Doctor of Philosophy
Department of Physics
Suters, Mark Gerard, Near and far infrared observations of protostars and dark clouds, Doctor of Philosophy thesis, Department of Physics, University of Wollongong, 1992. http://ro.uow.edu.au/theses/1629
Far infrared point source and extended emission data from the Infrared Astronomical Satellite (IRAS) survey are used to investigate the properties of star formation in the regions of high galactic latitude dark cloud complexes. The properties of individual sources are examined using near infrared spectroscopy and broad band spectral energy distributions.
The IRAS signature of star formation is derived by comparing the far infrared colours of a sample of protostars with those of other common far infrared objects. The quality of the IRAS data is ignored for the purposes of this investigation. The criteria developed for identifying protostars from the IRAS Point Source Catalog discriminates against most non-protostellar objects, with the exception of galaxies and Hfl regions. Objects identified as protostellar according to other criteria are also likely to be identified by the criteria developed.
Extended emission data in the far infrared is used to estimate the column density and temperature of several dark cloud complexes, and the optical extinction in the same regions is estimated with the Guide Star Catalog. Temperature and column density share an inverse relationship: cloud cores are characterised by column densities above 1024 hydrogen atoms m-2 and temperatures around 20 K, while the inter cloud medium has column densities below 1023 atoms m-2 and temperatures above 50 K. The column density, as measured by IRAS, and the optical extinction appear to be related up to values of around 1025 atoms m-2 and 5 magnitudes respectively, but the IRAS detectors appear insensitive to material at higher densities than these.
Near infrared spectra of a variety of objects chosen for their youth, including IRAS sources which satisfy the protostar criteria, are investigated. These spectra are categorised into three distinct groups of increasing youth: 1. T Tauri-like spectra, with flat H and K band continua, lacking both Br-γ emission and CO absorption; 2. FU Ori-like spectra, with CO absorption, 1.9 μm water absorption, and possibly Br-γ emission, and 3. embedded protostar spectra, with red continuum, and perhaps Br-γ emission, but lacking CO absorption.
The spectral energy distributions (SEDs) of the sources are also investigated, using data at wavelengths from 0.3 μm to 100 μm. All of the objects studied in the near infrared have SEDs characteristic of either T Tauri stars or of embedded protostars. There seems little correlation between the evolutionary status assigned to an object on the basis of its SED and that assigned from near infrared spectral features, perhaps because the shape of the SED is independent of the evolution of the central object, and depends on geometric considerations such as the orientation of the circumstellar disk in relation to the line of sight from the Earth.