High-Resolution Spectroscopy of Ursa Major Moving Group Stars

We use new and extant literature spectroscopy to address abundances and membership for UMa moving group stars. We first compare the UMa, Coma, and Hyades H-R diagrams via a homogeneous set of isochrones, and find that these three aggregates are essentially coeval. Our spectroscopy of cool UMa dwarfs reveals striking abundance anomalies--trends with Teff, ionization state, and excitation potential--like those recently seen in young cool M34, Pleaides, and Hyades dwarfs. In particular, the trend of rising 7774 Ang-based OI abundance with declining Teff is markedly subdued in UMa compared to the Pleiades, suggesting a dependence on age or metallicity. Despite disparate sources of Li data,our homogeneous analysis indicates that UMa members evince remarkably small scatter in the Li-Teff plane for Teff>5200 K. Significant star-to-star scatter suggested by previous studies is seen for cooler stars. Comparison with the consistently determined Hyades Li-Teff trend reveals differences qualitatively consistent with this cluster's larger [Fe/H] (and perhaps slightly larger age). However, quantitative comparison with standard stellar models indicates the differences are smaller than expected, suggesting the action of a fourth parameter beyond age, mass, and [Fe/H] controlling Li depletion.Comment: To appear in Publ. Astron. Soc. Pacif. (September 2005

Fe I and Fe II Abundances of Solar-Type Dwarfs in the Pleiades Open Cluster

We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an equivalent width analysis of Fe I and Fe II lines in high-resolution spectra obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph. Abundances derived from Fe II lines are larger than those derived from Fe I lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and the discrepancy (deltaFe = [Fe II/H] - [Fe I/H]) increases dramatically with decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The Pleiades joins the open clusters M 34, the Hyades, IC 2602, and IC 2391, and the Ursa Major moving group, demonstrating ostensible over-ionization trends. The Pleiades deltaFe abundances are correlated with Ca II infrared triplet and Halpha chromospheric emission indicators and relative differences therein. Oxygen abundances of our Pleiades sample derived from the high-excitation O I triplet have been previously shown to increase with decreasing Teff, and a comparison with the deltaFe abundances suggests that the over-excitation (larger abundances derived from high excitation lines relative to low excitation lines) and over-ionization effects that have been observed in cool open cluster and disk field main sequence (MS) dwarfs share a common origin. Star-to-star Fe I abundances have low internal scatter, but the abundances of stars with Teff < 5400 K are systematically higher compared to the warmer stars. The cool star [Fe I/H] abundances cannot be connected directly to over-excitation effects, but similarities with the deltaFe and O I triplet trends suggest the abundances are dubious. Using the [Fe I/H] abundances of five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of [Fe/H] = +0.01 +/- 0.02.Comment: 32 pages, 7 figures, 7 tables; accepted by PAS

Alkali-Activity Correlations in Open Clusters

We present a census of correlations between activity measures and neutral resonance lines of the alkali elements Li i and K i in open clusters and star-forming regions. The majority of very young associations and star formation regions show no evidence of Li-activity correlations, perhaps because their chromospheric activity indicators have a dominant origin in accretion processes with implied disk-clearing timescales in the range of a few times 106 to $4 ;107 yr. Alkali-alkali and/or alkali-activity correlations are newly noted within IC 2391, M34, and perhaps Blanco 1 and NGC 6475. Global X-ray luminosities are not as robust indicators as traditional optical indicators of alkali-activity correlations, nor are Li i–K i relations. Intracluster alkali-activity correlations are not global but are seen only within different intracluster subsamples, evincing rich behavior. Li- and K-activity correlations appear to go hand in hand, likely suggesting that at least some part of intracluster Li variance is not due to real differential Li depletion. Although up to$90% of the star-to-star variance in Li i and K i within such a subsample can be related to that in optical chromospheric emission, significant Li dispersion above observational scatter may remain even after accounting for this. We suggest, for example, that at least three independent mechanisms (including a possible intracluster age spread) influence the distribution in the M34 Li-Teff plane. We argue that Li-activity correlations are not illusory manifestations of a physical Li-rotation connection. Although an unexpected corre-lation between Li, chromospheric emission, and the k6455 Ca i feature in cool M34 dwarfs indicates that the role of ‘‘activity’’ is played by spots/plages, we note that the alkali-activity correlations are qualitatively opposite in sign to other abundance anomalies being rapidly delineated in active, young, cool stars

