bluuebunny/crossref_metadata_2025 huggingface dataset:
The Most Luminous Protostars in Molecular Clouds: A Hint to Understand the Stellar Initial Mass Function
Authors: Dobashi Kazuhito , Yonekura Yoshinori , Matsumoto Tomoaki , Momose Munetake , Sato Fumio , Bernard Jean-Philippe , Ogawa Hideo
Published: March 2014

The maximum luminosity of protostars forming in molecular clouds has been investigated as a function of the parent cloud mass on the basis of a rich cloud sample searched for in the literature. In total, we gathered 499 molecular clouds among the published data, out of which 243 clouds were found to be associated with protostellar candidates selected from the IRAS point-source catalog. A diagram of the maximum stellar luminosity in each cloud and the parent cloud mass shows that the protostars in the clouds associated with H II regions are apparently more luminous than those in clouds away from H II regions over the entire cloud mass range investigated ($ 1 \lt M_\mathrm{CL}/M_{{\odot }} \lt 10^6$). In addition, we found that there are well-defined upper and lower limits in the maximum stellar luminosity distribution with the lower limit having a steeper dependence on the cloud mass ($ L_\mathrm{MAX} \propto M_\mathrm{CL}^{1.5}$) than the upper one ($ L_\mathrm{MAX}\propto M_\mathrm{CL}^{0.8}$). All of these features can be naturally accounted for if we assume that the luminosity function of protostars is controlled by the cloud mass and the external pressure imposed on the cloud surface. We introduce a simple model for the stellar luminosity function as a function of these quantities, which should be closely related to the stellar initial mass function.
The Ortho-to-Para Ratio and the Chemical Properties of C3 H2 in Dark Cloud Cores
Authors: Takakuwa Shigehisa , Kawaguchi Kentarou , Mikami Hitomi , Saito Masao
Published: March 2014

We have observed cyclic C$_3$H$_2$ ($J_{K_{a}K_{c}}= 2_{12}$–$1_{01}, 2_{02}$–$1_{11}, 3_{12}$–$3_{03}$) lines at the 3 mm wavelength region toward the starless TMC-1C cloud and the protostellar core of L 1527 with the 45 m telescope at Nobeyama Radio Observatory. In both clouds, the $2_{12}$–$1_{01}$ and $2_{02}$–$1_{11}$ lines are strongly detected, while the $3_{12}$–$3_{03}$ line is only detected toward the center of the protostellar core L 1527. From our statistical equilibrium analyses of the ortho-C$_3$H$_2$ ($2_{12}$–$1_{01}$) and the para-C$_3$H$_2$ ($2_{02}$–$1_{11}$) lines, the ortho-to-para ratios of C$_3$H$_2$ are determined to be $2.4\pm0.1$ and $2.5\pm0.5$ in TMC-1C and L 1527, respectively. These values are lower than the statistical value of 3, although the error of the ratio in L 1527 is large. Since thermal equilibrium with a dust temperature of 10 K still gives a ratio of 3 in c-C$_3$H$_2$, this result should suggest the lower ortho-to-para ratio of the precursor molecule, c-C$_3$H$_{3}^{+}$, which is thought to be mainly produced by C$_3$H$^{+} +$ H$_2$. Thus, we conclude that the lower ortho-to-para ratio of c-C$_3$H$_2$ is due to a lower ortho-to-para ratio of H$_{2}$ than the statistical value.
The Gas-Drag Effect on the Orbital Instability of a Protoplanet System
Authors: Iwasaki Kazunori , Tanaka Hidekazu , Nakazawa Kiyoshi , Emori Hiroyuki
Published: March 2014

We have investigated numerically the orbital instability of a protoplanet system while taking account of the gas-drag force due to the solar nebula. In the present work, we considered an equally spaced five-protoplanet (with the same mass of $1 \times 10^{-7} {{{M}_{\odot}}}$) system, in which their initial orbits are coplanar and circular, and assumed that the gas-drag force is proportional to the square of the relative velocity between the gas and a protoplanet. We first re-examined and confirmed that, under a gas-free condition, $\log_{10} T_{\mathrm{inst}}$ can be approximately written as a linear function of the initial orbital separation distance, $\Delta \tilde{a}_{0}$, where $T_{\mathrm{inst}}$ is the time of the orbital instability (i.e., the time of the first orbital crossing between any two protoplanets). Next, we investigated the instability time under the gas-drag effect, $T_{\mathrm{inst}}^{\mathrm{gas}}$, and found that $T_{\mathrm{inst}}^{\mathrm{gas}}$ suddenly becomes large compared with $T_{\mathrm{inst}}$, when ${\Delta \tilde{a}}_{0}$ is larger than a certain critical separation distance, ${({\Delta \tilde{a}}_{0})}_{\mathrm{crit}}$. Furthermore, we showed that ${({\Delta \tilde{a}}_{0})}_{\mathrm{crit}}$ can be described semi-analytically as a function of the gaseous density. From a function extrapolated with a density in the minimum mass nebula model, we estimated ${({\Delta \tilde{a}}_{0})}_{\mathrm{crit}}$ in the nebula as being about 10 Hill radius at 1 AU.
OHS: OH-Airglow Suppressor for the Subaru Telescope
Authors: Iwamuro Fumihide , Motohara Kentaro , Maihara Toshinori , Hata Ryuji , Harashima Takashi
Published: March 2014

