bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation of Molecular Cloud Properties across the Spiral Arm in M 51
Authors: Tosaki Tomoka , Hasegawa Takashi , Shioya Yasuhiro , Kuno Nario , Matsushita Satoki 
Published: March 2014

Abstract
We present the results of high-resolution ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) mapping observations with the NRO 45m telescope of the area toward the southern bright arm region of M 51, including the galactic center, in order to study the physical conditions of the molecular clouds in the arm and the interarm. The obtained map shows the central depression of the ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) emission, the circumnuclear ring (radius $ \sim$$ {10{}^{\mathrm {\prime \prime }}}$–$ {20{}^{\mathrm {\prime \prime }}}$), and the spiral arm structure. The arm-to-interarm ratio of the ${{13\atop} \mathrm{CO}}$ ($ J = 1 \hbox{--} 0$) integrated intensity is 2–4. We also have found a feature different from that found in the ${{12\atop} \mathrm{CO}}$ results. For example, the ${{13\atop} \mathrm{CO}}$ distribution shows a depression in part of the spiral arm. The $ {{12\atop} \mathrm{CO}}/{{13\atop} \mathrm{CO}}$ ratio spatially varies, and shows high values ($ \sim 20$) for the interarm and the central region, but low values ($ \sim 10$) for the arm. Their values indicate that there is a denser gas in the spiral arm than in the interarm.
The distribution of the ${{13\atop} \mathrm{CO}}$ shows a better correspondence with that of the $ \mathrm{H}\alpha$ emission than with the ${{12\atop} \mathrm{CO}}$ in the disk region, except for the central region. We found that the ${{13\atop} \mathrm{CO}}$ emission is located on the downstream side of the ${{12\atop} \mathrm{CO}}$ arm, namely there is an offset between the ${{12\atop} \mathrm{CO}}$ and the ${{13\atop} \mathrm{CO}}$ as well as the $ \mathrm{H}\alpha$ emission. This suggests that there is a time delay between the accumulation of gas caused by the density wave and dense gas formation, accordingly star formation. This time delay is estimated to be $ \sim 10^7 \,\mathrm{yr}$ based on the assumption of galactic rotation derived by the rotation curve and the pattern speed of the M 51 spiral pattern. It is similar to the growth timescale of a gravitational instability in the spiral arm of M 51, suggesting that the gravitational instability plays an important role for dense gas formation.
Observation of Kes 27: A Typical Mixed-Morphology SNR
Authors: Enoguchi Hideyuki , Tsunemi Hiroshi , Miyata Emi , Yoshita Kumi 
Published: March 2014

Abstract
We report here on the observation of Kes 27, a proto-typical mixed-morphology SNR, using ASCA. It clearly shows a filled-center structure in the X-ray region while a shell structure in the radio region. There are two radio bright regions: one is in the center, while the other is in the east rim. The X-ray intensity peak coincides well with the radio bright region at the center. The X-ray spectrum was well-fitted by a collisional ionization equilibrium model with the solar abundances. Taking into account the ionization parameter ($ \gt 10^{12} \,\mathrm{cm}^{-3} \,\mathrm{s}$$ \gt 10^{12} \,\mathrm{cm}^{-3} \,\mathrm{s}$) and the plasma density ($ 0.39^{+0.03}_{-0.02} \,\mathrm{cm}^{-3}$), we found that the age of the SNR is longer than $ 8 \times 10^{4} \,\mathrm{yr}$. The hardness ratio map indicates that the inner region shows a harder spectrum than that in the outer region, which does not come from the heavier interstellar absorption feature, but from the higher temperature. There is a temperature gradient from the innner region ($ 0.84 \pm 0.08 \,\mathrm{keV}$) toward the outer region ($ 0.59^{+0.04}_{-0.06} \,\mathrm{keV}$), indicating that the thermal conduction does not play an important role.
Optical Observations of XTE J1118 + 480 during the 2000 Outburst
Authors: Uemura Makoto , Kato Taichi , Matsumoto Katsura , Iwamatsu Hidetoshi , Ishioka Ryoko , Cook Lewis M. , Dmitrienko Elena , Šimon Vojtěch , Honkawa Masami , Oksanen Arto , Moilanen Marko , Novák Rudolf , Martin Brian , Lipkin Yiftah , Leibowitz Elia M. , Masi Gianluca , Sano Yasuo , Nogami Daisaku , Buczynski Denis , Yamaoka Hitoshi , Takamizawa Kesao , Haseda Katsumi 
Published: March 2014

