ORCID Profile
0000-0002-4716-4235
Current Organisation
Monash University
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Astronomical and Space Sciences | Stellar Astronomy and Planetary Systems | Galactic Astronomy | Astronomical and Space Sciences not elsewhere classified | Astronomy And Astrophysics | Numerical Analysis
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in the Mathematical Sciences | Physical sciences | Mathematical sciences |
Publisher: Oxford University Press (OUP)
Date: 28-10-2016
Publisher: EDP Sciences
Date: 11-2022
DOI: 10.1051/0004-6361/202243540
Abstract: Aims. We present the implementation of the treatment of particle ejection and dust nucleation in the smoothed particle hydrodynamics (SPH) code P HANTOM . These developments represent the first step toward a more complete modeling of dust-driven winds emanating from asymptotic giant branch (AGB) stars that can be used for comparison with high resolution imaging of these stars. Methods. The AGB outflow is modeled by injecting the SPH particles from a spherical inner boundary. This boundary is a series of concentric shells, with the AGB star at its center, and the particles are positioned on these shells on the vertices of an isocahedron geodesic surface. The outermost shell is ejected with a predefined radial velocity, and subsequent lower shells replenish the ejected ones, all rotated randomly to improve the isotropy of the outflow. The physical properties of the particles on these shells are set by solving the 1D analytic steady wind equations. The formation of dust is calculated starting from a compact chemical network for carbon-rich material, which creates the building blocks of the solid-state particles. Subsequently, the theory of the moments is used to obtain dust growth rates, without requiring knowledge on the grain size distribution. Results. We tested our implementation against a series of 1D reference solutions. We demonstrate that our method is able to reproduce Parker-type wind solutions. For the trans-sonic solution, small oscillations are present in the vicinity of the sonic point, but these do not impact the trans-sonic passage or terminal wind velocity. Supersonic solutions always compare nicely with 1D analytic profiles. We also tested our implementation of dust using two formalisms: an analytic prescription for the opacity devised by Bowen and the full treatment of carbon-dust formation. Both simulations reproduce the 1D analytic solution displaying the expected additional acceleration when the gas temperature falls below the condensation temperature.
Publisher: Elsevier BV
Date: 09-2018
DOI: 10.1016/J.NUTRES.2018.05.005
Abstract: Food cravings are common in type 2 diabetes (T2D). Higher-protein diets are effective in improving satiety but their effect on cravings is unclear. It was hypothesized that a high protein (HP) diet would provide greater reductions in cravings than an isocaloric higher-carbohydrate diet (HC). In a randomized controlled trial, 61 adults (54% males) with T2D (means ± SD: BMI 34.3 ± 5.1 kg/m
Publisher: Oxford University Press (OUP)
Date: 19-09-2016
Publisher: Springer International Publishing
Date: 2014
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-05-2006
Abstract: We report an extremely rapid mechanism for magnetic field lification during the merger of a binary neutron star system. This has implications for the production of the short class of gamma-ray bursts, which recent observations suggest may originate in such mergers. In detailed magnetohydrodynamic simulations of the merger process, the fields are lified by Kelvin-Helmholtz instabilities beyond magnetar field strength and may therefore represent the strongest magnetic fields in the universe. The lification occurs in the shear layer that forms between the neutron stars and on a time scale of only 1 millisecond, that is, long before the remnant can collapse into a black hole.
Publisher: Oxford University Press (OUP)
Date: 14-03-2023
Abstract: We present the re-detection of a compact source in the face-on protoplanetary disc surrounding HD 169142, using VLT/SPHERE data in YJH bands. The source is found at a separation of 0${_{.}^{\\prime\\prime}}$319 (∼37 au) from the star. Three lines of evidence argue in favour of the signal tracing a protoplanet: (i) it is found in the annular gap separating the two bright rings of the disc, as predicted by theory (ii) it is moving at the expected Keplerian velocity for an object at ∼37 au in the 2015, 2017, and 2019 data sets and (iii) we also detect a spiral-shaped signal whose morphology is consistent with the expected outer spiral wake triggered by a planet in the gap, based on dedicated hydrodynamical simulations of the system. The YJH colours we extracted for the object are consistent with tracing scattered starlight, suggesting that the protoplanet is enshrouded in a significant amount of dust, as expected for a circumplanetary disc or envelope surrounding a gap-clearing Jovian-mass protoplanet.
Publisher: Oxford University Press (OUP)
Date: 11-11-2011
Publisher: Oxford University Press (OUP)
Date: 27-11-2021
Abstract: We examine whether stellar flyby simulations can initiate FU Orionis outbursts using 3D hydrodynamics simulations coupled to live Monte Carlo radiative transfer. We find that a flyby where the secondary penetrates the circumprimary disc triggers a 1–2 yr rise in the mass accretion rate to 10−4 M⊙ yr−1 that remains high (≳10−5 M⊙ yr−1) for more than a hundred years, similar to the outburst observed in FU Ori. Importantly, we find that the less massive star becomes the dominant accretor, as observed.
Publisher: Springer Science and Business Media LLC
Date: 23-08-2018
DOI: 10.1007/S40279-018-0969-2
Abstract: Intensified training is important for inducing adaptations to improve athletic performance, but detrimental performance effects can occur if prescribed inappropriately. Monitoring biomarker responses to training may inform changes in training load to optimize performance. This systematic review and meta-analysis aimed to identify biomarkers associated with altered exercise performance following intensified training. Embase, MEDLINE, CINAHL, Scopus and SPORTDiscus were searched up until September 2017. Included articles were peer reviewed and reported on biomarkers collected at rest in well-trained male athletes before and after periods of intensified training. The full text of 161 articles was reviewed, with 59 included (708 participants) and 42 (550 participants) meta-analysed. In total, 118 biomarkers were evaluated, with most being cellular communication and immunity markers (n = 54). Studies most frequently measured cortisol (n = 34), creatine kinase (n = 25) and testosterone (n = 20). Many studies reported decreased immune cell counts following intensified training, irrespective of performance. Moreover, reduced performance was associated with a decrease in neutrophils (d = - 0.57 95% confidence interval (CI) - 1.07 to - 0.07) and glutamine (d = - 0.37 95% CI - 0.43 to - 0.31) and an increase in urea concentration (d = 0.80 95% CI 0.30 to 1.30). In contrast, increased performance was associated with an increased testosterone:cortisol ratio (d = 0.89 95% CI 0.54 to 1.24). All remaining biomarkers showed no consistent patterns of change with performance. Many biomarkers were altered with intensified training but not in a manner related to changes in exercise performance. Neutrophils, glutamine, urea and the testosterone:cortisol ratio exhibited some evidence of directional changes that corresponded with performance changes therefore indicating potential to track performance. Additional investigations of the potential for these markers to track altered performance are warranted.
Publisher: Oxford University Press (OUP)
Date: 27-04-2021
Abstract: A new technique to detect protoplanets is by observing the kinematics of the surrounding gas. Gravitational perturbations from a planet produce peculiar ‘kinks’ in channel maps of different gas species. In this paper, we show that such kinks can be reproduced using semi-analytic models for the velocity perturbation induced by a planet. In doing so we (i) confirm that the observed kinks are consistent with the planet-induced wake (ii) show how to quantify the planet mass from the kink litude in particular, we show that the kink litude scales with the square root of the planet mass for channels far from the planet velocity, steepening to linear as the channels approach the planet and (iii) show how to extend the theory to include the effect of d ing, which may be needed in order to have localized kinks.
Publisher: Oxford University Press (OUP)
Date: 19-04-2021
Abstract: We present ALMA observations of the 12CO, 13CO, C18O J = 2-1 transitions and the 1.3 mm continuum emission for the circumbinary disc around HD 142527, at an angular resolution of ≈ 0${_{.}^{\\prime\\prime}}$3. We observe multiple spiral structures in intensity, velocity, and velocity dispersion for the 12CO and 13CO gas tracers. A newly detected 12CO spiral originates from the dust horseshoe, and is rotating at super-Keplerian velocity or vertically ascending, whilst the interspiral gas is rotating at sub-Keplerian velocities. This new spiral possibly connects to a previously identified spiral, thus spanning & °. A spatial offset of 30 au is observed between the 12CO and 13CO spirals, to which we hypothesize that the gas layers are propagating at different speeds (surfing) due to a non-zero vertical temperature gradient. Leveraging the varying optical depths between the CO isotopologues, we reconstruct temperature and column density maps of the outer disc. Gas surface density peaks at r ≈ 180 au, coincident with the peak of continuum emission. Here, the dust grains have a Stokes number of ≈ 1, confirming radial and azimuthal trapping in the horseshoe. We measure a cavity radius at half-maximum surface density of ≈ 100 au, and a cavity eccentricity between 0.3 and 0.45.
