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Title: From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing

Abstract

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 largermore » 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.« less

Authors:
 [1];  [1];  [1];  [1];  [1]
  1. Department of Physics, University of Warwick, Coventry CV4 7AL, UK
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1594190
Resource Type:
Published Article
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Name: Monthly Notices of the Royal Astronomical Society Journal Volume: 492 Journal Issue: 3; Journal ID: ISSN 0035-8711
Publisher:
Oxford University Press
Country of Publication:
United Kingdom
Language:
English

Citation Formats

Cunningham, Tim, Tremblay, Pier-Emmanuel, Gentile Fusillo, Nicola Pietro, Hollands, Mark, and Cukanovaite, Elena. From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing. United Kingdom: N. p., 2020. Web. doi:10.1093/mnras/stz3638.
Cunningham, Tim, Tremblay, Pier-Emmanuel, Gentile Fusillo, Nicola Pietro, Hollands, Mark, & Cukanovaite, Elena. From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing. United Kingdom. doi:10.1093/mnras/stz3638.
Cunningham, Tim, Tremblay, Pier-Emmanuel, Gentile Fusillo, Nicola Pietro, Hollands, Mark, and Cukanovaite, Elena. Tue . "From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing". United Kingdom. doi:10.1093/mnras/stz3638.
@article{osti_1594190,
title = {From hydrogen to helium: the spectral evolution of white dwarfs as evidence for convective mixing},
author = {Cunningham, Tim and Tremblay, Pier-Emmanuel and Gentile Fusillo, Nicola Pietro and Hollands, Mark and Cukanovaite, Elena},
abstractNote = {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.},
doi = {10.1093/mnras/stz3638},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 3,
volume = 492,
place = {United Kingdom},
year = {2020},
month = {1}
}

Journal Article:
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DOI: 10.1093/mnras/stz3638

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