1,659 research outputs found
Parent Stars of Extrasolar Planets. XI. Trends with Condensation Temperature Revisited
We report the results of abundance analyses of new samples of stars with
planets and stars without detected planets. We employ these data to compare
abundance-condensation temperature trends in both samples. We find that stars
with planets have more negative trends. In addition, the more metal-rich stars
with planets display the most negative trends. These results confirm and extend
the findings of Ramirez et al. (2009) and Melendez et al. (2009), who
restricted their studies to solar analogs. We also show that the differences
between the solar photospheric and CI meteoritic abundances correlate with
condensation temperature.Comment: 7 pages, 11 figures; to be published in MNRA
Planning, Managing and Monitoring Technological Security Infrastructures
Over the past few decades many different Information Technologies (IT) policies have been introduced, including COSO, ITIL, PMBook, CMM,ISO 2700x, Six Sigma, being COBIT IT (Control Objectives for IT) the framework that encompasses all IT and Information Systems (IS) governance activities at the organizationâs level. As part of the applicability of quality services certification (ISO 9001) in all IT services of a public institution, it is presented a case study aimed at planning, managing and monitoring technological security infrastructures. It followed the guidelines for the ISO 2700x family, COBIT, ITIL and other standards and conducted a survey to complement the IT processâs objectives. With regard to an action-research methodology for problem-solving (i.e., a kind of attempt to improve or investigate practice) and according to the issue under analyze, the question is put into the terms, viz. âHow can the ISO 2700x, COBIT, ITIL and other guidelines help with the planning, management and monitoring of technological security infrastructures and minimize the risk management of IT and IS?â. Indeed, it may be resolved that it is possible to achieve the goals of planning, managing and monitoring a technological security infrastructure. In the future, we will use Artificial Intelligence based approaches to problem solving such as Artificial Neural Networks and Cased Based Reasoning, to evaluate this issue
Searching for the signatures of terrestial planets in solar analogs
We present a fully differential chemical abundance analysis using very
high-resolution (R >~ 85,000) and very high signal-to-noise (S/N~800 on
average) HARPS and UVES spectra of 7 solar twins and 95 solar analogs, 24 are
planet hosts and 71 are stars without detected planets. The whole sample of
solar analogs provide very accurate Galactic chemical evolution trends in the
metalliciy range -0.3<[Fe/H]<0.5. Solar twins with and without planets show
similar mean abundance ratios. We have also analysed a sub-sample of 28 solar
analogs, 14 planet hosts and 14 stars without known planets, with spectra at
S/N~850 on average, in the metallicity range 0.14<[Fe/H]<0.36 and find the same
abundance pattern for both samples of stars with and without planets. This
result does not depend on either the planet mass, from 7 Earth masses to 17.4
Jupiter masses, or the orbital period of the planets, from 3 to 4300 days. In
addition, we have derived the slope of the abundance ratios as a function of
the condensation temperature for each star and again find similar distributions
of the slopes for both stars with and without planets. In particular, the peaks
of these two distributions are placed at a similar value but with opposite sign
as that expected from a possible signature of terrestial planets. In
particular, two of the planetary systems in this sample, containing each of
them a Super-Earth like planet, show slope values very close to these peaks
which may suggest that these abundance patterns are not related to the presence
of terrestial planets.Comment: Accepted for publication in The Astrophysical Journa
Overabundance of alpha-elements in exoplanet host stars
We present the results for a chemical abundance analysis between
planet-hosting and stars without planets for 12 refractory elements for a total
of 1111 nearby FGK dwarf stars observed within the context of the HARPS GTO
programs. Of these stars, 109 are known to harbour high-mass planetary
companions and 26 stars are hosting exclusively Neptunians and super-Earths. We
found that the [X/Fe] ratios for Mg, Al, Si, Sc, and Ti both for giant and
low-mass planet hosts are systematically higher than those of comparison stars
at low metallicities ([Fe/H] < from -0.2 to 0.1 dex depending on the element).
The most evident discrepancy between planet-hosting and stars without planets
is observed for Mg. Our data suggest that the planet incidence is greater among
the thick disk population than among the thin disk for mettallicities bellow
-0.3 dex. After examining the [alpha/Fe] trends of the planet host and non-host
samples we conclude that a certain chemical composition, and not the Galactic
birth place of the stars, is the determinating factor for that. The inspection
of the Galactic orbital parameters and kinematics of the planet-hosting stars
shows that Neptunian hosts tend to belong to the "thicker" disk compared to
their high-mass planet-hosting counterparts.We also found that Neptunian hosts
follow the distribution of high-alpha stars in the UW vs V velocities space,
but they are more enhanced in Mg than high-alpha stars without planetary
companions. Our results indicate that some metals other than iron may also have
an important contribution to planet formation if the amount of iron is low.
