Are superflares on solar analogues caused by extra-solar planets?

Stellar flares with ${10^2-10^7}$ times more energy than the largest solar flare have been detected from 9 normal F and G main sequence stars (Schaefer, King & Deliyannis 1999). These superflares have durations of hours to days and are visible from at least x-ray to optical frequencies. The absence of world-spanning aurorae in historical records and of anomalous extinctions in the geological record indicate that our Sun likely does not suffer superflares. In seeking to explain this new phenomenon, we are struck by its similarity to large stellar flares on RS Canum Venaticorum binary systems, which are caused by magnetic reconnection events associated with the tangling of magnetic fields between the two stars. The superflare stars are certainly not of this class, although we propose a similar flare mechanism. That is, superflares are caused by magnetic reconnection between fields of the primary star and a close-in Jovian planet. Thus, by only invoking known planetary properties and reconnection scenarios, we can explain the energies, durations, and spectra of superflares, as well as explain why our Sun does not have such events.Comment: 13 pages, Accepted for publication in Ap

Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space

Astronomically, there are viable mechanisms for distributing organic material throughout the Milky Way. Biologically, the destructive effects of ultraviolet light and cosmic rays means that the majority of organisms arrive broken and dead on a new world. The likelihood of conventional forms of panspermia must therefore be considered low. However, the information content of dam-aged biological molecules might serve to seed new life (necropanspermia).Comment: Accepted for publication in Space Science Review

Piecing together the puzzle of NGC 5253: abundances, kinematics and WR stars

We present Gemini-S/GMOS-IFU optical spectroscopy of four regions near the centre of the nearby (3.8 Mpc) dwarf starburst galaxy NGC 5253. This galaxy is famous for hosting a radio supernebula containing two deeply embedded massive super star clusters, surrounded by a region of enhanced nitrogen abundance that has been linked to the presence of WR stars. We detected 11 distinct sources of red WR bump (CIV) emission over a 20" (~350 pc) area, each consistent with the presence of ~1 WCE-type star. WC stars are not found coincident with the supernebula, although WN stars have previously been detected here. We performed a multi-component decomposition of the H\alpha\ line across all four fields and mapped the kinematics of the narrow and broad (FWHM = 100-250 km/s) components. These maps paint a picture of localised gas flows, as part of multiple overlapping bubbles and filaments driven by the star clusters throughout the starburst. We confirm the presence of a strong H\alpha\ velocity gradient over ~4.5" (~80 pc) coincident with the region of N/O enhancement, and high gas density known from previous study, and interpret this as an accelerating ionized gas outflow from the supernebula clusters. We measure the ionized gas abundances in a number of regions in the outer IFU positions and combine these with measurements from the literature to assess the radial abundance distribution. We find that the O/H and N/H profiles are consistent with being flat. Only the central 50 pc exhibits the well-known N/O enhancement, and we propose that the unusually high densities/pressures in the supernebula region have acted to impede the escape of metal-enriched hot winds from the star clusters and allow them to mix with the cooler phases, thus allowing these freshly processed chemicals to be seen in the optical.Comment: 16 pages, accepted to A&

A Prediction Formula of Supersoft X-ray Phase of Classical Novae

On the basis of the recently developed universal decline law of classical novae, we propose prediction formulae for supersoft X-ray on and off times, i.e., t_{X-on} = (10 \pm 1.8) t_3 days and t_{X-off} = (5.3 \pm 1.4) (t_3)^{1.5} days for 8 < t_3 < 80 days. We have determined the absolute magnitude of our free-free emission model light curves and derived maximum magnitude vs. rate of decline (MMRD) relations. Our theoretical MMRD relations are governed by two parameters, one is the white dwarf (WD) mass and the other is the initial envelope mass at a nova outburst; this second parameter explains the scatter of MMRD points of individual novae. Our theoretical MMRD relations are also in good agreement with the well-known empirical formulae. We also show another empirical relation of M_V(15) ~ -5.7 \pm 0.3 based on the absolute magnitude of our model light curves, i.e., the absolute magnitude at 15 days after optical maximum is almost common among various novae. We analyzed ten nova light curves, in which a supersoft X-ray phase was detected, and estimated their WD masses. The models best reproducing simultaneously the optical and supersoft X-ray observations are ONeMg WDs with 1.28 \pm 0.04 M_\sun (V598 Pup), 1.23 \pm 0.05 M_\sun (V382 Vel), 1.15 \pm 0.06 M_\sun (V4743 Sgr), 1.13 \pm 0.06 M_\sun (V1281 Sco), 1.2 \pm 0.05 M_\sun (V597 Pup), 1.06 \pm 0.07 M_\sun (V1494 Aql), 1.04 \pm 0.07 M_\sun (V2467 Cyg), 1.07 \pm 0.07 M_\sun (V5116 Sgr), 1.05 \pm 0.05 M_\sun (V574 Pup), and a CO WD with 0.93 \pm 0.08 M_\sun (V458 Vul). The newly proposed relationships are consistent with the emergence or decay epoch of the supersoft X-ray phase of these ten novae. Finally, we discuss the mechanism of shock-origin hard X-ray component in relation to the emergence of companion star from the WD envelope.Comment: 36 pages, 29 figures, to appear in the Astrophysical Journa