This paper describes an OH-airglow Suppressor (OHS) for the infrared Nasmyth focus of the Subaru telescope. OHS has the capability of eliminating 224 airglow-lines in the J- and H-bands, which are major sources of background radiation at near-infrared wavelengths up to 2 ${\mu \mathrm {m}}$. Specifically, it is a pre-optics system installed between the telescope and an infrared camera/spectrograph (CISCO). The suppressor reduces sky background emissions to 1/25 and its throughput is 40%. As a result, the S/N gain achieved with OHS is more than 1 mag compared to the typical spectroscopic approach. The limiting magnitude measured during a test observing run was found to be H = 21.1 mag ($\lambda/\Delta\lambda = 210, S/N = 5$) in the standard 4000 s exposure sequence.
ASCA Deep Survey in the Lockman Hole Field
Authors: Ishisaki Yoshitaka , Ueda Yoshihiro , Yamashita Akiko , Ohashi Takaya , Lehmann Ingo , Hasinger Günther
Published: March 2014

We present the results of deep observations of the Lockman Hole field with the ASCA SIS, covering $926\,\mathrm{arcmin}^2$ in the 1–7 keV energy range, with a sensitivity 3–5 times deeper than the previous ASCA larger area surveys. Utilizing the results of the ROSAT Ultra Deep survey, we have detected 32, 25, and 15 sources in the 1–7, 1–2, and 2–7 keV bands, and only 4, 4, and 1 sources remain unidentified, respectively. The average hardness of the sources detected in the 1–7 keV band with fluxes of between $10^{-14}$ and $10^{-13}\,\mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ corresponds to a photon index of $1.65\pm 0.10$. Type-2 AGNs show significantly harder spectra than type-1s, which can be explained by absorption column densities of $N_{\mathrm{H}} \simeq 10^{22-23}\,\mathrm{cm}^{-2}$ at the source redshifts. Fifteen sources are detected in the hard-band (2–7 keV), consisting of six type-1 AGNs, six type-2 AGNs, one star, one cluster of galaxies, and one unidentified source. Type-2 AGNs make up a major part of hard X-ray populations in the 2–7 keV band at a flux level of $3\times 10^{-14}\,\mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$ (2–7 keV). The redshift distributions of type-1 and type-2 AGNs suggest a lack of high luminosity (optically-defined) type-2 AGNs with intrinsic $N_{\mathrm{H}} \lt 10^{23}\,\mathrm{cm}^{-2}$, in the redshift range $z\simeq 1$–$2$ and/or with intrinsic luminosities larger than $3\times 10^{44}\,\mathrm{erg}\,\mathrm{s}^{-1}$ (2–10 keV at source frame).
Water Maser Survey in the Andromeda Galaxy
Authors: Imai Hiroshi , Ishihara Yuko , Kameya Osamu , Nakai Naomasa
Published: March 2014

We report on a water maser survey in the Andromeda galaxy (M 31). The surveyed H II regions with $^{12}$CO clouds are expected to be regions of ongoing star formation with water maser activity. Nevertheless, we could not detect any water maser emission with an upper limit of around 0.35 Jy or $4.9\times 10^{-3}\,L_{ {\odot }}$ in isotropic luminosity. These results indicate a low activity of the present star formation in M 31.
Photometric Observation of a New in-the-Gap SU UMa-Type Dwarf Nova V 725 Aquilae during the 1999 Superoutburst
Authors: Uemura Makoto , Kato Taichi , Pavlenko Elena , Baklanov Alex , Pietz Jochen
Published: March 2014

