Far-infrared spectroscopy across the asymmetric bipolar outflows from Cepheus A and L 1448

Details Far-infrared spectroscopy across the asymmetric bipolar outflows from Cepheus A and L 1448 Far-infrared spectroscopy across the asymmetric bipolar outflows from Cepheus A and L 1448

Apr 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...385..239f&link_type=abstract

Astronomy and Astrophysics, v.385, p.239-256 (2002)

Astronomy and Astrophysics

Astrophysics

20

Shock Waves, Molecular Processes, Ism: Jets And Outflows, Ism: Kinematics And Dynamics, Ism: Molecules, Stars: Mass-Loss

Scientific paper

Bipolar outflows are driven from protostars within molecular cores. They drive into molecular clouds, generating shock waves whose molecular emission lines have been observed in the infrared with ISO. We present spectroscopic data for seven locations within two asymmetric outflows, Cepheus A and L 1448, in order to test the shock physics and shock dynamics. Here, we simultaneously interpret the CO and H2 data sets which are generated by shocked gas, radiating at temperatures from 300 to 2000 K. We find that large-scale spatial variations in the excitation are absent across both outflows and that the excitation is low everywhere. Planar shock models are inconsistent with the data sets. Models with configurations or ensembles of shocks, in the form of bow shocks or supersonic turbulence, are consistent. This solves the previously reported problem that the CO abundances were anomalously high. Cool gas is dominant, from which we infer bow shocks with flanks more extended than for paraboloids. As a consequence, the atomic oxygen abundances must be quite low. J-type bow models require implausibly long wings. C-type physics is thus favoured. The density and the ratio of molecules to atoms are constrained by the CO/H2 flux levels as well as the H2 vibrational level distributions. Other C-shock parameters, such as the magnetic field strength, ion fraction and speed, are not tightly constrained. The total shock powers are derived and are comparable to the mechanical outflow luminosities for both outflows, consistent with the outflows being momentum-driven. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

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