Publisher: Oxford University Press (OUP)
Date: 17-08-2021
Abstract: Planet–disc interactions build up local pressure maxima that may halt the radial drift of protoplanetary dust, and pile it up in rings and crescents. ALMA observations of the HD 135344B disc revealed two rings in the thermal continuum stemming from ∼mm-sized dust. At higher frequencies the inner ring is brighter relative to the outer ring, which is also shaped as a crescent rather than a full ring. In near-IR scattered light images, the disc is modulated by a two-armed grand-design spiral originating inside the ALMA inner ring. Such structures may be induced by a massive companion evacuating the central cavity, and by a giant planet in the gap separating both rings, that channels the accretion of small dust and gas through its filamentary wakes while stopping the larger dust from crossing the gap. Here we present ALMA observations in the J = (2 − 1) CO isotopologue lines and in the adjacent continuum, with up to 12 km baselines. Angular resolutions of ∼0${_{.}^{\\prime\\prime}}$03 reveal the tentative detection of a filament connecting both rings, and which coincides with a local discontinuity in the pitch angle of the IR spiral, proposed previously as the location of the protoplanet driving this spiral. Line diagnostics suggests that turbulence, or superposed velocity components, is particularly strong in the spirals. The 12CO(2-1) 3D rotation curve points at stellocentric accretion at radii within the inner dust ring, with a radial velocity of up to ${\\sim}5{{\\ \\rm per\\ cent}}\\pm 0.5{{\\ \\rm per\\ cent}}$ Keplerian, which corresponds to an excessively large accretion rate of ${\\sim}2\\times 10^{-6}\\, M_\\odot \\,$yr−1 if all of the CO layer follows the 12CO(2-1) kinematics. This suggests that only the surface layers of the disc are undergoing accretion, and that the line broadening is due to superposed laminar flows.
Publisher: Oxford University Press (OUP)
Date: 07-11-2013
Publisher: Oxford University Press (OUP)
Date: 03-2016
Publisher: Oxford University Press (OUP)
Date: 04-2021
Abstract: Misalignments within protoplanetary discs are now commonly observed, and features such as shadows in scattered light images indicate departure from a co-planar geometry. VLT/SPHERE (Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch) observations of the disc around HD 143006 show a large-scale asymmetry and two narrow dark lanes that are indicative of shadowing. ALMA (Atacama Large Millimeter/submillimeter Array) observations also reveal the presence of rings and gaps in the disc, along with a bright arc at large radii. We present new hydrodynamic simulations of HD 143006, and show that a configuration with both a strongly inclined binary and an outer planetary companion is the most plausible to explain the observed morphological features. We compute synthetic observations from our simulations, and successfully reproduce both the narrow shadows and the brightness asymmetry seen in infrared scattered light. Additionally, we reproduce the large dust observed in the mm continuum, due to a 10 Jupiter-mass planet detected in the CO kinematics. Our simulations also show the formation of a circumplanetary disc, which is misaligned with respect to the outer disc. The narrow shadows cast by the inner disc and the planet-induced ‘kink’ in the disc kinematics are both expected to move on a time-scale of ∼5–10 yr, presenting a potentially observable test of our model. If confirmed, HD 143006 would be the first known ex le of a circumbinary planet on a strongly misaligned orbit.
Publisher: EDP Sciences
Date: 10-2009
Publisher: Oxford University Press (OUP)
Date: 25-08-2015
Publisher: Oxford University Press (OUP)
Date: 22-06-2023
Abstract: We present five morphological and kinematic criteria to aid in asserting the binary nature of a protoplanetary disc, based on 3D hydrodynamical simulations of circumbinary discs post-processed with Monte Carlo radiative transfer. We find that circumbinary discs may be identified by (i) a central cavity, (ii) spiral arms both in and outside of their central cavities, (iii) non-localized perturbations in their iso-velocity curves, (iv) asymmetry between the lines of maximum speed of the blueshifted and redshifted wings, and (v) asymmetry between the area of the blueshifted and redshifted wings. We provide quantitative metrics for the last two criteria that can be used, in conjunction with the morphological criteria, to signal whether a protoplanetary disc is likely to be a circumbinary disc.
Publisher: Oxford University Press (OUP)
Date: 25-09-2020
Abstract: We study the mutual evolution of the orbital properties of high-mass ratio, circular, co-planar binaries and their surrounding discs, using 3D Smoothed Particle Hydrodynamics simulations. We investigate the evolution of binary and disc eccentricity, cavity structure, and the formation of orbiting azimuthal overdense features in the disc. Even with circular initial conditions, all discs with mass ratios q & 0.05 develop eccentricity. We find that disc eccentricity grows abruptly after a relatively long time-scale (∼400–700 binary orbits), and is associated with a very small increase in the binary eccentricity. When disc eccentricity grows, the cavity semimajor axis reaches values $a_{\\rm cav}\\approx 3.5\\, a_{\\rm bin}$. We also find that the disc eccentricity correlates linearly with the cavity size. Viscosity and orbit crossing appear to be responsible for halting the disc eccentricity growth – eccentricity at the cavity edge in the range ecav ∼ 0.05–0.35. Our analysis shows that the current theoretical framework cannot fully explain the origin of these evolutionary features when the binary is almost circular (ebin ≲ 0.01) we speculate about alternative explanations. As previously observed, we find that the disc develops an azimuthal overdense feature in Keplerian motion at the edge of the cavity. A low-contrast overdensity still co-moves with the flow after 2000 binary orbits such an overdensity can in principle cause significant dust trapping, with important consequences for protoplanetary disc observations.
Publisher: Oxford University Press (OUP)
Date: 09-08-2019
Abstract: We present results from the first radiation non-ideal magnetohydrodynamics (MHD) simulations of low-mass star cluster formation that resolve the fragmentation process down to the opacity limit. We model 50 M⊙ turbulent clouds initially threaded by a uniform magnetic field with strengths of 3, 5 10, and 20 times the critical mass-to-magnetic flux ratio, and at each strength, we model both an ideal and non-ideal (including Ohmic resistivity, ambipolar diffusion, and the Hall effect) MHD cloud. Turbulence and magnetic fields shape the large-scale structure of the cloud, and similar structures form regardless of whether ideal or non-ideal MHD is employed. At high densities (106 ≲ nH ≲ 1011 cm−3), all models have a similar magnetic field strength versus density relation, suggesting that the field strength in dense cores is independent of the large-scale environment. Albeit with limited statistics, we find no evidence for the dependence of the initial mass function on the initial magnetic field strength, however, the star formation rate decreases for models with increasing initial field strengths the exception is the strongest field case where collapse occurs primarily along field lines. Protostellar discs with radii ≳ 20 au form in all models, suggesting that disc formation is dependent on the gas turbulence rather than on magnetic field strength. We find no evidence for the magnetic braking catastrophe, and find that magnetic fields do not hinder the formation of protostellar discs.
Publisher: Oxford University Press (OUP)
Date: 04-2008
Publisher: Cambridge University Press (CUP)
Date: 2016
DOI: 10.1017/PASA.2016.45
Abstract: The Protoplanetary Discussions conference—held in Edinburgh, UK, from 2016 March 7th–11th—included several open sessions led by participants. This paper reports on the discussions collectively concerned with the multi-physics modelling of protoplanetary discs, including the self-consistent calculation of gas and dust dynamics, radiative transfer, and chemistry. After a short introduction to each of these disciplines in isolation, we identify a series of burning questions and grand challenges associated with their continuing development and integration. We then discuss potential pathways towards solving these challenges, grouped by strategical, technical, and collaborative developments. This paper is not intended to be a review, but rather to motivate and direct future research and collaboration across typically distinct fields based on community-driven input , to encourage further progress in our understanding of circumstellar and protoplanetary discs.
