bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of the Ring-Like Structure in the SN 1987A Nebula due to the Magnetic Pressure of the Toroidal Field
Authors: Washimi Haruichi , Shibata Shinpei , Mori Masao 
Published: March 2014

Abstract
Several weeks after the explosion of supernova (SN) 1987A, the UV flash of the SN illuminated a ring-like structure in the circumstellar material at about 0.65 ly from the SN. The interaction between the stellar winds from the SN progenitor is considered to be the candidate for the formation of the circumstellar structure. In the case that the stellar winds are spherically symmetric, the interaction should result in a shell-like structure. However, in this paper we show that the magnetic field in the winds causes an anisotropy which leads to the formation of a ring-like structure. When the fast wind of the blue supergiant phase of the progenitor sweeps up the surrounding slow wind of the red-supergiant phase, the magnetic field as well as the wind material are piled up in the interaction region. Since the magnetic energy increases in proportion to the square of the amplitude, the magnetic field exhibits its effect prominently at the interaction region; due to the magnetic pressure force the material at lower latitudes is compressed into a ring-like structure. It is suggested that this magnetic process can also explain the newly observed pair of rings of the SN 1987A nebula.
Enhanced He I Absorption at the Feet of Solar X-Ray Loops
Authors: Venkatakrishnan P. , Sakurai Takashi , Suematsu Yoshinori , Ichimoto Kiyoshi 
Published: March 2014

Abstract
A comparison of He I spectroheliograms and Yohkoh soft X-ray images of active regions indicates that He I absorption is enhanced at the feet of hot X-ray loops. It is suggested that the conduction of heat from the loops into the transition region at their feet would produce enhanced transition-region emission around 50 eV that would in turn cause enhanced excitation of He I leading to the excess He I absorption that is observed.
CO-to-H2 Conversion Factor in Galaxies
Authors: Arimoto Nobuo , Sofue Yoshiaki , Tsujimoto Takuji 
Published: March 2014

Abstract
A general method and formulae to derive the CO-to-H2 conversion factor in galaxies as a function of the metallicity are presented based on an analysis of the observed data for the conversion factor obtained for nearby spiral and dwarf irregular galaxies. From the CO data for eight galaxies we obtained the following formula, which gives the conversion factor (X*) as a function of metallicity:
log X*= −1.0 (12 +log O/H)+ A,
where X* = NH2 / ICO × 10−20 H2/(K km s−1) and A is a constant. Since the metallicity is dependent on the luminosity of galaxies, we derived a correlation between the conversion factor and the absolute magnitude of galaxies. We also investigated dependence of the conversion factor on the distance from the center of individual galaxies. We also present a formula to calculate X* as a function of the radius in a galaxy.
Discovery of Two Types of Superhumps in WZ Sge-Type Dwarf Nova AL Comae Berenices
Authors: Kato Taichi , Nogami Daisaku , Baba Hajime , Matsumoto Katsura , Arimoto Jun'ichi , Tanabe Kazuhito , Ishikawa Kaoru 
Published: March 2014

Abstract
A dwarf nova, AL Com, was photometrically observed during an outburst in 1995 April, which occurred for the first time since 1975. The star showed two distinct types of periodic variation: (1) a 0.05666-day variation with decaying amplitudes during the earliest stage of the outburst, and (2) 0.0572-day super humps which grew ∼ 11 d after the onset of the outburst. The present observations are the one first to clearly established the SU UMa-type nature of AL Com. Furthermore, the appearance of these two periods, together with the whole course of the superoutburst, makes AL Com an almost perfect twin of an enigmatic dwarf nova, WZ Sge. We attributed the former period to be the orbital period of this cataclysmic binary. The double-humped profile of this variation seems to preclude an explantion based on an enhanced hot spot by a mass-transfer burst from the secondary, which has been believed to be the best observational evidence of a mass-transfer burst in WZ Sge obtained during its 1978 outburst.
Growth of Velocity Dispersions for Collapsing Spherical Stellar Systems
Authors: Hozumi Shunsuke , Fujiwara Takao , Kan-ya Yukitoshi 
Published: March 2014

