2006A&A...448..589P

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 A_V≃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.