15542603
Sulphur abundances in disk stars: A correlation with silicon
We have performed new determinations of sulphur and silicon abundances for a sample of 26 disk stars based on high-resolution, high signal-to-noise spectra. The results indicate a solar (S/Fe) for (Fe/H) > 0:3, below which (S/Fe) increases to0.25 dex at (Fe/H) = 1:0. We find that there is a good correlation between (S/H) and (Si/H), indicating the same nucleosynthetic origin of the two elements. It seems that the ratio of sulphur to silicon does not depend on metallicity for (Fe/H)> 1:0. The implications of these results on models for the nucleosynthesis of-capture elements and the chemical evolution of the Galaxy are discussed.
55427109
THE CHROMOSPHERIC ACTIVITY, AGE, METALLICITY, AND SPACE MOTIONS OF 36 WIDE BINARIES
We present the chromospheric activity (CA) levels, metallicities, and full space motions for 41 F, G, K, and M dwarf stars in 36 wide binary systems. Thirty-one of the binaries contain a white dwarf (WD) component. In such binaries, the total age can be estimated by adding the cooling age of the WD to an estimate of the progenitor's main-sequence lifetime. To better understand how CA correlates to stellar age, 14 cluster member stars were also observed. Our observations demonstrate for the first time that, in general, CA decays with age from 50 Myr to at least 8 Gyr for stars with 1.0 {<=} V - I {<=} 2.4. However, little change occurs in the CA level for stars with V - I < 1.0 between 1 Gyr and 5 Gyr, consistent with the results of Pace et al. Our sample also exhibits a negative correlation between the stellar age and metallicity, a positive correlation between the stellar age and W space velocity component, and the W velocity dispersion increases with age. Finally, the population membership of these wide binaries is examined based upon their U, V, W kinematics, metallicity, and CA. We conclude that wide binaries are similar tomore » field and cluster stars in these respects. More importantly, they span a much more continuous range in age and metallicity than is afforded by nearby clusters.« less
16273589
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. (1993a) in order to re-inspect their re- sults and to reveal new information on the chemical evo- lution of the Galactic disk. Compared to Edvardsson et al. the present study in- cludes several improvements. Eective temperatures are based on the Alonso et al. (1996) calibration of color in- dices by the infrared flux method and surface gravities are calculated from Hipparcos parallaxes, which also allow more accurate ages to be calculated from a comparison of MV and Te with isochrones. In addition, more reli- able kinematical parameters are derived from Hipparcos distances and proper motions in combination with accu- rate radial velocities. Finally, a larger spectral coverage, 5600 8800 A, makes it possible to improve the abundance accuracy by studying more lines and to discuss several el- ements 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 andRm. Abundance ratios with respect to Fe show, on the other hand, no signicant scatter at a given (Fe/H). The derived
14138593
Sc and Mn abundances in disk and metal-rich halo stars
Sc and Mn abundances are determined for 119 F and G main-sequence stars with 1:4 < (Fe/H) < +0:1, represent- ing stars from the thin disk, the thick disk and the halo. The results indicate that Sc behaves like an element, showing a decreasing (Sc/Fe) with increasing metallicity in disk stars and a dual pattern in the kinematically selected halo stars. In contrast, Mn shows an increase from (Mn/Fe) ' 0:5 at (Fe/H) = 1:4 to zero at solar metallicity. There appears to be a discontinuity or sharp increase of (Mn/Fe) at (Fe/H) ' 0:7 corresponding to the transition between the thick and the thin disk. It is dis- cussed if supernovae of Type Ia are a major source of Mn in the Galactic disk or if the trend of (Mn/Fe) vs. (Fe/H) can be ex- plained by nucleosynthesis in Type II supernovae with a strong metallicity dependence of the yield.
