The Dispersing Cloud Core around T Tauri

Abstract

We have made <SUP>13</SUP>CO (J = 1-0) observations of T Tauri with the Nobeyama Millimeter Array (NMA) and with the Nobeyama 45 m telescope. The <SUP>13</SUP>CO (J = 1-0) emission detected with the NMA shows three different features: (1) a pair of ringlike features surrounding T Tauri with a radius of 30" (corresponding to 4200 AU at the distance of 140 pc to T Tauri) at the velocities blueshifted and redshifted by less than 1 km s<SUP>-1</SUP> from the systemic velocity, (2) a blueshifted compact feature 3" east of T Tauri, and (3) another compact feature 7" southwest of T Tauri at velocities redshifted by more than 1 km s<SUP>-1</SUP>. On the other hand, the <SUP>13 </SUP>CO maps obtained with the 45 m telescope show a smoothly extended feature near the systemic velocity, which is missed in the NMA observations, as well as the above- mentioned three features. The total masses of gas detected with the NMA and the 45 m telescope are estimated to be (0.054-0.23) M<SUB>sun</SUB> and (0.31-1.3) M<SUB>sun</SUB>, respectively. The difference in the estimated mass between the two observations is mainly due to resolving out of the smoothly extended feature in the NMA observations. <P />The <SUP>13</SUP>CO rings are interpreted as biconical outfiowing shells in a nearly pole-on configuration. The high-velocity stellar wind ejected from T Tauri is estimated to be energetic enough to drive these out- flowing shells. We have analyzed the three-dimensional structure of the shells by correcting for the projection effect on the plane of the sky, and we have found that the spatial extent of the shells is nearly equal to or slightly smaller than the typical size of the molecular cloud cores in the Taurus Molecular Cloud. This fact indicates that the outflowing shells are part of the parent cloud core that still remains around T Tauri, which is now dispersing under the influence of the stellar wind. Such an environment around T Tauri is quite different from those around typical T Tauri stars, which are associated only with compact gaseous components. These results suggest strongly that T Tauri is one of the objects in the transitional phase from the protostar stage, in which a central star is deeply embedded in an infalling envelope, to the T Tauri stage, in which a central star is surrounded by a compact circumstellar disk instead of a spatially extended envelope.