NEW FIELD RR LYRAE VARIABLES IN THE OUTER PARTS OF THE LMC AND THE PROPERTIES OF THE LMC HALO

Four new type-ab RR Lyrae variables that belong to the field of the LMC were found in the direction of NGC 1466; a possible field variable was found near the Reticulum system. A King model that fits the surface densities of the known LMC field RR Lyrae stars of type ab has a limiting radius of 15 kpc. An exponential disk model that fits these densities has a scale length of 2.6 kpc. These models contain approximately 10(4) type-ab RR Lyrae stars and have a central surface density of approximately 200 of these stars per square degree. The LMC field halo of Population II stars has M-upsilon approximately -15.2 and a mass of approximately 1.6 x 10(8) M. This halo therefore makes up about 2% of the mass of the LMC, a similar percentage to that found for our Galactic halo. Thus, the efficiencies of the earliest star-formation processes may have been comparable in the two systems. The LMC field RR Lyraes have a period-frequency distributions similar to those found in the outer halo of our Galaxy. The ratio (rho) of the surface density of these RR Lyraes to that of the older long-period variables (OLPV) (found by Hughes et al. 1991) is approximately 13 at some 3 to 4 kpc from the LMC center. This measure of the relative strengths of the halo to an "old-disk" population is within a factor of two of that which would be seen in our Galaxy at the solar distance from its center. The central visual surface brightness of the LMC halo is approximately 25.5 mag per square arc sec. Its average visual surface brightness (over the area within the effective radius (approximately 4 kpc) is approximately 26.4 mag per square arc sec. It would be difficult to detect a halo of this faintness in an external galaxy unless the halo could be resolved into individual stars.