151 research outputs found
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu
To understand the formation and evolution of the different stellar
populations within our Galaxy it is essential to combine detailed kinematical
and chemical information for large samples of stars. We derive chemical
abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu for a large sample of more
than 1000 FGK dwarf stars with high-resolution (\,115000) and
high-quality spectra from the HARPS-GTO program. The abundances are derived by
a standard Local Thermodinamyc Equilibrium (LTE) analysis using measured
Equivalent Widths (EWs) injected to the code MOOG and a grid of Kurucz ATLAS9
atmospheres. We find that thick disk stars are chemically disjunct for Zn and
Eu and also show on average higher Zr but lower Ba and Y when compared to the
thin disk stars. We also discovered that the previously identified
high- metal-rich population is also enhanced in Cu, Zn, Nd and Eu with
respect to the thin disk but presents Ba and Y abundances lower on average,
following the trend of thick disk stars towards higher metallities and further
supporting the different chemical composition of this population. The ratio of
heavy-s to light-s elements of thin disk stars presents the expected behaviour
(increasing towards lower metallicities) and can be explained by a major
contribution of low-mass AGB stars for s-process production at disk
metallicities. However, the opposite trend found for thick disk stars suggests
that intermediate-mass AGB stars played an important role in the enrichment of
the gas from where these stars formed. Previous works in the literature also
point to a possible primary production of light-s elements at low metallicities
to explain this trend. Finally, we also find an enhancement of light-s elements
in the thin disk at super solar metallicities which could be caused by the
contribution of metal-rich AGB stars. (short version)Comment: 20 pages, 19 figures, accepted by A&
NIR spectroscopy of the Sun and HD20010 - Compiling a new linelist in the NIR
Context: Effective temperature, surface gravity, and metallicity are basic
spectroscopic stellar parameters necessary to characterize a star or a
planetary system. Reliable atmospheric parameters for FGK stars have been
obtained mostly from methods that relay on high resolution and high
signal-to-noise optical spectroscopy. The advent of a new generation of high
resolution near-IR spectrographs opens the possibility of using classic
spectroscopic methods with high resolution and high signal-to-noise in the NIR
spectral window. Aims: We aim to compile a new iron line list in the NIR from a
solar spectrum to derive precise stellar atmospheric parameters, comparable to
the ones already obtained from high resolution optical spectra. The spectral
range covers 10 000 {\AA} to 25 000 {\AA}, which is equivalent to the Y, J, H,
and K bands. Methods: Our spectroscopic analysis is based on the iron
excitation and ionization balance done in LTE. We use a high resolution and
high signal-to-noise ratio spectrum of the Sun from the Kitt Peak telescope as
a starting point to compile the iron line list. The oscillator strengths (log
gf) of the iron lines were calibrated for the Sun. The abundance analysis was
done using the MOOG code after measuring equivalent widths of 357 solar iron
lines. Results: We successfully derived stellar atmospheric parameters for the
Sun. Furthermore, we analysed HD20010, a F8IV star, from which we derived
stellar atmospheric parameters using the same line list as for the Sun. The
spectrum was obtained from the CRIRES- POP database. The results are compatible
with the ones found in the literature, confirming the reliability of our line
list. However, due to the quality of the data we obtain large errors.Comment: 9 pages and 9 figure
New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection
It is still being debated whether the well-known metallicity - giant planet
correlation for dwarf stars is also valid for giant stars. For this reason,
having precise metallicities is very important. Different methods can provide
different results that lead to discrepancies in the analysis of planet hosts.
