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R.P. Olling (USNO-DC/USRA), D.M. Peterson (SUNY, Stony Brook)
Astrometry is one of the foundations of astrophysics. Accurate trigonometric distances for large numbers of stars are attainable with space astrometry missions such as the successful HIPPARCOS, and the planned FAME, DIVA, SIM, GAIA satellites. However, external galaxies remain too distant for even these missions. In this paper we show that rotational parallaxes technique can be used to obtain 1-5% distances for Local Group spiral galaxies. The determination of trigonometric parallaxes allows for significant tests of stellar evolution. Astrometric distances to the Local Group galaxies will provide a solid foundation for the calibration of the zero points of the Cepheid's period-luminosity relation and the Tully-Fisher linewidth-luminosity relation, and hence the extra-galactic distance scale.
The rotational parallax method employs the common motions of a number of stars to determine the distance to the group as a whole. Assuming that a given target star in an external galaxy is on a circular orbit, three observables --the two proper motions and the radial velocity-- suffice to determine the three unknowns: the orbital inclination, the rotational velocity and the distance. We discuss the factors that complicate the application of this simple technique, and show that NASA's Space Interferometry Mission will be able to determine the distance to M31 to within a few percent.
The author(s) of this abstract have provided an email address for comments about the abstract: olling@usno.navy.mil