J/A+A/586/A67 G64-12 and G64-37 linelist and EWs (Reggiani+, 2016)
First high-precision differential abundance analysis of extremely metal-poor
stars.
Reggiani H., Melendez J., Yong D., Ramirez I., Asplund M.
<Astron. Astrophys. 586, A67 (2016)>
=2016A&A...586A..67R 2016A&A...586A..67R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, population II ; Spectroscopy ; Equivalent widths
Keywords: stars: abundances - stars: evolution - stars: Population II -
Galaxy: abundances - Galaxy: evolution - Galaxy: halo
Abstract:
Studies of extremely metal-poor stars indicate that chemical abundance
ratios [X/Fe] have a root mean square scatter as low as 0.05dex
(12%). It remains unclear whether this reflects observational
uncertainties or intrinsic astrophysical scatter arising from physical
conditions in the ISM at early times.
We measure differential chemical abundance ratios in extremely
metal-poor stars to investigate the limits of precision and to
understand whether cosmic scatter or observational errors are
dominant.
We used high-resolution (R∼95000) and high signal-to-noise (S/N=700
at 5000Å) HIRES/Keck spectra to determine high-precision
differential abundances between two extremely metal-poor stars through
a line-by-line differential approach. We determined stellar parameters
for the star G64-37 with respect to the standard star G64-12. We
performed EW measurements for the two stars for the lines recognized
in both stars and performed spectral synthesis to study the carbon
abundances. Results. The differential approach allowed us to obtain
errors of σ(Teff)=27K, σ(logg)=0.06dex,
σ([Fe/H])=0.02dex and σ(vt)=0.06km/s. We estimated
relative chemical abundances with a precision as low as
σ([X/Fe])∼0.01dex. The small uncertainties demonstrate that
there are genuine abundance differences larger than the measurement
errors. The observed Li difference cannot be explained by the
difference in mass because the less massive star has more Li.
It is possible to achieve an abundance precision around ∼0.01-0.05dex
for extremely metal-poor stars, which opens new windows on the study
of the early chemical evolution of the Galaxy.
Description:
The linelist employed in the differential analysis. Includes
wavelength, species, excitation potential, log(gf), and equivalent
widths for both stars analyzed.
Objects:
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RA (ICRS) DE Designation(s)
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13 40 02.50 -00 02 18.8 G64-12 = HIP 66673
14 02 30.09 -05 39 05.2 G64-37 = HIP 68592
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 38 166 Linelist and EWs measurements for both stars,
G64-12 and G64-37
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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- 8 F8.3 0.1nm lambda Wavelength
10- 13 F4.1 --- Species Species Identification
15- 19 F5.3 eV EP Excitation Potential of the line
21- 26 F6.3 [-] log(gf) log(gf) of the line
28- 32 F5.2 0.1pm EWG64-12 Equivalent width of the line for star G64-12
34- 38 F5.2 0.1pm EWG64-37 Equivalent width of the line for star G64-37
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Acknowledgements:
Henrique Reggiani, hreggiani(at)gmail.com
(End) Henrique Reggiani [USP, Brazil], Patricia Vannier [CDS] 28-Dec-2015