"PAH" emission bands in selected planetary nebulae: a study of the behaviour with gas phase C/O ratio

Airborne and space-based low-resolution spectroscopy in the 1980s discovered tantalizing quantitative relationships between the gas phase C/O abundance ratio in planetary nebulae (PNe) and the fractions of total far-infrared luminosity radiated by the 7.7 and 11.3 micron bands (the C=C stretch and C-H bend, respectively), of polycyclic aromatic hydrocarbons. Only a very small sample of nebulae was studied in this context, limited by airborne observations of the 7.7 micron band, or the existence of adequate IRAS Low Resolution Spectrometer data for the 11.3 micron band. To investigate these trends further, we have expanded the sample of planetaries available for this study using Infrared Space Observatory (ISO) low-resolution spectra secured with the Short Wavelength Spectrometer (SWS) and the Long Wavelength Spectrometer (LWS). The new sample of 43 PNe, of which 17 are detected in PAH emission, addresses the range from C/O=0.2-13 with the objective of trying to delineate the pathways by which carbon dust grains might have formed in planetaries. For the 7.7-micron and 11.3- micron bands, we confirm that the ratio of band strength to total infrared luminosity is correlated with the nebular C/O ratio. Expressed in equivalent width terms, the cut-on C/O ratio for the 7.7-micron band is found to be 0.6(+0.2,-0.4), in good accord with that found from sensitive ground-based measurements of the 3.3-micron band too.Comment: 10 pages, LaTeX (mn2e.cls), incl. 5 PostScript (eps) figures and 3 tables. Accepted by MNRA

Circumcision for prevention against HIV: marked seasonal variation in demand and potential public sector readiness in Soweto, South Africa

The public sector delivery of male circumcision in the only public sector hospital in Soweto, South Africa was examined to gauge local capacity to deliver this procedure as an intervention for prevention of HIV acquisition. During the period from July 1998 to March 2006, approximately 360 procedures were performed per annum. Striking seasonal variations and the relatively few procedures performed may create challenges for program planning, if male circumcision is increased to a level required to have an impact on the incidence of HIV among this population

From Unpleasant to Unbearable - Why And How to Implement an Upper Limit to Pain And Other Forms of Suffering in Research with Animals

The focus of this paper is the requirement that the use of live animals in experiments and in vivo assays should never be allowed if those uses involve severe suffering. This requirement was first implemented in Danish legislation, was later adopted by the European Union, and has had limited uptake in North America. Animal suffering can arise from exposure to a wide range of different external and internal events that threaten biological or social functions, while the severity of suffering may be influenced by the animals’ perceptions of their own situation and the degree of control they are able to exert. Severe suffering is more than an incremental increase in negative state(s) but involves a qualitative shift whereby the normal mechanisms to contain or keep negative states at arm’s length no longer function. The result of severe suffering will be a loss of the ability of cope. The idea of putting a cap on severe suffering may be justified from multiple ethical perspectives. In most, if not all, cases it is possible to avoid imposing severe suffering on animals during experiments without giving up the potential benefits of finding new ways to cure, prevent, or alleviate serious human diseases and generate other important knowledge. From this it follows that there is a strong ethical case to favor a regulatory ban on animal experiments involving severe suffering

