KOI-3278: A Self-Lensing Binary Star System

Abstract

Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a "self-lensing" system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler's laws and stellar models, we constrain the mass of the white dwarf to be ~63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution.Comment: Published in Science. Main text 6 pages, 3 figures. Supplement 16 pages, 7 figures. Code used for analysis is available at http://github.com/ethankruse/koi3278 . Animation showing ingress of the lensing event at https://www.dropbox.com/s/eb3pznxi990vn00/KOI3278_pulse_starspots2_1024.mp4 . Executive summary for non-astronomers available at http://www.astro.washington.edu/users/eakruse/papers.ph