4,870 research outputs found
Chemical abundances of stars with brown-dwarf companions
It is well-known that stars with giant planets are on average more metal-rich
than stars without giant planets, whereas stars with detected low-mass planets
do not need to be metal-rich. With the aim of studying the weak boundary that
separates giant planets and brown dwarfs (BDs) and their formation mechanism,
we analyze the spectra of a sample of stars with already confirmed BD
companions both by radial velocity and astrometry. We employ standard and
automatic tools to perform an EW-based analysis and to derive chemical
abundances from CORALIE spectra of stars with BD companions. We compare these
abundances with those of stars without detected planets and with low-mass and
giant-mass planets. We find that stars with BDs do not have metallicities and
chemical abundances similar to those of giant-planet hosts but they resemble
the composition of stars with low-mass planets. The distribution of mean
abundances of -elements and iron peak elements of stars with BDs
exhibit a peak at about solar abundance whereas for stars with low-mass and
high-mass planets the [X/H] and [X/H] peak abundances
remain at ~dex and ~dex, respectively. We display these
element abundances for stars with low-mass and high-mass planets, and BDs
versus the minimum mass, , of the most-massive substellar companion
in each system, and we find a maximum in -element as well as Fe-peak
abundances at jupiter masses. We discuss the
implication of these results in the context of the formation scenario of BDs in
comparison with that of giant planets.Comment: Accepted for publication in Astronomy & Astrophysic
Light elements in stars with exoplanets
It is well known that stars orbited by giant planets have higher abundances
of heavy elements when compared with average field dwarfs. A number of studies
have also addressed the possibility that light element abundances are different
in these stars. In this paper we will review the present status of these
studies. The most significant trends will be discussed.Comment: 10 pages, 6 figures. Submitted to the proceedings of IAU symposium
268: Light elements in the universe
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&
Detección específica de Arcobacter Butzleri en carne de pollo mediante una técnica de PCR
En este trabajo se describe el desarrollo de una técnica de PCR para la detección específica de Arcobacter butzleri en carne fresca de pollo empleando cebadores específicos de especie diseñados en gen 16S ARN ribosómico. Los cebadores seleccionados amplifican un fragmento de 195 pb en A. butzleri, sin producir señal de amplificación en otras especies de Arcobacter, Campylobacter, Helicobacter, ni en otros microorganismos presentes en los alimentos. La técnica de PCR se ha aplicado al análisis de 42 muestras comerciales de carne fresca de pollo adquiridas en diversos comercios minoristas. Tras un pre enriquecimiento selectivo durante 18 h a 30ºC, A. butzleri se detectó en un 85,7% de las muestras analizadas. Se observó una total concordancia entre los resultados obtenidos por PCR y el método convencional de recuento en placas de agar selectivo.A PCR technique was developed for the specific detection of Arcobacter butzleri in fresh chicken meat using species-specific primers designed on the 16S ribosomal ARN gene. The selected primers amplify a 195 bp fragment from A. butzleri whereas no PCR product is generated for other Arcobacter, Campylobacter, Helicobacter species, and other food bacteria. The PCR technique was used to screen 42 retail-purchased chicken samples for the presence of A. butzleri. Following a selective enrichment for 18 h at 30ºC, A butzleri was detected in 85.7% of the analyzed samples, showing a total concordance between the PCR results and the conventional selective plating method
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
The effect of Redbull on human enamel surface
Poster presented at the 63rd ORCA Congress (European Organization for Caries Research). July 6–9 2016, Athens, Greece.info:eu-repo/semantics/publishedVersio
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