Nebular emission-line profiles of Type Ib/c supernovae – probing the ejecta asphericity

In order to assess qualitatively the ejecta geometry of stripped-envelope core-collapse supernovae (SNe), we investigate 98 late-time spectra of 39 objects, many of them previously unpublished. We perform a Gauss-fitting of the [O  i ]  λλ6300, 6364  feature in all spectra, with the position, full width at half maximum and intensity of the  λ6300  Gaussian as free parameters, and the  λ6364  Gaussian added appropriately to account for the doublet nature of the [O  i ] feature. On the basis of the best-fitting parameters, the objects are organized into morphological classes, and we conclude that at least half of all Type Ib/c SNe must be aspherical. Bipolar jet models do not seem to be universally applicable, as we find too few symmetric double-peaked [O  i ] profiles. In some objects, the [O  i ] line exhibits a variety of shifted secondary peaks or shoulders, interpreted as blobs of matter ejected at high velocity and possibly accompanied by neutron-star kicks to assure momentum conservation. At phases earlier than ∼200 d, a systematic blueshift of the [O  i ]  λλ6300, 6364  line centroids can be discerned. Residual opacity provides the most convincing explanation of this phenomenon, photons emitted on the rear side of the SN being scattered or absorbed on their way through the ejecta. Once modified to account for the doublet nature of the oxygen feature, the profile of Mg  i ]  λ4571  at sufficiently late phases generally resembles that of [O  i ]  λλ6300, 6364  , suggesting negligible contamination from other lines and confirming that O and Mg are similarly distributed within the ejecta.     

The first confirmed Perseid lunar impact flash

The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18^h28^m27^s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48±1° N and 72±2° E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of 2×¹⁰⁻³. Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles.     

Notes on extended–range atmospheric prediction in the Northern Hemisphere winter

We examined the characteristic feature and predictability of low frequency variability (LFV) of the atmosphere in the Northern Hemisphere winter (January and February) by using the empirical orthogonal functions (EOFs) of the geopotential height at 500 hPa. In the discussion, we used the EOFs for geostrophic zonal wind (Uznl) and the height deviation from the zonal mean (Zeddy). The set of EOFs for Uznl and Zeddy was denoted as Uznl-1. Uznl-2, …, Zeddy-1, Zeddy-2…, respectively. We used the data samples of 396 pentads derived from 33 years of NMC, ECMWF and JMA analyses, from January 1963 to 1995. From the calculated scores for Uznl-1, Uznl-2, Zeddy-1, Zeddy-2 and so on we found that Uznl-1 and Zeddy-1 were statistically stable and their scores were more persistent than those of the other EOFs. A close relationship existed between the scores of Uznl-1 and those of Zeddy-1 30-day forecast experiments were carried out with the medium resolution version of JMA global spectral model for 20 cases in January and February for the period of 1984-1992. Results showed that Zeddy-1 was more predicta?ble than the other EOFs for Zeddy Considering these results, we argued that prediction of the Zeddy-1 was to be one of the main target of extended range forecasting     

Fluctuation in volume transport distribution accompanied by the Kuroshio front migration in the Tokara Strait

A relation between migration of the Kuroshio front and fluctuation of distribution of volume transport in the Tokara Strait was described, using sea level records at five tide gauge stations around the strait and data which were composed of sea surface temperature, XBT casts, sea surface salinity and velocities at 20 m, 75 m and 150 m depths taken en route a ferryboat. The Kuroshio front extends to about 150 m depth. The sea surface salinity and the horizontal velocities abruptly change at the front. There is a good correlation in a period range from half a month to two months between the migration of the front, which is not only at the surface but also in the subsurface, and the sea level fluctuation at Nakano-shima. A northward migration of the front with a period range from 17 to 50 days decreases the transport in the southern strait between Naze and Nakano-shima but increases in the northern strait between Nakano-shima and Sata-misaki. The northward migration intensifies inflow into Kagoshima Bay and the Ohsumi Branch Current. Correlation between the transport in the northern strait and the Ohsumi Branch Current is significant in the period range from 30 to 50 days. In this significant period range, the former leads the latter by about 3 days.     

Stratospheric ozone response to a solar proton event: Hemispheric asymmetries

Ozone depression in the polar stratosphere during the energetic solar proton event on 4 August 1972 was observed by the backscattered ultraviolet (BUV) experiment on the Nimbus 4 satellite. Distinct asymmetries in the columnar ozone content, the amount of ozone depressions and their temporal variations above 4 mb level (38 km) were observed between the two hemispheres. The ozone destroying solar particles precipitate rather symmetrically into the two polar atmospheres due to the geomagnetic dipole field These asymmetries can be therefore ascribed to the differences mainly in dynamics and partly in the solar illumination and the vertical temperature structure between the summer and the winter polar atmospheres. The polar stratosphere is less disturbed and warmer in the summer hemisphere than the winter hemisphere since the propagation of planetary wave from the troposphere is inhibited by the wind system in the upper troposphere, and the air is heated by the prolonged solar insolation. Correspondingly, the temporal variations of stratospheric ozone depletion and its recovery appear to be smooth functions of time in the (northern) summer hemisphere and the undisturbed ozone amount is slighily, less than that of its counterpart. On the other hand, the tempotal variation of the upper stratospheric ozone in the winter polar atmosphere (southern hemisphere) indicates large amplitudes and irregularities due to the disturbances produced by upward propagating waves which prevail in the polar winter atmosphere. These characteristic differences between the two polar atmospheres are also evident in the vertical distributions of temperature and wind observed by balloons and rocker soundings.     

Microbial ecology concerning to the degradation of nucleic acid in the marine environment

This article summarizes the author's current work on microbial degradation of nucleic acid. The aim of this work is to elucidate parts of the saprogenic process in the marine ecosystem through the study of the behavior of nucleic acid-hydrolyzing bacteria inhabiting seawater and sediments.Considerably large population of nucleic acid-hydrolyzing bacteria was found to occur in seawater and sediments. The main genera of these microbes areVibrio spp. in coastal seas, andPseudomonas spp. in the oceanic waters. As a result of microbial attack, nucleic acid components are released into seawater. The properties of extracellular nuclease produced by a marineVibrio sp. are well adapted to the seawater environment; consequently this enzyme has high activity and stability in seawater. By determining nuclease activity in seawater and sediments, the intensities of nucleic acid-hydrolysisin situ were evaluated.Distribution patterns of marine bacteria are also discussed in reference to the occurrence of phytoplankton in seawater.