Coronae of He-rich white dwarfs

Details Coronae of He-rich white dwarfs Coronae of He-rich white dwarfs

Sep 1978

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978a%26a....69..113m&link_type=abstract

Astronomy and Astrophysics, vol. 69, no. 1, Sept. 1978, p. 113-117.

Astronomy and Astrophysics

Astronomy

14

Abundance, Helium, Stellar Atmospheres, Stellar Coronas, White Dwarf Stars, Convective Heat Transfer, Stellar Spectra, Stellar Winds, Ultraviolet Astronomy, X Ray Astronomy

Scientific paper

A modified version of Hearn's (1975) 'minimum flux' corona method is used to compute model coronae for non-DA (He-rich) white dwarfs. Radiative flux emissivities for a helium plasma are included which are due to permitted lines, bremsstrahlung with a mean Gaunt factor of 1.4, and radiative recombination based on the hydrogenic approximation. Coronal temperatures, pressures, and continuous EUV and X-ray spectra are determined. The results show that: (1) a hot non-DA white dwarf with an effective temperature of about 20,000 K could have a corona with temperatures up to about 2.5 million K and base pressures up to approximately 30,000 dynes/sq cm; (2) the corona and transition zone together can emit up to more than 10 to the 28th power erg/s in the form of far-UV and soft X radiation; and (3) the maximum flux in soft X-rays is of the order of 10 to the 28th power erg/s in the 0.2-0.28-keV band.

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