Systematic Differences in Spectroscopic Analysis of Red Giants

Abstract

A spectroscopic analysis of stellar spectra can be carried out using different approaches; different methods, line lists, atomic parameters, solar abundances etc. The resulting atmospheric parameters from these choices can vary beyond quoted uncertainties in the literature. Here we characterize these differences by systematically comparing some of the commonly adopted ingredients; line lists, equivalent width measurements and atomic parameters. High resolution and high signal-to-noise spectroscopic data of one helium-core-burning red giant star in each of the three open clusters, NGC6819, M67 and NGC188 have been obtained with the FIES spectrograph at the Nordic Optical Telescope. The M67 target has been used to benchmark the analysis, as it is a well studied cluster with asteroseismic data from the K2 mission. For the other two clusters we have obtained higher quality data than previously analyzed, which allows us to establish their chemical composition more securely. Using a line by line analysis, we tested several different combinations of line lists and programs to measure equivalent widths of absorption lines to characterize systematic differences within the same spectroscopic method. The obtained parameters for the benchmark star in M67 vary up to ~170 K in T_eff, ~0.4 dex in log g and ~0.25 dex in [Fe/H] between the tested setups. Using the combination of equivalent width measurement program and line list that best reproduce the inferred log g from asteroseismology, we determined the atmospheric parameters for the three stars and securely established the chemical composition of NGC6819 to be ~solar, [Fe/H]=-0.02+-0.01 dex. We have highlighted the significantly different results obtained with different combinations of line lists, programs and atomic parameters, which emphasize the importance of benchmark stars studied with several different methods to anchor spectroscopic analyses.

arXiv commentAccepted for publication in Astronomy and Astrophysics

References in corpus (62)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• The K2 Mission: Characterization and Early results
• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• ASPCAP: The Apogee Stellar Parameter and Chemical Abundances Pipeline
• Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
• The effective temperature scale of FGK stars. II. Teff : color : [Fe/H] calibrations
• On the use of empirical bolometric corrections for stars
• NLTE line formation of Fe for late-type stars. I. Standard stars with 1D and <3D> model atmospheres
• NLTE line formation of Fe in late-type stars II: 1D spectroscopic stellar parameters
• Asteroseismology of old open clusters with Kepler: direct estimate of the integrated RGB mass loss in NGC6791 and NGC6819
• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• A new code for automatic determination of equivalent widths: Automatic Routine for line Equivalent widths in stellar Spectra (ARES)
• Gaia FGK Benchmark Stars - Metallicity
• The Second APOKASC Catalog: The Empirical Approach
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• The elemental composition of the Sun II. The iron group elements Sc to Ni
• High-precision abundances of elements in solar twin stars: Trends with stellar age and elemental condensation temperature
• A non-LTE study of neutral and singly-ionized iron line spectra in 1D models of the Sun and selected late-type stars
• Fundamental Properties of Stars using Asteroseismology from Kepler & CoRoT and Interferometry from the CHARA Array
• DAOSPEC: an automatic code for measuring equivalent widths in high-resolution stellar spectra
• Accurate fundamental parameters for 23 bright solar-type stars
• Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars
• Accurate parameters of 93 solar-type Kepler targets
• Galactic archaeology: mapping and dating stellar populations with asteroseismology of red-giant stars
• 3D Hydrodynamical Simulations of Surface Convection in Red Giant Stars. Impact on spectral line formation and abundance analysis
• The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample
• Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars
• Metal Abundances of Red Clump Stars in Open Clusters: I. NGC 6819
• Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. II. age dependencies and new insights
• Verifying asteroseismically determined parameters of Kepler stars using hipparcos parallaxes: self-consistent stellar properties and distances
• Deriving precise parameters for cool solar-type stars. Optimizing the iron line list
• Asteroseismology of the open clusters NGC 6791, NGC 6811, and NGC 6819 from nineteen months of Kepler photometry
• Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA
• Interferometric radii of bright Kepler stars with the CHARA Array: θ Cygni and 16 Cygni A and B
• Ground-based CCD astrometry with wide field imagers. II. A star catalogue for M67: [email protected] MPG/ESO astrometry, FLAMES@VLT radial velocities
• Stroemgren survey for Asteroseismology and Galactic Archaeology: let the SAGA begin
• An accurate and self-consistent chemical abundance catalogue for the APOGEE/Kepler sample
• NGC 6819: testing the asteroseismic mass scale, mass loss, and evidence for products of non-standard evolution
• Abundances and possible diffusion of elements in M67 stars
• Establishing the accuracy of asteroseismic mass and radius estimates of giant stars. I. Three eclipsing systems at [Fe/H]~ -0.3 and the need for a large high-precision sample
• The Hyades open cluster is chemically inhomogeneous
• WIYN Open Cluster Study. XXIV. Stellar Radial-Velocity Measurements in NGC 6819
• Detection of solar-like oscillations in relics of the Milky Way: asteroseismology of K giants in M4 using data from the NASA K2 mission
• Age and distance for the old open cluster NGC188 from the eclipsing binary member V12
• The K2 M67 Study: Revisiting old friends with K2 reveals oscillating red giants in the open cluster M67
• High-precision abundances of elements in Kepler LEGACY stars. Verification of trends with stellar age
• A Comparison of Stellar Elemental Abundance Techniques and Measurements
• Comparative Modelling of the Spectra of Cool Giants
• OCCASO II. Physical parameters and Fe abundances of Red Clump stars in 18 Open Clusters
• Evolution of lithium beyond the solar age: a Li survey of the old open cluster NGC 188
• A Star Catalog for the Open Cluster NGC188
• Spectroscopic Abundances in the Open Cluster, NGC 6819
• The [Y/Mg] clock works for evolved solar metallicity stars
• Tool for Automatic Measurement of Equivalent width (TAME)
• Data Compression for the Tomo-e Gozen with Low-rank Matrix Approximation
• Chemical abundance analysis of the old, rich open cluster Trumpler 20
• Atmospheric parameters of red giants in the Kepler field
• Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia
• The CoRoT-GES Collaboration. Improving Red Giants spectroscopic surface gravity and abundances with asteroseismology
• The Homogenous Study of Transiting Systems (HoSTS). II. The influence of the line list on stellar parameters

