Physical Properties of the Outflow Sources in Taurus

Abstract

We have searched for CO outflows in eight embedded IRAS sources located in the Taurus molecular cloud using the 45m telescope of Nobeyama Radio Observatory. We have detected CO wing emission in four of these sources. CO outflow associated with TMC1A (04365+2535) is strong and spatially compact (radius ≤ 0.04 pc). The dynamical timescale of ~2.5 x 10³ yr suggests this outflow is the youngest one in Taurus.

We have combined our data with previously published survey data and have analyzed the physical properties of the outflow sources. We found that 12 out of 16 embedded sources (~75%) have CO outflows associated with them; this indicates that almost all stars experience a phase of molecular outflow in their embedded stage. The IRAS color of the outflow sources suggests that the outflows appear in considerably early phase of the evolution of YSOs, that is, as early as YSOs became observable with IRAS and that visible outflow sources are in a transient phase of evolution between embedded sources and visible T Tauri stars without outflow. Visible outflow sources are systematically more luminous than visible no-outflow sources, while embedded outflow sources have comparable luminosities with visible no-outflow sources. Such luminosity function suggests that the YSOs with outflow undergo mass accretion and increase their stellar mass as they progress from embedded sources to visible outflow sources. Typical mass accretion rate derived from the bolometric luminosity is ~2 x10^-6 M _⊙ yr ^-1. The timescale for mass accretion to acquire typical stellar mass, 0.5-0.8 M _⊙ , is~2.5-4 x 10⁵ yr.