WATER MASERS ASSOCIATED WITH CIRCUMSTELLAR SHELLS

We report observational parameters for 62 H2O maser sources, 23 not pr eviously reported, and upper limits of H2O maser emission for 223 nond etected sources. The detected long-period variables (LPVs) are at D < 1.8 kpc for a detection limit of about 1 Jy. The distance adjusted det ection rate varies from 18% for Miras variables with P < 200 days to o ver 50% for stars with P > 300 days and seems to be determined primari ly by the amount of material in their associated circumstellar shells, since detected stars have infrared to photospheric flux ratios [flux( 12 mu m)/flux(2.2 mu m)] > 0.2, whereas nondetected stars have ratios less than 0.3. Stars in the overlap region, 0.2 < r < 0.3, may have be en observed at the wrong phase. The minimum mass-loss rate needed to s ustain detectable H2O maser emission from stars in this program is 0.5 x 10(-7) M. yr(-1). The mass-loss rate increases with period. Mira va riables with H2O masers have more asymmetric light curves (f = 43) com pared to nondetected Miras variables (f = 46). The average H2O maser f lux (normalized to 1 kpc) for Mira variables in our observing program with P < 300 days is about 15 Jy km s(-1), corresponding to L(H2O)/L(s tar) approximate to 1 x 10(-10) or L(H2O)/L. approximate to 3 x 10(-7) and to a photon luminosity approximate to 10(43)-10(44) s(-1). The lo w detection rates for Mira variables with P < 200 days is primarily du e to the smaller amount of material in their circumstellar shells as c ompared to the longer period Mira variables and does not appear to be a strong function of their lower metallicities.