118624022
Metallicity and Kinematic Distributions of Red Horizontal-branch Stars from the SDSS Survey
On the basis of a recently derived color-metallicity relation and stellar parameters from the Sloan Digital Sky Survey Data Release 7 spectroscopic survey, a large sample of red horizontal-branch (RHB) candidates have been selected to serve as standard candles. The metallicity and kinematic distributions of these stars indicate that they mainly originate from the thick-disk and the halo populations. The typical thick disk is characterized by the first group peaking at [Fe/H] ~ –0.6, V rot ~ 170 km s–1 with a vertical scale height around |Z| ~ 1.2 kpc, while stars with [Fe/H] 0 km s–1 (Halo I) shows a sign of metallicity gradient in the [Fe/H] versus |Z| diagram, while the other with V rot 10 kpc based on the star distribution in the R versus |Z| diagram.
15339664
Lithium abundances for 185 main-sequence stars - Galactic evolution and stellar depletion of lithium
We present a survey of lithium abundances in 185 main-sequence field stars with $5600 \la T_{\rm eff} \la 6600$ K and $-1.4 \la {\rm [Fe/H]} \la +0.2$ based on new measurements of the equivalent width of the $\lambda 6708$ Lii line in high-resolution spectra of 130 stars and a reanalysis of data for 55 stars from Lambert et al. ([CITE]). The survey takes advantage of improved photometric and spectroscopic determinations of effective temperature and metallicity as well as mass and age derived from Hipparcos absolute magnitudes, offering an opportunity to investigate the behaviour of Li as a function of these parameters. An interesting result from this study is the presence of a large gap in the $\log \varepsilon ({\rm Li}) - T_{\rm eff}$ plane, which distinguishes "Li-dip"stars like those first identified in the Hyades cluster by Boesgaard & Tripicco ([CITE]) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 $M_{\odot}$ at solar metallicity to 1.1 $M_{\odot}$ at ${\rm [Fe/H]} \simeq -1.0$. Excluding the Li-dip stars and a small group of lower mass stars with $T_{\rm eff} < 5900$ K and $\log \varepsilon ({\rm Li}) < 1.5$, the remaining stars, when divided into four metallicity groups, may show a correlation between Li abundance and stellar mass. The dispersion around the $\log \varepsilon ({\rm Li})$-mass relation is about 0.2 dex below ${\rm [Fe/H]} \simeq -0.4$ and 0.3 dex above this metallicity, which cannot be explained by observational errors or differences in metallicity. Furthermore, there is no correlation between the residuals of the $\log \varepsilon ({\rm Li})$-mass relations and stellar age, which ranges from 1.5 Gyr to about 15 Gyr. This suggests that Li depletion occurs early in stellar life and that parameters other than stellar mass and metallicity affect the degree of depletion, e.g. initial rotation velocity and/or the rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a given metallicity contributes to the dispersion in Li abundance. These problems make it difficult to determine the Galactic evolution of Li from the data, but a comparison of the upper envelope of the distribution of stars in the $\log \varepsilon ({\rm Li}) - {\rm [Fe/H]}$ plane with recent Galactic evolutionary models by Romano et al. ([CITE]) suggests that novae are a major source for the Li production in the Galactic disk; their occurrence seems to be the explanation for the steep increase of Li abundance at ${\rm [Fe/H]} \simeq -0.4$.
10522140
Evolution of the most massive galaxies to z ∼ 0.6 – II. The link between radio AGN activity and star formation
We analyze the optical spectra of massive (log M∗/M⊙ > 11.4) radio-loud galaxies at z � 0.2 and z � 0.6. Our samples are generated by crossmatching the SDSS DR7 and BOSS spectroscopic galaxy catalogues with the FIRST and NVSS radio continuum surveys. By comparing stellar population parameters of these radio-loud samples with radio-quiet control samples matched in stellar mass, velocity dispersion and redshift, we investigate how the presence of a radio-emitting jet relates to the recent star formation history of the host galaxy. We also investigate how the emissionline properties of the radio galaxies evolve with redshift by stacking their spectra. Our main results are the following. (1) Both at low and at high redshift, half as many radio-loud as radio-quiet galaxies have experienced significant star formation in the past Gyr. This difference in star formation history is independent of the luminosity of the radio AGN, except at radio luminosities greater than 10 25.5 W Hz −1 , where it disappears. (2) The Balmer absorption line properties of massive galaxies that have experienced recent star formation show that star formation occurred as a burst in many of these systems. (3) Both the radio and the emission-line luminosity of radio AGN evolve significantly with redshift. The average [O iii] rest equivalent width increases by 1 dex from z = 0.2 to z = 0.6, and emission line ratios change from LINER-like at low redshift to Seyfert-like at high redshift. However, radio galaxies with similar stellar population parameters, have similar emission-line properties both at high- and at low-redshift. These results suggest that massive galaxies experience cyclical episodes of gas accretion, star formation and black hole growth, followed by the production of a radio jet that shuts down further activity. The behaviour of galaxies with log M∗/M⊙ > 11.4 is the same at z = 0.6 as it is at z = 0.2, except that higher redshift galaxies experience more star formation and black hole growth and produce more luminous radio jets during each accretion cycle.