Publisher: Oxford University Press (OUP)
Date: 28-03-2012
Publisher: Oxford University Press (OUP)
Date: 17-01-2019
DOI: 10.1093/MNRAS/STZ111
Publisher: Oxford University Press (OUP)
Date: 14-11-2016
Publisher: Elsevier BV
Date: 10-2016
Publisher: Oxford University Press (OUP)
Date: 21-01-2010
Publisher: Oxford University Press (OUP)
Date: 09-2022
Abstract: At least one in five of all planetary nebulae are the product of a common envelope (CE) interaction, where the companion in-spirals into the envelope of an asymptotic giant branch (AGB) star ejecting the nebula and leaving behind a compact binary. In this work we carry out 3D smoothed particle hydrodynamics simulations of the CE interaction between a 1.7 M⊙ AGB star and a 0.6 M⊙ companion. We model the AGB structure using a 1D stellar model taken at the seventh thermal pulse. The interaction takes place when the giant is on the expanding phase of the seventh thermal pulse and has a radius of 250 R⊙. The post-CE orbital separations varies between 20 and 31 R⊙, with the inclusion of recombination energy resulting in wider separations. Based on the observed short in-spiral time-scales, we suggest that thermal pulses can trigger CEs, extending the ability of AGB stars to capture companions into CEs, that would lead to the prediction of a larger population of post-AGB, post-CE binaries. Simulations that include a tabulated equation of state unbind a great deal more gas, likely unbinding the entire envelope on short time-scales. The shape of the CE after the in-spiral is more spherical for AGB than red giant branch stars, and even more so if recombination energy is included. We expect that the planetary nebula formed from this CE will have different features compared to those formed from red giant branch stars.
Publisher: AIP
Date: 2010
DOI: 10.1063/1.3460126
Publisher: Springer Science and Business Media LLC
Date: 07-02-2019
Publisher: Oxford University Press (OUP)
Date: 03-2010
Publisher: Oxford University Press (OUP)
Date: 27-05-2015
DOI: 10.1093/MNRAS/STV957
Publisher: Oxford University Press (OUP)
Date: 03-2003
Publisher: Oxford University Press (OUP)
Date: 20-12-2011
Publisher: Oxford University Press (OUP)
Date: 30-03-2012
Publisher: Oxford University Press (OUP)
Date: 20-12-2018
Publisher: American Astronomical Society
Date: 26-08-2014
Publisher: Cambridge University Press (CUP)
Date: 05-2013
DOI: 10.1017/S1743921313006431
Abstract: We present the current standing of an investigation into the structure of the Milky Way. We use smoothed particle hydrodynamics (SPH) to simulate the ISM gas in the Milky Way under the effect of a number of different gravitational potentials representing the spiral arms and nuclear bars, both fixed and time-dependent. The gas is subject to ISM cooling and chemistry, enabling us to track the CO and HI density. We use a 3D grid-based radiative transfer code to simulate the emission from the SPH output, allowing for the construction of synthetic longitude-velocity maps as viewed from the Earth. By comparing these maps with the observed emission in CO and HI from the Milky Way ([Dame et al . 2001, Kalberla et al . 2005]), we can infer the arm/bar geometry that provides a best fit to our Galaxy. By doing so we aim to answer key questions concerning the morphology of the Milky Way such as the number of the spiral arms, the pattern speeds of the bar(s) and arms, the pitch angle of the arms and shape of the bar(s).
Publisher: Oxford University Press (OUP)
Date: 10-11-2018
Publisher: Elsevier BV
Date: 11-2015
DOI: 10.1016/J.CCT.2015.11.001
Abstract: Hypocaloric low-fat diets, high in protein with moderate carbohydrate (HP) can enhance weight loss, improve glycaemic control and improve cardiometabolic health risk factors in type 2 diabetes mellitus (T2DM). However, it is unclear whether the metabolic benefits observed during weight loss are sustained during energy-balance and weight maintenance. Furthermore, there is a lack of evidence regarding the effect of HP diets on food cravings, cognitive function and psychological wellbeing in T2DM, despite carbohydrate food cravings, cognitive impairment and depression being associated with hyperglycaemia. Overweight/obese adults with T2DM were randomised to consume either a HP diet (n=32, ~32% protein, 33% carbohydrate, 30% fat) or a higher-carbohydrate diet (HC, n=29, ~22% protein, 51% carbohydrate, 22% fat) for 24 weeks with 30 min of moderate intensity exercise five days/week for the study duration. There were 2 phases: a 12 week weight loss phase followed by a 12 week weight maintenance phase. Primary outcome was glycaemic control (glycosylated haemoglobin HbA1c). Secondary outcomes were cardiometabolic risk factors (body composition, fasting blood pressure, blood lipids, glucose, insulin and C-reactive protein), food cravings, cognitive function (memory psychomotor and executive function and psychological well-being. Outcomes were measured at baseline and the end of each 12-week intervention phase. Data will be analysed as intention-to-treat using linear mixed effects models. This study will examine the effects of two dietary interventions on health outcomes in T2DM during weight loss and notably following weight maintenance where there is a paucity of evidence.
Publisher: Oxford University Press (OUP)
Date: 04-09-2018
Publisher: Cambridge University Press (CUP)
Date: 05-2010
DOI: 10.1017/S1743921311000330
Abstract: Firstly, we give a historical overview of attempts to incorporate magnetic fields into the Smoothed Particle Hydrodynamics method by solving the equations of Magnetohydrodynamics (MHD), leading an honest assessment of the current state-of-the-art in terms of the limitations to performing realistic calculations of the star formation process. Secondly, we discuss the results of a recent comparison we have performed on simulations of driven, supersonic turbulence with SPH and Eulerian techniques. Finally we present some new results on the relationship between the density variance and the Mach number in supersonic turbulent flows, finding σ 2 ln ρ = ln(1 + b 2 2 with b = 0.33 up to Mach 20, consistent with other numerical results at lower Mach number (Lemaster & Stone 2008) but inconsistent with observational constraints on σ ρ and in Taurus and IC5146.
Publisher: EDP Sciences
Date: 2015
DOI: 10.1051/EAS/1571038
Publisher: Oxford University Press (OUP)
Date: 26-09-2020
Abstract: The protoplanetary disc HD 100453 exhibits a curious combination of spirals, shadows, and a relative misalignment between the observed outer disc and inferred inner disc. This disc is accompanied by a secondary star on a bound orbit exterior to the disc. Recent observations have suggested there may be an additional low-mass companion residing within the disc inner cavity. In our companion paper, the orbit of the secondary was shown to be misaligned by 61° to the plane of the outer disc. Here, we investigate the properties of the inner companion and the origin of the misalignment between the inner and outer discs. Using numerical simulations and synthetic observations, we show that the disc structure and kinematics are consistent with a ≲ 5 MJ planet located at 15 − 20 au. We find that the disc evolution over ∼50 binary orbits (∼105 yr) is governed by differential precession and to a lesser extent, the Kozai–Lidov effect. In our proposed model, the misalignment observed between the outer and inner disc arises naturally as a result of the misaligned outer companion driving the outer disc to precess more rapidly than the inner disc.
Publisher: Oxford University Press (OUP)
Date: 28-09-2016
Publisher: American Astronomical Society
Date: 04-2022
Abstract: We map the planetary wake associated with the embedded protoplanet creating the CO kink in the disk of HD 163296. We show that the wake can be traced by a series of correlated perturbations in the peak velocity map. The sign change of the perturbations across the disk’s major axis confirms that the wake induces predominantly radial motion, as predicted by models of planet–disk interaction. These results provide the first direct confirmation of planet wakes generated by Lindblad resonances. Mapping the wake provides a constraint on the disk aspect ratio, which is required to measure the mass of the planet.
Publisher: Oxford University Press (OUP)
Date: 16-04-2010
Publisher: American Astronomical Society
Date: 10-02-2020
Publisher: American Astronomical Society
Date: 14-02-2022
Publisher: Elsevier BV
Date: 08-2012
Publisher: Oxford University Press (OUP)
Date: 08-05-2019
Publisher: Oxford University Press (OUP)
Date: 18-01-2022
Abstract: Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1 M⊙ rotating, magnetized molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between 105 and 3 × 107 particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1 kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long time-scales given that the diffusion time-scale for the magnetic field exceeds the age of the Universe.
Publisher: Oxford University Press (OUP)
Date: 07-12-2018
Publisher: American Astronomical Society
Date: 26-08-2022
Abstract: Companions at subarcsecond separation from young stars are difficult to image. However, their presence can be inferred from the perturbations they create in the dust and gas of protoplanetary disks. Here we present a new interpretation of SPHERE polarized observations that reveal the previously detected inner spiral in the disk of HD 100546. The spiral coincides with a newly detected 12 CO inner spiral and the previously reported CO emission Doppler flip, which has been interpreted as the signature of an embedded protoplanet. Comparisons with hydrodynamical models indicate that this Doppler flip is instead the kinematic counterpart of the spiral, which is likely generated by an inner companion inside the disk cavity.
