Searching for molecular hydrogen mid-infrared emission in the circumstellar environments of Herbig Be stars
Laboratoire d'Astrophysique de Grenoble, CNRS, Université Joseph-Fourier, UMR 5571, 38041 Grenoble Cedex 09, France e-mail: firstname.lastname@example.org
2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
3 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
4 Laboratoire AIM, CEA/DSM, CNRS, Université Paris Diderot, DAPNIA/Service d'Astrophysique, Bât. 709, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
Accepted: 30 June 2008
Context. Molecular hydrogen (H2) is the most abundant molecule in the circumstellar (CS) environments of young stars, and is a key element in giant planet formation. The measurement of the H2 content provides the most direct probe of the total amount of CS gas, especially in the inner warm planet-forming regions of the disks.
Aims. Most Herbig Be stars (HBes) are distant from the Sun and their nature and evolution are still debated. We therefore conducted mid-infrared observations of H2 as a tracer of warm gas around HBes known to have gas-rich CS environments.
Methods. We report a search for the H2 S(1) emission line at 17.0348 μm in the CS environments of 5 HBes with the high resolution spectroscopic mode of VISIR (ESO VLT Imager and Spectrometer for the mid-InfraRed).
Results. No source shows evidence for H2 emission at 17.0348 μm. Stringent 3σ upper limits on the integrated line fluxes are derived. Depending on the adopted temperature, limits on column densities and masses of warm gas are also estimated. These non-detections constrain the amount of warm (>150 K) gas in the immediate CS environments of our target stars to be less than ∼.
Key words: stars: circumstellar matter / stars: formation / stars: pre-main sequence / ISM: molecules
© ESO, 2008