J/A+A/463/981 BV CCD photometry in Westerlund 2 (Rauw+, 2007)
Early-type stars in the core of the young open cluster Westerlund 2.
Rauw G., Manfroid J., Gosset E., Naze Y., Sana H., De Becker M., Foellmi C.,
Moffat A.F.J.
<Astron. Astrophys. 463, 981 (2007)>
=2007A&A...463..981R 2007A&A...463..981R
ADC_Keywords: Clusters, open ; Photometry, CCD ; Photometry, UBV
Keywords: Galaxy: open clusters and associations: individual: Westerlund 2 -
stars: early-type - stars: binaries: eclipsing -
stars: fundamental parameters - stars: individual: WR20a
Abstract:
The properties of the early-type stars in the core of the Westerlund 2
cluster are examined in order to establish a link between the cluster
and the very massive Wolf-Rayet binary WR20a as well as the H II
complex RCW 49.
Photometric monitoring as well as spectroscopic observations of
Westerlund 2 are used to search for light variability and to establish
the spectral types of the early-type stars in the cluster core. The
first light curves of the eclipsing binary WR 20a in B and V filters
are analysed and a distance of 8kpc is inferred. Three additional
eclipsing binaries, which are probable late O or early B-type cluster
members, are discovered, but none of the known early O-type stars in
the cluster displays significant photometric variability above 1% at
the 1-sigma level. The twelve brightest O-type stars are found to have
spectral types between O3 and O6.5, significantly earlier than
previously thought.
The distance of the early-type stars in Westerlund 2 is established to
be in excellent agreement with the distance of WR20a, indicating that
WR20a actually belongs to the cluster. Our best estimate of the
cluster distance thus amounts to 8.0±1.4kpc. Despite the earlier
spectral types, the currently known population of early-type stars in
Westerlund 2 does not provide enough ionizing photons to account for
the radio emission of the RCW 49 complex. This suggests that there
might still exist a number of embedded early O-stars in RCW49.
Description:
Photometric time series are given for the eclipsing binary systems
WR20a, MSP223, MSP96 and MSP44. In addition, we provide a table with
the average BV photometry of 1073 stars in the field of the open
cluster Westerlund 2. The data were obtained with the ANDICAM CCD
camera at the 1.3m telescope at CTIO.
Objects:
------------------------------------------------------------------------
RA (2000) DE Designation(s) (Period(d))
------------------------------------------------------------------------
10 23 58.0 -57 45 49 WR20a = WR 20a (P=3.68475)
10 23 59.2 -57 45 40 MSP223 = Cl* Westerlund 2 MSP 223 (P=29.21)
10 24 01.0 -57 45 06 MSP096 = Cl* Westerlund 2 MSP 96 (P=1.0728)
10 24 00.5 -57 44 45 MSP044 = Cl* Westerlund 2 MSP 44 (P=5.176)
------------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table23.dat 48 1284 B and V photometric time series of WR20a and
3 eclipsing binaries in Westerlund 2
table4.dat 47 1073 BV mean photometry of 1073 stars in the field
of view around Westerlund 2
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See also:
J/A+AS/127/423 : VI photometry of Westerlund 1 and 2 (Piatti+ 1998)
Byte-by-byte Description of file: table23.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Object name (WR20a, MSP223, MSP096 or MSP044) (1)
8- 20 F13.5 d JD Julian Day
22 A1 --- Filter [BV] Filter Name (either Johnson B or V)
24- 28 F5.3 --- sec(z) Airmass at the time of observation
30- 36 F7.4 mag mag B or V magnitude
38- 42 F5.3 mag e_mag Uncertainty on the magnitude
44- 48 F5.3 pix Seeing Seeing (FWHM) in pixels (1pix=0.37arcsec)
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Note (1): MSP223, MSP096 and MSP044 identified as Cl* Westerlund 2 MSP 223,
Cl* Westerlund 2 MSP 096 and Cl* Westerlund 2 MSP 044, respectively.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right Ascension J2000 (hours)
4- 5 I2 min RAm Right Ascension J2000 (minutes)
7- 10 F4.1 s RAs Right Ascension J2000 (seconds)
12 A1 --- DE- Declination J2000 (sign)
13- 14 I2 deg DEd Declination J2000 (degrees)
16- 17 I2 arcmin DEm Declination J2000 (minutes)
19- 22 F4.1 arcsec DEs Declination J2000 (seconds)
24- 29 F6.3 mag Vmag Mean observed Johnson V magnitude
31- 35 F5.3 mag e_Vmag Uncertainty on the V magnitude
37- 41 F5.3 mag B-V Mean observed Johnson B-V colour
43- 47 F5.3 mag e_B-V Uncertainty on the B-V colour
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Acknowledgements:
Gregor Rauw, rauw(at)astro.ulg.ac.be
(End) Gregor Rauw [IAGL, Belgium], Patricia Vannier [CDS] 21-Dec-2006