The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere White Dwarfs

TL;DR

This survey used direct imaging to search for ultra-low mass companions around white dwarfs, aiming to detect objects cooler than known brown dwarfs and understand planetary survival after stellar evolution.

Contribution

It presents the first multi-epoch J band survey of 23 white dwarfs, setting constraints on the frequency of substellar companions with temperatures above 500 K.

Findings

No common proper motion companions detected.

Less than 5% of white dwarfs have substellar companions > 500 K at 60-200 AU.

Limits established for companion masses based on observation completeness.

Abstract

The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower (< 500 K) than the coolest brown dwarfs currently observed. These ultra-low mass substellar objects would have spectral types > T8.5 and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 - 8 solar masses, i.e., early B to mid F). This paper presents the results of a multi-epoch J band common proper motion survey of 23 nearby equatorial and northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non-moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that < 5% of white dwarfs have substellar companions with effective temperatures > 500 K between projected physical separations of 60 - 200 AU.