Aims. We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for the two ions of iron and check the ionization equilibrium between Fe i and Fe ii in model atmospheres of the cool ...reference stars based on the best available complete model atom for neutral and singly-ionized iron. Methods. We present a comprehensive model atom for Fe with more than 3000 measured and predicted energy levels. As a test and first application of the improved model atom, iron abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. The efficiency of inelastic collisions with hydrogen atoms in the statistical equilibrium of iron is empirically estimated from inspection of their different influence on the Fe i and Fe ii lines in the selected stars. Results. Non-LTE leads to systematically depleted total absorption in the Fe i lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of such corrections is smaller compared to the earlier results. These non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient stars, and they vary within 0.21 dex and 0.35 dex in the very metal-poor stars HD 84937 and HD 122563, respectively, depending on the assumed efficiency of collisions with hydrogen atoms. Based on the analysis of the Fe i/Fe ii ionization equilibrium in these two stars, we recommend to apply the Drawin formalism in non-LTE studies of Fe with a scaling factor of 0.1. For the Fe ii lines non-LTE corrections do not exceed 0.01 dex in absolute value over the whole range of stellar parameters that are considered. This study reveals two problems. The first one is that gf-values available for the Fe i and Fe ii lines are not accurate enough to pursue high-accuracy absolute stellar abundance determinations. For the Sun, the mean non-LTE abundance obtained from 54 Fe i lines is 7.56 ± 0.09 and the mean abundance from 18 Fe ii lines varies between 7.41 ± 0.11 and 7.56 ± 0.05 depending on the source of the gf-values. The second problem is that lines of Fe i give, on average, a 0.1 dex lower abundance compared with those of Fe ii lines for HD 61421 and HD 102870, even when applying a differential line-by-line analysis with regard to the Sun. A disparity between neutral atoms and first ions points to problems of stellar atmosphere modelling or/and effective temperature determination.
Abstract
In this study, a mathematical model is developed to scrutinize the transient magnetic flow of Cross nanoliquid past a stretching sheet with thermal radiation effects. Binary chemical ...reactions and heat source/sink effects along with convective boundary condition are also taken into the consideration. Appropriate similarity transformations are utilized to transform partial differential equations (PDE’s) into ordinary ones and then numerically tackled by shooting method. The impacts of different emerging parameters on the thermal, concentration, velocity, and micro-rotation profiles are incorporated and discussed in detail by means of graphs. Results reveal that, the escalation in magnetic parameter and Rayleigh number slowdowns the velocity and momentum of the fluid. The increase in Biot number, radiation and heat sink/source parameters upsurges the thermal boundary but, converse trend is seen for escalating Prandtl number. The density number of motile microorganisms acts as a growing function of bioconvection Lewis number and declining function of bioconvection Peclet number.
The nearly continuous light curves with micromagnitude precision provided by the space mission Kepler are revolutionizing our view of pulsating stars. They have revealed a vast sea of low-amplitude ...pulsation modes that were undetectable from Earth. The long time base of Kepler light curves allows for the accurate determination of the frequencies and amplitudes of pulsation modes needed for in-depth asteroseismic modeling. However, for an asteroseismic study to be successful, the first estimates of stellar parameters need to be known and they cannot be derived from the Kepler photometry itself. The Kepler Input Catalog provides values for the effective temperature, surface gravity, and metallicity, but not always with sufficient accuracy. Moreover, information on the chemical composition and rotation rate is lacking. We are collecting low-resolution spectra for objects in the Kepler field of view with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, Xinglong observatory, China). All of the requested fields have now been observed at least once. In this paper, we describe those observations and provide a useful database for the whole astronomical community.
