Showing papers in "Publications of the Astronomical Society of Japan in 2008"

Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars

Abstract: We describe the construction of a database of extremely metal-poor (EMP) stars in the Galaxy. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the literature that report on studies of EMP halo stars with [Fe=H] �� 2.5. The compilation procedures for this database were designed to assemble data effectively from electronic tables available from online journals. We have also developed ad ata retrieval system that enables data searches by various criteria and illustrations to explore relationships between stored variables. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering relevant papers published by 2007 December. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe=H] �� 2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amounts to � 30% for [Fe=H] �� 2.5. We find that known binaries exhibit different distributions of the orbital period, according to whether they are giants or dwarfs, and also as a function of the metallicity, although the total sample of such stars is still quite small.

Reproducibility of Non-X-ray Background for the X-ray Imaging Spectrometer aboard Suzaku

Abstract: One of the advantages of the X-ray Imaging Spectrometer (XIS) system on board Suzaku is its low and stable non-X-ray background (NXB). In order to make the best use of this advantage, modeling the NXB spectra with high accuracy is important to subtract them from the spectra of on-source observations. We construct an NXB database by collecting XIS events when the dark Earth covers the XIS FOV. The total exposure time of the NXB data is about 785 ks for each XIS. It is found that the count rate of the NXB anti-correlates with the cut-off-rigidity and correlates with the count rate of the PIN upper discriminator (PIN-UD) in Hard X-ray Detector on board Suzaku. We thus model the NXB spectrum for a given on-source observation by employing either of these parameters and obtain a better reproducibility of the NXB for the model with PIN-UD than that with the cut-off-rigidity. The reproducibility of the NXB model with PIN-UD is 4.55-5.63% for each XIS NXB in the 1-7 keV band and 2.79-4.36% for each XIS NXB in the 5-12 keV band for each 5 ks exposure of the NXB data. This NXB reproducibility is much smaller than the spatial fluctuation of the cosmic X-ray background in the 1-7 keV band, and is almost comparable to that in the 5-12 keV band.

Astrometry of H2O Masers in Nearby Star-Forming Regions with VERA II SVS 13 in NGC 1333

Abstract: We report on the results of multiepoch very long baseline interferometry (VLBI) observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with the young stellar object SVS 13 in the NGC 1333 region. We carried out phase-referencing VLBI astrometry, and measured the annual parallax of the maser features in SVS 13 of 4.25 ˙ 0.32 mas, corresponding to a distance of 235 ˙ 18 pc from the Sun. Our result is consistent with a photometric distance of 220 pc, previously reported. Even though the maser features were detectable only for 6 months, the present result provides the distance to NGC 1333 with much higher accuracy than photometric methods. The absolute positions and proper motions have been derived, revealing that the H2O masers with LSR (local standard of rest) velocities of 7–8 km s � 1 are most likely associated with VLA 4A, which is a radio counterpart of SVS 13. It is currently difficult to attribute the observed proper motions of the maser features to either the jet or the rotating circumstellar disk associated with VLA 4A, which should be investigated through future high-resolution astrometric observations of VLA 4A and other radio sources in NGC 1333.

Delay Time Distribution Measurement of Type Ia Supernovae by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor

Abstract: The delay time distribution (DTD) of type Ia supernovae (SNe Ia) from star formation is an important clue to reveal the still unknown progenitor system of SNe Ia. Here we report on a measurement of the SN Ia DTD in a delay time range of t_Ia = 0.1-8.0 Gyr by using the faint variable objects detected in the Subaru/XMM-Newton Deep Survey (SXDS) down to i' ~ 25.5. We select 65 SN candidates showing significant spatial offset from nuclei of the host galaxies having old stellar population at z ~ 0.4-1.2, out of more than 1,000 SXDS variable objects. Although spectroscopic type classification is not available for these, we quantitatively demonstrate that more than ~80% of these should be SNe Ia. The DTD is derived using the stellar age estimates of the old galaxies based on 9 band photometries from optical to mid-infrared wavelength. Combined with the observed SN Ia rate in elliptical galaxies at the local universe, the DTD in t_Ia ~ 0.1-10 Gyr is well described by a featureless power-law as f_D(t_Ia) \propto t_Ia^{-1}. The derived DTD is in excellent agreement with the generic prediction of the double-degenerate scenario, giving a strong support to this scenario. In the single-degenerate (SD) scenario, although predictions by simple analytic formulations have broad DTD shapes that are similar to the observation, DTD shapes calculated by more detailed binary population synthesis tend to have strong peaks at characteristic time scales, which do not fit the observation. This result thus indicates either that the SD channel is not the major contributor to SNe Ia in old stellar population, or that improvement of binary population synthesis theory is required. Various sources of systematic uncertainties are examined and tested, but our main conclusions are not affected significantly.

