J/A+A/661/A153 Metal-poor red giant branch stars (Mucciarelli+, 2022)
Discovery of a thin lithium plateau among metal-poor red giant branch stars.
Mucciarelli A., Monaco L., Bonifacio P., Salaris M., Deal M., Spite M.,
Richard O., Lallement R.
<Astron. Astrophys. 661, A153 (2022)>
=2022A&A...661A.153M 2022A&A...661A.153M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, metal-deficient ; Radial velocities ;
Optical
Keywords: stars: abundances - techniques: spectroscopic - Galaxy: abundances
Abstract:
The surface lithium abundance A(Li) of warm metal-poor dwarf stars
exhibits a narrow plateau down to [Fe/H]~-2.8dex, while at lower
metallicities the average value drops by 0.3dex with a significant
star-by-star scatter (called lithium meltdown). This behaviour is in
conflict with predictions of standard stellar evolution models
calculated with the initial A(Li) provided by the standard Big Bang
nucleosynthesis.
The lower red giant branch (LRGB) stars provide a complementary tool
to understand the initial A(Li) distribution in metal-poor stars. We
have collected a sample of high-resolution spectra of 58 LRGB stars
spanning a range of [Fe/H] between ~-7.0dex and ~-1.3dex. The LRGB
stars display an A(Li) distribution clearly different from that of the
dwarfs, without signatures of a meltdown and with two distinct
components: (a) a thin A(Li) plateau with an average
A(Li)≃1.09±0.01dex (σ≃0.07dex), and (b) a small fraction of
Li-poor stars with A(Li) lower than ∼0.7dex.
The A(Li) distribution observed in LRGB stars can be reconciled with
an initial abundance close to the cosmological value, by including an
additional chemical element transport in stellar evolution models. The
required efficiency of this transport allows us to match also the
Spite plateau lithium abundance measured in the dwarfs.
The emerging scenario is that all metal-poor stars formed with the
same initial A(Li) but those that are likely the product of
coalescence or that experienced binary mass transfer and show lower
A(Li). We conclude that A(Li) in LRGB stars is qualitatively
compatible with the cosmological A(Li) value and that the meltdown
observed in dwarf stars does not reflect a real drop of the abundance
at birth.
Description:
Instrument, spectral range and resolution, ID program and PI for each
spectrum used in this work. radial velocity is listed only for the
stars for which we analysed spectra not already discussed in previous
papers (the quoted errors are computed as the dispersion divided by
the root mean square of the measured).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 88 115 Main information on the used spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Star name
26- 31 A6 --- Instr Instrument
33- 36 I4 0.1nm lambda1 Starting wavelength
38- 41 I4 0.1nm lambda2 Ending wavelength
43- 48 I6 --- resol Spectral resolution
50- 57 F8.2 km/s RV ? Radial velocity
59- 62 F4.2 km/s e_RV ? Uncertainty on radial velocity
64- 75 A12 --- ID Program Identification Number
77- 88 A12 --- PI Principal Investigator
--------------------------------------------------------------------------------
Acknowledgements:
Alessio Mucciarelli, alessio.mucciarelli2(at)unibo.it
(End) Patricia Vannier [CDS] 04-Apr-2022