On the inconsistency of [C/Fe] abundances and the fractions of carbon-enhanced metal-poor stars among various stellar surveys

Abstract

Carbon-enhanced metal-poor (CEMP) stars are a unique resource for Galactic archaeology because they probe the properties of the First Stars, early chemical evolution and binary interactions at very low metallicity. Comparing the fractions and properties of CEMP stars in different Galactic environments can provide us with unique insights into the formation and evolution of the Milky Way halo and its building blocks. In this work, we investigate whether directly comparing fractions of CEMP stars from different literature samples of very metal-poor ([Fe/H] < -2.0) stars is valid. We compiled published CEMP fractions and samples of Galactic halo stars from the past 25 years, and find that they are not all consistent with each other. Focusing on giant stars, we find significant differences between various surveys when comparing their trends of [Fe/H] versus [C/Fe] and their distributions of CEMP stars. To test the role of the analysis pipelines for low-resolution spectroscopic samples, we re-analysed giant stars from various surveys with the SSPP and FERRE pipelines. We found systematic differences in [C/Fe] of ~0.1-0.4 dex, partly independent of degeneracies with the stellar atmospheric parameters. These systematics are likely due to the different pipeline approaches, different assumptions in the employed synthetic grids, and/or the comparison of different evolutionary phases. We conclude that current biases in (the analysis of) very metal-poor samples limit the conclusions one can draw from comparing different surveys. We provide some recommendations and suggestions that will hopefully aid the community to unlock the full potential of CEMP stars for Galactic archaeology.

Published in MNRAS, only very minor changes compared to submitted version

References in corpus (50)

• Array Programming with NumPy
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Radial Velocity Experiment (RAVE): first data release
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• 4MOST: Project overview and information for the First Call for Proposals
• CH in stellar atmospheres: an extensive linelist
• A strong case for fast stellar rotation at very low metallicities
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies
• Binarity in Carbon-Enhanced Metal-Poor stars
• Dynamical Relics of the Ancient Galactic Halo
• Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars
• Four-hundred Very Metal-Poor Stars Studied with LAMOST and Subaru. II. Elemental abundances
• Center-to-Limb Variation of Solar 3-D Hydrodynamical Simulations
• The Best and Brightest Metal-Poor Stars
• Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-Metal" Stars - Confirmation of Metal-Poor Stars in the Thick Disk of the Galaxy
• A high-resolution spectral analysis of three carbon-enhanced metal-poor stars
• Deep SDSS optical spectroscopy of distant halo stars I. Atmospheric parameters and stellar metallicity distribution
• Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods
• The Gaia-ESO Survey: the most metal-poor stars in the Galactic bulge
• The Pristine Survey -- VI. The first three years of medium-resolution follow-up spectroscopy of Pristine EMP star candidates
• Detailed Abundances in the Ultra-faint Magellanic Satellites Carina II and III
• The SkyMapper DR1.1 Search for Extremely Metal-Poor Stars
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis
• The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way
• Carbon and oxygen in metal-poor halo stars
• The Photometric Metallicity and Carbon Distributions of the Milky Way's Halo and Solar Neighborhood from S-PLUS Observations of SDSS Stripe 82
• The Most Metal-Poor Stars. V. The CEMP-no Stars in 3D and Non-LTE
• Chemical Cartography. I. A Carbonicity Map of the Galactic Halo
• WHT follow-up observations of extremely metal-poor stars identified from SDSS and LAMOST
• Dynamically Tagged Groups of Metal-Poor Stars from the Best \& Brightest Survey
• The S2 Stream: the shreds of a primitive dwarf galaxy
• High resolution spectroscopic follow-up of the most metal-poor candidates from SkyMapper DR1.1
• Stellar metallicities from SkyMapper photometry I: A study of the Tucana II ultra-faint dwarf galaxy
• Origin of the CEMP-no Group Morphology in the Milky Way
• The Pristine Inner Galaxy Survey (PIGS) III: carbon-enhanced metal-poor stars in the bulge
• Chemical Cartography. II. The Assembly History of the Galactic Stellar Halo Traced by Carbon-Enhanced Metal-Poor Stars
• Four-hundred Very Metal-poor Stars studied with LAMOST and Subaru. I. Survey Design, Follow-up Program, and Binary Frequency
• An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres. II. Carbon-enhanced metal-poor 3D model atmospheres
• Identification of a Group III CEMP-no Star in the Dwarf Spheroidal Galaxy Canes Venatici I
• Targeting Bright Metal-poor Stars in the Disk and Halo Systems of the Galaxy
• The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations
• Metal-Poor Stars Observed with the Southern African Large Telescope II. An Extended Sample
• Carbon-enhanced metal-poor stars in the SDSS-APOGEE database

Cited by in corpus (5)

• The Pristine Inner Galaxy Survey (PIGS) V: a chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge
• Carbon-Enhanced Metal-Poor star candidates from BP/RP Spectra in $Gaia$ DR3
• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
• Mining S-PLUS for Metal-Poor Stars in the Milky Way
• The Pristine survey -- XX: GTC follow-up observations of extremely metal-poor stars identified from Pristine and LAMOST