Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995adil...mw...02w&link_type=abstract
NCSA Astronomy Digital Image Library
Astronomy and Astrophysics
Astronomy
Scientific paper
We have mapped the Orion-KL region in 28 transitions of 14 molecular species (H2CO, DCN, HDO, CH3CH2CN, HC3N, SO2, OCS, SO, SiO, HCN, HCO+, CH3CN, CH3OH, CO) near 3 millimeters wavelength using the BIMA array. The observations were obtained with 1-6 arcsecond angular resolution and 0.3-4 km/s velocity resolution. The images show two principal molecular concentrations in a ridge of dense gas, one at the Kleinmann-Low nebula and a second located 25 arcseconds to the northeast. These molecular concentrations correspond to column density enhancements inferred from dust continuum emission. The southern concentration shows broad line widths, high temperatures, high excitation emission, and it is associated with luminous infrared sources, masers, and powerful outflow from at least one embedded young stellar object. By contrast, the northern concentration shows narrower line widths, lower temperatures, and only weak indications of star formation. We discuss the observed spatial distributions of molecular emission in terms of the "ridge", "hot core", and "plateau" spectral components inferred from lower resolution data. The extended "ridge" gas is traced by six of the observed species (HCN, H13CN, HC3N, CH3CN, CH3OH). While most of the observed transitions of these species have similar excitation properties, the maps show differences in detail that likely reflect chemical processing in an environment of enhanced radiation and dynamic outflow. The "hot core" is prominent in almost all of the observed species as a cluster of bright peaks 2" to the southeast of the infrared source IRc2. However, only emission from CH3CH2CN and vibrationally excited HC3N appear co-spatial with the hot core dust peak. Emission from SiO and 29SiO peak close by, at radio source I, and the emission from most other species extends to the southwest. The "plateau" spectral component represents a mixture of features and may be further broken down into the "compact ridge" and "low velocity" and "high velocity" outflows, roughly divided at about 20 km/s from the velocity of the ambient cloud. The compact ridge extends from the hot core towards the south and is prominent in the oxygen rich species CH3OH, HDO, H2CO, and SO2. This region may be associated with grain mantles ablated from dense clumps by the action of the outflow. The low velocity outflow shows clear chemical gradients. In particular, the species SiO, SO, SO2, and HC3N appear to delineate three zones: (1) outflow from the IRc2 region, traced principally by SiO; (2) a doughnut of shocked gas, traced by SO and SO2; and (3) ablation from clumps, traced by HC3N. The SO and SO2 emission are red-shifted to the northwest and blue-shifted to the southeast, consistent with formation in an expanding doughnut or shell of shocked gas. The high velocity outflow appears bipolar, with blueshifted emission dominating to the west, redshifted emission to the east, and center is close to the SiO v=1 J=2-1 maser position and radio source I. To the northwest, red-shifted and blue-shifted emission overlap, perhaps the projection of outflowing gas in a wide angle cone. To the southeast, the outflow is smaller in extent and may be obstructed by dense material associated with the hot core. In an appendix, we present a table of column densities derived at 9 positions for each species observed in the BIMA survey for comparison with chemical models.
Plambeck Richard L.
Wilner David J.
Wright Mel C. H.
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