WD0141-675: A case study on how to follow-up astrometric planet candidates around white dwarfs

TL;DR

This study explores methods to confirm and characterize astrometric planet candidates around white dwarfs by combining spectroscopic, photometric, and astrometric data, focusing on the case of WD0141-675.

Contribution

It demonstrates how radial velocity and infrared photometry can effectively constrain the mass of potential planets around white dwarfs, aiding in confirmation and characterization.

Findings

Radial velocity campaigns can confirm close-in giant exoplanets around polluted white dwarfs.

Infrared emission detection with JWST MIRI can provide constraints on planetary formation.

Combining data types helps rule out brown dwarf and planet mass ranges for candidates.

Abstract

This work combines spectroscopic and photometric data of the polluted white dwarf WD0141-675 which has a now retracted astrometric super-Jupiter candidate and investigates the most promising ways to confirm Gaia astrometric planetary candidates and obtain follow-up data. Obtaining precise radial velocity measurement for white dwarfs is challenging due to their intrinsic faint magnitudes, lack of spectral absorption lines, and broad spectral features. However, dedicated radial velocity campaigns are capable of confirming close in giant exoplanets (a few M$_{\textrm{Jup}}$) around polluted white dwarfs, where additional metal lines aid radial velocity measurements. Infrared emission from these giant exoplanets is shown to be detectable with JWST MIRI and will provide constraints on the formation of the planet. Using the initial Gaia astrometric solution for WD0141-675 as a case study, if there were a planet with a 33.65 d period or less with a nearly edge on orbit, 1) ground-based radial velocity monitoring limits the mass to $<$ 15.4 M$_{\textrm{Jup}}$, and 2) space-based infrared photometry shows a lack of infrared excess and in a cloud-free planetary cooling scenario, a sub-stellar companion would have to be $<$ 16 M$_{\textrm{Jup}}$ and be older than 3.7 Gyr. These results demonstrate how radial velocities and infrared photometry can probe the mass of the objects producing some of the astrometric signals, and rule out parts of the brown dwarf and planet mass parameter space. Therefore, combining astrometric data with spectroscopic and photometric data is crucial to both confirm, and characterise astrometric planet candidates around white dwarfs.