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Astron. Astrophys. 352, 167-176 (1999)

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Locating the emission line regions in polars

II. Doppler imaging of BL Hydri

R.E. Mennickent  *  1, M.P. Diaz 2 and J. Arenas 3

1 Dpto. de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Concepción, Casilla 4009, Concepción, Chile (rmennick@stars.cfm.udec.cl)
2 Instituto Astronômico e Geofísico, Universidade de São Paulo, CP9638, 010065-970, São Paulo, Brazil (marcos@binary.iagusp.usp.br)
3 Department of Physics, Keele University, Keele, Staffordshire ST5 5BG, UK (jla@astro.keele.ac.uk)

Received 29 March 1999 / Accepted 4 October 1999


Phase-resolved spectroscopic observations of BL Hyi obtained during the high mass transfer state are presented. The H[FORMULA], He I 5875 and He I 6678 emission line profiles are analyzed with the Doppler tomography technique. It is shown that these emissions arise from a single region in the accretion stream. No emission from the secondary star, either in the H[FORMULA] or in the He I line, could be identified. The accretion column could not be detected on the tomographic reconstructions of the system. An orbital ephemeris based on the radial velocities of the Na I D emission line is derived, assuming a chromospheric origin in the secondary star. The spectroscopic observations provide a consistent picture of the accretion geometry in the system. Most of the optical emission line flux was found to be formed in a reservoir of low angular momentum gas filling a substantial fraction of the Roche lobe. Combining our results with literature data it was possible to constrain the absolute longitude of the magnetic axis in this classical polar.

Key words: stars: individual: BL Hyi – stars: novae, cataclysmic variables – stars: fundamental parameters – stars: evolution – stars: binaries: general

* On leave in Harvard-Smithsonian Center for Astrophysics, 60 Garden St, MA 02138, Cambridge, USA

Send offprint requests to: R.E. Mennickent

© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999