Self-consistent massive disks in triaxial dark matter halos

Galactic disks in triaxial dark matter halos become deformed by the elliptical potential in the plane of the disk in such a way as to counteract the halo ellipticity. We develop a technique to calculate the equilibrium configuration of such a disk in the combined disk-halo potential, which is based on the method of Jog (2000) but accounts for the radial variation in both the halo potential and the disk ellipticity. This crucial ingredient results in qualitatively different behavior of the disk: the disk circularizes the potential at small radii, even for a reasonably low disk mass. This effect has important implications for proposals to reconcile cuspy halo density profiles with low surface brightness galaxy rotation curves using halo triaxiality. The disk ellipticities in our models are consistent with observational estimates based on two-dimensional velocity fields and isophotal axis ratios.Comment: ApJ, in pres

Oxygen in Open Cluster Dwarfs: Pleiades and M34

We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] lambda6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]6300=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]Trip at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures

Microbiome-host systems interactions: protective effects of propionate upon the blood-brain barrier.

Background: Gut microbiota composition and function are symbiotically linked with host health, and altered in metabolic, inflammatory and neurodegenerative disorders. Three recognized mechanisms exist by which the microbiome influences the gut--brain axis: modification of autonomic/sensorimotor connections, immune activation, and neuroendocrine pathway regulation. We hypothesized interactions between circulating gut-derived microbial metabolites and the blood--brain barrier (BBB) also contribute to the gut--brain axis. Propionate, produced from dietary substrates by colonic bacteria, stimulates intestinal gluconeogenesis and is associated with reduced stress behaviours, but its potential endocrine role has not been addressed. Results: After demonstrating expression of the propionate receptor FFAR3 on human brain endothelium, we examined the impact of a physiologically relevant propionate concentration (1 μM) on BBB properties in vitro. Propionate inhibited pathways associated with non-specific microbial infections via a CD14-dependent mechanism, suppressed expression of LRP-1 and protected the BBB from oxidative stress via NRF2 (NFE2L2) signaling. Conclusions: Together, these results suggest gut-derived microbial metabolites interact with the BBB, representing a fourth facet of the gut--brain axis that warrants further attention

Reduced dimensionality spin-orbit dynamics of CH3 + HCl reversible arrow CH4 Cl on ab initio surfaces

A reduced dimensionality quantum scattering method is extended to the study of spin-orbit nonadiabatic transitions in the CH3 + HCl reversible arrow CH4 + Cl(P-2(J)) reaction. Three two-dimensional potential energy surfaces are developed by fitting a 29 parameter double-Morse function to CCSD(T)/IB//MP2/cc-pV(T+d)Z-dk ab initio data; interaction between surfaces is described by geometry-dependent spin-orbit coupling functions fit to MCSCF/cc-pV(T+d)Z-dk ab initio data. Spectator modes are treated adiabatically via inclusion of curvilinear projected frequencies. The total scattering wave function is expanded in a vibronic basis set and close-coupled equations are solved via R-matrix propagation. Ground state thermal rate constants for forward and reverse reactions agree well with experiment. Multi-surface reaction probabilities, integral cross sections, and initial-state selected branching ratios all highlight the importance of vibrational energy in mediating nonadiabatic transition. Electronically excited state dynamics are seen to play a small but significant role as consistent with experimental conclusions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3592732

Spectroscopic Abundances of Solar-Type Dwarfs in the Open Cluster M34 (NGC 1039)

