THE EVOLUTIONARY STATUS OF THE STELLAR POPULATION IN THE RHO-OPHIUCHI CLOUD CORE

This contribution reports the results of an infrared imaging survey aimed at characterizing the stellar populations associated with the three densest star-forming cores in the Ophiuchus molecular cloud complex. The survey has sufficient sensitivity at J, H, and K (at 5 sigma limits of 16.5, 15.4, and 14.2) to provide a complete census of embedded young stellar objects (YSOs) with masses greater than the hydrogen-burning 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. Our data suggest (1) a large fraction (> 70%) of the sources located within the cores are still surrounded by circumstellar disks and/or envelopes; and (2) the shape of the initial mass function for masses, M < 1 M., appears to be consistent with that derived from the solar neighborhood. We also report the results of a deeper imaging survey of centimeter continuum sources (14 sources) in these star-forming cores and in the larger Ophiuchus complex (eight sources). A large fraction (11/14) of the radio sources associated with the cores appear to have infrared excesses diagnostic of circumstellar accretion disks and/or infalling circumstellar envelopes. In these cases, the centimeter continuum radiation most likely diagnoses the ionized component of energetic winds or jets which characterize YSOs during the disk accretion phase. By contrast, of the eight radio sources located outside dense cores, only two show infrared excesses. For the sources which lack infrared excesses, the centimeter continuum emission is probably produced by gyrosynchrotron radiation arising in the stellar magnetospheres of weak emission T Tauri stars. There is some evidence that the frequency of binary companions among the sample of centimeter continuum sources in the molecular 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.