and Spitzer space telescopes. Carlson L.R., Sewilo M., Meixner M., Romita K.A., Whitney B., Hora J.L., Cignoni M., Sabbi E., Nota A., Sirianni M., Smith L.J., Gordon K., Babler B., Bracker S., Gallagher J.S., Meade M., Misselt K., Pasquali A., Shiao B. <Astrophys. J., 730, 78 (2011)> =2011ApJ...730...78C
ADC_Keywords: YSOs ; Clusters, open ; Photometry, HST ; Photometry, infrared Keywords: ISM: individual objects (NGC 602, N90) - Magellanic Clouds - stars: formation - stars: pre-main sequence - stars: protostars Abstract: We present the photometric catalogs for the star-forming cluster NGC 602 in the wing of the Small Magellanic Cloud covering a range of wavelengths from optical (HST/ACS F555W, F814W, and SMARTS/ANDICAM V, I) to infrared (Spitzer/IRAC 3.6, 4.5, 5.8, and 8um and MIPS 24um). Combining this with Infrared Survey Facility near-infrared photometry (J, H, Ks), we compare the young main sequence (MS) and pre-main sequence (PMS) populations prominent in the optical with the current young stellar object (YSO) populations revealed by the infrared. We analyze the MS and PMS population with isochrones in color-magnitude diagrams to derive ages and masses. The optical data reveal ∼565 PMS candidates, low-mass Stage III YSOs. We characterize ∼40 YSOs by fitting their spectral energy distributions to a grid of models (Robitaille et al. 2007ApJS..169..328R) to derive luminosities, masses, and evolutionary phase (Stages I-III). The higher resolution HST images reveal that ∼70% of the YSO candidates are either multiples or protoclusters. For YSOs and PMS sources found in common, we find a consistency in the masses derived. We use the YSO mass function to derive a present-day star formation rate of ∼0.2-1.0M☉/yr/kpc2, similar to the rate derived from the optical star formation history suggesting a constant star formation rate for this region. Description: Observations of NGC 602 (J2000=01:29:31-73:33:15) were taken from the optical to the mid-IR (Figure 2). We use optical data primarily from the HST/ACS Wide Field Channel (WFC) in F555W (V), F658N (Hα), and F814W (I). We add ground-based observations from the SMARTS (Small and Moderate Aperture Research Telescope System) ANDICAM instrument on a 1.3m telescope in Johnson-Cousins V and I bands. Five mid-IR images were taken through each of the four Spitzer/IRAC bands (Program ID 125, PI: Fazio, AOR 12485120). We also use near-IR photometry from the Magellanic Clouds Point Source Catalog of Kato et al. (2007, Cat. II/288). This imaging survey was performed with the simultaneous three-color Infrared Imager for Unbiased Surveys (SIRIUS) aboard the Infrared Survey Facility (IRSF) 1.4m telescope at the South African Astronomical Observatory's Southland. Multiwavelength Imaging Photometer for Spitzer (MIPS) 24um data are taken from the first epoch observations of SAGE-SMC (K. Gordon et al. 2011AJ....142..102G). These observations were performed in 2007 October. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 98 4535 Optical photometry table table3.dat 201 500 IRAC photometry table table4.dat 202 81 Fluxes of all 77 fitter sources including those fit in multiple ways table5.dat 107 51 *Young stellar object parameters
Note on table5.dat: For those sources with optical counterparts, we list the number of visually identifiable optical sources. Where possible, we determine masses of the optical sources; others either have no good optical photometry or are so young or of such low mass (M≲0.5M☉) that their masses cannot be determined from our evolutionary tracks (see Figure 3 (b)).
