B. Gelly - Academia.edu (original) (raw)
Papers by B. Gelly
VizieR Online Data Catalog, May 1, 2019
HAL (Le Centre pour la Communication Scientifique Directe), Nov 12, 2013
International audienc
Astronomy & Astrophysics, 2019
Measuring the atmospheric circulation of Venus at different altitudes is important for understand... more Measuring the atmospheric circulation of Venus at different altitudes is important for understanding its complex dynamics, in particular the mechanisms driving super-rotation. Observationally, Doppler imaging spectroscopy is in principle the most reliable way to measure wind speeds of planetary atmospheres because it directly provides the projected speed of atmospheric particles. However, high-resolution imaging spectroscopy is challenging, especially in the visible domain, and most knowledge about atmospheric dynamics has been obtained with the cloud tracking technique. The objective of the present work is to measure the global properties of the atmospheric dynamics of Venus at the altitude of the uppermost clouds, which is probed by reflected solar lines in the visible domain. Our results are based on high-resolution spectroscopic observations with the long-slit spectrometer of the solar telescope THEMIS. We present the first instantaneous “radial-velocity snapshot” of any planet ...
In the golden age of solar spacecraft observatories, the use of similar instruments observing sam... more In the golden age of solar spacecraft observatories, the use of similar instruments observing same targets offers us the possibility to get more accurate information of the physical processes taking place on them. We present a comparison between the vector magnetic field and thermodynamic quantities obtained by three different spectropolarimetric instruments. We have used the simultaneous multi-wavelength capabilities of THEMIS/MTR as bridge between the observations at Fe I 6173 Å provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP observations. The official inversion codes for these instruments (PCA based-on, VFISV and MERLIN respectively) have been used with the data properly arranged for them. Therefore, we compare the final products usually offered to the community, i.e. after the inversion, using different codes and these different wavelengths. The cross-calibration of these products shall allow us to go forward from one instrument result to other one in an easy, con...
Solar observations would benefit from simultaneous imaging and spectroscopy. To approach in an op... more Solar observations would benefit from simultaneous imaging and spectroscopy. To approach in an optimal manner such an ideal goal we have designed and built in THEMIS a spectro-imager based upon the concept of subtractive double pass through a diffraction grating spectrograph called TUNIS. In its basic design it produces an image at a wavelength which changes linearly in one of the directions of the image. To improve the simultaneity of the spectral coverage, we have implemented a spectral multiplexing, based upon Hadamard spectroscopy. We present the first observations of TUNIS and give the main specifications. TUNIS has been proposed for the European Solar Telescope (EST) project.
Amongst the different techniques applied up to now to the search for solar g--modes (peaks identi... more Amongst the different techniques applied up to now to the search for solar g--modes (peaks identification, study of the phase/power coherence, the P0 - nur diagrams, etc ldots), some ones are primarily based on the use of their asymptotic behaviour: the constant separation in period between consecutive modes of the same degree ell. The exact fractions technique is one of
Astronomy & Astrophysics, 1993
It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities me... more It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities measured with the resonance scattering technique show variations with time scales of weeks to months. The cause can be understood in terms of the effects of solar activity as was pointed out by Edmunds & Gough (1983) and Andersen & Maltby (1983). The latter authors
SPIE Proceedings, 2008
The European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based te... more The European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based telescope, to be located in the Canary Islands. EST will be optimized for studies of magnetic coupling between the deep photosphere and upper chromosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry. The design of EST will strongly emphasize the use of a large number of visible and near-infrared instruments simultaneously. To achieve these goals, EST will specialize in high spatial and temporal resolution using instruments that can efficiently produce twodimensional spectral information. In this communication, the present situation of the design is outlined, as well as the expected future phases and scheduling.
Full solar disk observations of radial velocity, obtained with the IRIS network of resonant scatt... more Full solar disk observations of radial velocity, obtained with the IRIS network of resonant scattering spectrometers, are used to analyze the acoustic p-mode spectrum around the acoustic cut-off frequency. Three different methods are used to determine it; two use the power spectrum, while the third uses the phase spectrum. The three values measured converge to a common value of 5.55
Le Centre pour la Communication Scientifique Directe - HAL - Inria, Jul 23, 2009
International audienc
An adaptive optics system with a single deformable mirror is being implemented on the THEMIS 90cm... more An adaptive optics system with a single deformable mirror is being implemented on the THEMIS 90cm solar telescope. This system is designed to operate in the visible and is required to be as robust as possible in order to deliver the best possible correction in any atmospheric conditions, even if wavefronts are sensed on some low-contrast solar granulation. In extreme conditions, the images given by the subapertures of the Shack-Hartmann wavefront sensor get randomly blurred in space, in the set of subapertures, and the distribution of blurred images is rapidly changing in time, some of them possibly fading away. The algorithms we have developed for such harsh conditions rely on inverse problem approach. As an example, with the gradients of the wavefronts, the wavefront sensor also estimates their errors, including their covariance. This information allows the control loop to promptly optimize itself to the fast varying conditions, both in space (wavefront reconstruction) and in time...
