PHOTOEVAPORATING STELLAR ENVELOPES OBSERVED WITH RAYLEIGH BEACON ADAPTIVE OPTICS

We present Halpha and I-band images of a approximately 1' diameter field centered on theta1C Ori made with a unique adaptive optics system that uses either starlight or Rayleigh-backscattered laser light to correct for atmospheric wavefront distortion. Approximately one-half of the stars in this region are positionally associated with knots of ionized gas, which are interpreted as photoevaporating envelopes of low-mass stars. The acronyms PIGs, EIDERs, or ProPlyDs all refer to these same 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 the primary source of ionization. The comet-like morphology of the bright nebulosities is modeled as the result of an equilibrium between photoionization, 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 envelopes all have the same density profile and mass-loss rate within a factor of 2. Faint, arcuate wisps are observed 1'' to 2'' distance from some of the cometary nebulosities; these are modeled as bow shocks caused by the wind from theta1C Ori. The positions of the stars associated with the PIGs in the observational H-R diagram indicate they are pre-main-sequence stars with masses less than approximately 3 M., with approximately 1 M. being typical. Their medium I-K color is 2.9.