Showing 1–50 of 206 results for author: Imai, H

Molecular absorption lines toward the Galactic ISM detected at 89 GHz with VLBI

Authors: Keisuke Nakashima, Hiroshi Imai, Youngjoo Yun

Abstract: As the first step to explore the Galactic foreground interstellar medium (ISM) with high angular resolution, we investigated the detectability of molecular absorption lines with very long baseline interferometry (VLBI). This paper reports our first observations of HCO+ J=1-0 and HCN J=1-0 molecular absorption lines toward four extragalactic compact radio sources with the Korean VLBI Network (KVN).… ▽ More As the first step to explore the Galactic foreground interstellar medium (ISM) with high angular resolution, we investigated the detectability of molecular absorption lines with very long baseline interferometry (VLBI). This paper reports our first observations of HCO+ J=1-0 and HCN J=1-0 molecular absorption lines toward four extragalactic compact radio sources with the Korean VLBI Network (KVN). HCO+ absorption lines were detected in all directions and HCN absorption lines in three directions. All of these detections, except for two HCO+ detections, are reported here for the first time with VLBI. We find that the column density ratio N(HCN)/N(HCO+) obtained with VLBI is consistent with the trend established from observations with connected-element interferometers, demonstrating the feasibility of future VLBI studies of molecular absorption. △ Less

Submitted 3 August, 2026; originally announced August 2026.

Comments: 5 pages, 2 figures, 3 tables. Accepted for publication in PASJ

Spatio-kinematical structure of the Galactic Nuclear Stellar Disk revealed in VLBI astrometry of circumstellar masers

Authors: Hiroshi Imai, Kohei Kurahara, Huib J. van Langevelde, Maria J. Rioja, Richard Dodson

Abstract: SKA-VLBI astrometry will enable us to measure up to thousands of three dimensional motions of OH masers associated with circumstellar envelopes (CSEs) of OH/IR stars in the Nuclear Stellar Disk (NSD) and sites of high mass star formation in the Central Molecular Zone (CMZ) of the Galactic Center (GC). It is expected that the spatio-kinematical distribution of those OH masers should indicate the ex… ▽ More SKA-VLBI astrometry will enable us to measure up to thousands of three dimensional motions of OH masers associated with circumstellar envelopes (CSEs) of OH/IR stars in the Nuclear Stellar Disk (NSD) and sites of high mass star formation in the Central Molecular Zone (CMZ) of the Galactic Center (GC). It is expected that the spatio-kinematical distribution of those OH masers should indicate the existence of a ring structure in the NSD, which has formed as a result of outward propagation of star-formation activities in the GC. This is likely visualized clearly by a group of OH/IR stars, some of which should have stellar pulsation periods of >400 days and the corresponding ages of <500 Myr, and some sites of ongoing star formation. These OH/IR stars should host 1612-MHz OH masers, some of which should become targets of huge-sample VLBI astrometry, in moderate accuracy, in SKA-MID Band 2 (~1.6 GHz). The data of maser source proper motions will exhibit a stream motion in the stellar ring structure. Furthermore, the information of accurate distances (error <100 pc) of the maser sources are necessary to directly find the major-axis direction of a possible elliptical ring of stars at ~8 kpc. These distances may be yielded through trigonometric parallaxes measurable in SKA-MID Band 5a (5--7 GHz) and/or photometric parallaxes derived from the pulsation period--luminosity relation of long period variable stars hosting the maser sources. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Comments: 11 pages, 4 figures, Published in Advancing Astrophysics with SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Imai01

Report number: AASKAII/Imai01

VLBI-Enabled Localization of Continuous GW Sources

Authors: Keitaro Takahashi, Takuya Akahori, Kenta Fujisawa, Hiroshi Imai, Hajime Kita, Hideyuki Kobayashi, Hiroaki Misawa, Kotaro Niinuma, Tomoaki Oyama, Kazuhiro Takefuji, Fuminori Tsuchiya

Abstract: Pulsar timing arrays (PTAs) are opening the nanohertz gravitational-wave (GW) band by timing millisecond pulsars (MSPs) to target signals from supermassive black hole binaries (SMBHBs). Beyond evidence for a stochastic background, a central SKA-era objective is detecting individual continuous-wave (CW) sources. The scientific payoff hinges on localization: conventional PTA searches yield uncertain… ▽ More Pulsar timing arrays (PTAs) are opening the nanohertz gravitational-wave (GW) band by timing millisecond pulsars (MSPs) to target signals from supermassive black hole binaries (SMBHBs). Beyond evidence for a stochastic background, a central SKA-era objective is detecting individual continuous-wave (CW) sources. The scientific payoff hinges on localization: conventional PTA searches yield uncertainties of tens-hundreds of deg$^2$, too large to identify a unique host, obtain a redshift, infer intrinsic masses, or pursue electromagnetic counterparts. This limitation is chiefly geometric: the CW response includes Earth and pulsar terms, and poorly known pulsar distances make the pulsar-term phase a free parameter that degrades triangulation. If distances to a few MSPs are known to better than a GW wavelength ($\sim$ 1 pc), these phases are fixed and localization improves by orders of magnitude. Simulations indicate that with sub-parsec distances for a handful of nearby MSPs, the uncertainty can shrink to $\sim 10^{-3}$ deg$^2$ (arcminute scale), enabling unique host association and multi-messenger follow-up. Achieving such distances requires $\sim$ 10 $μ$arcsec parallaxes for MSPs within a few hundred parsecs, a precision now approached with Very Long Baseline Interferometry (VLBI) and expected to become practical with phased-array SKA1-Mid operating as a sensitive VLBI element. SKA1's multi-beam, multi-calibrator astrometry will provide the independent distance priors needed for PTAs to localize nanohertz GW sources and measure SMBHB parameters and environments. We assess VLBI's role in PTA CW searches and propose a concrete SKA1-Mid observing strategy for nearby MSPs to deliver the required sub-parsec distances. △ Less

Submitted 27 June, 2026; originally announced June 2026.

Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Takahashi01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Report number: AASKAII/Takahashi01

All-valid-state HOBO encoding for constrained combinatorial optimization on NISQ devices

Authors: Juncheng Wang, Takumi Kanezashi, Daisuke Tsukayama, Koki Awaya, Reo Saito, Jun-ichi Shirakashi, Tetsuo Shibuya, Hiroshi Imai

Abstract: Continued advancements in quantum computing have stimulated growing interest in translating quantum technologies into real-world applications. Consequently, the investigation of practically motivated NP-hard problems is of significant value. This study investigates the performance of a variational quantum eigensolver (VQE) in addressing the traveling salesperson problem (TSP) through noiseless sim… ▽ More Continued advancements in quantum computing have stimulated growing interest in translating quantum technologies into real-world applications. Consequently, the investigation of practically motivated NP-hard problems is of significant value. This study investigates the performance of a variational quantum eigensolver (VQE) in addressing the traveling salesperson problem (TSP) through noiseless simulations representative of noisy intermediate-scale quantum (NISQ) devices using higher-order binary optimization (HOBO) encodings. We construct a HOBO Hamiltonian with an efficient binary representation and propose an all-valid-state HOBO (AVS-HOBO) scheme based on cyclic mapping that eliminates one penalty term and reuses states that would otherwise be invalid. Using TSP instances of up to 20 cities, we compare the original HOBO and AVS-HOBO encodings from multiple perspectives, including the energy convergence behavior and the approximation, tour-length, and feasibility ratios. In addition to simulations, we perform computations on real quantum hardware with different device architectures, where we not only compare the performances of different chips but also investigate the effects of different error-mitigation methods on actual quantum machines. The results indicate that AVS-HOBO encoding enhances the practical reliability of VQE on NISQ devices and improves scalability for larger TSP instances, with broader applicability to constrained quantum optimization problems. △ Less

Submitted 18 June, 2026; originally announced June 2026.

Comments: 14 pages, 11 figures. Corresponding author: Jun-ichi Shirakashi

Measurement of dijet transverse momentum imbalance and azimuthal acoplanarity in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV with the sPHENIX detector

Authors: sPHENIX Collaboration, M. I. Abdulhamid, U. Acharya, E. R. Adams, G. Adawi, I. Ahmed, C. A. Aidala, Y. Akiba, M. Alfred, S. Ali, A. Alsayegh, S. Altaf, H. Amedi, D. M. Anderson, V. V. Andrieux, A. Angerami, N. Applegate, M. U. Ashraf, H. Aso, S. Aune, B. Azmoun, V. R. Bailey, D. Baranyai, S. Bathe, A. Bazilevsky , et al. (305 additional authors not shown)

Abstract: This Letter reports on measurements of dijet transverse momentum ($p_\mathrm{T}$) imbalance and azimuthal acoplanarity in proton-proton collisions at $\sqrt{s} = 200$~GeV, using data recorded by the sPHENIX detector at the Relativistic Heavy Ion Collider corresponding to an integrated luminosity of $41$~pb$^{-1}$. Jets are reconstructed using the anti-$k_t$ algorithm with radius parameters… ▽ More This Letter reports on measurements of dijet transverse momentum ($p_\mathrm{T}$) imbalance and azimuthal acoplanarity in proton-proton collisions at $\sqrt{s} = 200$~GeV, using data recorded by the sPHENIX detector at the Relativistic Heavy Ion Collider corresponding to an integrated luminosity of $41$~pb$^{-1}$. Jets are reconstructed using the anti-$k_t$ algorithm with radius parameters $R = 0.3$ to $0.8$ from electromagnetic and hadronic calorimeter energy deposits. The jet $p_\mathrm{T}$ resolution is determined directly in data using two independent methods. The dijet $p_\mathrm{T}$ imbalance is characterized by the ratio $x_\mathrm{J} = p_\mathrm{T,2}/p_\mathrm{T,1}$ where $p_\mathrm{T,1(2)}$ is the highest (second-highest) jet $p_\mathrm{T}$ in the event. The dijet azimuthal acoplanarity $Δφ= |φ_1 - φ_2|$ is also reported. Results are reported for different $p_\mathrm{T,1}$ selections and jet radius parameters, normalized per dijet pair, and compared to the results of \textsc{Pythia} and \textsc{Herwig} Monte Carlo event generators. These measurements provide a stringent quantitative test of the modeling of QCD parton shower and hadronization dynamics, place important constraints on event-generator descriptions at RHIC energies, and establish a comprehensive proton-proton baseline for forthcoming measurements of jet modification in heavy ion collisions. △ Less

Submitted 15 June, 2026; originally announced June 2026.

Comments: 19 pages total, 8 figures, 1 tables. All figures and tables can be found at https://www.sphenix.bnl.gov/PublicResults/sPH-JET-2026-01

Vacuum structure of a scalar field on a torus with uniform magnetic flux

Authors: Mayumi Akamatsu, Hiroki Imai, Makoto Sakamoto, Maki Takeuchi

Abstract: We investigate the vacuum expectation value of a complex scalar field on a two-dimensional torus with quantized magnetic flux $M$. A characteristic feature of this system is the emergence of a critical area: when the area of the torus exceeds this critical value, the vacuum expectation value becomes nonvanishing. Furthermore, any nonzero vacuum expectation value necessarily exhibits nontrivial dep… ▽ More We investigate the vacuum expectation value of a complex scalar field on a two-dimensional torus with quantized magnetic flux $M$. A characteristic feature of this system is the emergence of a critical area: when the area of the torus exceeds this critical value, the vacuum expectation value becomes nonvanishing. Furthermore, any nonzero vacuum expectation value necessarily exhibits nontrivial dependence on the coordinates of the torus. Employing the lowest-mode approximation, we find a single vacuum configuration for $M=1$, whereas two and six degenerate vacuum configurations arise for $M=2$ and $M=3$, respectively. We then analyze the symmetry properties of these vacuum configurations and determine whether they preserve or spontaneously break the symmetry of the underlying system. △ Less

Submitted 24 April, 2026; originally announced April 2026.

