| Co-Investigator(Kenkyū-buntansha) |
KAJINO Toshitaka Theoretical Astrophysics Division , Assistant Professor, 理論天文学研究系, 助教授 (20169444)
GOUDA Naoteru Faculty of Science, University of Osaka, Assistant Professor, 大学院・理学研究科, 助教授 (50202073)
SOFUE Yoshiaki Faculty of Science, University of Tokyo, Professor, 大学院・理学研究科, 教授 (10022667)
YOSHII Yuzuru Faculty of Science, University of Tokyo, Professor, 大学院・理学研究科, 教授 (00158388)
TOSA Makoto Faculty of Science, Tohoku University, Professor, 大学院・理学研究科, 教授 (50022728)
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| Research Abstract |
The Hipparcos mission was the first space experiment dedicated to astrometry, and was accepted within the ESA scientific program in 1980. The primary objective of the mission was the determination of accurate astrometric data - positions, annual proper motions and absolute trigonometric parallaxes, at levels of I milliarcsec - for about 120000 stars. The Hipparcos Catalogue, the primary result of the observations and reduction of the satellite-acquired data, has provided great impacts on various research fields that include positional astronomy, stellar evolution, galactic astronomy, and cosmology.
Among the whole sample in the catalogue, the astrometric observations of RR Lyrae variables and metal-deficient red giants have been parts of the Hipparcos program assigned to our research group. Analyzing the data of these stars which arrived us prior to the release of the catalogue, we have found that (1) ages of old globular clusters, calibrated from the absolute magnitudes of RR Lyrae var
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iables, put severe limits on the range of cosmological parameters, and that (2) the formation of the Galaxy from the halo to disk components, as probed by kinematics of metal-poor stars, involved the slow collapse lasting several billion years.
We have also conducted the assembly of spectroscopic and photometric information for numerous metal-poor stars, for the purpose of studying early dynamical evolution of the Galaxy in the cosmological context. This is mainly because in recent years, the numbers of recognized stars with metal abundances significantly less than solar has grown enormously. So too has the quality and quantity of information available concerning their detailed abundances, velocities, and proper motions. Using newly determined (and/or refined) proper motions for over 1000 of these stars, based on results from the Hipparcos mission and various catalogs including the Southern Proper Motion catalog, the Northern Proper Motion catalog, the Astrographic Catalog, and the Digital Sky Survey obtained at STScI, we have arrived at the comprehensive view of the kinematics of the thick disk and halo components of the Galaxy. A number of interesting differences were also found between the observed properties of our non-kinematically selected sample, as compared with similar-sized, but kinematically biased samples of metal-poor stars. Less
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