Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998astl...24..650k&link_type=abstract
Astronomy Letters, Volume 24, Issue 5, September 1998, pp.650-661; Pis'ma v Astronomicheskii Zhurnal, Vol. 24, p. 754
Astronomy and Astrophysics
Astronomy
11
Scientific paper
We use high-resolution CCD spectra from the LYNX echelle spectrometer of the 6-m telescope to determine the fundamental parameters T_eff and log g and the detailed chemical composition for four pulsating RV Tau stars in the Galactic field - AC Her, U Mon, RV Tau, and AI CMi - by the method of model atmospheres. Based on high-resolution spectra, we have studied the chemical composition of RV Tau, the prototype of this class of pulsating variables, for the first time. Our main conclusion is that the group of stars under consideration is inhomogeneous in metallicity ([Fe/H] ranges from +0.05 to -1.16 dex) and elemental abundances. The pattern of chemical composition for RV Tau suggests that this star belongs to the young Galactic population (the mean abundance of the iron-group elements Ti, V, Cr, and Fe for RV Tau is [X/H]_solar = 0.04 dex) and that there are no traces of selective fractionation of chemical elements. The atmospheric chemical composition of AC Her was modified by nucleosynthesis (C/O > 1) and by selective fractionation on dust grains of the circumstellar envelope: while the easily condensable iron-group elements are appreciably underabundant, the atmospheric Zn and S abundances of AC Her differ only slightly from their solar values: [Zn/Fe]_solar = +0.68 and [S/Fe]_solar = +0.50. The atmosphere of AC Her exhibits appreciable lanthanide overabundances: the mean value of [X/Fe]_solar for La, Ce, Pr, Nd, Sm, and Eu is 0.41. The chemical composition of AI CMi is rather typical of post-AGB metal-poor supergiants with a great underabundance of the s-process elements. The four stars all show a great sodium overabundance, which is commonly observed in high-luminosity stars over a wide range of masses. The great sodium overabundance can be a product of the synthesis during the previous evolutionary stage of the star and partly a result of systematic errors in the abundance analysis due to failure to take into account non-LTE effects. We offer an explanation for the phenomenon of semiregular light variations in RV Tau stars.
Klochkova Valentina G.
Panchuk Vladimir E.
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