Interferometric Observations of the L 1157 and HH 211 Molecular Outflows

Details Interferometric Observations of the L 1157 and HH 211 Molecular Outflows Interferometric Observations of the L 1157 and HH 211 Molecular Outflows

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt........27g&link_type=abstract

Ph.D. thesis, Univ. Grenoble, France, (1997)

Mathematics

Logic

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Scientific paper

One of the signatures of the powerful ejections of matter that occur during the very first steps of star formation is the presence of bipolar molecular outflows around most protostars. This thesis studies the internal structure of two extremely young outflows, through millimeter interferometric observations performed with the IRAM Plateau de Bure interferometer. Large mosaics (of one complete lobe of L 1157 and of the whole HH 211 flow) are presented, for various molecular transitions at λ 3 mm and/or λ 1.3 mm. These maps belong to the very first images of molecular outflows that have been obtained at such a high angular resolution (1--3 arcsecond). The main results of this thesis can be summarized as follows: • Two distinct CO cavities are present in the southern lobe of the L 1157 outflow, with slightly different axes. Their brightness distributions and kinematical properties have been explained by a precession model. The SiO emission traces two main shocks, which present a remarkable morphological agreement with the CO flow. Each CO cavity is associated with a shock placed exactly at its apex. The density and velocity distributions of the cavities and (bow-)shocks have also been investigated. • Continuum and spectral observations of the protostar L 1157-mm have been obtained and provide a detailed description of the close environment of such an extremely young (Class 0) source. The protostellar envelope is strongly perturbated by the powerful outflow. Modelisation shows that such an interacting structure can explain the observed λ 3 mm continuum morphology and the spectral energy distribution of the source. A signature of gravitational infall has also been detected in the 13CO J = 1 --> 0 line. • The HH 211 outflow, observed through the CO J = 2 --> 1 line, presents a remarkable structure in which a fast, extremely collimated, molecular jet emerges from a flattened protostellar condensation. This jet terminates exactly at the position of strong H2 bow-shocks. It is surrounded by a low-velocity CO cavity, whose shape can be accurately reproduced by simple shock-travelling models. HH 211 appears thus to be a prime test-case for the jet-driven outflow paradigm. Several aspects of the L 1157 and HH 211 observations are also discussed, among which the formation mechanisms of molecular outflows (the propagation of large bow-shocks seems to be the most promising model) and the formation processes of the SiO molecule within the flows. Finally, the second part of this thesis presents the algorithms that have been developped to reconstruct and deconvolve images in the case of mosaic interferometric observations. These methods have been used for the L 1157 and HH 211 observations. A multi-resolution algorithm based on CLEAN and adapted to the case of mosaics is also presented.

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