bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conditions of Gravitational Instability in Protoplanetary Disks
Authors: Kimura Shigeo S. , Tsuribe Toru 
Published: March 2014

Abstract
Gravitational instability is one of the considerable mechanisms to explain the formation of giant planets. We have studied the gravitational stability in protoplanetary disks around a protostar. The temperature and Toomre's $ Q$ value were calculated by assuming local equilibrium between viscous heating and radiative cooling (local thermal equilibrium). We assumed a constant $ \alpha$ viscosity and used a cooling function with realistic opacity. Then, we derived the critical surface density, $ \Sigma_{\rm {c}}$ , that is needed in order for a disk to become gravitationally unstable as a function of $ r$ . This critical surface density, $ \Sigma _{\rm c}$ , is strongly affected by the temperature dependence of the opacity. At a radius of $ r_{\rm c}$$ \sim$ 20 AU, where ices form, the value of $ \Sigma _{\rm c}$ changes discontinuously by one order of magnitude. This $ \Sigma _{\rm c}$ is determined only by a local thermal process and the criterion of gravitational instability. By comparing a given surface density profile with $ \Sigma _{\rm c}$ , one can discuss the gravitational instability of protoplanetary disks. As an example, we discuss the gravitational instability of two semianalytic models for protoplanetary disks. One is a steady state accretion disk, which is realized after viscous evolution. The other is a disk that has the same angular-momentum distribution as its parent cloud core, which corresponds to the disk that has just formed. As a result, it is found that the disk tends to become gravitationally unstable for $ r$$ \ge$$ r_{\rm c}$ because ices make the disk temperature low. In a region closer to the protostar than $ r_{\rm c}$ , it is difficult for a typical protoplanetary disk to fragment because of the high temperature and the large Coriolis force. Based on this result, we conclude that fragmentation near the central star is possible, but difficult.
Optimization by Smoothed Bandpass Calibration in Radio Spectroscopy
Authors: Yamaki Haruka , Kameno Seiji , Beppu Hirohisa , Mizuno Izumi , Imai Hiroshi 
Published: March 2014

Abstract
We have developed the Smoothed Bandpass Calibration (SBC) method and the best suitable scan pattern to optimize radio spectroscopic observations. Adequate spectral smoothing is applied to the spectrum toward OFF-source blank sky adjacent to a target source for the purpose of bandpass correction. Because the smoothing process reduces noise, we can reduce the integration time for OFF-source scans while keeping the signal-to-noise ratio. Since smoothing is not applied to ON-source scans, the spectral resolution for line features is maintained. An optimal smoothing window is determined by the bandpass flatness evaluated by the spectral Allan variance (SAV). An efficient scan pattern is designed for OFF-source scans within the bandpass-stability time scale estimated by the time-based Allan variance (TAV). We tested the SBC using a digital spectrometer, VESPA, at the VERA Iriki station. For a targeted noise level of 5 $ \times$10$ ^{-4}$ as its ratio to the system noise, the optimal smoothing window was 32–60 channels (ch) over the whole bandwidth of 1024 ch, and the optimal scan pattern was designed as a sequence of 70 s ON $ +$ 10 s OFF scan pairs. The noise level by the SBC has been improved by a factor of 1.74, compared with that by the conventional method. The total telescope-time to reach our target with the SBC was 400 s, which is 1$ /$ 3 of 1200 s required in the conventional way. Improvements in the telescope-time efficiency with the SBC were calculated to be 3$ \times$ (for single-beam scans), 2$ \times$ (dual-beam), and 1.3$ \times$ (on-the-fly). The SBC is useful for optimizing scan patterns for observations from now on, and also for improving the signal-to-noise ratios of archival data if ON- and OFF-source spectra are separately recorded, though the efficiency depends on the spectral stability of the receiving system.
Chromospheric Running Wave from a Solar Cyclone Produced through the Emergence of a Twisted Magnetic Flux Tube
Authors: Magara Tetsuya , An Jun-Mo , Lee Hwanhee , Kang Jihye , Inoue Satoshi , Choe Gwangson 
Published: March 2014

