ZTFJ0038+2030: a long period eclipsing white dwarf and a substellar companion

TL;DR

This paper reports the discovery and characterization of a deep eclipsing white dwarf with a substellar companion, likely a brown dwarf, using ZTF data, and discusses the implications for understanding such systems.

Contribution

It presents the first detailed characterization of a white dwarf with a substellar companion discovered via ZTF, highlighting the potential for future discoveries.

Findings

The white dwarf has a mass of 0.50 solar masses and a temperature of 10900 K.

The companion has a mass of 0.059 solar masses and a radius of 0.0783 solar radii.

The system's orbital period is 10 hours, and the companion is likely an old brown dwarf.

Abstract

In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with a dark, substellar companion. The lack of an infrared excess and an orbital period of 10 hours made this a potential exoplanet candidate. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of $0.50\pm0.02\,\mathrm{M_{\odot}}$ and a temperature of $10900\pm200\,$K. The companion has a mass of $0.059\pm0.004\,\mathrm{M_{\odot}}$ and a small radius of $0.0783\pm0.0013\,\mathrm{R_{\odot}}$. It is one of the smallest transiting brown dwarfs known and likely old, $\gtrsim 8\,$Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems. This will allow us to measure period and mass distributions and allows us to understand the formation channels of white dwarfs with substellar companions.