GHRS Profiles of Hot UV Lines in T Tauri Stars
Session 40 -- Young Stars and T Tauri Stars
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [40.07] GHRS Profiles of Hot UV Lines in T Tauri Stars

J.A. Valenti, G. Basri (UCB), F. Walter (SUNY), L. Hartmann (CfA), N. Calvet (CIDA)

We present the first good line profiles of transition region'' lines in typical'' T Tauri stars. In particular, we discuss the C IV and Si IV doublets at 1400\AA\ and 1550\AA\ for BP Tau, DF Tau, DR Tau, and RW Aur. These line profiles were obtained with the GHRS on HST, and they are supplemented with concurrent observations of the Mg II doublet at 2800\AA\ and various optical lines such as H$\alpha$, H$\beta$, the Ca II infrared triplet, Na D, and He I at 5876\AA.

The C IV emission profiles have broad wings indicative of high velocity gas ($\pm$200 km/s). For DR Tau and RW Aur the velocity structure seen in C IV is similar to that seen in H$\alpha$ and Mg II. Line flux ratios imply that the gas is close to optically thin in the C IV lines. In addition, blueshifted absorption may be present in 3 of the 4 stars.

The Si IV profiles are narrower than the C IV profiles, but still broader than expected from a classical transition region. There is also evidence of a stellar'' (very narrow) component in several of the profiles. This is particularly striking for RW Aur, where the weaker line has a distinct narrow core, while the stronger line is broad and has a flat top. Furthermore, the broad (500 km/s) Si IV emission in RW Aur is significantly redshifted.

In each of the stars, the Mg II profile looks very similar to the H$\alpha$ profile, and C IV and Ca II bear an intriguing relation to each other. We do not claim to fully understand these profiles yet, but it is obvious that they are primarily formed outside the stellar atmosphere.