314 research outputs found
VINCI / VLTI observations of Main Sequence stars
Main Sequence (MS) stars are by far the most numerous class in the Universe.
They are often somewhat neglected as they are relatively quiet objects (but
exceptions exist), though they bear testimony of the past and future of our
Sun. An important characteristic of the MS stars, particularly the solar-type
ones, is that they host the large majority of the known extrasolar planets.
Moreover, at the bottom of the MS, the red M dwarfs pave the way to
understanding the physics of brown dwarfs and giant planets. We have measured
very precise angular diameters from recent VINCI/VLTI interferometric
observations of a number of MS stars in the K band, with spectral types between
A1V and M5.5V. They already cover a wide range of effective temperatures and
radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as
well as the asteroseismic information available for some of these stars, the
angular diameters put strong constraints on the detailed models of these stars,
and therefore on the physical processes at play.Comment: 5 pages, 3 figures. To appear in the Proceedings of IAU Symposium
219, "Stars as Suns", Editors A. Benz & A. Dupree, Astronomical Society of
the Pacifi
Testing real-time systems using TINA
The paper presents a technique for model-based black-box conformance testing of real-time systems using the Time Petri Net Analyzer TINA. Such test suites are derived from a prioritized time Petri net composed of two concurrent sub-nets specifying respectively the expected behaviour of the system under test and its environment.We describe how the toolbox TINA has been extended to support automatic generation of time-optimal test suites. The result is optimal in the sense that the set of test cases in the test suite have the shortest possible accumulated time to be executed. Input/output conformance serves as the notion of implementation correctness, essentially timed trace inclusion taking environment assumptions into account. Test cases selection is based either on using manually formulated test purposes or automatically from various coverage criteria specifying structural criteria of the model to be fulfilled by the test suite. We discuss how test purposes and coverage criterion are specified in the linear temporal logic SE-LTL, derive test sequences, and assign verdicts
Formal Verification Integration Approach for DSML
International audienceThe application of formal methods (especially, model check- ing and static analysis techniques) for the verification of safety critical embedded systems has produced very good results and raised the inter- est of system designers up to the application of these technologies in real size projects. However, these methods usually rely on specific verifica- tion oriented formal languages that most designers do not master. It is thus mandatory to embed the associated tools in automated verification toolchains that allow designers to rely on their usual domain-specific modeling languages (DSMLs) while enjoying the benefits of these power- ful methods. More precisely, we propose a language to formally express system requirements and interpret verification results so that system designers (DSML end-users) avoid the burden of learning some formal verification technologies. Formal verification is achieved through trans- lational semantics. This work is based on a metamodeling pattern for executable DSML that favors the definition of generative tools and thus eases the integration of tools for new DSML
Modeling of Alpha Cen and Procyon using VLTI observations
We present a novel approach to model the nearby stars Alpha Cen A & B and
Procyon A using asteroseismic and interferometric constraints. Using the VINCI
instrument installed at the VLT Interferometer (VLTI), the angular diameters of
the Alpha Centauri system were measured with a relative precision of 0.2% and
0.6%, respectively. From these values, we derive linear radii of R[A] = 1.224
+/- 0.003 R_sun and R[B] = 0.863 +/- 0.005 R_sun. These radii are in excellent
agreement with the models of Thevenin et al. (2002), that use asteroseismic
frequencies as constraints (Bouchy & Carrier 2001; Bouchy & Carrier 2002). With
the same instrument, we also measured the angular diameter of Procyon A. Using
the Hipparcos parallax, we obtain a linear radius of 2.048 +/- 0.025 R_sun. We
use this result together with spectroscopic and photometric constraints to
model this star with the CESAM code. We also computed the adiabatic oscillation
spectrum of our model of Procyon A, giving a mean large frequency separation of
Delta nu_0 = 54.8 uHz, in agreement with the seismic observations by Martic et
al. (2001). Our model favours a mass around 1.4 M_sun for Procyon A.Comment: 8 pages, 5 figures, poster presented at the JD 12 of the IAU General
Assembly, Sydney 200
Algorithms for zero-dimensional ideals using linear recurrent sequences
Inspired by Faug\`ere and Mou's sparse FGLM algorithm, we show how using
linear recurrent multi-dimensional sequences can allow one to perform
operations such as the primary decomposition of an ideal, by computing the
annihilator of one or several such sequences.Comment: LNCS, Computer Algebra in Scientific Computing CASC 201
Gravity modes in rapidly rotating stars. Limits of perturbative methods
CoRoT and Kepler missions are now providing high-quality asteroseismic data
for a large number of stars. Among intermediate-mass and massive stars, fast
rotators are common objects. Taking the rotation effects into account is needed
to correctly understand, identify, and interpret the observed oscillation
frequencies of these stars. A classical approach is to consider the rotation as
a perturbation. In this paper, we focus on gravity modes, such as those
occurring in gamma Doradus, slowly pulsating B (SPB), or Be stars. We aim to
define the suitability of perturbative methods. With the two-dimensional
oscillation program (TOP), we performed complete computations of gravity modes
-including the Coriolis force, the centrifugal distortion, and compressible
effects- in 2-D distorted polytropic models of stars. We started with the modes
l=1, n=1-14, and l=2-3, n=1-5,16-20 of a nonrotating star, and followed these
modes by increasing the rotation rate up to 70% of the break-up rotation rate.
