CO J = 3→2 and J = 2→1 mapping and spectroscopy of NGC 7027

Phillips, J. P.; White, G. J. and Richardson, K. J. (1985). CO J = 3→2 and J = 2→1 mapping and spectroscopy of NGC 7027. Astronomy & Astrophysics, 151(2) pp. 421–426.

URL: http://adsabs.harvard.edu/full/1985A&A...151..421P

Abstract

We present spectra and mapping for NGC 7072 in the J = 3→2 and J = 2→1 transitions of CO. The central profile at J = 2→1 is shown to be very similar to the J = 1→0 spectrum measured by Thronson (1983), and this implies a source expansion at roughly constant velocity. The J = 3→2 line however appears weaker, with evidence for appreciable quenching of the higher velocity components. Detailed modelling f the source indicates that densities n must vary appreciably with shell radius R(as nα R^-a, where α≥2), and this leads to a corresponding steep radial decrease in the radiation temperature T_R. In consequence, the source FWHM is found to decrease appreciably iwth increasing transition frequency, a trend which appears also to be confirmed by our central J = 3→2 scans. It is not however possible to constrain gas kinetic tempertures T_K, the level of CO thermalisation, or shell mass M with any degree of confidence - both low and high mass models appear capable of replicating our spectra. Finally, the J = 2→1 spatial velocity map displays evidence for a decrease in velocity width towards the outer regions of the nebula; a feature which is expected of most outflow models. The J = 3→2 map also indicates the presence of a nebular extension to the north-west of the peak emission core, although this is not reproduced in the corresponding J = 1→0 map of Mufson et al. (1975).

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