The production of strong broad He II emission after the tidal disruption
  of a main-sequence star by a supermassive black hole
  The tidal disruption event (TDE) PS1-10jh lacked strong Balmer lines but
showed strong, broad, He II emission both before maximum light and for at least
8 months thereafter. Gezari et al. interpreted this as evidence for the
disruption of a rare hydrogen-deficient star. However, Guillochon et al. have
argued instead that the disrupted star was a normal main-sequence star and that
the strength of the He II emission compared with the Balmer lines is a result
the emission being similar to the broad-line region (BLR) of an AGN, but
lacking the outer, lower-ionization BLR gas. We show that the profile of He II
4686 in PS1-10jh is similar to the blueshifted profiles of high-ionization
lines in AGNs. We find an He II 4686/Halpha ratio for PS1-10jh of ~ 3.7. We
show that both the high-velocity gas of the inner BLR of normal AGNs and the
spectra of type II-P supernovae right after shock break out also produce very
high He II 4686/Halpha ratios. A high He II 4686/Halpha ratio can thus be
produced with a solar H/He abundance ratio. We demonstrate from photoionization
modelling that the estimated He II 4686/Halpha ratio can be produced with a BLR
truncated before the He++ Stroemgren length if the density is ~ 10^{11}
cm^{-3}. The similarity of the He II 4686 emission in PS1-10jh to the emission
from the inner BLRs of AGNs supports the idea that the emission after a TDE
event is similar to that of normal AGNs.
