Modelling the circumstellar medium in RS Ophiuchi and its link to Type Ia supernovae

Recent interpretations of narrow, variable absorption lines detected in some Type Ia supernovae suggest that their progenitors are surrounded by dense, circumstellar material. Similar variations detected in the symbiotic recurrent nova system RS Oph, which undergoes thermonuclear outbursts every ~20 years, making it an ideal candidate to investigate the origin of these lines. To this end, we present simulations of multiple mass transfer-nova cycles in RS Oph. We find that the quiescent mass transfer produces a dense, equatorial outflow, i.e., concentrated towards the binary orbital plane, and an accretion disc forms around the white dwarf. The interaction of a spherical nova outburst with these aspherical circumstellar structures produces a bipolar outflow, similar to that seen in HST imaging of the 2006 outburst. In order to produce an ionization structure that is consistent with observations, a mass-loss rate of $5 \times 10^{-7}\,\mathrm{M}_{\odot}\,\mathrm{yr}^{-1}$ from the red giant is required. The simulations also produce a polar accretion flow, which may explain the broad wings of the quiescent H {\alpha} line and hard X-rays. By comparing simulated absorption line profiles to observations of the 2006 outburst, we are able to determine which components arise in the wind and which are due to the novae. We explore the possible behaviour of absorption line profiles as they may appear should a supernova occur in a system like RS Oph. Our models show similarities to supernovae like SN 2006X, but require a high mass-loss rate, $\dot{M} \sim 10^{-6}$ to $10^{-5}\,\mathrm{M_\odot}\,\mathrm{yr}^{-1}$, to explain the variability in SN 2006X

Evolution of Our Understanding of XIAP Deficiency

X-linked inhibitor of apoptosis (XIAP) deficiency is a rare inborn error of immunity first described in 2006. XIAP deficiency is characterised by immune dysregulation and a broad spectrum of clinical manifestations, including haemophagocytic lymphohistiocytosis (HLH), inflammatory bowel disease (IBD), hypogammaglobulinemia, susceptibility to infections, splenomegaly, cytopaenias, and other less common autoinflammatory phenomena. Since the first description of the disease, many XIAP deficient patients have been identified and our understanding of the disease has grown. Over 90 disease causing mutations have been described and more inflammatory disease manifestations, such as hepatitis, arthritis, and uveitis, are now well-recognised. Recently, following the introduction of reduced intensity conditioning (RIC), outcomes of allogeneic haematopoietic stem cell transplantation (HSCT), the only curative treatment option for XIAP deficiency, have improved. The pathophysiology of XIAP deficiency is not fully understood, however it is known that XIAP plays a role in both the innate and adaptive immune response and in immune regulation, most notably through modulation of tumour necrosis factor (TNF)-receptor signalling and regulation of NLRP3 inflammasome activity. In this review we will provide an up to date overview of both the clinical aspects and pathophysiology of XIAP deficiency

Smoothed particle hydrodynamics simulations of gas and dust mixtures

We present a 'two-fluid' implementation of dust in smoothed particle hydrodynamics (SPH) in the test particle limit. The scheme is able to handle both short and long stopping times and reproduces the short friction time limit, which is not properly handled in other implementations. We apply novel tests to verify its accuracy and limitations, including multi-dimensional tests that have not been previously applied to the drag-coupled dust problem and which are particularly relevant to self-gravitating protoplanetary discs. Our tests demonstrate several key requirements for accurate simulations of gas-dust mixtures. Firstly, in standard SPH particle jitter can degrade the dust solution, even when the gas density is well reproduced. The use of integral gradients, a Wendland kernel and a large number of neighbours can control this, albeit at a greater computational cost. Secondly, when it is necessary to limit the artificial viscosity we recommend using the Cullen & Dehnen (2010) switch, since the alternative, using ${\alpha} \sim 0.1$, can generate a large velocity noise up to ${{\sigma}_v} \lesssim 0.3 c_s$ in the dust particles. Thirdly, we find that an accurate dust density estimate requires $>400$ neighbours, since, unlike the gas, the dust particles do not feel regularization forces. This density noise applies to all particle-based two-fluid implementations of dust, irrespective of the hydro solver and could lead to numerically induced fragmentation. Although our tests show accurate dusty gas simulations are possible, care must be taken to minimize the contribution from numerical noise

A dusty origin for the correlation between protoplanetary disc accretion rates and dust masses