These results may provide strong constraints for the models of planet
formation, especially for planets with low mass.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in Astronomy
& Astrophysic
Higher depletion of lithium in planet host stars: no age and mass effect
Recent observational work by Israelian et al. has shown that sun-like planet
host stars in the temperature range 5700K < Teff < 5850K have lithium
abundances that are significantly lower than those observed for "single" field
stars. In this letter we use stellar evolutionary models to show that
differences in stellar mass and age are not responsible for the observed
correlation. This result, along with the finding of Israelian et al., strongly
suggest that the observed lithium difference is likely linked to some process
related to the formation and evolution of planetary systems.Comment: 4 pages, 4 figures, letter accepted for publication in Astronomy &
Astrophysic
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program.Galactic stellar populations and planets
We performed a uniform and detailed abundance analysis of 12 refractory
elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn and V) for a sample of
1111 FGK dwarf stars from the HARPS GTO planet search program. 109 of these
stars are known to harbour giant planetary companions and 26 stars are hosting
exclusively Neptunians and super-Earths. The main goals of this paper are i) to
investigate whether there are any differences between the elemental abundance
trends for stars of different stellar populations; ii) to characterise the
planet host and non-host samples in term of their [X/H]. The extensive study of
this sample, focused on the abundance differences between stars with and
without planets will be presented in a parallel paper. The equivalent widths of
spectral lines are automatically measured from HARPS spectra with the ARES
code. The abundances of the chemical elements are determined using a LTE
abundance analysis relative to the Sun, with the 2010 revised version of the
spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To
separate the Galactic stellar populations we applied both a purely kinematical
approach and a chemical method. We found that the chemically separated (based
on the Mg, Si, and Ti abundances) thin and thick discs are also chemically
disjunct for Al, Sc, Co and Ca. Some bifurcation might also exist for Na, V,
Ni, and Mn, but there is no clear boundary of their [X/Fe] ratios. We confirm
that an overabundance in giant-planet host stars is clear for all the studied
elements.We also confirm that stars hosting only Neptunian-like planets may be
easier to detect around stars with similar metallicities as non-planet hosts,
although for some elements (particulary alpha-elements) the lower limit of
[X/H] are very abrupt.Comment: 14 pages, 12 figures, 6 tables. accepted for publication in Astronomy
& Astrophysic
Chemical abundances of 451 stars from the HARPS GTO planet search program: Thin disc, thick disc, and planets
We present a uniform study of the chemical abundances of 12 elements (Si, Ca,
Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg, and Al) derived from the spectra of 451
stars observed as part of one of the HARPS GTO planet search programs. Sixty
eight of these are planet-bearing stars. The main goals of our work are: i) the
investigation of possible differences between the abundances of stars with and
without planets; ii) the study of the possible differences in the abundances of
stars in the thin and the thick disc. We confirm that there is a systematically
higher metallicity in planet host stars, when compared to non planet-hosts,
common to all studied species. We also found that there is no difference in the
galactic chemical evolution trends of the stars with and without planets. Stars
that harbour planetary companions simply appear to be in the high metallicity
tail of the distribution. We also confirm that Neptunian and super-Earth class
planets may be easier to find at lower metallicities. A statistically
significative abundance difference between stars of the thin and the thick disc
was found for [Fe/H] 0. However, the populations from the thick and the
thin disc cannot be clearly separated.Comment: Astronomy & Astrophysics, in pres
Chemical abundances in the protoplanetary disk LV2 (Orion): clues to the causes of the abundance anomaly in HII regions
Optical integral field spectroscopy of the archetype protoplanetary disk LV2
in the Orion Nebula is presented, taken with the VLT FLAMES/Argus fibre array.
The detection of recombination lines of CII and OII from this class of objects
is reported, and the lines are utilized as abundance diagnostics. The study is
complemented with the analysis of HST Faint Object Spectrograph ultraviolet and
optical spectra of the target contained within the Argus field of view. By
subtracting the local nebula background the intrinsic spectrum of the proplyd
is obtained and its elemental composition is derived for the first time. The
proplyd is found to be overabundant in carbon, oxygen and neon compared to the
Orion Nebula and the sun. The simultaneous coverage over LV2 of the CIII]
1908-A and [OIII] 5007-A collisionally excited lines (CELs) and CII and OII
recombination lines (RLs) has enabled us to measure the abundances of C++ and
O++ for LV2 with both sets of lines. The two methods yield consistent results
for the intrinsic proplyd spectrum, but not for the proplyd spectrum
contaminated by the generic nebula spectrum, thus providing one example where
the long-standing abundance anomaly plaguing metallicity studies of HII regions
has been resolved. These results would indicate that the standard
forbidden-line methods used in the derivation of light metal abundances in HII
regions in our own and other galaxies underestimate the true gas metallicity.Comment: Accepted by MNRAS November 8; 16 pages, 9 figs; typos corrected,
error in FWHMs in table 4 corrected in this versio
Measurement of the (90,91,92,93,94,96)Zr(n,gamma) and (139)La(n,gamma) cross sections at n_TOF
Open AccessNeutron capture cross sections of Zr and La isotopes have important implications in the field of nuclear astrophysics as well as in the nuclear technology. In particular the Zr isotopes play a key role for the determination of the neutron density in the He burning zone of the Red Giant star, while the (139)La is important to monitor the s-process abundances from Ba up to Ph. Zr is also largely used as structural materials of traditional and advanced nuclear reactors. The nuclear resonance parameters and the cross section of (90,91,92,93,94,96)Zr and (139)La have been measured at the n_TOF facility at CERN. Based on these data the capture resonance strength and the Maxwellian-averaged cross section were calculated
Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV
The neutron capture cross section of 204Pb has been measured at the CERN
n_TOF installation with high resolution in the energy range from 1 eV to 440
keV. An R-matrix analysis of the resolved resonance region, between 1 eV and
100 keV, was carried out using the SAMMY code. In the interval between 100 keV
and 440 keV we report the average capture cross section. The background in the
entire neutron energy range could be reliably determined from the measurement
of a 208Pb sample. Other systematic effects in this measurement could be
investigated and precisely corrected by means of detailed Monte Carlo
simulations. We obtain a Maxwellian average capture cross section for 204Pb at
kT=30 keV of 79(3) mb, in agreement with previous experiments. However our
cross section at kT=5 keV is about 35% larger than the values reported so far.
The implications of the new cross section for the s-process abundance
contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.
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