Spectroscopic Signatures of the Tidal Disruption of Stars by Massive
  Black Holes
  During the tidal disruption of a star by a massive black hole (BH) of mass
MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the
Eddington rate. A fraction of this gas is subsequently blown away from the BH,
producing an optically bright flare of radiation. We predict the spectra and
spectral evolution of tidal disruption events, focusing on the photoionized gas
outside this outflow's photosphere. The spectrum will show absorption lines
that are strongly blueshifted relative to the host galaxy, very broad
(0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI),
lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei
are a significant source of confusion in optical surveys for tidal disruption
events: we estimate that nuclear Type Ia supernovae are two orders of magnitude
more common than tidal disruption events at z ~ 0.1 for ground-based surveys.
Nuclear Type II supernovae occur at a comparable rate but can be excluded by
pre-selecting red galaxies. Supernova contamination can be reduced to a
manageable level using high-resolution follow-up imaging with adaptive optics
or the Hubble Space Telescope. Our predictions should help optical transient
surveys capitalize on their potential for discovering tidal disruption events.
