Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...181..103s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 181, no. 1, July 1987, p. 103-111.
Astronomy and Astrophysics
Astronomy
35
Calcium, Infrared Astronomy, Line Spectra, Stellar Spectra, Abundance, Metallicity, Near Infrared Radiation, Stellar Atmospheres, Stellar Temperature
Scientific paper
Profiles of the IR triplet lines of ionized Ca (8494, 8542, and 8662 A) have been calculated in the LTE approximation using model atmospheres representative of solar-type stars. The depth of absorption in the line wings is found to be particularly insensitive to surface gravity. Provided that the relative abundance (RA) of Ca is consistent with the metallicity of the model atmosphere, the depth of absorption becomes more sensitive to metallicity with increasing effective temperature. These conclusions have been tested against accurate measurements of IR triplet line profiles in Tau Ceti (G8 V) and Eta Cas A (G0 V). Using spectra recorded at a dispersion of 1 A/mm and with S/N of about 100, the T(eff), log g, Fe/H, and Ca/H were derived. Line profiles in Tau Ceti were found to be extremely narrow, indicating low rotational and turbulent broadening. The difference in RA between Ca and Fe in this star is consistent with other recent analyses of metal-deficient dwarfs in the Galactic disk. If the RAs of the alpha-particle elements are assumed to follow the Ca abundance rather than the Fe abundance, there is good agreement between observed and calculated profiles. In the case of Eta Cas A, where there appears to be no difference in RA between Ca and Fe, a small discrepancy between observed and calculated line wings is found.
Drake Jeremy J.
Smith Gordon
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