3,795 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&
Searching for the signatures of terrestrial planets in F-, G-type main-sequence stars
We have studied the volatile-to-refractory abundance ratios to investigate
their possible relation with the low-mass planetary formation. We present a
fully differential chemical abundance analysis using high-quality HARPS and
UVES spectra of 61 late F- and early G-type main-sequence stars, 29 are planet
hosts and 32 are stars without detected planets. As the previous sample of
solar analogs, these stars slightly hotter than the Sun also provide very
accurate Galactic chemical abundance trends in the metallicity range . Stars with and without planets show similar mean abundance
ratios. Moreover, when removing the Galactic chemical evolution effects, these
mean abundance ratios, , versus condensation
temperature tend to exhibit less steep trends with nearly null or slightly
negative slopes. We have also analyzed a sub-sample of 26 metal-rich stars, 13
with and 13 without known planets and find the similar, although not equal,
abundance pattern with negative slopes for both samples of stars with and
without planets. Using stars at S/N provides equally steep abundance
trends with negative slopes for both stars with and without planets. We revisit
the sample of solar analogs to study the abundance patterns of these stars, in
particular, 8 stars hosting super-Earth-like planets. Among these stars having
very low-mass planets, only four of them reveal clear increasing abundance
trends versus condensation temperature. Finally, we have compared these
observed slopes with those predicted using a simple model which enables us to
compute the mass of rocks which have formed terrestrial planets in each
planetary system. We do not find any evidence supporting the conclusion that
the volatile-to-refractory abundance ratio is related to the presence of rocky
planets.Comment: Accepted for publication in A&
CNO behaviour in planet-harbouring stars. II. Carbon abundances in stars with and without planets using the CH band
Context. Carbon, oxygen and nitrogen (CNO) are key elements in stellar
formation and evolution, and their abundances should also have a significant
impact on planetary formation and evolution.
Aims. We present a detailed spectroscopic analysis of 1110 solar-type stars,
143 of which are known to have planetary companions. We have determined the
carbon abundances of these stars and investigate a possible connection between
C and the presence of planetary companions. Methods. We used the HARPS
spectrograph to obtain high-resolution optical spectra of our targets. Spectral
synthesis of the CH band at 4300\AA was performed with the spectral synthesis
codes MOOG and FITTING.
Results. We have studied carbon in several reliable spectral windows and have
obtained abundances and distributions that show that planet host stars are
carbon rich when compared to single stars, a signature caused by the known
metal-rich nature of stars with planets. We find no different behaviour when
separating the stars by the mass of the planetary companion.
Conclusions. We conclude that reliable carbon abundances can be derived for
solar-type stars from the CH band at 4300\AA. We confirm two different slope
trends for [C/Fe] with [Fe/H] because the behaviour is opposite for stars above
and below solar values. We observe a flat distribution of the [C/Fe] ratio for
all planetary masses, a finding that apparently excludes any clear connection
between the [C/Fe] abundance ratio and planetary mass.Comment: 10 pages, 10 figures. Accepted to A&
C/O vs Mg/Si ratios in solar type stars: The HARPS sample
Aims. We present a detailed study of the Mg/Si and C/O ratios and their
importance in determining the mineralogy of planetary companions. Methods.
Using 499 solar-like stars from the HARPS sample, we determine C/O and Mg/Si
elemental abundance ratios to study the nature of the possible planets formed.
We separated the planetary population in low-mass planets ( < 30 ) and high-mass planets ( > 30 ) to test for possible
relation with the mass. Results. We find a diversity of mineralogical ratios
that reveal the different kinds of planetary systems that can be formed, most
of them dissimilar to our solar system. The different values of the Mg/Si and
C/O ratios can determine different composition of planets formed. We found that
100\% of our planetary sample present C/O < 0.8. 86\% of stars with high-mass
companions present 0.8 > C/O > 0.4, while 14\% present C/O values lower than
0.4. Regarding Mg/Si, all stars with low-mass planetary companion showed values
between 1 and 2, while 85% of the high-mass companion sample does. The other
15\% showed Mg/Si values below 1. No stars with planets were found with Mg/Si >
2. Planet hosts with low-mass companions present C/O and Mg/Si ratios similar
to those found in the Sun, whereas stars with high-mass companions have lower
C/O.Comment: 9 pages, 12 figues. Accepted in A&
Volatiles and refratories in solar analogs: no terrestial planet connection
We have analysed very high-quality HARPS and UVES spectra of 95 solar
analogs, 24 hosting planets and 71 without detected planets, to search for any
possible signature of terrestial planets in the chemical abundances of volatile
and refractory elements with respect to the solar abundances. We demonstrate
that stars with and without planets in this sample show similar mean abundance
ratios, in particular, a sub-sample of 14 planet-host and 14 "single" solar
analogs in the metallicity range 0.14<[Fe/H]<0.36. In addition, two of the
planetary systems in this sub-sample, containing each of them a
super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have
different volatile-to-refratory abundance ratios to what would be expected from
the presence of a terrestial planets. Finally, we check that after removing the
Galactic chemical evolution effects any possible difference in mean abundances,
with respect to solar values, of refratory and volatile elements practically
dissappears.Comment: 2 pages, 2 figures, to appear in the proceedings of the 276th IAU
Symposium "The Astrophysics of Planetary Systems
Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals
(Abbr.) We present high resolution (R~20000) spectra in the blue and the far
red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals
(NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics
of stars and ionized gas in these structures and, for the first time, the
derivation of their dynamical masses for the first two. In some cases these
regions, about 100 to 150 pc in size, are seen to be composed of several
individual star clusters with sizes between 1.5 and 4.9 pc estimated from
Hubble Space Telescope (HST) images. The stellar dispersions have been obtained
from the Calcium triplet (CaT) lines at 8494,8542,8662 \AA,
while the gas velocity dispersions have been measured by Gaussian fits to the
H and [OIII] 5007 \AA lines on the high dispersion
spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s.