Comments: 25 pages, 5 figures

Utility of NISQ devices: optimizing experimental parameters for the fabrication of Au atomic junction using gate-based quantum computers

Authors: Takumi Kanezashi, Daisuke Tsukayama, Jun-ichi Shirakashi, Tetsuo Shibuya, Hiroshi Imai

Abstract: Feedback-controlled electromigration (FCE) enables precise regulation of atomic migration by carefully optimizing multiple experimental parameters. However, manually fine-tuning these parameters poses significant challenges. This study investigated the feasibility of autonomously fabricating Au atomic junctions through gate-based quantum computing using a noisy intermediate-scale quantum (NISQ) de… ▽ More Feedback-controlled electromigration (FCE) enables precise regulation of atomic migration by carefully optimizing multiple experimental parameters. However, manually fine-tuning these parameters poses significant challenges. This study investigated the feasibility of autonomously fabricating Au atomic junctions through gate-based quantum computing using a noisy intermediate-scale quantum (NISQ) device, which effectively approximates solutions to combinatorial optimization problems. We compared the computational accuracy of the NISQ device against a previously reported D-Wave quantum annealer. The results indicate that the NISQ device achieved lower residual energies and produced higher-quality approximate solutions for large-scale problems than the quantum annealing system. △ Less

Submitted 14 April, 2026; originally announced April 2026.

Comments: 8 pages, 5 figures. Corresponding author: Jun-ichi Shirakashi

Journal ref: Applied Physics Express 18 (2025) 047001

Decomposition of Multi-Qubit Gates for Circuit Cutting

Authors: Ryota Tamura, Tomoya Kashimata, Yohei Hamakawa, Kosuke Tatsumura, Hiroshi Imai

Abstract: A large-scale quantum circuit can be partitioned into multiple subcircuits through circuit cutting, where each subcircuit is executed multiple times and the expectation value of the original circuit is reconstructed by classical post-processing from their measurement (sampling) results. In this process, appropriate cut locations are identified after the user-designed quantum circuit, including mul… ▽ More A large-scale quantum circuit can be partitioned into multiple subcircuits through circuit cutting, where each subcircuit is executed multiple times and the expectation value of the original circuit is reconstructed by classical post-processing from their measurement (sampling) results. In this process, appropriate cut locations are identified after the user-designed quantum circuit, including multi-qubit gates that act on three or more qubits, has been decomposed into single-qubit gates and two-qubit gates such as the CNOT gate. Here, we present a method for reducing the sampling overhead, which refers to the increase in the number of samples required due to the cutting process, by modifying the decomposition strategy of multi-qubit gates. Using MCX and CCCX gates as representatives of multi-qubit gates, we demonstrate that the proposed decomposition method, which introduces a small number of ancilla qubits according to the identified cut locations, effectively decreases the sampling overhead. △ Less

Submitted 27 March, 2026; originally announced March 2026.

Comments: 8 pages, 7 figures, 1 table

Efficient time-series prediction on NISQ devices via time-delayed quantum extreme learning machine

Authors: Mio Kawanabe, Saud Cindrak, Kathy Ludge, Jun-ichi Shirakashi, Tetsuo Shibuya, Hiroshi Imai

Abstract: We proposed a time-delayed quantum extreme learning machine (TD-QELM) for efficient time-series prediction on noisy intermediate-scale quantum (NISQ) devices. By encoding multiple past inputs simultaneously, TD-QELM achieves shallow circuit depth independent of sequence length, thereby, mitigating noise accumulation and reducing computational complexity. Experiments using the NARMA benchmark on bo… ▽ More We proposed a time-delayed quantum extreme learning machine (TD-QELM) for efficient time-series prediction on noisy intermediate-scale quantum (NISQ) devices. By encoding multiple past inputs simultaneously, TD-QELM achieves shallow circuit depth independent of sequence length, thereby, mitigating noise accumulation and reducing computational complexity. Experiments using the NARMA benchmark on both noiseless simulations and IBM's 127-qubit processor demonstrate that TD-QELM consistently outperforms conventional quantum reservoir computing in prediction accuracy and noise robustness. These results highlight TD-QELM as a practical and scalable framework for time-series learning on current NISQ hardware. △ Less

Submitted 16 June, 2026; v1 submitted 24 February, 2026; originally announced February 2026.

Comments: 9 pages, 5 figures, 4 Tables. Corresponding author: Jun-ichi Shirakashi

The Nearby Evolved Stars Survey III: First data release of JCMT CO-line observations

Authors: S. H. J. Wallström, P. Scicluna, S. Srinivasan, J. G. A. Wouterloot, I. McDonald, L. Decock, M. Wijshoff, R. Chen, D. Torres, L. Umans, B. Willebrords, F. Kemper, G. Rau, S. Feng, M. Jeste, T. Kaminski, D. Li, F. C. Liu, A. Trejo-Cruz, H. Chawner, S. Goldman, H. MacIsaac, J. Tang, S. T. Zeegers, T. Danilovich , et al. (15 additional authors not shown)

Abstract: Low- to intermediate-mass ($\sim$0.8$-$8 M$_\odot$) evolved stars contribute significantly to the chemical enrichment of the interstellar medium in the local Universe, making accurate mass-return estimates in their final stages crucial. The Nearby Evolved Stars Survey (NESS) is a large multi-telescope project targeting a volume-limited sample of $\sim$850 stars within 3 kpc in order to derive the… ▽ More Low- to intermediate-mass ($\sim$0.8$-$8 M$_\odot$) evolved stars contribute significantly to the chemical enrichment of the interstellar medium in the local Universe, making accurate mass-return estimates in their final stages crucial. The Nearby Evolved Stars Survey (NESS) is a large multi-telescope project targeting a volume-limited sample of $\sim$850 stars within 3 kpc in order to derive the dust and gas return rates in the Solar Neighbourhood, and to constrain the physics underlying these processes. We present an initial analysis of the CO-line observations, including detection statistics, carbon isotopic ratios, initial mass-loss rates, and gas-to-dust ratios. We describe a new data reduction pipeline to analyse the available NESS CO data from the JCMT, measuring line parameters and calculating empirical gas mass-loss rates. We present the first release of the available data on 485 sources, one of the largest homogeneous samples of CO data to date. Comparison with a large literature sample finds that high mass-loss rate and especially carbon-rich sources are over-represented in literature, while NESS is probing significantly more sources at low mass-loss rates, detecting 59 sources in CO for the first time and providing useful upper limits. CO line detection rates are 81% for the CO (2--1) line and 75% for CO (3--2). The majority (82%) of detected lines conform to the expected soft parabola shape, while eleven sources show a double wind. Calculated mass-loss rates show power-law relations with both the dust-production rates and expansion velocities up to $\sim 5 \times 10^{-6}$~\msunyr. Median gas-to-dust ratios of 250 and 680 are found for oxygen-rich and carbon-rich sources, respectively. Our analysis of CO observations in this first data release highlights the importance of our volume-limited approach in characterizing the local AGB population as a whole. △ Less

Submitted 16 October, 2025; originally announced October 2025.

Comments: 18 pages, 12 figures, accepted for publication in Astronomy & Astrophysics, data to be made available at https://evolvedstars.space

Journal ref: A&A 704, A276 (2025)

Identification and characterization of nascent planetary nebulae with OH and H$_2$O masers

Authors: Roldán A. Cala, José F. Gómez, Luis F. Miranda, Hiroshi Imai, Guillem Anglada, Itziar de Gregorio-Monsalvo, Keiichi Ohnaka, Olga Suárez, Daniel Tafoya, Lucero Uscanga

Abstract: Stars like the Sun expel their outer layers and form planetary nebulae (PNe) as they evolve into white dwarfs. PNe exhibit diverse morphologies, the origins of which are not fully understood. PNe with OH (OHPNe) and H$_{2}$O (H$_{2}$OPNe) masers are thought to be nascent PNe. However, the number of known OHPNe and H$_{2}$OPNe remains small, and only in eight cases the position of the maser emissio… ▽ More Stars like the Sun expel their outer layers and form planetary nebulae (PNe) as they evolve into white dwarfs. PNe exhibit diverse morphologies, the origins of which are not fully understood. PNe with OH (OHPNe) and H$_{2}$O (H$_{2}$OPNe) masers are thought to be nascent PNe. However, the number of known OHPNe and H$_{2}$OPNe remains small, and only in eight cases the position of the maser emission has been found to coincide with the PN, using the high astrometric accuracy of interferometric observations. In order to identify more OHPNe and H$_{2}$OPNe, we used public databases and our own ATCA/VLA observations to match the positions of OH and H$_{2}$O masers with known PNe and radio continuum emitters, considering radio continuum emission as a possible tracer of the photoionized gas that characterizes PNe. Here we report the confirmation of positional coincidence of maser emission with one more PN, and 12 PN candidates. Moreover, we have confirmed three evolved stars as `water fountains' (WFs) hosting H$_2$O masers. These WFs are associated with radio continuum emission, but their possible nature as PNe has not yet been confirmed. Although a final characterization of maser-emitting PNe as a group still requires confirmation of more objects, their distribution in the infrared color-color diagrams suggests that they are a heterogeneous group of PNe. In particular, the new OHPN IRAS 07027$-$7934 has been reported to contain a late [WC]-type central star, while the maser emission implies an O-rich envelope. This property is found in only one other known maser-emitting PN, although we found evidence that other confirmed and candidate OHPNe may also have mixed chemistry, since they show emission from polycyclic aromatic hydrocarbons. The new WF IRAS 18443$-$0231 shows radio continuum that is dominated by strong and variable non-thermal emission, as in magnetized outflows. △ Less

Submitted 5 October, 2025; v1 submitted 19 September, 2025; originally announced September 2025.

Comments: 31 pages, 13 figures, 14 tables, accepted for publication in A&A

Beam test results of the Intermediate Silicon Tracker for sPHENIX

Authors: C. W. Shih, G. Nukazuka, Y. Sugiyama, Y. Akiba, D. Cacace, H. En'yo, T. Hachiya, S. Hasegawa, M. Hata, H. Imai, C. M. Kuo, M. Morita, I. Nakagawa, Y. Nakamura, G. Nakano, Y. Namimoto, R. Nouicer, R. Pisani, M. Shibata, M. Shimomura, R. Takahama, K. Toho, H. Tsujibata, M. Tsuruta, M. Watanabe

Abstract: The Intermediate Silicon Tracker (INTT), a two-layer barrel silicon strip tracker, is a key component of the tracking system for sPHENIX at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The INTT is designed to enable the association of reconstructed tracks with individual RHIC bunch crossings. To evaluate the performance of preproduction INTT ladders and the readout… ▽ More The Intermediate Silicon Tracker (INTT), a two-layer barrel silicon strip tracker, is a key component of the tracking system for sPHENIX at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The INTT is designed to enable the association of reconstructed tracks with individual RHIC bunch crossings. To evaluate the performance of preproduction INTT ladders and the readout chain, a beam test was conducted at the Research Center for Accelerator and Radioisotope Science, Tohoku University, Japan. This paper presents the performance of the INTT evaluated through studies of the signal-to-noise ratio, residual distribution, spatial resolution, hit-detection efficiency, and multiple track reconstruction. △ Less

Submitted 5 February, 2026; v1 submitted 31 August, 2025; originally announced September 2025.

Comments: 11 pages, 11 figures, 2 tables

Journal ref: Nucl. Instrum. Methods A, 1086 (2026), Article 171312

The Nearby Evolved Stars Survey (NESS) V: properties of volume-limited samples of Galactic evolved stars

Authors: I. McDonald, S. Srinivasan, P. Scicluna, O. C. Jones, A. A. Zijlstra, S. H. J. Wallström, T. Danilovich, J. H. He, J. P. Marshall, J. Th. van Loon, R. Wesson, F. Kemper, A. Trejo-Cruz, J. Greaves, T. Dharmawardena, J. Cami, H. Kim, K. E. Kraemer, C. J. R. Clark, H. Shinnaga, C. Haswell, H. Imai, J. G. A. Wouterloot, A. J. Pérez Vidal, G. Rau , et al. (1 additional authors not shown)

Abstract: We provide a meta-study of the statistical and individual properties of two volume-complete sets of evolved stars in the Solar Neighbourhood: (1) 852 stars from the Nearby Evolved Stars Survey (NESS), and (2) a partially overlapping set of 507 evolved stars within 300 pc. We also investigate distance determinations to these stars, their luminosity functions and their spatial distribution. Gaia APS… ▽ More We provide a meta-study of the statistical and individual properties of two volume-complete sets of evolved stars in the Solar Neighbourhood: (1) 852 stars from the Nearby Evolved Stars Survey (NESS), and (2) a partially overlapping set of 507 evolved stars within 300 pc. We also investigate distance determinations to these stars, their luminosity functions and their spatial distribution. Gaia APSIS GSP-Phot AENEAS temperatures of bright giant stars often appear to be underestimated. Existing literature on AGB stars under-samples both the most and least extreme nearby dust-producing stars. We reproduce the literature star-formation history of the solar neighbourhood, though stellar-evolution models over-predict the number of AGB stars of ages around 500 Myr. The distribution of AGB stars broadly matches the known 300 pc scale height of the Galactic disc and shows concentration in the direction of the Galactic centre. Most dust-producing carbon stars belong to the Galactic thick-disc population. △ Less

Submitted 12 June, 2025; originally announced June 2025.

