Author name code: paletou ADS astronomy entries on 2022-09-14 author:"Paletou, Frederic" ------------------------------------------------------------------------ Title: The Gaia-ESO Public Spectroscopic Survey: Motivation, implementation, GIRAFFE data processing, analysis, and final data products Authors: Gilmore, G.; Randich, S.; Worley, C. C.; Hourihane, A.; Gonneau, A.; Sacco, G. G.; Lewis, J. R.; Magrini, L.; Francois, P.; Jeffries, R. D.; Koposov, S. E.; Bragaglia, A.; Alfaro, E. J.; Allende Prieto, C.; Blomme, R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Zwitter, T.; Bensby, T.; Flaccomio, E.; Irwin, M. J.; Franciosini, E.; Morbidelli, L.; Damiani, F.; Bonito, R.; Friel, E. D.; Vink, J. S.; Prisinzano, L.; Abbas, U.; Hatzidimitriou, D.; Held, E. V.; Jordi, C.; Paunzen, E.; Spagna, A.; Jackson, R. J.; Maiz Apellaniz, J.; Asplund, M.; Bonifacio, P.; Feltzing, S.; Binney, J.; Drew, J.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Bergemann, M.; Casey, A. R.; de Laverny, P.; Frasca, A.; Hill, V.; Lind, K.; Sbordone, L.; Sousa, S. G.; Adibekyan, V.; Caffau, E.; Daflon, S.; Feuillet, D. K.; Gebran, M.; Gonzalez Hernandez, J. I.; Guiglion, G.; Herrero, A.; Lobel, A.; Merle, T.; Mikolaitis, S.; Montes, D.; Morel, T.; Ruchti, G.; Soubiran, C.; Tabernero, H. M.; Tautvaisiene, G.; Traven, G.; Valentini, M.; Van der Swaelmen, M.; Villanova, S.; Viscasillas Vazquez, C.; Bayo, A.; Biazzo, K.; Carraro, G.; Edvardsson, B.; Heiter, U.; Jofre, P.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Walton, N. A.; Zaggia, S.; Aguirre Borsen-Koch, V.; Alves, J.; Balaguer-Nunez, L.; Barklem, P. S.; Barrado, D.; Bellazzini, M.; Berlanas, S. R.; Binks, A. S.; Bressan, A.; Capuzzo-Dolcetta, R.; Casagrande, L.; Casamiquela, L.; Collins, R. S.; D'Orazi, V.; Dantas, M. L. L.; Debattista, V. P.; Delgado-Mena, E.; Di Marcantonio, P.; Drazdauskas, A.; Evans, N. W.; Famaey, B.; Franchini, M.; Fremat, Y.; Fu, X.; Geisler, D.; Gerhard, O.; Gonzalez Solares, E. A.; Grebel, E. K.; Gutierrez Albarran, M. L.; Jimenez-Esteban, F.; Jonsson, H.; Khachaturyants, T.; Kordopatis, G.; Kos, J.; Lagarde, N.; Ludwig, H. -G.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.; Messina, S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.; Monteiro, M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.; Murphy, D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palous, J.; Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read, J. I.; Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.; Spina, L.; Steinmetz, M.; Stonkute, E.; Sutorius, E.; Thevenin, F.; Tosi, M.; Tsantaki, M.; Wright, N.; Wyse, R. F. G.; Zoccali, M.; Zorec, J.; Zucker, D. B. Bibcode: 2022arXiv220805432G Altcode: The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100,000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper (arXiv:2206.02901) introduces the survey results. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. The Gaia-ESO Survey obtained 202,000 spectra of 115,000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022. Title: The Gaia-ESO Public Spectroscopic Survey: Implementation, data products, open cluster survey, science, and legacy Authors: Randich, S.; Gilmore, G.; Magrini, L.; Sacco, G. G.; Jackson, R. J.; Jeffries, R. D.; Worley, C. C.; Hourihane, A.; Gonneau, A.; Viscasillas Vàzquez, C.; Franciosini, E.; Lewis, J. R.; Alfaro, E. J.; Allende Prieto, C.; Blomme, T. Bensby R.; Bragaglia, A.; Flaccomio, E.; François, P.; Irwin, M. J.; Koposov, S. E.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Zwitter, T.; Asplund, M.; Bonifacio, P.; Feltzing, S.; Binney, J.; Drew, J.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Bayo, A.; Bergemann, M.; Biazzo, K.; Carraro, G.; Casey, A. R.; Damiani, F.; Frasca, A.; Heiter, U.; Hill, V.; Jofré, P.; de Laverny, P.; Lind, K.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone, L.; Sousa, S. G.; Zaggia, S.; Adibekyan, V.; Bonito, R.; Caffau, E.; Daflon, S.; Feuillet, D. K.; Gebran, M.; González Hernández, J. I.; Guiglion, G.; Herrero, A.; Lobel, A.; Maíz Apellániz, J.; Merle, T.; Mikolaitis, S.; Montes, D.; Morel, T.; Soubiran, C.; Spina, L.; Tabernero, H. M.; Tautvaišienė, G.; Traven, G.; Valentini, M.; Van der Swaelmen, M.; Villanova, S.; Wright, N. J.; Abbas, U.; Aguirre Børsen-Koch, V.; Alves, J.; Balaguer-Núnez, L.; Barklem, P. S.; Barrado, D.; Berlanas, S. R.; Binks, A. S.; Bressan, A.; Capuzzo--Dolcetta, R.; Casagrande, L.; Casamiquela, L.; Collins, R. S.; D'Orazi, V.; Dantas, M. L. L.; Debattista, V. P.; Delgado-Mena, E.; Di Marcantonio, P.; Drazdauskas, A.; Evans, N. W.; Famaey, B.; Franchini, M.; Frémat, Y.; Friel, E. D.; Fu, X.; Geisler, D.; Gerhard, O.; González Solares, E. A.; Grebel, E. K.; Gutiérrez Albarrán, M. L.; Hatzidimitriou, D.; Held, E. V.; Jiménez-Esteban, F.; Jönsson, H.; Jordi, C.; Khachaturyants, T.; Kordopatis, G.; Kos, J.; Lagarde, N.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.; Messina, S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.; Monteiro, M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.; Murphy, D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palouus, J.; Paunzen, E.; Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read, J. I.; Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.; Spagna, A.; Steinmetz, M.; Stonkuté, E.; Sutorius, E.; Thévenin, F.; Tosi, M.; Tsantaki, M.; Vink, J. S.; Wright, N.; Wyse, R. F. G.; Zoccali, M.; Zorec, J.; Zucker, D. B.; Walton, N. A. Bibcode: 2022arXiv220602901R Altcode: In the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large samples of Galactic stars, complementing Gaia astrometry. Among those surveys, the Gaia-ESO Public Spectroscopic Survey (GES), the only one performed on a 8m class telescope, was designed to target 100,000 stars using FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering all the Milky Way populations, with a special focus on open star clusters. This article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. A companion article (Gilmore et al.) reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow. The GES has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110,000 unique target stars. Elemental abundances were derived for up to 31 elements for targets observed with UVES. Lithium abundances are delivered for about 1/3 of the sample. The analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the Gaia-ESO consortium and the community, with many highlight results achieved. The final catalogue has been released through the ESO archive at the end of May 2022, including the complete set of advanced data products. In addition to these results, the Gaia-ESO Survey will leave a very important legacy, for several aspects and for many years to come. Title: Deep learning application for stellar parameters determination: I-constraining the hyperparameters Authors: Gebran, Marwan; Connick, Kathleen; Farhat, Hikmat; Paletou, Frédéric; Bentley, Ian Bibcode: 2022OAst...31...38G Altcode: 2022arXiv220112476G Machine learning is an efficient method for analysing and interpreting the increasing amount of astronomical data that are available. In this study, we show a pedagogical approach that should benefit anyone willing to experiment with deep learning techniques in the context of stellar parameter determination. Using the convolutional neural network architecture, we give a step-by-step overview of how to select the optimal parameters for deriving the most accurate values for the stellar parameters of stars: Teff, log g, [M/H], and vesin i. Synthetic spectra with random noise were used to constrain this method and to mimic the observations. We found that each stellar parameter requires a different combination of network hyperparameters and the maximum accuracy reached depends on this combination as well as the signal-to-noise ratio of the observations, and the architecture of the network. We also show that this technique can be applied to other spectral-types in different wavelength ranges after the technique has been optimized. Title: The use of Deep Learning in stellar classification Authors: Connick, Kathleen; Gebran, Marwan; Paletou, Frédéric Bibcode: 2021scgr.confE...1C Altcode: We are applying various ML/DL techniques for the purpose of stellar spectroscopy. Having already ran tests with Principal Component Analysis (PCA) and Sliced Inverse Regression (SIR), we now turn our focus to Convolution Neural Network (CNN), among other techniques, in order to find the most accurate derivations for stellar parameters: effective temperature, surface gravity, projected equatorial rotational velocity, microturbulence velocity and metallicity. Title: VizieR Online Data Catalog: ESPaDOnS and NARVAL spectropolarimeters (IRAP) (Petit P., 2021) Authors: Petit, P.; Paletou, F.; Mathias, P.; Glorian, Jm.; Amato, A. Bibcode: 2021yCat....102043P Altcode: We list the stellar spectroscopic and spectropolarimetric observations available in the PolarBase data base. For each star equatorial coordinates, first Julian date of observation, last Julian date of observation, number of observations are given, and a detection diagnosis of polarized signatures (in cross-correlated pseudo-line profiles) are given.

(1 data file). Title: Full non-LTE spectral line formation. I. Setting the stage Authors: Paletou, F.; Peymirat, C. Bibcode: 2021A&A...649A.165P Altcode: 2021arXiv210312009P Radiative transfer out of local thermodynamic equilibrium (NLTE) has been increasingly adressed, mostly numerically, for about six decades now. However, the standard NLTE problem most often refers to the only deviation of the distribution of photons from their equilibrium, that is to say a Planckian distribution. Hereafter we revisit after Oxenius (1986, Kinetic theory of particles and Photons - Theoretical Foundations of non-LTE Plasma Spectroscopy, Springer) the so-called full NLTE problem, which considers coupling and therefore solving self-consistently for deviations from equilibrium distributions of photons as well as for massive particles constituting the atmospheric plasma. Title: An adaptive Gaussian quadrature for the Voigt function Authors: Paletou, F.; Peymirat, C.; Anterrieu, E.; Böhm, T. Bibcode: 2020A&A...633A.111P Altcode: 2019arXiv191208427P We evaluate an adaptive Gaussian quadrature integration scheme suitable for the numerical evaluation of generalized redistribution in frequency functions. The latter are indispensable ingredients for "full non-LTE" radiation transfer computations, assuming potential deviations of the velocity distribution of massive particles from the usual Maxwell-Boltzmann distribution. A first validation is made with computations of the usual Voigt profile. Title: VizieR Online Data Catalog: Stellar parameters of M and K dwarfs (Houdebine+, 2019) Authors: Houdebine, E. R.; Mullan, D. J.; Doyle, J. G.; de La Vieuville, G.; Butler, C. J.; Paletou, F. Bibcode: 2019yCat..51580056H Altcode: Observations of (R-I)C (Cousin's photometric system) or (R-I)<SU photometric system) for our samples of K and M dwarfs were taken from several papers. We selected eight samples of K and M dwarfs according to their (R-I)C colors. This represents a total sample of 2765 K and M dwarfs. Most stars in this sample are nearby or large proper motion stars. We also completed these samples of stars with a ninth sample of stars: the M0-M1 sample, which includes some stars from the samples of stars from B12 and M15 (see Table 1), as well as several stars initially from the M2 sample, which were found to have higher temperatures (we included in the M0-M1 sample stars down to the spectral type dM1.5).

(3 data files). Title: The Mass-Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs Authors: Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de La Vieuville, Geoffroy; Butler, C. J.; Paletou, F. Bibcode: 2019AJ....158...56H Altcode: 2019arXiv190507921H Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between red/infrared colors (e.g., (R - I) C ) and effective temperatures have been well established for a long time. The more recent (R - I) C color-T eff correlation using the data of Mann et al. (hereafter M15) and Boyajian et al. (hereafter B12) shows that this color can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in T eff relative to the (R - I) C -T eff relationship of B12 and M15 data is only ±3σ = 44.6 K for K dwarfs and ±3σ = 39.4 K for M dwarfs. These figures are small and show that the (R - I) C color can be used as a first-guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of (R - I) C color-T eff from B12 and M15 data. We also compiled T eff and metallicity measurements available in the literature using the VizieR database. We determine T eff for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and one triple system from our high-resolution spectra.

Based on Gaia DR2 and Hipparcos parallax measurements. Title: Sliced Inverse Regression: application to fundamental stellar parameters Authors: Kassounian, Sarkis; Gebran, Marwan; Paletou, Frédéric; Watson, Victor Bibcode: 2019OAst...28...68K Altcode: 2019arXiv190111003K We present a method for deriving the stellar fundamental parameters. It is based on a regularized sliced inverse regression (RSIR).We first tested it on noisy synthetic spectra of A, F, G, and K-type stars, and inverted simultaneously their atmospheric fundamental parameters: Teff., log g, [M/H] and v sin i. Different learning databases were calculated using a range of sampling in Teff., log g, v sin i, and [M/H]. Combined with a principal component analysis (PCA) nearest neighbors (NN) search, the size of the learning database is reduced. A Tikhonov regularization is applied, given the ill-conditioning of SIR. For all spectral types, decreasing the size of the learning database allowed us to reach internal accuracies better than PCA-based NN-search using larger learning databases. For each analyzed parameter, we have reached internal errors that are smaller than the sampling step of the parameter. We have also applied the technique to a sample of observed FGK and A stars. For a selection of well-studied stars, the inverted parameters are in agreement with the ones derived in previous studies. The RSIR inversion technique, complemented with PCA pre-processing proves to be efficient in estimating stellar parameters of A, F, G, and K-type stars. Title: Toulouse 2D numerical radiative transfer codes Authors: Paletou, F.; Léger, L.; Chane-Yook, M.; Auer, L. H. Bibcode: 2019arXiv190305971P Altcode: A tutorial associated with the distribution of 2D non-LTE multilevel atom radiative transfer codes. Title: Deep learning determination of stellar atmospheric fundamental parameters Authors: Kou, R.; Petit, P.; Paletou, F.; Kulenthirarajah, L.; Glorian, J. -M. Bibcode: 2018sf2a.conf..167K Altcode: In order to estimate fundamental parameters (effective temperature, surface gravity and metallicity) of the large amount of stars in the PolarBase data base, we need a fast and reliable algorithm. With this aim, we developed a convolutional neural network able to derive this parameter triplet. Our neural network was trained on observed spectra from the PolarBase and Elodie data bases (M to F stars). We used the spectral region between 6095 and 6185 Angströms which has proved its efficiency in a number of previous studies. We analyzed the outcome of our approach for a sample of spectra from the same data bases. We discuss the accuracy and reliability of the neural network depending on the parameter domain, size and quality of the training data set. Title: On Milne-Barbier-Unsöld relationships Authors: Paletou, Frédéric Bibcode: 2018OAst...27...76P Altcode: 2017arXiv171107026P This short review aims to clarify upon the origins of so-called Eddington-Barbier relationships, which relate the emergent specific intensity and the flux to the photospheric source function at specific optical depths. Here we discuss the assumptions behind the original derivation of Barbier (1943).We also point to the fact that Milne had already formulated these two relations in 1921. Title: VizieR Online Data Catalog: Rotation-Activity Correlations in K-M dwarfs. I. (Houdebine+, 2016) Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M. Bibcode: 2017yCat..18220097H Altcode: We selected a sample of 419 late-K dwarfs on the basis of (R-I) measurements available in the literature. Searching through databases at the European Southern Observatory (ESO) and Observatoire de Haute Provence (OHP), we identified spectra of 112 different stars that are suitable for our purposes. The spectra that we use to determine vsini came from two different echelle spectrographs: HARPS (High Accuracy Radial velocity Planet Search, ESO; R=115000) and SOPHIE (OHP; R=75000).

