J/AJ/170/144 GTC catalog of cluster members in the W51A region (Dawson+, 2025)
How massive star clusters form and evolve: A near-IR survey of the W51 complex.
Dawson A., Ginsburg A., Roman-Zuniga C.G.
<Astron. J., 170, 144 (2025)>
=2025AJ....170..144D 2025AJ....170..144D
ADC_Keywords: Clusters, open; YSOs; Photometry, infrared; Stars, masses;
Cross identifications
Keywords: Near infrared astronomy ; Infrared photometry ; Protoclusters
Abstract:
We present near-infrared JHKs and narrowband H2(1-0) photometric
observations of the W51A region, obtained with GTC EMIR, aiming to
characterize its young stellar population, and provide mass estimates
for individual cluster members and the protoclusters. Our observations
reveal over 3000 new sources, out of which 88 are located in the
protoclusters, W51 IRS2 and W51 Main. The average extinction (AV),
measured from the J-H color, of sources is 19AV in W51 IRS2 and
14AV in W51 Main. We document 17 new instances of H2 emission in
the region by utilizing observations from the H2(1-0) narrowband
filter. Despite limited completeness, we estimated masses for each
cluster member and estimated the total cluster mass to be in the range
of 900-4700M☉ for W51 IRS2 and 500-2700M☉ for W51 Main,
using an assumed age range of 1-3Myr. We measured the initial mass
function (IMF) in the proto-clusters assuming a range of ages from
1-3Myr and found that the IMF slopes for both protoclusters are
consistent with the Salpeter IMF in the mass range M≥8M☉ within
1σ-2σ.
Description:
NIR J-, H-, Ks-band filters, and the narrowband H2 filter
observations of the W51 GMC were conducted on 2020 June 7, and 2020
July 12. The observations were carried out using the NIR imaging
camera and spectrograph EMIR (Espectrografo Multiobjeto Infra-Rojo),
installed on the Gran Telescopio Canarias (GTC) at the Roque de los
Muchachos Observatory in the Canaries, Spain. Individual frames in all
filters had exposure times of 10s.
The reduced images had incorrect world coordinate system (WCS)
information, causing the centroid of stars to be slightly offset from
their true positions. The location of the bright stars from each frame
were compared to their on-sky location measured by Gaia (Gaia EDR3, I/350)
and the WCS was shifted accordingly to provide a closer match.
We compared the GTC catalog to 2MASS (II/246), the UKIDSS galactic
plane survey (GPS, II/316), as well as the catalogs of
Kumar+2004 (J/MNRAS/353/1025) and Bik+2019 (J/A+A/624/A63), and our
own photometric catalog covering the NACO images of W51 IRS2. The
high-resolution images of W51 IRS2, taken by the adaptive optics NIR
camera NACO (NaCo Nasmyth Adaptive Optics System Near-Infrared Imager
and Spectrograph, NAOS CONICA) at the ESO Very Large Telescope (VLT)
8.2m Unit Telescope (UT4) in Chile, were obtained from
Figueredo+ (2008AJ....136..221F 2008AJ....136..221F). There is a total of 3003 stars in
our field that were not documented in any previous NIR catalog of the
region, with 88 of these sources being located within the protoclusters.
There are 2265 newly detected sources with corresponding H-band
detections, and 1298 with corresponding J-band detections.
Objects:
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RA (2000) DE Designation(s)
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19 23 29.29 +14 31 37.9 W51a = [OMN2000] Region 3
19 23 39.93 +14 31 09.3 [WBN74] W 51 IRS 2 = BBRW W51 (b)
19 23 43.80 +14 30 37.0 NAME W 51 Main = [HLB98] Onsala 106
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 210 11946 Gran Telescopio Canarias (GTC) catalog
tablea1.dat 67 100 Catalog of cross-matched Gaia sources used to
correct world coordinate system (WCS) offset
tableb1.dat 44 198 NACO Ks-band source catalog of W51 IRS2
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/316 : UKIDSS-DR6 Galactic Plane Survey (Lucas+ 2012)
II/321 : IPHAS DR2 Source Catalogue (Barentsen+, 2014)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/MNRAS/353/1025 : JHK photometry of 4 W51 star clusters (Nanda+, 2004)
J/A+A/466/137 : Westerlund 2 JHKs photometry (Ascenso+, 2007)
J/ApJ/706/83 : Embedded YSO candidates in W51 (Kang+, 2009)
J/ApJ/720/1055 : VBLA observations of W51 Main/South (Sato+, 2010)