Comments: 36 pages, 22 figures, accepted MNRAS

Measurement of the transverse energy density in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV with the sPHENIX detector

Authors: sPHENIX Collaboration, M. I. Abdulhamid, U. Acharya, E. R. Adams, G. Adawi, C. A. Aidala, Y. Akiba, M. Alfred, S. Ali, A. Alsayegh, S. Altaf, H. Amedi, D. M. Anderson, V. V. Andrieux, A. Angerami, N. Applegate, H. Aso, S. Aune, B. Azmoun, V. R. Bailey, D. Baranyai, S. Bathe, A. Bazilevsky, S. Bela, R. Belmont , et al. (281 additional authors not shown)

Abstract: This paper reports measurements of the transverse energy per unit pseudorapidity ($dE_{T}/dη$) produced in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, performed with the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The results cover the pseudorapidity range $\left|η\right| < 1.1$ and constitute the first such measurement performed using a hadronic calorimeter at RHIC. Measure… ▽ More This paper reports measurements of the transverse energy per unit pseudorapidity ($dE_{T}/dη$) produced in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV, performed with the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The results cover the pseudorapidity range $\left|η\right| < 1.1$ and constitute the first such measurement performed using a hadronic calorimeter at RHIC. Measurements of $dE_{T}/dη$ are presented for a range of centrality intervals and the average $dE_{T}/dη$ as a function of the number of participating nucleons, $N_{\mathrm{part}}$, is compared to a variety of Monte Carlo heavy-ion event generators. The results are in agreement with previous measurements at RHIC, and feature an improved granularity in $η$ and improved precision in low-$N_{\mathrm{part}}$ events. △ Less

Submitted 29 August, 2025; v1 submitted 2 April, 2025; originally announced April 2025.

Comments: 18 pages total, 6 figures, 2 tables. All figures and tables can be found at https://www.sphenix.bnl.gov/PublicResults/sPH-BULK-2025-02 , data available at https://www.hepdata.net/record/159889

Journal ref: Phys. Rev. C 112 (2025) 024908

Measurement of charged hadron multiplicity in Au+Au collisions at $\sqrt{\text{s}_{\text{NN}}} = 200$ GeV with the sPHENIX detector

Authors: sPHENIX Collaboration, M. I. Abdulhamid, U. Acharya, E. R. Adams, G. Adawi, C. A. Aidala, Y. Akiba, M. Alfred, S. Ali, A. Alsayegh, S. Altaf, H. Amedi, D. M. Anderson, V. V. Andrieux, A. Angerami, N. Applegate, H. Aso, S. Aune, B. Azmoun, V. R. Bailey, D. Baranyai, S. Bathe, A. Bazilevsky, S. Bela, R. Belmont , et al. (281 additional authors not shown)

Abstract: The pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of $\sqrt{s_\mathrm{NN}} = 200$ GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction effic… ▽ More The pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of $\sqrt{s_\mathrm{NN}} = 200$ GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction efficiency, combinatorial pairs, and contributions from secondary decays. The measured distributions cover $|η| < 1.1$ across various centralities, and the average pseudorapidity density of charged hadrons at mid-rapidity is compared to predictions from Monte Carlo heavy-ion event generators. This result, featuring full azimuthal coverage at mid-rapidity, is consistent with previous experimental measurements at the Relativistic Heavy Ion Collider, thereby supporting the broader sPHENIX physics program. △ Less

Submitted 31 August, 2025; v1 submitted 2 April, 2025; originally announced April 2025.

Comments: 22 pages total, 6 figures, 4 tables. All figures and tables can be found at https://www.sphenix.bnl.gov/PublicResults/sPH-BULK-2025-01 , data available at https://www.hepdata.net/record/ins2907537

Journal ref: JHEP 08 (2025) 075

The Ladder and Readout Cables of Intermediate Silicon Strip Detector for sPHENIX

Authors: Y. Akiba, H. Aso, J. T. Bertaux, D. Cacace, K. Y. Chen, K. Y. Cheng, A. Enokizono, H. Enyo, K. Fujiki, Y. Fujino, M. Fujiiwara, T. Hachiya, T. Harada, S. Hasegawa, M. Hata, B. Hong, J. Hwang, T. Ichino, M. Ikemoto, H. Imagawa, H. Imai, Y. Ishigaki, M. Isshiki, K. Iwatsuki, R. Kane M. Kano , et al. (46 additional authors not shown)

Abstract: A new silicon-strip-type detector was developed for precise charged-particle tracking in the central rapidity region of heavy ion collisions. A new detector and collaboration at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is sPHENIX, which is a major upgrade of the PHENIX detector. The intermediate tracker (INTT) is part of the advanced tracking system of the sPHENIX dete… ▽ More A new silicon-strip-type detector was developed for precise charged-particle tracking in the central rapidity region of heavy ion collisions. A new detector and collaboration at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is sPHENIX, which is a major upgrade of the PHENIX detector. The intermediate tracker (INTT) is part of the advanced tracking system of the sPHENIX detector complex together with a CMOS monolithic-active-pixel-sensor based silicon-pixel vertex detector, a time-projection chamber, and a micromegas-based detector. The INTT detector is barrel shaped and comprises 56 silicon ladders. Two different types of strip sensors of 78~$μm$ pitch and 320~$μm$ thick are mounted on each half of a silicon ladder. Each strip sensor is segmented into 8$\times$2 and 5$\times$2 blocks with lengths of 16 and 20 mm. Strips are read out with a silicon strip-readout (FPHX) chip. In order to transmit massive data from the FPHX to the down stream readout electronics card (ROC), a series of long and high speed readout cables were developed. This document focuses on the silicon ladder, the readout cables, and the ROC of the INTT. The radiation hardness is studied for some parts of the INTT devices in the last part of this document, since the INTT employed some materials from the technology frontier of the industry whose radiation hardness is not necessarily well known. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: Submitted to NIM-A

First VLBI Imaging of SiO $v=0$, $J=1 \rightarrow 0$ Masers in VY Canis Majoris

Authors: Hiroko Shinnaga, Miyako Oyadomari, Hiroshi Imai, Tomoaki Oyama, Mark J. Claussen, Masumi Shimojo, Satoshi Yamamoto, Anita M. S. Richards, Sandra Etoka, Malcolm Gray, Takeru Suzuki

Abstract: We achieved the first VLBI detections of the ground vibrational state ($v=0$) $^{28}$SiO (hereafter, SiO) and $^{29}$SiO masers of the $J=1\rightarrow 0$ rotational transitions, towards the 25 \Msun ~red supergiant (RSG) star, VY Canis Majoris (VY CMa), taking advantage of the high sensitivity of the VLBI Exploration of Radio Astrometry (VERA) telescopes that coordinate with the Nobeyama 45 m tele… ▽ More We achieved the first VLBI detections of the ground vibrational state ($v=0$) $^{28}$SiO (hereafter, SiO) and $^{29}$SiO masers of the $J=1\rightarrow 0$ rotational transitions, towards the 25 \Msun ~red supergiant (RSG) star, VY Canis Majoris (VY CMa), taking advantage of the high sensitivity of the VLBI Exploration of Radio Astrometry (VERA) telescopes that coordinate with the Nobeyama 45 m telescope. In addition, we successfully detected the SiO $J=1\rightarrow 0$ transition in the $v=3$ state towards VY CMa for the first time with VLBI. The SiO $J=1\rightarrow 0$ maser spot in $v=0$ state was detected in the cross-power spectra taken with the baselines involving the Nobeyama 45-m telescope. The combination of previously reported absolute astrometry and the relative astrometry technique allowed us to derive the location of the SiO $v=0$ maser spot, {(RA, DEC) = ( 7${\rm ^h}$ 22${\rm ^m}$ 58.$^{\rm s}$32, $-$25$^{\circ}$ 46$^{\prime}$ 3.$^{\prime\prime}$4) in J2000 at an absolute positional accuracy of $\sim$100 milliarcseconds (mas). The SiO $v=0$ maser spot is offset by the amount of ($Δ$RA, $Δ$DEC)=($-$150, $-$300) (mas) to the southwest of the stellar position, suggesting that the $v = 0$ maser spot is associated with its outflow activity.} This observational study demonstrates that the brightest SiO $v=0$ maser spot is compact (3 mas), producing an extremely high brightness of $\sim$ 10$^7$ K. This indicates that the SiO $v=0$ maser action may originate from strong shocks in the stellar wind emanating from this extreme RSG that leads to its intense mass ejection. △ Less

Submitted 7 March, 2025; originally announced March 2025.

Comments: 10 pages, 4 figures, accepted for the publication of the Publication of Astronomical Society of Japan (PASJ)

ALMA observations of CO isotopologues towards six obscured post-AGB stars

Authors: T. Khouri, D. Tafoya, W. H. T. Vlemmings, H. Olofsson, C. Sánchez Contreras, J. Alcolea, J. F. Gómez, L. Velilla-Prieto, R. Sahai, M. Santander-García, V. Bujarrabal, A. Karakas, M. Saberi, I. Gallardo Cava, H. Imai, A. F. Pérez-Sánchez

Abstract: Low- and intermediate-mass stars evolve through the asymptotic giant branch (AGB), when an efficient mass-loss process removes a significant fraction of their initial mass. A substantial increase in the mass-loss rate at the end of the AGB is observed for at least some stars for unknown reasons. This creates post-AGB objects that are completely enshrouded in thick dusty envelopes and might be asso… ▽ More Low- and intermediate-mass stars evolve through the asymptotic giant branch (AGB), when an efficient mass-loss process removes a significant fraction of their initial mass. A substantial increase in the mass-loss rate at the end of the AGB is observed for at least some stars for unknown reasons. This creates post-AGB objects that are completely enshrouded in thick dusty envelopes and might be associated with binary interactions. We observed the $J=2-1$ line of $^{13}$CO, C$^{17}$O, and C$^{18}$O with the Atacama Large Millimeter / submillimeter Array (ALMA) towards six obscured post-AGB stars (four C-rich and two O-rich sources) to constrain the properties of their circumstellar envelopes, recent mass-loss histories, and initial mass of the central stars. Based on the inferred $^{17}$O/$^{18}$O isotopic ratios, we find all stars to have relatively low initial masses ($< 2~M_\odot$) contrary to suggestions in the literature of higher masses for some sources. We infer a mass for HD~187885 $\sim 1.15~M_\odot$, which is relatively low for a carbon star. For all but one source (GLMP~950), we observe kinematic components with velocities $\gtrsim 30$~km~s$^{-1}$, which are faster than typical AGB wind expansion velocities. For most sources, these higher-velocity outflows display point-symmetric morphologies. The case of Hen~3-1475 is particularly spectacular, with the high-velocity molecular outflow interleaved with the high-velocity outflow of ionised gas observed at optical wavelengths. Based on the size of the emission regions of the slow components of the outflows, we derive typical kinematic ages associated with the C$^{18}$O~$J=2-1$ emission $\lesssim 1500$~years and obtain relatively high associated mass-loss rates ($\gtrsim10^{-4}~M_\odot~{\rm yr}^{-1}$). The sources with known spectral types are found to have evolved faster than expected based on stellar evolutionary models. △ Less

Submitted 8 January, 2025; originally announced January 2025.

