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D. M. Peterson, G. Schaeffer (SUNY Stony Brook)
The Space Interferometry Mission offers the potential of measuring the distance to a handful of nearby spiral galaxies through the technique of ``Rotational Parallaxes'', ie, by measuring and analyzing both the proper motions and radial velocities of a number of objects that take part in the circular rotation of the systems. A and F supergiants are the ideal targets, being among the brightest stellar objects with nearly all their energy emitted in the visible and near IR.
We report our initial efforts at identifying the 100 or so such objects needed to apply this technique in M31. From the photometry of Magnier et al.\ (1992 A&A Supp 96, 379) we have identified about a 1000 candidates having the colors of A-F stars in the range -8.5 < MV < -6.5. The biggest difficulty is with foreground Pop II Halo giants in this color range. As a preliminary test we obtained WIYN Hydra 2-hour time and obtained spectra of 75 candidates in the 7800 Å region. Of these, only one is clearly an F Ia in M31, based on radial velocity and the Oxygen IR triplet (Slowik & Peterson 1996 AJ, 109, 2193). The other objects are apparently all in our halo, one having a blue shift of 300 km/s.
Compiling a list of 100 A-F Ia's in M31 will clearly be a demanding problem.
The author(s) of this abstract have provided an email address for comments about the abstract: dpeterson@astro.sunysb.edu