bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Reconnection as the Origin of Galactic-Ridge X-Ray Emission
Authors: Tanuma Syuniti , Yokoyama Takaaki , Kudoh Takahiro , Matsumoto Ryoji , Shibata Kazunari , Makishima Kazuo
Published: March 2014

We present a scenario for the origin of the hot plasma in our Galaxy as a model of strong X-ray emission [∼ 3 – 10 keV; LX(2 – 10 keV) ∼ 1038 erg s−1], called Galactic Ridge X-ray Emission (GRXE), which has been observed near to the galactic plane. GRXE is thermal emission from a hot component (∼ 7 keV) and a cool component (∼ 0.8 keV). Observations suggest that the hot component is diffuse, and that it is not escaping away freely. Both what heats the hot component and what confines it in the galactic ridge still remain puzzling, while the cool component is believed to be created by supernovae. We propose a new scenario: the hot component is heated by magnetic reconnection, and confined by a helical magnetic field produced by magnetic reconnection. We solved two-dimensional magnetohydrodynamic equations numerically to study how magnetic reconnection, triggered by a supernova explosion, creates hot plasmas and magnetic islands (helical tubes), and how the magnetic islands confine the hot plasmas in the Galaxy. This is one of the possible mechanisms to trigger reconnection in the Galaxy. We conclude that magnetic reconnection is able to heat the GRXE plasma if the magnetic field is localized in an intense flux tube with Blocal ∼ 30 μG.
Analysis of the Photospheric Lines of the Magnetic CP Star HR 7575
Authors: Kato Ken-ichi , Sadakane Kozo
Published: March 2014

The photospheric lines in the visual region of the cool magnetic CP star HR 7575 have been analyzed using a high-dispersion spectrogram obtained at the Dominion Astrophysical Observatory. The fully line-blanketed ATLAS9 model atmospheres of 10-times the solar metal content were employed to calculate the elemental abundances. The effective temperature Teff, derived from the optical and ultraviolet energy distributions, points to 8500 ± 300 K, while the ionization balance of iron is not reproduced at this effective temperature. The abundances derived from individual Cr I, Cr II, and Fe II lines apparently depend on their effective Lande factors. This implies that the Cr and Fe lines are intensified by the strong magnetic field on HR 7575. Their abundance enhancement is estimated to be about 0.7 dex based on a computation of the Unno-Beckers equation. The overall abundance patterns of HR 7575 are comparable to other cool magnetic CP stars. Of the analyzed elements, only Mg and Sc have nearly solar abundances, while Cr, Mn, Sr, and rare earths are overabundant by 1 to 5 dex.
Evolution of Lyman α Clouds at Low Redshifts
Authors: Okoshi Katsuya , Ikeuchi Satoru
Published: March 2014

Numerous and narrow absorption lines in quasar spectra, the so-called Lyman α forest, can be a unique probe to explore the early universe. In addition, several detections of an absorption trough in the spectra have placed stringent constraints on the physical properties of the intergalactic medium at high redshifts. They would play an important role in relation to the evolution of the UV background radiation field. Focusing on the mutual relations between the quasar absorption system and the UV background radiation field, we examine the evolution of minihalos, gas clouds confined by the gravity of cold dark matter, and explore reasonable possibilities for minihalos to reproduce the redshift distribution of Lyα clouds at 0 ≲ z ≲ 4. We can find that the redshift distribution of minihalos shows good agreement with the observations over the whole range of redshifts 0 ≲ z ≲ 4 under two alternative cases: first, the UV background radiation has a peak intensity at z ∼ 1; second, the Lyα forest has a comoving number density that decreases exponentially with a characteristic timescale, τ ∼ a few Gyr.
SiO Masers in Stars in the Inner and Outer Galactic Disk
Authors: Jiang B. W. , Deguchi Shuji , Ramesh B.
Published: March 2014

Observations in the J = 1–0, v = 1 and v = 2 28SiO and v = 0 29SiO maser lines were made towards 97 outer- and 19 inner-disk IRAS sources with typical IRAS colors of AGB stars. 21 new 28SiO and 1 new 29SiO maser sources were detected above the 5 σ level of ∼ 1 Jy with the Nobeyama 45 m telescope. Collecting all of the observational data in SiO J = 1–0 maser lines taken with a 45 m telescope, a comparison is made between the outer-disk, inner-disk, and bulge samples. The samples, themselves, align a sequence of mid-infrared color, flux at 12 μm and IRAS variability index. The detection rates are 66%, 51%, and 31%, respectively, in the bulge, inner disk, and outer disk. This fact is consistent with the tendency of increasing proportion of C-rich stars in the IRAS sample and metallicity gradient with the galactocentric distance.
A Millimeter Polarimeter for the 45-m Telescope at Nobeyama
Authors: Shinnaga Hiroko , Tsuboi Masato , Kasuga Takashi
Published: March 2014

We have designed and constructed a tunable polarimeter to cover frequencies from 35 GHz to 250 GHz (8.6 mm and 1.2 mm in wavelength) for the 45-m telescope at Nobeyama Radio Observatory. Both circular and linear polarizations can be measured by the polarimeter. The insertion loss was measured to be 0.14 ± 0.05 dB in the 100-GHz band. The overall instrumental polarization of the system in the 100 GHz band is as low as < 3%. The performance of the polarimeter in astronomical observations was tested by simultaneously measuring the linear polarization of the J = 2–1 transition of SiO in the v = 0 and 1 states at 86 GHz toward VY Canis Majoris. The observation revealed that the J = 2–1 emission in the v — 0 state of the object is highly linear polarized, which suggests that the emission originates through maser action in the circumstellar region. The details of the design, construction, and tests are presented.
A Very Dense Low-Mass Molecular Condensation in Taurus: Evidence for the Moment of Protostellar Core Formation
Authors: Onishi Toshikazu , Mizuno Akira , Fukui Yasuo
Published: March 2014

