ORCID Profile
0000-0003-4871-9535
Current Organisation
University of Western Australia
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Astronomical sciences | Communications Technologies | Microwave and Millimetrewave Theory and Technology | Galactic astronomy | Astronomical and Space Instrumentation | Satellite Communications
Publisher: Elsevier BV
Date: 2000
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317010547
Abstract: We report on the astrometric registration of VLBI images of the SiO and H 2 O masers in OH 231.8+4.2, the iconic Proto-Planetary Nebula also known as the Calabash nebula, using the KVN and Source/Frequency Phase Referencing. This, for the first time, robustly confirms the alignment of the SiO masers, close to the AGB star, which drives the bi-lobe structure with the water masers in the out-flow.
Publisher: MDPI AG
Date: 24-01-2017
Publisher: IEEE
Date: 08-2016
Publisher: MDPI AG
Date: 12-12-2017
Publisher: American Astronomical Society
Date: 15-12-2017
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317010274
Abstract: The Korean VLBI Network (KVN) is a unique millimeter VLBI system which is consisted of three 21 m telescopes with relatively short baselines. We present the preliminary results of simultaneous monitoring observations of the 22.2 GHz H 2 O and 43.1/42.8/86.2/129.3 GHz SiO masers based on the KVN Key Science Project (KSP). We obtained the astrometrically registered maps of the H 2 O and SiO masers toward nine evolved stars using the source frequency phase referencing method (SFPR). The SFPR maps of the H 2 O and SiO masers enabled us to investigate the spatial structure and kinematics from the SiO to H 2 O maser regions including the development of an outward motion from the ring-like or elliptical structures of SiO masers to the asymmetric structures of the 22.2 GHz H 2 O maser features. In particular, the 86.2/129.3 GHz SiO ( v =1, J =2–1 and J =3–2) masers were clearly imaged toward several objects for the first time. The SiO v =1, J =3–2 maser shows different distributions compared to those of the SiO v =1, 2, J =1–0 and v =1, J =2–1 masers implying a different physical condition.
Publisher: Oxford University Press (OUP)
Date: 25-06-2004
Publisher: American Astronomical Society
Date: 06-2022
Abstract: Very Long Baseline Interferometry (VLBI) astrometry is a well established technique for achieving ±10 μ as parallax accuracies at frequencies well above 10 GHz. At lower frequencies, uncompensated interferometer delays associated with the ionosphere play the dominant role in limiting the astrometric accuracy. Multiview is a novel VLBI calibration method, which uses observations of multiple quasars to accurately model and remove time-variable, directional-dependent changes to the interferometer delay. Here we extend the Multiview technique by phase-referencing data to the target source (“inverse Multiview”) and test its performance. Multiple observations with a four-antenna VLBI array operating at 8.3 GHz show single-epoch astrometric accuracies near 20 μ as for target–reference quasar separations up to about 7°. This represents an improvement in astrometric accuracy by up to an order of magnitude compared to standard phase-referencing.
Publisher: Oxford University Press (OUP)
Date: 25-10-2008
Publisher: American Astronomical Society
Date: 09-10-2014
Publisher: Elsevier BV
Date: 1997
Publisher: Oxford University Press (OUP)
Date: 25-08-2005
Publisher: American Astronomical Society
Date: 28-07-2023
Abstract: We present the first results from the Southern Hemisphere Parallax Interferometric Radio Astrometry Legacy Survey: 10 μ as accurate parallaxes and proper motions for two Southern Hemisphere 6.7 GHz methanol masers obtained using the inverse MultiView calibration method. Using an array of radio telescopes in Australia and New Zealand, we measured trigonometric parallaxes and proper motions for the masers associated with the star formation region G232.62+00.99 of π = 0.610 ± 0.011 mas, μ x = −2.266 ± 0.021 mas yr −1 , and μ y = 2.249 ± 0.049 mas yr −1 , which implies its distance to be d = 1.637 ± 0.029 kpc. These measurements represent an improvement in accuracy by more than a factor of 3 over the previous measurements obtained through Very Long Baseline Array observations of the 12 GHz methanol masers associated with this region. We also measure the trigonometric parallax and proper motion for G323.74–00.26 as π = 0.364 ± 0.009 mas, μ x = −3.239 ± 0.025 mas yr −1 , and μ y = − 3.976 ± 0.039 mas yr −1 , which implies a distance of d = 2.747 ± 0.068 kpc. These are the most accurate measurements of trigonometric parallax obtained for 6.7 GHz class II methanol masers to date. We confirm that G232.62+00.99 is in the Local Arm and find that G323.74–00.26 is in the Scutum–Centaurus arm. We also investigate the structure and internal dynamics of both masers.
