The surprising Far-UV spectrum of the polar BY Camelopardalis
Autor: | D. de Martino, Paula Szkody, Roger Ferlet, K. Beuermann, Steve B. Howell, R. E. Fried, Koji Mukai, Jean-Marc Bonnet-Bidaud, E. Roueff, Boris T. Gaensicke, Jean-Michel Desert, D. Porquet, M. Mouchet |
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Jazyk: | angličtina |
Rok vydání: | 2003 |
Předmět: |
Physics
Accretion (meteorology) 010308 nuclear & particles physics H0538+608 ultraviolet emission [accretion stars individual BY Cam white dwarfs cataclysmic variables binaries close X-rays] Interstellar cloud Astrophysics (astro-ph) Resonance Flux FOS: Physical sciences Astronomy and Astrophysics Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics 01 natural sciences 13. Climate action Space and Planetary Science 0103 physical sciences Polar Astrophysics::Solar and Stellar Astrophysics Absorption (electromagnetic radiation) 010303 astronomy & astrophysics Equivalent width Astrophysics::Galaxy Astrophysics Line (formation) |
Popis: | We report on the first far-UV observations of the asynchronous polar BY Cam made by the Far-Ultraviolet Spectroscopic Explorer (FUSE). The source is known to exhibit the most extreme NV/CIV emission resonance line ratio observed among polars. The FUSE observations reveal a OVI resonance line weaker than in the prototype of polars, AM Her, with the absence of a detectable narrow component. The OVI broad line is detected with an equivalent width of the same order as in AM Her, the blueward doublet component is clearly present but the redward component is strongly affected by H2 absorption. The presence of a strong NIII line and weak CIII lines also confirms the peculiar CNO line flux. We compare the resonance CNO line intensities with the predictions of the CLOUDY plasma code coupled to a geometrical model of the accretion column. Varying the temperature and/or intensity of the ionising spectrum is unable to reproduce the observed broad line ratios. A solution is obtained by significantly altering the element abundances with a strong depletion of C, overabundance of N and a weak underabundance of O. This confirms previous suggestions of non-solar abundances which may result from redistribution in the accreted material following nova outbursts and/or the secondary nuclear evolution. A very significant H2 absorption is observed in front of the source, a possible indication for either the existence of a dense interstellar cloud or of circumstellar material. Comment: 6 pages, 4 Postscript figures, accepted by Astronomy and Astrophysics, uses aa.sty |
Databáze: | OpenAIRE |
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