PHOTOEVAPORATING STELLAR ENVELOPES OBSERVED WITH RAYLEIGH BEACON ADAPTIVE OPTICS

We present Halpha and I-band images of a approximately 1' diameter fie ld centered on theta1C Ori made with a unique adaptive optics system t hat uses either starlight or Rayleigh-backscattered laser light to cor rect for atmospheric wavefront distortion. Approximately one-half of t he stars in this region are positionally associated with knots of ioni zed gas, which are interpreted as photoevaporating envelopes of low-ma ss stars. The acronyms PIGs, EIDERs, or ProPlyDs all refer to these sa me knots. The Halpha fluxes of the PIGs are proportional to their 2 cm radio continuum flux densities, and for nearly all the ionized knots, the 2 cm brightness temperatures are consistent with theta1C Ori as t he primary source of ionization. The comet-like morphology of the brig ht nebulosities is modeled as the result of an equilibrium between pho toionization, recombination, and shadowing. The radii of the ionized ' 'head'' of the cometary PIGs grow with distance from theta1C Ori; the radii range from less-than-or-similar-to0''.05 to approximately 0''.25 . We interpret the size-distance relationship as evidence that the env elopes all have the same density profile and mass-loss rate within a f actor of 2. Faint, arcuate wisps are observed 1'' to 2'' distance from some of the cometary nebulosities; these are modeled as bow shocks ca used by the wind from theta1C Ori. The positions of the stars associat ed with the PIGs in the observational H-R diagram indicate they are pr e-main-sequence stars with masses less than approximately 3 M., with a pproximately 1 M. being typical. Their medium I-K color is 2.9.