A consortium study of Antarctic micrometeorites recovered from the Dome Fuji Station

Deposits in the water tank at the Dome Fuji Station were collected by the 37th Japanese Antarctic Research Expedition team in 1996. We recovered 233 micrometeorites from the deposits. A consortium study was started in late 1998 to investigate mineralogy, petrology, bulk chemistry, and isotopic compositions of the micrometeorites. This is the first case of an organized study of micrometeorites in Japan, in order to establish the methods to investigate micrometeorites routinely. Consortium results on mineralogy, petrology, minor and trace element compositions, isotopic compositions of noble gases of the micrometeorites are reported in this volume. We also found a sequence of mineralogical and compositional changes of micrometeorites experienced from frictional heating during atmospheric entry. INAA and ion probe studies are now in progress

General characterization of Antarctic micrometeorites collected by the 39th Japanese Antarctic Research Expedition: Consortium studies of JARE AMMs (III)

From November 1998 to January 1999,the 39th Japanese Antarctic Research Expedition (JARE-39) undertook Japanese first large-scale collection of Antarctic micrometeorites (AMMs), with sizes larger than 10μm, at the Meteorite Ice Field around the Yamato Mountains in Antarctica (at three different locations, for a total of 24 collection sites). The number of collected AMMs larger than 40μm is estimated to be about 5000. Here we present the general characterization (i.e., micro-morphology and surface chemical composition using SEM/EDS) of ∿810 AMMs chosen from 5 of the 24 sites. Additionally, the mineral composition of 61 out of 810 AMMs was determined by Synchrotron X-ray radiation. Preliminary results on mineralogical and chemical compositions show similarities with that of previous studies, even though a pronounced alteration of some AMMs is noticed. A correlation is found between the Mg/Si ratio at the sample\u27s surfaces of unmelted AMMs and the age of snow/ice in which the AMMs are embedded

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0.08 d show positive period derivatives. Contrary to the earlier claim, we found no clear evidence for variation of period derivatives between superoutburst of the same object. We present an interpretation that the lengthening of the superhump period is a result of outward propagation of the eccentricity wave and is limited by the radius near the tidal truncation. We interpret that late stage superhumps are rejuvenized excitation of 3:1 resonance when the superhumps in the outer disk is effectively quenched. Many of WZ Sge-type dwarf novae showed long-enduring superhumps during the post-superoutburst stage having periods longer than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently, mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives and are excellent candidate for the systems around or after the period minimum of evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte