Spectrophotometry of the Huygens Region of the Orion Nebula, the Extended Orion Nebula, and M~43; Scattered Light Systematically Distorts Conditions Derived from Emission-Lines

摘要

We report on medium resolution spectrophotometry of the Orion Nebula region,including for the first time the Extended Orion Nebula and the nearby M~43. The49 long slit observations were divided into 99 smaller samples, which haveallowed determinations of the amount of extinction, extinction corrected\Hbeta\ surface brightness, electron temperatures (from [S~II], [N~II], and[O~III]), and electron densities (from [S~II] and [Cl~III]) throughout much ofthis complex region. We verify an earlier conclusion from a radio/optical study that beyond about5\arcmin\ from \ori\ local emission begins to be contaminated by scattering oflight from the much brighter central Huygens Region of M~42 and this scatteredlight component becomes dominant at large distances. This contamination meansthat the derived properties for the outer regions are not accurate. Fromcomparison of the light from the dominant star in M~43 with the continuum ofthat nebula (which is almost entirely scattered star light) it is determinedthat scattered light is enhanced in the blue, which can lead to observed Balmerline ratios that are theoretically impossible and erroneous electrontemperatures. This blue scattering of emission-lines is important even in the HuygensRegion because it means that at anything except very high spectroscopicresolution the observed lines are a blend of the original and scattered light,with shorter wavelength lines being artificially enhanced. This can lead toover-estimates of the electron temperatures derived from the nebular andauroral line ratios of forbidden lines. This phenomenon is probably applicableto many other H~II regions.