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著者人数: 36名, Accepted: 2018-09-14, 資料番号: SA1180348000

Giant radio pulses (GRPs) are sporadic bursts emitted by some pulsars, lasting a few microseconds. GRPs are hundreds to thousands of times brighter than regular pulses from these sources. The only GRP-associated emission outside radio wavelengths is from the Crab Pulsar, where optical emission is enhanced by a few percent during GRPs. We observed the Crab Pulsar simultaneously at X-ray and radio wavelengths, finding enhancement of the X-ray emission by $3.8\pm0.7\%$ (a 5.4$\sigma$ detection) coinciding with GRPs. This implies that the total emitted energy from GRPs is tens to hundreds of times higher than previously known. We discuss the implications for the pulsar emission mechanism and extragalactic fast radio bursts., Comment: 63 pages, 23 figures, 7 Tables. Published in Science

The Perseus arm has a gap in Galactic longitudes (l) between 50 and 80 deg (hereafter the Perseus arm gap) where the arm has little star formation activity. To better understand the gap, we conducted astrometric observations with VERA and analyzed archival H I data. We report on parallax and proper motion results from four star-forming regions, of which G050.28-00.39 and G070.33+01.59 are likely associated with the gap. The measured parallaxes are 0.140+/-0.018 (mas), 0.726+/-0.038 (mas), 0.074+/-0.037 (mas), and 0.118+/-0.035 (mas) for G050.28-00.39, G053.14+00.07, G070.33+01.59, and G079.08+01.33, respectively. Since the fractional parallax error of G070.33+01.59 is large (0.5), we estimated a 3D kinematic distance of the source to be 7.7+/-1.0 kpc using both the LSR velocity (VLSR) and the measured proper motion. Perseus-arm sources G049.41+00.32 and G050.28-00.39 lag relative to a Galactic rotation by 77+/-17 km/s and 31+/-10 km/s, respectively. The noncircular motion of G049.41+00.32 cannot be explained by the gravitational potential of the Perseus arm. We discovered rectangular holes with integrated brightness temperatures of < 30 K arcdeg in l vs. VLSR of the H I data. One of the holes is centered near (l, VLSR) = (47 deg, -15 km/s), and G049.41+00.32 is associated with the rim of the hole. However, G050.28-00.39 is not associated with the hole. We found extended H I emission on one side of the Galactic plane when integrating the H I data over the velocity range covering the hole (i.e., VLSR = [-25, -5] km/s). G049.41+00.32 and G050.28-00.39 are moving toward the emission. The Galactic H I disk at the same velocity range showed an arc structure, indicating that the disk was pushed from the lower side of the disk. All the observational results might be explained by a cloud collision with the Galactic disk., Accepted for publication in PASJ. 7 figures; 6 tables

We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric annual parallax and proper motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported while the rest of 78 sources are referred to previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry are revisited and compared with those from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould's Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameter of $R_{0}=7.92\pm0.16_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~kpc and $\Omega_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $\Omega_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively., Comment: 35 pages, 7 figures, accepted for publication in the Publications of the Astronomical Society of Japan

In this proceeding paper, we introduce the recent results of Galactic maser astrometry by mainly focusing on those obtained with Japanese VLBI array VERA. So far we have obtained parallaxes for 86 sources including preliminary results, and combination with the data obtained with VLBA/BeSSeL provides astrometric results for 159 sources. With these most updated results we conduct preliminary determinations of Galactic fundamental parameters, obtaining R0 = 8.16 ± 0.26 kpc and Θ0 = 237 ± 8 km/s. We also derive the rotation curve of the Milky Way Galaxy and confirm the previous results that the rotation curve is fairly flat between 5 kpc and 16 kpc, while a remarkable deviation is seen toward the Galactic center region. In addition to the results on the Galactic structure, we also present brief overviews on other science topics related to masers conducted with VERA, and also discuss the future prospect of the project.

Magnetic field is ubiquitous in the Universe and it plays essential roles in various astrophysical phenomena, yet its real origin and evolution are poorly known. This article reviews current understanding of magnetic fields in the interstellar medium, the Milky Way Galaxy, external galaxies, active galactic nuclei, clusters of galaxies, and the cosmic web. Particularly, the review concentrates on the achievements that have been provided by centimeter and meter wavelength radio observations. The article also introduces various methods to analyze linear polarization data, including synchrotron radiation, Faraday rotation, depolarization, and Faraday tomography., 40 pages, 16 figures, accepted for publication in PASJ

We report the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the HW3d object within the Cepheus A star-forming region. We measured proper motions of 30 water maser features, tracing a compact bipolar outflow. This outflow is highly collimated, extending through ~400 mas (290 AU), and having a typical proper motion velocity of ~6 mas yr−1 (~21 km s−1). The dynamical timescale of the outflow was estimated to be ~100 years, showing that the outflow is tracing a very early star-formation phase. Our results provide strong support that the HW3d object harbors an internal massive protostar, as previous observations suggested. In addition, we have analyzed Very Large Array (VLA) archive 1.3 cm continuum data of the 1995 and 2006 epochs obtained towards Cepheus A. These results indicate possible different protostars around HW3d and/or strong variability in its radio continuum emission.

We present the results of the first simultaneous dual-frequency phase referencing VLBI observation with VLBI Exploration of Radio Astrometry (VERA). The experiment was designed to simultaneously observe two adjacent VLBI sources at two different frequencies to test the feasibility of multifrequency phase referencing for the Korean VLBI Network (KVN). The KVN has introduced a multifrequency receiver system that performs simultaneous observations at four frequencies, such as 22, 43, 86, and 129 GHz, in order to calibrate the atmospheric phase fluctuations at 43, 86, or 129 GHz from the phase at 22 GHz. A pair of two bright continuum sources, a BL Lac object NRAO 512 (22 GHz) and a quasar 3C 345 (43 GHz), with a separation angle of 0. $^{\!\!\!\circ}$ 5 were observed simultaneously. The connected fringe phases of 22 and 43 GHz show very tight correlation that is proportional to the frequency, exhibiting a clearly non-dispersive characteristic of the neutral troposphere to the radio systems. The residual phase, which is the difference of the fringe phase between 43 GHz and a scaled-up phase of 22 GHz by multiplying the frequency ratio of 1.926 ( $\nu_{43}/\nu_{22}$ ), remained constant for more than 2 hr, and showed a weak sinusoidal variation at the first and second half of the observations, respectively. The Allan standard deviation of the residual phase is mostly dominated by white phase noise, implying that the dual-frequency phase referencing can compensate for the atmospheric phase fluctuation effectively. The coherence function of the residual phase indicates that an arbitrarily long-time integration of the fringe visibility is attainable. There is an excellent agreement between the self-calibrated and the phase referenced images of 3C 345. These results are promising for realizing multifrequency phase referencing with the KVN and opening new perspectives in the multifrequency study of VLBI.

We present a distance measurement for the semiregular variable S Crateris (S Crt) based on its annual parallax. With the unique dual beam system of the VLBI Exploration for Radio Astrometry (VERA) telescopes, we measured the absolute proper motion of a water maser spot associated with S Crt, referred to the quasar J1147-0724 located at an angular separation of 1.23$^{\circ}$. In observations spanning nearly two years, we have detected the maser spot at the LSR velocity of 34.7 km s$^{-1}$, for which we measured the annual parallax of 2.33$\pm$0.13 mas corresponding to a distance of 430$^{+25}_{-23}$ pc. This measurement has an accuracy one order of magnitude better than the parallax measurements of HIPPARCOS. The angular distribution and three-dimensional velocity field of maser spots indicate a bipolar outflow with the flow axis along northeast-southwest direction. Using the distance and photospheric temperature, we estimate the stellar radius of S Crt and compare it with those of Mira variables., 9 pages, 4 figures, accepted for publication in PASJ (Vol.60, No.5, October 25, VERA special issue)

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) x 10^5 L_sun 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., Comment: 7 pages, 4 figures, accepted for publication in PASJ, VERA special issue