Abstract
First, we have ensured that spherical nonrotating collisionless systems collapse while almost retaining their spherical configurations during the initial contraction phases, even if they are allowed to collapse three-dimensionally. Next, based on the assumption of spherical symmetry, we examine the evolution of the velocity dispersions with collapse for those systems having uniform or power-law density profiles with Maxwellian velocity distributions by directly integrating the collisionless Boltzmann equation. The results show that as far as the initial contraction phases are concerned, the radial velocity dispersion never grows faster than the tangential velocity dispersion, except at small radii, where the nearly isothermal nature remains, irrespective of the density profiles and virial ratios. This implies that the velocity anisotropy as an initial condition should be a poor indicator of the radial orbit instability. The growing behavior of the velocity dispersions is briefly discussed from the viewpoint that phase-space density is conserved in collisionless systems.
Detection of a Water-Vapor Megamaser in the Active Galaxy NGC 5793
Authors: Hagiwara Yoshiaki , Kohno Kotaro , Kawabe Ryohei , Nakai Naomasa 
Published: March 2014

Abstract
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⊙.
Wave Dispersion in a Two-Phase Gas Mixture : Comments on Random Motions and Void Modes
Authors: Kamaya Hideyuki , Shchekinov Yuri A. 
Published: March 2014

Abstract
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.
Spectroscopic Study of the Vela-Shrapnel
Authors: Tsunemi Hiroshi , Miyata Emi , Aschenbach Bernd 
Published: March 2014

Abstract
Several shrapnels have been detected in the vicinity of Vela SNR by the ROSAT all-sky survey. We present here the spectral properties of shrapnel ‘A’ observed with the ASCA satellite. A prominent Si-K emission line with relatively weak emission lines from other elements have been detected, revealing that the relative abundance of Si is a few ten-times higher than those of other elements. Combining with the ROSAT PSPC results, we obtained the electron temperature, kTe, to be 0.33 ± 0.01 keV. The total mass of shrapnel ‘A’ is estimated to be ∼ 0.01 M⊙. If it is an ejecta of a supernova explosion, the interstellar matter would be swept up in the leading edge while the ejecta material would be peeled off in the trailing edge, which should be confirmed by future observations.
A Study of Dense Molecular Gas and Star Formation toward the Vela Molecular Ridge with NANTEN
Authors: Yamaguchi Nobuyuki , Mizuno Norikazu , Saito Hiro , Matsunaga Ken'ichi , Mizuno Akira , Ogawa Hideo , Fukui Yasuo 
Published: March 2014

Abstract
New observations of the J=1−0 12CO, 13CO, and C18O emission lines have been extensively made toward the Vela Molecular Ridge (VMR) with NANTEN. The most prominent cloud is the giant molecular cloud, corresponding to the VMR-C region (Vela C). The present C18O distribution has been identified as 29 clouds. Among them, the most massive one is included in Vela C, having a total mass of ∼ 4.4 × 104M⊙. The rest of them are smaller C18O clouds of 102-103M⊙. Star formation in the region is almost exclusively occurring in the C18O clouds. The luminosities of the associated protostellar IRAS sources range from 5 L⊙ to 1.1 × 104L⊙, and the luminosity distribution is found to be well represented by the relation dNstar/dLIR ∞ L-1.65±0.14IR. We find that the ratios of the total luminosity of the sources associated with given C18O clouds to the cloud masses are significantly enhanced for those clouds associated with H II regions by an order of magnitude. This is interpreted as meaning that the formation of massive stars is enhanced due to the effects of H II regions, as is consistent with the preceding work. We have also newly found molecular outflow toward IRAS 08588–4347 as well as five possible candidates for outflows.
Accretion Disks Phase Transitions: 2-D or Not 2-D?
Authors: Abramowicz Marek A. , Björnsson Gunnlaugur , Igumenshchev Igor V. 
Published: March 2014

Abstract
We argue that the proper way to treat thin-thick accretion-disk transitions should take into account the 2-D nature of the problem. We illustrate the physical inconsistency of the 1-D vertically integrated approach by discussing a particular example of the convective transport of energy.
Super-Eddington Accretion-Disk Models for SS 433
Authors: Okuda Toru , Fujita Mitsutaka 
Published: March 2014

