Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aj....125.1519f&link_type=abstract
The Astronomical Journal, Volume 125, Issue 3, pp. 1519-1529.
Astronomy and Astrophysics
Astronomy
6
Ism: Clouds, Stars: Kinematics, Surveys
Scientific paper
The visual interstellar extinction in the Northern and Southern Coalsack regions is estimated from a photographic survey of proper motion and B,V photometry of 6×104 stars as faint as apparent magnitude 14 over a field of view of 6°×6° in each region. Each cloud is located at a distance of about 160+/-50 pc from the Sun and exceeds the mean interstellar extinction by more than 0.7+/-0.1 mag. Galactic plane orbits of 103 stars located at the same distance of 160+/-50 pc from the Sun in these regions show a semimajor axis of 8.45+/-0.15 kpc and a mean inclination of 0.3d+/-0.2d over the Galactic plane, suggesting a mean impact parameter of 9+/-3 pc with diffuse clouds of relative velocity on the order of 4+/-1 km s-1. The weak distant encounter of stars with the cold neutral medium can be explained by a mean mass of about 2500+/-1250 Msolar for the gas and dust content in order to account for the diffusion of stellar orbits. A mean displacement of 0.012"+/-0.001" yr-1 of the western limb of the Southern Coalsack is estimated in the northwest direction and permits a search for strong close stellar encounters. The transfer of angular momentum between the interstellar medium and the scattering of stellar orbits resulting from the encounters suggests a dissipation rate of (2.0+/-0.7)×10-4 Msolar yr-1, leading to an equipartition time of 12+/-4 Myr. A spin rate of 0.25+/-0.05 km s-1 pc-1 of the diffuse clouds in the Southern Coalsack is measured and interpreted as the result of the perturbation induced by stellar systems during flyby encounters with a crossing time of 3 Myr, suggesting a cloud core radius of 1 pc.
Argyle Robert W.
Fresneau Alain
Vaughan Alan E.
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