ORCID Profile
0000-0001-9525-7981
Current Organisation
University of Tasmania
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Publisher: Oxford University Press (OUP)
Date: 09-08-2018
Publisher: Oxford University Press (OUP)
Date: 16-03-2018
DOI: 10.1093/MNRAS/STY694
Publisher: American Astronomical Society
Date: 25-10-2018
Publisher: Oxford University Press (OUP)
Date: 22-10-2021
Abstract: We have performed a molecular line search towards the flaring 6.7-GHz masers G 24.33+0.13, and G 359.6−0.24 using the Australia Telescope Compact Array. We present spectra of the 6.7-GHz class II methanol and 22.2-GHz water masers towards these sources and provide a comparison with other recent flaring events these sources have experienced. We also detect the fourth ex le of a 23.4-GHz class I methanol maser and the 11th ex le of a 4.8-GHz formaldehyde maser towards G 24.33+0.13. Alongside these results, we also observe the previously detected ammonia (3,3) emission and report upper limits on the presence of various other cm-wavelength methanol, ammonia, and OH transitions. Our results are consistent with the flaring of G 24.33+0.13 being driven by a variable accretion rate in the host high mass young stellar object.
Publisher: Oxford University Press (OUP)
Date: 05-09-2022
DOI: 10.1093/PASJ/PSAC067
Abstract: In 2019 September, a sudden flare of the 6.7 GHz methanol maser was observed toward the high-mass young stellar object (HMYSO) G24.33+0.14. This may represent the fourth detection of a transient mass accretion event in an HMYSO after S255IR NIRS3, NGC 6334I-MM1, and G358.93−0.03-MM1. G24.33+0.14 is unique among these sources as it clearly shows a repeating flare with an 8 yr interval. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we observed the millimeter continuum and molecular lines toward G24.33+0.14 in the pre-flare phase in 2016 August (ALMA Cycle 3) and the mid-flare phase in 2019 September (ALMA Cycle 6). We identified three continuum sources in G24.33+0.14, and the brightest source, C1, which is closely associated with the 6.7 GHz maser emission, shows only a marginal increase in flux density with a flux ratio (Cycle 6$/$Cycle 3) of 1.16 ± 0.01, considering an additional absolute flux calibration uncertainty of $10\\%$. We identified 26 transitions from 13 molecular species other than methanol, and they exhibit similar levels of flux differences with an average flux ratio of 1.12 ± 0.15. In contrast, eight methanol lines observed in Cycle 6 are brighter than those in Cycle 3 with an average flux ratio of 1.23 ± 0.13, and the higher excitation lines tend to show a larger flux increase. If this systematic increasing trend is real, it would suggest radiative heating close to the central HMYSO due to an accretion event which could expand the size of the emission region and/or change the excitation conditions. Given the low brightness temperatures and small flux changes, most of the methanol emission is likely to be predominantly thermal, except for the 229.759 GHz (8−1–70 E) line known as a class I methanol maser. The flux change in the millimeter continuum of G24.33+0.14 is smaller than in S255IR NIRS3 and NGC 6334I-MM1 but is comparable with that in G358.93−0.03-MM1, suggesting different amounts of accreted mass in these events.
Publisher: Oxford University Press (OUP)
Date: 05-11-2020
Abstract: We have used the Australia Telescope Compact Array (ATCA) to make new observations of the 36.2-GHz (4−1 → 30E) methanol transition towards NGC 4945 and NGC 253. These observations have revealed the presence of new maser components towards these galaxies, and have provided the first clear evidence for variability in extragalactic class I methanol masers. Alongside the new observations of NGC 4945 and NGC 253, we present the results of recent 36.2-GHz methanol maser searches towards 12 galaxies, placing upper limits on the emission from the 36.2-GHz class I transition and the 37.7-GHz (72 → 81E) class II maser line towards these sources. Flux density values for the 7-mm continuum emission towards these sources are also reported where applicable. A re-analysis of the published 36.2-GHz methanol observations of Arp 220 undertaken as part of the search revealed some issues with previous imaging procedures. The re-analysis, combined with non-detections in independent follow-up observations, suggests that there is no 36.2-GHz methanol emission towards Arp 220 stronger than 3.5 mJy in a 10 km s−1 channel (5σ upper limit).
