Issue |
A&A
Volume 635, March 2020
|
|
---|---|---|
Article Number | A103 | |
Number of page(s) | 9 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/202037530 | |
Published online | 16 March 2020 |
New white dwarf envelope models and diffusion
Application to DQ white dwarfs
1
Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany
e-mail: koester@astrophysik.uni-kiel.de
2
Instituto de Fisica, Universidade Federal do Rio Grande do Sul, 91501-900 Porto-Alegre, RS, Brazil
3
Department of Physics and Astronomy, University of Victoria, PO Box 1700 STN CSC, Victoria, BC V8W 2Y2, Canada
Received:
20
January
2020
Accepted:
20
February
2020
Context. Recent studies of the atmospheres of carbon-rich (DQ) white dwarfs have demonstrated the existence of two different populations that are distinguished by the temperature range, but more importantly, by the extremely high masses of the hotter group. The classical DQ below 10 000 K are well understood as the result of dredge-up of carbon by the expanding helium convection zone. The high-mass group poses several problems regarding their origin and also an unexpected correlation of effective temperature with mass.
Aims. We propose to study the envelopes of these objects to determine the total hydrogen and helium masses as possible clues to their evolution.
Methods. We developed new codes for envelope integration and diffusive equilibrium that are adapted to the unusual chemical composition, which is not necessarily dominated by hydrogen and helium.
Results. Using the new results for the atmospheric parameters, in particular, the masses obtained using Gaia parallaxes, we confirm that the narrow sequence of carbon abundances with Teff in the cool classical DQ is indeed caused by an almost constant helium to total mass fraction, as found in earlier studies. This mass fraction is smaller than predicted by stellar evolution calculations. For the warm DQ above 10 000 K, which are thought to originate from double white dwarf mergers, we obtain extremely low hydrogen and helium masses. The correlation of mass with Teff remains unexplained, but another possible correlation of helium layer masses with Teff as well as the gravitational redshifts casts doubt on the reality of both and suggests possible shortcomings of current models.
Key words: white dwarfs / stars: carbon / stars: evolution / convection / diffusion
© ESO 2020
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.