ABSTRACT Recent observations have uncovered a correlation between the accretion rates (measured from the UV continuum excess) of protoplanetary discs and their masses inferred from observations of the submm continuum. While viscous evolution models predict such a correlation, the predicted values are in tension with data obtained from the Lupus and Upper Scorpius star-forming regions; for example, they underpredict the scatter in accretion rates, particularly in older regions. Here, we argue that since the submm observations trace the discs’ dust, by explicitly modelling the dust grain growth, evolution, and emission, we can better understand the correlation. We show that for turbulent viscosities with α ≲ 10−3, the depletion of dust from the disc due to radial drift means we can reproduce the range of masses and accretion rates seen in the Lupus and Upper Sco data sets. One consequence of this model is that the upper locus of accretion rates at a given dust mass does not evolve with the age of the region. Moreover, we find that internal photoevaporation is necessary to produce the lowest accretion rates observed. In order to replicate the correct dust masses at the time of disc dispersal, we favour relatively low photoevaporation rates ≲ 10−9 M⊙ yr−1 for most sources but cannot discriminate between EUV or X-ray-driven winds. A limited number of sources, particularly in Lupus, are shown to have higher masses than predicted by our models which may be evidence for variations in the properties of the dust or dust trapping induced in substructures.</jats:p

Evidence of a past disc-disc encounter: HV and DO Tau

© 2018 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society. Theory and observations suggest that star formation occurs hierarchically due to the fragmentation of giant molecular clouds. In this case we would expect substructure and enhanced stellar multiplicity in the primordial cluster. This substructure is expected to decay quickly in most environments, however historic stellar encounters might leave imprints in a protoplanetary disc (PPD) population. In a low-density environment such as Taurus, tidal tails from violent star-disc or disc-disc encounters might be preserved over timescales sufficient to be observed. In this work, we investigate the possibility that just such an event occurred between HV Tau C (itself a component of a triple system) and DO Tau ~0.1 Myr ago, as evidenced by an apparent 'bridge' structure evident in the 160 μ m emission. By modelling the encounter using smoothed particle hydrodynamics (SPH) we reproduce the main features of the observed extended structure ('V'-shaped emission pointing west of HV Tau and a tail-like structure extending east of DO Tau). We suggest that HV Tau and DO Tau formed together in a quadruple system on a scale of ~5000 au (0.025 pc)

Slope, grain size, and roughness controls on dry sediment transport and storage on steep hillslopes

Existing hillslope sediment transport models developed for low-relief, soil-mantled landscapes are poorly suited to explain the coupling between steep rocky hillslopes and headwater channels. Here we address this knowledge gap using a series of field and numerical experiments to inform a particle-based model of sediment transport by dry ravel—a mechanism of granular transport characteristic of steep hillslopes. We find that particle travel distance increases as a function of the ratio of particle diameter to fine-scale (1 m) topographic variability associated with rocky landscapes. Applying a 2-D dry-ravel-routing model to lidar-derived surface topography, we show how spatial patterns of local and nonlocal transport control connectivity between hillslopes and steep headwater channels that generate debris flows through failure of ravel-filled channels following wildfire. Our results corroborate field observations of a patchy transition from soil-mantled to bedrock landscapes and suggest that there is a dynamic interplay between sediment storage, roughness, grain sorting, and transport even on hillslopes that well exceed the angle of repose

The influence of vegetation on the ITCZ and South Asian monsoon in HadCM3

The role of global vegetation on the large-scale tropical circulation is examined in the version 3 Hadley Centre climate model (HadCM3). Alternative representations of global vegetation cover from observations and a dynamic global vegetation model (DGVM) were used as the landcover component for a number of HadCM3 experiments under a nominal present day climate state, and compared to the simulations using the standard land cover map of HadCM3. The alternative vegetation covers result in a large scale cooling of the Northern Hemisphere extra-tropics relative to the HadCM3 standard, resulting in a southward shift in the location of the inter-tropical convergence zone (ITCZ). A significant reduction in Indian monsoon precipitation is also found, which is related to a weakening of the South Asian monsoon circulation, broadly consistent with documented mechanisms relating to temperature and snow perturbations in the Northern Hemisphere extra-tropics in winter and spring, delaying the onset of the monsoon. The role of the Northern Hemisphere extra-tropics on tropical climate is demonstrated, with an additional representation of vegetation cover based on DGVM simulated changes in Northern Hemisphere vegetation from the end of the 21st Century. This experiment shows that through similar processes the simulated extra-tropical vegetation changes in the future contribute to a strengthening of the South Asian monsoon in this model. These findings provide renewed motivation to give careful consideration to the role of global scale vegetation feedbacks when looking at climate change, and its impact on the tropical circulation and South Asian monsoon in the latest generation of Earth System models

A super-resolution analysis of the DSHARP survey: Substructure is common in the inner 30 au

