The 2.35 year itch of Cyg OB2 #9. II. Radio monitoring

Cyg OB2 #9 is one of a small set of non-thermal radio emitting massive O-star binaries. The non-thermal radiation is due to synchrotron emission in the colliding-wind region. Cyg OB2 #9 was only recently discovered to be a binary system and a multi-wavelength campaign was organized to study its 2011 periastron passage. We report here on the results of the radio observations obtained in this monitoring campaign. We used the Expanded Very Large Array (EVLA) radio interferometer to obtain 6 and 20 cm continuum fluxes. The observed radio light curve shows a steep drop in flux sometime before periastron. The fluxes drop to a level that is comparable to the expected free-free emission from the stellar winds, suggesting that the non-thermal emitting region is completely hidden at that time. After periastron passage, the fluxes slowly increase. We introduce a simple model to solve the radiative transfer in the stellar winds and the colliding-wind region, and thus determine the expected behaviour of the radio light curve. From the asymmetry of the light curve, we show that the primary has the stronger wind. This is somewhat unexpected if we use the astrophysical parameters based on theoretical calibrations. But it becomes entirely feasible if we take into account that a given spectral type - luminosity class combination covers a range of astrophysical parameters. The colliding-wind region also contributes to the free-free emission, which can help to explain the high values of the spectral index seen after periastron passage. Combining our data with older Very Large Array (VLA) data allows us to derive a period P = 860.0 +- 3.7 days for this system. With this period, we update the orbital parameters that were derived in the first paper of this series.Comment: 10 pages, 4 figures, accepted for publication in A&

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

Exploiting indigenous knowledge of subsistence farmers’ for the management and conservation of Enset (Ensete ventricosum (Welw.) Cheesman) (musaceae family) diversity on-farm

Enset (Ensete ventricosum (Welw.) Cheesman) belongs to the order sctaminae, the family musaceae. The Musaceae family is subdivided into the genera Musa and Ensete. Enset is an important staple crop for about 20 million people in the country. Recent publications on enset ethnobotany are insignificant when compared to the diverse ethnolingustic communities in the country. Hence, this paper try to identify and document wealth of indigenous knowledge associated with the distribution, diversity, and management of enset in the country. Methods: The study was conducted in eight ethnic groups in the Southern Nations, Nationalities and Peoples’ Regional State. In order to identify and document wealth of indigenous knowledge, the data was collected mainly through individual interviews and direct on-farm participatory monitoring and observation with 320 farm households, key informant interviews. Relevant secondary data, literature and inter-personal data were collected from unpublished progress report from National Enset Research Project, elderly people and senior experts. Results: Enset-based farming system is one of a major agricultural system in Ethiopia that serves as a backbone for at least ¼ of country’s population. Farmers used three morphological characters, two growth attributes, disease resistance and five use values traits in folk classification and characterization of enset. A total of 312 folk landraces have been identified. The number of landraces cultivated on individual farms ranged from one to twenty eight (mean of 8.08 ± 0.93). All ethnic groups in the study area use five use categories in order of importance: kocho yield and quality, bulla quality, amicho use, fiber quality and medicinal/ritual value. Of the 312 landraces 245 landraces having more than two use types. Management and maintenance of on-farm enset diversity is influenced by systematic propagation of the landraces, exchange of planting material and selective pressure. Conclusion: It can be concluded that the existing farmers’ knowledge on naming, classification and diversity should be complemented with maintenance of the creative dynamics of traditional knowledge and transmission of the knowledge are crucial for constructing sustainable management

Variable millimetre radiation from the colliding-wind binary Cygnus OB2 #8A

Context. Massive binaries have stellar winds that collide. In the colliding-wind region, various physically interesting processes occur, leading to enhanced X-ray emission, non-thermal radio emission, as well as non-thermal X-rays and gamma-rays. Non-thermal radio emission (due to synchrotron radiation) has so far been observed at centimetre wavelengths. At millimetre wavelengths, the stellar winds and the colliding-wind region emit more thermal free-free radiation, and it is expected that any non-thermal contribution will be difficult or impossible to detect. Aims. We aim to determine if the material in the colliding-wind region contributes substantially to the observed millimetre fluxes of a colliding-wind binary. We also try to distinguish the synchrotron emission from the free-free emission. Methods. We monitored the massive binary Cyg OB2 #8A at 3 mm with the NOrthern Extended Millimeter Array (NOEMA) interferometer of the Institut de Radioastronomie Millimétrique (IRAM). The data were collected in 14 separate observing runs (in 2014 and 2016), and provide good coverage of the orbital period. Results. The observed millimetre fluxes range between 1.1 and 2.3 mJy, and show phase-locked variability, clearly indicating that a large part of the emission is due to the colliding-wind region. A simple synchrotron model gives fluxes with the correct order of magnitude, but with a maximum that is phase-shifted with respect to the observations. Qualitatively this phase shift can be explained by our neglect of orbital motion on the shape of the colliding-wind region. A model using only free-free emission results in only a slightly worse explanation of the observations. Additionally, on the map of our observations we also detect the O6.5 III star Cyg OB2 #8B, for which we determine a 3 mm flux of 0.21 ± 0.033 mJy. Conclusions. The question of whether synchrotron radiation or free-free emission dominates the millimetre fluxes of Cyg OB2 #8A remains open. More detailed modelling of this system, based on solving the hydrodynamical equations, is required to give a definite answer

