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Slow convection and fast rotation in crystallization-driven white dwarf dynamos

Ginzburg, Sivan and Fuller, Jim and Kawka, Adela and Caiazzo, Ilaria (2022) Slow convection and fast rotation in crystallization-driven white dwarf dynamos. Monthly Notices of the Royal Astronomical Society, 514 (3). pp. 4111-4119. ISSN 0035-8711. doi:10.1093/mnras/stac1363. https://resolver.caltech.edu/CaltechAUTHORS:20220707-305638000

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Abstract

It has been recently suggested that white dwarfs generate magnetic fields in a process analogous to the Earth. The crystallization of the core creates a compositional inversion that drives convection, and combined with rotation, this can sustain a magnetic dynamo. We reanalyse the dynamo mechanism, arising from the slow crystallization of the core, and find convective turnover times tconv of weeks to months – longer by orders of magnitude than previously thought. With white dwarf spin periods P ≪ t_(conv), crystallization-driven dynamos are almost always in the fast-rotating regime, where the magnetic field B is at least in equipartition with the convective motion and is possibly further enhanced by a factor of B ∝ (t_(conv)/P)^(1/2), depending on the assumed dynamo scaling law. We track the growth of the crystallized core using mesa and compute the magnetic field B(T_(eff)) as a function of the white dwarf’s effective temperature T_(eff). We compare this prediction with observations and show that crystallization-driven dynamos can explain some – but not all – of the ∼MG magnetic fields measured for single white dwarfs, as well as the stronger fields measured for white dwarfs in cataclysmic variables, which were spun up by mass accretion to short P. Our B(T_(eff)) curves might also explain the clustering of white dwarfs with Balmer emission lines around T_(eff) ≈ 7500 K.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/mnras/stac1363DOIArticle
https://doi.org/10.48550/arXiv.2202.12902arXivDiscussion Paper
ORCID:
AuthorORCID
Fuller, Jim0000-0002-4544-0750
Kawka, Adela0000-0002-4485-6471
Caiazzo, Ilaria0000-0002-4770-5388
Additional Information:© 2022 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) Received: 25 February 2022. Revision received: 01 May 2022. Accepted: 11 May 2022. Published: 16 May 2022. Corrected and typeset: 29 June 2022. We thank Wenbin Lu for interesting discussions and the anonymous reviewer for a useful report that has improved the paper. SG thanks the Heising-Simons Foundation for generous support through a 51 Pegasi b Fellowship. IC is a Sherman Fairchild Fellow at Caltech and thanks the Burke Institute at Caltech for supporting her research. DATA AVAILABILITY. The data underlying this article will be shared on reasonable request to the corresponding author.
Group:Astronomy Department, Walter Burke Institute for Theoretical Physics, TAPIR
Funders:
Funding AgencyGrant Number
Heising-Simons Foundation51 Pegasi b Fellowship
Sherman Fairchild FoundationUNSPECIFIED
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
Subject Keywords:dynamo, stars: magnetic field, white dwarfs
Issue or Number:3
DOI:10.1093/mnras/stac1363
Record Number:CaltechAUTHORS:20220707-305638000
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20220707-305638000
Official Citation:Sivan Ginzburg, Jim Fuller, Adela Kawka, Ilaria Caiazzo, Slow convection and fast rotation in crystallization-driven white dwarf dynamos, Monthly Notices of the Royal Astronomical Society, Volume 514, Issue 3, August 2022, Pages 4111–4119, https://doi.org/10.1093/mnras/stac1363
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115385
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:08 Jul 2022 23:07
Last Modified:25 Jul 2022 23:13

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