VLBI Exploration Of Radio Astrometry Research Articles

Trigonometric parallax and proper motion of Sagittarius A* measured by VERA using the new broad-band back-end system OCTAVE-DAS

Abstract We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be 117 ± 17 micro-arcseconds ($\, \mu \mbox{as}$) using the VLBI Exploration of Radio Astrometry (VERA) with the newly developed broad-band signal-processing system named “OCTAVE-DAS.” The measured parallax corresponds to a Galactocentric distance at the Sun of $R_0 = 8.5^{+1.5}_{-1.1}\:$kpc. By combining the astrometric results with VERA and the Very Long Baseline Array (VLBA) over a monitoring period of 25 yr, the proper motion of Sgr A* is obtained to be (μα, μδ) = (−3.133 ± 0.003, −5.575 ± 0.005) mas yr−1 in equatorial coordinates, corresponding to (μl, μb) = (−6.391 ± 0.005, −0.230 ± 0.004) mas yr−1 in Galactic coordinates. This gives an angular orbital velocity of the Sun of Ω⊙ = 30.30 ± 0.02 km s−1 kpc−1. We find upper limits to the core wander, Δθ < 0.20 mas (1.6 au), peculiar motion, Δμ < 0.10 mas yr−1 (3.7 km s−1), and acceleration, a < 2.6 $\, \mu \mbox{as} \:$yr−2 (0.10 km s−1 yr−1) for Sgr A*. Thus, we obtained upper mass limits of $\approx 3 \times 10^{4}\, M_{\odot }$ and $\approx 3 \times 10^{3}\, M_{\odot }$ for the supposed intermediate-mass black holes at 0.1 and 0.01 pc from the Galactic center, respectively.

Limits of water maser kinematics: insights from the high-mass protostar AFGL 5142-MM1

ABSTRACT Multi-epoch very long baseline interferometry (VLBI) observations measure three-dimensional water maser motions in protostellar outflows, enabling analysis of inclination and velocity. However, these analyses assume that water masers and shock surfaces within outflows are co-propagating. We compare VLBI data on maser-traced bow shocks in the high-mass protostar AFGL 5142-MM1, from seven epochs of archival data from the VLBI Exploration of Radio Astrometry (VERA), obtained from 2014 April to 2015 May, and our newly conducted data from the KVN and VERA Array (KaVA), obtained in 2016 March. We find an inconsistency between the expected displacement of the bow shocks and the motions of individual masers. The separation between two opposing bow shocks in AFGL 5142-MM1 was determined to be 337.17 ± 0.07 mas in the KaVA data, which is less than an expected value of 342.1 ± 0.7 mas based on extrapolation of the proper motions of individual maser features measured by VERA. Our measurements imply that the bow shock propagates at a velocity of 24 ± 3 km s−1, while the individual masing gas clumps move at an average velocity of 55 ± 5 km s−1; that is ,the water masers are moving in the outflow direction at double the speed at which the bow shocks are propagating. Our results emphasize that investigations of individual maser features are best approached using short-term high-cadence VLBI monitoring, while long-term monitoring on timescales comparable to the lifetimes of maser features is better suited to tracing the overall evolution of shock surfaces. Observers should be aware that masers and shock surfaces can move relative to each other, and that this can affect the interpretation of protostellar outflows.

Water maser distributions and their internal motions in the Sagittarius B2 complex

Abstract We conducted a multi-epoch very long baseline interferometry (VLBI) observation of 22 GHz H2O maser sources, which are associated with the Sagittarius B2 (Sgr B2) complex, one of the most active star-forming regions in the Galactic center. Using the VLBI exploration of radio astrometry (VERA) array, we detected 29, 90, and seven maser features in Sgr B2(North), (Main), and (South), respectively. We also discovered two H2O maser features in Sgr B2 (Mid-North). Moreover, we successfully measured spatial distributions and internal motions of the H2O maser sources in Sgr B2(M). We then discovered that the H2O maser features in Sgr B2(M) are located at the outer edge of H ii regions detected by using the centimeter radio continuum emission, and observationally demonstrated that they have outward motions from the two H ii regions separated by 1′. We obtained an absolute proper motion of (μαcos δ, μδ) = (−2.17 ± 0.03, −2.63 ± 0.06) mas yr−1 and marginally detected a parallax of Sgr B2, which is consistent with other measurements. The absolute proper motion corrected by the internal motions of the H2O maser features implies that the Sgr B2 complex is located at the near side of the Galactic center and is moving toward the positive galactic longitude. We estimate that Sgr B2 is at 160 ± 10 pc in front of Sgr A* by assuming a simple circular orbit of the central molecular zone (CMZ).

A kinematic study of the disc-outflow system around a high-mass protostar G59.783+0.065 probed by methanol and water masers

ABSTRACT Class II CH3OH masers are used as a convenient tracer of disc-like structures in high-mass star formation. However, more than half of them show a complex distribution in Very Long Baseline Interferometry (VLBI) maps. The origin of such a complex distribution is still unknown. We conducted VLBI monitoring observations to unveil the origin of a complex class II CH3OH maser in the high-mass star-forming region G59.783+0.065. We observed the CH3OH maser at 6.7 GHz and the H2O maser at 22 GHz to probe detailed circumstellar kinematics and structures by the Japanese VLBI network and the VLBI Exploration of Radio Astrometry. We found similar bipolar distributions in both masers, specifically two clusters located 2000 au apart along the east–west direction. We detected a linear distribution of CH3OH masers in the western cluster. A position–velocity diagram shows that the western CH3OH masers trace a rotating disc-wind or infalling component inside an edge-on disc-like structure. In contrast to the simple bipolar expanding motions of the H2O masers, the CH3OH masers exhibited complex motions despite their spatial coincidence. Some of the eastern CH3OH masers showed bipolar expansions similar to the H2O masers, while others displayed random or even inward motions. Such complex kinematics and their close association with the H2O maser could occur at the boundary between outflow and inflow. We suggest that the complex distribution of class II CH3OH masers, like G59.783+0.065 arises from several distinct circumstellar structures that simultaneously achieve maser excitation.

Astrometric VLBI observations of H2O masers in an extreme OH/IR star candidate NSV 17351

Abstract The results of astrometric very long baseline interferometry (VLBI) observations toward an extreme OH/IR star candidate NSV 17351 are presented. Using the VERA (VLBI Exploration of Radio Astrometry) VLBI array , we observed 22 GHz H2O masers of NSV 17351 and derived an annual parallax of 0.247 ± 0.035 mas, which corresponds to a distance of 4.05 ± 0.59 kpc, from the observation. By averaging proper motions of 15 maser spots further, we determined the systemic proper motion of NSV 17351 to be (μαcos δ, μδ)avg. = (−1.19 ± 0.11, 1.30 ± 0.19) mas yr−1. The maser spots spread out over a region of 20 × 30 mas, which can be converted to a spatial distribution of ∼80 × 120 au at the source distance. Internal motions of the maser spots suggest an outward-moving maser region with respect to the estimated position of the central star. From single-dish monitoring of the H2O maser emission, we estimate the pulsation period of NSV 17351 to be 1122 ± 24 d. This is the first report of the periodic activity of NSV 17351, indicating that NSV 17351 could have a mass of ∼4 M⊙. We confirmed that the time variation of H2O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H2O maser spectra for the last 40 years, we discovered the long-term acceleration in the radial velocity of the circumstellar matter to be 0.17 ± 0.03 km s−1 yr−1. We finally determined the position and kinematics in the Milky Way Galaxy and found that NSV 17351 is located in an interarm region between the Outer and Perseus arms. We note that the astrometric VLBI observation toward extreme OH/IR stars shows us a useful sample of the Galactic dynamics.

East Asian VLBI Network astrometry toward the extreme outer Galaxy: Kinematic distance with the proper motion of G034.84−00.95

Abstract We aim to reveal the structure and kinematics of the Outer Scutum–Centaurus (OSC) arm located on the far side of the Milky Way through very long baseline interferometry (VLBI) astrometry using KaVA, which is composed of KVN (the Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H2O maser source, which is associated with the star-forming region G034.84−00.95, to be (μαcos δ, μδ) = (−1.61 ± 0.18, −4.29 ± 0.16) mas yr−1 in equatorial coordinates (J2000.0). We estimate the 2D kinematic distance to the source to be 18.6 ± 1.0 kpc, which is derived from the variance weighted average of kinematic distances with local standard of rest velocity and the galactic-longitude component of the measured proper motion. Our result places the source in the OSC arm and implies that G034.84−00.95 is moving away from the Galactic plane with a vertical velocity of −38 ± 16 km s−1. Since the H i supershell GS033+06−49 is located at a kinematic distance roughly equal to that of G034.84−00.95, it is expected that gas circulation occurs between the outer Galactic disk around G034.84−00.95 with a Galactocentric distance of $12.8^{+1.0}_{-0.9}\:$kpc and the halo. We evaluate possible origins of the fast vertical motion of G034.84−00.95, which are (1) supernova explosions and (2) cloud collisions with the Galactic disk. However, neither of these possibilities are matched with the results of VLBI astrometry or the spatial distributions of H ii regions and H i gas.

