Two-horn quiescent prominence observed in H-alpha and MgII h&k lines with THEMIS and IRIS

Prominences are large magnetic structures in the corona filled by cool plasma with fast evolving fine structure. We aim to better understand the plasma conditions in the fine structure of a quiescent prominence including two transient horns observed at the bottom of the cavity using the high-resolution spectrograph IRIS and the MulTi-Raies (MTR) spectrograph of the THEMIS in the Canary Islands. We analysed the spectra obtained in H-alpha by THEMIS and MgII by IRIS and compare them with a grid of 23940 1D radiative transfer models which include a prominence-to-corona transition region (PCTR). The full observed profiles of MgII in each pixel are fitted completely by synthesised profiles with xRMS (Cross RMS; an improved version of the rolling root mean square (rRMS) method). When the RMS is below a certain threshold value, we recover the plasma conditions from the parameters of the model best fitting the observed line profile. This criterion is met in two regions (the horns and edge of the prominence) where the line profiles can generally be described as single peaked. The 1D models suggest that two different kinds of model atmospheres correspond to these two regions. The region at the edge is found to be fitted mainly with isothermal and isobaric models, while the other area (the horns) is seen to be fitted with models with a PCTR that have optical thicknesses <5. In the prominence edge, the theoretical relationship between the integrated intensities in H-alpha and MgII is verified and corresponds to low emission measure values. In these regions the electron density is ~10^10 cm^{-3}, while it is one order of magnitude less in the horn regions. In the horns, we find some profiles are best fitted with models with high mean temperatures. This suggests that the hot PCTR found in the horns could be interpreted as prominence plasma in condensation phase at the bottom of the coronal cavity.Comment: 24 pages, 19 figures, manuscript accepted to publication in A&

Venus wind map at cloud top level with the MTR/THEMIS visible spectrometer. I. Instrumental performance and first results

Solar light gets scattered at cloud top level in Venus' atmosphere, in the visible range, which corresponds to the altitude of 67 km. We present Doppler velocity measurements performed with the high resolution spectrometer MTR of the Solar telescope THEMIS (Teide Observatory, Canary Island) on the sodium D2 solar line (5890 \AA). Observations lasted only 49 min because of cloudy weather. However, we could assess the instrumental velocity sensitivity, 31 m/s per pixel of 1 arcsec, and give a value of the amplitude of zonal wind at equator at 151 +/- 16 m/s.Comment: 17 pages, 12 figure

Closing the loop as an inverse problem: the real-time control of THEMIS adaptive optics

We have taken advantage of the implementation of an adaptive optics system on the Themis solar telescope to implement innovative strategies based on an inverse problem formulation for the control loop. Such an approach encompassing the whole system implies the estimation of the pixel variances of the Shack-Hartmann wavefront sensor, a novel real-time method to extract the wavefront slopes as well as their associated noise covariance, and the computation of pseudo-open loop data. The optimal commands are computed by iteratively solving a regularized inverse problem with spatio-temporal constraints including Kolmogorov statistics. The latency of the dedicated real-time control software with conventional CPU is shorter than 300 $\mu$s from the acquisition of the raw 400 x 400 pixel wavefront sensor image to the sending of the commands

Estimation spectrale paramétrique de modes corrélés, application à l'héliosismologie

Cette communication porte sur l'estimation des paramètres de modes vibratoires ayant des excitations corrélées. L'application visée est l'analyse des modes vibratoires du soleil. Deux algorithmes d'estimation sont proposés. Le premier, qui est une extension de la méthode habituellement utilisée en héliosismologie, repose sur les propriétées asymptotiques du périodogramme. Cette méthode présente l'avantage de permettre une prise en compte immédiate des contraintes sur le profil des modes. Le second repose sur une modélisation temporelle du signal par une somme bruitée de processus autorégressifs ayant des excitations corrélées. Après une estimation des paramètres dynamiques la matrice de covariance des excitations est estimée par un algorithme EM. Les performances des deux méthodes sont évaluées par des simulations de Monte Carlo et comparées à la borne de Rao Cramèr. Enfin, des résultats sur des signaux mesurés par le satellite SOHO sont présentées

Two-horn quiescent prominence observed in Hα and Mg II h&k lines with THEMIS and IRIS