Abstract
We report on photometric and spectroscopic observations of a possible halo black-hole X-ray nova, XTE J1118$ +$480 ($ =$ KV UMa) during outburst. Our photometric monitoring during the main outburst revealed that the optical maximum as well as the onset of the outburst precede those in the X-ray region. This indicates that the event was an “outside-in” type outburst and that its optical flux was dominated by viscous heating, itself, and not the effect of X-ray irradiation. Based on these results, we suggest an outburst scenario analogous to superoutbursts in SU UMa-type dwarf novae. This scenario predicts a superhump phenomenon, which we indeed detected throughout the outburst. We determined its period to be $ 0.170529\pm 0.000006 \,\mathrm{d}$, which is slightly longer than the orbital periods suggested from spectroscopic observations. We have furthermore revealed the first evidence of a continuous period decreasing in X-ray novae. The most prominent feature in our optical spectrum is a double-peak He II 4686Å emission line having an asymmetric profile with an outstanding blue side peak. Using a Doppler mapping method, we found that the He II emission originates from the accretion disk, which particularly concentrates on the hot spot. The time that the blue peak becomes strongest corresponds to a superhump peak. This implies that we see an elongated side of an eccentric disk at that time and, hence, it may cause an asymmetric emission profile. Substituting the observed fractional superhump excess for a theoretically expected relation between it and the mass ratio, we estimate that the black-hole mass is larger than $9.5 \,{{{M}_{\odot}}}$. XTE J1118$ +$480 thus has a large mass of a compact object compared with the typical black-hole X-ray novae.
On the Origin of Early Superhumps in WZ Sge-Type Stars
Authors: Kato Taichi 
Published: March 2014

Abstract
The origin of early superhumps, which are double-wave periodic modulations seen only during the earliest stage of a WZ Sge-type outburst, has not been well understood. Based on a recent discovery of two-armed arch-like patterns on Doppler tomograms in conjunction with early superhumps, we propose a new interpretation on the origin of early superhumps, following a new interpretation by Smak (2001, Acta Astron., 51, 295) and Ogilvie (2002, MNRAS, 330, 937) of the two-armed pattern seen in IP Peg. If we consider irradiation of the elevated surface of the accretion disk caused by vertical tidal deformation, we can consistently explain the observed features on Doppler tomograms and photometric waves at the same time. We interpret that a combination of low mass-ratios ($ q$) and low mass-transfer rates, necessary to give rise to these tidal effects, discriminate WZ Sge-type stars from other SU UMa-type dwarf novae. Based on recent fluid calculations, such an effect would be observable in higher $ q$ systems. We interpret that RZ Leo is an example of such objects.
Detection of Water Maser Flare in the Seyfert/LINER, NGC 6240
Authors: Nakai Naomasa , Sato Naoko , Yamauchi Aya 
Published: March 2014

Abstract
We report on a flare-up of water-vapor maser emission in a prototypical ultraluminous FIR galaxy with an AGN, NGC 6240. The flux density of the detected maser line was $ \approx 0.1 \,\mathrm{Jy}$ with $ \mathit{FWHM} \approx 5 \,\mathrm{km} \,\mathrm{s}^{-1}$, indicating an apparent isotropic luminosity of $\approx 100 \,{L}_{\odot}$ at a distance of 100 Mpc, which is typical for water megamasers. The maser line was redshifted by $ \approx 200 \,\mathrm{km} \,\mathrm{s}^{-1}$ relative to the systemic velocity of the galaxy, while no systemic-velocity feature was detected. The previous possible detection or observed upper limits were at a level lower than the flux density in the present paper, indicating that the water maser in NGC 6240 flared up by more than a factor of 5 in 2001.
Evolution of Hard X-Ray Radiation from Clusters of Galaxies: Bremsstrahlung or Inverse Compton Scattering?
Authors: Takizawa Motokazu 
Published: March 2014