Abstract
An innovative solar observing satellite, Hinode, has successfully observed the detailed evolution of an emerging magnetic field, starting from its appearance at the solar surface, to forming a developed bipolar region. The high spatial and temporal resolutions provided by the satellite has enabled us to capture prominent dynamic phenomena caused by the emerging magnetic field, such as a running wave in a chromospheric layer and the rotation of a magnetic polarity region on the Sun, which is reminiscent of a cyclone on Earth. A possible mechanism for producing the chromospheric running wave spreading from a solar cyclone has been demonstrated with a three-dimensional magnetohydrodynamic simulation for the emergence of a twisted flux tube. The simulation shows that as the emergence proceeds, an arc-shaped region with enhanced plasma density propagates outwards from the site of emergence.
The Light and Period Variations of the Eclipsing Binary BX Draconis
Authors: Park Jang-Ho , Lee Jae Woo , Kim Seung-Lee , Lee Chung-Uk , Jeon Young-Beom 
Published: March 2014

Abstract
New CCD photometric observations of BX Dra were carried out on 26 nights during the period from 2009 April to 2010 June. The long-term photometric behaviors of the system are obtained from detailed studies of the period and light variations, based on historical data and our new observations. All available light curves display total eclipses at secondary minima and inverse O'Connell effects with Max I fainter than Max II, which were satisfactorily modeled by adding a slightly time-varying hot spot on the primary star. A total of 87 times of minimum lights spanning over $ \sim$ 74 yr, including our 22 timing measurements, were used for ephemeris computations. A detailed analysis of the $ O$$-$$ C$ diagram disclosed that the orbital period shows an upward parabola in combination with a sinusoidal variation. The continuous increase of period at a rate of $ +$ 5.65 $ \times$ 10$ ^{-7}$ d yr$ ^{-1}$ is consistent with that calculated from the Wilson–Devinney synthesis code. It can be interpreted as a mass transfer from the secondary star to the primary at a rate of 2.74 $ \times$ 10$ ^{-7}$$ M_{\odot}$ yr$ ^{-1}$ , which is one of the largest rates between components of the contact system. The most likely explanation of the sinusoidal variation having a period of 30.2 yr and a semiamplitude of 0.0062 d is a light-travel-time effect due to the existence of a circumbinary object. We suggest that BX Dra is probably a triple system, consisting of a primary star with a spectral type of F0, its secondary component of spectral type F1–2, and an unseen circumbinary object with a minimum mass of $ M_3$$ =$ 0.23 $ M_{\odot}$.
A New Galactic Extinction Map in High Ecliptic Latitudes
Authors: Kohyama Tsunehito , Shibai Hiroshi , Fukagawa Misato , Sumi Takahiro , Hibi Yasunori 
Published: March 2014

Abstract
In this study, we derived a galactic extinction map in high ecliptic latitudes for $ \mid{\beta}\mid$$ &gt;$ 30$ ^\circ$ . The dust temperature distribution was derived from the intensities at 100 and 140 $ \mu$ m with a spatial resolution of 5$ '$ . The intensity at 140 $ \mu$ m was derived from the intensities at 60 and 100 $ \mu$ m of the IRAS data, assuming two tight correlations between the intensities at 60, 100, and 140 $ \mu$ m of the COBE/DIRBE data. We found that these correlations can be separated into two correlations by the antenna temperature of the radio continuum at 41 GHz. Because the present study can trace the 5$ '$-scale spatial variation in the dust temperature distribution, it has an advantage over the extinction map derived by Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525), who used the DIRBE maps to derive the dust temperature distribution with a spatial resolution of 1$ ^\circ$ . We estimated the accuracy of our method by comparing it with that of Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525). The spatial-resolution difference was found to be significant. The area in which the significant difference is confirmed occupies 28% of the region for $ \mid{\beta}\mid$$ &gt;$ 30$ ^\circ$ . With respect to the estimated extragalactic reddening, the present study has an advantage over the extinction map derived by Dobashi (2011, PASJ, 63, 1), which was based on the 2MASS Point Source Catalog, because our extinction map was derived based on far-infrared emission. Dobashi's extinction map exhibits a maximum value that is lower than that of our map in the galactic plane, and a signal-to-noise ratio that is lower than that of our map in high galactic latitudes. This significant difference is confirmed in 81% of the region for $ \mid{\beta}\mid$$ &gt;$ 30$ ^\circ$ . In the areas where the significant differences are confirmed, the extinction should be estimated using our method, rather than the previous methods.
Properties of Molecular Gas in Galaxies in Early and Mid Stages of the Interaction. I. Distribution of Molecular Gas
Authors: Kaneko Hiroyuki , Kuno Nario , Iono Daisuke , Tamura Yoichi , Tosaki Tomoka , Nakanishi Koichiro , Sawada Tsuyoshi 
Published: March 2014

