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The stellar mass distribution in star-forming regions, stellar clusters and associations, the initial mass function (IMF), appears to be invariant across different star-forming environments, and is consistent with the IMF observed in the Galactic field. Deviations from the field, or standard, IMF, if genuine, would be considered strong evidence for a different set of physics at play during the formation of stars in the birth region in question. We analyse N -body simulations of the evolution of spatially and kinematically substructured star-forming regions to identify the formation of binary star clusters, where two (sub)clusters which form from the same Giant Molecular Cloud orbit a common centre of mass. We then compare the mass distributions of stars in each of the subclusters and compare them to the standard IMF, which we use to draw the stellar masses in the star-forming region from which the binary cluster(s) form. In each binary cluster that forms, the mass distributions of stars in one subcluster deviates from the standard IMF, and drastically so when we apply similar mass resolution limits as for the observed binary clusters. Therefore, if a binary subcluster is observed to have an unusual IMF, this may simply be the result of dynamical evolution, rather than different physical conditions for star formation in these systems. [ABSTRACT FROM AUTHOR]

Observations of star-forming regions provide snapshots in time of the star formation process, and can be compared with simulation data to constrain the initial conditions of star formation. In order to make robust inferences, different metrics must be used to quantify the spatial and kinematic distributions of stars. In this paper, we assess the suitability of the INdex to Define Inherent Clustering And TEndencies (INDICATE) method as a diagnostic to infer the initial conditions of star-forming regions that subsequently undergo dynamical evolution. We use INDICATE to measure the degree of clustering in N -body simulations of the evolution of star-forming regions with different initial conditions. We find that the clustering of individual stars, as measured by INDICATE, becomes significantly higher in simulations with higher initial stellar densities, and is higher in subvirial star-forming regions where significant amounts of dynamical mixing have occurred. We then combine INDICATE with other methods that measure the mass segregation (ΛMSR), relative stellar surface density ratio (ΣLDR), and the morphology (Q -parameter) of star-forming regions, and show that the diagnostic capability of INDICATE increases when combined with these other metrics. [ABSTRACT FROM AUTHOR]

Whilst the formation of Solar system planets is constrained by meteoritic evidence, the geophysical history of low-mass exoplanets is much less clear. The bulk composition and climate states of rocky exoplanets may vary significantly based on the composition and properties of the planetesimals they form. An important factor influenced by planetesimal composition is water content, where the desiccation of accreting planetesimals impacts the final water content of the resultant planets. While the inner planets of the Solar system are comparatively water-poor, recent observational evidence from exoplanet bulk densities and planetary formation models suggests that rocky exoplanets engulfed by substantial layers of high-pressure ices or massive steam atmospheres could be widespread. Here, we quantify variations in planetesimal desiccation due to potential fractionation of the two short-lived radioisotopes 26Al and 60Fe relevant for internal heating on planetary formation time-scales. We focus on how order of magnitude variations in 60Fe can affect the water content of planetesimals, and how this may alter the formation of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause of planetesimal heating in any Solar system analogue scenario, thus validating previous works focussing only on this radioisotope. However, 60Fe can become the primary heating source in the case of high levels of supernova enrichment in massive star-forming regions. These diverging scenarios can affect the formation pathways, bulk volatile budget, and climate diversity of low-mass exoplanets. [ABSTRACT FROM AUTHOR]

Cognitive functioning in older age profoundly impacts quality of life and health. While most research on cognition in older age has focused on mean levels, intraindividual variability (IIV) around this may have risk factors and outcomes independent of the mean value. Investigating risk factors associated with IIV has typically involved deriving a summary statistic for each person from residual error around a fitted mean. However, this ignores uncertainty in the estimates, prohibits exploring associations with time-varying factors, and is biased by floor/ceiling effects. To address this, we propose a mixed-effects location scale beta-binomial model for estimating average probability and IIV in a word recall test in the English Longitudinal Study of Ageing. After adjusting for mean performance, an analysis of 9,873 individuals across 7 (mean = 3.4) waves (2002–2015) found IIV to be greater at older ages, with lower education, in females, with more difficulties in activities of daily living, in later birth cohorts, and when interviewers recorded issues potentially affecting test performance. Our study introduces a novel method for identifying groups with greater IIV in bounded discrete outcomes. Our findings have implications for daily functioning and care, and further work is needed to identify the impact for future health outcomes. [ABSTRACT FROM AUTHOR]

Simulations of the effects of stellar fly-bys on planetary systems in star-forming regions show a strong dependence on subtle variations in the initial spatial and kinematic substructure of the regions. For similar stellar densities, the more substructured star-forming regions disrupt up to a factor of 2 more planetary systems. We extend this work to look at the effects of substructure on stellar binary populations. We present N -body simulations of substructured, and non-substructured (smooth) star-forming regions in which we place different populations of stellar binaries. We find that for binary populations that are dominated by close (<100 au) systems, a higher proportion are destroyed in substructured regions. However, for wider systems (>100 au), a higher proportion are destroyed in smooth regions. The difference is likely due to the hard–soft or fast–slow boundary for binary destruction. Hard (fast/close) binaries are more likely to be destroyed in environments with a small velocity dispersion (kinematically substructured regions), whereas soft (slow/wide) binaries are more likely to be destroyed in environments with higher velocity dispersions (non-kinematically substructured regions). Due to the vast range of stellar binary semimajor axes in star-forming regions (10−2 to 104 au), these differences are small and hence unlikely to be observable. However, planetary systems have a much smaller initial semimajor axis range (likely ∼1–100 au for gas giants) and here the difference in the fraction of companions due to substructure could be observed if the star-forming regions that disrupt planetary systems formed with similar stellar densities. [ABSTRACT FROM AUTHOR]

The dominant formation mechanism of brown dwarfs and planetary-mass objects (PMOs) in star-forming regions is presently uncertain. Do they form like stars, via the collapse and fragmentation of cores in giant molecular clouds, or do they form like planets in the discs around stars and are ejected via dynamical interactions? In this paper, we quantify the spatial distribution of substellar objects in NGC 1333, in particular focusing on PMOs that have been the target of recent deep imaging observations. We find that these objects have a spatial distribution that is indistinguishable from the stars, and more massive brown dwarfs. We also analyse N -body simulations and find that a population of ejected planets would have a significantly different spatial and kinematic distribution from stars, and brown dwarfs that also formed through gravitational collapse and fragmentation. We therefore conclude that the low-mass substellar objects in NGC 1333 formed more like stars than planets, although we predict that a population of hitherto undetected ejected PMOs may be lurking in this and other star-forming regions. [ABSTRACT FROM AUTHOR]

