Serendipitous observation of a white dwarf companion to a JWST/MIRI coronagraphic calibrator

TL;DR

This paper reports the serendipitous mid-infrared detection of a white dwarf companion to a star observed with JWST/MIRI, demonstrating the instrument's capability to study white dwarfs in close binary systems.

Contribution

It presents the first mid-infrared detection of a white dwarf companion to a bright star using JWST/MIRI, highlighting new observational possibilities.

Findings

White dwarf companion detected at 10-16 μm with JWST/MIRI

Photometry consistent with a 10,000 K, 0.8 M_sun white dwarf

Mid-infrared observations can effectively study white dwarf companions

Abstract

We present the unplanned detection of a white dwarf companion to the star HD 218261 in mid-infrared (10-16 $\mu$m) observations with JWST/MIRI. This star was observed as a calibrator for coronagraphic observations of the exoplanet host HR 8799. HD 218261 B has only previously been detected by Gaia, and only in visible light. We confidently detect the companion in the mid-infrared, where it is less luminous than the primary by a factor of ~10$^4$. The visible and mid-infrared photometry are consistent with a white dwarf of $T_\text{eff}\approx10000$ K, $M\approx0.8 M_\odot$, though observation of its optical spectrum is required to precisely constrain its physical parameters. These results demonstrate that precise mid-infrared photometry of white dwarf companions to bright stars can be obtained with MIRI, opening up new possibilities for studying white dwarfs in close binaries.