THE EVOLUTIONARY STATUS OF THE STELLAR POPULATION IN THE RHO-OPHIUCHICLOUD CORE

This contribution reports the results of an infrared imaging survey ai med at characterizing the stellar populations associated with the thre e densest star-forming cores in the Ophiuchus molecular cloud complex. The survey has sufficient sensitivity at J, H, and K (at 5 sigma limi ts of 16.5, 15.4, and 14.2) to provide a complete census of embedded y oung stellar objects (YSOs) with masses greater than the hydrogen-burn ing limit, provided that their ages are less than 3 Myr and that they are obscured by no more than similar to 18 mag of visual extinction. O ur data suggest (1) a large fraction (> 70%) of the sources located wi thin the cores are still surrounded by circumstellar disks and/or enve lopes; and (2) the shape of the initial mass function for masses, M < 1 M., appears to be consistent with that derived from the solar neighb orhood. We also report the results of a deeper imaging survey of centi meter continuum sources (14 sources) in these star-forming cores and i n the larger Ophiuchus complex (eight sources). A large fraction (11/1 4) of the radio sources associated with the cores appear to have infra red excesses diagnostic of circumstellar accretion disks and/or infall ing circumstellar envelopes. In these cases, the centimeter continuum radiation most likely diagnoses the ionized component of energetic win ds or jets which characterize YSOs during the disk accretion phase. By contrast, of the eight radio sources located outside dense cores, onl y two show infrared excesses. For the sources which lack infrared exce sses, the centimeter continuum emission is probably produced by gyrosy nchrotron radiation arising in the stellar magnetospheres of weak emis sion T Tauri stars. There is some evidence that the frequency of binar y companions among the sample of centimeter continuum sources in the m olecular cores may be higher (by as much as a factor of 3-4) than that among the older, distributed population of young stars in the larger Ophiuchus cloud complex.