Discovery of eclipsing white dwarf systems in a search for Earth-size companions

TL;DR

This paper explores white dwarfs as prime targets for exoplanet detection, especially Earth-sized and smaller objects, using their large eclipses and high-precision photometry, leading to the discovery of 20 new eclipsing systems.

Contribution

It introduces a novel search strategy combining synoptic and multi-colour data to detect eclipsing white dwarf systems, doubling known cases and identifying potential substellar companions.

Findings

Discovered 20 new eclipsing white dwarf systems.

Identified candidates with substellar radii.

Demonstrated white dwarfs' suitability for detecting small exoplanets.

Abstract

Although white dwarfs are believed to be the end point of most stellar evolution, unlike main sequence stars, they have not yet been the subject of dedicated time-domain surveys for exoplanets. We discuss how their size and distinctive colour make them excellent targets for wide-field searches for exoplanets. In particular, we note that planets of Earth-size can give rise to multi-magnitude eclipses of massive white dwarfs. Such a large signal is almost unmistakable and would be detectable even with very low-precision photometry. For objects of smaller size, the high accuracy photometry currently being used to detect Super-Earth and smaller planets transiting Sun-sized stars, is capable of revealing minor planets down to R~100km as they transit white dwarfs. Such observations can be used to test current evidence for asteroid-size objects being the cause for dust rings which have recently been observed for a number of white dwarfs. No other current exoplanet search method is capable of detecting such exo-asteroids. As an initial test of this search strategy, we combine synoptic data from the Catalina Sky Survey with multi-colour photometry and spectra from the Sloan Digital Sky Survey to search ~12,000 white dwarf lightcurves for eclipsing events. We find 20 new eclipsing white dwarf binary systems with low-mass companions. This doubles the number of known eclipsing white dwarfs and is expected to enable the determination of accurate white dwarf radii. Three of the discoveries have radii consistent with substellar systems and show no evidence of flux from the eclipsing object in their SDSS optical spectra, or near-IR data.