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

Carbon and oxygen in metal-poor halo stars

Carbon and oxygen are key tracers of the Galactic chemical evolution; in particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor halo stars could be a signature of nucleosynthesis by massive Population III stars. We reanalyse carbon, oxygen, and iron abundances in thirty-nine metal-poor turn-off stars. For the first time, we take into account three-dimensional (3D) hydrodynamic effects together with departures from local thermodynamic equilibrium (LTE) when determining both the stellar parameters and the elemental abundances, by deriving effective temperatures from 3D non-LTE H$\beta$ profiles, surface gravities from Gaia parallaxes, iron abundances from 3D LTE Feii equivalent widths, and carbon and oxygen abundances from 3D non-LTE Ci and Oi equivalent widths. We find that [C/Fe] stays flat with [Fe/H], whereas [O/Fe] increases linearly up to $0.75$ dex with decreasing [Fe/H] down to $-3.0$ dex. As such [C/O] monotonically decreases towards decreasing [O/H], in contrast to previous findings, mainly by virtue of less severe non-LTE effects for Oi at low [Fe/H] with our improved calculations.Comment: 5 pages, 2 figures; published in A&A Letter

The Rolodex model: understanding relationship complexity as a precursor to the design of organizational forms for chaotic environments

The emerging business environment is increasingly complex, characterized by hypercompetition, compound interdependence, and electronic webs This heightened complexity is triggering a slew of new organizational forms and shifts in the underlying logics of organizational forms These new organizational forms are not only more complex, but they have new kinds of complexity - increasingly hybrid and heterarchical, more flexible, and dynamically reconfigurable. The report argues that in such new conditions we need to rethink how we conceive the structural dimensions of organizational form and base them on a process model of inter-organizational relationships. This report examines relationship complexity as a structural topology that underlies organizational form It identifies three structural dimensions of relationship complexity reach, range, and reciprocity and combines them in a model that allows dynamic reconfigurability. The model is based on the primacy of perspective of practicing managers and we have termed it the Rolodex Model as it has overtones of an organizational version of a manager's card file of contacts. Using the concepts of energy and phase space from physics to enrich the Rolodex Model, the report shows how it can be used to explain existing archetypes of organizational forms, to identity new organizational forms, and to provide insights for organizational design The report then argues that further elaboration of energy concepts and relationship complexity may be necessary before we can fully respond to, and anticipate, the complex, dynamic, hypercompetitive organizational environment of today , much less that likely to exist tomorrow.Approved for public release; distribution is unlimited

s/alpha/Fe Abundance Ratios in Halo Field Stars: Is there a Globular Cluster Connection?

We try to understand the s- and r-process elements vs Ti/Fe plots derived by Jehin et al. (1999) for mildly metal-poor stars within the framework of the analytical semi-empirical models for these elements by Pagel & Tautvaisiene (1995, 1997). Jehin et al. distinguished two Pop II subgroups: IIa with alpha/Fe and s-elements/Fe increasing together, which they attribute to pure SNII activity, and IIb with constant alpha/Fe and a range in s/Fe which they attribute to a prolonged accretion phase in parent globular clusters. However, their sample consists mainly of thick-disk stars with only 4 clear halo members, of which two are `anomalous' in the sense defined by Nissen & Schuster (1997). Only the remaining two halo stars (and one in Nissen & Schuster's sample) depart significantly from Y/Ti (or s/alpha) ratios predicted by our model.Comment: 6 pages, 5 figures To appear in: Roma-Trieste Workshop 1999: `The Chemical Evolution of the Milky Way: Stars vs Clusters', Vulcano Sept. 1999. F. Giovanelli & F. Matteucci (eds), Kluwer, Dordrech