Abstract
We have calculated the evolution of a non-thermal electron population from super-thermal (but weakly relativistic) to highly relativistic energy range in clusters of galaxies. We investigate the evolution of hard X-ray radiation due to both bremsstrahlung and inverse Compton scattering of the cosmic microwave background photons. The bremsstrahlung component is more significant than that of inverse Compton scattering when the momentum spectra of the electron sources are steeper than $\sim P_\mathrm{e}^{-3.0}$ and vice versa in the case of Coma, where $P_\mathrm{e}$ is the electron momentum. The resultant hard X-ray spectra are flatter when the bremsstrahlung component is dominant. When the spectral indices of the source term are in the intermediate range (from $-2.5$ to $-3.5$), too much extreme ultraviolet emission is produced. Inverse-Compton-dominant models can reproduce Coma cluster results with reasonable injection rates, which are possible in cluster mergers and/or ambient gas accretion.
Interstellar Gas Mass Functions: Fractality and Scale Dependence
Authors: Casuso Emilio , Beckman John 
Published: March 2014

Abstract
We present a theoretical model for the observed mass functions (MF’s) of interstellar clouds, and test it by comparison with interferometrically observed MF’s. We consider the time evolution of velocities using the stochastic differential Langevin equation for the objects (in fact gas clumps of sizes below 1 pc) under Brownian motion, with friction and magnetic field. We also study geometrical binding, and hence the implications of sizes of the regions in which the gas clouds move, and also of the departures from sphericity of the clouds themselves. The size of the global region in which the objects move under the influence of the general dynamics of the galaxy leads to a box-effect modelled as a Chandrasekhar barrier, which naturally leads to the superposition of Gaussian distributions over different ranges of displacement, and with progressively decreasing amplitude. This accounts for the general power law trend observed for the MF’s, as well as its accompanying peaked structure. These results fit well the observed distributions even in very low mass ranges, which show global power law characteristics (scale independence, fractality, departures from sphericity for individual clouds), accompanied by turnovers, for a wide range of masses, characteristics of Gaussians (scale dependence, a tendency for clouds to be spherical).
A Helical Magnetic Field in the Jet of 3C 273
Authors: Asada Keiichi , Inoue Makoto , Uchida Yutaka , Kameno Seiji , Fujisawa Kenta , Iguchi Satoru , Mutoh Mutsumi 
Published: March 2014

Abstract
Both in the Faraday Rotation Measure and the intrinsic polarization angle, new features are revealed to indicate a helical magnetic field operating along the jet of the bright active galactic nucleus 3C 273. The helical field has been suggested to be related to the formation and collimation of jets by magnetohydrodynamic models. The distribution of the rotation measure shows a systematic gradient with respect to the jet axis, which is expected by a helical magnetic field. In addition, the helical field can consistently explain two types in the direction of the projected magnetic field: parallel and perpendicular to the jet axis. Further, if the helical magnetic field is generated by winding up of an initial field by rotation of the accretion disk, we can uniquely determine the direction of the disk rotation, since the jet is approaching us.
Multi-Wavelength Variation Properties of γ-Ray-Loud Blazars
Authors: Fan Jun-Hui , Cheng K. S. , Zhang Li 
Published: March 2014

