Wolf-Rayet spin at low metallicity and its implication for Black Hole formation channels

ArticleThis is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Context. The spin of Wolf-Rayet (WR) stars at low metallicity (Z) is most relevant for our understanding of gravitational wave sources such as GW150914, as well as the incidence of long-duration gamma-ray bursts (GRBs). Two scenarios have been suggested for both phenomena: one of them involves rapid rotation and quasi-chemical homogeneous evolution (CHE), the other invokes classical evolution through mass loss in single and binary systems. Aims. The stellar spin of Wolf-Rayet stars might enable us to test these two scenarios. In order to obtain empirical constraints on black hole progenitor spin we infer wind asymmetries in all 12 known WR stars in the Small Magellanic Cloud (SMC) at Z = 1/5Z⊙, as well as within a significantly enlarged sample of single and binary WR stars in the Large Magellanic Cloud (LMC at Z = 1/2Z⊙), tripling the sample of Vink (2007). This brings the total LMC sample to 39, making it appropriate for comparison to the Galactic sample. Methods. We measure WR wind asymmetries with VLT-FORS linear spectropolarimetry, a tool uniquely poised to perform such tasks in extragalactic environments. Results. We report the detection of new line effects in the LMC WN star BAT99-43 and the WC star BAT99-70, as well as the famous WR/LBV HD5980 in the SMC, which might be evolving chemically homogeneously. With the previous reported line effects in the late-type WNL (Ofpe/WN9) objects BAT99-22 and BAT99-33, this brings the total LMCWR sample to 4, i.e. a frequency of ∼10%. Perhaps surprisingly, the incidence of line effects amongst low Z WR stars is not found to be any higher than amongst the Galactic WR sample, challenging the rotationally-induced CHE model. Conclusions. AsWR mass loss is likely Z-dependent, our Magellanic Cloud line-effectWR stars may maintain their surface rotation and fulfill the basic conditions for producing long GRBs, both via the classical post-red supergiant (RSG) or luminous blue variable (LBV) channel, as well as resulting from CHE due to physics specific to very massive stars (VMS).We would like to thank the anonymous referee for their constructive comments. This research made use of the SIMBAD database, operated at CDS, Strasbourg, France. JSV is funded by the Northern Ireland Department of Communities (DfC). TJH was funded by ST/M0012174/1

Massive star feedback in clusters: variation of the FUV interstellar radiation field in time and space (article)

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.1803We investigate radiative feedback from a 34 M star in a 104 M turbulent cloud using threedimensional radiation-hydrodynamics (RHD) models. We use Monte Carlo radiative transfer to accurately compute photoionization equilibrium and radiation pressure, with multiple atomic species and silicate dust grains. We include the diffuse radiation field, dust absorption/reemission, and scattering. The cloud is efficiently dispersed, with 75 per cent of the mass leaving the (32.3 pc) 3 grid within 4.3 Myr (1.1 htffi). This compares to all mass exiting within 1.6 Myr (0.74 htffi) in our previously published 103 M cloud. At most 20 per cent of the mass is ionized, compared to 40 per cent in the lower mass model, despite the ionized volume fraction being 80 per cent in both, implying the higher mass cloud is more resilient to feedback. The total Jeans-unstable mass increases linearly up to 1500 M before plateauing after 2 Myr, corresponding to a core formation efficiency of 15 per cent. We also measure the time-variation of the far-ultraviolet (FUV) radiation field, G0, impinging on other cluster members, taking into account for the first time how this changes in a dynamic cluster environment with intervening opacity sources and stellar motions. Many objects remain shielded in the first 0.5 Myr whilst the massive star is embedded, after which G0 increases by orders of magnitude. Gas motions later on cause comparable drops which happen instantaneously and last for ∼ 1 Myr before being restored. This highly variable UV field will influence the photoevaporation of protoplanetary discs near massive stars.Science and Technology Facilities Counci

Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer II. The formation of a 25 solar-mass star

