bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of a Water-Vapor Megamaser in the Active Galaxy NGC 5793
Authors: Hagiwara Yoshiaki , Kohno Kotaro , Kawabe Ryohei , Nakai Naomasa
Published: March 2014

We have found an extragalactic water-vapor megamaser source in NGC 5793, an edge-on spiral galaxy. Its spectral profile shows two distinct high-velocity maser features, one on each side of the systemic velocity of the galaxy. They are almost symmetrically offset from the systemic velocity. The isotropic luminosity of the features is as large as 125 L⊙ at a distance of 50 Mpc. Weaker features at the systemic velocity were possibly detected. We have constructed a model which explains our observational data. The HO maser emission is emitted from a nearly edge-on circumnuclear disk, or torus, whose diameter is estimated to be larger than 4–20 pc, with a rotation velocity of Vrot = 245 km s−1 at an inferred inclination angle of 73°. The high-velocity features arise from gas at the tangential regions of the disk, or torus, and the systemic features from the region in our line of sight toward the center. In our model, the nuclear mass confined within the disk or torus is larger than 1.5 × 108M⊙.
The Proper Motion of Individual Sunspots
Authors: Herdiwijaya Dhani , Makita Mitsugu , Anwar Bachtiar
Published: March 2014

The proper motions of 276 individual sunspots were observed with a triple-exposures method, and then analyzed. Their linear drifts give the mean motions (degree day−1), which, depending on the heliographic latitude B, are the differential rotation, ω(B) = 14.5 – 2.5sin2B, and the equatorward meridional flow, vB = −0.05sin 2B. The deviations of the linear drift from the mean motions have a small correlation between the longitudinal and latitudinal ones, which correspond to the equatorial acceleration. The deviations in longitude are clearly separated by the sunspot polarities. The average separation velocity between the preceding and following polarities is 52 m s−1. The drifts of individual sunspots corrected for the mean motion are the smallest for the Zürich GHJ class. However, they are fairly large and may influence the determination of the mean motion. Short-term variations appear as positional deviations from the linear-drift curve. These fast drifts are detected in the active Zürich classes, and are one order of magnitude larger than the linear drift.
Two-Millimeter Observations of the Starburst Galaxy M82
Authors: Kuno Nario , Matsuo Hiroshi
Published: March 2014

The 2 mm continuum emission in the nuclear region of the archetypal starburst galaxy M82 was mapped with the Nobeyama 45-m telescope using a bolometer array (NOBA). The 2 mm map shows a central concentration with a single peak which is coincident with the 1.3 mm and 3.3 mm continuum peaks and an extended component that reaches up to 400 pc above and below the galactic plane. The good agreement in size and morphology between the extended structures and the dust lanes seen in the optical image or the spurlike features seen in CO maps suggests that these structures are associated with dust outflows. From a comparison between a 2 mm map and CO maps, it is suggested that the 2 mm continuum traces the distribution of neutral gas more precisely than does the CO emission.
A Nonlinear-Open-System Model for Star Formation in Spiral Galaxies
Authors: Kamaya Hideyuki , Takeuchi Tsutomu T.
Published: March 2014

We re-examine the discovery of short star-forming duration in late-type galaxies by Tomita et al. (1996 PASJ 48, 285) and propose another interpretation about their results. According to their discussion, in spiral galaxies, especially in early-type spirals, star-formation eras continue for no more than several times 107) years. Moreover, they showed the number distribution of star-formation activities in spiral galaxies and concluded that the dispersion of the distribution is at least 1.5 orders of magnitude. From the above results, we interpret that galaxies must have repetitive star-formation histories. This is because the dispersions easily emerge if recurrent star formations take place. Here, we also note that their results are derived mainly from the data expressing information of the cold component of the interstellar medium (ISM). Turning now to theoretical studies, it is known that a galaxy can exchange its phase of ISM recurrently as a nonlinear open system. Previously, this model was restricted to classes of dwarf galaxies, since there have been no observational evidence indicating cyclic phenomena in an extent of giant galaxies before Tomita et al. We must note that the period of the cycle is about several times 107 years. This period of a cyclic model of ISM is also determined by the evolution of the cold component of ISM. Thus, we comment that both the observational and theoretical periods of cyclic star formation are of the same order. This coincidence indicates that spiral galaxies are nonlinear open systems.
Kinematical Properties of Giant Molecular Clouds and Star Forming Efficiency
Authors: Ikuta Chisato , Sofue Yoshiaki
Published: March 2014

We are interested in the relationship between interacting luminous galaxies and their star forming efficiency. However, because of the limitation of available data, we have studied kinematic properties of giant molecular clouds (GMCs) associated with the star-forming regions in our Galaxy. We found that the star-forming efficiency (SFE) is correlated not only with the gas density (n), but also strongly with the velocity dispersion (σv) and the mass of a GMC. We obtained a modified Schmidt's law by fitting the derived SFE to the gas density and velocity dispersion to be: SFE ∝ nα σ αv, where the indices were determined as α ∼ 0.03 and β ∼ −3.3. This implies that stars are born more efficiently in a quiet cloud than in a disturbed cloud, and that the SFE is strongly dependent on the kinematical property of gas clouds.
Stability Condition of the Kelvin-Helmholtz Instability for the Two-Component Protogalaxy
Authors: Kamaya Hideyuki
Published: March 2014