(6 data files). Title: VizieR Online Data Catalog: Rotation-Activity Correlations in K-M dwarfs II. (Houdebine+, 2017) Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.; Gebran, M. Bibcode: 2017yCat..18370096H Altcode: The spectra that we use for determining the CaII and Hα equivalent widths in the present study of dK4-dM4 stars came from three different echelle spectrographs; HARPS (High Accuracy Radial velocity Planet Search, ESO), SOPHIE (OHP), and FEROS (The Fiber-fed Extended Range Optical Spectrograph).

The stars in our samples include all stars from all observing programs that have been carried out with HARPS and SOPHIE for stars belonging to the following spectral sub-types: dK4, dK6, dM2, and dM3. For dM4 stars, we compiled all measurements of vsini available in the literature (see Paper I; Houdebine+ 2016, J/ApJ/822/97). For the dK6 and dM3 samples, we also supplemented our own measurements with measurements available in the literature, notably for active stars (see Paper I).

(7 data files). Title: Inference of an explanatory variable from observations in a high-dimensional space: application to high-resolution spectra of stars Authors: Watson, V.; Trouilhet, JF.; Paletou, F.; Girard, S. Bibcode: 2017arXiv170602213W Altcode: Our aim is to evaluate fundamental parameters from the analysis of the electromagnetic spectra of stars. We may use $10^3$-$10^5$ spectra; each spectrum being a vector with $10^2$-$10^4$ coordinates. We thus face the so-called "curse of dimensionality". We look for a method to reduce the size of this data-space, keeping only the most relevant information.As a reference method, we use principal component analysis (PCA) to reduce dimensionality. However, PCA is an unsupervised method, therefore its subspace was not consistent with the parameter. We thus tested a supervised method based on Sliced Inverse Regression (SIR), which provides a subspace consistent with the parameter. It also shares analogies with factorial discriminant analysis: the method slices the database along the parameter variation, and builds the subspace which maximizes the inter-slice variance, while standardizing the total projected variance of the data. Nevertheless the performances of SIR were not satisfying in standard usage, because of the non-monotonicity of the unknown function linking the data to the parameter and because of the noise propagation. We show that better performances can be achieved by selecting the most relevant directions for parameter inference. Preliminary tests are performed on synthetic pseudo-line profiles plus noise. Using one direction, we show that compared to PCA, the error associated with SIR is 50$\%$ smaller on a non-linear parameter, and 70$\%$ smaler on a linear parameter. Moreover, using a selected direction, the error is 80$\%$ smaller for a non-linear parameter, and 95$\%$ smaller for a linear parameter. Title: Sliced Inverse Regression for the inference of stellar fundamental parameters Authors: Watson, V.; Trouilhet, JF.; Paletou, F.; Gebran, M. Bibcode: 2017arXiv170610121W Altcode: We aim at finding the value of an explanatory variable, through its expression in a large data-vector, without knowing the link function between the explanatory variable and the data-space. Sliced Inverse Regression (SIR) method allows for the projection of a data-vector onto a subspace consistent with the explanatory variable variation. We suggest a method based on the SIR subspace, that gives the most efficient estimation of an unknown explanatory variable. Title: The Rotation-Activity Correlations in K and M Dwarfs. II. New Constraints on the Dynamo Mechanisms in Late-K and M Dwarfs Before and At the Transition to Complete Convection Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.; Gebran, M. Bibcode: 2017ApJ...837...96H Altcode: 2017arXiv170107608H We study the rotation-activity correlations (RACs) in a sample of stars from spectral type dK4 to dM4. We study RACs using chromospheric data and coronal data. We study the Ca II line surface fluxes-P/\sin I RACs. We fit the RACs with linear homoscedastic and heteroscedastic regression models. We find that these RACs differ substantially from one spectral sub-type to another. For dM3 and dM4 stars, we find that the RACs cannot be described by a simple model, but instead that there may exist two distinct RAC behaviors for the low-activity and the high-activity stellar sub-samples, respectively. Although these results are preliminary and will need confirmation, the data suggest that these distinct RACs may be associated with different dynamo regimes. We also study {R}{HK}\prime as a function of the Rossby number R 0. We find (I) for dK4 stars, {R}{HK}\prime as a function of R 0 agrees well with previous results for F-G-K stars and (II) in dK6, dM2, dM3, and dM4 stars, at a given R 0, the values of {R}{HK}\prime lie at a factor of 3, 10, 20, and 90, respectively, below the F-G-K RAC. Our results suggest a significant decrease in the efficiency of the dynamo mechanism(s) as regards chromospheric heating before and at dM3, I.e., before and at the transition to complete convection. We also show that the ratio of coronal heating to chromospheric heating L X/L HK increases by a factor of 100 between dK4 and dM4 stars.

Based on observations available at Observatoire de Haute Provence and the European Southern Observatory databases and on Hipparcos parallax measurements. Title: Discovery of a complex linearly polarized spectrum of Betelgeuse dominated by depolarization of the continuum Authors: Aurière, M.; López Ariste, A.; Mathias, P.; Lèbre, A.; Josselin, E.; Montargès, M.; Petit, P.; Chiavassa, A.; Paletou, F.; Fabas, N.; Konstantinova-Antova, R.; Donati, J. -F.; Grunhut, J. H.; Wade, G. A.; Herpin, F.; Kervella, P.; Perrin, G.; Tessore, B. Bibcode: 2016A&A...591A.119A Altcode: 2016arXiv160504702A Context. Betelgeuse is an M supergiant that harbors spots and giant granules at its surface and presents linear polarization of its continuum.
Aims: We have previously discovered linear polarization signatures associated with individual lines in the spectra of cool and evolved stars. Here, we investigate whether a similar linearly polarized spectrum exists for Betelgeuse.
Methods: We used the spectropolarimeter Narval, combining multiple polarimetric sequences to obtain high signal-to-noise ratio spectra of individual lines, as well as the least-squares deconvolution (LSD) approach, to investigate the presence of an averaged linearly polarized profile for the photospheric lines.
Results: We have discovered the existence of a linearly polarized spectrum for Betelgeuse, detecting a rather strong signal (at a few times 10-4 of the continuum intensity level), both in individual lines and in the LSD profiles. Studying its properties and the signal observed for the resonant Na I D lines, we conclude that we are mainly observing depolarization of the continuum by the absorption lines. The linear polarization of the Betelgeuse continuum is due to the anisotropy of the radiation field induced by brightness spots at the surface and Rayleigh scattering in the atmosphere. We have developed a geometrical model to interpret the observed polarization, from which we infer the presence of two brightness spots and their positions on the surface of Betelgeuse. We show that applying the model to each velocity bin along the Stokes Q and U profiles allows the derivation of a map of the bright spots. We use the Narval linear polarization observations of Betelgeuse obtained over a period of 1.4 yr to study the evolution of the spots and of the atmosphere.
Conclusions: Our study of the linearly polarized spectrum of Betelgeuse provides a novel method for studying the evolution of brightness spots at its surface and complements quasi-simultaneous observations obtained with PIONIER at the VLTI.

Based on observations obtained at the Télescope Bernard Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse, France. Title: A new method for the inversion of atmospheric parameters of A/Am stars Authors: Gebran, M.; Farah, W.; Paletou, F.; Monier, R.; Watson, V. Bibcode: 2016A&A...589A..83G Altcode: 2016arXiv160301146G Context. We present an automated procedure that simultaneously derives the effective temperature Teff, surface gravity log g, metallicity [Fe/H], and equatorial projected rotational velocity vsini for "normal" A and Am stars. The procedure is based on the principal component analysis (PCA) inversion method, which we published in a recent paper .
Aims: A sample of 322 high-resolution spectra of F0-B9 stars, retrieved from the Polarbase, SOPHIE, and ELODIE databases, were used to test this technique with real data. We selected the spectral region from 4400-5000 Å as it contains many metallic lines and the Balmer Hβ line.
Methods: Using three data sets at resolving powers of R = 42 000, 65 000 and 76 000, about ~6.6 × 106 synthetic spectra were calculated to build a large learning database. The online power iteration algorithm was applied to these learning data sets to estimate the principal components (PC). The projection of spectra onto the few PCs offered an efficient comparison metric in a low-dimensional space. The spectra of the well-known A0- and A1-type stars, Vega and Sirius A, were used as control spectra in the three databases. Spectra of other well-known A-type stars were also employed to characterize the accuracy of the inversion technique.
Results: We inverted all of the observational spectra and derived the atmospheric parameters. After removal of a few outliers, the PCA-inversion method appeared to be very efficient in determining Teff, [Fe/H], and vsini for A/Am stars. The derived parameters agree very well with previous determinations. Using a statistical approach, deviations of around 150 K, 0.35 dex, 0.15 dex, and 2 km s-1 were found for Teff, log g, [Fe/H], and vsini with respect to literature values for A-type stars.
Conclusions: The PCA inversion proves to be a very fast, practical, and reliable tool for estimating stellar parameters of FGK and A stars and for deriving effective temperatures of M stars.

Based on data retrieved from the Polarbase, SOPHIE, and ELODIE archives.Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A83 Title: Rotation-Activity Correlations in K and M Dwarfs. I. Stellar Parameters and Compilations of v sin I and P/sin I for a Large Sample of Late-K and M Dwarfs Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M. Bibcode: 2016ApJ...822...97H Altcode: 2016arXiv160407920H The reliable determination of rotation-activity correlations (RACs) depends on precise measurements of the following stellar parameters: T eff, parallax, radius, metallicity, and rotational speed v sin I. In this paper, our goal is to focus on the determination of these parameters for a sample of K and M dwarfs. In a future paper (Paper II), we will combine our rotational data with activity data in order to construct RACs. Here, we report on a determination of effective temperatures based on the (R-I) C color from the calibrations of Mann et al. and Kenyon & Hartmann for four samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar parameters (T eff, log(g), and [M/H]) using the principal component analysis-based inversion technique for a sample of 105 late-K dwarfs. We compile all effective temperatures from the literature for this sample. We determine empirical radius-[M/H] correlations in our stellar samples. This allows us to propose new effective temperatures, stellar radii, and metallicities for a large sample of 612 late-K and M dwarfs. Our mean radii agree well with those of Boyajian et al. We analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have detected v sin I in 92 stars. In combination with our previous v sin I measurements in M and K dwarfs, we now derive P/sin I measures for a sample of 418 K and M dwarfs. We investigate the distributions of P/sin I, and we show that they are different from one spectral subtype to another at a 99.9% confidence level.

Based on observations available at Observatoire de Haute Provence and the European Southern Observatory databases and on Hipparcos parallax measurements. Title: VizieR Online Data Catalog: PCA-based inversion of stellar parameters (Gebran+, 2016) Authors: Gebran, M.; Farah, W.; Paletou, F.; Monier, R.; Watson, V. Bibcode: 2016yCat..35890083G Altcode: Inverted effective temperatures, surface gravities, projected rotational velocities, metalicities, and radial velocities for the selected A stars. The "closest" are the values found in Vizier catalogues closest to our inverted parameters, while "median" are the median of the catalogue values. Outliers are marked as "1" in the "outliers" column (see sect. 6)

(1 data file). Title: Numerical radiative transfer with state-of-the-art iterative methods made easy Authors: Lambert, Julien; Paletou, Frédéric; Josselin, Eric; Glorian, Jean-Michel Bibcode: 2016EJPh...37a5603L Altcode: 2015arXiv150901158L This article presents an on-line tool and its accompanying software resources for the numerical solution of basic radiation transfer out of local thermodynamic equilibrium (LTE). State-of-the-art stationary iterative methods such as Accelerated Λ-iteration and Gauss-Seidel schemes, using a short characteristics-based formal solver are used. We also comment on typical numerical experiments associated to the basic non-LTE radiation problem. These resources are intended for the largest use and benefit, in support to more classical radiation transfer lectures usually given at the Master level. Title: Estimating Stellar Fundamental Parameters Using PCA: Application to Early Type Stars of GES Data Authors: Farah, W.; Gebran, M.; Paletou, F.; Blomme, R. Bibcode: 2015sf2a.conf....3F Altcode: 2015arXiv150803978F This work addresses a procedure to estimate fundamental stellar parameters such as T_{eff}, log g, [Fe/H], and v sin i using a dimensionality reduction technique called principal component analysis (PCA), applied to a large database of synthetic spectra. This technique shows promising results for inverting stellar parameters of observed targets from Gaia Eso Survey. Title: The GSO Data Centre Authors: Paletou, F.; Glorian, J. -M.; Génot, V.; Rouillard, A.; Petit, P.; Palacios, A.; Caux, E.; Wakelam, V. Bibcode: 2015sf2a.conf...37P Altcode: 2015arXiv150803163P Hereafter we describe the activities of the Grand Sud-Ouest Data Centre operated for INSU (CNRS) by the OMP--IRAP and the Université Paul Sabatier in Toulouse, in a collaboration with the OASU--LAB in Bordeaux and OREME--LUPM in Montpellier. Title: Principal component analysis-based inversion of effective temperatures for late-type stars Authors: Paletou, F.; Gebran, M.; Houdebine, E. R.; Watson, V. Bibcode: 2015A&A...580A..78P Altcode: 2015arXiv150704202P We show how the range of application of the principal component analysis-based inversion method of Paletou et al. (2015, A&A, 573, A67) can be extended to data for late-type stars. Besides being an extension of its original application domain, which applied to FGK stars, we also used synthetic spectra for our learning database. We discuss our results for effective temperatures in comparison with previous evaluations made available from VizieR and Simbad services at CDS.

