Roudier Thierry

Roudier Thierry
French National Centre for Scientific Research | CNRS · astrophysique

About

160
Publications
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Introduction
Dr Thierry Roudier was born in 1957, and started his thesis at the Pic du Midi Observatory in 1983 under the supervision of Richard Muller. He got the degree of Docteur en Astrophysique in 1986 and started his career as a solar physicist at the Centre National de la Recherche Scientifique (CNRS) the same year. He built the national solar data base BASS2000 in 1996 and contributed to the management and exploitation of the French solar telescope THEMIS. Thierry devoted 25 years to observations and

Publications

Publications (160)
Article
Full-text available
Context. Exploding granules on the solar surface play a major role in the dynamics of the outer part of the convection zone, especially in the diffusion of the magnetic field. Aims. We aim to develop an automated procedure able to investigate the location and evolution of exploding granules over the solar surface and to get rid of visual detection....
Preprint
Full-text available
Exploding granules on the solar surface play a major role in the dynamics of the outer part of the convection zone, especially in the diffusion of magnetic field. We aimed at developing an automated procedure able to investigate the location and evolution of exploding granules over the solar surface and to get rid of visual detection. We used seque...
Article
Full-text available
Context. The interaction between magnetic fields and convection in sunspots during their decay process remains poorly understood, whereas the formation of sunspots is relatively well studied and fully modeled. Works on the velocity scales at the solar surface have pointed to the existence of the family of granules, whose interaction with the magnet...
Preprint
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We summarize in this paper the spectro-polarimetric methods used at the Pic du Midi Turret Dome in spectroscopic or imagery mode. The polarimeters and spectrograph allow the cartography of solar magnetic fields at high spatial resolution through the Zeeman effect or measurements of the unresolved turbulent magnetic fields in the quiet Sun through t...
Article
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Context. Detailed knowledge of surface dynamics is one of the key points in understanding magnetic solar activity. The motions of the solar surface, to which we have direct access via the observations, tell us about the interaction between the emerging magnetic field and the turbulent fields. Aims. The flows computed with the coherent structure tra...
Preprint
Full-text available
Detailed knowledge of surface dynamics is one of the key points in understanding magnetic solar activity. The motions of the solar surface, to which we have direct access via the observations, tell us about the interaction between the emerging magnetic field and the turbulent fields. The flows computed with the coherent structure tracking (CST) tec...
Article
Full-text available
Context. The Sun is the only star where the superficial turbulent convection can be observed at very high spatial resolution. The Solar Dynamics Observatory (SDO) has continuously observed the full Sun from space with multi-wavelength filters since July 2010. In particular, the Helioseismic and Magnetic Imager (HMI) instrument takes high-cadence fr...
Preprint
Full-text available
The Sun is the only star where the superficial turbulent convection can be observed at very high spatial resolution. The Solar Dynamics Observatory (SDO) has continuously observed the full Sun from space with multi-wavelength filters since July 2010. In particular, the Helioseismic and Magnetic Imager (HMI) instrument takes high-cadence frames (45...
Preprint
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Downflows on the solar surface are suspected to play a major role in the dynamics of the convection zone. We investigate the existence of the long-lasting downflows whose effects influence the interior of the Sun and the outer layers. We study the sets of Dopplergrams and magnetograms observed with SDO and Hinode spacecrafts and a MHD simulation. A...
Article
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Downflows on the solar surface are suspected to play a major role in the dynamics of the convection zone, at least in its outer part. We investigate the existence of the long-lasting downflows whose effects influence the interior of the Sun but also the outer layers. We study the sets of Dopplergrams and magnetograms observed with Solar Dynamics Ob...
Article
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Context. Pollux is considered as an archetype of a giant star hosting a planet since its radial velocity (RV) presents very stable sinusoidal variations with a period of about 590 d. We then discovered a weak magnetic field at its surface using spectropolarimetry, questioning the planetary hypothesis. Aims. We followed up our investigations on Poll...
Preprint
Full-text available
Context: Pollux is considered as an archetype of a giant star hosting a planet. We then discovered a weak magnetic field at its surface using spectropolarimetry. Aims and Methods: We followed up our investigations on Pollux first using ESPaDOnS at CFHT and then Narval at TBL to obtain Stokes I and Stokes V spectra to study their variations for a du...
Preprint
Full-text available
Exploding granules constitute the strongest horizontal flows on the quiet Sun and contribute to the structure of the surface horizontal velocity fields which build the large-scale organization of the discrete magnetic field. In this work we explore exploding granule expansion through the observations of the ground-based THEMIS telescope, IRIS, SDO,...
