Near-infrared and optical observations of IRAS sources in and near dense cores

This paper reports observations of 34 IRAS sources associated with dense cores in dark clouds at wavelengths 0.4-20 microns. The stars near cores tend to be visible T Tauri stars, while stars in cores tend to have circumstellar extinction 30-90 mag and luminosity about one solar, similar to that of T Tauri stars. The typical highly obscured star is probably accompanied by a luminous structure of substellar temperature, such as a circumstellar disk. In Taurus-Auriga, stars in cores probably become visible T Tauri stars less than 100,000 yr after they become detectable by IRAS; i.e., after they attain luminosity greater than about 0.1 solar. This implies that they are extremely young and may still be accreting. 54 references.