ISO Spectroscopy of Young Intermediate-Mass Stars in the BD+40 4124 Group

Abstract

We present the results of ISO SWS and LWS grating scans towards the three brightest members of the BD+40 4124 group in the infrared: BD+40 4124 (B2Ve), LkHalpha 224 (A7e) and the embedded source LkHalpha 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 (approx 10^2 cm^-3) H II region with a clumpy PDR in the case of BD+40 4124. The lower transitions of the infrared H I lines observed in BD+40 4124 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 LkHalpha 224 and LkHalpha 225, the observed emission lines arise in a non-dissociative shock produced by a slow (approx 20 km/s) outflow arising from LkHalpha 225. Toward LkHalpha 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 LkHalpha 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 LkHalpha 225, making this the first line of sight where the bulk of the CO_2 is in the gas-phase.