AAS 195th Meeting, January 2000
Session 127. Variable Stars
Oral, Saturday, January 15, 2000, 2:00-3:30pm, Centennial III

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[127.03] Luminous Blue Variables and Related High Mass Evolved Stars in M31 and Their Surprising Environments

N. L. King (NMSU)

Luminous Blue Variables (LBVs) are erratically eruptive massive stars near the Eddington limit thought to be descendants of blue supergiants and progenitors of Wolf-Rayet stars. In order to constrain the evolution of these massive stars we would like to know their bolometric luminosities, effective temperatures, current masses, progenitor masses, ages, and abundances. With the use of 3.5-m class telescopes (WIYN and ARC) we are able to constrain all but the abundances for these LBV-type stars in M31.

We began the study by developing a method for identifying candidate LBVs through deep narrow-band images. A target list was drawn for the NE half of M31. We obtained follow-up spectroscopy that confirmed the success of our search criteria. The spectra provided mass-loss rates for the objects with P-Cygni type profiles and spectral-type constraints from the presence of high or low excitation lines.

With WIYN images we measured color-magnitude diagrams for the resolved luminous stars and we charted the locations of HII regions and HI holes as indicators of stellar ages in the areas around our program stars. Surprisingly the majority of the LBV-type objects were found to be in or near associations older than the LBV-type objects themselves. The age discrepancies between LBV and environment might be explained if the LBVs or candidate LBVs are runaways, are products of discrete massive star forming events, have lived longer than theoretically expected, or are exotic binaries such as Thorne-Zytkow or mass-transferring close binaries.

We note that with the development of the wind-momentum-luminosity relation (WMLR) by Kudritzki et al. LBVs may one day be secondary distance indicators. We find that M31 LBV V15 is located in the same place of the WMLR diagram as Galactic and LMC LBVs and we hope to investigate this for a few more stars. [Support for thesis provided by NM Space Grant Consortium and NSF grant AST96-17014.]

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