Iron and helium emission lines in classical T Tauri stars
Results are presented for the He emission in 31 CTTS from the Taurus-Auriga molecular cloud spanning two orders of magnitude in the mass accretion rate, and for the Fe emission in DR Tau, based on a series of high resolution echelle spectra.
The He lines admit a description in terms of a narrow component ( NC) and a broad component (BC). The NC has FWHM between 32–55 km/s and centroid velocities near zero km/s or moderately redshifted, consistent with an origin in the postshock region of the magnetospheric accretion model. The BC, with FWHM between 128 and 287 km/s and centroid velocities between –93 and +35 km/s, includes a wind and an accretion component; we argue the BC is predominantly formed in the wind. Estimates of the wind and accretion component equivalent widths are oppositely related to the NC, so the NC equivalent width increases with the accretion component but decreases as the wind component increases. The NC is undetectable where profiles appear dominated by the wind, requiring a source of veiling other than the accretion shock to account for the observed continuum excess. Intensity ratios indicate that physical conditions are nearly uniform in the NC but span a range in the BC.
For DR Tau, the range of morphologies in 62 unblended Fe I and Fe II lines can be resolved in terms of a narrow component (NC) that dominates the weakest lines, and a broad component (BC) that dominates the strongest lines. The (NC) has FWHM ∼20 km/s and centroid velocity near zero km/s. The (BC) has FWHM ∼100 km/s, and a tendency to be blueshifted by ≤10 km/s. Estimates of iron line opacities τ and column densities N yield τNC ∼ 3 × τBC, NFeI [special characters omitted] 1017 – 1018 cm–2 , and NFeII [special characters omitted] 1018 – 1019 cm–2 for the BC. Estimates of kinetic temperature for iron suggest that the NC gas is hotter than the BC by several thousand degrees. For iron, the NC is consistent with an origin in the postshock gas while the BC may originate in the inner accretion disk close to the corotation radius.