OBSERVATIONS AND BOWSHOCK MODELS OF HERBIG-HARO OBJECTS (STAR FORMATION, BIPOLAR OUTFLOWS).

Abstract

Herbig-Haro (HH) objects are small nebulous regions of shock excited gas associated with bipolar outflows from newly formed stars. This dissertation presents an extensive set of observational data on Herbig-Haro objects, including deep CCD images, medium resolution long-slit spectra, and high resolution echelle spectra. The CCD survey indicates that HH objects cannot be identified reliably on the basis of morphology alone. The spectral line data show that HH objects exhibit enormous linewidths even though the objects are only about 1500 AU in size. The spectra sometimes have two velocity peaks, and show spatial separation of the high and low radial velocity gas. A radiative bowshock model constructed from a series of planar shock models accounts for the large linewidths, unusual line profiles, line ratios, and spatial structure seen in HH objects. A simple formula is derived that relates the shock velocity and orientation angle of a radiating bowshock to the observed maximum and minimum radial velocities seen in a line profile. The bowshock forms around a 'bullet' of material ejected from the forming star. The most likely acceleration mechanism for the bullet seems to be a breakup of a collimated stellar jet.