J/A+A/645/A61 Abundances of 25 metal-poor stars (Karinkuzhi+, 2021)
Low-mass low-metallicity AGB stars as an efficient i-process site explaining
CEMP-rs stars.
Karinkuzhi D., Van Eck S., Goriely S., Siess L., Jorissen A., Merle T.,
Escorza A., Masseron T.
<Astron. Astrophys. 645, A61 (2021)>
=2021A&A...645A..61K 2021A&A...645A..61K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Spectroscopy ; Abundances
Keywords: nuclear reactions, nucleosynthesis, abundances -
stars: AGB and post-AGB - binaries: spectroscopic -
stars: fundamental parameters
Abstract:
Among carbon-enhanced metal-poor (CEMP) stars, some are found to be
enriched in slow-neutron capture (s-process) elements (and are then
tagged CEMP-s), some have overabundances in rapid-neutron capture
(r-process) elements (tagged CEMP-r), and some are characterized by
both s- and r-process enrichments (tagged CEMP-rs). The current
distinction between CEMP-s and CEMP-rs is based on their [Ba/Fe] and
[Eu/Fe] ratios, since barium and europium are predominantly produced
by the s- and the r-process, respectively. The origin of the abundance
differences between CEMP-s and CEMP-rs stars is presently unknown. It
has been claimed that the i-process, whose site still remains to be
identified, could better reproduce CEMP-rs abundances than the
s-process. We propose a more robust classification method for CEMP-s
and CEMP-rs stars using additional heavy elements other than Ba and
Eu. Once a secure classification is available, it should then be
possible to assess whether the i-process or a variant of the s-process
better fits the peculiar abundance patterns of CEMP-rs stars. We
analyse high-resolution spectra of 24 CEMP stars and one r-process
enriched star without carbon-enrichment, observed mainly with the
high-resolution HERMES spectrograph mounted on the Mercator telescope
(La Palma) and also with the UVES spectrograph on VLT (ESO Chile) and
HIRES spectrograph on KECK (Hawaii). Stellar parameters and abundances
are derived using MARCS model atmospheres. Elemental abundances are
computed through spectral synthesis using the TURBOSPECTRUM radiative
transfer code. Stars are re-classified as CEMP-s or -rs according to a
new classification scheme using eight heavy element abundances. Within
our sample of 25 objects, the literature classification is globally
confirmed, except for HE 1429-0551 and HE 2144-1832, previously
classified as CEMP-rs and now as CEMP-s stars. The abundance profiles
of CEMP-s and CEMP-rs stars are compared in detail, and no clear
separation is found between the two groups; it seems instead that
there is an abundance continuum between the two stellar classes. There
is an even larger binarity rate among CEMP-rs stars than among CEMP-s
stars, indicating that CEMP-rs stars are extrinsic stars as well. The
second peak s-process elements (Ba, La, Ce) are slightly enhanced in
CEMP-rs stars with respect to first-peak s-process elements (Sr, Y,
Zr), when compared to CEMP-s stars. Models of radiative s-process
nucleosynthesis during the interpulse phases reproduce well the
abundance profiles of CEMP-s stars, whereas those of CEMP-rs stars are
explained well by low-metallicity 1M☉ models experiencing proton
ingestion. The global fitting of our i-process models to CEMP-rs stars
is as good as the one of our s-process models to CEMP-s stars. Stellar
evolutionary tracks of an enhanced carbon composition (consistent with
our abundance determinations) are necessary to explain the position of
CEMP-s and CEMP-rs stars in the Hertzsprung-Russell (HR) diagram using
Gaia DR2 parallaxes; they are found to lie mostly on the red giant
branch (RGB). CEMP-rs stars present most of the characteristics of
extrinsic stars such as CEMP-s, CH, barium, and extrinsic S stars;
they can be explained as being polluted by a low-mass, low-metallicity
thermally-pulsing asymptotic giant branch (TP-AGB) companion
experiencing i-process nucleosynthesis after proton ingestion during
its first convective thermal pulses. As such, they could be renamed
CEMP-sr stars, since they represent a particular manifestation of the
s-process at low-metallicities. For these objects a call for an exotic
i-process site may not necessarily be required anymore.
Description:
We present the abundances of 25 metal-poor stars and the lines used to
derive these abundances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 86 25 Programme stars and adopted atmospheric parameters
tablea1.dat 29 439 *Line list
tableb2.dat 66 701 Elemental abundances
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Note on tablea1.dat: Isotopic shifts are included for some lines.
