On the anomalous Balmer decrement in the Orion nebula

Details On the anomalous Balmer decrement in the Orion nebula On the anomalous Balmer decrement in the Orion nebula

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26at....6..197g&link_type=abstract

Astronomical and Astrophysical Transactions (ISSN 1055-6796), vol. 6, no. 3, p. 197-211

Astronomy and Astrophysics

Astrophysics

Anomalies, Atomic Energy Levels, Balmer Series, Orion Nebula, Quantum Numbers, Reduction, Absorption Spectra, Electron Transitions, Optical Thickness, Radiative Transfer, Radio Emission, Radio Spectra

Scientific paper

New measurements of Balmer lines in the cental part of the Orion nebula have been made on the 6-m telescope. The generalized curve of the level population is compiled from the Balmer line and radio line measurements. A new approach to the problem of the anamalous Balmer decrement is proposed. The relative level populations obtained from our relative intensity measurements are referred to the theoretical population curve in the range of high principal quantum numbers n = 20-30. It provides matching of our populations with the level populations derived from radio recombination line observations and from high-n Balmer line measurements by Goad et al. (1972). However, the low-n level population proves to be much lower than the theoretical ones. When interpreting the results of the observations, the inhomogeneity of the population structure of the low-l states is taken into account. The radiative transitions nd goes to 2p is shown to play the main role in the Balmer line emission. Absorption from the metastable level 2s also can be be important in the Balmer line radiation transfer. We show that the anomalously low intensity of the low-n Balmer lines cannot be explained only with the use of the effect of optical depth. It is possible that the anomaly in the low-n Balmer line intensities is caused by the real underpopulation of the nd-states when n is less than 15.

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