Based on data obtained from the ESO Science Archive Facility. Title: Discovery of starspots on Vega. First spectroscopic detection of surface structures on a normal A-type star Authors: Böhm, T.; Holschneider, M.; Lignières, F.; Petit, P.; Rainer, M.; Paletou, F.; Wade, G.; Alecian, E.; Carfantan, H.; Blazère, A.; Mirouh, G. M. Bibcode: 2015A&A...577A..64B Altcode: 2014arXiv1411.7789B Context. The theoretically studied impact of rapid rotation on stellar evolution needs to be compared with these results of high-resolution spectroscopy-velocimetry observations. Early-type stars present a perfect laboratory for these studies. The prototype A0 star Vega has been extensively monitored in recent years in spectropolarimetry. A weak surface magnetic field was detected, implying that there might be a (still undetected) structured surface. First indications of the presence of small amplitude stellar radial velocity variations have been reported recently, but the confirmation and in-depth study with the highly stabilized spectrograph SOPHIE/OHP was required.
Aims: The goal of this article is to present a thorough analysis of the line profile variations and associated estimators in the early-type standard star Vega (A0) in order to reveal potential activity tracers, exoplanet companions, and stellar oscillations.
Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy with the highly stabilized velocimeter SOPHIE/OHP. A total of 2588 high signal-to-noise spectra was obtained during 34.7 h on five nights (2 to 6 of August 2012) in high-resolution mode at R = 75 000 and covering the visible domain from 3895-6270 Å. For each reduced spectrum, least square deconvolved equivalent photospheric profiles were calculated with a Teff = 9500 and log g = 4.0 spectral line mask. Several methods were applied to study the dynamic behaviour of the profile variations (evolution of radial velocity, bisectors, vspan, 2D profiles, amongst others).
Results: We present the discovery of a spotted stellar surface on an A-type standard star (Vega) with very faint spot amplitudes ΔF/Fc ~ 5 × 10-4. A rotational modulation of spectral lines with a period of rotation P = 0.68 d has clearly been exhibited, unambiguously confirming the results of previous spectropolarimetric studies. Most of these brightness inhomogeneities seem to be located in lower equatorial latitudes. Either a very thin convective layer can be responsible for magnetic field generation at small amplitudes, or a new mechanism has to be invoked to explain the existence of activity tracing starspots. At this stage it is difficult to disentangle a rotational from a stellar pulsational origin for the existing higher frequency periodic variations.
Conclusions: This first strong evidence that standard A-type stars can show surface structures opens a new field of research and ask about a potential link with the recently discovered weak magnetic field discoveries in this category of stars.

Based on observations obtained with the SOPHIE spectrograph at the 2 m OHP telescope operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS). Title: VizieR Online Data Catalog: Fundamental stellar parameters from PolarBase (Paletou+, 2015) Authors: Paletou, F.; Boehm, T.; Watson, V.; Trouilhet, J. -F. Bibcode: 2015yCat..35730067P Altcode: 2015yCat..35739067P Our reference spectra are taken from the Elodie stellar library (Prugniel et al. 2007, astro-ph/0703658, Cat. III/251; Prugniel & Soubiran 2001A&A...369.1048P, Cat. III/218).

Our main purpose is inverting of stellar parameters from high-resolution spectra coming from Narval and ESPaDOnS spectropolarimeters. These data are now available from the public database PolarBase (Petit et al., 2014PASP..126..469P, Cat. J/PASP/126/469). Narval is a modern spectropolarimeter operating in the 380-1000nm spectral domain, with a spectral resolution of 65000 in its polarimetric mode. It is an improved copy, adapted to the 2m TBL telescope, of the ESPaDOnS spectropolarimeter, which is in operations since 2004 at the 3.6m aperture CFHT telescope.

(1 data file). Title: Inversion of stellar fundamental parameters from ESPaDOnS and Narval high-resolution spectra Authors: Paletou, F.; Böhm, T.; Watson, V.; Trouilhet, J. -F. Bibcode: 2015A&A...573A..67P Altcode: 2014arXiv1411.4859P The general context of this study is the inversion of stellar fundamental parameters from high-resolution Echelle spectra. We aim at developing a fast and reliable tool for the post-processing of spectra produced by ESPaDOnS and Narval spectropolarimeters. Our inversion tool relies on principal component analysis. It allows reducing dimensionality and defining a specific metric for the search of nearest neighbours between an observed spectrum and a set of observed spectra taken from the Elodie stellar library. Effective temperature, surface gravity, total metallicity, and projected rotational velocity are derived. Various tests presented in this study that were based solely on information coming from a spectral band centred on the Mg i b-triplet and had spectra from FGK stars are very promising.

Based on observations obtained at the Télescope Bernard Lyot (TBL, Pic du Midi, France), which is operated by the Observatoire Midi-Pyrénées, Université de Toulouse, Centre National de la Recherche Scientifique (France) and the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, CNRS/INSU and the University of Hawaii (USA). Title: Using Virtual Observatory with Python: querying remote astronomical databases Authors: Paletou, F.; Zolotukhin, I. Bibcode: 2014arXiv1408.7026P Altcode: This tutorial is devoted to extending an existing catalogue with data taken elsewhere, either from CDS Vizier or Simbad database. As an example, we used the so-called 'Spectroscopic Survey of Stars in the Solar Neighborhood' (aka. S4N, Allende Prieto et al. 2004) in order to retrieve all objects with available data for the set of fundamental stellar parameters effective temperature, surface gravity and metallicity. Then for each object in this dataset we query Simbad database to retrieve the projected rotational velocity. This combines Vizier and Simbad queries made using Python astroquery module. The tutorial covers remote database access, filtering tables with arbitrary criteria, creating and writing your own tables, and basics of plotting in Python. Title: VizieR Online Data Catalog: PolarBase catalogue of stellar spectra (Petit+, 2014) Authors: Petit, P.; Louge, T.; Theado, S.; Paletou, F.; Manset, N.; Morin, J.; Marsden, S. C.; Jeffers, S. V. Bibcode: 2014yCat..61260469P Altcode: We list the stellar spectroscopic and spectropolarimetric observations available in the PolarBase data base. For each star equatorial coordinates, first Julian date of observation, last Julian date of observation, number of observations are given, and a detection diagnosis of polarized signatures (in cross-correlated pseudo-line profiles) are given.

(1 data file). Title: PolarBase: A Database of High-Resolution Spectropolarimetric Stellar Observations Authors: Petit, P.; Louge, T.; Théado, S.; Paletou, F.; Manset, N.; Morin, J.; Marsden, S. C.; Jeffers, S. V. Bibcode: 2014PASP..126..469P Altcode: 2014arXiv1401.1082P PolarBase is an evolving data base that contains all stellar data collected with the ESPaDOnS and NARVAL high-resolution spectropolarimeters, in their reduced form, as soon as they become public. As of early 2014, observations of 2,000 stellar objects throughout the Hertzsprung-Russell diagram are available. Intensity spectra are available for all targets, and the majority of the observations also include simultaneous spectra in circular or linear polarization, with the majority of the polarimetric measurements being performed only in circularly polarized light (Stokes V). Observations are associated with a cross-correlation pseudo-line profile in all available Stokes parameters, greatly increasing the detectability of weak polarized signatures. Stokes V signatures are detected for more than 300 stars of all masses and evolutionary stages, and linear polarization is detected in 35 targets. The detection rate in Stokes V is found to be anti-correlated with the stellar effective temperature. This unique set of Zeeman detections offers the first opportunity to run homogeneous magnetometry studies throughout the H-R diagram. The web interface of PolarBase is available at http://polarbase.irap.omp.eu. Title: PCA-based inversion of stellar fundamental parameters from high-resolution Echelle spectra Authors: Paletou, F.; Trouilhet, J. -F.; Boehm, T. Bibcode: 2014arXiv1401.1083P Altcode: The general context of this study is the inversion of stellar fundamental parameters from high-resolution Echelle spectra. We aim at developing a fast and reliable tool for the post-processing of spectra produced, in particular, by the Espadons and Narval spectropolarimeters. Our inversion tool relies on principal component analysis. It allows reduction of dimensionality and the definition of a specific metric for the search of nearest neighbours between an observed spectrum and a set of synthetic spectra. Effective temperature, surface gravity, total metallicity and projected rotation velocity are derived. Our first tests, essentially done from the sole information coming from the spectral band that the RVS spectrometer will soon observe from the GAIA space observatory, and with spectra from mainly FGK-dwarfs are very promising. We also tested our method with a few targets beyond this domain of the H-R diagram. Title: Conceptual design of the data handling system for the European Solar Telescope Authors: Ermolli, Ilaria; Cauzzi, Gianna; Collados, Manuel; Paletou, Frederic; Reardon, Kevin; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario; Del Moro, Dario; Di Marcantonio, Paolo; Giorgi, Fabrizio; Lafon, Martine; Pietropaolo, Ermanno; Romano, Paolo Bibcode: 2012SPIE.8448E..1SE Altcode: We present an overview of the conceptual design of the data handling unit of the ECS, the Control System for the European Solar Telescope (EST). We will focus on describing the critical requirements for this unit resulting from the overall design of the telescope, together with its architecture and the results of the feasibility analysis carried out to date. Title: A critical evaluation of the principal component analysis detection of polarized signatures using real stellar data Authors: Paletou, F. Bibcode: 2012A&A...544A...4P Altcode: 2012arXiv1206.5139P The general context of this study is the post-processing of multiline spectropolarimetric observations of stars, and in particular the numerical analysis techniques aiming at detecting and characterizing polarized signatures. Using real observational data, we compare and clarify several points concerning various methods of analysis. We applied and compared the results of simple line addition, least-squares deconvolution, and denoising by principal component analysis to polarized stellar spectra available from the TBLegacy database of the Narval spectropolarimeter. This comparison of various approaches of distinct sophistication levels allows us to make a safe choice for the next implementation of on-line post-processing of our unique database for the stellar physics community. Title: Laboratory Measurements of the Zeeman Effect in the - System of Iron Monohydride Authors: Crozet, Patrick; Tourasse, Guillaume; Ross, Amanda J.; Tokaryk, D. W.; Paletou, Frederic; Ariste, Arturo Lopez Bibcode: 2012mss..confERA09C Altcode: We have used a hollow cathode sputtering source, flowing a mixture of 10 % H_2 in Ar ∼45 standard cm^3/minute to form FeH radicals. Sputtering from iron required currents ≥ 250 mA. A permanent magnet was placed 2--3 cm below the cathode, generating magnetic fields 3000--4500 Gauss. Output from a Sirah Matisse Ti:sapphire laser was focused to a beamwaist &lt; 1mm to probe a reasonably homogeneous region of the magnetic field, with the laser operating around 1 μm for the 0-0 band and 890 nm for the 1-0 band of the F ^4Δ←X ^4Δ system in FeH. The magnetic field is calibrated to 0.5 % accuracy from the Zeeman response of the Ar I line at 10958.339 cm-1. Several spectra have been taken for lines of the R branches of the F ^4Δ7/2←X ^4Δ7/2 and F ^4Δ5/2←X ^4Δ5/2 sub-bands, showing resolved structures at Doppler resolutions. Unresolved structures are seen for the Q and P transitions. Landé factors have been determined for the upper state (relying on ground state data from LMR work.

We gratefully acknowledge financial support from the French agency ANR, and from the CNRS (PNPS programme) for this work.}) either from fits to peak positions, or by simulating observed profiles when this was impossible. The Landé factors have been used to deduce a magnetic field of 2200 Gauss in sunspots from lines near 1 μm observed at the solar telescope THEMIS (Tenerife) in July 2011. Stokes V profiles were recorded at the telescope, for optimum sensitivity. The magnetic field deduced from atomic lines (Ti,Fe) is around 10 % higher than that found from FeH, compatible with molecules forming at higher altitudes in the solar atmosphere.

J.M. Brown, H. Korsgen, S.P. Beaton, & K.M. Evenson, J. Chem. Phys. 124 234309 (2006) Title: Long-term magnetic field monitoring of the Sun-like star ξ Bootis A Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin, J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.; Théado, S.; Van Grootel, V. Bibcode: 2012A&A...540A.138M Altcode: 2011arXiv1109.5066M
Aims: We aim to investigate the long-term temporal evolution of the magnetic field of the solar-type star ξ Bootis A, both from direct magnetic field measurements and from the simultaneous estimate of indirect activity indicators.
Methods: We obtained seven epochs of high-resolution, circularly-polarized spectra from the NARVAL spectropolarimeter between 2007 and 2011, for a total of 76 spectra. Using approximately 6100 photospheric spectral lines covering the visible domain, we employed a cross-correlation procedure to compute a mean polarized line profile from each spectrum. The large-scale photospheric magnetic field of the star was then modelled by means of Zeeman-Doppler Imaging, allowing us to follow the year-to-year evolution of the reconstructed magnetic topology. Simultaneously, we monitored the width of several magnetically sensitive spectral lines, the radial velocity, the line asymmetry of intensity line profiles, and the chromospheric emission in the cores of the Ca II H and Hα lines.
Results: During the highest observed activity states, in 2007 and 2011, the large-scale field of ξ Bootis A is almost completely axisymmetric and is dominated by its toroidal component. The toroidal component persists with a constant polarity, containing a significant fraction of the magnetic energy of the large-scale surface field through all observing epochs. The magnetic topologies reconstructed for these activity maxima are very similar, suggesting a form of short cyclicity in the large-scale field distribution. The mean unsigned large-scale magnetic flux derived from the magnetic maps varies by a factor of about 2 between the lowest and highest observed magnetic states. The chromospheric flux is less affected and varies by a factor of 1.2. Correlated temporal evolution, due to both rotational modulation and seasonal variability, is observed between the Ca II emission, the Hα emission and the width of magnetically sensitive lines. The rotational dependence of polarimetric magnetic measurements displays a weak correlation with other activity proxies, presumably due to the different spatial scales and centre-to-limb darkening associated with polarimetric signatures, as compared to non-polarized activity indicators. Better agreement is observed on the longer term. When measurable, the differential rotation reveals a strong latitudinal shear in excess of 0.2 rad d-1.

Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France.Tables 3-6 are available in electronic form at http://www.aanda.org Title: Laboratory determination of Landé factors for the molecular radical FeH Authors: Crozet, P.; Tourasse, G.; Ross, A.; Paletou, F.; López Ariste, A. Bibcode: 2012EAS....58...63C Altcode: We report laboratory measurements of the Zeeman response of lines in the 0-0 Wing-Ford band of the F-X system (λ ~ 1 μm) of FeH, measured in magnetic fields 0.3 - 0.5 Tesla. New Landé factors are used to deduce the magnetic field in sunspots from Stokes V profiles recorded at the solar telescope THEMIS. The magnetic field deduced from atomic lines (Ti, Fe) is slightly higher than that found from FeH. Title: Data handling and control of the European Solar Telescope Authors: Ermolli, I.; Bettonvil, F.; Cauzzi, G.; Cavaller, L.; Collados, M.; Di Marcantonio, P.; Grivel, C.; Paletou, F.; Romano, P.; Aboudarham, J.; Cirami, R.; Cosentino, R.; Giorgi, F.; Lafon, M.; Laforgue, D.; Reardon, K.; Sliepen, G. Bibcode: 2012MSAIS..19..380E Altcode: We describe some aspects of the facility operation that have been considered for the design of the data handling and control of the European Solar Telescope. The main sub-systems of the EST relevant for the control are summarized, together with some information on current solar data models. Title: Detection of a weak surface magnetic field on Sirius A: are all tepid stars magnetic? Authors: Petit, P.; Lignières, F.; Aurière, M.; Wade, G. A.; Alina, D.; Ballot, J.; Böhm, T.; Jouve, L.; Oza, A.; Paletou, F.; Théado, S. Bibcode: 2011A&A...532L..13P Altcode: 2011arXiv1106.5363P
Aims: We aim at a highly sensitive search for weak magnetic fields in main sequence stars of intermediate mass, by scanning classes of stars with no previously reported magnetic members. After detecting a weak magnetic field on the normal, rapidly rotating A-type star Vega, we concentrate here on the bright star Sirius A, taken as a prototypical, chemically peculiar, moderately rotating Am star.
Methods: We employed the NARVAL and ESPaDOnS high-resolution spectropolarimeters to collect 442 circularly polarized spectra, complemented by 60 linearly polarized spectra. Using a list of about 1100 photospheric spectral lines, we computed a cross correlation line profile from every spectrum, leading to a signal-to-noise ratio of up to 30 000 in the polarized profile.
Results: We report the repeated detection of circularly polarized, highly asymmetric signatures in the line profiles, interpreted as Zeeman signatures of a large-scale photospheric magnetic field, with a line-of-sight component equal to 0.2 ± 0.1 G.
Conclusions: This is the first polarimetric detection of a surface magnetic field on an Am star. Using rough estimates of the physical properties of the upper layers of Sirius A, we suggest that a dynamo operating in the shallow convective envelope cannot account for the field strength reported here. Together with the magnetic field of Vega, this result confirms that a new class of magnetic objects exists among non Ap/Bp intermediate-mass stars, and it may indicate that a significant fraction of tepid stars are magnetic.

Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Title: Exploring the magnetic topologies of cool stars Authors: Morin, J.; Donati, J. -F.; Petit, P.; Albert, L.; Auriére, M.; Cabanac, R.; Catala, C.; Delfosse, X.; Dintrans, B.; Fares, R.; Forveille, T.; Gastine, T.; Jardine, M.; Konstantinova-Antova, R.; Lanoux, J.; Lignires, F.; Morgenthaler, A.; Paletou, F.; Velez, J. C. Ramirez; Solanki, S. K.; Thado, S.; Van Grootel, V. Bibcode: 2011IAUS..273..181M Altcode: 2010arXiv1009.2589M Magnetic fields of cool stars can be directly investigated through the study of the Zeeman effect on photospheric spectral lines using several approaches. With spectroscopic measurement in unpolarised light, the total magnetic flux averaged over the stellar disc can be derived but very little information on the field geometry is available. Spectropolarimetry provides a complementary information on the large-scale magnetic topology. With Zeeman-Doppler Imaging (ZDI), this information can be retrieved to produce a map of the vector magnetic field at the surface of the star, and in particular to assess the relative importance of the poloidal and toroidal components as well as the degree of axisymmetry of the field distribution.

The development of high-performance spectropolarimeters associated with multi-lines techniques and ZDI allows us to explore magnetic topologies throughout the Hertzsprung-Russel diagram, on stars spanning a wide range of mass, age and rotation period. These observations bring novel constraints on magnetic field generation by dynamo effect in cool stars. In particular, the study of solar twins brings new insight on the impact of rotation on the solar dynamo, whereas the detection of strong and stable dipolar magnetic fields on fully convective stars questions the precise role of the tachocline in this process. Title: Broyden's method for the solution of the multilevel non-LTE radiation transfer problem Authors: Nicolas, S.; Bigarré, L.; Paletou, F. Bibcode: 2011A&A...527A...1N Altcode: 2010arXiv1012.3841N This study concerns the fast and accurate solution of multilevel non-LTE radiation transfer problems. We propose and evaluate an alternative iterative scheme to the classical MALI method. Our study is instead based on the application of Broyden's method for the solution of nonlinear systems of equations. Comparative tests, in 1D plane-parallel geometry, of the popular MALI method and our alternative method are discussed. The Broyden method is typically 4.5 times faster than MALI. This makes it also fairly competitive with the Gauss-Seidel and Successive Over-Relaxation methods developed after MALI. Title: Polarized Line Formation in Multi-dimensional Media. II. A Fast Method to Solve Problems with Partial Frequency Redistribution Authors: Anusha, L. S.; Nagendra, K. N.; Paletou, F. Bibcode: 2011ApJ...726...96A Altcode: In the previous paper of this series, we presented a formulation of the polarized radiative transfer equation for resonance scattering with partial frequency redistribution (PRD) in multi-dimensional media for a two-level atom model with unpolarized ground level, using the irreducible spherical tensors {T}^K_Q(i,Ω) for polarimetry. We also presented a polarized approximate lambda iteration method to solve this equation using the Jacobi iteration scheme. The formal solution used was based on a simple finite volume technique. In this paper, we develop a faster and more efficient method which uses the projection techniques applied to the radiative transfer equation (the Stabilized Preconditioned Bi-Conjugate Gradient method). We now use a more accurate formal solver, namely the well-known two-dimensional (2D) short characteristics method. Using the numerical method developed in Paper I, we can consider only simpler cases of finite 2D slabs due to computational limitations. Using the method developed in this paper, we could compute PRD solutions in 2D media in the more difficult context of semi-infinite 2D slabs also. We present several solutions which may serve as benchmarks in future studies in this area. Title: Data handling and control for the European Solar Telescope Authors: Ermolli, Ilaria; Bettonvil, Felix; Cauzzi, Gianna; Cavaller, Lluis; Collados, Manuel; Di Marcantonio, Paolo; Paletou, Frederic; Romano, Paolo; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario; Giorgi, Fabrizio; Lafon, Martine; Laforgue, Didier; Reardon, Kevin; Sliepen, Guus Bibcode: 2010SPIE.7740E..0GE Altcode: 2010SPIE.7740E..13E We introduce the concepts for the control and data handling systems of the European Solar Telescope (EST), the main functional and technical requirements for the definition of these systems, and the outcomes from the trade-off analysis to date. Concerning the telescope control, EST will have performance requirements similar to those of current medium-sized night-time telescopes. On the other hand, the science goals of EST require the simultaneous operation of three instruments and of a large number of detectors. This leads to a projected data flux that will be technologically challenging and exceeds that of most other astronomical projects. We give an overview of the reference design of the control and data handling systems for the EST to date, focusing on the more critical and innovative aspects resulting from the overall design of the telescope. Title: Magnetic field and velocity of early M dwarfs (Donati+, 2008) Authors: Donati, J. -F.; Morin, J.; Petit, P.; Delfosse, X.; Forveille, T.; Auriere, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.; Jardine, M. M.; Lignieres, F.; Paletou, F.; Ramirez Velez, J. C.; Theado, S. Bibcode: 2010yCat..73900545D Altcode: Spectropolarimetric observations of the selected M dwarfs were collected with NARVAL and the 2m Telescope Bernard Lyot (TBL), between 2007 January and 2008 February (in three different runs).

(2 data files). Title: Magnetic field and velocity of early M dwarfs (Morin+, 2008) Authors: Morin, J.; Donati, J. -F.; Petit, P.; Delfosse, X.; Forveille, T.; Albert, L.; Auriere, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.; Jardine, M. M.; Lignieres, F.; Paletou, F.; Ramirez Velez, J. C.; Theado, S. Bibcode: 2010yCat..73900567M Altcode: We have collected 107 pairs of Stokes I (unpolarised) and V (circularly polarised) spectra with the twin instruments ESPaDOnS at CFHT (2003ASPC..307...41D) and NARVAL at TBL between January 2006 and February 2008. All spectra were reduced using the Libre-Esprit pipeline, and the mean I and V line profiles were extracted using the Least-Squares Deconvolution (LSD) technique (1997MNRAS.291..658D). The star V374 Peg (2008MNRAS.384...77M) is also included in the discussion and in table1.dat.

(2 data files). Title: A conjugate gradient method for solving the non-LTE line radiation transfer problem Authors: Paletou, F.; Anterrieu, E. Bibcode: 2009A&A...507.1815P Altcode: 2009arXiv0905.3258P This study concerns the fast and accurate solution of the line radiation transfer problem, under non-LTE conditions. We propose and evaluate an alternative iterative scheme to the classical ALI-Jacobi method, and to the more recently proposed Gauss-Seidel and successive over-relaxation (GS/SOR) schemes. Our study is indeed based on applying a preconditioned bi-conjugate gradient method (BiCG-P). Standard tests, in 1D plane parallel geometry and in the frame of the two-level atom model with monochromatic scattering are discussed. Rates of convergence between the previously mentioned iterative schemes are compared, as are their respective timing properties. The smoothing capability of the BiCG-P method is also demonstrated. Title: Preconditioned Bi-conjugate Gradient Method for Radiative Transfer in Spherical Media Authors: Anusha, L. S.; Nagendra, K. N.; Paletou, F.; Léger, L. Bibcode: 2009ApJ...704..661A Altcode: 2009arXiv0906.2926A A robust numerical method called the Preconditioned Bi-Conjugate Gradient (Pre-BiCG) method is proposed for the solution of the radiative transfer equation in spherical geometry. A variant of this method called Stabilized Preconditioned Bi-Conjugate Gradient (Pre-BiCG-STAB) is also presented. These are iterative methods based on the construction of a set of bi-orthogonal vectors. The application of the Pre-BiCG method in some benchmark tests shows that the method is quite versatile, and can handle difficult problems that may arise in astrophysical radiative transfer theory. Title: Multi-Line Stokes Inversion for Prominence Magnetic-Field Diagnostics Authors: Casini, R.; López Ariste, A.; Paletou, F.; Léger, L. Bibcode: 2009ApJ...703..114C Altcode: 2009arXiv0906.2144C We present test results on the simultaneous inversion of the Stokes profiles of the He I lines at 587.6 nm (D3) and 1083.0 nm in prominences (90° scattering). We created data sets of synthetic Stokes profiles for the case of quiescent prominences (B < 200 G), assuming a conservative value of 10-3 of the peak intensity for the polarimetric sensitivity of the simulated observations. In this work, we focus on the error analysis for the inference of the magnetic field vector, under the usual assumption that the prominence can be assimilated to a slab of finite optical thickness with uniform magnetic and thermodynamic properties. We find that the simultaneous inversion of the two lines significantly reduces the errors on the inference of the magnetic field vector, with respect to the case of single-line inversion. These results provide a solid justification for current and future instrumental efforts with multi-line capabilities for the observations of solar prominences and filaments. Title: Freeware Solutions for Spectropolarimetric Data Reduction Authors: Paletou, F.; Rezaei, R.; Léger, L. Bibcode: 2009ASPC..405...51P Altcode: Most of the solar physicists use very expensive software for data reduction and visualization. We present hereafter a reliable freeware solution based on the Python language. This is made possible by the association of the latter with a small set of additional libraries developed in the scientific community. It provides then a very powerful and economical alternative to other interactive data languages. Although it can also be used for any kind of post-processing of data, we demonstrate the capabilities of such a set of freeware tools using THéMIS observations of the second solar spectrum. Title: The Ground-Based Solar Observations Database BASS 2000 Authors: Paletou, F.; Lafon, M.; Maeght, P.; Grimaud, F.; Louge, T.; Aboudarham, J. Bibcode: 2009ASPC..405..397P Altcode: BASS 2000 is the French solar database for ground-based instruments. We describe hereafter our organization, our tasks and the products we can deliver to the international community. Our prospects cover data mining into the THéMIS archive, a participation to the EST endeavour and the creation and curation of the ESPaDOnS/NARVAL stellar spectra database. Title: Why are Some A Stars Magnetic, while Most are Not? Authors: Wade, G. A.; Silvester, J.; Bale, K.; Johnson, N.; Power, J.; Aurière, M.; Ligniéres, F.; Dintrans, B.; Donati, J. -F.; Hui Bon Hoa, A.; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Rincon, F.; Toque, N.; Bagnulo, S.; Folsom, C. P.; Landstreet, J. D.; Gruberbauer, M.; Lueftinger, T.; Jeffers, S. V.; Lèbre, A.; Marsden, S. C. Bibcode: 2009ASPC..405..499W Altcode: A small fraction of intermediate-mass main sequence (A and B type) stars have strong, organised magnetic fields. The large majority of such stars, however, show no evidence for magnetic fields, even when observed with very high precision. In this paper we describe a simple model, motivated by qualitatively new observational results, that provides a natural physical explanation for the small fraction of observed magnetic stars. Title: 2D Radiative Modeling of He I Spectral Lines Formed in Solar Prominences Authors: Léger, L.; Paletou, F. Bibcode: 2009ASPC..405..325L Altcode: We present preliminary results of 2D radiative modeling of He I lines in solar prominences, using a new numerical code developed by us \citep*{leger_leger07}. It treats self-consistently the radiation transfer and the non-LTE statistical equilibrium of H and, in a second stage, the one of He using a detailed atomic model. Preliminary comparisons with new visible plus near-infrared observations made at high spectral resolution with THéMIS are very satisfactory. Title: 2D non-LTE radiative modelling of He I spectral lines formed in solar prominences Authors: Léger, L.; Paletou, F. Bibcode: 2009A&A...498..869L Altcode: 2008arXiv0811.4753L Context: The interpretation of high-resolution spectropolarimetric observations of solar prominences completed primarily at visible and near-infrared wavelengths, requires radiative modelling that takes into account both multi-dimensional geometry and complex atomic models.
Aims: We enhance the interpretation of observations of He i multiplets, by considering 2D non-LTE unpolarized radiation transfer, and taking into account of the atomic fine-structure of helium.
Methods: We apply our 2D non-LTE radiative transfer code, which is based on the multi-grid Gauss-Seidel/SOR iterative schemes.
Results: It allows us to compute realistic emergent intensity profiles for the He i λ 10 830 Å and D3 multiplets, which can be directly compared to the simultaneous and high-resolution observations completed at THéMIS. A preliminary 2D multi-thread modelling is also discussed. Title: Magnetic geometries of Sun-like stars: exploring the mass-rotation plane Authors: Petit, Pascal; Dintrans, B.; Aurière, M.; Catala, C.; Donati, J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morgenthaler, A.; Morin, J.; Paletou, F.; Ramirez Velez, J.; Solanki, S. K.; Théado, S. Bibcode: 2009IAUS..259..441P Altcode: Sun-like stars are able to continuously generate a large-scale magnetic field through the action of a dynamo. Various physical parameters of the star are able to affect the dynamo output, in particular the rotation and mass. Using the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France), it is now possible to measure the large-scale magnetic field of solar analogues (i.e. stars very close to the Sun in the mass-rotation plane, including strict solar twins). From spectropolarimetric time-series, tomographic inversion enables one to reconstruct the field geometry and its progressive distortion under the effect of surface differential rotation. We show the first results obtained on a sample of main-sequence dwarfs, probing masses between 0.7 and 1.4 solar mass and rotation rates between 1 and 3 solar rotation rate. Title: Magnetic geometries of Sun-like stars : impact of rotation Authors: Petit, P.; Dintrans, B.; Aurière, M.; Catala, C.; Donati, J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morin, J.; Paletou, F.; Ramirez, J.; Solanki, S. K.; Théado, S. Bibcode: 2008sf2a.conf..523P Altcode: Sun-like stars are able to continuously generate a large-scale magnetic field through the action of a dynamo. Various physical parameters of the star are able to affect the dynamo output, in particular the rotation and mass. Using new generation stellar spectropolarimeters (ESPaDOnS@CFHT, NARVAL@TBL), it is now possible to measure the large-scale magnetic field of solar analogues (i.e. stars very close to the Sun in the stellar-parameter plane, including strict solar twins). From spectropolarimetric time-series, tomographic inversion of polarized Zeeman signatures allows us to reconstruct the field geometry and its progressive distortion under the effect of surface differential rotation. We detail the first results obtained on a sample of four main-sequence dwarfs, with masses close to 1 solar mass and rotation rates between 1 and 3 solar rotation rate. Title: The magnetic field of solar prominences. Authors: Paletou, F. Bibcode: 2008sf2a.conf..559P Altcode: 2008arXiv0810.2662P In his famous monographs, Einar Tandberg-Hanssen writes that ``the single, physically most important parameter to study in prominences may be the magnetic field. Shapes, motions, and in fact the very existence of prominences depend on the nature of the magnetic field threading the prominence plasma''. Hereafter we sumarize recent contributions and advances in our knowledge about the magnetic field of solar prominences. It mostly relies on high resolution and high sensitivity spectropolarimetry made both in the visible and in the near infrared. Title: Large-scale magnetic topologies of early M dwarfs Authors: Donati, J. -F.; Morin, J.; Petit, P.; Delfosse, X.; Forveille, T.; Aurière, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.; Jardine, M. M.; Lignières, F.; Paletou, F.; Ramirez Velez, J. C.; Théado, S. Bibcode: 2008MNRAS.390..545D Altcode: 2008MNRAS.tmp.1077D; 2008arXiv0809.0269D We present here additional results of a spectropolarimetric survey of a small sample of stars ranging from spectral type M0 to M8 aimed at investigating observationally how dynamo processes operate in stars on both sides of the full convection threshold (spectral type M4).

