bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Spectral Properties of Hot Gas Cavities around NGC 4636
Authors: Ohto Akimitsu , Kawano Naomi , Fukazawa Yasushi
Published: March 2014

A Chandra observation of NGC 4636 revealed that X-ray hot gas is violently disturbed. We investigated the detailed distributions of the temperature and absorption of hot gas, in order to derive information about the gas dynamics. The temperature gradually increases from 0.6 keV at the center to 0.78 keV at 2 arcmin of the galaxy center; this is consistent with previous measurements. On the other hand, the azimuthal profiles of the temperature and absorption strongly correlate with the disturbance of hot gas. The west part, at 80 arcsec from the galaxy center, exhibits a higher temperature by 0.1–0.2 keV and an excess absorption by $\sim 5 \times 10^{20} \,\mathrm{cm}^{-2}$ compared with the azimuthal averages. This unusual region corresponds to the western X-ray cavity with a size of 20 arcsec radius. The same behavior is also seen around the northeast cavity with a smaller size than the west part. It is suggested that these unusual regions were caused by dramatic outflow or jet from the galactic nuclei, considering the east–west symmetry. The outflow gas or jet might have disturbed the surrounding hot gas and created hole-like regions. The observed high temperature and excess absorption of unusual regions indicate that the rims of holes might have been compressed, heated, and then cooled down at the end stage. We also discuss the past possible nuclear activity in NGC 4636.
The Influence of a Dipole Magnetic Field on the Structures of Cyclotron Lines
Authors: Nishimura Osamu
Published: March 2014

We examined the structures of cyclotron resonant lines in a large-scaled atmosphere threaded by a dipole magnetic field. We found that the ratio of the centroid energies of the lines at the second harmonic and at the fundamental can be more than 2. This is mainly due to different values of the cross sections of cyclotron resonant scattering in each harmonic. Our calculations suggest that the effect of the dipole magnetic field could be confirmed by the variation of the ratio of these centroid energies. Our results also indicate that the 5 keV absorption feature detected in the observed spectra of the Soft Gamma Repeater SGR 1806$-$20 is not due to an electron-cyclotron resonance.
Four Probable T Tauri Stars in MBM 12
Authors: Ogura Katsuo , Sugitani Koji , Magakian Tigran Yu. , Movsessian Tigran A. , Nikogossian Elena H. , Itoh Yoichi , Tamura Motohide
Published: March 2014

Survey observations were carried out in the MBM 12 (sometimes referred to as Lynds 1457) dark cloud in search of $\mathrm{H}\alpha$ emission stars by using a slitless grism spectrograph on the 2.6-m reflector of Byurakan Astrophysical Observatory, Armenia. Four new $\mathrm{H}\alpha$ stars were detected by the survey and identified as candidate T Tauri stars by follow-up low-dispersion spectroscopy and/or near-infrared photometry.
Hydrogen Abundance in the Tachocline Layer of the Sun
Authors: Takata Masao , Shibahashi Hiromoto
Published: March 2014

Sound speed inversions of the Sun show that the profile of the relative difference between the Sun and the standard solar model has a sharp peak around $r / {{{R}_{\odot}}} = 0.65$, which is the location of the tachocline layer found by rotation inversions. It has been suggested that this sharp peak would be due to the difference, between the Sun and the model, in the hydrogen abundance in the tachocline layer, possibly caused by the weak-mixing process. In this paper, we quantitatively discuss the hydrogen abundance in the tachocline layer based on a seismic solar model, which was constructed using the sound speed and density profiles as well as the depth of the convection zone obtained by helioseismology. One of the important characteristics of the seismic solar model is that it gives us a hydrogen profile as a part of the solution. We find that the hydrogen abundance of the seismic solar model decreases more mildly than that of the standard solar models constructed by incorporating the diffusion process. This feature hardly depends on the profile of the heavy elements as well as the uncertainties in the opacity and the equation of state.
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
Authors: Shirasaki Yuji , Kawai Nobuyuki , Yoshida Atsumasa , Matsuoka Masaru , Tamagawa Toru , Torii Ken’ichi , Sakamoto Takanori , Suzuki Motoko , Urata Yuji , Sato Rie , Nakagawa Yujin , Takahashi Daiki , Fenimore Edward E. , Galassi Mark , Lamb Donald Q. , Graziani Carlo , Donaghy Timothy Q. , Vanderspek Roland , Yamauchi Makoto , Takagishi Kunio , Hatsukade Isamu
Published: March 2014

The Wide-field X-ray Monitor (WXM) is one of the scientific instruments carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on 2000 October 9. HETE-2 is an international mission consisting of a small satellite dedicated to provide broad-band observations and accurate localizations of gamma-ray bursts (GRBs). A unique feature of this mission is its capability to determine and transmit GRB coordinates in almost real-time through the burst alert network. The WXM consists of three elements: four identical Xe-filled one-dimensional position-sensitive proportional counters, two sets of one-dimensional coded apertures, and the main electronics. The WXM counters are sensitive to X-rays between 2 keV and 25 keV within a field-of-view of about 1.5 sr, with a total detector area of about $350 \,\mathrm{cm}^2$. The in-flight triggering and localization capability can produce a real-time GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of $10^{-7} \,\mathrm{erg} \,\mathrm{cm}^{-2}$. In this report, the details of the mechanical structure, electronics, on-board software, ground and in-flight calibration, and in-flight performance of the WXM are discussed.
An Experimental Study of Submillimeter-Wave Horn Antennae for a Submillimeter-Wave Array
Authors: Matsunaga Mayumi , Sekimoto Yutaro , Matsunaga Toshiaki , Sakai Takeshi
Published: March 2014

