Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood

Two distinct halo populations were found in the solar neighborhood by a series of works. They can be clearly separated by [alpha\Fe] and several other elemental abundance ratios including [Cu/Fe]. Very recently, a non-local thermodynamic equilibrium (non-LTE) study revealed that relatively large departures exist between LTE and non-LTE results in copper abundance analysis. We aim to derive the copper abundances for the stars from the sample of Nissen et al (2010) with both LTE and non-LTE calculations. Based on our results, we study the non-LTE effects of copper and investigate whether the high-alpha population can still be distinguished from the low-alpha population in the non-LTE [Cu/Fe] results. Our differential abundance ratios are derived from the high-resolution spectra collected from VLT/UVES and NOT/FIES spectrographs. Applying the MAFAGS opacity sampling atmospheric models and spectrum synthesis method, we derive the non-LTE copper abundances based on the new atomic model with current atomic data obtained from both laboratory and theoretical calculations. The copper abundances determined from non-LTE calculations are increased by 0.01 to 0.2 dex depending on the stellar parameters compared with the LTE results. The non-LTE [Cu/Fe] trend is much flatter than the LTE one in the metallicity range -1.6<[Fe/H]<-0.8. Taking non-LTE effects into consideration, the high- and low-alpha stars still show distinguishable copper abundances, which appear even more clear in a diagram of non-LTE [Cu/Fe] versus [Fe/H]. The non-LTE effects are strong for copper, especially in metal-poor stars. Our results confirmed that there are two distinct halo populations in the solar neighborhood. The dichotomy in copper abundance is a peculiar feature of each population, suggesting that they formed in different environments and evolved obeying diverse scenarios.Comment: 9 pages, 7 figures, 2 table

Chemical composition of 90 F and G disk dwarfs

High resolution, high S/N spectra have been obtained for a sample of 90 F and G main-sequence disk stars covering the metallicity range -1.0 < [Fe/H] < +0.1, and have been analysed in a parallel way to the work of Edvardsson et al. (1993). Effective temperatures are based on the Alonso et al. (1996) calibration of color indices and surface gravities are calculated from Hipparcos parallaxes, which also allow more accurate ages to be calculated. In addition, more reliable kinematical parameters are derived from Hipparcos distances and proper motions. Finally, a larger spectral coverage, 5600 - 8800 A, makes it possible to improve the abundance accuracy by studying more lines and to discuss several elements not included in the work of Edvardsson et al. The present paper provides the data and discusses some general results of the abundance survey. A group of stars in the metallicity range of -1.0 < [Fe/H] < -0.6 having a small mean Galactocentric distance in the stellar orbits, Rm < 7 kpc, are shown to be older than the other disk stars and probably belong to the thick disk. Excluding these stars, a slight decreasing trend of [Fe/H] with increasing Rm and age is found, but a large scatter in [Fe/H] (up to 0.5 dex) is present at a given age and Rm. The derived trends of O, Mg, Si, Ca, Ti, Ni and Ba as a function of [Fe/H] agree rather well with those of Edvardsson et al., but the overabundance of Na and Al for metal-poor stars found in their work is not confirmed. Furthermore, the Galactic evolution of elements not included in Edvardsson et al., K, V and Cr, is studied.Comment: 16 pages with 10 figures. Accepted for publication in A&A

Cosmological Cosmic Rays and the observed Li6 plateau in metal poor halo stars

Very recent observations of the Li6 isotope in halo stars reveal a Li6 plateau about 1000 times above the predicted BBN abundance. We calculate the evolution of Li6 versus redshift generated from an initial burst of cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that the pregalactic production of the Li6 isotope can account for the Li6 plateau observed in metal poor halo stars without additional over-production of Li7. The derived relation between the amplitude of the CCR energy spectra and the redshift of the initial CCR production puts constraints on the physics and history of the objects, such as pop III stars, responsible for these early cosmic rays. Consequently, we consider the evolution of Li6 in the Galaxy. Since Li6 is also produced in Galactic cosmic ray nucleosynthesis, we argue that halo stars with metallicities between [Fe/H] = -2 and -1, must be somewhat depleted in Li6.Comment: 8 pages, 6 figures, version accepted for publication in Ap

The Importance of Forming and Funding Collaborative Marketing Groups for the Survival of Smallholder Farmers in Asia

In developed countries such as the USA and Western Europe, the market share of fresh fruit and vegetable sales by the major supermarket chains can be as high as 80%. In China, with growth rates averaging between 30% and 40%, it is anticipated that supermarket chains will gain a greater market share in Asia. Because of their size, supermarket chains source their product globally and focus on maximizing returns for shareholders, keeping costs low for consumers, and providing a safe product. To be competitive, smallholder farmers need to supply a large volume of safe and high-quality fruit. However, unless they increase their bargaining power, they will become price-takers. Regrettably, most smallholder farmers in Asia lack the income to introduce new technologies such as fertilizing and irrigation to improve fruit quality. Sometimes these management inputs are funded by the trader and supermarket chains though outgrower schemes. However, this leaves the farmer vulnerable to exploitation. We suggest that the best means for smallholder farmers to remain viable in global supply chains is to establish economically sustainable collaborative marketing groups. We propose a new way to fund the establishment of these groups, whereby international aid agencies or national governments fund a core nucleus of farmers (10 to 50) and contract them to implement new technologies. This will deliver a greatly improved product and significantly increase grower returns, often in the order of 5 to 10 times their current net farm profit. We suggest that a portion of the improved profits from this core group be retained to provide short-term start-up funds for additional groups of farmers to implement new technologies. Consequently, the process of farmer improvement will become self-generating and self-sustainable without the need for additional support. Furthermore, we propose that the more successful farmers levy themselves to establish and maintain marketing infrastructure and activities such as training and cool chain management. Governments and aid agencies will need to support these marketing groups by providing long-term technical assistance as well as social facilitators to develop trust and maintain unity within the groups

