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Preprint 11/09

EC 11481-2303 - A Peculiar Subdwarf OB Star Revisited

T.Rauch (1), K. Werner (1), J. W. Kruk (2)

(1) Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076 Tübingen, Germany
(2) Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, U.S.A.

To be published in: Proceedings of The Fourth Meeting On Hot Subdwarf Stars And Related Objects, Shanghai

Abstract. EC 11481-2303 is a peculiar, hot, high-gravity pre-white dwarf. Previous optical spectroscopy revealed that it is a sdOB star with an effective temperature (T_eff) of 41790 K, a surface gravity log(g)= 5.84, and He/H = 0.014 by number. We present an on-going spectral analysis by means of non-LTE model-atmosphere techniques based on high-resolution, high-S/N optical (VLT-UVES) and ultraviolet (FUSE, IUE) observations.
We are able to reproduce the optical and UV observations simultaneously with a chemically homogeneous NLTE model atmosphere with a significantly higher effective temperature and lower He abundance (T_eff = 55000 K, log (g) = 5.8, and He / H =  0.0025 by number). While C, N, and O appear less than 0.15 times solar, the iron-group abundance is strongly enhanced by at least a factor of ten.
 
Key words: Stars: individual: EC 11481-2303 -- Stars: abundances -- Stars: atmospheres -- Stars: chemically peculiar -- subdwarfs

Preprint (584 kb PDF file including figures)

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