Thierry Appourchaux | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)

Papers by Thierry Appourchaux

Advances in Space Research, 2003

ASTROD I is the first planned space mission in a series of ASTROD missions for testing relativity... more ASTROD I is the first planned space mission in a series of ASTROD missions for testing relativity in space using optical devices. The main aims are: (i) to test General Relativity with an improvement of three orders of magnitude compared to current results, (ii) to measure solar and solar system parameters with improved accuracy, (iii) to test the constancy of the gravitational constant and in general to get a deeper understanding of gravity. The first ideas for the ASTROD missions go back to the last century when new technologies in the area of laser physics and time measurement began to appear on the horizon. ASTROD is a mission concept that is supported by a broad international community covering the areas of space technology, fundamental physics, high performance laser and clock technology and drag free control. While ASTROD I is a single-spacecraft concept that performes measurements with pulsed laser ranging between the spacecraft and earthbound laser ranging stations, ASTROD-GW is planned to be a three spacecraft mission with inter-spacecraft laser ranging. ASTROD-GW would be able to detect gravitational waves at frequencies below the eLISA/NGO bandwidth. As a third step Super-ASTROD with larger orbits could even probe primordial gravitational waves. This article gives an overview on the basic principles especially for ASTROD I.

ABSTRACT The m-dependence of the amplitudes of the multiplets of low-degree p modes contains info... more ABSTRACT The m-dependence of the amplitudes of the multiplets of low-degree p modes contains information about the latitudinal distribution of the power in the excitation of the oscillations. We present estimates of those amplitudes from 4 years of VIRGO/LOI observations. Variation of the excitation with magnetic activity is studied.

Astronomy and Astrophysics a European Journal, 2004

Astronomy and Astrophysics, Apr 29, 1999

Low-degree solar p modes observed by the GONG network have been analysed for l ≤ 6, yielding accu... more Low-degree solar p modes observed by the GONG network have been analysed for l ≤ 6, yielding accurate measurements of their frequencies, splittings and linewidths. The results obtained here show significant improvement on previous determinations, especially for increasing the number of identified modes with l ≤ 3 and for minimizing the bias on the splitting determination and the error bars. A more realistic approach was used to fit the helioseismic data assuming that the observed spectra are statistically dependent upon one another. This is in contrast to what is commonly done and the result is a better treatment of the leakage between the modes. Moreover, the effect of an imperfect knowledge of the leakage within the elements of the l = 1 multiplets upon their splitting determination is analysed. In addition, the effect of the leakage between the modes of different degrees upon the p-mode parameters determination is shown, and a procedure for 'cleaning' the spatial alias is described leading to splitting coefficients with smaller systematic errors than before.

Structure and Dynamics of the Interior of the Sun and Sun Like Stars, 1998

Using continuous time series of 610 days of velocity (MDI, LOI-proxy) and intensity (VIRGO, SPM a... more Using continuous time series of 610 days of velocity (MDI, LOI-proxy) and intensity (VIRGO, SPM and LOI) we show that Lorentzian profiles as a model of low-degree p-mode line leads to systematic differences in the determination of intensity and velocity mode frequencies. These differences, as large as 0.1 muHz for degrees l = 0, 1, 2 and 3, are frequency-dependent. The use of a physics-based asymmetrical line shape (Rakesh et al., 1998) to fit the same lines has allowed us to significantly reduce differences in the frequency determination. P-mode lines in velocity exhibit a significant negative asymmetry (excess of power in the left wing) whereas p-modes lines in intensity have a positive asymmetry (excess of power in the right wing). The magnitude and sign of this asymmetry are directly related to the location of the source of p-mode excitation and to the correlation between mode and solar noise.

ABSTRACT The PRISMA mission addresses one of the most fundamental areas of astronomy: the structu... more ABSTRACT The PRISMA mission addresses one of the most fundamental areas of astronomy: the structure and evolution of the stars. It uses the new technique of asteroseismology, measuring the surface amplitude of oscillations which penetrate deep into the interior of stars, whilst simultaneously monitoring surface activity.