We present evidence for a protostellar condensation that is very close to the moment of the formation of a protostellar core within a time scale of ∼ 104 yr. This starless condensation, named MC 27 in complete surveyed molecular condensations in Taurus, is ∼ 0.1 pc in size and ∼ 3M® in mass. It exhibits fairly strong and narrow H13CO+ emission of the J = 4–3, 3–2, and 1–0 transitions, as well as self-reversed profiles of HCO+ J = 4–3 and 3–2. MC 27 has a density of – 106 cm″3 within – 1000 AU at the center, which is the highest value among the ∼ 40 starless condensations in Taurus. MC 27 shows a sharply peaked density distribution; the molecular intensity is well fitted by a power-law density distribution of $\textrm r\sim\sim^2$ over 0.02 pc < r < 0.2 pc. A statistical analysis indicates a very short time scale of ∼ 104 yr, which is consistent with a free-fall time scale for a density of ∼ 106 cm−3. These properties strongly suggest that MC 27 is in a very early stage of star formation. A Monte Carlo simulation of the present profiles indicates that the infall velocity at 2000–3000 AU should be 0.2–0.3 km s″1 while it is less than 0.3 km s−1 at < 1000 AU. This derived infall velocity profile can be explained by a dynamical-collapse model of supercritical condensation prior to formation of the first protostellar core by ∼ 103−4 yr.
X-Ray Evidence of an AGN in M82
Authors: Matsumoto Hironori , Tsuru Takeshi Go
Published: March 2014

The X-ray spectrum of the famous starburst galaxy M82 consists of three components: soft, medium, and hard (Tsuru et al. 1997, AAA 68.157.702). The spectrum of the hard component, which is spatially unresolved, is well represented by an absorbed thermal bremsstrahlung, or an absorbed power-law model. However, the origin of the hard component is unclear. Thus, we conducted a monitoring observation with ASCA in 1996. Although the X-ray flux of the soft and medium components remained constant, a significant time variability of the hard component was found between 3×1040 erg s−1 and 1†1041 erg s−1 at various time scales from 10 ks to one month. The temperature or photon index of the hard component also changed. We proved that the spatial position of the hard component is the center of M82. The spectrum of the variable source obtained by subtracting the spectrum of the lowest state from the highest state suggests strong absorption of NH ∼ 1022 cm2, which means a variable source is embedded in the center of M82. All of these observations suggest that a low-luminosity AGN exists in M82.
Black-Hole X-Ray Transients: The Effect of Irradiation on Time-Dependent Accretion Disk Structure
Authors: Kim Soon-Wook , Wheeler J. Craig , Mineshige Shin
Published: March 2014

Some effects of irradiation on time-dependent accretion-disk models for black hole X-ray novae are presented. Two types of irradiation are considered: direct irradiation from the inner hot disk and indirect irradiation as might be reflected by a corona or chromosphere above the disk. The shadowing effect of the time-dependent evolution of the disk height and consequent blocking of the outer disk by the inner and middle portions of the disk from the direct irradiation is included. The direct irradiation of the disk by inner layers where the soft X-ray flux is generated is found to have only a small effect on the outer disk because of shadowing. Mild indirect irradiation that flattens, but otherwise does not affect the light curve substantially, still has interesting non-linear effects on the structure of the disk as heating and cooling waves propagate. The irradiated disks do not always make simple transitions between the hot and cold states, but can linger at intermediate temperatures or even return temporarily to the hot state, depending on the irradiation and the activity in adjacent portions of the disk.
Shocked Molecular Gas Associated with the Supernova Remnant W28
Authors: Arikawa Yuji , Tatematsu Ken'ichi , Sekimoto Yutaro , Takahashi Tadayuki
Published: March 2014

We report on mapping observations of the CO J = 3-2 and CO J = 1–0 lines toward supernova remnant (SNR) W28, which is supposed to be an EGRET 7-ray source. A broad CO line emission (maximum linewidth reaches 70 km s−1), which suggests an interaction between the molecular cloud and W28 SNR, was detected. Moreover, the distribution of the unshocked and shocked gas is clearly resolved. The distribution of the shocked gas is similar to that of the radio-continuum emission, and tends to be stronger along the radio-continuum ridge. The unshocked gas is displaced by 0.4–1.0 pc outward with respect to the shocked gas. The spatial relationship between shocked and unshocked gas has been clarified for the first time for the SNR-cloud interaction. All of the known OH maser spots are located along the filament of the shocked gas. These facts convincingly indicate that W28 SNR interacts with the molecular cloud.
Damping Efficiency of the Void Mode in a Two-Phase Gas Mixture with a Phase Transition
Authors: Kamaya Hideyuki
Published: March 2014

We have discussed the wave properties in a two-phase gas mixture, which is composed of a diffuse medium [phase I (PI)] and dense clouds [phase II (PII)]. Interestingly, there are two wave modes when PII has mobility relative to PI. One is the acoustic mode, and the other is the void mode (or pattern-propagating mode). In this paper, we present a more careful discussion concerning the restoring force of the void mode. After that, we estimate the damping rate of the void mode due to the thermal process, which acts as a friction effect. We call this thermal friction. For a typical interstellar medium (ISM), where the cold cloud phase is PII and the warm phase gas is PI, friction is not so significant within the galaxy evolution timescales. However, if the coronal phase is PI, PII of the warm clouds suffers thermal friction efficiently. Thus, when the evolution of ISM is described by the classical three-phase model, we can adopt a modified two-phase model within the context of multi-phase flow; in which PI corresponds to a mixture of the hot and warm phases and PII corresponds to the cold clouds.
Possible Young Stellar Objects without Detectable CO Emission
Authors: Iwata Ikuru , Okumura Shin-ichiro , Saitō Mamoru
Published: March 2014