Within the context of the evolution of two-component protogalaxies, we discuss the stability condition of the Kelvin-Helmholtz (KH) instability on a boundary where evaporation of a denser component (cloud) or condensation of a diffuser component (hot gas) is expected. It has been stressed that the stability condition for the KH instability may determine the global properties of protogalaxies. However, discontinuous phase transition layer was assumed between the two phases in previous studies, though that layer is never a step condition. It is known that when a density continuity on the boundary is concerned, the KH instability is stabilized by gravity if the well-known Richardson criterion is satisfied : J > 0.25, where J is called the Richardson number. Especially, for the physical parameters of the two-component model of a protogalaxy, we find that J is much smaller than 0.25. The Richardson criterion is the stable condition due to gravity (we do not judge whether the adopted condition becomes unstable). Then, the smallness of J means that we can neglect the stabilization due to the self-gravity of the denser cloud component. Our conclusion supports the justification of the stability condition for the cloud phase given by the previous study.
Oxygen-Line Formation in Population-II A-Type Stars
Authors: Takeda Yoichi
Published: March 2014

The non-LTE formation of neutral oxygen lines in the visible (λ 6156–8) and near-IR (λ 7771–5) region was studied, and extensive grids of theoretical non-LTE equivalent widths and abundance corrections were computed in the parameter range of −2 ≤ [Fe/H] ≤ 0, 7000 K ≤Teff ≤ 14000 K, and 3.0 ≤ log g ≤ 4.0, with the intention of applying them to A-type stars, especially Population-II stars such as horizontal-branch objects. It was found that the inclusion of UV Lyman lines (such as Lyman β overlapping with a strong OI resonance transition) in the background opacity may be important, which tends to suppress the non-LTE effect, especially for the metal-deficient case. Nevertheless, the resulting non-LTE correction for OI 7771–5 is still of considerable amount (≳ 0.5–1.0 dex), even in the weak-line cases of low abundance, and should inevitably be taken into account when determining oxygen abundance from this near-IR triplet.
Repetitive Rebrightening in the Dwarf Nova EG CANCRI
Authors: Osaki Yoji , Shimizu Soichi , Tsugawa Motohiko
Published: March 2014

A dwarf nova of the WZ Sge-type, EG Cnc, which had a superoutburst in 1996 December after 19 years of dormancy, exhibited, after the end of the main outburst, six repetitive short outbursts with a mean interval of about 7 days. We propose that this rebrightening phenomenon of EG Cnc may have been produced by a thermal disk instability, which could in turn have been caused by a temporal increase in the viscosity at a cold state. We suggest that an increase in viscosity in quiescence could be produced by a highly turbulent state in the disk due to an after-effect of the main outburst. Our numerical simulations based on this model can reproduce very well the observed light curve of EG Cnc. We discuss a possible cause why the WZ Sge-type dwarf novae show post-outburst rebrightening.
On the Keplerian Rotation Curves of Galaxies
Authors: Honma Mareki , Sofue Yoshiaki
Published: March 2014

We propose a criterion for examining whether or not the uncertainty of the outer rotation curves is sufficiently small to distinguish a Keplerian rotation curve from flat ones. We have applied this criterion to both Keplerian and non-Keplerian rotation curves so far obtained, and investigated their relative fraction. We also studied the minimum extent of the dark halos indicated by non-Keplerian rotation curves using the criterion. We have found that one cannot rule out the possibility that a significant fraction of rotation curves become Keplerian within 10-times the disk scale length. If the Keplerian rotation curves so far observed trace the mass truncation, several galaxies may have rather small halos, the extent of which is not larger than twice that of the optical disk.
The PCI Interface for GRAPE Systems: PCI-HIB
Authors: Kawai Atsushi , Fukushige Toshiyuki , Taiji Makoto , Makino Junichiro , Sugimoto Daiichiro
Published: March 2014

We developed a PCI interface for GRAPE systems. GRAPE (GRAvity piPE) is a special-purpose computer for gravitational N-body simulations. A GRAPE system consists of GRAPE processor boards and a host computer. GRAPE processors perform the calculation of gravitational forces between particles. The host computer performs the remaining calculations. The newest of the GRAPE machines, GRAPE-4, has achieved a peak performance of 1.08 Tflop. The GRAPE-4 system uses TURBOChannel for the interface to the host, which limits the selection of the host computer. The TURBOChannel bus is not supported by any of recent workstations. We have developed a new host interface board which adopts the PCI bus instead of the TURBOChannel. PCI is an I/O bus standard developed by Intel. It has a fairly high peak transfer speed, and is available on a wide range of computers, from PCs to supercomputers. Thus, the new interface allows us to connect GRAPE-4 to a wide variety of host computers. In test runs with a Barnes-Hut treecode, we found that the performance of the new system with the PCI interface is 40% better than that of the original system.
Detection of Synchronic Bands in the Dust Tail of Comet C/Hale-Bopp 1995 O1
Authors: Watanabe Jun-Ichi , Fukushima Hideo , Kinoshita Daisuke , Sugawara Ken , Takata Masayuki
Published: March 2014

An imaging observation of the dust tail of Comet C/Hale-Bopp 1995O1 was carried out from 1997 March 5 through 9, using a wide-field CCD imaging camera. We detected several striae of degree scale in the dust tail, which could be recognized for the whole observed period. On the basis of a synchrone-syndyne analysis, these striae do not follow any synchrone or syndyne curves. We conclude that these are synchronic bands, which are thought to be made of dust grains originating through secondary processes in the outer coma or in the dust tail. The heliocentric distance of the comet was about 1 AU, which is the greatest distance at which any such synchronic bands have been detected. We report preliminary results of an analysis of these striae, and discuss some of their characteristics, in this paper.
Effects of Mean Magnetic Fields on Turbulence in Accretion Disks
Authors: Nakao Yasushi
Published: March 2014