To study the impact of different analyses on the metallicity scale for evolved
stars, we compare different iron line lists to use in the atmospheric parameter
derivation of evolved stars. Therefore, we use a sample of 71 evolved stars
with planets. With these new homogeneous parameters, we revisit the metallicity
- giant planet connection for evolved stars. A spectroscopic analysis based on
Kurucz models in local thermodynamic equilibrium (LTE) was performed through
the MOOG code to derive the atmospheric parameters. Two different iron line
list sets were used, one built for cool FGK stars in general, and the other for
giant FGK stars. Masses were calculated through isochrone fitting, using the
Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the
metallicity distributions of various different samples of evolved stars and red
giants. All parameters compare well using a line list set, designed
specifically for cool and solar-like stars to provide more accurate
temperatures. All parameters derived with this line list set are preferred and
are thus adopted for future analysis. We find that evolved planet hosts are
more metal-poor than dwarf stars with giant planets. However, a bias in giant
stellar samples that are searched for planets is present. Because of a colour
cut-off, metal-rich low-gravity stars are left out of the samples, making it
hard to compare dwarf stars with giant stars. Furthermore, no metallicity
enhancement is found for red giants with planets (\,dex) with
respect to red giants without planets.Comment: 22 pages, 10 figures, 12 tables, accepted to A&
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
Due to the importance that the star-planet relation has to our understanding
of the planet formation process, the precise determination of stellar
parameters for the ever increasing number of discovered extra-solar planets is
of great relevance. Furthermore, precise stellar parameters are needed to fully
characterize the planet properties. It is thus important to continue the
efforts to determine, in the most uniform way possible, the parameters for
stars with planets as new discoveries are announced. In this paper we present
new precise atmospheric parameters for a sample of 48 stars with planets. We
then take the opportunity to present a new catalogue of stellar parameters for
FGK and M stars with planets detected by radial velocity, transit, and
astrometry programs. Stellar atmospheric parameters and masses for the 48 stars
were derived assuming LTE and using high resolution and high signal-to-noise
spectra. The methodology used is based on the measurement of equivalent widths
for a list of iron lines and making use of iron ionization and excitation
equilibrium principles. For the catalog, and whenever possible, we used
parameters derived in previous works published by our team, using well defined
methodologies for the derivation of stellar atmospheric parameters. This set of
parameters amounts to over 65% of all planet host stars known, including more
than 90% of all stars with planets discovered through radial velocity surveys.
For the remaining targets, stellar parameters were collected from the
literature.Comment: Astronomy & Astrophysics, accepted for publicatio
The AMBRE Project: searching for the closest solar siblings
Finding solar siblings, that is, stars that formed in the same cluster as the
Sun, will yield information about the conditions at the Sun's birthplace. We
search for solar sibling candidates in AMBRE, the very large spectra database
of solar vicinity stars. Since the ages and chemical abundances of solar
siblings are very similar to those of the Sun, we carried out a chemistry- and
age-based search for solar sibling candidates. We used high-resolution spectra
to derive precise stellar parameters and chemical abundances of the stars. We
used these spectroscopic parameters together with Gaia DR2 astrometric data to
derive stellar isochronal ages. Gaia data were also used to study the
kinematics of the sibling candidates. From the about 17000 stars that are
characterized within the AMBRE project, we first selected 55 stars whose
metallicities are closest to the solar value (-0.1 < [Fe/H] < 0.1 dex). For
these stars we derived precise chemical abundances of several iron-peak, alpha-
and neutron-capture elements, based on which we selected 12 solar sibling
candidates with average abundances and metallicities between -0.03 to 0.03 dex.
