Astronomy & Astrophysics

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Issue		A&A Volume 418, Number 2, May I 2004
Page(s)		663 - 673
Section		Stellar structure and evolution
DOI		10.1051/0004-6361:20034518

A&A 418, 663-673 (2004)
DOI: 10.1051/0004-6361:20034518

Mid-infrared observations of young stellar objects in the vicinity of $\mathsf{\sigma}$ Orionis

J. M. Oliveira and J. Th. van Loon

Astrophysics Group, School of Chemistry & Physics, Keele University, Staffordshire ST5 5BG, UK
(Received 15 October 2003 / Accepted 26 January 2004)

Abstract
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 $\mu$ m range in order to investigate the chemistry of the dust grains. TX Ori exhibits a typical silicate emission feature at 10 $\mu$ m, with a feature at about 11.2 $\mu$ m 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 $\mu$ m 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.

Key words: stars: circumstellar matter -- stars: pre-main sequence -- stars: planetary systems: protoplanetary disks -- infrared: stars -- Galaxy: open clusters and associations: individual: $\sigma$ Orionis

Offprint request: J. M. Oliveira, joana@astro.keele.ac.uk

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Mid-infrared observations of young stellar objects in the vicinity of Orionis

Mid-infrared observations of young stellar objects in the vicinity of $\mathsf{\sigma}$ Orionis