Observational Signature of Tidal Disruption of a Star by a Massive Black Hole

We have modeled the time-variable profiles of the Balmer alpha emission from the nonaxisymmetric disk and debris tail created in the tidal disruption of a solar-type star by a million solar mass black hole. Two tidal disruption events were simulated using a three dimensional relativistic smoothed particle hydrodynamic code to describe the early evolution of the debris during the first 50-90 days. We have calculated the physical conditions and radiative processes in the debris using the photoionization code CLOUDY. We model the emission-line profiles in the period immediately after the accretion rate onto the black hole becomes significant. We find that the line profiles at these very early stages of the evolution of the postdisruption debris do not resemble the double-peaked profiles expected from a rotating disk, since the debris has not yet settled into such a stable structure. As a result of the uneven distribution of the debris and the existence of a ``tidal tail'' (the stream of returning debris), the line profiles depend sensitively on the orientation of the tail relative to the line of sight. Moreover, the predicted line profiles vary on fairly short time scales (of order hours to days). Given the accretion rate onto the black hole we also model the Balmer alpha light curve from the debris.