Accurate determination of stellar atmospheric parameters and elemental abundances is crucial for Galactic archaeology via large-scale spectroscopic surveys. In this paper, we estimate stellar ...atmospheric parameters -- effective temperature T sub( eff), surface gravity log g and metallicity Fe/H, absolute magnitudes M sub( V) and M sub( Ks), ...-element to metal (and iron) abundance ratio .../M (and .../Fe), as well as carbon and nitrogen abundances C/H and N/H from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra with a multivariate regression method based on kernel-based principal component analysis, using stars in common with other surveys (Hipparcos, Kepler, Apache Point Observatory Galactic Evolution Experiment) as training data sets. Both internal and external examinations indicate that given a spectral signal-to-noise ratio (SNR) better than 50, our method is capable of delivering stellar parameters with a precision of ~100 K for T sub( eff), ~0.1 dex for log g, 0.3-0.4 mag for M sub( V) and M sub( Ks), 0.1 dex for Fe/H, C/H and N/H, and better than 0.05 dex for .../M (.../Fe). The results are satisfactory even for a spectral SNR of 20. The work presents first determinations of C/H and N/H abundances from a vast data set of LAMOST, and, to our knowledge, the first reported implementation of absolute magnitude estimation directly based on a vast data set of observed spectra. The derived stellar parameters for millions of stars from the LAMOST surveys will be publicly available in the form of value-added catalogues. (ProQuest: ... denotes formulae/symbols omitted.)
Oxide-confined vertical cavity surface emitting lasers (VCSELs) with anti-waveguiding AlAs-rich core presently attract a lot of attention. Anti-waveguiding cavity enables the maximum possible optical ...confinement of the VCSEL mode ("λ/2 design"), increases its oscillator strength and reduces dramatically the optical power accumulated in the VCSEL mesa regions outside the aperture. VCSEL designs are suggested that favor single transverse mode operation. Modeling including current-induced and absorption-induced overheating shows that the preference for the transverse fundamental mode persists up to 10 mA current at 5 µm aperture diameter. Error-free data transmission is realized up to 160 Gb/s in digital-multitone (DMT) format using single-mode anti-waveguiding VCSELs. The approach to single-mode anti-waveguiding VCSELs is extended over a broad spectral range realizing error-free high-speed data transmission at both 850 nm and 910 nm.
Mutations in a tubulin gene caused infertility due to oocyte arrest in about a third of families tested. The investigators found that the mutant tubulins wreak havoc on microtubule assembly in the ...oocyte.
Successful human reproduction starts when a metaphase II oocyte fuses with a sperm cell to form a fertilized egg. In human oocytes, the meiotic cell cycle begins in the neonatal ovary and pauses at prophase I of meiosis until puberty, when a surge of luteinizing hormone stimulates the resumption of meiosis and ovulation. This leads to progression of the oocyte from metaphase I to metaphase II.
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Oocytes arrested in prophase I have an intact nucleus, termed the germinal vesicle, whereas oocytes that have resumed meiosis are characterized by the breakdown of the germinal vesicle. After germinal-vesicle breakdown, metaphase I . . .
Close white dwarf binaries consisting of a white dwarf and an A-, F-, G-, or K-type main-sequence star, henceforth close WD+AFGK binaries, are ideal systems to understand the nature of type Ia ...supernovae progenitors and to test binary evolution models. In this work we identify 775 WD+AFGK candidates from TGAS (The Tycho-Gaia Astrometric Solution) and Gaia Data Release 2 (DR2), a well-defined sample of stars with available parallaxes, and we measure radial velocities (RVs) for 275 of them with the aim of identifying close binaries. The RVs have been measured from high-resolution spectra obtained at the Xinglong 2.16 m Telescope and the San Pedro Mártir 2.12 m Telescope and/or from available LAMOST DR6 (low-resolution) and RAVE DR5 (medium-resolution) spectra. We identify 23 WD+AFGK systems displaying more than 3 RV variation among 151 systems for which the measured values are obtained from different nights. Our WD+AFGK binary sample contains both AFGK dwarfs and giants, with a giant fraction ∼43%. The close binary fractions we determine for the WD+AFGK dwarf and giant samples are 24% and 15%, respectively. We also determine the stellar parameters (i.e., effective temperature, surface gravity, metallicity, mass, and radius) of the AFGK companions with available high-resolution spectra. The stellar parameter distributions of the AFGK companions that are members of close and wide binary candidates do not show statistically significant differences.