Comments: Accepted for publication in Astronomy & Astrophysics

Journal ref: A&A 694, A222 (2025)

An interferometric search for SiO maser emission in planetary nebulae

Authors: Roldán A. Cala, José F. Gómez, Luis F. Miranda, Hiroshi Imai, Itziar de Gregorio-Monsalvo, Florin Placinta Mitrea, Mayra Osorio, Guillem Anglada

Abstract: Maser emission of SiO, H$_2$O and, OH is widespread in Asymptotic Giant Branch (AGB) stars with oxygen(O)-rich envelopes. This emission quickly disappear during the post-AGB phase and is extremely rare in planetary nebulae (PN). So far, only eight PNe have been confirmed to show OH and/or H$_2$O maser emission, and none has ever been found to show SiO maser emission. We intend to obtain the first… ▽ More Maser emission of SiO, H$_2$O and, OH is widespread in Asymptotic Giant Branch (AGB) stars with oxygen(O)-rich envelopes. This emission quickly disappear during the post-AGB phase and is extremely rare in planetary nebulae (PN). So far, only eight PNe have been confirmed to show OH and/or H$_2$O maser emission, and none has ever been found to show SiO maser emission. We intend to obtain the first detection of a SiO maser from a PNe. Such a detection would provide us with a useful tool to probe mass-loss in PNe at a scales of a few AU from the central star, much shorter than the scales traced by H$_2$ or OH masers. We compiled two different samples. The first one comprises all known PNe with confirmed OH and/or H$_2$O maser emission, as well as two candidate PNe showing OH masers. For the second sample we compiled single-dish SiO maser detections in the literature, and compared them with catalogs of PNe and radio continuum emission (which could trace photoionized gas in a PNe). We identified five targets (either PN or radio continuum sources) within the beam of the single-dish SiO maser observations. We then carried out interferometric observations of both samples with the Australia Telescope Compact Array, to confirm the spatial association between continuum and SiO maser emission. We found no SiO maser emission associated with any confirmed or candidate PN. In all targets, except IRAS 17390$-$3014, there is no spatial coincidence between SiO masers and radio continuum emission. While in IRAS 17390$-$3014 we cannot completely rule out a possible association, it is unlikely that the radio continuum emission arises from a planetary nebula. The absence of SiO maser emission in PNe showing OH or H$_2$O masers is of special interest, since thermal SiO emission has been reported in at least one of these targets, indicating that SiO molecules can be present in gas phase. △ Less

Submitted 30 October, 2024; originally announced October 2024.

Comments: 15 pages, 7 figures, 4 tables. Accepted for publication in A&A

Spatio-temporal reconstruction of substance dynamics using compressed sensing in multi-spectral magnetic resonance spectroscopic imaging

Authors: Utako Yamamoto, Hirohiko Imai, Kei Sano, Masayuki Ohzeki, Tetsuya Matsuda, Toshiyuki Tanaka

Abstract: The objective of our study is to observe dynamics of multiple substances in vivo with high temporal resolution from multi-spectral magnetic resonance spectroscopic imaging (MRSI) data. The multi-spectral MRSI can effectively separate spectral peaks of multiple substances and is useful to measure spatial distributions of substances. However it is difficult to measure time-varying substance distribu… ▽ More The objective of our study is to observe dynamics of multiple substances in vivo with high temporal resolution from multi-spectral magnetic resonance spectroscopic imaging (MRSI) data. The multi-spectral MRSI can effectively separate spectral peaks of multiple substances and is useful to measure spatial distributions of substances. However it is difficult to measure time-varying substance distributions directly by ordinary full sampling because the measurement requires a significantly long time. In this study, we propose a novel method to reconstruct the spatio-temporal distributions of substances from randomly undersampled multi-spectral MRSI data on the basis of compressed sensing (CS) and the partially separable function model with base spectra of substances. In our method, we have employed spatio-temporal sparsity and temporal smoothness of the substance distributions as prior knowledge to perform CS. The effectiveness of our method has been evaluated using phantom data sets of glass tubes filled with glucose or lactate solution in increasing amounts over time and animal data sets of a tumor-bearing mouse to observe the metabolic dynamics involved in the Warburg effect in vivo. The reconstructed results are consistent with the expected behaviors, showing that our method can reconstruct the spatio-temporal distribution of substances with a temporal resolution of four seconds which is extremely short time scale compared with that of full sampling. Since this method utilizes only prior knowledge naturally assumed for the spatio-temporal distributions of substances and is independent of the number of the spectral and spatial dimensions or the acquisition sequence of MRSI, it is expected to contribute to revealing the underlying substance dynamics in MRSI data already acquired or to be acquired in the future. △ Less

Submitted 1 March, 2024; originally announced March 2024.

Journal ref: Expert Systems with Applications, Vol. 232 (2023) p. 120744

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

Authors: Tomoaki Oyama, Takumi Nagayama, Aya Yamauchi, Daisuke Sakai, Hiroshi Imai, Mareki Honma, Yu Asakura, Kazuhiro Hada, Yoshiaki Hagiwara, Tomoya Hirota, Takaaki Jike, Yusuke Kono, Syunsaku Suzuki, Hideyuki Kobayashi, Noriyuki Kawaguchi

Abstract: We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be $117\pm17$ micro-arcseconds ($μ$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 w… ▽ More We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be $117\pm17$ micro-arcseconds ($μ$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 years, the proper motion of Sgr A* is obtained to be $(μ_α, μ_δ) = (-3.133\pm0.003, -5.575\pm0.005)$ mas yr$^{-1}$ in equatorial coordinates, corresponding to $(μ_l, μ_b) = (-6.391\pm0.005, -0.230\pm0.004)$ mas yr$^{-1}$ in Galactic coordinates. This gives an angular orbital velocity of the Sun of $Ω_\odot = 30.30 \pm 0.02$ 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, $a < 2.6$ $μ$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. △ Less

Submitted 4 January, 2024; originally announced January 2024.

Comments: 15 pages, 9 figures, accepted for publication in the Publications of the Astronomical Society of Japan

Toward Realistic Models in $T^2/\mathbb{Z}_2$ Flux Compactification

Authors: Hiroki Imai, Nobuhito Maru

Abstract: We consider a six dimensional gauge theory compactified on $T^2/\mathbb{Z}_2$ with magnetic flux. The configurations of models are classified by winding numbers at the fixed points. Requiring the existence of generation numbers and Yukawa coupling, we see that allowed and forbidden configurations are described by geometry of winding numbers. We consider a six dimensional gauge theory compactified on $T^2/\mathbb{Z}_2$ with magnetic flux. The configurations of models are classified by winding numbers at the fixed points. Requiring the existence of generation numbers and Yukawa coupling, we see that allowed and forbidden configurations are described by geometry of winding numbers. △ Less

Submitted 8 May, 2024; v1 submitted 16 November, 2023; originally announced November 2023.

Comments: 27 pages, 8 figures

Report number: NITEP-189

Systematic Search for Water Fountain Candidates using the Databases of Circumstellar Maser Sources

Authors: Haichen Fan, Jun-ichi Nakashima, D. Engels, Yong Zhang, Jian-Jie Qiu, Huan-Xue Feng, Jia-Yong Xie, Hiroshi Imai, Chih-Hao Hsia

Abstract: Water fountains (WFs) are thought to be objects in the morphological evolution of the circumstellar envelopes of low- and intermediate-mass evolved stars, transitioning from spherically symmetric to asymmetric shapes. We used databases of circumstellar 1612 MHz OH and 22.235 GHz H$_2$O maser sources to search for new WF candidates using the criterion of a larger velocity range of the H$_2$O maser… ▽ More Water fountains (WFs) are thought to be objects in the morphological evolution of the circumstellar envelopes of low- and intermediate-mass evolved stars, transitioning from spherically symmetric to asymmetric shapes. We used databases of circumstellar 1612 MHz OH and 22.235 GHz H$_2$O maser sources to search for new WF candidates using the criterion of a larger velocity range of the H$_2$O maser emission compared to that of the OH maser emission. Thus, it is in principle possible to identify WFs with an H$_2$O velocity ranges smaller than those for the previously known WFs. For the OH maser line, we analyzed database entries of 8,474 observations from 2,195 sources, and 6,085 observations from 3,642 sources for H$_2$O maser line. After a close examination of the velocity ranges and line profiles, we identified 11 sources that meet the criterion mentioned above. We examined the IRAS colors of the selected sources and found that two of them (IRAS 19069+0916 and IRAS 19319+2214) are in the color region for post-AGB stars. We find that the maser velocity criterion can discover other astrophysically interesting objects than just WFs. Such objects may include peculiar planetary nebulae with maser emissions and stellar merger remnants. △ Less

Submitted 8 October, 2023; originally announced October 2023.

Comments: 34 pages, 10 figures, Accepted for publication in ApJS

FLASHING: Project Overview

Authors: Hiroshi Imai, Yuhki Hamae, Kei Amada, Keisuke Nakashima, Ka-Yiu Shum, Rina Kasai, Jose F. Gomez, Lucero Uscanga, Daniel Tafoya, Gabor Orosz, Ross A. Burns

Abstract: This paper describes the overview of the FLASHING (Finest Legacy Acquisitions of SiO-/ H$_2$O-maser Ignitions by the Nobeyama Generation) project promoted using the 45 m telescope of Nobeyama Radio Observatory, which aims to intensively monitor H$_2$O (22 GHz) and SiO (43 GHz) masers associated with so-called "water fountain" sources. Here we show scientific results on the basis of the data taken… ▽ More This paper describes the overview of the FLASHING (Finest Legacy Acquisitions of SiO-/ H$_2$O-maser Ignitions by the Nobeyama Generation) project promoted using the 45 m telescope of Nobeyama Radio Observatory, which aims to intensively monitor H$_2$O (22 GHz) and SiO (43 GHz) masers associated with so-called "water fountain" sources. Here we show scientific results on the basis of the data taken in for the first five seasons of FLASHING, from 2018 December to 2023 April). We have found the evolution of the H$_2$O maser spectra, such as new spectral components breaking the record of the jet's top speed and/or systematic velocity drifts in the spectrum indicating acceleration or deceleration of the maser gas clumps. For the 43 GHz SiO maser emission, we have found its new detection in a source while its permanent disappearance in other source. Our finding may imply that the jets from these water fountains can be accelerated or decelerated, and show how cicumstellar envelopes have been destroyed. △ Less

Submitted 1 September, 2023; originally announced September 2023.

Comments: 31 pages, 22 figures, to be published in the Publications of the Astronomical Society of Japan

Evolution of the outflow in the water fountain source IRAS 18043$-$2116

Authors: L. Uscanga, H. Imai, J. F. Gómez, D. Tafoya, G. Orosz, T. P. McCarthy, Y. Hamae, K. Amada

Abstract: We present the spectral and spatial evolution of H$_2$O masers associated with the water fountain source IRAS 18043$-$2116 found in the observations with the Nobeyama 45 m telescope and the Australia Telescope Compact Array. We have found new highest velocity components of the H$_2$O masers (at the red-shifted side $V_{\rm LSR}\simeq376~\mathrm{km~s}^{-1}$ and at the blue-shifted side… ▽ More We present the spectral and spatial evolution of H$_2$O masers associated with the water fountain source IRAS 18043$-$2116 found in the observations with the Nobeyama 45 m telescope and the Australia Telescope Compact Array. We have found new highest velocity components of the H$_2$O masers (at the red-shifted side $V_{\rm LSR}\simeq376~\mathrm{km~s}^{-1}$ and at the blue-shifted side $V_{\rm LSR}\simeq$ $-165~\mathrm{km~s}^{-1}$), and the resulting velocity spread of $\simeq 540~\mathrm{km~s}^{-1}$ breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow ($\sim60^{\circ}$). The evolution of the maser cluster separation of $\sim$2.9 mas yr$^{-1}$ and the compact ($\sim0.''2$) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short ($\sim$30 yr) timescale of the outflow. We also confirmed the increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed. △ Less

Submitted 2 March, 2023; originally announced March 2023.

