bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Ionization and Abundance of C and Si in QSO Absorbers
Authors: Khare Pushpa , Ikeuchi Satoru 
Published: March 2014

Abstract
We have analyzed high-resolution data of absorption lines of Si and C in absorption systems observed in the spectra of QSOs, in order to study the ionization state and the overabundance of Si with respect to C in absorbers, and also to study the change in these properties with the redshift. No correlation was found between the column-density ratios of Si IV to C IV of intervening systems and the redshift. The data do not provide any evidence for an abrupt change in the values of the ratio at any particular redshift, unlike that for Lyman alpha forest clouds. We have compared the observed ratios of column-densities of Si II and Si IV and of Si IV and C IV in different classes of absorption systems with the predictions of photo-ionization models for different shapes of the background-radiation field. An overabundance of Si over C can be ruled out in several of the intervening systems for any shape of the background radiation. For these systems we can also rule out any contribution from stellar sources to the background, which is then entirely from the AGNs. No overabundance is needed in other intervening systems if the radiation field from stellar sources significantly contributes to the UV background. An overabundance, however, is present in Lyman alpha forest clouds at redshifts larger than 3 and in systems associated with the QSOs. For all of the intervening systems a minimum of 10% of the background is contributed by the AGNs.
High-Resolution VSOP Imaging of the Southern Blazar PKS 1921-293 at 1.6 GHz
Authors: Shen Zhi-Qiang , Edwards Philip G. , Lovell James E. J. , Fujisawa Kenta , Kameno Seiji , Inoue Makoto 
Published: March 2014

Abstract
We present a high-resolution 1.6 GHz VSOP image of the southern blazar PKS 1921-293. The image shows a typical core-jet morphology, consistent with ground-based VLBI images. However, the addition of data from the space antenna has greatly improved the angular resolution (especially along the north-south direction for this source), thus allowing us to clearly identify the core. Model fitting has revealed an inner jet component of ∼ 1.5 mas north of the core. This jet feature may be moving on a common curved path connecting the jet within a few parsecs to the 10-parsec-scale jet. The compact core has a brightness temperature of 2.6 × 1012 K (in the rest frame of the quasar), an indication of relativistic beaming. We analyzed the source in terms of three models involving the inverse Compton catastrophe, an inhomogeneous relativistic jet, and the equipartition of energy between the radiating particles and the magnetic field. Our analysis of this 7-ray-quiet blazar shows no preference to any particular one of these models.
ASCA Observation of a Radio-Loud Quasar and a New Candidate for a Cluster of Galaxies
Authors: Akimoto Fumie , Furuzawa Akihiro , Tawara Yuzuru , Kamata Yuichi , Yamashita Koujun 
Published: March 2014

Abstract
During an X-ray observation of the distant galaxy cluster CL 0107+31 (z = 0.69) with ASCA, an extended X-ray source was detected in the field of view. Based on an image analysis in two different energy bands of 1–3 keV and 3–10 keV, we found that this source consists of a hard point-like component and an additional soft diffuse X-ray source extended over ≥ 3′ in radius. However, due to poor photon statistics, we could not distinguish whether their X-ray spectra are thermal or non-thermal. The peak position of the central X-ray source coincides with a radio-loud quasar, NRAO 58. NRAO 58 is found to have a power-law spectrum with a photon index $1.6^{+0.3}_{-0.2}$ and a (2–10 keV) luminosity of ∼ 4×46 erg s−1 (in the quasar rest frame). The extended component is likely to be a candidate for a nearby galaxy group which accidentally coincides with the quasar.
A Dark-Cloud Complex in Aquila: Small Molecular Clouds Possibly Associated with the Aquila Rift
Authors: Kawamura Akiko , Onishi Toshikazu , Mizuno Akira , Ogawa Hideo , Fukui Yasuo 
Published: March 2014

Abstract
A 12CO(J = 1−0) survey for local molecular clouds was performed toward dark clouds in Aquila (26° &lt; l ≤ 42° and −25° ≤ b &lt; −2°) by using the 4-meter millimeter wave telescope, NANTEN, at Las Campanas Observatory, Chile. A cloud complex consisting of 64 small clouds has been discovered in −25° ≲ b ≲ −12°; at a distance of 220 pc, its height from the galactic plane is ∼ 50–100 pc and the total mass is ∼ 4 × 103M⊙. The spatial and velocity distributions of the complex suggest that it may be connected to the Great Rift in Aquila. This complex, as a whole, has a significantly large virial mass compared with the mass derived from the CO intensities by an order of magnitude, though H I gas of ∼ 104M⊙, possibly associated, may contribute to bind them gravitationally. The individual CO clouds have velocity dispersion and mass similar to those of the high-latitude clouds; also, the clouds are not in gravitational equilibrium. There is no indication of active star formation.
Stability of a Dynamically Collapsing Gas Sphere
Authors: Hanawa Tomoyuki , Matsumoto Tomoaki 
Published: March 2014

