Tomoaki Oyama
A5068454302- Astrophysics and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Pulsars and Gravitational Waves Research
- Astrophysics and Star Formation Studies
- Stellar, planetary, and galactic studies
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- GNSS positioning and interference
- Geophysics and Gravity Measurements
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Particle Accelerators and Free-Electron Lasers
- Mechanics and Biomechanics Studies
- Superconducting and THz Device Technology
- Wireless Communication Networks Research
- Microwave Engineering and Waveguides
- Advanced Adaptive Filtering Techniques
- Atmospheric Ozone and Climate
- Particle Detector Development and Performance
- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Radio Wave Propagation Studies
- Black Holes and Theoretical Physics
- Photonic and Optical Devices
National Astronomical Observatory of Japan
2016-2025
Korean Association for the Study of Intestinal Diseases
2024
Korea Astronomy and Space Science Institute
2012-2024
Toyo University
2023
The Graduate University for Advanced Studies, SOKENDAI
2023
University College Cork
2023
National Institutes of Natural Sciences
2013-2020
Astronomical Observatory
2000-2008
Institute of Astronomy
2008
The University of Tokyo
2000-2008
Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by accretion matter onto super massive black holes. While the measured width profiles such jets on large scales agree with theories magnetic collimation, predicted structure disk at jet launch point has not been detected. We report radio interferometry observations 1.3mm wavelength elliptical galaxy M87 that spatially resolve base in this source. The derived size 5.5 +/- 0.4 Schwarzschild radii is...
We report on the results of multi-epoch VLBI observations with VERA (VLBI Exploration Radio Astrometry) 22 GHz H2O masers associated young stellar object SVS 13 in NGC 1333 region. have carried out phase-referencing astrometry and measured an annual parallax maser features 4.25+/-0.32 mas, corresponding to distance 235+/-18 pc from Sun. Our result is consistent a photometric 220 previously reported. Even though were detectable only for 6 months, present provide much higher accuracy than...
Sagittarius A*, the ~4 x 10^6 solar mass black hole candidate at Galactic Center, can be studied on Schwarzschild radius scales with (sub)millimeter wavelength Very Long Baseline Interferometry (VLBI). We report 1.3 mm observations of Sgr A* using a VLBI array consisting JCMT Mauna Kea, ARO/SMT Mt. Graham in Arizona, and two telescopes CARMA Cedar Flat California. Both quasar calibrator 1924-292 were observed over three consecutive nights, both sources clearly detected all baselines. For...
We present the initial results of multi-epoch VLBI observations 22 GHz H2O masers in Orion KL region with VERA (VLBI Exploration Radio Astrometry). With dual-beam receiving system, we have carried out phase-referencing astrometry and successfully detected an annual parallax to be 2.29+/-0.10 mas, corresponding distance 437+/-19 pc from Sun. The is determined for first time method these observations. Although this value consistent that previously reported, 480+/-80 pc, which estimated...
We present analyses to determine the fundamental parameters of Galaxy based on VLBI astrometry 52 Galactic maser sources obtained with VERA, VLBA and EVN. model Galaxy's structure a set including center distance R_0, angular rotation velocity at LSR Omega_0, mean peculiar motion respect (U_src, V_src, W_src), rotation-curve shape index, V component Solar motions V_sun. Based Markov chain Monte Carlo method, we find that is constrained 5% level be R_0 = 8.05 +/- 0.45 kpc, where error bar...
Abstract We present results of phase-referencing VLBI observations SiO masers in the Orion-KL region made with VERA. Using a strong maser spot 43GHz $v =$ 2 $J=$ 1-0 emission, we derived trigonometric parallax to be 2.39$\pm$0.03mas, corresponding distance 418$\pm$6pc, highest accuracy among existing measurements source. superimposed image 1 and features based on absolute positions obtained from astrometry common reference The both transitions show similar X-shaped distributions centered at...
We present the first astrometry catalog from Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). have compiled all results VERA, providing accurate trigonometric annual parallax and proper motion measurements. In total, 99 maser sources are listed in catalog. Among them, 21 newly reported while rest 78 referred to previously published or those preparation for forthcoming papers. The accuracy revisited compared with other projects such as...
We have performed high-precision astrometry of H2O maser sources in Galactic star forming region Sharpless 269 (S269) with VERA. successfully detected a trigonometric parallax 189+/-8 micro-arcsec, corresponding to the source distance 5.28 +0.24/-0.22 kpc. This is smallest ever measured, and first one beyond 5 The as well proper motions are used constrain outer rotation curve Galaxy, demonstrating that difference velocities at Sun S269 (which 13.1 kpc away from Galaxy's center) less than 3%....
The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve 1.3 mm emission from this source on angular scales comparable to that of general relativistic shadow. Previous EHT observations have used visibility amplitudes infer morphology millimeter-wavelength emission. Potentially much richer information contained in phases. We report phase Sgr obtained with total 13 nights over 4 years. Closure phases, sum phases...
The Atacama Millimeter/submillimeter Array (ALMA) Phasing Project (APP) has developed and deployed the hardware software necessary to coherently sum signals of individual ALMA antennas record aggregate in Very Long Baseline Interferometry (VLBI) Data Exchange Format. These beamforming capabilities allow array collectively function as equivalent a single large aperture participate global VLBI arrays. inclusion phased current networks operating at (sub)millimeter wavelengths provides an order...
We report on astrometric observations of H$_2$O masers around the red supergiant VY Canis Majoris carried out with VLBI Exploration Radio Astrometry (VERA). Based monitoring for 13 months, we successfully measured a trigonometric parallax 0.88$\pm$0.08mas, corresponding to distance 1.14$^{+0.11} _{-0.09}$kpc. This is most accurate determined CMa and first one based an annual measurement. The luminosity has been overestimated due previously accepted distance. With our result, re-estimated be...
