bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Properties of the Nucleus of M81
Authors: Ishisaki Yoshitaka , Makishima Kazuo , Iyomoto Naoko , Hayashida Kiyoshi , Inoue Hajime , Mitsuda Kazuhisa , Tanaka Yasuo , Uno Shin'ichiro , Kohmura Yoshiki , Mushotzky Richard F. , Petre Robert , Serlemitsos Peter J. , Terashima Yuichi
Published: March 2014

Due to the appearance of SN 1993J, the region of M81 (NGC 3031) was observed with ASCA ten times between 1993 April and 1995 April. Data from eight of these observations have been used to study the 0.5–10 keV spectral and temporal properties of the source designated X-5, coincident with the M81 nucleus. The 2–10 keV luminosity of X-5 varied by a factor of 1.7 over a period of two years, around a mean of ∼ 2 × 1040 erg s−1 . Variations by ∼ 20% on a time scale of one day were also detected. The average spectrum of X-5 can be represented in the 2–10 keV range by a power-law continuum of the photon index, Γ = 1.85± 0.04, and a relatively low intrinsic absorption column of NH ∼ 1 × 1021 cm−2 . In the soft (< 2 keV) energy range, an additional thermal component with a temperature of 0.6–0.8 keV has been detected. An apparently broad or complex Fe-K emission line centered at 6.6–6.7 keV was also detected at an equivalent width of 170 ± 60 eV. These results indicate that the M81 nucleus is a low-luminosity active galactic nucleus, and suggest that similar objects are relatively numerous. A comparison is made between the nucleus of M81 and those of Seyfert galaxies.
A Variation in the Present Star Formation Activity of Spiral Galaxies
Authors: Tomita Akihiko , Tomita Yoshio , Saitō Mamoru
Published: March 2014

The star formation rate in spiral galaxies is considered to be continuously decreasing with time on a time scale of 109 yr. The present star formation activity, on the other hand, occurs in molecular clouds with a time scale of 107 yr, and shows various degrees among galaxies. We have made a new data set of 1681 nearby spiral galaxies from available databases, and have studied the statistics of the present star formation activity. We analyzed the far-infrared and optical B-band surface brightnesses of the HII regions and the non-HII regions in M31, and have shown that the far-infrared-to-optical B-band flux ratio (ƒFIR/ ƒB) is a useful indicator of the present star formation activity of spiral galaxies. For the sample galaxies, we made a distribution diagram of log(ƒFIR/ ƒB) versus log LB for each morphological type. The distribution of ƒFIR/ ƒB has a dispersion of one to two orders of magnitude, even within the same morphological type of galaxies, implying that the star formation activities of spiral galaxies change discontinuously within a short time scale. After analyzing the log(ƒFIR/ ƒB) versus log LB correlation, we suggest that the most active star formation in galaxies does not continue longer than 108 yr. We also constructed a universal histogram of log(ƒFIR/ ƒB) for each morphological type. The earlier-type spirals tend to show a larger variation in the present star formation activity. We discuss the correlation between the present star formation activity and the structures and environments of galaxies. We suggest that a short-term variation occurs primarily due to internal processes which may change with the morphological type of galaxies.
Numerical Simulation of Solar Coronal X-Ray Jets Based on the Magnetic Reconnection Model
Authors: Yokoyama Takaaki , Shibata Kazunari
Published: March 2014

We performed two-dimensional numerical simulations of solar coronal X-ray jets by solving the resistive magnetohydrodynamic (MHD) equations. The simulations were based on the magnetic reconnection model, in which the plasma of an X-ray jet is accelerated and heated by reconnection between the emerging flux and a pre-existing coronal field. Many observed characteristics of X-ray jets could be successfully reproduced. Morphologically, the two observed types of jets, two-sided-loop type and anemone-jet type, were well reproduced. Here, the two-sided-loop type is a pair of horizontal jets (or loops), which occurs when an emerging flux appears in a quiet region where the coronal field is approximately horizontal. In contrast, the anemone-jet type is a vertical jet, which takes place when an emerging flux appears in a coronal hole where the coronal field is vertical or oblique. Quantitatively, the velocity, temperature, thermal energy, kinetic energy, and other parameters obtained in the simulation are in good agreement with the observations. Furthermore, the simulations reveal new features which might be associated with X-ray jets: (1) A fast-mode MHD shock is produced at the collision site of each reconnection jet with the ambient magnetic field. (2) Reconnection produces a cool jet as well as a hot jet (X-ray jet). The hot and cool jets are adjacent to each other, which is consistent with the observed simultaneous coexistence of X-ray jets and Hα surges in the sun.
Metal Abundance of an X-Ray Emitting Gas in Two Groups of Galaxies: The NGC 5044 Group and HCG 51
Authors: Fukazawa Yasushi , Makishima Kazuo , Matsushita Kyoko , Yamasaki Noriko , Ohashi Takaya , Mushotzky Richard F. , Sakima Yasuhiro , Tsusaka Yoshiyuki , Yamashita Koujun
Published: March 2014

