Infrared spectroscopy of the sources in S235 and its implication for the line excess problem

Abstract

Infrared and radio spectroscopy of four heavily obscured infrared sources in the region of S235 is presented: IRS 1-4 in the list of Evans and Blair. All of the sources show emission in the Br..gamma.. line of hydrogen which indicates the presence of regions with enhanced amounts of ionized gas around them. Each is therefore considered a separate source of luminosity apart from the central ionizing star of the visible nebula. Three of the four sources show excess line emission which indicates higher ionization than expected from a ZAMS star of the same luminosity. The only source not showing a line excess is IRS 3 which does show radio emission in an extended structure. This fits a pattern in which line excess sources are very compact, dense H II regions which, due to a high optical depth at radio frequencies, have little or no radio emission. The CO spectra of these sources show no evidence for high-velocity molecular outflow. This is contrary to the results in other line excess sources.