The presence of short-lived radioisotopes (SLRs) 26Al and 60Fe in the Solar system places constraints on the initial conditions of our planetary system. Most theories posit that the origin of 26Al and 60Fe is in the interiors of massive stars, and they are either delivered directly to the protosolar disc from the winds and supernovae of the massive stars, or indirectly via a sequential star formation event. However, massive stars that produce SLRs also emit photoionizing far and extreme ultraviolet radiation, which can destroy the gas component of protoplanetary discs, possibly precluding the formation of gas giant planets like Jupiter and Saturn. Here, we perfom N -body simulations of star-forming regions and determine whether discs that are enriched in SLRs can retain enough gas to form Jovian planets. We find that discs are enriched and survive the photoionizing radiation only when the dust radius of the disc is fixed and not allowed to move inwards due to the photoevaporation, or outwards due to viscous spreading. Even in this optimal scenario, not enough discs survive until the supernovae of the massive stars and so have zero or very little enrichment in 60Fe. We therefore suggest that the delivery of SLRs to the Solar system may not come from the winds and supernovae of massive stars. [ABSTRACT FROM AUTHOR]

The abundance of the short-lived radioisotopes 26Al and 60Fe in the early Solar system is usually explained by the Sun either forming from pre-enriched material, or the Sun's protosolar disc being polluted by a nearby supernova explosion from a massive star. Both hypotheses suffer from significant drawbacks: the former does not account for the dynamical evolution of star-forming regions, while in the latter the time for massive stars to explode as supernovae can be similar to, or even longer than, the lifetime of protoplanetary discs. In this paper, we extend the disc enrichment scenario to include the contribution of 26Al from the winds of massive stars before they explode as supernovae. We use N -body simulations and a post-processing analysis to calculate the amount of enrichment in each disc, and we vary the stellar density of the star-forming regions. We find that stellar winds contribute to disc enrichment to such an extent that the Solar system's 26Al/60Fe ratio is reproduced in up to 50 per cent of discs in dense (⁠|$\tilde{\rho } = 1000$|  M⊙ pc−3) star-forming regions. When winds are a significant contributor to the SLR enrichment, we find that Solar system levels of enrichment can occur much earlier (before 2.5 Myr) than when enrichment occurs from supernovae, which start to explode at later ages (>4 Myr). We find that Solar system levels of enrichment all but disappear in low-density star-forming regions (⁠|$\tilde{\rho } \le 10$|  M⊙ pc−3), implying that the Solar system must have formed in a dense, populous star-forming region if 26Al and 60Fe were delivered directly to the protosolar disc from massive-star winds and supernovae. [ABSTRACT FROM AUTHOR]

The multidimensional phase space density (both position and velocity) of star-forming regions may encode information on the initial conditions of star and planet formation. Recently, a new metric based on the Mahalanobis distance has been used to show that hot Jupiters are more likely to be found around exoplanet host stars in high six-dimensional phase space density, suggesting a more dynamic formation environment for these planets. However, later work showed that this initial result may be due to a bias in the age of hot Jupiters and the kinematics of their host stars. We test the ability of the Mahalanobis distance and density to differentiate more generally between star-forming regions with different morphologies by applying it to static regions that are either substructured or smooth and centrally concentrated. We find that the Mahalanobis distance is unable to distinguish between different morphologies, and that the initial conditions of the N -body simulations cannot be constrained using only the Mahalanobis distance or density. Furthermore, we find that the more dimensions in the phase space, the less effective the Mahalanobis density is at distinguishing between different initial conditions. We show that a combination of the mean three-dimensional (x, y, z) Mahalanobis density and the Q -parameter for a region can constrain its initial virial state. However, this is due to the discriminatory power of the Q -parameter and not from any extra information imprinted in the Mahalanobis density. We therefore recommend continued use of multiple diagnostics for determining the initial conditions of star-forming regions, rather than relying on a single multidimensional metric. [ABSTRACT FROM AUTHOR]

Protoplanetary discs are crucial to understanding how planets form and evolve, but these objects are subject to the vagaries of the birth environments of their host stars. In particular, photoionizing radiation from massive stars has been shown to be an effective agent in disrupting protoplanetary discs. External photoevaporation leads to the inward evolution of the radii of discs, whereas the internal viscous evolution of the disc causes the radii to evolve outwards. We couple N -body simulations of star-forming regions with a post-processing analysis of disc evolution to determine how the radius and mass distributions of protoplanetary discs evolve in young star-forming regions. To be consistent with observations, we find that the initial disc radii must be of the order of 100 au, even though these discs are readily destroyed by photoevaporation from massive stars. Furthermore, the observed disc radius distribution in the Orion Nebula Cluster (ONC) is more consistent with moderate initial stellar densities (100 M⊙ pc−3), in tension with dynamical models that posit much higher initial densities for the ONC. Furthermore, we cannot reproduce the observed disc radius distribution in the Lupus star-forming region if its discs are subject to external photoevaporation. A more detailed comparison is not possible due to the well-documented uncertainties in determining the ages of pre-main-sequence (disc-hosting) stars. [ABSTRACT FROM AUTHOR]

Exoplanets display incredible diversity, from planetary system architectures around Sun-like stars that are very different from our Solar system, to planets orbiting post-main-sequence stars or stellar remnants. Recently, the B-star Exoplanet Abundance STudy (BEAST) reported the discovery of at least two super-Jovian planets orbiting massive stars in the Sco Cen OB association. Whilst such massive stars do have Keplerian discs, it is hard to envisage gas giant planets being able to form in such hostile environments. We use N -body simulations of star-forming regions to show that these systems can instead form from the capture of a free-floating planet or the direct theft of a planet from one star to another, more massive star. We find that this occurs on average once in the first 10 Myr of an association's evolution, and that the semimajor axes of the hitherto confirmed BEAST planets (290 and 556 au) are more consistent with capture than theft. Our results lend further credence to the notion that planets on more distant (>100 au) orbits may not be orbiting their parent star. [ABSTRACT FROM AUTHOR]

We investigate whether spatial-kinematic substructure in young star-forming regions can be quantified using Moran's I statistic. Its presence in young star clusters would provide an indication that the system formed from initially substructured conditions, as expected by the hierarchical model of star cluster formation, even if the cluster were spatially smooth and centrally concentrated. Its absence, on the other hand, would be evidence that star clusters form monolithically. The Moran's I statistic is applied to N -body simulations of star clusters with different primordial spatial-velocity structures, and its evolution over time is studied. It is found that this statistic can be used to reliably quantify spatial-kinematic substructure, and can be used to provide evidence as to whether the spatial-kinematic structure of regions with ages ≲6 Myr is best reproduced by the hierarchical or monolithic models of star formation. Moran's I statistic is also able to conclusively say whether the data are not consistent with initial conditions that lack kinematic substructure, such as the monolithic model, in regions with ages up to, and potentially beyond, 10 Myrs. This can therefore provide a kinematic signature of the star cluster formation process that is observable for many Myr after any initial spatial structure has been erased. [ABSTRACT FROM AUTHOR]

