Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..250m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 1, p. 250-260
Astronomy and Astrophysics
Astrophysics
18
Carbon, Carbon Monoxide, H Ii Regions, Interstellar Matter, Jet Flow, Molecular Clouds, Ultraviolet Radiation, Angular Resolution, Atmospheric Density, Fine Structure, Red Shift, Rotational Spectra
Scientific paper
We present high resolution maps (10-14 arcsec full width at half maximum (FWHM)) of the atomic carbon (CI) (3)P1 (492.1607 GHz) fine structure line and the C(17)O J = 3 goes to 2 (337.0611 GHz) rotational line from the outflow and photon-dominated region (PDR) in S 140. These observations reveal remarkable, previously unresolved structure. There is a marked variation in CI line profiles across the mapped region. Towards the outflow the lines are broad (FWHM approximately 5-6 km/s) with peak values of Tmb approximately 10-12K, yet towards the PDR the lines are distinctly narrower (approximately 3-4 km/s) with higher values of peak Tmb up to 18K. Both the CI and C(17)O intergrated intensity maps show a similar morphology. The emision peak lies towards the molecular outflow source, and there is an arc of emission extending from the peak towards the South. The CI and C(17)O arcs are offset, with the CI arc offset to the northeast. This CI arc feature is observed at blue and redshifted velocities, while the C(17) arc feature is only observed in blueshifted emission. This implies the CI emission lies on the inner edge of the blueshifted molecular outflow wall (traced by the C(17)O emission). Towards the molecular outflow source the abundance ratio N(CI)/N(CO) = 0.14, with a similar ratio found for the blue wing and core velocity intervals (0.12). The red wing has a particularly high abundance, N(CI)/N(CO) = 0.67. The most plausible mechanism for producing the CI emission is the effect of shocks on the chemical and physical processes at the interface between the stellar wind and the blueshifted outflow cavity wall. The PDR is a clumpy, narrow (approximately 0.1-0.15pc) elongated ridge-like feature, adjacent to the south-western edge of the molecular cloud. Emission from the PDR is observed across a relatively narrow velocity range, -10 to -6 km/s. There is a localized intergrated emission peak (at offset position -28, -42 arcsec), which we have designated PDRc1 (PDR clump 1). The abundance of CI is particularly high, N(CI)/N(CO) = 0.29 at the position of PDRc1. The observed column density (9.7 +/- 0.8 x 1017/sq. cm) and emergent intensity (8.7 +/- .07 x 10-6 erg/sq. cm/s/sr) towards PDRc1 are in close agreement with recent modelling of low-density PDRs.
Krause Dirk
Minchin Nigel R.
Stutzki Juergen
White Glenn J.
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