Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...678..394f&link_type=abstract
The Astrophysical Journal, Volume 678, Issue 1, pp. 394-407.
Astronomy and Astrophysics
Astronomy
1
Stars: Abundances, Stars: Atmospheres, Stars: Individual (Gd 605), Stars: Subdwarfs, Techniques: Spectroscopic
Scientific paper
We present an analysis of the atmospheric properties of the evolved, hydrogen-rich object GD 605 using FUSE, IUE, and optical spectra in conjunction with non-LTE (NLTE) model atmospheres and synthetic spectra. We also present an analysis of the interstellar medium along the line of sight toward this star. Our effective temperature determination relies on the constraints on the ionization balance O IV/O V imposed by the FUSE data, while the surface gravity relies on a match to the Balmer lines in the optical spectrum. Our analysis yields Teff~85,000 K, logg~5.25, and a helium abundance close to the solar value. These parameters suggest that GD 605 is in a post-AGB evolutionary phase and belongs to the class of hydrogen-rich central star of planetary nebulae, subclass O(H). Apart from lines of hydrogen and helium, about two dozen photospheric lines are observed in the FUSE data, which are dominated by the O VI λλ1031.9 and 1037.6 transitions. In addition, we detect lines associated with the following ions: N IV, O IV, O V, Si IV, S VI, Ar VII, as well as Fe VII. Synthetic spectra based on NLTE line-blanketed model atmospheres reproduce most of the line profiles observed in what appears to be an atmosphere deficient in heavy elements. Our calculations do not fully reproduce the strength of the strongest ultraviolet lines seen, the O VI doublet, perhaps a sign that some contribution to this structure may arise in the interstellar medium or in a circumstellar environment. We discuss various scenarios to account for the absence of a visible nebula and the dearth of heavy elements in the atmosphere of GD 605.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by Johns Hopkins University under NASA contract NAS5-32985.
Chayer Pierre
Fontaine Gérard
Fontaine M.
Oliveira Cristina M.
Wesemael François
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