Stellar Parameters and Elemental Abundances of Late-G Giants

Abstract: The properties of 322 intermediate-mass late-G giants (comprising 10 planet-host stars) selected as the targets of the Okayama Planet Search Program, many of which are red-clump giants, were comprehensively investigated by establishing their various stellar parameters (atmospheric parameters, including turbulent velocity fields, metallicity, luminosity, mass, age, projected rotational velocity, etc.), and their photospheric chemical abundances for 17 elements, in order to study their mutual dependence, connection with the existence of planets, and possible evolution-related characteristics. The metallicity distribution of planet-host giants was found to be almost the same as that of non-planet-host giants, making marked contrast to the case of planet-host dwarfs tending to be metal-rich. Generally, the metallicities of these comparatively young (typical age of � 10 9 yr) giants tend to be somewhat lower than those of dwarfs at the same age, and super-metal-rich ([Fe=H] > 0.2) giants appear to be lacking. Apparent correlations were found between the abundances of C, O, and Na, suggesting that the surface compositions of these elements have undergone appreciable changes due to dredge-up of H-burning products by evolution-induced deep

SiO Maser Observations toward Orion-KL with VERA

Abstract: We present results of phase-referencing VLBI observations of SiO masers in the Orion-KL region made with VERA. Using a strong maser spot in the 43 GHz v = 2 J = 1–0 emission, we derived the trigonometric parallax of Orion-KL to be 2.39˙0.03mas, corresponding to a distance of 418˙6pc, with the highest accuracy among existing parallax measurements of the source. We made a superimposed image of v = 1 J = 1–0 and v = 2 J = 1–0 maser features in Orion-KL based on absolute positions obtained from the phase-referencing astrometry with a common reference source. The maser features of both transitions show similar X-shaped distributions centered at Source I. However, in each of the four arms of the X-shape, the SiO v = 2 features tend to lie closer to Source I than the SiO v = 1 features. The radial velocities of the maser emission decrease with the distance from Source I. The spatial and radial velocity distributions of the SiO masers suggest that the SiO masers lie in the rotating materials associated with a disk around Source I, rather than a decelerating outflow.

Subaru Weak Lensing Study of Seven Merging Clusters: Distributions of Mass and Baryons

Abstract: We present and compare projected distributions of mass, galaxies, and the intracluster medium (ICM) for a sample of merging clusters of galaxies based on the joint weak-lensing, optical photometric, and X-ray analysis. Our sample comprises seven nearby Abell clusters, for which we have conducted systematic, deep imaging observations with Suprime-Cam on Subaru telescope. Our seven target clusters, representing various merging stages and conditions, allow us to investigate in details the physical interplay between dark matter, ICM, and galaxies associated with cluster formation and evolution. A1750 and A1758 are binary systems consisting of two cluster-sized components, A520, A754, A1758N, A1758S, and A1914 are on-going cluster mergers, and A2034 and A2142 are cold-front clusters. In the binary clusters, the projected mass, optical light, and X-ray distributions are overall similar and regular without significant substructures. On-going and cold-front merging clusters, on the other hand, reveal highly irregular mass distributions. Overall the mass distribution appears to be similar to the galaxy luminosity distribution, whereas their distributions are quite different from the ICM distribution in a various ways. We also measured for individual targets the global cluster parameters such as the cluster mass,the mass-to-light ratio, and the ICM temperature. A comparison of the ICM and virial temperatures of merging clusters from X-ray and weak-lensing analyses, respectively, shows that the ICM temperature of on-going and cold-front clusters is significantly higher than the cluster virial temperature by a factor of $\sim 2$. This temperature excess in the ICM could be explained by the effects of merger boosts.