We present phase-referenced maps of the SiO maser transitions v = 1 J = 1–0 and v = 2 J = 1–0 from the symbiotic stellar system R Aquarii, which hosts an evolved AGB star plus a hot companion. Observations were performed at two epochs: 2004.98 and 2005.98. Accurate absolute coordinates and proper motions of the emission centroid were obtained; the errors expected for these parameters are also given. We compare the VERA data with the previous astrometry by Hipparcos. This represents a possibility to improve the orbital parameters of the system in a different way than that done before. Thanks to our accurate astrometry, we have also estimated the percentage of spot coincidences between both maser transitions, a parameter that has been proposed to be relevant to discriminate between different maser pumping schemes. Although the overall distributions of both lines are always similar, the spots are rarely coincident, in a percentage ranging between 3% and 20% of the cases. The lack of systematic coincidence favors, in principle, radiative pumping. However, we argue that no firm conclusion can be reached due to a lack of models that include an overlap of rovibrational lines, and that accurately address the coincidence of very intense spots of different maser transitions.

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

We observed the SiO (v = 1 and v = 2, J = 1–0) maser emissions toward the Mira variable IK Tauri (IK Tau, NML Tau, IRC +10050) over nine epochs from 2003 November to 2005 April using the VLBI Exploration of Radio Astrometry (VERA) telescope array. We found that the SiO maser distributions around IK Tau are highly variable, depending on the stellar pulsation phase. The velocity structures were complex and also time-variable, and are inconsistent with a simply rotating shell that was suggested by previous observations. Based on fittings of the SiO maser distributions to elliptical ring models, we found that the ring size seems to vary in correlation with the pulsation phase, as previously found for TX Cam. Comparisons of the v = 1 and v = 2 maser distributions reveal that 42–50% of the maser pairs have a positional offset less than 0.5 mas, suggesting that the maser pumping in these spots is likely to be dominated by line overlapping or collisional pumping, rather than pure radiative pumping. In order to model the velocity structure of the spoke-like features observed in IK Tau, we propose a ballistic-orbit model, in which a gas clump ejected from the stellar surface moves radially outward with a gravitational deceleration, and argue that the stellar mass can be deduced from that model.

We report on results of five-epoch VLBI observations of H2O maser emission in the M-type star IRC � 10414, carried out with the VLBI Exploration of Radio Astrometry (VERA). The maser distribution extends over an area of 70 mas � 260 mas and exhibits a bipolar structure. The relative proper motions of 17 maser features were measured during the monitoring observations spanning nine months. The distance to IRC � 10414 was re-estimated on the basis of the statistical treatment of parallax and the model-fitting method, yielding D = 3.1 ˙ 0.4 kpc and D = 2.0 ˙ 0.2 kpc, respectively. The estimated distance, D = 2–3 kpc, is much larger than that previously adopted. The stellar luminosity of IRC � 10414 is also re-estimated to be L� � 9 � 10 4 (D=2 kpc) 2 Lˇ, much brighter by a factor of 10–20 than previously adopted (L� � 10000 Lˇ). The maser motions exhibit not only a spherically expanding flow with a velocity of � 10 (D=2 kpc) km s � 1 , but also a faster bipolar outflow with a major axis in the north–south direction and at a small inclination angle with respect to the celestial sphere. These characteristics of the star and the

著者人数：20名, 資料番号: SA1000216000

We report on the results of multi-epoch 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 have carried out phase-referencing VLBI astrometry and measured an annual parallax of the maser features in SVS 13 of 4.25+/-0.32 mas, corresponding to the 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 results provide 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 the LSR (local standard of rest) velocities of 7-8 km s-1 are most likely associated with VLA4A, which is a radio counterpart of SVS 13. The origin of the observed proper motions of the maser features are currently difficult to attribute to either the jet or the rotating circumstellar disk associated with VLA4A, which should be investigated through future high-resolution astrometric observations of VLA4A and other radio sources in NGC 1333.

We report on results of multi-epoch VLBI observations of H2O masers associated with a low-mass young stellar object, IRAS 16293 2422 in Oph East, and a fringe-phase and position reference source, ICRF J162546.8 252738, using the VLBI Exploration of Radio Astrometry (VERA) for high-precision astrometry. We obtained an annual parallax of a maser feature to be = 5.6 0:5 mas, corresponding to a distance of D= 178 +18 37 pc. We also found 10 relative proper motions of maser features with respect to the maser feature mentioned above. The motion of the accompanying young stellar object (YSO) has already been found in thermal continuum emission previously observed with the Very Large Array. The intrinsic motions of masers have been estimated from the relative proper motions after the YSO’s motion is subtracted from, and a systemic secular motion of the position reference feature is added to the proper motions originally measured. The intrinsic maser kinematical structure may trace a bipolar outflow.

VERA aims at astrometric observations using phase referencing VLBI techniques, whose goal is a 10 micro arc-second accuracy for annual parallax measurements. VERA has four 20-m diameter VLBI radio telescopes in Japanese archipelago with the maximum baseline length of 2,300 km. They have the two-beam observing system, which makes simultaneous observations of two objects possible. This leads to very accurate phase referencing VLBI observations. An important science goal is to make a 3-dimensional map of the Galaxy and reveal its dynamics. In order to achieve this, VERA has the 22GHz and 43GHz bands for H2O and SiO maser objects, respectively. Maser objects are compact and suitable for astrometry observations. VERA's construction was started in 2000 and the array became operational in 2004. We have already measured annual parallaxes and proper motions of some galactic objects. In the future, VERA will collaborate with Korean and Chinese VLBI stations.

We report on absolute proper-motion measurements of an H2O maser source in the NGC 281 West molecular cloud, which is located ~320 pc above the Galactic plane and is associated with an HI loop extending from the Galactic plane. We have conducted multi-epoch phase-referencing observations of the maser source with VERA (VLBI Exploration of Radio Astrometry) over a monitoring period of 6 months since May 2006. We find that the H2O maser features in NGC 281 West are systematically moving toward the southwest and further away from the Galactic plane with a vertical velocity of ~20-30 km/s at its estimated distance of 2.2-3.5 kpc. Our new results provide the most direct evidence that the gas in the NGC 281 region on the HI loop was blown out from the Galactic plane, most likely in a superbubble driven by multiple or sequential supernova explosions in the Galactic plane., Comment: 10 pages, 5 figures, PASJ in press (Vol. 59, No. 4; August 25, 2007 issue)

The beacon signals from a geostationary satellite were observed using three-element very long baseline interferometry (VLBI), and the phase fluctuations along the baselines between three sites were obtained. The atmospheric phase fluctuations at each observation site were derived from the baseline phase fluctuation data. The fluctuations were classified into three time-interval regions based on the dependence of the Allan standard deviation of the fluctuations on the time interval. In the region where the interval was less than a few seconds and in the one where it was greater than one hundred seconds, the curve of the Allan standard deviation was steep and showed the property of white phase noise. In the region between these two regions, the dependence of the Allan standard deviation on the time interval was weak. The magnitude of the Allan standard deviations for the three observation sites showed time variations in the region where the time interval was longer than a few seconds. Comparison with the weather conditions suggested that the time variations of the Allan standard deviation reflected atmospheric instability above the sites.

Phase characteristics, which are systematic phase offsets across the main beam of an actual telescope, may be a problem for achieving the same-beam differential very long baseline interferometer (VLBI) technique. This technique is essential for differential phase delay measurements such as those used in the Japanese Selenological and Engineering Explorer (SELENE) project, where the phase has to be determined to an accuracy of 0.075 radians rms. Accurate measurement and correction of phase characteristics are very important. The phase characteristics at 2.2375 and 2.2807 GHz of the 20-m and 10-m telescopes at Mizusawa were measured to an error of approximately 0.04 radians rms. The phase characteristics were 0.06 radians rms for the 20-m and 0.055 radians rms for the 10-m telescopes in the main beams, and the post-fit residuals decreased to 0.03 and 0.04 radians rms, respectively, after correcting by using quadratic formulas. These results confirmed the effectiveness of the same-beam differential VLBI technique for VLBI observations of SELENE

We present results of astrometric observations of S269 H2O maser performed with VERA (VLBI Exploration of Radio Astrometry). We have monitored the positions of S269 H2O masers for 1 year and successfully detected its parallax to be 189±8 micro-arcsecond. This corresponds to a source distance of 5.28+0.24−0.22kpc, and is the smallest parallax (and thus the largest distance) that has ever been measured by means of annual parallax. Proper motions of S269 H2O maser were also measured and used to determine the Galactic rotation velocity at the position of S269. Our measurements show that the Galactic rotation velocity at S269 is the same to that at the Sun within 3%, indicating that the Galactic rotation curve is flat out to R~13 kpc.