We observed two groups of galaxies, the NGC 5044 group (WP 23) and Hickson's compact group HCG 51, with ASCA. We detected an extended bright soft X-ray emission, which indicates the existence of large amounts of a hot X-ray emitting gas in both targets. The temperature of the hot gas is ∼ 1 keV for both objects, which is equivalent to their galaxy velocity dispersion. The metal abundance of the gas is 0.3–0.5 solar value for both objects, which is similar to that of rich clusters of galaxies. The Si to Fe abundance ratio is smaller than that of rich clusters of galaxies, although the iron abundances determined by the Fe-L lines are somewhat uncertain. The X-ray luminosities in the 0.5–10 keV band are 1 × 1043 erg s−1 and 5 × 1042 erg s−1 for the NGC 5044 group and HCG 51, respectively, which are higher by an order of magnitude than those of X-ray bright elliptical galaxies. This makes HCG 51 one of the most X-ray luminous compact groups. Both objects have a total gravitating mass of Mtotal ∼ 2.0 × 1013M⊙, and a gas mass and a galaxy mass of Mgas ∼ Mgalaxy ∼ 1.5 × 1012M⊙. The ratios among these mass components are Mgas/Mgalaxy ∼ 1 and (Mgas + Mgalaxy)/ Mtotal ∼ 0.2 within ∼ 350 kpc for both objects. The latter is similar to previous ROSAT results for many groups of galaxies, while the former is larger than the average value of the ROSAT-observed groups. Moreover, the metal abundances of the present two groups are significantly higher than those of the NGC 2300 group and HCG 62, and are comparable to those of clusters. These suggest that the hot-gas mass and metal abundances can scatter widely among groups, compared to the small variance found among rich clusters.
A New Eclipsing X-Ray Burster near the Galactic Center: A Quiescent State of the Old Transient A1742—289
Authors: Maeda Yoshitomo , Koyama Katsuji , Sakano Masaaki , Takeshima Toshiaki , Yamauchi Shigeo
Published: March 2014

With ASCA, we found highly absorbed X-rays from the position of the bright transient source A1742–289 with a variable flux ranging from 8 × 10−12 to 4 × 10−11 erg s−1 cm−2 in the 3–10 keV band. We discovered an X-ray burst and eclipses from A1742–289, establishing that A1742–289 is an eclipsing low-mass X-ray binary. Using the black-body radius during an X-ray burst, we estimated the distance of A1742–289 to be about 10 kpc, or near to the galactic center. The burst peak flux was then found below the Eddington limit of a neutron star. Excess soft X-rays during the eclipse were detected, which are interpreted to be scattering by interstellar dust-grains. Since A1742–289 was found to be an X-ray emitter, even in the quiescent state with a moderate but variable flux, and since A1742–289 is lying only 1′.3 from the galactic center, previously reported X-ray fluxes of the galactic center (Sgr A*) with non-imaging instruments might have suffered due to possible contamination of A1742–289.
Line-Profile Analysis of KI 7699 in the Sun and in Procyon
Authors: Takeda Yoichi , Kato Ken-ichi , Watanabe Yoshiya , Sadakane Kozo
Published: March 2014

The profiles of the resonance line of potassium (KI 7698.98) in the flux spectrum of the Sun and Procyon were studied in detail using the multi-parameter fitting method, in order to extract information regarding the fundamental atomic parameters responsible for the formation of this line as well as to diagnose the nature of the velocity fields in their atmospheres. It was concluded from an analysis of the solar KI 7699 profile that neutral-hydrogen collisions are practically negligible compared to electron collisions in the rate equation of statistical equilibrium, and that an empirical correction to the Unsöld's standard (van der Waals effect) damping constant is Δ log C6 ≃ + 1.0 with the most consistent microturbulent velocity of ξ ≃ 0.8 km s−1 . Based upon these results, the atmospheric-velocity parameters of Procyon were determined to be ξ ≃ 1.4 km s−1, ζRT≃ 6.7 km s−1 (the radial-tangential macroturbulence), and ve sin i ≃ 3.3 km s−1 (the projected rotational velocity). The potassium abundances of the Sun and Procyon derived from this resonance line, which are significantly affected by the non-LTE effect amounting to ∼ 0.4 dex (Sun) and ∼ 0.7 dex (Procyon), turned out to be nearly the same and log εK ≃ 5.1. It also appears that the microturbulence tends to decrease with an increase in the atmospheric height of the Sun as well as of Procyon.
Atmospheric Abundances of Light Elements in the F-Type Star Procyon
Authors: Kato Ken-ichi , Watanabe Yoshiya , Sadakane Kozo
Published: March 2014

High-dispersion spectra in the near-infrared region of the F-type star Procyon (α CMi, F5 IV–V) were obtained and the absorption lines of eight light elements, including phosphorus P and potassium K were analyzed with ATLAS9 model atmospheres. The LTE abundance was found to be solar for N, Mg, Al, Si, and P, which is consistent with previous studies in the visible region. However, two CI lines, triplet lines of OI at λ7771–5 Å, and the resonance line of KI at λ7699 Å are fairly strong; their estimated LTE abundances are greater than the solar values by more than 0.2 dex. These discrepancies are discussed in terms of non-LTE line formation.
Observation of Superhumps during the 1995 October Superoutburst of AW Geminorum
Authors: Kato Taichi
Published: March 2014

An SU UMa-type dwarf nova, AW Gem, was observed during the 1995 October superoutburst. Time-resolved CCD photometry yielded a refined estimate of the superhump period of 0.07943 (±0.00002) d. Observations of the initial stage of the superoutburst revealed that the superhumps started to grow within one day of the start of the superoutburst, until attaining their full amplitude during an additional two days. Marked QPOs with periods of 4–5 min were observed during the growing stage of the superhumps, showing their maximal amplitudes on the declining branches from the superhump maxima. These facts suggest that QPOs during the early stage of a superoutburst may be physically related to the growth mechanism of the superhumps.
Detection of the Mid-Infrared Unidentified Bands in the Diffuse Galactic Emission by IRTS
Authors: Onaka Takashi , Yamamura Issei , Tanabé Toshihiko , Roellig Thomas L. , Yuen Lunming
Published: March 2014