On-The-Fly Observing System of the Nobeyama 45-m and ASTE 10-m Telescopes

Abstract: We have developed a spectral line On-The-Fly (OTF) observing mode for the Nobeyama Radio Observatory 45-m and the Atacama Submillimeter Telescope Experiment 10-m telescopes. Sets of digital autocorrelation spectrometers are available for OTF with heterodyne receivers mounted on the telescopes, including the focal-plane 5 $\times$ 5 array receiver, BEARS, on the 45-m. During OTF observations, the antenna is continuously driven to cover the mapped region rapidly, resulting in a high observing efficiency and accuracy. Pointing of the antenna and readouts from the spectrometer are recorded as fast as 0.1s. In this paper we report on improvements made to the software and instruments, requirements and optimization of observing parameters, the data-reduction process, and verification of the system. It is confirmed that, using optimal parameters, the OTF is about twice as efficient as the conventional position-switch observing method.

Toward First-Principle Simulations of Galaxy Formation: I. How Should We Choose Star-Formation Criteria in High-Resolution Simulations of Disk Galaxies?

Abstract: We performed three-dimensional N -body/SPH simulations to study how mass resolution and other model param- eters, such as the star-formation efficiency parameter, Cand the threshold density for star formation, nth affect structures of the galactic gaseous/stellar disk We employed 10 6 -10 7 particles to resolve a cold ( T 100 cm � 3 ) phase as well as diffuse, hot phases We found that structures of the interstellar medium (ISM) and the distribution of young stars were sensitive to the assumed values of nth High-nth models with nth = 100 cm � 3 yielded clumpy multi-phase features in the ISM Young stars were distributed in a thin disk, of which the half-mass scale height was 10-30 pc In low-nth models with nth = 01 cm � 3 , which is usually employed in cosmological galaxy-formation simulations, the gas disk appears to be smoother and the stellar disk is found to be several-times thicker than the high-nth models A high-resolution simulation with high-nth is necessary to reproduce the complex structure of the gas disk The global star-formation properties of galaxies, such as the star-formation history, in low-nth models are similar to those in high-nth models when we tune the value of Cso that they repro- duce the observed relation between the surface gas density and the surface star-formation rate density We however emphasize that high-nth models automatically reproduce the relation, regardless of the values of C� T he ISM structure, phase distribution and distributions of young star-forming regions are quite similar in runs with different values of C� We found that the timescale of the flow from the reservoir (nH � 1c m � 3 ) to the star-forming regions (nH & 100cm � 3 ) is about five-times as long as the local dynamical time, and this evolution timescale is independent

Multi-Object Infrared Camera and Spectrograph (MOIRCS) for the Subaru Telescope* I. Imaging

Abstract: MOIRCS is a fully cryogenic near-infrared instrument for the 8.2 m Subaru Telescope. MOIRCS has two observation modes: a wide-field imaging mode and a multiobject spectroscopy mode. This paper describes the imaging mode, its specifications, and actual performances that we confirmed through laboratory tests and commissioning observations. The imaging mode provides a 40 70 field of view with a pixel scale of 0:00117 pixel 1 in the wavelength range of 0.85 to 2.5 m using cooled optics and two 2048 2048 HgCdTe HAWAII-2 focal plane arrays. Good-quality images are obtained over the entire field of view with practically no chromatic aberration. The limiting magnitudes for a point source estimated from observed background brightness and throughput are 23.7 in the J band, 23.0 in the H band, and 22.6 in the Ks band (Vega) with S=N = 5, 0:005 seeing, 1:000 aperture, and 1 hr exposure.

