Discovery of close companions to the nearby young stars HD 199143 and HD 358623

Abstract

Young stellar systems in the solar neighborhood provide valuable laboratories for detailed studies of star and planet formation. The bright F8V star HD 199143 and the Li-rich late-type emission line star HD 358623 are among the nearest young stars identified to date, and may be members of a young association in Capricornus. We present high-resolution near-infrared images of these two sources, obtained using the adaptive optics system on the 3.6-meter telescope at the European Southern Observatory in La Silla, Chile. Our observations reveal that both are in fact close binary systems. The newly discovered companion at a separation of $\sim$1'' may account for the unusual characteristics of HD 199143 --rapid rotation, emission lines, ultraviolet variability, and excess infrared emission-- recently discussed by van den Ancker and co-workers. HD 199143 may be a rare example of a close binary with only a circum{\it secondary} disk. With the detection of a $\sim$2'' companion, HD 358623 is now possibly one of the closest known T Tauri binaries. Both binary systems are prime targets for follow-up spectroscopic and astrometric observations.