9,872 research outputs found
Red Runaways II: Low mass Hills stars in SDSS Stripe 82
Stars ejected from the Galactic centre can be used to place important
constraints on the Milky Way potential. Since existing hypervelocity stars are
too distant to accurately determine orbits, we have conducted a search for
nearby candidates using full three-dimensional velocities. Since the efficacy
of such studies are often hampered by deficiencies in proper motion catalogs,
we have chosen to utilize the reliable, high-precision SDSS Stripe 82 proper
motion catalog. Although we do not find any candidates which have velocities in
excess of the escape speed, we identify 226 stars on orbits that are consistent
with Galactic centre ejection. This number is significantly larger than what we
would expect for halo stars on radial orbits and cannot be explained by disk or
bulge contamination. If we restrict ourselves to metal-rich stars, we find 29
candidates with [Fe/H] > -0.8 dex and 10 with [Fe/H] > -0.6 dex. Their
metallicities are more consistent with what we expect for bulge ejecta, and so
we believe these candidates are especially deserving of further study. We have
supplemented this sample using our own radial velocities, developing an
algorithm to use proper motions for optimizing candidate selection. This
technique provides considerable improvement on the blind spectroscopic sample
of SDSS, being able to identify candidates with an efficiency around 20 times
better than a blind search.Comment: 13 pages, accepted for publication in Ap
Nearby Low-Mass Hypervelocity Stars
Hypervelocity stars are those that have speeds exceeding the escape speed and
are hence unbound from the Milky Way. We investigate a sample of low-mass
hypervelocity candidates obtained using data from the high-precision SDSS
Stripe 82 catalogue, which we have combined with spectroscopy from the 200-inch
Hale Telescope at Palomar Observatory. We find four good candidates, but
without metallicities it is difficult to pin-down their distances and therefore
total velocities. Our best candidate has a significant likelihood that it is
escaping the Milky Way for a wide-range of metallicities.Comment: 5 pages; Contribution to proceedings for "The Milky Way Unravelled by
Gaia" conference, Barcelona, Dec 201
Significant Refugee Crises Since World War II and the Response of the International Community
This article analyzes some of the significant post-World War II refugee crises and describes in summary how the international community responded to each. Overpopulation, legal and illegal migration, and repatriation of thousands of colonials have had a negative influence on public opinion with respect to rescuing and assisting refugees. Yet today the refugee problem and the attendant human suffering is growing. There are serious apprehensions about the mounting costs and the ability of those concerned to cope. The international machinery is stretched; inflation and unemployment in the industrialized world have further complicated the search for solutions. Present and future refugee crises will thus continue to test the adequacy of the international community\u27s response, and the experiences of the past may provide some, though surely not all, the answers
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