Our further selection left us with 4 candidates with stellar ages that are
compatible with the solar age within observational uncertainties. For the 2 of
the hottest candidates, we derived the carbon isotopic ratios, which are
compatible with the solar value. HD186302 is the most precisely characterized
and probably the most probable candidate of our 4 best candidates. Very precise
chemical characterization and age estimation is necessary to identify solar
siblings. We propose that in addition to typical chemical tagging, the study of
isotopic ratios can give further important information about the relation of
sibling candidates with the Sun. Ideally, asteroseismic age determinations of
the candidates could solve the problem of imprecise isochronal ages.Comment: Accepted for publication in A&
Deriving precise parameters for cool solar-type stars. Optimizing the iron line list
Temperature, surface gravity, and metallicitity are basic stellar atmospheric
parameters necessary to characterize a star. We aim to improve the description
of the spectroscopic temperatures especially for the cooler stars where the
differences with the Infrared Flux Method are higher, as presented in previous
work. Our spectroscopic analysis is based on the iron excitation and ionization
balance, assuming Kurucz model atmospheres in LTE. The abundance analysis is
determined using the code MOOG. We optimize the line list using a cool star
with high resolution and high signal-to-noise spectrum, as a reference in order
to check for weak, isolated lines. We test the quality of the new line list by
re-deriving stellar parameters for 451 stars with high resolution and
signal-to-noise HARPS spectra, that were analyzed in a previous work with a
larger line list. The comparison in temperatures between this work and the
latest IRFM shows that the differences for the cooler stars are significantly
smaller and more homogeneously distributed than in previous studies for stars
with temperatures below 5000 K. We use the new line list to re-derive
parameters for some of the cooler stars that host planets. Finally, we present
the impact of the new temperatures on the [Cr I/Cr II] and [Ti I/Ti II]
abundance ratios that previously showed systematic trends with temperature.Comment: 11 pages, 14 figures, accepted to A&
Search for lithium-rich giants in 32 open clusters with high-resolution spectroscopy
Lithium-rich giant stars are rare and their existence challenges our
understanding of stellar structure and evolution. We profit from the
high-quality sample gathered with HARPS and UVES, in order to search for
Li-rich giants and to identify the Li enrichment mechanisms responsible. We
derive stellar parameters for 247 stars belonging to 32 open clusters, with
0.07 Ga < ages < 3.6 Ga. We employed the spectral synthesis technique code
FASMA for the abundance analysis of 228 stars from our sample. We also
determined ages, distances, and extinction using astrometry and photometry from
Gaia and PARSEC isochrones to constrain their evolutionary stage. Our sample
covers a wide range of stellar masses from 1 to more than 6 solar masses where
the majority of the masses are above 2 solar masses. We have found 14 canonical
Li-rich giant stars which have experienced the first dredge-up. This
corresponds to 6% of our total sample, which is higher than what is typically
found for field stars. Apart from the canonical limit, we use the maximum Li
abundance of the progenitor stars as a criterion for Li enrichment. We find Li
enhancement also among eight stars which have passed the first dredge up and
show strong Li lines based on the fact that stars at the same evolutionary
stage in the same cluster have significantly different Li abundances. We
confirm that giants with higher Li abundance correspond to a higher fraction of
fast-rotating giants, suggesting a connection between Li enhancement and
stellar rotation as predicted by stellar models. Our Li-rich giants are found
in various evolutionary stages implying that no unique Li production mechanism
is responsible for Li enrichment but rather different intrinsic or external
mechanisms can be simultaneously at play.Comment: accepted in A&A, online data will be available in CD
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period
While giant extrasolar planets have been studied for more than two decades
now, there are still some open questions such as their dominant formation and
migration process, as well as their atmospheric evolution in different stellar
environments. In this paper, we study a sample of giant transiting exoplanets
detected by the Kepler telescope with orbital periods up to 400 days. We first
defined a sample of 129 giant-planet candidates that we followed up with the
SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This
allow us to unveil the nature of these candidates and to measure a
false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting
within 400 days of period. Based on a sample of confirmed or likely planets, we
then derive the occurrence rates of giant planets in different ranges of
orbital periods. The overall occurrence rate of giant planets within 400 days
is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the
different populations of giant planets reported by radial velocity surveys.
Comparing these rates with other yields, we find that the occurrence rate of
giant planets is lower only for hot jupiters but not for the longer period
planets. We also derive a first measurement on the occurrence rate of brown
dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we
discuss the physical properties of the giant planets in our sample. We confirm
that giant planets receiving a moderate irradiation are not inflated but we
find that they are in average smaller than predicted by formation and evolution
models. In this regime of low-irradiated giant planets, we find a possible
correlation between their bulk density and the Iron abundance of the host star,
which needs more detections to be confirmed.Comment: To appear in Astronomy and Astrophysic
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