Comments: 14 pages, 7 figures. Accepted by ApJ

H$_2$O MegaMaser emission in NGC 4258 indicative of a periodic disc instability

Authors: Wiillem A. Baan, Tao AN, Christian Henkel, Hiroshi Imai, Vladimir Kostenko, Andrej Sobolev

Abstract: H$_2$O MegaMaser emission may arise from thin gas discs surrounding the massive nuclei of galaxies such as NGC\,4258, but the physical conditions responsible for the amplified emission are unclear. A detailed view of these regions is possible using the very high angular resolution afforded by space very long baseline interferometry (SVLBI). Here we report SVLBI experiments conducted using the orbi… ▽ More H$_2$O MegaMaser emission may arise from thin gas discs surrounding the massive nuclei of galaxies such as NGC\,4258, but the physical conditions responsible for the amplified emission are unclear. A detailed view of these regions is possible using the very high angular resolution afforded by space very long baseline interferometry (SVLBI). Here we report SVLBI experiments conducted using the orbiting RadioAstron Observatory that have resulted in detections of the H$_2$O 22 GHz emission in NGC\,4258, with Earth-space baselines of 1.3, 9.5 and 19.5 Earth diameters. Observations at the highest angular resolution of 11 and 23 $μ$as show distinct and regularly spaced regions within the rotating disc, at an orbital radius of about 0.126 pc. These observations at three subsequent epochs also indicate a time evolution of the emission features, with a sudden rise in amplitude followed by a slow decay. The formation of the emission regions, their regular spacing and their time-dependent behaviour appear consistent with the occurrence of a periodic magneto-rotational instability in the disc. This type of shear-driven instability within the differentially rotating disc has been suggested to be the mechanism governing the radial momentum transfer and viscosity within a mass-accreting disc. The connection of the H$_2$O MegaMaser activity with the magneto-rotational instability activity would make it an indicator of the mass-accretion rate in the nuclear disc of the host galaxy. △ Less

Submitted 28 February, 2023; originally announced February 2023.

Comments: 23 pages, 5 figures

Quantum-Relaxation Based Optimization Algorithms: Theoretical Extensions

Authors: Kosei Teramoto, Rudy Raymond, Eyuri Wakakuwa, Hiroshi Imai

Abstract: Quantum Random Access Optimizer (QRAO) is a quantum-relaxation based optimization algorithm proposed by Fuller et al. that utilizes Quantum Random Access Code (QRAC) to encode multiple variables of binary optimization in a single qubit. The approximation ratio bound of QRAO for the maximum cut problem is $0.555$ if the bit-to-qubit compression ratio is $3$x, while it is $0.625$ if the compression… ▽ More Quantum Random Access Optimizer (QRAO) is a quantum-relaxation based optimization algorithm proposed by Fuller et al. that utilizes Quantum Random Access Code (QRAC) to encode multiple variables of binary optimization in a single qubit. The approximation ratio bound of QRAO for the maximum cut problem is $0.555$ if the bit-to-qubit compression ratio is $3$x, while it is $0.625$ if the compression ratio is $2$x, thus demonstrating a trade-off between space efficiency and approximability. In this research, we extend the quantum-relaxation by using another QRAC which encodes three classical bits into two qubits (the bit-to-qubit compression ratio is $1.5$x) and obtain its approximation ratio for the maximum cut problem as $0.722$. Also, we design a novel quantum relaxation that always guarantees a $2$x bit-to-qubit compression ratio which is unlike the original quantum relaxation of Fuller~et~al. We analyze the condition when it has a non-trivial approximation ratio bound $\left(>\frac{1}{2}\right)$. We hope that our results lead to the analysis of the quantum approximability and practical efficiency of the quantum-relaxation based approaches. △ Less

Submitted 2 April, 2023; v1 submitted 19 February, 2023; originally announced February 2023.

Comments: 23 pages, 5 figures

The Role of Entanglement in Quantum-Relaxation Based Optimization Algorithms

Authors: Kosei Teramoto, Rudy Raymond, Hiroshi Imai

Abstract: Quantum Random Access Optimizer (QRAO) is a quantum-relaxation based optimization algorithm proposed by Fuller et al. that utilizes Quantum Random Access Code (QRAC) to encode multiple variables of binary optimization in a single qubit. Differing from standard quantum optimizers such as QAOA, it utilizes the eigenstates of local quantum Hamiltonians that are not diagonal in the computational basis… ▽ More Quantum Random Access Optimizer (QRAO) is a quantum-relaxation based optimization algorithm proposed by Fuller et al. that utilizes Quantum Random Access Code (QRAC) to encode multiple variables of binary optimization in a single qubit. Differing from standard quantum optimizers such as QAOA, it utilizes the eigenstates of local quantum Hamiltonians that are not diagonal in the computational basis. There are indications that quantum entanglement may not be needed to solve binary optimization problems with standard quantum optimizers because their maximal eigenstates of diagonal Hamiltonians include classical states. In this study, while quantumness does not always improve the performance of quantum relaxations, we observed that there exist some instances in which quantum relaxation succeeds to find optimal solutions with the help of quantumness. Our results suggest that QRAO not only can scale the instances of binary optimization problems solvable with limited quantum computers but also can benefit from quantum entanglement. △ Less

Submitted 9 April, 2023; v1 submitted 1 February, 2023; originally announced February 2023.

Comments: 14 pages, 8 figures

Overview of the Observing System and Initial Scientific Accomplishments of the East Asian VLBI Network (EAVN)

Authors: Kazunori Akiyama, Juan-Carlos Algaba, Tao An, Keiichi Asada, Kitiyanee Asanok, Do-Young Byun, Thanapol Chanapote, Wen Chen, Zhong Chen, Xiaopeng Cheng, James O. Chibueze, Ilje Cho, Se-Hyung Cho, Hyun-Soo Chung, Lang Cui, Yuzhu Cui, Akihiro Doi, Jian Dong, Kenta Fujisawa, Wei Gou, Wen Guo, Kazuhiro Hada, Yoshiaki Hagiwara, Tomoya Hirota, Jeffrey A. Hodgson , et al. (79 additional authors not shown)

Abstract: The East Asian VLBI Network (EAVN) is an international VLBI facility in East Asia and is operated under mutual collaboration between East Asian countries, as well as part of Southeast Asian and European countries. EAVN currently consists of 16 radio telescopes and three correlators located in China, Japan, and Korea, and is operated mainly at three frequency bands, 6.7, 22, and 43 GHz with the lon… ▽ More The East Asian VLBI Network (EAVN) is an international VLBI facility in East Asia and is operated under mutual collaboration between East Asian countries, as well as part of Southeast Asian and European countries. EAVN currently consists of 16 radio telescopes and three correlators located in China, Japan, and Korea, and is operated mainly at three frequency bands, 6.7, 22, and 43 GHz with the longest baseline length of 5078 km, resulting in the highest angular resolution of 0.28 milliarcseconds at 43 GHz. One of distinct capabilities of EAVN is multi-frequency simultaneous data reception at nine telescopes, which enable us to employ the frequency phase transfer technique to obtain better sensitivity at higher observing frequencies. EAVN started its open-use program in the second half of 2018, providing a total observing time of more than 1100 hours in a year. EAVN fills geographical gap in global VLBI array, resulting in enabling us to conduct contiguous high-resolution VLBI observations. EAVN has produced various scientific accomplishments especially in observations toward active galactic nuclei, evolved stars, and star-forming regions. These activities motivate us to initiate launch of the 'Global VLBI Alliance' to provide an opportunity of VLBI observation with the longest baselines on the earth. △ Less

Submitted 14 December, 2022; originally announced December 2022.

Comments: 27 pages, appeared in Galaxies special issue 'Challenges in Understanding Black Hole Powered Jets with VLBI' as an invited review

Journal ref: Galaxies 2022, 10(6), 113

Index and winding numbers on $T^2/\mathbb{Z}_N$ orbifolds with magnetic flux

Authors: Hiroki Imai, Makoto Sakamoto, Maki Takeuchi, Yoshiyuki Tatsuta

Abstract: We analyze the number of independent chiral zero modes and the winding numbers at the fixed points on $T^2/{\mathbb{Z}}_N$ ($N=2,3,4,6$) orbifolds with magnetic flux. In the case of $N=2$, we derive the index formula $n_{+}-n_{-}=M/2+(-V_{+}+V_{-})/4=M/2-V_{+}/2+1$ by using the trace formula, where $n_{\pm}$ are the numbers of the $\pm$ chiral zero modes and $V_{\pm}$ are the sums of the winding n… ▽ More We analyze the number of independent chiral zero modes and the winding numbers at the fixed points on $T^2/{\mathbb{Z}}_N$ ($N=2,3,4,6$) orbifolds with magnetic flux. In the case of $N=2$, we derive the index formula $n_{+}-n_{-}=M/2+(-V_{+}+V_{-})/4=M/2-V_{+}/2+1$ by using the trace formula, where $n_{\pm}$ are the numbers of the $\pm$ chiral zero modes and $V_{\pm}$ are the sums of the winding numbers at the fixed points on $T^2/{\mathbb{Z}}_2$. We also obtain the formula $n_{+}-n_{-}=M/N+(-V_{+}+V_{-})/(2N)=M/N-V_{+}/N+1$ for $N=3,4,6$ under an assumption. △ Less

Submitted 28 November, 2022; originally announced November 2022.

Comments: 37 pages, 2 figures

Report number: KOBE-TH-22-04

EAVN Astrometry toward the Extreme Outer Galaxy: Kinematic distance with the proper motion of G034.84-00.95

Authors: Nobuyuki Sakai, Bo Zhang, Shuangjing Xu, Daisuke Sakai, Yoshiaki Tamura, Takaaki Jike, Taehyun Jung, Chungsik Oh, Jeong-Sook Kim, Noriyuki Kawaguchi, Hiroshi Imai, Wu Jiang, Lang Cui, Soon-Wook Kim, Pengfei Jiang, Tomoharu Kurayama, Jeong Ae Lee, Kazuya Hachisuka, Dong-Kyu Jung, Bo Xia, Guanghui Li, Mareki Honma, Kee-Tae Kim, Zhi-Qiang Shen, Na Wang

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 (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H$_{2}$O maser source, which is associated with the star-forming… ▽ More 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 (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H$_{2}$O maser source, which is associated with the star-forming region G034.84$-$00.95, to be ($μ_α \rm{cos}δ$, $μ_δ$) = ($-$1.61$\pm$0.18, $-$4.29$\pm$0.16) mas yr$^{-1}$ in equatorial coordinates (J2000). We estimate the 2D kinematic distance to the source to be 18.6$\pm$1.0 kpc, which is derived from the variance-weighted average of kinematic distances with LSR velocity and the Galactic-longitude component of the measured proper motion. Our result places the source in the OSC arm and implies that G034.84$-$00.95 is moving away from the Galactic plane with a vertical velocity of $-$38$\pm$16 km s$^{-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 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 the possibilities are matched with the results of VLBI astrometry as well as spatial distributions of H II regions and H I gas. △ Less

Submitted 22 November, 2022; originally announced November 2022.

Comments: Accepted for publication in PASJ. 14 figures; 8 tables

Sciences with Thai National Radio Telescope

Authors: Phrudth Jaroenjittichai, Koichiro Sugiyama, Busaba H. Kramer, Boonrucksar Soonthornthum, Takuya Akahori, Kitiyanee Asanok, Willem Baan, Sherin Hassan Bran, Shari L. Breen, Se-Hyung Cho, Thanapol Chanapote, Richard Dodson, Simon P. Ellingsen, Sandra Etoka, Malcolm D. Gray, James A. Green, Kazuhiro Hada, Marcus Halson, Tomoya Hirota, Mareki Honma, Hiroshi Imai, Simon Johnston, Kee-Tae Kim, Michael Kramer, Di Li , et al. (22 additional authors not shown)

Abstract: This White Paper summarises potential key science topics to be achieved with Thai National Radio Telescope (TNRT). The commissioning phase has started in mid 2022. The key science topics consist of "Pulsars and Fast Radio Bursts (FRBs)", "Star Forming Regions (SFRs)", "Galaxy and Active Galactic Nuclei (AGNs)", "Evolved Stars", "Radio Emission of Chemically Peculiar (CP) Stars", and "Geodesy", cov… ▽ More This White Paper summarises potential key science topics to be achieved with Thai National Radio Telescope (TNRT). The commissioning phase has started in mid 2022. The key science topics consist of "Pulsars and Fast Radio Bursts (FRBs)", "Star Forming Regions (SFRs)", "Galaxy and Active Galactic Nuclei (AGNs)", "Evolved Stars", "Radio Emission of Chemically Peculiar (CP) Stars", and "Geodesy", covering a wide range of observing frequencies in L/C/X/Ku/K/Q/W-bands (1-115 GHz). As a single-dish instrument, TNRT is a perfect tool to explore time domain astronomy with its agile observing systems and flexible operation. Due to its ideal geographical location, TNRT will significantly enhance Very Long Baseline Interferometry (VLBI) arrays, such as East Asian VLBI Network (EAVN), Australia Long Baseline Array (LBA), European VLBI Network (EVN), in particular via providing a unique coverage of the sky resulting in a better complete "uv" coverage, improving synthesized-beam and imaging quality with reducing side-lobes. This document highlights key science topics achievable with TNRT in single-dish mode and in collaboration with VLBI arrays. △ Less

Submitted 10 October, 2022; originally announced October 2022.

