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From hydrogen to helium : the spectral evolution of white dwarfs as evidence for convective mixing
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Cunningham, T. J., Tremblay, Pier-Emmanuel, Gentile Fusillo, Nicola Pietro, Hollands, Mark A. and Cukanovaite, Elena (2020) From hydrogen to helium : the spectral evolution of white dwarfs as evidence for convective mixing. Monthly Notices of the Royal Astronomical Society, 492 (3). pp. 3540-3552. doi:10.1093/mnras/stz3638
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Official URL: https://doi.org/10.1093/mnras/stz3638
Abstract
We present a study of the hypothesis that white dwarfs undergo a spectral change from hydrogen- to helium-dominated atmospheres using a volume-limited photometric sample drawn from the Gaia-DR2 catalogue, the Sloan Digital Sky Survey (SDSS), and the Galaxy Evolution Explorer (GALEX). We exploit the strength of the Balmer jump in hydrogen-atmosphere DA white dwarfs to separate them from helium-dominated objects in SDSS colour space. Across the effective temperature range from 20 000 to 9000 K, we find that 22 per cent of white dwarfs will undergo a spectral change, with no spectral evolution being ruled out at 5σ. The most likely explanation is that the increase in He-rich objects is caused by the convective mixing of DA stars with thin hydrogen layers, in which helium is dredged up from deeper layers by a surface hydrogen convection zone. The rate of change in the fraction of He-rich objects as a function of temperature, coupled with a recent grid of 3D radiation-hydrodynamic simulations of convective DA white dwarfs – which include the full overshoot region – lead to a discussion on the distribution of total hydrogen mass in white dwarfs. We find that 60 per cent of white dwarfs must have a hydrogen mass larger than MH/MWD = 10−10, another 25 per cent have masses in the range MH/MWD = 10−14–10−10, and 15 per cent have less hydrogen than MH/MWD = 10−14. These results have implications for white dwarf asteroseismology, stellar evolution through the asymptotic giant branch and accretion of planetesimals on to white dwarfs.
| Item Type: | Journal Article | ||||||||
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| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
| SWORD Depositor: | Library Publications Router | ||||||||
| Journal or Publication Title: | Monthly Notices of the Royal Astronomical Society | ||||||||
| Publisher: | Oxford University Press (OUP) | ||||||||
| ISSN: | 1365-2966 | ||||||||
| Official Date: | March 2020 | ||||||||
| Dates: |
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| Volume: | 492 | ||||||||
| Number: | 3 | ||||||||
| Page Range: | pp. 3540-3552 | ||||||||
| DOI: | 10.1093/mnras/stz3638 | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Access rights to Published version: | Open Access |
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