Context. Prominences are large magnetic structures in the corona filled by cool plasma with fast evolving fine structure. Aims. We aim to better understand the plasma conditions in the fine structure of a quiescent prominence including two transient horns observed at the bottom of the cavity using the high resolution Interface Region Imaging Spectrograph (IRIS) and the MulTi-Raies (MTR) spectrograph of the Télescope Heliographique pour l’Etude du Magnétisme et des Instabilités Solaires (THEMIS) in the Canary Islands. Methods. We analysed the spectra obtained in Hα by THEMIS and Mg II by IRIS and compare them with a grid of 23 940 1D radiative transfer models which include a prominence-to-corona transition region (PCTR). The full observed profiles of Mg II in each pixel are fitted completely by synthesised profiles with ×RMS (Cross RMS; an improved version of the rolling root mean square (rRMS) method). When the RMS is below a certain threshold value, we recover the plasma conditions from the parameters of the model best fitting the observed line profile. This criterion is met in two regions (the horns and edge of the prominence) where the line profiles can generally be described as single peaked. Results. The 1D models suggest that two different kinds of model atmospheres correspond to these two regions. The region at the edge is found to be fitted mainly with isothermal and isobaric models, while the other area (the horns) is seen to be fitted with models with a PCTR that have optical thicknesses of less than 5. In the prominence edge, the theoretical relationship between the integrated intensities in Hα and Mg II is verified and corresponds to low emission measure values. In these regions the electron density is around 1010 cm−3, while it is one order of magnitude less in the horn regions around 109 cm−3. Conclusions. In the horns, we find some profiles are best fitted with models with high mean temperatures. This suggests that the hot PCTR found in the horns could be interpreted as prominence plasma in condensation phase at the bottom of the coronal cavity

A short survey on protein blocks.

International audienceProtein structures are classically described in terms of secondary structures. Even if the regular secondary structures have relevant physical meaning, their recognition from atomic coordinates has some important limitations such as uncertainties in the assignment of boundaries of helical and β-strand regions. Further, on an average about 50% of all residues are assigned to an irregular state, i.e., the coil. Thus different research teams have focused on abstracting conformation of protein backbone in the localized short stretches. Using different geometric measures, local stretches in protein structures are clustered in a chosen number of states. A prototype representative of the local structures in each cluster is generally defined. These libraries of local structures prototypes are named as "structural alphabets". We have developed a structural alphabet, named Protein Blocks, not only to approximate the protein structure, but also to predict them from sequence. Since its development, we and other teams have explored numerous new research fields using this structural alphabet. We review here some of the most interesting applications

Séismologie du soleil et d'étoiles de type solaire

Optical resonance is essential in building spectrophotometers with an excellent spectral quality. Their application to the seismology of the Sun and solar-type stars allowed to show evidence of pressure modes on Procyon and Alpha Centauri. The eigenmodes we observe are the stationary combination of traveling acoustic waves, and carry information on integral properties of the star (e.g. integral of the speed of the sound), and of some parameters of the thermonuclear core.In the solar case, the importance of seismological observations to the tests of the internal structure is now above the measurement of neutrinos flux. We now have enough coherent measurements to study the changes in eigenmodes with solar activity. We show a variation of modes eigenfrequencies between the 1980 SMM data and our own observation from South Pole in 1985.The scientific counterpart of solar seismology is important enough so as to make obvious the need for networks of observation. The IRIS network will bring a temporal coverage allowing the study of the internal structure of the Sun (dynamic, chemical, magnetic...) over duration comparable to the solar cycle. The IRIS-01 experiment was the first site of the Nice network.L'utilisation de la résonance optique permet de construire des spectrophotomètre d'une excellente qualité spectrale. Leur application à la sismologie du soleil et des étoiles de type solaire a permis la mise en évidence des modes propres de pression sur Procyon et Alpha Centauri. Les modes propres que nous avons observés sont la composition stationnaire d'ondes acoustiques se propageant et sont porteurs d'information sur les propriétés intégrale de l'étoile (intégrale de la vitesse du son) ainsi que sur certains paramètres du cœur thermonucléaire. Dans le cas du soleil, la contribution des observations sismologique aux tests de la structure interne dépasse celle des mesures de flux de neutrinos . Nous disposons maintenant de suffisamment de mesures cohérente pour étudier le changement des modes propres avec l'activité solaire. Nous mettons en évidence variation des fréquences propres d'oscillation entre les données fournies par le satellite SMM en 1980 et nos propres observations au Pôle Sud en 1985.La contrepartie scientifique de la séismologie du soleil est suffisamment importante pour que l'intérêt des réseaux d'observation devienne une évidence. Le réseau IRIS apportera une couverture temporelle permettant l'étude de la structure profonde du soleil (dynamique, chimique, magnétique...) sur des durées comparables au cycle solaire. l'expérience IRIS-01 à constitué le premier maillon du réseau Niçois

Vector magnetic field and vector current density in and around the δ-spot NOAA 10808

International audienc

Vector magnetic field and vector current density in and around the δ-spot NOAA 10808

International audienc