Publisher: Springer Science and Business Media LLC
Date: 12-08-2019
Publisher: Oxford University Press (OUP)
Date: 13-02-2018
DOI: 10.1093/MNRAS/STY367
Publisher: Oxford University Press (OUP)
Date: 16-03-2018
DOI: 10.1093/MNRAS/STY642
Publisher: American Astronomical Society
Date: 28-07-2023
Abstract: We use numerical simulations of circumplanetary disks to determine the boundary between disks that are radially truncated by the tidal potential and those where gas escapes the Hill sphere. We consider a model problem, in which a coplanar circumplanetary disk is resupplied with gas at an injection radius smaller than the Hill radius. We evolve the disk using the Phantom smoothed particle hydrodynamics code until a steady state is reached. We find that the most significant dependence of the truncation boundary is on the disk aspect ratio H / R . Circumplanetary disks are efficiently truncated for H / R ≲ 0.2. For H / R ≃ 0.3, up to about half of the injected mass, depending on the injection radius, flows outward through the decretion disk and escapes. As expected from analytic arguments, the conditions ( H / R and Shakura–Sunyaev α ) required for tidal truncation are independent of planet mass. A simulation with larger α = 0.1 shows stronger outflow than one with α = 0.01, but the dependence on transport efficiency is less important than variations of H / R . Our results suggest two distinct classes of circumplanetary disks: tidally truncated thin disks with dust-poor outer regions, and thicker actively decreting disks with enhanced dust-to-gas ratios. Applying our results to the PDS 70 c system, we predict a largely truncated circumplanetary disk, but it is possible that enough mass escapes to support an outward flow of dust that could explain the observed disk size.
Publisher: Oxford University Press (OUP)
Date: 10-12-2020
Abstract: We present 1.3 mm continuum ALMA long-baseline observations at 3–5 au resolution of 10 of the brightest discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project. We identify a total of 26 narrow rings and gaps distributed in 8 sources and 3 discs with small dust cavities (r & au). We find that two discs around embedded protostars lack the clear gaps and rings that are ubiquitous in more evolved sources with Class II SEDs. Our s le includes five objects with previously known large dust cavities (r & au). We find that the 1.3 mm radial profiles of these objects are in good agreement with those produced by numerical simulations of dust evolution and planet–disc interactions, which predict the accumulation of mm-sized grains at the edges of planet-induced cavities. Our long-baseline observations resulted in the largest s le of discs observed at ∼3–5 au resolution in any given star-forming region (15 objects when combined with Ophiuchus objects in the DSHARP Large Program) and allow for a demographic study of the brightest $\\sim\\! 5{{\\ \\rm per\\ cent}}$ of the discs in Ophiuchus (i.e. the most likely formation sites of giant planets in the cloud). We use this unique s le to propose an evolutionary sequence and discuss a scenario in which the substructures observed in massive protoplanetary discs are mainly the result of planet formation and dust evolution. If this scenario is correct, the detailed study of disc substructures might provide a window to investigate a population of planets that remains mostly undetectable by other techniques.
Publisher: Oxford University Press (OUP)
Date: 14-06-2017
Publisher: Oxford University Press (OUP)
Date: 16-05-2020
Abstract: We present a fix to the overd ing problem found by Laibe & Price when simulating strongly coupled dust–gas mixtures using two different sets of particles using smoothed particle hydrodynamics. Our solution is to compute the drag at the barycentre between gas and dust particle pairs when computing the drag force by reconstructing the velocity field, similar to the procedure in Godunov-type solvers. This fixes the overd ing problem at negligible computational cost, but with additional memory required to store velocity derivatives. We employ slope limiters to avoid spurious oscillations at shocks, finding the van Leer Monotonized Central limiter most effective.
Publisher: Oxford University Press (OUP)
Date: 20-07-2010
Publisher: Oxford University Press (OUP)
Date: 11-10-2013
Publisher: Springer Berlin Heidelberg
Date: 2008
Publisher: Oxford University Press (OUP)
Date: 23-04-2012
Publisher: Oxford University Press (OUP)
Date: 17-06-2013
DOI: 10.1093/MNRAS/STT877
Publisher: American Astronomical Society
Date: 04-09-2019
Publisher: Oxford University Press (OUP)
Date: 21-12-2011
Publisher: American Astronomical Society
Date: 03-06-2019
Publisher: Oxford University Press (OUP)
Date: 30-07-2013
Publisher: Oxford University Press (OUP)
Date: 15-03-2018
DOI: 10.1093/MNRAS/STY647
Publisher: Oxford University Press (OUP)
Date: 13-02-2015
DOI: 10.1093/MNRAS/STV014
Publisher: Oxford University Press (OUP)
Date: 09-12-2016
Publisher: American Physical Society (APS)
Date: 20-03-2019
Publisher: American Astronomical Society
Date: 10-02-2020
Publisher: Oxford University Press (OUP)
Date: 27-08-2012
Publisher: Oxford University Press (OUP)
Date: 14-06-2016
Publisher: Oxford University Press (OUP)
Date: 06-2004
Publisher: Zenodo
Date: 2017
Publisher: Oxford University Press (OUP)
Date: 11-04-2010
Publisher: Oxford University Press (OUP)
Date: 12-06-2020
Abstract: In this work we demonstrate that the inner spiral structure observed in AB Aurigae can be created by a binary star orbiting inside the dust cavity. We find that a companion with a mass-ratio of 0.25, semimajor axis of 40 au, eccentricity of 0.5, and inclination of 90° produces gaseous spirals closely matching the ones observed in 12CO (2-1) line emission. Based on dust dynamics in circumbinary discs (Poblete, Cuello & Cuadra 2019), we constrain the inclination of the binary with respect to the circumbinary disc to range between 60° and 90°. We predict that the stellar companion is located roughly 0.18 arcsec from the central star towards the east-southeast, above the plane of the disc. Should this companion be detected in the near future, our model indicates that it should be moving away from the primary star at a rate of 6 mas yr−1 on the plane of the sky. Since our companion is inclined, we also predict that the spiral structure will appear to change with time, and not simply corotate with the companion.
Publisher: Oxford University Press (OUP)
Date: 05-05-2021
Abstract: Of the 21 known gaseous debris discs around white dwarfs, a large fraction of them display observational features that are well described by an eccentric distribution of gas. In the absence of embedded objects or additional forces, these discs should not remain eccentric for long time-scales, and should instead circularize due to viscous spreading. The metal pollution and infrared excess we observe from these stars is consistent with the presence of tidally disrupted sub-stellar bodies. We demonstrate, using smoothed particle hydrodynamics, that a sublimating or partially disrupting planet on an eccentric orbit around a white dwarf will form and maintain a gas disc with an eccentricity within 0.1 of, and lower than, that of the orbiting body. We also demonstrate that the eccentric gas disc observed around the white dwarf SDSS J1228 + 1040 can be explained by the same hypothesis.
Publisher: Oxford University Press (OUP)
Date: 07-10-2022
Abstract: We perform 3D hydrodynamic simulations of disc–disc stellar flybys with on-the-fly Monte Carlo radiative transfer. We show that pre-existing circumstellar discs around both stars result in fast rising (∼years) outbursts lasting two to five times longer than for a star–disc flyby. The perturber always goes into outburst ($\\dot{M}\\gt 10^{-5}~{\\rm M_{\\odot }~ yr^{-1}}$). Whereas we find that the primary goes into a decades long outburst only when the flyby is retrograde to the circumprimary disc rotation. High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter. A large fraction of accreted material is alien.
Publisher: Oxford University Press (OUP)
Date: 27-01-2016
DOI: 10.1093/MNRAS/STW034
Publisher: Oxford University Press (OUP)
Date: 18-08-2020
Abstract: Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an ≈10MJup companion on an eccentric orbit internal to the spiral arms. Previous studies on MWC 758 have assumed an external companion. We compare simulated observations from three-dimensional hydrodynamics simulations of disc–companion interaction to scattered light, infrared and CO molecular line observations, taking into account observational biases. The inner companion hypothesis is found to explain the double spiral arms, as well as several additional features seen in MWC 758 – the arc in the north-west, substructures inside the spiral arms, the cavity in CO isotopologues, and the twist in the kinematics. Testable predictions include detection of fainter spiral structure, detection of a point source south-southeast of the primary, and proper motion of the spiral arms.