Publisher: American Astronomical Society
Date: 06-05-2019
Publisher: Oxford University Press (OUP)
Date: 21-01-2019
DOI: 10.1093/MNRAS/STZ192
Publisher: American Astronomical Society
Date: 28-04-2023
Abstract: We present the spectral and spatial evolution of H 2 O masers associated with the water fountain source IRAS 18043−2116, found in 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 redshifted side V LSR ≃ 376 km s −1 and at the blueshifted side V LSR ≃ −165 km s −1 ), and the resulting velocity spread of ≃540 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 (∼60°). The evolution of the maser cluster separation of ∼2.9 mas yr −1 and the compact (∼0.″2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (∼30 yr) timescale of the outflow. We also confirmed an 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.
Publisher: Springer Science and Business Media LLC
Date: 27-09-2022
DOI: 10.1007/S00190-022-01657-2
Abstract: Global geodetic VLBI is upgrading to its next-generation observing system, VGOS. This upgrade has turned out to be a process over multiple years, until VGOS reaches its full capabilities with the envisaged continuous observations. Until then, for the Australian stations, the upgrade means ceasing their legacy S/X observations, leaving a large gap in the global network as well as in the station time series. The Australian mixed-mode observing program is a series of sessions where the VGOS stations in Hobart and Katherine observe legacy S/X VLBI together with other stations in the region. This paper describes the technical details of these observations and their processing strategies and discusses their suitability for geodetic results by comparison with those of standard legacy S/X sessions. The presented mixed-mode sessions allow a continuation of the station time series, a benefit for the stations themselves as well as for future realisations of the terrestrial and celestial reference frames. A novel mode of observing is introduced and tested. The results are promising and it is suggested for acceptance into standard legacy S/X IVS observations, overcoming current gaps in the network due to VGOS upgrades and preventing a worsening of global results otherwise.
Publisher: EDP Sciences
Date: 2020
DOI: 10.1051/0004-6361/201936330
Abstract: Methanol (CH 3 OH) is one of the most abundant interstellar molecules, offering a vast number of transitions to be studied, including many maser lines. However, while the strongest Galactic CH 3 OH lines, the so-called class II masers, show no indications for the presence of superluminous counterparts in external galaxies, the less luminous Galactic class I sources appear to be different. Here we report class I 36 GHz ( λ ≈ 0.8 cm) CH 3 OH 4 −1 → 3 0 E line emission from the nearby galaxies Maffei 2 ( D ≈ 6 Mpc) and IC 342 ( D ≈ 3.5 Mpc), measured with the 100 m telescope at Effelsberg at three different epochs within a time span of about five weeks. The 36 GHz methanol line of Maffei 2 is the second most luminous among the sources detected with certainty outside the Local Group of galaxies. This is not matched by the moderate infrared luminosity of Maffei 2. Higher-resolution data are required to check whether this is related to its prominent bar and associated shocks. Upper limits for M 82, NGC 4388, NGC 5728 and Arp 220 are also presented. The previously reported detection of 36 GHz maser emission in Arp 220 is not confirmed. Nondetections are reported from the related class I 44 GHz ( λ ≈ 0.7 cm) methanol transition towards Maffei 2 and IC 342, indicating that this line is not stronger than its 36 GHz counterpart. In contrast to the previously detected 36 GHz CH 3 OH emission in NGC 253 and NGC 4945, our 36 GHz profiles towards Maffei 2 and IC 342 are similar to those of previously detected nonmasing lines from other molecular species. However, by analogy to our Galactic center region, it may well be possible that the 36 GHz methanol lines in Maffei 2 and IC 342 are composed of a large number of faint and narrow maser features that remain spatially unresolved. In view of this, a search for a weak broad 36 GHz line component would also be desirable in NGC 253 and NGC 4945.
