J/A+A/622/A111 Systematic diff. in spectroscopic analysis (Slumstrup+ 2019)
Systematic differences in spectroscopic analysis of red giants.
Slumstrup D., Grundahl F., Silva Aguirre V., Brogaard K.
<Astron. Astrophys. 622, A111 (2019)>
=2019A&A...622A.111S 2019A&A...622A.111S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Abundances ; Equivalent widths
Keywords: stars: fundamental parameters - stars: abundances -
open clusters and associations: individual: NGC 6819 -
open clusters and associations: individual: M67 -
open clusters and associations: individual: NGC 188 - stars: late-type
Abstract:
A spectroscopic analysis of stellar spectra can be carried out using
multiple approaches such as different methods, line lists, atmospheric
models, atomic parameters, and solar abundances. The resulting
atmospheric parameters from these choices can vary beyond the quoted
uncertainties in the literature. We characterize these differences by
systematically comparing some of the commonly adopted ingredients such
as line lists, equivalent width measurements, and atomic parameters.
High-resolution and high signal-to-noise (S/N) spectroscopic data of
one helium-core-burning red giant star in each of the three open
clusters, NGC 6819, M67, and NGC 188 were obtained with the FIES
spectrograph at the Nordic Optical Telescope. The M67 target was 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
obtained higher quality data than had been analyzed before, 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 stellar
absorption lines to characterize systematic differences within the
same spectroscopic method.
The obtained parameters for the benchmark star in M67 vary up to ∼170K
in effective temperature, ∼0.4dex in logg and ∼0.25dex in [Fe/H]
between the tested setups. Using the combination of an equivalent
width measurement program and line list that best reproduce the
inferred surface gravity from asteroseismology, we determined the
atmospheric parameters for the three stars and securely established
the chemical composition of NGC 6819 to be close to solar,
[Fe/H]=-0.02±0.01dex.
We highlighted the significantly different results obtained with
different combinations of line lists, programs, and atomic parameters.
The results emphasize the importance of benchmark stars studied with
several methods to anchor spectroscopic analyses.
Description:
Systematic differences were characterized in a line-by-line
spectroscopic analysis of high resolution and high signal-to-noise
spectra of red clump stars in three open clusters occuring due to
changes in line list, program for measuring equivalent widths and
atomic parameters. Surface gravities determined with asteroseismology
was used to constrain the result. The metallicity of NGC 6819 was
determined to be close to solar.
The final line list for NGC 6819, M67 and NGC 188 targets.
Objects:
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RA (ICRS) DE Designation(s)
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19 41 18 +40 11.2 NGC 6819 = Cl Melotte 223
08 51 18 +11 48.0 M67 = NGC 2682
00 48 26 +85 15.3 NGC 188 = Cl Melotte 2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 61 214 Line list
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 0.1nm lambda Central wavelength of line
14- 17 F4.1 --- El Numeric description of element
22- 26 F5.3 eV EP Excitation potential
31- 36 F6.3 --- loggf Oscillator strength
41- 45 F5.1 0.1pm EW6819 ?=-99.9 Equivalent Width for NGC 6819 target
49- 53 F5.1 0.1pm EW67 ?=-99.9 Equivalent Width for M67 target
57- 61 F5.1 0.1pm EW188 ?=-99.9 Equivalent Width for NGC 188 target
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Acknowledgements:
Ditte Slumstrup, ditte(at)phys.au.dk
(End) Ditte Slumstrup [Aarhus University], Patricia Vannier [CDS] 11-Jan-2019