Suzaku Results on Cygnus X-1 in the Low/Hard State

Abstract: The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005October, while it was in a low/hard state with a 0.7–300 keV luminosity of 4.6×10 37 erg s −1 . The XIS andHXD spectra, spanning 0.7–400 keV, were reproduced successfully incorporating a cool accretion disk anda hot Comptonizing corona. The corona is characterized by an electron temperature of ∼100 keV, and twooptical depths of ∼0.4 and ∼1.5 which account for the harder and softer continua, respectively. The disk hasthe innermost temperature of ∼0.2 keV, and is though to protrude half way into the corona. The disk notonly provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflectionhump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655−40 revealsseveral interesting spectral differences, which can mostly be attributed to inclination effects assuming thatthe disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicatesthat the continuum becomes less Comptonized when the source flares up on times scales of 1–200 s, whilethe underlying disk remains unchanged.Key words: accretion disks — black hole physics — stars: individual (Cygnus X-1)— X-ray: binaries1. IntroductionLuminous soft X-ray radiation of accreting stellar-massblack holes (BHs) has generally been explained as thermalemission from optically-thick (in particular “standard”)accretion disks (Shakura & Sunyaev 1973; Makishimaet al. 1986; Dotani et al. 1997; Remillard & McClintock2006), which are expected to form around them underrather high accretion rates. In contrast, their hard X-rayproduction process is much less understood, even thoughintense hard X-ray emission characterizes black-hoe bina-ries (BHBs) among varioustypes of compact X-raysourcesin the Milky Way and Magellanic clouds.Indeed, BHBs often emit a major fraction of their ra-diative luminosity in the hard X-ray band, in the formof spectral hard-tail component if they are in so-calledhigh/soft state, or as the entire power-law (hereafter PL)like continua if they are in so-called low/hard state (here-after LHS) which appears under relatively low accretionrates. Furthermore, the hard X-ray emission (partic-ularly in the LHS) involves another interesting aspect,namely the long-known aperiodic variation over a widefrequency range (e.g., Oda et al. 1971; Oda 1977; Nolanet al. 1981; Miyamoto et al. 1991; Pottschmidt et al.2003; Remillard & McClintock 2006). These spectral andtiming studies are not limited to stellar-mass BHs, since a

High Metallicity of the X-Ray Gas Up to the Virial Radius of a Binary Cluster of Galaxies: Evidence of Galactic Superwinds at High-Redshift

Abstract: We present an analysis of a Suzaku observation of the link region between the galaxy clusters A 399 and A 401. We obtained the metallicity of the intracluster medium (ICM) up to the cluster virial radii for the first time. We determined the metallicity where the virial radii of the two clusters cross each other ( 2 Mpc away from their centers) and found that it is comparable to that in their inner regions ( 0:2Zˇ). It is unlikely that the uniformity of metallicity up to the virial radii is due to mixing caused by a cluster collision. Since the ram-pressure is too small to strip the interstellar medium of galaxies around the virial radius of a cluster, the fairly high metallicity that we found there indicates that the metals in the ICM are not transported from member galaxies by ram-pressure stripping. Instead, the uniformity suggests that the proto-cluster region was extensively polluted with metals by extremely powerful outflows (superwinds) from galaxies before the clusters formed. We also searched for the oxygen emission from the warm–hot intergalactic medium in that region and obtained a strict upper limit of the hydrogen density (nH < 4:1 10 5 cm ).

Planetary Companions around Three Intermediate-Mass G and K Giants : 18 Delphini, ξ Aquilae, and HD 81688

Abstract: We report on the detection of 3 new extrasolar planets from a precise Doppler survey of G and K giants at Okayama Astrophysical Observatory. The host stars, 18 Del (G6 III), � Aql (K0 III) and HD 81688 (K0 III–IV), are located in the clump region on the HR diagram with estimated masses of 2.1–2.3Mˇ .1 8 Del b has a minimum mass of 10:3MJ and resides in a nearly circular orbit with period of 993 d, which is the longest one around evolved stars. � Aq lb and HD 81688 b have minimum masses of 2.8 and 2.7MJ ,a nd reside in nearly circular orbits with periods of 137 and 184 d, respectively, which are the shortest ones around evolved stars. All of the substellar companions ever discovered around intermediate-mass (1.7–3.9Mˇ )c lump giants have semimajor axes larger than 0.68 AU, suggesting a lack of short-period planets. Our numerical calculations suggest that Jupiter-mass planets within about

Tropospheric Delay Calibrations for VERA

Abstract: We present techniques for the tropospheric delay calibration, which is the key to increasing the accuracy of the phase-referencing astrometry with Very Long Baseline Interferometry (VLBI). We study three methods, and make a comparison of these methods to discuss the accuracy in calibration. Our results show that all three methods can calibrate the tropospheric zenith delay within accuracy of � 2 cm. We also present simulations of positional errors in VLBI Exploration of Radio Astrometry (VERA) at the presence of an error in the tropospheric zenith delay, showing that parallax measurements with accuracy of 10 � as can be readily achieved for sources at high declination and with