Gravitational interactions in star-forming regions are capable of disrupting and destroying planetary systems, as well as creating new ones. In particular, a planet can be stolen, where it is directly exchanged between passing stars during an interaction; or captured, where a planet is first ejected from its birth system and is free-floating for a period of time, before being captured by a passing star. We perform sets of direct N -body simulations of young, substructured star-forming regions, and follow their evolution for 10 Myr in order to determine how many planets are stolen and captured, and their respective orbital properties. We show that in high-density star-forming regions, stolen and captured planets have distinct properties. The semimajor axis distribution of captured planets is significantly skewed to wider orbits compared to the semimajor axis distribution of stolen planets and planets that are still orbiting their parent star (preserved planets). However, the eccentricity and inclination distributions of captured and stolen planets are similar, but in turn very different to the inclination and eccentricity distributions of preserved planets. In low-density star-forming regions these differences are not as distinct but could still, in principle, be used to determine whether observed exoplanets have likely formed in situ or have been stolen or captured. We find that the initial degree of spatial and kinematic substructure in a star-forming region is as important a factor as the stellar density in determining whether a planetary system will be altered, disrupted, captured, or stolen. [ABSTRACT FROM AUTHOR]

The ability to make meaningful comparisons between theoretical and observational data of star-forming regions is key to understanding the star formation process. In this paper, we test the performance of INDICATE, a new method to quantify the clustering tendencies of individual stars in a region, on synthetic star-forming regions with substructured, and smooth, centrally concentrated distributions. INDICATE quantifies the amount of stellar affiliation of each individual star, and also determines whether this affiliation is above random expectation for the star-forming region in question. We show that INDICATE cannot be used to quantify the overall structure of a region due to a degeneracy when applied to regions with different geometries. We test the ability of INDICATE to detect differences in the local stellar surface density and its ability to detect and quantify mass segregation. We then compare it to other methods such as the mass segregation ratio ΛMSR, the local stellar surface density ratio ΣLDR, and the cumulative distribution of stellar positions. INDICATE detects significant differences in the clustering tendencies of the most massive stars when they are at the centre of a smooth, centrally concentrated distribution, corresponding to areas of greater stellar surface density. When applied to a subset of the 50 most massive stars, we show INDICATE can detect signals of mass segregation. We apply INDICATE to the following nearby star-forming regions: Taurus, ONC, NGC 1333, IC 348, and ρ Ophiuchi and find a diverse range of clustering tendencies in these regions. [ABSTRACT FROM AUTHOR]

We quantify the spatial distribution of stars for two subclusters centred around the massive/intermediate-mass stars S Mon and IRS 1/2 in the NGC 2264 star-forming region. We find that both subclusters have neither a substructured nor a centrally concentrated distribution according to the |$\mathcal {Q}$| -parameter. Neither subcluster displays mass segregation according to the ΛMSR ratio, but the most massive stars in IRS 1/2 have higher relative surface densities according to the ΣLDR ratio. We then compare these quantities to the results of N -body simulations to constrain the initial conditions of NGC 2264, which are consistent with having been dense (⁠|$\tilde{\rho } \sim 10^4$| M⊙ pc−3), highly substructured and subvirial. These initial conditions were also derived from a separate analysis of the runaway and walkaway stars in the region, and indicate that star-forming regions within 1 kpc of the Sun likely have a broad range of initial stellar densities. In the case of NGC 2264, its initial stellar density could have been high enough to cause the destruction or truncation of protoplanetary discs and fledgling planetary systems due to dynamical encounters between stars in the early stages of its evolution. [ABSTRACT FROM AUTHOR]

Planets are observed to orbit the component star(s) of stellar binary systems on so-called circumprimary or circumsecondary orbits, as well as around the entire binary system on so-called circumbinary orbits. Depending on the orbital parameters of the binary system, a planet will be dynamically stable if it orbits within some critical separation of the semimajor axis in the circumprimary case, or beyond some critical separation for the circumbinary case. We present N -body simulations of star-forming regions that contain populations of primordial binaries to determine the fraction of binary systems that can host stable planets at various semimajor axes, and how this fraction of stable systems evolves over time. Dynamical encounters in star-forming regions can alter the orbits of some binary systems, which can induce long-term dynamical instabilities in the planetary system and can even change the size of the habitable zone(s) of the component stars. However, the overall fraction of binaries that can host stable planetary systems is not greatly affected by either the assumed binary population or the density of the star-forming region. Instead, the critical factor in determining how many stable planetary systems exist in the Galaxy is the stellar binary fraction – the more stars that are born as singles in stellar nurseries, the higher the fraction of stable planetary systems. [ABSTRACT FROM AUTHOR]

The first stages of planet formation usually occur when the host star is still in a (relatively) dense star-forming region, where the effects of the external environment may be important for understanding the outcome of the planet formation process. In particular, star-forming regions that contain massive stars have strong far-ultraviolet (FUV) and extreme ultraviolet (EUV) radiation fields, which can induce mass-loss from protoplanetary discs due to photoevaporation. In this paper, we present a parameter-space study of the expected FUV and EUV fields in N -body simulations of star-forming regions with a range of initial conditions. We then use recently published models to determine the mass-loss due to photoevaporation from protoplanetary discs. In particular, we focus on the effects of changing the initial degree of spatial structure and initial virial ratio in the star-forming regions, as well as the initial stellar density. We find that the FUV fields in star-forming regions are much higher than in the interstellar medium, even when the regions have stellar densities as low as in the Galactic field, due to the presence of intermediate-mass, and massive, stars (>5 M⊙). These strong radiation fields lead to the destruction of the gas component in protoplanetary discs within 1 Myr, implying that gas giant planets must either form extremely rapidly (<1 Myr), or that they exclusively form in star-forming regions like Taurus, which contain no intermediate-mass or massive stars. The latter scenario is in direct tension with meteoritic evidence from the Solar system that suggests the Sun and its protoplanetary disc was born in close proximity to massive stars. [ABSTRACT FROM AUTHOR]

Within-individual variability of repeatedly measured exposures might predict later outcomes (e.g. blood pressure (BP) variability (BPV) is an independent cardiovascular risk factor above and beyond mean BP). Because 2-stage methods, known to introduce bias, are typically used to investigate such associations, we introduce a joint modeling approach, examining associations of mean BP and BPV across childhood with left ventricular mass (indexed to height; LVMI) in early adulthood with data (collected 1990–2011) from the UK Avon Longitudinal Study of Parents and Children cohort. Using multilevel models, we allowed BPV to vary between individuals (a "random effect") as well as to depend on covariates (allowing for heteroskedasticity). We further distinguished within-clinic variability ("measurement error") from visit-to-visit BPV. BPV was predicted to be greater at older ages, at higher body weights, and in female participants and was positively correlated with mean BP. BPV had a weak positive association with LVMI (10% increase in within-individual BP variance was predicted to increase LVMI by 0.21%, 95% credible interval: −0.23, 0.69), but this association became negative (−0.78%, 95% credible interval: −2.54, 0.22) once the effect of mean BP on LVMI was adjusted for. This joint modeling approach offers a flexible method of relating repeatedly measured exposures to later outcomes. [ABSTRACT FROM AUTHOR]

Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such as dynamical interactions with other stars and photoevaporation from massive stars. These interactions can also cause young stars to be ejected from their birth regions and become runaways. We present examples of such runaway stars in the vicinity of the Orion Nebula Cluster (ONC) found in Gaia DR2 data that have retained their discs during the ejection process. Once set on their path, these runaways usually do not encounter any other dense regions that could endanger the survival of their discs or young planetary systems. However, we show that it is possible for star–disc systems, presumably ejected from one dense star-forming region, to encounter a second dense region, in our case the ONC. While the interactions of the ejected star–disc systems in the second region are unlikely to be the same as in their birth region, a second encounter will increase the risk to the disc or planetary system from malign external effects. [ABSTRACT FROM AUTHOR]

Galactic Wolf–Rayet (WR) star membership of star-forming regions can be used to constrain the formation environments of massive stars. Here, we utilize Gaia DR2 parallaxes and proper motions to reconsider WR star membership of clusters and associations in the Galactic disc, supplemented by recent near-infrared studies of young massive clusters. We find that only 18–36 per cent of 553 WR stars external to the Galactic Centre region are located in clusters, OB associations or obscured star-forming regions, such that at least 64 per cent of the known disc WR population are isolated, in contrast with only 13 per cent of O stars from the Galactic O star Catalogue. The fraction located in clusters, OB associations or star-forming regions rises to 25–41 per cent from a global census of 663 WR stars including the Galactic Centre region. We use simulations to explore the formation processes of isolated WR stars. Neither runaways, nor low-mass clusters, are numerous enough to account for the low cluster membership fraction. Rapid cluster dissolution is excluded as mass segregation ensures WR stars remain in dense, well-populated environments. Only low-density environments consistently produce WR stars that appeared to be isolated during the WR phase. We therefore conclude that a significant fraction of WR progenitors originate in low-density association-like surroundings which expand over time. We provide distance estimates to clusters and associations host to WR stars, and estimate cluster ages from isochrone fitting. [ABSTRACT FROM AUTHOR]

The |$\mathcal {Q}$| -parameter is used extensively to quantify the spatial distributions of stars and gas in star-forming regions as well as older clusters and associations. It quantifies the amount of structure using the ratio of the average length of the minimum spanning tree, |$\bar{m}$|⁠ , to the average length within the complete graph, |$\bar{s}$|⁠. The interpretation of the |$\mathcal {Q}$| -parameter often relies on comparing observed values of |$\mathcal {Q}$|⁠ , |$\bar{m}$|⁠ , and |$\bar{s}$| to idealized synthetic geometries, where there is little or no match between the observed star-forming regions and the synthetic regions. We measure |$\mathcal {Q}$|⁠ , |$\bar{m}$|⁠ , and |$\bar{s}$| over 10 Myr in N -body simulations, which are compared to IC 348, NGC 1333, and the ONC. For each star-forming region, we set up simulations that approximate their initial conditions for a combination of different virial ratios and fractal dimensions. We find that the dynamical evolution of idealized fractal geometries can account for the observed |$\mathcal {Q}$|⁠ , |$\bar{m}$|⁠ , and |$\bar{s}$| values in nearby star-forming regions. In general, an initially fractal star-forming region will tend to evolve to become more smooth and centrally concentrated. However, we show that different initial conditions, as well as where the edge of the region is defined, can cause significant differences in the path that a star-forming region takes across the |$\bar{m}{-}\bar{s}$| plot as it evolves. We caution that the observed |$\mathcal {Q}$| -parameter should not be directly compared to idealized geometries. Instead, it should be used to determine the degree to which a star-forming region is either spatially substructured or smooth and centrally concentrated. [ABSTRACT FROM AUTHOR]

Background The Life-Space Assessment (LSA) has demonstrable validity and reliability among people sampled from nonclinical settings. Its properties in clinical settings, especially physical therapy services, are less well established. Objective The aim of this study was to test the construct/convergent validity, responsiveness, and floor/ceiling effects of the LSA among patients who had musculoskeletal, orthopedic, neurological, or general surgical presentations and were receiving individually tailored, community-based physical therapist interventions to address gait/balance impairments in an urban location in the United Kingdom. Design A prospective, repeated-measures, comparative cohort design was used. Methods Two hundred seventy-six community-dwelling, newly referred patients were recruited from three cohorts (outpatients; domiciliary, nonhospitalized; and domiciliary, recent hospital discharge). Data were collected from the LSA and the Performance-Oriented Mobility Assessment (POMA1) at initial assessment and discharge. Two hundred twenty-eight participants were retained at follow-up. Results The median age was 80.5 years, 73.6% were women, and the median number of physical therapist contacts over 53 days was five. LSA scores at assessment and changes over treatment distinguished between cohorts, even after adjustment for covariates. Weak correlations (0.14–0.41) were found between LSA and POMA1 scores. No LSA floor/ceiling effects were found. Significant improvements in the LSA score after the intervention were found for each cohort and for the sample overall. For the whole sample, the mean change in the LSA score was 10.5 points (95% CI = 8.3–12.8). Limitations The environmental demands participants faced were not measured. Caregivers answered the LSA questions on behalf of participants when necessary. Assessors were not always masked with regard to the measurement point. Conclusions The LSA has utility as an outcome measure in routine community-based physical therapist practice. It has satisfactory construct validity and is sensitive to change over a short time frame. The LSA is not a substitute for the POMA1; these measures complement each other, with the LSA bringing the added value of measuring real-life functional mobility. [ABSTRACT FROM AUTHOR]

Observations of pre- and proto-stellar cores in young star-forming regions show them to be mass segregated, i.e. the most massive cores are centrally concentrated, whereas pre-main-sequence stars in the same star-forming regions (and older regions) are not. We test whether this apparent contradiction can be explained by the massive cores fragmenting into stars of much lower mass, thereby washing out any signature of mass segregation in pre-main-sequence stars. Whilst our fragmentation model can reproduce the stellar initial mass function, we find that the resultant distribution of pre-main sequence stars is mass segregated to an even higher degree than that of the cores, because massive cores still produce massive stars if the number of fragments is reasonably low (between one and five). We therefore suggest that the reason cores are observed to be mass segregated and stars are not is likely due to dynamical evolution of the stars, which can move significant distances in star-forming regions after their formation. [ABSTRACT FROM AUTHOR]

