Astronomy and Astrophysics, volume 448, 589-596 (2006/3-3)
The birth-cluster of the galactic luminous blue variable WRA 751.
PASQUALI A., COMERON F. and NOTA A.
Abstract (from CDS):
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 (B-V)≃1.67, which in turn defines a mean extinction AV≃6.1mag. The 5 brighter (V≤16.2) and bluer (Q≤-0.9) 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 4Myr, 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 2.2x103M☉. Our discovery is only the second known instance of a Galactic Luminous Blue Variable associated with its birth-cluster.
stars: early-type - stars: evolution - stars: fundamental parameters - stars: Hertzsprung-Russell (HR) and C-M diagrams
Table 1: [PCN2006] NN (Nos 1-24).
Stellar cluster = NAME WRAY 15-751 CLUSTER
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