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
56306739
Abundances of neutron-capture elements in G 24-25 - A halo-population CH subgiant
Aims. The differences between the neutron-capture element abundances of halo stars are important to our understanding of the nucleosynthesis of elements heavier than the iron group. We present a detailed abundance analysis of carbon and twelve neutron-capture elements from Sr up to Pb for a peculiar halo star G 24-25 with [Fe/H] = −1.4 in order to probe its origin. Methods. The equivalent widths of unblended lines are measured from high resolution NOT/FIES spectra and used to derive abundances based on Kurucz model atmospheres. In the case of CH, Pr, Eu, Gd, and Pb lines, the abundances are derived by fitting synthetic profiles to the observed spectra. Abundance analyses are performed both relative to the Sun and to a normal halo star G 16-20 that has similar stellar parameters as G 24-25. Results. We find that G 24-25 is a halo subgiant star with an unseen component. It has large overabundances of carbon and heavy s-process elements and mild overabundances of Eu and light s-process elements. This abundance distribution is consistent with that of a typical CH giant. The abundance pattern can be explained by mass transfer from a former asymptotic giant branch component, which is now a white dwarf.
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 ${\rm [Fe/H]} \simeq -0.4$.
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.
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.
119292768
THE KINEMATICS AND CHEMISTRY OF RED HORIZONTAL BRANCH STARS IN THE SAGITTARIUS STREAMS
We have selected 556 red horizontal branch stars along the streams of the Sagittarius (Sgr) dwarf galaxy from Sloan Digital Sky Survey DR7 spectroscopic data using a theoretical model. The metallicity and ?-element distributions are investigated for stars in the Sgr streams and for Galactic stars at the same locations. We find that the Sgr stars have two peaks in the metallicity distribution while the Galactic stars have a more prominent metal-poor peak. Meanwhile, [?/Fe] ratios of the Sgr stars are lower than those of the Galactic stars. Among the Sgr stars, we find a difference in the metallicity distribution between the leading and trailing arms of the Sgr tidal tails. The metallicity and [?/Fe] distribution of the leading arm is similar to that of the Galaxy. The trailing arm is composed mainly of a metal-rich component and [?/Fe] is obviously lower than that of the Galactic stars. The metallicity gradient is ?(1.8 ? 0.3)? 10?3?dex?deg?1 in the first wrap of the trailing arm and ?(1.5 ? 0.4)? 10?3?dex?deg?1 in the first wrap of the leading arm. No significant gradient exists along the second wraps of the leading or trailing arms. It seems that the Sgr dwarf galaxy initially lost the metal-poor component in the second wrap (older) arms due to the tidal force of our Galaxy and then the metal-rich component is disrupted in the first wrap (younger) arms. Finally, we found that the velocity dispersion of the trailing arm from 88? < ?? < 112? is ? = 9.808 ? 1.0?km?s?1, which is consistent with previous work in the literature.
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.
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.
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.
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.
15744505
Radio Luminosity, Black Hole Mass and Eddington Ratio for Quasars from the Sloan Digital Sky Survey
We investigate the MBH-O''.relation for radio-loud quasars with redshift z＜0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS).The sample consists of 3772 quasars with better models of the H/~ and [O III] lines and available radio luminosity,including 306 radio-loud quasars,3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity (181 radio-quiet quasars with measured radio luminosity).The virial supermassive black hole mass (MBH) is calculated from the broad H/line,and the host stellar velocity dispersion (σ*) is traced by the core [O III] gaseous velocity dispersion.The radio luminosity and radio loudness are derived from the FIRST catalog.Our results are as follows:(1) For radio-quiet quasars,we confirm that there is no obvious deviation from the MBH-O.relation defined for inactive galaxies when the uncertainties in MBH and the luminosity bias are concerned.(2) We find that the radio-loud quasars deviate more from the MBH-σ.relation than do the radio-quiet quasars.This deviation is only partly due to a possible cosmological evolution of the MBH-σ* relation and the luminosity bias.(3) The radioluminosity is proportional to M128+0.23-0.16 BH(LBol/LEdd)1.29+0.31-0.24 for radio-quiet quasars and to M3.10+0.6.-0.70(LBol.LEdd)4.18+1.40-1.10 for radio-loud quasars.The weaker dependence of the radio luminosity on the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities,such as the spin of the black hole.