X-RAY AND MOLECULAR-EMISSION FROM THE NEAREST REGION OF RECENT STAR-FORMATION

The isolated, young, sunlike star TW Hya and four other young stars in its vicinity are strong x-ray sources. Their similar x-ray and optica l properties indicate that the stars make up a physical association th at is on the order of 20 million years old and that lies between about 40 and 60 parsecs (between about 130 and 200 light years) from Earth. TW Hya itself displays circumstellar CO, HCN, CN, and HCO+ emission. These molecules probably orbit the star in a solar-system-sized disk v iewed more or less face-on, whereas the star is likely viewed pole-on. Being at least three times closer to Earth than any well-studied regi on of star formation, the TW Hya Association serves as a test-bed for the study of x-ray emission from young stars and the formation of plan etary systems around sunlike stars.