Abstract
We present the results of $ ^{12}$ CO (J$ =$ 1–0) mapping observations toward four interacting galaxies in early and mid stages of the interaction in order to understand the behavior of molecular gas in galaxy–galaxy interactions. The observations were carried out using the 45-m telescope at Nobeyama Radio Observatory (NRO). We compared our CO total flux to those previously obtained with single-dish observations, and found that there is no discrepancy between them. By applying a typical CO–H$ _{2}$ conversion factor, it was found that all constituent galaxies have molecular gas mass of more than 10$ ^{9}$ . Comparisons to H I, K$ _{\rm s}$, and tracers of star formation, such as H$ \alpha$ , FUV, 8 $ \mu$ m, and 24 $ \mu$ m, revealed that the distribution of molecular gas in interacting galaxies in the early stage of the interaction differs from atomic gas, stars, and star-forming regions. These differences can not be explained without the result of the interaction. The central concentration of molecular gas of interacting galaxies in the early stage of the interaction is lower than that of isolated galaxies, which suggests that molecular gas is distributed off-centre, and/or extends in the beginning of the interaction.
Measurements of an Antenna Surface for a Millimeter-Wave Space Radio Telescope. II. Metal Mesh Surface for Large Deployable Reflector
Authors: Kamegai Kazuhisa , Tsuboi Masato 
Published: March 2014

Abstract
Large deployable antennas with a mesh surface woven by fine metal wires are an important technology for communications satellites and space radio telescopes. However, it is difficult to make metal mesh surfaces with sufficient radio-frequency (RF) performance for frequencies higher than millimeter waves. In this paper, we present the RF performance of metal mesh surfaces at 43 GHz. For this purpose, we developed an apparatus to measure the reflection coefficient, transmission coefficient, and radiative coefficient of the mesh surface. The reflection coefficient increases as a function of the metal mesh surface tension, whereas the radiative coefficient decreases. The anisotropic aspects of the reflection coefficient and the radiative coefficient are also clearly seen. They depend on the front and back sides of the metal mesh surface and the rotation angle. The transmission coefficient was measured to be almost constant. The measured radiative coefficients and transmission coefficients would cause significant degradation of the system noise temperature. In addition, we carried out an astronomical observation of a well-known SiO maser source, R Cas, by using a metal mesh mirror on the NRO 45-m radio telescope Coudé system. The metal mesh mirror considerably increases the system noise temperature, and slightly decreases the peak antenna temperature. These results are consistent with laboratory measurements.
X-Ray and Optical Monitoring of a Gamma-Ray-Emitting Radio Galaxy, NGC 1275
Authors: Yamazaki Syoko , Fukazawa Yasushi , Sasada Mahito , Itoh Ryosuke , Nishino Sho , Takahashi Hiromitsu , Takaki Katsutoshi , Kawabata Koji S. , Yoshida Michitoshi , Uemura Makoto 
Published: March 2014

Abstract
We performed monitoring observations of a gamma-ray-emitting radio galaxy, NGC 1275, in the X-ray and optical bands with the Suzaku/XIS, Kanata telescope, and the Okayama telescope. The X-ray flux of the nucleus was estimated by imaging spectroscopy in the hard X-ray band. In the optical band, a continuum flux, a broad H$ \alpha$ line flux, and the polarization degree were measured. We could not find any time variability of the X-ray (2006–2011) and optical continuum (2010–2011) within 30%, regardless of the recent radio and gamma-ray variability by a factor of 3. The observed optical polarization was very small at $ \sim$ 0.4% and showed little variability; it would be mostly of interstellar origin within our Galaxy. Furthermore, we confirmed with the XMM-Newton data that the X-ray spectrum of NGC 1275 in 2006 exhibited the Fe-K line, whose equivalent width was typical for other radio and Seyfert galaxies. These results indicate that the jet emission is not a major component in the optical and X-ray bands. Following these results, we discuss the jet emission of NGC 1275.
X-Ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*
Authors: Ryu Syukyo Gando , Nobukawa Masayoshi , Nakashima Shinya , Tsuru Takeshi Go , Koyama Katsuji , Uchiyama Hideki 
Published: March 2014

