ALMA observations of the supergiant B[e] star Wd1-9

Mass-loss in massive stars plays a critical role in their evolution, although the precise mechanism(s) responsible – radiatively driven winds, impulsive ejection and/or binary interaction – remain uncertain. In this Letter, we present Atacama Large Millimetre/Submillimeter Array line and continuum observations of the supergiant B[e] star Wd1-9, a massive post-main-sequence object located within the starburst cluster Westerlund 1 (Wd1). We find it to be one of the brightest stellar point sources in the sky at millimetre wavelengths, with (serendipitously identified) emission in the H41α radio recombination line. We attribute these properties to a low velocity (∼100 km s-1 ) ionized wind, with an extreme mass-loss rate ≳6.4 × 105(d/5 kpc)1.5 Mȯyr-1. External to this is an extended aspherical ejection nebula indicative of a prior phase of significant mass-loss. Taken together, the millimetre properties of Wd1-9 show a remarkable similarity to those of the highly luminous stellar source MWC349A. We conclude that these objects are interacting binaries evolving away from the main sequence and undergoing rapid case-A mass transfer. As such they – and by extension the wider class of supergiant B[e] stars – may provide a unique window into the physics of a process that shapes the life-cycle of ∼70 per cent of massive stars found in binary systems

Non-thermal radio emission from O-type stars III. Is Cyg OB2 No. 9 a wind-colliding binary?

The star Cyg OB2 No. 9 is a well-known non-thermal radio emitter. Recent theoretical work suggests that all such O-stars should be in a binary or a multiple system. However, there is no spectroscopic evidence of a binary component. Re-analysis of radio observations from the VLA of this system over 25 years has revealed that the non-thermal emission varies with a period of 2.35+-0.02 yr. This is interpreted as a strong suggestion of a binary system, with the non-thermal emission arising in a wind-collision region. We derived some preliminary orbital parameters for this putative binary and revised the mass-loss rate of the primary star downward from previous estimates.Comment: 13 pages, 5 figures, includes online data, accepted by A&

Can single O stars produce non-thermal radio emission?

We present a model for the non-thermal radio emission from presumably single O stars, in terms of synchrotron emission from relativistic electrons accelerated in wind-embedded shocks. These shocks are associated with an unstable, chaotic wind. The main improvement with respect to earlier models is the inclusion of the radial dependence of the shock velocity jump and compression ratio, based on 1D hydrodynamical simulations. The decrease of the velocity jump and the compression ratio as a function of radius produces a rapidly decreasing synchrotron emissivity. This effectively prohibits the models from reproducing the spectral shape of the observed non-thermal radio emission. We investigate a number of "escape routes" by which the hydrodynamical predictions might be reconciled with the radio observations. Although these escape routes reproduce the observed spectral shape, none of these escape routes are physically plausible. In particular, re-acceleration by feeding an electron distribution through a number of shocks, is in contradiction with current hydrodynamical simulations. These hydrodynamical simulations have their limitations, most notably the use of 1D. At present, it is not feasible to perform 2D simulations of the wind out to the distances required for synchrotron-emission models. Based on the current hydrodynamic models, we suspect that the observed non-thermal radio emission from O stars cannot be explained by wind-embedded shocks associated with the instability of the line-driving mechanism. The most likely alternative mechanism is synchrotron emission from colliding winds. That would imply that all O stars with non-thermal radio emission should be members of binary or multiple systems.Comment: 10 pages, 8 figures, accepted for publication by A&

Enset‐based agricultural systems in Ethiopia: A systematic review of production trends, agronomy, processing and the wider food security applications of a neglected banana relative

Enset (Ensete ventricosum (Welw.) Cheesman) is the major starch staple of the Ethiopian Highlands, where its unique attributes enhance the food security of approximately 20 million people and have earned it the title “The Tree Against Hunger”. Yet enset‐based agriculture is virtually unknown outside of its narrow zone of cultivation, despite growing wild across much of East and Southern Africa. Here, we review historical production data to show that the area of land under enset production in Ethiopia has reportedly increased 46% in two decades, whilst yield increased 12‐fold over the same period, making enset the second most produced crop species in Ethiopia—though we critically evaluate potential issues with these data. Furthermore, we address a major challenge in the development and wider cultivation of enset, by reviewing and synthesizing the complex and fragmented agronomic and ethnobotanic knowledge associated with this species; including farming systems, processing methods, products, medicinal uses and cultural importance. Finally, we provide a framework to improve the quality, consistency and comparability of data collected across culturally diverse enset‐based agricultural systems to enhanced sustainable use of this neglected starch staple. In conclusion, we discuss the challenges and opportunities for enset cultivation beyond its restricted distribution, and the regional food security potential it could afford smallholders elsewhere in Southern and East Africa

Musa germplasm diversity status across a wide range of agro-ecological zones in Rwanda