We report on multi-epoch observations of H2O maser emission in the star-forming region OH 43.8−0.1, carried out with VLBI Exploration of Radio Astrometry. The large-scale maser distributions obtained by single-beam VLBI mapping reveal new maser spots scattered over the area of 0. 7 ×1. 0, in addition to a ‘shell-like’ structure with a scale of 0. 3 ×0. �� 5, which was mapped previously. Proper motions were also obtained for 43 spots based on 5-epoch monitoring with a time span of 281 days. The distributions of the proper motions show a systematic outflow in the north–south direction with an expansion velocity of ∼ 8kms −1 . The overall distributions of the maser spots as well as the proper motions are better represented by a bipolar flow plus a central maser cluster with a complex structure, rather than a shell with uniform expansion, such as those found in Cep A R5 and W75N VLA2. The distance to OH 43.8−0.1 was also estimated based on the statistical parallax, yielding D =2 .8 ±0.5kpc. This distance is consistent with a near kinematic distance, and rules out a far kinematic distance (∼ 9kpc). Also, the radial velocity of the OH 43.8−0.1 combined with the distance provides a constraint on the flatness of the galactic rotation curve, indicating that there is no systematic difference in the rotation speeds at the Sun and at the position of OH 43.8−0.1, which is located at a galacto-centric radius of ∼ 6.3kpc.

This paper reports the statistical characteristics of phase fluctuations obtained by a very long baseline interferometry, which received beacon waves from a geostationary satellite. Observations were made in different weather conditions by the 6-m Kagoshima and the 10-m Mizusawa radio telescopes, which were 1284 km apart from one another. Atmospheric phase fluctuations ranging from 0.2 to about 1000 s were detected. To study a variety of statistical characteristics of these phase fluctuations, the Allan standard deviation, /spl sigma//sub y/(/spl tau/), the temporal structure function, D/sub /spl phi//(/spl tau/), and the square root of power spectrum, G/sub /spl phi//(f), were calculated from the observation results. These qualities were found to depend on the time interval /spl tau/ or the frequency f (f=1/2/spl tau/) as follows: /spl sigma//sub y/(/spl tau/)/spl prop//spl tau//sup -0.6/, /spl tau//sup -0.3/, D/sub /spl phi//(/spl tau/)/spl prop//spl tau//sup 0.9/, /spl tau//sup 1.3/ for 0.2 s f>0.33 Hz and G/sub /spl phi//(f)/spl prop/f/sup -1.3/ for 0.33 Hz>f>0.00125 Hz. The curves of /spl sigma//sub y/(/spl tau/) and D/sub /spl phi//(/spl tau/) exhibited shifts whose magnitudes followed the weather order clear, cloudy, and rainy. For /spl tau/>1.5 s (or f 0.33 Hz), the model has to be modified to explain the experimental results.

We have been monitoring the flux density of Sagittarius A* (Sgr A*) at 22 GHz since DOY=42 (11 Feb. 2013) with a sub-array of the Japanese VLBI Network in order to search the increase of 22-GHz emission from Sgr A* induced by the interaction of the G2 cloud with the accretion disk. The flux densities observed until DOY=322 (18 Nov. 2013) are consistent with the previously observed values before the approaching of the cloud. We have detected no large flare during this period.

