LAMAp-LERMA Observatoire de Paris et Université Cergy-Pontoise
Observatoire de Meudon
SF2A- ASHRA- ENS
92195
Meudon Cedex, F
Presentation 1 : Poster
Detection of a protostellar region, in BHR 71, revealed by the IR emission of H$_2$ in K band
JL Lemaire$^1$, D Field$^2$, G Pineau des Forêts$^3$, G Callejo$^1$ // 1 LAMAp-LERMA (FRE 2460 du CNRS), Universit\'e de Cergy-Pontoise \& Observatoire de Paris // 2 Institute for Physics and Astronomy, University of Aarhus, Denmark // 3 Institut d'Astrophysique Spatial, Orsay \& Observatoire de Paris
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.
Presentation 2 : Poster
Probing the H$_2$ formation on the surface of grains in the laboratory, in connection with observations of H$_2$ emission in the interstellar medium
J-H Fillion, F. Dulieu, S. Baouche, G. Callejo, J-L.Lemaire //LAMAp, Université de Cergy-Pontoise 95031 Cedex France // and LERMA - FRE2460 du CNRS. Observatoire de Paris France
It is well-established that the gas-grain interaction plays an important
role for the formation of molecules, in particular in the case of H2, whose
abundance relative to H atoms in the ISM cannot be accounted for by gas-phase
reactions. Whilst theoretical models of the gas-grain interaction have been
recently developed, very few experimental studies of the processes involved
have been performed to test their predictions. In particular data concerning
the internal energy state of nascent H2 molecules are still scarce or
conspicuously absent. These data relating to H2 are of fundamental importance
with respect to the energy balance in the ISM.
An experimental facility devoted to the study of molecular hydrogen formation
on surfaces that mimics dust grains under physical conditions relevant to
the interstellar medium is being developed in our laboratory. Our measurements
will provide both internal energy and velocity distributions of the desorbed molecules.
This work is of direct and fundamental interest for the understanding of
H2 infrared observations in the ISM (dark clouds, Bok globules, star forming
regions and molecular cloud in general) which are performed in collaboration
in our group. The interpretation of such observations makes use of theoretical
astrophysical models which include detailed chemical pathways and physical
processes save data related to grain-surface processes which are only
treated at the moment in a phenomenological way.