MOBSTER – III. HD 62658: a magnetic Bp star in an eclipsing binary with a non-magnetic 'identical twin'

Creators: Shultz, M. E.; Johnston, C.; Labadie-Bartz, J.; Petit, V.; David-Uraz, A.; Kochukhov, Ø.; Wade, G. A.; Pepper, J.; Stassun, K. G.; Rodriguez, J. E.; Lund, M. B.; James, D. J.

Abstract

HD 62658 (B9p V) is a little-studied chemically peculiar star. Light curves obtained by the Kilodegree Extremely Little Telescope (KELT) and Transiting Exoplanet Survey Satellite (TESS) show clear eclipses with a period of about 4.75 d, as well as out-of-eclipse brightness modulation with the same 4.75 d period, consistent with synchronized rotational modulation of surface chemical spots. High-resolution ESPaDOnS circular spectropolarimetry shows a clear Zeeman signature in the line profile of the primary; there is no indication of a magnetic field in the secondary. PHOEBE modelling of the light curve and radial velocities indicates that the two components have almost identical masses of about 3 M_⊙. The primary's longitudinal magnetic field〈B_z〉 varies between about +100 and −250 G, suggesting a surface magnetic dipole strength B_d = 850 G. Bayesian analysis of the Stokes V profiles indicates B_d = 650 G for the primary and B_d < 110 G for the secondary. The primary's line profiles are highly variable, consistent with the hypothesis that the out-of-eclipse brightness modulation is a consequence of rotational modulation of that star's chemical spots. We also detect a residual signal in the light curve after removal of the orbital and rotational modulations, which might be pulsational in origin; this could be consistent with the weak line profile variability of the secondary. This system represents an excellent opportunity to examine the consequences of magnetic fields for stellar structure via comparison of two stars that are essentially identical with the exception that one is magnetic. The existence of such a system furthermore suggests that purely environmental explanations for the origin of fossil magnetic fields are incomplete.

Additional Information

© 2019 The Author(s) Published by Oxford University Press on behalf of the 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 2019 October 6. Received 2019 September 24; in original form 2019 August 12. Published: 14 October 2019. This project makes use of data from the KELT survey, including support from The Ohio State University, Vanderbilt University, and Lehigh University, along with the KELT follow-up collaboration. This work has made use of the VALD data base, operated at Uppsala University, the Institute of Astronomy RAS in Moscow, and the University of Vienna. This work is based on observations obtained at the Canada–France–Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-2655. MES acknowledges support from the Annie Jump Cannon Fellowship, supported by the University of Delaware and endowed by the Mount Cuba Astronomical Observatory. CJ acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement N°670519: MAMSIE), as well as from the Research Foundation Flanders (FWO) under grant agreement G0A2917N (BlackGEM). CJ acknowledges the use of computational resources and services provided by the VSC (Flemish Supercomputer Center), funded by the Research Foundation – Flanders (FWO) and the Flemish Government – department EWI. JLB acknowledges support from FAPESP (grant 2017/23731-1). ADU acknowledges support from the National Science and Engineering Research Council of Canada (NSERC). OK acknowledges support by the Knut and Alice Wallenberg Foundation (project grant 'The New Milky Way'), the Swedish Research Council (project 621-2014-5720), and the Swedish National Space Board (projects 185/14, 137/17). GAW acknowledges support from a Discovery Grant from NSERC. DJJ was supported through the Black Hole Initiative at Harvard University, through a grant (60477) from the John Templeton Foundation and by National Science Foundation award AST-1440254.

Attached Files

Published - stz2846.pdf

Accepted Version - 1910.02928.pdf

Files

1910.02928.pdf

Files (2.7 MB)

Name	Size	Download all
1910.02928.pdf md5:a78f52b607d935dda3e3258f6ba56c5c	741.0 kB	Preview Download
stz2846.pdf md5:53ec3d521386fbfa8f59bfeb75bf3ec8	1.9 MB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes