ISO spectroscopy of young intermediate-mass stars in the BD+40^deg4124 group

Abstract

We present the results of ISO SWS and LWS grating scans towards the three brightest members of the BD+40^deg4124 group in the infrared: BD+40^deg4124 (B2Ve), LkHα 224 (A7e) and the embedded source LkHα 225. Emission from the pure rotational lines of H_2, from ro-vibrational transitions of CO, from PAHs, from H i recombination lines and from the infrared fine structure lines of [Fe ii], [Si ii], [S i], [O i], [O iii] and [C ii] was detected. These emission lines arise in the combination of a low-density (~ 10² cm^-3) H ii region with a clumpy PDR in the case of BD+40^deg4124. The lower transitions of the infrared H i lines observed in BD+40^deg4124 are optically thick; most likely they arise in either a dense wind or a circumstellar disk. This same region is also responsible for the optical H i lines and the radio continuum emission. In the lines of sight towards LkHα 224 and LkHα 225, the observed emission lines arise in a non-dissociative shock produced by a slow (~ 20 km s^-1) outflow arising from LkHα 225. Toward LkHα 225 we also observe a dissociative shock, presumably located closer to the outflow source than the non-dissociative shock. In the line of sight towards LkHα 225 we observed absorption features due to solid water ice and amorphous silicates, and due to gas-phase H_2O, CO and CO_2. No solid CO_2 was detected towards LkHα 225, making this the first line of sight where the bulk of the CO_2 is in the gas-phase. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.