Date of Original Version
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 R⊙ 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 M⊙, 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 M⊙. Independently, our radius and recent log g determinations yield 0.44 M⊙ < MDA < 0.47 M⊙. 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.
Benedict, G. F., McArthur, B. E., Franz, O. G., Wasserman, L. H., Nelan, E., Lee, J., Fredrick, L. W.,...Bradley, A. (2000). 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. The Astromomical Journal, 119(5), 2382-2390. doi: 10.1086/301355.
Available at: https://doi.org/10.1086/301355