bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Equilibrium Ionization State and Two-Temperature Structure in the Bullet Cluster 1E 0657−56
Authors: Akahori Takuya , Yoshikawa Kohji
Published: March 2014

We investigate a non-equilibrium ionization state and an electron–ion two-temperature structure of the intracluster medium in the merging galaxy cluster, 1E 0657$-$56 (Bullet cluster), using a series of $N$-body and hydrodynamic simulations. We find that the electron temperature at the shock layer associated with the X-ray sub-peak (bullet) is quite different depending on the thermal relaxation model between electrons and ions; $\sim $25 keV for the Coulomb thermal relaxation model and $\sim $45 keV for the instantaneous thermal relaxation model in the simulations which reproduce the observed X-ray morphology. Furthermore, both of Fe XXV and Fe XXVI are overabundant compared with the ionization equilibrium state around the shock layer, and thus, the intensity ratio between Fe XXV and Fe XXVI K$\alpha$ lines are significantly altered from that in the ionization equilibrium state. We also carry out the simulations with various sets of merger parameters, and discuss a possible range of the non-equilibrium effects in this system. Our results could be tested with future X-ray observations such as Astro-H with better sensitivity in high energy band.
Destructible Bars in Disk Galaxies under the Dynamical Influence of a Massive Central Black Hole
Authors: Hozumi Shunsuke
Published: March 2014

The characteristics of the galactic bars that are prone to suffer a damaging impact from a massive central black hole are examined using flat stellar disks. We construct three disk model groups that consist of exponential disks with one type of velocity distribution and Kuzmin–Toomre disks with two different types of exact equilibrium distribution functions. For each disk model group, three disks that have different typical Toomre’s $Q$ values are evolved to form bars through dynamical instability. Once a bar is fully developed, a black hole (BH), whose mass is 1% of the disk mass, is adiabatically added at the center of the disk. Our results show that lower-amplitude bars, that is weaker bars, are dissolved more easily by that BH. We have found that this destructibility is rooted in the characteristic feature that the bar formed spontaneously becomes shorter in length and rounder in shape with decreasing bar amplitude. Since such weaker bars are found to originate from colder disks in each disk model group, it follows that for a given form of velocity structure, the coldness of an initial disk determines whether the bar produced in that disk is favorable to dissolution induced by a massive central BH. In addition, the existence of bar-dissolved galaxies of the kind studied here is also discussed.
VLBI Astrometry of the Semiregular Variable RX Bootis
Authors: kamezaki Tatsuya , nakagawa Akiharu , omodaka Toshihiro , kurayama Tomoharu , imai Hiroshi , tafoya Daniel , matsui Makoto , nishida Yoshiro , nagayama Takumi , honma Mareki , kobayashi Hideyuki , miyaji Takeshi , takeuti Mine
Published: March 2014

We present distance measurements of the semiregular variable RX Bootis (RX Boo) with its annual parallax. Using the unique dual-beam system of the VLBI Exploration of Radio Astrometry (VERA) telescope, we conducted astrometric observations of a water maser spot accompanying RX Boo, referred to the quasar J1419$+$2706 separated by 1$^\circ\!\!\!.$69 from RX Boo. We measured the annual parallax of RX Boo to be 7.31$\ \pm\ $0.50 mas, corresponding to a distance of 136$^{+10}_{-9}\ $pc, from one-year monitoring observation data of one maser spot at $V_{{\rm LSR}}$$=$ 3.2 km s$^{-1}$. The distance, itself, is consistent with that obtained with Hipparcos. The distance uncertainty was reduced by a factor of two, allowing us to determine the stellar properties more accurately. Using our distance, we discuss the location of RX Boo in various sequences of Period–Luminosity (PL) relation. We found that RX Boo is located in the Mira sequence of the PL relation. In addition, we calculated the radius of the photosphere and the mass limitation of RX Boo, and evaluated its evolutionary status.
Evolution of Supernova Remnants Expanding out of the Dense Circumstellar Matter into the Rarefied Interstellar Medium
Authors: Shimizu Takafumi , Masai Kuniaki , Koyama Katsuji
Published: March 2014

We carried out 3D-hydrodynamical calculations for the interaction of expanding supernova ejecta with the dense circumstellar matter (CSM) and the rarefied interstellar medium (ISM) outside. The CSM is composed of stellar-wind matter from the progenitor in its pre-supernova phase, and assumed to be axially symmetric: more matter around the equator than in the polar direction driven by rotation of the progenitor. Because of the high density of the CSM, the ionization state of the shock-heated ejecta quickly becomes equilibrium with the electron temperature. When the blast wave breaks out of the CSM into the rarefied ISM, the shocked ejecta cools rapidly due to adiabatic expansion, and hence an over-ionized/recombining plasma would be left. The ejecta is reheated by the second reverse shock due to the interaction with the ISM. We calculated the emission measure of the supernova remnant (SNR) along the line of sight, and found that the over-ionized plasma appears to be bar-like with wings in the edge-on (equatorial view), while shell-like in the face-on (polar view) geometry with respect to the rotation axis. Hot gas heated by the blast wave exists in the outermost region of the SNR with a nearly complete shell, but the X-rays therefrom are too faint to be observable. Thus, depending on the viewing angle, the SNR of the over-ionized plasma would exhibit a center-filled morphology in X-rays, like W 49 B, a mixed-morphology SNR. The bar-like structure is swept out by the second reverse shock and disappears eventually, and then the SNR becomes shell-like in both the equatorial and polar views in the later phase of evolution.
Maser Emission toward the Infrared Dark Cloud G359.94+0.17 Seen in Silhouette against the Galactic Center
Authors: Deguchi Shuji , Tafoya Daniel , Shino Nagisa
Published: March 2014

