A multi-transition CO study of the GL 490 outflow

Abstract

The high-velocity GL 490 outflow has been observed at high spatial resolution with the JCMT in three rotational transitions (J = 2[right arrow]1 of HBBW = 21", J = 3[right arrow]2 of HPBW = 15" and J = 6[right arrow] 5)of [superscript 12]CO and [superscript 13]CO. A number of moving clumps can be detected in the channel maps, which indicates that the outflow is bipolarity but complex in structure. The main red wing emission from GL 490 consists of two spatially separate clumps of similar mass. The estimated masses of the clumps are found to be higher (from 0.01 to 0.5 solar mass) than those of previously studied clumps from other outflows.

The moving clumps velocities exceed the estimated escape velocity of the parent molecular cloud. Total clump mass is 0.3% of the cloud mass confined within a radius of 0.4 pc and 15% of the total outflow mass. Therefore, the clumps represent a kinematically insignificant component of the molecular cloud.

The detection of CO J = 6[right arrow]5 emission shows that warm rest velocity gas exists near GL 490. This warm region is estimated to be about 6000 AU in radius, assuming spherical geometry. Combined with infrared absorption spectroscopy data, the average density of this region is estimated to be ~10[superscript 6]cm[superscript minus 3].

The [superscript 12]CO J = 6[right arrow]5 spectral line map shows that line profiles changes markedly within 20" of GL 490. A strong blue wing emission is seen at the position of the main blue lobe. The line profile displays no emission from the rest velocity gas at this location. This fact, coupled with the derived high temperature and density, is consistent with shocked CO in the blue lobe.