J/ApJ/746/154 : Improved kinematic plx for Sco-Cen members (Pecaut+, 2012)
J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)
J/ApJS/213/1 : The MSFRs Omnibus X-ray Catalog (MOXC) (Townsley+, 2014)
J/A+A/595/A27 : JVLA images of W51A (Ginsburg+, 2016)
J/ApJ/839/108 : YSOs in the star-forming regions W51 & W43 (Saral+, 2017)
J/MNRAS/477/3369 : Young stellar objects in W49A and W51 (Eden+, 2018)
J/A+A/624/A63 : W51 OB stars NIR spectroscopy (Bik+, 2019)
J/AJ/162/153 : X-ray propert. of A,B-types, T-Tauri stars & YSOs (Nunez+, 2021)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- ID Source ID
26- 27 I2 h RAh Hour of right ascension (J2000)
29- 30 I2 min RAm Minute of right ascension (J2000)
32- 36 F5.2 s RAs Second of right ascension (J2000)
38 A1 --- DE- Sign of declination (J2000)
39- 40 I2 deg DEd Degree of declination (J2000)
42- 43 I2 arcmin DEm Arcminute of declination (J2000)
45- 49 F5.2 arcsec DEs Arcsecond of declination (J2000)
51- 55 F5.2 mag Jmag [8.3/26.7]? Apparent J-band magnitude
57- 64 F8.3 mag e_Jmag [1e-3/3443]? Uncertainty in Jmag
66- 70 F5.2 mag Hmag [6.7/25.7]? Apparent H-band magnitude
72- 81 F10.4 mag e_Hmag [3e-4/91464]? Uncertainty in Hmag
83- 87 F5.2 mag Ksmag [6.1/28.3]? Apparent Ks magnitude
89- 97 F9.4 mag e_Ksmag [5e-4/5672]? Uncertainty in Ksmag
99- 103 F5.2 mag AV [0.03/53.6]? Average extinction
105- 113 F9.2 mag e_AV [0.02/854796]? Uncertainty in AV
115- 120 F6.2 mag AVmin [-35.1/45.2]? Minimum extinction
122- 126 F5.2 mag AVmax [5.2/73.2]? Maximum extinction
128- 133 F6.2 Msun M1 [0.09/275]? Mass estimate at 1 Myr
135- 140 F6.2 Msun e_M1 [0/137.3]? Uncertainty in mass1
142- 147 F6.2 Msun M1min [0.09/275]? Minimum mass at 1 Myr
149- 154 F6.2 Msun M1max [0.09/275]? Maximum mass at 1 Myr
156- 160 F5.2 Msun M2 [0.09/93]? Mass estimate at 2 Myr
162- 166 F5.2 Msun e_M2 [0/46.4]? Uncertainty in mass2
168- 172 F5.2 Msun M2min [0.09/93]? Minimum mass at 2 Myr
174- 178 F5.2 Msun M2max [0.09/93]? Maximum mass at 2 Myr
180- 184 F5.2 Msun M3 [0.09/55.3]? Mass estimate at 3 Myr
186- 190 F5.2 Msun e_M3 [0.01/27.5]? Uncertainty in mass3
192- 196 F5.2 Msun M3min [0.09/55.3]? Minimum mass at 3 Myr
198- 202 F5.2 Msun M3max [0.09/55.2]? Maximum mass at 3 Myr
204- 210 A7 --- Notes Additional notes (1)
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Note (1): Notes as follows:
A = Foreground source; 1924 occurrences
B = Extinction estimated using surrounding sources (see Section 3.2);
3540 occurrences
C = Extinction measured using the NICE method; 8377 occurrences
D = NACO Ks-band magnitude adopted; 5 occurrences
E = UKIDSS (II/316) Ks-band magnitude adopted; 53 occurrences
F = UKIDSS (II/316) H-band magnitude adopted; 75 occurrences
G = UKIDSS (II/316) J-band magnitude adopted; 0 occurrence
H = 2MASS (II/246) H- and Ks-band magnitudes adopted; 24 occurrences
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Hour of right ascension (J2000)
4- 5 I2 min RAm Minute of right ascension (J2000)
7- 11 F5.2 s RAs Second of right ascension (J2000)
13- 13 A1 --- DE- Sign of declination (J2000)
14- 15 I2 deg DEd Degree of declination (J2000)
17- 18 I2 arcmin DEm Arcminute of declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of declination (J2000)
26- 30 F5.2 mag Jmag [12.5/20.6]? Apparent J-band magnitude
32- 36 F5.2 mag Hmag [11.9/18.9]? Apparent H-band magnitude
38- 42 F5.2 mag Ksmag [11/17.2] Apparent Ks-band magnitude
44- 47 F4.2 arcsec Offset [0.01/1.3] Gaia offset
49- 67 I19 --- GaiaDR3 Gaia DR3 (I/355) source ID
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Hour of right ascension (J2000)
4- 5 I2 min RAm Minute of right ascension (J2000)
7- 11 F5.2 s RAs Second of right ascension (J2000)
13- 13 A1 --- DE- Sign of declination (J2000)
14- 15 I2 deg DEd Degree of declination (J2000)
17- 18 I2 arcmin DEm Arcminute of declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of declination (J2000)
26- 30 F5.2 mag Ksmag [9.4/18.5] Apparent Ks-band magnitude
32- 35 F4.2 mag e_Ksmag [0.01/3.3] Uncertainty in Ksmag
37- 40 F4.2 arcsec Offset [0.02/4.5] GTC offset
42- 44 A3 --- Match GTC matched? (Yes/No) (1)
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Note (1): Match as follows:
Yes = 90 occurrences
No = 108 occurrences
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 22-Jun-2026