Astronomy and Astrophysics, 1988
ABSTRACT
Themis is a 90 cm solar telescope which undergoes a rejuvenation of its scientific instruments. I... more Themis is a 90 cm solar telescope which undergoes a rejuvenation of its scientific instruments. In particular, it is about to be equipped with an adaptive optics (AO) system with a bandwidth of at least 1 kHz and featuring a 97 actuator deformable mirror and 10×10 Shack-Hartmann wavefront sensor. Nowadays, the computational power required by such a system can be provided by current multi-core CPU. We have therefore implemented from scratch the real-time control system in pure software using Julia,1 a new language for technical computations, and running on Linux OS. Our main motivation was to be able to exploit new advances in wavefront sensing and adaptive optics control. With a computational cost comparable to state-of-the-art but sub-optimal methods used in solar AO, our wavefront sensing algorithm estimates the local slopes and their covariances following a maximum likelihood registration method. Themis AO system has a modest size but can be used to assert the benefits of maximum...
Based on the principle of optical resonance spectrophotometry, a new instrument has been designed... more Based on the principle of optical resonance spectrophotometry, a new instrument has been designed to be devoted to the search for stellar eigenmodes similar to the 5-min. p-modes observed in integrated sunlight. Used at the Cassegrain focus of the E.S.O. 3.6 m telescope in Chile, this instrument has made it possible to detect these oscillations on Alpha Centauri. The power envelope around five-minutes is almost identical to the solar one (Fig. 3) but the spacing between consecutive peaks in this envelope appears to be 81.3 μHz for Alpha Centauri, (Figs. 1, 2) instead of 68 μHz for the Sun, thus indicating that the radial order of eigenmodes excited within this 5-min. range is somewhat lower Au moyen d'un spectrophotometre specialise et du telescope de 3,60 m de l'E.S.O., des modes propres d'oscillation de periodes voisines de 5 mn ont ete pour la premiere fois detectes sur l'etoile Alpha du Centaure. Ces oscillations sont comparables a celles du Soleil
Astronomy and Astrophysics
We estimate the statistical uncertainties of low-l solar p-modes parameters based on a Monte Carl... more We estimate the statistical uncertainties of low-l solar p-modes parameters based on a Monte Carlo approach. Random perturbations of ideal Lorentz profiles L(a, ν i) can provide many estimations of the set of p-modes parameters a and allow one to estimate statistical error-bars σ a by modelling the parameters' distribution function. Unlike frequencies, which show symmetric distributions, amplitudes and linewidths have asymmetric probability density function similar to the distribution function for time-averaged energies of stochastically excited solar p-modes (Kumar, 1988). A comparison between σ ν and uncertainties based on Hessian's computation (Libbrecht 1992, Toutain and Appourchaux 1994) shows a nice agreement. However, our error-bars take into account more statistical effects, and rely less on the initial parameters' estimation. Such a technique has been used on the IRIS power spectra computed from gapped data, and on one GONG power spectrum computed from almost continuous data. We also present IRIS linewidths and error bars averaged over the years 1989-92 and computed with a fitting strategy using imposed frequency which improves the value of both the parameter and its uncertainty.
The context is that of the so-called ``fundamental ambiguity'' (also azimuth ambiguity, o... more The context is that of the so-called ``fundamental ambiguity'' (also azimuth ambiguity, or 180° ambiguity) in magnetic field vector measurements: two field vectors symmetrical with respect to the line-of-sight have the same polarimetric signature, so that they cannot be discriminated. We propose a method to solve this ambiguity by applying the ``simulated annealing'' algorithm to the minimization of the field divergence, added to the longitudinal current absolute value, the line-of-sight derivative of the magnetic field being inferred by the interpretation of the Zeeman effect observed by spectropolarimetry in two lines formed at different depths. We find that the line pair Fe I lambda 6301.5 and Fe I lambda 6302.5 is appropriate for this purpose. We treat the example case of the delta-spot of NOAA 10808 observed on 13 September 2005 between 14:25 and 15:25 UT with the THEMIS telescope. Besides the magnetic field resolved map, the electric current density vector map ...