We report our photometric observation of the 1999 September outburst of a dwarf nova, V725 Aql. Our detection of superhumps established that it belongs to SUUMa stars. By performing a period analysis of the superhumps, we revealed a long superhump period of $0.09909 \pm 0.00015\,\mathrm{d}$, which implies that its orbital period is well over 2 hr. The outburst light curve is typical for a superoutburst, though, after the superoutburst, the object experienced a re-brightening which can be seen in some SUUMa stars with short orbital periods. The 1999 superoutburst occurred about 1650 d after the last possible superoutburst in 1995. This indicates the supercycle of V725 Aql to be long, over 1000 d. This long supercycle implies a low mass-transfer rate of this star.
ASCA Observations of the Temperature Structure and Metal Distribution in the Perseus Cluster of Galaxies
Authors: Ezawa Hajime , Yamasaki Noriko Y. , Ohashi Takaya , Fukazawa Yasushi , Hirayama Masaharu , Honda Hirohiko , Kamae Tuneyoshi , Kikuchi Ken’ichi , Shibata Ryo
Published: March 2014

Large-scale distributions of hot-gas temperature and Fe abundance in the Perseus cluster have been studied with multi-pointing observations by the GIS instrument onboard ASCA. Within a radius of $ {20{}^{\mathrm {\prime }}}$ from the cluster center, the energy spectra requires two temperature components, in which the cool component indicates $ kT \sim 2\;\mathrm{keV}$ and the hot-component temperature shows a significant decline from about 8 keV to 6 keV toward the center. In the outer region of the cluster, the temperature shows a fluctuation with an amplitude of about 2 keV, which suggest that a western region at $ \sim {16{}^{\mathrm {\prime }}}$ from the cluster center is relatively hotter. As for the Fe abundance, a significant decline with radius is detected from 0.44 solar at the center to $ \sim 0.1$ solar at a $ {50{}^{\mathrm {\prime }}}$ offset region. If the observed Fe-K line intensity within $ {4{}^{\mathrm {\prime }}}$ from the center is suppressed by a factor of 2 due to the resonance scattering effect, the corrected Fe mass density follows the galaxy distribution. Finally, our results do not support the large-scale velocity gradients previously reported from the same GIS data.
Seyfert-Type Dependences of Narrow Emission-Line Ratios and Physical Properties of High-Ionization Nuclear Emission-Line Regions in Seyfert Galaxies
Authors: Nagao Tohru , Murayama Takashi , Taniguchi Yoshiaki
Published: March 2014

In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission lines, [Fe VII]$ \lambda6087$, [Fe X]$ \lambda6374$, and [Ne V]$ \lambda3426$, tend to be stronger in Seyfert 1 galaxies than in Seyfert 2 galaxies. In addition to these lines, [O III]$ \lambda4363$ and [Ne III]$ \lambda3869$, whose ionization potentials are not high ($ < 100 \,\mathrm{eV}$), but whose critical densities are significantly high ($ \gtrsim 10^7 \,\mathrm{cm}^{-3}$), also exhibit the same tendency. On the other hand, the emission-line flux ratios among low-ionization emission lines do not show such a tendency. We point out that the most plausible interpretation of these results is that the high-ionization emission lines arise mainly from highly-ionized, dense gas clouds, which are located very close to nuclei, and thus can be hidden by dusty tori. To examine the physical properties of these highly-ionized dense gas clouds, photoionization model calculations were performed. As a result, we find that the hydrogen density and the ionization parameter of these highly-ionized dense gas clouds are constrained to be $ n_\mathrm{H}> 10^6 \,\mathrm{cm}^{-3}$ and $ U > 10^{-2}$, respectively. These lower limits are almost independent both from the metallicity of gas clouds and from the spectral energy distribution of the nuclear ionizing radiation.
Estimation of Central Black Hole Masses in Low-Luminosity Active Galactic Nuclei
Authors: Awaki Hisamitsu , Terashima Yuichi , Hayashida Kiyoshi , Sakano Masaaki
Published: March 2014

We analyzed six low-luminosity active galactic nuclei (hereafter LLAGNs), which consist of two bright LINERs (low-ionization nuclear emission line region) with broad H$ \alpha$, and of four bright low-luminosity Seyferts observed by the X-ray satellite ASCA. We examined the time variabilities of these targets, and found that most targets show no significant time variabilities, although these galaxies belong to LLAGNs. By applying Fourier analysis to their light curves in the 2–10keV band, we obtained the lower limits of their time variability scales, which correspond to their central black hole masses greater than several times $10^{6}\,{{{M}_{\odot}}}$. Our result suggests that these LLAGNs are harbors of super-massive black holes, but the emitting powers are only $ < 1 \%$ of the Eddington luminosities of the central engines in the LLAGNs due to their small accretion rates. Since a black hole would grow by mass accretion, it is hard to create such a super-massive black hole under a small accretion rate. Therefore, the mass-accretion rates in the past must have been larger than those at present, and the galaxies have probably been as luminous as QSOs. This will be a hint to find out the cause of the lack of QSOs in the local universe.
An X-Ray Emitting Supernova Remnant Candidate, M 33 X-4
Authors: Okada Yuu , Takahashi Hiromitsu , Makishima Kazuo
Published: March 2014