Young stellar objects (YSOs) usually appear in molecular clouds as infrared objects associated with a molecular envelope. Wouterloot and Brand (1989, AAA 50.133.012) searched 1302 IRAS point sources with reliable fluxes at 25, 60, and 100 μm near to the galactic plane for 12CO (J = 1–0) emission; 1077 sources were detected. Among their far-infrared sources without detectable CO emission, we found that at least 18 objects are invisible at optical and near-infrared wavelengths. The infrared spectral indices between 2.2 μm and 25 μm correspond to those of class I YSOs, and the IRAS colors are similar to those of the usual YSOs. These peculiar far-infrared objects are highly concentrated around the galactic plane and the distances are estimated to be ∼1 kpc. Although their distribution is away from molecular clouds, some of them seem to be associated with large dark clouds or weak radio sources. These objects are possible YSOs with low CO abundance in the envelopes.
Dense Cores and Star-Formation Activities in the Chamaeleon Dark-Cloud Complex
Authors: Mizuno Akira , Hayakawa Takahiro , Tachihara Kengo , Onishi Toshikazu , Yonekura Yoshinori , Yamaguchi Nobuyuki , Kato Shigeo , Hara Atsushi , Mizuno Norikazu , Kawamura Akiko , Abe Rihei , Saito Hiro , Yamaguchi Reiko , Ogawa Hideo , Fukui Yasuo
Published: March 2014

We carried out a C18O (J = 1−0) survey for dense molecular cores in the Chamaeleon (Cha) I, II, and III dark clouds with the NANTEN millimeter-wave telescope. The present survey covered ∼ 93% of the area where the molecular column density is greater than ∼ 4 × 1021 cm-2, estimated from preceding 13CO(J = 1−0) observations. We identified 23 C18O cores, whose typical mass, radius, peak column density, line width are 22 M⊙ , 0.22 pc, 9.7 × 1021 cm-2, and 0.82 km s-1, respectively. The surface density of classical T Tauri stars abruptly increases for the area whose column density is greater than 1022 cm-2, suggesting that this value gives a certain threshold value for star formation. The star-formation efficiency varies over a wide range among the three clouds: 13%, 1%, and 0% in Cha I, II, and III, respectively. The C18O cores in Cha I are characterized by (1) a high column density, (2) being almost in virial equilibrium, and (3) a high Mcore/Mcloud ratio. The cores in Cha III show the opposite trend, and those in Cha II are in between. Such trends suggest that Cha I is a well-evolved or well gravitationally relaxed cloud-core system, which is probably related to the very high star-formation activity in the cloud.
ASCA Discovery of a Be X-Ray Pulsar in the SMC: AX J0051–733
Authors: Imanishi Kensuke , Yokogawa Jun , Tsujimoto Masahiro , Koyama Katsuji
Published: March 2014

ASCA observed the central region of the Small Magellanic Cloud, and found a hard X-ray source, AX J0051–733, at the position of the ROSAT source RX J0050.8–7316, which has an optical counterpart of a Be star. Coherent X-ray pulsations of 323.1 ± 0.3 s were discovered from AX J0051–733. The pulse profile shows several sub-peaks in the soft (0.7–2.0 keV) X-ray band, but becomes nearly sinusoidal in the harder (2.0–7.0 keV) X-ray band. The X-ray spectrum was found to be hard, and is well fitted by a power-law model with a photon index of 1.0 ± 0.4. The long-term flux history was examined with the archival data of Einstein observatory and ROSAT; a flux variability with a factor ≳10 was found.
Galactic Black-Hole Candidates Shining at the Eddington Luminosity
Authors: Watarai Ken-ya , Fukue Jun , Takeuchi Mitsuru , Mineshige Shin
Published: March 2014

We discuss distinctive features of luminous accretion disks shining at the Eddington luminosity in the context of galactic black-hole candidates (GBCs). We first note that the standard-disk picture is not applicable, although it is often postulated. Rather, the disk becomes advection-dominated while remaining optically thick (the so-called slim disk). The slim disk exhibits several noteworthy signatures: (1) The disk luminosity is insensitive to the mass-flow rates, Ṁ, and is always kept around the Eddington luminosity, LE, even if Ṁ greatly exceeds LE/c2. This reflects the fact that radiative cooling is no longer balanced by viscous heating and excess energy is carried by accreting matter to black holes. (2) The spectra of the slim disks are multi-color blackbody characterized by (i) a high maximum temperature, kTin ∼ a few keV, (ii) a small size of an emitting region, rin < 3 rg (with rg being Schwarzschild radius), due to substantial radiation coming out from inside 3 rg, and (iii) flatter spectra in the soft-X bands, vSv ∼ v0, because of a flatter effective temperature profile of the slim disk, Teff ∝ r−1/2 (in contrast with Teff ∝ r−3/4 in the standard disk). Thus, a small rin (≪ 3rg) does not necessarily mean the presence of a Kerr hole. Furthermore, (3) as Ṁ increases, Tin increases, while rin decreases as rin ∝ (Tin)−1 approximately. That is, the changes in rin derived from the fitting do not necessarily mean the changes in the physical boundary of the optically thick portions of the disk. Observational implications are discussed in relation to binary jet sources.
Infrared Imaging of z = 2.43 Radio Galaxy B3 0731+438 with the Subaru Telescope — Detection of Hα a Ionization Cones of a Powerful Radio Galaxy
Authors: Motohara Kentaro , Iwamuro Fumihide , Terada Hiroshi , Goto Miwa , Iwai Jun'ichi , Tanabe Hirohisa , Taguchi Tomoyuki , Hata Ryuji , Maihara Toshinori , Oya Shin , Iye Masanori , Kosugi George , Noumaru Jun'ichi , Ogasawara Ryusuke , Sasaki Toshinori , Takata Tadafumi
Published: March 2014