We examine the mass dependence of the velocity dispersion of stars in the young cluster NGC 6530 to better understand how it formed. Using a large sample of members we find that the proper motion velocity dispersion increases with stellar mass. While this trend is the opposite of that predicted if the cluster were developing energy equipartition, it is in agreement with recent N -body simulations that find such a trend develops because of the Spitzer instability. In these simulations the massive stars sink to the centre of the cluster and form a self-gravitating system with a higher velocity dispersion. If the cluster has formed by the cool collapse of an initially substructured distribution, then this occurs within 1–2 Myr, in agreement with our observations of NGC 6530. We therefore conclude that NGC 6530 formed from much more extended initial conditions and has since collapsed to form the cluster we see now. This cluster formation model is inconsistent with the idea that all stars form in dense, compact clusters and provides the first dynamical evidence that star clusters can form by hierarchical mergers between subclusters. [ABSTRACT FROM AUTHOR]

We use N -body simulations to probe the early phases of the dynamical evolution of star-forming regions and focus on mass and velocity distributions of unbound stars. In this parameter space study, we vary the initial virial ratio and degree of spatial and kinematic substructure and analyse the fraction of stars that become unbound in two different mass classes (above and below 8 M |$\odot$| ). We find that the fraction of unbound stars differs depending on the initial conditions. After 10 Myr, in initially highly subvirial, substructured simulations, the high-mass and lower mass unbound fractions are similar at ∼23 per cent. In initially virialized, substructured simulations, we find only ∼16 per cent of all high-mass stars are unbound, whereas ∼37 per cent of all lower mass stars are. The velocity distributions of unbound stars only show differences for extremely different initial conditions. The distributions are dominated by large numbers of lower mass stars becoming unbound just above the escape velocity of ∼3 km s−1 with unbound high-mass stars moving faster on average than lower mass unbound stars. We see no high-mass runaway stars (velocity > 30 km s−1) from any of our initial conditions and only an occasional lower mass runaway star from initially subvirial/substructured simulations. In our simulations, we find a small number of lower mass walkaway stars (with velocity 5–30 km s−1) from all of our initial conditions. These walkaway stars should be observable around many nearby star-forming regions with Gaia. [ABSTRACT FROM AUTHOR]

Understanding how the birthplace of stars affects planet-forming discs is important for a comprehensive theory of planet formation. Most stars are born in dense star-forming regions where the external influence of other stars, particularly the most massive stars, will affect the survival and enrichment of their planet-forming discs. Simulations suggest that stellar dynamics play a central role in regulating how external feedback affects discs, but comparing models to observations requires an estimate of the initial stellar density in star-forming regions. Structural analyses constrain the amount of dynamical evolution a star-forming region has experienced; regions that maintain substructure and do not show mass segregation are likely dynamically young, and therefore close to their birth density. In this paper, we present a structural analysis of two clusters in the Carina Nebula, Tr14 and Tr16. We show that neither cluster shows evidence for mass segregation or a centrally concentrated morphology, suggesting that both regions are dynamically young. This allows us to compare to simulations from Nicholson et al. who predict disc survival rates in star-forming regions of different initial densities. The surviving disc fractions in Tr14 and Tr16 are consistent with their predictions (both are ∼10 per cent), supporting a growing body of evidence that the star-forming environment plays an important role in the survival and enrichment of protoplanetary discs. [ABSTRACT FROM AUTHOR]

We analyse N -body simulations of star-forming regions to investigate the effects of external far- and extreme-ultraviolet photoevaporation from massive stars on protoplanetary discs. By varying the initial conditions of simulated star-forming regions, such as the spatial distribution, net bulk motion (virial ratio), and density, we investigate which parameters most affect the rate at which discs are dispersed due to external photoevaporation. We find that disc dispersal due to external photoevaporation is faster in highly substructured star-forming regions than in smooth and centrally concentrated regions. Subvirial star-forming regions undergoing collapse also show higher rates of disc dispersal than regions that are in virial equilibrium or are expanding. In moderately dense (∼100 M⊙ pc−3) regions, half of all protoplanetary discs with radii ≥100 au are photoevaporated within 1 Myr, three times faster than is currently suggested by observational studies. Discs in lower density star-forming regions (∼10 M⊙ pc−3) survive for longer, but half are still dispersed on short time-scales (∼2 Myr). This demonstrates that the initial conditions of the star-forming regions will greatly impact the evolution and lifetime of protoplanetary discs. These results also imply that either gas giant planet formation is extremely rapid and occurs before the gas component of discs is  evaporated, or gas giants only form in low-density star-forming regions where no massive stars are present to photoevaporate gas from protoplanetary discs. [ABSTRACT FROM AUTHOR]

Habitable zones are regions around stars where large bodies of liquid water can be sustained on a planet or satellite. As many stars form in binary systems with non-zero eccentricity, the habitable zones around the component stars of the binary can overlap and be enlarged when the two stars are at periastron (and less often when the stars are at apastron). We perform N -body simulations of the evolution of dense star-forming regions and show that binary systems where the component stars originally have distinct habitable zones can undergo interactions that push the stars closer together, causing the habitable zones to merge and become enlarged. Occasionally, overlapping habitable zones can occur if the component stars move further apart, but the binary becomes more eccentric. Enlargement of habitable zones happens to one to two binaries from an average initial total of 352 in each simulated star-forming region, and demonstrates that dense star-forming regions are not always hostile environments for planet formation and evolution. [ABSTRACT FROM AUTHOR]

Here, we confirm Melnick 34, an X-ray bright star in the 30 Dor region of the Large Magellanic Cloud, as an SB2 binary comprising WN5h + WN5h components. We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS spectra. Radial velocity monitoring and automated template-fitting methods both reveal a similar high-eccentricity system with a mass ratio close to unity, and an orbital period in agreement with the 155.1 ± 1 d X-ray light-curve period previously derived by Pollock et al. Our favoured solution derived an eccentricity of 0.68 ± 0.02 and mass ratio of 0.92 ± 0.07, giving minimum masses of MAsin3(i)  = 65 ± 7 M⊙ and MBsin3(i)  = 60 ± 7 M⊙. Spectral modelling using WN5h templates with cmfgen reveals temperatures of T ∼ 53 kK for each component and luminosities of log(LA/L⊙)  = 6.43 ± 0.08 and log(LB/L⊙)  = 6.37 ± 0.08, from which BONNSAI evolutionary modelling gives masses of MA  = 139 |$^{+21}_{-18}$|  M⊙ and MB  = 127 |$^{+17}_{-17}$|  M⊙ and ages of ∼0.6 Myr. Spectroscopic and dynamic masses would agree if Mk34 has an inclination of i ∼ 50°, making Mk34 the most massive binary known and an excellent candidate for investigating the properties of colliding wind binaries. Within 2–3 Myr, both components of Mk34 are expected to evolve to stellar mass black holes, which, assuming the binary system survives, would make Mk34 a potential binary black hole merger progenitor and a gravitational wave source. [ABSTRACT FROM AUTHOR]