Abstract We present results of multi-epoch VLBI observations with VERA (VLBI Exploration Radio Astrometry) the 22GHz H$_{2}$O masers associated a young stellar object (YSO) IRAS22198$+$6336 in dark cloud, L1204G. Based on phase-referencing astrometry, we derived an annual parallax to be 1.309$\pm$0.047mas, corresponding distance 764$\pm$27pc from Sun. Although most principal error source our astrometry is attributed internal structure maser spots, successfully reduced errors by employing...
Abstract We present the technique of instrumental delay calibration for dual-beam system VLBI Exploration Radio Astrometry (VERA), namely, horn-on-dish method, in which artificial noise sources are mounted on antenna feedome base and a wide-band radio is injected into receivers after reflection by subreflector. introduce basic concept with also results experiments to evaluate its accuracy. Detailed comparisons between model path calculations measured paths from show that method can calibrate...
Abstract The Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) is the first international array dedicated to high-frequency (23–43 GHz bands) observations in East Asia. Here, we report imaging three bright active galactic nuclei (AGNs) known for their complex morphologies: 4C 39.25, 3C 273, M 87. This one initial results KaVA's early operation. Our KaVA images reveal extended outflows with substructures such as knots...
Sagittarius A* (Sgr A*), the Galactic Center supermassive black hole (SMBH), is one of best targets to resolve innermost region SMBH with very long baseline interferometry (VLBI). In this study, we have carried out observations toward Sgr at 1.349 cm (22.223 GHz) and 6.950 mm (43.135 East Asian VLBI Network, as a part multi-wavelength campaign Event Horizon Telescope (EHT) in 2017 April. To mitigate scattering effects, physically motivated kernel model from Psaltis et al. (2018) parameters...
Context. Because of its proximity and the large size black hole, M 87 is one best targets for studying launching mechanism active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in accelerating jet. However, current observational estimates field strength jet limited innermost part (≲100 r s ) or HST-1 (∼10 5 ). No attempt has yet been made measure between. Aims. We aim infer out a distance several thousand by tracking distance-dependent changes...
We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in Galactic star-forming region NGC 281 West, which has been considered be part a 300-pc superbubble. successfully detected trigonometric parallax 0.355+/-0.030 mas, corresponding distance 2.82+/-0.24 kpc. Our direct determination resolved large discrepancy between previous photometric and kinematic studies; likely is far side Perseus spiral arm. The as well absolute proper motions were...
Abstract We report on results of multi-epoch VLBI observations H$_2$O masers associated with a low-mass young stellar object, IRAS 16293$-$2422 in $\rho$ Oph East, and fringe-phase position reference source, ICRF J162546.8$-$252738, using the Exploration Radio Astrometry (VERA) for high-precision astrometry. obtained an annual parallax maser feature to be $\pi=$ 5.6$^{+1.5}_{-0.5}$ mas, corresponding distance $D=178^{+18}_{-37}$ pc. also found 10 relative proper motions features respect...
Abstract We carry out astrometric Very Long Baseline Interferometry (VLBI) observations for Cygnus X-3, a high-mass X-ray binary (HMXB), with the Korean–Japanese joint VLBI array (KaVA) from 2020 to 2021. The have been optimized subdued phase when X-3 is relatively faint, sidestepping giant flare between and position of core in was measured through observations. Based on accumulating positions available archival data, obtained over $\sim$38 yr Large Array (VLA), (VLBA), European Network...
Abstract We report on the results of monitoring observations 242 stellar H$_2$O masers, which have been made with Iriki 20m telescope VLBI Exploration Radio Astrometry (VERA) from 2003 July to 2006 November. The present paper mainly focuses 85 masers that tightly observed a time spacing typically 1−2 months. In particular, 46 out them recognized concerning their periodic flux variation and light−curve data visual light. Thus, shows some statistical views variability properties masers. found...
A prototype for a space-borne smart reconfigurable reflector, whose reflector surface can be changed intentionally using adjustment actuators, has been developed, and its performance was evaluated through experiments. The designed as sub-reflector of space antenna observations in the extremely highfrequency band (frequency range: 30 -300 GHz) is used correcting path length errors system caused by deformations main reflector. It consists solid surface, supporting members, actuators. actuators...
We present a detection of bright burst from FRB 20201124A, which is one the most active repeating FRBs, based on S-band observations with 64-m radio telescope at Usuda Deep Space Center/JAXA. This first observed by using Japanese facility. Our 2 GHz in February 2022 highest frequency for this and fluence $>$ 189 Jy ms brightest bursts source. place an upper limit spectral index $\alpha$ = -2.14 S band non-detection X same time. compare event rate detected ones previous research, suggest that...
Abstract We have achieved the first VLBI detections of ground vibrational state (v = 0) 28SiO (hereafter, SiO) and 29SiO masers J 1→0 rotational transitions, towards 25 $M_{\odot }$ red supergiant (RSG) star, VY Canis Majoris (VY CMa), taking advantage high sensitivity Exploration Radio Astrometry (VERA) telescopes that coordinate with Nobeyama 45 m telescope. In addition, we successfully detected SiO transition in v 3) CMa for time VLBI. The maser spot 0 was cross-power spectra taken...
We present the results of first dual-beam observations with VERA (VLBI Exploration Radio Astrometry). The a pair H2O maser sources W49N and OH43.8-0.1 have been carried out on 2002 May 29 July 23, fringes lines at 22 GHz successfully detected. While residual fringe phases both show rapid variations over 360 degree due to atmospheric fluctuation, differential phase between two remains constant for 1 hour r.m.s. 8 degree, demonstrating that fluctuation is removed effectively by referencing....