Astrometry of H2O Masers in Nearby Star-Forming Regions with VERA III. IRAS22198+6336 in Lynds1204G

Abstract: We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud, L 1204 G. Based on phase-referencing VLBI astrometry, we derived an annual parallax of IRAS 22198+6336 to be 1.309˙ 0.047 mas, corresponding to the distance of 764˙ 27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduced the errors in the derived annual parallax by employing position measurements for all of the 26 detected maser spots. Based on this result, we reanalyzed the spectral energy distribution of IRAS 22198+6336 and found that the bolometric lumi— —

Systematic Infrared 2.5—5μm Spectroscopy of Nearby Ultraluminous Infrared Galaxies with AKARI

Abstract: We report on the results of systematic infrared 2.5–5 � m spectroscopy of 45 nearby ultraluminous infrared galaxies (ULIRGs) at z 0.15. We estimate the intrinsic luminosities of extended (several kpc), modestly obscured (AV < 15 mag) starburst activity based on the observed 3.3 � m PAH emission luminosities measured in AKARI IRC slitless spectra, and confirm that such starbursts are energetically unimportant in nearby ULIRGs. In roughly half of the observed ULIRGs classified optically as nonSeyferts, we find signatures of luminous buried AGNs. The fraction of ULIRGs with detectable buried AGN signatures increases with increasing infrared luminosity. Our overall results support the scenario that luminous buried AGNs are important in many ULIRGs at z< 0.3 classified optically as non-Seyferts, and that the optical undetectability of such buried AGNs occurs merely because of a large amount of nuclear dust, which can make the sightline of even the lowest dust column density opaque to the ionizing radiation of the AGNs.

Distance to VY Canis Majoris with VERA

Abstract: We report astrometric observations of H2O masers around the red supergiant VY Canis Majoris (VY CMa) carried out with VLBI Exploration of Radio Astrometry (VERA). Based on astrometric monitoring for 13 months, we successfully measured a trigonometric parallax of 0.88 ± 0.08 mas, corresponding to a distance of 1.14 +0.11 −0.09 kpc. This is the most accurate distance to VY CMa and the first one based on an annual parallax measurement. The luminosity of VY CMa has been overestimated due to a previously accepted distance. With our result, we re-estimate the luminosity of VY CMa to be (3 ± 0.5) × 10 5 L⊙ using the bolometric flux integrated over optical and IR wavelengths. This improved luminosity value makes location of VY CMa on the Hertzsprung-Russel (HR) diagram much closer to the theoretically allowable zone (i.e. the left side of the Hayashi track) than previous ones, though uncertainty in the effective temperature of the stellar surface still does not permit us to make a final conclusion.

Restoring the Suzaku Source Position Accuracy and Point-Spread Function

Abstract: We present an empirical correction of sky coordinates of X-ray photons obtained with the X-ray Imaging Spectrometer (XIS) aboard the Suzaku satellite to improve the source position accuracy and restore the point-spread function (PSF). The XIS images are known to have an uncertainty in position of up to 1 0 , and to show considerable degradations of the PSF. These problems are caused by a drifting of the satellite attitude due to thermal distortion of the side panel #7, where the attitude control system is mounted. We found that the position error averaged over a pointing observation can be largely reduced by using the relation between the deviation of the source position in the DETX direction and the ecliptic latitude of the pointing target. We parameterized the wobbling of the source position synchronized with the 96-minute satellite orbital period with temperatures of onboard radiators and elapsed time since the night–day transition of the spacecraft. We developed software, aeattcor, to correct the image drift using these parameters, and applied it to 27 point-source images taken in the Suzaku initial science-operation phase. We show that the radius of the 90% error circle of the source position was reduced to 19 00 and the PSF was sharpened. These improvements have enhanced the scientific capability of the Suzaku XIS.