A model of magnetohydrodynamic (MHD) turbulence in accretion disks with mean magnetic fields has been constructed using a second-order closure modeling of turbulence. The transport equations of the Reynolds stress tensor, the Maxwell stress tensor, and the cross-helicity tensor (the correlation of the velocity fluctuation and the magnetic fluctuation) are closed by second-order quantities using a two-scale direct interaction approximation (TSDIA). The quantities appearing in these equations are considered to be those averaged in the vertical direction of the disks; also, stationary turbulence is assumed. We are interested only in the effects of the mean magnetic fields on the turbulence in the disk, i.e., no dynamo processes are considered, and the mean magnetic fields are supposed to be embedded in the disk a priori. The results show that the presence of a radial mean field enhances the turbulent viscosity (and the so-called α-parameter value) in the disk. This suggests that the radial mean magnetic field has something to do with advection-dominated disks, in which a rather large viscosity is needed. On the other hand, a toroidal mean field diminishes the strength of the turbulence. Therefore, the strength of the turbulence in the accretion disk is determined by competition between the above-mentioned two opposite effects of the mean fields.
Radiative Avalanche Driven by Spherical Starbursts
Authors: Fukue Jun , Umemura Masayuki , Mineshige Shin
Published: March 2014

We examine a radiative avalanche for the case of spherically distributed sources. A radiative avalanche is a new mechanism, in which the mass-accretion of the nuclear disk is driven via radiation drag exerted by stellar radiation from circumnuclear starburst regions, and which is expected to be a link between starburst activities and AGNs. The results of the present spherical case are qualitatively similar to those of the ring-like case. However, the solid angle subtended by the starburst region is large and the radiation field of the starburst region has no angular momentum, which are in favor for the avalanche model. In addition, an avalanche can take place continuously from the outside to the inside of the starburst region in the spherical case.
Cosmological Implications of Number Counts of Clusters of Galaxies: log N–log S in X-Ray and Submm Bands
Authors: Kitayama Tetsu , Sasaki Shin , Suto Yasushi
Published: March 2014

We have computed the number counts of clusters of galaxies, the log N–log S relations, in X-ray and submm bands based on the Press-Schechter theory. We paid particular attention to a set of theoretical models which well reproduce the ROSAT soft X-ray log N–log S, and explored possibilities to further constrain the models from future observations in hard X-ray and submm bands. The former is closely related to the ASCA, AXAF, and Astro-E missions, while the latter to the PLANCK and LMSA projects. We have shown that one can break the degeneracy in an acceptable parameter region on the Ω0–σ8 plane by combining the X-ray and submm number counts. Models which reproduce the ROSAT 0.5–2 keV band log N–log S will have N(> S) ∼ (150–300)(S/10−12 erg cm−2 s−1)−1.3 str−1 at S ≳ 10−12 erg cm−2 s−1 in the 2–10 keV band, and N(> Sv) ∼ (102–104)(Sv/100 mJy)−1.5 str−1 at Sv ≳ 100 mJy in the submm (0.85 mm) band. The amplitude of log N–log S is very sensitive to the model parameters in the submm band. We also computed the redshift evolution of the cluster number counts and compared it with that of the X-ray brightest Abell-type clusters. The results, although still preliminary, point to low density (Ω0 ∼ 0.3) universes. The contribution of clusters to the X-ray and submm background radiations is shown to be insignificant in any model compatible with the ROSAT log N–log S relation.
The Magnetic Ordering of Graphite Grains and an Experimental Application to Grain Alignment
Authors: Chihara Hiroki , Uyeda Chiaki , Tsuchiyama Akira , Yamanaka Takamitsu
Published: March 2014

The temperature dependence of diamagnetic grain orientation is reported for the first time concerning micron-sized graphite samples. An experimental method was developed for the purpose of studying the mechanism of interstellar grain alignment. The experiment was carried out in the temperature range from room temperature to 180 K, using ethanol as the suspending medium. The field of full orientation HS decreased from 380 G to 260 G as the temperature decreased from room temperature to 180 K. The average sizes of the samples were 2.5 ± 0.2 μm and 3.8 ± 0.2 μm in diameter, and the thickness was 0.3 ± 0.2 μm. This temperature dependence of HS agrees with a theoretical relation, which was derived from the theory of the Boltzmann distribution of suspended particles. A quantitative consistency in applying the conventional theory on interstellar grain alignment has not yet been achieved for the dense region, such as molecular clouds. The possibility of applying a diamagnetic-orientation experiment to the mechanism of interstellar grain alignment is discussed. The method for observing grain alignment established in the present work, can be applied for a quantitative evaluation of the star-light polarization mechanism.
ASCA Observation of Bright X-Ray Sources in the Nearby Spiral Galaxy IC 342
Authors: Okada Kyoko , Dotani Tadayasu , Makishima Kazuo , Mitsuda Kazuhisa , Mihara Tatehiro
Published: March 2014