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

3D non-LTE iron abundances in FG-type dwarfs

Spectroscopic measurements of iron abundances are prone to systematic modelling errors. We present 3D non-LTE calculations across 32 STAGGER-grid models with effective temperatures from 5000 K to 6500 K, surface gravities of 4.0 dex and 4.5 dex, and metallicities from $-$3 dex to 0 dex, and study the effects on 171 Fe I and 12 Fe II optical lines. In warm metal-poor stars, the 3D non-LTE abundances are up to 0.5 dex larger than 1D LTE abundances inferred from Fe I lines of intermediate excitation potential. In contrast, the 3D non-LTE abundances can be 0.2 dex smaller in cool metal-poor stars when using Fe I lines of low excitation potential. The corresponding abundance differences between 3D non-LTE and 1D non-LTE are generally less severe but can still reach $\pm$0.2 dex. For Fe II lines the 3D abundances range from up to 0.15 dex larger, to 0.10 dex smaller, than 1D abundances, with negligible departures from 3D LTE except for the warmest stars at the lowest metallicities. The results were used to correct 1D LTE abundances of the Sun and Procyon (HD 61421), and of the metal-poor stars HD 84937 and HD 140283, using an interpolation routine based on neural networks. The 3D non-LTE models achieve an improved ionisation balance in all four stars. In the two metal-poor stars, they remove excitation imbalances that amount to 250 K to 300 K errors in effective temperature. For Procyon, the 3D non-LTE models suggest [Fe/H] = 0.11 $\pm$ 0.03, which is significantly larger than literature values based on simpler models. We make the 3D non-LTE interpolation routine for FG-type dwarfs publicly available, in addition to 1D non-LTE departure coefficients for standard MARCS models of FGKM-type dwarfs and giants. These tools, together with an extended 3D LTE grid for Fe II from 2019, can help improve the accuracy of stellar parameter and iron abundance determinations for late-type stars.Comment: 17 pages, 11 figures, 5 tables; arXiv abstract abridged; accepted for publication in Astronomy & Astrophysic

2014 Murmuri Earthquake

We present source models for the August 2014 Murmuri (Dehloran) earthquake sequence in the Zagros Mountains of Iran. An Mw6.2 mainshock was followed by an aftershock sequence containing 5 events of Mw ≥ 5.4. Models of P and SH waveforms show that all events had dominantly thrust-faulting mechanisms, and had centroid depths that place them within the thick sedimentary sequence, above the crystalline basement. The combination of our estimated focal mechanisms, relative relocations of the event hypocentres, and the surface displacement patterns observed using InSAR, imply that the mainshock and largest aftershock ruptured different fault planes and both contributed to the surface deformation. The fault planes both slipped in horizontally-elongated patches, possibly due to rheological layering limiting the up- and down-dip extent of rupture. The slip vector of the Murmuri mainshock implies that the decollement beneath the Lorestan Arc is weaker than any such feature beneath the Dezful Embayment, providing an explanation for the plan-view sinuosity of the range-front of the Zagros Mountains.This work form part of the NERC- and ESRC-funded project ‘Earthquakes Without Frontiers’. JRE is funded by the NERC projects ‘COMET’ and ‘LiCS’.This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/gji/ggv36

The [Y/Mg] clock works for evolved solar metallicity stars

Previously [Y/Mg] has been proven to be an age indicator for solar twins. Here, we investigate if this relation also holds for helium-core-burning stars of solar metallicity. High resolution and high signal-to-noise ratio (S/N) spectroscopic data of stars in the helium-core-burning phase have been obtained with the FIES spectrograph on the NOT 2.56m telescope and the HIRES spectrograph on the Keck I 10 m telescope. They have been analyzed to determine the chemical abundances of four open clusters with close to solar metallicity; NGC 6811, NGC 6819, M67 and NGC 188. The abundances are derived from equivalent widths of spectral lines using ATLAS9 model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Results from asteroseismology and binary studies were used as priors on the atmospheric parameters, where especially the $\log g$ is determined to much higher precision than what is possible with spectroscopy. It is confirmed that the four open clusters are close to solar metallicity and they follow the [Y/Mg] vs. age trend previously found for solar twins. The [Y/Mg] vs. age clock also works for giant stars in the helium-core burning phase, which vastly increases the possibilities to estimate the age of stars not only in the solar neighborhood, but in large parts of the Galaxy, due to the brighter nature of evolved stars compared to dwarfs.Comment: 5 pages, 3 figures, accepted for publication as a Letter to A&