See also: II/288 : IRSF Magellanic Clouds Point Source Catalog (Kato+ 2007) II/305 : SAGE LMC and SMC IRAC Source Catalog (IPAC 2009) J/ApJ/681/290 : HST/ACS photometry in the SMC (Schmalzl+, 2008) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 I4 --- Seq [1/4535] Source index number 6- 14 A9 --- --- [HSTNGC602] 16- 36 A21 --- Name Source designation (JHHMMSS.sss+DDMMSS.ss) 38- 45 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000) 47- 55 F9.5 deg DEdeg Declination in decimal degrees (J2000) 57- 62 F6.3 mag Vmag ?=0 HST/ACS F555W filter magnitude 64- 68 F5.3 mag e_Vmag ?=0 Uncertainty in Vmag 70- 75 F6.3 mag Imag [13.51/27.91] HST/ACS F814W filter magnitude 77- 81 F5.3 mag e_Imag Uncertainty in Imag 83- 84 I2 --- s [2/12] Source of photometry (1) 86- 89 I4 --- S08 Schmalzl et al. 2008, Cat. J/ApJ/681/290 identifier (<Cl* NGC 602 SGD NNNN> for Simbad) 91- 92 I2 --- H91 ?=0 Hutchings et al. 1991AJ....101..933H spectroscopic O/B star number (<Cl* NGC 602 HTCP NN> in Simbad) 94- 96 I3 --- IRAC [1/598]?=0 Matching IRAC source identifier from Table 3 98 I1 --- N [0/9] Total number of optical sources matching the same IRAC source
Note (1): Flags indicate the photometric data used: 2 = ACS; 6 = ground-based (SMARTS); 12 = ACS/SMARTS combination.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 3 I3 --- ID [7/703] Source index number 5- 34 A30 --- Name Source designation (SSTNGC602/SSTISAGE1A JHHMMSS.ss+DDMMSS.s) 36 A1 --- f_Name [f] Flag for SAGE name (1) 38- 46 A9 --- OName Other identifier (G1) 48- 58 F11.8 deg RAdeg Right Ascension in decimal degrees (J2000) 60- 71 F12.8 deg DEdeg Declination in decimal degrees (J2000) 73- 78 F6.3 mag [3.6] ?=99.99 Spitzer/IRAC 3.6 micron band magnitude 80- 85 F6.3 mag e_[3.6] ?=99.99 Uncertainty in [3.6] 87- 92 F6.3 mag [4.5] ?=99.99 Spitzer/IRAC 4.5 micron band magnitude 94- 99 F6.3 mag e_[4.5] ?=99.99 Uncertainty in [4.5] 101-106 F6.3 mag [5.8] ?=99.99 Spitzer/IRAC 5.8 micron band magnitude 108-113 F6.3 mag e_[5.8] ?=99.99 Uncertainty in [5.8] 115-121 F7.3 mag [8.0] ?=99.99 Spitzer/IRAC 8.0 micron band magnitude 123-128 F6.3 mag e_[8.0] ?=99.99 Uncertainty in [8.0] 130-135 F6.3 mag  ?=99.99 Spitzer/MIPS 24 micron band magnitude 137-142 F6.3 mag e_ ?=99.99 Uncertainty in  144 I1 --- N [0/2] Total number of optical sources matching the same IRAC source 146-192 A47 --- Match ID(s)s of all optical sources matched from Table 2 194-195 I2 --- H91 [1/12]?=0 Hutchings et al. 1991AJ....101..933H spectroscopic O/B star number 197-201 A5 --- G07 Gouliermis et al. 2007ApJ...665..306G YSO candidate identifier(s) (<[GQH2007] NN> in Simbad)
Note (1): Source designation from SAGE-SMC (Surveying the Agents of Galaxy Evolution in the SMC; K. Gordon et al. 2011AJ....142..102G, 2011AJ....142..103B); see Cat. II/305
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 4 A4 --- ID Source name, <[CSM2011] NNN> in Simbad 5 A1 --- n_ID [io] Notes for source 270 (1) 7- 36 A30 --- Name IRAC designation (SSTNGC602/SSTISAGE1A JHHMMSS.ss+DDMMSS.s) 38- 45 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000) 47- 55 F9.5 deg DEdeg Declination in decimal degrees (J2000) 57- 62 F6.4 mJy F(V) ? HST/ACS F555W filter flux density (2) 64- 69 F6.4 mJy e_F(V) ? Uncertainty in S(V) (3) 71- 77 F7.4 mJy F(I) ? HST/ACS F814W filter flux density (2) 79- 84 F6.4 mJy e_F(I) ? Uncertainty in S(I) (3) 86- 92 F7.4 mJy F(J) ? IRSF J band flux density (4) 94- 99 F6.4 mJy e_F(J) ? Uncertainty in S(J) (3) 101-107 F7.4 mJy F(H) ? IRSF H band flux density (4) 109-114 F6.4 mJy e_F(H) ? Uncertainty