The Friends of Friends algorithm identifies groups of objects with similar spatial and kinematic properties, and has recently been used extensively to quantify the distributions of gas and stars in young star-forming regions. We apply the Friends of Friends algorithm to N -body simulations of the dynamical evolution of subvirial (collapsing) and supervirial (expanding) star-forming regions. We find that the algorithm picks out a wide range of groups (1–25) for statistically identical initial conditions, and cannot distinguish between subvirial and supervirial regions in that we obtain similar mode and median values for the number of groups it identifies. We find no correlation between the number of groups identified initially and either the initial or subsequent spatial and kinematic tracers of the regions' evolution, such as the amount of spatial substructure, dynamical mass segregation, or velocity dispersion. We therefore urge caution in using the Friends of Friends algorithm to quantify the initial conditions of star formation. [ABSTRACT FROM AUTHOR]

We quantify the spatial distributions of dense cores in three spatially distinct areas of the Orion B star-forming region. For L1622, NGC2068/NGC 2071, and NGC2023/NGC 2024, we measure the amount of spatial substructure using the Q-parameter and find all three regions to be spatially substructured (Q < 0.8). We quantify the amount of mass segregation using MSR and find that the most massive cores are mildly mass segregated in NGC2068/NGC 2071 (ΛMSR ~ 2), and very mass segregated in NGC2023/NGC 2024 (ΛMSR = 28+13 -10 for the four most massive cores). Whereas the most massive cores in L1622 are not in areas of relatively high surface density, or deeper gravitational potentials, the massive cores in NGC2068/NGC 2071 and NGC2023/NGC 2024 are significantly so. Given the low density (10 cores pc-2) and spatial substructure of cores in Orion B, the mass segregation cannot be dynamical. Our results are also inconsistent with simulations in which the most massive stars form via competitive accretion, and instead hint that magnetic fields may be important in influencing the primordial spatial distributions of gas and stars in star-forming regions. [ABSTRACT FROM AUTHOR]

Aims The UK has a socialized healthcare system that provides treatment that is free at the point of care for acute and chronic health disorders (the National Health Service—NHS), which is currently experiencing a period of unprecedented challenge. Methods A narrative review that discusses present and future arrangements for transplantation of alcohol-related liver disease (ArLD) in the UK. Results Liver disease in the UK is reaching epidemic proportions due to obesity and metabolic disease compounding alcohol-mediated liver damage. Unfortunately, hepatology services in the UK are geographically disparate and subject to significant variations in liver morbidity and mortality, prompting concerns that this may negatively impair access to transplantation. In an attempt to improve referrals to tertiary liver services, the UK listing criteria for alcohol-associated liver disease were revised in 2016 by a working party under the aegis of the UK-Liver Advisory Group with the ambition of increasing opportunities for disease evaluation and improving the condition of candidates referred for assessment. Conclusion Liver transplantation for ArLD is well established in the UK. Recent organizational changes seek to reduce inequities in access to transplant services. Short Summary Liver disease in the UK is reaching epidemic proportions. Concerns over equity of access to liver transplantation prompted revision of the UK listing criteria for alcohol-associated liver disease in 2016, to improve to the availability of tertiary hepatology services. Transplanting patients with alcohol-related liver disease in the National Health System: New Rules and Decisions '...The second property of your excellent sherris is, the warming of the blood; which, before cold and settled, hath left the liver white and pale...' Falstaff; Henry IV Part 2: Act 4, Scene 3 [ABSTRACT FROM AUTHOR]

We quantify the structure of a very large number of Galactic open clusters and look for evidence of mass segregation for themostmassive stars in the clusters.We characterize the structure and mass segregation ratios of 1276 clusters in the Milky Way Stellar Cluster (MWSC) catalogue containing each at least 40 stars and that are located at a distance of up to ≈2 kpc from the Sun. We use an approach based on the calculation of the minimum spanning tree of the clusters, and for each one of them, we calculate the structure parameter Q and the mass segregation ratio ΛMSR. Our findings indicate that most clusters possess a Q parameter that falls in the range 0.7-0.8 and are thus neither strongly concentrated nor do they show significant substructure. Only 27 per cent can be considered centrally concentrated with Q values >0.8. Of the 1276 clusters, only 14 per cent show indication of significant mass segregation (ΛMSR > 1.5). Furthermore, no correlation is found between the structure of the clusters or the degree of mass segregation with their position in the Galaxy. A comparison of the measured Q values for the young open clusters in the MWSC to N-body numerical simulations that follow the evolution of the Q parameter over the first 10 Myr of the clusters life suggests that the young clusters found in the MWSC catalogue initially possessed local mean volume densities of ρ⋆ ≈ 10-100 M☉ pc- 3. [ABSTRACT FROM AUTHOR]

We examine the level of substructure and mass segregation in the massive, young cluster Westerlund 1. We find that it is relatively smooth, with little or no mass segregation, but with the massive stars in regions of significantly higher than average surface density. While an expanding or bouncing-back scenario for the evolution of Westerlund 1 cannot be ruled out, we argue that the most natural model to explain these observations is one in which Westerlund 1 formed with no primordial mass segregation and at a similar or larger size than we now observe. [ABSTRACT FROM AUTHOR]

Approximately 10 per cent of star clusters are found in pairs, known as binary clusters. We propose a mechanism for binary cluster formation; we use N-body simulations to show that velocity substructure in a single (even fairly smooth) region can cause binary clusters to form. This process is highly stochastic and it is not obvious from a region's initial conditions whether a binary will form and, if it does, which stars will end up in which cluster.We find the probability that a region will divide is mainly determined by its virial ratio, and a virial ratio above 'equilibrium' is generally necessary for binary formation. We also find that the mass ratio of the two clusters is strongly influenced by the initial degree of spatial substructure in the region. [ABSTRACT FROM AUTHOR]

We analyse N-body and smoothed particle hydrodynamic (SPH) simulations of young starforming regions to search for differences in the spatial distributions of massive stars compared to lower mass stars. The competitive accretion theory of massive star formation posits that the most massive stars should sit in deeper potential wells than lower mass stars. This may be observable in the relative surface density or spatial concentration of the most massive stars compared to other lower mass stars. Massive stars in cool-collapse N-body models do end up in significantly deeper potentials and are mass segregated. However, in models of warm (expanding) star-forming regions, whilst the massive stars do come to be in deeper potentials than average stars, they are not mass segregated. In the purely hydrodynamical SPH simulations, the massive stars do come to reside in deeper potentials, which is due to their runaway growth. However, when photoionization and stellar winds are implemented in the simulations, these feedback mechanisms regulate the mass of the stars and disrupt the inflow of gas into the clouds' potential wells. This generally makes the potential wells shallower than in the control runs, and prevents the massive stars from occupying deeper potentials. This in turn results in the most massive stars having a very similar spatial concentration and surface density distribution to lower mass stars. Whilstmassive stars do form via competitive accretion in our simulations, this rarely translates to a different spatial distribution and so any lack of primordial mass segregation in an observed star-forming region does not preclude competitive accretion as a viable formation mechanism for massive stars. [ABSTRACT FROM AUTHOR]