Publisher: Oxford University Press (OUP)
Date: 27-09-2016
Publisher: Oxford University Press (OUP)
Date: 05-2007
Publisher: Oxford University Press (OUP)
Date: 12-05-2016
Publisher: Oxford University Press (OUP)
Date: 22-06-2010
Publisher: Oxford University Press (OUP)
Date: 05-09-2019
Abstract: Recent observations of protoplanetary discs reveal disc substructures potentially caused by embedded planets. We investigate how the gas surface density in discs changes the observed morphology in scattered light and dust continuum emission. Assuming that disc substructures are due to embedded protoplanets, we combine hydrodynamical modelling with radiative transfer simulations of dusty protoplanetary discs hosting planets. The response of different dust species to the gravitational perturbation induced by a planet depends on the drag stopping time — a function of the generally unknown local gas density. Small dust grains, being stuck to the gas, show spirals. Larger grains decouple, showing progressively more axisymmetric (ring-like) substructure as decoupling increases with grain size or with the inverse of the gas disc mass. We show that simultaneous modelling of scattered light and dust continuum emission is able to constrain the Stokes number, St. Hence, if the dust properties are known, this constrains the local gas surface density, Σgas, at the location of the structure, and hence the total gas mass. In particular, we found that observing ring-like structures in mm-emitting grains requires St ≳ 0.4 and therefore Σgas ≲ 0.4 g/cm2. We apply this idea to observed protoplanetary discs showing substructures both in scattered light and in the dust continuum.
Publisher: Oxford University Press (OUP)
Date: 08-2022
Abstract: We present new high-contrast images in near-infrared wavelengths (λc = 1.04, 1.24, 1.62, 2.18, and 3.78 μm) of the young variable star CQ Tau, aiming to constrain the presence of companions in the protoplanetary disc. We reached a Ks-band contrast of 14 mag with SPHERE/IRDIS at separations greater than 0${_{.}^{\\prime\\prime}}$4 from the star. Our mass sensitivity curve rules out giant planets above 4 MJup immediately outside the spiral arms at ∼60 au and above 2–3 MJup beyond 100 au to 5σ confidence assuming hot-start models. We do, however, detect four spiral arms, a double-arc and evidence for shadows in scattered light cast by a misaligned inner disc. Our observations may be explained by an unseen close-in companion on an inclined and eccentric orbit. Such a hypothesis would also account for the disc CO cavity and disturbed kinematics.
Publisher: Springer Science and Business Media LLC
Date: 15-06-2018
Publisher: Oxford University Press (OUP)
Date: 12-10-2015
Publisher: American Astronomical Society
Date: 11-09-2012
Publisher: Elsevier BV
Date: 12-2008
Publisher: Elsevier BV
Date: 02-2012
Publisher: Oxford University Press (OUP)
Date: 30-10-2015
Publisher: Oxford University Press (OUP)
Date: 17-08-2018
Publisher: Oxford University Press (OUP)
Date: 09-2009
Publisher: Oxford University Press (OUP)
Date: 02-10-2021
Abstract: Gas and dust in inclined orbits around binaries experience precession induced by the binary gravitational torque. The difference in precession between gas and dust alters the radial drift of weakly coupled dust and leads to density enhancements where the radial drift is minimized. We explore this phenomenon using 3D hydrodynamical simulations to investigate the prominence of these ‘dust traffic jams’ and the evolution of the resulting dust sub-structures at different disc inclinations and binary eccentricities. We then derive evolution equations for the angular momentum of warped dust discs and implement them in a 1D code and present calculations to further explain these traffic jams. We find that dust traffic jams in inclined circumbinary discs provide significant dust density enhancements that are long lived and can have important consequences for planetesimal formation.
Publisher: Oxford University Press (OUP)
Date: 23-03-2015
DOI: 10.1093/MNRAS/STV347
Publisher: IOP Publishing
Date: 05-2016
Publisher: Cambridge University Press (CUP)
Date: 2018
DOI: 10.1017/PASA.2018.25
Abstract: We present Phantom , a fast, parallel, modular, and low-memory smoothed particle hydrodynamics and magnetohydrodynamics code developed over the last decade for astrophysical applications in three dimensions. The code has been developed with a focus on stellar, galactic, planetary, and high energy astrophysics, and has already been used widely for studies of accretion discs and turbulence, from the birth of planets to how black holes accrete. Here we describe and test the core algorithms as well as modules for magnetohydrodynamics, self-gravity, sink particles, dust–gas mixtures, H 2 chemistry, physical viscosity, external forces including numerous galactic potentials, Lense–Thirring precession, Poynting–Robertson drag, and stochastic turbulent driving. Phantom is hereby made publicly available.
Publisher: Springer Science and Business Media LLC
Date: 27-07-2007
Publisher: Oxford University Press (OUP)
Date: 20-12-2016
Publisher: Oxford University Press (OUP)
Date: 17-05-2017
Publisher: SAGE Publications
Date: 08-08-2017
Abstract: To investigate the reliability of a clinically applicable method of dynamometry to assess and monitor hip abductor muscle strength in older persons. Bilateral isometric hip abductor muscle strength measured with a handheld dynamometer, patients supine with the contralateral hip positioned directly against a wall for stabilization. Reliability determined by comparing intra-assessor and inter-assessor results and comparison to a criterion standard (stabilized dynamometer with patients in the standing position). UniSA Nutritional Physiology Research Centre. Twenty-one patients older than 65 years were recruited from the Royal Adelaide Hospital. Intraclass correlation coefficients (ICCs), bias, and limits of agreement calculated to determine reliability. Intra-assessor and inter-assessor ICCs were high (0.94 and 0.92-0.94, respectively). There was no intra-assessor bias and narrow limits of agreement (±2.4%). There was a small inter-assessor bias but narrow limits of agreement (0.6%-0.9% and ± 2.3%, respectively). There was a wide variation comparing results to the criterion standard (±5.0%-5.2% limits of agreement), highlighting problems attributed to difficulties that the test population had with the standing position used in the criterion standard test. Testing older persons’ hip abductor muscle strength while in the supine position with optimal pelvic stabilization using a handheld dynamometer is highly reliable. While further studies must be done to assess patients with specific pathologies, this test has potential application to monitor and evaluate the effects of surgical interventions and/or rehabilitation protocols for a variety of conditions affecting hip abductor function such as hip fractures and arthritis.
Publisher: Oxford University Press (OUP)
Date: 09-10-2019
Abstract: We test the hypothesis that the disc cavity in the ‘transition disc’ Oph IRS 48 is carved by an unseen binary companion. We use 3D dust–gas smoothed-particle hydrodynamics simulations to demonstrate that marginally coupled dust grains concentrate in the gas overdensity that forms in the cavity around a low binary mass ratio binary. This produces high contrast ratio dust asymmetries at the cavity edge similar to those observed in the disc around IRS 48 and other transition discs. This structure was previously assumed to be a vortex. However, we show that the observed velocity map of IRS 48 displays a peculiar asymmetry that is not predicted by the vortex hypothesis. We show the unusual kinematics are naturally explained by the non-Keplerian flow of gas in an eccentric circumbinary cavity. We further show that perturbations observed in the isovelocity curves of IRS 48 may be explained as the product of the dynamical interaction between the companion and the disc. The presence of an ∼0.4 M⊙ companion at an ∼10 au separation can qualitatively explain these observations. High spatial resolution line and continuum imaging should be able to confirm this hypothesis.
Publisher: Oxford University Press (OUP)
Date: 11-11-2022
Abstract: We present ALMA band 6 images of the 12CO, 13CO, and C18O J = 2-1 line emissions for the circumstellar disc around HD 169142, at ∼8 au spatial resolution. We resolve a central gas-depleted cavity, along with two independent near-symmetric ring-like structures in line emission: a well-defined inner gas ring [∼25 au] and a second relatively fainter and diffuse outer gas ring [∼65 au]. We identify a localized super-Keplerian feature or vertical flow with a magnitude of ∼75 ms−1 in the 12CO map. This feature has the shape of an arc that spans azimuthally across a position angle range of −60° to 45° and radially in between the B1[26au] and B2[59au] dust rings. Through reconstruction of the gas surface density profile, we find that the magnitude of the background perturbations by the pressure support and self-gravity terms are not significant enough to account for the kinematic excess. If of planetary origin, the relative depletion in the gas-density profile would suggest a 1 MJ planet. In contrast, the central cavity displays relatively smooth kinematics, suggesting either a low-mass companion and/or a binary orbit with a minimal vertical velocity component.
