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[123.01] Post-Asymptotic Giant Branch Stars in the Local Group

M. H. Siegel, H. E. Bond (STScI)

We report results of a search of Local Group galaxies for bright post-asymptotic-giant-branch (PAGB) stars. PAGB stars of spectral types A and F are the brightest members of Population II, and should have an extremely narrow luminosity function. PAGB stars are easily identifiable because their low surface gravities give them very large Balmer jumps. These factors should make PAGB stars excellent standard candles.

We have established a system of standard stars in a photometric system that combines the Gunn u filter (whose bandpass lies entirely below the Balmer jump) with the standard BVI system. We have obtained uBVI photometry of most of the members of the Local Group, including WLM, NGC 147, NGC 185, NGC 205, Phoenix, Fornax, and NGC~6822, and fields in the halos of M31 and M33. We have identified a number of PAGB candidates for spectroscopic follow-up, and confirm that the luminosity distribution is sharply peaked. Adopting a luminosity of M_V=-3.4 based on PAGB stars in Galactic globular clusters, we present a tally of distance measures to these objects and compare them to those derived from other standard candles.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.