This letter presents the first results of the mid-infrared spectrum (4.5–11.7 μ m) of the diffuse emission near to the galactic plane (l ∼ 50°; |b| ≤ 5° obtained by the mid-infrared spectrometer on board the Infrared Telescope in Space mission. The results clearly demonstrate the presence of unidentified infrared emission (UIR) bands at 6.2, 7.7, 8.6, and 11.3 μm in the diffuse galactic emission. The distribution of the UIR bands correlates well with the IRAS 100 μm map, suggesting that the UIR-band emitting material is well mixed with the classical dust grains in general interstellar space. The present results indicate that more than 70% of the IRAS 12 μm flux diffuse emission is emitted in the spectral range 8–11.7 μm, and that most of the 12 μm excess comes from the features associated with the UIR bands.
Submillimeter Observations of the Galactic Plane by IRTS
Authors: Hirao Takanori , Matsumoto Toshio , Sato Shinji , Ganga Ken , Lange Andrew E. , Smith Beverly J. , Freund Minoru M.
Published: March 2014

We report on observations of interstellar dust emission at |b| ≤ 3.°5 and l ∼ 46° with the Far Infrared Photometer (FIRP) on board the Infrared Telescope in Space (IRTS). The FIRP is a four-channel photometer with bands centered at 150, 250, 400, and 700 μm and with a spatial resolution of 0.°5 (FWHM). The 150–250 μm and the 250–400 μm brightness ratios of the interstellar dust emission show a slight decrease with increasing galactic latitude at |b| ≤ 3.°5, consistent with the 140–240 μm brightness ratio observed by COBE/DIRBE. The 250–700 μm brightness ratio shows a much stronger dependence on the galactic latitude. The effect may be due to a single component of warm (T ∼ 20 K) dust with an emissivity index of n < 2, that decreases with galactic latitude. Alternatively, the effect may be due to the existence of two components of dust, a warm (T ∼ 20 K) component and a cold (T ∼ 4–7 K) component, each with an emissivity index of n = 2. In the latter case, either the temperature or the optical depth of the cold component increases as a function of the galactic latitude. In either case, the physical properties of the interstellar dust must be assumed to vary significantly over the range |b| ≤ 3.°5.
Detecting Accretion Disks in Active Galactic Nuclei
Authors: Fanton Claudio , Calvani Massimo , de Felice Fernando , Čadež Andrej
Published: March 2014

Recent X-ray observations of active galactic nuclei with ASCA suggest that we may be observing Fe-K line emission from very close to the central black-black hole. We provide here the relevant formalism to interpret those observations. We show how to model the appearance of an accretion disk around a rotating black hole and line profiles from disk emission. We try to present in a coherent way results that are scattered in the litterature and/or that are limited to particular cases. We extend these results to the more general case of a rotating black hole (Kerr metric). We finally discuss the relation of the full width at zero intensity of the line to the angular momentum of the black hole.
ASCA Observations of Two Ultraluminous IRAS Galaxies: IRAS 15307+3252 and IRAS 20460+1925
Authors: Ogasaka Yasushi , Inoue Hajime , Brandt William N. , Fabian Andrew C. , Kii Tsuneo , Nakagawa Takao , Fujimoto Ryuichi , Otani Chiko
Published: March 2014

We report on ASCA observations of two ultraluminous far-infrared galaxies, IRAS 15307+3252 and IRAS 20460+1925. An X-ray flux of 1.53 × 10−12 erg cm−2 s−1 in the 2–10 keV band was detected from IRAS 20460+1925. The continuous spectrum is well represented by a power law with a photon index of 1.99+0.18−0.15 and excess photoelectric absorption by a column of (2.6+0.29−0.32 × 1022 cm−2 in the rest frame. The spectrum also shows an iron K emission line with an equivalent width of 260+145−137 eV and a centroid energy of 6.36±0.08 keV in the rest frame. These spectral properties are consistent with those of Seyfert-2 galaxies, although the intrinsic 2–10 keV X-ray luminosity (corrected for absorption) of 1.20 × 1044 erg s−1 is high and close to that of quasars. No X-rays were detected from IRAS 15307+3252, and the upper limit to the X-ray flux is 7.2 × 10−14 erg cm−2 s−1 in the 2–10 keV band. However, the upper limit on the ratio of the X-ray flux to the far-infrared flux is not inconsistent with a source containing a highly obscured quasar.
Disk Accretion onto a Magnetized Young Star and Associated Jet Formation
Authors: Hirose Shigenobu , Uchida Yutaka , Shibata Kazunari , Matsumoto Ryoji
Published: March 2014

We investigated disk accretion onto a magnetized young star by performing MHD numerical simulations. We considered the case in which the stellar magnetosphere truncates the accretion disk carrying the interstellar magnetic field, and the star is magnetized in the same direction as the disk. In such a case, the interface between the accretion disk and the magnetosphere contains a magnetically neutral ring in the equatorial plane. The numerical results show that the disk accretion drives the magnetic reconnection between the magnetospheric field and the disk magnetic field, which allows mass transfer from the disk to the magnetosphere. Most of the transferred mass accretes to the star along the reconnected magnetospheric field, while the rest of the mass is accelerated to the bipolar directions by a Lorentz force along the stellar open magnetic field. This “reconnection-driven” jet is further accelerated magneto-centrifugally due to stellar rotation, and corresponds to optical jets from young stars. The magnetic braking as a reaction of the magneto-centrifugal acceleration of the jet may explain the observed slow rotations of young stars in the disk-accretion stage.
Preflare Heating and Mass Motion in a Solar Flare Associated with Hot Plasma Ejection: 1993 November 11 C9.7 Flare
Authors: Ohyama Masamitsu , Shibata Kazunari
Published: March 2014