Abstract
We discuss the stability of dynamically collapsing gas spheres. We use a similarity solution for a dynamically collapsing sphere as the unperturbed state. In the similarity solution the gas pressure is approximated by a polytrope of P = K ργ. We examined three types of perturbations: bar ( l = 2) mode, spin-up mode, and Ori-Piran mode. When γ &lt; 1.097 , it is unstable against the bar mode. It is unstable against the spin-up mode for any γ . When γ &lt; 0.961 , the similarity solution is unstable against the Ori-Piran mode. The unstable mode grows in proportion to | t - t0 | -σ , while the central density increases in proportion to ρc ∝ (t - t0) -2 in the similarity solution. The growth rate, σ, is obtained numerically as a function of γ for the bar mode and the Ori-Piran mode. The growth rate of the bar mode is larger for a smaller γ . The spin-up mode has a growth rate of σ = 1/3 for any γ.
Two-Epoch Space VLBI Observations of the Gamma-Ray Loud Quasar PKS 1741–038
Authors: Wajima Kiyoaki , Lovell James E. J. , Kobayashi Hideyuki , Hirabayashi Hisashi , Fujisawa Kenta , Tsuboi Masato 
Published: March 2014

Abstract
We present the results of high-resolution imaging of the gamma-ray loud quasar PKS 1741–038 with the HALCA satellite and ground radio telescopes. Observations were made at two epochs at an interval of nine months with the first-epoch observation at 1.6 and 5 GHz and with the second-epoch observation at 5 GHz. The source shows a very compact structure, but is clearly resolved in the space-ground baseline visibility data. The core component of the source has a brightness temperature, Tb, greater than 1012 K in the source's rest frame at each frequency. We applied three individual jet models in order to derive the Doppler factor, δ . The core component has δ ∼ 14, considering the Tb limit due to the inverse Compton catastrophe, while a 2.5-times larger δ is obtained assuming that the particles and magnetic field are in equipartition. Two-epoch images at 5 GHz show almost no change of the structure. Assuming that the component motion in this interval is less than our resolution, we derived the upper limit of the viewing angle as being 4.°8. The smaller viewing angle and higher Doppler factor favor the inverse Compton gamma-ray emission model; we conclude that the gamma-ray emission from this source is highly Doppler-boosted.
A Universal Phase Function for Jovian Clouds from the Visible to Near-IR Wavelength Region. I. Zone Phase Function
Authors: Satoh Takehiko , Itoh Seigo , Kawabata Kiyoshi , Tenma Takafumi , Akabane Tokuhide 
Published: March 2014

Abstract
A set of wavelength-dependent scattering phase functions for Jupiter's clouds has been obtained; the Mie theory was employed to simulate well-defined scattering phase functions deduced from an analysis of the Pioneer 10 photometry data (Tomasko et al. 1978, AAA 021.099.011). A reasonable fit to the cloud-phase functions for the bright zone (STrZ) was obtained with a particle effective radius, reff, of 0.96 μ m and the real part of the refractive index, nr, being 1.591 for the blue and 1.535 for the red, slightly higher than the nominal values for ammonia ice. The derived Mie phase functions were tested against several STrZ data. The appropriateness of these phase functions has been demonstrated through the fact that they reproduce not only the observed limb-to-limb intensity profiles, but also the correct wavelength dependence of the haze optical thickness for a wide wavelength range from visible to near-infrared.
The Nuclear Region of the Seyfert 2 Galaxy NGC 3079
Authors: Sawada-Satoh Satoko , Inoue Makoto , Shibata Katsunori M. , Kameno Seiji , Migenes Victor , Nakai Naomasa , Diamond Philip J. 
Published: March 2014

