J/A+A/635/A104 Chemical abundance analysis of HD 20 (Hanke+, 2020)
A high-precision abundance analysis of the nuclear benchmark star HD 20.
Hanke M., Hansen C.J., Ludwig H.-G., Cristallo S., McWilliam A.,
Grebel E. K., Piersanti L.
<Astron. Astrophys. 635, A104 (2020)>
=2020A&A...635A.104H 2020A&A...635A.104H (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics; Spectroscopy; Abundances; Stars, metal-deficient;
Equivalent widths
Keywords: stars: abundances - stars: chemically peculiar -
stars: individual: HD 20 - stars: evolution - Galaxy: halo -
nuclear reactions, nucleosynthesis, abundances
Abstract:
Metal-poor stars with available detailed information about their
chemical inventory pose powerful empirical benchmarks for nuclear
astrophysics. Here we present our spectroscopic chemical abundance
investigation of the metal-poor ([Fe/H]=-1.60dex), r-process-enriched
([Eu/Fe]=0.73dex) halo star HD 20 using novel and archival
high-resolution data at outstanding signal-to-noise ratios (up to 1000
per Angstroem). By combining one of the first asteroseismic gravity
measurements in the metal-poor regime from a TESS light curve with the
spectroscopic analysis of iron lines under non-local thermodynamic
equilibrium conditions, we derive a set of highly accurate and precise
stellar parameters. These allow us to delineate a reliable chemical
pattern that is comprised of solid detections of 48 elements,
including 28 neutron-capture elements. Hence, we establish HD 20 among
the few benchmark stars that have almost complete patterns and possess
low systematic dependencies on the stellar parameters. Our
light-element (Z<30) abundances are representative of other, similarly
metal-poor stars in the Galactic halo with contributions from
core-collapse supernovae of type II. In the realm of the
neutron-capture elements, our comparison to the scaled solar r-pattern
shows that the lighter neutron-capture elements (Z<60) are poorly
matched. In particular, we find imprints of the weak r-process acting
at low metallicities. Nonetheless, by comparing our detailed
abundances to the observed metal-poor star BD +17 3248, we find a
persistent residual pattern involving mainly the elements Sr, Y, Zr,
Ba, and La. These are indicative of enrichment contributions from the
s-process and we show that mixing with material from predicted yields
of massive, rotating AGB stars at low metallicity considerably
improves the fit. Based on a solar ratio of heavy- to light-s elements
-- at odds with model predictions for the i-process -- and a missing
clear residual pattern with respect to other stars with claimed
contributions from this process, we refute (strong) contributions from
such astrophysical sites providing intermediate neutron densities.
Finally, nuclear cosmochronology is used to tie our detection of the
radioactive element Th to an age estimate for HD 20 of 11.0±3.8Gyr.
Description:
Equivalent widths (EWs) measured from HD 20's spectra using EWCODE are
presented alongside individual transition parameters and deduced
abundances. Profiles for which a standard EW analysis was prohibited
were analyzed using spectrum synthesis. NLTE corrections were
performed and are listed whenever available.
Objects:
-------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------
00 05 15.32 -27 16 18.1 HD 20 = HIP 434
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 74 464 Atomic data, equivalent widths, and abundances
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Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 8 F8.3 0.1nm lambda Wavelength
10- 15 A6 --- Ion Ion designation
17- 21 F5.3 eV chiex ? Excitation potential
23- 29 F7.3 [-] loggf ? Oscillator strength
31- 35 F5.1 0.1pm EW ? Equivalent width
37- 40 F4.1 0.1pm e_EW ? Equivalent width error
42- 46 F5.2 [-] logeps LTE abundance
48- 51 F4.2 [-] e_logeps ? LTE abundance error
53- 56 F4.2 [-] logepsNLTE ? NLTE abundance
58- 62 F5.2 [-] deltaNLTE ? NLTE correction
64- 68 A5 --- Ref Reference flag (1)
70- 72 A3 --- Note [12, ]? Special note flag (2)
74 I1 --- l_logeps [3]? 3 for upper limit abundance
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Acknowledgements:
Michael Hanke, mhanke(at)ari.uni-heidelberg.de
(End) Michael Hanke [ARI, Germany], Patricia Vannier [CDS] 04-Feb-2020