The Dusty Progenitor Star of the Type II Supernova 2017eaw
  We present pre-explosion photometry of the likely progenitor star of the Type
II supernova (SN II) 2017eaw in NGC 6946. We use a Hubble Space Telescope (HST)
image of SN 2017eaw to perform relative astrometry with HST and Spitzer Space
Telescope (Spitzer) imaging, finding a single point source consistent with its
position. We detect the progenitor star in $>$40 epochs of HST and Spitzer
imaging covering 12.9 years to 43 days before discovery. While the progenitor
luminosity was roughly constant for most of this period, there was a $\sim$20%
increase in its $4.5~\mu$m luminosity over the final 3 years before explosion.
We interpret the bright mid-infrared emission as a signature of circumstellar
dust around the progenitor system. Using the pre-explosion photometry and
assuming some circumstellar dust, we find the progenitor is most likely a red
supergiant with $\log(L/L_{\odot}) = 4.9$ and $T = 3350$ K, obscured by a
$>2\times10^{-5}~M_{\odot}$ dust shell with $R = 4000~R_{\odot}$ and $T = 960$
K. Comparing to single-star evolutionary tracks, we find that the progenitor
star had an initial mass of $13~M_{\odot}$ and a mass-loss rate of
$2\times10^{-7}~M_{\odot}~\text{yr}^{-1}$, consistent with the population of SN
II progenitor stars.