Abstract
We present a discussion on high-resolution studies of the nuclear region of NGC 3079 using observations of an H2O maser and continuum emission as well as H I absorption with a global VLBI network including the VLBA, the phased VLA and the Effelsberg 100 m telescope. Multi-frequency observations of the continuum emission reveal the spectra of continuum components and suggest a core-jet morphology. The H2O maser spots lie in a series of clusters distributed along a north-south direction, while we rule out any possibility that the masering disk lies along the north-south direction. H I absorption features towards the continuum components have a velocity gradient opposite to that observed in the galaxy as a whole. We identify the nucleus and rotation axis of the central 10 pc region, and discuss the properties of a postulated rotating torus in the nuclear region.
Evolution of Cluster Galaxies in Hierarchical Clustering Universes
Authors: Okamoto Takashi , Habe Asao 
Published: March 2014

Abstract
Using cosmological N-body simulations of critical (SCDM) and open (Ω = 0.3, OCDM) cold dark matter models, we investigated the evolution of cluster galaxies. Based on our numerical simulation, we constructed merging history trees of the galaxies. By following their merging history, we could show that the major merger fractions of the galaxies in cluster-forming regions is roughly proportional to (1+z)4.5 at low redshifts (z &lt; 2), and has a steep peak at z ≃ 2.5 and z ≃ 3 in SCDM and OCDM, respectively. We also show that the cluster galaxies are affected by the tidal interaction after the clusters are formed. Because the formation redshift of the cluster in SCDM, zform = 0.15, is much more recent than that of the cluster in OCDM, zform = 1.6, the cluster galaxies in SCDM show more rapid evolution by tidal interactions from z = 0.5 than those in OCDM.
Magnetic Field Evolution Leading to Solar Flares II. Cases with High Magnetic Shear and Flare-Related Shear Change
Authors: Li Hui , Sakurai Takashi , Ichimoto Kiyoshi , UeNo Satoru 
Published: March 2014

Abstract
Following Paper I in which we considered five solar flares, we have selected another three solar flares greater than GOES X-ray class M/Hα importance 1. The three active regions discussed here are characterized by high magnetic shear. We investigated the spatial relationships among Hα flare ribbons, soft X-ray (SXR) flare loops, and magnetic configurations for the three flares produced in these active regions. Our results show that only one of these three flares satisfies the sufficient conditions for a flare to occur proposed by Hagyard (1990, AAA 052.075.047). We also discuss the magnetic shear changes around the flaring time only along the neutral lines associated with the studied flares and over the whole flaring area. The flare-related changes on the neutral line are small (2°–4°) and the association of these changes with the flares is not conclusive. The average shear in the flaring areas of the flares associated with high shear decreases significantly after the flares and it may be a better parameter to characterize the flare-related shear changes in such cases.
Fragmentation of Cosmologically Collapsed Layers
Authors: Hosokawa Tamaki , Ôishi Tomohiro , Yoshida Tatsuo , Yokosawa Masayoshi 
Published: March 2014

Abstract
The fragmentation and dynamics of pancake-like collapsed layers are discussed. The fragmentation theory for an isothermal gas layer is extended to the case of the transverse expansion or contraction of a layer with two components. The expansion of a layer suppresses the growth of a perturbation and the contraction enhances the perturbation. It is shown that the growth rate increases exponentially with the deceleration of expansion. The critical wave number for the instability is almost constant for various rates of the expansion. The linear interaction of a perturbation between the cooled layer and a hot layer composed of dark matter changes the growth rate. The growth rate of the cooled layer is superior to the maximum value of the growth rate in isolated cases when the scale heights of both layers are not so different. This fragmentation theory is applied to cosmologically collapsed layers that were calculated by numerical simulations. The cooled layers produced by t he collapse with transverse expansion have nearly the same density and temperature over a wide scale range of primordial density fluctuations, λ = 1–20 Mpc. The mass of fragmentation is determined by evaluating the growth time of the perturbation and the accretion time of the cooled layer. The typical masses of the fragmentation are distributed over a narrow mass scale of 107–8M⊙ . A large dynamic range of the calculation, 106–8, is required to simulate the central region of the collapsed layer for the fluctuation wavelength, λ = 10 Mpc. A calculation method with extremely large dynamic range is also presented.
Interstellar-Cloud Formation in the Extended Envelopes of Blue Compact Dwarf Galaxies
Authors: Saitō Mamoru , Kamaya Hideyuki , Tomita Akihiko 
Published: March 2014