We report on infrared imaging observations of the z = 2.429 radio galaxy B3 0731+438 with the Subaru telescope. The images were taken with the K′-band filter and the 2.25 μm narrow-band filter to examine the structure and properties of the Hα+[NII] λλ 6548, 6583 emission-line components. The Hα+[NII] emission-line image shows biconical lobes with an extent of 40 kpc, which are aligned with the radio axis. The rest-frame equivalent widths of the emission lines at these cones are as large as 1100 Å, and can be well explained by a gas-cloud model photoionized by power-law continuum radiation. The isotropic ionizing photon luminosity necessary to ionize the hydrogen gas in these cones amounts to 1057 (photons s−1), which is larger than that in the majority of radio-loud QSOs. From these results, we propose that the Hα alignment effect in this object is produced by biconical gas clouds, which are swept up by the passage of radio jets, and are ionized by strong UV radiation from a hidden AGN. The continuum image consists of two components, a stellar-like point source and an extended diffuse galaxy. These are supposed to be a type-2 AGN and its host galaxy. The SED is fitted by a combination of spectra of a reddened dust-scattered AGN and an instantaneous starburst population of 500 Myr old. The stellar mass of the galaxy is estimated to be 3 × 1011M⊙, which is as large as that of typical 3C radio galaxies at z = 1.
A Pair of Twisted Jets of Ionized Iron from L 1551 IRS 5
Authors: Itoh Yoichi , Kaifu Norio , Hayashi Masahiko , Hayashi Saeko S. , Yamashita Takuya , Usuda Tomonori , Noumaru Jun'ichi , Maihara Toshinori , Iwamuro Fumihide , Motohara Kentaro , Taguchi Tomoyuki , Hata Ryuji
Published: March 2014

High-resolution near-infrared J-band imaging with the Subaru Telescope has demonstrated, for the first time from the ground, two independent jets emanating from the protostar L 1551 IRS 5. Successive near-infrared spectroscopy has revealed that the jet emission is dominated by [FeII] lines in the J- and H-bands. While the visual-extinction estimated from the [FeII] line ratios reaches more than 20 mag in the close vicinity of IRS 5, it decreases rapidly at ∼ 1″ from IRS 5 and remains constant around 7 mag at larger distances. The electron density in the jets is estimated to be 106 cm−3 near IRS 5 and is 104 to 105 cm−3 in their outer section. The twisted appearance of the jets, with bright knots especially prominent in the northern jet, is similar to the R-band jets observed with the Hubble Space Telescope. These results suggest that the twisted structure and bright emission knots are intrinsic to the jets and are not due to a spatial variation of the extinction.
Emergence of Twisted Magnetic-Flux Bundles and Flare Activity in a Large Active Region, NOAA 4201
Authors: Ishii Takako T. , Kurokawa Hiroki , Takeuchi Tsutomu T.
Published: March 2014

To reveal what is the key agent for strong flare activity, we studied the evolution of a large sunspot group, NOAA 4201, and its flare activity. We analyzed high-resolution Hα images obtained with the Domeless Solar Telescope at Hida Observatory, and Kitt Peak full disk magnetograms. We examined the sunspot proper motions and evolutionary changes of Hα fine structures and magnetic fields in this active region, and constructed a schematic model of emerging twisted magnetic-flux bundles. We also found that the occurrence of high flare activity was restricted to the rapidly emerging region of the twisted flux bundle. This fact suggests that the emergence of a twisted emerging flux bundle should be the key to high flare productivity of the sunspot group.
Evolution of the Blue Luminosity-to-Baryon Mass Ratio of Clusters of Galaxies
Authors: Shimasaku Kazuhiro
Published: March 2014

We derive the ratio of the total blue luminosity to the total baryon mass, LB/Mb, for massive (Mgas at the Abell radius is ≥ 1 × 1013 h−2.5 M⊙ ) clusters of galaxies up to z ≃ 1 from the literature. Twenty-two clusters in our sample are at z > 0.1. Assuming that the relative mix of hot gas and galaxies in clusters does not change during cluster evolution, we use LB/Mb to probe the star-formation history of the galaxy population as a whole in clusters. We find that LB/Mb of clusters increases with redshift from LB/Mb=0.024 (LB/M)⊙ at z = 0 to ≃ 0.06 (LB/M)⊙ at z = 1, indicating a factor of 2–3 brightening (we assume H0=70 km s−1 Mpc−1). This amount of brightening is almost identical to the brightening of the M/LB ratio of early-type galaxies in clusters at 0.02 ≤ z ≤ 0.83 reported by van Dokkum et al. (1998, AAA 70.160.065). We compare the observed brightening of LB/Mb with luminosity evolution models for the galaxy population as a whole, changing the e-folding time of star formation, τ , by 0.1 ≤ τ ≤ 5 Gyr and the formation redshift, zF, by 2 ≤ zF < ∞. We find that τ = 0.1 Gyr for ‘single burst’ models with zF ≥ 3 and τ = 5 Gyr for ‘disk’ models with arbitrary zF are consistent with the observed brightening, while models with τ = 1–2 Gyr tend to predict brightening that is too steep. We also derive the ratio of the blue luminosity density to the baryon density for field galaxies, adopting Ωb h2 = 0.02, and find that the blue luminosity per unit baryon is similar in clusters and in fields up to z ≃ 1 within the observational uncertainties.
Spiral Structures and Shocks in Accretion Discs in Close Binary Systems: the Role of the Stellar Mass Ratio.
Authors: Lanzafame Giuseppe , Maravigna Fabio , Belvedere Gaetano
Published: March 2014

