Interferometric Astrometry of the Detached White Dwarf-M Dwarf Binary Feige 24 Using HST Fine Guidance Sensor 3: White Dwarf Radius and Component Mass Estimates
Abstract
With Hubble Space Telescope Fine Guidance Sensor 3 we have determined a parallax for the white dwarf-M dwarf interacting binary, Feige 24. The white dwarf (DA) component has an effective temperature Teff~56,000 K. A weighted average with past parallax determinations (πabs=14.6+/-0.4 mas) narrows the range of possible radius values, compared with past estimates. We obtain RDA=0.0185+/-0.0008 Rsolar with uncertainty in the temperature and bolometric correction the dominant contributors to the error. Fine Guidance Sensor 3 photometry provides a light curve entirely consistent with reflection effects. A recently refined model mass-luminosity relation for low-mass stars provides a mass estimate for the M dwarf companion, MdM=0.37+/-0.20 Msolar, where the mass range is due to metallicity and age uncertainties. Radial velocities from Vennes and Thorstensen provide a mass ratio from which we obtain MDA=0.49+0.19-0.05 Msolar. Independently, our radius and recent logg determinations yield 0.44 Msolar<MDA<0.47 Msolar. In each case, the minimum DA mass is that derived by Vennes & Thorstensen from their radial velocities and Keplerian circular orbits with i<=90°. Locating Feige 24 on an (M,R)-plane suggests a carbon core. Our radius and these mass estimates yield a value of γgrav inconsistent with that derived by Vennes & Thorstensen. We speculate on the nature of a third component whose existence would resolve the discrepancy. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 2000
- DOI:
- 10.1086/301355
- arXiv:
- arXiv:astro-ph/0001387
- Bibcode:
- 2000AJ....119.2382B
- Keywords:
-
- ASTROMETRY;
- STARS: BINARIES: GENERAL;
- STARS: DISTANCES;
- STARS: INDIVIDUAL: NAME: FEIGE 24;
- STARS: LATE-TYPE;
- STARS: WHITE DWARFS;
- Astrophysics
- E-Print:
- 29 pages, 12 figures. accepted for publication May 2000 issue of The Astronomical Journal