This paper aims to introduce two types of submillimeter-wave horn antennae designed by the authors and to present numerical findings obtained by an evaluative testing system that has also been developed by the authors. Submillimeter-wave components are widely used in radio-astronomical observation systems. There is a need to minimize (1) the various losses possibly incurred in the wave-receiving unit, and (2) the quantity of the unwanted electromagnetic waves mixing in. It is a well-known fact that a corrugated horn antenna possesses very low levels of cross-polarized field intensity, loss, and side lobes. It is for this reason that the authors have chosen to use corrugated horn antennae as two types of such antennae—one designed for use in the range of 280 GHz to 360 GHz frequencies and tested at 280 GHz, 332 GHz, and 360 GHz, and the other designed for use in the range of 385 GHz to 500 GHz frequencies and tested at 385 GHz, 442.5 GHz, and 500 GHz. The measurements of the antenna beam patterns have been found to largely correspond to those of the numerical analyses; it may be concluded that the antennae are functionally as efficient as they were designed and the testing system doubtless serves the desired purpose.
Minkowski Functionals of SDSS Galaxies I : Analysis of Excursion Sets
Authors: Hikage Chiaki , Schmalzing Jens , Buchert Thomas , Suto Yasushi , Kayo Issha , Taruya Atsushi , Vogeley Michael S. , Hoyle Fiona , Gott J. Richard , Brinkmann Jon
Published: March 2014

We present a first morphometric investigation of a preliminary sample from the SDSS of 154287 galaxies with apparent magnitude $14.5 < m_r < 17.5$ and redshift $0.001 < z < 0.4$. We measure the Minkowski Functionals, which are a complete set of morphological descriptors. To account for the complicated wedge-like geometry of the present survey data, we construct isodensity contour surfaces from the galaxy positions in redshift space and employ two complementary methods of computing the Minkowski Functionals. We find that the observed Minkowski Functionals for SDSS galaxies are consistent with the prediction of a $\Lambda$-dominated spatially-flat Cold Dark Matter model with random-Gaussian initial conditions, within the cosmic variance estimated from the corresponding mock catalogue. We expect that future releases of the SDSS survey will allow us to distinguish morphological differences in the galaxy distribution with regard to different morphological types and luminosity ranges.
Radiative Collimation of Electron–Positron Jets II
Authors: Orihara Shiho , Fukue Jun
Published: March 2014

We consider a collimation and acceleration mechanism for relativistic jets emanating from an inner region of a relativistic accretion disk surrounding a Kerr black hole, with Keplerian angular momentum under disk radiation fields, taking into account the effect of radiation drag. When the jets consist of electron–positron pair plasmas and the disk luminosity is of the order of the Eddington luminosity, we found that the terminal speed is about $0.9 \,c$ for a Schwarzschild case, while it becomes $\sim 0.96 \,c$ for an extreme Kerr case. In such a case, the opening angle of jets is of the order of $5^\circ$. We also examined the opening angle and the listing degree when the disk radiation is not axisymmetric, but has a one-armed pattern. For the case of 0.3 amplitude, the opening angle is of the order of a few degrees, and the jet direction is bent by several degrees to $10^\circ$.
Abundance Analysis of the Silicon Star HR 6958
Authors: Kato Ken-ichi
Published: March 2014

The elemental composition of the chemically peculiar star HR 6958 has been studied with emphasis on doubly ionized rare earths. A visual region spectrum taken with the ELODIE spectrograph at the Haute-Provence Observatory was analyzed. A total of 40 elements including Pr III, Nd III, Tb III, Dy III, Ho III, and Er III were identified and their abundances computed. He is deficient by over 1 dex with respect to the Sun; the light elements (C-Ca), except for Si, have solar abundances; the iron group elements (Sc–Fe) are overabundant by 1 dex to 2 dex, with Ti and Cr highly overabundant; and the lanthanide rare earths are overabundant by 3 dex to 4 dex. This abundance pattern with He deficient, Si, Ti, Cr, Sr, and Pr overabundant indicates that HR 6958 is a member of Si stars.
TV Observation of the Leonid Meteor Shower in 2002: First Observation of a Faint Meteor Storm
Authors: Fujiwara Yasunori , Ueda Masayoshi , Kawasaki Yasuhiro , Nakamura Takuji
Published: March 2014

TV observations of the Leonid meteor shower were carried out between ${18{}^{\mathrm {h}}}$ (UT) and ${20\rlap {.}{}^{\mathrm {h}}5}$ (UT) on 2002 November 17. In total, 412 Leonid meteors were observed along with 303 non-Leonid meteors. Enhanced activity of faint ($\mbox{mag} \lt +10$ mag$< +10$) Leonid meteors was observed between ${19\rlap {.}{}^{\mathrm {h}}5}$ (UT) and ${20\rlap {.}{}^{\mathrm {h}}5}$ (UT), with a peak influx of $1.8 \times 10^{-4} \,\mathrm{km}^{-2} \,\mathrm{s}^{-1}$. The activity of this peak was rich in faint meteors, without visible meteors, which was different from the storm observed in 2001 over Japan. Comparisons between the observed peak and several theoretical predictions are discussed.
GRAPE-6: Massively-Parallel Special-Purpose Computer for Astrophysical Particle Simulations
Authors: Makino Junichiro , Fukushige Toshiyuki , Koga Masaki , Namura Ken
Published: March 2014

In this paper, we describe the architecture and performance of the GRAPE-6 system, a massively-parallel special-purpose computer for astrophysical $N$-body simulations. GRAPE-6 is the successor of GRAPE-4, which was completed in 1995 and achieved the theoretical peak speed of 1.08 Tflops. As was the case with GRAPE-4, the primary application of GRAPE-6 is simulations of collisional systems, though it can also be used for collisionless systems. The main differences between GRAPE-4 and GRAPE-6 are (a) the processor chip of GRAPE-6 integrates 6 force-calculation pipelines, compared to one pipeline of GRAPE-4 (which needed 3 clock cycles to calculate one interaction), (b) the clock speed is increased from 32 to 90 MHz, and (C) the total number of processor chips is increased from 1728 to 2048. These improvements resulted in a peak speed of 64 Tflops. We also discuss the design of the successor of GRAPE-6.
The Infrared Counterpart of the X-Ray Nova XTE J1720—318
Authors: Tetsuya Nagata , Kato Daisuke , Baba Daisuke , Nishiyama Shogo , Nagayama Takahiro , Nagashima Chie , Kurita Mikio , Sato Shuji , Kato Taichi , Uemura Makoto , Yamaoka Hitoshi , Monard Berto , Ita Yoshifusa , Matsunaga Noriyuki , Nakajima Yasushi , Tamura Motohide , Nakaya Hidehiko , Sugitani Koji
Published: March 2014