VizieR Online Data Catalog, May 1, 2019
HAL (Le Centre pour la Communication Scientifique Directe), Nov 12, 2013
International audienc
Astronomy & Astrophysics, 2019
Measuring the atmospheric circulation of Venus at different altitudes is important for understand... more Measuring the atmospheric circulation of Venus at different altitudes is important for understanding its complex dynamics, in particular the mechanisms driving super-rotation. Observationally, Doppler imaging spectroscopy is in principle the most reliable way to measure wind speeds of planetary atmospheres because it directly provides the projected speed of atmospheric particles. However, high-resolution imaging spectroscopy is challenging, especially in the visible domain, and most knowledge about atmospheric dynamics has been obtained with the cloud tracking technique. The objective of the present work is to measure the global properties of the atmospheric dynamics of Venus at the altitude of the uppermost clouds, which is probed by reflected solar lines in the visible domain. Our results are based on high-resolution spectroscopic observations with the long-slit spectrometer of the solar telescope THEMIS. We present the first instantaneous “radial-velocity snapshot” of any planet ...
In the golden age of solar spacecraft observatories, the use of similar instruments observing sam... more In the golden age of solar spacecraft observatories, the use of similar instruments observing same targets offers us the possibility to get more accurate information of the physical processes taking place on them. We present a comparison between the vector magnetic field and thermodynamic quantities obtained by three different spectropolarimetric instruments. We have used the simultaneous multi-wavelength capabilities of THEMIS/MTR as bridge between the observations at Fe I 6173 Å provided by SDO/HMI and at Fe I 6301 & 6302 Å by Hinode-SOT/SP observations. The official inversion codes for these instruments (PCA based-on, VFISV and MERLIN respectively) have been used with the data properly arranged for them. Therefore, we compare the final products usually offered to the community, i.e. after the inversion, using different codes and these different wavelengths. The cross-calibration of these products shall allow us to go forward from one instrument result to other one in an easy, con...
Solar observations would benefit from simultaneous imaging and spectroscopy. To approach in an op... more Solar observations would benefit from simultaneous imaging and spectroscopy. To approach in an optimal manner such an ideal goal we have designed and built in THEMIS a spectro-imager based upon the concept of subtractive double pass through a diffraction grating spectrograph called TUNIS. In its basic design it produces an image at a wavelength which changes linearly in one of the directions of the image. To improve the simultaneity of the spectral coverage, we have implemented a spectral multiplexing, based upon Hadamard spectroscopy. We present the first observations of TUNIS and give the main specifications. TUNIS has been proposed for the European Solar Telescope (EST) project.
Amongst the different techniques applied up to now to the search for solar g--modes (peaks identi... more Amongst the different techniques applied up to now to the search for solar g--modes (peaks identification, study of the phase/power coherence, the P0 - nur diagrams, etc ldots), some ones are primarily based on the use of their asymptotic behaviour: the constant separation in period between consecutive modes of the same degree ell. The exact fractions technique is one of
Astronomy & Astrophysics, 1993
It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities me... more It has been known since the work by Claverie et al. (1982) that integrated-sunlight velocities measured with the resonance scattering technique show variations with time scales of weeks to months. The cause can be understood in terms of the effects of solar activity as was pointed out by Edmunds & Gough (1983) and Andersen & Maltby (1983). The latter authors
SPIE Proceedings, 2008
The European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based te... more The European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based telescope, to be located in the Canary Islands. EST will be optimized for studies of magnetic coupling between the deep photosphere and upper chromosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry. The design of EST will strongly emphasize the use of a large number of visible and near-infrared instruments simultaneously. To achieve these goals, EST will specialize in high spatial and temporal resolution using instruments that can efficiently produce twodimensional spectral information. In this communication, the present situation of the design is outlined, as well as the expected future phases and scheduling.
Full solar disk observations of radial velocity, obtained with the IRIS network of resonant scatt... more Full solar disk observations of radial velocity, obtained with the IRIS network of resonant scattering spectrometers, are used to analyze the acoustic p-mode spectrum around the acoustic cut-off frequency. Three different methods are used to determine it; two use the power spectrum, while the third uses the phase spectrum. The three values measured converge to a common value of 5.55
Le Centre pour la Communication Scientifique Directe - HAL - Inria, Jul 23, 2009
International audienc
An adaptive optics system with a single deformable mirror is being implemented on the THEMIS 90cm... more An adaptive optics system with a single deformable mirror is being implemented on the THEMIS 90cm solar telescope. This system is designed to operate in the visible and is required to be as robust as possible in order to deliver the best possible correction in any atmospheric conditions, even if wavefronts are sensed on some low-contrast solar granulation. In extreme conditions, the images given by the subapertures of the Shack-Hartmann wavefront sensor get randomly blurred in space, in the set of subapertures, and the distribution of blurred images is rapidly changing in time, some of them possibly fading away. The algorithms we have developed for such harsh conditions rely on inverse problem approach. As an example, with the gradients of the wavefronts, the wavefront sensor also estimates their errors, including their covariance. This information allows the control loop to promptly optimize itself to the fast varying conditions, both in space (wavefront reconstruction) and in time...
