Abstract
With increasing numbers infected by SARS-CoV-2, understanding long-COVID is essential to inform health and social care support. A Scottish population cohort of 33,281 laboratory-confirmed ...SARS-CoV-2 infections and 62,957 never-infected individuals were followed-up via 6, 12 and 18-month questionnaires and linkage to hospitalization and death records. Of the 31,486 symptomatic infections,1,856 (6%) had not recovered and 13,350 (42%) only partially. No recovery was associated with hospitalized infection, age, female sex, deprivation, respiratory disease, depression and multimorbidity. Previous symptomatic infection was associated with poorer quality of life, impairment across all daily activities and 24 persistent symptoms including breathlessness (OR 3.43, 95% CI 3.29–3.58), palpitations (OR 2.51, OR 2.36–2.66), chest pain (OR 2.09, 95% CI 1.96–2.23), and confusion (OR 2.92, 95% CI 2.78–3.07). Asymptomatic infection was not associated with adverse outcomes. Vaccination was associated with reduced risk of seven symptoms. Here we describe the nature of long-COVID and the factors associated with it.
Planet formation is generally described in terms of a system containing the host star and a protoplanetary disk
, of which the internal properties (for example, mass and metallicity) determine the ...properties of the resulting planetary system
. However, (proto)planetary systems are predicted
and observed
to be affected by the spatially clustered stellar formation environment, through either dynamical star-star interactions or external photoevaporation by nearby massive stars
. It is challenging to quantify how the architecture of planetary sysems is affected by these environmental processes, because stellar groups spatially disperse within less than a billion years
, well below the ages of most known exoplanets. Here we identify old, co-moving stellar groups around exoplanet host stars in the astrometric data from the Gaia satellite
and demonstrate that the architecture of planetary systems exhibits a strong dependence on local stellar clustering in position-velocity phase space. After controlling for host stellar age, mass, metallicity and distance from the star, we obtain highly significant differences (with p values of 10
to 10
) in planetary system properties between phase space overdensities (composed of a greater number of co-moving stars than unstructured space) and the field. The median semi-major axis and orbital period of planets in phase space overdensities are 0.087 astronomical units and 9.6 days, respectively, compared to 0.81 astronomical units and 154 days, respectively, for planets around field stars. 'Hot Jupiters' (massive, short-period exoplanets) predominantly exist in stellar phase space overdensities, strongly suggesting that their extreme orbits originate from environmental perturbations rather than internal migration
or planet-planet scattering
. Our findings reveal that stellar clustering is a key factor setting the architectures of planetary systems.
Planet-forming disc evolution is not independent of the star formation and feedback process in giant molecular clouds. In particular, OB stars emit UV radiation that heats and disperses discs in a ...process called ‘external photoevaporation’. This process is understood to be the dominant environmental influence acting on planet-forming discs in typical star-forming regions. Our best studied discs are nearby, in sparse stellar groups where external photoevaporation is less effective. However, the majority of discs are expected to reside in much stronger UV environments. Understanding external photoevaporation is therefore key to understanding how most discs evolve, and hence, how most planets form. Here, we review our theoretical and observational understanding of external photoevaporation. We also lay out key developments for the future to address existing unknowns and establish the full role of external photoevaporation in the disc evolution and planet formation process.
ABSTRACT
The exotic range of known planetary systems has provoked an equally exotic range of physical explanations for their diverse architectures. However, constraining formation processes requires ...mapping the observed exoplanet population to that which initially formed in the protoplanetary disc. Numerous results suggest that (internal or external) dynamical perturbation alters the architectures of some exoplanetary systems. Isolating planets that have evolved without any perturbation can help constrain formation processes. We consider the Kepler multiples, which have low mutual inclinations and are unlikely to have been dynamically perturbed. We apply an adaption of previous modelling efforts, accounting for the two-dimensionality of the radius ($R_\mathrm{pl} =0.3\!-\!20\, R_\oplus$) and period (Porb = 0.5–730 d) distribution. We find that an upper limit in planet mass of the form $M_\mathrm{lim} \propto a_\mathrm{pl}^{\beta } \exp (-a_\mathrm{in}/a_\mathrm{pl})$, for semimajor axis apl and a broad range of ain and β, can reproduce a distribution of Porb, Rpl that is indistinguishable from the observed distribution by our comparison metric. The index is consistent with β = 1.5, expected if growth is limited by accretion within the Hill radius. This model is favoured over models assuming a separable PDF in Porb, Rpl. The limit, extrapolated to longer periods, is coincident with the orbits of RV-discovered planets (apl > 0.2 au, $M_\mathrm{pl}\gt 1\, M_\mathrm{J}$) around recently identified low density host stars, hinting at isolation mass limited growth. We discuss the necessary circumstances for a coincidental age-related bias as the origin of this result; such a bias is possible but unlikely. We conclude that, in light of the evidence suggesting that some planetary systems have been dynamically perturbed, simple models for planet growth during the formation stage are worth revisiting.
