2004A&A...418..663O

We present new mid-infrared observations of objects in the vicinity of the O-star σ Orionis, obtained with TIMMI-2 at ESO. By constraining their near- and mid-infrared spectral energy distributions, we established the nature of previously known IRAS sources and identified new mid-infrared sources as young stellar objects with circumstellar disks, likely massive members of the σ Ori cluster. For two of these objects we have obtained spectroscopy in the 8-13µm range in order to investigate the chemistry of the dust grains. TX Ori exhibits a typical silicate emission feature at 10µm, with a feature at about 11.2µm that we identify as due to crystalline olivine. The IRAS05358-0238 spectrum is very unusual, with a weak silicate feature and structure in the range 10-12µm that may be explained as due to self-absorbed forsterite. We also provide the first evidence for the presence of circumstellar disks in the jet sources Haro 5-39/HH 447, V510 Ori/HH 444 and V603 Ori/HH 445.