Astronomy and Astrophysics, 1988
ABSTRACT
Themis is a 90 cm solar telescope which undergoes a rejuvenation of its scientific instruments. I... more Themis is a 90 cm solar telescope which undergoes a rejuvenation of its scientific instruments. In particular, it is about to be equipped with an adaptive optics (AO) system with a bandwidth of at least 1 kHz and featuring a 97 actuator deformable mirror and 10×10 Shack-Hartmann wavefront sensor. Nowadays, the computational power required by such a system can be provided by current multi-core CPU. We have therefore implemented from scratch the real-time control system in pure software using Julia,1 a new language for technical computations, and running on Linux OS. Our main motivation was to be able to exploit new advances in wavefront sensing and adaptive optics control. With a computational cost comparable to state-of-the-art but sub-optimal methods used in solar AO, our wavefront sensing algorithm estimates the local slopes and their covariances following a maximum likelihood registration method. Themis AO system has a modest size but can be used to assert the benefits of maximum...
Based on the principle of optical resonance spectrophotometry, a new instrument has been designed... more Based on the principle of optical resonance spectrophotometry, a new instrument has been designed to be devoted to the search for stellar eigenmodes similar to the 5-min. p-modes observed in integrated sunlight. Used at the Cassegrain focus of the E.S.O. 3.6 m telescope in Chile, this instrument has made it possible to detect these oscillations on Alpha Centauri. The power envelope around five-minutes is almost identical to the solar one (Fig. 3) but the spacing between consecutive peaks in this envelope appears to be 81.3 μHz for Alpha Centauri, (Figs. 1, 2) instead of 68 μHz for the Sun, thus indicating that the radial order of eigenmodes excited within this 5-min. range is somewhat lower Au moyen d'un spectrophotometre specialise et du telescope de 3,60 m de l'E.S.O., des modes propres d'oscillation de periodes voisines de 5 mn ont ete pour la premiere fois detectes sur l'etoile Alpha du Centaure. Ces oscillations sont comparables a celles du Soleil
Astronomy and Astrophysics
We estimate the statistical uncertainties of low-l solar p-modes parameters based on a Monte Carl... more We estimate the statistical uncertainties of low-l solar p-modes parameters based on a Monte Carlo approach. Random perturbations of ideal Lorentz profiles L(a, ν i) can provide many estimations of the set of p-modes parameters a and allow one to estimate statistical error-bars σ a by modelling the parameters' distribution function. Unlike frequencies, which show symmetric distributions, amplitudes and linewidths have asymmetric probability density function similar to the distribution function for time-averaged energies of stochastically excited solar p-modes (Kumar, 1988). A comparison between σ ν and uncertainties based on Hessian's computation (Libbrecht 1992, Toutain and Appourchaux 1994) shows a nice agreement. However, our error-bars take into account more statistical effects, and rely less on the initial parameters' estimation. Such a technique has been used on the IRIS power spectra computed from gapped data, and on one GONG power spectrum computed from almost continuous data. We also present IRIS linewidths and error bars averaged over the years 1989-92 and computed with a fitting strategy using imposed frequency which improves the value of both the parameter and its uncertainty.
The context is that of the so-called ``fundamental ambiguity'' (also azimuth ambiguity, o... more The context is that of the so-called ``fundamental ambiguity'' (also azimuth ambiguity, or 180° ambiguity) in magnetic field vector measurements: two field vectors symmetrical with respect to the line-of-sight have the same polarimetric signature, so that they cannot be discriminated. We propose a method to solve this ambiguity by applying the ``simulated annealing'' algorithm to the minimization of the field divergence, added to the longitudinal current absolute value, the line-of-sight derivative of the magnetic field being inferred by the interpretation of the Zeeman effect observed by spectropolarimetry in two lines formed at different depths. We find that the line pair Fe I lambda 6301.5 and Fe I lambda 6302.5 is appropriate for this purpose. We treat the example case of the delta-spot of NOAA 10808 observed on 13 September 2005 between 14:25 and 15:25 UT with the THEMIS telescope. Besides the magnetic field resolved map, the electric current density vector map ...