We report on a strong outburst of the W49N H2O maser observed with VERA. Single-dish monitoring with VERA 20 m telescopes detected a strong outburst of the maser feature at V_LSR = -30.7 km/s in 2003 October. The outburst had a duration of ~100 days and a peak intensity of 7.9 x 10^4 Jy, being one of the strongest outbursts in W49N observed so far. VLBI observations with the VERA array were also carried out near to the maximum phase of the outburst, and the outburst spot was identified in the VLBI map. While the map was in good agreement with previous studies, showing three major concentrations of maser spots, we found a newly formed arc-like structure in the central maser concentration, which may be a shock front powered by a forming star or a star cluster. The outburst spot was found to be located on the arc-like structure, indicating a possible connection of the present outburst to a shock phenomenon., Comment: 4 pages, 2 figures included, to appear in PASJ letter (Vol.56, #3, 2004 June)

We present a magnetic field mapping of water maser clouds in the star-forming region W3 IRS5, which has been made on the basis of the linear polarization VLBI observation. Using the Very Long Baseline Array (VLBA) at 22.2 GHz, 16 of 61 detected water masers were found to be linearly polarized with polarization degrees up to 13%. Although 10 polarized features were widely distributed in the whole W3 IRS5 water maser region, they had similar position angles of the magnetic field vectors (~75 deg from the north). The magnetic field vectors are roughly perpendicular to the spatial alignments of the maser features. They are consistent with the hourglass model of the magnetic field, which was previously proposed to explain the magnetic field in the whole W3 Main region (r~0.1 pc). They are, on the other hand, not aligned to the directions of maser feature proper motions observed previously. This implies that the W3 IRS5 magnetic field was controlled by a collapse of the W3 Main molecular cloud rather than the outflow originated from W3 IRS5., 19 pages, 5 files, 1 table, accepted for publication in the Astrophysical Journal vol. 595, No.1 (2003 September 20 issue)

We describe the proper motion measurements of water masers in the massive-star forming region W 51A and the analysis of the 3-D kinematics in three maser clusters of W 51A. We found a systematic expanding motion in one of the clusters named W 51 North, while no systematic motion was detected in other two clusters named W 51 Main and South. The 3-D motions of the clusters relative to the position reference feature in W 51 North indicate a separating motion between the W 51 North and the W 51 Main/South clusters. We estimated the distance to W 51 North as to be 6.7±2.1 kpc on basis of the statistical parallax and the model fitting methods.

著者人数: 14名, Accepted: 2014-10-26, 資料番号: SA1004968000

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

A survey has been made in the SiO J = 1-0, v = 1 and 2 transitions (~43 GHz) for the color-selected IRAS sources in the central region of the Galaxy, -10? < l < 15? (except |l| ? 3?) and |b| ? 3?, with the Nobeyama 45 m telescope. We have detected 124 out of 200 observed sources in SiO masers. Distances to the sources range approximately from 2 to 11 kpc, if estimated from the IRAS 12 and 25 ?m flux densities. Radial velocities of the detected sources spread between ?260 km s-1. The distribution of SiO sources in the longitude-velocity diagram is compared with the H I contours. A number of sources are out of the H I limiting velocities; a group of negative-velocity (~-200 to -80 km s-1) sources is found at l = 3?-12? region. The subsamples of sources exhibit negative and positive shifts of the average radial velocity depending on distance, suggesting evidence of a streaming motion of stars in the bulge bar.

We have made multiepoch VLBA observations of water masers in the massive-star forming region W3 IRS 5. We measured radial velocities and proper motions of 108 water maser features during three observing sessions. The masers are clustered in two groups, which are associated with at least two different outflows. Positions of the outflow origins are close to the hypercompact radio continuum sources, which are clustered within a scale of 6000 AU. The continuum sources are probably driving sources of the outflows. We performed a three-dimensional kinematic model analysis of the maser motions in one of the two outflows, assuming a spherically symmetric expanding flow. We obtained a distance to the W3 IRS 5 region as 1.83 ? 0.14 kpc. The directions of the two outflows are roughly in the north-south direction, which is not significantly different from the direction of the global outflow seen in CO (J = 2-1) emission. This suggests that the massive-star cluster in the W3 IRS 5 region was created during formation of hierarchical structure in a parent molecular-cloud core. Such a structure is expected to preserve the angular momentum vector during star formation process, which may be along the directions of the present outflows.

