A5032534031- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Gear and Bearing Dynamics Analysis
- Metal Alloys Wear and Properties
- Astronomy and Astrophysical Research
- Tribology and Lubrication Engineering
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Mechanical Engineering and Vibrations Research
- Tribology and Wear Analysis
- Molecular Spectroscopy and Structure
- Lubricants and Their Additives
- Mechanical stress and fatigue analysis
- Fatigue and fracture mechanics
- Fluid Dynamics and Turbulent Flows
- Metallurgy and Material Forming
- Combustion and flame dynamics
- Advanced Sensor Technologies Research
- Mechanical Failure Analysis and Simulation
- Thermochemical Biomass Conversion Processes
- Coal Combustion and Slurry Processing
- Adhesion, Friction, and Surface Interactions
- Metal and Thin Film Mechanics
- Advanced machining processes and optimization
University of Sheffield
2011-2024
Royal Society
2017-2020
Liverpool John Moores University
2014-2016
ETH Zurich
2010-2014
University of Cambridge
2007
Bridge University
2007
Monash University
1997-2002
Australian National University
2002
Rolls-Royce (United Kingdom)
1984-1995
Alberta Energy
1993-1994
Spectroscopic analyses of hydrogen-rich WN 5–6 stars within the young star clusters NGC 3603 and R136 are presented, using archival Hubble Space Telescope Very Large spectroscopy, high spatial resolution near-IR photometry, including Multi-Conjugate Adaptive Optics Demonstrator (MAD) imaging R136. We derive stellar temperatures for in (T*∼ 42 ± 2 kK) 53 3 plus clumping-corrected mass-loss rates 2–5 × 10−5 M⊙ yr−1 which closely agree with theoretical predictions from Vink et al. These make a...
We discuss the observations and theory of star cluster formation to argue that clusters form dynamically cool (subvirial) with substructure. then perform an ensemble simulations cool, clumpy (fractal) show they often mass segregate on timescales far shorter than expected from simple models. The segregation comes about through production a short-lived, but very dense core. This shows in like Orion Nebula Cluster stars ⩾ 4 M☉ can within current age cluster. Therefore, observed apparently young...
We present a new method to detect and quantify mass segregation in star clusters. It compares the minimum spanning tree (MST) of massive stars with that random stars. If is present, MST length most will be shorter than This difference can quantified (with an associated significance) measure degree segregation. test on simulated clusters both 2D 3D show works as expected. apply Orion Nebula Cluster (ONC) able Trapezium `mass ratio' Λ_{MSR}=8.0 \pm 3.5 (where Λ_{MSR}=1 no segregation) down 16...
Over the past few decades, numerous wide (>1000 au) binaries in Galactic field and halo have been discovered. Their existence cannot be explained by process of star formation or dynamical interactions field, their origin has long a mystery. We explain these during dissolution phase young clusters: an initially unbound pair stars may form binary when distance phase-space is small. Using N-body simulations, we find that resulting fraction semi-major axis range 1000 au - 0.1 pc for individual...
We model the dynamical evolution of star-forming regions with a wide range initial properties. follow regions’ substructure using |$\mathcal {Q}$|-parameter, we search for mass segregation ΛMSR technique, and also quantify local density around stars as function ΣLDR method. The amount measured by is generally only significant subvirial virialized, substructured – which usually evolve to form bound clusters. method shows that massive attain higher densities than median value in all regions,...
We present N-body simulations of young substructured star clusters undergoing various dynamical evolutionary scenarios and examine the direct effects interactions in cluster on planetary systems. model initially cool collapse, virial equilibrium expanding, place a 1-Jupiter-mass planet at either 5 or 30 au from their host stars, with zero eccentricity. find that after 10 Myr ∼10 per cent planets orbiting have been liberated parent form population free-floating planets. A small number these...
We examine substructure and mass segregation in the massive OB association Cygnus OB2 to better understand its initial conditions. Using a well understood Chandra X-ray selected sample of young stars we find that Cyg exhibits considerable physical has no evidence for segregation, both indications is not dynamically evolved. Combined with previous kinematical studies conclude very young, what observe now close conditions: formed as highly substructured, unbound low volume density (< 100...
We present a large-scale, volume-limited companion survey of 245 late-K to mid-M (K7-M6) dwarfs within 15 pc. Infrared adaptive optics (AO) data were analysed from the Very Large Telescope, Subaru Canada–France–Hawaii and MMT Observatory detect close companions sample ∼ 1 100 au, while digitized wide-field archival plates searched for wide 10 000 au. With sensitivity bottom main sequence over separation range 3 multiple AO epochs allow us confirm candidates with common proper motions,...
Around 4 per cent of O-stars are observed in apparent isolation, with no associated cluster, and indication having been ejected from a nearby cluster. We define an isolated O-star as star >17.5 M⊙ cluster total mass <100 which contains other massive (>10 M⊙) stars. show that the fraction apparently is reproduced when stars sampled (randomly) standard initial function form N(M) ∝M−2. This result difficult to reconcile idea there fundamental relationship between most suggest such typical...
Observations and theory both suggest that star clusters form sub-virial (cool) with highly sub-structured distributions. We perform a large ensemble of N-body simulations moderate-sized (N=1000) cool, fractal to investigate their early dynamical evolution. find clumpy dynamically mass segregate on short timescale, Trapezium-like massive higher-order multiples are commonly formed, stars often ejected from velocities > 10 km/s (c.f. the average escape velocity 2.5 km/s). The properties also...
