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Long-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at work

Bours, MCP and Marsh, TR and Parsons, SG and Dhillon, VS and Ashley, RP and Bento, JP and Breedt, E and Butterley, T and Caceres, C and Chote, P and Copperwheat, CM and Hardy, LK and Hermes, JJ and Irawati, P and Kerry, P and Kilkenny, D and Littlefair, SP and McAllister, MJ and Rattanasoon, S and Sahman, DI and Vuckovic, M and Wilson, RW (2016) Long-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at work. Monthly Notices of the Royal Astronomical Society, 460 (4). pp. 3873-3887. ISSN 0035-8711

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Abstract

We present a long-term programme for timing the eclipses of white dwarfs in close binaries to measure apparent and/or real variations in their orbital periods. Our programme includes 67 close binaries, both detached and semi-detached and with M-dwarfs, K-dwarfs, brown dwarfs or white dwarfs secondaries. In total, we have observed more than 650 white dwarf eclipses. We use this sample to search for orbital period variations and aim to identify the underlying cause of these variations. We find that the probability of observing orbital period variations increases significantly with the observational baseline. In particular, all binaries with baselines exceeding 10 yr, with secondaries of spectral type K2 – M5.5, show variations in the eclipse arrival times that in most cases amount to several minutes. In addition, among those with baselines shorter than 10 yr, binaries with late spectral type (>M6), brown dwarf or white dwarf secondaries appear to show no orbital period variations. This is in agreement with the so-called Applegate mechanism, which proposes that magnetic cycles in the secondary stars can drive variability in the binary orbits. We also present new eclipse times of NN Ser, which are still compatible with the previously published circumbinary planetary system model, although only with the addition of a quadratic term to the ephemeris. Finally, we conclude that we are limited by the relatively short observational baseline for many of the binaries in the eclipse timing programme, and therefore cannot yet draw robust conclusions about the cause of orbital period variations in evolved, white dwarf binaries.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society] ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 20 Jan 2017 09:58
Last Modified: 20 Jan 2017 09:58
DOI or Identification number: 10.1093/mnras/stw1203
URI: http://researchonline.ljmu.ac.uk/id/eprint/5325

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