The temperature dependence of photodiodes quantum efficiency for different processes (deep diffus... more The temperature dependence of photodiodes quantum efficiency for different processes (deep diffused and ion implanted) and resistivities (10 and 100 (Omega) .cm) were measured. To better predict their behavior, a comparison was made with a simple uni-dimensional p-n junction model. This includes band-gap, depletion region width, diffusion constants, mobilities, intrinsic carrier concentration, absorption coefficient, and refractive index temperature functions. The

Astronomy & Astrophysics, 1995

The Luminosity Oscillations Imager is a part of the VIRGO instrument to be flown aboard the Solar... more The Luminosity Oscillations Imager is a part of the VIRGO instrument to be flown aboard the Solar and Heliospheric Observatory in mid 1995. Using a ground-based version of the instrument, we have detected low-l modes with a time series spanning 163 days. The low resolution capability of the instrument allows the identification of individual tesseral orders for l=2 to 5.

We report on results from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-a... more We report on results from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-and-hounds exercise. The group is concerned with the development of methods for extracting the parameters of low-l solar p mode data ('peak bagging'), collected by Sun-as-a-star observations. Accurate and precise estimation of the fundamental parameters of the p modes is a vital pre-requisite of all subsequent studies. Nine members of the FLAG (the 'hounds') fitted an artificial 3456-d dataset. The dataset was made by the 'hare' (WJC) to simulate full-disc Doppler velocity observations of the Sun. The rotational frequency splittings of the l = 1, 2 and 3 modes were the first parameter estimates chosen for scrutiny. Significant differences were uncovered at l = 2 and 3 between the fitted splittings of the hounds. Evidence is presented that suggests this unwanted bias had its origins in several effects. The most important came from the different way in which the hounds modeled the visibility ratio of the different rotationally split components. Our results suggest that accurate modelling of the ratios is vital to avoid the introduction of significant bias in the estimated splittings. This is of importance not only for studies of the Sun, but also of the solar analogues that will targets for asteroseismic campaigns.

Proceedings of the International Astronomical Union, 2014

The Solar Orbiter is the next solar physics mission of the European Space Agency, ESA, in collabo... more The Solar Orbiter is the next solar physics mission of the European Space Agency, ESA, in collaboration with NASA, with a launch planned in 2018. The spacecraft is designed to approach the Sun to within 0.28 AU at perihelion of a highly eccentric orbit. The proximity with the Sun will also allow its observation at uniformly high resolution at EUV and visible wavelengths. Such observations are central for learning more about the magnetic coupling of the solar atmosphere. At a later phase in the mission the spacecraft will leave the ecliptic and study the enigmatic poles of the Sun from a heliographic latitude of up to 33 • .

Progress in the development of an instrument with very high (1:10 billion) wavelength stability d... more Progress in the development of an instrument with very high (1:10 billion) wavelength stability designed to measure solar surface velocities and magnetic fields is reported. The instrument determines Doppler and Zeeman shifts in solar spectral lines by a 6-point weighted average. It is built around an electrically tunable solid lithium-niobate Fabry-Perot etalon that is stabilized against a diode laser which itself is locked to a resonance line of cesium 133. Key features are the etalon, which acts as a wide-angle 0.017-nm solar filter, the camera with a specially stabilized shutter, and the instrument control and data collection system. Use of the instrument in helioseismological research is emphasized.

The quest for the solar gravity modes (or g modes) is key for the understanding of the structure ... more The quest for the solar gravity modes (or g modes) is key for the understanding of the structure and dynamics of the solar core. In this paper, we review the history of the solar g-mode detection which is separated in three nearly distinct era which corresponds to: the theory of g modes, the detections from the ground and the detections from space. The prospects of definitive solar g-mode detection are also discussed.