Based on ASCA observations of the Local-Group spiral galaxy M 33, a report is made on the X-ray properties of luminous X-ray source called X-4, which is located in a giant H ii region in M 33. The 0.8-8.0keV spectrum of X-4 is described by a two-component model, consisting of a thin thermal plasma emission with a temperature of $ \sim 1.0 \,\mathrm{keV}$, and a power law emission with a photon index of $ \sim 2.0$. The two spectral components cross over at $ \sim 3.0 \,\mathrm{keV}$. These spectral properties are similar to those of a young supernova remnant (SNR), except that the 0.8-8.0keV luminosity of M 33 X-4, $ \sim 1.0 \times 10^{38} \,\mathrm{erg} \,\mathrm{s}^{-1}$, is considerably higher than those of the SNRs in the Milky Way. There is also evidence of excess absorption, or an over-abundance of $ \alpha$-elements relative to iron. If this source is an SNR, the hard component is thought to be synchrotron radiation from high-energy particles, produced either by shock acceleration, like in SN 1006, or by a central neutron star, like in the Crab Nebula.
CO Survey of Nearby Spiral Galaxies with the Nobeyama 45-m Telescope: I. The Data
Authors: Nishiyama Kohta , Nakai Naomasa
Published: March 2014

We mapped the 12CO($J = 1 -0$) emission along the major and minor axes of disks or bars of 25 nearby galaxies using the Nobeyama 45-m telescope with a spatial resolution of $0.01$–$0.12 D_{25}$ ($D_{25}$: de Vaucouleurs’ diameter), and detected the CO emission at 8–42 positions along each axis. The galaxy sample includes morphological type Sab and Scd as well as barred and nonbarred. These data are useful to statistically study the internal distribution and dynamics of molecular gas in galaxies and to deduce common characteristic properties. In this paper, we describe the sample and observations, present all spectra and measured line parameters, and examine the relations between the global molecular gas mass and the Hubble type, the total mass of the galaxies, and the star-formation rate.
CO Survey of Nearby Spiral Galaxies with the Nobeyama 45-m Telescope: II. Distribution and Dynamics of Molecular Gas
Authors: Nishiyama Kohta , Nakai Naomasa , Kuno Nario
Published: March 2014

We have studied the distribution and dynamics of molecular gas in galaxies by observing CO emission mainly along the major and minor axes of 28 nearby spiral galaxies with the 45-m telescope of the Nobeyama Radio Observatory. The observations showed that the surface density of molecular gas indicates an exponential distribution in the region of the flat (differential) rotation curve for all spiral galaxies. This could be because the radial distribution is determined by gas inflow due to the viscosity of molecular clouds. The surface density of molecular gas in barred galaxies also shows a characteristic distribution in the region of the bar, suggesting gas inflow along the bar by the bar potential and perpendicular to the bar by viscosity. Such a transfer of molecular gas increases the gas density in the central region, probably causing the evolution of the rotation curve, which is determined by the mass distribution, on the time scale of the galaxy age. We compared the radial distribution of the surface density of H I with that of $\mathrm{H}_{2}$, and found same scale length of the exponential distribution in the Virgo galaxies and a much larger scale length in field galaxies for H I. This could be due to a difference in the viscosity coefficient of the H I gas.
A Hyperenergetic CO Shell in the Galactic Center Molecular Cloud Complex
Authors: Oka Tomoharu , Hasegawa Tetsuo , Sato Fumio , Tsuboi Masato , Miyazaki Atsushi
Published: March 2014

We report on the detection of a high-velocity feature, CO 1.27$+$0.01, in the Galactic-center molecular-cloud complex. In our 12CO images taken with the NRO 45 m telescope, CO 1.27$+$0.01 appears as the second prominent high-velocity feature, next to CO 0.02–0.02, having a velocity width of $\Delta V \simeq 100 \,\mathrm{km} \,\mathrm{s}^{-1}$ and a size of $9 \,\mathrm{pc} \times 12 \,\mathrm{pc}$. It seems to consist of two expanding shells with sizes of $\sim 10 \,\mathrm{pc}$. The major shell has a kinetic energy of about an order of magnitude larger than the gravitational energy, indicating that the shell is apparently gravitationally unbound. We propose that CO 1.27$+$0.01 may have been accelerated by a series of supernova explosions which occurred within the last $\sim 6 \times 10^4 \,\mathrm{yr}$. No association of a nonthermal radio continuum source suggests a strong magnetic field ($B \gtrsim 0.4 \,\mathrm{mG}$) in the vicinity of CO 1.27$+$0.01.
Possible Kreutz Sungrazing Comets Found in Historical Records
Authors: Hasegawa Ichiro , Nakano Syuichi
Published: March 2014