Parameters and relative abundances of Fe, Ni, Ti, Cr, Ca, Si, Al, and Mg have been derived for nine M34 G and K dwarfs from high-resolution, modest signal-to-noise ratio Keck HIRES spectra. Effective temperatures have been derived spectroscopically and fall in the range 4750 K Teff 6130 K. Despite modest scatter in Fe, Ti, Cr, Ca, Al, and Mg (none of which is found to be correlated with Li scatter in M34), our two coolest stars are slightly though consistently underabundant in these elements relative to the warmer stars. The two cool stars are slightly overabundant in Si, whose abundances are derived from higher excitation lines. This and our finding that Fe ii–based abundances are significantly higher than Fe i–based values in the cool stars seem to point toward the action of non-LTE effects (overionization, overexcitation, or both), though additional analysis is required to exclude inadequacies in the model atmospheres. Final mean cluster abundances are based on five warm stars, which indicate [Fe/H] = +0.07 Æ0.04, and are void of any statistically significant scatter. The other elements scale well with Fe except for Ni, which appears to be slightly underabundant with respect to Fe. Potassium abundances are derived and show a surprising marked trend with temperature, which further supports our suspicion of the presence of non-LTE effects. Moreover, similar trends with temperature suggest that the Li and K underabundances in cool M34 dwarfs are partially related; thus, some portion of the well-known Li-Teff trend in cool M34 dwarfs may be illusory

Hyades Oxygen Abundances from the k6300 [O i] Line: The Giant-Dwarf Oxygen Descrepancy Revisited

We present the results of our abundance analysis of Fe, Ni, and O in high signal-to-noise ratio, high-resolution Very Large Telescope UVES and McDonald 2dcoude´ spectra of nine dwarfs and three giants in the Hyades open cluster. The difference in Fe abundances derived from Fe ii and Fe i lines ([Fe ii/HÀ½Fe i/H)and Ni i abundances derived from moderately high-excitation ( %4:20 eV) lines is found to increase with decreasing Teff for the dwarfs. Both of these findings are in concordance with previous results of overexcitation/overionization in cool young dwarfs. Oxygen abundances are derived from the [O i] k6300 line, with careful attention given to the Ni i blend. The dwarf O abundances are in star-to-star agreement within uncertainties, but the abundances of the three coolest dwarfs (4573 K TeA 4834 K) evince an increase with decreasing Teff. Possible causes for the apparent trend are considered,including the effects of overdissociation of O-containing molecules.O abundances are derived from the near-UV OH k3167 line in high-quality Keck HIRES spectra, and no such effects are found; indeed, the OH-based abundances show an increase with decreasing Teff, leaving the nature and reality of the cool dwarf [O i]-based O trend uncertain. The mean relative O abundance of the six warmest dwarfs (5075 K TeA 5978 K) is ½O/H¼þ0:14 Æ0:02, and we find a mean abundance of ½O/H¼þ0:08 Æ0:02for the giants. Thus, our updated analysis of the [O i] k6300 line does not confirm the Hyades giant-dwarf oxygen discrepancy initially reported by King & Hiltgen, suggesting that the discrepancy was a consequence of analysis-related systematic errors. LTE oxygen abundances from the near-IR, high-excitation O i triplet are also derived for the giants, and the resulting abundances are approximately 0.28 dex higher than those derived from the [O i] line, in agreement with non-LTE predictions. Non-LTE corrections from the literature are applied to the giant triplet abundances; the resulting mean abundance is ½O/H¼þ0:17 Æ0:02, in decent concordance with the giant and dwarf [O i] abundances. Finally, Hyades giant and dwarf O abundances derived from the [O i] k6300 line and high-excitation triplet, as well as dwarf O abundances derived from the near-UV OH k3167 line, are compared, and a mean cluster O abundance of ½O/H¼þ0:12 Æ0:02 is achieved, which represents the best estimate of the Hyades O abundance

A spread spectrum approach to time-domain near-infrared diffuse optical imaging using inexpensive optical transceiver modules

We introduce a compact time-domain system for near-infrared spectroscopy using a spread spectrum technique. The proof-of-concept single channel instrument utilises a low-cost commercially available optical transceiver module as a light source, controlled by a Kintex 7 field programmable gate array (FPGA). The FPGA modulates the optical transceiver with maximum-length sequences at line rates up to 10Gb/s, allowing us to achieve an instrument response function with full width at half maximum under 600ps. The instrument is characterised through a set of detailed phantom measurements as well as proof-of-concept in vivo measurements, demonstrating performance comparable with conventional pulsed time-domain near-infrared spectroscopy systems