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Session 96 - Cepheids and Supergiant Variable Stars.
Display session, Thursday, January 16
Metropolitan Ballroom,

[96.01] The Lack of Miras in the Galactic Halo

K. Sarin, M. Jura (UCLA)

An automated search for variable stars in a 16 deg^2 field centered at l = 356^\circ, b = -47^\circ was conducted by Hawkins (1983, MNRAS, 202, 571). The survey did not identify any Mira variables although they should have been easy to find due to their high luminosity. Assuming that the halo has a density that varies as R^-3.5 where R is the galactocentric radius and assuming a local density of the halo equal to 1/500 of that of the disk and using the estimates of Jura amp; Kleinmann (1992, ApJS, 79, 105) for the number density of local Miras, we calculate that Hawkins should have been able to identify at least 11 Miras in the observed field, depending upon the amount of interstellar extinction and the degree of amplitude variability that these stars undergo. The absence of any detected Miras suggests that Galactic Halo stars in this field do not evolve into Mira stars and affirms the results (for example, Frogelamp; Elias 1988, ApJ, 324, 823) that Miras are only found in Globular Clusters with Z \geq 0.1 Z_ødot and that the metallicity in the halo is less han 0.1 solar.

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