A VLA Survey of Radio-Emitting Young Stars in the Rho Ophiuchi Dark Cloud

An extensive radio-continuum survey of the ρ Ophiuchi molecular cloud was conducted with the Very Large Array to look for counterparts of several dozen pre-main-sequence stars found in X-ray, optical, and infrared surveys. Four square degrees were mapped at 1.4 GHz, with a sensitivity of 1.5 - 3 mJy; in addition, the central part of the cloud was mapped at 5 GHz with a sensitivity of 1 mJy. The authors detect 93 radio sources, significantly more than in previous observations. Thirteen radio sources are found to be probably stellar. They include five variable X-ray stars, seven near- or far-infrared sources, five stars visible on the Palomar Sky Survey, and ten sources with flat or ascending radio spectra. No optical T Tauri star is detected. The remaining sources are extragalactic, in agreement with radio-source counts. The stellar radio sources in the cloud constitute a population distinct from T Tauri stars, and they tend to have unusual infrared energy distributions. The authors suggest that they correspond to somewhat evolved young stars born in the cloud.