Resonant Excitation of Disk Oscillations in Deformed Disks II: A Model of High-Frequency QPOs

Abstract: The amplification of disk oscillations resulting from nonlinear resonant couplings between the oscillations and a disk deformation is examined. The disk is geometrically thin and general relativistic with a non-rotating central source. A Lagrangian formulation is adopted. The author examined the same problem a few years ago, but here we derive a general stability criterion in a more perspective way. Another distinct point from the previous work is that in addition to the case where the deformation is a warp, the case where the deformation is a one-armed pattern symmetric with respect to the equatorial plane is considered. The results obtained show that in addition to the previous results that the inertial-acoustic mode and g-mode oscillations are amplified by horizontal resonance in warped disks, they also amplified by horizontal resonance in disks deformed by one-armed pattern symmetric with respect to the equatorial plane. If we consider local oscillations that are localized around boundaries of their propagation region, the resonance occurs at 4rg, where rg is the Schwarzschild radius. If nonlocal oscillations are considered, frequency ranges of oscillations where oscillations are resonantly amplified are specified.

Planetary Companions to Evolved Intermediate-Mass Stars: 14 Andromedae, 81 Ceti, 6 Lyncis, and HD167042

Abstract: We report on the detection of four extrasolar planets orbiting evolved intermediate-mass stars from a precise Doppler survey of G-K giants at Okayama Astrophysical Observatory. All of the host stars are considered to be formerly early F-type or A-type dwarfs when they were on the main sequence. 14 And (K0 III) is a clump giant with a mass of 2.2 Mand has a planet of minimum mass m2 sin i = 4.8 MJ in a nearly circular orbit with a 186 d period. This is one of the innermost planets around evolved intermediate-mass stars, and such planets have only been discovered in clump giants. 81 Cet (G5 III) is a clump giant with 2.4 Mhosting a planet of m2 sin i = 5.3 MJ in a 953 d orbit with an eccentricity of e = 0.21. 6 Lyn (K0 IV) is a less-evolved subgiant with 1.7Mˇ, and has a planet of m2 sin i = 2.4 MJ in a 899 d orbit with e = 0.13. HD 167042 (K1 IV) is also a less-evolved star with 1.5 Mˇ hosting a planet of m2 sin i = 1.6 MJ in a 418 d orbit with e = 0.10. This planet was independently announced by Johnson et al. (2008, ApJ, 675, 784). All of the host stars have solar or sub-solar metallicity, which supports the lack of a metal-rich tendency in planet-harboring giants in contrast to the case of dwarfs.

Dual-Beam Delay Calibration for VERA

Abstract: We present the technique of instrumental delay calibration for the dual-beam system of VLBI Exploration of Radio Astrometry (VERA), namely, the horn-on-dish method, in which artificial noise sources are mounted on the antenna feedome base and a wide-band radio noise is injected into the dual-beam receivers after reflection by a subreflector. We introduce the basic concept of calibration with the horn-on-dish method, and also present results of the experiments to evaluate its calibration accuracy. Detailed comparisons between model path calculations and measured paths from the noise sources show that the horn-on-dish method can calibrate the dual-beam delay difference in the antenna structure and receiver within an � 0.1 mm level. We estimated that the systematic error in

Performance of the Charge-Injection Capability of Suzaku XIS

Abstract: A charge-injection technique is applied to the X-ray CCD camera, XIS (X-ray Imaging Spectrometer) aboard Suzaku. The charge transfer inefficiency (CTI) in each CCD column (vertical transfer channel) is measured by the injection of charge packets into a transfer channel and subsequent readout. This paper reports on the performances of the charge-injection capability based on the ground experiments using a radiation-damaged device, and in-orbit measurements of the XIS. The ground experiments show that charges are stably injected with a dispersion of 91 eV in FWHM in a specific column for the charges equivalent to an X-ray energy of 5.1 keV. This dispersion width is significantly smaller than that of the X-ray events of 113 eV (FWHM) at approximately the same energy. The amount of charge loss during transfer in a specific column, which is measured with the charge-injection capability, is consistent with that measured with the calibration source. These results indicate that the charge-injection technique can accurately measure column-dependent charge losses, rather than the calibration sources. The column-to-column CTI correction to the calibration source spectra significantly reduces the line widths compared to those with a columnaveraged CTI correction (from 193 eV to 173 eV in FWHM on an average at the time of one year after the launch). In addition, this method significantly reduces the low-energy tail in the line profile of the calibration source spectrum.