Abstract
We examine highly super-Eddington accretion disk models onto a neutron star for SS 433, based on two-dimensional hydrodynamical calculations. The super-Eddington accretion flows form a kind of standing shock elongated along the rotational axis of the disk. This results in a very rarefied, hot, optically thin region between the shock and the axis. The anisotropic radiation fields in this region accelerate the flows to relativistic jets of ∼ 0.2 c with a collimation angle of ∼ 10°–25°. The accretion disk is highly convective or turbulent near to the equatorial plane, and is very geometrically thick. Most of the input accreting matter is blown off from the system through the jets and the disk wind. The super-Eddington accretion disk models are promising to explain SS 433.
Metal Abundances in the Hot Interstellar Medium in Early-Type Galaxies Observed with ASCA
Authors: Matsushita Kyoko , Ohashi Takaya , Makishima Kazuo 
Published: March 2014

Abstract
We have analyzed ASCA data of 27 early-type galaxies, and studied the properties of their X-ray emitting ISM (InterStellar Medium) in detail. We found that overlapping lines and free-bound continuum cause strong coupling in the derived abundances of various elements. The abundance determination is also difficult due to the uncertainties in the Fe-L atomic physics, because the Fe-L lines couple with the O and Ne K-lines. However, when the abundances of α-elements are fixed, all of the plasma codes give similar Fe abundances with a scattering of only 20–30%. To relax the strong coupling among the elements, we included 20% systematic errors in the Fe-L region of the spectra. Then, in X-ray luminous galaxies, the derived abundance of Fe and α-elements both became ∼ 1 solar within a factor of 2. This result relaxes the previous severe discrepancy between the ISM and stellar metallicities. The ISM metallicity in X-ray fainter galaxies is still uncertain, but we can at least constrain that the contribution from type-Ia SN to the ISM abundance is lower than in X-ray luminous systems. These results strongly suggest that a large fraction of SN Ia products have escaped into intergalactic space.
Detection Rate of Molecular Gas in Elliptical Galaxies: Constraints on Galaxy-Formation Theories
Authors: Fujita Yutaka , Nagashima Masahiro , Gouda Naoteru 
Published: March 2014

Abstract
We calculated the detection rate of cold gas in elliptical galaxies using a semi-analytic model of galaxy formation, and compared it with observations. We have shown that a model with a long star-formation time-scale ( ∼ 20 Gyr) is inconsistent with observations. Thus, some mechanisms of reducing the mass of interstellar medium, such as the consumption of molecular gas by star formation and/or reheating from supernovae, are certainly effective in galaxies. Our model predicts that star formation is induced when galaxies in a halo collide with each other and it reduces the cold gas left until the present. However, we find that the reduction through random collisions of satellite (non-central) galaxies in the mean-free time-scale in a halo is not required to explain the observations. For cD galaxies, the predicted detection rate of cold gas is consistent with observations as long as the transformation of hot gas into cold gas is prevented in halos whose circular velocities are larger than 500;km; s−1. Moreover, we find that the cold gas brought into cDs through capturing gas-rich galaxies is small. We also show that the fraction of galaxies with observable cold gas should be small for cluster ellipticals in comparison with that for field ellipticals. Our fiducial models and the models with a large reheating efficiency can reproduce the observations well, although a comparison with a larger and complete sample of elliptical galaxies will constrain the physical parameters in galaxy-formation theories more strictly.
ASCA Observations of Three Shakhbazyan's Compact Groups of Galaxies
Authors: Takahashi Isao , Fukazawa Yasushi , Kodaira Keiichi , Makishima Kazuo , Nakazawa Kazuhiro , Xu Haiguang 
Published: March 2014

Abstract
X-ray observations of three Shakhbazyan's Compact Groups of Galaxies are presented for the first time. Extended X-ray emission was detected from SCGG 202 and SCGG 223 with 0.5–2 keV luminosity of 1 ' 1042 erg s−1 and 3 ' 1042 erg s−1 (for H0 = 75 km s−1 Mpc−1), respectively, while no significant emission was detected from SCGG 205 with an upper limit of 0.7 ' 1042 erg s−1. The X-ray spectra of SCGG 202 and SCGG 223 can be described with thin-thermal plasma emission with a temperature of about 1 keV. The X-ray properties of SCGG 202 and SCGG 223 are in good agreement with those of other known groups of galaxies, proving the physical nature of their grouping.
Stellar Contents of the Galactic Giant H II Region NGC 3603
Authors: Pandey Anil K. , Ogura Katsuo , Sekiguchi Kaz 
Published: March 2014