Agro-ecological niche of bacterial wilt (Xanthomonas campestris pv. musacearum) of enset (Ensete ventricosum (Welw.) Cheessman) in Gamo highlands of Ethiopia

In Ethiopia, nearly 20 million people depend on Enset (Ensete ventricosum (Welw.) Cheessman) for food, animal feed and fibre. Most of its cultivation is concentrated in the South and South-Western parts of the country. Enset based farming system is common in the Gamo highlands, with 11, 150 ha currently covered by it. Enset is supplemented with the cultivation of cereals, pulses and other root and tuber crops. Diverse high yielding clones of different ages are available all year round and can withstand dry spells, making Enset the most important food security crop in these densely populated highlands. Despite its relevance, Enset remains very poorly studied. One of the most important problems is Bacterial Wilt disease caused by Xanthomonas campestris pv. musacearum, destructive to Enset at all growth stages and present in all Enset growing areas of the country. As a plant takes up to 8 years to mature, an attack of Bacterial Wilt can leave a family vulnerable to famine for years. It is most likely spread by infected farm tools, harvesting knives, plant debris and repeated transplanting of corms. Adoption of the control package by farmers has been less effective and all known varieties are susceptible, putting a great challenge on controlling the epidemic. Despite being present in the entire Enset belt, the severity of a Bacterial Wilt infection varies greatly from region to region. Hence, this study aims at correlating the distribution and severity of the disease to environmental factors such as soil type, fertility, climate and altitude, and to the socio-economical status of the farm households. A better knowledge of the influence of these factors would help in developing more targeted measures to control the disease

Agronomic practices with a special focus on transplanting methods for optimum growth and yield of enset [Ensete ventricosum (Welw.) Cheesman] in Ethiopia.

Introduction Transplanting enset suckers or plants is practiced by the majority of small-scale farmers across the enset-growing belt in Ethiopia. Enset suckers, obtained from a multiplication nursery, are first intensely managed in a small plot (one plant 0.5 1.0 m-2) from where plants are consecutively transplanted into ever more widely spaced arrangements with a final minimal spacing of one plant 2 4 m-2. This review summarizes relevant information on transplanting methods from randomized controlled field trials and on-farm observations. Results and discussion Transplanting frequency impacts the crop cycle duration and yield. Transplanting once results in plants with a higher growth rate and hence a shorter crop cycle, while more frequent transplanting results in higher yields per plant. For example, plants transplanted once were harvested at 2 years and yielded 27 kg dry matter (DM) plant-1, while plants transplanted two or three times were both harvested at 4.5 years and yielded, respectively, 44 and 31 kg DM plant-1. Conclusion This review endeavours to help determine the enset transplanting methods that give optimum growth, biomass production and yield

Traditional enset [Ensete ventricosum (Welw.) Cheesman] sucker propagation methods and opportunities for crop improvement

This review focuses on the enset seed systems in Ethiopia and explores opportunities to improve the system. Cultivated enset is predominantly vegetatively propagated by farmers. Reproduction of an enset plant from seed is seldom practiced by farmers and has been reported only from the highlands of Gardula. Seedlings arising from seed are reported to be less vigorous than the suckers obtained through vegetative propagation. Rhizomes from immature plants, between 2 and 6 years old, are preferred for the production of suckers. The average number of suckers produced per rhizome ranges from 40 to 200, depending on soil conditions, cultivar type, size and age of the parent plant, amount of rainfall, land preparation and time of planting. Traditional macro-propagation of enset suckers involves both men and women farmers. Sucker propagation and transplanting activities often contribute to the dissemination or maintenance of pests (e.g., the enset root mealy bug or nematodes) and diseases (e.g., enset bacterial wilt). Conclusion Macro- and micro-propagation are useful technologies to improve the efficiency of sucker production and to provide clean replacement plants in locations where diseases have affected plantations or to locally multiply newly introduced cultivars for distribution

Testing common classical LTE and NLTE model atmosphere and line-formation codes for quantitative spectroscopy of early-type stars

It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere structures, spectral energy distributions and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE are compared. Their ability to reproduce observations for effective temperatures between 15000 and 35000 K are verified. Strengths and weaknesses of the different approaches are identified. Recommendations are made as to how to improve the models in order to derive unbiased stellar parameters and chemical abundances in future applications, with special emphasis on Gaia science.Comment: 12 pages, 8 figures; accepted for publication in Journal of Physics: Conference Series, GREAT-ESF Workshop: Stellar Atmospheres in the Gaia Er