J/A+A/587/A42 weak G-band stars abundances (Palacios+, 2016)
New determination of abundances and stellar parameters for a set of
weak G-band stars.
Palacios A., Jasniewicz G., Masseron T., Thevenin F., Itam-Pasquet J.,
Parthasarathy M.
<Astron. Astrophys., 587, A42-42 (2016)>
=2016A&A...587A..42P 2016A&A...587A..42P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Stars, peculiar ; Abundances
Keywords: stars: abundances - stars: carbon - stars: chemically peculiar -
stars: late-type - stars: evolution
Abstract:
Weak G-band (wGb) stars are a very peculiar class of red giants; they
are almost devoided of carbon and often present mild lithium
enrichment. Despite their very puzzling abundance patterns, very few
detailed spectroscopic studies existed up to a few years ago, which
prevented any clear understanding of the wGb phenomenon. We recently
proposed the first consistent analysis of published data for a sample
of 28 wGb stars and were able to identify them as descendants of early
A-type to late B-type stars, although we were not able to conclude on
their evolutionary status or the origin of their peculiar abundance
pattern. Using new high-resolution spectra, we present the study of a
new sample of wGb stars with the aim of homogeneously deriving their
fundamental parameters and surface abundances for a selected set of
chemical species that we use to improve our insight on this peculiar
class of objects. We obtained high-resolution and high signal-to-noise
spectra for 19 wGb stars in the southern and northern hemisphere that
we used to perform consistent spectral synthesis to derive their
fundamental parameters and metallicities, as well as the spectroscopic
abundances for Li, C, 12C/13C, N, O, Na, Sr, and Ba. We also
computed dedicated stellar evolution models that we used to determine
the masses and to investigate the evolutionary status and chemical
history of the stars in our sample. We confirm that the wGb stars are
stars with initial masses in the range 3.2 to 4.2M☉. We suggest
that a large fraction could be mildly evolved stars on the subgiant
branch currently undergoing the first dredge-up, while a smaller
number of stars are more probably in the core He burning phase at the
clump. After analysing their abundance pattern, we confirm their
strong nitrogen enrichment anti-correlated with large carbon
depletion, characteristic of material fully processed through the CNO
cycle to an extent not known in evolved intermediate-mass stars in the
field and in open clusters. However, we demonstrate here that such a
pattern is very unlikely owing to self-enrichment. In the light of the
current observational constraints, no solid self-consistent pollution
scenario can be presented either, leaving the wGb puzzle largely
unsolved.
Description:
Seventeen southern wGb stars were observed at La Silla, ESO Chile,
with the high-efficiency Fiber-fed Extended Range Optical Spectrograph
FEROS spectrograph mounted on the 2.2m telescope. FEROS is a
bench-mounted, thermally controlled, prism-cross-dispersed echelle
spectrograph, providing, in a single spectrogram spread over 39
orders, almost complete spectral coverage from ∼350 to ∼920nm at a
resolution of 48000. The FEROS observations were carried out during
an observing run between May 10 and 13, 2012. All these spectra were
flat-fielded and calibrated by means of ThArNe exposures using
standard processing tools available at ESO.
In addition, two northern wGb stars, HD 18474 and HD 166208, were
observed in service mode at the Observatoire du Pic du Midi, France,
with the NARVAL spectrograph mounted on the Bernard Lyot 2.0m
telescope. The NARVAL instrument consists of a bench-mounted
cross-dispersed echelle spectrograph, fibre-fed from a
Cassegrain-mounted polarimeter unit. It was used in its
non-polarimetric mode; it provided almost complete spectral coverage
from ∼375 to ∼1050nm at a resolution of 75000 in a single spectrogram
spread over 40 orders.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 99 19 Observation log of the target stars observed
in this paper
table1.dat 66 19 Basic data and atmospheric parameters of weak
G-band stars
table2.dat 69 19 Abundances of light elements in wGb stars
table3.dat 42 19 Abundances of heavy elements in wGb stars
table5.dat 42 13 Comparison of atmospheric parameters and
abundances derived for wGb stars common to our
sample and that of Adamczak and Lambert,
2013ApJ...765..155A 2013ApJ...765..155A
table7.dat 42 19 Masses and radii of program stars
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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 A9 --- Name HD name (HD NNNNNN)
11- 12 I2 h RAh Right ascension (J2000) (1)
14- 15 I2 min RAm Right ascension (J2000) (1)
17- 24 F8.5 s RAs Right ascension (J2000) (1)
26 A1 --- DE- Declination sign (J2000) (1)
27- 28 I2 deg DEd Declination (J2000) (1)
30- 31 I2 arcmin DEm Declination (J2000) (1)
33- 39 F7.4 arcsec DEs Declination (J2000) (1)
41- 44 F4.2 mag Vmag V magnitude (1)
46- 59 A14 --- SpType Spectral type (1)
61- 63 A3 --- Obser Observatory (2)
65- 74 A10 "YYYY-MM-DD" Obs.date Observation date
76- 83 A8 "h:m:s" Obs.time Observation time
85- 88 I4 s Exptime Exposure time
90- 92 I3 --- SNR Signal-to-noise ratio
94- 99 F6.2 km/s RV Radial velocity (3)
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Note (1): Coordinates, V magnitude, and spectral types are from SIMBAD.