The present paper focuses on early M stars (M0-M3), that is above the full convection threshold. Applying tomographic imaging techniques to time series of rotationally modulated circularly polarized profiles collected with the NARVAL spectropolarimeter, we determine the rotation period and reconstruct the large-scale magnetic topologies of six early M dwarfs. We find that early-M stars preferentially host large-scale fields with dominantly toroidal and non-axisymmetric poloidal configurations, along with significant differential rotation (and long-term variability); only the lowest-mass star of our subsample is found to host an almost fully poloidal, mainly axisymmetric large-scale field resembling those found in mid-M dwarfs.

This abrupt change in the large-scale magnetic topologies of M dwarfs (occurring at spectral type M3) has no related signature on X-ray luminosities (measuring the total amount of magnetic flux); it thus suggests that underlying dynamo processes become more efficient at producing large-scale fields (despite producing the same flux) at spectral types later than M3. We suspect that this change relates to the rapid decrease in the radiative cores of low-mass stars and to the simultaneous sharp increase of the convective turnover times (with decreasing stellar mass) that models predict to occur at M3; it may also be (at least partly) responsible for the reduced magnetic braking reported for fully convective stars.

Based on observations obtained at the Télescope Bernard Lyot (TBL), operated by the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France.

E-mail: donati@ast.obs-mip.fr (J-FD); jmorin@ast.obs-mip.fr (JM); petit@ast.obs-mip.fr (PP); xavier.delfosse@obs.ujf-grenoble.fr (XD); thierry.forveille@obs.ujf-grenoble.fr (TF); auriere@ast.obs-mip.fr (MA); remi.cabanac@ast.obs-mip.fr (RC); dintrans@ast.obs-mip.fr (BD); rfares@ast.obs-mip.fr (RF); tgastine@ast.obs-mip.fr (TG); mmj@st-and.ac.uk (MMJ); lignieres@ast.obs-mip.fr (FL); fpaletou@ast.obs-mip.fr (FP); julio.ramirez@obspm.fr (JCRV); sylvie.theado@ast.obs-mip.fr (ST) Title: Large-scale magnetic topologies of mid M dwarfs Authors: Morin, J.; Donati, J. -F.; Petit, P.; Delfosse, X.; Forveille, T.; Albert, L.; Aurière, M.; Cabanac, R.; Dintrans, B.; Fares, R.; Gastine, T.; Jardine, M. M.; Lignières, F.; Paletou, F.; Ramirez Velez, J. C.; Théado, S. Bibcode: 2008MNRAS.390..567M Altcode: 2008arXiv0808.1423M; 2008MNRAS.tmp.1071M We present in this paper, the first results of a spectropolarimetric analysis of a small sample (~20) of active stars ranging from spectral type M0 to M8, which are either fully convective or possess a very small radiative core. This study aims at providing new constraints on dynamo processes in fully convective stars.

This paper focuses on five stars of spectral type ~M4, i.e. with masses close to the full convection threshold (~=0.35Msolar), and with short rotational periods. Tomographic imaging techniques allow us to reconstruct the surface magnetic topologies from the rotationally modulated time-series of circularly polarized profiles. We find that all stars host mainly axisymmetric large-scale poloidal fields. Three stars were observed at two different epochs separated by ~1 yr; we find the magnetic topologies to be globally stable on this time-scale.

We also provide an accurate estimation of the rotational period of all stars, thus allowing us to start studying how rotation impacts the large-scale magnetic field.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) and the Télescope Bernard Lyot (TBL). CFHT is operated by the National Research Council of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France (INSU/CNRS) and the University of Hawaii, while the TBL is operated by CNRS/INSU.

E-mail: jmorin@ast.obs-mip.fr (JM); donati@ast.obs-mip.fr (J-FD); petit@ast.obs-mip.fr (PP); xavier.delfosse@obs.ujf-grenoble.fr (XD); thierry.forveille@obs.ujf-grenoble.fr (TF); albert@cfht.hawaii.edu (LA); auriere@ast.obs-mip.fr (MA); remi.cabanac@ast.obs-mip.fr (RC); dintrans@ast.obs-mip.fr (BD); rfares@ast.obs-mip.fr (RF); tgastine@ast.obs-mip.fr (TG); mmj@st-andrews.ac.uk (MMJ); ligniere@ast.obs-mip.fr (FL); fpaletou@ast.obs-mip.fr (FP); jramirez@mesiog.obspm.fr (JR); sylvie.theado@ast.obs-mip.fr (ST) Title: Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold Authors: Petit, P.; Dintrans, B.; Solanki, S. K.; Donati, J. -F.; Aurière, M.; Lignières, F.; Morin, J.; Paletou, F.; Ramirez Velez, J.; Catala, C.; Fares, R. Bibcode: 2008MNRAS.388...80P Altcode: 2008MNRAS.tmp..715P; 2008arXiv0804.1290P From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars.

We reconstruct the large-scale magnetic geometry of the targets as a low-order (l < 10) spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ~12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component. Title: Magnetospheric accretion on the T Tauri star BP Tauri Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.; Paletou, F.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron, A.; Harries, T. J.; Hussain, G. A. J.; Unruh, Y.; Morin, J.; Marsden, S. C.; Manset, N.; Aurière, M.; Catala, C.; Alecian, E. Bibcode: 2008MNRAS.386.1234D Altcode: 2008MNRAS.tmp..461D; 2008arXiv0802.2052D From observations collected with the ESPaDOnS and NARVAL spectropolarimeters, we report the detection of Zeeman signatures on the classical T Tauri star (cTTS) BP Tau. Circular polarization signatures in photospheric lines and in narrow emission lines tracing magnetospheric accretion are monitored throughout most of the rotation cycle of BP Tau at two different epochs in 2006. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized spectral proxies tracing the photosphere and the footpoints of accretion funnels.

From the complete data sets at each epoch, we reconstruct the large-scale magnetic topology and the location of accretion spots at the surface of BP Tau using tomographic imaging. We find that the field of BP Tau involves a 1.2 kG dipole and 1.6 kG octupole, both slightly tilted with respect to the rotation axis. Accretion spots coincide with the two main magnetic poles at high latitudes and overlap with dark photospheric spots; they cover about 2 per cent of the stellar surface. The strong mainly axisymmetric poloidal field of BP Tau is very reminiscent of magnetic topologies of fully convective dwarfs. It suggests that magnetic fields of fully convective cTTSs such as BP Tau are likely not fossil remants, but rather result from vigorous dynamo action operating within the bulk of their convective zones.

Preliminary modelling suggests that the magnetosphere of BP Tau extends to distances of at least 4R* to ensure that accretion spots are located at high latitudes, and is not blown open close to the surface by a putative stellar wind. It apparently succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of BP Tau.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope Bernard Lyot (TBL). CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France (INSU/CNRS) and the University of Hawaii, while TBL is operated by CNRS/INSU.

E-mail: donati@ast.obs-mip.fr (J-FD); mmj@st-andrews.ac.uk (MMJ); sg64@st-andrews.ac.uk (SGG); petit@ast.obs-mip.fr (PP); fpaletou@ast.obs-mip.fr (FP); jerome.bouvier@obs.ujf-grenoble.fr (JB); catherine.dougados@obs.ujf-grenoble.fr (CD); francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk (ACC); th@astro.ex.ac.uk (TJH); ghussain@eso.org (GAJH); y.unruh@imperial.ac.uk (YU); jmorin@ast.obs-mip.fr (JM); scm@aao.gov.au (SCM); manset@cfht.hawaii.edu (NM); auriere@ast.obs-mip.fr (MA); claude.catala@obspm.fr (CC); evelyne.alecian@obspm.fr (EA) Title: Magnetic Topologies of Cool Stars Authors: Donati, J. -F.; Jardine, M. M.; Petit, P.; Morin, J.; Bouvier, J.; Collier Cameron, A.; Delfosse, X.; Dintrans, B.; Dobler, W.; Dougados, C.; Ferreira, J.; Forveille, T.; Gregory, S. G.; Harries, T.; Hussain, G. A. J.; Menard, F.; Paletou, F. Bibcode: 2008ASPC..384..156D Altcode: 2007astro.ph..2159D; 2008csss...14..156D Stellar magnetic fields can be investigated using several, very complementary approaches. While conventional spectroscopy is capable of estimating the average magnetic strength of potentially complex field configurations thanks to its low sensitivity to the vector properties of the field, spectropolarimetry can be used to map the medium- and large-scale structure of magnetic topologies. In particular, the latter approach allows one to retrieve information about the poloidal and toroidal components of the large-scale dynamo fields in low-mass stars, and thus to investigate the physical processes that produce them. Similarly, this technique can be used to explore how magnetic fields couple young stars to their massive accretion disc and thus to estimate how much mass and angular momentum are transfered to the newly-born low-mass star. We present here the latest results in this field obtained with spectropolarimetry, with special emphasis on the surprising discoveries obtained on very-low mass fully-convective stars and classical T Tauri stars thanks to the ESPaDOnS spectropolarimeter recently installed on the 3.6m Canada-France-Hawaii Telescope. Title: Weak magnetic fields in Ap/Bp stars. Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy Authors: Aurière, M.; Wade, G. A.; Silvester, J.; Lignières, F.; Bagnulo, S.; Bale, K.; Dintrans, B.; Donati, J. F.; Folsom, C. P.; Gruberbauer, M.; Hui Bon Hoa, A.; Jeffers, S.; Johnson, N.; Landstreet, J. D.; Lèbre, A.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Power, J.; Rincon, F.; Strasser, S.; Toqué, N. Bibcode: 2007A&A...475.1053A Altcode: 2007arXiv0710.1554A Aims:We investigated a sample of 28 well-known spectroscopically-identified magnetic Ap/Bp stars, with weak, poorly-determined or previously undetected magnetic fields. The aim of this study is to explore the weak part of the magnetic field distribution of Ap/Bp stars.
Methods: Using the MuSiCoS and NARVAL spectropolarimeters at Télescope Bernard Lyot (Observatoire du Pic du Midi, France) and the cross-correlation technique Least Squares Deconvolution (LSD), we obtained 282 LSD Stokes V signatures of our 28 sample stars, in order to detect the magnetic field and to infer its longitudinal component with high precision (median σ=40 G).
Results: For the 28 studied stars, we obtained 27 detections of Stokes V Zeeman signatures from the MuSiCoS observations. Detection of the Stokes V signature of the 28th star (HD 32650) was obtained during science demonstration time of the new NARVAL spectropolarimeter at Pic du Midi. This result clearly shows that when observed with sufficient precision, all firmly classified Ap/Bp stars show detectable surface magnetic fields. Furthermore, all detected magnetic fields correspond to longitudinal fields which are significantly greater than some tens of G. To better characterise the surface magnetic field intensities and geometries of the sample, we phased the longitudinal field measurements of each star using new and previously-published rotational periods, and modeled them to infer the dipolar field intensity (B_d, measured at the magnetic pole) and the magnetic obliquity (β). The distribution of derived dipole strengths for these stars exhibits a plateau at about 1 kG, falling off to larger and smaller field strengths. Remarkably, in this sample of stars selected for their presumably weak magnetic fields, we find only 2 stars for which the derived dipole strength is weaker than 300 G. We interpret this “magnetic threshold” as a critical value necessary for the stability of large-scale magnetic fields, and develop a simple quantitative model that is able to approximately reproduce the observed threshold characteristics. This scenario leads to a natural explanation of the small fraction of intermediate-mass magnetic stars. It may also explain the near-absence of magnetic fields in more massive B and O-type stars.

Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS and Université Paul Sabatier, France. Figures 7 to 32 are only available in electronic form at http://www.aanda.org Table 3 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/1053 Title: 2D radiative modelling of He I spectral lines formed in solar prominences Authors: Leger, L.; Paletou, F. Bibcode: 2007arXiv0712.1701L Altcode: We present preliminary results of 2D radiative modelling of He I lines in solar prominences, using a new numerical code developed by us (Leger, Chevallier and Paletou 2007). It treats self-consistently the radiation transfer and the non-LTE statistical equilibrium of H and, in a second stage, the one of He using a detailed atomic model. Preliminary comparisons with new visible plus near-infrared observations made at high spectral resolution with THeMIS are very satisfactory. Title: Freeware solutions for spectropolarimetric data reduction Authors: Paletou, F.; Rezaei, R.; Leger, L. Bibcode: 2007arXiv0712.1522P Altcode: Most of the solar physicists use very expensive software for data reduction and visualization. We present hereafter a reliable freeware solution based on the Python language. This is made possible by the association of the latter with a small set of additional libraries developed in the scientific community. It provides then a very powerful and economical alternative to other interactive data languages. Although it can also be used for any kind of post-processing of data, we demonstrate the capabities of such a set of freeware tools using THeMIS observations of the second solar spectrum. Title: Why are some A stars magnetic, while most are not? Authors: Wade, G. A.; Silvester, J.; Bale, K.; Johnson, N.; Power, J.; Aurière, M.; Ligniéres, F.; Dintrans, B.; Donati, J. -F.; Bon Hoa, A. Hui; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Rincon, F.; Toque, N.; Bagnulo, S.; Folsom, C. P.; Landstreet, J. D.; Gruberbauer, M.; Lueftinger, T.; Jeffers, S.; Lèbre, A.; Marsden, S. Bibcode: 2007arXiv0712.3614W Altcode: A small fraction of intermediate-mass main sequence (A and B type) stars have strong, organised magnetic fields. The large majority of such stars, however, show no evidence for magnetic fields, even when observed with very high precision. In this paper we describe a simple model, motivated by qualitatively new observational results, that provides a natural physical explanation for the small fraction of observed magnetic stars. Title: The ground-based solar observations database BASS 2000 Authors: Paletou, F.; Lafon, M.; Maeght, P.; Grimaud, F.; Louge, T.; Aboudarham, J. Bibcode: 2007arXiv0712.2421P Altcode: BASS 2000 is the French solar database for ground-based instruments. We describe hereafter our organization, our tasks and the products we can deliver to the international community. Our prospects cover data mining into the THeMIS archive, a participation to the EST endeavour and the creation and curation of the ESPaDOnS/NARVAL stellar spectra database. Title: Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron, A.; Harries, T. J.; Jeffers, S. V.; Paletou, F. Bibcode: 2007MNRAS.380.1297D Altcode: 2007MNRAS.tmp..760D; 2007arXiv0709.1414D From observations collected with the ESPaDOnS spectropolarimeter, we report the discovery of magnetic fields at the surface of the mildly accreting classical T Tauri star (cTTS) V2129 Oph. Zeeman signatures are detected, both in photospheric lines and in the emission lines formed at the base of the accretion funnels linking the disc to the protostar, and monitored over the whole rotation cycle of V2129 Oph. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized line profiles.

We reconstruct the large-scale magnetic topology at the surface of V2129 Oph from both sets of Zeeman signatures simultaneously. We find it to be rather complex, with a dominant octupolar component and a weak dipole of strengths 1.2 and 0.35 kG, respectively, both slightly tilted with respect to the rotation axis. The large-scale field is anchored in a pair of 2-kG unipolar radial field spots located at high latitudes and coinciding with cool dark polar spots at photospheric level. This large-scale field geometry is unusually complex compared to those of non-accreting cool active subgiants with moderate rotation rates.

As an illustration, we provide a first attempt at modelling the magnetospheric topology and accretion funnels of V2129 Oph using field extrapolation. We find that the magnetosphere of V2129 Oph must extend to about 7R* to ensure that the footpoints of accretion funnels coincide with the high-latitude accretion spots on the stellar surface. It suggests that the stellar magnetic field succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of V2129 Oph. The magnetospheric geometry we derive qualitatively reproduces the modulation of Balmer lines and produces X-ray coronal fluxes typical of those observed in cTTSs.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

E-mail: donati@ast.obs-mip.fr (J-FD); mmj@st-andrews.ac.uk (MMJ); sg64@st-andrews.ac.uk (SGG); petit@ast.obs-mip.fr (PP); jerome.bouvier@obs.ujf-grenoble.fr (JB); catherine.dougados@obs.ujf-grenoble.fr (CD); francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk (ACC); th@astro.ex.ac.uk (TJH); s.v.jeffers@phys.uu.nl (SVJ); fpaletou@ast.obs-mip.fr (FP) Title: VizieR Online Data Catalog: Magnetic fields in Ap/Bp stars (Auriere+, 2007) Authors: Auriere, M.; Wade, G. A.; Silvester, J.; Lignieres, F.; Bagnulo, S.; Bale, K.; Dintrans, B.; Donati, J. F.; Folsom, C. P.; Gruberbauer, M.; Hui Bon Hoa, A.; Jeffers, S.; Johnson, N.; Landstreet, J. D.; Lebre, A.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Naseri, S.; Paletou, F.; Petit, P.; Power, J.; Rincon, F.; Strasser, S.; Toque, N. Bibcode: 2007yCat..34751053A Altcode: We have investigated a sample of 28 well-known spectroscopically-identified magnetic Ap/Bp stars, with weak, poorly-determined or previously undetected magnetic fields. The aim of this study is to explore the weak part of the magnetic field distribution of Ap/Bp stars. Using the MuSiCoS and NARVAL spectropolarimeters at Telescope Bernard Lyot (Observatoire du Pic du Midi, France) and the cross-correlation technique Least Squares Deconvolution (LSD), we have obtained 282 LSD Stokes $V$ signatures of our 28 sample stars, in order to detect the magnetic field and to infer its longitudinal component with high precision (median sigma=40G).

(2 data files). Title: Multidimensional NLTE Radiative Transfer Authors: Léger, L.; Paletou, F.; Navarre, F. Bibcode: 2007sf2a.conf..592L Altcode: We present the main capabilities and performances of a new 2D numerical radiative transfer code (Léger et al. 2007). It treats self-consistently the radiative transfer and the NLTE statistical equilibrium of H. It includes also the possibility of modelling moving 2D structures such as eruptive prominences. Title: Fast 2D non-LTE radiative modelling of prominences. Numerical methods and benchmark results Authors: Léger, L.; Chevallier, L.; Paletou, F. Bibcode: 2007A&A...470....1L Altcode: 2007astro.ph..3689L Context: New high-resolution spectropolarimetric observations of solar prominences require improved radiative modelling capabilities in order to take into account both multi-dimensional - at least 2D - geometry and complex atomic models.
Aims: This makes necessary the use of very fast numerical schemes for the resolution of 2D non-LTE radiative transfer problems considering freestanding and illuminated slabs.
Methods: The implementation of Gauss-Seidel and successive over-relaxation iterative schemes in 2D, together with a multi-grid algorithm, is thoroughly described in the frame of the short characteristics method for the computation of the formal solution of the radiative transfer equation in cartesian geometry.
Results: We propose a new test for multidimensional radiative transfer codes and we also provide original benchmark results for simple 2D multilevel atom cases which should be helpful for the further development of such radiative transfer codes, in general. Title: Differential speckle interferometry: in-depth analysis of the solar photosphere Authors: Grec, C.; Aime, C.; Faurobert, M.; Ricort, G.; Paletou, F. Bibcode: 2007A&A...463.1125G Altcode: Aims:We present the results of an experiment performed at the solar telescope THEMIS in 2002 to measure the depth over which the solar granulation extends in the photosphere.
Methods: Observations made in the 523.3 nm and 557.6 nm photospheric non-magnetic iron lines were correlated with images in the continuum using spectrograms. The difference in depth between the different levels in the photosphere is projected into a difference of position along the slit of the spectrograph, using a perspective effect similar to the well-known Wilson effect for sunspots. This requires measuring displacements, ones much smaller than the telescope resolution. This is made possible by using a differential speckle interferometric technique, cross-correlating images taken in the continuum and the line. The method is not adapted to following displacements of structures in the core of strong lines, due to their difference in shapes with the structures observed in the continuum. In this case, a sequential cross-spectrum method is developed to cross-correlate images taken at close wavelengths.
Results: The raw results are surprising: displacements measured in the blue and the red wings of a line have opposite signs! North and South observations, however, clearly show the expected behavior attributed to a perspective effect. After a description of the observations, we give a first interpretation of the results. The main part of the observed displacement comes from the effect of unresolved Doppler shifts produced by horizontal velocities in the solar photosphere. The perspective effect we seek appears as a second-order term; we find that its amplitude is 2 or 3 times larger than predicted by theoretical 1D models. In the core of strong lines we detect a contrast inversion that also shows up in the cross-correlation function as an anti-correlation peak at line center.
Conclusions: .This first use of the differential speckle interferometry technique on the Sun is quite promising for 3D studies at high spatial resolution. Further observations with very good image quality are needed to take advantage of this new technique.

THEMIS is operated on the Island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias. Title: Fast multilevel radiative transfer Authors: Paletou, Frédéric; Léger, Ludovick Bibcode: 2007JQSRT.103...57P Altcode: 2005astro.ph..7021P The vast majority of recent advances in the field of numerical radiative transfer relies on approximate operator methods better known in astrophysics as Accelerated Lambda-Iteration (ALI). A superior class of iterative schemes, in term of rates of convergence, such as Gauss-Seidel and Successive Overrelaxation methods were therefore quite naturally introduced in the field of radiative transfer by Trujillo Bueno & Fabiani Bendicho (1995); it was thoroughly described for the non-LTE two-level atom case. We describe hereafter in details how such methods can be generalized when dealing with non-LTE unpolarised radiation transfer with multilevel atomic models, in monodimensional geometry. Title: Contrast inversion in the 557.6 nm line detected with differential speckle interferometry Authors: Grec, C.; Aime, C.; Faurobert, M.; Ricort, G.; Paletou, F. Bibcode: 2007MmSAI..78...48G Altcode: We report on some aspects of the use of a Differential speckle interferometry technique on the Sun. The method consists in cross-correlating images of the granulation taken in the line absorption and in the continuum, outside the solar disk center. Due to a perspective effect, the difference in depth between different photospheric levels results in a difference in position along the spectrograph slit. Observations were done in 2002, 2005 and 2006, at the telescope THEMIS in the 557.6 nm iron line. As expected from the perspective effect, we obtain opposite results at opposite latitudes on the Sun disk. Surprisingly, the displacements measured in the blue and the red wings of the line have opposite signs. This may be the result of unresolved Doppler shifts produced by horizontal granular velocity fields. We also detect an anti-correlation peak in the core of strong lines, that is the signature of a contrast inversion. Title: A Spectro-Polarimetric Survey of the Coolest Magnetic Ap Stars Authors: Johnson, N.; Wade, G. A.; Allen, A.; Folsom, C.; Welland, M.; Aurière, M.; Donati, J. -F.; Jeffers, S.; Lignires, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Petit, P.; Toqué, N.; Bagnulo, S.; Landstreet, J. D.; Lüftinger, T.; Ryabchikova, T. Bibcode: 2006ASPC..358..393J Altcode: This article describes the first results of a systematic spectro-polarimetric survey of the coolest magnetic Ap stars, undertaken with the MuSiCoS spectro-polarimeter, with the aim of clarifying the magnetic field and atmospheric characteristics of these enigmatic objects. Title: The surprising magnetic topology of τ Sco: fossil remnant or dynamo output? Authors: Donati, J. -F.; Howarth, I. D.; Jardine, M. M.; Petit, P.; Catala, C.; Landstreet, J. D.; Bouret, J. -C.; Alecian, E.; Barnes, J. R.; Forveille, T.; Paletou, F.; Manset, N. Bibcode: 2006MNRAS.370..629D Altcode: 2006MNRAS.tmp..680D; 2006astro.ph..6156D We report the discovery of a medium-strength (~0.5 kG) magnetic field on the young, massive star τ Sco (B0.2V), which becomes the third-hottest magnetic star known. Circularly polarized Zeeman signatures are clearly detected in observations collected mostly with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada-France-Hawaii Telescope; temporal variability is also clearly established in the polarimetry, and can be unambiguously attributed to rotational modulation with a period close to 41 d. Archival ultraviolet (UV) spectra confirm that this modulation repeats over time-scales of decades, and refine the rotation period to 41.033 +/- 0.002 d.

Despite the slow rotation rate of τ Sco, we none the less succeed in reconstructing the large-scale structure of its magnetic topology. We find that the magnetic structure is unusually complex for a hot star, with significant power in spherical-harmonic modes of degree up to 5. The surface topology is dominated by a potential field, although a moderate toroidal component is probably present. We fail to detect intrinsic temporal variability of the magnetic structure over the 1.5-yr period of our spectropolarimetric observations (in agreement with the stable temporal variations of the UV spectra), and infer that any differential surface rotation must be very small.

