Mass ratios of the components in T Tauri binary systems and implications for multiple star formation

Using near-infrared speckle interferometry we have obtained resolved JHK-ph otometry for the components of 58 young binary systems. From these measurem ents, combined with other data taken from literature, we derive masses and particularly mass ratios of the components. We use the J-magnitude as an in dicator for the stellar luminosity and assign the optical spectral type of the system to the primary. On the assumption that the components within a b inary are coeval we can then also place the secondaries into the HRD and de rive masses and mass ratios for both components by comparison with differen t sets of current theoretical pre-main sequence evolutionary tracks. The re sulting distribution of mass ratios is comparatively at for M-2=M-1 greater than or equal to 0.2, but depends on assumed evolutionary tracks. The mass ratio is neither correlated with the primary's mass or the components' sep aration. These findings are in line with the assumption that for most multi ple systems in T associations the components' masses are principally determ ined by fragmentation during formation and not by the following accretion p rocesses. Only very few unusually red objects were newly found among the de tected companions. This finding shows that the observed overabundance of bi naries in the Taurus-Auriga association compared to nearby main sequence st ars should be real and not the outcome of observational biases related to i nfrared observing.