Comparisons for Esta-Task3: Cles and Cesam

We present the results of comparing three different implementations of the microscopic diffusion process in the stellar evolution codes CESAM and CLES. For each of these implementations we computed models of 1.0, 1.2 and 1.3 M$_{\odot}$. We analyse the differences in their internal structure at three selected evolutionary stages, as well as the variations of helium abundance and depth of the stellar convective envelope. The origin of these differences and their effects on the seismic properties of the models are also considered.Comment: 10 pages, 8 figures, Joint HELAS and CoRoT/ESTA Workshop on Solar/Stellar Models and Seismic Analysis Tools, Novembre, Porto 2007 To be published in EAS Publications Serie

Calibrations of alpha Cen A & B

Detailed evolutionary models of the visual binary alpha Centauri, including pre main-sequence evolution, have been performed using the masses recently determined by Pourbaix et al. (1999). Models have been constructed using the CEFF equation of state, OPAL opacities, NACRE thermonuclear reaction rates and microscopic diffusion. A chi^2-minimization is performed to derive the most reliable set of modeling parameters wp={t_alpha Cen, Yi, [Fe/H]i, alpha A, alpha B}, where t alpha Cen is the age of the system, Yi the initial helium content, [Fe/H]i the initial metallicity and, alpha A and alpha B the convection parameters of the two components. Using the basic Bohm-Vitense (1958) mixing-length theory of convection, we derive wp BV={2710 Myr, 0.284,0.257, 1.53, 1.57}. We obtain a noticeably smaller age than estimated previously, in agreement with Pourbaix et al. (1999), mainly because of the larger masses. If convective core overshoot is considered we get wp ov={3530 Myr, 0.279,0.264,1.64,1.66}. The use of Canuto & Mazitelli (1991, 1992) convection theory leads to the set wp CM={4086 Myr, 0.271, 0.264, 0.964, 0.986}. Using the observational constraints adopted by Guenther & Demarque (2000), and the basic mixing-length theory, we obtain wp GD={5640 Myr, 0.300, 0.296, 1.86, 1.97} and surface lithium depletions close to their observed values. A seismological analysis of our calibrated models has been performed. The determination of large and small spacings between the frequencies of acoustic oscillations from seismic observations would help to discriminate between the models of alpha Cen computed with different masses and to confirm or rules out the new determination of masses.Comment: accepted for publication by A&

Seismic diagnostics for transport of angular momentum in stars 2. Interpreting observed rotational splittings of slowly-rotating red giant stars

Asteroseismology with the space-borne missions CoRoT and Kepler provides a powerful mean of testing the modeling of transport processes in stars. Rotational splittings are currently measured for a large number of red giant stars and can provide stringent constraints on the rotation profiles. The aim of this paper is to obtain a theoretical framework for understanding the properties of the observed rotational splittings of red giant stars with slowly rotating cores. This allows us to establish appropriate seismic diagnostics for rotation of these evolved stars. Rotational splittings for stochastically excited dipolar modes are computed adopting a first-order perturbative approach for two $1.3 M_\odot$ benchmark models assuming slowly rotating cores. For red giant stars with slowly rotating cores, we show that the variation of the rotational splittings of $\ell=1$ modes with frequency depends only on the large frequency separation, the g-mode period spacing, and the ratio of the average envelope to core rotation rates (${\cal R}$). This leds us to propose a way to infer directly ${\cal R}$ from the observations. This method is validated using the Kepler red giant star KIC 5356201. Finally, we provide a theoretical support for the use of a Lorentzian profile to measure the observed splittings for red giant stars.Comment: 15 pages, 15 figures, accepted for publication in A&

Measurement of the electron drift velocity for directional dark matter detectors

Three-dimensional track reconstruction is a key issue for directional Dark Matter detection. It requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures : $\rm CF_4$ and $\rm CF_4+CHF_3$. We also show that adding $\rm CHF_3$ allows us to lower the electron drift velocity while keeping almost the same Fluorine content of the gas mixture.Comment: Proceedings of the 4th international conference on Directional Detection of Dark Matter (CYGNUS 2013), 10-12 June 2013, Toyama, Japa

