Detection of a protostellar region, in BHR 71, revealed by the IR emission of H2 in K band
Abstract
The observation of protostars in early stages of formation, is at the moment one of the major scientific goal of galactic astronomy. Important advances have been made in mm-wave radio-interferometry in identifying infall and accretion of material and in establishing the structure and evolution of circumstellar disks, in the inner reaches of which planets may form. In conjunction with still scarce observations, numerous theoretical models describe how disks may be created, which role is played by the angular momentum and the magnetic fields and how fast outflows of matter, recognised to be the signature of early star-formation, may develop. We exploit in this work the capability of the ISAAC instrument at ESO-VLT to detect extremely weak signals in the infrared (IR), reporting for the first time deep IR observations, in K band around 2 m, of vibrationally excited molecular hydrogen in the direction of the Bok globule BHR 71, a region already known as protostellar. There have been very few observations of H2 emission demonstrably associated with protostellar cores, as opposed to jets and outflows which characterize them at longer distances, and the results presented here are the first of their kind for imaging and spectroscopy of H2 in the direction of a zone around a deeply embedded protostar, opening a new window on early star formation. Our data show clearly, in the region of the IRS2 protostar (Class 0), two zones of vibrationally excited H2, separated by a narrow and darker lane. The morphology, dimensions and orientation of this lane, located at right-angles to the known outflow from IRS2, suggest its identification as a circumstellar disk. This interpretation is corroborated by the similitude of the H2 emission spectrum observed in this region with the spectrum observed at the bright apex of the other known protostar IRS1 (Class 1). An analysis of the H2 emission spectra, related to J-shocks models, shows that the gas is heated largely by processes of outflow and accretion intrinsic to the protostar.
- Publication:
-
SF2A-2002: Semaine de l'Astrophysique Francaise
- Pub Date:
- June 2002
- Bibcode:
- 2002sf2a.conf...31L