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The Astrophysical Journal Letters


The American Astronomical Society


We present spectrally resolved observations of the young multiple system T Tau in atomic and molecular lines obtained with the Heterodyne Instrument for the Far Infrared on board Herschel. While CO, H2O, [Cii], and SO lines trace the envelope and the outflowing gas up to velocities of 33 km s−1 with respect to systemic, the CN 5–4 hyperfine structure lines at 566.7, 566.9 GHz show a narrow double-peaked profile centered at systemic velocity, consistent with an origin in the outer region of the compact disk of T Tau N. Disk modeling of the T Tau N disk with the thermo-chemical code ProDiMo produces CN line fluxes and profiles consistent with the observed ones and constrain the size of the gaseous disk (Rout=110+10−20AU) and its inclination (i=25◦±5◦). The model indicates that the CN lines originate in a disk upper layer at 40–110 AU from the star, which is irradiated by the stellar UV field and heated up to temperatures of 50–700 K. With respect to previously observed CN 2–1 millimeter lines, the CN 5–4 lines appear to be less affected by envelope emission, due to their larger critical density and excitation temperature. Hence, high-J CN lines are a unique confusion-free tracer of embedded disks, such as the disk of T Tau N.


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