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THE APPLICATION OF MULTIVIEW METHODS FOR HIGH-PRECISION ASTROMETRIC SPACE VLBI AT LOW FREQUENCIES
Dodson, R.,Rioja, M.,Asaki, Y.,Imai, H.,Hong, X.-Y.,Shen, Z. American Institute of Physics 2013 The Astronomical journal Vol.145 No.6
<P>High-precision astrometric space very long baseline interferometry (S-VLBI) at the low end of the conventional frequency range, i.e., 20 cm, is a requirement for a number of high-priority science goals. These are headlined by obtaining trigonometric parallax distances to pulsars in pulsar-black hole pairs and OH masers anywhere in the Milky Way and the Magellanic Clouds. We propose a solution for the most difficult technical problems in S-VLBI by the MultiView approach where multiple sources, separated by several degrees on the sky, are observed simultaneously. We simulated a number of challenging S-VLBI configurations, with orbit errors up to 8 m in size and with ionospheric atmospheres consistent with poor conditions. In these simulations we performed MultiView analysis to achieve the required science goals. This approach removes the need for beam switching requiring a Control Moment Gyro, and the space and ground infrastructure required for high-quality orbit reconstruction of a space-based radio telescope. This will dramatically reduce the complexity of S-VLBI missions which implement the phase-referencing technique.</P>
KAMEYA, O.,TSUBOI, M.,ASAKI, Y.,YONEKURA, Y.,MIYAMOTO, Y.,KANEKO, H.,SETA, M.,NAKAI, N.,MIYOSHI, M.,TAKABA, H.,WAKAMATSU, K.,FUKUZAKI, Y.,MORIMITSU, T.,SEKIDO, M. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
We have been performing daily VLBI monitoring of the flux density of Sagittarius (Sgr) $A^{\ast}$ at 22 GHz from February 2013 to August 2014 using a sub-array of the Japanese VLBI Network (JVN). The purpose of this monitoring is to explore the flux density variability at daily time resolution for a period longer than one year with the G2 cloud approaching. The flux density of Sgr $A^{\ast}$ is basically stable during the observational period, though there are some small variations. The average and scattering range are consistent with the previously observed values. We have observed no strong flare of Sgr $A^{\ast}$ although it is near the expected peri-center passing.
Evidence of a Rattling Transition in the Caged Compounds LaRu2Zn20 and LaIr2Zn20: 139La NMR Studies
Hideki Tou,Kenji Asaki,Hisashi Kotegawa,Takahiro Onimaru,Keisuke T. Matsumoto,Yukihiro F. Inoue,Toshiro Takabatake 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report a study of 139La(I=7/2) nuclear magnetic resonance (NMR) to investigate the structuralphase transition in the two caged compounds LaIr2Zn20 and LaRu2Zn20 from microscopic viewpoints. The former compound shows a second-order structural phase transition around Ts = 200 Kwhereas the latter one shows a first-order structural phase transition at Ts = 150 K. For both compounds,quite narrow La-NMR lines of less that 10 kHz without any electric field gradient (EFG) atthe La site were observed at temperatures above Ts, indicating that the local symmetry at the Lasite holds a cubic symmetry. On the other hand, an EFG at La site appears at temperatures belowTs, evidencing symmetry lowering occurs at the La site at temperatures below Ts. At temperaturesaround Ts, both the nuclear spin-lattice relaxation rate (1/T1) and the nuclear spin-spin relaxationrate (1/T2) show unusual enhancements associated with the slowing down of the EFG fluctuations. However, the temperature dependences of 1/T1T and 1/T2 are different from the typical slowingdownphenomena of the EFG fluctuations due to the classical motional narrowing. The lowering ofthe local symmetry at the La site is ascribed to a freezing of the rattling motion.