ABSTRACT
Globular clusters exhibit abundance variations, defining ‘multiple populations’, which have prompted a protracted search for their origin. Properties requiring explanation include the high ...fraction of polluted stars (∼40−90 per cent, correlated with cluster mass), the absence of pollution in young clusters, and the lower pollution rate with binarity and distance from the cluster centre. We present a novel mechanism for late delivery of pollutants into stars via accretion of substellar companions. In this scenario, stars move through a medium polluted with asymptotic giant branch (AGB) and massive star ejecta, accreting material to produce companions with typical mass ratio q ∼ 0.1. These companions undergo eccentricity excitation due to dynamical perturbations by passing stars, culminating in a merger with their host star. The accretion of the companion alters surface abundances via injected pollutant. Alongside other self-enrichment models, the companion accretion model can explain the dilution of pollutant and correlation with intracluster location. The model also explains the ubiquity and discreteness of the populations and correlations of enrichment rates with cluster mass, cluster age, and stellar binarity. Abundance variations in some clusters can be broadly reproduced using AGB and massive binary ejecta abundances from the literature. In other clusters, some high companion mass ratios (q ≳ 1) are required. In these cases, the available mass budget necessitates a variable degree of mixing of the polluted material with the primary star, deviations from model ejecta abundances, or mixing of internal burning products. We highlight the avenues of further investigation that are required to explore some of the key processes invoked in this model.
A solution to the proplyd lifetime problem Winter, Andrew J; Clarke, Cathie J; Rosotti, Giovanni P ...
Monthly Notices of the Royal Astronomical Society,
12/2019, Letnik:
490, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Protoplanetary discs (PPDs) in the Orion Nebula Cluster (ONC) are irradiated by UV fields from the massive star θ1C. This drives thermal winds, inducing mass-loss rates of up to ...$\dot{M}_\mathrm{wind}\sim 10^{-7}\, \mathrm{M}_\odot$ yr−1 in the ‘proplyds’ (ionized PPDs) close to the centre. For the mean age of the ONC and reasonable initial PPD masses, such mass-loss rates imply that discs should have been dispersed. However, $\sim 80{\,{\rm {per\, cent}}}$ of stars still exhibit a near-infrared excess, suggesting that significant circumstellar mass remains. This ‘proplyd lifetime problem’ has persisted since the discovery of photoevaporating discs in the core of the ONC by O’Dell & Wen (1994). In this work, we demonstrate how an extended period of star formation can solve this problem. Coupling N-body calculations and a viscous disc evolution model, we obtain high disc fractions at the present day. This is partly due to the migration of older stars outwards, and younger stars inwards such that the most strongly irradiated PPDs are also the youngest. We show how the disc mass distribution can be used to test the recent claims in the literature for multiple stellar populations in the ONC. Our model also explains the recent finding that host mass and PPD mass are only weakly correlated, in contrast with other regions of similar age. We conclude that the status of the ONC as the archetype for understanding the influence of environment on planet formation is undeserved; the complex star formation history (involving star formation episodes within ∼0.8 Myr of the present day) results in confusing signatures in the PPD population.
The Biological General Repository for Interaction Datasets (BioGRID: http://thebiogrid.org) is an open access database that houses genetic and protein interactions curated from the primary biomedical ...literature for all major model organism species and humans. As of September 2014, the BioGRID contains 749,912 interactions as drawn from 43,149 publications that represent 30 model organisms. This interaction count represents a 50% increase compared to our previous 2013 BioGRID update. BioGRID data are freely distributed through partner model organism databases and meta-databases and are directly downloadable in a variety of formats. In addition to general curation of the published literature for the major model species, BioGRID undertakes themed curation projects in areas of particular relevance for biomedical sciences, such as the ubiquitin-proteasome system and various human disease-associated interaction networks. BioGRID curation is coordinated through an Interaction Management System (IMS) that facilitates the compilation interaction records through structured evidence codes, phenotype ontologies, and gene annotation. The BioGRID architecture has been improved in order to support a broader range of interaction and post-translational modification types, to allow the representation of more complex multi-gene/protein interactions, to account for cellular phenotypes through structured ontologies, to expedite curation through semi-automated text-mining approaches, and to enhance curation quality control.
ABSTRACT
The formation of gas giant planets must occur during the first few Myr of a star’s lifetime, when the protoplanetary disc still contains sufficient gas to be accreted on to the planetary ...core. The majority of protoplanetary discs are exposed to strong ultraviolet irradiation from nearby massive stars, which drives winds and depletes the mass budget for planet formation. It remains unclear to what degree external photoevaporation affects the formation of massive planets. In this work, we present a simple one dimensional model for the growth and migration of a massive planet under the influence of external FUV fields. We find that even moderate FUV fluxes $F_\mathrm{FUV}\gtrsim 100 \, G_0$ have a strong influence on planet mass and migration. By decreasing the local surface density and shutting off accretion on to the planet, external irradiation suppresses planet masses and halts migration early. The distribution of typical stellar birth environments can therefore produce an anticorrelation between semi-major axis and planet mass, which may explain the apparent decrease in planet occurrence rates at orbital periods Porb ≳ 103 d. Even moderate fluxes FFUV strongly suppress giant planet formation and inward migration for any initial semi-major axis if the stellar host mass $M_*\lesssim 0.5\, {\rm M}_\odot$, consistent with findings that massive planet occurrence is much lower around such stars. The outcomes of our prescription for external disc depletion show significant differences to the current approximation adopted in state-of-the-art population synthesis models, motivating future careful treatment of this important process.
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