In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors

Three-dimensional track reconstruction is a key issue for directional Dark Matter detection and it requires a precise knowledge of the electron drift velocity. Magboltz simulations are known to give a good evaluation of this parameter. However, large TPC operated underground on long time scale may be characterized by an effective electron drift velocity that may differ from the value evaluated by simulation. In situ measurement of this key parameter is hence needed as it is a way to avoid bias in the 3D track reconstruction. We present a dedicated method for the measurement of the electron drift velocity with the MIMAC detector. It is tested on two gas mixtures: CF4 and CF4 + CHF3. The latter has been chosen for the MIMAC detector as we expect that adding CHF3 to pure CF4 will lower the electron drift velocity. This is a key point for directional Dark Matter as the track sampling along the drift field will be improved while keeping almost the same Fluorine content of the gas mixture. We show that the drift velocity at 50 mbar is reduced by a factor of about 5 when adding 30% of CHF3.Comment: 19 pages, 14 figures. Minor corrections, matches published version in JINS

Seismic diagnostics for transport of angular momentum in stars 1. Rotational splittings from the PMS to the RGB

Rotational splittings are currently measured for several main sequence stars and a large number of red giants with the space mission Kepler. This will provide stringent constraints on rotation profiles. Our aim is to obtain seismic constraints on the internal transport and surface loss of angular momentum of oscillating solar-like stars. To this end, we study the evolution of rotational splittings from the pre-main sequence to the red-giant branch for stochastically excited oscillation modes. We modified the evolutionary code CESAM2K to take rotationally induced transport in radiative zones into account. Linear rotational splittings were computed for a sequence of $1.3 M_{\odot}$ models. Rotation profiles were derived from our evolutionary models and eigenfunctions from linear adiabatic oscillation calculations. We find that transport by meridional circulation and shear turbulence yields far too high a core rotation rate for red-giant models compared with recent seismic observations. We discuss several uncertainties in the physical description of stars that could have an impact on the rotation profiles. For instance, we find that the Goldreich-Schubert-Fricke instability does not extract enough angular momentum from the core to account for the discrepancy. In contrast, an increase of the horizontal turbulent viscosity by 2 orders of magnitude is able to significantly decrease the central rotation rate on the red-giant branch. Our results indicate that it is possible that the prescription for the horizontal turbulent viscosity largely underestimates its actual value or else a mechanism not included in current stellar models of low mass stars is needed to slow down the rotation in the radiative core of red-giant stars.Comment: 15 pages, 13 figures, accepted for publication in A&

The TSS-1 mission: Results on satellite charging

In the present paper we first give a short account of the mission TSS-1 flown on the Shuttle sts-46 in August 1992 and its basic electrical configurations. We then show some results obtained from the experiment RETE on board the satellite which are relevant for the issue of satellite charging

The CoRoT Evolution and Seismic Tools Activity: Goals and Tasks

The forthcoming data expected from space missions such as CoRoT require the capacity of the available tools to provide accurate models whose numerical precision is well above the expected observational errors. In order to secure that these tools meet the specifications, a team has been established to test and, when necessary, to improve the codes available in the community. The CoRoT evolution and seismic tool activity (ESTA) has been set up with this mission. Several groups have been involved. The present paper describes the motivation and the organisation of this activity, providing the context and the basis for the presentation of the results that have been achieved so far. This is not a finished task as future even better data will continue to demand more precise and complete tools for asteroseismology.Comment: 11 pages, 3 figures, accepted for publication in Astrophysics and Space Science, 'CoRoT ESTA' special volum

Laboratory measurements of the performances of the Sweeping Langmuir Probe instrument aboard the PICASSO CubeSat

The Sweeping Langmuir Probe (SLP) is one of the instruments on board the triple-unit CubeSat PICASSO, an ESA in-orbit demonstrator launched in September 2020, which is flying at about 540 km altitude. SLP comprises four small cylindrical probes mounted at the tip of the solar panels. It aims to perform in situ measurements of the plasma parameters (electron density and temperature together with ion density) and of the spacecraft potential in the ionosphere. Before the launch, the instrument, accommodated on an electrically representative PICASSO mock-up, was tested in a plasma chamber. It is shown that the traditional orbital-motion-limited collection theory used for cylindrical Langmuir probes cannot be applied directly for the interpretation of the measurements because of the limited dimensions of the probes with respect to the Debye length in the ionosphere. Nevertheless, this method can be adapted to take into account the short length of the probes. To reduce the data downlink while keeping the most important information in the current-voltage characteristics, SLP includes an on-board adaptive sweeping capability. This functionality has been validated in both the plasma chamber and in space, and it is demonstrated that with a reduced number of data points the electron retardation and electron saturation regions can be well resolved. Finally, the effect of the contamination of the probe surface, which can be a serious issue in Langmuir probe data analysis, has been investigated. If not accounted for properly, this effect could lead to substantial errors in the estimation of the electron temperature.</p