This paper presents Suzaku results obtained for the Sagittarius (Sgr) C region using the concept of X-ray reflection nebulae (XRNe) as the echo of past flares from a super-massive black hole, Sgr A*. The Sgr C complex is composed of several molecular clouds proximately located in projected distance. The X-ray spectra of Sgr C were analyzed based on the view that XRNe are located inside the Galactic center plasma X-ray emission with an oval distribution around Sgr A*. We found that XRNe are largely separated in the line-of-sight position, and are associated with molecular clouds in different velocity ranges detected by radio observations. We also applied the same analysis to Sgr B XRNe, and completed a long-term light curve for Sgr A* occurring in the past. As a new finding, we determined that Sgr A* has already experienced periods of high luminosity, $ \sim$ 500 years ago, which is longer than the previously reported value. Our results are consistent with a scenario that Sgr A* was continuously active with sporadic flux variabilities of $ L_{\rm X}$ $ =$ (1–3) $ \times$ 10$ ^{39}$ erg s$ ^{-1}$ in the past 50 to 500 years. The average past luminosity was approximately 4–6 orders of magnitude higher than that presently observed. In addition, two short-term flares of 5–10 years have been found. Thus, the past X-ray flare should not be a single short-term flare, but can be interpreted as multiple flares superposed on a long-term high state.
Detection of Far-Infrared Emission from Galaxies and Quasars in the Galactic Extinction Map by Stacking Analysis
Authors: Kashiwagi Toshiya , Yahata Kazuhiro , Suto Yasushi 
Published: March 2014

Abstract
We performed stacking image analyses of galaxies over a Galactic extinction map constructed by Schlegel, Finkbeiner, and Davis (1998, AJ, 500, 525). We selected $ \sim$ 10$ ^{7}$ galaxies in total from the Sloan Digital Sky Survey (SDSS) DR7 photometric catalog. We detected clear signatures of the enhancement of the extinction in the $ r$-band, $ \Delta A_r$ , around galaxies, indicating that the extinction map is contaminated by their FIR (far-infrared) emission. The average amplitude of the contamination per galaxy was well-fitted to $ \Delta A_r$ ($ m_r$ ) $ =$ 0.64 $ \times$ 10$ ^{0.17(18-m_r)}$ [mmag]. While this value is very small, it is directly associated with galaxies, and may have a systematic effect on galaxy statistics. Indeed, this correlated contamination leads to a relatively large anomaly of galaxy surface number densities against the SFD extinction, $ A_{\rm SFD}$ , discovered by Yahata et al. (2007, PASJ, 59, 205). We modeled the radial profiles of stacked galaxy images, and found that the FIR signal around each galaxy does not originate from the central galaxy alone, but is dominated by the contributions of nearby galaxies via galaxy angular clustering. The separation of the single galaxy and the clustering terms enables us to infer the statistical relation of the FIR and $ r$-band fluxes of galaxies, and also to probe the flux-weighted cross-correlation of galaxies, down to magnitudes that are difficult to probe directly for individual objects. We repeated the same stacking analysis for SDSS DR6 photometric quasars, and discovered similar signatures, but with weaker amplitudes. The implications of the present results for galaxy and quasar statistics, and for corrections to the Galactic extinction map, are briefly discussed.
An X-Ray Study of the Galactic-Scale Starburst-Driven Outflow in NGC 253
Authors: Mitsuishi Ikuyuki , Yamasaki Noriko Y. , Takei Yoh 
Published: March 2014

The X-ray properties of hot interstellar gas in a bright, nearby edge-on starburst galaxy, NGC 253, were investigated so as to gain a further understanding of starburst-driven outflow activity by utilizing XMM-Newton and Suzaku. Spectroscopic analyses for three regions of the galaxy characterized by multiwavelength observations, i.e., the superwind region, the disk region, and the halo region, were conducted. Various emission lines from O, Ne, Mg, Si, and Fe were observed in the spectra of each region. The hot gas was represented by two thin thermal plasmas with temperatures of $ kT$ $ \sim$ 0.2 and $ \sim$ 0.6 keV. The abundance ratios, i.e., O$ /$ Fe, Ne$ /$ Fe, Mg$ /$ Fe, and Si$ /$ Fe, are consistent between the three regions, which suggests a common origin of the hot gas. The abundance patterns are consistent with those of type II supernova ejecta, indicating that the starburst activity in the central region provides metals toward the halo through a galactic-scale starburst-driven outflow. The energetics can also support this indication on the condition that 0.01–50 $ \eta^{1/2}$ % of the total emission in the nuclear region has flowed to the halo region. To constrain the dynamics of hot interstellar gas, surface brightness, and hardness ratio profiles, which trace the density and temperature, were extracted. Assuming a simple polytropic equation of state for gas, $ T\rho^{1-\gamma}$ $ =$ const, we constrained the physical condition; $ \gamma$ is consistent with 5$ /$ 3 at a hot disk of $ &lt;$ 3 kpc from the center along with the minor axis, and $ T$ is constant ($ \gamma$ $ =$ 1) in the halo, the distance of which is between 3 and 10 kpc from the center. It is suggested that the hot gas expands adiabatically from the central region towards the halo region while it moves as free expansion from the inner part of the halo towards the outer part of the halo as the outflow. We constrained the outflow velocity to be $ &gt;$ 100 km s$ ^{-1}$ based on the observed temperature gradient in the halo. In comparison with the escape velocity of $ \sim$ 220 km s$ ^{-1}$ for NGC 253, it is indicated that the hot interstellar gas can escape from the gravitational potential of NGC 253 by combining the outflow velocity and the thermal velocity.
High-Precision Measurements of the Brightness Variation of Nereid
Authors: Terai Tsuyoshi , Itoh Yoichi 
Published: March 2014

