Mid-infrared observations of young stellar objects in the vicinity of   sigma Orionis
  We present new mid-infrared observations of objects in the vicinity of the O-star sigma 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 sigma Ori cluster. For two of these objects we have obtained spectroscopy in the 8-13 micron range in order to investigate the chemistry of the dust grains. TX Ori exhibits a typical silicate emission feature at 10 micron, with a feature at about 11.2 micron that we identify as due to crystalline olivine. The IRAS 05358-0238 spectrum is very unusual, with a weak silicate feature and structure in the range 10-12 micron 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. 
Joana M. Oliveira, Jacco Th. van Loon (Keele University)