Origins of the H, He I, and Ca II Line Emission in Classical T Tauri Stars

We perform local excitation calculations to obtain line opacities and emissivity ratios and compare them with observed properties of H, He I, O I, Ca II, and Na I lines to determine the density, temperature, and photon ionization rate. We find that UV photoionization is the most probable excitation mechanism for generating the He I 10830 opacities that produce all the associated absorption features. We also calculate the specific line flux at an observed velocity of v_obs = +/- 150 km/s for both radial wind and infall models. All the model results, together with observed correlations between absorption and emission features and between narrow and broad emission components, are used to deduce the origins of the strong H, He I, and Ca II broad line emission. We conclude that the first two arise primarily in a radial outflow that is highly clumpy. The bulk of the wind volume is filled by gas at a density ~10^9 cm^-3 and optically thick to He I 10830 and H alpha, but optically thin to He I 5876, Pa gamma, and the Ca II infrared triplet. The optically thick He I 5876 emission occurs mostly in regions of density greater than or equal to 10^11 cm^-3 and temperature greater than or equal to 1.5x10^4 K, while the optically thick H alpha and Pa gamma emission occur mostly in regions of density around 10^11 cm^-3 and temperature between 8750 and 1.25x10^4 K. In producing the observed line fluxes at a given v_obs, the covering factor of these emission clumps is sufficiently small not to incur significant absorption of the stellar and veiling continua in either He I or H lines. The strong Ca II broad line emission likely arises in both the magnetospheric accretion flow and the disk boundary layer, where the gases dissipate part of their rotational energies before infalling along magnetic field lines. The needed density and temperature are ~10^12 cm^-3 and less than or equal to 7500 K.Comment: Accepted to MNRAS, 88 pages, 24 figure

Redshifted Absorption at He I 10830 as a Probe of the Accretion Geometry of T Tauri Stars

We probe the geometry of magnetospheric accretion in classical T Tauri stars by modeling red absorption at He I 10830 via scattering of the stellar and veiling continua. Under the assumptions that the accretion flow is an azimuthally symmetric dipole and helium is sufficiently optically thick that all incident 1-micron radiation is scattered, we illustrate the sensitivity of He I 10830 red absorption to both the size of the magnetosphere and the filling factor of the hot accretion shock. We compare model profiles to those observed in 21 CTTS with subcontinuum redshifted absorption at He I 10830 and find that about half of the stars have red absorptions and 1-micron veilings that are consistent with dipole flows of moderate width with accretion shock filling factors matching the size of the magnetospheric footpoints. However, the remaining 50% of the profiles, with a combination of broad, deep absorption and low 1-micron veiling, require very wide flows where magnetic footpoints are distributed over 10-20% of the stellar surface but accretion shock filling factors are < 1%. We model these profiles by invoking large magnetospheres dilutely filled with accreting gas, leaving the disk over a range of radii in many narrow "streamlets" that fill only a small fraction of the entire infall region. In some cases accreting streamlets need to originate in the disk between several stellar radii and at least the corotation radius. A few stars have such deep absorption at velocities greater than half the stellar escape velocity that flows near the star with less curvature than a dipole trajectory seem to be required.Comment: 26 pages, emulateapj format, Accepted by ApJ, to appear 2008 November 1