in S(K) (3) 116-122 F7.4 mJy F(K) ? IRSF K_S_ band flux density (4) 124-129 F6.4 mJy e_F(K) ? Uncertainty in S(K) (3) 131-137 F7.4 mJy F(3.6) Spitzer/IRAC 3.6 micron band flux density 139-144 F6.4 mJy e_F(3.6) Uncertainty in S(3.6) (3) 146-152 F7.4 mJy F(4.5) ? Spitzer/IRAC 4.5 micron band flux density 154-159 F6.4 mJy e_F(4.5) ? Uncertainty in S(4.5) (3) 161-166 F6.4 mJy F(5.8) ? Spitzer/IRAC 5.8 micron band flux density 168-173 F6.4 mJy e_F(5.8) ? Uncertainty in S(5.8) (3) 175-180 F6.4 mJy F(8.0) ? Spitzer/IRAC 8.0 micron band flux density 182-187 F6.4 mJy e_F(8.0) ? Uncertainty in S(8.0) (3) 189-195 F7.4 mJy F(24) ? Spitzer/MIPS 24 micron band flux density 197-202 F6.4 mJy e_F(24) ? Uncertainty in S(24) (3)
Note (1): Optically, source 270 appears to be a protocluster emerging from a pillar of dust (Figure 12). We fit source 270 in the three ways shown in Figure 12: (A270) fitting all data points, (Y270o) fitting optical plus NIR, and (Y270i) fitting IRAC plus MIPS 24um. See section 4.7.2 for further explanations. Note (2): Calculated from aperture photometry magnitudes, which are adapted from ACS/WFC F555W and F814W bands to V and I according to the prescription of Sirianni et al. (2005PASP..117.1049S). Note (3): Where 0.90 or 0.95 are reported in the error columns that data point is set as an upper with 0.90 or 0.95 certainty. Note (4): Adapted from IRSF to 2MASS as described in Kato et al. (2007, Cat. II/288).
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 6 A6 --- Name YSO designation (G1) 8- 12 A5 --- f_Name [fghk, ] Flag on Name (1) 14- 18 A5 --- G07 Identification number(s) from Gouliermis et al. (2007ApJ...665..306G; <[GQH2007] NN> in Simbad) 20 A1 --- l_Nopt Limit flag on Nopt 21- 22 I2 --- Nopt ? Approximate number of optical sources within the 1.6" IRAC aperture radius 23 A1 --- f_Nopt [il] Flag on Nopt (1) 25- 28 F4.2 --- Chi2 χ2min (cpd) per data point 30- 33 I4 --- Nfits Number of fits with cpd between cpdmin and cpdmin+0.5 35- 39 F5.2 Msun Mopt ? Sum of the optical masses 40 A1 --- f_Mopt [j] Flag on Mopt (1) 42- 46 F5.2 Msun <M*> ? Mean IR mass 48- 51 F4.2 Msun e_<M*> ? Standard deviation of <M*> 53- 58 F6.3 10+3Lsun <L*> ? Luminosity 60 A1 --- le<L*> Limit flag on e_<L*> 61- 65 F5.3 10+3Lsun e_<L*> ? Uncertainty on <L*> 67 A1 --- l_dM/dt Limit flag on dM/dt 68- 74 F7.3 10-4Msun/yr dM/dt ? Accretion rate 76 A1 --- ledM/dt Limit flag on e_dM/dt 77- 82 F6.3 10-4Msun/yr e_dM/dt ? Uncertainty on dM/dt 84 A1 --- l_<Mdisk> Limit flag on <Mdisk> 85- 91 F7.5 Msun <Mdisk> ? Disk mass 93 A1 --- le<Mdisk> Limit flag on e_<Mdisk> 94- 99 F6.4 Msun e_<Mdisk> ? Uncertainty on <Mdisk> 101-107 A7 --- Stage Evolutionary stage (U=unclassified probable YSO)
Note (1): Flag as follows: f = These sources are likely YSOs based on CMD examination and physical location, but they are not considered well fit. g = These sources are fit with optical fluxes set as upper limits. h = Fit using the error bar method of correcting for PAH emission. k = These are in environments of illuminated dust, mostly along ridges or in the tips of "pillars". i = Corresponds to one or more PMS star. j = These optical masses neglect one or more optical source. l = Outside optical FOV.
Global note: Note (G1): ID number with prefixes: Y (YSO candidate), G (galaxy), K (naked star), S (stellar in images but not fit), and U (unclassified); NA= Not applicable (see "[CSM2011]" column of table 4). See section 2.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 17-Sep-2012
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