We apply the virial theorem to estimate dynamical masses of the clusters,
assuming that systems are gravitationally bounded and spherically symmetric,
and using previously measured sizes. The measured values of the stellar
velocity dispersions yield dynamical masses of the order of 10 to 10
solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are
found to differ by about 20 to 30 km/s with the H emission lines being
narrower than both the stellar lines and the [OIII] 5007 \AA
lines. The twice ionized oxygen, on the other hand, shows velocity dispersions
comparable to those shown by stars, in some cases, even larger. We have found
indications of the presence of two different kinematical components in the
ionized gas of the regions...Comment: 4 pages, proceeding of the meeting "Young massive star clusters -
Initial conditions and environments", Granada, Spain, 200
Li depletion in solar analogues with exoplanets: Extending the sample
We want to study the effects of the formation of planets and planetary
systems on the atmospheric Li abundance of planet host stars. In this work we
present new determinations of lithium abundances for 326 Main Sequence stars
with and without planets in the T range 5600-5900 K. 277 stars
come from the HARPS sample, the remaining targets have been observed with a
variety of high resolution spectrographs. We confirm significant differences in
the Li distribution of solar twins (T = T 80 K,
log g = log g 0.2 and [Fe/H] = [Fe/H] 0.2): the
full sample of planet host stars (22) shows Li average values lower than
"single" stars with no detected planets (60). If we focus in subsamples with
narrower ranges in metallicity and age, we observe indications of a similar
result though it is not so clear for some of the studied subsamples.
Furthermore, we compare the observed spectra of several couples of stars with
very similar parameters which show different Li abundances up to 1.6 dex.
Therefore we show that neither age, nor mass nor metallicity of a parent star
is the only responsible for enhanced Li depletion in solar analogues. We
conclude that another variable must account for that difference and suggest
that this could be the presence of planets which causes additional rotationally
induced mixing in the external layers of planet host stars. Moreover, we find
indications that the amount of depletion of Li in planet host solar-type stars
is higher when the planets are more massive than Jupiter.Comment: 16 pages, accepted for publication in A&
Multivariate statistical analysis applied to water quality of a tropical Coastal Lagoon, Cartagena, Colombian Caribbean
Coastal lagoons are one of the most threatened ecosystems in the world, because of population growth, habitat destruction, pollution, wastewater, overexploitation and invasive species which are the main causes of their degradation. The objective of this paper was to evaluate the water quality behavior in a stressed coastal lagoon in Cartagena, Colombian Caribbean. Environmental data was analyzed using hypothesis testing, confidence intervals, and also Principal components analysis (PCA). The study was focused on water parameters such as dissolved oxygen (DO), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), salinity, pH, total dissolved solids, total coliforms (TC), Fecal coliforms (FC), ammonium (NH4+) and total phosphorus (TP). The analysis was conducted in line with the Colombian national water standard. Results showed that BOD5, COD, phosphorus, and coliforms are out of the limits permitted for these variables in Colombia and are reaching levels that may be a threat to human health. Principal components analysis detected five components that explained 79.4% of the variance of data and showed that anthropogenic and temporal factors might be affecting the variation of the parameters. © 2020, Gadjah Mada University. All rights reserved.Fundacion Universitaria Konrad LorenzThe authors would like to thank Fundacion Universitaria Tecnologico Comfenalco, University of Cartagena and SENA for financially supporting this research
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