Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........19t&link_type=abstract
PhD Dissertation, California Univ. Berkeley, CA United States
Astronomy and Astrophysics
Astronomy
5
Bipolarity, Stellar Evolution, Stellar Envelopes, Stellar Models, Stellar Structure, Stellar Winds, Asymmetry, Clumps, Dust, Infrared Astronomy Satellite, Kinematics, Spatial Distribution
Scientific paper
Stars begin their lives deeply embedded in clouds of gas and dust, and in order to become visible, they have to disperse their obscuring environment. How this transition from embedded object to visible star occurs is not yet well understood, although it is often assumed that a strong wind from the star, in the form of a bipolar outflow, clears the stellar environment. In this thesis, we study the dense gas around two young stars that excite bipolar outflows, paying special attention to its kinematics and spatial distribution. We find that despite differences in the mass and evolutionary status of the two objects, in both cases the dense gas appears in the process of acceleration by the outflow, and that its spatial distribution has been already affected by the acceleration. Our study of the Mon R2 outflow, powered by a massive and relatively evolved young star, shows the long term effect of the outflow-core interaction. A large cavity has been evacuated in the core, and the accelerated gas moves along its walls. This accelerated gas is composed of discrete clumps that have the same density, temperature, and chemical abundance as the gas in the ambient cloud. The clumps, therefore, represent fragments of the dense core that have been accelerated, and the whole outflow, in fact, seems to consist of clumbs, of which only the largest ones are well distinguished by our observations. The outflow around IRAS 3282, on the other hand, is one of the youngest and most collimated outflows known. Despite being surrounded by a rather asymmetric gas distribution, the two opposed lobes present similar collimation, indicating that the mechanism that causes it (most likely a jet) is able to maintain the collimation under different environments. The two outflow lobes, however, present different distributions of mass with velocity, with the lobe that travels through more dense gas having a larger amount of low velocity material. This slower lobe, in addition, presents a shear-like velocity pattern, with the fastest gas moving along the outflow axis and the slower gas moving at some distance from it.
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