Open AccessThe ages and colours of cool helium‐core white dwarf stars
Author(s) -
Serenelli A.M.,
Althaus L.G.,
Rohrmann R.D.,
Benvenuto O.G.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04449.x
Subject(s) - white dwarf , physics , astrophysics , stars , helium , astronomy , stellar evolution , blue dwarf , core (optical fiber) , black dwarf , atomic physics , optics
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 0.169 M ⊙ 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 4000 K, 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 0.3 M ⊙ can reach the turn‐off in their colours and become blue again within cooling times much less than 15 Gyr and then remain brighter than M V ≈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.