the star. If the GQ Lup companion is a planet, however, it probably has not formed at its current wide separation, but further inward, and was then moved to a larger separation by an encounter with another, more massive inner protoplanet (Debes & Sigurdsson 2006; Boss 2006). An encounter with another star could have resulted in a dynamical perturbation of the forming GQ Lup (system) resulting in a binary with large mass ratio, i.e., a companion forming as a brown dwarf (embryo) by fragmentation, and/or would also have increased the orbital inclination and/or eccentricity of the (forming) companion significantly.

Deviations of the separation and PA values from being constant could also be due to other reasons:\
(i) If either GQ Lup A or b were an unresolved multiple, one would expect a periodic variation in the separation. If, e.g., GQ Lup A was an unresolved close binary made up of two stars with different brightness, its photocenter would show periodic variations according to the Keplerian motion of the two stars around its common center-of-mass. Then, the apparent separation between this photocenter and GQ Lup b would also vary with the same period. Quantitatively, this effect depends on the separation between 