Abstract
Nereid, the outer satellite of Neptune, has a highly eccentric prograde orbit with a semimajor axis of larger than 200 in units of Neptune's radius, and is classified as an irregular satellite. Although the capture origin of irregular satellites has been widely accepted, several previous studies suggest that Nereid was formed in the circumplanetary disk of Neptune and ejected outward to the present location by Triton. A series of our photometric observations confirm that Nereid's rotation period, 11.5 hr, is stable and nonchaotic, as indicated by Grav, Holman, and Kavelaars (2003, ApJ, 591, L71). The optical colors of Nereid are indistinguishable from those of trans-Neptunian objects and Centaurs, especially from these objects with neutral colors. We also found the consistency of Nereid's rotation period based on the size–rotation distribution of small outer bodies. It is likely that Nereid originated as an immigrant body captured from the heliocentric orbit that was 4–5 AU away from Neptune's orbit.
Can Superflares Occur on Our Sun?
Authors: Shibata Kazunari , Isobe Hiroaki , Hillier Andrew , Choudhuri Arnab Rai , Maehara Hiroyuki , Ishii Takako T. , Shibayama Takuya , Notsu Shota , Notsu Yuta , Nagao Takashi , Honda Satoshi , Nogami Daisaku 
Published: March 2014

Abstract
Recent observations of Sun-like stars, similar to our Sun in their surface temperature (5600–6000 K) and slow rotation (rotational period $ &gt;$ 10 d), using the Kepler satellite by Maehara et al. (2012, Nature, 485, 478) have revealed the existence of superflares (with energy of 10$ ^{33}$ –10$ ^{35}$ erg). From statistical analyses of these superflares, it was found that superflares with energy of 10$ ^{34}$ erg occur once in 800 yr, and superflares with 10$ ^{35}$ erg occur once in 5000 yr. In this paper, we examine whether superflares with energy of 10$ ^{33}$ –10$ ^{35}$ erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas related to the mechanisms of the solar dynamo. If magnetic flux is generated by differential rotation at the base of the convection zone, as assumed in typical dynamo models, it is possible that the present Sun would generate a large sunspot with a total magnetic flux of $ \sim$ 2 $ \times$ 10$ ^{23}$ Mx ($ =$ G cm$ ^{2}$ ) within one solar cycle period, and lead to superflares with an energy of 10$ ^{34}$ erg. To store a total magnetic flux of $ \sim$ 10$ ^{24}$ Mx, necessary for generating 10$ ^{35}$ erg superflares, it would take $ \sim$ 40 yr. Hot Jupiters have often been argued to be a necessary ingredient for the generation of superflares, but we found that they do not play any essential role in the generation of magnetic flux in the star itself, if we consider only the magnetic interaction between the star and the hot Jupiter. This seems to be consistent with Maehara et al.'s finding of 148 superflare-generating solar-type stars that do not have a hot Jupiter-like companion. Altogether, our simple calculations, combined with Maehara et al.'s analysis of superflares on Sun-like stars, show that there is a possibility that superflares of 10$ ^{34}$ erg would occur once in 800 yr on our present Sun.
Detection of Change in Supercycles in ER Ursae Majoris
Authors: Zemko Polina , Kato Taichi , Shugarov Sergei Yu. 
Published: March 2014

Abstract
We examined data from observations of ER UMa during a period of $ \sim$ 20 years available in the AAVSO, VSNET, AFOEV, NSVS, and VSOLJ databases together with published light curves. The obtained $ O$$-$$ C$ diagram revealed a systematic change of the supercycle (time interval between two successive superoutbursts) ranging from 43.6 to 59.2 d. The time-scale of this cycle variation is from 300 to $ \sim$ 1900 d. The number of normal outbursts within the supercycles also varied between 4 and 6, although no strong correlation between this number and the supercycle length was found. We suggest that the appearance of negative superhumps is responsible for the observed variations in the number of normal outbursts. Our results generally confirm the expectations based on the thermal-tidal instability theory.