Abstract
Blue compact dwarf galaxies (BCDs) have an interesting feature in their central region where stars are actively forming. In this paper, we show that shock waves produced by the starbursts there are able to trigger self-gravitating interstellar clouds in extended envelopes, which are often observed in typical BCDs. The criterion adopted for the formation of interstellar clouds is very simple, that is, $\rho \gt 2 \Gamma{\bar{\rho}}/3$. Here, ρ is the gas density of the shocked layer, ${\bar{\rho}}$ is a mean density including the dark matter, and Γ is a numerical factor between 0.5 and 1.0, depending on the mass distribution of the galaxy. Hence, we suggest that the infalling of the clouds onto the central regions causes subsequent starbursts after ∼ 0.1 Gyr of the event, and that the episodic starbursts continue during sub-Gyr.
Infrared Properties of SiO Maser Sources in Late-Type Stars
Authors: Matsuura Mikako , Yamamura Issei , Murakami Hiroshi , Onaka Takashi , Ootsubo Takafumi , Tohya Takanao , Okamura Yoshihiko , Freund Minoru M. , Tanaka Masahiro 
Published: March 2014

Abstract
The results of an SiO maser survey for late-type stars selected by the IRTS (Infrared Telescope in Space) are presented. We have detected SiO J = 1–0, v = 1 and/or v = 2 lines in 27 stars out of 59 stars. The maser intensity increases with the depth of the H2O absorption in the infrared spectra and redness of the 2.2 and 12 μm color. The column densities of the water vapor in the target stars were estimated from the depth of the water absorption in the IRTS spectra. We found that the SiO maser was detected mostly in the stars with a column density of water vapor higher than 3 × 1019–3 ×20 cm−2. We further estimated the density of hydrogen molecules in the outer atmosphere corresponding to these column densities, obtaining 109–1010 cm−3 as a lower limit. These values are roughly in agreement with the critical hydrogen density predicted by models for the excitation of SiO masers. It is possible that the SiO masers are excited in clumps with column density even higher than this value. The present results provide useful information for the understanding of the physical conditions of the outer atmospheres in late-type stars.
OASIS: A Multi-Purpose Near-Infrared Camera and Spectrograph
Authors: Okumura Shin-ichiro , Nishihara Eiji , Watanabe Etsuji , Mori Atsushi , Kataza Hirokazu , Yamashita Takuya 
Published: March 2014

Abstract
We have developed a near-infrared (1–2.5 μm) camera and spectrograph, called OASIS (Okayama Astrophysical System for Infrared imaging and Spectroscopy). OASIS was designed for the 188 cm telescope at Okayama Astrophysical Observatory, and developed as a common-use facility instrument. It has two observing capabilities: imaging with a field of view of 4′ × 4′ and long-slit spectroscopy with a resolving power of ∼ 1000. This paper describes the design of OASIS and reports on the total system performance of the camera+telescope+atmosphere at the Okayama Observatory, together with the performance of an array detector, NICMOS 3, which OASIS utilizes.
Hard X-Ray Emission from Massive Star Clusters in a Giant Molecular Cloud NGC 6334
Authors: Sekimoto Yutaro , Matsuzaki Keiichi , Kamae Tuneyoshi , Tatematsu Ken'ichi , Yamamoto Satoshi , Umemoto Tomofumi 
Published: March 2014

Abstract
We report on detection with the ASCA satellite of hard X-rays from far infrared (FIR) star clusters in the giant molecular cloud (GMC) cores of the NGC 6334 star-forming region. Five FIR cores are visible in the hard X-ray band (E &gt; 2 keV), while in the soft X-ray band (E &lt; 2 keV) the emission is absorbed, except for one core. The observed spectra can be fitted with thermal emission from a hot plasma, whose temperature of ∼ 9 keV is significantly higher than those reported of low-mass Class I pre-main-sequence stars (PMSs) ( ∼ 3 keV) in nearby dark clouds and those of OB-type main-sequence stars (∼ 1 keV). The X-ray luminosity of each core is typically 1033 erg s−1 or 103 times that of typical low-mass PMSs. The observed hard X-rays may be emitted from young massive stars and loss-mass/intermediate-mass PMSs in the FIR cores. The observed hard X-ray flux can ionize the inner part (r ∼ 0.3 pc) of the GMC cores at a rate comparable to that by cosmic-ray particles. If the LX/M ratio of ∼ 10−5L⊙/M⊙ observed in NGC 6334 is typical among GMCs, the X-ray flux from all GMCs in the Galaxy ( ∼ 109L⊙) can account for about 20% of the diffuse galactic ridge hard X-ray emission.
First-Epoch VSOP Observation of 3C 380: Kinematics of the Parsec-Scale Jet
Authors: Kameno Seiji , Inoue Makoto , Fujisawa Kenta , Shen Zhi-Qiang , Wajima Kiyoaki 
Published: March 2014