We report on the discovery of an infrared counterpart to the X-ray transient XTE J1720$-$318 on 2003 January 18, nine days after an X-ray outburst, and the infrared light curve during the first 130 days after the outburst. The infrared light curve shows a decline of $\sim 1.2 \,\mathrm{mag}$ from the peak magnitude of $K_\mathrm{s} \sim 15.3$ over the observation period, and a secondary maximum, about 40 days after the outburst. Another small increase in the flux was also recorded about 20 days after the outburst. These increases were also detected in the X-ray light curve. The $J H K_\mathrm{s}$ colors are consistent with an X-ray irradiated accretion disk suffering an extinction of $A_V \sim 8$, which is also inferred from its X-ray spectrum and the extinction map constructed from far-infrared dust emission of this line of sight. These $J, H$, and $K_\mathrm{s}$ observations demonstrate that useful data can be obtained even for such an object, which suffers heavy optical extinction, possibly located beyond the galactic center.
Performance of Subaru Cassegrain Adaptive Optics System
Authors: Takami Hideki , Takato Naruhisa , Hayano Yutaka , Iye Masanori , Oya Shin , Kamata Yukiko , Kanzawa Tomio , Minowa Yosuke , Otsubo Masashi , Nakashima Koji , Gaessler Wolfgang , Saint-Jacques David
Published: March 2014

The design and performance of the Cassegrain Adaptive Optics (AO) system for the 8.2 m Subaru Telescope are reported. The system is based on a curvature wavefront sensor with 36 photon-counting avalanche photodiode modules and a bimorph wavefront correcting deformable mirror with 36 driving electrodes. The engineering first light of the AO system took place in 2000 December. The AO system has been in service since 2002 April for two open-use instruments, an infrared camera and spectrograph and a coronagraph imager with adaptive optics. The Strehl ratio in the $K$-band is around 0.3 for bright guide stars under ${0\rlap {.}{}^{\mathrm {\prime \prime }}4} K$-band seeing condition. The control loop performs with 2060 corrections per second. High sensitivity of the wavefront sensor allows significant improvement in the image quality, even for faint guide stars down to $R = 18 \,\mathrm{mag}$. The FWHM of stellar images in a globular cluster was measured to derive an estimation of the isoplanatic angle and was found nearly constant out to $30''$ from the guide star, indicating that the height of the effective turbulent layer of that particular night was less than 1.8 km. The on-going upgrade plans for a fivefold increase in the number of control elements and for the installation of a laser guide AO system are described.
Spectral Evolution of the GRB 030329 Afterglow: Detection of the Supernova Nebular Phase Emissions
Authors: Kosugi George , Mizumoto Yoshihiko , Kawai Nobuyuki , Yoshida Atsumasa , Kawabata Koji S. , Totani Tomonori , Iye Masanori , Sekiguchi Kazuhiro , Aoki Kentaro , Ohyama Youichi , Aoki Wako , Kobayashi Naoto , Komiyama Yutaka , Noumaru Jun’ichi , Ogasawara Ryusuke , Sakamoto Takanori , Shirasaki Yuji , Takata Tadafumi , Tamagawa Toru , Torii Ken’ichi , Urata Yuji , Watanabe Jun-ichi , Yamada Toru , Qiu Yulei
Published: March 2014

GRB 030329 is the first Gamma-ray burst event for which a connection with a supernova (SN 2003dh) has been confirmed spectroscopically in its early phase. We present optical spectroscopy of this object 40 and 85 days after the burst (35 and 73 rest-frame days, respectively) obtained with the Subaru 8.2-m telescope. After subtracting the host galaxy template spectrum, the second-epoch spectrum shows nebular-phase emission lines emerging from the dominated photospheric-phase spectrum. The transition from the photospheric phase to the nebular phase has just started, or was slowly progressing at the time of our second-epoch observations. Our spectral analysis of the nebular-phase emission lines suggests that the explosion of the progenitor of the GRB 030329 was aspherical, and that the axis of an asphericity is well aligned to both the GRB relativistic jet and our line of sight. Although the decay index and the color evolution in the rest frame during our two epochs are very consistent with those of the Type Ic supernovae SN 1998bw and SN 1997ef, the nebular-phase lines emerged slightly earlier than in the case of these supernovae. These results infer that the most important factor that distinguishes SNe with GRB from SNe without GRB is the scale of the jet activity, or a viewing-angle effect, or both of them.
13CO (J=1–0) Survey of Molecular Clouds toward the Monoceros and Canis Major Region
Authors: Kim Bong Gyu , Kawamura Akiko , Yonekura Yoshinori , Fukui Yasuo
Published: March 2014

Through a large-scale ${{13\atop} \mathrm{CO}}$ ($J = 1 \hbox{--} 0$) survey toward a region in Monoceros and Canis Major, we present following results: (1) We identified in total 115 clouds. (2) Group I (CMa OB1 and G220.8$-$1.7) may physically connected with Group II (Mon R2 and NGC 2149). (3) 496 YSO candidates were chosen from IRAS point source catalog (IPC). (4) The mass spectrum of the Local clouds shows a power-law relation with an index of $-1.55 \pm 0.09$. (5) The number fraction of star-forming clouds increases as the cloud mass increases. Especially, massive clouds of $M_\mathrm{cloud} \ge 10^{3.5} \,{{{M}_{\odot}}}$ are all star-forming clouds. (6) The line width–cloud radius relation is best fitted as $\Delta V_\mathrm{comp} \propto r_\mathrm{cloud}^{0.47}$ ($\mbox{correlation coefficient} = 0.87$ correlation coefficient$= 0.87$). (7) The distribution of $(M_\mathrm{vir} / M_\mathrm{cloud})$ shows that star-forming clouds tend to be more virialized than no star-forming clouds. (8) Star formation in Group I is more active than that in Group II. (9) Unexpected small number of low-mass clouds in Group I may be due to strong UV radiation from O-type stars in the vicinity of the clouds. (10) Star formation in Group II might occurred by self-gravitational, except for the most massive cloud.
Critical Accretion Disk
Authors: Fukue Jun
Published: March 2014

