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Abstract: Cold cores in interstellar molecular clouds represent the very first phase instar formation. The physical conditions of these objects are studied in orderto understand how molecular clouds evolve and how stellar masses aredetermined. The purpose of this study is to probe conditions in the dense,starless clump Ophichus D Oph D. The ground-state 110-111 rotationaltransition of ortho-H2D+ was observed with APEX towards the density peak of OphD. The width of the H2D+ line indicates that the kinetic temperature in thecore is about 6 K. So far, this is the most direct evidence of such cold gas inmolecular clouds. The observed H2D+ spectrum can be reproduced with ahydrostatic model with the temperature increasing from about 6 K in the centreto almost 10 K at the surface. The model is unstable against any increase inthe external pressure, and the core is likely to form a low-mass star. Theresults suggest that an equilibrium configuration is a feasible intermediatestage of star formation even if the larger scale structure of the cloud isthought to be determined by turbulent fragmentation. In comparison with theisothermal case, the inward decrease in the temperature makes smaller, i.e.less massive, cores susceptible to externally triggered collapse.



Autor: J. Harju 1, M. Juvela 1, S. Schlemmer 2, L.K. Haikala 1, K. Lehtinen 1, K. Mattila 1 1 Observatory, University of Helsinki, Finla

Fuente: https://arxiv.org/



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