55754943
A doubly rotating black ring with dipole charge
A bstractWe present a dipole-charged generalisation of the Pomeransky-Sen’kov black ring in five-dimensional Kaluza-Klein theory. It rotates in two independent directions, although one of the rotations has been tuned to achieve balance, so that the space-time does not contain any conical singularities. This solution was constructed using the inverse-scattering method in six-dimensional vacuum gravity. We then study various physical properties of this solution, with particular emphasis on the new features that the dipole charge introduces.
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.
17292810
Rotating black lens solution in five dimensions
It has recently been shown that a stationary, asymptotically flat vacuum black hole in five space-time dimensions with two commuting axial symmetries must have an event horizon with either a spherical, ring or lens-space topology. In this paper, we study the third possibility, a so-called black lens with $L(n,1)$ horizon topology. Using the inverse scattering method, we construct a black-lens solution with the simplest possible rod structure, and possessing a single asymptotic angular momentum. Its properties are then analyzed; in particular, it is shown that there must either be a conical singularity or a naked curvature singularity present in the space-time.
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
118555570
The Metallicity Gradient of the Thick Disk Based on Red Horizontal-branch Stars from SDSS DR8
Based on SDSS DR8, we have selected a sample of 1728 red horizontal-branch (RHB) stars with |Z| < 3 kpc by using a color-metallicity relation and stellar parameters. The sample stars clearly trace a typical thick disk population with peaks at |Z| = 1.26 kpc and [Fe/H] = –0.54. The vertical metallicity gradient of the thick disk is estimated in two ways. One is a fit to the Gaussian peaks of the metallicity histograms of the thick disk by subtracting minor contributions from the thin disk and the inner halo based on the Besancon Galaxy Model. The resulting gradient is –0.12 ± 0.01 dex kpc–1 for 0.5 < |Z| < 3 kpc. The other method is to linearly fit the data based on stars with 1 < |Z| < 3 kpc being the main component of the thick disk. Five subgroups are then selected in different directions in the X-|Z| plane to investigate the difference in the vertical metallicity gradient between the Galactocenter and anti-Galactocenter directions. We found that a vertical gradient of –0.22 ± 0.07 dex kpc–1 is detected for five directions except for one involving the pollution of stars from the bulge. The results indicate that the vertical gradient is dominant, but a radial gradient has a minor contribution for the thick disk population represented by RHB stars with 1 < |Z| < 3 kpc. The present work strongly suggests the existence of a metallicity gradient in the thick disk, which is thought to be negligible in most previous works in the literature.
118576878
Evolution of the most massive galaxies to z= 0.6 – I. A new method for physical parameter estimation
We use principal component analysis (PCA) to estimate stellar masses, mean stellar ages, star formation histories (SFHs), dust extinctions and stellar velocity dispersions for a set of ∼290 000 galaxies with stellar masses greater than 1011 M⊙ and redshifts in the range 0.4 < z < 0.7 from the Baryon Oscillation Spectroscopic Survey (BOSS). We find that the fraction of galaxies with active star formation first declines with increasing stellar mass, but then flattens above a stellar mass of 1011.5 M⊙ at z∼ 0.6. This is in striking contrast to z∼ 0.1, where the fraction of galaxies with active star formation declines monotonically with stellar mass. At stellar masses of 1012 M⊙, therefore, the evolution in the fraction of star-forming galaxies from z∼ 0.6 to the present day reaches a factor of ∼10. When we stack the spectra of the most massive, star-forming galaxies at z∼ 0.6, we find that half of their [O iii] emission is produced by active galactic nuclei. The black holes in these galaxies are accreting on average at ∼0.01 the Eddington rate. To obtain these results, we use the stellar population synthesis models of Bruzual & Charlot to generate a library of model spectra with a broad range of SFHs, metallicities, dust extinctions and stellar velocity dispersions. The PCA is run on this library to identify its principal components over the rest-frame wavelength range 3700–5500 A. We demonstrate that linear combinations of these components can recover information equivalent to traditional spectral indices such as the 4000-A break strength and HδA, with greatly improved signal-to-noise ratio (S/N). In addition, the method is able to recover physical parameters such as stellar mass-to-light ratio, mean stellar age, velocity dispersion and dust extinction from the relatively low S/N BOSS spectra. We examine in detail the sensitivity of our stellar mass estimates to the input parameters in our model library, showing that almost all changes result in systematic differences in logM* of 0.1 dex or less. The biggest differences are obtained when using different population synthesis models – stellar masses derived using Maraston et al. models are systematically smaller by up to 0.12 dex at young ages.
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.
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 ${\rm [Fe/H]} \simeq -0.4$.