The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees

TL;DR

This study analyzes 238 Cepheids, including 150 new ones, to refine the galactic abundance gradient, examine the metallicity island, and report a Cepheid with a notable lithium feature, ensuring systematic effects are minimized.

Contribution

It provides a new, internally consistent measurement of the galactic abundance gradient using a large Cepheid sample, and reevaluates the metallicity island with improved data.

Findings

Galactic abundance gradient d[Fe/H]/dRG = -0.062 0.002 dex/kpc.

No significant evidence for the previously suggested metallicity island.

First report of a Cepheid (V1033 Cyg) with a pronounced lithium feature.

Abstract

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.