The ages and colours of cool helium-core white dwarf stars
Abstract
The purpose of this work is to explore the evolution of helium-core white dwarf stars in a self-consistent way with the predictions of detailed non-grey model atmospheres and element diffusion. To this end, we consider helium-core white dwarf models with stellar masses of 0.406, 0.360, 0.327, 0.292, 0.242, 0.196 and 0.169Msolar and follow their evolution from the end of mass-loss episodes, during their pre-white dwarf evolution, down to very low surface luminosities. We find that when the effective temperature decreases below 4000K, the emergent spectrum of these stars becomes bluer within time-scales of astrophysical interest. In particular, we analyse the evolution of our models in the colour-colour and in the colour-magnitude diagrams and find that helium-core white dwarfs with masses ranging from ~0.18 to 0.3Msolar can reach the turn-off in their colours and become blue again within cooling times much less than 15Gyr and then remain brighter than MV~16.5. In view of these results, many low-mass helium white dwarfs could have had enough time to evolve to the domain of collision-induced absorption from molecular hydrogen, showing blue colours.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2001
- DOI:
- 10.1046/j.1365-8711.2001.04449.x
- arXiv:
- arXiv:astro-ph/0102417
- Bibcode:
- 2001MNRAS.325..607S
- Keywords:
-
- STARS: ATMOSPHERES;
- STARS: EVOLUTION;
- STARS: FUNDAMENTAL PARAMETERS;
- STARS: INTERIORS;
- WHITE DWARFS;
- Astrophysics
- E-Print:
- 11 pages, 9 figures. Accepted for publication in MNRAS