Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26as..110..441b&link_type=abstract
Astronomy and Astrophysics Supplement, v.110, p.441
Astronomy and Astrophysics
Astrophysics
21
Stars: Abundances, Stars: Chemically Peculiar, Stars: Horizontal Branch, Stars: Individual: Feige 86, {Iota} Her, 3 Cen A
Scientific paper
IUE and visible high resolution spectra of the halo B-type star Feige 86 are analyzed with the aim to get further insight into the atmospheric parameters and surface chemical composition of this Pop II star. The analysis is mostly based on the comparison of photometric, spectrophotometric, and spectroscopic observations with color indices, fluxes, and spectra computed by using Kurucz (1993a,b) codes, Kurucz (1993a) LTE ATLAS9 model atmospheres, and Kurucz (1993b) line lists. The atmospheric parameters T_eff_=16430+/-250K and logg=4.20+/-0.02 are determined from the Stroemgren photometry, visual energy distribution, and Balmer profiles. A colour excess E(B-V) between 0.02 and 0.08mag is deduced on the basis of both photometric and spectrophotometric data. Although the star's kinematics implies that it is a Pop II object (hence on the HB, given its spectral type) we find that its chemical composition is peculiar and unlike that of Pop II stars. We find that light elements (up to S) are underabundant, with the exception of P; iron-peak elements are solar or slightly overabundant; heavy elements, with the exception of Ge, are overabundant. In particular, we identify lines of Pt II, Au III, and Hg II consistent with overabundances from 3.5 to 4.0dex. Several Mo III lines are also identified. He I lines are carefully analyzed and the detection of the ^3^He line at 667.8nm is discussed. Some ultraviolet lines arising from a lower level with energy close to 0eV are affected by an additional slightly red-shifted absorption, probably of interstellar or circumstellar origin. We compare the spectra of Feige 86 with those of the normal Pop I B-type star ι Her and with those of the peculiar Pop I B-type star 3 Cen A, to which Feige 86 has always been associated. We show that the similarity with 3 Cen A is marginal, because, although nearly all the same elements are affected by abundance anomalies, these occur in a different degree in the two stars, except for He, P, and Cu. No Mo, Pt, and Au lines have been identified in 3 Cen A. To what extent the different abundances of the two stars can be explained in terms of the different evolutionary history or of different atmospheric phenomena, such as diffusion, is still an open question.
Bonifacio Piercarlo
Castelli Fabio
Hack Margherita
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