X-ray plasma ejection associated with an impulsive flare was observed near to the solar limb on 1993 November 11 with the Yohkoh soft X-ray telescope. We examined the physical condition as well as the morphological evolution of the ejecta and flare. The results are the following: (1) The shape of the ejecta was a loop before the start of ejection. (2) The ejected loop appeared after its footpoint brightened, and started to slowly rise long before the impulsive phase (at ∼ 10 km s−1, the preflare slow rise), but was suddenly accelerated to ∼ 130 km s−1 just before or at about the onset of the impulsive phase (the main rise). (3) The ejected material was already heated to ∼ 11.3 ± 4 MK before the main rise. (4) The electron density of the ejecta (∼ 4.5 × 109−1.4 × 1010 cm−3) was larger than the typical density of the active-region corona. The mass of the ejecta was ∼ 1014 g. These results suggest chromospheric evaporation due to preflare heating. It is suggested that magnetic reconnection may already be occurring in the preflare phase, leading to heating of the ejected material (possibly plasmoids) and causing chromospheric evaporation. The reconnection rate (or the speed of the inflow into the neutral point) is also estimated for the preflare, the impulsive, and the gradual phases.
Gravothermal Expansion in N-Body Systems
Authors: Endoh Hitoshi , Fukushige Toshiyuki , Makino Junichiro
Published: March 2014

We investigated whether gravothermal expansion occurs in N-body systems. As the most idealized case, we studied the evolution of an N-body system in a spherical adiabatic wall which is initially in thermal equilibrium. Such a system is thermodynamically unstable if the central density is more than 709 times higher than the density just inside the wall. We performed simulation of a 2048-body system with and without artificial perturbations. We found that gravothermal expansion took place as well as gravothermal contraction. Whether gravothermal expansion occurs or not is determined by the perturbation or statistical fluctuation on the temperature structure in the initial model. The results were compared with that of a self-gravitating gas system.
The Dipping Source X1254-690 Observed with GINGA
Authors: Uno Shin'ichiro , Mitsuda Kazuhisa , Aoki Takashi , Makino Fumiyoshi
Published: March 2014

The results of Ginga observations of the dipping X-ray source X1254-690 are presented. The persistent emission spectrum cannot be represented with conventional two-component models; an additional spectral structure, which can be represented either by a broad emission line or by reflection by warm matter, is required. The energy spectra during dips can be represented by the sum of a non-absorbed component, which has the same spectral shape as the persistent emissions just before or after the dip, and an absorbed component, which is described by the persistent spectrum with additional absorption. The intensity of the non-absorbed component first decreases with decreasing intensity; then, the decrease saturates at about 8% of the persistent intensity. This strongly supports the existence of an accretion-disk corona of an electron-scattering optical depth of about 0.1. The column density of the absorbed component obtained from spectral fit stays at about 1 × 1023 cm−2 when the intensity of the non-absorbed component is above about 20% of the persistent intensity, but increases to 1 × 1024 cm−2 at the bottom of the dip. The electron-scattering optical depth of the accretion-disk corona and the column density of the absorber are roughly consistent with the double-phase model of X-ray irradiated accretion matter.
Radiation Damage on X-Ray CCDs and Restoration Technique for Space Astronomy
Authors: Tomida Hiroshi , Matsumoto Hironori , Ozaki Masanobu , Tazawa Yuji , Awaki Hisamitsu , Tsuru Takeshi , Koyama Katsuji , Tsunemi Hiroshi , Yamamoto Koei
Published: March 2014

We studied the proton damage effects of the X-ray CCD, and searched for a possible restoration technique in orbit. We measured the X-ray CCD performances after irradiation at energies of 2 and 9.5 MeV, and confirmed a clear degradation of the charge transfer efficiency (CTE) and the energy resolution. To restore the degraded CTE and energy resolution, we tried a charge injection technique, and found the improvement in the CTI (= 1 − CTE) and energy resolution to be 1/4 and 1/3, respectively. We also estimated the energy level of the deep trap, which causes a quantization of the dark current from the radiation-damaged pixels. The trap energy level was about 0.57 eV, or near to the center of forbidden band.
X-Ray Analysis of the ρ Ophiuchi Dark Cloud with ASCA: Source Identification, X-Ray Spectra, and Temporal Variability
Authors: Kamata Yuichi , Koyama Katsuji , Tsuboi Yohko , Yamauchi Shigeo
Published: March 2014

This paper presents a comprehensive study with the Japanese X-ray astronomical satellite ASCA on X-rays from the main body of the ρ Ophiuchi dark cloud. We have constructed separate X-ray images using 3 energy bands and 12 time-sliced data, and thereby detected 19 X-ray sources, doubling the previous ASCA results of 11 X-ray sources. Three of the sources are associated with class-I infrared sources, which precede the T Tauri phase. Half of the 19 sources were found to be time variable, and 5 flare-like events with an averaged energy of > 3 × 1035 erg were observed. With the analogy of solar flares, we estimated the flare loop height and plasma density to be 3 × 1011 cm and 3 × 1011 cm−3, respectively. Among these sources, a flare from the class-I source EL 29 exhibited an order-of-magnitude larger absorption (NH) than in quiescence states, which may indicate the exsistence of a dense protostellar disk.
Isothermal Shocks in Adiabatic Black-Hole Accretion Flows
Authors: Lu Ju-Fu , Yuan Feng
Published: March 2014

