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 ~50% 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 × 10 5 to 1 × 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.