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TOPIC: Star-forming regions

Blobrana

L

Posts: 131433

Date: Jun 14 18:38 2009

Star-forming complexes	Permalink

Title: Filamentary structure of star-forming complexes Authors: Philip C. Myers The nearest young stellar groups are associated with "hubs" of column density exceeding 10^22 cm^-2, according to recent observations. These hubs radiate multiple "filaments" of parsec length, having lower column density and fewer stars. Systems with many filaments tend to have parallel filaments with similar spacing. Such "hub-filament structure" is associated with all of the nine young stellar groups within 300 pc, forming low-mass stars. Similar properties are seen in infrared dark clouds forming more massive stars. In a new model, an initial clump in a uniform medium is compressed into a self-gravitating, modulated layer. The outer layer resembles the modulated equilibrium of Schmid-Burgk (1967) with nearly parallel filaments. The filaments converge onto the compressed clump, which collapses to form stars with high efficiency. The initial medium and condensations have densities similar to those in nearby star-forming clouds and clumps. The predicted structures resemble observed hub-filament systems in their size, shape, and column density, and in the appearance of their filaments. These results suggest that hub-filament structure associated with young stellar groups may arise from compression of clumpy gas in molecular clouds. Read more (2226kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Apr 29 13:51 2009

Star-forming regions	Permalink

Title: The origin of large peculiar motions of star-forming regions and spiral structures of our Galaxy Authors: Junichi Baba, Yoshiharu Asaki, Junichiro Makino, Makoto Miyoshi, Takayuki R. Saitoh, Keiichi Wada Recent VLBI (Very Long Baseline Interferometer) observations (Xu et al. 2006; Sato et al. 2008) determined the distances and proper motions of star-forming regions in spiral arms directly. They showed that star forming regions and young stars have large non-circular motions, as large as 30 km s-1 with complex structures. Such a large motion is incompatible with the prediction of the standard theory of stationary spiral arms. We use a high-resolution, self-consistent N-body+hydrodynamical simulation to explore how the spiral arms are formed and maintained, and how star-forming regions move. We found that arms are not stationary but transient and recurrent, as suggested in alternative theories of spiral structures. Because of this transient nature of the spiral arms, star-forming regions exhibit large and complex non-circular motions, which is consistent with the VLBI observations. Due to this large non-circular motions, a kinematically estimated gas map does not represent true spiral structures in our Galaxy. Read more (1069kb, PDF) __________________

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