Article
Full-text available
Exploding granules constitute the strongest horizontal flows on the quiet Sun and contribute to the structure of the surface horizontal velocity fields which build the large-scale organization of the discrete magnetic field. In this work we explore exploding granule expansion through the observations of the ground-based THEMIS telescope, IRIS, SDO,...
Preprint
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We studied the dynamics of the solar atmosphere in the region of a large quiet-Sun filament, which erupted on 21 October 2010. The filament eruption started at its northern end and disappeared from the H$\alpha$ line-core filtergrams line within a few hours. The very fast motions of the northern leg were recorded in ultraviolet light by AIA. We aim...
Preprint
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Trees of fragmenting granules (TFG) and associated flows are suspected to playa major role in the formation of the network in the quiet Sun. We investigate the counterparts, in terms of dynamics, of surface structures detectable by high resolution observations in deeper layers up to 15 Mm, which are only available from numerical simulations. The fi...
Article
Context . Trees of fragmenting granules (TFG) and associated flows are suspected to play a major role in the formation of the network in the quiet Sun. We investigate the counterparts, in terms of dynamics, of surface structures detectable by high resolution observations in deeper layers up to 15 Mm, which are only available from numerical simulati...
Article
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Context . A large filament composed principally of two sections erupted sequentially in the southern hemisphere on January 26, 2016. The central, thick part of the northern section was first lifted up and lead to the eruption of the full filament. This event was observed in H α with the Global Oscillation Network Group (GONG) and Christian Latouche...
Preprint
Full-text available
A large filament composed principally of two sections erupted sequentially in the southern hemisphere on January 26 2016. The central, thick part of the northern section was first lifted up and lead to the eruption of the full filament. This event was observed in H-alpha with GONG and CLIMSO, and in ultraviolet (UV) with the AIA/SDO imager. The aim...
Article
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Direct measurements of plasma motions in the photosphere are limited to the line-of-sight component of the velocity. Several algorithms have therefore been developed to reconstruct the transverse components from observed continuum images or magnetograms. We compare the space and time averages of horizontal velocity fields in the photosphere inferre...
Article
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We compare horizontal velocities, vertical magnetic fields, and the evolution of trees of fragmenting granules (TFG, also named families of granules) derived in the quiet Sun at disk center from observations at solar minimum and maximum of the Solar Optical Telescope (SOT on board Hinode) and results of a recent 3D numerical simulation of the magne...
Article
The Sun provides us with the only spatially well-resolved astrophysical example of turbulent thermal convection. While various aspects of solar photospheric turbulence, such as granulation (one-Megameter horizontal scale), are well understood, the questions of the physical origin and dynamical organization of larger-scale flows, such as the 30-Mega...
Article
Context: The determination of the underlying mechanisms of the magnetic elements diffusion over the solar surface is still a challenge. Understanding the formation and evolution of the solar network (NE) is a challenge, because it provides a magnetic flux over the solar surface comparable to the flux of active regions at solar maximum. Aims: We inv...
Article
We investigate the relationship between trees of fragmenting granules (TFG), horizontal and vertical flows, and acoustic events (AE) in the photospheric network. AE are spatially concentrated and short-duration locations of acoustic energy flux. We performed observations at disk center of a 2D field of view (FOV) with high spatial and temporal reso...
Article
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We investigate the magnetic field at the surface of 48 red giants selected as promising for detection of Stokes V Zeeman signatures in their spectral lines. We use the spectropolarimeters Narval and ESPaDOnS to detect circular polarization within the photospheric absorption lines of our targets and use the least-squares deconvolution (LSD) method....
Article
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We model the solar horizontal velocity power spectrum at scales larger than granulation using a two-component approximation to the mass continuity equation. The model takes four times the density scale height as the integral (driving) scale of the vertical motions at each depth. Scales larger than this decay with height from the deeper layers. Thos...
Article
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Context: Studying the motions on the solar surface is fundamental for understanding how turbulent convection transports energy and how magnetic fields are distributed across the solar surface. Aims: From horizontal velocity measurements all over the visible disc of the Sun and using data from the Solar Dynamics Observatory/Helioseismic and Magnetic...
Article
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Dynamics of a filament is investigated in Hα. Counterstreaming flows are observed along the filament. Photospheric horizontal motions have been computed by using a Coherent Structure Tracking algorithm in the filament environment.
Article
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Context. An extended filament in the central part of the active region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in the southern hemisphere. It has been observed in Hα with the THEMIS telescope in the Canary Islands and in 304 Å with the EUV imager (AIA) onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the Hα thre...
Article
Full-text available
Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval d...