The DSHARP survey evidenced the ubiquity of substructure in the mm dust distribution of large, bright protoplanetary discs. Intriguingly, these datasets have yet higher resolution information that is not recovered in a CLEAN image. We first show that the intrinsic performance of the CLEAN algorithm is resolution-limited. Then analyzing all 20 DSHARP sources using the 1D, super-resolution code Frankenstein (frank), we accurately fit the 1D visibilities to a mean factor of 4.3 longer baseline than the Fourier transform of the CLEAN images and a factor of 3.0 longer baseline than the transform of the CLEAN component models. This yields a higher resolution brightness profile for each source, identifying new substructure interior to 30 au in multiple discs; resolving known gaps to be deeper, wider, and more structured; and known rings to be narrower and brighter. Across the survey, high contrast gaps are an average 14% wider and 44% deeper in the frank profiles relative to CLEAN, and high contrast rings are an average 26% narrower. Categorizing the frank brightness profiles into trends, we find that the relative scarcity of features interior to 30 au in the survey's CLEAN images is an artifact of resolving power, rather than an intrinsic rarity of inner disc (or compact disc) substructure. Finally the rings in the frank profiles are narrower than the previously inferred deconvolved widths, indicating smaller alpha / St ratios in the local gas disc

Assessment of best single sample for finding chlamydia in women with and without symptoms: a diagnostic test study

Objective: to compare vulvovaginal swabs with endocervical swabs as optimal diagnostic sample for detection of Chlamydia trachomatis infection. Design: a diagnostic test study. Setting: an urban sexual health centre. Participants: 3973 women aged ≥16 years requesting testing for sexually transmitted infections. Interventions: participants took a vulvovaginal swab before routine examination, and clinicians took an endocervical swab during examination. Main outcome measure: diagnosis of chlamydia infection with samples analysed using the Aptima Combo-2 assay; positive results confirmed with the Aptima CT assay. Results: of the 3973 participants, 410 (10.3%) were infected with C trachomatis. Infected women were significantly younger (22 v 25 years, P<0.0001) and more likely to have symptoms suggestive of a bacterial sexually transmitted infection (53% v 41%, odds ratio 1.63 (95% CI 1.30 to 2.04)), be a contact of someone with a sexually transmitted infection (25% v 5%, odds ratio 6.18 (4.61 to 8.30)), clinically diagnosed with cervicitis (17% v 4%, odds ratio 4.92 (3.50 to 6.91)), and have pelvic inflammatory disease (9% v 3%, odds ratio 2.85 (1.87 to 4.33)). When women co-infected with gonorrhoea were included in the analysis, there was an association with mixed ethnicity (10% v 7%, odds ratio 1.53 (1.07 to 2.17)); but when those with gonorrhoea were removed, women of white ethnicity were significantly more likely to have chlamydia (85% v 80%, odds ratio 1.40 (1.03 to 1.91)). On analysis of complete paired results, vulvovaginal swabs were significantly more sensitive than endocervical swabs (97% (95% CI 95% to 98%) v 88% (85% to 91%), P<0.00001); corresponding specificities were 99.9% and 100%. In women with symptoms suggestive of a bacterial sexually transmitted infection, vulvovaginal swabs were significantly more sensitive than endocervical swabs (97% (93% to 98%) v 88% (83% to 92%), P=0.0008), as they were in women without symptoms (97% (94% to 99%) v 89% (84% to 93%), P=0.002). Conclusions: vulvovaginal swabs are significantly better than endocervical swabs at detecting chlamydia in women with and without symptoms suggestive of sexually transmitted infections. In those with symptoms, using endocervical samples rather than vulvovaginal swabs would have missed 9% of infections, or 1 in every 11 cases of chlamydia

The origin of the eccentricity of the hot Jupiter in CI Tau

Following the recent discovery of the first radial velocity planet in a star still possessing a protoplanetary disc (CI Tau), we examine the origin of the planet's eccentricity (e $\sim 0.3$). We show through long timescale ($10^5$ orbits) simulations that the planetary eccentricity can be pumped by the disc, even when its local surface density is well below the threshold previously derived from short timescale integrations. We show that the disc may be able to excite the planet's orbital eccentricity in $<$ a Myr for the system parameters of CI Tau. We also perform two planet scattering experiments and show that alternatively the observed planet may plausibly have acquired its eccentricity through dynamical scattering of a migrating lower mass planet, which has either been ejected from the system or swallowed by the central star. In the latter case the present location and eccentricity of the observed planet can be recovered if it was previously stalled within the disc's magnetospheric cavity.This work has been supported by the DISCSIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG, and from STFC through grant ST/L000636/1. This work used the DIRAC Shared Memory Processing and Data Analytic systems, both at the University of Cambridge and operated, respectively, by the COSMOS Project at the Department of Applied Mathematics and Theoretical Physics and the Cambridge High Performance Computing Service, on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk). This equipment was funded by BIS National E-infrastructure capital grants ST/J005673/1 and ST/K001590/1, STFC capital grants ST/H008586/1, ST/H008861/1 and ST/H00887X/1, STFC DiRAC Operations grant ST/K00333X/1, and STFC DiRAC Operations grant ST/K00333X/1. DiRAC is part of the National E-Infrastructure.This is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/mnrasl/slw18