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[116.09] Spectra of Post-AGB Stars in the Halo of M31

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

Using a photometric system that combines the Gunn-Thuan u filter with the standard BVI filters, we have identified more than two dozen candidate post-asymptotic-giant-branch (PAGB) A- and F-type stars in the halo of M31. In order to confirm that these are indeed M31 stars with extremely large Balmer jumps, we have obtained moderate-resolution spectra of a sample of the candidates, using the 6.5-m MMT blue channel spectrograph. The vast majority of the PAGB candidates are indeed extremely low-gravity A-F stars with radial velocities suggestive of M31 membership; only one ``interloper'' was a high-z QSO. At V~q21, these are the visually brightest stars in the M31 halo, and they show great utility both as halo tracers and as standard extragalactic candles.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.