J/A+A/624/A63 W51 OB stars NIR spectroscopy (Bik+, 2019)
Near-infrared spectroscopy of the massive stellar population of W51:
evidence for multi-seeded star formation.
Bik A., Henning T., Wu S.-W., Zhang M., Brandner W., Pasquali A., Stolte A.
<Astron. Astrophys. 624, A63 (2019)>
=2019A&A...624A..63B 2019A&A...624A..63B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, OB ; Photometry, CCD;
Photometry, infrared; Spectra, infrared
Keywords: stars: formation - stars: early type - techniques: spectroscopic -
Hertzsprung-Russell and C-M diagrams -
open clusters and associations: individual: W51 - infrared : stars
Abstract:
The interplay between the formation of stars, stellar feedback and
cloud properties strongly influences the star formation history of
giant molecular clouds. The formation of massive stars leads to a
variety of stellar clusters, ranging from low stellar density OB
associations to dense, gravitationally bound starburst clusters. We
aimed at identifying the massive stellar content and reconstructing
the star formation history of the W51 giant molecular cloud. We
performed near-infrared imaging and K-band spectroscopy of the massive
stars in W51. We analysed the stellar populations using
colour-magnitude and colour-colour diagrams and compared the
properties of the spectroscopically identified stars with stellar
evolution models. We derive the ages of the different sub-clusters in
W51 and, based on our spectroscopy derive an age for W51 of 3Myrs or
less. The age of the P Cygni star LS1 and the presence of two still
forming proto- clusters suggests that the star formation history of
W51 is more complex than a single burst. We did not find evidence for
triggered star formation and we concluded that the star formation in
W51 is multi seeded. We finally concluded that W51 is a OB association
where different sub-clusters form over a time span of at least 3-5Myrs.
Description:
Near-infrared J, H and Ks photometry obtained with SOFI/NTT of the
stellar content of the 4 observed fields in W51 (Fields I, II, III and
IV). Only the objects with a detection in all three bands with a
photometric error less than 0.2mag in each band. For each star the ra
and dec, field and magnitudes and errors in J,H and Ks are given.
Additionally, the reduced fits files with the K-band spectra obtained
with LUCI/LBT from the OB stars (nr 1 to 16) are included. The
numbering is that of table 3. The spectra of the stars added from the
literature are not included.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
w51-phot.dat 77 15145 Near-infrared photometry of the stars in W51
list.dat 154 16 Spectroscopically classified OB stars in W51
(table 3) with spectra
fits/* . 16 Individual fits spectra
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See also:
J/ApJ/706/83 : Embedded YSO candidates in W51 (Kang+, 2009)
J/ApJ/839/108 : YSOs in the star-forming regions W51 + W43 (Saral+, 2017)
Byte-by-byte Description of file: w51-phot.dat
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Bytes Format Units Label Explanations
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3- 7 I5 --- Object [1/15145] object number
10- 12 A3 --- Field Observed Field (I, II III or IV)
15- 16 I2 h RAh Right ascension (J2000.0)
18- 19 I2 min RAm Right ascension (J2000.0)
21- 25 F5.2 s RAs Right ascension (J2000.0)
28 A1 --- DE- Declination sign (J2000.0)
29- 30 I2 deg DEd Declination (J2000.0)
32- 33 I2 arcmin DEm Declination (J2000.0)
35- 38 F4.1 arcsec DEs Declination (J2000.0)
41- 45 F5.2 mag Jmag SOFI/NTT J magnitude
48- 51 F4.2 mag e_Jmag rms uncertainty on Jmag
54- 58 F5.2 mag Hmag SOFI/NTT H magnitude
61- 64 F4.2 mag e_Hmag rms uncertainty on Hmag
67- 71 F5.2 mag Ksmag SOFI/NTT Ks magnitude
74- 77 F4.2 mag e_Ksmag rms uncertainty on Ksmag
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- No [1/16] Seauential number
3 A1 --- n_No [ac] Note on No (1)
5- 14 A10 --- ObsID Observation ID
16- 18 A3 --- Field Field designation
20- 21 I2 h RAh Right ascension (J2000)
23- 24 I2 min RAm Right ascension (J2000)
26- 30 F5.2 s RAs Right ascension (J2000)
32 A1 --- DE- Declination sign (J2000)
33- 34 I2 deg DEd Declination (J2000)
36- 37 I2 arcmin DEm Declination (J2000)
39- 42 F4.1 arcsec DEs Declination (J2000)
44- 48 F5.2 mag Jmag SOFI/NTT J magnitude
50- 53 F4.2 mag e_Jmag rms uncertainty on Jmag
55- 59 F5.2 mag Hmag SOFI/NTT H magnitude
61- 64 F4.2 mag e_Hmag rms uncertainty on Hmag
66- 70 F5.2 mag Ksmag SOFI/NTT Ks magnitude
72- 75 F4.2 mag e_Ksmag rms uncertainty on Ksmag
77- 83 A7 --- SpType Spectral type (2)
85- 88 I4 --- Nx Number of pixels along X-axis
90-113 A24 "datime" Obs.date Observation date
115-121 F7.1 0.1nm blambda Lower value of wavelength interval
123-129 F7.1 0.1nm Blambda Upper value of wavelength interval
131-137 F7.5 0.1nm dlambda Wavelength resolution
139-140 I2 Kibyte size Size of FITS file
142-154 A13 --- FileName Name of the fits spectrum in subdirectory fits
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Note (1): Notes as follows:
a = Source 44 in Figueredo et al. (2008AJ....136..221F 2008AJ....136..221F)
c = Not detected in theJ-band in our catalogue, hence we used the value from
the UKIDDS Galactic Plane Survey DR6 (Lucas et al.,
2008MNRAS.391..136L 2008MNRAS.391..136L, Cat. II/316)
Note (2): Spectral types obtained by comparison with reference stars from
Hanson et al. (1996, Cat. J/ApJS/107/281; 2005, Cat. J/ApJS/161/154) and
Bik et al. (2005, Cat. J/A+A/440/121).
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Acknowledgements:
Arjan Bik, arjan.bik(at)astro.su.se
(End) Arjan Bik [SU, Sweden], Patricia Vannier [CDS] 23-Feb-2019