Comments: 75 pages, 16 figures, 15 tables. White Paper for Potential Key Sciences to be Achieved with Thai National Radio Telescope (TNRT)

The Astrometric Animation of Water Masers towards the Mira Variable BX Cam

Authors: Shuangjing Xu, Hiroshi Imai, Youngjoo Yun, Bo Zhang, Maria J. Rioja, Richard Dodson, Se-Hyung Cho, Jaeheon Kim, Lang Cui, Andrey M. Sobolev, James O. Chibueze, Dong-Jin Kim, Kei Amada, Jun-ichi Nakashima, Gabor Orosz, Miyako Oyadomari, Sejin Oh, Yoshinori Yonekura, Yan Sun, Xiaofeng Mai, Jingdong Zhang, Shiming Wen, Taehyun Jung

Abstract: We report VLBI monitoring observations of the 22 GHz water (H$_{2}$O) masers around the Mira variable BX Cam, which were carried out as a part of the EAVN Synthesis of Stellar Maser Animations (ESTEMA) project. Data of 37 epochs in total were obtained from 2018 May to 2021 June with a time interval of 3-4 weeks, spanning approximately three stellar pulsation periods ($P= \sim$440 d). In particular… ▽ More We report VLBI monitoring observations of the 22 GHz water (H$_{2}$O) masers around the Mira variable BX Cam, which were carried out as a part of the EAVN Synthesis of Stellar Maser Animations (ESTEMA) project. Data of 37 epochs in total were obtained from 2018 May to 2021 June with a time interval of 3-4 weeks, spanning approximately three stellar pulsation periods ($P= \sim$440 d). In particular, the dual-beam system equipped on the VERA stations was used to measure the kinematics and parallaxes of the H$_{2}$O maser features. The measured parallax, $π=1.79\pm 0.08$ mas, is consistent with $Gaia$ EDR3 and previously measured VLBI parallaxes within a 1-$σ$ error level. The position of the central star was estimated, based on both the $Gaia$ EDR3 data and the center position of the ring-like 43 GHz silicon-monoxide (SiO) maser distribution imaged with the KVN. The three-dimensional H$_{2}$O maser kinematics indicates that the circumstellar envelope is expanding at a velocity of $13\pm4$ km s$^{-1}$, while there are asymmetries in both the spatial and velocity distributions of the maser features. Furthermore, the H$_{2}$O maser animation achieved by our dense monitoring program manifests the propagation of shock waves in the circumstellar envelope of BX Cam. △ Less

Submitted 6 October, 2022; originally announced October 2022.

Comments: 31 pages, 16 figures, accepted by ApJ

Searching for nascent planetary nebulae: OHPNe candidates in the SPLASH survey

Authors: Roldán A. Cala, José F. Gómez, Luis F. Miranda, Lucero Uscanga, Shari L. Breen, Joanne R. Dawson, Itziar de Gregorio-Monsalvo, Hiroshi Imai, Hai-Hua Qiao, Olga Suárez

Abstract: The evolution of asymptotic giant branch stars from the spherical symmetry into the diverse shapes of planetary nebulae (PNe) is a topic of intensive research. Young PNe provide a unique opportunity to characterize the onset of this transitional phase. In particular, OH maser-emitting PNe (OHPNe) are considered nascent PNe. In fact, only 6 OHPNe have been confirmed to date. In order to identify an… ▽ More The evolution of asymptotic giant branch stars from the spherical symmetry into the diverse shapes of planetary nebulae (PNe) is a topic of intensive research. Young PNe provide a unique opportunity to characterize the onset of this transitional phase. In particular, OH maser-emitting PNe (OHPNe) are considered nascent PNe. In fact, only 6 OHPNe have been confirmed to date. In order to identify and characterize more OHPNe, we processed the unpublished continuum data of the interferometric follow-up of the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH). We then matched the interferometric positions of OH maser and radio continuum emission, considering the latter as a possible tracer of free-free emission from photoionized gas, characteristic of PNe. We report 8 objects with a positive coincidence, 4 of which are classified as candidate OHPNe here for the first time (IRAS 16372-4808, IRAS 17494-2645, IRAS 18019-2216 and OH 341.6811+00.2634). Available evidence strongly indicates that they are evolved stars, while the comparison with confirmed OHPNe indicates that they are likely to be PNe. Their final confirmation as bona fide PNe, however, requires optical/infrared spectroscopy. The obtained spectral indices of the radio continuum emission (between $\simeq$ 0.4 - 1.3) are consistent with partially optically thick free-free emission from photoionized gas. Also, they cluster in the same region of a WISE colour-colour diagram as that of the confirmed OHPNe ($9.5 \lesssim [3.4]-[22] \lesssim 13.5$, and $4.0 \lesssim [4.6]-[12] \lesssim 7.0$), thus this diagram could help to identify more OHPNe candidates in the future. △ Less

Submitted 19 August, 2022; originally announced August 2022.

Comments: 17 pages, 7 figures, 5 tables. Accepted for publication in MNRAS

GASKAP-HI Pilot Survey Science III: An unbiased view of cold gas in the Small Magellanic Cloud

Authors: James Dempsey, N. M. McClure-Griffiths, Claire Murray, John M. Dickey, Nickolas M. Pingel, Katherine Jameson, Helga Dénes, Jacco Th. van Loon, D. Leahy, Min-Young Lee, S. Stanimirović, Shari Breen, Frances Buckland-Willis, Steven J. Gibson, Hiroshi Imai, Callum Lynn, C. D. Tremblay

Abstract: We present the first unbiased survey of neutral hydrogen (HI) absorption in the Small Magellanic Cloud (SMC). The survey utilises pilot HI observations with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope as part of the Galactic ASKAP HI (GASKAP-HI) project whose dataset has been processed with the GASKAP-HI absorption pipeline, also described here. This dataset provides absorpt… ▽ More We present the first unbiased survey of neutral hydrogen (HI) absorption in the Small Magellanic Cloud (SMC). The survey utilises pilot HI observations with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope as part of the Galactic ASKAP HI (GASKAP-HI) project whose dataset has been processed with the GASKAP-HI absorption pipeline, also described here. This dataset provides absorption spectra towards 229 continuum sources, a 275% increase in the number of continuum sources previously published in the SMC region, as well as an improvement in the quality of absorption spectra over previous surveys of the SMC. Our unbiased view, combined with the closely matched beam size between emission and absorption, reveals a lower cold gas faction (11%) than the 2019 ATCA survey of the SMC and is more representative of the SMC as a whole. We also find that the optical depth varies greatly between the SMC's bar and wing regions. In the bar we find that the optical depth is generally low (correction factor to the optically thin column density assumption of $\mathcal{R}_{\rm HI} \sim 1.04$) but increases linearly with column density. In the wing however, there is a wide scatter in optical depth despite a tighter range of column densities. △ Less

Submitted 13 April, 2022; originally announced April 2022.

Comments: Accepted for publication in PASA, 19 pages, 17 figures, 5 tables

SPLASH: The Southern Parkes Large-Area Survey in Hydroxyl -- Data Description & Release

Authors: J. R. Dawson, P. A. Jones, C. Purcell, A. J. Walsh, S. L. Breen, C. Brown, E. Carretti, M. R. Cunningham, J. M. Dickey, S. P. Ellingsen, S. J. Gibson, J. F. Gomez, J. A. Green, H. Imai, V. Krishnan, N. Lo, V. Lowe, M. Marquarding, N. M. McClure-Griffiths, .

Abstract: We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667 and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone and Galactic Centre over the range $|b|<$ 2$^{\circ}$, 332$^{\circ}$… ▽ More We present the full data release for the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH), a sensitive, unbiased single-dish survey of the Southern Galactic Plane in all four ground-state transitions of the OH radical at 1612, 1665, 1667 and 1720 MHz. The survey covers the inner Galactic Plane, Central Molecular Zone and Galactic Centre over the range $|b|<$ 2$^{\circ}$, 332$^{\circ}$ $< l <$ 10$^{\circ}$, with a small extension between 2$^{\circ}$ $< b <$ 6$^{\circ}$, 358$^{\circ}$ $< l <$ 4$^{\circ}$. SPLASH is the most sensitive large-scale survey of OH to-date, reaching a characteristic root-mean-square sensitivity of $\sim15$ mK for an effective velocity resolution of $\sim0.9$ km/s. The spectral line datacubes are optimised for the analysis of extended, quasi-thermal OH, but also contain numerous maser sources, which have been confirmed interferometrically and published elsewhere. We also present radio continuum images at 1612, 1666 and 1720 MHz. Based on initial comparisons with $^{12}$CO(J=1-0), we find that OH rarely extends outside CO cloud boundaries in our data, but suggest that large variations in CO-to-OH brightness temperature ratios may reflect differences in the total gas column density traced by each. Column density estimation in the complex, continuum-bright Inner Galaxy is a challenge, and we demonstrate how failure to appropriately model sub-beam structure and the line-of-sight source distribution can lead to order-of-magnitude errors. Anomalous excitation of the 1612 and 1720 MHz satellite lines is ubiquitous in the inner Galaxy, but is disabled by line overlap in and around the Central Molecular Zone. △ Less

Submitted 9 March, 2022; originally announced March 2022.

Comments: Main paper: 22 pages, 15 figures. Online-only material (appended to ArXiv PDF): 11 pages, 3 figure sets. Accepted to MNRAS. Survey data is available from: https://docs.datacentral.org.au/splash/

Proper Motions of Water Masers in the Star-forming Region IRAS 23139+5939

Authors: Miguel A. Trinidad, Hiroshi Imai, Eduardo de la Fuente, Ivan Toledano-Juárez, Joseph M. Masqué, Tatianna Rodríguez-Esnard

Abstract: We observed H$_2$O (6$_{16}$ $\rightarrow$ 5$_{23}$) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA a combination of VLBI arrays between the KVN (Korea) and VERA (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 (VLA)… ▽ More We observed H$_2$O (6$_{16}$ $\rightarrow$ 5$_{23}$) maser emission associated with the high-mass star-forming region IRAS 23139+5959 using the KaVA a combination of VLBI arrays between the KVN (Korea) and VERA (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 (VLA). By determining the maser proper motions, we found that the first of maser groups exhibit 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 \hii region. We discuss the star formation activity in IRAS 23139+5939, which may be reflected in the high variability of H$_2$O masers associated with an outflow seen from the front. △ Less

Submitted 7 February, 2022; originally announced February 2022.

Comments: 13 pages, 5 Figures, Published on Publications of the Astronomical Society of Japan, 2021

Journal ref: Publications of the Astronomical Society of Japan, Volume 73, Issue 6, December 2021, Pages 1669-1680

Physical properties of the molecular cloud, N4, in SS433; Evidence for an interaction of molecular cloud with the jet from SS433

Authors: Hiroaki Yamamoto, Ryuji Okamoto, Yasuhiro Murata, Hiroyuki Nakanishi, Hiroshi Imai, Kohei Kurahara

Abstract: We conducted observations and analyses of the molecular cloud, N4, which is located at ~40 pc from SS433 and the same line of sight as that of the radio shell, in 12CO(J=1-0), 12CO(J=3-2), 13CO(J=3-2), and grand-state OH emissions.N4 has a strong gradient of the integrated intensity of 12CO(J=1-0, 3-2) emission at the northern, eastern and western edges. The main body of N4 also has a velocity gra… ▽ More We conducted observations and analyses of the molecular cloud, N4, which is located at ~40 pc from SS433 and the same line of sight as that of the radio shell, in 12CO(J=1-0), 12CO(J=3-2), 13CO(J=3-2), and grand-state OH emissions.N4 has a strong gradient of the integrated intensity of 12CO(J=1-0, 3-2) emission at the northern, eastern and western edges. The main body of N4 also has a velocity gradient of ~0.16 km s^-1 20"^-1. A velocity shift by up to 3 km s^-1 from the systemic velocity at ~49 km s^-1 is detected at only the northwestern part of N4. The volume density of the molecular hydrogen gas and the kinematic temperature are estimated at eight local peaks of 12CO(J=1-0) and 13CO(J=3-2) emissions by the RADEX code. The calculated n(H2) is an order of 10^3 cm^-3, and T_k ranges ~20 K to ~56 K. The mass of N4 is estimated to be ~7300 Mo. The thermal and turbulent pressures in N4 are estimated to be ~10^5 K cm^-3 and ~10^7 K cm^-3, respectively. The relation of the thermal and turbulent pressures in N4 tends to be similar to that of the molecular clouds in the Galactic plane. However, these values are higher than those in the typical molecular clouds in the Galactic plane. Several pieces of circumstantial evidence representing the physical properties of N4 and comparison with the data of infrared and X-ray radiation suggest that N4 is interacting with a jet from SS433. However, no gamma-ray radiation is detected toward N4. Compared to the previous study, it is hard to detect the gamma-ray radiation by cosmic-ray proton origin due to the low sensitivity of the current gamma-ray observatories. Any OH emission was not detected toward N4 due to the low sensitivity of the observation and antenna beam dilution. △ Less

Submitted 31 January, 2022; v1 submitted 30 January, 2022; originally announced January 2022.