We present analyses of the spatial distributions of stars in the young (1-3 Myr) star-forming regions IC 348 and NGC 1333 in the Perseus giant molecular cloud. We quantify the spatial structure using the Q-parameter and find that both IC 348 and NGC 1333 are smooth and centrally concentrated with Q-parameters of 0.98 and 0.89, respectively. Neither region exhibits mass segregation (ΛMSR = 1.1-0.3+0.2 for IC 348 and ΛMSR = 1.2-0.3+0.4 for NGC 1333, where ΛMSR ∼ 1 corresponds to no mass segregation) nor do the most massive stars reside in areas of enhanced stellar surface density compared to the average surface density, according to the ΣLDR method. We then constrain the dynamical histories and hence initial conditions of both regions by comparing the observed values to N-body simulations at appropriate ages. Stars in both regions likely formed with subvirial velocities that contributed to merging of substructure and the formation of smooth clusters. The initial stellar densities were no higher than ρ ∼ 100-500 M⊚ pc-3 for IC 348 and ρ ∼ 500-2000 M⊚ pc-3 for NGC 1333. These initial densities, in particular that of NGC 1333, are high enough to facilitate dynamical interactions that would likely affect ∼10 per cent of protoplanetary discs and binary stars. [ABSTRACT FROM AUTHOR]

Objectives: Telehealth is promoted as a strategy to support self-management of long-term conditions. The aim of this systematic review is to identify which information and communication technology features implemented in mobile apps to support asthma self-management are associated with adoption, adherence to usage, and clinical effectiveness.Methods: We systematically searched 9 databases, scanned reference lists, and undertook manual searches (January 2000 to April 2016). We include randomized controlled trials (RCTs) and quasiexperimental studies with adults. All eligible papers were assessed for quality, and we extracted data on the features included, health-related outcomes (asthma control, exacerbation rate), process/intermediate outcomes (adherence to monitoring or treatment, self-efficacy), and level of adoption of and adherence to use of technology. Meta-analysis and narrative synthesis were used.Results: We included 12 RCTs employing a range of technologies. A meta-analysis (n = 3) showed improved asthma control (mean difference -0.25 [95% CI, -0.37 to -0.12]). Included studies incorporated 10 features grouped into 7 categories (education, monitoring/electronic diary, action plans, medication reminders/prompts, facilitating professional support, raising patient awareness of asthma control, and decision support for professionals). The most successful interventions included multiple features, but effects on health-related outcomes were inconsistent. No studies explicitly reported adoption of and adherence to the technology system.Conclusion: Meta-analysis of data from 3 trials showed improved asthma control, though overall the clinical effectiveness of apps, typically incorporating multiple features, varied. Further studies are needed to identify the features that are associated with adoption of and adherence to use of the mobile app and those that improve health outcomes. [ABSTRACT FROM AUTHOR]

The presence and abundance of short-lived radioisotopes 26Al and 60Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe).Massive stars are more likely to form in massive star clusters (>1000M⊙) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of ~1 pc. We investigate whether low-mass (50-200 M⊙) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse N-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience SN enrichment than in high-mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first SN even in clusters with relatively low (100 stars pc-3) initial densities. However, because of the high number of low-mass clusters containing one or twomassive stars, the absolute number of enriched stars is the same, if not higher than formore populous clusters. Our results show that direct enrichment of protoplanetary discs from SNe occurs as frequently in low-mass clusters containing one or two massive stars (>20M⊙) as in more populous star clusters (1000 M⊙). This relaxes the constraints on the direct enrichment scenario and therefore the birth environment of the Solar system. [ABSTRACT FROM AUTHOR]

Heating by short-lived radioisotopes (SLRs) such as 26Al and 60Fe fundamentally shaped the thermal history and interior structure of Solar system planetesimals during the early stages of planetary formation. The subsequent thermo-mechanical evolution, such as internal differentiation or rapid volatile degassing, yields important implications for the final structure, composition and evolution of terrestrial planets. SLR-driven heating in the Solar system is sensitive to the absolute abundance and homogeneity of SLRs within the protoplanetary disc present during the condensation of the first solids. In order to explain the diverse compositions found for extrasolar planets, it is important to understand the distribution of SLRs in active planet formation regions (star clusters) during their first few Myr of evolution. By constraining the range of possible effects, we show how the imprint of SLRs can be extrapolated to exoplanetary systems and derive statistical predictions for the distribution of 26Al and 60Fe based on N-body simulations of typical to large clusters (103–104 stars) with a range of initial conditions. We quantify the pollution of protoplanetary discs by supernova ejecta and show that the likelihood of enrichment levels similar to or higher than the Solar system can vary considerably, depending on the cluster morphology. Furthermore, many enriched systems show an excess in radiogenic heating compared to Solar system levels, which implies that the formation and evolution of planetesimals could vary significantly depending on the birth environment of their host stars. [ABSTRACT FROM AUTHOR]

We follow the dynamical evolution of young star-forming regions with a wide range of initial conditions and examine how the radial velocity dispersion, ι, evolves over time. We compare this velocity dispersion to the theoretically expected value for the velocity dispersion if a region were in virial equilibrium, ιvir and thus assess the virial state (ι/ιvir) of these systems. We find that in regions that are initially subvirial, or in global virial equilibrium but subvirial on local scales, the system relaxes to virial equilibrium within several million years, or roughly 25-50 crossing times, according to the measured virial ratio. However, the measured velocity dispersion, ι, appears to be a bad diagnostic of the current virial state of these systems as it suggests that they become supervirial when compared to the velocity dispersion estimated from the virial mass, ιvir. We suggest that this discrepancy is caused by the fact that the regions are never fully relaxed, and that the early non-equilibrium evolution is imprinted in the one-dimensional velocity dispersion at these early epochs. If measured early enough (<2Myr in our simulations, or ~20 crossing times), the velocity dispersion can be used to determine whether a region was highly supervirial at birth without the risk of degeneracy. We show that combining ι, or the ratio of ι to the interquartile range (IQR) dispersion, with measures of spatial structure, places stronger constraints on the dynamical history of a region than using the velocity dispersion in isolation. [ABSTRACT FROM AUTHOR]