Demonstration of Ultrawideband Polarimetry Using VLBI Exploration of Radio Astrometry (VERA)

We report on recent technical developments in the front- and back-ends for the four 20 m radio telescopes of the Japanese Very-Long-Baseline Interferometry (VLBI) project, VLBI Exploration of Radio Astrometry (VERA). We present a brief overview of a dual-circular polarization receiving and ultrawideband (16 Giga bit s−1) recording systems that were installed on each of the four telescopes operating at 22 and 43 GHz bands. The wider-band capability improves the sensitivity of VLBI observations for continuum emission, and the dual-polarization capability enables the study of magnetic fields in relativistic jets ejected from supermassive black holes in active galactic nuclei and in sites of star formation and around evolved stars.We present the linear polarization intensity maps of extragalactic sources at 22 and 43 GHz obtained from the most recent test observations to show the state of the art of the VERA polarimetric observations. At the end of this article, given the realization of VLBI polarimetry with VERA, we describe the future prospects for scientific aims and further technical developments.

Intensity monitor of water maser emission associated with massive YSOs

AbstractWe are carrying out the intensity monitoring of the water maser emission associated with massive young stellar objects (YSOs) using the VLBI Exploration of Radio Astrometry (VERA) antennas. We are currently monitoring 108 sources. During our long monitoring period, we could find flares on several YSOs. As an example, we show the results from IRAS 16293–2422 and NGC2071 IRS1 here. We also show the results of monitoring of the water maser emission from G36.115+0.552, which the methanol maser flare was reported. We observed it as often as possible, usually once a day.

The origin of the Perseus-arm gap revealed with VLBI astrometry

AbstractThe Perseus arm has a gap in Galactic longitudes (l) between 50° and 80° where the arm has little star formation activity. To understand the gap, we conducted VERA (VLBI Exploration of Radio Astrometry) astrometry and analyzed archival H <SC>I</SC> 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 associated with the gap. Perseus-arm sources G049.41+00.32 and G050.28–00.39 lag relative to a Galactic rotation by 77 ± 17 km s-1 and 31 ± 10 km s-1, respectively. The noncircular motion of G049.41+00.32 cannot be explained by the gravitational potential of the arm. We discovered rectangular holes with integrated brightness temperatures less than 30 K arcdeg in l vs. VLSR of the H <SC>I</SC> data. Also, we found extended H <SC>I</SC> emission on one side of the Galactic plane when integrating the H <SC>I</SC> data over the velocity range covering the hole. G049.41+00.32 and G050.28–00.39 are moving toward the emission. The Galactic H <SC>I</SC> 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.

Implications from the Velocity Profile of the M87 Jet: A Possibility of a Slowly Rotating Black Hole Magnetosphere

Motivated by the measured velocity profile of the M87 jet using the Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) by Park et al. indicating that the starting position of the jet acceleration is farther from the central engine of the jet than predicted in general relativistic magnetohydrodynamic simulations, we explore how to mitigate the apparent discrepancy between the simulations and the KaVA observation. We use a semi-analytic jet model proposed by Tomimatsu & Takahashi consistently solving the transmagnetic field structure but neglecting any dissipation effects. By comparing the jet model with the observed M87 jet velocity profile, we find that the model can reproduce the logarithmic feature of the velocity profile and can fit the observed data when choosing c/(100r g ) ≲ Ω F ≲ c/(70r g ), where r g is the gravitational radius. While a total specific energy () of the jet changes the terminal bulk Lorentz factor of the jet, a slower angular velocity of the black hole magnetosphere (Ω F ) makes a light-cylinder radius (r lc) larger, and it consequently pushes out a location of a starting point of the jet acceleration. Using the estimated Ω F we further estimate the magnetic field strength on the event horizon scale in M87 by assuming Blandford–Znajek process is in action. The corresponding magnetic flux threading the event horizon of M87 is in good agreement with a magnetically arrested disk regime.