Comments: 31 pages, 12 figures, accepted for publication in PASJ

Observational identification of a sample of likely recent Common-Envelope Events

Authors: Theo Khouri, Wouter Vlemmings, Daniel Tafoya, Andrés F. Pérez-Sánchez, Carmen Sánchez Contreras, José F. Gómez, Hiroshi Imai, Raghvendra Sahai

Abstract: One of the most poorly understood stellar evolutionary paths is that of binary systems undergoing common-envelope evolution, when the envelope of a giant star engulfs the orbit of a companion. Although this interaction leads to a great variety of astrophysical systems, direct empirical studies are difficult because few objects experiencing common-envelope evolution are known. We present ALMA obser… ▽ More One of the most poorly understood stellar evolutionary paths is that of binary systems undergoing common-envelope evolution, when the envelope of a giant star engulfs the orbit of a companion. Although this interaction leads to a great variety of astrophysical systems, direct empirical studies are difficult because few objects experiencing common-envelope evolution are known. We present ALMA observations towards sources known as water fountains that reveal they had low initial masses ($<4~{\rm M}_\odot$) and ejected a significant fraction of it over less than a few hundred years. The only mechanism able to explain such rapid mass ejection is common-envelope evolution. Our calculations show that the water-fountain sample accounts for a large fraction of the systems in our Galaxy which have just experienced the common-envelope phase. Since water-fountain sources show characteristic fast bipolar outflows, outflows and jets likely play an important role right before, during or immediately after the common-envelope phase. △ Less

Submitted 17 December, 2021; originally announced December 2021.

Comments: Published on Nature Astronomy on Dec 16, 2021: https://rdcu.be/cDlX8

GASKAP-HI Pilot Survey Science I: ASKAP Zoom Observations of HI Emission in the Small Magellanic Cloud

Authors: N. M. Pingel, J. Dempsey, N. M. McClure-Griffiths, J. M. Dickey, K. E. Jameson, H. Arce, G. Anglada, J. Bland-Hawthorn, S. L. Breen, F. Buckland-Willis, S. E. Clark, J. R. Dawson, H. Dénes, E. M. Di Teodoro, B. -Q. For, Tyler J. Foster, J. F. Gómez, H. Imai, G. Joncas, C. -G. Kim, M. -Y. Lee, C. Lynn, D. Leahy, Y. K. Ma, A. Marchal , et al. (31 additional authors not shown)

Abstract: We present the most sensitive and detailed view of the neutral hydrogen (HI) emission associated with the Small Magellanic Cloud (SMC), through the combination of data from the Australian Square Kilometre Array Pathfinder (ASKAP) and Parkes (Murriyang), as part of the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) pilot survey. These GASKAP-HI pilot observations, for the first time… ▽ More We present the most sensitive and detailed view of the neutral hydrogen (HI) emission associated with the Small Magellanic Cloud (SMC), through the combination of data from the Australian Square Kilometre Array Pathfinder (ASKAP) and Parkes (Murriyang), as part of the Galactic Australian Square Kilometre Array Pathfinder (GASKAP) pilot survey. These GASKAP-HI pilot observations, for the first time, reveal HI in the SMC on similar physical scales as other important tracers of the interstellar medium, such as molecular gas and dust. The resultant image cube possesses an rms noise level of 1.1 K (1.6 mJy/beam) per 0.98 km s$^{-1}$ spectral channel with an angular resolution of 30$''$ ($\sim$10 pc). We discuss the calibration scheme and the custom imaging pipeline that utilizes a joint deconvolution approach, efficiently distributed across a computing cluster, to accurately recover the emission extending across the entire $\sim$25 deg$^2$ field-of-view. We provide an overview of the data products and characterize several aspects including the noise properties as a function of angular resolution and the represented spatial scales by deriving the global transfer function over the full spectral range. A preliminary spatial power spectrum analysis on individual spectral channels reveals that the power-law nature of the density distribution extends down to scales of 10 pc. We highlight the scientific potential of these data by comparing the properties of an outflowing high velocity cloud with previous ASKAP+Parkes HI test observations. △ Less

Submitted 10 December, 2021; v1 submitted 9 November, 2021; originally announced November 2021.

Comments: Accepted for publication in PASA, 34 pages, 18 figures, 5 tables

The Nearby Evolved Stars Survey II: Constructing a volume-limited sample and first results from the James Clerk Maxwell Telescope

Authors: P. Scicluna, F. Kemper, I. McDonald, S. Srinivasan, A. Trejo, S. H. J. Wallström, J. G. A. Wouterloot, J. Cami, J. Greaves, Jinhua He, D. T. Hoai, Hyosun Kim, O. C. Jones, H. Shinnaga, C. J. R. Clark, T. Dharmawardena, W. Holland, H. Imai, J. Th. van Loon, K. M. Menten, R. Wesson, H. Chawner, S. Feng, S. Goldman, F. C. Liu , et al. (67 additional authors not shown)

Abstract: The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of $\sim$850 Galactic evolved stars within 3\,kpc at (sub-)mm wavelengths, observed in the CO $J = $ (2$-$1) and (3$-$2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a n… ▽ More The Nearby Evolved Stars Survey (NESS) is a volume-complete sample of $\sim$850 Galactic evolved stars within 3\,kpc at (sub-)mm wavelengths, observed in the CO $J = $ (2$-$1) and (3$-$2) rotational lines, and the sub-mm continuum, using the James Clark Maxwell Telescope and Atacama Pathfinder Experiment. NESS consists of five tiers, based on distances and dust-production rate (DPR). We define a new metric for estimating the distances to evolved stars and compare its results to \emph{Gaia} EDR3. Replicating other studies, the most-evolved, highly enshrouded objects in the Galactic Plane dominate the dust returned by our sources, and we initially estimate a total DPR of $4.7\times 10^{-5}$ M$_\odot$ yr$^{-1}$ from our sample. Our sub-mm fluxes are systematically higher and spectral indices are typically shallower than dust models typically predict. The 450/850 $μ$m spectral indices are consistent with the blackbody Rayleigh--Jeans regime, suggesting a large fraction of evolved stars have unexpectedly large envelopes of cold dust. △ Less

Submitted 24 October, 2021; originally announced October 2021.

Comments: 20 pages, 13 figures, 5 tables, accepted for publications in MNRAS

Fallback in bipolar Planetary Nebulae ?

Authors: Willem A. Baan, Hiroshi Imai, Gabor Orosz

Abstract: The subclass of bipolar Planetary Nebulae (PN) exhibits well-defined low-power outflows and some show shock-related equatorial spiderweb structures and hourglass structures surrounding these outflows. These structures are distinctly different from the phenomena associated with spherical and elliptical PN and suggest a non-standard way to simultaneously energise both kind of structures. This paper… ▽ More The subclass of bipolar Planetary Nebulae (PN) exhibits well-defined low-power outflows and some show shock-related equatorial spiderweb structures and hourglass structures surrounding these outflows. These structures are distinctly different from the phenomena associated with spherical and elliptical PN and suggest a non-standard way to simultaneously energise both kind of structures. This paper presents evidence from the published literature on bipolar PN Hb\,12 and other sources in support of an alternative scenario for energizing these structures by means of accretion from material shells deposited during earlier post-AGB and pre-PN evolutionary stages. In addition to energizing the bipolar outflow, a sub-Eddington accretion scenario could hydrodynamically explain the spiderweb and outer hourglass structures as oblique shockwaves for guiding the accreting material into the equatorial region of the source. Estimates of the accretion rate resulting from fallback-related spherical accretion could indeed help to drive a low-power outflow and contribute to the total luminosity of these sources. △ Less

Submitted 9 September, 2021; v1 submitted 29 July, 2021; originally announced July 2021.

Comments: To be published in Research in Astronomy and Astrophysics

Testing Scalable Bell Inequalities for Quantum Graph States on IBM Quantum Devices

Authors: Bo Yang, Rudy Raymond, Hiroshi Imai, Hyungseok Chang, Hidefumi Hiraishi

Abstract: Testing and verifying imperfect multi-qubit quantum devices are important as such noisy quantum devices are widely available today. Bell inequalities are known useful for testing and verifying the quality of the quantum devices from their nonlocal quantum states and local measurements. There have been many experiments demonstrating the violations of Bell inequalities but they are limited in the nu… ▽ More Testing and verifying imperfect multi-qubit quantum devices are important as such noisy quantum devices are widely available today. Bell inequalities are known useful for testing and verifying the quality of the quantum devices from their nonlocal quantum states and local measurements. There have been many experiments demonstrating the violations of Bell inequalities but they are limited in the number of qubits and the types of quantum states. We report violations of Bell inequalities on IBM Quantum devices based on the scalable and robust inequalities maximally violated by graph states as proposed by Baccari et al. (Ref.[1]). The violations are obtained from the quantum states of path graphs up to 57 and 21 qubits on the 65-qubit and 27-qubit IBM Quantum devices, respectively, and from those of star graphs up to 8 and 7 qubits with error mitigation on the same devices. We are able to show violations of the inequalities on various graph states by constructing low-depth quantum circuits producing them, and by applying the readout error mitigation technique. We also point out that quantum circuits for star graph states of size N can be realized with circuits of depth $O(\sqrt n)$ on subdivided honeycomb lattices which are the topology of the 65-qubit IBM Quantum device. Our experiments show encouraging results on the ability of existing quantum devices to prepare entangled quantum states, and provide experimental evidences on the benefit of scalable Bell inequalities for testing them. △ Less

Submitted 15 May, 2025; v1 submitted 25 January, 2021; originally announced January 2021.

Journal ref: IEEE Journal on Emerging and Selected Topics in Circuits and Systems 12.3 (2022): 638-647

FLASHING: New high-velocity H$_2$O masers in IRAS 18286$-$0959

Authors: Hiroshi Imai, Yuri Uno, Daichi Maeyama, Ryosuke Yamaguchi, Kei Amada, Yuhki Hamae, Gabor Orosz, José F. Gómez, Daniel Tafoya, Lucero Uscanga, Ross A. Burns

Abstract: We discovered new high-velocity components of H$_2$O maser emission in one of the "water fountain" sources, IRAS~18286$-$0959, which has been monitored using the Nobeyama 45 m telescope in the new FLASHING (Finest Legacy Acquisitions of SiO- and H$_2$O-maser Ignitions by Nobeyama Generation) project since 2018 December. The maser spectra show new, extremely high expansion velocities ($>$200~km~s… ▽ More We discovered new high-velocity components of H$_2$O maser emission in one of the "water fountain" sources, IRAS~18286$-$0959, which has been monitored using the Nobeyama 45 m telescope in the new FLASHING (Finest Legacy Acquisitions of SiO- and H$_2$O-maser Ignitions by Nobeyama Generation) project since 2018 December. The maser spectra show new, extremely high expansion velocities ($>$200~km~s$^{-1}$ projected in the line of sight) components, some of which are located symmetrically in the spectrum with respect to the systemic velocity. They were also mapped with KaVA (KVN and VERA Combined Array) in 2019 March. We located some of these maser components closer to the central stellar system than other high velocity components (50--200~km~s$^{-1}$) that have been confirmed to be associated with the known bipolar outflow. The new components would flash in the fast collimated jet at a speed over 300~km~s$^{-1}$ (soon) after 2011 when they had not been detected. The fastest of the new components seem to indicate rapid deceleration in these spectra, however our present monitoring is still too sparse to unambiguously confirm it (up to 50~km~s$^{-1}$yr$^{-1}$) and too short to reveal their terminal expansion velocity, which will be equal to the expansion velocity that has been observed ($v_{\rm exp}\sim$120~km~s$^{-1}$). Future occurrences of such extreme velocity components may provide a good opportunity to investigate possible recurrent outflow ignitions. Thus sculpture of the parental envelope will be traced by the dense gas that is entrained by the fast jet and exhibits spectacular distributions of the relatively stable maser features. △ Less

Submitted 26 September, 2020; originally announced September 2020.

