2002/07/01 by L. E. Hartley, J. E. Drew, K. S. Long · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #astro-ph
paper · pdf · doi:10.1046/j.1365-8711.2002.05823.x
published as Mon.Not.Roy.Astron.Soc. 336 (2002) 808 · Accepted for publication in MNRAS. Higher resolution versions of greyscale figures are available on request from [email protected]
arxiv created 2002/07/01 · openalex publication_date 2002/11/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/01
We present <it>Hubble Space Telescope</it> STIS (1160–1700 Å) echelle spectra of the cataclysmic variable (CV) star QU Car, at three epochs. In catalogues this binary is classified as a nova-like variable. QU Car was observed three times in time-tag mode for 2300, 2600 and 2600 s, allowing us to study the spectral time evolution on time-scales down to ∼10 s. We find evidence of a high-state non-magnetic CV at low inclination, with unusually high ionization. We observed narrow absorption lines (approximately a few hundred km s−1 wide) in N <scp>V</scp>λ1240, O <scp>V</scp>λ1371 and Si <scp>IV</scp>λ1398, and broader (HWZI ∼ 1000 km s−1) emission in C <scp>III</scp>λ1176, C <scp>IV</scp>λ1549 and He <scp>II</scp>λ1640, all with a superposed absorption component. High ionization is indicated by the He <scp>II</scp> emission, which is unusually strong in comparison with C <scp>IV</scp>, and the relative strength of the O <scp>V</scp> absorption line. The dereddened ultraviolet continuum spectral index of, on average, −2.3 suggests that disc accretion dominates the spectral energy distribution. In two observations velocity shifting is noted in the absorption lines on a time-scale long enough not to repeat within the ∼ 2600-s exposures. The absorption superposed on the C <scp>IV</scp> emission line moves coherently with the N <scp>V</scp> and Si <scp>IV</scp> absorption, suggesting the same origin for all absorption lines – most likely to be in the accretion disc atmosphere. Weak blueshifted absorption in N <scp>V</scp> and C <scp>IV</scp> provides evidence of an outflow component and we estimate a maximum outflow velocity of ∼ 2000 km s−1. This may be linked to a wind launched from further out in the disc than is typically seen in those high-state non-magnetic CVs, the wind speeds of which are observed to reach to &gsim; 4000 km s−1. Unusually, three ionization stages of carbon (C <scp>II</scp>, C <scp>III</scp> and C <scp>IV</scp>) are present in emission, with the linewidth increasing with higher ionization. The presence of C <scp>II</scp> in emission and the positive linewidth/ionization correlation are most easily reconciled with an origin in a disc chromosphere, beyond the influence of the extreme ultraviolet-emitting inner disc.