EPISODIC OUTFLOWS FROM HIGH-MASS PROTOSTARS

A program of high-resolution infrared spectroscopy at 4.7-mu-m has resulted in the detection of outflowing gas from the seven deeply embedded, luminous young stellar objects M8E-IR, GL 490, GL 2591, W3 IRS 5, NGC 7538 IRS 1, NGC 7538 IRS 9, and S140 IRS 1. The outflows are seen as blueshifted absorption features in lines of the fundamental band of CO. New CO J = 2-1 emission line data are presented for the sources M8E-IR, GL 490, GL 2591, W3 IRS 5, and NGC 7538 IRS 9. The kinematics and physical properties of the outflowing gas are discussed and the CO outflows seen in absorption are compared to the spatially extended outflows seen in millimeter emission lines of CO. Differences in velocity structure and temperature show that the absorbing gas is distinct from the millimeter line emitting gas. The new CO J = 2-1 data show, unambiguously for the first time, that M8E-IR, GL 2591, W3 IRS 5, and NGC 7538 IRS 9 are sources of bipolar outflow. All seven of the young stellar objects showing absorption outflows are sources of extended bipolar outflows. Two candidate protostars, W33A and GL 2136, which are not known to have bipolar outflows, have no absorption outflows. The multicomponent absorption outflows seen from M8E-IR and W3 IRS 5 strongly resemble the outflows seen in the visible from the FU Orionis object V1057 Cyg. The outflow from GL 2591 is kinematically much like the outflow from FU Orionis itself. We suggest that these embedded objects may be FUors, and that the extended bipolar flows are the cumulative result of many outburst episodes over the accretion lifetime of the star. For the four objects NGC 7538 IRS 9, W3 IRS 5, GL 2591, and M8E-IR, the total momentum in the infrared outbursts, over the lifetime of the activity, is estimated. For three of the four, the total momentum in outbursts is comparable to the momentum found in the extended bipolar outflows of luminous young stellar objects. The mass loss rates inferred for the same four sources on the basis of the infrared flows are of the same order of magnitude as mass loss rates deduced for other luminous young stellar objects from their bipolar outflows. The episodic outflows we observe in the infrared are, therefore, capable of producing extended bipolar flows. An emission component to the CO upsilon = 0-1 line profiles is seen in four sources. The profiles are of the P Cygni form and imply gas expanding from the central source. The size of the region producing the fundamental band emission lines, for the source S140 IRS 1, is calculated to be small, some 10 or 20 AU in radius. The observations presented here do not favor a particular outflow model. Unlike low-mass protostars, the luminous objects studied here may produce copious ultraviolet radiation. Low-velocity outflowing gas, as seen in GL 490, S140 IRS 1, and NGC 7538 IRS 1, might be accelerated by the uv radiation acting on surrounding gas. The higher velocity outflows require some other mechanism.