Hermes, JJ;
Gaensicke, BT;
Koester, D;
Bours, MCP;
Townsley, DM;
Farihi, J;
Marsh, TR;
... Raddi, R; + view all
(2014)
Heavy metals in a light white dwarf: abundances of the metal-rich, extremely low-mass GALEX J1717+6757.
Monthly Notices of the Royal Astronomical Society
, 444
(2)
pp. 1674-1682.
10.1093/mnras/stu1518.
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Abstract
Using the Hubble Space Telescope, we detail the first abundance analysis enabled by far-ultraviolet spectroscopy of a low-mass (≃0.19 M⊙) white dwarf (WD), GALEX J1717+6757, which is in a 5.9-h binary with a fainter, more-massive companion. We see absorption from nine metals, including roughly solar abundances of Ca, Fe, Ti, and P. We detect a significantly sub-solar abundance of C, and put upper limits on N and O that are also markedly sub-solar. Updated diffusion calculations indicate that all metals should settle out of the atmosphere of this 14 900 K, log g = 5.67 WD in the absence of radiative forces in less than 20 yr, orders of magnitude faster than the cooling age of hundreds of Myr. We demonstrate that ongoing accretion of rocky material that is often the cause of atmospheric metals in isolated, more massive WDs is unlikely to explain the observed abundances in GALEX J1717+6757. Using new radiative levitation calculations, we determine that radiative forces can counteract diffusion and support many but not all of the elements present in the atmosphere of this WD; radiative levitation cannot, on its own, explain all of the observed abundance patterns, and additional mechanisms such as rotational mixing may be required. Finally, we detect both primary and secondary eclipses using ULTRACAM high-speed photometry, which we use to constrain the low-mass WD radius and rotation rate as well as update the ephemeris from the discovery observations of this WD+WD binary.
| Type: | Article |
|---|---|
| Title: | Heavy metals in a light white dwarf: abundances of the metal-rich, extremely low-mass GALEX J1717+6757 |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stu1518 |
| Publisher version: | http://dx.doi.org/10.1093/mnras/stu1518 |
| Language: | English |
| Additional information: | This article has been accepted for publication in the Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| Keywords: | stars: abundances, binaries: close, binaries: eclipsing, stars: individual: (GALEX J171708.5+675712), white dwarfs, Galaxy: stellar content |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1477438 |
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