Publisher: Springer Science and Business Media LLC
Date: 28-07-2022
DOI: 10.1186/S40623-022-01671-W
Abstract: The deviation of Universal Time from atomic time, expressed as UT1−UTC, reflects the irregularities of the Earth rotation speed and is key to precise geodetic applications which depend on the transformation between celestial and terrestrial reference frames. A rapidly varying quantity such as UT1−UTC demands observation scenarios enabling fast delivery of good results. These criteria are currently met only by the Very Long Baseline Interferometry (VLBI) Intensive sessions. Due to stringent requirements of a fast UT1−UTC turnaround, the observations are limited to a few baselines and a duration of one hour. Hence, the estimation of UT1−UTC from Intensives is liable to constraints and prone to errors introduced by inaccurate a priori information. One aspect in this context is that the regularly operated Intensive VLBI sessions organised by the International VLBI Service for Geodesy and Astrometry solely use stations in the northern hemisphere. Any potential systematic errors due to this northern hemisphere dominated geometry are so far unknown. Besides the general need for stimulating global geodetic measurements with southern observatories, this served as a powerful motivation to launch the SI (Southern Intensive) program in 2020. The SI sessions are observed using three VLBI antennas in the southern hemisphere: Ht (South Africa), Hb (Tasmania) and Yg (Western Australia). On the basis of UT1−UTC results from 53 sessions observed throughout 2020 and 2021, we demonstrate the competitiveness of the SI with routinely operated Intensive sessions in terms of operations and UT1−UTC accuracy. The UT1−UTC values of the SI reach an average agreement of 32 µs in terms of weighted standard deviation when compared with the conventional Intensives results of five independent analysis centers and of 27 µs compared with the 14C04 series. The mean scatter of all solutions of the considered northern hemisphere Intensives with respect to C04 is at a comparable level of 29 µs. The quality of the results is only slightly degraded if just the baseline HtHb is evaluated. In combination with the e-transfer capabilities from Ht to Hb, this facilitates continuation of the SI by ensuring rapid service UT1−UTC provision. Graphical Abstract
Publisher: Oxford University Press (OUP)
Date: 29-04-2023
Abstract: We report the detection of ammonia masers in the non-metastable (6, 3), (7, 5), and (6, 5) transitions the latter being the first unambiguous maser detection of that transition ever made. Our observations include the first very long baseline interferometry detection of ammonia maser emission, which allowed effective constraining of the (6, 5) maser brightness temperature. The masers were detected towards G 358.931−0.030, a site of 6.7-GHz class II methanol maser emission that was recently reported to be undergoing a period of flaring activity. These ammonia masers appear to be flaring contemporaneously with the class II methanol masers during the accretion burst event of G 358.931−0.030. This newly detected site of ammonia maser emission is only the 12th such site discovered in the Milky Way. We also report the results of an investigation into the maser pumping conditions, for all three detected masing transitions, through radiative transfer calculations constrained by our observational data. These calculations support the hypothesis that the ammonia (6, 5) maser transition is excited through high colour temperature infrared emission, with the (6, 5) and (7, 5) transition line ratio implying dust temperatures & K. Additionally, we detect significant linearly polarized emission from the ammonia (6, 3) maser line. Alongside our observational and radiative transfer calculation results, we also report newly derived rest frequencies for the ammonia (6, 3) and (6, 5) transitions.
Publisher: American Astronomical Society
Date: 13-09-2017
Publisher: American Astronomical Society
Date: 02-04-2018
Publisher: American Astronomical Society
Date: 02-2022
Abstract: We report the detection of class I methanol maser at the 36.2 GHz transition toward the nearby starburst galaxy Maffei 2 with the Karl G. Jansky Very Large Array. Observations of the 36.2 GHz transition at two epochs separated by ∼4 yr show consistencies in both the spatial distribution and flux density of the methanol emission in this transition. Similar to the detections in other nearby starbursts the class I methanol masers sites are offset by a few hundred pc from the center of the galaxy and appear to be associated with the bar edges of Maffei 2. Narrow spectral features with line widths of a few km s −1 are detected, supporting the hypothesis that they are masing. Compared to other nearby galaxies with the detections in the 36.2 GHz methanol maser transition, the maser detected in Maffei 2 has about an order of magnitude higher isotropic luminosity, and thus represents the first confirmed detection of class I methanol megamasers. The spatial distribution of the 36.2 GHz maser spot clusters may trace the rotational gas flow of the galactic bar, providing direct evidence that the class I methanol maser is related to shocks induced by galactic bar rotation. A tentative detection in the 6.7 GHz class II methanol maser (at a 5 σ level) is also reported. This is comparable in luminosity to some of the 6.7 GHz maser sources detected in Galactic star-forming regions. The 6.7 GHz methanol emission appears to be associated with star formation activity in a smaller volume, rather than related to the larger-scale galactic activities.
Start Date: 2021
End Date: 2021
Funder: FrontierSI
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