Other
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........3c&link_type=abstract
Phd Thesis
Other
3
Pre-Main-Sequence Stars, Ultraviolet, X-Ray
Scientific paper
Newly calibrated IUE spectra and ROSAT data for a sample of T Tauri stars have been investigated. In the ultraviolet band a complete spectral atlases for our sample of stars is presented. We have identified the main spectral lines and the continuous emission. While for some stars the continuum is well explained by the sum of the stellar black body emission plus a hydrogenic component with a temperature in the range 1.4 to 5 × 104 K, there are however others which require a third component, i.e., black body emission at temperatures in the range 5900--9700 K covering a few percent of the stellar surface. In addition, we have utilised the observed line fluxes together with Emission Measure techniques to derive the temperature structure in the atmosphere of the stars. The behaviour of the stars is analysed showing noticeable differences. For the star LkHα 264 we have also established the connection between the UV analysis into optical ranges in terms of the continuum. The combined emission in the UV also fits the observed optical continuum well and we conclude that this star is an analogue of the Sun but displaying a much higher level of activity. The stars in the sample have also been studied in X-ray allowing for some newly detections. Also fundamental parameters have been derived. Within the sample we analysed in more detail those stars for which there are more than one set of observations and looked for X-ray variability. Three stars in our sample, V410 Tau, TW Hya and CS Cha, allow a detailed spectral analysis and we have also searched for variability, both short- and long-term within the limits of the data. The results of the spectral analysis for these stars can be successfully described by a model of emission from two-temperature, hot, optically thin plasma in collisional equilibrium. We have established the connection from the UV to the X-ray band extending the spectroscopic analysis from regions with plasma at temperatures below 104K to regions at ≍107K. From comparison with the Sun we concluded that the behaviour of the stars can be tentatively classified in three types.
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