A multitransition CO study of GL 490

Abstract

The environment of the young stellar object GL 490 has been studied using submillimeter emission lines of CO and fundamental vibrational band absorption lines of CO. High spatial resolution observations were made in the emission lines of CO J = 3-2, (13)CO J = 3-2, and CO J = 6-5. A high spectral resolution (lambda/delta lambda = 43,000) M-band (4.7 micrometers spectrum of GL 490 was obtained and shows fundamental vibrational band lines of CO and (13)CO from a range of rotational states. CO J = 3-2 maps reveal numerous moving clumps with outflow speeds from a few km/s to 40 km/s. The CO J = 3-2 emission, combined with (13)CO J = 3-2 and CO J = 2-1 emission, shows that the outflowing gas has temperatures from 10 K to 30 K. The CO J = 6-5 emission demonstrates that the clumps also contain hotter gas, with excitation temperatures from 30 K to 100 K. A range of temperatures is consistent with the preence of shocks. The masses of the clumps range from 0.01 to 0.5 solar mass. The absence of alignment of the clumps argues against their ejection from the central object as interstellar 'bullets'. The range of speeds of the outflowing gas is consistent with a wind-driven outflow, in which a fast stellar wind sweeps up a shell of ambient gas. The clumps would represent shell fragments. The acceleration of preexisting clumps of ambient gas by the ram pressure of a fast wind can also produce the moving clumps. The CO lines in the absorption spectrum show a strong absorption component blueshifted by 13 km/s with respect to the ambient cloud. The absence of an enhancement in CO J = 3-2 emission at the same velocity suggests that the blueshifted absorbing gas fills only a small fraction of the 15 sec beam.