In historical records, twenty four candidates of possible Kreutz sungrazing comets have been found, and their times of perihelion passage estimated. Translated original records of comets with presumed ephemerides are given. Some uncertain candidates are also presented. Although already suggested by Marsden (1967, Astron. Jahresber. 67.9133), our calculations on the motions of comets 1882 R1 and 1965 S1 confirm that the progenitor of these comets is a comet that appeared in 1106; some trials on the linkage of sungrazing comets are discussed.
Detection of Eight Molecular Supershells in the Southern Milky Way with NANTEN
Authors: Matsunaga Ken’ichi , Mizuno Norikazu , Moriguchi Yoshiaki , Onishi Toshikazu , Mizuno Akira , Fukui Yasuo
Published: March 2014

We carried out a new CO survey for molecular supershells in the southern Milky Way with NANTEN. We covered an area of $300^{\circ} \lt l \lt 350^{\circ}$ and $-9^{\circ} \lt b \lt 9^{\circ}$ at $4^{\prime}$ or $8^{\prime}$ grid spacings with a 2.$^\prime$6 beamsize. In addition to the disk component at $\vert b\vert \lt 2^{\circ}$, we found numerous filamentary or arc-like CO distributions by inspecting the velocity channel maps. As a result, we identified 8 supershell candidates, 3 of which are associated with CO holes in the galactic disk. Six of the supershells had not been identified by the previous studies, while 2 of them were known from H i and low-resolution CO surveys. The size of the supershells ranges from 100 pc to 450 pc and the average is 230 pc; their age ranges from $2.2 \times 10^6 \;\mathrm{yr}$ to $1.1 \times 10^7 \,\mathrm{yr}$. We note that two of the supershells are also associated with observable indications of supershells at other wavelengths, including H i, far-infrared, soft X-ray, and SNRs. The implications of these findings are discussed in terms of the impact of supershells on star formation in the Galaxy.
A 12CO $J = 1 \hbox{--} 0$) Survey of Molecular Clouds toward the Vela Supernova Remnant with NANTEN
Authors: Moriguchi Yoshiaki , Yamaguchi Nobuyuki , Onishi Toshikazu , Mizuno Akira , Fukui Yasuo
Published: March 2014

The molecular distribution toward the whole extent of the Vela SNR has been obtained at a linear resolution of 0.15 pc in 12CO ($J = 1 \hbox{--} 0$) emission with the NANTEN telescope. The CO distribution is generally anti-correlated with the SNR. The X-ray distribution has a sharp boundary toward the CO clouds, especially in the east, suggesting an interaction between them. There is only weak CO emission in the west, and the X-ray emission extends smoothly toward this direction. This indicates that the absence of dense gas probably allowed hot gas to escape freely. The CO clouds are highly filamentary, exhibiting a spatial correlation with regions of optical shocked features on a large scale. In the north of the SNR, enhanced X-ray emission is found toward network-like optical filaments. We suggest that this enhancement is due to the evaporation of molecular gas by shock heating caused by the interaction between the blast wave and the molecular gas. Comparisons with a few simple theoretical models of SNR evolution and expansion indicate that the clouds are mostly pre-existent, are being accelerated, and are evaporating now.
12CO Molecular Cloud Survey and Global Star Formation in Lupus
Authors: Tachihara Kengo , Toyoda Shuichiro , Onishi Toshikazu , Mizuno Akira , Fukui Yasuo , Neuhäuser Ralph
Published: March 2014

The Lupus star-forming region has been surveyed for molecular clouds in 12CO with the NANTEN radio telescope, and a cloud mass of $1.7 \times 10^{4} \,{{{M}_{\odot}}}$ has been revealed. We were able to detect 105 molecular clouds, most of which are relatively small and of low mass. The members of the Sco OB 2 association and the X-ray detected pre-main-sequence stars (PMSs) are distributed all around this region. The OB stars and the molecular clouds show exclusive distributions. Large fractions of the PMSs are located away from the molecular clouds, and are thus isolated. The origin of the isolated PMSs is discussed. About 40% of the PMSs have candidates of their parent clouds less massive than 20${M}_{\odot}$ within 4 pc, which suggests in-situ star formation in the small clouds and their rapid dissipation. The separations from the PMSs to the clouds are typically larger than those in the Chamaeleon region, probably because of coexisting OB stars. From the cloud structures and the distributions of the OB stars, PMSs, and H i expanding shell, it is suggested that the molecular clouds have been effectively dissipated by the OB stars and a shock wave, which may also have triggered star formation in Lupus and the $\rho$ Oph clouds.
Study of L 688/L 694/L 700: a Complex of Dark Clouds in Aquila
Authors: Kawamura Akiko , Kun Maria , Onishi Toshikazu , Vavrek Roland , Domsa István , Mizuno Akira , Fukui Yasuo
Published: March 2014