The topology of the extended magnetic field that we derive from the photospheric magnetic maps is also more complex than a global dipole, and features in particular a significantly warped torus of closed magnetic loops encircling the star (tilted at about 90° to the rotation axis), with additional, smaller, networks of closed-field lines. This topology appears to be consistent with the exceptional X-ray properties of τ Sco and also provides a natural explanation of the variability observed in wind-formed UV lines. Although we cannot completely rule out the possibility that the field is produced through dynamo processes of an exotic kind, we conclude that its magnetic field is most probably a fossil remnant from the star formation stage.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

E-mail: donati@ast.obs-mip.fr (J-FD); idh@star.ucl.ac.uk (IDH); mmj@st-andrews.ac.uk (MMJ); petit@ast.obs-mip.fr (PP); claude.catala@obspm.fr (CC); jlandstr@uwo.ca (JDL); jean-claude.bouret@oamp.fr (J-CB); evelyne.alecian@obspm.fr (EA); jrb3@st-andrews.ac.uk (JRB); forveill@cfht.hawaii.edu (TF); fpaletou@ast.obs-mip.fr (FP); manset@cfht.hawaii.edu (NM) Title: A search for magnetic fields in the variable HgMn star α Andromedae Authors: Wade, G. A.; Aurière, M.; Bagnulo, S.; Donati, J. -F.; Johnson, N.; Landstreet, J. D.; Lignières, F.; Marsden, S.; Monin, D.; Mouillet, D.; Paletou, F.; Petit, P.; Toqué, N.; Alecian, E.; Folsom, C. Bibcode: 2006A&A...451..293W Altcode: 2006astro.ph..1616W Context: .The chemically peculiar HgMn stars are a class of Bp stars which have historically been found to be both non-magnetic and non-variable. Remarkably, it has recently been demonstrated that the bright, well-studied HgMn star α And exhibits clear Hg ii line profile variations indicative of a non-uniform surface distribution of this element.
Aims: .With this work, we have conducted an extensive search for magnetic fields in the photosphere of α And.
Methods: .We have acquired new circular polarisation spectra with the MuSiCoS and ESPaDOnS spectropolarimeters. We have also obtained FORS1 circular polarisation spectra from the ESO Archive, and considered all previously published magnetic data. This extensive dataset has been used to systematically test for the presence of magnetic fields in the photosphere of α And. We have also examined the high-resolution spectra for line profile variability.
Results: .The polarimetric and magnetic data provide no convincing evidence for photospheric magnetic fields. The highest-S/N phase- and velocity-resolved Stokes V profiles, obtained with ESPaDOnS, allow us to place a 3σ upper limit of about 100 G on the possible presence of any undetected pure dipolar, quadrupolar or octupolar surface magnetic fields (and just 50 G for fields with significant obliquity). We also consider and dismiss the possible existence of more complex fossil and dynamo-generated fields, and discuss the implications of these results for explaining the non-uniform surface distribution of Hg. The very high-quality ESPaDOnS spectra have allowed us to confidently detect variability of Hg ii λ 6149, λ 5425 and λ 5677. The profile variability of the Hg ii lines is strong, and similar to that of the Hg ii λ 3984 line. On the other hand, variability of other lines (e.g. Mn, Fe) is much weaker, and appears to be attributable to orbital modulation, continuum normalisation differences and weak, variable fringing.
Title: Direct detection of a magnetic field in the innermost regions of an accretion disk Authors: Donati, Jean-François; Paletou, Fréderic; Bouvier, Jérome; Ferreira, Jonathan Bibcode: 2005Natur.438..466D Altcode: 2005astro.ph.11695D Models predict that magnetic fields play a crucial role in the physics of astrophysical accretion disks and their associated winds and jets. For example, the rotation of the disk twists around the rotation axis the initially vertical magnetic field, which responds by slowing down the plasma in the disk and by causing it to fall towards the central star. The magnetic energy flux produced in this process points away from the disk, pushing the surface plasma outwards, leading to a wind from the disk and sometimes a collimated jet. But these predictions have hitherto not been supported by observations. Here we report the direct detection of the magnetic field in the core of the protostellar accretion disk FU Orionis. The surface field reaches strengths of about 1kG close to the centre of the disk, and it includes a significant azimuthal component, in good agreement with recent models. But we find that the field is very filamentary and slows down the disk plasma much more than models predict, which may explain why FU Ori fails to collimate its wind into a jet. Title: Large-scale magnetic field of the G8 dwarf ξ Bootis A Authors: Petit, P.; Donati, J. -F.; Aurière, M.; Landstreet, J. D.; Lignières, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Toqué, N.; Wade, G. A. Bibcode: 2005MNRAS.361..837P Altcode: 2005MNRAS.tmp..591P; 2005astro.ph..5438P We investigate the magnetic geometry of the active G8 dwarf ξ Bootis A (ξ Boo A), from spectropolarimetric observations obtained in 2003 with the MuSiCoS échelle spectropolarimeter at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France). We repeatedly detect a photospheric magnetic field, with periodic variations consistent with rotational modulation. Circularly polarized (Stokes V) line profiles present a systematic asymmetry, showing up as an excess in amplitude and area of the blue lobe of the profiles. Direct modelling of Stokes V profiles suggests that the global magnetic field is composed of two main components, with an inclined dipole and a large-scale toroidal field. We derive a dipole intensity of about 40 G, with an inclination of 35° of the dipole with respect to the rotation axis. The toroidal field strength is of the order of 120 G. A noticeable evolution of the field geometry is observed over the 40 nights of our observation window and results in an increase in field strength and dipole inclination.

This study is the first step of a long-term monitoring of ξ Boo A and other active solar-type stars, with the aim of investigating secular fluctuations of stellar magnetic geometries induced by activity cycles. Title: Full Stokes Spectropolarimetry of Hα in Prominences Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.; Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno, J.; Balasubramaniam, K. S. Bibcode: 2005ApJ...621L.145L Altcode: We report on spectropolarimetric observations of Hα in prominences made with the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires and the High Altitude Observatory/Advanced Stokes Polarimeter. Stokes Q and U show the expected profile shape from resonance scattering polarization and the Hanle effect. In contrast, most of the time, Stokes V does not show the antisymmetric profile shape typical of the Zeeman effect but a profile that indicates the presence of strong atomic orientation in the hydrogen levels, to an extent that cannot be explained by invoking the alignment-to-orientation transfer mechanism induced by the prominence magnetic field. We found that the largest signal amplitudes of Stokes V (comparable to that of Stokes Q and U) could be produced by a process of selective absorption of circularly polarized radiation from the photosphere, which requires that the prominence be in the vicinity of an active region. Although recent observations of active region filaments indicate such a selective absorption mechanism as a plausible explanation of the anomalous signals observed, the particular set of conditions that must be met suggest that a different explanation may be required to explain the almost ubiquitous symmetric V signal observed in Hα prominences. Therefore, we speculate that an alternative mechanism inducing strong atomic orientation at the observed level could be due to the presence of electric fields inducing an electric Hanle effect on Hα. Although we are still working toward a careful modeling of this effect, including both electric and magnetic fields, we present some preliminary considerations that seem to support this possibility. Title: Near Infrared Spectropolarimetry from Dome C Authors: Donati, J. -F.; Collier Cameron, A.; Bouvier, J.; Dougados, C.; Ménard, F.; Catala, C.; Petit, P.; Paletou, F.; Pello, R.; Contini, T.; Harries, T. Bibcode: 2005EAS....14..115D Altcode: We discuss in this paper the new science perspectives that a near infrared (NIR) spectropolarimeter installed on a 4m class telescope at Dome C in Antartica would offer to the astrophysics community worldwide, in very diverse research fields such as stellar formation, extra solar planets, stellar magnetism and activity, asteroseismology, circumstellar environments, interstellar medium, galactic and extragalactic physics. We also propose an instrument concept with estimated performances, as well as an example 2-step scenario for the construction of this instrument. Title: Dome C astronomy and astrophysics meeting Authors: Giard, Martin; Casoli, Fabienne; Paletou, Frederic Bibcode: 2005EAS....14.....G Altcode: No abstract at ADS Title: Rotational periods of four roAp stars Authors: Ryabchikova, T.; Wade, G. A.; Aurière, M.; Bagnulo, S.; Donati, J. -F.; Jeffers, S. V.; Johnson, N.; Landstreet, J. D.; Lignières, F.; Lueftinger, T.; Marsden, S.; Mouillet, D.; Paletou, F.; Petit, P.; Reegen, P.; Silvester, J.; Strasser, S.; Toque, N. Bibcode: 2005A&A...429L..55R Altcode: Forty-five new measurements of the mean longitudinal magnetic fields and mean equivalent widths of 4 roAp stars have obtained using the MuSiCoS spectropolarimeter at Pic du Midi observatory. These new high-precision data have been combined with archival measurements in order to constrain the rotational periods of HD 12098, HD 24712 = HR 1217, HD 122970 and HD 176232 = 10 Aql. We report a revised rotational period for HD 24712 (Prot = 12.45877 ± 0.00016 d, crucial for interpretation of upcoming MOST observations of this star), new rotational periods for HD 12098 and HD 122970 (Prot=5.460 ± 0.001 d and Prot=3.877 ± 0.001 d, respectively) and evidence for an extremely long period for HD 176232.

Table 1 is only available in electonic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / / cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/L55 Title: A spectropolarimetric survey of the coolest magnetic Ap stars Authors: Johnson, N.; Wade, G. A.; Aurière, M.; Donati, J. -F.; Lignires, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Toqué, N.; Petit, P.; Bagnulo, S.; Landstreet, J. D.; Lüftinger, T. Bibcode: 2004IAUS..224..599J Altcode: We describe the first results of a systematic spectropolarimetric survey of the coolest magnetic Ap stars, undertaken with the MuSiCoS spectropolarimeter, with the aim of clarifying the magnetic field and atmospheric characteristics of these enigmatic objects. Title: A survey of the weakest-field magnetic Ap stars: discovery of a threshold magnetic field strength? Authors: Aurière, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati, J. -F.; Johnson, N.; Lignières, F.; Landstreet, J. D.; Lüftinger, T.; Mouillet, D.; Paletou, F.; Petit, P.; Strasser, S. Bibcode: 2004IAUS..224..633A Altcode: We are conducting a magnetic survey of a sample of about 30 spectroscopically identified Ap stars, with weak or previously undetected magnetic fields. For 28 studied stars, we have obtained 25 detections of Stokes V Zeeman signatures. Our results suggest that all Ap stars are magnetic. Further there may exist a minimum field strength for which Ap-type characteristics are produced. Title: Exact vs. Gauss-Seidel numerical solutions of the non-LTE radiation transfer problem Authors: Quang, Carine; Paletou, Frédéric; Chevallier, Loïc Bibcode: 2004sf2a.conf..317Q Altcode: 2006astro.ph..1462Q; 2004sf2a.confE.322Q Although published in 1995 (Trujillo Bueno & Fabiani Bendicho, ApJ 455, 646), the Gauss-Seidel method for solving the non-LTE radiative transfer problem has deserved too little attention in the astrophysical community yet. Further tests of the performances and of the accuracy of the numerical scheme are provided. Title: A survey of Ap stars for weak longitudinal magnetic fields Authors: Auriere, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati, J. F.; Johnson, N.; Landstreet, J. D.; Lignieres, F.; Lueftinger, T.; Mouillet, M.; Paletou, F.; Petit, P.; Strasser, S. Bibcode: 2004mast.conf..114A Altcode: We are conducting a magnetic survey of a sample of about 30 spectroscopically-identified Ap stars (selected from the HD catalogue), but with faint or previously undetected magnetic fields. We use the MuSiCoS spectropolarimeter at Telescope Bernard Lyot (Pic du Midi Observatory, France) and the cross-correlation technique Least Squares Deconvolution (LSD; Donati et al. 1997). For 24 studied stars, we have obtained 21 detections of Stokes V Zeeman signatures (data quality and phase coverage may explain our lack of detection of any field in some objects). Our results suggest that all Ap stars are magnetic and, furthermore, that there may exist a minimum field strength for which Ap-type characteristics are produced. Title: No weak magnetic field detected in the variable HgMn star α Andromedae Authors: Wade, G. A.; Abecassis, M.; Auriere, M.; Donati, J. -F.; Ligneres, F.; Marsden, S.; Mouillet, D.; Paletou, F.; Petit, P.; Toque, N.; Monin, D.; Landstreet, J. D.; Bagnulo, S.; Luftinger, T. Bibcode: 2004mast.conf..108W Altcode: High-S/N, phase-distributed circular polarisation spectra of the variable HgMn star α And provide no evidence of any photospheric magnetic field, with an upper limit for oblique dipolar fields of 280 G (approximately the equipartition field at log τ5000 = 0.0). We therefore propose that the variability of the Hg λ3984 line and the inferred nonuniform distribution of Hg (reported by Adelman et al. 2002) most plausibly result from a separation mechanism unrelated to the presence of a magnetic field. Title: Photospheric magnetic field and surface differential rotation of the FK Com star HD 199178 Authors: Petit, P.; Donati, J. -F.; Oliveira, J. M.; Aurière, M.; Bagnulo, S.; Landstreet, J. D.; Lignières, F.; Lüftinger, T.; Marsden, S.; Mouillet, D.; Paletou, F.; Strasser, S.; Toqué, N.; Wade, G. A. Bibcode: 2004MNRAS.351..826P Altcode: 2004astro.ph..3284P We present spectropolarimetric observations of the FK Com star HD 199178 obtained between 1998 December and 2003 August at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France). We report the detection of a photospheric magnetic field and reconstruct its distribution by means of Zeeman-Doppler imaging. We observe large regions where the magnetic field is mainly azimuthal, suggesting that the dynamo processes generating the magnetic activity of HD 199178 may be active very close to the stellar surface. We investigate the rapid evolution of surface brightness and magnetic structures from a continuous monitoring of the star over several weeks in 2002 and 2003. We report that significant changes occur in the distribution of cool-spots and magnetic regions on typical time-scales of the order of two weeks. Our spectropolarimetric observations also suggest that the surface of HD 199178 is sheared by differential rotation, with a difference in rotation rate between equatorial and polar regions of the order of 1.5 times that of the Sun. Title: Surface Differential Rotation of Evolved Fast Rotators Authors: Petit, P.; Donati, J. -F.; MUSICOS Collaboration; Wade, G. A.; Landstreet, J. D.; Sigut, T. A. A.; Shorlin, S. L. S.; Bagnulo, S.; Lüftinger, T.; Strasser, S.; Oliveira, J. M.; Aurière, M.; Lignières, F.; Mouillet, D.; Paletou, F. Bibcode: 2004IAUS..215..294P Altcode: No abstract at ADS Title: On the accuracy of the ALI method for solving the radiative transfer equation Authors: Chevallier, L.; Paletou, F.; Rutily, B. Bibcode: 2003A&A...411..221C Altcode: 2006astro.ph..1341C We solve the integral equation describing the propagation of light in an isothermal plane-parallel atmosphere of optical thickness tau *, adopting a uniform thermalization parameter epsilon . The solution given by the ALI method, widely used in the field of stellar atmosphere modelling, is compared to the exact solution. Graphs are given that illustrate the accuracy of the ALI solution as a function of the parameters epsilon , tau * and optical depth variable tau . Title: Escape probability methods versus ``exact" transfer for modelling the X-ray spectrum of Active Galactic Nuclei and X-ray binaries Authors: Dumont, A. -M.; Collin, S.; Paletou, F.; Coupé, S.; Godet, O.; Pelat, D. Bibcode: 2003A&A...407...13D Altcode: 2003astro.ph..6297D In the era of XMM-Newton and Chandra missions, it is crucial to use codes able to compute correctly the line spectrum of X-ray irradiated thick media (Thomson thickness of the order of unity), in order to build models for the structure and the emission of the central regions of Active Galactic Nuclei (AGN), or of X-ray binaries. In all photoionized codes except in our code Titan, the line intensities are computed with the so-called ``escape probability approximation". In its last version, Titan solves the transfer of a thousand lines and of the continuum with the ``Accelerated Lambda Iteration" method, which is one of the most efficient and at the same time the most secure for line transfer. We first review the escape probability formalism and mention various reasons why it should lead to wrong results concerning the line fluxes. Then we check several approximations commonly used instead of line transfer in photoionization codes, by comparing them to the full transfer computation. We find that for conditions typical of the AGN or X-ray binary emission medium, all approximations lead to an overestimation of the emitted X-ray line spectrum, which can reach more than one order of magnitude. We show that it is due mainly to the local treatment of line photons, implying a delicate balance between excitations of X-ray transitions by the very intense underlying diffuse X-ray continuum (which are not taken properly into account in escape probability approximations) and the net rate of excitations by the diffuse line flux. The most affected lines are those in the soft X-ray range. Such processes are much less important in cooler and thinner media (like the Broad Line Region of AGN), as the most intense lines lie in the optical and near ultraviolet range where the diffuse continuum is small. We conclude that it is very important to treat correctly the transfer of the continuum to get the best results for the line spectrum. On the other hand the approximations used for the escape probabilities have a relatively small influence on the computed thermal and ionization structure of the surface layers, but in the deep layers, they lead to an overestimation of the ionization state. As a consequence the computed continuum emitted by the back (non-irradiated) side is not correct, and might be strongly overestimated in the EUV range. Title: A survey of magnetic Ap/Bp stars for weak longitudinal magnetic fields Authors: Auriere, M.; Silvester, J.; Wade, G. A.; Bagnulo, S.; Donati, J. -F.; Johnson, N.; Landstreet, J. D.; Ligneres, F.; Lueftinger, T.; Mouillet, D.; Paletou, F.; Petit, P.; Strasser, S. Bibcode: 2003APN....39.....A Altcode: We describe an ongoing observational programme, using the MuSiCoS spectropolarimeter at Pic du Midi Observatory, aimed at detecting the weakest magnetic fields of Ap/Bp stars. For the 21 stars observed up to now, we have obtained 19 detections of Stokes V Zeeman signatures. This remarkable detection rate strongly suggests that all Ap stars having "magnetic" behaviour (Preston 1974; i.e. essentially all stars classified spectroscopically as Ap/Bp) actually harbour magnetic fields. In other words, all Ap stars appear to be observably magnetic.

