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Tidally excited oscillations in hot white dwarfs

Yu, Hang and Fuller, Jim and Burdge, Kevin B. (2021) Tidally excited oscillations in hot white dwarfs. Monthly Notices of the Royal Astronomical Society, 501 (2). pp. 1836-1851. ISSN 0035-8711. https://resolver.caltech.edu/CaltechAUTHORS:20201203-151022085

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Abstract

We study the flux variation in helium white dwarfs (WDs) induced by dynamical tides for a variety of WD models with effective temperatures ranging from T=10kK to T=26kK⁠. At linear order, we find the dynamical tide can significantly perturb the observed flux in hot WDs. If the temperature T≳14kK⁠, then the dynamical tide may induce a fractional change in the flux by >1 per cent when the orbital period is P_(orb) ≃ 20−60min⁠. The ratio between the flux modulation due to the dynamical tide and that due to the equilibrium tide (i.e. ellipsoidal variability) increases as the WD’s radius decreases, and it could exceed O(10) if the WD has a radius R ≲ 0.03 R_⊙. Unlike the ellipsoidal variability which is in phase with the orbital motion, the pulsation caused by the dynamical tide may have a substantial phase shift. A cold WD with T≃10kK⁠, on the other hand, is unlikely to show observable pulsations due to the dynamical tide. At shorter orbital periods, the dynamical tide may break and become highly non-linear. We approximate this regime by treating the waves as one-way travelling waves and find the flux variation is typically reduced to 0.1–1 per cent and the excess phase is ∼90° (though with large uncertainty). Even in the travelling-wave limit, the flux perturbation due to dynamical tide could still exceed the ellipsoidal variability for compact WDs with R ≲ 0.02 R_⊙. We further estimate the non-linear flux perturbations oscillating at four times the orbital frequency dominated by a self-coupled parent g-mode driving low-order daughter p modes. The non-linear flux variation could be nearly 50 per cent of the linear variation for very hot WD models with T≳26kK and 1 per cent linear flux variation. We thus predict that both the linear and non-linear flux variations due to dynamical tides are likely to have significant observational signatures.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/mnras/staa3717DOIArticle
https://arxiv.org/abs/2010.15279arXivDiscussion Paper
ORCID:
AuthorORCID
Yu, Hang0000-0002-6011-6190
Fuller, Jim0000-0002-4544-0750
Burdge, Kevin B.0000-0002-7226-836X
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2020 November 25. Received 2020 November 25; in original form 2020 October 28. Published: 30 November 2020. HY acknowledges support from the Sherman Fairchild Foundation. JF is thankful for support through an Innovator Grant from The Rose Hills Foundation, and the Alfred P. Sloan Foundation through grant FG-2018-10515. KBB thanks the National Aeronautics and Space Administration and the Heising-Simons Foundation for supporting his research. Data Availability: The MESA and GYRE input files to generate the background models and to obtain the WD eigenmodes are available on reasonable requests to the corresponding author.
Group:TAPIR, Astronomy Department
Funders:
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
Rose Hills FoundationUNSPECIFIED
Alfred P. Sloan FoundationFG-2018-10515
NASAUNSPECIFIED
Heising-Simons FoundationUNSPECIFIED
Subject Keywords:asteroseismology – binaries: close – stars: oscillations – white dwarfs
Issue or Number:2
Record Number:CaltechAUTHORS:20201203-151022085
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201203-151022085
Official Citation:Hang Yu, Jim Fuller, Kevin B Burdge, Tidally excited oscillations in hot white dwarfs, Monthly Notices of the Royal Astronomical Society, Volume 501, Issue 2, February 2021, Pages 1836–1851, https://doi.org/10.1093/mnras/staa3717
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106898
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:05 Dec 2020 01:41
Last Modified:11 Feb 2021 20:45

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