Weird RV variations of Theta Cygni A

arXiv: Extrasolar planets and brown dwarfs around A-F type stars - VII. Theta Cygni radial velocity variations: planets or stellar phenomenon?

Some very odd radial velocity variations of the star Theta Cygni A. There seems to be some link between the radial velocity variations and the shape of the spectral lines, which indicates stellar activity may be to blame. Alternatively there may be a planetary system, but would perhaps require some exotic planetary configuration.

Reading over the paper, it discusses Bisector Velocities, what are these?

I found something from a paper that described it as "The locus of midpoints of horizontal segments spamming the line profile from the core to the continuum".
What does this mean exactly? The distance between absorption lines?

And would "bisector velocity variations" imply that the distance between absorption lines are variable?

Part of these RV variations appear to come from stellar pulsations.

A new interferometric study of four exoplanet host stars : θ Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
http://arxiv.org/abs/1208.3895

Quote :

The interferometric measurements of {\theta} Cyg show a significant diameter variability that remains unexplained up to now. We propose that the presence of these discrepancies in the interferometric data is caused by either an intrinsic variation of the star or an unknown close companion orbiting around it.