Physics
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........25s&link_type=abstract
Ph.D. Thesis Colorado Univ., Boulder.
Physics
Pre-Main Sequence Stars, Radio Emission, Spectral Energy Distribution, A Stars, B Stars, Circular Polarization, Cosmic Dust, Luminosity, Stellar Envelopes, Stellar Magnetic Fields, T Tauri Stars
Scientific paper
This study focuses on the properties and physical origin of radio continuum emission from pre-main-sequence (PMS) stars. These are young stars, typically less than a few million years old, and are still in a phase of gravitational contraction that will ultimately be halted by the onset of hydrogen burning in their cores. First, I address the question of the origin of centimeter continuum emission in intermediate mass (approx. equal to 3-20 solar mass) PMS stars, the so-called 'Herbig Ae/Be stars'. A high-sensitivity radio survey of 57 such stars was undertaken using the Very Large Array and Australia Telescope, resulting in the detection of twelve stars. These observations provide a homogenous data base consisting of information on source sizes, radio luminosities, variability timescales, circular polarization, and spectral energy distributions in the wavelength range 2-20 cm. Using these data along with previously published spectroscopy, I conclude that centimeter radio emission from Herbig Ae/Be stars is predominantly thermal and in many cases wind-related. An unexpected result of the above program was the serendipitous detection of circularly polarized radio emission in the low mass (approx. equal to 1 solar mass) PMS star Hubble 4, a member of the class of 'weak-lined T Tauri stars' (WTTS). This provides some of the most convincing evidence to date for the existence of ordered magnetic fields in WTTS. In a second observing program, I have searched for evidence of cold (less than or equal to 50 K) circumstellar dust around WTTS, which might exist in the form of remnant disks. Of the sixteen WTTS that were observed in the wavelength range 450-1100 microns using the James Clerk Maxwell Telescope, only V836 Tau was detected. Its spectral energy distribution longward of 10 microns is consistent with that expected for a flat, axisymmetric circumstellar disk of mass approx. equal to 0.04 solar mass (= 42 Jupiter masses). This star may be a rare example of an object in which disk dispersal is underway, but not yet complete.
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