An empirical metallicity tracer in CEMP and C-normal stars
arXiv:2001.02684 · doi:10.1051/0004-6361/201936305
Abstract
Deriving the metallicity, [Fe/H], in low-resolution spectra of carbon-enhanced metal-poor (CEMP) stars is a tedious task that, owing to the large number of line blends, often leads to uncertainties on [Fe/H] exceeding 0.25dex. The CEMP stars increase in number with decreasing [Fe/H] and some of these are known to be bona fide second generation halo stars. Hence, knowing their [Fe/H] is important for tracing the formation and chemical evolution of the Galaxy. Here, we aim to improve the [Fe/H] measurements in low-resolution spectra by avoiding issues related to blends. We improve our chemical tagging in such spectra at low metallicities. We developed an empirical way of deriving [Fe/H] in CEMP (and C-normal) stars that relates the equivalent width (EW) of strong lines, which remain detectable in lower-resolution, metal-poor spectra. The best [Fe/H] tracers are found to be Cr I and Ni I, which both show strong transitions in spectral regions that are free of molecular bands (between ~5200-6800A, a region accessible to most surveys). We derive different relations for dwarfs and giants. The relations are valid in the ranges ~-3<[Fe/H]<-0.5 and 10<EW<800mA (Cr) or [Fe/H]>-3.2 and EW>5mA (Ni), depending on the element and line as well as the stellar evolutionary stage. The empirical relations are valid for both CEMP and C-normal stars and have been proven to be accurate tracers in a sample of ~400 stars (mainly giants). The metallicities are accurate to within ~0.2 depending on the sample and resolution, and the empirical relations are robust to within 0.05-0.1dex. Our relations will improve the metallicity determination in future surveys, which will encounter a large number of CEMP stars, and will greatly speed up the process of determining [Fe/H] as the EWs only need to be measured in two or three lines in relatively clean regions compared to dealing with numerous blended Fe lines. Abrigded.
12 pages, 15 figures, 7 pages appendix. Accepted by A&A
References in corpus (16)
- Determining stellar atmospheric parameters and chemical abundances of FGK stars with iSpec
- Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
- A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
- An extremely primitive halo star
- Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
- The intermediate neutron-capture process and carbon-enhanced metal-poor stars
- TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
- The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars
- An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
- Silver and palladium help unveil the nature of a second r-process
- Lithium abundances in CEMP stars
- Observational Constraints on First-Star Nucleosynthesis. II. Spectroscopy of an Ultra Metal-Poor CEMP-no Star
- Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
- Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars
- Carbon and oxygen in metal-poor halo stars
- The Most Metal-Poor Stars. V. The CEMP-no Stars in 3D and Non-LTE