Statistics – Computation
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........11f&link_type=abstract
Ph.D. thesis, Queen Mary & Westfield College, University of London, United Kingdom (Available on-line at URL: www.astro.up.pt/us
Statistics
Computation
5
Scientific paper
The magnetospheric accretion model for T Tauri stars provides a possible answer for the long standing problem in low mass star formation of how angular momentum is shed in order to keep the rotational velocities as low as observed despite accreting matter from a quasi-Keplerian accretion disk. Given its importance for a better understanding of T Tauri stars the model should be thoroughly tested observationally. The work presented in this Thesis tests some aspects of the magnetospheric accretion model by using high spectral resolution observations of near infrared hydrogen lines. The presence of winds in T Tauri stars and their possible influence on the line profiles of near infrared hydrogen lines is also investigated. These lines are optically thinner than the more commonly studied Balmer lines and may give better indications of accretion. A sample of 50 T Tauri stars, mostly from the Taurus-Auriga complex, was chosen. Paβ line profiles were obtained for 49 of these stars and Brγ profiles for 37 of the stars in the sample. Emission at Paβ was observed for 41 stars and emission at Brγ was found for 30 stars. The most conspicuous features in the line profiles is the almost complete absence of blueshifted absorption components and the high frequency of inverse P Cygni profiles (IPC). At Paβ, 34% of the profiles are IPC while at Brγ 20% are IPC. The redshifted absorption features indicate infall at velocities of about 200 kms-1, compatible with free fall from a few radii out as expected in a magnetospheric accretion picture. In general, line profiles are broad centrally peaked with slightly blueshifted line peaks. These observations are consistent with the Paβ and Brγ lines forming predominantly in infalling material. Radiative transfer calculations of the Paβ and Brγ line profiles in a very simplified spherically symmetric situation are discussed and the results compared with the observations. The identification of photospheric lines in the observed spectra allows the computation of the veiling at J for 75% of the observed stars and at K for 70% of the stars. Average values are < rJ > = 0.56 and < rK > = 1.31. In the remaining 25% of the stars at J and 30% of stars at K no photospheric lines were identified, i.e. they were observed to be 'continuum' stars in the observed wavelengths regions. The implications of these results are discussed. Thesis available through http://astro.up.pt/users/dfmf/Thesis/thesis.html
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