The Extremely Low Luminosity White Dwarf ESO 439-26
Abstract
We present a detailed analysis of the extremely low luminosity white dwarf ESO 439-26. The measured trigonometric parallax of pi = 0."0237 +/- 0."0030, together with the observed V magnitude of 20.52, yields an absolute visual magnitude of MV = 17.4 +/- 0.3. ESO 439-26 thus lies more than 1 mag faintward of the observed cutoff of the white-dwarf luminosity function in the Galactic disk and could therefore be the coolest and hence oldest white dwarf ever detected. However, we show from a detailed analysis of the optical energy distribution that the intrinsic low luminosity of ESO 439-26 is the result of its small radius, or large mass. Our best solution is reached with Teff = 4560 +/- 100 K, log g = 9.04 +/- 0.14, and a pure-helium atmospheric composition. Evolutionary models are used to derive a mass of M = 1.21 +/- 0.07 M⊙ and a cooling age of 6.4 +/- 0.3 Gyr, a value that is smaller than the current estimates of the age of the Galactic disk.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1995
- DOI:
- 10.1086/309845
- Bibcode:
- 1995ApJ...455L.159R
- Keywords:
-
- STARS: EVOLUTION;
- STARS: INDIVIDUAL ALPHANUMERIC: ESO 439-26;
- STARS: WHITE DWARFS