This is the author accepted manuscript. The final version is available from OUP via the DOI in this record.We present a numerical simulation of the formation of a massive star using Monte- Carlo-based radiation hydrodynamics (RHD). The star forms via stochastic disc ac- cretion and produces fast, radiation-driven bipolar cavities. We nd that the evolution of the infall rate (considered to be the mass ux across a 1500 au spherical boundary), and the accretion rate onto the protostar, are broadly consistent with observational constraints. After 35 kyr the star has a mass of 25M and is surrounded by a disc of mass 7 M and 1500 au radius, and we nd that the velocity eld of the disc is close to Keplerian. Once again these results are consistent with those from recent high-resolution studies of discs around forming massive stars. Synthetic imaging of the RHD model shows good agreement with observations in the near- and far-IR, but may be in con ict with observations that suggests that MYSOs are typically circularly symmetric on the sky at 24.5 m. Molecular line simulations of a CH3CN transition compare well with observations in terms of surface brightness and line width, and indicate that it should be possible to reliably extract the protostellar mass from such observations.The calculations for this paper were performed on the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital fund of BIS, and the University of Exeter, and on the Complexity DiRAC Facility jointly funded by STFC and the Large Facilities Capital Fund of BIS. TJH and TAD acknowledge funding from Exeter's STFC Consolidated Grant (ST/M00127X/1). We thank Takashi Hosokawa for kindly providing us with the protostellar evolutionary model. We are grateful to Maite Beltran for providing the data for Figure 4, and we thank Dave Acreman, John Ilee and Tom Haworth for useful discussions. We thank the anonymous referee for a helpful report

Ten eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance

This is the author accepted manuscript. The final version is available from OUP via the DOI in this record.We present the first results of an observational programme to measure the fundamental parameters of over 100 eclipsing binaries in the Small Magellanic Cloud (SMC). The spectroscopic data have been obtained by using the two degree field (2dF) multi-object spectrograph on the 3.9-m Anglo-Australian Telescope, and have been used in conjunction with photometry from the Optical Gravitational Lensing Experiment (OGLE) data base of SMC eclipsing binaries. In this first paper, we discuss 10 systems: three are detached early-B binaries, six are in a semi-detached configuration, and one is in a marginal contact state. We conclude that the semi-detached systems are undergoing the slow mass-transfer phase of case-A binary evolution, in which the mass donor has reached its Roche lobe while still on the main sequence. Each system provides a primary distance indicator. By constructing a new calibration between spectral type and temperature for O and early B stars, we find a mean distance modulus to the SMC of 18.89±0.04 (statistical) ±0.10 (systematic). This value represents one of the most precise determinations to date of the distance to the SMC

Synthetic molecular line observations of the first hydrostatic core from chemical calculations

This is the final version. Available from OUP via the DOI in this recordThe first stable object to develop in the low-mass star formation process has long been predicted to be the first hydrostatic core (FHSC). Despite much effort, it has still yet to be definitively observed in nature. More specific observational signatures are required to enable observers to distinguish the FHSC from young, faint, but more evolved protostars. Here we present synthetic spectral line observations for CO, SO, CS and HCO$^+$ that were calculated from radiation (magneto)hydrodynamical models, chemical modelling and Monte Carlo radiative transfer. HCO$^+$ $(1-0)$ and SO $(8_7 - 7_6)$ spectra of the FHSC show variations for observations at a low inclination which may allow a candidate FHSC to be distinguished from a more evolved object. We find that the FHSC outflow is unlikely to be detectable with ALMA, which would discount the observed sources with slow outflows that are currently identified as candidate FHSCs. We compare the results of simulated ALMA observations with observed candidate FHSCs and recommend Oph A SM1N and N6-mm as the most promising candidates to follow up.European Commissio

Monte Carlo simulations of heat deposition during photothermal skin cancer therapy using nanoparticles

