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The Far-Ultraviolet Spectra of Two Hot PG1159 StarsPG 1159 stars are hot, hydrogen-deficient (pre-) white dwarfs with atmospheres mainly composed of helium, carbon, and oxygen. The unusual surface chemistry is the result of a late helium-shell flash. Observed element abundances enable us to test stellar evolution models quantitatively with respect to their nucleosynthesis products formed near the helium-burning shell of the progenitor asymptotic giant branch stars. Because of the high effective temperatures (T(sub eff)), abundance determinations require ultraviolet spectroscopy and non-local thermodynamic equilibrium model atmosphere analyses. Up to now, we have presented results for the prototype of this spectral class and two cooler members (T(sub eff) in the range 85,000-140,000 K). Here we report on the results for two even hotter stars (PG 1520+525 and PG 1144+005, both with T(sub eff) = 150,000 K) which are the only two objects in this temperature-gravity region for which useful far-ultraviolet spectra are available, and revisit the prototype star. Previous results on the abundances of some species are confirmed, while results on others (Si, P, S) are revised. In particular, a solar abundance of sulphur is measured in contrast to earlier claims of a strong S deficiency that contradicted stellar evolution models. For the first time, we assess the abundances of Na, Al, andCl with newly constructed non-LTE model atoms. Besides the main constituents (He, C, O), we determine the abundances (or upper limits) of N, F, Ne, Na, Al, Si, P, S, Cl, Ar, and Fe. Generally, good agreement with stellar models is found.
Document ID
20170003250
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Werner, K.
(Eberhard Karls Universitat Tuebingen Tuebingen, Germany)
Rauch, T.
(Eberhard Karls Universitat Tuebingen Tuebingen, Germany)
Kruk, J. W.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
April 7, 2017
Publication Date
September 30, 2016
Publication Information
Publication: Astronomy & Astrophysics
Publisher: EDP Sciences
Volume: 593
ISSN: 0004-6361
e-ISSN: 1432-0746
Subject Category
Astronomy
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN41363
Funding Number(s)
CONTRACT_GRANT: DLR 50OR1507
Distribution Limits
Public
Copyright
Other

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