This paper presents global solutions of adiabatic accretion flows with isothermal shocks in the potential of a non-rotating black hole. It is known that in the previously studied cases, where flow including shock is either entirely adiabatic or entirely isothermal, there can be no more than one stable shock solution, and the solution can only be of the α-x type; however, the solution topology in the present case shows new remarkable characteristics: for the same flow parameters there can be two stable shock solutions satisfying the physical boundary conditions, and the solution can be of three types, namely α-x, x-α, and α-αtype. In addition, shocks in the present case occur for a parameter region that is different from that for Rankine-Hugoniot shocks to occur. These results greatly increase the possibilities of shock formation in astrophysical flows. It is also noted that in the present case the efficiency of energy release at the shock can be as high as a few percent. Finally, a brief comparison is made between shocked inviscid flows and two types of shock-free viscous flow, namely that of Shakura and Sunyaev (1973, AAA 09.066.049) and that of Narayan and Yi (1994, AAA 61.064.083).
CO(J=3–2) Observations of MS 1512-cB58 at z=2.72
Authors: Nakanishi Kouichiro , Ohta Kouji , Takeuchi Tsutomu T. , Akiyama Masayuki , Yamada Toru , Shioya Yasuhiro
Published: March 2014

We report on a search for 12CO(J = 3–2) emission line toward MS 1512-cB58, a forming galaxy candidate at z = 2.72. We have observed the object with the 45-m telescope of the Nobeyama Radio Observatory, and found no significant emission. The 3σ upper limit of the CO(J = 3–2) line luminosity is 4.4 × 1010 K km s−1 pc2, assuming a line velocity width of 300 km s−1; this corresponds to a molecular hydrogen mass of 2.0 × 1011M⊙, if we assume the Galactic CO-to-H2 conversion factor. A lower limit on the ratio of the Hα line luminosity to the CO luminosity of MS 1512-cB58 is at an upper part of, but within, the range of ratios for nearby galaxies.
Wide-Band X-Ray Spectra and Images of the Starburst Galaxy M82
Authors: Tsuru Takeshi Go , Awaki Hisamitsu , Koyama Katsuji , Ptak Andy
Published: March 2014

The ASCA results of the starburst galaxy M82 are presented. The X-rays in the 0.5–10 keV band exhibit a thin thermal spectrum with emission lines from highly ionized magnesium, silicon, and sulfur, as well as a hard tail extending to higher than 10 keV energy. The soft X-rays are spatially extended, while the hard X-rays show an unresolved point-like structure with possible a long-term flux variability. The flux ratio of the emission lines and the spatially extended structure in the low-energy band indicate that at least two-temperature thin thermal plasmas are present. The abundances of the oxygen, neon, magnesium, silicon, sulfur, and iron in the thin thermal plasmas are found to be significantly lower than the cosmic value. Neither type-Ia nor type-II supernova explosions can reproduce the observed abundance ratio. The origin of the unresolved hard X-rays is uncertain, but is probably an obscured low-luminosity AGN.
K-4 VLBI Data-Acquisition System
Authors: Kiuchi Hitoshi , Amagai Jun , Hama Shin'ichi , Imae Michito
Published: March 2014

We have developed a new VLBI system based on the conventional K-4 system, whose data-acquisition mode includes VLBA and VSOP data modes. In developing the new VLBI data-acquisition system, multi-bit quantization sampling, high-speed (wide-bandwidth) data sampling, and the data acquisition mode were taken into consideration. The new acquisition system has one-bit and two-bit quantization sampling modes for VLBI, and four-bit and eight-bit sampling modes for general-purpose use. The total data rate is up to 256 Mbps, and up to 16 video channels can be selected. Anti-aliasing filtering is carried out in analog (32 MHz), and after sampling, the 16-MHz, 8-MHz, etc. filterings are carried out in the digital filter. The digital filter is used because it results in good phase characteristics. This system is specially designed for the Key Stone Project, and an input interface unit is incorporated in the VSOP.
3D Velocity-Field Observation of Solar Convection I. Characteristics of Mesogran
Authors: Ueno Satoru , Kitai Reizaburo
Published: March 2014

In this series we report on the results of our 3D velocity-field observation of the solar photosphere. The observation consisted of a 2D granulation imaging observation and a 1D slit spectroscopic observation. Both observations were performed simultaneously using the Domeless Solar Telescope of Hida Observatory, Kyoto University. In this paper we focus on the solar meso-sized velocity structure, i.e., mesogranulation. We investigated its spatial size, lifetime, velocity amplitude, and the relation between horizontal velocity and radial velocity. Our results are as follows: (1)The characteristic size of meso-granular cells is about 18″. (2)Especially at the region where the slit was placed, the patterns of the horizontal velocity divergence and of the radial velocity are closely related to each other, and their spatial sizes are also very consistent. (3)The peak of its lifetime distribution is located at 30–40 min, and (4)the relative frequency of mesogranular cells having a longer lifetime than 60 min is only 26%. (5)Solar mesogranulation is confirmed to be a convective phenomenon. An exceptional example of upward gas flow at the boundary of a strong mesogranulation cell was found. Discussions are also given concerning this abnormal phenomenon.
Computer Simulations of Stellar-Coronagraph Observations
Authors: Itoh Yoichi , Takato Naruhisa , Takami Hideki , Tamura Motohide
Published: March 2014

An infrared camera optimized for stellar coronagraphic observations is now under construction for use on the Subaru 8 m telescope. This instrument, called CIAO (Coronagraphic Imager with Adaptive Optics), aims to observe faint infrared objects in the very close vicinity of a bright source, such as brown dwarfs in binary systems and protoplanetary disks. We have conducted extensive computer simulations in order to optimize the transmittance patterns of the stellar coronagraph components and to evaluate the performance of the camera for various astronomical objects. The simulations took into account atmospheric turbulence and telescope aberration, where the wavefront is expanded in terms of Zernike polynomials. We examined the effect of the truncation of the Zernike expansion to the properties of the resultant PSFs, and found that the higher terms of the Zernike expansion omitted by former studies should be included rather in the simulation for coronagraphic observations than in the simulation for direct imaging observations. The results of the simulations show that a few minute integrations will be required for the detection of a young brown dwarf in a binary system in the Pleiades, while it will take a few nights for a protoplanetary disk in the Taurus molecular cloud.
Initial Shock Waves for Explosive Nucleosynthesis in Type II Supernova
Authors: Nagataki Shigehiro , Hashimoto Masa-Aki , Yamada Shoichi
Published: March 2014