The infrared dark cloud G359.94$+$0.17 is a conspicuous, opaque cloud, which is seen in silhouette against the Galactic center. We found unexpectedly strong ($\sim\ $50 Jy) maser emission of CH$_3$OH at 44 GHz with additional weak 22 GHz H$_2$O maser and 43 GHz SiO thermal emissions toward this cloud. Detections of these molecular lines indicate that strong star-forming activities are proceeding in this cloud, which was not reported previously despite of numerous studies toward the Galactic center. The line profiles of the NH$_3$ inversion lines at 23 GHz indicate that G359.94$+$0.17 is composed of mainly two clouds with $V_{\rm lsr}$$=$ 0, and 15 km s$^{-1}$ overlapped on the line of sight. The maser emission is associated with the 15 km s$^{-1}$ cloud, suggesting that it is located at the Norma spiral arm.
A Method of Identifying AGNs Based on Emission-Line Excess and the Nature of Low-Luminosity AGNs in the Sloan Digital Sky Survey. I. A New Method
Authors: Tanaka Masayuki
Published: March 2014

We developed a new technique for identifying active galactic nuclei (AGNs) and studied the nature of low-luminosity AGNs in the Sloan Digital Sky Survey. This is the former part of a series of papers. We develop a new, sensitive method of identifying AGNs in this paper. The emission-line luminosity in a spectrum is the sum of a star-formation component and an AGN component (if present). We demonstrate that an accurate estimate of the star-formation component can be achieved by fitting model spectra, generated with a recent stellar population synthesis code, to a continuum spectrum. By comparing the observed total line luminosity with that attributed to star formation, we can tell whether a galaxy hosts an AGN or not. We compare our method with the commonly used emission-line diagnostics proposed by Baldwin, Phillips, and Terlevich (1981, PASP, 93, 5; hereafter BPT). By this method, we classify 85% of the strong emission-line objects in the same star-formation/AGN as BPT. One unique feature of our method is its sensitivity; it is applicable to nearly twice as many objects as BPT. We further make a comparison between our method and the BPT diagnostics using stacked spectra and selections in X-ray and radio wavelengths. We show that it is overall a sensitive method of identifying AGNs, while our method suffers from incompleteness and contamination as any AGN identification method does so. We emphasize that our method can be applied at high redshifts (up to ${z}$$\sim$ 1.7 with red-sensitive optical spectrograph) without making any a priori assumptions about the host-galaxy properties. Another unique feature is that it allows us to subtract the emission-line luminosity due to star formation, and to extract the intrinsic AGN luminosity.
Behavior of [S/Fe] in Very Metal-Poor Stars from the S I 1.046 μm Lines Revisited
Authors: Takeda Yoichi , Takada-Hidai Masahide
Published: March 2014

With an aim to establish how the [S$ /$Fe] ratios behave in the very low metallicity regime down to [Fe$ /$ H] $ \sim$  $-$ 3, we conducted a non-LTE analysis of near-IR S I triplet lines (multiplet 3) at 10455–10459 Å for a dozen very metal-poor stars ($-$ 3.2 $ \lesssim$ [Fe$ /$ H] $ \lesssim$  $-$ 1.9) based on new observational data obtained with IRCS$ +$ AO188 of the Subaru Telescope. It turned out that the resulting [S$ /$ Fe] values are only moderately supersolar at [S$ /$ Fe] $ \sim$  $ +$ 0.2–0.5, irrespective of the metallicity. While this ``flat'' tendency is consistent with a trend recently corroborated by Spite et al. (2011, A&A, 528, A9) based on the S I 9212/9228/9237 lines (multiplet 1), it disaffirms the possibility of a conspicuously large [S$ /$ Fe] (up to $ \sim$  $ +$ 0.8) at [Fe$ /$ H] $ \sim$  $-$ 3 that we once suggested in our first report on the S abundances of disk/halo stars using S I 10455–10459 lines (Takeda & Takada-Hidai 2011, PASJ, 63, S537). Given these new observational facts, we withdraw our previous argument, since we consider that [S$ /$ Fe]'s of some most metal-poor objects were overestimated in that paper; the likely cause for this failure is also discussed.
A Dynamic Era-Based Time-Symmetric Block Time-Step Algorithm with Parallel Implementations
Authors: Kaplan Murat , Saygin Hasan
Published: March 2014

The time-symmetric block time-step (TSBTS) algorithm is a newly developed efficient scheme for $N$-body integrations. It is constructed on an era-based iteration. In this work, we re-designed the TSBTS integration scheme with a dynamically changing era size. A number of numerical tests were performed to show the importance of choosing the size of the era, especially for long-time integrations. Our second aim was to show that the TSBTS scheme is as suitable as previously known schemes for developing parallel $N$-body codes. In this work, we relied on a parallel scheme using the copy algorithm for the time-symmetric scheme. We implemented a hybrid of data and task parallelization for force calculation to handle load balancing problems that can appear in practice. Using the Plummer model initial conditions for different numbers of particles, we obtained the expected efficiency and speedup for a small number of particles. Although parallelization of the direct $N$-body codes is negatively affected by the communication/calculation ratios, we obtained good load-balanced results. Moreover, we were able to conserve the advantages of the algorithm (e.g., energy conservation for long-term simulations).
Wide-Band Optical Filter Optimized for Deep Imaging of Small Solar-System Bodies
Authors: Okumura Shin-ichiro , Nishiyama Kota , Urakawa Seitaro , Sakamoto Tsuyoshi , Takahashi Noritsugu , Yoshikawa Makoto
Published: March 2014

This paper describes a newly designed wide-band optical filter. It is optimized for deep imaging of small solar-system bodies. The new filter, which we denote as $Wi$, is designed to reduce contamination by light pollution from street lamps, especially strong mercury and sodium emission lines. It is also useful for reducing unwanted scattered moonlight. Compared with the use of a commercially available long-wave cut wide-band filter, the signal-to-noise ratios in the detection of asteroids are improved by about 6% by using the $Wi$ filter.
Properties of Molecular Gas in the Bar of Maffei 2
Authors: Sorai Kazuo , Kuno Nario , Nishiyama Kohta , Watanabe Yoshimasa , Matsui Hidenori , Habe Asao , Hirota Akihiko , Ishihara Yuko , Nakai Naomasa
Published: March 2014

