Other
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt........61d&link_type=abstract
PhD Thesis, Centro de Astrofísica and Faculdade de Ciências, Universidade do Porto, 1996.
Other
Scientific paper
T Tauri stars constitute a peculiar class of irregular variable young (< 107 yr) and low mass stars (< 3 Modot), still evolving to the main sequence. Their spectral characteristics and other related phenomena, such as winds or accretion, are important for the study of stellar evolution and to improve our understanding of the Sun's earlier phases. A sample of ten classic T Tauri stars has been extensively observed (one week) in the optical, at high resolution (λ Δ λ > 2× 104) and high signal-to-noise (> 40). Profiles of the Hα, He I and Na I D lines have been ob tained with the objective of studying the conditions prevailing both in the cooler and the hotter regions of the stellar atmosphere as well as the stellar activity. The high quality spectra and the quasi-simultaneous exposures in the two wavelength b ands allow the discussion of possible correlations (in equivalent width) between different lines and their variability in what concern the shape of the profiles. The high non-photospheric continuum of T Tauri stars, quite variable in some stars, need s to be accounted for. This has been done only for the stars displaying weak veiling, shown by the analysis of behaviour of the photospheric lines intensity during the week. In this work we find, for some of stars in the sample, strong correlations between the lines of He I and Na D. Such correlations can be used to further constrain the physical parameters in the emitting regions and the dimension of such regions. In a complementary analysis, we measured the rotational velocity, v sin i, for some of the stars, using Fourier analysis technique of the photospheric lines. The presence of a strong optical and ultraviolet continua may result in the shallowing and widening of the photospheric lines. Numerous simulations were carried out in order to estimate the limiting (smallest) rotational velocity that can be measured as a function of resolution and signal-to-noise ratio of the observations. As a consequence we were able to identify photospheric lines only in five out of the ten stars in th e sample. For the star LkHα 264, this was the first determination of v sin i.
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