We present atmospheric parameters for 51 nearby F and G dwarf and subgiant stars uniformly distributed over the -2.60 < Fe/H < +0.20 metallicity range that is suitable for the Galactic chemical ...evolution research. Lines of iron in the two ionization stages, Fe sub(I) and Fe sub(II), were used to derive a homogeneous set of effective temperatures, surface gravities, iron abundances, and microturbulence velocities. Our spectroscopic analyses took advantage of employing high-resolution (R > or =, slanted 60,000) Shane/Hamilton and Canada-France-Hawaii Telescope/ESPaDOnS observed spectra and non-LTE (NLTE) line formation for Fe sub(I) and Fe sub(II) in the classical one-dimensional model atmospheres. The spectroscopic method was tested in advance with the 20 benchmark stars, for which there are multiple measurements of the infrared flux method effective temperature and their Hipparcos parallax error is less than 10%. We found NLTE abundances from lines of Fe sub(I) and Fe sub(II) to be consistent within 0.06 dex for every benchmark star, when applying a scaling factor of S sub(H) = 0.5 to the Drawinian rates of inelastic Fe+H collisions. The obtained atmospheric parameters were checked for each program star by comparing its position in the log g-T sub(eff) plane with the theoretical evolutionary track of given metallicity and alpha -enhancement in the Yi et al. grid. Our final effective temperatures lie exactly in between the T sub(IRFM) scales of Alonso et al., and Casagrande et al., with a mean difference of +46 and -51 K, respectively. NLTE leads to higher surface gravity compared with that for LTE. The shift in log g is smaller than 0.1 dex for stars with Fe/H > or =, slanted -0.75, T sub(eff) < or =, slant 5750 K, or log g > or =, slanted 4.20. NLTE analysis is crucial for the very metal-poor turnoff and subgiant stars, for which the shift in log g between NLTE and LTE can be up to 0.5 dex. The obtained accurate atmospheric parameters will be used in the forthcoming papers to determine NLTE abundances of important astrophysical elements from lithium to europium and to improve observational constraints on the chemodynamical models of the Galaxy evolution.
The goal of this study was to determine the effects of genetic variation in the organic cation transporter 1, OCT1, on the pharmacokinetics of the antidiabetic drug, metformin. Twenty healthy ...volunteers with known OCT1 genotype agreed to participate in the study. Each subject received two oral doses of metformin followed by collection of blood and urine samples. OCT1 genotypes had a significant (P<0.05) effect on metformin pharmacokinetics, with a higher area under the plasma concentration–time curve (AUC), higher maximal plasma concentration (Cmax), and lower oral volume of distribution (V/F) in the individuals carrying a reduced function OCT1 allele (R61C, G401S, 420del, or G465R). The effect of OCT1 on metformin pharmacokinetics in mice was less than in humans possibly reflecting species differences in hepatic expression level of the transporter. Our studies suggest that OCT1 genotype is a determinant of metformin pharmacokinetics.
Clinical Pharmacology & Therapeutics (2008) doi:10.1038/sj.clpt.6100275
As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC) aims to survey a significant volume of the Galactic thin/thick discs and halo ...for a contiguous sky area of over 3400 deg2 centred on the Galactic anticentre (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3700–9000 low-resolution (R ∼ 1800) spectra for a statistically complete sample of ∼3 M stars of all colours down to a limiting magnitude of r ∼ 17.8 mag (to 18.5 mag for limited fields). Together with Gaia, the LSS-GAC will yield a unique data set to advance our understanding of the structure and assemblage history of the Galaxy, in particular its disc(s). In addition to the main survey, the LSS-GAC will also target hundreds of thousands objects in the vicinity fields of M 31 and M 33 and survey a significant fraction (over a million) of randomly selected very bright stars (r ≤ 14 mag) in the Northern hemisphere. During the Pilot and the first year Regular Surveys of LAMOST, a total of 1042 586 750 867 spectra of a signal-to-noise ratio S/N(7450 Å) ≥ 10 S/N(4650 Å) ≥ 10 have been collected. In this paper, we present a detailed description of the target selection algorithm, survey design, observations and the first data release of value-added catalogues (including radial velocities, effective temperatures, surface gravities, metallicities, values of interstellar extinction, distances, proper motions and orbital parameters) of the LSS-GAC.
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