We investigated the physical properties of molecular gas in one of the nearest barred spiral galaxies, Maffei 2, using the C12O ($J$$=$ 1–0) emission line taken for the Nobeyama CO Atlas of Nearby Spiral Galaxies. Position–velocity diagrams perpendicular to the apparent major axis of the bar show an abrupt velocity change across the bar, which is caused by molecular gas motion of $\sim\ $100 km s$^{-1}$ along the leading edges of the bar. The distribution of the peak temperature ($T_{\rm peak}$), velocity width ($\Delta V$), and integrated intensity of the C12O spectra ($I_{\rm CO}$) in the ridges of the bar is quite different from that in the spiral arms in $T_{\rm peak}$–$\Delta V$–$I_{\rm CO}$ space, suggesting that molecular-gas properties are different in these regions. Simple model calculations assuming an ensemble of uniform and spherical molecular clouds in a large velocity-gradient approximation indicate that molecular gas in the bar ridge regions may be gravitationally unbound, which suggests that molecular gas is hard to become dense, and to form stars. Moreover, the gravitationally unbound condition makes the CO-to-H$_{2}$ conversion factor in the bar ridges smaller than in the arms. A lower star-formation efficiency in bars indicated by previous studies is caused by such a condition that molecular gas is gravitationally unbound, as well as by an overestimation of molecular gas mass in the bar regions relative to spiral arms using a constant CO-to-H$_{2}$ conversion factor.
SGRs and AXPs as Rotation-Powered Massive White Dwarfs
Authors: Malheiro Manuel , Rueda Jorge A. , Ruffini Remo
Published: March 2014

SGR 0418$+$5729 is a “Rosetta Stone” for deciphering the energy source of Soft Gamma Ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs). We present a model based on canonical physics and astrophysics for SGRs and AXPs powered by massive highly magnetized rotating white dwarfs (WDs), in total analogy with pulsars powered by rotating neutron stars (NSs). We predict for SGR 0418$+$5729 a lower limit for its spin-down rate, $\dot{P}~\geq~L_{\rm X} P^3/$(4$\pi^2 I$) $=$ 1.18 $\times$ 10$^{-16}$, where $I$ is the moment of inertia of the WD. We show for SGRs and AXPs that the occurrence of the glitch and the gain of rotational energy is due to the release of gravitational energy associated to the contraction and decrease of the moment of inertia of the WDs. The steady emission and the outburst following the glitch are explained by the loss of rotational energy of the WDs, in view of the much larger moment of inertia of the WDs, as compared to that of NSs and/or quark stars. There is no need here to invoke the unorthodox concept of magnetic energy release due to the decay of overcritical magnetic fields, as assumed in the magnetar model. A new astrophysical scenario for the SGRs and AXPs associated to Supernova remnants is presented. The observational campaigns of the X-ray Japanese satellite Suzaku on AE Aquarii and the corresponding theoretical works by Japanese groups and recent results of the Hubble Space Telescope, give crucial information for our theoretical model. Follow-on missions of Hubble Telescope and VLT are highly recommended to give further observational evidence of this most fundamental issue of relativistic astrophysics: the identification of the true SGRs/AXPs energy source.
Low-Resolution Spectroscopy of Hot Post-AGB Candidates II. LS, LSS, LSE Stars and Additional IRAS Sources
Authors: Parthasarathy Mudumba , Drilling John S. , Vijapurkar Jyotsna , Takeda Yoichi
Published: March 2014

Hot (OB) post-asymptotic giant branch (post-AGB) stars are immediate progenitors of planetary nebulae (PNe). Very few hot post-AGB stars are known. Detecting new hot post-AGB candidates and follow-up multiwavelength studies will enable us to further understand the processes during the post-AGB evolution that lead to the formation of PNe. Case-Hamburg OB star surveys and their extension (LS, LSS, and LSE catalogues) and IRAS (point source) catalogues are good sources for detecting new hot post-AGB candidates from low-resolution spectroscopy. Spectral types are determined from low-resolution optical spectra of 44 stars selected from the LS, LSS, and LSE catalogues. Unlike the stars mentioned in the first paper, the stars discussed in this paper were selected using criteria other than positional coincidence with an IRAS source with far-IR (IRAS) colours similar to post-AGB supergiants and planetary nebulae. These included high galactic latitude, spectral types of O, B, A supergiants, emission lines in the spectrum and known spectral peculiarity. From the present study we find that LSS 1179, LSS 1222, LSS 1256, LSS 1276, LSS 1341, LSS 1394, LSS 2241, LSS 2429, LSS 4560, LSE 3, LSE 16, LSE 42, and LSE 67 to be new hot post-AGB candidates. Further studies of these candidates are needed.
Multi-Wavelength Photometric and Polarimetric Observations of the Outburst of 3C 454.3 in 2009 December
Authors: Sasada Mahito , Uemura Makoto , Fukazawa Yasushi , Kawabata Koji S. , Itoh Ryosuke , Sakon Itsuki , Fujisawa Kenta , Kadota Akiko , Ohsugi Takashi , Yoshida Michitoshi , Yasuda Hajimu , Yamanaka Masayuki , Sato Shuji , Kino Masaru
Published: March 2014