Suzaku Observation of the Ophiuchus Galaxy Cluster: One of the Hottest Cool Core Clusters

Abstract: We present the analysis of a Suzaku observation of the Ophiuchus galaxy cluster. We confirmed that the cluster has a cool core. While the temperature of the intracluster medium (ICM) decreases toward the center, the metal abundance increases. Except for the core (r . 50 kpc), the cluster is hot (� 9–10 keV) and is almost isothermal for r . 1 Mpc; the latter contradicts a previous study. We do not detect any variation of the redshift of the ICM in the cluster; the upper limit of the velocity difference is 3000 km s � 1 . The iron-line ratios in X-ray spectra indicate that the ICM has reached the ionization equilibrium state. From these results, we conclude that the Ophiuchus cluster is not a major merger cluster, but one of the hottest clusters with a cool core. We obtain the upper limit of non-thermal emission from the cluster, which is consistent with both the recent claimed detection with INTEGRAL and the recent upper limits with the Swift/BAT. If the cluster has bright non-thermal emission, as suggested by the INTEGRAL measurement, it is probably not due to a recent major cluster merger.

Absolute photometric calibration of the infrared camera (IRC) aboard AKARI

Abstract: The absolute photometric calibration of imaging observations with the Infrared Camera (IRC) aboard the AKARI satellite was performed by monitoring the same stars regularly and by observing a set of standard stars. By our monitoring observations, we confirmed that all channels of the IRC were stable to within 4% and that their sensitivities were constant until the liquid helium was exhausted. Using the data of these repeated observations, we evaluated the intrinsic errors as a function of the brightnesses of objects and found that the errors increase rapidly toward fainter objects. We also checked the consistency between short and long exposure times, and confirmed that the data sampling had been executed as designed. Finally, by comparing the estimated in-band flux densities and the observed data values of standard stars, we obtained conversion factors to the absolute flux densities of all the band/exposure configurations. Their absolute uncertainties are estimated to be less than 6%.

AKARI/IRC Deep Survey in the North Ecliptic Pole Region

Abstract: We have made adeep and wide imaging survey with all nine AKARI/IRC bands from 2 to 24 μm within ahalf degree of the North Ecliptic Pole. The survey covered acircular area of 0.38deg2 centered at RA = 17h56m, Dec = 66°37' where adeep optical multi-band survey has been conducted by Subaru/Suprime-Cam. The 5σ sensitivity of the survey for point sources is 11.0, 48, 117, and 275 μJy at wavelengths 3, 7, 15, and 24 μm, respectively. The survey is limited by sky noise at wavelengths from 7 to 24 μm, and limited by source confusion from 2 to 4 μm. We have also made apoint source catalog at each band, consisting of more than 5000 sources with a 50% completeness limit of 93 μ Jy at 15 μm. Our results are consistent with the pilot survey at faint fluxes and has better statistical significance at the bright fluxes. This is the first near- and mid-infrared sub-mJy extragalactic survey with contiguous wavelength coverage from 2 to 24 μm and a large band-merged catalogue. It will provide powerful and unique diagnostics of obscured star-formation and AGN activities in the galaxies up to z = 2.

X-Ray Spectroscopy of SN 1006 with Suzaku

Abstract: We report on observations of SN 1006 with Suzaku. We firmly detected K-shell emission from Fe, for the first time, and found that the Fe ionization state is quite low. The broad-band spectrum extracted from southeast of the remnant was well-fitted with a model consisting of three optically thin thermal non-equilibrium ionization plasmas and a power-law component. Two of the thermal models are highly overabundant in heavy elements, and hence are likely due to ejecta. These components have different ionization parameters, net∼ 1.4×10 10 cm s and net∼ 7.7×10 8 cm s; it is the later one that produces Fe-K emission. This suggests that Fe has been heated by reverse shock more recently than the other elements, consistent with a picture where the ejecta are stratified by composition with Fe in the interior. On the other hand, the third thermal component is assumed to be solar abundance, and we associate it with emission from the interstellar medium (ISM). The electron temperature (kTe ∼ 0.5 keV) is lower than that expected from the shock velocity, which suggests a lack of collisionless electron heating at the forward shock. The extremely low ionization parameter and extreme non-equilibrium state are due to the low density of the ambient medium.