Publisher: Oxford University Press (OUP)
Date: 07-12-2007
Publisher: Oxford University Press (OUP)
Date: 21-12-2011
Publisher: Oxford University Press (OUP)
Date: 12-2015
Publisher: Oxford University Press (OUP)
Date: 29-05-2015
DOI: 10.1093/MNRAS/STV996
Publisher: EDP Sciences
Date: 03-2023
DOI: 10.1051/0004-6361/202245141
Abstract: Context. Dust grain dynamics in molecular clouds is regulated by its interplay with supersonic turbulent gas motions. The conditions under which interstellar dust grains decouple from the dynamics of gas in molecular clouds remain poorly constrained. Aims. We first aim to investigate the critical dust grain size for dynamical decoupling, using both analytical predictions and numerical experiments. Second, we aim to set the range of validity of two fundamentally different numerical implementations for the evolution of dust and gas mixtures in turbulent molecular clouds. Methods. We carried out a suite of numerical experiments using two different schemes to integrate the dust grain equation of motion within the same framework. First, we used a monofluid formalism (or often referred to as single fluid) in the terminal velocity approximation. This scheme follows the evolution of the barycentre of mass between the gas and the dust on a Eulerian grid. Second, we used a two-fluid scheme, in which the dust dynamics is handled with Lagrangian super-particles, and the gas dynamics on a Eulerian grid. Results. The monofluid results are in good agreement with the theoretical critical size for decoupling. We report dust dynamics decoupling for Stokes number St 0.1, that is, dust grains of s 4 μm in size. We find that the terminal velocity approximation is well suited for grain sizes of 10 μm in molecular clouds, in particular in the densest regions. However, the maximum dust enrichment measured in the low-density material - where St 1 - is questionable. In the Lagrangian dust experiments, we show that the results are affected by the numerics for all dust grain sizes. At St ≪ 1, the dust dynamics is largely affected by artificial trapping in the high-density regions, leading to spurious variations of the dust concentration. At St 1 , the maximum dust enrichment is regulated by the grid resolution used for the gas dynamics. Conclusions. Dust enrichment of submicron dust grains is unlikely to occur in the densest parts of molecular clouds. Two fluid implementations using a mixture of Eulerian and Lagrangian descriptions for the dust and gas mixture dynamics lead to spurious dust concentration variations in the strongly and weakly coupled regimes. Conversely, the monofluid implementation using the terminalvelocity approximation does not accurately capture dust dynamics in the low-density regions, that is, where St 1 . The results of previous similar numerical work should therefore be revisited with respect to the limitations we highlight in this study.
Publisher: Oxford University Press (OUP)
Date: 21-10-2019
Abstract: Tidal encounters in star clusters perturb discs around young protostars. In Cuello et al., we detailed the dynamical signatures of a stellar flyby in both gas and dust. Flybys produce warped discs, spirals with evolving pitch angles, increasing accretion rates, and disc truncation. Here, we present the corresponding observational signatures of these features in optical/near-infrared scattered light and (sub) millimetre continuum and CO line emission. Using representative prograde and retrograde encounters for direct comparison, we post-process hydrodynamical simulations with radiative transfer methods to generate a catalogue of multiwavelength observations. This provides a reference to identify flybys in recent near-infrared and submillimetre observations (e.g. RW Aur, AS 205, HV Tau and DO Tau, FU Ori, V2775 Ori, and Z CMa).
Publisher: Oxford University Press (OUP)
Date: 02-2004
Publisher: Oxford University Press (OUP)
Date: 11-05-2023
Abstract: Young protostellar discs are likely to be both self-gravitating, and to support grain growth to sizes where the particles decoupled from the gas. This combination could lead to short-wavelength fragmentation of the solid component in otherwise non-fragmenting gas discs, forming Earth-mass solid cores during the Class 0/I stages of young stellar object evolution. We use three-dimensional smoothed particle hydrodynamics simulations of two-fluid discs, in the regime where the Stokes number of the particles St & 1, to study how the formation of solid clumps depends on the disc-to-star mass ratio, the strength of gravitational instability, and the Stokes number. Gravitational instability of the simulated discs is sustained by local cooling. We find that the ability of the spiral structures to concentrate solids increases with the cooling time and decreases with the Stokes number, while the relative dynamical temperature between gas and dust of the particles decreases with the cooling time and the disc-to-star mass ratio and increases with the Stokes number. Dust collapse occurs in a subset of high disc mass simulations, yielding clumps whose mass is close to linear theory estimates, namely 1–10 M⊕. Our results suggest that if planet formation occurs via this mechanism, the best conditions correspond to near the end of the self-gravitating phase, when the cooling time is long and the Stokes number close to unity.
Publisher: Oxford University Press (OUP)
Date: 11-08-2021
Abstract: We present the implementation of a dust growth and fragmentation module in the public smoothed particle hydrodynamics (SPH) code phantom. This module is made available for public use with this paper. The coagulation model considers locally monodisperse dust size distributions around single values that are carried by the SPH particles. Along with the presentation of the model, implementation, and tests, we showcase growth and fragmentation in a few typical circumstellar disc simulations and revisit previous results. The module is also interfaced with the radiative transfer code mcfost, which facilitates the comparison between simulations and ALMA observations by generating synthetic maps. Circumstellar disc simulations with growth and fragmentation reproduce the ‘self-induced dust trap’ mechanism first proposed in 2017, which supports its existence. Synthetic images of discs featuring this mechanism suggest it would be detectable by ALMA as a bright axisymmetric ring at several tens of au from the star. With this paper, our aim is to provide a public tool to be able to study and explore dust growth in a variety of applications related to planet formation.
Publisher: Oxford University Press (OUP)
Date: 12-2021
Abstract: Stellar binaries represent a substantial fraction of stellar systems, especially among young stellar objects. Accordingly, binaries play an important role in setting the architecture of a large number of protoplanetary discs. Binaries in coplanar and polar orientations with respect to the circumbinary disc are stable configurations and could induce non-axisymmetric structures in the dust and gas distributions. In this work, we suggest that the structures shown in the central region of the protoplanetary disc HD 169142 are produced by the presence of an inner stellar binary and a circumbinary (P-type) planet. We find that a companion with a mass ratio of 0.1, semimajor axis of 9.9 au, eccentricity of 0.2, and inclination of 90°, together with a 2 MJ coplanar planet on a circular orbit at 45 au reproduce the structures at the innermost ring observed at 1.3 mm and the shape of spiral features in scattered light observations. The model predicts changes in the disc’s dust structure, and star’s astrometric parameters, which would allow testing its veracity by monitoring this system over the next 20 yr.
Publisher: American Astronomical Society
Date: 14-06-2018
Publisher: Oxford University Press (OUP)
Date: 26-08-2014
Publisher: American Astronomical Society
Date: 18-09-2018
Publisher: Cambridge University Press (CUP)
Date: 2007
DOI: 10.1071/AS07022
Abstract: This paper presents SPLASH , a publicly available interactive visualisation tool for Smoothed Particle Hydrodynamics (SPH) simulations. Visualisation of SPH data is more complicated than for grid-based codes because the data are defined on a set of irregular points and therefore requires a mapping procedure to a two dimensional pixel array. This means that, in practise, many authors simply produce particle plots which offer a rather crude representation of the simulation output. Here we describe the techniques and algorithms which are utilised in SPLASH in order to provide the user with a fast, interactive and meaningful visualisation of one, two and three dimensional SPH results.
Publisher: Springer Science and Business Media LLC
Date: 14-01-2019
Publisher: Oxford University Press (OUP)
Date: 28-01-2016
DOI: 10.1093/MNRAS/STW013
Publisher: MDPI AG
Date: 14-02-2014
DOI: 10.3390/NU6020682
Publisher: Oxford University Press (OUP)
Date: 12-2001
Publisher: Oxford University Press (OUP)
Date: 14-02-2018
DOI: 10.1093/MNRAS/STY392
Publisher: Oxford University Press (OUP)
Date: 07-11-2017
Publisher: Oxford University Press (OUP)
Date: 07-07-2016
Publisher: Oxford University Press (OUP)
Date: 10-01-2022
Abstract: We perform 3D hydrodynamical simulations of a common-envelope event involving a 12$\\, \\rm {M}_{\\odot }$ red supergiant donor. Massive stars are expected to be qualitatively different from low-mass stars as their envelopes have significant support from radiation pressure, which increases both the final separation and amount of mass ejected through the common-envelope interaction. We perform adiabatic simulations that include radiation energy through the equation of state, which results in ejecting 60 per cent more mass (up to two thirds of the total envelope mass becoming unbound, or more) and yield a 10 per cent larger final separation compared to simulations that assume an ideal gas. When also including recombination energy, we find that at least three quarters of the envelope, and possibly the entire envelope, may be unbound. The final separation further increases by almost 20 per cent. The additional amount of ejected material is mainly due to energy injected from helium recombination. Hydrogen recombination plays a comparatively small role, as it mainly occurs in gas that has already become unbound. We conclude that the internal energy of the envelope can be a significant energy source for ejecting the common envelope, but ultimately radiation transport and convection need to be included.