A survey has been made in the SiO J = 1-0, v = 1 and 2 transitions (~43 GHz) for color-selected IRAS sources in the Galactic-center region of |l| ≤ 3° and |b| ≤ 3° using the Nobeyama 45 m telescope. We have detected 86 of 176 observed sources in the SiO masers. Distances to the sources are deduced from IRAS 12 and 25 μm flux densities and range approximately from 5 to 12 kpc. Radial velocities of the detected sources spread between -300 and 310 km s-1. The longitude-velocity (l-v) diagram exhibits an empty region of sources at l = -04-10 and Vlsr = 20-150 km s-1, which is interpreted as an undersampling effect of sources in the IRAS catalog at the Galactic central disk. The rotation rate, velocity dispersion, tilt angle of the rotation axis, and velocity shift at l = 0° are derived by fitting the velocities of the sources with a straight line as a function of Galactic longitude. These quantities are compatible with those obtained from previous observations of bulge stars with |b| > 3°. The average radial velocity of subsamples of stars tends to increase with distance, suggesting the presence streaming motion of stars in a barlike bulge. We conclude that most of the IRAS sources in the sample belong to the bulge.

We discuss the results on 26 water masers candidates observed with the 45 m millimeter wave telescope of the NRO of Japan, and propose using the tail length and integration intensity of the spectral line profile as criteria for molecular outflow. 9 out of the 26 candidates are shown to be without outflows.

CS (2-1) data of the Orion A Cloud obtained with the FCRAO 14 m telescope are shown. The CS (2-1) image shows the clumpy and filamentary structure of the Orion A cloud, as did our previous CS (1-0) image, obtained with the NRO 45 m telescope. The peak intensity TMB (CS 2-1) decreases more steeply than TMB (CS 1-0) toward the south along the filament. It is found that the gas density of the CS cores tends to be lower in the south of the cloud, and this explains the above difference in the line-intensity decrease. From CS and C34S data, we estimated the optical depth of CS (2-1) to be moderately high (2-5) and that of CS (1-0) to be typically less than unity.

We present aperture synthesis CO (J = 1-0) observations of the compact molecular outflow in the dark cloud B1 (Barnard 1). We have detected strong blueshifted emission having a peak brightness temperature of 14.3 K, while no significant emission was detected in the redshifted velocity range. The most prominent feature in our map is a distinct ringlike structure having a size of 25'' (8700 AU) × 14'' (5000 AU) at velocities blueshifted by 1.9-2.7 km s-1 from the systemic velocity. The central hole of the CO ring coincides well with the IRAS position, suggesting that this outflow is driven by the IRAS source, 03301+3057. The CO ring structure is interpreted as a conical outflow lobe with a brightened limb observed from its polar direction. The high-velocity gas that is blueshifted more than 4 km s-1 shows a V-shaped structure open to the southwest. This structure well delineates the northeast edge of the CO blue lobe observed with the single dish, where the CO lobe faces to the dense gas traced by the C18O emission. The strong peak of SiO emission observed by Yamamoto et al. is located at the interface between the CO outflow and the dense gas traced by the C18O and H13CO+ emission. This suggests that the outflow which emanates from the young star strongly interacts with the dense material and causes a shock that propagates into the surrounding cloud. The presence of strong SiO emission and the cold IRAS spectrum (log [Fν(60 μm)/Fν(100 μm)] < -0.76) suggest that the central source of B1 is a candidate for a protostar in the earliest evolutionary stage having an outflow in a nearly pole-on configuration.

Search for evidences of the dissipative core-mantle coupling is probably the most interesting subject for VLBI Earth rotation observations in view of physical informations to be obtained about the core-mantle boundary region. It is shown that the VLBI detected out-of-phase component of the retrograde annual nutation term is most likely to be a manifestation of the dissipative coupling because the coupling coefficient required to explain the observed out-of-phase component is just in the same order of magnitude as the one associated with the decade fluctuations in the rotation rate of the Earth, which are commonly attributed to the dissipative core-mantle coupling. Several observational tests are proposed to clarify the mechanism and frequency characteristics of the coupling. Researches along this direction require accuracy and time resolution of the VLBI observations beyond their present-day level. It is shown that a VLBI system of new design, 'antennacluster-antennacluster VLBI system', will be able to realize the high performance required.