Distance to NGC 281 in a Galactic Fragmenting Superbubble: Parallax Measurements with VERA

Abstract: We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in the Galactic star-forming region NGC 281 West, which has been considered to be part of a 300-pc superbubble. We successfully detected a trigonometric parallax of 0.355 ˙ 0.030 mas, corresponding to a source distance of 2.82 ˙ 0.24 kpc. Our direct distance determination of NGC 281 has resolved a large distance discrepancy between previous photometric and kinematic studies; likely NGC 281 is in the far side of the Perseus spiral arm. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, � 650 pc in size parallel to the Galactic disk and with a shape slightly elongated along the disk or spherical, but not vertically elongated, indicating that the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as being � 20 km s � 1 , both perpendicular to and parallel to the Galactic disk with a consistent timescale of � 20 Myr.

Suzaku Observations of AWM 7 Cluster of Galaxies: Temperatures, Abundances, and Bulk Motions

Abstract: We carried out 3 observations of the cluster of galaxies AWM 7, for the central region and 200-east and 200-west offset regions, with Suzaku. Temperature and abundance profiles were measured out to 270 ' 570 h 1 70 kpc, which corresponded to 0.35r180. The temperature of the intra-cluster medium (ICM) slightly decreased from 3.8 keV at the center to 3.4 keV in the 0.35 r180 region, indicating a flatter profile than those in other nearby clusters. The abundance ratio of Si to Fe was almost constant in our observations, while the Mg-to-Fe ratio increased with radius from the cluster center. The O to Fe ratio in the west region showed an increase with radius, while that in the east region was almost flat, though the errors were relatively large. These features suggest that the enrichment process is significantly different between products of type II supernovae (O and Mg) and those by type Ia supernovae (Si and Fe). We also examined the positional shift of the central energy of a He-like Fe-K line, in search of possible rotation of the ICM. The 90% upper limit for the line-of-sight velocity difference was derived to be ∆v . 2000 km s , suggesting that the ellipticity of AWM 7 is rather caused by a recent directional infall of gas along the large-scale filament.

N2H+ and HC3N observations of the orion a cloud

Abstract: The “ R -shaped filament” of the Orion A giant molecular cloud was mapped in N2H, and its northern end, the OMC-2/3 region, was also observed in HC3N and CCS. The results were compared with maps of other molecular lines and the dust continuum emission. The N2H distribution is similar to the dust continuum distribution, except for the central part of the Orion Nebula. The distribution of HCO holds a resemblance to that of the dust continuum, but the N2H distribution looks more similar to the dust continuum distribution. The N-bearing molecules, N2H and NH3, seem to be more intense in OMC-2, compared with the HCO and CS distribution. This suggests that OMC-2 has a higher abundance of N-bearing molecules, or a higher filling factor of the quiescent gas. We identified 34 cloud cores from N2H data. Over the Orion Nebula region, the N2H linewidth is large (1.1–2.1 km s ). In the OMC-2/3 region, it becomes moderate (0.5–1.3 km s ), and it is smaller (0.3–1.1 km s ) in the south of the Orion Nebula. On the other hand, the gas kinetic temperature of the quiescent cores observed in N2H is rather constant ( 20 K) over the R -shaped filament. We detected no CCS emission in the OMC-2/3 region. In general, the N2H and HC3N distribution is quite similar in the OMC-2/3 region, but we observed a displacement between N2H and HC3N over a 20 scale in OMC-3, which has a chain of Class 0–I protostars (candidates).

Detection of Polarimetric Variations Associated with the Shortest Time-Scale Variability in S5 0716+714

Abstract: We present the results of near-infrared and optical observations of the BL Lac object S5 0716+714, carried out with the KANATA telescope. S5 0716+714 has both a long-term, high-amplitude variability and a short-term variability within one night. The shortest variability (microvariability) time-scale is important for understanding the geometry of jets and the magnetic field, because it provides a possible minimum size of variation sources. Here, we report on the detection of 15-min variability in S5 0716+714, which is one of the shortest time scales in optical and near-infrared variations observed in blazars. The detected microvariation had an amplitude of 0.061 0.005 mag in the V band and a blue color of Δ(V J ) = 0.025 0.011. Furthermore, we successfully detected an unprecedented, short time-scale polarimetric variation, which correlated with the brightness change. We revealed that the microvariation had a specific polarization component. The polarization degree of the variation component was higher than that of the total flux. These results suggest that the microvariability originated from a small and local region where the magnetic field was aligned.