Accretion disk parameters in HLX-1
  We estimate the outer radius of the accretion disk in HLX-1 from its optical
brightness and from the exponential timescale of the decline in the X-ray
lightcurve after an outburst. We find that the disk is an order of magnitude
smaller than the semimajor axis of the orbit. If the disk size is determined by
the circularization radius near periastron, the eccentricity of the binary
system must be >~ 0.95. We report on the discovery of H-alpha emission during
the 2012 outburst, with a single-peaked, narrow profile (consistent with a
nearly face-on view), and a central velocity displaced by ~490 km/s from that
of the host galaxy.
