Other
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........13w&link_type=abstract
PhD Thesis, Max-Planck-Institut für Astronomie, Heidelberg, Germany, 1999.
Other
Scientific paper
Using near-infrared speckle-interferometry we have obtained resolved JHK-photometry for the components of 58 young binary systems. By placing the components into a color-color diagram we identify some unusual red objects that are candidates for infrared companions or substellar objects. We place a subsample that consists of the components of 14 weak-lined TTS systems (where no significant circumstellar excess emission is expected) into a color-magnitude diagram and show that in all these systems the components are coeval within the uncertainties. Particularly this is the case for the triple system HBC 358. Using the J-magnitude as an indicator for the stellar luminosity, the optical spectral type of the system and the previously justified assumption that all components are coeval we can place the components into the HRD and derive their masses by comparison with theoretical pre-main sequence evolutionary tracks. The results are the following: The distribution of mass ratios is neither clustered towards M2 / M1 = 1 nor is it a function of the primary's mass or the components' projected separation. Comparison of these results with predictions of theoretical multiple star formation models suggests that most of the systems have formed by fragmentation during protostellar collapse, and that the components' masses are principally determined by fragmentation and not by the following accretion processes. Furthermore the infrared source HV Tau C is discussed using new observational data. We show that this source is no Herbig-Haro object, but an active T Tauri star. So the HV Tau-system does not impose a problem on current models of T Tauri stars and their environment. From relative positions of the components at different epochs we derive their relative velocities and show that in most close systems orbital motion can be proved. The analysis of this orbital motion leads to an empirical mass estimate for T Tauri-stars which is larger than the masses one would expect from the HRD. We have also used speckle interferometry to obtain the relative astrometry for the components of nearby low-mass binary systems at different epochs. This has led to an improved orbit determination for the visual pair in the nearby M-dwarf triple Gliese 866. We show that all components of this system have masses only close above the hydrogen burning limit. For eight other systems the combination of our relative astrometry with radial velocity data will lead to precise mass determinations for the components of nearby late type binaries in the near future.
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