For a supercritical accretion regime, we propose a critical accretion disk, where the mass-accretion rate is regulated just at the critical rate with the help of wind mass-loss. We first derive a critical radius, inside of which the standard picture is violated, using the condition that the radiative force is balanced by the gravity in the vertical direction. The critical radius $r_\mathrm{cr}$ is found to be $r_\mathrm{cr} = (9\sqrt{3}\sigma_\mathrm{T} / 16\pi c m_\mathrm{p}) \dot{M}_\mathrm{input} = 1.95 (\dot{M}_\mathrm{input} / \dot{M}_\mathrm{crit}) r_\mathrm{g}$, where $\dot{M}_\mathrm{input}$ is the mass-accretion rate at the outer edge of the disk, $\dot{M}_\mathrm{crit}$ the critical accretion rate, and $r_\mathrm{g}$ the Schwarzschild radius of the central object. Outside of this critical radius, the disk is in a radiation-pressure dominated standard state, while inside this radius the disk is in a critical state, where the excess mass is expelled by wind and the accretion rate is kept to be just at the critical rate at any radius inside $r_\mathrm{cr}$. In such a critical accretion disk, the disk thickness is $H \sim (1/6\sqrt{3})r$ and the surface temperature is $\sigma T^4 \sim (2/3\sqrt{3}) L_\mathrm{E} / 4\pi r^2$, where $L_\mathrm{E}$ is the Eddington luminosity. The total disk luminosity becomes $L_\mathrm{disk} \sim (2/3\sqrt{3}) [\ln (r_\mathrm{cr}/r_\mathrm{in})+1] L_\mathrm{E}$, where $r_\mathrm{in}$ is the inner radius. We apply the present model to microquasars and narrow-line Seyfert 1 galaxies, which are supposed to be under supercritical accretion.
Wave–Warp Resonant Interactions in Relativistic Disks and kHz QPOs
Authors: Kato Shoji
Published: March 2014

Non-linear resonant interactions between disk oscillations and relativistic disks are examined under the assumption that the disks are deformed by a warp. There are three types of resonances: horizontal and vertical resonances of $g$-mode oscillations, and horizontal resonances of $p$-mode oscillations. In the limit of long-wavelength oscillations, the resonances occur at $3 \,r_{\mathrm{g}}, 3.62 \,r_{\mathrm{g}}, 4 \,r_{\mathrm{g}}$, and $6.46 \,r_{\mathrm{g}}$, depending on the types of resonances and the wave modes. The frequencies of the resonant oscillations at these points also depend on the modes of oscillations. There are sets of resonant oscillations whose frequency ratio is close to $2:3$. The frequencies of the resonant oscillations can change as a wave packet propagates in the radial direction.
Chandra Observation of Luminous Sources in the Nearby Irregular Galaxy NGC 4449
Authors: Miyawaki Ryohei , Sugiho Masahiko , Kokubun Motohide , Makishima Kazuo
Published: March 2014

Using archival Chandra ACIS-S data, $0.5 \hbox{--} 8.0 \,\mathrm{keV}$ X-ray spectra of two luminous X-ray sources in the nearby dwarf irregular galaxy NGC 4449 were studied. One, with an extremely high luminosity of $1.3 \times 10^{39} \;\mathrm{erg} \,\mathrm{s}^{-1}$ in the $0.5 \hbox{--} 8.0 \;\mathrm{keV}$ band, shows a spectrum that is well described with a power-law model of photon index $\sim 2$. Its properties are consistent with those of ultraluminous compact X-ray sources observed in nearby galaxies. The spectrum of the other, with a luminosity of $2.7 \times 10^{38} \,\mathrm{erg} \,\mathrm{s}^{-1}$ in the same band, is successfully represented with a so-called multi-color disk blackbody emission model with an inner-most disk temperature of $\sim 0.59 \,\mathrm{keV}$. Its spectral parameters are typical of ordinary black hole binaries observed in our Galaxy and the Large Magellanic Cloud. These young population objects, together with a bright supernova remnant and diffuse hot gas already reported, suggest that the X-ray emission from irregular galaxies is generally enhanced by their recent star-forming activities.
A Subaru Search for Lyman$\alpha$
Emitters at
z
= 5.8 with an Intermediate-Band Filter
Authors: Ajiki Masaru , Taniguchi Yoshiaki , Fujita Shinobu S. , Shioya Yasuhiro , Nagao Tohru , Murayama Takashi , Yamada Sanae F. , Umeda Kazuyoshi , Sasaki Shunji S. , Sumiya Ryoko , Komiyama Yutaka
Published: March 2014

We present the results of a survey for Ly $\alpha$ emitters at $z \approx 5.8$ using a new intermediate-band filter centered at $\lambda_\mathrm{c} \approx 8275 \,{Å$ with $\Delta\lambda_\mathrm{FWHM} \approx 340 \,{Å$ (i.e., spectroscopic resolution is $R \approx 24$ ) and a combination with a traditional narrow-band centered at $\lambda_\mathrm{c} \approx 8150 \,{Å$ with $\Delta\lambda_\mathrm{FWHM} \approx 120 \,{Å$ ( $R \approx 68$ ). Our observations were made using the Subaru Prime Focus Camera, Suprime-Cam, on the 8.2m Subaru telescope in a sky area surrounding the high-redshift quasar SDSSp J104433.04 $-$ 012522.2 at $z = 5.74$ , covering an effective sky area of $\approx 720 \;\mathrm{arcmin}^2$ . In this survey, we have found four Ly $\alpha$ -emitter candidates from the intermediate-band image ( $z \approx 5.8$ with $\Delta z \approx 0.3$ ). Combined with our previous results based on the NB816 imaging, we discuss the star-formation activity in galaxies between $z \approx 5.7$ and $z \approx 5.9$ .
Global Structures of Optically Thin Black Hole Accretion Flows Obtained from Direct Magnetohydrodynamic Simulations
Authors: Machida Mami , Nakamura Kenji , Matsumoto Ryoji
Published: March 2014