Publisher: Sissa Medialab
Date: 18-04-2023
DOI: 10.22323/1.428.0058
Publisher: Elsevier BV
Date: 1997
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We report very long baseline interferometry (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 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 = ∼440 days). 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 ± 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 Korean VLBI Network. The three-dimensional H 2 O maser kinematics indicates that the circumstellar envelope is expanding at a velocity of 13 ± 4 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.
Publisher: American Astronomical Society
Date: 15-10-2018
Publisher: American Astronomical Society
Date: 09-02-2017
Publisher: EDP Sciences
Date: 18-07-2005
Publisher: American Astronomical Society
Date: 25-04-2016
Publisher: Cambridge University Press (CUP)
Date: 09-2018
DOI: 10.1017/S1743921317010560
Abstract: Observations at low frequencies ( GHz ) are dominated by distinct direction dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase referencing calibrator and astrometry. To increase the capability for high precision astrometric measurements an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. The MultiView technique holds the key to the compensation of atmospheric spatial-structure errors, by using observations of multiple calibrators and two dimensional interpolation. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ~100micro-arcseconds astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit.
Publisher: IEEE
Date: 08-2016
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-03-2021
Abstract: If a black hole interacts with a binary companion star, the system emits x-rays and can form a radio jet. The masses of black holes in these x-ray binaries are all lower than those detected using gravitational waves, challenging models of black hole formation from massive stars. Miller-Jones et al. used radio astrometry to refine the distance to Cygnus X-1, a well-studied x-ray binary. They found a larger distance than previous estimates, raising the mass of the black hole in the system to 21 solar masses. The results challenge the wind mass loss rates implemented in stellar evolution models. Science , this issue p. 1046
Publisher: American Astronomical Society
Date: 12-01-2017
Publisher: EDP Sciences
Date: 18-07-2013
Publisher: IOP Publishing
Date: 07-2016
Publisher: American Astronomical Society
Date: 10-10-2011
Publisher: American Astronomical Society
Date: 28-05-2015
Publisher: Springer Science and Business Media LLC
Date: 29-09-2020
Publisher: American Astronomical Society
Date: 30-04-2013
Publisher: MDPI AG
Date: 24-04-2023
Abstract: The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide.
Publisher: American Astronomical Society
Date: 17-10-2014
Publisher: MDPI AG
Date: 12-01-2023
Abstract: (Sub) mm VLBI observations are strongly hindered by limited sensitivity, with the fast tropospheric fluctuations being the dominant culprit. We predict great benefits from applying next-generation frequency phase transfer calibration techniques for the next generation Event Horizon Telescope (ngEHT), using simultaneous multi-frequency observations. We present comparative simulation studies to characterise its performance, the optimum configurations, and highlight the benefits of including observations at 85 GHz along with the 230 and 340 GHz bands. The results show a transformational impact on the ngEHT array capabilities, with orders of magnitude improved sensitivity, observations routinely possible over the whole year, and ability to carry out micro-arcsecond astrometry measurements at the highest frequencies, amongst others. This will enable the addressing of a host of innovative open scientific questions in astrophysics. We present a solution for highly scatter-broadened sources such as SgrA*, a prime ngEHT target. We conclude that adding the 85 GHz band provides a pathway to an optimum and robust performance for ngEHT in sub-millimeter VLBI, and strongly recommmend its inclusion in the simultaneous multi-frequency receiver design.