18353027
An Observation of Autocorrelation of Wilson Loops on Lattice
An observation of the autocorrelation of Wilson loops on lattice is presented, especially for the small separation in Markov chain. We give a possible explanation for such behavior. We also present the dependence of autocorrelation behavior on the chosen operators in this paper.
119299152
Spectral Classification and Redshift Measurement for the SDSS-III Baryon Oscillation Spectroscopic Survey
We describe the automated spectral classification, redshift determination, and parameter measurement pipeline in use for the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III (SDSS-III) as of the survey's ninth data release (DR9), encompassing 831,000 moderate-resolution optical spectra. We give a review of the algorithms employed, and describe the changes to the pipeline that have been implemented for BOSS relative to previous SDSS-I/II versions, including new sets of stellar, galaxy, and quasar redshift templates. For the color-selected "CMASS" sample of massive galaxies at redshift 0.4 ≲ z ≲ 0.8 targeted by BOSS for the purposes of large-scale cosmological measurements, the pipeline achieves an automated classification success rate of 98.7% and confirms 95.4% of unique CMASS targets as galaxies (with the balance being mostly M stars). Based on visual inspections of a subset of BOSS galaxies, we find that approximately 0.2% of confidently reported CMASS sample classifications and redshifts are incorrect, and about 0.4% of all CMASS spectra are objects unclassified by the current algorithm which are potentially recoverable. The BOSS pipeline confirms that ~51.5% of the quasar targets have quasar spectra, with the balance mainly consisting of stars and low signal-to-noise spectra. Statistical (as opposed to systematic) redshift errors propagated from photon noise are typically a few tens of km s–1 for both galaxies and quasars, with a significant tail to a few hundreds of km s–1 for quasars. We test the accuracy of these statistical redshift error estimates using repeat observations, finding them underestimated by a factor of 1.19-1.34 for galaxies and by a factor of two for quasars. We assess the impact of sky-subtraction quality, signal-to-noise ratio, and other factors on galaxy redshift success. Finally, we document known issues with the BOSS DR9 spectroscopic data set and describe directions of ongoing development.
119228842
A New AF gravitational instanton
Abstract It has long been conjectured that the Euclidean Schwarzschild and Euclidean Kerr instantons are the only non-trivial asymptotically flat (AF) gravitational instantons. In this Letter, we show that this conjecture is false by explicitly constructing a new two-parameter AF gravitational instanton with a U ( 1 ) × U ( 1 ) isometry group, using the inverse-scattering method. It has Euler number χ = 3 and Hirzebruch signature τ = 1 , and its global topology is C P 2 with a circle S 1 removed appropriately. Various other properties of this gravitational instanton are also discussed.
119107777
The Roper Puzzle
We carried out a calculation of the Roper state with the Sequential Empirical Bayesian (SEB) method with overlap valence fermion on 2+1-flavor domain-wall fermion configurations on the 24^3 x 64 lattice with a^{-1} = 1.73 GeV. The light sea quark mass corresponds to a pion mass of 330 MeV. The mass of the Roper, chirally extrapolated to the physical pion mass, is 1404(112) MeV which is consistent with the experimental value at 1440 MeV. When compared to the Roper state calculation with variational method for Clover and twisted mass fermions, it is found that the Roper states from SEB with overlap fermion are systematically lower by 400 - 800 MeV for all the quark masses ranging from light to the strange mass region. We study the origin of the difference by exploring the size of the interpolation field in relation to the radial wavefunction of the Roper and also the dynamical influence of the higher Fock space.