We have performed 1-dimensional calculations for explosive nucleosynthesis in collapse-driven supernova and investigated its sensitivity to the initial form of the shock wave. We have found the tendency that the peak temperature becomes higher around the mass cut if the input energy is injected more in the form of kinetic energy rather than internal energy. Then, the mass cut becomes larger, and, as a result, neutron-rich matter is less included in the ejecta; this is favorable for producing the observational data compared with a previous model. Our results imply that the standard method to treat various processes for stellar evolution, such as convection and electron capture during the silicon burning stage, is still compatible with the calculation of explosive nucleosynthesis.
Dispersion of Inferred SNe Ia/SNe II Ratios for Current Models of Supernova Nucleosynthesis
Authors: Nagataki Shigehiro , Hashimoto Masa-aki , Sato Katsuhiko
Published: March 2014

We have estimated the dispersion of the inferred relative frequencies of Type-Ia and Type-II supernovae (NIa/NII) in our Galaxy by fitting the numerical results of supernova nucleosynthesis to the solar-system abundances. The ratio NIa/NII is estimated to be 0.056–0.14, which is consistent with the observation, if the model of Woosley and Weaver (1995, AAA 64.065.030 WW95) is adopted for Type-II supernovae (SNe II). On the other hand, the upper limit of NIa/NII becomes too large for the model of Hashimoto (1995, AAA 64.065.034 Ha95). However, Ha95 can fit the solar values better than WW95 as far as the abundant nuclei are concerned. These results mean that Ha95 can reproduce the main nuclei of the solar-system well and that WW95 can reproduce the solar values over a wide mass-number range. We also note that NIa/NII tends to become smaller if the delayed detonation model is adopted for Type-Ia supernovae (SNe Ia). The dispersion of NIa/NII obtained in the present investigation is larger than that concluded by Tsujimoto et al. (1995, AAA 64.125.075), which will have an influence on the estimate of the average life time of SNe Ia's progenitors and/or the star-formation rate history in our galaxy.
Irradiated Accretion Disk in the Galactic Supersoft X-Ray Source RX J0019.8 + 2156
Authors: Matsumoto Katsura , Fukue Jun
Published: March 2014

We considered the X-ray irradiated accretion disk in the galactic supersoft X-ray source RX J0019.8+2156, and estimated the contribution in UV and optical fluxes due to the reprocessing effect of X-ray radiation on the surface of the accretion disk and main sequence companion star. In the nuclear-burning white dwarf model of supersoft X-ray sources, radiation near the Eddington luminosity is generated on the white dwarf. For an assumed distance of 2 kpc to the object, however, a simple model with the standard accretion-disk model can not reproduce the observed fluxes in the UV and optical wavelengths of the object. This fact suggests the existence of reprocessing processes by the irradiated components in the binary system at relatively lower frequencies. We thus calculated the irradiation effects on the accretion disk and the mass donor companion in this system, and estimated their contributions to the flux of the lower frequency regions in the energy distribution. As a result, the reprocessed radiation from the irradiated accretion disk and companion star can well reproduce the observed fluxes.
Discovery of the First in-the-Gap SU UMa-Type Dwarf Nova, NY Serpentis (=PG 1510+234)
Authors: Nogami Daisaku , Kato Taichi , Baba Hajime , Masuda Seiji
Published: March 2014

We performed photometric monitoring and time-resolved observations of NY Ser between 1995 July 25 and 1997 March 11. NY Ser shows normal outbursts with a recurrence time of 6–9 days and superoutbursts with a recurrence time of 85–100 days in the range of 14.6–18.0 mag in the V band. The superhump period is 0.106 (± 0.001) d, which suggests that the orbital period is located near to the middle of the period gap.
Cosmological Accretion Disk Embedded in Background Radiation: Interplay of Viscosity and Radiation Drag
Authors: Mineshige Shin , Tsuribe Tohru , Umemura Masayuki
Published: March 2014

The time-evolutionary properties of a standard α-type disk under the influence of a strong radiation field (“β drag”) is investigated. Viscous diffusion tends to transport angular momentum from the inner portions outward, whereas Compton drag efficiently removes angular momentum at large radii. As a result, both effects reinforce each other, promoting a more rapid accretion, compared with those cases in the absence of either of the two processes. The effects of radiation drag can be understood by simple transformations of the radius and time; if the kinematic viscosity varies as v ∝ ra with a being a constant, and if the angular frequency is Ω ∝ r−3/2 , for example, the surface density evolves as $ \Sigma(r,t)= e^{4\beta t} f(r^\prime,t^\prime)$ with $r^\prime \equiv re^{2\beta t}$ and $t^\prime \equiv (e^{n\beta t}-1)/(n\beta)$, where $ f(r,t)$ is the Σ evolution without radiation drag, β is the reciprocal of the drag timescale, and n=4–2a. As a consequence, the disk is exponentially contracting with time.
12CO(J=1–0) and 13CO(J=1–0) Mapping of the Starburst Galaxy M82
Authors: Kikumoto Takahiro , Taniguchi Yoshiaki , Nakai Naomasa , Ishizuki Sumio , Matsushita Satoki , Kawabe Ryohei
Published: March 2014

We have mapped the central 1 kpc region of the nearby starburst galaxy M82 in both the 12CO(J=1–0) and 13CO(J=1–0) emission lines under the same angular resolution $(\sim 7^{\prime \prime} \times 6^{\prime \prime})$. The intensity ratio (R) of 12CO(J=1–0) to 13CO(J=1–0) emission shows the significant spatial variation: $(\sim 7^{\prime \prime} \times 6^{\prime \prime})$ (the NE lobe), $R\simeq 20-25$ (the SW lobe), and R >70 (the 2.2 μm secondary peak). These values are significantly higher than those of giant molecular clouds in our Galaxy and molecular gas in other normal spiral galaxies. We also find that a very high ratio (R > 90) is achieved around the brightest radio continuum source, 41.9+58, which is considered to be a supernova remnant (or remnants). Based on the LTE model, we show that the molecular gas in M82 tends to be optically thin, even for the 12CO emission; its optical depth is a few or less. The smaller optical depths may naturally explain the higher R values observed in M82. We discuss the possibility that a superwind causes the formation of such clouds.
Spectroscopic Observation of Comet P/de Vico: Comparison with P/Halley and P/Brorsen-Metcalf
Authors: Kawakita Hideyo , Ayani Kazuya , Matsubara Keiji
Published: March 2014

A spectroscopic observation of Comet P/de Vico in the visible region was made at Bisei Astronomical Observatory on 1995 October 11. The obtained spectrum covers the wavelengths from 5200 to 7200 Å, and includes several emissions, such as C2, NH2, and [OI]. The ratios of the gas-production rates of C2 and NH2 relative to that of H2O, Q(C2)/Q(H2O), and Q(NH2)/Q(H2O), were determined from our observation based on the Haser model. The production-rate ratio and gas-to-dust ratio were: Q(C2)/Q(H2O) = 0.25%, Q(NH2)/Q(H2O) = 0.14%, and log10[ Q(H2O)/Af ρ] = 26.9 at the time of observation. Comet P/de Vico was similar to P/Halley from the viewpoint of the chemical composition (C2 and NH2 relative to the H2O), and P/de Vico was comparable to P/Brorsen-Metcalf concerning the gas-to-dust ratio. P/de Vico was one of the most gas-rich comets ever known.
ASCA Observations of the Chamaeleon II Dark Cloud
Authors: Yamauchi Shigeo , Hamaguchi Kenji , Koyama Katsuji , Murakami Hiroshi
Published: March 2014

ASCA results of eight X-ray sources in the Chamaeleon II dark cloud are presented. Six sources were identified as low-mass young stellar objects, either Class II–III sources or T Tauri stars with X-ray temperatures and luminosities in the range of 0.8–3 keV and 1029.9–1031.1 erg s−1, respectively. Two of them showed time variability: one with typical flare profile and the other with a light curve showing fast-rise and gradual decay. These variable sources exhibited a higher temperature than did those of the other sources with less time variability. We found a high-temperature, time-variable, and moderately absorbed X-ray source which has no cataloged counterpart at any other wavelength. We also found hard X-rays at the position of a Herbig Ae candidate with an extremely large NH of 2×1023 H cm−2 , one order of magnitude higher than that estimated from the optical extinction. The origin of the X-rays, including these two sources, are discussed.
Asteroid Lightcurve Observations near Stationary Points: (4179) Toutatis in 1997 February
Authors: Nakamura Tsuko , Fuse Tetsuharu
Published: March 2014

Lightcurve observations of asteroids with long-spin periods (say, more than a few days) are particularly important regarding the detection of a non-principal axis spin state. However, it is not easy for such observations to achieve photometric accuracy comparable to that for short-period spin asteroids, since slow-spin asteroids inevitably require long duration and coordinated observations and the use of different reference stars during a run. We propose here the advantage of observations near stationary points for long-spin asteroids, where the same reference stars can be used throughout. This proposal was tested for CCD lightcurve observations of asteroid (4179) Toutatis, which were performed near its stationary point in 1997 February. From six night observations spanning 11 days, a spin period of 7.50 ±0.2 d was obtained using two independent methods of period analysis; this value has been found to be in fairly good agreement with the periods obtained by Hudson and Ostro(1995, AAA 64.098.037), and Spencer et al. (1995, AAA 64.098.052).
Evidence for a Black Hole in the X-Ray Transient GRS 1009–45
Authors: Kubota Aya , Tanaka Yasuo , Makishima Kazuo , Ueda Yoshihiro , Dotani Tadayasu , Inoue Hajime , Yamaoka Kazutaka
Published: March 2014

We report on the result of an X-ray observation of the X-ray Nova Velorum 1993 (GRS 1009–45), made with ASCA on 1993 November 10-11. The energy spectrum was extremely soft and accompanied by a hard tail, characteristics of the Galactic black-hole binaries in the soft state. It is well represented by a two-component model consisting of a multicolor disk model or a general relativistic accretion disk model, both describing emission from an optically thick accretion disk, and a power-law component with a photon index of ∼ 2.5. A spectral analysis of the soft component allows an estimation of the mass of the central object. For the optically-estimated distance (> 1 kpc) and inclination (> 37°), the mass is estimated to be $\gt 3.1 M_\odot$. These results strongly support that the compact object is a black hole.
Nest of Molecular Outflows in the Circinus Cloud
Authors: Dobashi Kazuhito , Sato Fumio , Mizuno Akira
Published: March 2014