X-ray observations of the nearby starburst galaxy IC 342 with ASCA led to the detection of three bright X-ray sources, whose positions are consistent with those from the Einstein and ROSAT observations. The X-ray luminosities of the two sources exceed the Eddington limit of a 1.4M⊙ object by two orders of magnitude for an assumed distance of 4.5 Mpc. The brightest one (source 1) among the three exhibited significant time variations on a time scale of a few hours during the ASCA observation. Thus, the size of the emission region must be smaller than about 1014 cm. The energy spectrum of the source can be represented either by a power-law with an exponential roll-over, or by an optically thick accretion disk model with a maximum color temperature of 1.77 keV. Although the large luminosity of source 1 may be explained by a ∼ 100M⊙ black hole at 4.5 Mpc, the observed energy spectrum is too hard to be accounted for by an optically thick accretion disk around the black hole. If source 1 is a relativistic jet source with strong X-ray beaming, both the large luminosity and the hard X-ray spectrum can be explained.
Non-LTE Analysis of the Oxygen λλ 7771–5 Triplet in Mid-G through Early-K Gaints
Authors: Takeda Yoichi , Kawanomoto Satoshi , Sadakane Kozo
Published: March 2014

An extensive spectral-synthesis analysis in the neighborhood of the OI 7771–5 lines (including also the lines of FeI, NdII, and CN) was carried out for thirty-two giant stars at the spectral type of mid-G through early-K, and their photospheric oxygen abundances were derived from these triplet lines based on detailed statistical-equilibrium calculations, aiming to assess the importance of the non-LTE effect quantitatively as well as to examine the reliability of the abundances derived from this near-IR triplet compared to those obtained from the forbidden line widely invoked. It turned out that the expected (negative) non-LTE correction ranges from 0.1 to 0.2 dex, the extent of which is somewhat smaller than has been reported by Eriksson and Toft (1979, AAA 25.114.007). The resulting non-LTE abundances were found to agree in most cases with those determined from the published equivalent widths of the forbidden O I 6300 line with no serious systematic descrepancy, though some showing appreciable scatters. The possible sources of uncertainties in oxygen-abundance determination are further examined, and the relevant characteristics of the resulting abundances, such as the [O/Fe] ratio in G–K giants, are discussed.
Trans-Fast MHD Winds in a Pulsar Magnetosphere
Authors: Takahashi Masaaki , Shibata Shinpei
Published: March 2014

We consider the problem of how a pulsar wind dominated by electro-magnetic energy converts itself into a kinetic energy-dominated wind, that is required by magnetohydrodynamical (MHD) models of interaction between the pulsar and the nebula. It is known that stationary, ideal-MHD wind models based on radial configurations are incapable of explaining the energy conversion from the electro-magnetic energy to the plasma's kinetic energy. For non-radial field geometries, we consider a detailed analysis of the critical conditions of trans-fast MHD winds and discuss the effects of the magnetic field on the wind acceleration. Although the flow properties associate with the magnetic flux tube divergence, we survey the acceptable ranges of the wind parameters as a pulsar wind. Further, we demonstrate the Crab pulsar wind with a magnetic flux tube diverging as ∝ x−0.4 . We see that the rapid acceleration is caused by a nearby Alfvén point; the velocity is almost terminated within several thouthand times of the fast magnetosonic point; thus, the kinetic energy-dominated wind is realized.
Accretion Corona Immersed in Disk Radiation Fields
Authors: Miwa Tadahiro , Fukue Jun , Watanabe Yoichi , Katayama Mako
Published: March 2014

We theoretically examined an accretion-disk corona, which is infalling toward the central black hole. The corona was supposed to be initially at rest far from the center. It was also assumed to be both geometrically and optically thin. During infall above and below the disk, the corona is suffered from the disk radiation fields. When the accretion disk is less luminous, the corona gas freely infalls to the center. When the accretion disk is sufficiently luminous, on the other hand, the corona gas gains angular momentum from the underlying disk via radiation drag. As a result, the infall of the corona gas is suppressed and the corona gas tends to corotate with the disk. When the disk is highly luminous, the infall of the corona gas stops in the inner disk and the corona gas may blow off from the disk as a radiatively driven wind.
FTS Measurements of Submillimeter-Wave Atmospheric Opacity at Pampa la Bola
Authors: Matsuo Hiroshi , Sakamoto Akihiro , Matsushita Satoki
Published: March 2014

The first measurements of submillimeter-wave atmospheric opacity spectra at the Pampa la Bola site (Northern Chile, Atacama, 4800 m altitude) have been performed during the winter season using a Fourier transform spectrometer (FTS). Atmospheric emission spectra, as a function of airmass, were measured under various weather conditions. Atmospheric opacity was evaluated from sky temperature at the zenith as well as from tipping measurements, which are independent measures but give consistent results. Correlation diagrams between 220 GHz and 345 GHz, 410 GHz, 492 GHz, 675 GHz, 691 GHz, 809 GHz, 875 GHz are shown. Correlations between millimeter-wave and submillimeter-wave opacities get worse when 220 GHz opacity is larger than 0.1. Deviations from the opacity correlation at each frequency show good correlations themselves, but have different relative variations at each frequency. This indicates that atmospheric transparency cannot be characterized only by millimeter-wave opacity, but requires simultaneous opacity measurements at millimeter and submillimeter-wavelengths.
A Hybrid N-Body/Cellular Automaton Scheme for Modelling Propagating Star Formation in Galaxies
Authors: Gardiner Lance T. , Turfus Colin , Wang Meishing
Published: March 2014