We present the results of optical and radio molecular observations of the small dark clouds L 688, L 694, and L 700 (CB 200). Based on star counts, we found a distance of $230 \pm 30\,\mathrm{pc}$ for the clouds. We present extinction maps of the clouds based on the USNO Catalog data. Our objective prism search for candidate pre-main-sequence stars resulted in the detection of an $\mathrm{H}\alpha$ emission star in the cloud area. We observed the clouds in the 12CO ($1\hbox{-}0$), and $\mathrm{C}{{18\atop} \mathrm{O}}$ ($1\hbox{-}0)$ lines. A ring-shaped cloud of $\sim 430\,{{{M}_{\odot}}}$ was detected from the 12CO observation. Five 13CO cores were identified. Three $\mathrm{C}{{18\atop} \mathrm{O}}$ cores with $N(\mathrm{H}_{2}) \sim (5.3\hbox{-}7.6) \times 10^{21}\mathrm{cm}^{-2}$ reside in two of the 13CO cores in the northern part of the cloud. The density gradient seen in optical, infrared and radio, and also the positions of the star-formation sites may suggest the possibility of shock compression due to some stars or SNRs near the galactic plane.
On the Mass Spectrum of Giant Molecular Clouds in the Large Magellanic Cloud
Authors: Fukui Yasuo , Mizuno Norikazu , Yamaguchi Reiko , Mizuno Akira , Onishi Toshikazu
Published: March 2014

Based on a new sensitive survey of the giant molecular clouds (GMCs) in the Large Magellanic Cloud, we derived the mass spectrum for them. In the mass range from $\sim8\times10^4\,{{{M}_{\odot}}}$ to $3\times10^6\,{{{M}_{\odot}}}$, a power law with an index value of $-1.9\pm0.1$ shows the best fit to the data. This is consistent with numerical simulations that explain both the H i and CO clumpy distributions by Wada et al. (2000; ApJ, 540, 797), but is significantly steeper than that of the GMCs in the Galaxy. This may be consistent with the drastic dissipation of the GMCs in the LMC due to higher UV radiation fields than in the Galaxy.
Average Curves of Emissivity of the Highest Pulses in Long and Short Gamma-Ray Bursts
Authors: Liang En-Wei , Xie Guang-Zhong , Su Cheng-Yue
Published: March 2014

The average curves of emissivity (ACEs) of the highest pulses in long and short groups of gamma-ray bursts(GRBs) observed by BATSE on board CGRO have been studied by an alignment method and a wavelet package de-noising technique. A developed pulse-finding has been applied to identify the highest pulses from the profiles of GRBs. A sample including 116 long GRBs and 95 short GRBs was selected. The results show that the ACEs of the pulses in the short group are shorter and narrower than that in the long group. The ACEs of pulses in two groups have a significant difference, which was measured by the K–S test. Compared to the ACEs, the normalized ACEs of the pulses in the two groups seem to be similar. We present a brief discussion of our results. Based on our results and the discussion, we conclude that two groups of bursts may be generated from different sizes of emission regions. These sources likely have an intrinsic difference. However, the emission mechanisms are the same. These results support the most accepted taxonomy of GRBs, and present an interpretation of why two groups of bursts have a notable difference in the burst–s duration, but other observed properties have no distinguishable difference.
Short-Period Noncontact Close Binary Systems. VI. V392 Orionis
Authors: Narusawa Shin-ya , Yamasaki Atsuma , Fukata Mitsuo , Takeda Masao , Nakamura Yasuhisa , Okazaki Akira
Published: March 2014

Photometric and spectroscopic observations in the optical region of the short-period eclipsing binary system V392 Ori (A5 V, $P = 0.6593 \,\mathrm{d}$) were performed and light and radial velocity curves were obtained. The light curves taken at various times are slightly different from one another. Analyses of the light and radial velocity curves yielded photometric and spectroscopic elements of the system. The derived mass function is quite small, $f(M) = 0.0108 \,{{{M}_{\odot}}}$. The masses of the primary and secondary components were found to be 1.2${M}_{\odot}$ and 0.3${M}_{\odot}$, respectively, and the radii are 1.7${R}_{\odot}$ and 0.9${R}_{\odot}$. V392 Ori was found to belong to a group of low-mass binary systems. Due to the semidetached nature of the system, the loss of mass/angular momentum from the system may occasionally occur, inducing a probable effect on the light curves of the system. We compare the system with other low-mass binary systems and discuss the evolutionary status of the system.
A Multi-Band Photometric Study of Tidal Debris in a Compact Group of Galaxies: Seyfert’s Sextet
Authors: Nishiura Shingo , Shioya Yasuhiro , Murayama Takashi , Sato Yasunori , Nagao Tohru , Taniguchi Yoshiaki , Sanders David B.
Published: March 2014

