Astronomy and Astrophysics, volume 284, 919-935 (1994/4-3)
An investigation of extinction diagnostics towards the Orion Nebula.
GREVE A., CASTLES J. and McKEITH C.D.
Abstract (from CDS):
We present for the Orion nebula long-slit spectroscopic observations of emission lines in the wavelength regions 10 000-11 000 A and 3700-7330 A. These wavelength regions contain the corresponding multiplet lines of common upper atomic level of hydrogen P6-H6 (= Pγ -Hδ) and P7-H7 (= Pδ-Hε) and of [S II] at 10 300 A and 4072 A. From these lines the extinction AV towards the Orion nebula is derived with minimal reliance on recombination line model calculations. We find good internal agreement for the extinction derived from the corresponding hydrogen and [S II] lines, except for deviations of the order of 20-30% for data based on Hε and Pδ, where deblending of the Hε line may be uncertain by this amount and the flux of the Pδ line contains a similar error. There exists good agreement with the extinction derived from the other Paschen and Balmer line combinations. We also discuss in particular the method of extinction determination proposed by Allen (1979). However, we find no advantage from this over the other methods based on Paschen-Balmer lines and corresponding [S II] lines, neither from a greater precision achieved nor from the observational requirements.
H II regions: individual: Orion nebula - emission lines - corresponding multiplet lines - extinction