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THE HOT SUBDWARF IN THE ECLIPSING BINARY HD185510 C.Simon Jeffery
 

Summary: 1
THE HOT SUBDWARF IN THE ECLIPSING BINARY HD185510
C.Simon Jeffery
Armagh Observatory
Theodore Simon
Institute for Astronomy, University of Hawaii
ABSTRACT: The importance of binarity in the origin and evolution of hot subdwarfs has
become widely recognised. The RS CVn binary HD185510 consists of a K0 III giant which
eclipses its faint blue companion every 21 days. The latter has been identified as an sdB
star: it is the only such object known in a wide eclipsing binary and can only be observed
in the ultraviolet, where its radial velocity amplitude and spectrum have been recorded. A
detailed analysis of the orbit from a new ultraviolet light curve and previous radial velocities
indicates a low mass (¸0.3 solar masses) for the blue star. We have derived atmospheric
parameters from multiwavelength photometry and from high­resolution ultraviolet spectra.
Both components appear to be metal poor, the hot star is intermediate between a classical
subdwarf B star and a helium white dwarf, with T eff ¸ 31 000K. In order to resolve a conflict
between the primary radius indicated by the rotational light curve and that indicated by
the eclipse geometry, it is necessary to assume that the incliniation i ¸ 90 ffi and that the
subdwarf is partially eclipsed by the atmosphere of the K giant with an optical scale height
of ¸ 0:03R ? . The evolutionary implications are considered.

  

Source: Armagh Observatory
Jeffery, Simon - Armagh Observatory

 

Collections: Physics