A Potential New Pathway for Staphylococcus aureus Dissemination: The Silent Survival of S. aureus Phagocytosed by Human Monocyte-Derived Macrophages

Although considered to be an extracellular pathogen, Staphylococcus aureus is able to invade a variety of mammalian, non-professional phagocytes and can also survive engulfment by professional phagocytes such as neutrophils and monocytes. In both of these cell types S. aureus promptly escapes from the endosomes/phagosomes and proliferates within the cytoplasm, which quickly leads to host cell death. In this report we show that S. aureus interacted with human monocyte-derived macrophages in a very different way to those of other mammalian cells. Upon phagocytosis by macrophages, S. aureus persisted intracellularly in vacuoles for 3–4 days before escaping into the cytoplasm and causing host cell lysis. Until the point of host cell lysis the infected macrophages showed no signs of apoptosis or necrosis and were functional. They were able to eliminate intracellular staphylococci if prestimulated with interferon-γ at concentrations equivalent to human therapeutic doses. S. aureus survival was dependent on the alternative sigma factor B as well as the global regulator agr, but not SarA. Furthermore, isogenic mutants deficient in α-toxin, the metalloprotease aureolysin, protein A, and sortase A were efficiently killed by macrophages upon phagocytosis, although with different kinetics. In particular α-toxin was a key effector molecule that was essential for S. aureus intracellular survival in macrophages. Together, our data indicate that the ability of S. aureus to survive phagocytosis by macrophages is determined by multiple virulence factors in a way that differs considerably from its interactions with other cell types. S. aureus persists inside macrophages for several days without affecting the viability of these mobile cells which may serve as vehicles for the dissemination of infection

A development study and randomised feasibility trial of a tailored intervention to improve activity and reduce falls in older adults with mild cognitive impairment and mild dementia

Background: People with dementia progressively lose abilities and are prone to falling. Exercise- and activity-based interventions hold the prospect of increasing abilities, reducing falls, and slowing decline in cognition. Current falls prevention approaches are poorly suited to people with dementia, however, and are of uncertain effectiveness. We used multiple sources, and a co-production approach, to develop a new intervention, which we will evaluate in a feasibility randomised controlled trial (RCT), with embedded adherence, process and economic analyses. Methods: We will recruit people with mild cognitive impairment or mild dementia from memory assessment clinics, and a family member or carer. We will randomise participants between a therapy programme with high intensity supervision over 12 months, a therapy programme with moderate intensity supervision over 3 months, and brief falls assessment and advice as a control intervention. The therapy programmes will be delivered at home by mental health specialist therapists and therapy assistants. We will measure activities of daily living, falls and a battery of intermediate and distal health status outcomes, including activity, balance, cognition, mood and quality of life. The main aim is to test recruitment and retention, intervention delivery, data collection and other trial processes in advance of a planned definitive RCT. We will also study motivation and adherence, and conduct a process evaluation to help understand why results occurred using mixed methods, including a qualitative interview study and scales measuring psychological, motivation and communication variables. We will undertake an economic study, including modelling of future impact and cost to end-of-life, and a social return on investment analysis. Discussion: In this study, we aim to better understand the practicalities of both intervention and research delivery, and to generate substantial new knowledge on motivation, adherence and the approach to economic analysis. This will enable us to refine a novel intervention to promote activity and safety after a diagnosis of dementia, which will be evaluated in a definitive randomised controlled trial.\ud Trial registration: ClinicalTrials.gov: NCT02874300; ISRCTN 10550694

The wide-field, multiplexed, spectroscopic facility WEAVE : survey design, overview, and simulated implementation

Funding for the WEAVE facility has been provided by UKRI STFC, the University of Oxford, NOVA, NWO, Instituto de Astrofísica de Canarias (IAC), the Isaac Newton Group partners (STFC, NWO, and Spain, led by the IAC), INAF, CNRS-INSU, the Observatoire de Paris, Région Île-de-France, CONCYT through INAOE, Konkoly Observatory (CSFK), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Lund University, the Leibniz Institute for Astrophysics Potsdam (AIP), the Swedish Research Council, the European Commission, and the University of Pennsylvania.WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20,000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ∼ 3 million stars and detailed abundances for ∼ 1.5 million brighter field and open-cluster stars; (ii) survey ∼ 0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey  ∼ 400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z 1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.PostprintPeer reviewe