Spectroscopic Validation of Low-metallicity Stars from RAVE

Abstract

We present results from a medium-resolution (R∼2000) spectroscopic follow-up campaign of 1694 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 α-element abundances, which are crucial for considering the nature and frequency of the carbon-enhanced metalpoor (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) versus [Fe/H] diagram. Inspection of the C a [ ] 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.

The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

“…Indeed, the spectroscopic parameters for J0937−0626 place it in the expected region for old, moderately metal-poor HB stars. The spectroscopic temperature is also in agreement with the photometric analysis by Munari et al (2014) and the spectroscopic RAVE DR5 value (Kunder et al 2017), while the temperature, surface gravity, and metallicity are in agreement with the medium-resolution analysis of Placco et al (2018). Gaia has provided a parallax for J0937−0626 in Data Release 2 (Gaia Collaboration et al 2016, which gives a distance; Bailer-Jones et al…”

“…The [X/Fe] ratios for Mg, Si, and Ca are subsolar, while [Ti/Fe] is roughly solar; these ratios are subsolar even when LTE parameters are used. Placco et al (2018) also found a low [α/Fe] = − 0.09 based on a medium-resolution spectrum.…”

“…OBSERVATIONS, DATA REDUCTION, AND ATMOSPHERIC PARAMETERS J0937−0626 was identified as a metal-poor star in Data Release 4 of the RAdial Velocity Experiment (RAVE; Steinmetz et al 2006;Kordopatis et al 2013a) and the subsequent re-analysis by Matijevic et al (2017). It was then targeted for a medium-resolution, optical analysis by Placco et al (2018). J0937−0626 was then observed at high spectral resolution in 2016 and 2017 using the Astrophysical Research Consortium (ARC) 3.5-m telescope at Apache Point Observatory, as part of the Northern Hemisphere survey of the RPA ).…”

Accuracy and Precision of Industrial Stellar Abundances

“…Their Table 5 is a nice summary of the situation, showing, in general, agreements for S/N > 50 spectra in T eff on the order of 100 K, and in log g and [Fe/H] of about 0.1 to 0.2 dex. Recent comparisons of the different sets of RAVE parameters (DR4, DR5, RAVE-on) to independent determinations by Placco et al (2018) in the low metallicity regime show significant discrepancies well above the errors mentioned above. Casey et al (2017) One special feature of this survey is that it targets stars of wider spectral ranges than FGK-type owing to different science cases for which groups within the consortium have developed their own analysis methods.…”

The R-Process Alliance: First Release from the Northern Search for r-process-enhanced Metal-poor Stars in the Galactic Halo

“…e "P18" indicates that the target was included in the medium-resolution follow-up of Placco et al (2018), while "Std" indicates that the star was previously observed by others. f Based on radial velocity variations, this object is a suspected or confirmed binary.…”