Note (2): Observatory code as follows:
TBL = 2.0m Bernard Lyot Telescope installed at the Pic du Midi (France)
ESO = ESO 2.2m telescope installed at La Silla (Chile)
Note (3): Accuracy on barycentric radial velocities (RV) is better than 0.07km/s
for all stars.
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name HD name (HD NNNNNN)
11- 14 I4 K T Temperature
16- 18 I3 K e_T rms uncertainty on T
20- 23 F4.2 [cm/s2] logg Surface gravity
25- 28 F4.2 [cm/s2] e_logg rms uncertainty on logg
30- 33 F4.2 [Lsun] logL Luminosity
35- 38 F4.2 [Lsun] e_logL rms uncertainty on logL
40- 43 F4.2 km/s Vturb Microturbulent velocity
45- 48 F4.2 km/s e_Vturb rms uncertainty on Vturb
50 A1 --- l_vsini Limit flag in vsini
51- 52 I2 km/s vsini Rotational velocity
54- 66 A13 --- Colour Colour coding
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name HD name (HD NNNNNN)
11- 15 F5.2 [-] [C/H] Abundance [C/H] (G1)
17- 20 F4.2 [-] e_[C/H] rms uncertainty on [C/H]
22- 25 F4.2 [-] [N/H] Abundance [N/H] (G1)
27- 30 F4.2 [-] e_[N/H] rms uncertainty on [N/H]
32- 36 F5.2 [-] [O/H] Abundance [O/H] (G1)
38- 41 F4.2 [-] e_[O/H] rms uncertainty on [O/H]
43- 47 F5.2 [-] [Na/H] Abundance [Na/H] (G1)
49- 52 F4.2 [-] e_[Na/H] rms uncertainty on [Na/H]
54- 55 A2 -- l_A(Li) [≤ ] Limit flag on A(Li)
56- 59 F4.2 [-] A(Li) Lithium Abundance, logε(Li)
61- 64 F4.2 [-] e_A(Li) ? rms uncertainty on A(Li)
66- 67 I2 [-] 12C/13C ?=- Abundance ratio 12C/13C
69 I1 [-] e_12C/13C ?=- rms uncertainty on 12C/13C
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name HD name (HD NNNNNN)
11- 15 F5.2 [-] [Fe/H] Metallicity, [Fe/H] (G1)
17- 20 F4.2 [-] e_[Fe/H] rms uncertainty on [Fe/H]
22- 26 F5.2 [-] [Sr/H] Abundance [Sr/H] (G1)
28- 31 F4.2 [-] e_[Sr/H] rms uncertainty on [Sr/H]
33- 37 F5.2 [-] [Ba/H] Abundance [Ba/H] (G1)
39- 42 F4.2 [-] e_[Ba/H] rms uncertainty on [Ba/H]
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name HD name (HD NNNNNN)
11- 13 I3 K DT ? Difference in temperature, ΔT (1)
15- 18 F4.1 [cm/s2] Dlogg ? Difference in logg, Δlogg (1)
20- 24 F5.2 [-] D[Fe/H] ? Difference in [Fe/H], Δ[Fe/H] (1)
26- 30 F5.2 [-] D[C/H] ? Difference in [C/H], Δ[C/H] (1)
32- 36 F5.2 [-] D[N/H] ? Difference in [N/H], Δ[N/H] (1)
38- 42 F5.2 [-] D[O/H] ? Difference in [O/H], Δ[O/H] (1)
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Note (1): this work minus Adamczak and Lambert, 2013ApJ...765..155A 2013ApJ...765..155A.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name HD name (HD NNNNNN)
11- 13 F3.1 Msun Mass Mass
16- 19 F4.2 Msun e_Mass Error on Mass (lower value)
21- 23 F3.1 Msun E_Mass Error on Mass (upper value)
25- 29 F5.2 Rsun Rad Radius
32- 36 F5.2 Rsun e_Rad Error on Rad (lower value)
38- 42 F5.2 Rsun E_Rad Error on Rad (upper value)
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Global notes:
Note (G1): Solar values are taken from Asplund et al. (2005A&A...431..693A 2005A&A...431..693A)
and are 8.39, 7.78, 8.66, 6.17, 7.45, 2.92, and 2.17
for C, N, O, Na, Fe, Sr, and Ba respectively.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 19-May-2016