J/A+A/555/A50 UBVIc photometry of stars in Westerlund 2 (Carraro+, 2013)
The distance to the young open cluster Westerlund 2.
Carraro G., Turner D., Majaess D., Baume G.
<Astron. Astrophys. 555, A50 (2013)>
=2013A&A...555A..50C 2013A&A...555A..50C
ADC_Keywords: Clusters, open ; Stars, early-type ; Photometry, CCD
Keywords: stars: Wolf-Rayet - open clusters and associations: general -
open clusters and associations: individual: Westerlund 2 -
HII regions - stars: massive
Abstract:
A new X-ray, UBVIc, and JHKs study of the young cluster Westerlund 2
was undertaken to resolve discrepancies tied to the cluster's
distance. Existing spectroscopic observations for bright cluster
members and new multi-band photometry imply a reddening relation
toward Westerlund 2 described by E(U-B)/E(B-V)=0.63+0.02E(B-V).
Variable-extinction analyses for Westerlund 2 and nearby IC 2581 based
upon spectroscopic distance moduli and ZAMS fitting yield values of
RV=AV/E(B-V)=3.88±0.18 and 3.77±0.19, respectively, and
confirm prior assertions that anomalous interstellar extinction is
widespread throughout Carina. The results were confirmed by applying
the color-difference method to UBVRIcJHKs data for 19
spectroscopically observed cluster members, yielding
RV=3.85±0.07. The derived distance to Westerlund 2 of
d=2.85±0.43kpc places the cluster on the far side of the Carina
spiral arm. The cluster's age is no more than τ∼2x106yr as
inferred from the cluster's brightest stars and an X-ray (Chandra)
cleaned analysis of its pre-main-sequence demographic. Four Wolf-Rayet
stars in the cluster core and surrounding corona (WR20a, WR20b, WR20c,
and WR20aa) are very likely cluster members, and their inferred
luminosities are consistent with those of other late-WN stars in open
clusters. The color-magnitude diagram for Westerlund 2 also displays a
gap at spectral type B0.5∼V with associated color spread at higher and
lower absolute magnitudes that might be linked to close binary
mergers. These features, in conjunction with the evidence for mass
loss from the WR stars, may help to explain the high flux of
γ-rays, cosmic rays, and X-rays from the direction toward
Westerlund 2.
Description:
Photometric data in UBVI for stars in the field of the open cluster
Westerlund 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cluster.dat 119 42215 UBVIc photometry and astrometry
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See also:
J/A+AS/127/423 : VI photometry of Westerlund 1 and 2 (Piatti+ 1998)
J/A+A/463/981 : BV CCD photometry in Westerlund 2 (Rauw+, 2007)
J/A+A/466/137 : Westerlund 2 JHKs photometry (Ascenso+, 2007)
Byte-by-byte Description of file: cluster.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [1/42215] Star sequential number
7- 17 F11.7 deg RAdeg Right ascension (J2000.0)
19- 29 F11.7 deg DEdeg Declination (J2000.0)
32- 38 F7.4 mag Umag ?=99.9999 Johnson U magnitude
42- 47 F6.4 mag e_Umag ?=9.9999 Error in U magnitude
50- 56 F7.4 mag Bmag ?=99.9999 Johnson B magnitude
60- 65 F6.4 mag e_Bmag ?=9.9999 Error in B magnitude
68- 74 F7.4 mag Vmag ?=99.9999 Johnson V magnitude
77- 83 F7.4 mag e_Vmag ?=9.9999 Error in V magnitude
86- 92 F7.4 mag Icmag ?=99.9999 Cousins I magnitude
95-101 F7.4 mag e_Icmag ?=9.9999 Error in I magnitude
104-110 F7.4 --- chi DAOPHOT χ value
113-119 F7.4 --- sharp DAOPHOT sharpness parameter (0=isolated star;
positive for blends or non-stellar objets)
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Acknowledgements:
Giovanni Carraro, gcarraro(at)eso.org
(End) Patricia Vannier [CDS] 07-Jun-2013