In order to investigate the properties of the prominent tidal debris feature extending to the northeast of a compact group of galaxies, Seyfert’s Sextet, we analyzed multi-band ($U$, $B$, $V$, $VR$, $R$, $I$, $J$, $H$, and $K^{\prime }$) photometric imaging data and obtained the following results: 1) The radial surface brightness distribution of this tidal debris in Seyfert’s Sextet (TDSS) in each band appears to be well approximated by an exponential profile. 2) The observed $B-V$ color of TDSS is similar to those of dwarf elliptical galaxies in nearby clusters. 3) Comparing the spectral energy distribution (SED) of TDSS with theoretical photometric evolution models and with the SED of the stars in the outer part of HCG 79b, we find that its SED is comparable to that of a $\sim 10 \,\mathrm{Gyr}$-old stellar population with solar metallicity, similar to the stellar population in the outer part of HCG 79b. This suggests that TDSS consists of stars that may have been liberated from HCG 79b by strong galaxy interactions, not a pre-existing dwarf galaxy as previously thought.
Observations of SiO Maser Sources within a Few Parsec from the Galactic Center
Authors: Deguchi Shuji , Fujii Takahiro , Miyoshi Makoto , Nakashima Jun-ichi
Published: March 2014

Mapping and monitoring observations of SiO maser sources near the Galactic center were made with the Nobeyama 45-m telescope at 43 GHz. Rectangular mapping an area of approximately $200^{\prime\prime} \times 100^{\prime\prime}$ in a ${30{}^{\mathrm {\prime \prime }}}$ grid, and triangular mapping in a ${20{}^{\mathrm {\prime \prime }}}$ grid toward the Galactic center, resulted in 15 detections of SiO sources; the positions of the sources were obtained with errors of 5 – ${10{}^{\mathrm {\prime \prime }}}$ , except for a few weak sources. Three-year monitoring observations found that the component at $V_\mathrm{lsr} =-27 \,\mathrm{km} \,\mathrm{s}^{-1}$ of IRS 10 EE flared to about 1.5 Jy during 2000 March–May, which was a factor of more than 5 brighter than its normal intensity. Using the radial velocities and positions of the SiO sources, we identified 5 which are counterparts of previously observed OH 1612 MHz sources. The other 10 SiO sources have no OH counterparts, but two were previously detected with VLA, and four are located close to the positions of large-amplitude variables observed at near-infrared wavelengths. A least-squares fit to a plot of velocities versus Galactic longitudes gives a rather high speed for the rotation of the star cluster around the Galactic center. The observed radial-velocity dispersion is roughly consistent with a value obtained before. It was found that all of the SiO sources with OH 1612 MHz counterparts have periods of light variation longer than 450 days, while SiO sources without OH masers often have periods shorter than 450 days. This fact suggests that lower-mass AGB stars are more often detected in SiO masers than in the OH 1612 MHz line.
Peak Frequency of the Synchrotron Emission and Classificatory Criteria of BL Lacertae Objects
Authors: Dong Yun-Ming , Mei Dong-Cheng , Liang En-Wei
Published: March 2014

In this short paper, we quantitatively consider how the peak frequency of the synchrotron emission can be used to distinguish RBLs and XBLs. A sample of RBLs and XBLs presented by Sambruna et al. (1996, AAA065.159.120) was employed and the peak frequency, $ \nu_{\mathrm{p}}$, of the synchrotron emission of each source was calculated by considering the proper physical origin of the X-ray emission for different classes of BL Lac objects. A plot of $ \alpha_{\mathrm{rx}} \hbox{--} \log \nu_{\mathrm{p}}$ can be divided into four different regions by lines of $ \alpha_{\mathrm{rx}} = 0.75$ and $ \log \nu_{\mathrm{p}} = 14.7 \pm 0.4$. All RBL-like objects, defined by $\alpha_{\mathrm{rx}} \gt 0.75$$ \alpha_{\mathrm{rx}} \gt 0.75$, are located in the upper-left region, while all XBL-like objects, defined by $ \alpha_{\mathrm{rx}} \leq 0.75$, are inside the lower-right region. No sources are in the lower-left and upper-right regions, suggesting that the classificatory criteria in terms of the peak frequency should be $ \log \nu_{\mathrm{p}} = 14.7 \pm 0.4$. This provides evidence supporting what Giommi et al. (1995, AAA063.158.163) proposed: RBL-like and XBL-like objects can be distinguished by the difference in the peak frequency of the synchrotron emission. The sometime confusing and observationally dependent RBL–XBL terminology should be replaced by the more physical LBL–HBL one.
Radial Distributions of the HCN/CO Ratio in Nearby CO Bright Galaxies
Authors: Sorai Kazuo , Nakai Naomasa , Kuno Nario , Nishiyama Kohta
Published: March 2014

