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Session 26 - Stars in the Visible & IR.
Display session, Tuesday, June 10
South Main Hall,

[26.12] Calibration of Post-AGB A and F Supergiants as Standard Candles

L. K. Fullton, H. E. Bond, A. Saha (STScI), R. A. Saffer (Villanova Univ.)

Low-mass stars leaving the asymptotic giant branch (AGB) and passing through spectral types F and A should make excellent Population II standard candles. Theoretically, they should have a very narrow luminosity function: the upper limit is set by the much shorter lifetimes of the more luminous post-AGB (PAGB) stars, and the lower limit corresponds to the turnoff mass of the oldest progenitors. Moreover, PAGB A-F stars are readily recognized because of their enormous Balmer jumps. They should be found in the halos of spiral galaxies where internal absorption is minimized and also in elliptical galaxies.

As part of an ongoing project to calibrate PAGB stars as standard candles, we are searching for them in old populations of Local Group galaxies. We employ a hybrid CCD photometric system that combines the Gunn u filter with Johnson-Kron-Cousins BVI. We have used Kurucz/Hubeny model atmospheres and stellar emergent spectra along with filter transmission functions and instrument sensitivity curves to generate synthetic photometric indices that can be parameterized in terms of stellar \logg and T_eff.

Calibration results from Local Group galaxies observed to dat will be presented.

Supported by NASA Grant NAGW-4361.

Program listing for Tuesday