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The Mass of the White Dwarf Companion in the Self-Lensing Binary KOI-3278: Einstein vs. Newton

Yahalomi, Daniel A. and Shvartzvald, Yossi and Agol, Eric and Shporer, Avi and Latham, David W. and Kruse, Ethan and Brewer, John M. and Buchhave, Lars A. and Fulton, Benjamin J. and Howard, Andrew W. and Isaacson, Howard and Petigura, Erik A. and Quinn, Samuel N. (2019) The Mass of the White Dwarf Companion in the Self-Lensing Binary KOI-3278: Einstein vs. Newton. Astrophysical Journal, 880 (1). Art. No. 33. ISSN 1538-4357. doi:10.3847/1538-4357/ab2649.

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KOI-3278 is a self-lensing stellar binary consisting of a white dwarf secondary orbiting a Sun-like primary star. Kruse & Agol noticed small periodic brightenings every 88.18 days in the Keplerphotometry and interpreted these as the result of microlensing by a white dwarf with about 63% of the mass of the Sun. We obtained two sets of spectra for the primary that allowed us to derive three sets of spectroscopic estimates for its effective temperature, surface gravity, and metallicity for the first time. We used these values to update the Kruse & Agol Einsteinian microlensing model, resulting in a revised mass for the white dwarf of 0.539^(+0.022)_(-0.020) M⊙. The spectra also allowed us to determine radial velocities and derive orbital solutions, with good agreement between the two independent data sets. An independent Newtonian dynamical MCMC model of the combined velocities yielded a mass for the white dwarf of 0.5122^(+0.0057)_(-0.0058) M⊙. The nominal uncertainty for the Newtonian mass is about four times better than for the Einsteinian, ±1.1% versus ±4.1%, and the difference between the two mass determinations is 5.2%. We then present a joint Einsteinian microlensing and Newtonian radial velocity model for KOI-3278, which yielded a mass for the white dwarf of 0.5250^(+0.0082)_(-0.0089) M⊙. This joint model does not rely on any white dwarf evolutionary models or assumptions on the white dwarf mass–radius relation. We discuss the benefits of a joint model of self-lensing binaries, and how future studies of these systems can provide insight into the mass–radius relation of white dwarfs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Shvartzvald, Yossi0000-0003-1525-5041
Agol, Eric0000-0002-0802-9145
Shporer, Avi0000-0002-1836-3120
Latham, David W.0000-0001-9911-7388
Brewer, John M.0000-0002-9873-1471
Buchhave, Lars A.0000-0003-1605-5666
Fulton, Benjamin J.0000-0003-3504-5316
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Petigura, Erik A.0000-0003-0967-2893
Quinn, Samuel N.0000-0002-8964-8377
Additional Information:© 2019 The American Astronomical Society. Received 2019 April 24; revised 2019 May 24; accepted 2019 June 1; published 2019 July 22. We thank George Zhou, Joseph Rodriguez, Allyson Bieryla, Jason Eastman, and Stephanie Douglas for stimulating conversations and guidance. Software: Brewer (Brewer et al. 2016), emcee (Foreman-Mackey et al. 2013), matplotlib (Hunter 2007), numpy (Walt et al. 2011), scipy (Jones et al. 2001), SPC (Buchhave et al. 2012), SpecMatch (Petigura et al. 2017).
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Subject Keywords:binaries: eclipsing – gravitational lensing: micro – white dwarfs
Issue or Number:1
Record Number:CaltechAUTHORS:20190515-080923158
Persistent URL:
Official Citation:Daniel A. Yahalomi et al 2019 ApJ 880 33
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95498
Deposited By: Tony Diaz
Deposited On:16 May 2019 02:35
Last Modified:16 Nov 2021 17:13

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