VERA astrometry toward the Perseus arm gap

Abstract The Perseus arm has a gap in Galactic longitudes (l) between 50° and 80° (hereafter the Perseus arm gap) where the arm has little star formation activity. To better understand the gap, we conducted astrometric observations with VERA (VLBI Exploration of Radio Astrometry) 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 of 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−1 and 31 ± 10 km s−1, 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°, −15 km s−1), 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−1). 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.

Proper motions of water masers in the star-forming region IRAS 23139+5939

Abstract We observed H2O (616→523) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA, a combination of very long baseline interferometry (VLBI) arrays between the Korean VLBI Network and the VLBI Exploration of Radio Astrometry (Japan). Through multi-epoch KaVA observations, we detected three groups of maser features, two of which coincide with those previously detected by the Karl G. Jansky Very Large Array. By determining the maser proper motions, we found that the first of maser groups exhibits an expanding motion that traces a wide-angle outflow almost along the line of sight, while the second one seems to be associated with the envelope of an H ii region. We discuss the star formation activity in IRAS 23139+5939, which may be reflected in the high variability of H2O masers associated with an outflow seen from the front.

East Asian VLBI Network observations of active galactic nuclei jets: imaging with KaVA+Tianma+Nanshan

The East Asian Very Long Baseline Interferometry (VLBI) Network (EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China, Japan and Korea. EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions. After the combination of the Korean VLBI Network (KVN) and the VLBI Exploration of Radio Astrometry (VERA) into KaVA, further expansion with the joint array in East Asia is actively promoted. Here we report the first imaging results (at 22 and 43 GHz) of bright radio sources obtained with KaVA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China. To test the EAVN imaging performance for different sources, we observed four active galactic nuclei (AGN) having different brightness and morphology. As a result, we confirmed that the Tianma 65-m Radio Telescope (TMRT) significantly enhances the overall array sensitivity, a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of KaVA only. The addition of the Nanshan 26-m Radio Telescope (NSRT) further doubled the east-west angular resolution. With the resulting high-dynamic-range, high-resolution images with EAVN (KaVA+TMRT+NSRT), various fine-scale structures in our targets, such as the counter-jet in M87, a kink-like morphology of the 3C 273 jet and the weak emission in other sources are successfully detected. This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general. Ongoing expansion of EAVN will further enhance the angular resolution, detection sensitivity and frequency coverage of the network.

Astrometry and infrared observations of the Mira variable stars AP Lyncis, V837 Herculis, and BX Camelopardalis: Implications for the period–luminosity relation of the Milky Way

Abstract AP Lyn and V837 Her are long-period Mira variable stars in the Milky Way. We performed VLBI Exploration of Radio Astrometry (VERA) phase-referenced observations towards H2O masers associated with AP Lyn and V837 Her. The annual parallaxes of AP Lyn and V837 Her were obtained to be 2.008 ± 0.038 mas and 1.090 ± 0.014 mas, corresponding to distances of 498 ± 10 pc and 917 ± 12 pc, respectively. From our multi-epoch infrared observations using the Kagoshima University 1 m telescope, we derived the mean J-, H-, and K′-band magnitudes of AP Lyn, V837 Her, and an additional long-period Mira variable BX Cam, whose parallax is known. We derived their pulsation periods to be 433 ± 1 d, 520 ± 1 d, and 458 ± 1 d, respectively, using the K′-band light curves. The MK–log P relation of long-period Mira variables seem to be violated by Mira variable stars with larger-than-expected MK values (like OZ Gem) in the Milky Way because of circumstellar extinction leading to an observed dimming effect. AP Lyn, V837 Her, and BX Cam (like OZ Gem) are dimming from the trend to O-rich stars in the Large Magellanic Cloud. This implies that the high metallicity of the Milky Way galaxy increases the opacity of the Mira-type variable stars and strengthens mass loss.