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• Testing asteroseismology with Gaia DR2: Hierarchical models of the Red Clump
• Li Evolution and the Open Cluster NGC 6819: A Correlation Between Li Depletion and Spindown in Dwarfs More Massive Than the F-Dwarf Li-Dip
• Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. III. Constraints from a subgiant
• Asteroseismology of the Hyades red giant and planet host epsilon Tauri
• Asteroseismology of overmassive, undermassive, and potential past members of the open cluster NGC6791
• SPECIES II. Stellar parameters of the EXPRESS program giant star sample
• An asteroseismic age estimate of the open cluster NGC 6866 using Kepler and Gaia
• Establishing the accuracy of asteroseismic mass and radius estimates of giant stars III. KIC4054905, an eclipsing binary with two 10 Gyr thick disk RGB stars
• An extended and refined grid of 3D STAGGER model atmospheres. Processed snapshots for stellar spectroscopy
• Properties of the Hyades, the eclipsing binary HD27130, and the oscillating red giant $\epsilon$ Tau
• Extremely precise age and metallicity of the open cluster NGC 2506 using detached eclipsing binaries
• Establishing the accuracy of asteroseismic mass and radius estimates of giant stars. II. Revised stellar masses and radii for KIC 8430105
• Exploring the dependence of chemical traits on metallicity: chemical trends for red giant stars with asteroseismic ages
• Anomalously low-mass core-He-burning star in NGC 6819 as a post-common-envelope phase product
• Advancing accuracy in age determinations of old-disk stars using an oscillating red giant in an eclipsing binary
• Pushing the boundaries of asteroseismic individual frequency modelling: unveiling two evolved very-low metallicity red giants
• Metallicities in M dwarfs: Investigating different determination techniques