Abstract
A recent study of the young cluster NGC 2264 resulted in the discovery of 300 young stellar objects in the brightness range 17< B <21. These objects were placed in the L, Teff diagram. When combined with previous observations of the brighter members of the cluster these data permit us to discuss the spread in stellar formation time (At > 10x106 years) and the rate of star formation as a function of time and mass; low mass (< 1 M0) stars form first and massive stars only later in the history of the cluster. High spectral resolution, high signal-to-noise ratio spectra of T Tau provide a list of spectral features in which incipient emission is apparent. These features are predicted to be formed in the upper atmosphere of T Tau and, in most cases, appear strongly in emission in more advanced T Tau stars. These data provide strong support for the view that T Tau stars have pronounced chromospheres. The same technique was applied to the Herbig Ae/Be star, HK Ori. Although this star was originally classified as Ae, our Echelle data show a variation in apparent absorption line type from early A in the blue and late F in the red. It may not be possible to model the Ae/Be stars as objects characterized by normal photospheres and an "envelope" which produces the emission line spectrum and IR excess. A study of rotational velocities for the Herbig Ae/Be stars demonstrates that the distribution of vsini values for Ae/Be stars later than B5 differs significantly from that for "normal" Be stars. Regions containing Herbig-Haro been imaged at v, R, I and Ha using the KPNO CCD. These images provide a "roadmap" for isolating the contributions of the shock-excited and scattered light components of these objects. In the case of the region near HHl2, the Ha image suggests the presence of a highly collimated bipolar flow.