Abstract
Based on multi-waveband (radio, optical, and X-ray) observation data of 61 $\gamma$-ray-loud blazars (Cheng et al. 2000, ApJ, 537, 80) and $\gamma$-ray data by Hartman et al. (1999, AAA72.002.011) we have studied the variability properties using the variability index, $v = (F_{\mathrm{max}}-F_{\mathrm{min}}) / (F_{\mathrm{max}} + F_{\mathrm{min}})$, and the relations between the flux density and both the redshift and the variability index. The mainly results are as follows: 1) the average variability indexes are almost the same within the error-bar range for the radio, optical, X-ray, and $\gamma$-ray bands. 2) The variabilities in the optical, X-ray, and $\gamma$-ray bands are found to be correlated with the flux densities of the source, implying that the more variable is the source, the brighter it is.
Diffuse and Gravitationally Stable Molecular Gas in the Post-Starburst Galaxy NGC 5195
Authors: Kohno Kotaro , Tosaki Tomoka , Matsushita Satoki , Vila-VilarÓ Baltasar , Shibatsuka Toshihito , Kawabe Ryohei 
Published: March 2014

Abstract
The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesis CO($1-0$) observations of the post-starburst galaxy NGC 5195. CO($1-0$) and HCN($1-0$) observations of NGC 5195 using the Nobeyama 45 m telescope are also presented. High-resolution (${1\rlap {.}{}^{\mathrm {\prime \prime }}9} \times {1\rlap {.}{}^{\mathrm {\prime \prime }}8}$ or $86 \,\mathrm{pc} \times 81 \,\mathrm{pc}$ resolution at $D = 9.3 \,\mathrm{Mpc}$) NMA maps show a strong concentration of CO emission toward the central a few $\times 100 \,\mathrm{pc}$ region of NGC 5195, despite the fact that the current massive star formation is suppressed there. The face-on gas surface density, $\Sigma_\mathrm{gas}$, within the $r&lt;2{}^{\prime\prime}$ or 90 pc region reaches $3.7 \times 10^3 M_\odot$ pc$^{-2}$ if a Galactic $N_\mathrm{H_2}/I_\mathrm{CO}$ conversion factor is applied. The extent of the central CO peak is about $5{}^{\prime\prime}$, or 230 pc, and is elongated along the E-W direction with two-armed spiral-like structures, which are typical for barred disk galaxies. The HCN-to-CO integrated intensity ratio on the brightness temperature scale, $R_\mathrm{HCN/CO}$, is about 0.02 within the central $r &lt; 400$ pc region. This $R_\mathrm{HCN/CO}$ is smaller than those in starburst regions by a factor of $5 \hbox{--} 15$. These molecular-gas properties would explain why NGC 5195 is in a post-starburst phase; most of the dense molecular cores (i.e., the very sites of massive star formation) have been consumed away by a past starburst event, and therefore a burst of massive star formation can no longer last, although a large amount of low density gas still exists. We find a steep rise of the rotation velocity toward the center of NGC 5195. As a consequence, the critical gas surface density for a local gravitational instability of the gas disk becomes very high ($\Sigma_\mathrm{crit} \sim 6.9 \times 10^3 \,{{{M}_{\odot}}} \,\mathrm{pc}^{-2}$), suggesting that the molecular gas in the central region of NGC 5195 is gravitationally stable, in contrast to that of starburst galaxies. We propose that dense molecular gas can not be formed from remaining diffuse molecular gas because the molecular gas in the center of NGC 5195 is too stable to form dense cores via gravitational instabilities of diffuse molecular gas. The deduced very high threshold density seems to be due to a high mass concentration in NGC 5195. The known trends on the occurrence and luminosity of nuclear star formation in early-type galaxies can be understood naturally if the high threshold density is characteristic for early-type galaxies.
Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud
Authors: Itoh Yoichi , Tamura Motohide , Tokunaga Alan T. 
Published: March 2014

Abstract
We carried out near-infrared spectroscopic observations of 23 very low-luminosity young stellar object (YSO) candidates and 5 of their companions in Heiles Cloud 2, one of the densest parts of the Taurus molecular cloud. Twelve objects were confirmed to be YSOs by the $\mathrm{B}\gamma$ feature. The effective temperatures of the YSOs and of the companions are estimated from the 2.26-${\mu \mathrm {m}}$ feature, the 2.21-${\mu \mathrm {m}}$ feature, and the $\mathrm{H}_{2}\mathrm{O}$ band strengths. Detailed comparisons of our photometric and spectroscopic observations with evolutionary tracks on the HR diagram suggest some objects to be very low-mass YSOs.
Asymmetrical Distribution of Sunspot Groups in the Solar Hemispheres
Authors: Li Ke-Jun , Liu Xiao-Hua , Yun Hong-Sik , Xiong Song-Ying , Liang Hong-Fei , Zhao Hai-Zhuan , Zhan La-Sheng , Gu Xiao-Ma 
Published: March 2014