The IntraCluster Medium: An Invariant Stellar IMF

Evidence supporting the hypothesis of an invariant stellar Initial Mass Function is strong and varied. The intra-cluster medium in rich clusters of galaxies is one of the few contrary locations where recent interpretations of the chemical abundances have favoured an IMF that is biased towards massive stars, compared to the `normal' IMF. This interpretation hinges upon the neglect of Type Ia supernovae to the ICM enrichment, and a particular choice of the nucleosynthesis yields of Type II supernovae. We demonstrate here that when one adopts yields determined empirically from observations of Galactic stars, rather than the uncertain model yields, a self-consistent picture may be obtained with an invariant stellar IMF, and about half of the iron in the ICM being produced by Type Ia supernovae.Comment: 9 pages, LateX (aaspp4 macro), including one postscript figure. Accepted, ApJ Letter

Improving the nutritional management of non-astringent persimmon in subtropical Australia

A series of experiments was conducted to evaluate the nutritional requirements of non-astringent persimmon in subtropical Australia. Three rates two times of application of the two major nutrients, N and K, were evaluated for two different soil types in south-east Queensland. Nitrogen and K were shown to be key manipulators of productivity. At both low (100 kg per hectare) annual rates of N, the total number of fruit per tree was reduced due to adverse effects on fruit set and increased fruit drop. With potassium, average fruit weight and yield increased with increasing rates of K applied up to 80 kg per hectare, and much more slowly thereafter. Multiple, sequential foliar applications of Ca were shown to increase leaf Ca concentrations by 20%, improve fruit firmness and storage life. A benchmarking survey of leading orchards was also undertaken to document current nutritional practices, and to determine if there was a relationship between leaf nutrient concentrations with productivity. Salinity was a major problem in some production regions; and at leaf CI concentrations above 0.8%, yield was severely reduced. Based on these studies, a new, narrower range of leaf nutrient standards at both fruit set and one month prior to harvest is being developed

A Survey of Cultivars and Management Practices in Australian Persimmon Orchards

Three surveys were conducted to determine the most commonly used cultivars and management practices across Australia. The persimmon industry is established from the semi-tropical far north of Queensland to the cool temperate zones of Victoria, South Australia and Western Australia. Fruit from warmer regions mature four months earlier, giving a harvest spread from February to June inclusive. The majority of the Australian industry is based on the non-astringent cultivar Fuyu. Only 26% of Australian orchards are planted with pollinizers. Yield and fruit size vary within and between regions. Factors contributing to lower yields and smaller size grades are temperature, salinity, pollination, and training and management systems. The most common tree training system is the freestanding vase, followed by palmette, the V- and Tatura trellises. Ruakura trellis is the least used. Trellised trees produce higher yields of marketable fruit through increased planting density, improved light interception and a tree structure that stabilises against tree movement, significantly reducing fruit blemish

Limits on the Boron Isotopic Ratio in HD 76932

Data in the 2090 A B region of HD 76932 have been obtained at high S/N using the HST GHRS echelle at a resolution of 90,000. This wavelength region has been previously identified as a likely candidate for observing the B11/B10 isotopic splitting. The observations do not match a calculated line profile extremely well at any abundance for any isotopic ratio. If the B abundance previously determined from observations at 2500 A is assumed, the calculated line profile is too weak, indicating a possible blending line. Assuming that the absorption at 2090 A is entirely due to boron, the best-fit total B abundance is higher than but consistent with that obtained at 2500 A, and the best-fit isotopic ratio (B11/B10) is in the range ~10:1 to ~4:1. If the absorption is not entirely due to B and there is an unknown blend, the best-fit isotopic ratio may be closer to 1:1. Future observations of a similar metal-poor star known to have unusually low B should allow us to distinguish between these two possibilities. The constraints that can be placed on the isotopic ratio based on comparisons with similar observations of HD 102870 and HD 61421 (Procyon) are also discussed.Comment: Accepted for Nov 1998 Ap

Extended Stromgren Photoelectric Photometry in NGC 752

Photoelectric photometry on the extended Stromgren system (uvbyCa) is presented for 7 giants and 21 main sequence stars in the old open cluster, NGC 752. Analysis of the hk data for the turnoff stars yields a new determination of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06 +/- 0.03, where the error quoted is the standard error of the mean and the Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20 stars within the limits of the hk metallicity calibration are included. The derived [Fe/H] is in excellent agreement with past estimates using properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and recent high dispersion spectroscopy.Comment: 14 tex'd pages including 2 tables; 2 separate files with eps figures Accepted for PASP March 200