Water Masers Associated with Circumstellar Shells

Details Water Masers Associated with Circumstellar Shells Water Masers Associated with Circumstellar Shells

Oct 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apjs..106..579b&link_type=abstract

Astrophysical Journal Supplement v.106, p.579

Other

30

Stars: Circumstellar Matter, Masers, Stars: Mass Loss, Stars: Variables: Other Long-Period Variables

Scientific paper

We report observational parameters for 62 H2O maser sources, 23 not previously reported, and upper limits of H2O maser emission for 223 nondetected sources. The detected long-period variables (LPVs) are at D < 1.8 kpc for a detection limit of about 1 Jy. The distance adjusted detection rate varies from 18% for Miras variables with P < 200 days to over 50% for stars with P> 300 days and seems to be determined primarily by the amount of material in their associated circumstellar shells, since detected stars have infrared to photospheric flux ratios [flux(12 μm flux(2.2 μm)] > 0.2, whereas nondetected stars have ratios less than 0.3. Stars in the overlap region, 0.2 < r <0.3, may have been observed at the wrong phase. The minimum mass-loss rate needed to sustain detectable H2O maser emission from stars in this program is 0.5 × 10-7 Msun yr-1. The mass-loss rate increases with period. Mira variables with H2O masers have more asymmetric light curves (f = 43) compared to nondetected Miras variables (f = 46). The average H2O maser flux (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(star) ≍ 1 × 10-10 or L(H20)/Lsun 3 x 10-7 and to a photon luminosity 1043-1044 s-1. The low detection rates for Mira variables with P < 200 days is primarily due to the smaller amount of material in their circumstellar shells as compared to the longer period Mira variables and does not appear to be a strong function of their lower metallicities.

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