We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the literature that report on studies of EMP halo stars with [Fe=H] Ä 2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe=H] Ä 2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to 30% for [Fe=H] Ä 2.5. We find that known binaries exhibit different distributions of the orbital period, according to whether they are giants or dwarfs, and also as a function of the metallicity, although the total sample of such stars is still quite small.

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We report systematic variations in the emission line ratio of the CO J = 2 − 1 and J = 1 − 0 transitions (R 2−1/1−0 ) in the grand-design spiral galaxy M51. The R 2−1/1−0 ratio shows clear evidence for the evolution of molecular gas from the upstream interarm regions, passage into the spiral arms and back into the downstream interarm regions. In the interarm regions, R 2−1/1−0 is typically < 0.7 (and often 0.4-0.6); this is similar to the ratios observed in Galactic giant molecular clouds (GMCs) with low far infrared luminosities. However, the ratio rises to > 0.7 (often 0.8-1.0) in the spiral arms, particularly at the leading (downstream) edge of the molecular arms. These trends are similar to those seen in Galactic GMCs with OB star formation (presumably in the Galactic spiral arms). R 2−1/1−0 is also high, ∼ 0.8 − 1.0, in the central region of M51. Analysis of the molecular excitation using a Large Velocity Gradient radiative transfer calculation provides insight into the changes in the physical conditions of molecular gas between the arm and interarm regions: cold and low density gas ( 10 K, 300 cm −3 ) is required for the interarm GMCs but this gas must become warmer and/or denser in the more active star forming spiral arms. The ratio R 2−1/1−0 is higher in areas of high 24µm dust surface brightness (which is an approximate tracer of star formation rate surface density) and high CO(1-0) integrated intensity (i.e., a well-calibrated tracer of total molecular gas surface density). The systematic enhancement of the CO(2-1) line relative to CO(1-0) in luminous star forming regions suggests that some caution is needed when using CO(2-1) as a tracer of bulk molecular gas mass, especially when galactic structures are resolved.

Recent paleomagnetic studies are reviewed in an effort to clarify the relationship between the intra-arc deformation of central Japan and the collision tectonics of the Izu-Bonin Arc. The cusp structure of the pre-Neogene terranes of central Japan, called the Kanto Syntaxis, suggests a collisional origin with the Izu-Bonin Arc. The paleomagnetic results and newly obtained radiometric ages of the Kanto Mountains revealed the Miocene rotational history of the east wing of the Kanto Syntaxis. More than 90" clockwise rotation of the Kanto Mountains took place after deposition of the Miocene Chichibu Basin (planktonic foraminifera1 zone of N.8: 16.6-15.2 Ma). After synthesizing the paleomagnetic data of the Japanese Islands and collision tectonics of central Japan, it appears that approximately a half rotation (40-50") probably occurred at ca 15Ma in association with the rapid rotation of Southwest Japan. The remainder (5040") continued until 6 Ma, resulting in the sharp bent structure of the pre-Neogene accretionary complexes (Kanto Syntaxis). The latter rotation seems t o have been caused by the collision of the Izu-Bonin Arc on the northwestward migrating Philippine Sea Plate.