A CHEOPS White Dwarf Transit Search

TL;DR

This study used CHEOPS to search for transiting planetesimals around six nearby white dwarfs, finding no significant signals but demonstrating sensitivity to Moon-sized objects with specific orbital periods.

Contribution

First systematic search for transiting planetesimals around white dwarfs using CHEOPS, employing both aperture and PSF photometry methods.

Findings

No significant transiting signals detected.

Sensitivity primarily to Moon-sized objects with periods 3-10 hours.

Photometric precision of <2 ppt achieved in 60s exposures.

Abstract

White dwarf spectroscopy shows that nearly half of white dwarf atmospheres contain metals that must have been accreted from planetary material that survived the red giant phases of stellar evolution. We can use metal pollution in white dwarf atmospheres as flags, signalling recent accretion, in order to prioritize an efficient sample of white dwarfs to search for transiting material. We present a search for planetesimals orbiting six nearby white dwarfs with the CHEOPS spacecraft. The targets are relatively faint for CHEOPS, $11$ mag $< G < 12.8$ mag. We use aperture photometry data products from the CHEOPS mission as well as custom PSF photometry to search for periodic variations in flux due to transiting planetesimals. We detect no significant variations in flux that cannot be attributed to spacecraft systematics, despite reaching a photometric precision of $<2$ ppt in 60 s exposures on each target. We simulate observations to show that the small survey is sensitive primarily to Moon-sized transiting objects with periods $3$ hr $< P < 10$ hr, with radii $R \gtrsim 1000$ km.