Coordinated observations for approved Chandra proposal 28200192 2137632896 Assigned ID: 7868 ----- Attempting Submission 1 (Tue Sep 08 20:33:22 GMT 2026) ----- No ephemeris is avalable for the variability period that these observations are phased to, so I picked an arbitary value (today's JD). Let me know if there is a better solution. Second submission: realised that for the 0.2x0.2as slit no ACQ PEAK is needed. 597063071 ----- Attempting Submission 1 (Thu Oct 01 20:52:08 GMT 2026) ----- HST Phase II Proposal 18484 successfully submitted. Receipt: # 18484-1 ----- Attempting Submission 2 (Mon Oct 05 20:37:32 GMT 2026) ----- Planet or EUV variation? Chandra and Hubble observations of a variable white dwarf We request Chandra and Hubble observations to characterise the X-ray and ultraviolet variability of the hot white dwarf HS 0209+0832. The white dwarf is accreting material from a remnant planetary system with chemical abundances that match no known object. TESS observations reveal a periodic 4.4 day signal, an extremely rare variability mode for hot white dwarfs. We suggest two hypotheses, both of which would be extraordinary discoveries: First, this may be only the second known example of an EUV variable white dwarf; Second, the signals could reveal an evaporating giant planet. We will obtain a soft X-ray light curve and spectrum of the system to search for EUV variation to test these hypotheses, along with phase-resolved ultraviolet spectra to search for metal line variability. The aim is to aquire phase resolved E140M spectra of the white dwarf HS0209+0832 (Feige 20). Eight exposures should be taken over the 4.399 day period identified with TESS. We estimate (etc run 2370262) that a single E140M observation should return S/N of about 10 to 20 over the spectrum. Data should be obtained in time-tag mode. The ephemeris of the periodic behaviour is unknown so the submission date was used. David Wilson is an expert on ultraviolet and X-ray observations of stars and white dwarfs. He led Chandra program 20200610 observing a similar star to this target, and has led multiple programs with Hubble and other observatories and published multiple multi-wavelength stellar Observations. Jamie Williams is a PhD student who has led the analysis of the archival data of the target. Boris Gaensicke is an expert in white dwarfs and their planetary systems and has led many HST programs obtaining ultraviolet spectroscopy of white dwarfs. Snehalata Sahu is an experienced user of the white dwarf model atmosphere code we will use in this analysis and an expert in analyzing ultraviolet spectroscopy of white dwarfs Andrew Swan is an expert in space telescope observations of variable white dwarfs Stellar Physics and Stellar Types Exoplanets and Exoplanet Formation 6 false false false false false false false true SECONDARY CHANDRA 28200192 false SUPPORTED STAR DA DZ NO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 J2000 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 STIS/FUV-MAMA Spectroscopic No No E140M 1425 /home/david/work/hot_white_dwarfs/chandra_prop/OP-cache/hs0209_hst_chandra_p2-v01.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. 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