NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

Abstract

We present a detailed analysis of narrow Na I and K I absorption resonance lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying their origin. The Na I λ5889.95 line is detected toward all but one source, while the weaker K I λ7698.96 line is detected in about two-thirds of the sample. The similarity in their peak centroids and the significant positive correlation between their equivalent widths demonstrate that these transitions trace the same atomic gas. The absorption lines are present toward both disk and diskless young stellar objects, which excludes cold gas within the circumstellar disk as the absorbing material. A comparison of Na I and CO detections and peak centroids demonstrates that the atomic gasand molecular gas are not co-located, the atomic gas being more extended than the molecular gas. The width of the atomic lines corroborates this finding and points to atomic gas about an order of magnitude warmer than the molecular gas. The distribution of Na I radial velocities shows a clear spatial gradient along the length of the Taurus molecular cloud filaments. This suggests that absorption is associated with the Taurus molecular cloud. Assuming that the gradient is due to cloud rotation, the rotation of the atomic gas is consistent with differential galactic rotation, whereas the rotation of the molecular gas, although with the same rotation axis, is retrograde. Our analysis shows that narrow Na I and K I absorption resonance lines are useful tracers of the atomic envelope of molecular clouds. In line with recent findings from giant molecular clouds, our results demonstrate that the velocity fields of the atomic and molecular gas are misaligned. The angular momentum of a molecular cloud is not simply inherited from the rotating Galactic disk from which it formed but may be redistributed by cloud-cloud interactions.

Tracing Slow Winds From T Tauri Stars via Low-Velocity Forbidden Line Emission

“…Our sample is presented in Table 1 and consists of 33 mostly single and bright (B16) TTS with disk spectral energy distributions encompassing: 26 Class II, full disks with optically thick inner regions; 5 transition disks (TDs), with absent or lowNIR to mid-infrared (MIR) excess emission from the inner disk but large far-infrared (FIR) emission; 2 Class II/III evolved disks with weak NIR to FIR excess. Additional information on this sample can be found in Pascucci et al (2015), who analyzed the Na D and K profiles (at 5889.95 and 7698.96 Å, respectively) from the same spectra as presented here. The spectral types (SpTy), extinctions (A v ), stellar bolometric luminosities (L * ), and stellar masses (M * ) in Table 1 are all taken from Herczeg & Hillenbrand (2014) who derived them in a homogeneous way from spectrophotometric data, while taking into account excess continuum emission (veiling) and extinction when deriving the stellar properties.…”

“…Resolved millimeter continuum images point to a highly inclined outer disk (∼70°, ∼35°, Isella et al 2009). However, MIR interferometric visibilities coupled with spectral Pascucci et al (2015). SpT, Av, L * , and M * values were taken from Herczeg & Hillenbrand (2014).…”

“…Pascucci et al (2015) independently calculated the spectral resolution achieved by HIRES in this setting and found a slightly better resolution of ∼45,000 corresponding to 6.6 km s −1 . The targets were observed in two campaigns with the same instrumental setting, one in 2006 and another in 2012.…”

“…An example of a spectrum before and after sky subtraction is discussed in Appendix A and the figure therein. Further details about the data reduction and source exposure times are given in Pascucci et al (2015). …”

“…The velocity is relative to the stellocentric frame, as determined from photospheric line centroids. The stellar radial velocities of our sources are given in Tables5 and6 of Pascucci et al (2015) and have a 1σ uncertainty of ∼1 km s −1 .…”