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

Abstract

KOI-3278 is a self-lensing stellar binary consisting of a white-dwarf secondary orbiting a Sun-like primary star. Kruse and Agol (2014) noticed small periodic brightenings every 88.18 days in the Kepler photometry 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 and Agol (2014) Einsteinian microlensing model, resulting in a revised mass for the white dwarf of $0.539_{-0.020}^{+0.022}{M}_{\odot }$. 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 $0.5122_{-0.0058}^{+0.0057}{M}_{\odot }$. The nominal uncertainty for the Newtonian mass is about four times better than for the Einsteinian, $\pm 1.1\%$ vs. $\pm 4.1\%$ 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 $0.5250_{-0.0089}^{+0.0082}{M}_{\odot }$. 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.

arXiv commentApJ Accepted; 22 Pages, 8 Figures, 6 Tables and 4 Supplementary Tables

References in corpus (32)

• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• Gaia Data Release 2. Summary of the contents and survey properties
• PARSEC: stellar tracks and isochrones with the PAdova and TRieste Stellar Evolution Code
• The Transiting Exoplanet Survey Satellite
• Analytic Lightcurves for Planetary Transit Searches
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Radial Velocities for 889 Late-type Stars
• RadVel: The Radial Velocity Modeling Toolkit
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
• An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• A library of high resolution synthetic stellar spectra from 300nm to 1.8 micron with solar and alpha-enhanced composition
• Spectroscopy Made Easy: Evolution
• A Comprehensive Spectroscopic Analysis of DB White Dwarfs
• Spectral Properties of Cool Stars: Extended Abundance Analysis of 1617 Planet Search Stars
• The California-Kepler Survey. I. High Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets
• The Initial-Final Mass Relation: Direct Constraints at the Low Mass End
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• Stellar Limb-Darkening Coefficients for CoRot and Kepler
• Planetary Candidates Observed by Kepler IV: Planet Sample From Q1-Q8 (22 Months)
• Analytic Approximations for Transit Light Curve Observables, Uncertainties, and Covariances
• Three's Company: An additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets
• KOI-3278: A Self-Lensing Binary Star System
• Spectral Properties of Cool Stars: Extended Abundance Analysis of Kepler Objects of Interest
• Microlensing of Large Sources
• Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: The effects of including recombination energy
• Discovery of three self-lensing binaries from Kepler
• Detection of Potential Transit Signals in Sixteen Quarters of Kepler Mission Data
• The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution
• Two Stars Two Ways: Confirming a Microlensing Binary Lens Solution with a Spectroscopic Measurement of the Orbit
• Solving Kepler's equation CORDIC-like
• Degeneracy between Lensing and Occultation in the Analysis of Self-lensing Phenomena

Cited by in corpus (5)

• Self-lensing Discovery of a $0.2M_{\odot }$ White Dwarf in an Unusually Wide Orbit Around a Sun-like Star
• Formation of long-period post-common-envelope binaries I. No extra energy is needed to explain oxygen-neon white dwarfs paired with AFGK-type main-sequence stars
• Formation of long-period post-common-envelope binaries II. Explaining the self-lensing binary KOI 3278
• No longer impossible: the self-lensing binary KIC 8145411 is a triple
• Four New Self-lensing Binaries from Kepler: Radial Velocity Characterization and Astrophysical Implications