The Asymptotic Giant Branches of GCs: Selective Entry Only

The handful of available observations of AGB stars in Galactic Globular Clusters suggest that the GC AGB populations are dominated by cyanogen-weak stars. This contrasts strongly with the distributions in the RGB (and other) populations, which generally show a 50:50 bimodality in CN band strength. If it is true that the AGB populations show very different distributions then it presents a serious problem for low mass stellar evolution theory, since such a surface abundance change going from the RGB to AGB is not predicted by stellar models. However this is only a tentative conclusion, since it is based on very small AGB sample sizes. To test whether this problem really exists we have carried out an observational campaign specifically targeting AGB stars in GCs. We have obtained medium resolution spectra for about 250 AGB stars across 9 Galactic GCs using the multi-object spectrograph on the AAT (2df/AAOmega). We present some of the preliminary findings of the study for the second parameter trio of GCs: NGC 288, NGC 362 and NGC 1851. The results indeed show that there is a deficiency of stars with strong CN bands on the AGB. To confirm that this phenomenon is robust and not just confined to CN band strengths and their vagaries, we have made observations using FLAMES/VLT to measure elemental abundances for NGC 6752.We present some initial results from this study also. Our sodium abundance results show conclusively that only a subset of stars in GCs experience the AGB phase of evolution. This is the first direct, concrete confirmation of the phenomenon.Comment: 4 pages, to appear in conference proceedings of "Reading the book of globular clusters with the lens of stellar evolution", Rome, 26-28 November 201

Effect of shot peening on the residual stress and mechanical behaviour of low-temperature and high-temperature annealed martensitic gear steel 18CrNiMo7-6

A martensitic gear steel (18CrNiMo7-6) was annealed at 180 \ub0C for 2h and at ∼ 750 \ub0C for 1h to design two different starting microstructures for shot peening. One maintains the original as-transformed martensite while the other contains irregular-shaped sorbite together with ferrite. These two materials were shot peened using two different peening conditions. The softer sorbite + ferrite microstructure was shot peened using 0.6 mm conditioned cut steel shots at an average speed of 25 m/s in a conventional shot peening machine, while the harder tempered martensite steel was shot peened using 1.5 mm steel shots at a speed of 50 m/s in an in-house developed shot peening machine. The shot speeds in the conventional shot peening machine were measured using an in-house lidar set-up. The microstructure of each sample was characterized by optical and scanning electron microscopy, and the mechanical properties examined by microhardness and tensile testing. The residual stresses were measured using an Xstress 3000 G2R diffractometer equipped with a Cr Kα x-ray source. The correspondence between the residual stress profile and the gradient structure produced by shot peening, and the relationship between the microstructure and strength, are analyzed and discussed

Asteroseismology of red giants & galactic archaeology

Red-giant stars are low- to intermediate-mass ($M \lesssim 10$~M$_{\odot}$) stars that have exhausted hydrogen in the core. These extended, cool and hence red stars are key targets for stellar evolution studies as well as galactic studies for several reasons: a) many stars go through a red-giant phase; b) red giants are intrinsically bright; c) large stellar internal structure changes as well as changes in surface chemical abundances take place over relatively short time; d) red-giant stars exhibit global intrinsic oscillations. Due to their large number and intrinsic brightness it is possible to observe many of these stars up to large distances. Furthermore, the global intrinsic oscillations provide a means to discern red-giant stars in the pre-helium core burning from the ones in the helium core burning phase and provide an estimate of stellar ages, a key ingredient for galactic studies. In this lecture I will first discuss some physical phenomena that play a role in red-giant stars and several phases of red-giant evolution. Then, I will provide some details about asteroseismology -- the study of the internal structure of stars through their intrinsic oscillations -- of red-giant stars. I will conclude by discussing galactic archaeology -- the study of the formation and evolution of the Milky Way by reconstructing its past from its current constituents -- and the role red-giant stars can play in that.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Phylogenetic inference using cytochrome c oxidase subunit I (COI) in the poultry red mite, Dermanyssus gallinae in the United Kingdom relative to a European framework

The poultry red mite (Dermanyssus gallinae), an obligatory blood feeding ectoparasite, is primarily associated with laying hens where it is estimated to cause losses of ~€231 million per annum to European farmers. Moderate to high infestation levels result in negative impacts on hen welfare, including increased cannibalism, irritation, feather pecking, restlessness, anaemia and mortality. Acaricides are currently the prevailing method of population control for D. gallinae, although resistance against some classes of acaricide has been widely reported. The development of resistance highlights a growing need for research into alternative control methods, including the development of a suitable and effective vaccine. Understanding the genetic structure of D. gallinae populations can support improved management of acaricide resistance and sustainability of future vaccines, but limited data are currently available. The aim of this study was to characterise D. gallinae isolates from Europe, targeting the cytochrome c oxidase subunit 1 (COI) gene to gain an insight into population structure and genetic diversity of currently circulating mites. Dermanyssus gallinae isolates were collected from Albania, Belgium, Croatia, Czech Republic, Denmark, France, Greece, Italy, the Netherlands, Portugal, Romania, Slovenia, Turkey and the United Kingdom. Genomic DNA was extracted from individual adult D. gallinae mites and a 681bp fragment of the COI gene was amplified and sequenced. Phylogenetic analyses of 195 COI sequences confirmed the presence of multiple lineages across Europe with 76 distinct haplotypes split across three main haplogroups and six sub-haplogroups. Importantly there is considerable inter- and intra-country variation across Europe, which could result from the movement of poultry or transfer of contaminated equipment and/or materials and husbandry practices

EXPLORING ANTICORRELATIONS AND LIGHT ELEMENT VARIATIONS IN NORTHERN GLOBULAR CLUSTERS OBSERVED BY THE APOGEE SURVEY

We investigate the light-element behavior of red giant stars in northern globular clusters (GCs) observed by the SDSS-III Apache Point Observatory Galactic Evolution Experiment. We derive abundances of 9 elements (Fe, C, N, O, Mg, Al, Si, Ca, and Ti) for 428 red giant stars in 10 GCs. The intrinsic abundance range relative to measurement errors is examined, and the well-known C–N and Mg–Al anticorrelations are explored using an extreme-deconvolution code for the first time in a consistent way. We find that Mg and Al drive the population membership in most clusters, except in M107 and M71, the two most metal-rich clusters in our study, where the grouping is most sensitive to N. We also find a diversity in the abundance distributions, with some clusters exhibiting clear abundance bimodalities (for example M3 and M53) while others show extended distributions. The spread of Al abundances increases significantly as cluster average metallicity decreases as previously found by other works, which we take as evidence that low metallicity, intermediate mass AGB polluters were more common in the more metal-poor clusters. The statistically significant correlation of [Al/Fe] with [Si/Fe] in M15 suggests that 28Si leakage has occurred in this cluster. We also present C, N, and O abundances for stars cooler than 4500 K and examine the behavior of A(C+N+O) in each cluster as a function of temperature and [Al/Fe]. The scatter of A(C+N +O) is close to its estimated uncertainty in all clusters and independent of stellar temperature. A(C+N+O) exhibits small correlations and anticorrelations with [Al/Fe] in M3 and M13, but we cannot be certain about these relations given the size of our abundance uncertainties. Star-to-star variations of a-element (Si, Ca, Ti) abundances are comparable to our estimated errors in all clusters