Multiple Outflows in the High-mass Cluster-forming Region G25.82–0.17

Abstract We present results of continuum and spectral line observations with Atacama Large Millimeter/submillimeter Array (ALMA) and 22 GHz water (H2O) maser observations using the KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry) array (KaVA) toward a high-mass star-forming region, G25.82–0.17. Multiple 1.3 mm continuum sources are revealed, indicating the presence of young stellar objects (YSOs) at different evolutionary stages, namely an ultracompact H ii region, G25.82–E, a high-mass young stellar object (HM-YSO), G25.82–W1, and starless cores, G25.82–W2 and G25.82–W3. Two SiO outflows, at N–S and SE–NW orientations, are identified. The CH3OH 8−1–70 E line, known to be a Class I CH3OH maser at 229 GHz, is also detected, showing a mixture of thermal and maser emission. Moreover, the H2O masers are distributed in a region ∼0.″25 shifted from G25.82–W1. The CH3OH 224–215 E line shows a compact ringlike structure at the position of G25.82–W1 with a velocity gradient, indicating a rotating disk or envelope. Assuming Keplerian rotation, the dynamical mass of G25.82–W1 is estimated to be >25 M ⊙ and the total mass of 20–84 M ⊙ is derived from the 1.3 mm continuum emission. The driving source of the N–S SiO outflow is G25.82–W1 while that of the SE–NW SiO outflow is uncertain. Detection of multiple high-mass starless/protostellar cores and candidates without low-mass cores implies that HM-YSOs could form in individual high-mass cores as predicted by the turbulent core accretion model. If this is the case, the high-mass star formation process in G25.82 would be consistent with a scaled-up version of low-mass star formation.

VEDA: VERA data analysis software for VLBI phase-referencing astrometry

Abstract We present the VEra Data Analyzer (VEDA) software package for Very Long Baseline Interferometry (VLBI) phase-referencing observations and parallax measurements. The Japanese VLBI project VLBI Exploration of Radio Astrometry (VERA) provides high-precision astrometric results at the 10 μas level. To achieve this precision, accurate calibration of the atmospheric phase fluctuation, the instrumental phase, and the source structural effect is required. VEDA specializes in phase-referencing data analysis, including these calibrations. In order to demonstrate its performance we analyzed H2O maser observations of W 3(OH) and Orion KL with VERA. Their parallaxes were obtained to be 0.527 ± 0.016 mas and 2.459 ± 0.029 mas, respectively. We also analyzed their data using AIPS, which is widely used for VLBI data analysis, and confirmed that the parallaxes obtained using VEDA and AIPS are coincident within 10 μas. VEDA is available for high-precision parallax and proper motion measurements of Galactic maser sources.

Trigonometric parallax of O-rich Mira variable star OZ Gem (IRAS 07308+3037): A confirmation of the difference between the P–L relations of the Large Magellanic Cloud and the Milky Way

Abstract OZ Geminorum (OZ Gem) is a galactic Mira variable in the Milky Way (MW). We measured its annual parallax with VLBI Exploration of Radio Astrometry to be π = 0.806 ± 0.039 mas, corresponding to a distance of D = 1.24 ± 0.06 kpc. Based on multi-epoch infrared observations with the Kagoshima University 1 m telescope, we also derived the mean J-, H-, and K′-band magnitudes of OZ Gem to be 5.75 ± 0.47 mag, 4.00 ± 0.16 mag, and 2.65 ± 0.16 mag, respectively. We derived a pulsation period of OZ Gem as 592 ± 1 d from the K′-band lightcurve. From the period–luminosity (P–L) relation and two-color diagram of the Large Magellanic Cloud (LMC), the property of OZ Gem suggests that OZ Gem is assigned among the carbon-rich Mira variables. However, our optical spectroscopic observational results (with the 1.5 m Kanata telescope) confirmed OZ Gem to be an oxygen-rich Mira star with the detection of multiple titanium oxide transition absorption lines. We suggest that OZ Gem is a low-mass star evolving to an OH/IR star with large mass loss and dust formation. It is predicted that the lower limit to the initial mass of AGB stars for developing the C-rich surface chemistry is larger in the MW than in the LMC because of larger metallicity, and OZ Gem is likely to be the first example to prove this. Our results highlight the necessity of deriving the PL relation of the Milky Way with high accuracy.

