[Previous] | [Session 85] | [Next]
P.L. Lim, J.A. Holtzman, R.A.M. Walterbos (New Mexico State University)
The evolution of massive stars is still poorly understood because of critical effects of mass loss during the post-main sequence phase. Of particular relevance is the Luminous Blue Variable phase, during which high mass loss may occur over a brief period. It would be useful to know the mass range of stars that enter this phase, and the life time of the phase. For that, better estimates of the numbers of LBVs in different environments is crucial. In a study of M31, we detected candidate LBVs as luminous stars with strong H\alpha emission-lines and no nebular [SII] emission. (King, N.L., Walterbos, R.A.M., & Braun, R., 1998, ApJ, 507:210-220). HST's sensitivity offers the capability to identify these candidate LBVs in galaxies beyond the Local Group.
We identify massive H\alpha emmision-line stars in nearby spiral galaxies within 10 Mpc, using data from the HST WFPC2 archive. We obtained stellar photometry in H\alpha (F656N) and various broadband filters, with methods developed for the HST Local Group Stellar Photometry archive (Holtzman, J., Afonso, C., & Dolphin, A., 2003, ApJS, submitted). We identify candidates based on the amount of H\alpha excess in two-color plots. We also require an absolute magnitude MV \leq -5, and photometry fit parameters consistent with point source characteristics. Candidates are inspected visually on the images for verification purpose.
We find promising candidates in several nearby galaxies. We will present a catalog of the objects, and discuss their properties and the environments in which they are found.
Support for this work was provided by NASA through grant numbers AR-08372.01-97A and HST-AR-08749.01-A from the Space Telescope Science Institute, which is operated by AURA, Inc. under NASA contract NAS5-26555.
[Previous] | [Session 85] | [Next]
Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.