The Birth-Cluster of the Galactic Luminous Blue Variable WRA751

Abstract

We present the results of NTT/VLT UBV imaging of a 260 square arcmin region containing the Galactic Luminous Blue Variable WRA751, 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 arcmin from WRA751, 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) = 6.1 mag. 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 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 2200 solar masses. Our discovery is only the second known instance of a Galactic Luminous Blue Variable associated with its birth-cluster.

8 pages, 6 figures, accepted by A&A

References in corpus (9)

• Stellar population synthesis at the resolution of 2003
• Starburst99: Synthesis Models for Galaxies with Active Star Formation
• The evolution of rotating stars
• Database of Geneva stellar evolution tracks and isochrones for UBVRIJHKLL'M, HST-WFPC2, Geneva and Washington photometric systems
• The Physical Properties and Effective Temperature Scale of O-type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars, and Results from the Complete Sample
• A Study of Cyg OB2: Pointing the Way Towards Finding Our Galaxy's Super Star Clusters
• The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turn-offs. II. Results from 12 Galactic Clusters and OB Associations
• The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turn-offs. I. Results from 19 OB Associations in the Magellanic Clouds
• The Star Formation History and Mass Function of the Double Cluster h and Chi Persei

Cited by in corpus (9)

• The Hα surface brightness - radius relation: a robust statistical distance indicator for planetary nebulae
• Luminous Blue Variables are Antisocial: Their Isolation Implies that they are Kicked Mass Gainers in Binary Evolution
• The first X-ray survey of Galactic Luminous Blue Variables
• On the Gaia DR2 distances for Galactic Luminous Blue Variables
• Herschel imaging and spectroscopy of the nebula around the luminous blue variable star WRAY 15-751
• NTT follow-up observations of star cluster candidates from the FSR catalogue
• Proper motions of OB stars in the far Carina Arm
• Nature Versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center
• Astrophysics in 2006