Abstract
In the present work, the north–south asymmetry of solar activity was examined by analyzing statistically the hemispheric distribution of annual numbers of sunspot groups, using the Royal Greenwich Observatory data set from the year 1874 through 2000. An interesting phenomenon is found that the solar activity of a cycle usually has the same beginning and end times, but different maximum amplitudes at different maximum times in the hemispheres. Some characteristics of the asymmetry of solar activity were investigated and explained. For solar cycle 23, a dominance of solar activity is predicted to occur in the southern hemisphere in several forthcoming years.
Effects of Relativistic Expansion on Late-Time Supernova Light Curves
Authors: Iwamoto Koichi 
Published: March 2014

Abstract
The effects of relativistic expansion on late-time supernova (SN) light curves (LCs) were investigated, and an analytic expression for a correction term to the (quasi-)exponential decay was obtained. It has been shown that the relativistic effects brighten the LC owing to (1) a delayed decay of radioactive nuclei (time-dilation) as well as to (2) Lorentz boosting of the photon energies. The leading correction term is quadratic in $\beta$, where $\beta$ is the maximum velocity of ejecta divided by the speed of light, and grows as a quadratic function of time. Thus, the relativistic effect is negligibly small at early times, but becomes of considerable size at late times. It was also shown that including the differential time-dilation effect is essential for an accurate LC prediction better than to first order in $\beta$. For ordinary SNe, the effect is too small to be detected. However, in SNe having a very large energy (hypernovae) or exploding in an aspherical geometry, radioactive ${{56\atop} \mathrm{Ni}}$ is likely to be boosted to higher velocities. We might then see an appreciable excess of the flux. The relative importance of the relativistic effects remain uncertain, depending on the abundances of various radioactive isotopes and other energy sources that may power the LC.
3-D Kinematics of Water Masers in the W 51A Region
Authors: Imai Hiroshi , Watanabe Teruhiko , Omodaka Toshihiro , Nishio Masanori , Kameya Osamu , Miyaji Takeshi , Nakajima Junichi 
Published: March 2014

Abstract
We report on proper-motion measurements of water masers in the massive-star forming region W 51A and analyses of the 3-D kinematics of the masers in three maser clusters of W 51A (W 51 North, Main, and South). In W 51 North, we found a clear expanding flow having an expansion velocity of $ \sim 70 \,\mathrm{km} \,\mathrm{s}^{-1}$, which indicates deceleration. The originating point of the flow coincides within $ {0\rlap {.}{}^{\mathrm {\prime \prime }}1}$ with a silicon-monoxide maser source near the H II region W 51d. In W 51 Main, no systematic motion was found over the whole velocity range ($- 58 \,\mathrm{km} \,\mathrm{s}^{-1} \leq V_{\mathrm{LSR}} &lt; 158 \,\mathrm{km} \,\mathrm{s}^{-1}$), although a stream motion was previously reported in a limited range of the Doppler velocity ($ 54 \,\mathrm{km} \,\mathrm{s}^{-1} \leq V_{\mathrm{LSR}} &lt; 68 \,\mathrm{km} \,\mathrm{s}^{-1}$). Multiple driving sources of outflows are thought to explain the kinematics of W 51 Main. In W 51 South, an expansion motion like a bipolar flow was marginally visible. Analyses based on diagonalization of the variance–covariance matrix of maser velocity vectors demonstrate that the maser kinematics in W 51 North and Main are significantly tri-axially asymmetric. We estimated the distance to W 51 North to be $ 6.1 \pm 1.3 \,\mathrm{kpc}$ based on a model-fitting method adopting a radially expanding flow.
VLBI Observations of Water Masers in the Circumstellar Envelope of IRC$ +$60169
Authors: Sudou Hiroshi , Omodaka Toshihiro , Imai Hiroshi , Sasao Tetsuo , Takaba Hiroshi , Nishio Masanori , Hasegawa Wataru , Nakajima Junichi 
Published: March 2014