In this work we investigated, in the Smooth Particle Hydrodynamics (SPH) framework, the development of spiral structures and shock fronts in the radial flow of accretion discs in close binary systems. These shock waves take place when the initially supersonic radial flow penetrating the disc bulk, reduces substantially its speed becoming suddenly subsonic. To this purpose, keeping constant the mass of the compact primary (M1 = 1 M⊙ ), the separation between the two components and the injection speed at the inner Lagrangian point L1 (close to the local sound speed), we carried out 2D SPH simulations for four values of the stellar mass ratio M2/M1. We worked out 2D models because the damping effect of the artificial viscosity is too strong in 3D. Furthermore, the 2D environment seems the most suitable in order to evidence shock fronts in highly compressible gases. The results show that spiral structures and shock fronts develop for low values of M2/M1, whilst they become less evident for higher values. This behaviour is interpreted in terms of initial specific angular momentum at L1, whose position, relative to the companions, depends on the stellar mass ratio.
Formation of Intermediate-Mass Black Holes in Circumnuclear Regions of Galaxies
Authors: Taniguchi Yoshiaki , Shioya Yasuhiro , Tsuru Takeshi G. , Ikeuchi Satoru
Published: March 2014

Recent high-resolution X-ray imaging studies have discovered possible candidates of intermediate-mass black holes with masses of M⋅ ∼ 102–4M⊙ in circumnuclear regions of many (disk) galaxies. It is known that a large number of massive stars are formed in a circumnuclear giant H II region. Therefore, we propose that a continual merger of compact remnants left from these massive stars is responsible for the formation of such an intermediate-mass black hole within a timescale of ∼ 109 yr. A necessary condition is that several hundreds of massive stars are formed in a compact region with a radius of a few parsecs.
Superwind-Driven Intense H2 Emission in NGC 6240
Authors: Ohyama Youichi , Yoshida Michitoshi , Takata Tadafumi , Imanishi Masatoshi , Usuda Tomonori , Saito Yoshihiko , Taguchi Hiroko , Ebizuka Noboru , Iwamuro Fumihide , Motohara Kentaro , Taguchi Tomoyuki , Hata Ryuji , Maihara Toshinori , Iye Masanori , Sasaki Toshiyuki , Kosugi George , Ogasawara Ryusuke , Noumaru Junichi , Mizumoto Yoshihiko , Yagi Masafumi , Chikada Yoshihiro
Published: March 2014

We have performed a long-slit K-band spectroscopic observation of the luminous infrared galaxy NGC 6240. Spatially extended H2 emission is detected over 3.3 kpc around the two nuclei. The peak position of the H2v = 1–0 S(1) emission is located at ∼ 0″.3–0″.4 north of the southern nucleus. Based on line-ratio analyses, we suggest that the excitation mechanism of H2 is pure thermal at most positions. We find the following three velocity components in the H2 emission around the southern nucleus and its south region: a blue-shifted component (≈ –250 km s−1 with respect to Vsys), which is recognized as a distinct C-shape distortion in the velocity field around the southern nucleus; a high-velocity blue-shifted “wing” component (∼ –1000 km s-1 with respect to Vsys); and a component indicating possible line splitting of ∼ 500 km s−1. We show that these kinematic properties can be reproduced by expanding motion of a shell-like structure around the southern nucleus. The offset peak position of the H2 emission can be understood if we assume that the shell expanding to the north interacts with the extragalactic molecular gas which has been transferred during the merging of the two nuclei. At the interface the cloud-crushing mechanism may work efficiently, and shock-excited intense H2 emission is thus expected there. With this mechanism, the H2 luminosity can be explained without global shock driven by the collision of two nuclei. All of these findings lead us to propose a model in which most of the H2 emission is attributed to shock excitation driven by the superwind activity of the southern nucleus.
Dust Growth Timescale and Mass Function of Molecular Clouds in the Galaxy
Authors: Hirashita Hiroyuki
Published: March 2014

We examine the characteristic growth time of dust grains in the Galaxy, where the grain growth in molecular clouds is the dominant factor for dust-mass increase. Since the timescale of grain growth depends on the gas density of molecular clouds, we reconsider the typical molecular-cloud density by using the “density function” of clouds [denoted as N(n) dn]. Here, the density function expresses the probability that a cloud has a volume-averaged gas density between n and n+dn, and it can be calculated by combining the observed mass function and the scaling law of molecular clouds. Through the formulation that combines N(n) with the characteristic dust growth timescale, we find that the typical dust growth timescale is in the range of 107–108 yr. This range is equivalent to the timescale of the dust growth in molecular clouds whose molecular number density is 3 × 102−3 × 103 cm−3. Thus, the dense molecular clouds (n > 104 cm−3) contribute little to dust growth. The timescale supports the value constrained in our previous model and provides an upper limit for the lifetimes of molecular clouds.
TV Observation of the Leonid Meteor Shower in 1999: Secondary Peak over Japan
Authors: Watanabe Jun-ichi , Takahashi Yoko , Sasaki Akiyuki , Abe Shinsuke , Kinoshita Daisuke , Shiki Shigetomo
Published: March 2014

We carried out a wide-field TV observation of the Leonid meteor shower at the Nobeyama Radio Observatory, from 12h30m UT through 20h15m UT on 1999 November 18. We detected 428 Leonid meteors, along with 55 sporadic meteors. A gentle peak of the activity was recognized at around 17h UT, when the peak influx rate of meteoroids was 1.1 × 10−6 km−2 s−1(mag < +5). This secondary peak was at least by one order smaller than the main peak of the Leonid storm observed at 02h UT over Europe.
ASCA Observation of the Lyman-Limit Quasar PKS 2145+067
Authors: Yamasaki Noriko Y. , Ishikawa Teru , Ohashi Takaya
Published: March 2014

An X-ray observation of a famous Lyman-limit quasar PKS 2145+067 at zem= 0.990 was carried out with ASCA. The source showed a 2–10 keV flux of 1.3 × 10−11 erg cm−2 s−1 (LX = 2.5 ' 1046 erg s−1 for H0= 50 km s−1 Mpc−1) described by a power-law spectrum with a photon index of the Γ = 1.63 ± 0.04. In the ASCA energy band, no excess absorption was detected, implying that absorption column density at zab = 0.791 was less than 1.6 ' 1021 cm−2 if the absorbing medium had a metal abundance of 0.5 solar. A comparison with previous Einstein Observatory and ROSAT observations shows that PKS 2145+067 has increased in luminosity by a factor of 2–3 between 1991 and 1998.
Distribution and Kinematics of Molecular Gas in Barred Spiral Galaxies. II. NGC 253
Authors: Sorai Kazuo , Nakai Naomasa , Kuno Nario , Nishiyama Kohta , Hasegawa Tetsuo
Published: March 2014

