Extreme Ultraviolet Photometry and Spectroscopy of BL Hydri

Details Extreme Ultraviolet Photometry and Spectroscopy of BL Hydri Extreme Ultraviolet Photometry and Spectroscopy of BL Hydri

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...487..916s&link_type=abstract

Astrophysical Journal v.487, p.916

Astronomy and Astrophysics

Astronomy

14

Stars: Novae, Cataclysmic Variables, Ultraviolet: Stars, Stars: White Dwarfs, Stars: Individual Constellation Name: Beta Hydri

Scientific paper

We have analyzed Extreme Ultraviolet Explorer (EUVE) observations of BL Hyi obtained during a high-accretion state in 1995 October. The light curve obtained with the Deep Survey instrument reveals a broad hump covering the phases in which both poles have been known to be active in X-ray emission. In contrast to the X-ray, both poles contribute a comparable extreme ultraviolet (EUV) flux. The short-wavelength spectrum can be fitted with either a relatively cool (5 eV), pure-hydrogen white dwarf or with a 17 eV blackbody; both fits imply a neutral hyrogen column density in the local interstellar medium of ~3 x 1019 cm-2. However, nearly simultaneous IUE far-ultraviolet (FUV) spectroscopic measurements rule out pure-hydrogen white dwarf models with temperatures of less than 8 eV. BL Hyi has a cooler accretion area than AM Her and VV Pup, but it is similar in temperature to QS Tel. The total EUV energy is 2--4 x 1032 ergs s-1, which is only slightly greater than the hard X-ray and cyclotron energy. This suggests that BL Hyi has a conventional accretion column and that the polar cap is primarily heated from above by radiation from the accretion shock, rather than from below by dense blobs that penetrate the photosphere.

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