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

Bours, M. C. P; Marsh, T. R; Parsons, S. G; Dhillon, V. S; Ashley, R. P; Bento, J. P; Breedt, E; Butterley, T; Caceres, C; Copperwheat, C. M; Hardy, L. K; Hermes, J. J; Irawati, P; Kerry, P; Kilkenny, D; Littlefair, S. P; McAllister, M. J; Rattanasoon, S; Sahman, D. I; Vuckovic, M; Wilson, R. W

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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...[Show more]

dc.contributor.authorBours, M. C. P
dc.contributor.authorMarsh, T. R
dc.contributor.authorParsons, S. G
dc.contributor.authorDhillon, V. S
dc.contributor.authorAshley, R. P
dc.contributor.authorBento, J. P
dc.contributor.authorBreedt, E
dc.contributor.authorButterley, T
dc.contributor.authorCaceres, C
dc.contributor.authorCopperwheat, C. M
dc.contributor.authorHardy, L. K
dc.contributor.authorHermes, J. J
dc.contributor.authorIrawati, P
dc.contributor.authorKerry, P
dc.contributor.authorKilkenny, D
dc.contributor.authorLittlefair, S. P
dc.contributor.authorMcAllister, M. J
dc.contributor.authorRattanasoon, S
dc.contributor.authorSahman, D. I
dc.contributor.authorVuckovic, M
dc.contributor.authorWilson, R. W
dc.date.accessioned2016-08-17T00:16:44Z
dc.date.available2016-08-17T00:16:44Z
dc.identifier.issn0035-8711
dc.identifier.urihttp://hdl.handle.net/1885/107204
dc.description.abstractWe 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 yrs, 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 yrs, 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.
dc.description.sponsorshipMCPB acknowledges support from Maja Vuckovic and the Joint Committee ESO-Government of Chile (grant 2014). TRM, EB, VSD, SPL, TB and RWW are grateful to the Science and Technology Facilities Council for financial support in the form of grant nos ST/L000733, ST/L00075X/1 and ST/M001350/1. SGP and CC acknowledge support from CONICYT FONDECYT grants 3140585 and 3140592, respectively. CC also acknowledges support from the Millennium Nucleus RC130007 (Chilean Ministry of Economy). JJH acknowledges support from NASA through Hubble Fellowship grant no. HST-HF2-51357.001-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. DK is partially funded by the University of the Western Cape and the National Research Foundation (NRF) of South Africa. The research leading to these results has also received funding from the European Research Council under ERC Grant Agreement n. 320964 (WDTracer).
dc.format15 pages
dc.publisherOxford University Press
dc.rights© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. http://www.sherpa.ac.uk/romeo/issn/0035-8711/Author can archive publisher's version/PDF (Sherpa/Romeo as of 17/8/2016).
dc.sourceMonthly Notices of the Royal Astronomical Society
dc.subjectmethods
dc.subjectobservational
dc.subjectbinaries
dc.subjecteclipsing
dc.subjectwhite dwarfs
dc.titleLong-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at work
dc.typeJournal article
local.identifier.citationvolume460
dcterms.dateAccepted2016-05-17
dc.date.issued2016-08-21
local.publisher.urlhttp://mnras.oxfordjournals.org/
local.type.statusPublished Version
local.contributor.affiliationBento, J. P., RSAA General, CPMS Research School of Astronomy and Astrophysics, The Australian National University
local.identifier.essn1365-2966
local.bibliographicCitation.issue4
local.bibliographicCitation.startpage3873
local.bibliographicCitation.lastpage3887
local.identifier.doi10.1093/mnras/stw1203
dcterms.accessRightsOpen Access
CollectionsANU Research Publications

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