ABSTRACT In the first part of this thesis, we present a tabulation of parameters for 50 globules, most of which are bright-rimmed clouds, observed in transitions of 12CO, 13CO, CS, and HCO+ with a 1 arcminute diameter beam. H-alpha images for many bright-rimmed clouds and long-slit H-alpha spectra of two such clouds are presented. The observations are interpreted in terms of the rocket effect and D-critical ionization fronts. The elongated clouds (the so called elephant trunk globules and cometary clouds) tend to point toward their source of ionization, although a possible counter-example is presented. They often have velocity gradients along their lengths; a few examples are newly presented along with others collected from the literature. Mechanisms for forming elongated clouds are discussed. Also, means of determining the three-dimensional geometry of an H II region are discussed. The hypothesis that bright rims implode clouds and induce star formation is reviewed and found to be controversial. In the second part, we present images of the Orion Trapezium made with a unique adaptive optics system that uses either starlight or Rayleigh-backscattered laser light to correct for atmospheric wavefront distortion. The H-alpha and I band images reveal the region around the bright Trapezium stars, which has been studied extensively at radio wavelengths. Approximately one half of the stars in this region are positionally associated with knots of ionized gas, known as pigs, which are interpreted as photoevaporating envelopes of low mass stars. Disks are not observed directly but are inferred from the relatively low extinction to the stars inside the pigs. The comet-like morphology of the pigs is the result of an equilibrium between photoionization, recombination, and shadowing; interaction with the wind from theta-1C ~Ori is not required. The sizes of the ionized component of the envelopes increase with distance from the source of ionization, theta-1C Ori. The size-distance relationship suggests that the mass loss rates from the pigs are all approximately the same. The actual value of the mass loss rate is model dependent, but is ~1.2 x 10-7 M⊙ yr-1. In the third and last part, we extend the laser beacon concept to a polychromatic beacon in order to infer the wavefront tilt by measuring the differential tilt caused by dispersion. The general concept of a polychromatic beacon is to make the atmosphere produce a second beacon of a different color at altitude. Two mechanisms capable of producing the color conversion are Raman scattering in the troposphere, and resonant florescence in the mesosphere. Because the differential tilt is quite small, high precision is required and thus also high photon return rates. Our analysis indicates that existing lasers may satisfy the theoretical requirements; however, the installation and operation of such lasers may be prohibitively expensive using current technology.
Read full abstract
Feb 1, 1995
K Sugitani + 1
Open Access