344 research outputs found
Remote balance weighs accurately amid high radiation
Commercial beam-type balance, modified and outfitted with electronic controls and digital readout, can be remotely controlled for use in high radiation environments. This allows accurate weighing of breeder-reactor fuel pieces when they are radioactively hot
Constraining angular momentum transport processes in stellar interiors with red-giant stars in the open cluster NGC6819
Clusters are excellent test benches for verification and improvement of
stellar evolution theory. The recent detection of solar-like oscillations in
G-K giants in the open cluster NGC6819 with Kepler provides us with independent
constraints on the masses and radii of stars on the red giant branch, as well
as on the distance to clusters and their ages. We present, for NGC6819,
evolutionary models by considering rotation-induced mixing ; and the
theoretical low-l frequencies of our stellar models.Comment: Submitted to EPJ Web of Conferences, to appear in the Proceedings of
the 3rd CoRoT Symposium, Kepler KASC7 joint meeting; 2 pages, 1 figur
Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities
The availability of asteroseismic constraints for a large sample of stars
from the missions CoRoT and Kepler paves the way for various statistical
studies of the seismic properties of stellar populations. In this paper, we
evaluate the impact of rotation-induced mixing and thermohaline instability on
the global asteroseismic parameters at different stages of the stellar
evolution from the Zero Age Main Sequence to the Thermally Pulsating Asymptotic
Giant Branch to distinguish stellar populations. We present a grid of stellar
evolutionary models for four metallicities (Z = 0.0001, 0.002, 0.004, and
0.014) in the mass range between 0.85 to 6.0 Msun. The models are computed
either with standard prescriptions or including both thermohaline convection
and rotation-induced mixing. For the whole grid we provide the usual stellar
parameters (luminosity, effective temperature, lifetimes, ...), together with
the global seismic parameters, i.e. the large frequency separation and
asymptotic relations, the frequency corresponding to the maximum oscillation
power {\nu}_{max}, the maximal amplitude A_{max}, the asymptotic period spacing
of g-modes, and different acoustic radii. We discuss the signature of
rotation-induced mixing on the global asteroseismic quantities, that can be
detected observationally. Thermohaline mixing whose effects can be identified
by spectroscopic studies cannot be caracterized with the global seismic
parameters studied here. But it is not excluded that individual mode
frequencies or other well chosen asteroseismic quantities might help
constraining this mixing.Comment: 15 pages, 11 figures, accepted for publication in A&
FastAlert-an automatic search system to alert about new entries in biological sequence databanks
This paper describes a new tool enabling awareness of new sequence databank entries of interest. The Fast Alert system relieves the researcher from the burden of repeating FASTA searches in order to keep up with the rapidly growing amount of information found in biological sequence databanks. The query sequence can be submitted from any computer connected to the Internet. Upon registration, the databank, including the updates, is scanned at periodic intervals with the sequence provided. The results, so-called FastAlert reports, are delivered via electronic mail. The reports contain the FASTA best-scores list and the similarity statistics for each entry liste
Stellar mass and age determinations - I. Grids of stellar models from Z=0.006 to 0.04 and M=0.5 to 3.5 Msun
We present dense grids of stellar models suitable for comparison with
observable quantities measured with great precision, such as those derived from
binary systems or planet-hosting stars. We computed new Geneva models without
rotation at metallicities Z=0.006, 0.01, 0.014, 0.02, 0.03 and 0.04 (i.e.
[Fe/H] from -0.33 to +0.54) and with mass in small steps from 0.5 to 3.5 Msun.
Great care was taken in the procedure for interpolating between tracks in order
to compute isochrones. Several properties of our grids are presented as a
function of stellar mass and metallicity. Those include surface properties in
the Hertzsprung-Russell diagram, internal properties including mean stellar
density, sizes of the convective cores, and global asteroseismic properties. We
checked our interpolation procedure and compared interpolated tracks with
computed tracks. The deviations are less than 1% in radius and effective
temperatures for most of the cases considered. We also checked that the present
isochrones provide nice fits to four couples of observed detached binaries and
to the observed sequences of the open clusters NGC 3532 and M67. Including
atomic diffusion in our models with M<1.1 Msun leads to variations in the
surface abundances that should be taken into account when comparing with
observational data of stars with measured metallicities. For that purpose,
iso-Zsurf lines are computed. These can be requested for download from a
dedicated web page together with tracks at masses and metallicities within the
limits covered by the grids. The validity of the relations linking Z and FeH is
also re-assessed in light of the surface abundance variations in low-mass
stars.Comment: Accepted for publication in A&
Analysis of 70 Ophiuchi AB including seismic constraints
The analysis of solar-like oscillations for stars belonging to a binary
system provides a unique opportunity to probe the internal stellar structure
and to test our knowledge of stellar physics. Such oscillations have been
recently observed and characterized for the A component of the 70 Ophiuchi
system. A model of 70 Ophiuchi AB that correctly reproduces all observational
constraints available for both stars is determined. An age of 6.2 +- 1.0 Gyr is
found with an initial helium mass fraction Y_i=0.266 +- 0.015 and an initial
metallicity (Z/X)_i=0.0300 +- 0.0025 when atomic diffusion is included and a
solar value of the mixing-length parameter assumed. A precise and independent
determination of the value of the mixing-length parameter needed to model 70
Oph A requires accurate measurement of the mean small separation, which is not
available yet. Current asteroseismic observations, however, suggest that the
value of the mixing-length parameter of 70 Oph A is lower or equal to the solar
calibrated value. The effects of atomic diffusion and of the choice of the
adopted solar mixture were also studied. We also tested and compared the
theoretical tools used for the modeling of stars for which p-modes frequencies
are detected by performing this analysis with three different stellar evolution
codes and two different calibration methods. We found that the different
evolution codes and calibration methods we used led to perfectly coherent
results.Comment: 9 pages, 8 figures, accepted for publication in A&
Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
A precise characterisation of the red giants in the seismology fields of the
CoRoT satellite is a prerequisite for further in-depth seismic modelling.