We present a numerical scheme for modelling star formation in galaxies based on the dual operation of gravitational instabilities and propagating star formation. Star formation is superposed on a mechanical N-body simulation of a collisional particle system by using a cellular automaton framework. The simulations involve 5000 particles representing gas clouds which can collide inelastically, and have been performed on a 2D square surface with quasiperiodic boundary conditions. The input of kinetic energy from star-forming regions leads to self-regulation of the global dynamics of star formation. The model naturally generates cloud complexes assembled from groups of cloud particles and simulates the ignition and propagation of star formation in such complexes leading to the formation of low density bubbles and expanding shells. The percentage of the model surface undergoing star formation and the ratio of the rates of stimulated to spontaneous star formation are shown to be consistent with models based on the theory of Stochastic Self-Propagating Star Formation (SSPSF). The code is shown to lead to star formation that propagates very nearly isotropically and can thus be adapted to the case of rotating disc galaxies without geometrical modification.
ASCA X-Ray Observations of Gamma Cassiopeiae
Authors: Kubo Shin , Murakami Toshio , Ishida Manabu , Corbet Robin H. D.
Published: March 2014

We present the results of X-ray observations of γ Cassiopeiae made with the ASCA satellite. Since the discovery of X-ray emission from this system, several possible models for the origin of X-rays have been proposed, including the corona of γ Cas, itself, a binary neutron-star companion, and a binary white-dwarf companion. However, there has been no clear way to distinguish which, if any, of these models is correct. In this paper we exploit the spectral resolution of the ASCA SIS detectors which, for the first time, enables the iron-line emission from this system to be studied in detail. The line and continuous spectrum of γ Cas is compared with the X-ray spectra of hot coronae of early type stars, low-mass X-ray binaries, high-mass X-ray binaries, and white-dwarf binaries. The observed properties of rapid fluctuations on timescales down to 10 s and a spectrum with a temperature of 10.6 keV, together with iron line emission, are very similar to those of binary white-dwarf systems. Assuming a white-dwarf binary origin for the X-rays, we estimated the luminosity of this system as a function of the binary separation using recent measurements of the circumstellar environment of γ Cas. Despite previous arguments that the X-ray luminosity is too large to be accounted for by accretion onto a white dwarf, we find that such a model is, in fact, consistent with the observed properties of the system.
Effect of Radiation Drag on Hoyle–Lyttleton Accretion
Authors: Nio Tomomi , Matsuda Takuya , Fukue Jun
Published: March 2014

Hoyle–Lyttleton type accretion was investigated by taking into account not only the effect of radiation pressure but also that of radiation drag. We calculated the trajectories of particles for three cases: only the effect of gravity is considered (case A); the effect of radiation pressure is taken into account (case B); the effect of radiation drag as well as radiation pressure is taken into account (case C). The accretion radii for the former two cases are 2GM/v2∞ for case A and 2GM(1-Γ )/v2∞ for case B, where M is the mass of the accreted object, v∞ the relative velocity, and Γ the normalized luminosity of the accreted object. We found that the accretion radius for case C is in between those of cases A and B under the present approximation; i.e., the accretion radius decreases due to radiation pressure, while it increases due to radiation drag. In addition, the accretion radius for case C becomes larger as the incident velocity becomes fast. The effect of radiation drag becomes ever more important when the velocity of the incident particle is comparable to the light speed.
ASCA Observations of the Sculptor Supercluster
Authors: Obayashi Hitoshi , Makishima Kazuo , Tamura Takayuki
Published: March 2014

We present ASCA results of the Sculptor supercluster, a rich supercluster with a redshift of 0.11, near to the south galactic pole. We searched for excess emission associated with the supercluster, and obtained the 3 σ upper limit as 16% of the brightness of the cosmic X-ray background in the 0.8–10 keV band. The X-ray properties of member clusters were analyzed and compared with other clusters. As for temperature-luminosity relation, no difference between the clusters in this supercluster and other clusters could be found. Applying the β model, we estimated the gas mass and the total gravitational mass associated with individual clusters, as well as those of the overall supercluster.
Gravitational Collapse of Filamentary Clouds
Authors: Kawachi Takeshi , Hanawa Tomoyuki
Published: March 2014

We consider gravitational collapse of a filamentary cloud under the assumption that it is axisymmetric and uniform along the axis. The pressure is approximated by a polytrope of P = K ρ γ. We found a similarity solution for the collapse when the polytropic index lies in the range 0 < γ < 1. According to the similarity solution, the collapse consits of two phases. In the first phase the filament becomes denser and thiner. The density at the center (ρc) increases in proportion to (t0 – t) −2, where t0 denotes the epoch at the end of the first phase. Meanwhile, the filament diameter (FWHM) decreases in proportion to (t0 – t) (2−γ). The line density of the central filament of ρ > 0.1 ρc vanishes at t = t0, since it is proportional to the central density and the square of the diameter [∝ (t0 – t)2(1− γ)]. In the second phase the central filament grows in mass by accretion. The collapse in the second phase is similar to the inside-out collapse of a spherical gas cloud. When the polytropic index γ is closer to unity, the collapse is slower. When γ = 0.999, the collapse is 12-times slower than the dynamical one. We also found from numerical simulations having various initial conditions that the collapse of a filamentary cloud approaches asymptotically the similarity solution irrespectively of the initial condition.
ASCA Observations of Transient X-Ray Sources in Quiescence
Authors: Asai Kazumi , Dotani Tadayasu , Hoshi Reiun , Tanaka Yasuo , Robinson Craig R. , Terada Kentaro
Published: March 2014