Abstract
We present CCD UBVRI and Hα photometry for the starburst cluster associated with the galactic giant H II region NGC 3603. The mean reddening of the cluster members comes out to be $\langle E(B-V)\rangle=1.48\pm0.21 $ (s.d.). The surface distribution of the reddening shows a radial variation with a minimum near to the cluster center and two local maxima at radii ∼ 30″ and ∼ 70″. Our photometric data indicate an anomalous reddening law for the dust inside the cluster region, and the ratio of the total to the selective extinction, R, is found to be ∼ 4.3. A comparison of the observational and intrinsic colour-magnitude digrams (CMDs) yields a mean distance modulus of (m – M)0 = 14.0, which corresponds to a distance of 6.3 ± 0.6 kpc. This distance is smaller than those obtained in earlier works (e.g., 7.2 kpc, Melnick et al. 1989, AAA 49.132.013) but is in good agreement with the kinematic distance (6.1 ± 0.6 kpc) recently reported by De Pree et al. (1999, AAA 71.132.041). The cluster shows a large age spread, containing stars as old as up to several Myr. However, the mean age of the cluster is found to be ≤ 1 Myr. We estimate a minimum star formation efficiency of ∼ 25 % and a gas removal time of τ ∼ 4.6 Myr.
Overabundance of Calcium in the Young SNR RX J0852–4622: Evidence of Over-Production of 44Ti
Authors: Tsunemi Hiroshi , Miyata Emi , Aschenbach Bernd , Hiraga Junko , Akutsu Daisuke 
Published: March 2014

Abstract
Recently, COMPTEL has detected γ-rays of 1157 keV from 44Ti in the direction of the SNR RX J0852–4622 (Iyudin et al. 1998, AAA 70.125.077). Since 44Ti is a product of explosive nucleosynthesis and its half lifetime, τ1/2, is about 60 yr, RX J0852–4622 must be a young supernova remnant and radiation is dominated by the ejecta rather than by interstellar matter. We have detected an X-ray emission line at 4.1 ± 0.2 keV which is thought to come from highly ionized Ca. The emission line is so far only seen in the north-west shell region of RX J0852–4622. The X-ray spectrum can be well fitted with that of a thin hot plasma of cosmic abundances, except that of Ca, which is overabundant by a factor of 8 ± 5. Assuming that most of the Ca is 44Ca, which originates from 44Ti by radioactive decay, we estimate a total Ca mass of about 1.1 × 10−3M⊙. Combining the amount of 44Ca and the observed flux of the 44Ti γ-ray line, the age of RX J0852–4622 is around 1000 yr.
PROGRAPE-1: A Programmable, Multi-Purpose Computer for Many-Body Simulations
Authors: Hamada Tsuyoshi , Fukushige Toshiyuki , Kawai Atsushi , Makino Junichiro 
Published: March 2014

Abstract
We have developed PROGRAPE-1 (PROgrammable GRAPE-1), a programmable multi-purpose computer for many-body simulations. The main difference between PROGRAPE-1 and “traditional” GRAPE systems is that the former uses FPGA (Field Programmable Gate Array) chips as the processing elements, while the latter relies on a hardwired pipeline processor specialized to gravitational interactions. Since the logic implemented in FPGA chips can be reconfigured, we can use PROGRAPE-1 to calculate not only gravitational interactions, but also other forms of interactions, such as the van der Waals force, hydrodynamical interactions in the SPHr calculation, and so on. PROGRAPE-1 comprises two Altera EPF10K100 FPGA chips, each of which contains nominally 100000 gates. To evaluate the programmability and performance of PROGRAPE-1, we implemented a pipeline for gravitational interactions similar to that of GRAPE-3. One pipeline is fitted into a single FPGA chip, operated at 16 MHz clock. Thus, for gravitational interactions, PROGRAPE-1 provided a speed of 0.96 Gflops-equivalent. PROGRAPE will prove to be useful for a wide-range of particle-based simulations in which the calculation cost of interactions other than gravity is high, such as the evaluation of SPH interactions.
Molecular Clouds around a Runaway O Star, ζ Ophiuchi
Authors: Tachihara Kengo , Abe Rihei , Onishi Toshikazu , Mizuno Akira , Fukui Yasuo 
Published: March 2014