In 2009 December, the bright blazar 3C 454.3 exhibited a strong outburst in the optical, X-ray, and gamma-ray regions. We performed photometric and polarimetric monitoring of this outburst in the optical and near-infrared bands with TRISPEC and HOWPol attached to the Kanata telescope. We also observed this outburst in the infrared band with AKARI, and the radio band with the 32-m radio telescope of Yamaguchi University. The object was in an active state from JD 2455055 to 2455159. It was 1.3 mag brighter than its quiescent state before JD 2455055 in the optical band. After the end of the active state in JD 2455159, a prominent outburst was observed in all wavelengths. The outburst continued for two months. Our optical and near-infrared polarimetric observations revealed that the position angle of the polarization (PA) apparently rotated clockwise by 240° within 11 d in the active state (JD 2455063-2455074); after this rotation, PA remained almost constant during our monitoring. In the outburst state, PA smoothly rotated counterclockwise by 350° within 35 d (JD 2455157-2455192). Thus, we detected two distinct rotation events of polarization vectors in opposite directions. We discuss these two events compared with the past rotation events observed in 2005, 2007, and 2008.
NIR Spectroscopy of Star-Forming Galaxies at z ∼ 1.4 with Subaru/FMOS: The Mass–Metallicity Relation
Authors: Yabe Kiyoto , Ohta Kouji , Iwamuro Fumihide , Yuma Suraphong , Akiyama Masayuki , Tamura Naoyuki , Kimura Masahiko , Takato Naruhisa , Moritani Yuuki , Sumiyoshi Masanao , Maihara Toshinori , Silverman John , Dalton Gavin , Lewis Ian , Bonfield David , Lee Hanshin , Curtis Lake Emma , Macaulay Edward , Clarke Fraser
Published: March 2014

We present near-infrared spectroscopic observations of star-forming galaxies at $z$$\sim $ 1.4 with FMOS on the Subaru Telescope. We observed $K$-band selected galaxies in the SXDS/UDS fields with $K$$\leq$ 23.9 mag, 1.2 $\leq$$z_{\rm ph}$$\leq$ 1.6, $M_{*}$$\geq$ 10$^{9.5}\ M_{\odot}$, and expected F(H$\alpha $) $\geq$ 10$^{-16}\ $erg s$^{-1}\ $cm$^{-2}$; 71 objects in the sample have significant detections of H$\alpha $. For these objects, excluding possible AGNs, identified from the BPT diagram, gas-phase metallicities were obtained from the [N II] / H$\alpha $ line ratio. The sample is split into three stellar-mass bins, and the spectra are stacked in each stellar-mass bin. The mass–metallicity relation obtained at $z$$\sim $ 1.4 is located between those at $z$$\sim $ 0.8 and $z$$\sim $ 2.2. We constrain the intrinsic scatter to be $\sim $ 0.1 dex, or larger in the mass–metallicity relation at $z$$\sim $ 1.4; the scatter may be larger at higher redshifts. We found trends that the deviation from the mass–metallicity relation depends on the SFR (Star-formation rate) and the half light radius: Galaxies with higher SFR and larger half light radii show lower metallicities at a given stellar mass. One possible scenario for the trends is the infall of pristine gas accreted from IGM, or through merger events. Our data points show larger scatter than the fundamental metallicity relation (FMR) at $z$$\sim $ 0.1, and the average metallicities slightly deviate from the FMR. The compilation of the mass–metallicity relations at $z$$\sim $ 3 to $z$$\sim $ 0.1 shows that they evolve smoothly from $z$$\sim $ 3 to $z$$\sim $ 0 without changing the shape so much, except for the massive part at $z$$\sim $ 0.
X-Ray View of the Shock Front in the Merging Cluster Abell 3376 with Suzaku
Authors: Akamatsu Hiroki , Takizawa Motokazu , Nakazawa Kazuhiro , Fukazawa Yasushi , Ishisaki Yoshitaka , Ohashi Takaya
Published: March 2014

We report on a Suzaku measurement of the shock feature associated with the western radio relic in the merging cluster A 3376. The temperature profile is characterized by an almost flat radial shape with $ kT$$ \sim$ 4 keV within 0.5$ \ r_{200}$ and a rise by about 1 keV inside the radio relic. Across the relic region (0.6–0.8$ \ r_{200}$ ), the temperature shows a remarkable drop from about 4.7 keV to 1.3 keV. This is clear evidence that the radio relic really corresponds to a shock front, possibly caused by a past major merger. The observed sharp changes of the temperature and electron density indicate the Mach number $ {\cal M}$$ \sim$ 3. The radial entropy profile is flatter than the prediction ($ r^{1.1}$ ) of numerical simulations within 0.5$ \ r_{200}$ , and becomes steeper around the relic region. These observed features and time-scale estimation consistently imply that the ICM around the radio relic has experienced a merger shock, and is in the middle of the process of dynamical and thermal relaxations.
An Accretion-Disk Model with Cooling through Molecular Lines
Authors: Kai Takashi , Baba Tamon , Arai Kenzo
Published: March 2014

We investigated an accretion-disk model with line-cooling of H$ _2$ O and CO. The abundances of molecules were calculated numerically by the chemical reaction network, along with the structure of the disk. It was found that, when the model is applied to the Keplerian disk observed in the nucleus of NGC 4258, the temperature is $ T$$ \simeq$ 400–500 K, the number density of molecular hydrogen is $ n$ (H$ _2$ ) $ \simeq$ 10$ ^{7}$ –10$ ^{9}$ cm$ ^{-3}$ , and the fractional abundance of H$ _2$ O amounts to 10$ ^{-3}$ in the maser emitting region for the mass-accretion rate $ \dot{M}$$ \simeq$ 10$ ^{-6}$ –10$ ^{-7}\ M_{\odot }$ yr$ ^{-1}$ and the viscosity parameter $ \alpha$$ =$ 0.1. In the outer region, the disk is both geometrically and optically thin, the drift time is at most 1 Gyr, self-gravity of the disk can be neglected, and irradiation from the inner disk is of also a negligible effect. The Toomre $ Q$ parameter is greater than unity, leading the disk to be gravitationally stable. It was also found that these physical circumstances cannot be achieved in the optically thick model cooled by blackbody radiation.
Cryogenic 36–45 GHz InP Low-Noise Amplifier MMIC's with Improved Noise Temperature by Eliminating Parasitic Parallel-Plate Modes
Authors: Nakano Hiroshi , Shimizu Takashi , Ohno Takeshi , Hirachi Yasutake , Kawaguchi Noriyuki
Published: March 2014

