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Astron. Astrophys. 327, 1177-1184

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Kinematics and electron temperatures in the core of Orion A*

T.L. Wilson, L. Filges, C. Codella, W. Reich, and P. Reich

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 23 May 1997 / Accepted 11 July 1997


A map of the core of Orion A, with a 42$^{\prime\prime}$ resolution in the 64$\alpha$ recombination line of hydrogen, covering $\sim$5$^{\prime}$ by $\sim$5$^{\prime}$, is presented. The Vlsr distribution shows a complex variation about the center of the ionized gas emission: From $\Delta \alpha$=-200'' to +300'', the Vlsr varies from -5 km s-1 to +2 km s-1 then to -4 km s-1, finally rising to +3 km s-1. A search for cold ($T_{\rm e} \sim $3000K) ionized gas toward the KL nebula has revealed no measurable differences in Te between this region and other parts of Orion A. The average Te from our data is 8300$\pm$200K. We find no significant difference between Te values determined from radio recombination lines and those determined from forbidden optical lines of [O III], although the Te value from Balmer decrement data is markedly lower. The turbulent velocity varies by <5% over the region mapped. On the basis of our 2.45' resolution, high dynamic range 6 cm continuum map, we find that the emission falls off faster in the East than in the West. We find support for the model in which Orion A is ionization bounded in the East but density bounded in the West. The ionized gas in the West is flowing in the direction of the Sun, while the more positive Vlsr values in the east may be caused by the flow of ionized gas off the foreground Dark Bay. This ionized region may have little fine scale structure, since there is little continuum emission in interferometer maps.

Key words: ISM: Orion A - ISM: HII regions - ISM: kinematics and dynamics - ISM: structure - radio lines: ISM

*Table 1 is only available in electronic form at the CDS (Strasbourg) via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: T.L. Wilson

© European Southern Observatory (ESO) 1997

Online publication: October 20, 1997
Last change: April 6, 1998