Comments: 11 pages, 5 figures, 2 tables

Journal ref: PASJ, 72, 58 (2020)

Compiling ONNX Neural Network Models Using MLIR

Authors: Tian Jin, Gheorghe-Teodor Bercea, Tung D. Le, Tong Chen, Gong Su, Haruki Imai, Yasushi Negishi, Anh Leu, Kevin O'Brien, Kiyokuni Kawachiya, Alexandre E. Eichenberger

Abstract: Deep neural network models are becoming increasingly popular and have been used in various tasks such as computer vision, speech recognition, and natural language processing. Machine learning models are commonly trained in a resource-rich environment and then deployed in a distinct environment such as high availability machines or edge devices. To assist the portability of models, the open-source… ▽ More Deep neural network models are becoming increasingly popular and have been used in various tasks such as computer vision, speech recognition, and natural language processing. Machine learning models are commonly trained in a resource-rich environment and then deployed in a distinct environment such as high availability machines or edge devices. To assist the portability of models, the open-source community has proposed the Open Neural Network Exchange (ONNX) standard. In this paper, we present a high-level, preliminary report on our onnx-mlir compiler, which generates code for the inference of deep neural network models described in the ONNX format. Onnx-mlir is an open-source compiler implemented using the Multi-Level Intermediate Representation (MLIR) infrastructure recently integrated in the LLVM project. Onnx-mlir relies on the MLIR concept of dialects to implement its functionality. We propose here two new dialects: (1) an ONNX specific dialect that encodes the ONNX standard semantics, and (2) a loop-based dialect to provide for a common lowering point for all ONNX dialect operations. Each intermediate representation facilitates its own characteristic set of graph-level and loop-based optimizations respectively. We illustrate our approach by following several models through the proposed representations and we include some early optimization work and performance results. △ Less

Submitted 30 September, 2020; v1 submitted 19 August, 2020; originally announced August 2020.

Comments: 8 pages

Shaping the envelope of the asymptotic giant branch star W43A with a collimated fast jet

Authors: Daniel Tafoya, Hiroshi Imai, Jose F. Gomez, Jun-ichi Nakashima, Gabor Orosz, Bosco H. K. Yung

Abstract: One of the major puzzles in the study of stellar evolution is the formation process of bipolar and multi-polar planetary nebulae. There is growing consensus that collimated jets create cavities with dense walls in the slowly-expanding (10--20 ~km~s$^{-1}$) envelope ejected in previous evolutionary phases, leading to the observed morphologies. However, the launching of the jet and the way it intera… ▽ More One of the major puzzles in the study of stellar evolution is the formation process of bipolar and multi-polar planetary nebulae. There is growing consensus that collimated jets create cavities with dense walls in the slowly-expanding (10--20 ~km~s$^{-1}$) envelope ejected in previous evolutionary phases, leading to the observed morphologies. However, the launching of the jet and the way it interacts with the circumstellar material to create such asymmetric morphologies have remained poorly known. Here we present for the first time CO emission from the asymptotic giant branch star W43A that traces the whole stream of a jet, from the vicinity of its driving stellar system out to the regions where it shapes the circumstellar envelope. We found that the jet has a launch velocity of 175~km~s$^{-1}$ and decelerates to a velocity of 130~km~s$^{-1}$ as it interacts with circumstellar material. The continuum emission reveals a bipolar shell with a compact bright dot in the centre that pinpoints the location of the driving source of the jet. The kinematical ages of the jet and the bipolar shell are equal, $τ$$\sim$60~years, indicating that they were created simultaneously, probably by a common underlying mechanism, and in an extremely short time. These results provide key initial conditions for the theoretical models that aim to explain the formation of bipolar morphologies in the circumstellar envelopes of low and intermediate mass stars. △ Less

Submitted 12 June, 2020; originally announced June 2020.

Comments: 11 pages, 6 figures. Published in ApJ Letters

Journal ref: The Astrophysical Journal Letters, Volume 890, Issue 1, id.L14 February 2020

Asymmetric distributions of H2O and SiO masers towards V627 Cas

Authors: Haneul Yang, Se-Hyung Cho, Youngjoo Yun, Dong-Hwan Yoon, Dong-Jin Kim, Hyosun Kim, Sung-Chul Yoon, Richard Dodson, María J. Rioja, Hiroshi Imai

Abstract: We performed simultaneous observations of the H2O 6(1,6) - 5(2,3) (22.235080 GHz) and SiO v= 1, 2, J = 1 - 0, SiO v = 1, J = 2 - 1, 3 - 2 (43.122080, 42.820587, 86.243442, and 129.363359 GHz) masers towards the suspected D-type symbiotic star, V627 Cas, using the Korean VLBI Network. Here, we present astrometrically registered maps of the H2O and SiO v = 1, 2, J = 1 - 0, SiO v = 1, J = 2 - 1 maser… ▽ More We performed simultaneous observations of the H2O 6(1,6) - 5(2,3) (22.235080 GHz) and SiO v= 1, 2, J = 1 - 0, SiO v = 1, J = 2 - 1, 3 - 2 (43.122080, 42.820587, 86.243442, and 129.363359 GHz) masers towards the suspected D-type symbiotic star, V627 Cas, using the Korean VLBI Network. Here, we present astrometrically registered maps of the H2O and SiO v = 1, 2, J = 1 - 0, SiO v = 1, J = 2 - 1 masers for five epochs from January 2016 to June 2018. Distributions of the SiO maser spots do not show clear ring-like structures, and those of the H2O maser are biased towards the north-north-west to west with respect to the SiO maser features according to observational epochs. These asymmetric distributions of H2O and SiO masers are discussed based on two scenarios of a bipolar outflow and the presence of the hot companion, a white dwarf, in V627 Cas. We carried out ring fitting of SiO v = 1, and v = 2 masers and estimated the expected position of the cool red giant. The ring radii of the SiO v = 1 maser are slightly larger than those of the SiO v = 2 maser, as previously known. Our assumption for the physical size of the SiO maser ring of V627 Cas to be the typical size of a SiO maser ring radius (\sim4 au) of red giants yields the distance of V627 Cas to be \sim1 kpc. △ Less

Submitted 1 June, 2020; originally announced June 2020.

Comments: 7 pages, 4 figures, 1 table, Published in MNRAS

Journal ref: MNRAS, 495, 1284-1290 (2020)

The First VERA Astrometry Catalog

Authors: VERA collaboration, Tomoya Hirota, Takumi Nagayama, Mareki Honma, Yuuki Adachi, Ross A. Burns, James O. Chibueze, Yoon Kyung Choi, Kazuya Hachisuka, Kazuhiro Hada, Yoshiaki Hagiwara, Shota Hamada, Toshihiro Handa, Mao Hashimoto, Ken Hirano, Yushi Hirata, Takanori Ichikawa, Hiroshi Imai, Daichi Inenaga, Toshio Ishikawa, Takaaki Jike, Osamu Kameya, Daichi Kaseda, Jeong Sook Kim, Jungha Kim , et al. (37 additional authors not shown)

Abstract: 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… ▽ More 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 $Ω_{\odot}=30.17\pm0.27_{\rm{stat.}}\pm0.3_{\rm{sys.}}$~km~s$^{-1}$~kpc$^{-1}$, where $R_{0}$ and $Ω_{\odot}$ are the distance from the Sun to the Galactic center and the Sun's angular velocity of the Galactic circular rotation, respectively. △ Less

Submitted 7 February, 2020; originally announced February 2020.

Comments: 35 pages, 7 figures, accepted for publication in the Publications of the Astronomical Society of Japan

Accurate OH Maser Positions From The SPLASH Survey III: The Final 96 Square Degrees

Authors: Hai-Hua Qiao, Shari L. Breen, Jose F. Gomez, J. R. Dawson, Andrew J. Walsh, James A. Green, Simon P. Ellingsen, Hiroshi Imai, Zhi-Qiang Shen

Abstract: We present high spatial resolution observations of ground-state OH masers achieved with the Australia Telescope Compact Array (ATCA). These observations targeted 253 pointing centres containing OH maser candidates at all four ground-state OH transitions identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) across 96 square degrees of the Southern Galactic plane (332\degree$<l<$3… ▽ More We present high spatial resolution observations of ground-state OH masers achieved with the Australia Telescope Compact Array (ATCA). These observations targeted 253 pointing centres containing OH maser candidates at all four ground-state OH transitions identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) across 96 square degrees of the Southern Galactic plane (332\degree$<l<$334\degree and $-$2\degree$<b<+$2\degree, 344\degree$<l<$355\degree and $-$2\degree$<b<+$2\degree, 358\degree$<l<$4\degree and $+$2\degree$<b<+$6\degree, 5\degree$<l<$10\degree and $-$2\degree$<b<+$2\degree). We detect maser emission towards 236 fields and suggest that 7 out of 17 non-detections are due to the slightly lower sensitivity of the ATCA observations, combined with some temporal variability. The superior resolution provided by the ATCA data has allowed us to identify 362 OH maser sites in the 236 target fields. Almost half (160 of 362) of these masers have been detected for the first time. Comparison between these 362 maser sites with information presented in the literature allowed us to categorize 238 sites as evolved star sites (66\%), 63 as star formation (17\%), eight as supernova remnants and 53 unknown maser sites (15\%). We present analysis of the OH masers across the full SPLASH survey range (176 square degrees) and find that the detection rate of 1.7 GHz radio continuum sources (18\%) is lower than that previously found at 8.2 and 9.2 GHz (38\%). We also find that the velocity separations of evolved star sites with symmetric 1612 MHz maser profiles are generally smaller than those with asymmetric profiles. △ Less

Submitted 6 December, 2019; originally announced December 2019.

Comments: 22 pages, 12 figures. arXiv admin note: text overlap with arXiv:1809.09304

Overall variation of the $H_2O$ masers around W Hydrae in 28 years

Authors: Hiroshi Imai, Akiharu Nakagawa, Hiroshi Takaba

Abstract: In this paper, we present the distribution of $H_2O$ masers associated with the semi-regular variable star W Hydrae (W Hya). We have collected the radio interferometric data of the maser distribution taken with the Very Large Array (VLA), the Kashima-Nobeyama InterFErometer (KNIFE), the Multi-Element Radio Link Network (MERLIN), the VLBI Exploration of Radio Astrometry (VERA), and the combined arr… ▽ More In this paper, we present the distribution of $H_2O$ masers associated with the semi-regular variable star W Hydrae (W Hya). We have collected the radio interferometric data of the maser distribution taken with the Very Large Array (VLA), the Kashima-Nobeyama InterFErometer (KNIFE), the Multi-Element Radio Link Network (MERLIN), the VLBI Exploration of Radio Astrometry (VERA), and the combined array of the Korean VLBI Network (KVN) and VERA (KaVA) in order to trace the maser distribution variation in two decades. Even though differences in the sensitivities and angular resolutions of the interferometric observations should be taken into account, we attempt to find possible correlation of the maser distribution with the stellar light curve. Our failure in the measurement of the annual parallax of the masers with VERA is likely caused by the properties of the maser features, which have been spatially resolved by the synthesized beam and survived for only half a year or less. No dependence of the maser spot flux density on its size is found in the KNIFE data, suggesting that maser spot size is determined by the physical boundary, as is expected for a clump affected by outward propagation of a stellar pulsation shock wave, rather than the (spherical) geometry of maser beaming in the maser gas clump. △ Less

Submitted 13 October, 2019; originally announced October 2019.

Comments: 27 pages, 10 figures, will be published in PASJ