We studied the global structures of radiatively inefficient black hole accretion flows by three-dimensional magnetohydrodynamic simulations. The initial state is a constant angular-momentum torus threaded by weak toroidal magnetic fields. The torus is assumed to be embedded in a low-density, spherical, isothermal halo. We found that in the innermost region ($\varpi < 15 \,r_g$: $r_g$ is the Schwarzschild radius) of optically thin hot disks formed by accretion from the torus, the radial structure can be described by a one-dimensional steady transonic ADAF (Advection Dominated Accretion Flow) solution that takes into account the radial dependence of $\alpha$. Numerical results indicate that the magnetic flux emerging from the disk creates a magnetically active layer in which magnetic reconnection generates outflows along magnetic field lines. We also studied the dependence of the disk structure on the external pressure of the initial torus. The saturation level of magnetic field amplification is higher for a model with a larger external pressure. Thus, external pressure enhances the magnetic activity of the disk. When the external pressure is 5–20% of the maximum pressure of the torus, the kinetic and Poynting energy flux of the outflow is about 1% of the energy flux advected to the black hole through accretion.
SiO Maser Survey of IRAS Sources in the Inner Galactic Disk
Authors: Deguchi Shuji , Fujii Takahiro , Glass Ian S. , Imai Hiroshi , Ita Yoshifusa , Izumiura Hideyuki , Kameya Osamu , Miyazaki Atsushi , Nakada Yoshikazu , Nakashima Jun-ichi
Published: March 2014

We surveyed 401 color-selected IRAS sources in the galactic disk in the SiO $J = 1 \hbox{--} 0, v = 1$ and 2 maser lines at 43 GHz, resulting in 254 (239 new) detections. The observed sources lie mostly in a strip of the inner galactic disk with boundaries $-10^{\circ} < l < 40^{\circ}$ and $\vert b\vert < 3^{\circ}$. This survey provides radial velocities of inner-disk stars for which optical measurements cannot be made due to interstellar extinction. The SiO $l \hbox{--} v$ diagram in the area $-10^{\circ} < l < 40^{\circ}$ exhibits fewer objects coincident with the molecular ring feature than does the OH 1612 MHz source $l \hbox{--} v$ map, indicating a slight difference of stellar type between SiO and OH emitting stars. After identifying all of the SiO detected sources in the 2MASS near-infrared catalog, we computed their luminosity distances based on the infrared fluxes. We then mapped these objects onto the first quadrant of the galactic plane. Combining the distances with the SiO radial velocities, we obtained a pattern speed for SiO maser sources, $\Omega_{\mathrm{P}} = 21 (\pm 13) \,\mathrm{km} \,\mathrm{s}^{-1} \,\mathrm{kpc}^{-1}$, between the distances 1 and 5.5 kpc, without the use of any dynamical models. The increase of the pattern speed toward the galactic center (up to $60 \,\mathrm{km} \,\mathrm{s}^{-1} \,\mathrm{kpc}^{-1}$ between the distances, 5.5 and 7 kpc) suggests the presence of two pattern speeds in the Galaxy.
Of NBOs and kHz QPOs: a Low-Frequency Modulation in Resonant Oscillations of Relativistic Accretion Disks
Authors: HorÁk Jiří , Abramowicz Marek A. , Karas Vladimír , Kluźniak Wodzimierz
Published: March 2014

The origin of quasi periodic modulations of flux in the kilohertz range (kHz QPOs), observed in low-mass X-ray binaries, is usually assumed to be physically distinct from that of the “normal branch oscillations” (NBOs) in the Z-sources. We show that a low-frequency modulation of the kHz QPOs is a natural consequence of the non-linear relativistic resonance suggested previously to explain the properties of the high-frequency twin peaks. The theoretical results discussed here are reminiscent of the 6 Hz variations of frequency and amplitude of the kHz QPOs reported by Yu, van der Klis, and Jonker (2001, ApJ, 559, L29).
2:3 Twin Quasi-Periodic Oscillations in Magnetohydrodynamic Accretion Flows
Authors: Kato Yoshiaki
Published: March 2014

We have studied the radial and vertical oscillations in three-dimensional magnetohydrodynamic (MHD) accretion flows around black holes. General-relativistic effects were taken into account by using a pseudo-Newtonian potential. We found that the structure of MHD flows is changed at $3.8 \,r_{\mathrm{s}} \leq r \leq 6.3 \,r_{\mathrm{s}}$, and that two pairs of quasi-periodic oscillations (twin QPOs) are excited in that region. The time evolution of the power spectrum density (PSD) indicates that these twin QPOs are most likely to be produced by a resonance between the Keplerian frequency, $\nu_\mathrm{K}$, and the epicyclic frequency, $\nu_{\kappa}$. The PSD shows that the lower peak frequency, $\nu_\mathrm{l}$, corresponds to, $\nu_\mathrm{K}$, while the upper peak frequency, $\nu_\mathrm{u}$, corresponds to $\nu_\mathrm{K} + \nu_{\kappa}$. The ratio of two peak frequencies is close to $2:3$. The results provide the first direct evidence for the excitation of resonant disk oscillation in MHD accretion flows.
Locating the Warm–Hot Intergalactic Medium in the Simulated Local Universe
Authors: Yoshikawa Kohji , Dolag Klaus , Suto Yasushi , Sasaki Shin , Yamasaki Noriko Y. , Ohashi Takaya , Mitsuda Kazuhisa , Tawara Yuzuru , Fujimoto Ryuichi , Furusho Tae , Furuzawa Akihiro , Ishida Manabu , Ishisaki Yoshitaka , Takei Yoh
Published: March 2014