This paper describes cryogenic 36–45 GHz InP low-noise amplifier monolithic microwave integrated circuits (MMIC's) with an improved noise temperature by eliminating parasitic parallel-plate resonance modes. These MMIC's are used for a Radio Astronomical receiver, which needs the ultimate super low-noise and wide-band frequency characteristics, such as those in ALMA Band 1. The MMIC chips were designed in the coplanar waveguide (CPW), and mounted to the AlN substrate with a flip-chip assembly, which was promising compared to wire bonding. The flip-chip assemblies, however, are prone to cause the parasitic parallel plate resonance mode (PPM). The relationship between the $S$-parameters and the PPM was investigated by using a 3D-electromagnetic simulation of the simple transmission-line test-chip with the same chip size as that of the actual MMIC. In order to eliminate the PPM, additional bumps were mounted on the simple transmission-line test-chip, and the effect of these bumps was confirmed by the simulation. These results obtained from the simple transmission-line test-chip were applied to an actual MMIC chip assembly. The MMIC assembled with the additional bumps had no abnormality in the measured $S$-parameters, and the PPM had been eliminated up to 65 GHz. Moreover, the stability factor, $K$, became more than 2.4 over 36–45 GHz. This InP low-noise amplifier MMIC exhibited a gain of 15 dB and a noise temperature of 180–240 K at room temperature in the frequency range of 36–45 GHz. When cooled to 28 K, a gain of 17 dB and a noise temperature of 22–35 K were obtained at a power consumption of 4.7 mW over 36–45 GHz. A high-gain amplifier module consisting of two cascaded chips, exhibited a gain of 27–30 dB and a noise temperature of 25–30 K at the ambient temperature of 22 K in the frequency range of 41–45 GHz.
Accretion Geometry of the Low-Mass X-Ray Binary Aquila X-1 in the Soft and Hard States
Authors: Sakurai Soki , Yamada Shin'Ya , Torii Shunsuke , Noda Hirofumi , Nakazawa Kazuhiro , Makishima Kazuo , Takahashi Hiromitsu
Published: March 2014

The neutron-star Low-Mass X-ray Binary Aquila X-1 was observed seven times in total with the Suzaku X-ray observatory from September 28 to October 30 in 2007, in the decaying phase of an outburst. In order to constrain the flux-dependent accretion geometry of this source over wider energy bands than employed in most previous studies, the present study utilized two out of seven data sets. The 0.8–31 keV spectrum on September 28, taken with the XIS and HXD-PIN for an exposure of 13.8 ks, shows an absorbed 0.8–31 keV flux of 3.6 $\times$ 10$^{-9}$ erg s$^{-1}$ cm$^{-2}$ , together with typical characteristics of the soft state of this type of object. The spectrum was successfully explained by an optically thick disk emission plus a Comptonized blackbody component. Although these results are in general agreement with previous studies, the significance of a hard tail recently reported using the same data was inconclusive in our analysis. The spectrum acquired on October 9 for an exposure of 19.7 ks was detected over a 0.8–100 keV band with the XIS, HXD-PIN, and HXD-GSO, at an absorbed flux of 8.5 $\times$ 10$^{-10}$ erg s$^{-1}$ cm$^{-2}$ (in 0.8–100 keV). It shows characteristics of the hard state, and was successfully explained by the same two continuum components, but with rather different parameters, including much stronger thermal Comptonization, of which the seed photon source was identified with blackbody emission from the neutron-star surface. As a result, the accretion flow in the hard state is inferred to take the form of an optically-thick and geometrically-thin disk down to a radius of 21 $\pm$ 4 km from the neutron star, and then turn into an optically thin nearly spherical hot flow.
Formation of Dense Gas and Stars near the End of the Galactic Bar
Authors: Ohishi Yukie , Sorai Kazuo , Habe Asao
Published: March 2014

We carried out H$ ^{13}$ CO$ ^{+}$ ($ J$  $ =$ 1–0) observations of a molecular cloud containing a massive star-forming region, G23.44$-$ 0.18, using the Nobeyama 45-m radio telescope. We identified three clumps, named Clumps A, B, and C, on the periphery of the H II region in the cloud. The most massive clump, Clump A, has a radius of 0.74 $ \pm$ 0.20 pc and a mass of 1100$ ^{+800}_{-\hskip.35mm 640}\ M\odot$ . Both Clumps B and C, however, have much smaller size and mass than Clump A. These three clumps seem not to be virialized. We also found four sub-clumps in Clump A. These sub-clumps may be affected by the strong outflow penetrating Clump A. The star-formation efficiency (SFE) of the entire cloud is $ \sim$ 0.4%, which is typical for galactic star-forming clouds. The SFE of Clump A is 25$ ^{+14}_{-\hskip.35mm 11}$ %. This value is higher than other embedded cluster-forming clumps, which implies that stars, including massive ones, are formed efficiently and actively in Clump A. The dense gas fraction estimated from H$ ^{13}$ CO$ ^{+}$ ($ J$  $ =$ 1–0) and $ ^{13}$ CO ($ J$  $ =$ 1–0) of the cloud are lower than those of other star-forming regions. The results mean that this star-forming region is young, and suggest that the formation of dense gas and stars in the cloud has just begun. Comparing the dynamical age of the H II region with the fragmentation timescale for the collect and collapse process, molecular gas is accumulating through expansion of the H II region in Clumps B and C. Since there are massive young stellar objects (YSOs) in Clump A, we suggest that this clump has already become denser than the other regions in the cloud due to converging flow, or some external factors, such as an old bubble and cloud–cloud interaction.
Trapped, Two-Armed, Nearly Vertical Oscillations in Disks with Toroidal Magnetic Fields II: Effects of Finite Thickness
Authors: Kato Shoji
Published: March 2014

We examine the radial trapping of two-armed ($ m$$ =$ 2) vertical p-mode oscillations in geometrically thin relativistic disks that are vertically isothermal, but terminated at a certain height by the presence of hot and low-density corona. The disks are assumed to be subject to toroidal magnetic fields. The oscillations are classified by $ n$ , a number related to the node number of oscillations in the vertical direction, and starting from $ n$$ =$ 1. In modes with $ n$$ =$ 1, the frequencies of trapped oscillations depend little on the height of termination, but in modes with $ n$$ =$ 2, 3, $ \cdots$ the frequencies decrease and the radial extentions of the trapped region become wide, as the termination height decreases. This study is a preparation to examine whether these oscillations can describe kilo-hertz quasi-periodic oscillations (kHz QPOs), horizontal branch oscillations (HBOs), and their correlations.
Statistical Analyses of White-Light Flares: Two Main Results about Flare Behaviour
Authors: Dal Hasan Ali
Published: March 2014

