| Theoretical models of star formation and stellar evolution have improved significantly over the past few decades. Their accuracy, however, is still limited. I present three investigations using high resolution spectroscopy in the infrared to make dynamical measurements of nearby stars, with the goal of providing useful constraints for improving models.;The Hyades cluster contains a well defined stellar sample with constrained age and metallicity, in a distinct star forming region, and is an excellent laboratory for testing models of star formation. I obtained H-band spectra of 32 spectroscopic binary stars with low mass companions. In 27 of these systems I detected the companion and derived the companion-to-primary mass ratio. Together with visible light measurements from Latham and colleagues, my results indicate a mass ratio distribution for Hyades spectroscopic binaries that decreases towards smaller mass ratios. If combined with the mass ratios derived by Patience and colleagues for a sample of wide Hyades binaries, the measured distribution is consistent with a flat distribution.;Gl569 is a nearby multiple system believed to contain an M-star, Gl569A, and a brown dwarf binary, Gl569B. Colleagues and I observed the system with high spectral and angular resolution, intending to measure the dynamical masses of the brown dwarf binary. My analysis did not yield this result, but instead revealed two surprises. First, at age ∼100 Myr, the system is younger than reported by earlier investigators. Second, the spectroscopic and photometric results support earlier indications that Gl569B is actually a hierarchical brown dwarf triple rather than a binary, and suggest that the three components have roughly equal masses of ∼0.04 M⊙ .;rho Coronae Borealis was among the first stars identified with a candidate extra-solar planet companion, but later reports suggested the companion is really a low-mass star with mass 0.14 +/- 0.05 M⊙ . Colleagues and I did not detect evidence of such a companion in high resolution spectra, and placed upper bounds on the flux ratio at 1.6 mum of less than 0.0024 and 0.005 at the 90% and 99% confidence levels, respectively. Using an H-band mass-luminosity relationship, the corresponding upper limits on the companion mass are 0.11 M⊙ and 0.15 M⊙ . |