We then derived perturbative coefficients and determined the domains of
validity of the perturbative methods. Second-order perturbative methods are
suited to computing low-order, low-degree mode frequencies up to rotation
speeds ~100 km/s for typical gamma Dor stars or ~150 km/s for B stars. The
domains of validity can be extended by a few tens of km/s thanks to the
third-order terms. For higher order modes, the domains of validity are
noticeably reduced. Moreover, perturbative methods are inefficient for modes
with frequencies lower than the Coriolis frequency 2Omega. We interpret this
failure as a consequence of a modification in the shape of the resonant cavity
that is not taken into account in the perturbative approach.Comment: 8 pages, 6 figures, Astronomy & Astrophysics (in press
Rotation profiles of solar-like stars with magnetic fields
The aim of this work is to investigate rotation profile of solar-like stars
with magnetic fields. A diffusion coefficient of magnetic angular momentum
transport is deduced. Rotating stellar models with different mass are computed
under the effect of the coefficient. Then rotation profiles are obtained from
the theoretical stellar models. The total angular momentum of solar model with
only hydrodynamic instabilities is about 13 times larger than that of the Sun
at the age of the Sun, and this model can not reproduce quasi-solid rotation in
the radiative region. However, not only can the solar model with magnetic
fields reproduce an almost uniform rotation in the radiative region, but its
total angular momentum is consistent with helioseismic result at the level of 3
at the age of the Sun. The rotation of solar-like stars with magnetic
fields is almost uniform in the radiative region. But there is an obvious
transition region of angular velocity between the convective core and the
radiative region of models with 1.2 - 1.5 , where angular velocity
has a sharp radial change, which is different from the rotation profile of the
Sun and massive stars with magnetic fields. Moreover the changes of the angular
velocity in the transition region increase with the increasing in the age and
mass.Comment: Accepted for publication in ChjA
The Central Temperature of the Sun can be Measured via the Be Solar Neutrino Line
A precise test of the theory of stellar evolution can be performed by
measuring the difference in average energy between the neutrino line produced
by electron capture in the solar interior and the corresponding
neutrino line produced in a terrestrial laboratory. The high temperatures in
the center of the sun broaden the line asymmetrically, FWHM = 1.6~keV, and
cause an average energy shift of 1.3~keV. The width of the Be neutrino line
should be taken into account in calculations of vacuum neutrino oscillations.Comment: RevTeX file, 9 pages. For hardcopy with figure, send to
[email protected]. Institute for Advanced Study number AST 93/4
Oscillations in Procyon A: First results from a multi-site campaign
Procyon A is a bright F5IV star in a binary system. Although the distance,
mass and angular diameter of this star are all known with high precision, the
exact evolutionary state is still unclear. Evolutionary tracks with different
ages and different mass fractions of hydrogen in the core pass, within the
errors, through the observed position of Procyon A in the Hertzsprung-Russell
diagram. For more than 15 years several different groups have studied the
solar-like oscillations in Procyon A to determine its evolutionary state.
Although several studies independently detected power excess in the
periodogram, there is no agreement on the actual oscillation frequencies yet.
This is probably due to either insufficient high-quality data (i.e., aliasing)
or due to intrinsic properties of the star (i.e., short mode lifetimes). Now a
spectroscopic multi-site campaign using 10 telescopes world-wide (minimizing
aliasing effects) with a total time span of nearly 4 weeks (increase the
frequency resolution) is performed to identify frequencies in this star and
finally determine its properties and evolutionary state.Comment: 7 pages, 4 figures to be published in the proceedings of HELAS II
International Conference: Helioseismology, Asteroseismology and MHD
Connections published in the Journal of Physics: Conference Series. High
resolution colour figures can be provided on reques
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