Probing Intermediate Mass Black Holes With Optical Emission Lines from
  Tidally Disrupted White Dwarfs
  We calculate the emission line spectrum produced by the debris released when
a white dwarf (WD) is tidally disrupted by an intermediate-mass black hole
(IMBH; $M\sim 10^{2}-10^{5}\msun$) and we explore the possibility of using the
emission lines to identify such events and constrain the properties of the
IMBH. To this end, we adopt and adapt the techniques developed by Strubbe &
Quataert to study the optical emission lines produced when a main sequence (MS)
star is tidally disrupted by a supermassive black hole. WDs are tidally
disrupted outside of the event horizon of a $< 10^{5}\msun$ black hole, which
makes these tidal disruption events good signposts of IMBHs. We focus on the
optical and UV emission lines produced when the accretion flare photoionizes
the stream of debris that remains unbound during the disruption. We find that
the spectrum is dominated by lines due to ions of C and O, the strongest of
which are \ion{C}{4} $\lambda$1549 at early times and [\ion{O}{3}]
$\lambda$5007 at later times. Furthermore, we model the profile of the emission
lines in the [\ion{O}{3}] $\lambda\lambda$4959, 5007 doublet and find that it
is highly asymmetric with velocity widths of up to $\sim 2500
\rm{\;km\;s^{-1}}$, depending on the properties of the WD-IMBH system and the
orientation of the observer. Finally, we compare the models with observations
of X-ray flares and optical emission lines in the cores of globular clusters
and propose how future observations can test if these features are due to a WD
that has been tidally disrupted by an IMBH.