Abstract
Molecular clouds around a runaway O star, ζ Oph, have been surveyed with the NANTEN telescope, and their streaming motion caused by ζ Oph has been detected. ζ Oph is the earliest (O9.5 V) member of the Sco OB 2 association and is rapidly moving accompanied by an H II region, S 27. We detected 2 major filamentary cloud complexes, L 156 and L 204 complexes. Their total masses traced by the 12CO emission are 520 M⊙ and 1110 M⊙ , respectively. Denser molecular cloud cores detected in C18O are locally distributed on the near side of the L 204 complex to ζ Oph, and lower density gas spreads toward the opposite side. Both complexes have radial velocity shifts that are correlated with the gas density. It is suggested that the low-density gas is accelerated outward away from ζ Oph relative to the embedded dense cores. These density and velocity structures indicate a dynamical interaction between the H II region and the molecular clouds. We calculated the kinetic energies and momenta for seven individual clouds, and examined the effects of the stellar wind and photo-evaporation by the UV field of ζ Oph. It is found that the stellar wind can hardly input the momentum during the crossing time of the rapid movement of ζ Oph. UV radiation seems to be a more likely origin of the streaming gas motion.
On the Detection of Solar Coronal High-Velocity Fields Using the XUV Doppler Telescope
Authors: Kobayashi Ken , Hara Hirohisa , Kano Ryohei , Nagata Shin'ichi , Sakao Taro , Shimizu Toshifumi , Tsuneta Saku , Yoshida Tsuyoshi 
Published: March 2014

Abstract
The XUV Doppler Telescope (XDT) is a sounding rocket experiment designed to detect flows in the solar corona using filter ratios. The XDT, successfully launched on 1998 January 31, is a normal incidence telescope composed of narrow-bandpass multilayer mirrors and capable of obtaining images 2 Å above and 2 Å below the Fe XIV 211 Å (T = 1.7 MK) emission line. It has the potential to make a velocity map of the entire solar disk with just a few minutes of observation. The image ratio maps show features that translate to Doppler shifts of 200 km s−1 or more, including several `redshift' features located near footpoints of coronal loops. However, no corresponding velocity features were seen by the Solar and Heliospheric Observatory (SOHO) Coronal Diagnostic Spectrometer (CDS) in the Mg IX 368 Å (T = 1 MK) line, suggesting that the features are not caused by Doppler shift. Instead, the features seem to be related to contamination of lower temperature (T &lt; 1 MK) emission lines and the nearby density-sensitive Fe XIII lines. We conclude that while no flows were positively identified by the XDT, this observing technique is capable of detecting flows of 1000 km s−1 independently, and 200 km s−1 when combined with simultaneous plasma diagnostic observation.
Sub-Parsec-Scale Acceleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251
Authors: Sudou Hiroshi , Taniguchi Yoshiaki , Ohyama Youichi , Kameno Seiji , Sawada-Satoh Satoko , Inoue Makoto , Kaburaki Osamu , Sasao Tetsuo 
Published: March 2014

Abstract
In order to investigate the genesis of a powerful radio jet, we have mapped the central 10 pc region of the nearby radio galaxy, NGC 6251, with a 0.2 pc resolution using Very Long Baseline Interferometer (VLBI) at two radio frequencies, 5 GHz and 15 GHz. We have found the sub-parsec-scale counterjet for the first time in this radio galaxy. This discovery allows us to investigate the jet acceleration based on the relativistic beaming model.
Discovery of a 9-s X-Ray Pulsar, AX J0049–732, in the Small Magellanic Cloud
Authors: Ueno Masaru , Yokogawa Jun , Imanishi Kensuke , Koyama Katsuji 
Published: March 2014

Abstract
We report on an ASCA discovery of a new X-ray pulsar, AX J0049−732, in the Small Magellanic Cloud (SMC). The pulse shape is sinusoidal with a barycentric period of 9.1320 ± 0.0004 s. The X-ray spectrum was fitted by an absorbed power-law model with a photon index of 0.6+1.0−0.7 and a column density of 1.3+2.9−1.3 × 1022 cm−2. An unabsorbed flux at 0.7−10.0 keV was estimated to be 8 × 10−13 erg cm−2 s−1 corresponding to an X-ray luminosity of 4 × 1035 erg s−1 at the SMC distance of 62 kpc.