Objectives: This study assessed the on-farm Musa germplasm diversity across different agro-ecologies of Rwanda and the socio-economic utilization options and selection practices that create/maintain this diversity on-farm.Methodology and results: A Musa germplasm diagnostic survey was carried out in 2007 in five Rwandan districts on a transect from Lake Kivu (West) to Kirehe district (East) bordering Tanzania. Across all sites, 118 farms, each having at least 50 mats were sampled for determining Musa diversity. Forty three Musa cultivars were recorded across the five districts. Higher diversity was observed in the east declining westwards to the Lake Kivu region as reflected by the number of cultivars and their relative abundance. Nearly half of the recorded cultivars had a low diversity index (Gini-Simpson 1-D < 0.2) and therefore prone to genetic erosion. Cooking cultivars only dominate in the district of Kirehe, while beer cultivars dominate the banana production landscape in the other districts. Taste/flavor, bunch size and market demand were the most important criteria for banana cultivar selection and thus greatly influenced cultivar conservation and distribution on-farm. Diseases such as Fusarium wilt and Xanthomonas wilt greatly contributed to genetic erosion.Conclusion and application of results: Musa cultivar diversity in Rwanda is under threat. Ex-situ conservation of the menaced cultivars is of crucial importance. Beer cultivars dominated the landscape. Cultivar diversity on-farm was influenced by the prevailing altitude; taste/flavor, bunch size, and market demand of the cultivars; and their susceptibility to diseases especially Fusarium and Xanthomonas wilt. Banana breeding or adaptation strategies therefore should take into account the farmer preferred traits. In addition, strategies for managing these diseases are critical for preventing the genetic erosion of the affected cultivars.Keywords: cultivar evenness, cultivar richness, diversity index, genetic erosio

Modular Air-Coupled Ultrasonic Multichannel System for Inline NDT

AbstractIn many production processes it is important to detect in a very early stage basic errors in the fabricatedmaterial. If the errors are not visible from the exterior, ultrasonic inspection is a convenient technique,at least if the nature of the error influences the characteristics of sound passing through the material.Examples are local density variations in non-wovens, delaminations in composites, bad bondings inlaminates, inclusions, cracks or other artefacts in plastic or metal plates, etc. There are two major,difficult requirements imposed by industry to the used detection technique: the sensors shouldn’t makephysical contact with the material and the speed of testing must be sufficiently high to enable testingin-line. The former requirement can be met by employing an air-coupled ultrasonic approach, the latterby using a multichannel system.We propose a modular air-coupled ultrasonic multichannel system.Each multichannel module contains12 air-coupled transducers and exists in a transmitter and a receiver version. The desired scan width isobtained by connecting several modules to each other. During the scanning all transducers are spatially fixed while the material is moving forward. This way, speeds up to 1m/s are possible, irrespective ofthe width of the material. To that purpose a FPGA based platform with parallel processing of largenumbers of data streams is implemented in the modules. This allows the implementation of all kind ofprocedures, going from point measurements to more sophisticated techniques.In spite of all measurements being performed in ambient air, the ultrasonic frequency is rather high(1MHz), but lower frequencies are possible as well. The most obvious set-up of the modules is a through-transmission configuration. However the system can also be used in a pitch-catch configuration which isvery suitable for one-sided testing of thick materials. An examples established in the laboratory is shownto illustrate the performance

Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD\168112 (O5.5III(f^+))

We report the results of a multiwavelength study of the non-thermal radio emitter HD168112 (O5.5III(f^+)). The detailed analysis of two quasi-simultaneous XMM-Newton and VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decrease of the X-ray flux of ~30%. The radio emission on the other hand increases by a factor 5-7 between the two observations obtained roughly simultaneously with the XMM-Newton pointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT ~2-3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD168112 is indeed a binary, it must be seen under a fairly low inclination.Comment: 17 pages, 11 figures (10 postscript + 1 gif

Can the timely removal of outer symptomatic leaves of enset plants following a tool-mediated infection with Xanthomonas vasicola pv. musacearum lead to recovery?

Xanthomonas wilt (XW) of enset is a major biotic constraint to enset cultivation in Ethiopia. Three enset cultivars, namely, ‘Mazia’ (tolerant), ‘Arkiya’ (susceptible) and ‘Kelisa’ (susceptible) were inoculated with Xanthomonas vasicola pv. musacearum (Xvm), the causal agent of XW at Hosanna (2,177 m a.s.l.) in Southern Ethiopia. The treatments included inoculation of one or three outer leaves, and subsequent removal or non-removal of symptomatic leaves and leaf sheaths. This study explored the potential effect of singly removing symptomatic outer enset leaves on the recovery of enset plants from XW disease. Removal of symptomatic outer leaves was postulated to remove a large percentage of inoculum from a plant, thus preventing further symptom development on more inner/adjacent/younger leaves, eventually leading to the recovery of infected enset plants. The ‘Mazia’ enset cultivar was tolerant as it recovered fully irrespective of the number of leaves inoculated and whether single symptomatic leaves were removed or not. Singly removing symptomatic leaves in this tolerant enset cultivar however significantly hastened the recovery of the plants by approximately two months. This practice could thus be promoted for hastening the recovery of tolerant enset cultivars. For the susceptible cultivars ‘Arkiya’ and ‘Kelisa’, leaf removal only improved recovery when single leaves were inoculated. However, infection levels still remained high by the close of the experiment, suggesting that the practice may not be suitable in the susceptible cultivars. This study was conducted on young enset plants; cutting symptomatic leaves on susceptible but more mature plants could be explored. For the tolerant cultivars, the practice needs validation through studies on a wider range of cultivars