The Japanese lunar mission, Selenological and Engineering Explorer (Kaguya), which was successfully launched on 14 September 2007, consists of a main satellite and two small satellites, Rstar and Vstar. Same-beam very long baseline interferometry (VLBI) observations of Rstar and Vstar were performed for 15.4 months from November 2007 to February 2009 using eight VLBI stations. In 2008, S band same-beam VLBI observations totaling 476 h on 179 days were undertaken. The differential phase delays were successfully estimated for most ( about 85%) of the same-beam VLBI observation periods. The high success rate was mainly due to the continuous data series measuring the differential correlation phase between Rstar and Vstar. The intrinsic measurement error in the differential phase delay was less than 1 mm RMS for small separation angles and increased to approximately 2.5 mm RMS for the largest separation angles ( up to 0.56 deg). The long-term atmospheric and ionospheric delays along the line of sight were reduced to a low level ( several tens of milimeters) using the same-beam VLBI observations, and further improved through application of GPS techniques. Combining the eight-station ( four Japanese telescopes of VLBI Exploration of Radio Astrometry and four international telescopes) S band same-beam VLBI data with Doppler and range data, the accuracy of the orbit determination was improved from a level of several tens of meters when only using Doppler and range data to a level of 10 m. As a preliminary test of the technique, the coefficient sigma degree variance of the lunar gravity field was compared with and without 4 months of VLBI data included. A significant reduction below around 10 deg ( especially for the second degree) was observed when the VLBI data were included. These observations confirm that the VLBI data contribute to improvements in the accuracy of the orbit determination and through this to the lunar gravity field model.

Taehyun Jung, Bong Won Sohn, Hideyuki Kobayashi, Tetsuo Sasao, Tomoya Hirota, Osamu Kameya, Yoon Kyung Choi, Hyun Soo Chung a Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea University of Science and Technology, Daejeon, Republic of Korea Mizusawa VERA Observatory, NAOJ, Mitaka, Tokyo, Japan Ajou University, Suwon 442-749, Republic of Korea Max-Planck-Institut fur Radioastronomie, Bonn, Germany E-mail: thjung@kasi.re.kr

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 the 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 the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as ~20 km/s both perpendicular to and parallel to the Galactic disk with a consistent timescale of ~20 Myr., 16 pages, 5 figures, accepted for publication in PASJ, VERA special issue

We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H$_{2}$O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud L1204G. Based on the phase-referencing VLBI astrometry, we derive an annual parallax of IRAS 22198+6336 to be 1.309$\pm$0.047 mas, corresponding to the distance of 764$\pm$27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduce the errors in the derived annual parallax by employing the position measurements for all of the 26 detected maser spots. Based on this result, we reanalyze the spectral energy distribution (SED) of IRAS 22198+6336 and find that the bolometric luminosity and total mass of IRAS 22198+6336 are 450$L_{\odot}$ and 7$M_{\odot}$, respectively. These values are consistent with an intermediate-mass YSO deeply embedded in the dense dust core, which has been proposed to be an intermediate-mass counterpart of a low-mass Class 0 source. In addition, we obtain absolute proper motions of the H$_{2}$O masers for the most blue-shifted components. We propose that the collimated jets aligned along the east-west direction are the most plausible explanation for the origin of the detected maser features., Comment: 15 pages, 7 figures, accepted for publication in PASJ (Vol.60, No.5, October 25, VERA special issue)

We present the results of the multi-frequency observations of radio outburst of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope. Since the prediction of a flare by RATAN-600, the source has been monitored from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the quench of the activity, successive flares exceeding 1 Jy were observed successfully. The time scale of the variability in the active phase is presumably shorter in higher frequency bands. We also present the result of a follow-up VLBI observation at 8.4 GHz with the Japanese VLBI Network (JVN) 2.6 days after the first rise. The VLBI image exhibits a single core with a size of, 17 pages,6 figures; accepted by PASJ