AAS 207th Meeting, 8-12 January 2006
Session 74 Planets in Binary Star Systems, Young Stars and Jets
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[74.08] Variability of FUV Emission Line in Classical T Tauri Stars as a Diagnostic for Disc Accretion

B. Ramkumar, C. M. Johns-Krull (Rice University)

We present our results of FUV emission line variability studies done on four classical T Tauri stars. We have used the IUE Final Archive spectra of pre-main sequence stars to analyze the sample of four stars BP Tau, DR Tau, RU Lup and RY Tau where each of these low-resolution (R ~ Å) spectra was observed in the IUE short-wavelength band pass (1150--1980Å). Given a broad time line of multiple observations being available from the IUE Final archive, an intrinsic variability study has been possible with this sample. Our results indicate that the transition region lines \ion{Si}{4} and \ion{C}{4}, produced near the accretion shocks at ~105 K, have a strong correlation between them in all four stars except DR Tau. We also observe a strong correlation between \ion{C}{4} & \ion{He}{2} on our entire sample with a correlation coefficient of 0.549 (false alarm probability = 7.9 x 10-2) or higher. In addition, \ion{He}{2} correlates with the molecular hydrogen (1503Å) line in all but RU Lup. If the \ion{He}{2} lines are produced because of X-ray ionization then the observed molecular hydrogen emission is indeed controlled by X-ray ionization and therefore \ion{He}{2} could serve as an X-ray proxy for future studies. Also, our correlation results strengthen the fact that \ion{C}{4} is a good predictor of \ion{Si}{4} and have a common origin i.e. in accretion shocks in the star formation process.

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