High resolution infrared spectra of silicon monoxide and silicon isotopic abundances in cool luminous stars

Details High resolution infrared spectra of silicon monoxide and silicon isotopic abundances in cool luminous stars High resolution infrared spectra of silicon monoxide and silicon isotopic abundances in cool luminous stars

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...289..469t&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 289, no. 2, p. 469-491

Astronomy and Astrophysics

Astronomy

30

Abundance, Giant Stars, Infrared Astronomy, Infrared Spectra, M Stars, Silicon Oxides, Stellar Composition, Stellar Spectra, Supergiant Stars, Isotope Ratios, Stellar Atmospheres, Turbulence

Scientific paper

We report on high spectral resolution observations of the 4 microns SiO first overtone bands in six late-type M giants (M5-8III) and two M supergiants. For M supergiants as well as for M5-6 giants, line intensities and profiles of most (28)SiO lines can be understood by a unique set of silicon abundances, micro- and macro-turbulence, once a model atmosphere is specified by a Teff which is confirmed by angular diameter measurement. In the latest M giants (M7-8III), strong lines of (28)SiO show excess emission over the predictions based on classical model atmospheres. We suggest that emission of SiO from the outer atmosphere fills in the photospheric absorption. Many resolved lines and band heads due to (29)SiO and (30)SiO can be clearly identified in all the late M giant spectral surveyed. Silicon isotopic ratios are determined by the analysis of the well isolated weak absorption features, including doublet features due to the returning R-branch. A reasonble number of weak spectral lines for use as abundance indicators were found for each isotopic species. Si-28/Si-29 and Si-28/Si-30 have approximately the terrestiral values but more neutron-rich nuclei tend to be more abundant. Si/29/Si-30 has slightly less than the terrestrial value of 1.51 in all the M giants surveyed. Similar analysis turned out to be more difficult in M supergiants, but Si-28/Si-29 shows the same tendency as in M giants. Information on silicon isotopic ratios may not be necessarily homogeneous throughout the Galaxy, possible reflecting different contributions of types I and II supernovae.

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