A rich cluster of radio stars in the Rho Ophiuchi cloud cores

Deep 6 cm VLA observations of the central regions of the Rho Ophiuchi star-forming cloud reveal a concentration of faint stellar radio sources. A sensitivity better than 0.09 mJy is achieved, corresponding to 2.3 x 10 to the 15th ergs/s/Hz, a factor of 10-20 more sensitive than previous observations of the cloud. In the northern molecular core, Rho Oph A, 22 sources are seen in a 13 arcmin x 13 arcmin map centered on the embedded B star S1. Below 0.4 mJy, the source density is several times that expected from extragalactic sources. At least seven radio sources are associated with young stars: six are coincident with infrared sources, and one with a strong millimeter source at the base of a bipolar flow. In the southern molecular core, Rho Oph E/F, 13 faint radio sources are detected; at least six are coincident with infrared stars. The low-mass stellar radio sources range in radio intensity from 0.2 to 3 mJy. These studies show that continuum radio emission far above levels present in main sequences stars is observed in one-third to one-half of low-mass pre-main-sequence stars. However, it is not clear whether the radio emission is generally thermal or nonthermal in origin.