Though your thread was posted on April, 01,
I checked the BBC news website today [April, 04] which confirms
the discovery and the historic image. The planetary object is about one to two jovian masses.

I was somewhat in error assuming it to have an orbital radius of about 80AU...It actually has an orbital radius of about 100AU.
The planet should then be orbiting its primary at a velocity of about
2700 meters/second, assuming the primary is nearly one solar mass.

Any large moons in orbit around the GQ Lupi gas-giant will obviously
fluctuate the gas-giant's orbital velocity...The effect would be measurable.

I hope to e-mail the German astronomers who recorded the image and petition them to try and record any possible Doppler-shift variations
in the gas-giant's orbital velocity caused by potential moons...of course R.L. might beat me to it by getting hold of the Subaru telescope astronomers on top of that Hawaiian peak.

cheers.

Jacob