Soft X-ray transients are most probably low-mass binary systems containing either a neutron star (NS-LMXB) or a black hole (BH-LMXB). We have systematically investigated thirteen soft X-ray transients (four NS-LMXBs and nine BH-LMXBs) in the quiescent state using the available ASCA data. The luminosities of the observed NS-LMXBs in quiescence are on the order of ∼ 1032−33 erg s−1, whereas those of the BH-LMXBs are found to be systematically lower, most of them giving upper limits in the range below 1032−33 erg s−1 . The quiescent luminosity of LMXBs may be explained in terms of an optically thin, advection-dominated accretion disk, for which most of the thermal and kinetic energies of accreting matter are advected into the compact object with little X-ray emission. However, this scenario predicts a much larger luminosity for NS-LMXBs than observed, if the advected energies are liberated at the neutron-star surface, which is absent in BH-LMXBs. Mass accretion onto the neutron-star surface may be suppressed through some mechanism, such as the so-called propeller effect. The soft component observed in the NS-LMXBs is most probably emission from the magnetic pole regions of the neutron star.
Wave Dispersion in a Two-Phase Gas Mixture : Comments on Random Motions and Void Modes
Authors: Kamaya Hideyuki , Shchekinov Yuri A.
Published: March 2014

The properties of linear waves in a mixture comprising diffuse and dense phases are discussed using two approaches: (i) In one approach, the repulsive pressure produced in the diffuse phase by ballistically moving dense clouds generates motion of the components when gradients of the volume-filling factor arise; (ii) in the other approach, where this effect is omitted, a mixture is dynamically insensitive to perturbations containing only variations in the volume-filling factor of dense clouds. We show that the wave dynamics in these two approaches is quite different: in the framework of the first approach, the dispersion relation contains two different branches — the acoustic and the void (pattern formation) modes, while in the second approach the void mode disappears. We argue that in most situations for astrophysical gas mixtures, the first approach is more applicable: since effects of repulsive pressure from randomly moving clouds do exist, the void mode must be important in determining the dynamics of small perturbations and the formation of structures.
Stability of the Transition Layer between Advection-Dominated and Cooling-Dominated Regions in Accretion Disks. I. Dynamical Instability of Thin Transition
Authors: Kato Shoji
Published: March 2014

The time variations and Fe fluorescence lines observed in the hard state of stellar black-hole candidates and AGNs might be related to both the instability of and cool gas supply from the transition layer between advection-dominated and cooling-dominated regions. As a first step to examine this possibility, we consider the dynamical instability of the transition layer against non-axisymmetric perturbations under some idealizations. That is, the transition layer is assumed to have an infinitesimal thickness, and perturbations occur inviscidly and adiabatically. No magnetic field is assumed. The results show that the perturbations with m  mcrit become overstable due to a density inversion (the Rayleigh-Taylor instability in a rotating system). Here, mcrit ∼ 0.085(r/H)2, r being the radius of the transition region and H the disk half-thickness outside the region. This means that perturbations grow if their size in the azimuthal direction is shorter than ∼ 74(H/r)H, which is ∼ 2H when H/r = 0.03. The limitations of applicability of our results and other possible mechanisms which make the transition layer unstable are discussed in the final section.
Distance Determination of Mass-Losing Stars
Authors: Yuasa Manabu , Unno Wasaburo , Magono Shigeko
Published: March 2014

Based on the Principal Component Analysis on IRAS colors and the radio data, the distances to 183 mass-losing red giant stars were determined using the radial velocity and Oort's galactic rotation model for a zero-point calibration in the distance modulus. Also, based on the requirement of higher accuracy of the distance determination, the mass-losing red giant stars were divided into two groups by means of the first-principal component representing an intrinsic photometric property of the expanding shell; then, the distances were estimated to be logd(kpc) = 0.458 p<i + 0.09 ± 0.13 for group 1 and logd(kpc) = 0.325 P2 + 0.45 ± 0.15 for group 2, where p<i is the principal component corresponding to the distance, as obtained from the IRAS flux, which was assumed to be inversely proportional to the square of the distance. Thus,these two groups differ from each other not only by their photometric properties, but also by their average distances, by a factor of about 2. Systematic differences exist between the two groups in their population characteristics and in their evolutionary stages.
Two-Dimensional Simulations of Relativistic Jet—Cloud Collisions
Authors: Zhang Hui-Min , Koide Shinji , Sakai Jun-Ichi
Published: March 2014

We have investigated the processes of both nonrelativistic and relativistic jet-cloud collisions using a relativistic hydrodynamic simulation code. Several runs were performed to study different aspects of these kinds of collisions. Simulations show that the collisions involve two kinds of processes: reflection and bending. Collisions of relativistic jets and high-Mach-number nonrelativistic jets appear as reflections, while the collisions of low-Mach-number nonrelativistic jets show a reflection feature at their early stage and a bending feature at their late stage. Downstream of the collisions point the flow is still supersonic. In the bending cases, the original supersonic state is maintained all the time, while in the reflection processes, the supersonic condition of the downstreams flow is re-established by high pressure. The deflection angle is not fixed; it depends on almost all parameters involved in the collisions. Even for a particular collision process, its deflection angle is not fixed, but rather changes with time. Two results are noticeable: (1) the deflection angle can be greater than 90°; (2) in the collision region of a reflection process, the temperature is high and the jet material suffers rapid deceleration and reacceleration.
Pairwise Infall Velocity and Acceleration in the ZePdovich Approximation
Authors: Seto Naoki , Yokoyama Jun'ichi
Published: March 2014

