Spectroscopic Validation of Low-Metallicity Stars from RAVE

TL;DR

This study spectroscopically confirms the metallicity and chemical properties of 1,694 RAVE star candidates, identifying numerous CEMP stars and demonstrating the effectiveness of Gaia data in selecting low-metallicity stars.

Contribution

It provides a large, spectroscopically validated sample of low-metallicity stars, including detailed carbon and alpha-element abundances, and introduces Gaia-based criteria for candidate selection.

Findings

88% of stars have [Fe/H] <= -1.0

306 CEMP star candidates identified

Gaia transverse velocities aid in low-metallicity selection

Abstract

We present results from a medium-resolution (R ~ 2, 000) spectroscopic follow-up campaign of 1,694 bright (V < 13.5), very metal-poor star candidates from the RAdial Velocity Experiment (RAVE). Initial selection of the low-metallicity targets was based on the stellar parameters published in RAVE Data Releases 4 and 5. Follow-up was accomplished with the Gemini-N and Gemini-S, the ESO/NTT, the KPNO/Mayall, and the SOAR telescopes. The wavelength coverage for most of the observed spectra allows for the determination of carbon and {\alpha}-element abundances, which are crucial for con- sidering the nature and frequency of the carbon-enhanced metal-poor (CEMP) stars in this sample. We find that 88% of the observed stars have [Fe/H] <= -1.0, 61% have [Fe/H] <= -2.0, and 3% have [Fe/H] <= -3.0 (with four stars at [Fe/H] <= -3.5). There are 306 CEMP star candidates in this sample, and we identify 169 CEMP Group I, 131 CEMP Group II, and 6 CEMP Group III stars from the A(C) vs. [Fe/H] diagram. Inspection of the [alpha/C] abundance ratios reveals that five of the CEMP Group II stars can be classified as "mono-enriched second-generation" stars. Gaia DR1 matches were found for 734 stars, and we show that transverse velocities can be used as a confirmatory selection criteria for low-metallicity candidates. Selected stars from our validated list are being followed-up with high-resolution spectroscopy, to reveal their full chemical abundance patterns for further studies.