Multi-wavelength observations of the EUV variable metal-rich white dwarf GD 394. (arXiv:1811.10614v1 [astro-ph.SR])

Multi-wavelength observations of the EUV variable metal-rich white dwarf GD 394. (arXiv:1811.10614v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_D/0/1/0/all/0/1">David J. Wilson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gaensicke_B/0/1/0/all/0/1">Boris T. Gaensicke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Koester_D/0/1/0/all/0/1">Detlev Koester</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toloza_O/0/1/0/all/0/1">Odette Toloza</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holberg_J/0/1/0/all/0/1">Jay B. Holberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Preval_S/0/1/0/all/0/1">Simon P. Preval</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barstow_M/0/1/0/all/0/1">Martin A. Barstow</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Belardi_C/0/1/0/all/0/1">Claudia Belardi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burleigh_M/0/1/0/all/0/1">Matthew R. Burleigh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Casewell_S/0/1/0/all/0/1">Sarah L. Casewell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cauley_P/0/1/0/all/0/1">P. Wilson Cauley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chote_P/0/1/0/all/0/1">Paul Chote</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Farihi_J/0/1/0/all/0/1">Jay Farihi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hollands_M/0/1/0/all/0/1">Mark A. Hollands</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Long_K/0/1/0/all/0/1">Knox S. Long</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Redfield_S/0/1/0/all/0/1">Seth Redfield</a>

We present new Hubble Space Telescope (HST) ultraviolet and ground-based
optical observations of the hot, metal-rich white dwarf GD 394.
Extreme-ultraviolet (EUV) observations in 1992-1996 revealed a 1.15d
periodicity with a 25 percent amplitude, hypothesised to be due to metals in a
surface accretion spot. We obtained phase-resolved HST/Space Telescope Imaging
Spectrograph (STIS) high-resolution far-ultraviolet (FUV) spectra of GD 394
that sample the entire period, along with a large body of supplementary data.
We find no evidence for an accretion spot, with the flux, accretion rate and
radial velocity of GD 394 constant over the observed timescales at ultraviolet
and optical wavelengths. We speculate that the spot may have no longer been
present when our observations were obtained, or that the EUV variability is
being caused by an otherwise undetected evaporating planet. The atmospheric
parameters obtained from separate fits to optical and ultraviolet spectra are
inconsistent, as is found for multiple hot white dwarfs. We also detect
non-photospheric, high-excitation absorption lines of multiple volatile
elements, which could be evidence for a hot plasma cocoon surrounding the white
dwarf.

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