The large scale mapping of the disk of a nearby barred galaxy, NGC 253 in CO (J = 1–0), was made with an angular resolution of 16″. Molecular gas concentrates in the nuclear region and the large-scale bar seen in near-infrared images. The radial distribution of molecular gas indicates a secondary peak, whose radius agrees with that of the Hα ring and the ends of the bar, as well as a central strong peak. The radial distribution is well fitted by an exponential function or a power law outside the secondary peak. A rotation curve is rising in the inner region and changes to flat at the ring. These facts suggest that molecular gas infalls from the outer disk by losing angular momentum due to gaseous viscosity in the region of the differential rotation, and accumulates at the ring. In the bar region (and within the corotation radius), molecular gas again loses its angular momentum due to the bar potential, and is infalling toward the nuclear region. The upper limit of the noncircular motion along the major axis of the bar in the leading edge of the bar is ≈ 70–130 km s−1 in the rest frame of the bar.
Basic Properties of Supercritical Accretion Disks
Authors: Fukue Jun
Published: March 2014

At the turn of the millennium, supercritical accretion disks (superdisks), where the mass-accretion rate highly exceeds the Eddington's one, are being resurrected under recent observational and theoretical progress. We examined the effects and properties of the self-irradiation, self-occultation, continuous and line spectra of superdisks, and found various distinct features of superdisks. Due to self-irradiation, the effective flux is enhanced by a factor of 1.1 to 1.8 all over the disk, depending on the relative disk thickness. For a superdisk with finite thickness, the flux at infinity is enhanced in the poleward direction, while it is zero in the equatorial direction. The continuous spectra are generally flat (vSv ∼ v0), as long as we see the disk pole-on. It, however, strongly depends on the inclination angle: for a larger inclination angle the central part of the disk is self-occulted and the flat nature of the continuum disappears. The line spectra are also greatly modified from those of the standard disk. In the non-relativistic standard model the line spectra have symmetrical double peaks. In the superdisk, however, the line spectra become asymmetric with strong blue peaks and weak red peaks, even for the non-relativistic case. This is due to the projection effect. The relations between the observables and model parameters are derived.
Some Features of Manifestations of Coronal Holes in Microwave Emission
Authors: Krissinel Boris B. , Kuznetsova Svetlana M. , Maksimov Vladimir P. , Prosovetsky Dmitry V. , Grechnev Victor V. , Stepanov Alexandr P. , Shishko Ludmila F.
Published: March 2014

Using observational data from the SSRT, we have investigated the behavior of four mid- and low-latitude coronal holes. The coronal holes under study appeared as regions of decreased emission intensity relative to the quiet Sun level totally or partially coincident with holes in EUV emission. Difference in the electron density and temperature in different holes or different parts of a hole can account for the diversity of manifestations of coronal holes. Estimates showed that the influence of these parameters is strongest in the wavelength range of 2–5 cm. Depending on particular values of the coronal electron density and temperature, coronal holes are either indistinguishable from the background of the quiet Sun, or show up as regions of decreased or increased microwave emission.
Solar Radio Radiation Bursts on 1998 April 15
Authors: Ning Zongjun , Fu Qijun , Lu Quankang
Published: March 2014

We present two remarkable “decimetric pulsation” events (DCIM) around the time 1998 0415 0800, detected by spectrometers (1.00–2.00 GHz and 2.60–3.80 GHz) at Beijing Astronomical Observatory (BAO). High-resolution dynamic spectra reveal various fine structures, such as spike groups, pulsations, type-III bursts, patches, and zebra patterns or evolving emission lines on the rising phase of the second DCIM around 3 GHz. It is the first time that such a wealth of fine features have been detected in a same type IV-DCIM event; it is also the first time that blips pairs simultaneously drifting towards the same frequency have been recorded; it is the second time to observe an evolving emission line, and the first above 1 GHz.
Moderate Dispersion Spectra of NH2 in Comet Hale-Bopp: Analysis of Population Distribution in $\widetilde X^{2} \textrm B_{1}(0,0,0)$
State of NH
2
Authors: Kawakita Hideyo , Ayani Kazuya , Kawabata Tetsuya
Published: March 2014

We carried out moderate-dispersion spectroscopic observations of comet Hale-Bopp (C/1995O1) on 1997 February 25, in order to study the fine structure of two NH 2 emission bands, $\widetilde A(0,9,0)-\widetilde X(0,0,0)$ and $\widetilde A(0,8,0)-\widetilde X(0,0,0)$ , which was resolved in our spectra. We compared the observed fine structure with that of the modeled spectra, which were computed based on the transition probabilities of NH 2 between the $\widetilde A(0,v^{\prime}_{2},0)$ and $\widetilde X(0,0,0)$ states determined by ourselves. From a comparison between the observation and the calculations we concluded that the population distribution of the NH 2 in the $\widetilde X(0,0,0)$ ground state can be approximated by the Boltzmann distribution at a temperature of 60 K.
Detections of SiO and H2O Masers in the Bipolar Nebula IRAS 19312+1950
Authors: Nakashima Jun-ichi , Deguchi Shuji
Published: March 2014