Performance of VERA in 10 micro-arcsecond astrometry

Abstract Very Long Baseline Interferometry (VLBI) astrometry using the phase-referencing technique remains an open issue for the quantitative characterization of the observing conditions to achieve a feasible parallax precision of 10 micro-arcseconds (μas). To address this issue, we evaluated the astrometric performance of the VLBI Exploration of Radio Astrometry (VERA) through the parallax measurements of five distant star-forming regions under good observing conditions of close separations (${0{^{\circ}_{.}}5}$–${1{_{.}^{\circ}}3}$) and high elevations (≥50°). Their parallaxes measured 89–200 μas, corresponding to distances of 5–11 kpc with an error of 11–20 μas. Furthermore, we investigated the contributions to the position error budget and concluded that the tropospheric residual contribution is the dominant error source. We also confirmed that the astrometric error propagation strongly depends on the term $\Delta \sec Z$, which stands for the difference between $\sec Z$ of the target and its reference source, where Z is the zenith angle during the observations. We found that for a source pair with a $\Delta \sec Z$ less than 0.01 (for example, a set of a close separation of $\le {{0{^{\circ}_{.}}5}}$ and a high elevation of ≥50°), we can achieve the parallax precision of 10 μas using a typical monitoring program comprising 10 observing epochs over a span of two years.

Astrometry of H2O masers in the W 48 A (G35.20−01.74) H ii region with VERA: A compact disk outflow inside core H-2a

Abstract W 48 A core H-2a is one of the young massive protostellar objects in the W 48 region. We conducted multi-epoch astrometric observations of the water (H2O) masers associated with the W 48 A core H-2a with VLBI Exploration of Radio Astrometry (VERA). The trigonometric annual parallax of W 48 A core H-2a was measured to be 0.433 ± 0.026 mas, corresponding to a distance of $2.31^{+0.15}_{-0.13}$ kpc. This agrees with the revised parallax of 0.412 ± 0.014 mas by Wu et al. (2019, ApJ, 874, 94). We obtained the systemic proper motion and local standard of rest velocity to be (μαcos δ, μδ) = (0.26 ± 0.73, −3.87 ± 0.33) mas yr−1 and vLSR = 41.9 ± 0.9 km s−1, respectively. The distribution of the H2O masers covers an area of 70 mas × 80 mas, corresponding to 160 au × 180 au at the distance of 2.31 kpc. The internal proper motions of the H2O masers trace an east–west bipolar outflow. With the recent absolute position measurement of the 6.7 GHz methanol (CH3OH) masers and their elliptical distribution, whose major axis is perpendicular to the axis of the bipolar outflow, we suggest the presence of a disk outflow system in core H-2a. The spectral energy distribution (SED) of the driving source of core H-2a was previously reported to yield a luminosity and envelope mass of 8000 ± 1000 $W_{\odot}$ and 170 ± 30 $M_{\odot}$, respectively. Refitting the SED with the new distance, we obtained the luminosity to be 3100 ± 388 $L_{\odot}$ and derived the zero age main sequence (ZAMS) stellar mass to be 9 ± 1 $M_{\odot}$. Using our distance measurement, we derived the peculiar motion of W 48 A to be (Us, Vs, Ws) = (1 ± 4, 5 ± 6, −15 ± 5) km s−1.

Development of a 22/43 GHz-band quasi-optical perforated plate and dual-band observation system of the Nobeyama 45 m telescope

Abstract We have developed a system of simultaneous observations in the 22 and 43 GHz bands using the Nobeyama 45 m telescope, and are also working to add the 86 GHz band. Multi-frequency observations are realized by mounting perforated plates in the optics as dichroic frequency-selective devices. This paper presents the development of the perforated plate for the 22 and 43 GHz bands and the results of the commissioning observations with this plate on the Nobeyama 45 m telescope. The perforated plate is designed to be installed in the large telescope optics with a physical beam diameter as large as $50\:$cm for transmitting the higher frequency (43 GHz) band and for reflecting the lower frequency (22 GHz) band. The developed plate achieves an insertion loss of $0.22\:$dB (5%) at $43\:$GHz. The effects of the mounted plate on the systematic offsets and on the accuracy degradation of pointing were confirmed to be negligible. The differences in the main-beam/aperture efficiencies from those without the plate were confirmed to be within a few percent points. In addition, we successfully detected interferometry fringes in a very long baseline interferometry (VLBI) observation using the 45 m telescope and the VLBI Exploration of Radio Astrometry (VERA) 20 m telescopes, which confirmed that the dual-band observation system is operationally effective in both single-dish and VLBI observations.