Publisher: Oxford University Press (OUP)
Date: 09-05-2020
Abstract: Recent millimetre-wavelength surveys performed with the Atacama Large Millimeter Array (ALMA) have revealed protoplanetary discs characterized by rings and gaps. A possible explanation for the origin of such rings is the tidal interaction with an unseen planetary companion. The protoplanetary disc around DS Tau shows a wide gap in the ALMA observation at 1.3 mm. We construct a hydrodynamical model for the dust continuum observed by ALMA assuming the observed gap is carved by a planet between one and five Jupiter masses. We fit the shape of the radial intensity profile along the disc major axis varying the planet mass, the dust disc mass, and the evolution time of the system. The best-fitting model is obtained for a planet with $M_{\\rm p}=3.5\\, \\mathrm{ M}_{\\rm Jup}$ and a disc with $M_{\\rm dust}= 9.6\\,\\times \\,10^{-5}\\, \\mathrm{ M}_{\\odot }$. Starting from this result, we also compute the expected signature of the planet in the gas kinematics, as traced by CO emission. We find that such a signature (in the form of a ‘kink’ in the channel maps) could be observed by ALMA with a velocity resolution between $0.2-0.5\\, \\rm {kms}^{-1}$ and a beam size between 30 and 50 mas.
Publisher: Oxford University Press (OUP)
Date: 05-09-2018
Publisher: MDPI AG
Date: 12-05-2016
DOI: 10.3390/NU8050289
Publisher: Oxford University Press (OUP)
Date: 11-08-2007
Publisher: Oxford University Press (OUP)
Date: 15-10-2020
Abstract: We present a method for simulating the dynamics of a mixture of gas and multiple species of large Stokes number dust grains, typical of evolved protoplanetary discs and debris discs. The method improves upon earlier methods, in which only a single grain size could be represented, by capturing the differential backreaction of multiple dust species on the gas. This effect is greater for large dust-to-gas ratios that may be expected in the later stages of the protoplanetary disc life. We benchmark the method against analytic solutions for linear waves, drag, and shocks in dust–gas mixtures, and radial drift in a protoplanetary disc showing that the method is robust and accurate.
Publisher: Oxford University Press (OUP)
Date: 12-2005
Publisher: Oxford University Press (OUP)
Date: 13-04-2020
Abstract: During the common-envelope binary interaction, the expanding layers of the gaseous common envelope recombine and the resulting recombination energy has been suggested as a contributing factor to the ejection of the envelope. In this paper, we perform a comparative study between simulations with and without the inclusion of recombination energy. We use two distinct setups, comprising a 0.88- and 1.8-M⊙ giants, that have been studied before and can serve as benchmarks. In so doing, we conclude that (i) the final orbital separation is not affected by the choice of equation of state (EoS). In other words, simulations that unbind but a small fraction of the envelope result in similar final separations to those that, thanks to recombination energy, unbind a far larger fraction. (ii) The adoption of a tabulated EoS results in a much greater fraction of unbound envelope and we demonstrate the cause of this to be the release of recombination energy. (iii) The fraction of hydrogen recombination energy that is allowed to do work should be about half of that which our adiabatic simulations use. (iv) However, for the heavier star simulation, we conclude that it is helium and not hydrogen recombination energy that unbinds the gas and we determine that all helium recombination energy is thermalized in the envelope and does work. (v) The outer regions of the expanding common envelope are likely to see the formation of dust. This dust would promote additional unbinding and shaping of the ejected envelope into axisymmetric morphologies.
Publisher: American Astronomical Society
Date: 10-2020
Abstract: ISO-Oph 2 is a wide-separation (240 au) binary system where the primary star harbors a massive ( M dust ∼ 40 M ⊕ ) ring-like disk with a dust cavity ∼50 au in radius and the secondary hosts a much lighter ( M dust ∼ 0.8 M ⊕ ) disk. As part of the high-resolution follow-up of the “Ophiuchus Disk Survey Employing ALMA” (ODISEA) project, we present 1.3 mm continuum and 12 CO molecular line observations of the system at 002 (3 au) resolution. We resolve the disk around the primary into two nonaxisymmetric rings and find that the disk around the secondary is only ∼7 au across and also has a dust cavity ( r ∼ 2.2 au). Based on the infrared flux ratio of the system and the M0 spectral type of the primary, we estimate the mass of the companion to be close to the brown-dwarf limit. Hence, we conclude that the ISO-Oph 2 system contains the largest and smallest cavities, the smallest measured disk size, and the resolved cavity around the lowest-mass object ( M ⋆ ∼ 0.08 M ⊙ ) in Ophiuchus. From the 12 CO data, we find a bridge of gas connecting both disks. While the morphology of the rings around the primary might be due to an unseen disturber within the cavity, we speculate that the bridge might indicate an alternative scenario in which the secondary has recently flown by the primary star causing the azimuthal asymmetries in its disk. The ISO-Oph 2 system is therefore a remarkable laboratory to study disk evolution, planet formation, and companion–disk interactions.
Publisher: Oxford University Press (OUP)
Date: 03-09-2022
Abstract: The role of recombination during a common-envelope event has been long debated. Many studies have argued that much of hydrogen recombination energy, which is radiated in relatively cool and optically thin layers, might not thermalize in the envelope. On the other hand, helium recombination contains ≈30 per cent of the total recombination energy, and occurs much deeper in the stellar envelope. We investigate the distinct roles played by hydrogen and helium recombination in a common-envelope interaction experienced by a 12 $\\, \\rm {M}_{\\odot }$ red supergiant donor. We perform adiabatic, 3D hydrodynamical simulations that (i) include hydrogen, helium, and H2 recombination, (ii) include hydrogen and helium recombination, (iii) include only helium recombination, and (iv) do not include recombination energy. By comparing these simulations, we find that the addition of helium recombination energy alone ejects 30 per cent more envelope mass, and leads to a 16 per cent larger post-plunge-in separation. Under the adiabatic assumption, adding hydrogen recombination energy increases the amount of ejected mass by a further 40 per cent, possibly unbinding the entire envelope, but does not affect the post-plunge separation. Most of the ejecta becomes unbound at relatively high (& per cent) degrees of hydrogen ionisation, where the hydrogen recombination energy is likely to expand the envelope instead of being radiated away.
Publisher: Oxford University Press (OUP)
Date: 28-03-2014
DOI: 10.1093/MNRAS/STU355
Publisher: Oxford University Press (OUP)
Date: 02-2007
Publisher: Oxford University Press (OUP)
Date: 03-12-2021
Abstract: We present an online, open, and comprehensive template library of gravitational waveforms produced during the tidal disruptions of stars by massive black holes, spanning a broad space of parameters. We build this library thanks to a new feature that we implement in the general relativistic version of phantom, a smoothed particle hydrodynamics code for three dimensional simulations in general relativity. We first perform a series of numerical tests to show that the gravitational wave (GW) signal obtained is in excellent agreement with the one expected from theory. This benchmark is done for well studied scenarios (such as binary stellar systems). We then apply our code to calculate the GW signals from tidal disruption events, finding that our results are consistent with the theoretical estimates obtained in previous studies for selected parameters. We illustrate interesting results from the catalog, where we stress how the gravitational signal is affected by variations of some parameters (like black hole spin, stellar orbital eccentricity, and inclination). The full catalog is available online. It is intended to be a living catalog.
Publisher: Oxford University Press (OUP)
Date: 21-01-2006
Publisher: Oxford University Press (OUP)
Date: 28-03-2014
DOI: 10.1093/MNRAS/STU359
Publisher: Oxford University Press (OUP)
Date: 30-07-2021
Abstract: IRAS 04158+2805 has long been thought to be a very low mass T-Tauri star (VLMS) surrounded by a nearly edge-on, extremely large disc. Recent observations revealed that this source hosts a binary surrounded by an extended circumbinary disc with a central dust cavity. In this paper, we combine ALMA multiwavelength observations of continuum and 12CO line emission, with H α imaging and Keck astrometric measures of the binary to develop a coherent dynamical model of this system. The system features an azimuthal asymmetry detected at the western edge of the cavity in Band 7 observations and a wiggling outflow. Dust emission in ALMA Band 4 from the proximity of the in idual stars suggests the presence of marginally resolved circumstellar discs. We estimate the binary orbital parameters from the measured arc of the orbit from Keck and ALMA astrometry. We further constrain these estimates using considerations from binary–disc interaction theory. We finally perform three SPH gas+dust simulations based on the theoretical constraints we post-process the hydrodynamic output using radiative transfer Monte Carlo methods and directly compare the models with observations. Our results suggest that a highly eccentric e ∼ 0.5–0.7 equal mass binary, with a semimajor axis of ∼55 au, and small/moderate orbital plane versus circumbinary disc inclination θ ≲ 30° provides a good match with observations. A dust mass of ${\\sim}1.5\\times 10^{-4} \\, {\\rm M_\\odot }$ best reproduces the flux in Band 7 continuum observations. Synthetic CO line emission maps qualitatively capture both the emission from the central region and the non-Keplerian nature of the gas motion in the binary proximity.