We report on the detection of SiO and H2O masers toward a newly found bipolar nebula, IRAS 19312+1950. This object exhibits extreme red IRAS color [log (F25/F12) = 0.5 and log (F60/F25) = 0.7] and a nebulosity having a size of about 30″ extended to the south-west in the 2MASS near-infrared image. Toward this object, we have detected emission from the H2O 6(1,6)–5(2,3) transition, the SiO J = 1–0, v = 1 and 2, and J = 2–1, v = 1 transitions, and the SO 2(2)–1(1) and H13CN J = 1–0 transitions. The thermal lines of SO and H13CN are shifted by about 12 km s−1 in radial velocity with respect to the maser lines, indicating that thermal emission comes from the background molecular cloud. However, the SiO J = 2−1, v = 2 spectrum shows another component of SiO emission separated by 26 km s−1 from the main component, that might be formed in a rotating or expanding shell.
Broad-Band Spectra Study of 213 VSOP 5-GHz Survey Sources
Authors: Kovalev Yuri A. , Kovalev Yuri Y. , Nizhelsky Nikolai A.
Published: March 2014

We present a statistical and model study of 1−22 GHz spectra and 5-GHz interpolated data for 213 of 230 sources with declinations δ > −30°, selected for survey observations with the HALCA space radio telescope. The spectra of two subsamples were specially surveyed and monitored in 1997-2000 as a ground spectra support for the space VLBI survey in the framework of the VSOP Survey Programme. Every 1–22 GHz spectrum was measured with the RATAN-600 radio telescope at six wavelengths of 1.4, 2.7, 3.9, 7.7, 13, and 31 cm over a period of a few minutes (ten minutes or more near the pole). (25–30)% of the sources studied are outside of the VSOP selection criteria in 1997-2000 because of the variability of the VSOP sources, which were compiled from catalogs spanning a period between 1985 and 1996. About 60% of 186 VSOP/HALCA sources, monitored in 8 epochs, have amplitudes of variability greater than ± 10% at 5 GHz over the three-year period. 45 new strong of 660 additionally surveyed sources have been found and can be added to the HALCA sample. 26 of 45 sources are new for the full VSOP list. Almost all VSOP sources are suggested to have continuous jets at milliarcsecond scales. This conclusion is supported by an analysis of the individual spectra for 213 objects, their mean statistical shape in the local frame, and the long-term variable spectra for 25 objects. Model and statistical analyses suggest a common physical origin of the radio sources of various types in the studied samples and in the majority of VSOP survey sources.
Penetration of Magneto-Rotationally Unstable Perturbations in SSD into ADAF through a Transition Surface
Authors: Kato Shoji
Published: March 2014

A linear deformation, by a magneto-rotational instability, of the transition suface between an outer Shakura-Sunyaev-type standard disk (SSD) and inner advection-dominated accretion flows (ADAF) is examined. The transition is assumed to be a discontinuous plane where a low-temperature, high-density gas is jointed to a high-temperature, low-density gas. No mass flow through the surface is considered. Magnetic fields directed in the vertical direction are assumed. We examine how the linear perturbations generated by the magneto-rotational instability in the outer region penetrate into the inner region. The perturbation penetrates into the inner region with an exponentially decreasing amplitude. We suppose that the perturbations of MHD turbulence invading into the inner ADAF region from the outer SSD region would be seed fluctuations of the strong time variabilities observed in the high state of X-ray black-hole candidates.
Discovery of a Slow X-Ray Pulsator, AX J1740.1-2847, in the Galactic Center Region
Authors: Sakano Masaaki , Torii Ken'ichi , Koyama Katsuji , Maeda Yoshitomo , Yamauchi Shigeo
Published: March 2014

We report the discovery of an X-ray pulsar, AX J1740.1–2847, from the Galactic center region. This source was found as a faint hard X-ray object on 1998 September 7–8 with the ASCA Galactic center survey observation. Then, coherent pulsations of P = 729± 14 s period were detected. The X-ray spectrum is described by a flat power-law of ∼ 0.7 photon index. The large absorption column of log NH ∼ 22.4 cm−2 indicates that AX J1740.1–2847 is a distant source, larger than 2.4 kpc, and possibly near to the Galactic center region. The luminosity in the 2–10 keV band is larger than 2.5×1033 erg s−1, or likely to be 3.2×1034 erg s−1 at the Galactic-center distance. Although the slow-pulse period does not discriminate whether AX J1740.1–2847 is a white dwarf or neutron-star binary, the flat power-law and moderate luminosity strongly favor a neutron-star binary.
Discovery of Non-Thermal X-Rays from the Shell of RCW 86
Authors: Bamba Aya , Koyama Katsuji , Tomida Hiroshi
Published: March 2014

We report the ASCA (Advanced Satellite for Cosmology and Astrophysics) results of RCW 86, a shell-like supernova remnant (SNR). The bright region in the X-ray band traces the radio clumpy shell, although details of the structure are different. The X-ray spectrum from each part of the shell can not be fitted to a thin thermal plasma model, but requires at least three components: a low-temperature plasma of 0.3 keV, a high-temperature plasma of ≥ several keV, and a power-law component with a photon index of ∼ 3. The abundances of O, Ne, Mg, and Si are significantly higher than that of Fe, indicating that RCW 86 is a type II SNR. The absorption column of ∼ 3×1021 H cm-2 indicates the distance to the SNR to be several kpc. The power-law component can be interpreted to be synchrotron radiation of high-energy electrons. Assuming an energy density equipartition between the magnetic field and the electrons, and using the radio and X-ray spectra, we argue that high-energy electrons are accelerated up to 20 TeV. The acceleration efficiency is, however, different from shell to shell.
The VLBI Space Observatory Programme and the Radio-Astronomical Satellite HALCA
Authors: Hirabayashi Hisashi , Hirosawa Haruto , Kobayashi Hideyuki , Murata Yasuhiro , Asaki Yoshiharu , Avruch Ian M. , Edwards Philip G. , Fomalont Edward B. , Ichikawa Tsutomu , Kii Tsuneo , Okayasu Rikako , Wajima Kiyoaki , Inoue Makoto , Kawaguchi Noriyuki , Chikada Yoshihiro , Bushimata Takeshi , Fujisawa Kenta , Horiuchi Shinji , Kameno Seiji , Miyaji Takeshi , Shibata Kazunori M. , Shen Zhi-Qiang , Umemoto Tomofumi , Kasuga Takashi , Nakajima Jun'ichi , Takahashi Yukio , Enome Shinzou , Morimoto Masaki , Ellis Jordan , Meier David L. , Murphy David W. , Preston Robert A. , Smith Joel G. , Wietfeldt Rick D. , Benson John M. , Claussen Mark J. , Flatters Chris , Moellenbrock George A. , Romney Jonathan D. , Ulvestad James S. , Langston Glen I. , Minter Anthony H. , D'Addario Larry R. , Dewdney Peter E. , Dougherty Sean M. , Jauncey David L. , Lovell James E. J. , Tingay Steven J. , Tzioumis Anastasios K. , Taylor A. Russell , Cannon Wayne H. , Gurvits Leonid I. , Schilizzi Richard T. , Booth Roy S. , Popov Misha V.
Published: March 2014

