Astrophysics of young star binaries

This paper describes our study of the astrophysics of individual components in close pre-main-sequence binaries. We observed both stars in 17 systems, located in four nearby star-forming regions, using low-resolution (R = 760) infrared spectroscopy and photometry. For 29 components we detected photospheric absorption lines and were able to determine spectral type, extinction, K-band excess, and luminosity. The other five objects displayed featureless or pure emission line spectra. In similar to50% of the systems, the extinction and K-band excess of the primary stars dominate those of the secondaries. Masses and ages were determined for these 29 objects by placing them on the H-R diagram, overlaid with theoretical pre-main-sequence tracks. Most of the binaries appear to be coeval. The ages span 5 x 10(5) to 1 x 10(7) yr. The derived masses range from the substellar, 0.06 M., to 2.5 M., and the mass ratios from M-2/M-1 = 0.04 to 1.0. Fourteen stars show evidence of circumstellar disks. The K-band excess is well correlated with the K-L color for stars with circumstellar material.