We present an analysis of mock spectral observations of warm–hot intergalactic medium (WHIM) using a constrained simulation of the local universe. The simulated map of oxygen emission lines from local WHIM well reproduces the observed structures traced by galaxies in the real local universe. We further attempt to perform mock observation of the outer parts of the simulated Coma cluster and A 3627 adopting the expected performance of DIOS (Diffuse Intergalactic Oxygen Surveyor), which is proposed as a dedicated soft X-ray mission to search for cosmic missing baryons. We find that WHIMs surrounding nearby clusters are detectable with a typical exposure time of one day, and thus constitute realistic and promising targets for DIOS. We also find that an X-ray emitting clump in front of Coma cluster, recently reported in the XMM-Newton observation, has a counterpart in the simulated local universe, and its observed spectrum can be well reproduced in the simulated local universe if the gas temperature is set to the observationally estimated value.
Sound Speed and the Pseudo-Newtonian Potential
Authors: Fukue Jun
Published: March 2014

We propose a special-relativistic correction to the sound speed calculated from the (Paczyński and Wiita 1980) pseudo-Newtonian potential, in order to avoid divergence to infinity at the Schwarzschild radius. Under this correction, the re-scaled sound speed approaches $c/\sqrt{3}$ at the Schwarzschild radius; otherwise, it diverges there. Spherical flows onto a black hole are briefly discussed.
Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova, EG Cancri
Authors: Kato Taichi , Nogami Daisaku , Matsumoto Katsura , Baba Hajime
Published: March 2014

We report on time-resolved photometric observations of the WZ Sge-type dwarf nova, EG Cnc (Huruhata’s variable), during its superoutburst in 1996–1997. EG Cnc, after the main superoutburst accompanied by the development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a series of six major rebrightenings. During these rebrightenings and the following long fading tail, EG Cnc persistently showed superhumps having a period equal to the superhump period observed during the main superoutburst. The persistent superhumps had a constant superhump flux with respect to the rebrightening phase. These findings suggest that the superhumps observed during the rebrightening stage and the fading tail are a “remnant” of the usual superhumps, and are not newly triggered by rebrightenings. By a comparison with the 1977 outburst of this object and outbursts of other WZ Sge-type dwarf novae, we propose an activity sequence of WZ Sge-type superoutbursts, in which the current outburst of EG Cnc is placed between a single-rebrightening event and distinct outbursts separated by a dip. The post-superoutburst behavior of WZ Sge-type dwarf novae can be understood in the presence of a considerable amount of remnant matter behind the cooling front in the outer accretion disk, even after the main superoutburst. We consider that a premature quenching of the hot state due to the weak tidal effect under the extreme mass ratio of the WZ Sge-type binary is responsible for the origin of the remnant mass.
V1494 Aql: Eclipsing Fast Nova with an Unusual Orbital Light Curve
Authors: Kato Taichi , Ishioka Ryoko , Uemura Makoto , Starkey Donn R. , Krajci Tom
Published: March 2014

We present the time-resolved photometry of V1494 Aql (Nova Aql 1999 No. 2) between 2001 November and 2003 June. The object is confirmed to be an eclipsing nova with a period of 0.1346138(2) d. The eclipses were present in all observed epochs. The orbital light curve shows a rather unusual profile, consisting of a bump-like feature at phase 0.6–0.7 and a dip-like feature at phase 0.2–0.4. These features were probably persistently present in all available observations between 2001 and 2003. A period analysis outside of the eclipses has confirmed that these variations have a period common to the orbital period, and are unlikely to be interpreted as superhumps. We suspect that the structure (probably in the accretion disk) fixed in the binary rotational frame is somehow responsible for this feature.
Unusual State in V Sagittae
Authors: Kato Taichi
Published: March 2014

It has recently been demonstrated that the recurring high/low states in the peculiar binary V Sge can be explained by considering limit-cycle oscillation involving negative feedback by the wind on the mass-transfer from the secondary star. We noticed, from recent observations reported to VSNET, the presence of a different state of recurring variations (recurrence time $\sim 30 \,\mathrm{d}$), showing a gradual rise and a sudden drop in brightness. The observed features of this light variation are unlikely to be reproduced by a limit-cycle oscillation mechanism involving a mass-transfer variation from the secondary star (Hachisu, Kato 2003). We suggest that this phenomenon originates from an unidentified intrinsic instability in the disk, or in the wind of a high-luminosity object, such as in V Sge.
Deep Fading of the New Herbig Be Star MisV1147
Authors: Uemura Makoto , Kato Taichi , Ishioka Ryoko , Yoshida Seiichi , Kadota Ken-ichi , Ohkura Nobuo , Henden Arne , Pejcha Ondrej , Kinugasa Kenzo , Fujii Mitsugu , Simonsen Mike , Greaves John , Dubovsky Pavol A. , Poyner Gary , West Doug , Stine Robert J. , Taylor Dan , Poxon Michael , Muyllaert Eddy , Ripero José , Reszelski Maciej , Jones Christopher P.
Published: March 2014

We report on the discovery of a new variable star, MisV1147, by the MISAO Project and its unusual photometric variations. The light curve of the object is characterized by two distinct states, that is, a relatively calm, bright state and an active state during which repetitive fadings with large amplitudes of $\sim 2 \,\mathrm{mag}$ were observed. The fading events were associated with optical reddening. The object is identified with a catalogued $\mathrm{H}\alpha$ emission star, which has been confirmed by our spectroscopic observations. The $\mathrm{H}\alpha$ emission line is narrow and symmetric both in the bright and faint phases. The object has infrared colors analogous to T Tau stars or Herbig Ae/Be stars. In conjunction with the detection of a NaD absorption line and its position close to Cep OB1, we conclude that MisV1147 is a Herbig Be star with its spectral type of B2. Its optical-infrared spectral energy distribution is typical for Herbig Ae/Be stars, which supports this classification. The overall properties of the light curve are reminiscent of a UX Ori sub-group, showing Algol-type minima. The most noteworthy feature of MisV1147 is that it has a spectral type B2, whereas known UX Ori stars have spectral types later than B8. The object, furthermore, has one of the largest amplitudes of variations among known Herbig Ae/Be stars. Hence the object breaks the very strong correlation between the variation amplitude and the spectral type. This implies that dust clumps in circumstellar matter can significantly obscure a central object even in the early-type system.
Metallicities in Four Planet-Harbouring K-Type Giants: HD 47536, HD 59686, HD 137759, and HD 219449
Authors: Sadakane Kozo , Ohnishi Takashi , Ohkubo Michiko , Takeda Yoichi
Published: March 2014

