Emission-line diagnostics of T Tauri magnetospheric accretion. I. Line profile observations

We present high-resolution spectra of classical T Tauri stars in Taurus in the range 5800-9000 Angstrom to critically examine the current theories of magnetospheric accretion. In this paper, we focus on the emission lines of hydrogen (the higher Paschen series and H alpha), He I lambda 5876, O I lambda 7773 and lambda 8446, the Na D lines, and the Ca II infrared triplet. We argue that the magnetospheric infall zone is the likely source of emission for the hydrogen, oxygen, and sodium lines for most of the stars in our sample. As has been previously shown, the calcium and helium lines have a narrow and a broad component; focusing on the broad components, we find that they are likely formed in the magnetosphere for at least several of the stars in the sample. Preliminary calculations indicate that the magnetospheric models developed to explain the Balmer lines predict significant Ca II, Paschen, and O I emission, roughly comparable to what is observed. However, in some of the stars, especially at high veilings, the case for line formation in the accretion flow is not clear. Finally, our results suggest that the Ca II IR triplet lines are good indicators of the accretion rate for all but the most weakly accreting T Tauri stars.