Article
Full-text available
We compare measurements of horizontal flows on the surface of the Sun using helioseismic time--distance inversions and coherent structure tracking of solar granules. Tracking provides 2D horizontal flows on the solar surface, whereas the time--distance inversions estimate the full 3-D velocity flows in the shallow near-surface layers. Both techniqu...
Article
Full-text available
Context. The measurement of the Sun's surface motions with a high spatial and temporal resolution is still a challenge. Aims: We wish to validate horizontal velocity measurements all over the visible disk of the Sun from Solar Dynamics Observatory/ Helioseismic and Magnetic Imager (SDO/HMI) data. Methods: Horizontal velocity fields are measured by...
Article
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We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux, in the quiet sun using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the Solar Optical Telescope (SOT) onboard \textit{Hinode}. Line profiles of Fe \textsc{i} 557.6 nm were record...
Article
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We briefly review the observations of the solar photosphere and pinpoint some open questions related to the magnetohydrodynamics of this layer of the Sun. We then discuss the current modelling efforts, addressing among other problems, that of the origin of supergranulation.
Article
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14 Ceti is a subgiant star of F spectral class that displays variations in the S-index of its CaII H & K lines and an X-ray emission that is stronger than the mean observed for its spectral class, which may be due to some magnetic activity. We attempt to Zeeman-detect and study the magnetic field of 14 Ceti and to infer its origin. We used the spec...
Article
We first present the important role played by the families of granule (or Tree of Fragmenting granules) in the formation of the photospheric network. Then, we describe the occurence and characteristics of acoustic events (AE), defined as spatially concentrated energy flux, in the quiet Sun. Finally, we present how horizontal velocities obtained fro...
Article
Full-text available
For the first time, the motion of granules (solar plasma on the surface on scales larger than 2.5 Mm) has been followed over the entire visible surface of the Sun, using SDO/HMI white-light data. Horizontal velocity fields are derived from image correlation tracking using a new version of the coherent structure tracking algorithm.The spatial and te...
Article
We have observed during 3 seasons the slow rotating but active G8 giant EK Eri with the new generation spectropolarimeter NARVAL at Telescope Bernard Lyot (Observatoire du Pic du Midi, France). We got 21 observations between 20 September 2007 and 22 March 2010. For all the spectra, we detected a significant Zeeman Stokes V signature and the corresp...
Article
Thanks to the Solar Optical Telescope onboard HINODE, we mainly aim at the understanding of temporal evolution and spatial characterization of solar granular and supergranular features and their relation with magnetic field. We study the photospheric motions and the network magnetic field interactions using the Tree of Fragmenting Granules (TFGs)....
Article
New observations have been obtained on September 4, 2010, by the Solar Optical Telescope on board the satellite HINODE, in the magnetically insensitive Fel 557.6-nm line formed in the solar atmosphere. Acoustic events (AEs, defined as spatially concentrated propagating waves) have been derived in the photosphere from amplitudes and phases of vertic...
Article
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EK Eri is one of the most slowly rotating active giants known, and has been proposed to be the descendant of a strongly magnetic Ap star. We have performed a spectropolarimetric study of EK Eri over 4 photometric periods with the aim of inferring the topology of its magnetic field. We used the NARVAL spectropolarimeter at the Bernard Lyot telescope...
Article
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We present the outcome of a highly-sensitive search for magnetic fields on the cool supergiant Betelgeuse. A time-series of six circularly-polarized spectra was obtained using the NARVAL spectropolarimeter at T\'elescope Bernard Lyot (Pic du Midi Observatory), between 2010 March and April. Zeeman signatures were repeatedly detected in cross-correla...
Article
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In this contribution we present our results regarding the study of small scale magnetic fields as seen by magnetic bright points (MBPs) in different wavelengths and hence different heights. By the determination of the size distribution of these features we are able to derive the value of the scale height parameter for the photosphere: 107 km ± 18.5...
Article
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We present a method to extract from a single image both object and point spread function using low contrast features of an extended field of view. Invoking the principal ergodic on stochastic turbulent phenomena, we show that the aberration parameters, characteristics of the earth’s turbulence, can be recovered from multiple features within an isop...
Article
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We investigate the magnetic dichotomy between Ap/Bp and other A-type stars by carrying out a deep spectropolarimetric study of Am and HgMn stars. Using the NARVAL spectropolarimeter at the Telescope Bernard Lyot (Observatoire du Pic du Midi, France), we obtained high-resolution circular polarisation spectroscopy of 12 Am stars and 3 HgMn stars. Usi...