Publisher: American Astronomical Society
Date: 21-02-2017
Publisher: No publisher found
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 12-2014
DOI: 10.1093/PASJ/PSU107
Publisher: Elsevier BV
Date: 11-2017
Publisher: American Astronomical Society
Date: 14-12-2015
Publisher: American Astronomical Society
Date: 11-1994
DOI: 10.1086/174799
Publisher: American Astronomical Society
Date: 04-2008
DOI: 10.1086/525025
Publisher: Oxford University Press (OUP)
Date: 31-01-2018
DOI: 10.1093/MNRAS/STY239
Publisher: American Astronomical Society
Date: 14-09-2012
Publisher: Elsevier BV
Date: 11-1999
Publisher: Oxford University Press (OUP)
Date: 05-05-2020
Abstract: We performed simultaneous observations of the $\\rm H_2O$ 61,6 − 52,3 (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 $\\rm H_2O$ 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 $\\rm H_2O$ 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 $\\rm H_2O$ 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 (∼4 au) of red giants yields the distance of V627 Cas to be ∼1 kpc.
Publisher: EDP Sciences
Date: 09-2016
Publisher: MDPI AG
Date: 21-12-2022
Abstract: The source-frequency phase-referencing (SFPR) technique has been demonstrated to have great advantages for mm-VLBI observations. By implementing simultaneous multi-frequency receiving systems on the next-generation Event Horizon Telescope (ngEHT) antennas, it is feasible to carry out a frequency phase transfer (FPT) which could calibrate the non-dispersive propagation errors and significantly increase the phase coherence in the visibility data. Such an increase offers an efficient approach for a weak source or structure detection. The SFPR also makes it possible for high-precision astrometry, including the core-shift measurements up to sub-mm wavelengths for Sgr A*, M 87*, etc. We also briefly discuss the technical and scheduling considerations for future SFPR observations with the ngEHT.
Publisher: Elsevier BV
Date: 1997
Publisher: Oxford University Press (OUP)
Date: 17-04-2013
DOI: 10.1093/MNRAS/STT471
Publisher: Elsevier BV
Date: 11-1999
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317011425
Abstract: We present the results from the Australian Long Baseline Array (LBA) observations of the ground- and excited-state OH masers at high resolutions towards the massive star-forming region G351.417+0.645 in 2012. We obtain the most accurate spatial gradient of magnetic fields at ground state transitions and verify the reliability of magnetic field strengths measured from previous lower resolution observations. In comparison with previous LBA observations in 2001 at 6.0 GHz, we identified several matched Zeeman pairs. We found that the OH maser features have no significant change of magnetic field strengths and directions with small internal proper motions, implying quite stable physical conditions. Additionally, we found that 1665- and 6035-MHz OH maser features reveal the same trend of reversal of magnetic fields. Moreover, we also analyzed the physical conditions at different locations from the coincidence of different OH maser transitions based on current OH maser models.
Publisher: American Astronomical Society
Date: 03-2011
Publisher: Oxford University Press (OUP)
Date: 05-2012
Publisher: EDP Sciences
Date: 22-12-2010
Publisher: Oxford University Press (OUP)
Date: 12-10-2018
Publisher: American Astronomical Society
Date: 13-06-2017
Publisher: Springer Science and Business Media LLC
Date: 28-06-2018
DOI: 10.1038/S41467-018-04767-8
Abstract: The supergiant VX Sagittarii is a strong emitter of both H 2 O and SiO masers. However, previous VLBI observations have been performed separately, which makes it difficult to spatially trace the outward transfer of the material consecutively. Here we present the astrometrically registered, simultaneous maps of 22.2 GHz H 2 O and 43.1/42.8/86.2/129.3 GHz SiO masers toward VX Sagittarii. The H 2 O masers detected above the dust-forming layers have an asymmetric distribution. The multi-transition SiO masers are nearly circular ring, suggesting spherically symmetric wind within a few stellar radii. These results provide the clear evidence that the asymmetry in the outflow is enhanced after the smaller molecular gas clump transform into the inhomogeneous dust layers. The 129.3 GHz maser arises from the outermost region compared to that of 43.1/42.8/86.2 GHz SiO masers. The ring size of the 129.3 GHz maser is maximized around the optical maximum, suggesting that radiative pumping is dominant.
Publisher: Oxford University Press (OUP)
Date: 08-05-2018
Publisher: Oxford University Press (OUP)
Date: 2004
DOI: 10.1143/PTPS.155.339
Start Date: 2023
End Date: 12-2025
Amount: $432,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 12-2013
Amount: $300,000.00
Funder: Australian Research Council
View Funded Activity