RR LYRAE VARIABLE-STAR DISTRIBUTION IN THE GALACTIC HALO

From the CCD/Transit Instrument (CTI) survey, we generated a list of 4 2 RR Lyrae variable stars, 34 of which were previously undiscovered (W etterer et al. 1996, AJ, 112, 742). The CTI survey is unique when comp ared to other surveys in that its survey area covers a large range of Galactic latitude and longitude in a single field. In this paper we us e these RR Lyrae variable stars to examine their number density from 7 to 35 kpc from the Galactic center. The RR Lyrae number density was f ound to follow a R(-3.34+/-0.11) power-law function when modeled as a spherically symmetric distribution and an a(-3.76+/-0.13) power-law fu nction when modeled as the ellipsoidal distribution of Preston et al. (1991, ApJ, 375, 121). We then combined the CTI results with that of o ther surveys to provide a more complete picture of the RR Lyrae number density throughout the Galactic halo (0.6-80 kpc). A spherically symm etric model for the RR Lyrae number density yields a R(-3.024+/-0.077) power-law function, although better agreement between surveys is reac hed if the number density is modeled as an ellipsoidal distribution, w hich yields an a(-3.530+/-0.077) power-law function. The wide range of number densities measured at the Sun's distance from the Galactic cen ter (>10 kpc-3 for both the local number density as calculated from br ight RR Lyrae stars and the CTI survey, to <1 kpc-3 for a fields in th e Lick RR Lyrae Survey and the Palomar-Groningen Variable Star Survey) , as well as the possible underdensity of RR Lyraes beyond 25 kpc, are also discussed. (C) 1996 American Astronomical Society.