Spectroscopic abundance analyses are carried out for four K-type giant stars that have recently been reported to be accompanied by giant planets, together with two reference stars of similar spectral types. The resulting metallicities, $\mathrm{[Fe/H]}$, for three stars (HD 59686, HD 137759, and HD 219449) coincide with the solar value, while that for HD 47536 is definitely lower than the Sun. Combining with the reported low metallicity found for the G9 III giant HD 104985 (which has a planet with an orbital period 198 days), there is no known metal-rich star with planets among giant stars. This may suggest a lower frequency of incidence of high-metallicity stars for giant stars with planets when compared with dwarf stars with planets.
High-Dispersion Spectra Collection of Nearby F–K Stars at Okayama Astrophysical Observatory: A Basis for Spectroscopic Abundance Standards
Authors: Yoichi Takeda , Sato Bun’ei , Kambe Eiji , Masuda Seiji , Izumiura Hideyuki , Watanabe Etsuji , Ohkubo Michiko , Yanagisawa Kenshi , Yasaka Yoshiro , Honda Satoshi , Kawanomoto Satoshi , Aoki Wako , Ando Hiroyasu , Sadakane Kozo , Takada-Hidai Masahide , Miyama Shoken M.
Published: March 2014

Towards constructing a system of high-dispersion spectroscopic standard stars with well-established abundances, so that adequate reference stars of similar properties may be found for precise differential abundance studies of any near-solar type stars, we have collected high-resolution ($R \sim 70000$) echelle spectra for 160 F–K dwarfs and subgiants of the solar neighborhood in three wavelength regions (5000–6200 Å, 5800–7000 Å, and 7600–8800 Å) at Okayama Astrophysical Observatory. This spectra database is open to the public.
The 2003 Superoutburst of an SU UMa-Type Dwarf Nova, GO Comae Berenicis
Authors: Imada Akira , Kato Taichi , Uemura Makoto , Ishioka Ryoko , Krajci Thomas , Sano Yasuo , Vanmunster Tonny , Starkey Donn R. , Cook Lewis M. , Pietz Jochen , Nogami Daisaku , Yeung Bill , Nakajima Kazuhiro , Tanabe Kenji , Koizumi Mitsuo , Taguchi Hiroki , Yamada Norimi , Nishi Yuichi , Martin Brian , Torii Ken’ichi , Kinugasa Kenzo , Jones Christopher P.
Published: March 2014

We photometrically observed a 2003 June superoutburst of GO Gom. The mean superhump period was 0.063059(13) d. The resultant data revealed that (1) the obtained light curve contained a precursor, (2) a plateau stage of the object lasted for 8 days, which is remarkably shorter than that of ordinary SU UMa-type dwarf novae, and (3) the amplitude of the superoutburst was less than 5 mag, which is unpredictably small when taking into account the fact that the supercycle of GO Com is about 2800 days. In order to explain these anomalies, a mass-elimination process from the accretion disk, such as evaporation, may play an important role.
Gigabit Digital Filter Bank: Digital Backend Subsystem in the VERA Data-Acquisition System
Authors: Iguchi Satoru , Kurayama Tomoharu , Kawaguchi Noriyuki , Kawakami Kazuyuki
Published: March 2014

The VERA terminal is a new data-acquisition system developed for the VERA project, which is a project to construct a new Japanese VLBI array dedicated to make a 3-D map of our Milky Way Galaxy in terms of high-precision astrometry. New technology, a gigabit digital filter, was introduced in the development. The importance and advantages of a digital filter for radio astronomy have been studied as follows: (1) the digital filter can realize a variety of observation modes and maintain compatibility with different data-acquisition systems (Kiuchi et al. 1997 and Iguchi et al. 2000a), (2) the folding noise occurring in the sampling process can be reduced by combination with a higher-order sampling technique (Iguchi, Kawaguchi 2002), (3) and an ideal sharp cut-off bandedge and a flat amplitude/phase responses are approached by using a large number of taps available to use LSI of a large number of logic cells (Iguchi et al. 2000a). We developed the custom Finite Impulse Response filter chips and manufactured the Gigabit Digital Filter Banks (GDFBs) as a digital backend subsystem in the VERA terminal. In this paper, the design and development of the GDFB are presented in detail, and the performances and demonstrations of the developed GDFB are shown.
Spectroscopic Study on the Atmospheric Parameters of Nearby F–K Dwarfs and Subgiants
Authors: Takeda Yoichi , Ohkubo Michiko , Sato Bun’ei , Kambe Eiji , Sadakane Kozo
Published: March 2014

Based on a collection of high-dispersion spectra obtained at Okayama Astrophysical Observatory, the atmospheric parameters ($T_{\mathrm{eff}}, \log g, v_{\mathrm{t}}$, and $\mathrm{[Fe/H]}$) of 160 mid-F through early-K stars were extensively determined by the spectroscopic method using the equivalent widths of Fe I and Fe II lines along with the numerical technique of Takeda et al. (2002, PASJ, 54, 451). The results are comprehensively discussed and compared with the parameter values derived by different approaches (e.g., photometric colors, theoretical evolutionary tracks, Hipparcos parallaxes, etc.) as well as with the published values found in various literature. It has been confirmed that our purely spectroscopic approach yields fairly reliable and consistent results.
Radial-Velocity Variability of G-Type Giants: First Three Years of the Okayama Planet Search Program
Authors: Sato Bun’ei , Kambe Eiji , Takeda Yoichi , Izumiura Hideyuki , Masuda Seiji , Ando Hiroyasu
Published: March 2014