Using perturbative methods, nonlinear corrections to the mean pairwise infall velocity and acceleration are investigated both in the ZePdovich approximation and in the higher order Eulerian perturbation theory. We calculate the second-order corrections to these two quantities, and find that for a typical cold-dark-matter model, predictions of the ZePdovich approximations are considerably different from that of the Eulerian perturbation theory, even on quasi-linear scales. This is an important caveat against the application of this approximation to quantities closely related to the dynamical nature of structure formation.
ASCA Measurements of Metallicity and Temperature Distributions in Three Clusters: A4059, MKW 3s,
and 2A 0335+096
Authors: Kikuchi Ken'ichi , Furusho Tae , Ezawa Hajime , Yamasaki Noriko Y. , Ohashi Takaya , Fukazawa Yasushi , Ikebe Yasushi
Published: March 2014

We present ASCA results on the distributions of the metallicity and temperature in 3 bright near-by clusters: A4059, MKW 3s, and 2A 0335+096. A significant gradient in the metal abundance is detected in A4059, while other clusters suggest similar gradients with low significance. These features together with recent results on AWM 7 and Perseus clusters suggest that metals injected in the ICM are not effectively mixed in the cluster space. An analysis of the GIS data, without explicitly including the cooling flow model, shows no substantial temperature drop at large radii (at half the virial radii) for the 3 systems. This is contrary to the recent results for 30 clusters by Markevitch et al. (1998, ApJ 503, 77), who assume rather strong cooling flows. The gas mass fraction of these clusters is 10-15% within 1 Mpc, which suggests that a baryonic fraction of about 20%, including the stellar mass, is a common level in galaxy groups and clusters.
Evolution of Hydromagnetic Disturbances in Low Ionized Cosmic Plasmas
Authors: Nomura Hideko , Kamaya Hideyuki , Mineshige Shin
Published: March 2014

We consider the propagation of hydromagnetic waves generated by a compact turbulent source in low ionized plasmas, applying the Lighthill theory. We assume the plasma to be isothermal, and adopt a uniform, stationary medium thread by ordered magnetic fields as an initial condition. Then, the distinct properties of the hydromagnetic waves originating from a source oscillating with a fixed frequency are studied in the linear regime. As is well known, in low ionized plasmas, the generated waves dissipate due to ion-neutral damping. In this paper, the dependence of the dissipation rate on the frequency of the oscillating source is investigated. The larger the frequency becomes, the more substantial is the wave dissipation. Implications of our results on the energy source in molecular clouds are also discussed. Interestingly, since the outflow lobes associated with young stellar objects act as compact turbulent sources, hydromagnetic waves are generated by them. From our order-estimations, about 70% of the energy of the outflow itself propagates as waves or turbulences, while the remaining 30% dissipates and heats the neutrals via ion-neutral damping. Then, we confirm that the outflows are significant energy sources in molecular clouds in the context of the Lighthill theory.
Comparative Studies of Visible and IRAS Interplanetary Dust Bands
Authors: Ishiguro Masateru , Nakamura Ryosuke , Fujii Yasumasa , Mukai Tadashi
Published: March 2014

We have examined the diversity and similarity of visible dust bands and infrared dust bands based on data obtained by our ground-based observations (Ishiguro et al. 1999, ApJ 511, 432) and by the Infrared Astronomy Satellite (IRAS). It is found that the latitude profile of visible dust bands at the solar elongation, λ - λ⊙ = 89°, is similar to that of infrared dust bands, except for the appearance of bands found at the ecliptic latitude, β = ± 5°, in only the visible region. Using the migration model for the spatial distribution of interplanetary dust bands, originally deduced from the infrared data (Reach et al. 1997, AAA 67.106.048), we predicted the visible band structure near to the anti-solar point in order to examine our observed evidence. Our results verify that the visible dust bands at β = +2° and −4° near to the anti-solar point comprise the dust particles originally supplied from the Themis and Koronis families.
Implication of Dark Matter in Dwarf Spheroidal Galaxies
Authors: Hirashita Hiroyuki , Kamaya Hideyuki , Takeuchi Tsutomu T.
Published: March 2014

We examine the correlation between physical quantities to explore the existence of dark matter (DM) in the Local Group dwarf spheroidal galaxies (dSphs). In order to clarify whether DM exists in the dSphs we compare two extreme models of their internal kinematics: [1] a tidal model (the mass of a dSph is estimated with the luminous mass, since the observed large velocity dispersions of the dSphs are attributed to the tidal force by the Galaxy), and [2] a DM model (the mass of a dSph is estimated with the virial mass, since the velocity dispersion is considered to reflect the DM potential). In both models, we find that the relation between the surface brightness of the dSphs and the tidal force by the Galaxy is consistently interpreted. This makes a critical remark about the previous studies that concluded that the tidal force is effective for the dSphs based only on model [1]. We also check the correlation between the Galactocentric distance and the tidal force. Consequently, both models are also supported in this test. Thus, we are unable to judge which of the two is more promising for the dSphs in correlation investigations. The physical process of tidal disruption is also considered. Since the timescale for the tidally perturbed stars to escape is much shorter than the orbital periods of the dSphs, it is difficult for the tidally perturbed dSphs to exist as an assembly. Thus, we suggest that the gravitational field of DM is necessary to bind the dSphs with a large velocity dispersion.
On the Continuum Shape of Broad Absorption Line Quasars
Authors: Yamamoto Tetsuo M. , Vansevičius Vladas
Published: March 2014