We present two main results, based on models and the statistical analyses of 1672 $ U$-band flares. We also discuss the behaviour of white-light flares. In addition, the parameters of the flares detected from two years of observations on CR Dra are presented. By comparing with flare parameters obtained from other UV Ceti-type stars, we examine the behaviour of the optical flare processes along with the spectral types. Moreover, we aimed, using large white-light flare data, to analyse the flare time-scales with respect to some results obtained from X-ray observations. Using SPSS V17.0 and GraphPad Prism V5.02 software, the flares detected from CR Dra were modelled with the OPEA function, and analysed with the $ t$-Test method to compare similar flare events in other stars. In addition, using some regression calculations in order to derive the best histograms, the time-scales of white-light flares were analysed. Firstly, CR Dra flares have revealed that white-light flares behave in a similar way as their counterparts observed in X-rays. As can be seen in X-ray observations, the electron density seems to be a dominant parameter in white-light flare process, too. Secondly, the distributions of the flare time-scales demonstrate that the number of observed flares reaches a maximum value in some particular ratios, which are 0.5, or its multiples, and especially positive integers. The thermal processes might be dominant for these white-light flares, while non-thermal processes might be dominant in the others. To obtain better results for the behaviour of the white-light flare process along with the spectral types, much more stars in a wide spectral range, from spectral type dK5e to dM6e, must be observed in white-light flare patrols.
Self-Charge-Filling (SCF) Effect of Suzaku XIS
Authors: Todoroki Shotaro , Kitamoto Shunji , Yoshida Yuki , Murakami Hiroshi
Published: March 2014

We demonstrate the importance of the self-charge-filling (SCF) effect for the analysis of bright and line-rich sources with the Suzaku X-ray imaging spectrometer (XIS) if spaced-row charge injection (SCI) is not applied. The SCF-effect changes the central energy of lines depending on the extracted region or the event densities of the images. We propose a correction method of the SCF-effect and show its validity by applying it to the extraction of the spectra of Cygnus X-3.
An Intrinsic Short-Term Radio Variability Observed in PKS 1510−089
Authors: Kadota Akiko , Fujisawa Kenta , Sawada-Satoh Satoko , Wajima Kiyoaki , Doi Akihiro
Published: March 2014

We searched a short-term radio variability in an active galactic nucleus, PKS 1510$-$ 089. Daily flux monitoring for 143 d at 8.4 GHz was performed, and VLBI observations at 8.4, 22, and 43 GHz were carried out 4 times during the flux monitoring period. As a result, variability with a time scale of 20 to 30 d was detected. The variation patterns were very much alike at three frequencies; moreover, those at 22 and 43 GHz were synchronized. These properties support that this short-term variability is an intrinsic one. The Doppler factor estimated from the variability time scale is 47. Since the Doppler factor is not extraordinary large for AGN, such intrinsic variability with a time scale of less than 30 d would exist in other AGNs.
Statistical Properties of Molecular Clumps in the Galactic Center 50 km s-1 Molecular Cloud
Authors: Tsuboi Masato , Miyazaki Atsushi
Published: March 2014

We present the statistical properties of molecular clumps in the Galactic center 50 km s$ ^{-1}$ molecular cloud (GCM-0.02-0.07) based on observations of the CS $ J$  $ =$ 1–0 emission line with the Nobeyama Millimeter Array. In the cloud, 37 molecular clumps with local thermodynamic equilibrium (LTE) masses of 2 $ \times$ 10$ ^{2}$ –6 $ \times$ 10$ ^{3}\ M_{\odot}$ were identified by using the clumpfind algorithm. The velocity widths of the molecular clumps are about five-fold those of Galactic disk molecular clouds with the same radius. The virial-theorem masses are three-fold the LTE masses. The mass and size spectra can be described by power laws of $ dN/dM$  $ \propto$  $ M^{-2.6\pm0.1}$ ($ M$  $ \gtrsim$ 900 $ M_{\odot}$ ) and $ dN/dR$  $ \propto$  $ R^{-5.9\pm0.3}$ ($ R$  $ \gtrsim$ 0.35 pc), respectively. The statistical properties of the region interacting with the Sgr A East shell and those of the non-interacting part of the cloud are significantly different. The interaction probably makes the mass function steeper, from $ dN/dM$  $ \propto$  $ M^{-2.0\pm0.1}$ in the non-interacting part to $ dN/dM$  $ \propto$  $ M^{-4.0\pm0.2}$ in the interacting region. On the other hand, the interaction presumably truncates the size spectrum on the larger side of $ R$  $ \sim$ 0.4 pc.
GRB 100418A: a Long GRB without a Bright Supernova in a High-Metallicity Host Galaxy
Authors: Niino Yuu , Hashimoto Tetsuya , Aoki Kentaro , Hattori Takashi , Yabe Kiyoto , Nomoto Ken'ichi
Published: March 2014

