ISO spectroscopy of shocked gas in the vicinity of T Tauri

Abstract

We present the results of ISO SWS and LWS spectroscopy of the young binary system T Tau. The spectrum shows absorption features due to H_2O ice, CO_2 ice, gas-phase CO and amorphous silicate dust, which we attribute to the envelope of T Tau S. We derive an extinction of A_V = 17.4m +/- 0.6m towards this source. Detected emission lines from H i arise in the same region which is also responsible for the optical H i lines of T Tau N. These lines most likely arise in a partially ionized wind. Emission from the infrared fine-structure transitions of [S i], [Ar ii], [Ne ii], [Fe ii], [Si ii], [O i] and [C ii] was also detected, which we explain as arising in a ~ 100 km s(-1) dissociative shock in a fairly dense (5 x 10(4) cm(-3) ) medium. Pure rotational and ro-vibrational emission from molecular hydrogen was detected as well. We show the H_2 emission lines to be due to two thermal components, of 440 and 1500 K respectively, which we attribute to emission from the dissociative shock also responsible for the atomic fine-structure lines and a much slower (~ 35 km s(-1) ) non-dissociative shock. The 1500 K component shows clear evidence for fluorescent UV excitation. Additionally, we found indications for the presence of a deeply embedded (A_V > 40() m) source of warm H_2 emission. We suggest that this component might be due to a shock, caused by either the outflow from T Tau S or by the infall of matter on the circumstellar disk of T Tau S. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.