Abstract
Water masers around an AGB star, IRC$ +$60169, were observed at four epochs using the Japanese VLBI networks. The distribution of the maser features is limited in a thick-shell region, which has inner and outer expansion velocities of $ 7 \,\mathrm{km} \,\mathrm{s}^{-1}$ and $ 14 \,\mathrm{km} \,\mathrm{s}^{-1}$ at radii of 25 mas and 120 mas, respectively. The distribution of the red-shifted features exhibits a ring-like structure, the diameter of which is 30 mas, and corresponds to the inner radius of the maser shell. This implies that dense gas around the star obscures red-shifted emission. Although a position–radial velocity diagram for the maser features is consistent with a spherical shell model, the relative proper motions do not indicate an expansion motion of the shell. A remarkable property has been found that is a possible periodic change of the alignment pattern of water maser spots.
Spectroscopic Studies of the Solar Corona II. Properties of Green and Red Emission Lines in Open and Closed Coronal Structures
Authors: Singh Jagdev , Sakurai Takashi , Ichimoto Kiyoshi , Suematsu Yoshinori , Takeda Aki 
Published: March 2014

Abstract
We obtained profiles of the green (Fe XIV 5303 Å) and red (Fe X 6374 Å) emission lines simultaneously on 1998 July 18–19 for about 4 hours with a cadence of 10 minutes, covering an area of about $ 200'' \times 500''$ in the solar corona. The line width (FWHM), intensity, and Doppler shift for both lines were computed using Gaussian fits to the observed line profiles. We then studied any systematic differences in these parameters between closed and open field structures, and their time variations. The derived line widths indicate that the FWHM of the red line increases with height above the limb at a rate of $ 0.5 \hbox{--} 2.6 \,\mathrm{m}$ Å$ \,\mathrm{arcsec}^{-1}$ and the green-line width decreases with height at a rate of $ 1.2 \hbox{--} 3.4 \,\mathrm{m}$ Å$ \,\mathrm{arcsec}^{-1}$. The difference in the time-averaged values of the widths of the green line in open and closed coronal structures at a given height above the limb is small, whereas the width of the red line in open structures is substantially larger than that in the closed loop-like coronal structures.
Spectroscopic Studies of the Solar Corona III. Density Diagnostics Using the Infrared Lines of Fe xiii
Authors: Singh Jagdev , Sakurai Takashi , Ichimoto Kiyoshi , Takeda Aki 
Published: March 2014

Abstract
We have obtained spectrographic observations of several coronal regions in three emission lines (6374 Å [Fe x ], 10747 Å [Fe xiii], and 10798 Å [Fe xiii]) simultaneously. The 25-cm coronagraph at Norikura Observatory and two large-format CCD cameras were used. The peak intensity, velocity, and line-width values were derived from Gaussian fits to the observed line profile at each location of the observed region. The ratio of the intensities of the 10747 Å and 10798 Å emission lines in the individual coronal structures range between 1.0 and 2.5 at $ 10''$ above the limb, which corresponds to a density range of $ 9.8 \times 10^9 \hbox{--} 2.4 \times 10^8 \,\mathrm{cm}^{-3}$. The scale-height temperature values, derived from the variations of the intensity ratio with height above the limb for all individual coronal structures, range between $ 0.6 \times 10^ 6 \,\mathrm{K}$ and $ 8.3 \times 10^6 \,\mathrm{K}$ with a most frequent value around $ 1.8 \times 10^6 \,\mathrm{K}$. The large values of the scale-height temperature for 70% of the structures indicate that these structures may not be in hydrostatic equilibrium nor be isothermal in nature.