The dusty aftermath of SN Hunt248: merger-burst remnant?
  SN Hun248 was classified as a nonterminal eruption (a SN "impostor") from a
directly identified and highly variable cool hypergiant star. The 2014 outburst
achieved peak luminosity equivalent to that of the historic eruption of
luminous blue variable (LBV) Eta Car, and exhibited a multipeaked optical light
curve that rapidly faded after ~100 days. We report ultraviolet (UV) through
optical observations of SN Hunt248 with the Hubble Space Telescope (HST) about
1 yr after the outburst, and mid-infrared observations with the Spitzer Space
Telescope before the burst and in decline. The HST data reveal a source that is
a factor of ~10 dimmer in apparent brightness than the faintest available
measurement of the precursor star. The UV-optical spectral energy distribution
(SED) requires a strong Balmer continuum, consistent with a hot B4-B5
photosphere attenuated by grey circumstellar extinction. Substantial
mid-infrared excess of the source is consistent with thermal emission from hot
dust with a mass of 10^{-6} - 10^{-5} MSun and a geometric extent that is
comparable to the expansion radius of the ejecta from the 2014 event. SED
modeling indicates that the dust consists of relatively large grains (>0.3 um),
which could be related to the grey circumstellar extinction that we infer for
the UV-optical counterpart. Revised analysis of the precursor photometry is
also consistent with grey extinction by circumstellar dust, and suggests that
the initial mass of the star could be twice as large as previously estimated
(nearly ~60 MSun). Reanalysis of the earlier outburst data shows that the peak
luminosity and outflow velocity of the eruption are consistent with a trend
exhibited by stellar merger candidates, prompting speculation that SN Hunt248
may also have stemmed from a massive stellar merger or common-envelope
ejection.
