bluuebunny/crossref_metadata_2025_split huggingface dataset:
Destructible Bars in Disk Galaxies under the Dynamical Influence of a Massive Central Black Hole
Authors: Hozumi Shunsuke 
Published: March 2014

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
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

Abstract
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

Abstract
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.
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Formation of Dense Gas and Stars near the End of the Galactic Bar
Authors: Ohishi Yukie , Sorai Kazuo , Habe Asao 
Published: March 2014

Abstract
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.
Statistical Analyses of White-Light Flares: Two Main Results about Flare Behaviour
Authors: Dal Hasan Ali 
Published: March 2014

Abstract
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.
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

Abstract
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

Abstract
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.