An extrasolar extreme-ultraviolet object. II. The nature of Hz 43
A variety of new data are presented on the white dwarf HZ 43, the first extrasolar object to be detected at extreme-ultraviolet (EUV) wavelengths. Optical spectrophotometry with 8 A resolution has been obtained separately for the white dwarf and the red companion; we classify the stars as DAwk and dM3.5e. The distance modulus from the red dwarf data is (m: M) =4.1 +- 0.7. A new trigonometric parallax is derived from 22 plates of the Allegheny Observatory, yielding ..pi..=0''/sub ./016 +- 0''/sub ./004((m: M) =4.0 +- 0.5). The combination of EUV and optical data require T=110,000 +- 10,000 K. Other optical and X-ray results are compatible with, although less restrictive than, this estimate. There is no firm evidence for variability of the EUV or X-ray flux on time scales from seconds to years; archival plate material shows no evidence for optical variability over an 80 year baseline. The volume density of neutral interstellar hydrogen implied by the observations is n/sub H/=0.02 cm/sup -3/, consistent with other estimates for the solar neighborhood.Several competing models postulating EUV emission from white dwarfs are shown to be unreasonable given the current data. The most tenable explanation of the data is blackbody radiation from a star with T=110,000 K and T=0.07 R/sub sun/. The bolometric magnitude and surface gravity are estimated as m/sub bol/=2.55 +- 0.06 and log g=8.6 +- 0.3, respectively, and the evolutionary implications of such a hot star are briefly considered. In particular, some DA stars must have progenitos hotter than the sdB's, i.e., planetary-nebula central stars or sdO's. (AIP)
- Research Organization:
- Univ. of California, Berkeley, CA (United States)
- OSTI ID:
- 7245420
- Journal Information:
- Astrophys. J.; (United States), Vol. 209:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
WHITE DWARF STARS
EXTREME ULTRAVIOLET RADIATION
SPECTROPHOTOMETRY
COSMIC X-RAY SOURCES
PHYSICAL PROPERTIES
STAR EVOLUTION
STAR MODELS
VARIATIONS
COSMIC RAY SOURCES
DWARF STARS
ELECTROMAGNETIC RADIATION
MATHEMATICAL MODELS
RADIATIONS
STARS
ULTRAVIOLET RADIATION
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources