bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic Study of NGC 1068 in the 3 μm Band
Authors: Imanishi Masatoshi , Terada Hiroshi , Sugiyama Kouji , Motohara Kentaro , Goto Miwa , Maihara Toshinori
Published: March 2014

The results of a near-infrared (2.9–4.1 μm) spectroscopic observation of NGC 1068 is presented. We detected an absorption feature near to 3.4 μm caused by an obscuring torus as well as a broad (FWHM ∼ 300 km s−1) Pfγ emission line near to 3.75 μm. The column density estimated from the 3.4 μm feature corresponds to AV = 18–30 mag, which is far smaller than that inferred from hard X-ray observations. We conclude that the obscuring torus is highly concentrated to a thin disk, the thickness of which is less than 10−1 pc, and that we view the obscuring torus from the exact edge-on direction. We have not detected the 3.3 μm UIR (Unidentified InfraRed emission) feature in the central 3.″8 × 3.″8 region. This result implies that starburst activity just outside of the obscuring torus is absent.
ASCA Observations of Eta Carinae
Authors: Tsuboi Yohko , Koyama Katsuji , Sakano Masaaki , Petre Robert
Published: March 2014

We present ASCA results on the peculiar star η Car in the center of the Carina Nebula. The X-ray emission from η Car was found to be attributable to two thermal components: the high-temperature component (kT ∼ 5 keV) is consistent with a point source, and is highly absorbed, while the low-temperature plasma (kT ∼ 0.7 keV) is extended, and shows no significant circumstellar absorption. We found a line-like structure around 0.5 keV, which is probably due to the Lyα line of nitrogen. Using a variable-abundance coronal plasma model, we found that the relative abundance of nitrogen to oxygen is extremely large in comparison with the solar value. This may be the first X-ray evidence of the enrichment of CNO-processed material in an evolved massive star.
ASCA Observation of the Poor Cluster of Galaxies AWM 7: Evidence of an Abundance Increase in the
Intra-Cluster Medium at the Center
Authors: Xu Haiguang , Ezawa Hajime , Fukazawa Yasushi , Kikuchi Ken'ichi , Makishima Kazuo , Ohashi Takaya , Tamura Takayuki
Published: March 2014

We present the results of the ASCA central-pointing observation of the poor cD cluster AWM 7. The Performance Verification phase data of GIS 2, GIS 3, SIS 0 chip 1, and SIS 1 chip 3 were used to study the properties of the intra-cluster medium (ICM) within 16′ around the X-ray centroid. We found that, compared with the outer regions, the equivalent width of the Fe-K lines increases in the central 4′ (∼ 123 h−150 kpc) region by a factor of ∼ 1.5. Although the ICM temperature tends to decrease in the same region, the observed increase in the Fe-K line equivalent width cannot be explained away by a possible temperature drop. The model fitting indicates that the abundance increases from ∼ 0.4 solar outside 4′ to ∼ 0.6 solar at the center. Thus, after the Centaurus cluster and the Virgo cluster, AWM 7 is the third poor cD cluster confirmed to show an abundance increase in the central region. The 0.5−3 keV flux of the cool emission within 4′ is constrained to be < 8 × 1042)h−250 erg s−1, or < 21% of the total 0.5–3 keV flux from the same spatial region. We discuss possible relations of these phenomena to the cD galaxy.
Effect of Shear on the Cosmological Distance and Image Amplification: Power Spectrum Approach
Authors: Nakamura Takahiro T.
Published: March 2014

The effect of shear on the cosmological distance and image in an inhomogeneous universe is investigated by solving the optical scalar equation perturbatively. We estimate the statistical properties of these quantities in cold dark-matter models for general cosmological parameters. We show that the effect of shear can be safely neglected for a light ray passing through a linear density inhomogeneity, which justifies the approximation used in previous studies. We also obtain an analytic expression for the skewness of the probability distribution of amplification in the Einstein-de Sitter universe.
Distribution of Forces in Gravitationally Clustered System
Authors: Ardi Eliani , Inagaki Shogo
Published: March 2014

We have studied the distribution of forces in gravitational systems through numerical experiments. Data were taken from an N-body simulation in an expanding universe. Before clustering, the distribution of random forces was represented as a Holtsmark distribution; the nearest-neighbor distribution is also shown as a comparison. The analytical and simulation distributions are in good agreement. When clustering becomes strong, the simulation result showed that the contribution of the forces acting on each galaxy, which is generated from all other galaxies, is almost entirely due to the gravitational attraction of its nearest neighbor. This implies that nearest-neighbor galactic encounters may play the main role in the dynamics of galaxy clustering.
Thermal Stability in Two-Temperature Advection-Dominated Accretion, Disks against Local Perturbations
Authors: Yamasaki Tatsuya
Published: March 2014

The stability of two-temperature advection-dominated accretion disks is examined against axisymmetric local thermal perturbations. The disks are optically thin. The results show that there is a weakly unstable mode due to radiation effects. In the case that thermal conduction is efficient, however, the mode is stabilized. The magnetic field also stabilizes the local thermal mode.
Evidence for a Dense, Cold Screen towards IRAS 18507+0121
Authors: Ramesh B. , Bronfman L. , Deguchi S.
Published: March 2014

Self-absorbed profiles has been seen towards the core containing IRAS 18507+0121, a probable high-mass protostar, in the millimeter wave lines of HCO+, H13 CO+, CS, and C34S. Especially, the J = 1 → 0 line of H13 CO+, is found to be stronger than that of HCO+. We have modeled this core in order to determine the physical conditions in it. To generate synthetic spectra from the model core, we used a multi-level, non-LTE radiative transfer code that employs a large-velocity-gradient approximation in order to estimate the level populations. It has been demonstrated that the line profiles can be explained by a collapsing hot core hidden behind a cold (∼ 4 K) and dense (3 × 104 cm−3) intervening, but comoving, screen or envelope. The model parameters adjusted to reproduce the observed profiles are (a) the temperature, density, and velocity fields in the model core and (b) the temperature, density, and linewidth in the screen. Comparing the observed profiles with the model spectra at both the on-center and one off-center positions, we have been able to reliably determine the physical conditions in the core.
Oxygen λ7771–5 Triplet in Hyades A-Type Stars: A Quest for the Key to the Am Phenomenon
Authors: Takeda Yoichi , Sadakane Kozo
Published: March 2014

An extensive profile-fitting analysis of the OI 7771–5 triplet (along with the nearby FeI line) was carried out for thirty-one A-type stars, eighteen of them belonging to the Hyades group, in order to clarify the key factor which plays the decisive role in the appearance of abundance anomalies of metallic-line stars (Am), by examining whether any meaningful relation exists between the microturbulence (ξ), the oxygen abundance (log ∊O), the iron abundance (log ∊Fe), the projected rotational velocity (ve sin i), and the stellar atmospheric parameters. It was clearly found based on the Hyades results that the abundance of O/Fe, both being good indicators of the Am phenomenon, because of the negative/positive correlation with the metallicity estimated from colors, progressively increases/decreases (i.e., toward the direction of disappearance of anomaly) with an increase in ve sin i as well as with a decrease in log g. It was thus concluded that the most important driver of the Am phenomenon, producing a significant deficiency/excess of O/Fe, is the rotational velocity which appears to be responsible for not only the triggering, but also the extent of the peculiarity. Meanwhile, the observed log g-dependence of the abundance e anomalies is considered to be nothing but superficial, which may be interpreted as being due to the correlation between log g and ve sin i, i.e., rotation-induced lowering of the effective gravity.
Three-Dimensional MHD Models for the Interaction between the Solar Wind and the Interstellar Medium
Authors: Nozawa Satoshi , Washimi Haruichi
Published: March 2014

We attempted to perform a global three-dimensional (3-D) MHD computer simulation of the outer heliosphere under the interaction of the solar wind plasma with the interstellar medium, and showed that MHD processes are important in analyzing 3-D global heliospheric structure. The magnetic pressure effect of the interplanetary spiral field, which has been discussed theoretically and analyzed by a 2-D simulation, was examined in detail in our 3-D global system. The contraction of the scale of the terminal shock due to the magnetic pressure effect was analyzed quantitatively. It was found that in the downstream side of the interstellar flow, the magnetic pressure force contracts the scale of the terminal shock more evidently, which produces an isotropic structure of the shock rather than a bullet-type shape which was obtained by a hydrodynamic simulation. Collimated polar streams of the solar wind due to the magnetic pressure are also found in the heliosheath. In addition, the magnetic pressure is found to make the sheet plasma more dominant along the equatorial disk in the heliosheath.
The Most Distant [OIII]-Emitting Quasar PKS 1937–101 at Redshift 3.8
Authors: Taniguchi Yoshiaki , Murayama Takashi , Kawara Kimiaki , Arimoto Nobuo
Published: March 2014

We report on the discovery of a high-z quasar with unambiguous [OIII]λ5007 emission: PKS 1937–101 at redshift 3.8. This quasar, however, shows little evidence for rest-frame ultraviolet and optical FeII emission. It is thus shown that PKS 1937–101 does not belong to a class of super-iron-rich high-z quasars reported by Elston, Thompson, and Hill (1994, AAA61.159.045). The epoch of major star formation in the host galaxy is briefly discussed.
X-Ray Imaging Spectroscopy of Stephan's Quintet and Seyfert 2 Galaxy NGC 7319
Authors: Awaki Hisamitsu , Koyama Katsuji , Matsumoto Hironori , Tomida Hiroshi , Tsuru Takeshi , Ueno Shiro
Published: March 2014

We observed Stephan's Quintet, a compact group of galaxies, with the Japanese X-ray satellite ASCA. The ASCA observation has revealed that the X-ray emission consists of two components. One is a soft X-ray emission characterized by thin thermal model with kT = 0.76+0.05−0.10 keV and a metal abundance of 0.08 ± 0.04 solar. Since the soft X-rays are extended and the centroid is located at the region between NGC 7318 and NGC 7319, thin thermal emission originates from diffuse hot gas filling the Quintet. The total mass of hot gas is about 2 × 1010M⊙, which is only 10% of the galaxy mass. The low metal abundance indicates that most of the hot gas consist of primordial gas. The binding mass is about 6 × 1012M⊙. The baryonic fraction is about 10%. The other component is hard X-ray emission located at NGC 7319, a Seyfert 2 galaxy. The X-ray spectrum is well fitted by the absorbed-power law emission plus a line. The photon index is 0.8+0.8−1.1, and the absorption column is about 1023 cm−2. The X-ray luminosity in the 2–10 keV band is about 1.7 × 1042 erg s−1. These characteristics are consistent with those of Seyfert 2 galaxies. We have revealed an obscured nucleus in NGC 7319. Our results well explain the flux of Hα and anisotropic radiation seen in the optical band.
1–4 μm Spectroscopy of Very Red Stars Found in an I-Band Objective Prism Survey
Authors: Goto Miwa , Sasaki Yoshinori , Imanishi Masatoshi , Nagata Tetsuya , Jones Terry Jay
Published: March 2014

We present the 1.2–4.2 μm spectroscopy of stars found in an objective prism survey of the galactic plane by Stephenson (1992, AAA 55.002.010). These stars were thought by Stephenson to be heavily reddened by interstellar absorption. However, almost all of them have turned out to be late-type stars with clear 2.3 μm CO absorption, which means that they are intrinsically red as well. A few stars have AV ∼ 9, but most of them are only moderately reddened (AV = 1–5).
Time Variation of X-Rays from GX 5–1
Authors: Kamado Yasuhide , Kitamoto Shunji , Miyamoto Sigenori
Published: March 2014

Long- and short-term variations of X-rays from GX 5–1 (a neutron-star X-ray binary) were investigated based on the Eastern energy spectral model: a disk-blackbody component plus a blackbody component model. In the horizontal branch (HB), an increase in the X-ray intensity is mainly due to the disk component; this increase is mainly due to an increase in Rin (the inner radius of the accretion disk), although Tin (the temperature of the inner edge of the accretion disk) decreases slightly. A fraction of the blackbody component decreases with the X-ray intensity in HB. In the normal branch (NB), an increase in the X-ray intensity is due to both components. The hardening of the X-ray energy spectrum with the X-ray intensity in NB is mainly due to an increase in the blackbody component: the fraction of the blackbody component increases with the X-ray intensity. The X-ray intensities of the disk component and the blackbody component show different long-term variations from each other, which are similar to the case of the disk component and the power-law component of black-hole candidate X-ray binaries (BHCXBs); GX 339–4 and GS 1124–683. It is possible that the behavior of the Z source from HB to NB is due to hysteretic behavior, such as that shown by the BHCXBs. Short-term variations of X-rays from GX 5–1 were investigated using normalized power spectral density functions (NPSDs), and were compared with those of a BHCXB, GS 1124–683. NPSD of the disk component has a power-law shape, and has an energy dependence: the higher is the X-ray energy, the larger is the variation. NPSD of the blackbody component has a flat-top shape, and has no energy dependence. These are the same as that of the disk component and the power-law energy spectral component of GS 1124–683, in spite of their different energy spectra and different category of X-ray stars. The very-low-frequency noise (VLFN) of GX 5–1 has minimum values in the transition part between HB and NB, where the total X-ray intensity has its maximum value. VLFN seems to be related to a variation of the mass-accretion rate.
Discovery of an 11-s X-Ray Pulsar in the Galactic-Plane Section of the Scorpius Constellation
Authors: Sugizaki Mutsumi , Nagase Fumiaki , Torii Ken'ichi , Kinugasa Kenzo , Asanuma Tatsuhiko , Matsuzaki Keiichi , Koyama Katsuji , Yamauchi Shigeo
Published: March 2014

During a galactic-plane survey with ASCA in 1996 September, we detected a relatively bright, soft source at R.A. = 17h8m46s.6, DEC. = −40°9′27″ (J2000), and discovered an 11-s X-ray pulsation from the source. This source has been identified with the ROSAT source 1RXS J170849.0−400910. From a timing analysis of the source, we obtained a barycentric pulse period of P = 10.99759±0.00005 s with a broad sinusoidal shape of a pulse fraction of ∼ 30%. The energy spectrum in the 0.8–10 keV region is very soft, and can be fitted by a power-law model with a photon index of 3.5 and an absorption column density of 1.8 × 1022 cm−2. The observed pulse-phase-averaged flux in the range 0.8–10 keV is 4.3 × 10−11 erg cm−2 s−1, which corresponds to 1.7 × 10−10 erg cm−2 s−1 after correcting for soft X-ray absorption. During an observation interval of about 14 hr, neither a significant change in the pulsation period, nor a significant variation in the phase-averaged flux was detected. From these X-ray properties, we suggest that this newly discovered X-ray pulsar might be a member of a small subgroup of “anomalous” X-ray pulsars with a period close to 6–9 s.
Why Can We Detect the High-Redshift Quasar BR 1202–0725 in CO?
Authors: Ikuta Chisato , Arimoto Nobuo , Sofue Yoshiaki , Taniguchi Yoshiaki
Published: March 2014

We present CO luminosity evolutions of both elliptical and spiral galaxies based on a galactic-wind model and a bulge-disk model, respectively. We have found that the CO luminosity peaks at around the epoch of the galactic wind caused by collective supernovae ∼ 0.85 Gyr after the birth of the elliptical with M = 2 · 1012M⊙, while ∼ 0.36 Gyr after the birth of the bulge with M = 2 · 1011M⊙. After these epochs, the CO luminosity decreased abruptly because the majority of the molecular gas was expelled from the galaxy system as wind. Taking account of typical masses of elliptical galaxies and the bulges of spiral galaxies, we suggest that CO emission can be hardly detected from galaxies with a redshift of z ∼ 1–4 unless some amplification either by galaxy mergers and/or by gravitational lensing is working. Therefore, our study explains reasonably well why CO emission was detected from the high-redshift quasar BR 1202 – 0725 at z = 4.7, while it was not detected from powerful radio galaxies with 1 < z < 4.
Star-Burst Galaxy M83 Observed from ASCA
Authors: Okada Kyoko , Mitsuda Kazuhisa , Dotani Tadayasu
Published: March 2014

Combined spectral and spatial analyses of the central region of the nearby spiral galaxy M83 shows the presence of two different emission components. One component has a spatial size of 2.′7, as defined by the rms radius of the emission region, and has an emission temperature of about 5 keV when it is approximated with a thermal-bremsstrahlung model. The other component has a much smaller radius with an upper limit of 1.′0 rms radius, and has a lower emission temperature of about 0.4 keV. The X-ray luminosities of the two components are, respectively, 2.1 × 1039 erg s−1 (soft component) and 4.8 × 1039 erg s−1 (hard component) in the 0.−10 keV band (for the distance of 3.75 Mpc). The soft, lower-temperature component is consistent to be emission from the hot gas originating from the star-burst activity in the galaxy. On the other hand, the hard component is consistent with being a collection of binary X-ray sources in the bulge region.
Cross-Section Variations of Coronal Magnetic Loops
Authors: Wang Huaning , Sakurai Takashi
Published: March 2014

Axisymmetric nonlinear force-free field models were employed to study the variation of the cross-section of coronal loops. In order to simulate these loops, we placed the point source of the fields under the photosphere and made the symmetric axis parallel to the photospheric surface. Based upon qualitative theoretical analyses and numerical simulations on the dipoles in these models, we compared the simulated magnetic loops with similar arclength and symmetric distributions of magnetic strength, and obtained the following results: The cross-section expansion of the current-free loops is fairly large and nearly isotropic, and that of highly sheared force-free loops is small and anisotropic. The anisotropy of the cross-section expansion, however, tends to vanish in extremely sheared loops. Magnetic loops with constant thickness, as an extreme case in the dipole nonlinear force-free fields, can be reached asymptotically when the magnetic shear increases. They tend to appear in the vicinity of the plane, vertically intersecting the symmetric axis at the point source, and their footpoints are not exactly located in the peak sites of vertical electric current density on the photospheric surface.
The Ionization and Abundance of C and Si in QSO Absorbers
Authors: Khare Pushpa , Ikeuchi Satoru
Published: March 2014

We have analyzed high-resolution data of absorption lines of Si and C in absorption systems observed in the spectra of QSOs, in order to study the ionization state and the overabundance of Si with respect to C in absorbers, and also to study the change in these properties with the redshift. No correlation was found between the column-density ratios of Si IV to C IV of intervening systems and the redshift. The data do not provide any evidence for an abrupt change in the values of the ratio at any particular redshift, unlike that for Lyman alpha forest clouds. We have compared the observed ratios of column-densities of Si II and Si IV and of Si IV and C IV in different classes of absorption systems with the predictions of photo-ionization models for different shapes of the background-radiation field. An overabundance of Si over C can be ruled out in several of the intervening systems for any shape of the background radiation. For these systems we can also rule out any contribution from stellar sources to the background, which is then entirely from the AGNs. No overabundance is needed in other intervening systems if the radiation field from stellar sources significantly contributes to the UV background. An overabundance, however, is present in Lyman alpha forest clouds at redshifts larger than 3 and in systems associated with the QSOs. For all of the intervening systems a minimum of 10% of the background is contributed by the AGNs.
Wave Excitation in Isothermal Disks by External Gravity
Authors: Takeuchi Taku , Miyama Shoken M.
Published: March 2014

Wave excitation in isothermal disks with finite thickness by external gravity is investigated. The main application of this study is to clarify the process of angular-momentum transfer in a protoplanetary disk by a protoplanet. It is found that waves with vertical motion (3D-waves) as well as waves without vertical motion (2D-waves) are excited, and that both waves can transfer angular-momentum. The 2D-waves have properties similar to the waves in infinitesimally thin disks. A protoplanet on the central plane of the disk excites mainly 2D-waves. On the other hand, 3D-waves have a minor effect on the angular-momentum transfer.
Near-Infrared Spectroscopic Observation of the High-z Quasar PKS 0201+113
Authors: Oya Shin , Iwamuro Fumihide , Tsukamoto Hiroyuki , Maihara Toshinori
Published: March 2014

A near-infrared spectroscopic observation of a high-redshift quasar, PKS 0201+113, made with the OH-airglow suppressor spectrograph (OHS) is presented. This quasar is known to have a damped Lyα system in the line of sight. Distinctive characteristics shown in the low-resolution spectrum of the quasar in the J- and H-bands are a large redshift difference between the Mg II emission line and high-excitation lines, the presence of Fe II emission features and a possibly reddened continuum spectrum. The difference in the velocity between the C IV and Mg II lines is consistent with a simple picture of the separated distribution of broad line regions made of two regions: i) high-excited clouds having a high outflow velocity and ii) relatively quiescent low-excited clouds surrounding the central hot region. The presence of Fe II emission implies that the metalicity of the central environmental gas of the high-redshift quasar is still similar to that of low-redshift quasars. A softening of the spectral slope toward short wavelengths could be explained if we take reddening by the damped Lyα system into account.
Elliptical Lens Model in PG 1115+080
Authors: Asano Katsuaki , Fukuyama Takeshi
Published: March 2014

The mass distribution of the lensing galaxy of the multiple quasar PG 1115+080 has been studied. Using the observational data of Christian et al. (1987, AAA 43.159.012), we applied a single elliptical lens model with a softened power-law behavior. It has been revealed that the image positions, amplifications, and time delays of this lensing system cannot be explained by the single transparent lens model. We compare this elliptical lens model with a multipole expansion model.
A Redshift Survey for Galaxies behind the Milky Way near the Galactic Center
Authors: Roman Adel T. , Takeuchi Tsutomu T. , Nakanishi Kouichiro , Saitō Mamoru
Published: March 2014

The galaxy search at the region near the galactic center is still highly incomplete. This paper presents results of our redshift measurements for a random sample of galaxies and galaxy candidates at l ≃ 18° to 41° and b ≃ −17° to 17°, most of which were newly identified through our previous optical search. We have obtained 78 new radial velocities, and found two regions with enhanced density at around l ≃ 32°, cz ≃ 1500 km s−1 and at l ≃ 30° to 40°, cz ≃ 6000 to 7000 km s−1. Our data rule out the possible presence of a nearby large void at the region cz < 6000 km s−1 around l = 30° , which has been induced from the results of a systematic search for IRAS galaxies.
Precessional Light Curves of SS 433
Authors: Fukue Jun , Obana Yoshimi , Okugami Masamitsu
Published: March 2014

We have calculated theoretical light curves of SS 433 during precession, using a model in which SS 433 consists of a geometrically thick torus around a compact star and a companion star filling the Roche lobe. In order to interpret a bright hump at the precession phase of 0 (the torus is seen from the “bottomside”), the configuration of the torus is not very thick, but should be rather thin (at least mildly thin). Combinations of light curves during eclipse and precession impose several constraints on the physical parameters: the binary mass ratio, torus configuration, and surface temperature of the companion. The favorite combination is a mass ratio of about 2 (a compact star is a black hole) and a surface temperature of the companion of around 17000 K.
The Complex X-Ray Spectrum of 3C 273: ASCA Observations
Authors: Cappi Massimo , Matsuoka Masaru , Otani Chiko , Leighly Karen Marie
Published: March 2014

The results obtained from 9 X-ray observations of 3C 273 performed by ASCA are presented (total exposure time ∼ 160000 s). The analysis and interpretation of the data was complicated by the fact that 4 of these observations were used for the on-board calibration of the CCDs spectral response. The present standard analysis shows that, in agreement with official recommendations, a conservative systematic error (at low energies) of 2–3 × 1020 cm−2 must be assumed when analyzing ASCA SIS data. A soft-excess, with variable flux and/or shape, has been clearly detected as well as flux and spectral variability. An anti-correlation has been found between the spectral index and the flux in the 2–10 keV energy range. Fitting the data with the latest available calibration matrices, we also detect an emission line at 5.4–5.7 keV (6.3–6.6 keV in the quasar frame) in only the two observations with lowest fluxes where it is weak (EW ∼ 20–30 eV), narrow and consistent with being produced by Fe Kα emission from neutral matter. Overall, the observations are qualitatively consistent with a variable, non-thermal X-ray continuum emission (a power law with Γ ∼ 1.6, possibly produced in the innermost regions of the radio-optical jet), plus underlying “Seyfert-like” features (a soft-excess and Fe Kα line emission). When the continuum (jet) emission is in a low state, the Seyfert-like spectral features (soft-excess, iron line, and possibly a steep power law plus reflection continuum) are more easily seen.
Low-Resolution Spectral Classification of Very Faint Emission-Line Galaxies
Authors: Murayama Takashi , Taniguchi Yoshiaki
Published: March 2014

In order to classify the emission-line activity of very faint galaxies, we present a new classification method based on low spectral-resolution $(\lambda/\Delta\lambda\sim50)$ spectroscopic data. Our new method enables us to classify faint emission-line objects with B < 26, which will be obtained by using deep optical and near-infrared spectroscopy with an 8-m class of telescope facilities.
Discovery of X-Ray Emission from a Radio Supernova Remnant G352.7-0.1
Authors: Kinugasa Kenzo , Torii Ken'ichi , Tsunemi Hiroshi , Yamauchi Shigeo , Koyama Katsuji , Dotani Tadayasu
Published: March 2014

We report on the first detection of X-rays from the radio supernova remnant (SNR) G352.7-0.1 with the ASCA Galactic Plane Survey Project. An X-ray image with a shell-like morphology similar to that of the radio band and a spectrum with prominent K-shell lines from highly ionized Si, S, and Ar are presented. These features provide convincing evidence that the X-rays are due to a shock-heated optically thin hot plasma. The spectra are represented by a non-equilibrium ionization (NEI) model with an electron temperature of kT ∼ 2.0 keV, an ionization parameter of $\tau\sim10^{11.0}$ cm−3 s, and an absorption of $N_\textrm H \sim 2.9 \times 10^{22}$ cm−2 . We report on evidence of overabundances of Si and S of ∼ 3.7 and ∼ 3.4, relative to the solar values, respectively. The large absorption indicates that G352.7–0.1 is near to the galactic center region and, after removing the absorption, the X-ray flux in the 1–10 keV band is estimated to be $F_\textrm X (1-10 \textrm {kev})\sim1.2\times10^{-11}\textrm {erg cm}^{-2} \textrm s^{-2}$ . Assuming the SNR to be in the Sedov phase and near to the galactic center (8.5 kpc), G352.7-0.1 is estimated to have a SN explosion energy and age of $E_\textrm {SN}\sim 2\times 10^{50}$erg and $t_{\textrm age}\sim 2200$ yr, respectively; hence, it is a middle-aged SNR.
Metal-Rich Plasma at the Center Portion of the Cygnus Loop
Authors: Miyata Emi , Tsunemi Hiroshi , Kohmura Takayoshi , Suzuki Seiji , Kumagai Shiomi
Published: March 2014

We observed the center portion of the Cygnus Loop supernova remnant with the ASCA observatory. The X-ray spectrum of the center portion was significantly different from that obtained at the North-East (NE) limb. The emission lines from Si and S were quite strong, while those of O and the continuum emission were similar to those obtained at the NE limb. Based on a spectral analysis, the Si and S emission lines originated from a high-kTe and low-ionization plasma, whereas O and most of the continuum emission arose from a low-kTe and high-ionization plasma. We suppose that Si and S emitting gases are present at the interior of the Loop, while the O lines and continuum emission mainly arise from the shell region. Therefore, we subtracted the spectrum of the NE limb from that of the center. The obtained abundances of Si, S, and Fe were 4 ± 1, 6 ± 2, and $1.3^{+0.6}_{-0.3}$times higher than those of the cosmic abundances, respectively, and ∼ 40 times richer than those obtained at the NE limb. These facts strongly support the idea that some of the crude ejecta must be left at the center portion of the Cygnus Loop. The low abundance of Fe relative to Si and S suggests a type II SN with a massive progenitor star as the origin of the Cygnus Loop.
Spectroscopic Analysis of the Cobalt Peculiar Star HR 5049 in the Red Spectral Region
Authors: Nishimura Masayoshi
Published: March 2014

A detailed LTE analysis of metallic lines in the red spectral region (between λ5700 Å and λ6700 Å) was carried out for the B-type peculiar star HR 5049. The abundances of 5 elements from 8 ions were determined. This star exhibits unusually strong lines of Co I and Co II, and this element is found to be overabundant by as much as 4.0 dex compared to the solar abundance. Weak Cl I lines have been detected in the observed region, and Cl was estimated to be overabundant by 3.0 dex. The abundances of Si, Cr, and Fe are also strongly enhanced. Although lines of Pr III were found to vary with the phase in the rotation period of the star, other elements were found not to vary. From its observed abundance-pattern, HR 5049 is suggested to be a member of a rare group of CP stars which are characterized by enhancements of chlorine and cobalt, as in HR 1094.
CCD Photometry of SW Ursae Majoris during the 1996 Superoutburst
Authors: Nogami Daisaku , Baba Hajime , Kato Taichi , Novák Rudolf
Published: March 2014

Differential CCD photometry of the 1996 April superoutburst of SW UMa was performed both at the Nicholas Copernicus Observatory and at the Ouda Station, Kyoto University. Although superhumps with a period of 0.05818 (± 0.00002) d and possible small-amplitude quasi periodic oscillations (QPOs) were detected, we failed to find the so-called super-QPOs. SW UMa has been proved to be the fourth SU UMa-type dwarf nova, following AL Com, V1028 Cyg, and HV Vir, in which an analysis of the superhump maxima timings revealed an increase in the superhump period.
CO (J = 2–1) Observations of the Quasar BR 1202–0725 at Z = 4.7
Authors: Ohta Kouji , Nakanishi Kouichiro , Akiyama Masayuki , Yamada Toru , Kohno Kotaro , Kawabe Ryohei , Kuno Nario , Nakai Naomasa
Published: March 2014

A 12CO (J=2–1) observation of the quasar BR 1202–0725 at z=4.7, in which a huge amount of molecular gas had been detected in the 12CO (J=5–4) emission line, was made with the Nobeyama 45-m radio telescope. An upper limit of 1.2 mK in TMB ( ∼ 2.8 mJy) was obtained at a velocity resolution of 25 km s−1 . The physical conditions of the molecular gas were examined using the CO emission-line ratios with the LVG model; the line ratios imply that the molecular gas is dense $[n(\textrm H_2)\sim 10^{3.5-5.5}\textrm {cm}^{-3}]$ with a high kinetic temperature (50–100 K). The value of the CO-to-H2 conversion factor in this system is discussed and the molecular-gas mass is estimated to be less than $5.4 \times 10^{11}M \odot$. Using these values, we tried to sketch the distribution of molecular gas in this system and find the possibility that the system consists of many small dense clouds.
The Orbital Period of the SU Ursae Majoris Star EK Trianguli Australis and Evidence for Ring-Like Accretion Disks in Long-Supercycle Length SU Ursae Majoris Stars
Authors: Mennickent Ronald E. , Arenas Jose
Published: March 2014

An orbital period of 0.06288(5) d has been found from a radial velocity study of the Hα emission line. In addition, we have detected an extra line emitting source located ≈ 80° apart from the vector joining the secondary–primary centers, as measured in the opposite sense to the binary rotational motion. This is not the expected location for the hotspot in dwarf novae. This anomaly could be removed by assuming a line emission lagging behind the white dwarf binary motion. In addition, we have estimated line emissivity (∝ r−α ) and disk radius $R \equiv r_{in}/r_{out}$ for 8 SU UMa stars. Most stars fit α = 1.8 ± 0.1 but AK Cnc and WZ Sge strongly deviate from the mean; their emission line shapes can be explained assuming a post-outburst accretion disk mostly emitting close to the white dwarf (AK Cnc) and a ring-like disk (WZ Sge). In addition, we have found a tendency of long-supercycle length SU UMa stars to show very compact (large R; probably ring-like) accretion disks. If the supercycle length were basically controlled by the mass transfer rate (Ṁ), the inner disk radius would be a function of Ṁ. A white dwarf magnetic field ∼ 5000 G is required to fit the truncation radius with the magnetosphere radius of SU UMa stars.
Angular Momentum Transfer due to Galactic Winds and Cooling Flows
Authors: Missoulis Vasilis
Published: March 2014

The interaction of a slowly rotating halo with an early galactic superwind is investigated. Two cases of the halo are assumed: a) rich in cold clouds, b) constituted by diffuse gas. In the first case, the clouds evaporate due to the shock-wave and their matter is mixed with the wind to a uniform mixture. In the second case, a cold shell is formed at large distance from the center. Fragmentation of this shell leads to the appearance of a stellar shell whereas the remaining clouds are free-falling to the center of the system. In both cases a strong redistribution of the mass is taking place which leads to angular momentum transfer from the outer to the inner regions. By the same way the mass and angular momentum can be redistributed by quasi-stationary cooling flows with cloud formation. Some applications of the above mechanisms to the structure of the disk of spiral galaxies are discussed.
X-Ray Constraints on Cluster Magnetic Fields
Authors: Henriksen Mark
Published: March 2014

Lower limits to the intracluster magnetic field are derived from modeling broad band X-ray spectra of 6 galaxy clusters with radio halos (A401, A754, A1367, Coma=A1656, A2256, and A2319). The 0.7–10 keV spectra for all clusters were obtained with the Advanced Satellite for Cosmology and Astrophysics (ASCA) Gas Imaging Spectrometer (GIS). For A401, A754, A1367, and A1656, data from the HEAO1-A2 High Energy Detector (HED) (2–60 keV) was included in a joint fit to further constrain the allowed non-thermal component. Upperlimits to the non-thermal X-ray emission are a factor of ∼ 10 improvement over previous values. Lower limits to the average magnetic field derived from these upperlimits and the radio spectral parameters range from 0.08–0.30 μ G. A seed intracluster field amplified by turbulence from galaxy motion through the intracluster medium should have an average value in the range ∼ 0.1–0.2, thus the lack of any detections makes it unlikely that field amplification is due to galaxy wakes. In addition, all of these clusters have an asymmetric surface brightness distribution while several also have X-ray spectroscopic evidence of a merger. We suggest that cluster mergers rather than galaxy wakes are the source of the magnetic field amplification.
“Huruhata's Variable” Revealed: The WZ Sge-Type Dwarf Nova EG Cancri
Authors: Matsumoto Katsura , Nogami Daisaku , Kato Taichi , Baba Hajime
Published: March 2014

Time-resolved CCD photometric observations of a dwarf nova EG Cnc were carried out during an outburst which occurred after a 19-year quiescent interval, since 1977 November. Our observations between 1996 December 2 and 14 revealed this outburst to be a definite superoutburst, eventually enabling a definite classification of this object as an SU UMa-type dwarf nova. This outburst was characterized by its long duration of more than two weeks and a large amplitude of at least 6.7 mag. The object showed two distinct types of superhumps: double-peaked modulations attributable to “early superhumps” with a period of 0.0582±0.00025 d in the earlier stage of the current outburst, followed by fully grown typical superhumps with a period of 0.0603±0.00006 d. We regard the period of 0.0582 d as being the orbital period of the object with a 3.7% superhump excess ratio. These characteristics suggest a strong resemblance to an extreme rare class of dwarf novae including WZ Sge, HV Vir, and AL Com with some other similarities between EG Cnc and the WZ Sge-type dwarf novae. The existence of double-peaked “early superhumps” in the early stage of superoutbursts may be a new defining criterion for the WZ Sge-type dwarf novae.
Two New SU UMa-Type Dwarf Novae with Superhump Periods of Over Two Hours: GX Cassiopeiae and V419 Lyrae
Authors: Nogami Daisaku , Kato Taichi , Masuda Seiji
Published: March 2014

We succeeded in detecting superhumps in GX Cas and V419 Lyr during the 1994 long outburst and the 1995 outburst, respectively, and identified those stars as SU UMa stars. A period analysis gives 0.09297 (± 0.00005) d as the best-estimated superhump period of GX Cas, which is the third-longest one following TU Men and NY Ser. This superhump period suggests GX Cas to be located at the upper edge of the period gap of dwarf novae. The superhump period of V419 Lyr is estimated to be close to GX Cas, though the short coverage of superhumps prevented us from determining an accurate value. The recurrence cycle of the superoutburst (supercycle) and the normal outburst of GX Cas is estimated to be 386 d and 50–70 d, respectively, based on the VSNET data archive. This supercycle predicts that the next superoutburst in GX Cas will occur around 1998 November 10. Detailed observations of these stars may give important information concerning the study of dwarf-nova evolution as well as the criterion of the tidal instability.
Nuclear-to-Disk Rotation Curves of Galaxies in the Ha and [N II] Emission Lines
Authors: Sofue Yoshiaki , Tomita Akihiko , Tutui Yoshinori , Honma Mareki , Takeda Yoichi
Published: March 2014

We have obtained optical CCD spectroscopy along the major axes of 22 nearby spiral galaxies of Sb and Sc types in order to analyze their rotation curves. By subtracting the stellar continuum emission, we have obtained position–velocity (PV) diagrams of the Hα and [N II] lines. We point out that the Hα line is often superposed by a broad stellar absorption feature (Balmer wing) in the nuclear regions, and, therefore, the [N II] line is a better tracer of kinematics in the central few hundred parsec regions. By applying the envelope-tracing technique to the Hα and [N II] PV diagrams, we have derived nucleus-to-disk rotation curves of the observed galaxies. The rotation curves rise steeply within the central few hundred parsecs, indicating a rapidly rotating nuclear disk and mass concentration near the nucleus.
Hydrogen Shell-Burning Models for RX J0925.7–4758
Authors: Hoshi Reiun
Published: March 2014

We have constructed models of accreting white dwarfs in steady hydrogen burning for the supersoft X-ray source RX J0925.7–4758. A white dwarf with a mass of around 1.4 M⊙ has been found to account for the blackbody temperature and the bolometric luminosity, determined from ASCA observations. Our models indicate that the color temperature is higher by up to 30% than the effective temperature. To be exact, the soft X-ray spectra differ considerably from the blackbody. The models discussed in this paper can also be applied to the other supersoft X-ray sources.
Oxygen and Nitrogen Abundances in Hyades F Type Dwarfs
Authors: Takeda Yoichi , Kawanomoto Satoshi , Takada-Hidai Masahide , Sadakane Kozo
Published: March 2014

The abundances of oxygen and nitrogen were investigated for eleven Hyades F type main-sequence stars, based on the line-profile of O I (+Fe I) 8446 and the equivalent-widths of N I 8629/8683, in order to examine whether any conspicuous abundance deficiency exists for O and N at Teff ∼ 6700 K similar to that observed for Li, since its possibility was suggested by the diffusion interpretation of this “Li-chasm”. It turned out, however, that the abundances appear to be nearly independent of Teff (and ve sin i) for both O and N, without showing any apparent dip larger than ∼ 0.2 dex (for O) or ∼ 0.3 dex (for N), being consistent with the results of García-López et al.'s (1993, AAA 58.114.068) study for oxygen. This may indicate that the diffusion process alone is probably not responsible for the origin of the Li-gap. Regarding the averaged O and N abundances in these Hyades F stars, a moderate N-excess by ∼ 0.3 dex relative to the Sun was suggested (though not definite), with oxygen being nearly normal.
Evolution of Accretion Disks with Mass Evaporation during the Quiescence of WZ Sge-Type Dwarf Novae and X-Ray Novae
Authors: Mineshige Shin , Liu Bifang , Meyer Friedrich , Meyer-Hofmeister Emmi
Published: March 2014

We propose a new scenario for disk evolution during the quiescence of WZ Sge-type dwarf novae and X-ray novae. A hole created by evaporation of the inner disk material steadily expands towards larger radii, eventually removing thermally unstable portions of the disk. The disk is, however, not in a steady state, since a certain amount of angular momentum is continuously brought in by an incoming stream, whereas angular-momentum losses due to the evaporation and to the tidal action by a companion star are likely to be small in the quiescence. Accordingly, the total angular momentum of the disk monotonically increases, whereas an increase in the disk mass is somewhat slower because of the mass evaporation. This results in an expansion of the disk and an accumulation of mass in the outermost part of the disk. The quiescence will be terminated if a thermal instability is ignited before the disk expands to the critical radius for the 3:1 resonance between Kepler and orbital angular frequencies. If not, superhumps are expected during quiescence.
Fragmentation of Collapsing Gas Disks in External Potentials
Authors: Kawata Daisuke , Hanami Hitoshi
Published: March 2014

The star-formation activity in protogalactic disks is regulated by the fragmentation process of self-gravitating gas disks formed by the collapse in dark halo potentials. In order to study this process, we numerically simulated the dynamical evolution of rotating gas clouds in external potentials. The fragmentation was found to occur only in the limited area of the parameter space defined by the initial ratios of the thermal and rotational energies to the gravitational energy. A linear instability analysis has been applied to rotating equilibrium disks resulting from the initial clouds. We found that the critical condition for the growth of axisymmetric perturbations nicely explains the fragmentation boundary found in the simulation results. The generalized fragmentation condition derived by the linear instability analysis consists of two criteria: the “Q-value” criterion, which requires existence of at least one unstable perturbation, and the “wavelength” criterion, which states that the wavelength of the most unstable perturbation is less than the radial scale length of the disk. The second criterion includes the first one automatically when the external gravitational field is absent, whereas the two criteria combine to control fragmentation process in the external potential.
Analysis of Toroidal Magnetic Fields in Accretion Disks Using the Cross-Helicity Effect and Estimate of the Jet Velocity
Authors: Nishino Satoru , Yokoi Nobumitsu
Published: March 2014

The magnetic fields in an accretion disk are examined using a magnetohydrodynamic (MHD) turbulent dynamo model consisting of transport equations for the mean fields, turbulent energy, dissipation rate, and cross helicity. The velocity of accreting gases is assumed to obey the Keplerian and rigid rotations in the outer and inner regions of a disk, respectively, except for the central part. Under the condition of axisymmetry around the rotation axis and uniformity in the direction perpendicular to the disk, the turbulent model is examined both numerically and analytically. As a result, it is pointed out that the cross-helicity effect generates a toroidal magnetic field, resulting in the occurrence of a current in a direction perpendicular to the disk in the central part. This toroidal magnetic field enables gas to escape from a central high-mass body as bipolar jets, because the magnetic energy may become comparable to the gravitational one. The velocity of the jets in a protoplanetary system was estimated by a numerical simulation of the preset model.
Outflows from Advection-Dominated Disks?
Authors: Nakamura Kenji E.
Published: March 2014

Narayan and Yi (1994, AAA 064.083) found that the Bernoulli parameter is a positive constant in advection-dominated accretion flows, thereby mass outflow being inevitable. We find, however, that their conclusion depends critically on their assumptions required to derive their self-similar solutions (i.e., substantial infall velocity, comparable to the rotational velocity, or high virial temperature at the outer boundary) . Rather, positive Bernoulli parameters are not the universal feature of advection-dominated flow. If boundary conditions are properly set, the Bernoulli parameter is mostly negative, as long as the viscosity parameter α is not very large (α < 1) and the specific heat ratio γ is 5/3. Our result shows that spontaneous outflows are not expected, even if accretion disks are advection-dominated. Still, outflow is possible if there exists some mechanism which puts most of the energy selectively into a small fraction of the disk material.