ESPRESSO observations of the debris-accreting white dwarf WD\,0141--675

TL;DR

This study uses high-resolution ESPRESSO spectroscopy to investigate potential planetary companions around white dwarf WD 0141-675, finding tentative signals that suggest the presence of a planetary-mass object with an orbital period around 15-16 days.

Contribution

First high-resolution spectroscopic analysis of WD 0141-675 indicating possible planetary signals, demonstrating ESPRESSO's capability to detect short-period planets around white dwarfs.

Findings

Tentative 15.6-day radial velocity signal.

Weak variability in Ca K line morphology.

Infrared photometry rules out brown dwarf companion.

Abstract

WD\,0141--675 was reported as the first astrometrically detected white dwarf planet host candidate as part of the third data release from \textit{Gaia}, just to be later retracted via a news item on the \textit{Gaia} web site$^1$. We present time-resolved, high-resolution optical ESPRESSO spectroscopy of \obj. A radial velocity analysis of the \Ion{Ca}~K absorption line reveals a tentative periodic signal of $15.6\pm0.9$\,d. Phase-folding the ESPRESSO spectroscopy on this signal exhibits weak variability in the morphology of \Ion{Ca}~K close to the core of the line. A violet-to-red ratio analysis of the Ca~K line shows a periodic signal of $16.1\pm0.9$\,d. The periods from both methods agree, within their uncertainties, with half the period of the astrometric planet candidate, however, both measurements are of low statistical significance. Nonetheless, our results imply possible solutions to the mass function within the planetary regime. And when combined with existing infrared photometry, which rules out a brown dwarf companion, yield a lower limit on the orbital inclination of $\sim7^\circ$. Our study demonstrates that ESPRESSO observations are well capable of detecting short-period (days to weeks) giant planets orbiting white dwarfs.