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See also:
II/180 : uvby-beta photometry of metal-poor stars (Schuster+ 1989)
J/A+A/587/A124 : Metal-poor stars towards the Galactic bulge (Koch+, 2016)
J/A+A/593/A28 : Halo metal-poor stars chemical data (Fernandez-Alvar+, 2016)
J/A+A/608/A89 : Very metal poor stars in MW halo (Mashonkina+, 2017)
J/ApJ/847/142 : Ultra-metal-poor stars LTE & NLTE abundances (Ezzeddine+ 2017)
J/A+A/614/A68 : Carbon-enhanced metal-poor stars sample (Caffau+, 2018)
J/A+A/622/L4 : Carbon and oxygen in metal-poor halo stars (Amarsi+, 2019)
J/A+A/623/A128 : Galactic halo CEMP stars abund. + kinematics (Hansen+, 2019)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Star Star name
13 A1 --- n_Star [a] Note on Star (1)
15- 18 I4 K Teff Effective temperature
20- 22 I3 K e_Teff rms uncertainty on Teff
24- 27 F4.2 [cm/s2] logg Surface gravity
29- 32 F4.2 [cm/s2] e_logg rms uncertainty on logg
34- 37 F4.2 km/s vt Microturbulent velocity
39- 42 F4.2 km/s e_vt rms uncertainty on vt
44- 48 F5.2 [-] [Fe/H] Metallicity
50- 53 F4.2 [-] e_[Fe/H] rms uncertainty on [Fe/H]
55- 59 F5.3 --- dS Signed distance (2)
61- 65 F5.3 --- dRMS RMS distance (2)
67- 68 A2 ---- OClass [rs ] Original classification (3)
70- 71 A2 --- NewClass [rs ] New classification (4)
73- 76 F4.1 ---- chi2 ? chi2 value (5)
78- 79 A2 --- Spec Spectrograph used (6)
81- 82 A2 --- Bin Binarity flag (7)
84- 86 A3 --- r_Bin Reference for Bin (8)
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Note (1): a: HD 221170 is an r-process-enriched star not enriched in carbon.
Note (2): average abundance distances (in dex) between the abundance profile of
a given star and the standard-r abundance profile (See Sect. 5)
Note (3): specifies the classification based on [La/Eu], adopting the criterion
suggested by Beers & Christlieb (1992AJ....103.1987B 1992AJ....103.1987B, Cat. J/AJ/103/1987)
Note (4): refers to the star assignment adopted in the present paper
(see Sect. 5).
Note (5): The chi2 indicator (Eq. 6 in Sect. 7) quantifies the agreement
between the AGB model predictions and the measured abundances of eight heavy
elements.
Note (6): Spectrograph used as follows:
U = UVES
H = HERMES
HI = HIRES
Note (7): Code as follows:
Y = spectroscopic binary
Y? = possible spectroscopic binary
Note (8): References as follows:
a = HERMES unpublished data
b = Jorissen et al. (2016A&A...586A.158J 2016A&A...586A.158J, Cat. J/A+A/586/A158)
c = Jorissen et al. (in preparation)
d = Preston & Sneden (2001AJ....122.1545P 2001AJ....122.1545P)
e = McClure & Woodsworth (1990ApJ...352..709M 1990ApJ...352..709M)
f = Hansen et al. (2016A&A...588A...3H 2016A&A...588A...3H)
g = Jorissen et al. (2005A&A...441.1135J 2005A&A...441.1135J)
h = Pereira et al. (2019MNRAS.488..482P 2019MNRAS.488..482P)
i = Hansen et al. (2015A&A...583A..49H 2015A&A...583A..49H)
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Element Species identifier with ionization stage
7- 14 F8.3 0.1nm Lambda Wavelength
17- 21 F5.3 eV EP Lower excitation potential
24- 29 F6.3 [-] loggf log of the oscillator strength
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Star Star identifier
15- 21 A7 --- Element Species identifier
(LTE and NLTE marked separately) (1)
24- 25 I2 --- Z ? Atomic number
29- 32 F4.2 [-] log(e)Sun ? Solar abundance
36- 40 F5.2 [-] log(e)Star ? log mean abundance
41 A1 --- u_log(e)Star [:] Uncertainty flag on log(e)Star
45- 48 F4.2 [-] sigmal ? Line-to-line scatter
51- 52 I2 --- Nl ? Number of used lines
55- 59 F5.2 [Sun] [X/Fe] ? Abundances relative to Fe (2)
63- 66 F4.2 --- sigmat ? Total uncertainty in [X/Fe]
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Note (1): LTE and NLTE abundances are shown separately for Sr, Ba, Eu and Pb in
columns log(e)_star and [X/Fe].
Note (2): [Sun] in Units column indicates log [Solar Unit].
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Acknowledgements:
Drisya Karinkuzhi, Drisya.Karinkuzhi(at)ulb.ac.be
References:
Asplund et al., 2009ARA&A..47..481A 2009ARA&A..47..481A
(End) Patricia Vannier [CDS] 20-Nov-2020