Detection of highly ionized O and Ne absorption lines in the X-ray spectrum of 4U1820-303 in the globular cluster, NGC 6624

We searched for absorption lines of highly ionized O and Ne in the energy spectra of two Low-mass X-ray binaries, 4U1820-303 in the globular cluster NGC6624 and Cyg X-2, observed with the Chandra LETG, and detected O VII, O VIII and Ne IX absorption lines for 4U1820-303. The equivalent width of the O VII K alpha line was 1.19 +0.47/-0.30 eV (90 % errors) and the significance was 6.5 sigma. Absorption lines were not detected for Cyg X-2 with a 90 % upper limit on the equivalent width of 1.06 eV for O VII K alpha. The absorption lines observed in 4U1820-303 are likely due to hot interstellar medium, because O will be fully photo-ionized if the absorbing column is located close to the binary system. The velocity dispersion is restricted to b = 200 - 420 km/s from consistency between O VII K alpha and K beta lines, Ne/O abundance ratio, and H column density. The average temperature and the O VII density are respectively estimated to be log(T[K]) = 6.2 - 6.3 and n(OVII) = (0.7 - 2.3) x 10^{-6} cm^{-3}. The difference of O VII column densities for the two sources may be connected to the enhancement of the soft X-ray background (SXB) towards the Galactic bulge region. Using the polytrope model of hot gas to account for the SXB we corrected for the density gradient and estimated the midplane O VII density at the solar neighborhood. The scale height of hot gas is then estimated using the AGN absorption lines. It is suggested that a significant portion of both the AGN absorption lines and the high-latitude SXB emission lines can be explained by the hot gas in our Galaxy.Comment: Accepted for publication in ApJ. 7 pages, 9 eps figure

Narrow linewidth, single frequency semiconductor laser with a phase conjugate external cavity mirror

We measure the spectral characteristics of an external cavity semiconductor laser which uses a phase conjugate mirror for its external reflection. This device has significant advantages over the conventional external cavity system owing to the self-aligning nature of the phase conjugate mirror. The fiber delay line self-heterodyne technique is used to measure the fundamental linewidth for single mode operation of this device. It shows the linewidth to be at least as narrow as the instrumental resolution of 100 kHz

Detection of Excess Hard X-ray Emission from the Group of Galaxies HCG62

From the group of galaxies HCG62, we detected an excess hard X-ray emission in energies above $\sim 4$ keV with \A SCA. The excess emission is spatially extended up to $\sim10'$ from the group center, and somewhat enhanced toward north. Its spectrum can be represented by either a power-law of photon index 0.8-2.7, or a Bremsstrahlung of temperature $>6.3$ keV. In the 2-10 keV range, the observed hard X-ray flux, $(1.0\pm0.3)\times10^{-12}$ erg cm$^{-2}$ s$^{-1}$, implies a luminosity of $(8.0\pm2.0)\times10^{41}$ erg s$^{-1}$ for a Hubble constant of 50 km s$^{-1}$ Mpc$^{-1}$. The emission is thus too luminous to be attributed to X-ray binaries in the memb er galaxies. We discuss possible origin of the hard X-ray emission.Comment: 6 pages, 3 Postscript figures, uses emulateapj.sty. Accepted for publication in the Astrophysical Journal Letter

The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

We describe the construction of a database of extremely metal-poor (EMP) stars in the Galactic halo whose elemental abundances have been determined. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the recent literature that report studies of EMP halo stars with [Fe/H] < -2.5. The compilation procedures for this database have been designed to assemble the 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 permits the user to explore relationships between the stored variables graphically. 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 all of the relevant papers published by December 2007. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] < -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) amount to ~30 % for [Fe/H] < -2.5. We find that known binaries exhibit different distributions of orbital period, according to whether they are giants or dwarfs, and also as a function of metallicity, although the total sample of such stars is still quite small.Comment: 24 pages, 10 figures, accepted by PASJ, final version. The SAGA database is available at http://saga.sci.hokudai.ac.j

Generalized Ginsparg-Wilson algebra and index theorem on the lattice

Recent studies of the topological properties of a general class of lattice Dirac operators are reported. This is based on a specific algebraic realization of the Ginsparg-Wilson relation in the form $\gamma_{5}(\gamma_{5}D)+(\gamma_{5}D)\gamma_{5} = 2a^{2k+1}(\gamma_{5}D)^{2k+2}$ where $k$ stands for a non-negative integer. The choice $k=0$ corresponds to the commonly discussed Ginsparg-Wilson relation and thus to the overlap operator. It is shown that local chiral anomaly and the instanton-related index of all these operators are identical. The locality of all these Dirac operators for vanishing gauge fields is proved on the basis of explicit construction, but the locality with dynamical gauge fields has not been established yet. We suggest that the Wilsonian effective action is essential to avoid infrared singularities encountered in general perturbative analyses.Comment: 11 pages. Talk given at APCTP-Nankai Joint Symposium on Lattice Statistics and Mathematical Physics, Tianjin, China, 8-11 October, 2001. To be published in the Proceedings and in Int. Jour. Mod. Phys.

Topological properties of Berry's phase

By using a second quantized formulation of level crossing, which does not assume adiabatic approximation, a convenient formula for geometric terms including off-diagonal terms is derived. The analysis of geometric phases is reduced to a simple diagonalization of the Hamiltonian in the present formulation. If one diagonalizes the geometric terms in the infinitesimal neighborhood of level crossing, the geometric phases become trivial for any finite time interval $T$. The topological interpretation of Berry's phase such as the topological proof of phase-change rule thus fails in the practical Born-Oppenheimer approximation, where a large but finite ratio of two time scales is involved.Comment: 9 pages. A new reference was added, and the abstract and the presentation in the body of the paper have been expanded and made more precis

Parachuting Behavior and Predation by Ants in the Nettle Caterpillar, Scopelodes contracta

This paper documents the bizarre descending behavior from the tree crown to the ground of the larvae of the moth, Scopelodes contracta Walker (Lepidoptera: Limacodidae) and the interaction of the larva with predatory ants. S. contracta larvae infest leaves of many tree species in urban areas and orchards in Japan. Mature larvae and leaves without basal leaf parts were found under trees of four species infested with S. contracta larvae in Osaka, Japan. Individual larvae riding on leaves were observed falling from tree crowns to the ground. Many S. contracta cocoons were found in the soil below the trees two weeks after the observed parachuting. These observations indicate that S. contracta larvae parachuted to the ground where they spin their cocoons in the soil. When a larva that had just parachuted down was returned to an arboreal twig, the larva repeated the parachuting behavior. This parachuting behavior appears to be adaptive, because larvae can descend to the ground safely and with low energy cost. Worker ants of Tetramorium tsushimae Emery (Hymenoptera: Formicidae) and Pristomyrmex punctatus Mayr (Hymenoptera: Formicidae) occasionally attacked larvae on the ground before they had a chance to burrow in the soil