Publisher: Oxford University Press (OUP)
Date: 22-12-2019
Publisher: Oxford University Press (OUP)
Date: 26-08-2020
Abstract: How does the cavity size in circumbinary discs depend on disc and binary properties? We investigate by simulating disc cavities carved by binary companions using smoothed particle hydrodynamics. We find that a cavity is quickly opened on the dynamical time, while the cavity size is set on the viscous time. In agreement with previous findings, we find long-term cavity sizes of 2–5 times the binary semimajor axis, increasing with eccentricity and decreasing with disc aspect ratio. When considering binaries inclined with respect to the disc, we find three regimes: (i) discs that evolve towards a coplanar orbit have a large cavity, slightly smaller than that of an initially coplanar disc (ii) discs that evolve towards a polar orbit by breaking have a small cavity, equal in size to that of an initially polar disc and (iii) discs that evolve towards a polar orbit via warping have an intermediate-sized cavity. We find typical gas depletions inside the cavity of ≳2 orders of magnitude in surface density.
Publisher: Oxford University Press (OUP)
Date: 25-09-2020
Abstract: The disc surrounding PDS 70, with two directly imaged embedded giant planets, is an ideal laboratory to study planet–disc interaction. We present 3D smoothed particle hydrodynamics simulations of the system. In our simulations, planets, which are free to migrate and accrete mass, end up in a locked resonant configuration that is dynamically stable. We show that features observed at infrared (scattered light) and millimetre (thermal continuum) wavelengths are naturally explained by the accretion stream on to the outer planet, without requiring a circumplanetary disc around Planet c. We post-processed our near-infrared synthetic images in order to account for observational biases known to affect high-contrast images. Our successful reproduction of the observations indicates that planet–disc dynamical interactions alone are sufficient to explain the observations of PDS 70.
Publisher: American Physical Society (APS)
Date: 17-03-2017
Publisher: Oxford University Press (OUP)
Date: 06-02-2023
Abstract: We report kinematic and thermal signatures associated with the directly imaged protoplanet candidate in the Elias 2–24 disc. Using the DSHARP (Disc Substructures at High Angular Resolution Project) ALMA (Atacama Large Millimetre/submillimetre Array) observations of the 12CO J = 2 − 1 line, we show that the disc kinematics are perturbed, with a detached CO emission spot at the location of the planet candidate and traces of spiral wakes, and also that the observed CO emission intensities require local heating. While the foreground extinction hides the velocity channels associated with the planet, preventing a planet mass estimate, the level of gas heating implied by the CO emission indicates the presence of a warm, embedded giant planet. Comparison with models shows that this could either be a ≳5 MJup or a lower mass (≳2 MJup) but accreting protoplanet.
Publisher: American Astronomical Society
Date: 29-12-2011
Publisher: Oxford University Press (OUP)
Date: 26-08-2014
Publisher: American Astronomical Society
Date: 07-2022
Abstract: We test the hypothesis that an embedded giant planet in the IM Lupi protostellar disk can produce velocity kinks seen in CO line observations as well as the spiral arms seen in scattered light and continuum emission. We inject planets into 3D hydrodynamics simulations of IM Lupi, generating synthetic observations using Monte Carlo radiative transfer. We find that an embedded planet of 2–3 M Jup can reproduce non-Keplerian velocity perturbations, or “kinks”, in the 12 CO J = 2–1 channel maps. Such a planet can also explain the spiral arms seen in 1.25 mm dust continuum emission and 1.6 μ m scattered-light images. We show that the wake of the planet can be traced in the observed peak velocity map, which appears to closely follow the morphology expected from our simulations and from analytic models of planet–disk interaction.
Publisher: Oxford University Press (OUP)
Date: 05-01-2018
Publisher: Oxford University Press (OUP)
Date: 22-02-2021
Abstract: Understanding how giant planets form requires observational input from directly imaged protoplanets. We used VLT/NACO and VLT/SPHERE to search for companions in the transition disc of 2MASS J19005804-3645048 (hereafter CrA-9), an accreting M0.75 dwarf with an estimated age of 1–2 Myr. We found a faint point source at ∼0.7-arcsec separation from CrA-9 (∼108 au projected separation). Our 3-epoch astrometry rejects a fixed background star with a 5σ significance. The near-IR absolute magnitudes of the object point towards a planetary-mass companion. However, our analysis of the 1.0–3.8$\\,\\mu$m spectrum extracted for the companion suggests it is a young M5.5 dwarf, based on both the 1.13-μm Na index and comparison with templates of the Montreal Spectral Library. The observed spectrum is best reproduced with high effective temperature ($3057^{+119}_{-36}$K) BT-DUSTY and BT-SETTL models, but the corresponding photometric radius required to match the measured flux is only $0.60^{+0.01}_{-0.04}$ Jovian radius. We discuss possible explanations to reconcile our measurements, including an M-dwarf companion obscured by an edge-on circum-secondary disc or the shock-heated part of the photosphere of an accreting protoplanet. Follow-up observations covering a larger wavelength range and/or at finer spectral resolution are required to discriminate these two scenarios.
Publisher: Oxford University Press (OUP)
Date: 05-09-2014
Publisher: Oxford University Press (OUP)
Date: 11-02-2020
Abstract: We use three-dimensional simulations with coupled hydrodynamics and Monte Carlo radiative transfer to show that shadows cast by the inner disc in broken circumbinary discs move within a confined range of position angles on the outer disc. Over time, shadows appear to rock back and forth in azimuth as the inner disc precesses. The effect occurs because the inner disc precesses around a vector that is not the angular momentum vector of the outer disc. We relate our findings to recent observations of shadows in discs.
Publisher: American Astronomical Society
Date: 02-06-2016
Publisher: Springer Science and Business Media LLC
Date: 2004
Publisher: American Astronomical Society
Date: 21-07-2014
Publisher: Oxford University Press (OUP)
Date: 17-12-2018
Publisher: Oxford University Press (OUP)
Date: 20-11-2015
Publisher: Oxford University Press (OUP)
Date: 02-2004
Publisher: Oxford University Press (OUP)
Date: 25-05-2022
Abstract: Young multiple systems accrete most of their final mass in the first few Myr of their lifetime, during the protostellar and protoplanetary phases. Previous studies showed that in binary systems the majority of the accreted mass falls on to the lighter star, thus evolving to mass equalization. However, young stellar systems often comprise more than two stars, which are expected to be in hierarchical configurations. Despite its astrophysical relevance, differential accretion in hierarchical systems remains to be understood. In this work, we investigate whether the accretion trends expected in binaries are valid for higher order multiples. We performed a set of three-dimensional smoothed particle hydrodynamics simulations of binaries and of hierarchical triples (HTs) embedded in an accretion disc, with the code phantom. We identify for the first time accretion trends in HTs and their deviations compared to binaries. These deviations, due to the interaction of the small binary with the infalling material from the circumtriple disc, can be described with a semi-analytical prescription. Generally, the smaller binary of an HT accretes more mass than a single star of the same mass as the smaller binary. We found that in an HT, if the small binary is heavier than the third body, the standard differential accretion scenario (whereby the secondary accretes more of the mass) is h ered. Reciprocally, if the small binary is lighter than the third body, the standard differential accretion scenario is enhanced. The peculiar differential accretion mechanism we find in HTs is expected to affect their mass ratio distribution.
Publisher: Oxford University Press (OUP)
Date: 06-05-2016
Publisher: Research Square Platform LLC
Date: 06-04-2023
DOI: 10.21203/RS.3.RS-2749842/V1
Abstract: Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, discs and bipolar outflows, with shaping attributed to interactions with a companion. For the first time, we have used a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W~Aquilae, a binary system containing an AGB star and a main sequence companion. Our results are based on anisotropic SiN emission, the first detections of NS and SiC towards an S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our new method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and establishes a template for future studies.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2008
End Date: 2011
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2007
End Date: 2008
Funder: The Royal Society
View Funded ActivityStart Date: 06-2010
End Date: 05-2013
Amount: $285,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 12-2020
Amount: $648,530.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2018
End Date: 12-2022
Amount: $369,365.00
Funder: Australian Research Council
View Funded ActivityStart Date: 12-2022
End Date: 12-2025
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2013
End Date: 10-2017
Amount: $325,000.00
Funder: Australian Research Council
View Funded Activity