We report on the discovery of a large and bright molecular outflow associated with an intense CO clump in the Circinus cloud, which was detected with the $\textrm CO (J = 1-0)$ emission line using the new Nagoya 4 meter radio telescope “Nanten” installed at Las Campanas Observatory (Chile). The outflow is quite large, extending over an area of $10^\prime \times 20^\prime (\sim 4 \times 8$ pc at its distance of 1.26 kpc) that covers most of the clump surface, and having very high radio brightness; actually, the CO brightness of the high velocity wings integrated over the outflow lobes amounts to as high as $1.5 \times 10^{-1} \textrm {K km s}^{-1} \textrm {deg}^2$, which makes this CO outflow one of the brightest reported so far. The outflow is also massive $(\sim 50 M_\odot)$ and energetic $(\sim 4300 {M_\odot} \textrm {km}^2\textrm {s}^{-2})$. The outflow exhibits a complex morphology, having 2 local peaks at each of the redand blue-shifted lobes. Comparing the outflow morphology with the locations of the protostellar candidates selected from the IRAS Point Source Catalog, we conclude that the detected outflow is most likely to be driven by at least 4 distinct protostars forming in the clump, namely, IRAS 14562–6248, 14563–6301, 14564–6254, and 14568–6304. Thereby, we suggest to designate the CO clump as the “Nest of Molecular Outflows” in the Circinus cloud.
X-Ray Observations of the Orion OB1b Association
Authors: Nakano Makoto , Yamauchi Shigeo , Sugitani Koji , Ogura Katsuo , Kogure Tomokazu
Published: March 2014

We report on the broad-band X-ray images and spectra for the Orion OB1b association obtained with ASCA. More than forty X-ray sources were detected in three fields, and about half of them have likely optical counterparts in the Guide Star Catalog. Their temperature and X-ray luminosities at the assumed distance of 450 pc are 4 keV and 1 × 1030−1 × 1031 erg s−1 in the total energy band (0.5–10 keV), respectively. In one field covering the Horsehead Nebula and NGC 2023, several X-ray sources were identified with known candidates for low-mass pre-main-sequence stars, including V615 Ori. Among them, four sources are emission-line stars with X-ray emission. Some X-ray sources were also found in the chain of small reflection nebulosities illuminated by OB association members near to ∊ Ori. The X-ray emission from sources having optical counterparts is consistent with thin thermal plasma of temperatures of 1–2 keV. X-ray emission from possible extragalactic sources is also reported.
Spectroscopic and Photometric Observations of a Z Cam-Type Dwarf Nova, AT Cancri, in Standstill
Authors: Nogami Daisaku , Masuda Seiji , Kato Taichi , Hirata Ryuko
Published: March 2014

We performed quasi-simultaneous spectroscopic and photometric observations of a Z Cam star, AT Cnc, in standstill in 1997 February. V-band time-resolved photometry marginally revealed small-amplitude (∼ 0.01 mag) oscillations with period candidates of 0.132 d, 0.124 d, 0.142 d, and 0.249 d. Low-resolution spectra show Balmer lines in emission and absorption, and Na D absorption. From the radial-velocity variation of Hα, we deduced the system parameters: the orbital period = 0.2011(±0.0006) d, the semi-amplitude = 80 (±4) km s−1, the systemic velocity = 11(±3) km s−1, the primary mass = 0.9 (±0.5) M⊙. The phase of the velocity variation of Hα is very close to that of Na D. There are two possibilities: the Hα emission line radiated (a) from the secondary star, or (b) from the accretion disk. The inclination is estimated to be 17° (± 5°) and 36° (± 12°) based on the respective possibilities. Doppler map drawn under possibility (a) revealed on a broadly extended component in the (−Vx, −Vy) region. In the Doppler map drawn under the possibility (b), the peak exists on the irradiated side of the Doppler position of the secondary and the (+Vx, +Vy) region. We discovered an absorption component in the blue wing at Hα . The P Cyg profile appeared during a limited period in its orbital phase, which is interpreted to be caused by transient mass ejection episodes.
Improvement of YOHKOH Hard X-Ray Imaging
Authors: Sato Jun , Kosugi Takeo , Makishima Kazuo
Published: March 2014

The Hard X-ray Telescope (HXT) on board Yohkoh is a Fourier-synthesis-type imager for solar flare observations; it measures a set of spatially modulated photon counts with sixty-four, independent, bigrid modulation collimators and an image is reconstructed from these data using sophisticated image synthesis procedures, such as the Maximum Entropy Method (MEM) and PIXON. The HXT-MEM imaging has been greatly improved by incorporating the following three improvements which we have recently achieved: (1) Accurately estimated instrumental response functions (X-ray transmission/modulation patterns), which are made available through self-calibration using solar flares as calibration sources; (2) Improvement of the MEM algorithm, which includes the total flux estimate in its iteration loop; and (3) Accurate error estimate and its proper inclusion in the MEM. Various problems seen in previous HXT-MEM imaging are drastically reduced and high-quality images are obtained.
ASCA Observations of the Supernova Remnant G156.2+5.7
Authors: Yamauchi Shigeo , Koyama Katsuji , Tomida Hiroshi , Yokogawa Jun , Tamura Keisuke
Published: March 2014

We report on the ASCA X-ray spectra from the north rim and the center of the supernova remnant (SNR) G156.2+5.7. The spectra are found to comprise soft and hard X-ray components. No clear shell structure has been found, either in the soft or in the hard X-ray bands. The soft X-rays are attributable to a non-equilibrium ionization plasma with a temperature of 0.4 keV and an ionization timescale of 1011.0−11.2 cm−3s. A Sedov solution with an explosion energy of 1051 erg leads to an age of ∼ 1.5 × 104 yr and a density of ambient gas of ∼ 0.2 cm−3. The distance to G156.2+5.7 is estimated to be ∼ 1.3 kpc. The abundances of silicon and sulfur vary between the center and the north rim of the SNR, while the abundances of all other elements do not. The hard component can be modeled with either thermal emission of a temperature higher than a few keV or a non-thermal process with a power-law spectrum of photon index 1.5–1.8. Since the former model requires an uncomfortably high temperature, we favor a non-thermal model. We also discuss the nature of a point source found at the edge of the SNR.