Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108.1924t&link_type=abstract
The Astronomical Journal (ISSN 0004-6256), vol. 108, no. 5, p. 1924-1930
Astronomy and Astrophysics
Astronomy
26
Binary Stars, Dwarf Stars, Hot Stars, Red Dwarf Stars, Stellar Envelopes, Stellar Evolution, Stellar Spectrophotometry, Ultraviolet Astronomy, Balmer Series, Extreme Ultraviolet Explorer Satellite, H Alpha Line, Ultraviolet Photometry, Ultraviolet Spectroscopy
Scientific paper
New optical spectroscopy shows a 0.706 d orbital period for Extreme Ultraviolet Explorer (EUVE) 2013+400 and confirms its membership in a class of close binary systems emerging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s (1994) optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (Teff approximately equals 50 000 K) and therefore very young (tage less than or equal 5 x 106 yr), and extreme ultraviolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of nH approximately equal to 1019/sq cm. The white dwarf is a DAO type and we obtained two independent estimates of the helium abundance from EUV photometric measurements (log(y) approximately equal to -3.2) and from the He II lambda-4686 line profile (log(y) approximately equal to -2.8). The data possibly indicate a level of heterogeneity expected in the context of on-going chemical separation in the photospheric layers. The Balmer lines show narrow emission that varies with binary phase with the equivalent widths of the emission trailing the radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectrophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total light near 6500 A; the resulting H-alpha emission is twice as strong as in Feige 24, with an equivalent width of 37-61 A with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to the class of close binary stars discovered in EUV all-sky surveys.
Shambrook Anouk
Thorstensen John R.
Vennes Stephane
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