  Planet formation is one explanation for the partial clearing of dust observed
in the disks of some T Tauri stars. Indeed studies using state-of-the-art high
angular resolution techniques have very recently begun to observe planetary
companions in these so-called transitional disks. The goal of this work is to
use spectra of the transitional disk object LkCa 15 obtained with X-Shooter on
the Very Large Telescope to investigate the possibility of using
spectro-astrometry to detect planetary companions to T Tauri stars. It is
argued that an accreting planet should contribute to the total emission of
accretion tracers such as H$\alpha$ and therefore planetary companions could be
detected with spectro-astrometry in the same way as it has been used to detect
stellar companions to young stars. A probable planetary-mass companion was
recently detected in the disk of LkCa 15. Therefore, it is an ideal target for
this pilot study. We studied several key accretion lines in the wavelength
range 300 nm to 2.2 $\mu$m with spectro-astrometry. While no
spectro-astrometric signal is measured for any emission lines the accuracy
achieved in the technique is used to place an upper limit on the contribution
of the planet to the flux of the H$\alpha$, Pa$\gamma$, and Pa$\beta$ lines.
The derived upper limits on the flux allows an upper limit of the mass
accretion rate, log($\dot{M}_{acc}$) = -8.9 to -9.3 for the mass of the
companion between 6 M$_{Jup}$ and 15 M$_{Jup}$, respectively, to be estimated
(with some assumptions).