The presence and abundance of the short-lived radioisotopes (SLRs) 26Al and 60Fe during the formation of the Solar system is difficult to explain unless the Sun formed in the vicinity of one or more massive star(s) that exploded as supernovae. Two different scenarios have been proposed to explain the delivery of SLRs to the protosolar nebula: (i) direct pollution of the protosolar disc by supernova ejecta, and (ii) the formation of the Sun in a sequential star formation event in which supernovae shockwaves trigger further star formation which is enriched in SLRs. The sequentially triggered model has been suggested as being more astrophysically likely than the direct pollution scenario. In this paper, we investigate this claim by analysing a combination of N-body and smoothed particle hydrodynamics simulations of star formation. We find that sequential star formation would result in large age spreads (or even bi-modal age distributions for spatially coincident events) due to the dynamical relaxation of the first star formation event(s). Secondly, we discuss the probability of triggering spatially and temporally discrete populations of stars and find this to be only possible in very contrived situations. Taken together, these results suggest that the formation of the Solar system in a triggered star formation event is as improbable, if not more so, than the direct pollution of the protosolar disc by a supernova. [ABSTRACT FROM AUTHOR]

We compare the spatial distribution of stars which form in hydrodynamical simulations to the spatial distribution of the gas, using the Q-parameter. The Q-parameter enables a selfconsistent comparison between the stars and gas because it uses a pixelated image of the gas as a distribution of points, in the same way that the stars (sink particles in the simulations) are a distribution of points. We find that, whereas the stars have a substructured, or hierarchical spatial distribution (Q ~ 0.4-0.7), the gas is dominated by a smooth, concentrated component and typically has Q ~ 0.9. We also find no statistical difference between the structure of the gas in simulations that form with feedback, and those that form without, despite these two processes producing visually different distributions. These results suggest that the link between the spatial distributions of gas, and the stars which form from them, is non-trivial. [ABSTRACT FROM AUTHOR]

We examine the performance of four different methods which are used to measure mass segregation in star-forming regions: the radial variation of the mass function MMF; the minimum spanning tree-based ΛMSR method; the local surface density ΣLDR method; and the ΩGSR technique, which isolates groups of stars and determines whether the most massive star in each group is more centrally concentrated than the average star. All four methods have been proposed in the literature as techniques for quantifying mass segregation, yet they routinely produce contradictory results as they do not all measure the same thing. We apply each method to synthetic star-forming regions to determine when and why they have shortcomings. When a star-forming region is smooth and centrally concentrated, all four methods correctly identify mass segregation when it is present. However, if the region is spatially substructured, the ΩGSR method fails because it arbitrarily defines groups in the hierarchical distribution, and usually discards positional information for many of the most massive stars in the region. We also show that the ΛMSR and ΣLDR methods can sometimes produce apparently contradictory results, because they use different definitions of mass segregation. We conclude that only ΛMSR measures mass segregation in the classical sense (without the need for defining the centre of the region), although ΣLDR does place limits on the amount of previous dynamical evolution in a star-forming region. [ABSTRACT FROM AUTHOR]

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 Telescope, Canada-France-Hawaii Telescope, and MMT Observatory to detect close companions to the sample from ~ 1 to 100 au, while digitized wide-field archival plates were searched for wide companions from ~ 100 to 10 000 au. With sensitivity to the bot-tom of the main sequence over a separation range of 3 to 10 000 au, multiple AO and wide-field epochs allow us to confirm candidates with common proper motions, minimize background contamination, and enable a measurement of comprehensive binary statistics. We detected 65 comoving stellar companions and find a companion star fraction of 23.5 ± 3.2 per cent over the 3 au to 10 000 au separation range. The companion separation distribution is observed to rise to a higher frequency at smaller separations, peaking at closer separations than measured for more massive primaries. The mass ratio distribution across the q = 0.2-1.0 range is flat, similar to that of multiple systems with solar-type primaries. The characterization of binary and multiple star frequency for low-mass field stars can provide crucial comparisons with star-forming environments and hold implications for the frequency and evolutionary histories of their associated discs and planets. [ABSTRACT FROM AUTHOR]

The gravitational instability model of planet/brown dwarf formation proposes that protostellar discs can fragment into objectswith masses above a fewJupitermasses at large semimajor axis. Tidal downsizing may reduce both the object mass and semimajor axis. However, most studies of tidal downsizing end when the protostellar disc disperses, while the system is embedded in its parent star-forming region. To compare disc fragment descendants with exoplanet and brown dwarf observations, the subsequent dynamical evolution must be explored. We carry out N-body integrations of fragment-fragment scattering in multi-object star systems, and star systems embedded in substructured clusters. In both cases, we use initial conditions generated by population synthesis models of tidal downsizing. The scattering simulations produce a wide range of eccentricities. The ejection rate is around 25 per cent. The ejecta mass distribution is similar to that for all objects, with a velocity dispersion consistent with those produced by full hydrodynamic simulations. The semimajor axis distribution after scattering extends to parsec scales. In the cluster simulations, 13 per cent of the objects are ejected from their planetary system, and around 10 per cent experience significant orbit modification. A small number of objects are recaptured on high-eccentricity, high-inclination orbits. The velocity distribution of ejecta is similar to that produced by fragment-fragment scattering. If fragment-fragment scattering and cluster stripping act together, then disc fragmentation should be efficient at producing free-floating substellar objects, and hence characterizing the free-floating planet population will provide strong constraints on the frequency of disc fragmentation. [ABSTRACT FROM AUTHOR]

We take the end result of smoothed particle hydrodynamics (SPH) simulations of star formation which include feedback from photoionization and stellar winds and evolve them for a further 10 Myr using N-body simulations. We compare the evolution of each simulation to a control run without feedback, and to a run with photoionization feedback only. In common with previous work, we find that the presence of feedback prevents the runaway growth of massive stars, and the resulting star-forming regions are less dense, and preserve their initial substructure for longer. The addition of stellar winds to the feedback produces only marginal differences compared to the simulations with just photoionization feedback. We search for mass segregation at different stages in the simulations; before feedback is switched on in the SPH runs, at the end of the SPH runs (before N-body integration) and during the N-body evolution. Whether a simulation is primordially mass segregated (i.e. before dynamical evolution) depends extensively on how mass segregation is defined, and different methods for measuring mass segregation give apparently contradictory results. Primordial mass segregation is also less common in the simulations when star formation occurs under the influence of feedback. Further dynamical mass segregation can also take place during the subsequent (gas-free) dynamical evolution. Taken together, our results suggest that extreme caution should be exercised when interpreting the spatial distribution of massive stars relative to low-mass stars in simulations. [ABSTRACT FROM AUTHOR]

The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the ‘density degeneracy problem’: an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the $\mathcal {Q}$-parameter and comparing the structure and present-day density to the results of N-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three – the Orion Nebula Cluster, ρ Oph, and Corona Australis – are consistent with having evolved from the Kroupa universal initial period distribution and a binary fraction of unity. [ABSTRACT FROM AUTHOR]