Article
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Context. Betelgeuse is an M supergiant with a complex and extended atmosphere, which also harbors spots and giant granules at its surface. A possible magnetic field could contribute to the mass loss and to the heating of the outer atmosphere. Aims: We observed Betelgeuse, to directly study and infer the nature of its magnetic field. Methods: We us...
Article
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We compare surface maps of the chemically peculiar star HD 50773 produced with a Bayesian technique and based on high quality CoRoT photometry with those derived from rotation phase resolved spectropolarimetry. The goal is to investigate the correlation of surface brightness with surface chemical abundance distribution and the stellar magnetic fiel...
Article
We study the characteristics of Magnetic Bright Points (MBPs) observed at different wave-lenghts and hence different heights of the photosphere and chromosphere. The data sets were obtained with the Solar Optical Telescope (SOT) of the Hinode satellite. Hinode delivers (among other data) high resolution seeing free filtergrams in the blue continuum...
Article
Full-text available
First results regarding the spatial alignment of observations taken at different wavelengths are presented. An exceptionally long time series (48 hours) of data, obtained by the Solar Optical Telescope (SOT) of the Hinode satellite, has been analysed. Hinode delivers (among other data) high resolution seeing free filtergrams in the magnetic sensiti...
Article
Full-text available
The variation of solar convection over the solar activity cycle is still discussed with controversial results. In this paper we study the solar granulation and its variation over the unusual long lasting solar minimum between cycle 23 and 24. Spatially highly resolved Hinode images were segmented and the mean value of the segmented granules as well...
Conference Paper
Many features of solar surface turbulence, like the supergranulation, are still poorly understood.We use long time series of images taken by the Solar Optical Telescope on board the Hinode satellite to determine the velocity fields. The dynamics in the subgranulation range can be investigated with unprecedented precision thanks to the absence of...
Conference Paper
In this paper, we analyse a a 48h high-resolution time sequence of the quiet Sun photosphere obtained with the Solar Optical Telescope onboard Hinode. Using floating corks advected by velocity fields inferred from photometry measurements, we show that long-living Trees of Fragmenting Granules play a crucial role in the advection of small-scale magn...
Article
Full-text available
The aim of this work is to give new observational constraints on solar surface flows by determining the horizontal scale dependence of the velocity and intensity fields, as represented by their power spectra, and to offer some theoretical guidelines to interpret these spectra. We use long time series of images taken by SOT/Hinode and reconstruct bo...
Book
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We present first results of the magnetic survey of a sample of slow rotating giant stars for which an X-ray emission or variations of CaII H & K lines have been already detected.
Article
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Aims: We observe the nearby, weakly-active single giant, Pollux, in order to directly study and infer the nature of its magnetic field. Methods: We used the new generation spectropolarimeters ESPaDOnS and NARVAL to observe and detect circular polarization within the photospheric absorption lines of Pollux. Our observations span 18 months from 2007-...
Article
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Aims: The interactions of velocity scales on the Sun's surface, from granulation to supergranulation are still not understood, nor are their interaction with magnetic fields. We thus aim at giving a better description of dynamics in the mesoscale range which lies between the two scales mentioned above. Method: We analyse a 48h high-resolution time...
Article
Since 2004, at the Laboratoire d'Astrophysique de Toulouse Tarbes (LATT), we work with CMOS APS detectors, firstly to develop a large-field,high-resolution camera for the observation of the solar supergranulation, secondly to develop a fast camera for an adaptive optics test bench. In these two projects, we use detectors from FillFactory, now conti...
Article
Full-text available
Long time series of solar granulation are extremely difficult to be obtained from ground based observations because of the unstable Earth's atmosphere. The Hinode-SOT instrument provided long term stable time series of solar granulation at different wavelengths in the visible. After appropriate calibration, these data can be used for studies of lon...
Article
Full-text available
We study the influence of large and small scales photospheric motions on the destabilization of an eruptive filament, observed on October 6, 7, and 8, 2004 as part of an international observing campaign (JOP 178). Large-scale horizontal flows are invetigated from a series of MDI/SOHO full-disc Dopplergrams and magnetograms from THEMIS. Small-scale...
Article
Full-text available
We observe the slowly-rotating, active, single giant, EK Eri, to study and infer the nature of its magnetic field directly. We used the spectropolarimeter NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least Square Deconvolution method to create high signal-to-noise ratio Stokes V profiles. We fitted the Stokes V profiles wi...
Article
We present the recent results obtained by the Toulouse-Tarbes group on the dynamics of the solar surface at meso and supergranular scale, and their interactions with the magnetic field. First, using the 14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained a 7.5h-long sequence of high resolution images with unprecedented field size (5...