Theory predicts that we should find fast, ejected (runaway) stars of all masses around dense, young star-forming regions. $N$-body simulations show the number and distribution these could be used to constrain initial spatial kinematic substructure We search for runaway slower walkaway within 100 pc Orion Nebula Cluster (ONC) using $Gaia$ DR2 astrometry photometry. compare our findings predictions velocity distributions from run 4 Myr with conditions tailored ONC. In DR2, 31 54 candidates...
We examine the dynamical destruction of binary systems in star clusters different densities. find that at high densities (10^4 - 10^5 Msun pc^-3) almost all binaries with separations > 10^3 AU are destroyed after a few crossing times. At low (order(10^2) many destroyed, and no 10^4 survive Therefore can be used as tracer age past density cluster. argue central region Orion Nebula Cluster was around 100 times denser half-mass radius only 0.1 0.2 pc (a) it is expanding, (b) has very AU, (c)...
We determine the distribution of stellar surface densities, Σ, from models static and dynamically evolving star clusters with different morphologies, including both radially smooth substructured clusters. find that Σ is degenerate, in sense many cluster morphologies (smooth or substructured) produce similar cumulative distributions. However, when used tandem a measure structure, such as -parameter, current spatial dynamical state can be inferred. The effect dynamics on -parameter...
The initial density of individual star-forming regions (and by extension the birth environment planetary systems) is difficult to constrain due "density degeneracy problem": an initially dense region expands faster than a more quiescent two-body relaxation and so two with same observed present-day may have had very different densities. We densities seven nearby folding in information on their spatial structure from $\mathcal{Q}$-parameter comparing results $N$-body simulations. This turn...
We quantify the structure of a very large number Galactic open clusters and look for evidence mass segregation most massive stars in clusters. characterise ratios 1276 Milky Way Stellar Cluster (MWSC) catalogue containing each at least 40 that are located distance up to $\approx 2$ kpc from Sun. use an approach based on calculation minimum spanning tree clusters, one them, we calculate parameter \Q\ ratio $\Lambda_{\rm MSR}$. Our findings indicate possess falls range 0.7-0.8 thus neither...
We present 3.7 arcsec (~0.05 pc) resolution 3.2 mm dust continuum observations from the IRAM PdBI, with aim of studying structure and fragmentation filamentary Infrared Dark Cloud G035.39-00.33. The emission is segmented into a series 13 quasi-regularly spaced (~0.18pc) cores, following major axis IRDC. compare spatial distribution cores that predicted by theoretical work describing hydrodynamic fluid cylinders, finding significant (a factor ~8) discrepancy between two. Our are consistent...
Heating by short-lived radioisotopes (SLRs) such as aluminum-26 and iron-60 fundamentally shaped the thermal history interior structure of Solar System planetesimals during early stages planetary formation. The subsequent thermo-mechanical evolution, internal differentiation or rapid volatile degassing, yields important implications for final structure, composition evolution terrestrial planets. SLR-driven heating in is sensitive to absolute abundance homogeneity SLRs within protoplanetary...
We analyse N-body simulations of star-forming regions to investigate the effects external far and extreme ultra-violet photoevaporation from massive stars on protoplanetary discs. By varying initial conditions simulated regions, such as spatial distribution, net bulk motion (virial ratio), density, we which parameters most affect rate at discs are dispersed due photoevaporation. find that disc dispersal is faster in highly substructured than smooth centrally concentrated regions. Sub-virial...
Recent years have seen a surge of interest in the community studying effect ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because significant fraction planetary systems, potentially including our own, formed close proximity to stars. rapidly developing field, with broad range observations across many regions recently obtained or scheduled. In this paper, stimulated series workshops topic, we take...
The formation of an elaborate H-bonding network between heptanuclear cations, consisting a hexacyanochromate capped by six [Mn(dmptacn)]2+ moieties, and counterions results in the assembly novel 1-D chains with short-range ferrimagnetic behaviour occurring S = 27/2 clusters 3/2 ions.
Whether massive stars can occasionally form in relative isolation or if they require a large cluster of lower-mass around them is key test the differentiation star formation theories as well how initial mass function sampled. Previous attempts to find O-type that formed were hindered by possibility such are merely runaways from clusters, i.e., their current does not reflect birth conditions. We introduce new method affected degeneracy. Using VLT-FLAMES Tarantula Survey and additional high...
We have measured the multiplicity fractions and separation distributions of seven young star-forming regions using a uniform sample binaries. Both are similar in different regions. A tentative decline fraction with increasing stellar density is apparent, even for binary systems separations too close (19–100 au) to been dynamically processed. The statistically indistinguishable over most ranges, higher densities do not exhibit lower proportion wide (300–620 relative (62–300 binaries as might...
Whether massive stars (≳30 M⊙) can occasionally form in relative isolation (e.g. clusters with M < 100 or if they require a large cluster of lower-mass around them is key test the differentiation star-formation theories as well how initial mass function sampled. Previous attempts to find O-type that formed were hindered by possibility such are merely runaways from clusters, i.e., their current does not reflect birth conditions. We introduce new method affected degeneracy. Using VLT-FLAMES...