SiO Maser Survey of Late-Type Stars. II. Statistical Study

Details SiO Maser Survey of Late-Type Stars. II. Statistical Study SiO Maser Survey of Late-Type Stars. II. Statistical Study

May 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aj....111.1987c&link_type=abstract

Astronomical Journal v.111, p.1987

Astronomy and Astrophysics

Astronomy

21

Masers, Surveys, Stars: Late-Type

Scientific paper

Using the results of a simultaneous survey of the six transitions of silicon monoxide 28SiO (v=0,1,2,3, J=1-0) and 29SiO (v=0, 1, j=1-0) [Cho et al. A&AS, 115, 117 (1996); hereafter referred to as Paper I] towards more than 100 late-type stars, we have carried out an extensive statistical analysis. We report a clear correlation between the 28SiO (v=1, 2, J=1-0) and IR (4 μm) flux densities. The integrated flux densities of the v=1 and v=2 lines were found to be nearly equal to the sources detected in the v=3 line. Moreover, the flux density ratios of SiO to IR of these sources are found to be considerably higher than those of the sources not detected in the v=3 line, suggesting IR pumping of the vibrationally excited masers. Clear evidence has been found for a correlation between SiO masing and the optical phase of the host star. Most of the v=3 and 29SiO v=0 maser lines were detected in stars at the optical phase around 0.2, which is the turnover phase from rising to infalling gas motion in stellar pulsation. The v=1 and v=2 masers also tend to have their flux maxima near the optical phase 0.2. The mean velocity of the 28SiO v=1 and v=2 masers as a function of the optical phase shows that the redshifted emission is dominating during the phases from 0.3 to 0.8, while the blueshifted emission appears from phase ˜0.85 and is dominant during phases 0.0-0.2 (or 1.0-1.2). The behavior is similar to that of the observed 1.6 μm CO velocity curves. This implies that the vibrationally excited 28SiO masers occur in a region close to the star, which is affected by the stellar pulsation. The effect on the 28SiO masers of the stellar pulsation suggests that shock waves may play an important role in achieving the maximum fluxes of the 28SiO v=1,2 masers, and the masing in the 25SiO v=3 line around the optical phase 0.2.

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