A CO J = 2-->1 study of the outflow sources GL 490 and NGC 7538 IRS 9

Abstract

This thesis presents new detailed [superscript 12]CO and [superscript 13]CO observations, using 21" resolution, around the two luminous infrared sources GL 490 and NGC 7538 IRS 9. Observations show strong evidence for bipolarity of the high-velocity outflows surrounding these two objects.

Calculations of optical depth indicate that [superscript 12]CO J =2[right arrow]1 emission is optically thick in the inner wings and optically thin in the outer wings. The total outflow masses were determined to be 9 MO for GL 490 and 50 MO for NGC 7538 IRS 9. The calculated mechanical luminosities of the outflows are much smaller than the stellar luminosities of the respective sources which is consistent with radiation pressure being the driving mechanism. The calculated force required to accelerate the molecular outflow is, however, much larger than the force that could be exerted on the gas if every photon emitted by the central object were absorbed.

Mass loss rates were calculated by dividing total outflow mass by the dynamical timescale and were found to be 1.7X10[superscript -3]MO/yr for NGC 7538 IRS 9 and 6X10[superscript -4]MO/yr for GL 490. Our observations imply that much of the emission arises from swept-up material which is possibly the result of the interaction of a collimated wind and the ambient molecular cloud. (Abstract shortened by UMI.)