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Arxiv: Serendipitous observation of a white dwarf companion to a JWST/MIRI coronagraphic calibrator Published: 10/15/2024 4:00:03 PM Updated: 10/15/2024 4:00:03 PM

Paper abstract: We present the unplanned detection of a white dwarf companion to the star HD218261 in mid-infrared (10-16 \mum) observations with JWST/MIRI. This starwas observed as a calibrator for coronagraphic observations of the exoplanethost HR 8799. HD 218261 B has only previously been detected by Gaia, and onlyin 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 visibleand mid-infrared photometry are consistent with a white dwarf ofT_\text{eff}~10000 K, M~0.8 M_\odot, though observation of itsoptical spectrum is required to precisely constrain its physical parameters.These results demonstrate that precise mid-infrared photometry of white dwarfcompanions to bright stars can be obtained with MIRI, opening up newpossibilities for studying white dwarfs in close binaries.