Volume 448, Number 2, March III 2006
|Page(s)||589 - 596|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||24 February 2006|
The birth-cluster of the galactic luminous blue variable WRA 751
Institute of Astronomy, ETH Hönggerberg, HPF, 8093 Zürich, Switzerland
2 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: email@example.com
3 ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: firstname.lastname@example.org
4 STScI, 3700 San Martin Drive, MD28201 Baltimore, USA e-mail: email@example.com
Accepted: 8 November 2005
We present the results of NTT/VLT UBV imaging of a 260 arcmin2 region containing the Galactic Luminous Blue Variable WRA 751, in search for its birth-cluster, i.e. a cluster of young and massive stars spatially and physically associated with it. On the basis of the classical reddening-free parameter Q, we have identified a sample of 24 early-type stars with colours typical of spectral types earlier than B3. Interestingly, these stars are clustered within a radius of 1' from WRA 751, corresponding to about 1% of the imaged field. These stars tightly distribute around , which in turn defines a mean extinction mag. The 5 brighter () and bluer () stars of the sample have been subsequently observed with FORS1 and classified as 3 late O- and 2 early B-stars. The absence of stars earlier than O8 indicates an age of the cluster older than 4 Myr, although it could be due to an incomplete sampling of the upper end of the main sequence. Nevertheless, the detection of OB stars of class I certainly indicates an age of a few million years. At an assumed distance of 6 kpc, we estimate a cluster radius of 3.4 pc and a total mass of 3 . Our discovery is only the second known instance of a Galactic Luminous Blue Variable associated with its birth-cluster.
Key words: stars: early-type / stars: evolution / stars: fundamental parameters / stars: Hertzsprung-Russell (HR) and C-M diagrams
© ESO, 2006
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