The orbital ephemeris and eclipse transitions of the low-mass X-ray binary EXO 0748 - 676

Details The orbital ephemeris and eclipse transitions of the low-mass X-ray binary EXO 0748 - 676 The orbital ephemeris and eclipse transitions of the low-mass X-ray binary EXO 0748 - 676

Jan 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991apj...366..253p&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 366, Jan. 1, 1991, p. 253-260.

Astronomy and Astrophysics

Astrophysics

31

Eclipsing Binary Stars, Main Sequence Stars, Stellar Evolution, X Ray Binaries, Dwarf Stars, Orbital Elements, Stellar Atmospheres, Stellar Luminosity, Stellar Mass Accretion, Stellar Models, Stellar Temperature

Scientific paper

Using the eclipses as fiducial markers, an updated ephemeris for EXO 0748 - 676 is derived and evidence is found that between February 1985 and March 1989 the 3.82-h orbital period of EXO 0748 - 676 decreased with a time scale of -5 x 10 to the 6th yr. The sense of this change is the same as that predicted by simple models for the evolution of low-mass X-ray binaries containing main-sequence companions, but is a factor about 100 faster than expected. This rapid change in orbital period could result from the expansion of the companion due to the effects of X-ray heating. The eclipse transition durations are variable, with the shortest observed taking 1.5 s and the longest 40 s. This latter figure is about an order of magnitude too large to be due to absorption effects in the atmosphere of the secondary assuming a Roche geometry and likely stellar temperature. Either flaring activity or the presence of an X-ray heated evaporative wind or a corona may enhance the scale height of the companion's atmosphere producing the extended eclipse transitions.

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