Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.3903g&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #39.03; Bulletin of the American Astronomical Society, Vol. 24, p.1180
Astronomy and Astrophysics
Astronomy
2
Scientific paper
High spatial resolution, narrow band, infrared line images and CO (1-0) mm interferometer data are presented for NGC 7027. These data trace emission from the central H II region (Bralpha ), the intermediate photodissociation region (H_2 1-0 S(1) &\ 3.3 microns dust feature), and the molecular circumstellar envelope (CO (1-0)). The H II region lies in a cavity in the CO envelope, and consists of a smooth elliptical shell. A striking change of morphology is seen in the H_2 emission and the dust feature. The H_2 1--0S(1) emission is composed of two components: 1) an incomplete elliptical ring of knots which bounds the ionized gas; 2) a remarkable thin shell which loops around the H II region with four--fold symmetry. The dust emission is similar to that from the ionized gas, but is displaced further from the center, and extends at low surface brightness into four ``ears'' which fill in the bays delineated by the outermost loops of H_2 emission. No 3.3 microns emission is detectable beyond the outer H_2 shell. The outer loops of H_2 emission and the 3.3 microns emission occupy the region between the edge of the H II region and the inner edge of the molecular gas. It is natural to ascribe the morphology of NGC 7027 to a photodissociation region which separates the ionized and molecular gas. If this is correct then the exterior H_2 loops are due to molecular gas heated by the far--UV emission escaping from the H II region, and delineate a photodissociation front. The H_2 and CO kinematics rule out shock excitation of the H_2 emission and favor UV excitation.
Beckwith Steve
Graham James R.
Herbst Thomas M.
Matthews Keith
Neugebauer Gernot
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