Dynamical masses of pre-main sequence stars.

摘要

Determining precise masses of pre-main sequence stars is important for understanding the physical processes of star formation. The goal of my thesis is to contribute to the set of known dynamical masses of young stars. Emphasis is placed on masses below 1 M⊙ , where few reliable measurements are available and theoretical tracks of stellar evolution are particularly discrepant. I used a variety of high spatial and spectral resolution techniques to measure the orbital motion in binary and triple star systems and to map the rotation of circumstellar disks around single stars. Most of the multiple systems that I have been monitoring have expected periods longer than 20 years. Through analysis of the astrometric orbits, I find that even if the complete orbit of a binary is not well-determined, the measurements can yield a useful value for the total mass of the system. I derive preliminary values for the total mass in DF Tau ( 0.78+0.26-0.14M ⊙ ), ZZ Tau, ( 0.68+0.18-0.14M ⊙ ), Elias 12 Na-Nb ( 0.97+0.83-0.36M ⊙ ), and T Tau Sa-Sb ( 4.7+2.4-1.8M⊙ ), assuming a distance of 140 pc. I also present infrared spectroscopic observations for these systems, with likely radial velocity detections for both components in DF Tau and V853 Oph A. Because the velocities of these long period systems vary slowly, these measurements could potentially provide data for a future determination of the mass ratio. I also present the first angularly resolved measurement of the projected separation of the double-lined spectroscopic binary, Haro 1-14c, using long baseline interferometry. With a period of 591 days, the measurement of the individual component masses, as well as the distance to the system, will be attained with observations over the next few years. By mapping the rotation of circumstellar disks in CO emission, I derive preliminary stellar masses for IRAS 04385+2550 (0.42 +/- 0.14 M⊙ ) and LkHalpha 358 (0.34 +/- 0.12 M⊙ ), at an assumed distance of 140 pc. Confusion with the parent molecular cloud is the main limitation to the precision of the derived masses. Continued advances in high spatial resolution instrumentation will provide access to a larger sample of pre-main sequence stars where dynamical mass measurements are possible.