High-resolution FEROS and HARPS spectra were obtained as part of the
ground-based follow-up campaigns for 19 targets holding great asteroseismic
potential. These data are used to accurately estimate their fundamental
parameters and the abundances of 16 chemical species in a self-consistent
manner. Some powerful probes of mixing are investigated (the Li and CNO
abundances, as well as the carbon isotopic ratio in a few cases). The
information provided by the spectroscopic and seismic data is combined to
provide more accurate physical parameters and abundances. The stars in our
sample follow the general abundance trends as a function of the metallicity
observed in stars of the Galactic disk. After an allowance is made for the
chemical evolution of the interstellar medium, the observational signature of
internal mixing phenomena is revealed through the detection at the stellar
surface of the products of the CN cycle. A contamination by NeNa-cycled
material in the most massive stars is also discussed. With the asteroseismic
constraints, these data will pave the way for a detailed theoretical
investigation of the physical processes responsible for the transport of
chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised
version after language editing
Survey for Transiting Extrasolar Planets in Stellar Systems: III. A Limit on the Fraction of Stars with Planets in the Open Cluster NGC 1245
We analyze a 19-night photometric search for transiting extrasolar planets in
the open cluster NGC 1245. An automated transit search algorithm with
quantitative selection criteria finds six transit candidates; none are bona
fide planetary transits. We characterize the survey detection probability via
Monte Carlo injection and recovery of realistic limb-darkened transits. We use
this to derive upper limits on the fraction of cluster members with close-in
Jupiter-radii, RJ, companions. We carefully analyze the random and systematic
errors of the calculation. For similar photometric noise and weather properties
as this survey, observing NGC 1245 twice as long results in a tighter
constraint on "Hot Jupiter", HJ, companions than observing an additional
cluster of similar richness as NGC 1245 for the same length of time as this
survey. This survey observed ~870 cluster members. If 1% of stars have 1.5 RJ
HJ companions, we expect to detect one planet for every 5000 dwarf stars
observed for a month. To reach a ~2% upper limit on the fraction of stars with
1.5 RJ HJ companions, we conclude a total sample size of ~7400 dwarf stars
observed for at least a month will be needed. Results for 1.0 RJ companions,
without substantial improvement in the photometric precision, will require a
small factor larger sample size.Comment: 24 pages, 15 figures, submitted A
Higher metal abundances do not solve the solar problem
Context. The Sun acts as a cornerstone of stellar physics. Thanks to
spectroscopic, helioseismic and neutrino flux observations, we can use the Sun
as a laboratory of fundamental physics in extreme conditions. The conclusions
we draw are then used to inform and calibrate evolutionary models of all other
stars in the Universe. However, solar models are in tension with helioseismic
constraints. The debate on the ``solar problem'' has hitherto led to numerous
publications discussing potential issues with solar models and abundances.
Aims. Using the recently suggested high-metallicity abundances for the Sun, we
investigate whether standard solar models, as well as models with macroscopic
transport reproducing the solar surface lithium abundances and analyze their
properties in terms of helioseismic and neutrino flux observations. Methods. We
compute solar evolutionary models and combine spectroscopic and helioseismic
constraints as well as neutrino fluxes to investigate the impact of macroscopic
transport on these measurements. Results. When high-metallicity solar models
are calibrated to reproduce the measured solar lithium depletion, tensions
arise with respect to helioseismology and neutrino fluxes. This is yet another
demonstration that the solar problem is also linked to the physical
prescriptions of solar evolutionary models and not to chemical composition
alone. Conclusions. A revision of the physical ingredients of solar models is
needed in order to improve our understanding of stellar structure and
evolution. The solar problem is not limited to the photospheric abundances if
the depletion of light elements is considered. In addition, tighter constraints
on the solar beryllium abundance will play a key role in the improvement of
solar models.Comment: Accepted for publication in Astronomy and Astrophysic
Extrasolar planets and brown dwarfs around A--F type stars. VIII. A giant planet orbiting the young star HD113337
In the frame of the search for extrasolar planets and brown dwarfs around
early-type main-sequence stars, we present the detection of a giant planet
around the young F-type star HD113337. We estimated the age of the system to be
150 +100/-50 Myr. Interestingly, an IR excess attributed to a cold debris disk
was previously detected on this star. The SOPHIE spectrograph on the 1.93m
telescope at Observatoire de Haute-Provence was used to obtain ~300 spectra
over 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A
and F stars, to derive the radial velocity variations. The data reveal a 324.0
+1.7/-3.3 days period that we attribute to a giant planet with a minimum mass
of 2.83 +- 0.24 Mjup in an eccentric orbit with e=0.46 +- 0.04. A long-term
quadratic drift, that we assign to be probably of stellar origin, is
superimposed to the Keplerian solution.Comment: 7 pages, 4 figure
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