For some of our stars with sufficient measurements and suitable phase sampling, dipolar oblique rotator models have been determined. Although results are preliminary, we find that magnetic geometry or rotational phase variations can explain the apparent faintness of the measured fields, and that the dipole strength for this small sample is at least several hundred G. In other words, at present we find no evidence for inferred dipolar surface fields weaker than a few hundred G in any Ap star. As suggested by Glagolevskij & Chountonov (2002), this result may indicate that there is a minimum field strength for which Ap-type characteristics are produced. This minimum strength appears to be of order the photospheric equipartition field (around 230 G for a main sequence A0 star). Title: Spectropolarimetry of Solar Prominences Authors: Paletou, F.; Aulanier, G. Bibcode: 2003ASPC..307..458P Altcode: No abstract at ADS Title: On the Need of High-Resolution Spectropolarimetric Observations of Prominences Authors: Paletou, F.; Aulanier, G. Bibcode: 2003ASPC..286...45P Altcode: 2003ctmf.conf...45P No abstract at ADS Title: The accuracy of the ALI method for solving the radiative transfer equation in stellar atmospheres Authors: Chevallier, L.; Paletou, F.; Rutily, B. Bibcode: 2003sf2a.conf..581C Altcode: 2006astro.ph..1460C; 2003sf2a.confE.240C We test the accuracy of the ALI method, widely used in stellar atmospheres modelling, by solving exactly a standard radiative transfer problem in plane-parallel geometry. Some recommendations are given for a practical use of this method in stellar atmospheres numerical codes. Title: Caution! Modelling the X-ray spectrum of AGN and X-ray binaries is not simple: Escape probabilities versus transfer computations Authors: Dumont, A. -M.; Collin, S.; Paletou, F.; Coupé, S.; Godet, O.; Pelat, D. Bibcode: 2003sf2a.conf..475D Altcode: 2003sf2a.confE.203D We compare different escape probability approximations commonly used for the line transfer in photoionisation codes, with a full transfer computation performed with the Accelerated Lambda Iteration method (ALI), using our code Titan specially designed for thick hot media. For a case typical of the UV-X emitting region in AGN or in X-ray binaries, we show that the emitted line intensities in the X-ray range are generally overestimated by the approximation procedures, sometimes by up to one order of magnitude. This is a strong problem at the era of XMM and Chandra missions which allow observing detailed X-ray features, used to deduce the physical conditions of the emission/absorbing regions. Title: The Advanced Technology Solar Telescope Authors: Paletou, F.; López Ariste, A.; Meunier, N.; Molodij, G. Bibcode: 2003sf2a.conf...97P Altcode: 2003sf2a.confE..30L The Advanced Technology Solar Telescope (ATST) is a 4-m aperture solar telescope project lead by the NSO and supported by all major solar US research institutes. Also a European initiative gathering 17 countries, so far, is currently being prepared in support of the project. ATST, intended for first light in 2010, will provide the high-angular resolution required for nowadays photospheric studies; but its large aperture and controlled scattered-light design makes it also a very promising tool for high sensitivity spectropolarimetric observations needed throughout the whole solar atmosphere up to the corona, and in spectral windows ranging from the visible to the thermal infrared. Title: Full-Stokes spectropolarimetry of solar prominences Authors: Paletou, F.; López Ariste, A.; Bommier, V.; Semel, M. Bibcode: 2001A&A...375L..39P Altcode: We report on first spectropolarimetric observations of solar prominences made at THEMIS. Hereafter we shall emphasis on the preliminary analysis of He I D3 full-Stokes observations. Our measurements clearly show manifestations of both the Hanle and Zeeman effects. More generally, we demonstrate the very favourable performances of the THEMIS multi-line spectropolarimetric mode for further new investigations of the magnetic field in solar prominences. Based on observations made at THEMIS, operated on the Island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias. Title: THÉMIS Observations of the Second Solar Spectrum Authors: Trujillo Bueno, J.; Collados, M.; Paletou, F.; Molodij, G. Bibcode: 2001ASPC..236..141T Altcode: 2001aspt.conf..141T No abstract at ADS Title: Scattering Induced Polarization and Hanle Effect Observations with THEMIS Authors: Arnaud, J.; Faurobert, M.; Vigneau, J.; Paletou, F. Bibcode: 2001ASPC..248...93A Altcode: 2001mfah.conf...93A No abstract at ADS Title: Transfert de rayonnement : méthodes itératives Authors: Paletou, F. Bibcode: 2001CRPhy...2..885P Altcode: Dans cet article, je décrirai diverses méthodes permettant de résoudre des problèmes de transfert de rayonnement considérant successivement l'atome à deux niveaux, puis les effets de redistribution partielle en fréquence, l'atome à plusieurs niveaux et, enfin, la polarisation du rayonnement. La méthode numérique dite ALI (pour Accelerated Lambda-Iteration) est le dénominateur commun à toutes ces méthodes. Title: THEMIS Multi-Line Spectropolarimetry Authors: Paletou, F.; Molodij, G. Bibcode: 2001ASPC..248..617P Altcode: 2001mfah.conf..617P No abstract at ADS Title: Scattering Polarization Measurements with THÉMIS Authors: Arnaud, J.; Vigneau, J.; Faurobert, M.; Paletou, F. Bibcode: 2001ASPC..236..151A Altcode: 2001aspt.conf..151A No abstract at ADS Title: Multi-line Spectropolarimetry at THÉMIS Authors: Paletou, F.; Molodij, G. Bibcode: 2001ASPC..236....9P Altcode: 2001aspt.conf....9P No abstract at ADS Title: An Operator Perturbation Method of Polarized Line Transfer V. Diagnosis of Solar Weak Magnetic Fields Authors: Nagendra, K. N.; Frisch, H.; Faurobeet-Scholl, M.; Paletou, F. Bibcode: 2000JApA...21..255N Altcode: No abstract at ADS Title: Observations à haute sensibilité polarimétrique à THEMIS Authors: Paletou, F.; Molodij, G. Bibcode: 2000CRPhy...1.1309P Altcode: 2000CRAS....1.1309P Une observation effectuée le 7 Avril 2000 nous a permis de mesurer avec une grande précision la polarisation linéaire dans la raie D2 de NaI observée près du bord solaire. Ceci nous permet de démontrer le très grand potentiel de performance du télescope solaire THEMIS en matière de mesure de signaux de polarisation faibles. Title: An operator perturbation method for polarized line transfer IV: Applications to the Hanle effect with partial frequency redistribution Authors: Nagendra, K. N.; Paletou, F.; Frisch, H.; Faurobert-Scholl, M. Bibcode: 1999ASSL..243..127N Altcode: 1999sopo.conf..127N No abstract at ADS Title: Polarized radiation transfer in 2D geometry Authors: Paletou, F.; Bommier, V.; Faurobert-Scholl, M. Bibcode: 1999ASSL..243..189P Altcode: 1999sopo.conf..189P No abstract at ADS Title: Polarized redistribution matrix for Hanle effect: Numerical tests Authors: Faurobert-Scholl, M.; Paletou, F.; Bommier, V. Bibcode: 1999ASSL..243..115F Altcode: 1999sopo.conf..115F No abstract at ADS Title: On the Bright Rims of H-alpha Filaments Authors: Paletou, F. Bibcode: 1998ASPC..150...70P Altcode: 1998IAUCo.167...70P; 1998npsp.conf...70P No abstract at ADS Title: An operator perturbation method for polarized line transfer. II. Resonance polarization with partial frequency redistribution effects Authors: Paletou, Frederic; Faurobert-Scholl, Marianne Bibcode: 1997A&A...328..343P Altcode: The effects of partial frequency redistribution are implemented in the Polarized Accelerated Lambda Iteration (PALI) method of Faurobert-Scholl et al. (1997). The numerical scheme is an extension of the core-wing technique of Paletou & Auer (1995) originally developed for non-polarized line transfer problems. Using a new code, we validate theoretical results against those given by a Feautrier type code. Title: On Hα source function vertical variations in filaments and bright rims visibility. Authors: Paletou, F. Bibcode: 1997A&A...317..244P Altcode: Using new radiative modelling capabilities in two-dimensional (2D) cartesian geometry, we investigate the vertical variations of the Hα source function in filaments. It is shown how the two-dimensional geometry can affect the transfer of the Hα line into filaments and, consequently, how assumptions on the geometry of the model may influence a further interpretation of observations. A special attention is paid to the possibility of formation of a bright rim inside the filament body by diffusive penetration of Hα radiation. Unlike recently proposed by Heinzel et al. (1995SoPh..160...19H), we can see from our 2D computations that the observable emergent intensities are not high enough to explain bright rims contrasts. Title: A note on improved computations of solar prominences: 2D radiative models. Authors: Paletou, F. Bibcode: 1996A&A...311..708P Altcode: We report on improved computations concerning two-dimensional (2D) radiative modelling of solar prominences. This report mainly concerns a more correct definition of the bound-free radiative rates (incident radiation and dilution factor). As a consequence, the difference (at a given height) between the Hα line integrated intensity computed respectively in 1D and 2D geometries is found to be less important than what was previously presented (Paletou 1995). Title: Transfert de rayonnement hors-ETL et applications en physique solaire. Authors: Faurobert-Scholl, M.; Paletou, F.; Frisch, H. Bibcode: 1996JAF....53...24F Altcode: No abstract at ADS Title: Two-dimensional multilevel radiative transfer with standard partial frequency redistribution in isolated solar atmospheric structures. Authors: Paletou, F. Bibcode: 1995A&A...302..587P Altcode: We have implemented standard partial frequency redistribution (PRD) in a two-dimensional multilevel non-LTE radiative transfer code. The Multilevel Accelerated Lambda Iteration (MALI) method is used. First, a numerical approach for treating standard PRD effects is described, as well as a simple method for treating an optically thick bound-free transition with MALI. Then, the method is validated in mono-dimensional geometry. Finally, preliminary results from two-dimensional radiative modelling of solar prominences are presented. Title: A new approximate operator method for partial frequency redistribution problems. Authors: Paletou, F.; Auer, L. H. Bibcode: 1995A&A...297..771P Altcode: Methods for the solution of non-lte partial frequency redistribution (prd) radiative transfer problems are presented. By explicitly treating the partial frequency coherence, convergence difficulties caused by using a Complete Redistribution Approximation are completely overcome. A new core-wing treatment of the redistribution both avoids the explicit solution of the frequency coupled system, and permits the use of simple Approximate Operator Iteration to solve prd problems extremely efficiently. Title: Two-dimensional radiative transfer with partial frequency redistribution I. General method Authors: Auer, L. H.; Paletou, F. Bibcode: 1994A&A...285..675A Altcode: We present a new method for the solution of non-LTE scattering problems in two dimensions. It is based on Accelerated Lambda Iteration and an improved short characteristic method. It is more than an order of magnitude faster than a direct approach for Complete Redistribution. We, further, have extended the method to the solution of Partial Redistribution problems. The computational cost of treating PRD with the new method is only a small factor larger than CRD. Results with the new iterative approach are in complete agreement with previously published results. Title: Two-dimensional radiative transfer with partial frequency redistribution. II. Application to resonance lines in quiescent prominences Authors: Paletou, F.; Vial, J. -C.; Auer, L. H. Bibcode: 1993A&A...274..571P Altcode: Theoretical emergent profiles in the resonance lines of H I Lyman α, Mg II h & k and Ca II H & K formed in quiescent prominences are presented. Both partial frequency redistribution effects and two-dimensional structure have been included in the calculations. The prominence model consists of a static, isobaric and isothermal freestanding slab irradiated by realistic chromospheric profiles (080-8 observations). We compare the differences between complete (CRD) and partial frequency redistribution (PRD). Vertical variations in the emergent profiles are displayed, and the importance of the geometrical effects is discussed. In addition, we have evaluated both emergent profiles for a filament as seen over the disk, and the back-scattered radiation towards the chromosphere. Title: Radiative modeling of solar prominences, two-dimensional transfer plus partial frequency redistribution. Authors: Paletou, F.; Vial, Jean-Claude; Auer, L. H. Bibcode: 1992ESASP.348..225P Altcode: 1992cscl.work..225P The two-dimensional, PRD radiative transfer code of Auer and Paletou (1992) has been used to compute the resonance lines of H I, Mg II and Ca II in quiescent prominences, which are modeled as isothermal freestanding slabs illuminated from the sides as well as from below. Partial redistribution (PRD) and 2D effects are evidenced and compared to complete redistribution computations for both 1D and 2D geometries. Important edge variations are fround at the bottom and the top that should be observed with a spatial resolution of one arcsecond. As in 1D, PRD effects allow for greater penetration of the incident radiation into the layer. The 2D code computes both the radial emergent intensity and the amount of radiation backscattered into the chromosphere. It can, accordingly, be used to estimate the visibility of filaments. It will be of special interest to build non-isothermal models and compare e.g. the Lyα profiles with the SUMER/SOHO observations.