Abstract
The space-VLBI mission VSOP provides high-quality imaging capabilities to investigate fine structures in quasar jets. We report on the first-epoch VSOP observation of the superluminal quasar 3C 380 at λ 6 cm. A high-quality image with a dynamic range of 1:1200 at a resolution of 0.74 mas × 0.36 mas reveals precise structure along the pc-scale jet. Components C2, A, and F, have been identified with those in previous ground-VLBI observations, and an apparent superluminal motion has been confirmed. We find a very straight motion with a constant apparent velocity for components A and F. Each motion vector is almost parallel to each position vector. This suggests a ballistic ejection from the core. In spite of better position accuracy than previous ground-VLBI observations, we cannot confirm any evidence of acceleration or changes of the position angle which were reported in Polatidis and Wilkinson (1998, AAA 069.159.023). We confirmed that the bent jet structure has kept its similarity and direction, compared with previous images. This suggests an oblique shock in relativistic flow rather than the Kelvin-Helmholtz instability.
Models for Accretion-Disk Fluctuations through Self-Organized Criticality Including Relativistic Effects
Authors: Xiong Ying , Wiita Paul J. , Bao Gang 
Published: March 2014

Abstract
The possibility that some of the observed X-ray and optical variability in active galactic nuclei and galactic black hole candidates are produced in accretion disks through the development of a self-organized critical state is reconsidered. New simulations, including more complete calculations of relativistic effects, do show that this model can produce light-curves and power-spectra for the variability which agree with the range observed in optical and X-ray studies of AGN and X-ray binaries. However, the universality of complete self-organized criticality has not quite been achieved. This is mainly because the character of the variations depend quite substantially on the extent of the unstable disk region. If it extends close to the innermost stable orbit, a physical scale is introduced and the scale-free character of self-organized criticality is vitiated. A significant dependence of the power spectrum density slope on the type of diffusion within the disk and a weaker dependence on the amount of differential rotation are noted. When general-relativistic effects are incorporated in the models, additional substantial differences are produced if the disk is viewed from directions far from the accretion disk axis.
Kinematics of the Galaxy from Hipparcos Proper Motions
Authors: Zhu Zi 
Published: March 2014

Abstract
From Hipparcos proper motions, we have analysed the local kinematics of the Milky Way from young O-B5 stars, classical Cepheids, and the late-type K-M giants. The components of solar motion along the direction pointing to the galactic center from the Sun u0 and along the direction pointing to the north galactic pole w0 are approximately 10 km s−1 and 8 km s−1 for all types of stars, while the component pointing to the direction of the galactic rotation varies over a wide range from 13 to 21 km s-1, depending on the type of stars. The galactic rotation derived from O-B5 stars is 269 ± 12 km s-1, which is apparently larger than that recommended by the IAU in 1985 (220 km s-1). Analysing the proper-motion data of O-B5 stars, we clarified a clear stellar warping motion that is a systematic rotation, ∂Vz/∂θ /R = −3.79 ± 1.05 km s−1 kpc−1, of stars around the axis pointing to the galactic center. Taking the kinematical solution from the K–M giants into account, and considering the possible systematic errors remaining in the Hipparcos proper-motion system, the warping motion of O–B5 stars might even be pronounced. The solution from classical Cepheids seems to show a slight contracting motion of the Galaxy in the solar neighbourhood, ∂Vθ/∂θ /R = −2.60±1.07 km s−1 kpc−1, which is along the solar circle. By comparing the thus-derived results, the kinematical discrepancies between each subset of stars are analysed, and the possible reasons for the kinematical differences are discussed.
Discovery of 101-s Pulsations from AX J0057.4–7325 in the SMC with ASCA
Authors: Yokogawa Jun , Torii Ken’ichi , Kohmura Takayoshi , Imanishi Kensuke , Koyama Katsuji 
Published: March 2014

Abstract
The results from two ASCA observations of AX J0057.4−7325 = RX J0057.3−7325 are presented. Coherent pulsations with a barycentric period of 101.45 ± 0.07 s were discovered in the second observation. The X-ray spectrum was found to be hard (photon index ∼ 0.9) and unchanged through these observations, except for the flux. The ROSAT archival data show that AX J0057.4−7325 exhibits a flux variation with a factor ≳ 10. A discussion on a possible optical counterpart is given.