Mass Determination of Sub-stellar Companions Around Young Stars - The Example of HR 7329

Lowrance et al. (2000) found a faint companion candidate about 4 arcsec south of the young A0-type star HR 7329. Its spectral type of M7-8 is consistent with a young brown dwarf companion. Here we report spectroscopic J band observations using the integral field spectrograph SINFONI at VLT, enabling a new estimation of effective temperature, extinction and surface gravity of the object and hence its mass. Although the data were reduced carefully, the presence of a spike within the point spread function of the object in each spectral image hampered the precise estimation of the properties of HR 7329. Nevertheless, we will show with the example of this sub-stellar companion how mass estimates independent of evolutionary models of directly imaged sub-stellar companions can be obtained, after removing most of the strong influence of the spike in the present data, and present a new mass estimation of HR, 7329 B/b based on the values gained.