Zirconium, Barium, Lanthanum and Europium Abundances in Open Clusters

We present an analysis of the s-process elements Zr, Ba, and La and the r-process element Eu in a sample of 50 stars in 19 open clusters. Stellar abundances of each element are based on measures of a minimum of two lines per species via both equivalent width and spectrum synthesis techniques. We investigate cluster mean neutron-capture abundance trends as a function of cluster age and location in the Milky Way disk and compare them to results found in other studies in the literature. We find a statistically significant trend of increasing cluster [Ba/Fe] as a function of decreasing cluster age, in agreement with recent findings for other open cluster samples, supporting the increased importance of low-mass asymptotic giant branch stars to the generation of s-process elements. However, the other s-process elements, [La/Fe] and [Zr/Fe], do not show similar dependences, in contrast to theoretical expectations and the limited observational data from other studies. Conversely, cluster [Eu/Fe] ratios show a slight increase with increasing cluster age, although with marginal statistical significance. Ratios of [s/r]-process abundances, [Ba/Eu] and [La/Eu], however, show more clearly the increasing efficiency of s-process relative to r-process enrichment in open cluster chemical evolution, with significant increases among younger clusters. Last, cluster neutron-capture element abundances appear to be independent of Galactocentric distance. We conclude that a homogeneous analysis of a larger sample of open clusters is needed to resolve the apparent discrepant conclusions between different studies regarding s-process element abundance trends with age to better inform models of galactic chemical evolution.Comment: 24 pages, 13 figures, 10 tables; published in The Astronomical Journa

Extended Stromgren Photoelectric Photometry in NGC 752

Photoelectric photometry on the extended Stromgren system (uvbyCa) is presented for 7 giants and 21 main sequence stars in the old open cluster, NGC 752. Analysis of the hk data for the turnoff stars yields a new determination of the cluster mean metallicity. From 10 single-star members, [Fe/H] = -0.06 +/- 0.03, where the error quoted is the standard error of the mean and the Hyades abundance is set at [Fe/H] = +0.12. This result is unchanged if all 20 stars within the limits of the hk metallicity calibration are included. The derived [Fe/H] is in excellent agreement with past estimates using properly-zeroed m1 data, transformed moderate-dispersion spectroscopy, and recent high dispersion spectroscopy.Comment: 14 tex'd pages including 2 tables; 2 separate files with eps figures Accepted for PASP March 200

1.6 W continuous-wave Raman laser using low-loss synthetic diamond

Low-birefringence (Δn<2x10−6), low-loss (absorption coefficient <0.006cm−1 at 1064nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240nm, CW output powers of 1.6W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%

Open clusters towards the Galactic center: chemistry and dynamics. A VLT spectroscopic study of NGC6192, NGC6404, NGC6583

In the framework of the study of the Galactic metallicity gradient and its time evolution, we present new high-resolution spectroscopic observations obtained with FLAMES and the fiber link to UVES at VLT of three open clusters (OCs) located within $\sim$7~kpc from the Galactic Center (GC): NGC~6192, NGC~6404, NGC~6583. We also present new orbit determination for all OCs with Galactocentric distances (R$_{\rm{GC}}) \leq$8~kpc and metallicity from high-resolution spectroscopy. We aim to investigate the slope of the inner disk metallicity gradient as traced by OCs and at discussing its implication on the chemical evolution of our Galaxy. We have derived memberships of a group of evolved stars for each clusters, obtaining a sample of 4, 4, and 2 member stars in NGC~6192, NGC~6404, and NGC~6583, respectively. Using standard LTE analysis we derived stellar parameters and abundance ratios for the iron-peak elements Fe, Ni, Cr, and for the $\alpha$-elements Al, Mg, Si, Ti, Ca. We calculated the orbits of the OCs currently located within 8~kpc from the GC, and discuss their implication on the present-time radial location. {The average metallicities of the three clusters are all oversolar: [Fe/H]= $+0.12\pm0.04$ (NGC~6192), $+0.11\pm0.04$ (NGC 6404), $+0.37\pm0.03$ (NGC 6583). They are in qualitative agreement with their Galactocentric distances, being all internal OCs, and thus expected to be metal richer than the solar neighborhood. The abundance ratios of the other elements over iron [X/Fe] are consistent with solar values. The clusters we have analysed, together with other OC and Cepheid data, confirm a steep gradient in the inner disk, a signature of an evolutionary rate different than in the outer disk.Comment: 17 pages, 13 figures, A&A accepted for publicatio

vbyCaHbeta CCD Photometry of Clusters. VI. The Metal-Deficient Open Cluster NGC 2420

CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-deficient open cluster, NGC 2420. Restricting the data to probable single members of the cluster using the CMD and the photometric indices alone generates a sample of 106 stars at the cluster turnoff. The average E(b-y) = 0.03 +/- 0.003 (s.e.m.) or E(B-V) = 0.050 +/- 0.004 (s.e.m.), where the errors refer to internal errors alone. With this reddening, [Fe/H] is derived from both m1 and hk, using b-y and Hbeta as the temperature index. The agreement among the four approaches is reasonable, leading to a final weighted average of [Fe/H] = -0.37 +/- 0.05 (s.e.m.) for the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When combined with the abundances from DDO photometry and from recalibrated low-resolution spectroscopy, the mean metallicity becomes [Fe/H] = -0.32 +/- 0.03. It is also demonstrated that the average cluster abundances based upon either DDO data or low-resolution spectroscopy are consistently reliable to 0.05 dex or better, contrary to published attempts to establish an open cluster metallicity scale using simplistic offset corrections among different surveys.Comment: scheduled for Jan. 2006 AJ; 33 pages, latex, includes 7 figures and 2 table

vbyCaHbeta CCD Photometry of Clusters. VIII. The Super-Metal Rich, Old Open Cluster NGC 6791

CCD photometry on the intermediate-band vbyCaHbeta system is presented for the metal-rich, old open cluster, NGC 6791. Preliminary analysis led to [Fe/H] above +0.4 with an anomalously high reddening and an age below 5 Gyr. A revised calibration between (b-y)_0 and [Fe/H] at a given temperature shows that the traditional color-metallicity relations underestimate the color of the turnoff stars at high metallicity. With the revised relation, the metallicity from hk and the reddening for NGC 6791 become [Fe/H] = +0.45 +/- 0.04 and E(b-y) = 0.113 +/- 0.012 or E(B-V) = 0.155 +/- 0.016. Using the same technique, reanalysis of the photometry for NGC 6253 produces [Fe/H] = +0.58 +/-0.04 and E(b-y) = 0.120 +/- 0.018 or E(B-V) = 0.160 +/- 0.025. The errors quoted include both the internal and external errors. For NGC 6791, the metallicity from m_1 is a factor of two below that from hk, a result that may be coupled to the consistently low metal abundance from DDO photometry of the cluster and the C-deficiency found from high dispersion spectroscopy. E(B-V) is the same value predicted from Galactic reddening maps. With E(B-V) = 0.15 and [Fe/H] = +0.45, the available isochrones predict an age of 7.0 +/- 1.0 Gyr and an apparent modulus of (m-M) = 13.60 +/- 0.15, with the dominant source of the uncertainty arising from inconsistencies among the isochrones. The reanalysis of NGC 6253 with the revised lower reddening confirms that on both the hk and m_1 metallicity scales, NGC 6253, while less than half the age of NGC 6791, remains at least as metal-rich as NGC 6791, if not richer.Comment: Accepted for Astronomical Journal. 42 p. latex file includes 11 figures and 3 tables, one of which is a short version of a data table to appear in online AJ in its entiret

Abundance Gradients and the Formation of the Milky Way

In this paper we adopt a chemical evolution model, which is an improved version of the Chiappini, Matteucci and Gratton (1997) model, assuming two main accretion episodes for the formation of the Galaxy. The present model takes into account in more detail than previously the halo density distribution and explores the effects of a threshold density in the star formation process, during both the halo and disk phases. In the comparison between model predictions and available data, we have focused our attention on abundance gradients as well as gas, stellar and star formation rate distributions along the disk. We suggest that the mechanism for the formation of the halo leaves detectable imprints on the chemical properties of the outer regions of the disk, whereas the evolution of the halo and the inner disk are almost completely disentangled. This is due to the fact that the halo and disk densities are comparable at large Galactocentric distances and therefore the gas lost from the halo can substantially contribute to building up the outer disk. We also show that the existence of a threshold density for the star formation rate, both in the halo and disk phase, is necessary to reproduce the majority of observational data in the solar vicinity and in the whole disk. Moreover, we predict that the abundance gradients along the Galactic disk must have increased with time and that the average [alpha/Fe] ratio in stars (halo plus disk) slightly decrease going from 4 to 10 Kpcs from the Galactic center. We also show that the same ratios increase substantially towards the outermost disk regions and the expected scatter in the stellar ages decreases, because the outermost regions are dominated by halo stars.Comment: 41 pages (including the figures), To be published in Ap

Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters

We present metallicity estimates for seven open clusters based on spectrophotometric indices from moderate-resolution spectroscopy. Observations of field giants of known metallicity provide a correlation between the spectroscopic indices and the metallicity of open cluster giants. We use \chi^2 analysis to fit the relation of spectrophotometric indices to metallicity in field giants. The resulting function allows an estimate of the target-cluster giants' metallicities with an error in the method of \pm0.08 dex. We derive the following metallicities for the seven open clusters: NGC 1245, [m/H]=-0.14\pm0.04; NGC 2099, [m/H]=+0.05\pm0.05; NGC 2324, [m/H]=-0.06\pm0.04; NGC 2539, [m/H]=-0.04\pm0.03; NGC 2682 (M67), [m/H]=-0.05\pm0.02; NGC 6705, [m/H]=+0.14\pm0.08; NGC 6819, [m/H]=-0.07\pm0.12. These metallicity estimates will be useful in planning future extra-solar planet transit searches since planets may form more readily in metal-rich environments.Comment: 38 pages, including 12 figures. Accepted for publication in A

Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood

A number of studies of abundance gradients in the galactic disk have been performed in recent years. The results obtained are rather disparate: from no detectable gradient to a rather significant slope of about -0.1 dex kpc -1. The present study concerns the abundance gradient based on the spectroscopic analysis of a sample of classical Cepheids. These stars enable one to obtain reliable abundances of a variety of chemical elements. Additionally, they have well determined distances which allow an accurate determination of abundance distributions in the galactic disc. Using 236 high resolution spectra of 77 galactic Cepheids, the radial elemental distribution in the galactic disc between galactocentric distances in the range 6-11 kpc has been investigated. Gradients for 25 chemical elements (from carbon to gadolinium) are derived...Comment: 28 pages, 14 postscript figures, LaTeX, uses Astronomy and Astrophysics macro aa.cls, graphicx package, to be published in Astronomy and Astrophysics (2002) also available at http://www.iagusp.usp.br/~maciel/index.htm

The Age of the Oldest Stars in the Local Galactic Disk From Hipparcos Parallaxes of G and K Subgiants

We review the history of the discovery of field subgiant stars and their importance in the age dating of the Galactic disk. We use the cataloged data from the Hipparcos satellite in this latter capacity. Based on Hipparcos parallaxes accurate to 10% or better, the absolute magnitude of the lower envelope of the nearly horizontal subgiant sequence for field stars in the H-R diagram for B-V colors between 0.85 and 1.05 is measured to be M_V = 4.03 +/- 0.06. The age of the field stars in the solar neighborhood is found to be 7.9 +/- 0.7 Gyr by fitting the theoretical isochrones for [Fe/H] = +0.37 to the lower envelope of the Hipparcos subgiants. The same grid of isochrones yields ages, in turn, of 4.0 +/- 0.2 Gyr, 6.2 +/- 0.5 Gyr, and 7.5 to 10 Gyr for the old Galactic clusters M67, NGC188, and NGC6791. The ages of both the Galactic disk in the solar neighborhood and of NGC6791 are, nevertheless, likely between 3 and 5 Gyr younger than the oldest halo globular clusters, which have ages of 13.5 Gyr. The most significant results are (1) the supermetallicity of the oldest local disk stars, and (2) the large age difference between the most metal-poor component of the halo and the thick and thin disk in the solar neighborhood. These facts are undoubtedly related and pose again the problem of the proper scenario for the timing of events in the formation of the halo and the Galactic disk in the solar neighborhood. [Abstract Abridged]Comment: 44 pages, 12 Figures; accepted for publication in PASP; high resolution versions of Figures 1, 2, 6 and 9 available at http://bubba.ucdavis.edu/~lubin/Sandage