We present results of a search for a supernova (SN) component associated with GRB 100418A at a redshift of 0.624. The field of GRB 100418A was observed with FOCAS on the Subaru 8.2 m telescope under a photometric condition (seeing 0$ .\!\!\!''$ 3–0$ .\!\!\!''$ 4) on 2010 May 14 (UT). The date corresponds to 25.6 days after the burst trigger (15.8 days in the restframe). We made imaging observations in the $ V,\ R_{\rm c}$ , and $ I_{\rm c}$ bands, and two hours of spectrophotometric observations. We obtained a resolved host galaxy image that is elongated 1$ .\!\!\!''$ 6 (= 11 kpc) from north to south. No point source was detected on the host galaxy. The time variation of the $ R_{\rm c}$-band magnitude shows that the afterglow of GRB 100418A has faded to $ R_{\rm c}$$ \gtrsim$ 24 without any SN-like rebrightening, when we compare our measurement to reports in GCN circulars. We could not identify any SN feature, such as broad emission-lines or bumps in our spectrum. Assuming the SN is fainter than the 3 $ \sigma$ noise spectrum of our observation, we estimated the upper limit on the SN absolute magnitude to be $ M_{I_{\rm c},{\rm obs}}$$ \gt$$-$ 17.2 in the observer frame $ I_{\rm c}$-band. This magnitude is comparable to the faintest type Ic SNe. We also estimated the host galaxy properties from the spectrum. The host galaxy of GRB 100418A is relatively massive (log$ \ M_\star/M_\odot$$ =$ 9.54) compared to typical long GRB host galaxies, and has 12 $ +$ log (O$ /$ H) $ =$ 8.75.
Superburst with Outburst from EXO 1745−248 in Terzan 5 with MAXI
Authors: Serino Motoko , Mihara Tatehiro , Matsuoka Masaru , Nakahira Satoshi , Sugizaki Mutsumi , Ueda Yoshihiro , Kawai Nobuyuki , Ueno Shiro
Published: March 2014

MAXI/GSC detected a superburst from EXO 1745$-$ 248 in the globular cluster Terzan 5 on 2011 October 24. The GSC light curve shows an exponential decay with an $ e$-folding time of 0.3 d. The spectra are consistent with the blackbody radiation, whose temperature is 2.2 keV and 1.2 keV at MJD 55858.56 and 55859.20, respectively. The fluence is 1.4 $ \times$ 10$ ^{42}$ erg in 2–20 keV, assuming an 8.7 kpc distance. The sphere radius of the blackbody and its luminosity are estimated to be 6.2 km and 1.1 $ \times$ 10$ ^{38}$ erg s$ ^{-1}$ , respectively, from a spectral fitting at the flux peak. Those $ e$-folding time, temperature, softening, fluence, and radius are typical of superbursts from low-mass X-ray binaries. The superburst was followed by an outburst 28 hours after the superburst onset. The outburst lasted for 5 d and the fluence was 4.3 $ \times$ 10$ ^{42}$ erg. The instability of the accretion disk caused by the superburst would be an explanation for the outburst, whereas the mass accretion of the matter evaporated from the surface of the companion star by the superburst would be another possibility.
Reconstruction of the Structure of Accretion Disks in Dwarf Novae from the Multi-Band Light Curves of Early Superhumps
Authors: Uemura Makoto , Kato Taichi , Ohshima Tomohito , Maehara Hiroyuki
Published: March 2014

We propose a new method to reconstruct the structure of accretion disks in dwarf novae using multi-band light curves of early superhumps. Our model assumes that early superhumps are caused by the rotation effect of non-axisymmetrically flaring disks. We have developed a Bayesian model for this reconstruction, in which a smoother disk-structure tends to have a higher prior probability. We analyzed simultaneous optical and near-infrared photometric data of early superhumps of the dwarf nova, V455 And using this technique. The reconstructed disk has two flaring parts in the outermost region of the disk. These parts are responsible for the primary and secondary maxima of the light curves. The height-to-radius ratio is $ h/r$$ =$ 0.20–0.25 in the outermost region. In addition to the outermost flaring structures, flaring arm-like patterns can be seen in an inner region of the reconstructed disk. The overall profile of the reconstructed disk is reminiscent of the disk structure that is deformed by the tidal effect. However, an inner arm-like pattern, which is responsible for the secondary minimum in the light curve, cannot be reproduced only by the tidal effect. It implies the presence of another mechanism that deforms the disk structure. Alternatively, the temperature distribution of the disk could be non-axisymmetric. We demonstrate that the disk structure with weaker arm-like patterns is optimal in the model including the irradiation effect. However, the strongly irradiated disk gives quite blue colors, which may conflict with the observation. Our results suggest that the amplitude of early superhumps depends mainly on the height of the outermost flaring regions of the disk. We predict that early superhumps can be detected with an amplitude of $ \gt$ 0.02 mag in about 90% of WZ Sge stars.
New Period Investigation of Near Contact Binary BF Virginis
Authors: Liying Zhu , Sheng-Bang Qian , Linjia Li
Published: March 2014

The near contact binary BF Virginis was monitored by us from 2007 to 2011 with the 60-cm telescope of Yunnan Observatory. Eight new observed times of light minimum were derived. All of the available eclipse times, spanning more than 100 yr, were analyzed. It is found that there exists a cyclic variation with a semi-amplitude of 0.034 d and a period of 63.3 yr, superposed by an upward parabolic variation. The upward parabolic change can be explained as a continuous period increase due to mass transfer from the secondary to the primary component of BF Vir, which supports the secondary filling near contact configuration. The period oscillation can be explained either by the light-time effect due to the presence of a third body or by magnetic activity. If it is caused by the light-time effect, the minimum mass and the corresponding orbital radius of the additional body should be $ m_{3}$$ =$ 0.93 $ M_{\odot}$ and $ a_{3}$$ =$ 19.4 AU, respectively. On the other hand, the period oscillation may be explained as a consequence of magnetic cycles in its secondary component. In this case, the required variation of the quadrupole moment is calculated to be $ \Delta{Q}$$ =$ 2.1 $ \times$ 10$ ^{50}$ g cm$ ^2$ .
Near-Infrared Survey of Bright Rimmed Clouds
Authors: Hayashi Miyuki , Itoh Yoichi , Oasa Yumiko
Published: March 2014