The continuum shape of 26 broad absorption line (BAL) QSOs is shown to be virtually identical to that of non-BAL QSOs when the spectra of the former are dereddened. A procedure for dereddening of BAL QSO spectra is introduced, based on measurement of the flux in three bands and determination of the colour excess in comparison with an unreddened spectrum. This method allows us to derive the type and amount of extinction. We show that reddening in high-ionization BAL QSOs is comparatively small and the range of extinction laws varies from Milky Way, LMC to SMC type. On the other hand, low-ionization BAL QSOs seem to experience reddening which can be attributed to SMC type extinction alone. Comparison of the colour indices of composite spectra from Francis et al. (1991) and Zheng et al. (1997) with those derived from individual BAL QSO spectra shows that the Francis et al. (1991) composite might be a more suitable representative of an unreddened spectrum. In general, we conclude that the spectral energy distribution of normal QSOs can be used as an incident continuum shape for BAL QSOs.
Dark Bulge, Exponential Disk, and Massive Halo in the Large Magellanic Cloud
Authors: Sofue Yoshiaki
Published: March 2014

The rotation curve of the Large Magellanic Cloud, which we derived from high-resolution H I position-velocity diagrams observed by Kim et al. (1998 ApJ 503, 674), shows a steep central rise and flat rotation with a gradual rise toward the edge. Using the rotation curve, we calculate the distribution of the surface mass density, and show that the LMC has a dark compact bulge, an exponential disk, and a massive halo. The bulge is 1.2 kpc away from the center of the stellar bar, and is not associated with an optical counterpart. This indicates that the “dark bulge„ has a large fraction of dark matter, with an anomalously high mass-to-luminosity (M/L) ratio. On the contrary, the stellar bar has a smaller M/L ratio compared to that of the surrounding regions.
Rotation-Infall Motion around the Protostar IRAS 16293-2422 Traced by Water Maser Emission
Authors: Imai Hiroshi , Iwata Takahiro , Miyoshi Makoto
Published: March 2014

We made VLBI observations of the water maser emission associated with a protostar, IRAS 16293-2422, using the Kashima-Nobeyama Interferometer (KNIFE)t and the Japanese domestic VLBI network (J-Net).* These distributions of water maser features showed the blue-shifted and red-shifted components separated in the north-south direction among three epochs spanning three years. The direction of the separation was perpendicular to the molecular outflow and parallel to the elongation of the molecular disk. These steady distributions were successfully modeled by a rotating-infalling disk with an outer radius of 100 AU around a central object with a mass of 0.3 M® . The local specific angular momentum of the disk was calculated to be 0.2–1.0 × 10∼3 km s−1 pc at a radius of 20–100 AU. This value is roughly equal to that of the disk of IRAS 00338+6312 in L1287 and those of the molecular disks around the protostars in the Taurus molecular cloud. The relatively large disk radius of about 100 AU traced by water maser emission suggests that impinging clumps onto the disk should be hotter than 200 K to excite the water maser emission.
Supersoft X-Ray Source in the Globular Cluster M3 (NGC 5272)
Authors: Dotani Tadayasu , Asai Kazumi , Greiner Jochen
Published: March 2014

We studied the nature of a transient supersoft X-ray source (SSS), 1E 1339.8+2837, in the globular cluster M3 (NGC 5272) using the ASCA data and the archival ROSAT data. We found that 1E 1339.8+2837 was observed most of the time as a CV-type X-ray source and had a hard energy spectrum approximated by a bremsstrahlung model of 5 keV. It switched to a high state only during 1991–92 at a luminosity of 1035 erg s−1, which is larger than that in the low state by nearly two orders of magnitude. We confirmed the very soft energy spectrum characteristic of the SSS during the high state. Thus, 1E 1339.8+2837 is considered to be a white-dwarf binary, making a transition between the SSS and the CV. We discuss a possible model of 1E 1339.8+2837, a dwarf nova including a massive white dwarf.
Astrometric VLBI Observation of PSR 0329+54
Authors: Sekido Mamoru , Imae Michito , Hanado Yuko , Ilyasov Yuri P. , Oreshko Vasilli V. , Rodin Alexander E. , Hama Shin'ichi , Nakajima Junichi , Kawai Eiji , Koyama Yasuhiro , Kondo Tetsuro , Kurihara Noriyuki , Hosokawa Mizuhiko
Published: March 2014

We conducted VLBI experiments on the pulsar PSR 0329+54 with the Kashima (Japan)-Kalyazin (Russia) baseline in 1995 March and 1996 May. An absolute astrometric measurement was applied by using the analysis software SOLVE and CALC, which were developed by NASA/GSFC for geodesy and astrometry. Our measurement results are consistent with the former results of a VLBI observation by Bartel et al. (1985, AAA 39.041.005) and a VLA observation by Fomalont et al. (1984, AAA 38.041.014) when proper motion (Harrison et al. 1993, AAA 57.126.049) is taken into account. By using our data set and Bartel et al.'s data, the most precise proper motion and pulsar position in ICRF were obtained. The proper motion as μα : 17.3 ± 0.8 mas yr−1, μδ : –11.5 ± 0.6 mas yr−1 and the coordinates at the epoch of 1995.0 are α : 03h32m59.s376 ± 0.001, and δ : 54°34′43.″504 ± 0.007.