Astrophysics of Young Star Binaries

This paper describes our study of the astrophysics of individual componentsin close pre-main-sequence binaries. We observed both stars in 17 systems,located in 4 nearby star forming regions, using low-resolution (R=760),infrared spectroscopy and photometry. For 29 components we detectedphotospheric absorption lines and were able to determine spectral type,extinction, K-band excess, and luminosity. The other 5 objects displayedfeatureless or pure emission line spectra. In ~50 % of the systems, theextinction and K-band excess of the primary stars dominate those of thesecondaries. Masses and ages were determined for these 29 objects by placingthem on the H-R diagram, overlaid with theoretical pre-main-sequence tracks.Most of the binaries appear to be coeval. The ages span 5x10^5 to 1x10^7 years.The derived masses range from the substellar, 0.06 M_sun, to 2.5 M_sun, and themass ratios from M_2/M_1=0.04 to 1.0. Fourteen stars show evidence ofcircumstellar disks. The K-band excess is well correlated with the K-L colorfor stars with circumstellar material.Comment: 63 pages, 14 figures, accepted for publication in the Ap