We report on the radial-velocity variability of G-type giants based on the results of precise Doppler measurements of 57 stars that were observed for the first 3 years of the Okayama Planet Search Program. This program aims to search for planets around intermediate-mass stars in their evolved stages as late-G giants. We found that most of the targets with $B-V<1.0$ have radial-velocity scatters of $\sigma \sim 10 \;\mathrm{m} \,\mathrm{s}^{-1}$, with the most stable reaching levels of $6 \hbox{--} 8 \,\mathrm{m} \,\mathrm{s}^{-1}$, while those with $B-V>1.0$ typically show $\sigma \sim 20 \,\mathrm{m} \,\mathrm{s}^{-1}$. In total, about 60% of the targets are stable in radial velocity to a level of $\sigma < 15 \,\mathrm{m} \,\mathrm{s}^{-1}$ over 1–3 years, and about 90% have $\sigma < 30 \,\mathrm{m} \,\mathrm{s}^{-1}$. We found that 4 stars (HD 30557, HD 34559, HD 68077, and HD 85444) show significant long-term radial-velocity trends, suggesting that they are probably orbited by unseen stellar or substellar companions. Three stars (HD 79181, HD 104985, and HD 141680) show periodic radial-velocity variations. HD 104985 is the first planet-harboring star discovered from our survey. The properties of the variations in these 3 stars have been, and will be, extensively discussed in separate papers. Relatively large, but not apparently periodic, radial-velocity variations of $\sigma \gt 30 \,\mathrm{m} \,\mathrm{s}^{-1} \sigma > 30 \,\mathrm{m} \,\mathrm{s}^{-1}$ are found in 4 stars (HD 41597, HD 134190, HD 161178, and HD 176598). For most of the stars without showing any significant periodicity, we can exclude companions with $K\gt50 \,\mathrm{m} \,\mathrm{s}^{-1} K>50 \,\mathrm{m} \,\mathrm{s}^{-1}$, or $m_2 \sin i \gt 1.8 \,M_\mathrm{J}(a/\mathrm{AU})^{1/2}(M_{*}/{{{M}_{\odot}}})^{1/2} m_2 \sin i > 1.8 \,M_\mathrm{J}(a/\mathrm{AU})^{1/2}(M_{*}/{{{M}_{\odot}}})^{1/2}$ for orbital radii $a \lesssim 1 \hbox{--} 2 \,\mathrm{AU}$.
Sulfur Abundances in Metal-Poor Stars Based on OAO-1.88 m/HIDES Spectra
Authors: Takada-Hidai Masahide , Saito Yu-ji , Takeda Yoichi , Honda Satoshi , Sadakane Kozo , Masuda Seiji , Izumiura Hideyuki
Published: March 2014

The LTE abundances of sulfur (S) of 21 metal-poor stars and one normal star were explored in the metallicity range of $-3 < \mathrm{[Fe/H]} \leq 0$, based on the equivalent widths of the S I (1) 9212, 9237 Å and S I (6) 8693, 9894 Å lines measured on high-resolution spectra, which were observed by the OAO 1.88-m telescope equipped with HIDES. Our main results are: (1) The abundances derived from the S I (6) lines are consistent with those from the S I (1) lines among our sample stars in the range of $\mathrm{[Fe/H]} \gt-2 \mathrm{[Fe/H]} \gt-2$ with an average difference of $+0.03 \pm 0.05 \,\mathrm{dex}$, whereas a significant discrepancy is observed in the range of $\mathrm{[Fe/H]} \leq-2$. (2) The behavior of $\mathrm{[S(6)/Fe]}$ versus $\mathrm{[Fe/H]}$ of our halo sample stars exhibits a nearly flat trend with an average of $+0.62 \pm 0.09 \,\mathrm{dex}$ in the range of $-3 < \mathrm{[Fe/H]} <-1.25$, and shows a distribution around $+0.29 \,\mathrm{dex}$ in $-1.25 \leq\mathrm{[Fe/H]}\leq-0.7$. Our sample stars with $-1.25 \leq \mathrm{[Fe/H]} \leq-0.5$ follow an increasing trend with decreasing $\mathrm{[Fe/H]}$. The behavior of $\mathrm{[S(1)/Fe]}$ of our sample stars also shows essentially the same trend as $\mathrm{[S(6)/Fe]}$, though it is quantitatively different. (3) The S behavior in the range of $-3 < \mathrm{[Fe/H]} \leq 0$ inferred from the abundances of multiplets 6 and 1 are qualitatively consistent with each other, and may be represented by a combination of a nearly flat trend and a linearly increasing trend with decreasing $\mathrm{[Fe/H]}$. A transition of the trend is likely to occur at $\mathrm{[Fe/H]} \sim-1.5 \,\mathrm{dex}$.
Core Structure of Intracluster Gas: Isothermal Hydrostatic Equilibrium
Authors: Akahori Takuya , Masai Kuniaki
Published: March 2014

We investigated the core structure of intracluster hot gas based on the so-called $\beta$-model. We found that the virial temperature, $T_{\mathrm{vir}}$, of a cluster may be represented better by $\beta T_{\mathrm{X}}$ than $T_{\mathrm{X}}$, where $\beta$ is a parameter obtained from the X-ray surface brightness, and $T_{\mathrm{X}}$ is the emission-weighted mean temperature of the gas. For 121 clusters observed by ROSAT and ASCA, the luminosity-temperature relation, $L_{\mathrm{X}} \hbox{--} \beta T_{\mathrm{X}}$, is found to be less steep than $L_{\mathrm{X}} \hbox{--} T_{\mathrm{X}}$. The clusters can be classified into large and small core groups, and the latter exhibits no significant correlation between the core and virial radii. We examined the properties of the small core clusters, and found that they have a shorter cooling time than the Hubble time, while no significant correlation was found with the presence of cD galaxies or asymmetry in the surface brightness. We carried out hydrodynamical calculations to simulate the $\beta$-model and confirmed the above results: $T_{\mathrm{vir}} \simeq \beta T$ for the gas temperature, $T$, and the gas core formed due to a central cD galaxy is too small to account for the cores of the smaller core clusters.