13,800 research outputs found
ARES v2 - new features and improved performance
Aims: We present a new upgraded version of ARES. The new version includes a
series of interesting new features such as automatic radial velocity
correction, a fully automatic continuum determination, and an estimation of the
errors for the equivalent widths. Methods: The automatic correction of the
radial velocity is achieved with a simple cross-correlation function, and the
automatic continuum determination, as well as the estimation of the errors,
relies on a new approach to evaluating the spectral noise at the continuum
level. Results: ARES v2 is totally compatible with its predecessor. We show
that the fully automatic continuum determination is consistent with the
previous methods applied for this task. It also presents a significant
improvement on its performance thanks to the implementation of a parallel
computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage:
www.astro.up.pt/~sousasag/are
Anomalous U(1)_A and Electroweak Symmetry Breaking
We suggest a new mechanism for electroweak symmetry breaking in the
supersymmetric Standard Model. Our suggestion is based on the presence of an
anomalous U(1)_A gauge symmetry, which naturally arises in the four dimensional
superstring theory, and heavily relies on the value of the corresponding
Fayet-Illiopoulos \xi-term.Comment: Latex, 11 pages, discussions and references adde
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&
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&
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&
New and updated stellar parameters for 90 transit hosts. The effect of the surface gravity
Context. Precise stellar parameters are crucial in exoplanet research for
correctly determining of the planetary parameters. For stars hosting a
transiting planet, determining of the planetary mass and radius depends on the
stellar mass and radius, which in turn depend on the atmospheric stellar
parameters. Different methods can provide different results, which leads to
different planet characteristics.}%Spectroscopic surface gravities have shown
to be poorly constrained, but the photometry of the transiting planet can
provide an independent measurement of the surface gravity.
Aims. In this paper, we use a uniform method to spectroscopically derive
stellar atmospheric parameters, chemical abundances, stellar masses, and
stellar radii for a sample of 90 transit hosts. Surface gravities are also
derived photometrically using the stellar density as derived from the light
curve. We study the effect of using these different surface gravities on the
determination of the chemical abundances and the stellar mass and radius.
Methods. A spectroscopic analysis based on Kurucz models in LTE was performed
through the MOOG code to derive the atmospheric parameters and the chemical
abundances. The photometric surface gravity was determined through isochrone
fitting and the use of the stellar density, directly determined from the light
curve. Stellar masses and radii are determined through calibration formulae.
Results. Spectroscopic and photometric surface gravities differ, but this has
very little effect on the precise determination of the stellar mass in our
spectroscopic analysis. The stellar radius, and hence the planetary radius, is
most affected by the surface gravity discrepancies. For the chemical
abundances, the difference is, as expected, only noticable for the abundances
derived from analyzing of lines of ionized species.Comment: 12 pages, 6 figures, 5 tables, accepted to A&
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