SiO MASERS AROUND WX PSC MAPPED WITH THE KVN AND VERA ARRAY (KaVA)
Yun, Youngjoo,Cho, Se-Hyung,Imai, Hiroshi,Kim, Jaeheon,Asaki, Yoshiharu,Chibueze, James O.,Choi, Yoon Kyung,Dodson, Richard,Kim, Dong-Jin,Kusuno, Kozue,Matsumoto, Naoko,Min, Cheulhong,Oyadomari, Miyak American Astronomical Society 2016 The Astrophysical journal Vol.822 No.1
<P>We present the first images of the v = 1 and v = 2 J = 1 -> 0 SiO maser lines taken with KaVA, i.e., the combined array of the Korean Very Long Baseline Interferometry (VLBI) Network and the VLBI Exploration of Radio Astrometry ( VERA), toward the OH/IR star WX Psc. The combination of long and short antenna baselines enabled us to detect a large number of maser spots, which exhibit a typical ring-like structure in both the v. =. 1 and v = 2 J = 1 -> 0 SiO masers as those that have been found in previous VLBI observational results of WX Psc. The relative alignment of the v = 1 and v = 2 SiO maser spots are precisely derived from astrometric analysis, due. to the absolute coordinates of the reference maser spot that were well determined in an independent astrometric observation with VERA. The superposition of the v = 1 and v = 2 maser spot maps shows a good spatial correlation between the v = 1 and v = 2 SiO maser features. Nevertheless, it is also shown that the v = 2 SiO maser spot is distributed in an inner region compared to the v - 1 SiO maser by about 0.5 mas on average. These results provide good support for the recent theoretical studies of the SiO maser pumping, in which both the collisional and the radiative pumping predict the strong spatial correlation and the small spatial discrepancy between the v = 1 and v = 2 SiO maser.</P>
THE 2014 ALMA LONG BASELINE CAMPAIGN: OBSERVATIONS OF ASTEROID 3 JUNO AT 60 KILOMETER RESOLUTION
Hunter, T. R.,Kneissl, R.,Moullet, A.,Brogan, C. L.,Fomalont, E. B.,Vlahakis, C.,Asaki, Y.,Barkats, D.,Dent, W. R. F.,Hills, R. E.,Hirota, A.,Hodge, J. A.,Impellizzeri, C. M. V.,Liuzzo, E.,Lucas, R.,M IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.808 No.1
<P>We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0 ''.042 (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of 10 consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259 +/- 4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215 +/- 13 K, while the median over the whole surface is 197 +/- 15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids and to measure accurately their position, geometric shape, rotational period, and soil characteristics.</P>
THE 2014 ALMA LONG BASELINE CAMPAIGN: AN OVERVIEW
Partnership, ALMA,Fomalont, E. B.,Vlahakis, C.,Corder, S.,Remijan, A.,Barkats, D.,Lucas, R.,Hunter, T. R.,Brogan, C. L.,Asaki, Y.,Matsushita, S.,Dent, W. R. F.,Hills, R. E.,Phillips, N.,Richards, A. M IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.808 No.1
Vlahakis, C.,Hunter, T. R.,Hodge, J. A.,Pé,rez, L. M.,Andreani, P.,Brogan, C. L.,Cox, P.,Martin, S.,Zwaan, M.,Matsushita, S.,Dent, W. R. F.,Impellizzeri, C. M. V.,Fomalont, E. B.,Asaki, Y.,Barka IOP Publishing 2015 ASTROPHYSICAL JOURNAL LETTERS - Vol.808 No.1
<P>We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the z = 3.042 gravitationally lensed submillimeter galaxy HATLAS J090311.6+003906 (SDP. 81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to similar to 15 km. We present continuum imaging at 151, 236, and 290 GHz at unprecedented angular resolutions as fine as 23 mas, corresponding to an unmagnified spatial scale of similar to 180 pc at z = 3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of similar to 1 ''.5. We also present imaging of CO J = 10 - 9, J = 8 - 7, and J = 5 - 4 and H2O (202-111) line emission. The CO emission, at an angular resolution of similar to 170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.</P>