Searches for far-infrared emission from dark clouds - Rho Ophiuchi, Heiles 2, L1529, and L183

Four dark clouds, Rho Ophiuchi, Heiles 2, L1529, and L183, have been surveyed at 70 and 130 microns. A new source of far-infrared radiation, with total luminosity between 5 solar luminosities and 9 solar luminosities, compatible with the presence of a low-mass star, has been detected in Rho Oph. The emission extends over a very small region coincident with a (C-18)O column density peak. The temperature of the emitting dust is determined to be about 13 K, considerably lower than the gas excitation temperature. No far-infrared emission was detected from Heiles 2, L1529, or L183, indicating that these clouds can harbor only very low-mass objects, of luminosity at most about 2 solar luminosities.