Detection of Lead in the Carbon-Rich, Very Metal-Poor Star LP625-44: A Strong Constraint on s-Process Nucleosynthesis at Low Metallicity

We report the detection of the Pb I 4057.8A line in the very metal-poor ([Fe/H]=-2.7), carbon-rich star, LP625-44. We determine the abundance of Pb ([Pb/Fe] = 2.65) and 15 other neutron-capture elements. The abundance pattern between Ba and Pb agrees well with a scaled solar system s-process component, while the lighter elements (Sr-Zr) are less abundant than Ba. The enhancement of s-process elements is interpreted as a result of mass transfer in a binary system from a previous AGB companion, an interpretation strongly supported by radial velocity variations of this system. The detection of Pb makes it possible, for the first time, to compare model predictions of s-process nucleosynthesis in AGB stars with observations of elements between Sr and Pb. The Pb abundance is significantly lower than the prediction of recent models (e.g., Gallino et al. 1998), which succeeded in explaining the metallicity dependence of the abundance ratios of light s-elements (Sr-Zr) to heavy ones (Ba-Dy) found in previously observed s-process-enhanced stars. This suggests that one should either (a) reconsider the underlying assumptions concerning the 13C-rich s-processing site (13C-pocket) in the present models, or (b) investigate alternative sites of s-process nucleosynthesis in very metal-poor AGB stars.Comment: 10 pages, 3 figures, Astrophysical Journal Letters, in pres

Effect of pesticides on integrated mite management in Washington State

The effect of pesticides used against codling moth, Cydia pomonella L., on integrated mite management was studied for three years in five or six commercial apple orchards in central Washington. Phytophagous and predatory mites were counted throughout the season in blocks ranging from 0.4-1.6 ha in size treated with four codling moth insecticides. In one year of the study (2006), five out of six orchards experienced elevated mite densities relative to the standard. In four orchards, novaluron caused a 3.0-16.9× increase in mite populations; acetamiprid caused a 2.6-3.4× increase, and thiacloprid caused a 1.7-13.8× increase. In the fifth orchard, the organophosphate standard had an extremely high mite population, in addition to all three experimental treatments. In 2005 and 2007, only one or two orchards had elevated mite levels in the novaluron, acetamiprid, and thiacloprid treatments. Additive effects of codling moth and thinning programs were evaluated in small plot research trials. Treatments with all three elements [1) codling moth insecticide; 2) calcium polysulfide; 3) carbaryl] produced the highest levels ofspider mites. Three sulfur-containing products (calcium polysulfide, ammonium thiosulfate, and dry flowable sulfur) were evaluated for their effect onGalandromus occidentalis (Nesbitt) and apple rust mite, Aculus schlechtendali (Nalepa). All three materials caused suppressed G. occidentalis numbers. Calcium polysulfide caused the greatest reduction in apple rust mite numbers, ammonium thiosulfate the least reduction, with dry flowable sulfur intermediate between the two. Additive effects of codling moth materials, carbaryl, and sulfur-containing products may be causing increased mite levels in Washington orchards

Extremely Metal-Poor Stars. VII. The Most Metal-Poor Dwarf, CS 22876-032

We report high-resolution, high-signal-to-noise, observations of the extremely metal-poor double-lined spectroscopic binary CS 22876-032. The system has a long period : P = 424.7 $\pm$ 0.6 days. It comprises two main sequence stars having effective temperatures 6300 K and 5600 K, with a ratio of secondary to primary mass of 0.89 $\pm$ 0.04. The metallicity of the system is [Fe/H] = -3.71 $\pm$ 0.11 $\pm$ 0.12 (random and systematic errors) -- somewhat higher than previous estimates. We find [Mg/Fe] = 0.50, typical of values of less extreme halo material. [Si/Fe], [Ca/Fe], and [Ti/Fe], however, all have significantly lower values, ~ 0.0-0.1, suggesting that the heavier elements might have been underproduced relative to Mg in the material from which this object formed. In the context of the hypothesis that the abundance patterns of extremely metal-poor stars are driven by individual enrichment events and the models of Woosley and Weaver (1995), the data for CS 22876-032 are consistent with its having been enriched by a zero-metallicity supernova of mass 30 M$_{\odot}$. As the most metal-poor near-main-sequence-turnoff star currently known, the primary of the system has the potential to strongly constrain the primordial lithium abundance. We find A(Li) (= log(N(Li)/N(H)) + 12.00) = 2.03 $\pm$ 0.07, which is consistent with the finding of Ryan et al. (1999) that for stars of extremely low metallicity A(Li) is a function of [Fe/H].Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical Journal, Sept. 1, 2000 issu