This is the final version. Available from the publisher via the DOI in this record.Photothermal therapy using nanoparticles is a promising new approach for the treatment of cancer. The principle is to utilise plasmonic nanoparticle light interaction for efficient heat conversion. However, there are many hurdles to overcome before it can be accepted in clinical practice. One issue is a current poor characterization of the thermal dose that is distributed over the tumour region and the surrounding normal tissue. Here, we use Monte Carlo simulations of photon radiative transfer through tissue and subsequent heat diffusion calculations, to model the spatial thermal dose in a skin cancer model. We validate our heat rise simulations against experimental data from the literature and estimate the concentration of nanorods in the tumor that are associated with the heat rise. We use the cumulative equivalent minutes at 43 °C (CEM43) metric to analyse the percentage cell kill across the tumour and the surrounding normal tissue. Overall, we show that computer simulations of photothermal therapy are an invaluable tool to fully characterize thermal dose within tumour and normal tissue.Wellcome TrustScience and Technology Facilities Council (STFC

Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph

From observations collected with the ESPaDOnS spectropolarimeter, we report the discovery of magnetic fields at the surface of the mildly accreting classical T Tauri star V2129 Oph. Zeeman signatures are detected, both in photospheric lines and in the emission lines formed at the base of the accretion funnels linking the disc to the protostar, and monitored over the whole rotation cycle of V2129 Oph. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized line profiles. We reconstruct the large-scale magnetic topology at the surface of V2129 Oph from both sets of Zeeman signatures simultaneously. We find it to be rather complex, with a dominant octupolar component and a weak dipole of strengths 1.2 and 0.35 kG, respectively, both slightly tilted with respect to the rotation axis. The large-scale field is anchored in a pair of 2-kG unipolar radial field spots located at high latitudes and coinciding with cool dark polar spots at photospheric level. This large-scale field geometry is unusually complex compared to those of non-accreting cool active subgiants with moderate rotation rates. As an illustration, we provide a first attempt at modelling the magnetospheric topology and accretion funnels of V2129 Oph using field extrapolation. We find that the magnetosphere of V2129 Oph must extend to about 7R* to ensure that the footpoints of accretion funnels coincide with the high-latitude accretion spots on the stellar surface. It suggests that the stellar magnetic field succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of V2129 Oph. The magnetospheric geometry we derive produces X-ray coronal fluxes typical of those observed in cTTSs.Comment: MNRAS, in press (18 pages, 17 figures

Circumstellar environment of RX Puppis

The symbiotic Mira, RX Pup, shows long-term variations in its mean light level due to variable obscuration by circumstellar dust. The last increase in extinction towards the Mira, between 1995 and 2000, has been accompanied by large changes in the degree of polarization in the optical and red spectral range. The lack of any obvious associated changes in the position angle may indicate the polarization variations are driven by changes in the properties of the dust grains (e.g. variable quantity of dust and variable particle size distribution, due to dust grain formation and growth) rather than changes in the viewing geometry of the scattering region(s), e.g. due to the binary rotation.Comment: Paper presented at Torun 2000 conference on Post-AGB objects as a phase of stellar evolution; 8 pages, 3 figure

A role for SPARC in the moderation of human insulin secretion.

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tAIMS/HYPOTHESIS: We have previously shown the implication of the multifunctional protein SPARC (Secreted protein acidic and rich in cysteine)/osteonectin in insulin resistance but potential effects on beta-cell function have not been assessed. We therefore aimed to characterise the effect of SPARC on beta-cell function and features of diabetes. METHODS: We measured SPARC expression by qRT-PCR in human primary pancreatic islets, adipose tissue, liver and muscle. We then examined the relation of SPARC with glucose stimulated insulin secretion (GSIS) in primary human islets and the effect of SPARC overexpression on GSIS in beta cell lines. RESULTS: SPARC was expressed at measurable levels in human islets, adipose tissue, liver and skeletal muscle, and demonstrated reduced expression in primary islets from subjects with diabetes compared with controls (p< = 0.05). SPARC levels were positively correlated with GSIS in islets from control donors (p< = 0.01). Overexpression of SPARC in cultured beta-cells resulted in a 2.4-fold increase in insulin secretion in high glucose conditions (p< = 0.01). CONCLUSIONS: Our data suggest that levels of SPARC are reduced in islets from donors with diabetes and that it has a role in insulin secretion, an effect which appears independent of SPARC's modulation of obesity-induced insulin resistance in adipose tissue.Diabetes Research Wellness Foundatio