We conducted wide-field near-infrared imaging observations of 32 bright rimmed clouds (BRCs). Given a detection limit of 17.7 mag at the $ K$-band, we identified 2099 objects as young stellar object (YSO) candidates that displayed near-infrared excesses. Their masses, estimated from luminosities, range from 0.006 $ M_{\odot}$ to 2.7 $ M_{\odot}$ . The candidates are not uniformly distributed. For 21 BRCs, more than half of the associated YSO candidates are located inside the cloud. We found clear evidence of triggered star formation. The number of YSO candidates is not correlated with the core mass of the molecular clouds. Instead, the YSO number increases with increasing UV photon flux from the exciting star illuminating the cloud surface. UV radiation activates star formation in the BRCs.
HAT-P-38b: A Saturn-Mass Planet Transiting a Late G Star
Authors: Sato Bun'ei , Hartman Joel D. , Bakos Gáspár Á. , BÉKy Bence , Torres Guillermo , Latham David W. , KovÁcs Géza , Csubry Zoltán , Penev Kaloyan , Noyes Robert W. , Buchhave Lars A. , Quinn Samuel N. , Everett Mark , Esquerdo Gilbert A. , Fischer Debra A. , Howard Andrew W. , Johnson John A. , Marcy Geoff W. , Sasselov Dimitar D. , SzklenÁr Tamás , LÁzÁr József , Papp István , SÁri Pál
Published: March 2014

We report on the discovery of HAT-P-38b, a Saturn-mass exoplanet, transiting the $ V$$ =$ 12.56 dwarf star GSC 2314-00559 on a $ P$$ =$ 4.6404 d circular orbit. The host star is a 0.89 $ M_{\odot}$ late G dwarf, with solar metallicity and a radius of 0.92 $ R_{\odot}$ . The planetary companion has a mass of 0.27 $ M_{\rm J}$ and a radius of 0.82 $ R_{\rm J}$ . HAT-P-38b is one of the planets the mass and radius of which have ever been discovered to be the closest to those of Saturn.
Extremely Strong 13CO J = 3→2 Line in the ``Water Fountain'' IRAS 16342−3814: Evidence for the Hot-Bottom Burning
Authors: Imai Hiroshi , Chong Sze Ning , He Jin-Hua , Nakashima Jun-Ichi , Hsia Chih-Hao , Sakai Takeshi , Deguchi Shuji , Koning Nico
Published: March 2014

We observed four ``water fountain'' sources in the CO $ J$  $ =$ 3$ \rightarrow$ 2 line emission with the Atacama Submillimeter Telescope Experiment (ASTE) 10 m telescope in 2010–2011. The water fountain sources are evolved stars that form high-velocity collimated jets traced by H$ _{2}$ O maser emission. The CO line was detected only from IRAS 16342$-$ 3814. The present work confirmed that the $ ^{12}$ CO to $ ^{13}$ CO line intensity ratio is $ \sim$ 1.5 at the systemic velocity. We discuss the origins of the very low $ ^{12}$ CO-to-$ ^{13}$ CO intensity ratio, as possible evidence for ``hot-bottom burning'' in an oxygen-rich star, and the CO intensity variation in IRAS 16342$-$ 3814.
Suzaku Observation of the Supergiant Fast X-Ray Transient AX J1841.0−0536
Authors: Kawabata Nobukawa Kumiko , Nobukawa Masayoshi , Tsuru Takeshi Go , Koyama Katsuji
Published: March 2014

We observed the supergiant fast X-ray transient AX J1841.0$-$ 0536 with Suzaku in 2011 March. Many short flares with time-scales of a few hundred seconds and a large flare with a peak flux (1.0–10 keV) of $ \gtrsim$ 2 $ \times$ 10$ ^{-10}$ erg s$ ^{-1}$ cm$ ^{-2}$ were detected. The broad-band (1.0–40 keV) spectrum was fitted with a cut-off power-law continuum plus a K$ \alpha$ line from a neutral iron absorbed by partial covering gas. In addition, a broad absorption feature was found in a high-energy band. The photon index of the power-law is 1.01 $ \pm$ 0.12 in a low-luminosity state, and decreases (becomes hard) with increasing luminosity. On the other hand, the absorption column density and the iron line equivalent width are nearly constant. The covering fraction does not vary significantly, except for the full coverage epoch at the end of the large flare. We thus propose that the X-ray emission is due to subsequent in-falls of many small blobs.
Discovery of Superhumps during a Normal Outburst of SU Ursae Majoris
Authors: Imada Akira , Izumiura Hideyuki , Kuroda Daisuke , Yanagisawa Kenshi , Kawai Nobuyuki , Omodaka Toshihiro , Miyanoshita Ryo
Published: March 2014

We report on time-resolved photometry during a 2012 January normal outburst of SU UMa. The light curve shows hump-like modulations with a period of 0.07903(11) d, which coincides with the known superhump period of SU UMa during superoutbursts. We interpret this as a superhump, based on the observed periodicity, profiles of the averaged light curve, and the $g'$$-$$I_{\rm c}$ variation during the normal outburst. This is the first case that superhumps have been detected during an isolated normal outburst of SU UMa-type dwarf novae. The present result strongly suggests that the radius of the accretion disk already reaches the 3:1 resonance, even in the midst of the supercycle.
Observational Report on the Classical Nova KT Eridani
Authors: Imamura Kazuyoshi , Tanabe Kenji
Published: March 2014

A report is presented on spectroscopic and multi-color photometric observations of the high Galactic latitude classical nova KT Eridani (Nova Eridani 2009). After 12.2 d from maximum light, broad and prominent emission lines of the Balmer series, Hei, Heii, Nii, Niii, and Oi can be seen on the spectra. The FWHM of the H${\alpha}$ line yields an expansion velocity of approximately 3400 km s$^{-1}$. After 279.4 d from maximum light, we can see prominent emission lines of Heii and [Oiii] on the spectrum. Among them, [Oiii] (4959, 5007) lines show multiple peaks. From the obtained light curve, KT Eri is classified to be a very fast nova, with a decline rate by two magnitudes of 6.2 $\pm$ 0.3 d and three of 14.3 $\pm$ 0.7 d. We tried to estimate the absolute magnitude ($M_V$) using the Maximum Magnitude versus Rate of Decline relationship and distance of KT Eri. The calculated $M_V$ is approximately $-$9. Accordingly, the distance and Galactic height are approximately 7 kpc and 4 kpc, respectively. Hence, KT Eri is concluded to be located outside of the Galactic disk.