Infrared and SiO maser observations of OH/IR stars

Details Infrared and SiO maser observations of OH/IR stars Infrared and SiO maser observations of OH/IR stars

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...280..551n&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 280, no. 2, p. 551-566

Astronomy and Astrophysics

Astronomy

36

Infrared Radiation, Infrared Stars, Interstellar Masers, Late Stars, Observation, Silicon Oxides, Stellar Atmospheres, Infrared Photometry, Sky Surveys (Astronomy), Spectrum Analysis, Stellar Luminosity

Scientific paper

We have performed quasisimultaneous infrared photometry and observations of the SiO 86 GHz ( v = 1, J = 2-1) and SiO 43 GHz (v = 1 and 2, J = 1-0) maser emission from a sample of 44 OH/IR stars. In contrast to masers associated with Mira variables the SiO 86 GHz integrated flux densities in OH/IR stars are weaker than those at 43 GHz, and the SiO 43 GHz (v = 2) emission is often stronger than the SiO 43 GHz (v = 1) emission. Our results show that it is useful to divide the sample into two groups because of the difference in their SiO maser properties: sources with warm, thin envelopes (K - L less than 4), and sources with cooler, thicker envelopes (K - L less than 4). In the warmer sources the average 43 GHz/86 GHz integrated flux density ratio of order 2, but in the cooler sources it is significantly larger, more than 10. The cooler sources also proved to be underluminous at 86 GHz with respect to their bolometric luminosities and their IRAS 12 micrometer flux densities. In addition, the 43 GHz maser intensity ratio (v = 2)/(v = 1) differs markedly between the two groups. Cooler sources show a significantly larger average ratio than the warmer sources, about 3.2 compared with 1.2. The low intensity of the SiO 86 GHz masers relative to the 43 GHz masers in OH/IR stars are explained in terms of a decrease in SiO intensity in stars with a high mass loss rate and an increased coupling between the two 43 GHz transitions due to an increase in line strength of an infrared line connecting the two transitions.

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