Simultaneous observations of HCN and CO lines were made along the major axes of six nearby CO bright galaxies with the Nobeyama 45-m telescope. The beam-averaged HCN/CO ratios are 0.01 to 0.1. The distributions of the HCN/CO ratio along the major axes (and the minor axis for M 51) show different patterns from one galaxy to another. By adding data obtained from the outer disk, however, we found gradual decreases in the HCN and CO intensities and the HCN/CO ratio with increasing radius in M 51 from the nuclear region to 3 kpc, similar to our previous result for NGC 253. The HCN/CO ratio is very sensitive to the observing beam size on a linear scale. The ratio, which reflects the fraction of dense molecular gas, correlates with the star-formation activity derived from the far-infrared luminosity.
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

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

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.
Are Jets Ejected from Locally Magnetized Accretion Disks?
Authors: Kudoh Takahiro , Matsumoto Ryoji , Shibata Kazunari
Published: March 2014

We investigated the jet formation from accretion disks in which a weak localized poloidal magnetic field is initially embedded. Previous MHD numerical simulations of jet formation from accretion disks initially assumed a large-scale vertical uniform magnetic field that threads the disk, which showed that jets are ejected from accretion disks by a magneto-centrifugal force and magnetic pressure. In contrast to a large-scale uniform magnetic field, what happens if the magnetic field is localized in the disk? Our MHD numerical simulation shows that the jet structure appears even if the initial magnetic field is localized in the disk. The disk material is ejected as a poloidal magnetic loop by magnetic pressure due to a toroidal magnetic field that is generated by the disk rotation. Though the ejection mechanism is different from that of the magneto-centrifugally driven jet model, the rising magnetic loop behaves like a jet; it is collimated by a pinching force of the toroidal magnetic field, and its velocity is on order of the Keplerian velocity of the disk.
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

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

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

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

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

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).
Spectroscopic Determination of Atmospheric Parameters of Solar-Type Stars: Description of the Method and Application to the Sun
Authors: Takeda Yoichi , Ohkubo Michiko , Sadakane Kozo
Published: March 2014

A computer program has been developed for determining the fundamental model atmosphere parameters ($T_\mathrm{eff}$, $\log g$, $v_\mathrm{t}$, $[\mathrm{Fe/H}]$) of solar-type stars, which is based on the equivalent widths for a well-chosen set of Fe i and Fe ii lines. The basic principle of this method is to find the solution in the $(T_\mathrm{eff}$, $\log g$, $v_\mathrm{t})$ space, which minimizes the sum of the dispersion of the Fe i abundances and the square of the Fe i–Fe ii abundance difference. An application of this code to the observed solar equivalent widths turned out to yield satisfactory results, which are more or less consistent with the actual parameters of the Sun. The numerical performance of this approach as well as the errors involved in the resulting solutions are discussed.
Orbital Stability of a Protoplanet System under a Drag Force Proportional to the Random Velocity
Authors: Iwasaki Kazunori , Emori Hiroyuki , Nakazawa Kiyoshi , Tanaka Hidekazu
Published: March 2014

We investigated the effects of a tidal interaction with a gas disk and the dynamical friction with a planetesimal disk on the orbital instability of a protoplanet system. Both effects are expressed as the drag force, which is proportional to the random velocity of a protoplanet. We calculated numerically the orbits of 5 protoplanets with the same separation distance under the drag-force effect and examined the orbital instability time under the drag force, $T_{\mathrm{inst}}^{\mathrm{df}}$. We found that $T_{\mathrm{inst}}^{\mathrm{df}}$ can become much larger than the instability time under the drag-free condition, and that the onset of the orbital instability is prevented when the separation distance exceeds a critical value. We obtained a relation between the critical separation distance and the surface density of the gas or planetesimal disk. By applying this relation, we found that, for the formation of terrestrial planets from a protoplanet system with a typical orbital separation (i.e., $\sim 10$ Hill radii), the surface density of the nebular gas must be reduced to about one-thousandth of that in the minimum-mass nebula model. Terrestrial planets would be formed after such a depletion of the solar nebula.