The radio astronomy satellite HALCA was launched by the Institute of Space and Astronautical Science in 1997 February to participate in Very Long Baseline Interferometry (VLBI) observations with arrays of ground radio telescopes. HALCA is the main element of the VLBI Space Observatory Programme (VSOP), a complex international endeavor involving over 25 ground radio telescopes, five tracking stations and three correlators. Simultaneous observations with HALCA's 8 meter diameter radio telescope and ground radio telescopes synthesize a radio telescope over twice the size of the Earth, enabling the highest resolution 1.6 GHz and 5 GHz images to be made.
HALCA's Onboard VLBI Observing System
Authors: Kobayashi Hideyuki , Wajima Kiyoaki , Hirabayashi Hisashi , Murata Yasuhiro , Kawaguchi Noriyuki , Kameno Seiji , Shibata Katsunori M. , Fujisawa Kenta , Inoue Makoto , Hirosawa Haruto
Published: March 2014

The first space VLBI satellite, HALCA, was launched on 1997 February 12. We report the characteristics of HALCA as an orbiting VLBI station with 8-m deployment antenna. It is required the high system gain, low system noise, and high stability of phase transfer. And the stabilities of system gain and system noise are needed for imaging of VLBI. HALCA achieved the requirement as a VLBI stations and has made almost 3 times longer baselines than ground global VLBI networks. It means observations with 3 times higher angular resolution have been carried out. We have measured aperture efficiencies of the deployment antenna, system noise temperatures, stability of onboard local oscillators, and stability of phase link. HALCA's onboard radio astronomy system has 1.60–1.73 GHz, 4.7–5.0 GHz, and 21.9–22.3 GHz receivers and two-channel high-rate samplers. Typical values of system noise temperature in orbit are 70 K and 90 K at 1.6 and 5 GHz respectively. At 22 GHz, the apparent system noise temperature is 400 K; however, this is mostly due to attenuation between the main antenna and the 22 GHz low noise amplifier. A reference tone signal is transmitted from a ground tracking station which is locked on a ground hydrogen maser oscillator. The internal phase stability of local oscillators is around 5° r.m.s. at 5 GHz. The total gain of the receiving system and the bit distribution of the high-rate samplers have also been checked. With the exception of the 22 GHz attenuation, the in-orbit performance of the VLBI observing system matches the ground-test results very well.
Viscous Transonic Decretion in Disks of Be Stars
Authors: Okazaki Atsuo T.
Published: March 2014

We consider the characteristics of the outflow in disks of Be stars, based on the viscous decretion disk scenario. In this scenario, the matter ejected from the equatorial surface of a star drifts outward because of the effect of viscosity, and forms the disk. For simplicity, we adopt the $ \alpha$-prescription for the viscous stress, and assume the disk to be isothermal. Solving the resulting wind equations, we find that a transonic solution exists for any value of $ \alpha$. The sonic point is located at $r \gt 100\;R$$ r \gt 100\;R$ for the plausible values of parameters, where $ R$ is the stellar radius. The sonic radius is smaller for a higher temperature and/or a larger radiative force. We also find that the topology of the sonic point is nodal for $ \alpha \gtrsim 0.95$, while it is of the saddle type for $ \alpha \lesssim 0.9$. We expect that the sonic point in the former case is unstable, whereas that in the latter case is stable. The outflow is highly subsonic in the inner part of the disk. Roughly, the outflow velocity increases linearly with $ r$ and the surface density decreases as $ r^{-2}$. Interestingly, the disk is near-Keplerian in the inner subsonic region, while it is angular-momentum conserving in the outer subsonic region and in the supersonic region. Our results, together with the observed range of the base density for Be star disks, suggest that the mass-loss rate in the equatorial region is at most comparable with that in the polar region.
Amplification of Magnetic Fields in an Accretion Disk with a Starburst Torus
Authors: Kamaya Hideyuki
Published: March 2014

It is widely believed that a black hole is surrounded by an accretion disk. Such an accretion disk should have magnetic fields whose evolution is important to understand the disk dynamics, since the viscosity in the disk must originate from magnetic turbulence. In the case of the accretion disk of AGN (active galactic nuclei) with a circum-disk star-burst region, we point out that the so-called $ \alpha $-dynamo effect via radiation drag due to an exterior radiation field around the disk works well. This is possible since the drag time-scale is longer than the dynamical time-scale. Importantly, we find that the starburst AGN satisfies this criterion. Thus, the magnetic field of the accretion disk of the starburst AGN is amplified by the dynamo effect owing to the radiation drag. This results in enhancing the mass-accretion rate to the massive black-hole of AGN within the star-burst region.
Intracluster Supernova as a Possible Extra Energy Source of Clusters
Authors: Sasaki Shin
Published: March 2014

The observed luminosity–temperature relation of clusters is considerably steeper than that expected from a simple scaling relation. Although extra energy input is a likely solution, its source has not been identified. We propose intracluster supernova as a possible source, and also predict the supernova rate in intracluster space as a critical test.