A multifrequency study of circumstellar envelopes of cool giants and supergiants

Astronomy and Astrophysics – Astrophysics

Scientific paper

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Giant Stars, Interstellar Masers, Interstellar Matter, Silicon Oxides, Stellar Envelopes, Supergiant Stars, H Alpha Line, Late Stars, Light Curve, Mira Variables, Stellar Evolution, Stellar Spectra

Scientific paper

A multifrequency study of all parts of circumstellar envelopes of cool giants and supergiants is presented. In order to investigate the influence of stellar parameters on spectral features of these envelopes, a sample of 77 cool giants and supergiants that occupies a horizontal strip in the Hertzsprung-Russell diagram was observed. Spectroscopic and photometric observations at optical, infrared and radio wavelengths led to the following results: (1) for giants there exists a strong correlation between H-alpha emission and SiO masers, which led to the suggestion that SiO masers are triggered by shock-waves and can be pumped by collisions, (2) the SiO expansion velocity was found to be systematically lower by 2 km/s compared to the CO expansion velocity, and (3) a relation between the asymmetry of the light curve and the intensity of the dust emission at 9.7 microns has been confirmed for a wide range of periods. Rather than luminosity alone, pulsational properties of the variable play a dominant role for the structure of circumstellar envelopes of cool giants and supergiants.

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