We report on results of rotation inversions using as in- put fitted splitting estimates from the ... more We report on results of rotation inversions using as in- put fitted splitting estimates from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-and- hounds exercise. The 'hounds in the group fitted an arti- ficial 9.5-yr dataset made by the 'hare to mimic full-disc Doppler velocity observations of the Sun.

Angular Momentum Evolution of Young Stars, 1991

New Eyes to See Inside the Sun and Stars, 1998

ABSTRACT The Luminosity Oscillations Imager (LOI) of the VIRGO experiment aboard SOHO provides co... more ABSTRACT The Luminosity Oscillations Imager (LOI) of the VIRGO experiment aboard SOHO provides continuous measurement of the solar irradiance in a 5 nm band around 500 nm. The solar image is broken down in 12 pixels distributed in 4 latitudinal bands. The first year of operation of the instrument has taken place during a period of solar minimum activity. The measurements provide an indication of the distribution of the solar irradiance variations versus latitude. Contributions to the observed variations due to the presence of active regions are discussed in relation to the possible effect of the evolving solar cycle (structure of the convection zone): short term variations versus long term variations. The problem of the photometric stability of the measurements needed for the investigation is thoroughly treated by self consistency and by comparison with other instruments on SOHO (VIRGO sun- photometers and MDI intensity measurements).

Passive Materials for Optical Elements II, 1993

ABSTRACT A multilayer filter, that will fly on the SOHO mission, has been designed to resist 3 - ... more ABSTRACT A multilayer filter, that will fly on the SOHO mission, has been designed to resist 3 - 4 major solar flares. This paper reports on the effects of the simulated solar flare on the glasses and filters. For the color filter glasses, transmittance drops could be up to 18% at 500 nm, for the 7-year simulated test, while for the heat absorbing glasses it was a few %. The filter transmittance dropped relatively by 2.6% and 15%, for the 2-year and 7- year doses, respectively. In most cases the filter profiles were slightly affected. The effect of the irradiations on the coatings, the adhesive and the glasses is discussed. Guidelines for minimizing effect of irradiations on coatings and glasses are given.

Advances in Helio- and Asteroseismology, 1987

ABSTRACT A unique solar lineshift analyzer described by Rust, Burton and Leistner (1986) has been... more ABSTRACT A unique solar lineshift analyzer described by Rust, Burton and Leistner (1986) has been used to study solar oscillations. Operation of this "Stabilized Solar Analyzer" depends on the electro-optic effect in crystalline lithium niobate, the substrate of the solid Fabry-Perot etalon. For 10 days in February, 1986, at the Vacuum Tower Telescope of the Sacramento Peak Observatory, the authors obtained full-disk observations of the solar oscillations.

Communications in Asteroseismology

SIAMOIS is a ground-based asteroseismology project, to pursue velocity measurements from the Dome... more SIAMOIS is a ground-based asteroseismology project, to pursue velocity measurements from the Dome C Concordia station in Antarctica. The scientific program of SIAMOIS is based on the very precise asteroseismic observation of nearby bright targets, focussing on the observations of solar-like oscillations in solar-like stars. Spectrometric observations with SIAMOIS will be able to detect l=3 oscillation modes that cannot be analyzed with space-borne photometric observations. The Doppler data, less affected by the stellar activity noise, will yield a more precise mode structure inversion, thus a high-precision determination of the stellar interior structure. The benefit of precise Doppler observations of nearby targets, with addition of interferometric and high-resolution spectrometric measurements, will allow us to investigate in detail the physical laws governing the stellar interior structure and evolution. Dome C appears to be the ideal place for ground-based asteroseismic observat...

Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, 2012

ABSTRACT Echoes is a project of a space-borne instrument which has been proposed as part of the J... more ABSTRACT Echoes is a project of a space-borne instrument which has been proposed as part of the JUICE mission which is selected in the Cosmic Vision program of the European Space Agency (ESA) to perform seismic and dynamics studies of Jupiter's interior and atmosphere. Based on an original Mach-Zehnder design, the instrument aims to measure Doppler shifts of solar spectral lines, which are reflected by cloud layers of Jupiter's upper troposphere, coupled with imaging capabilities. It is specified to detect global oscillations with degree up to l = 50 and amplitude as low as 1 cm/s at the surface of Jupiter. In order to check the compliance of the instrument, and its capability to operate in representative environment (TRL5), we build a prototype to perform tests. In this paper, we present the prototype implemented at Observatoire de la Côte d'Azur in collaboration with Institut d'Astrophysique Spatiale. We describe the design of the Mach-Zehnder and the procedure of control and adjustment. We present the necessary tests and we show on simulation that the measurements will provide the required precision. In conclusion, we will explain the perspective for such a new instrument.

Advances in Space Research, 2003

Astronomy and Astrophysics a European Journal, 2004

Astronomy and Astrophysics, Apr 29, 1999

Structure and Dynamics of the Interior of the Sun and Sun Like Stars, 1998

Astronomy & Astrophysics, 1995

Proceedings of the International Astronomical Union, 2014

Angular Momentum Evolution of Young Stars, 1991

New Eyes to See Inside the Sun and Stars, 1998

Passive Materials for Optical Elements II, 1993

Advances in Helio- and Asteroseismology, 1987

Communications in Asteroseismology

Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, 2012

Proceedings: Second Eddington Workshop: Stellar structure and habitable planet finding, Jan 2004

With more than 30 years of experience in extraction of eigenmodes from power spectra of solar sig... more With more than 30 years of experience in extraction of eigenmodes from power spectra of solar signals, we are now almost ready to apply this knowledge onto the forecoming missions: COROT and Eddington. However the fitting task differs by 3 orders of magnitude; COROT will be able to get time series of stellar light for some 30 stars, while Eddington will be able to gather such data for about 50000 stars. While for COROT, our current tools can be applied by hand, the case of Eddington is significantly more complex. We are looking forward having automatic fitting procedures that will allow to recover mode parameters for about 90% of the solar-like stars. Unfortunately, about 10% of these stars will require some more delicate attention that will cost time to take care of. We will use the example of the infamous HD 57006, known to be quite evolved with a difficult eigenmode spectrum, to explain how a star can evolve from an easy-to-fit target (90% of the solar-like stars) to a difficult-to-fit (10% of the remaining stars). In the latter case, new techniques for detecting narrow peaks (g-mode like) out of broad peaks (p-mode like) has been devised in the context of the hare-and-hound exercise of COROT. This and other techniques will be used to implement the automatic fitting procedure for the remaining 10% of Eddington solar-like stars.

Peered Reviewed Article, Jan 12, 2005

The mode identification and fitting of solar oscillations provide an observational tool to derive... more The mode identification and fitting of solar oscillations provide an observational tool to derive the physical properties of the Sun's interior. What has been devised for helioseismology can now be used for future asteroseismology ground-based instruments and space missions, such as the High-Accuracy Radial Velocity Planetary Searcher (HARPS) and Convection, Rotation and Planetary Transits (COROT). In the coming decade, numerous stars will be observed for which new tools will be needed. For instance, it is very likely that g and p modes will be detected, rendering the identification difficult. In addition, modes having both characteristics, known as mixed modes, are also likely to be detected in evolved stars; these latter modes are crucial for the understanding of the internal structure of the stars as they propagate deeply inside the stars, unlike the p modes. Unfortunately, the mixing will not only occur physically but also in the frequency domain: mixed modes will appear very close to stochastically excited p modes. In this paper, we have devised a new technique for detecting long-lived modes (mixed or g modes) embedded in a common p-mode spectrum. The technique has been validated using Monte Carlo simulations. In the framework of the hare-and-hound exercise of COROT, this technique has been applied to synthetic time series of the evolved solar-like star HD 57006. The results show that we can detect most of the mixed modes embedded by the hare. We also discuss the impact of how the long-lived modes are excited on the detection level. The technique described here can be applied to stars with a mass greater than 1.2 M⊙, having evolved possibly beyond the terminal-age main sequence, such as Procyon.