ISO spectroscopy of young intermediate-mass stars in the BD+40 degrees 4124 group

We present the results of ISO SWS and LWS grating scans towards the three b rightest members of the BD+40 degrees 4124 group in the infrared: BD+40 deg rees 4124 (B2Ve), LkH alpha 224 (A7e) and the embedded source LkH alpha 225 . Emission from the pure rotational lines of H-2. from re-vibrational trans itions of CO. from PAHs. from H I recombination lines and from the infrared line structure lines of [Fe II], [Si II], [S I], [O I], [O III] and [C III was detected. These emission lines arise in the combination of a low-densi ty (approximate to 10(2) cm(-3)) H II region with a clumpy PDR in the case of BD+40 degrees 4124. The lower transitions of the infrared H I lines obse rved in BD+40 degrees 4124 are optically thick: most likely they arise in e ither a dense wind or a circumstellar disk. This same region is also respon sible for the optical H1 lines and the radio continuum emission. In the lin es of sight towards LkH alpha 224 and LkH alpha 225, the observed emission lines arise in a non-dissociative shock produced by a slow (approximate to 20 km s(-1)) outflow arising from LkHa 225. Toward LkH alpha 225 WE also ob serve a dissociative shock, presumably located closer to the outflow source than the non-dissociative shock. Tn the line of sight towards LkH alpha 22 5 we observed absorption features due to solid water ice and amorphous sili cates, and due to gas-phase H2O, CO and CO2. No solid CO2 was detected towa rds LkH alpha 225. making this the first line of sight where the bulk of th e CO2 is in the gas-phase.