The radio recombination line spectrum of Orion A: Observations and analysis

Journal Article · Wed Oct 01 04:00:00 EDT 1975 · Astrophys. J., v. 201, no. 1, pp. 134-150

DOI:https://doi.org/10.1086/153867· OSTI ID:4108605

Lockman, F J; Brown, R L

The entire body of radio observations of Orion A has been considered, and the means by which the temperature and density can be derived from the ratio T/subL//T/subC/ and the line width $delta$v of the hydrogen radio recombination lines is examined. Since it is critical to determine the extent to which low- frequency line measurements are contaminated by ''baseline-subtraction'' problems, new observations are presented which, together with general considerations of the line shape and data reduction processes, support the following conclusions: T/subL//T/subC/ and $delta$v can be accurately determined in the low-frequency observations even when erroneous baselines are removed; in accord with other studies, a density gradient must exist in the nebula; isothermal models cannot reproduce the observed line strenghts; the most dense parts of the nebula must be somewhat cooler than the surrounding gas. A model of Orion A has been constructed that is derived directly from the radio continuum observations. These observations demand that the simplest possible model of the nebula be comprised of three regions whose gross properties: the electrons density and the size: are defined by the continuum measurements. This model has been used for an analysis of the radio recombination line data, and virtually all known radio data on the Orion Nebula including $delta$v and T/subL//T/subC/ of the H n$alpha$ lines from 610 MHz to 85 GHz $delta$v and T/subL//T/subC/ of all the observed H n$beta$ lines; the shape and magnitude of the radio continuum spectrum can be reproduced. The application of this model to the problem of the abundance and distribution of ionized helium with the nebula is also considered. (AIP)

• Research Organization: National Radio Astronomy Observatory, Green Bank, West Virginia
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-018173
• OSTI ID: 4108605
• Journal Information: Astrophys. J., v. 201, no. 1, pp. 134-150, Journal Name: Astrophys. J., v. 201, no. 1, pp. 134-150; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

*NEBULAE-- EMISSION SPECTRA
640105* --Physics Research--Astrophysics & Cosmology-- Galaxies
COSMOCHEMISTRY
HELIUM
HYDROGEN
N56500* --Physics (Astrophysics & Cosmology)--Galaxies
RADIOWAVE RADIATION
RECOMBINATION
STRUCTURAL MODELS
TEMPERATURE DEPENDENCE
VARIATIONS