R. Earle Luck

Using an Non-Local Thermodynamic Equilibrium (NLTE) analysis and a homogenous spectral data base, we have determined Ba abundances in a sample of 210 Galactic Cepheids and related objects. We confirm the previous result reported in Andrievsky et al. that the barium distribution in the range of Galactocentric distances from 5 to 18 kpc shows very small gradient value. The value determined here – d[Ba/H]/dR ≈ −0.01 dex kpc⁻¹ – is smaller than that for other s-process elements, such as La, Pr, Nd and Sm (Luck & Lambert), that typically show gradients of −0.03 dex kpc⁻¹.

This paper reports on the spectroscopic investigation of 238 Cepheids in the northern sky. Of these stars, about 150 are new to the study of the galactic abundance gradient. These new Cepheids bring the total number of Cepheids involved in abundance distribution studies to over 400. In this work we also consider systematics between various studies and also those which result from the choice of models. We find systematic variations exist at the 0.06 dex level both between studies and model atmospheres. In order to control the systematic effects our final gradients depend only on abundances derived herein. A simple linear fit to the Cepheid data from 398 stars yields a gradient d[Fe/H]/dRG = -0.062 \pm 0.002 dex/kpc which is in good agreement with previously determined values. We have also reexamined the region of the "metallicity island" of Luck et al. (2006). With the doubling of the sample in that region and our internally consistent abundances, we find there is scant evidence for a distinct island. We also find in our sample the first reported Cepheid (V1033 Cyg) with a pronounced Li feature. The Li abundance is consistent with the star being on its red-ward pass towards the first giant branch.

This paper reports on the spectroscopic investigation of 101 Cepheids in the Carina region. These Cepheids extend previous samples by about 35% in number and increase the amount of the galactic disk coverage especially in the direction of l \approx 270{\deg}. The new Cepheids do not add much information to the radial gradient, but provide a substantial increase in azimuthal coverage. We find no azimuthal dependence in abundance over an 80{\deg} angle from the galactic center in an annulus of 1 kpc depth centered on the Sun. A simple linear fit to the Cepheid data yields a gradient d[Fe/H]/dRG = -0.055 \pm 0.003 dex/kpc which is somewhat shallower than found from our previous, smaller Cepheid sample.

We present an abundance analysis for stars within 15 pc of the Sun located north of -30° declination. We have limited our abundance sample to absolute magnitudes brighter than +7.5 and have eliminated several A stars in the local vicinity. Our final analysis list numbers 114 stars. Unlike Allende Prieto et al. in their consideration of a very similar sample, we have enforced strict spectroscopic criteria in the determination of atmospheric parameters. Nevertheless, our results are very similar to theirs. We determine the mean metallicity of the local region to be = -0.07 using all stars and -0.04 when interlopers from the thick disk are eliminated.

We present atmospheric parameters and iron abundances derived from high-resolution spectra for three samples of dwarf stars: stars which are known to host close-in giant planets (CGP), stars for which radial velocity data exclude the presence of a close-in giant planetary companion (no-CGP), as well as a random sample of dwarfs with a spectral type and magnitude distribution similar to that of the planetary host stars (control). All stars have been observed with the same instrument and have been analyzed using the same model atmospheres, atomic data and equivalent width modeling program. Abundances have been derived differentially to the Sun, using a solar spectrum obtained with Callisto as the reflector with the same instrumentation. We find that the iron abundances of CGP dwarfs are on average by 0.22 dex greater than that of no-CGP dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are different than that of the control dwarfs, while the combined iron abundances have a distribution which is very similar to that of the control dwarfs. All four samples (CGP, no-CGP, combined, control) have different effective temperature distributions. We show that metal enrichment occurs only for CGP dwarfs with temperatures just below solar and approximately 300 K higher than solar, whereas the abundance difference is insignificant at Teff around 6000 K.Comment: 52 pages (aastex 11pt, preprint style), including 17 figures and 13 tables; accepted for publication in AJ (scheduled for the October 2003 issue