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Author name code: paletou
ADS astronomy entries on 2022-09-14
author:"Paletou, Frederic"
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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.
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.
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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.
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.
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Title: Deep learning application for stellar parameters determination:
I-constraining the hyperparameters
Authors: Gebran, Marwan; Connick, Kathleen; Farhat, Hikmat; Paletou,
Frédéric; Bentley, Ian
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: T<SUB>eff</SUB>, log g, [M/H],
and v<SUB>e</SUB>sin 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.
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Title: The use of Deep Learning in stellar classification
Authors: Connick, Kathleen; Gebran, Marwan; Paletou, Frédéric
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.
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Title: VizieR Online Data Catalog: ESPaDOnS and NARVAL
spectropolarimeters (IRAP) (Petit P., 2021)
Authors: Petit, P.; Paletou, F.; Mathias, P.; Glorian, Jm.; Amato, A.
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. <P />(1 data file).
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Title: Full non-LTE spectral line formation. I. Setting the stage
Authors: Paletou, F.; Peymirat, C.
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.
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Title: An adaptive Gaussian quadrature for the Voigt function
Authors: Paletou, F.; Peymirat, C.; Anterrieu, E.; Böhm, T.
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.
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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.
2019yCat..51580056H Altcode:
Observations of (R-I)<SUB>C</SUB> (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)<SUB>C</SUB> 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). <P />(3 data files).
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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.
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)<SUB> C </SUB>) and effective temperatures have been
well established for a long time. The more recent (R - I)<SUB> C
</SUB> color-T <SUB>eff</SUB> 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 <SUB>eff</SUB> relative
to the (R - I)<SUB> C </SUB>-T <SUB>eff</SUB> 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)<SUB> C </SUB>
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)<SUB> C </SUB> color-T
<SUB>eff</SUB> from B12 and M15 data. We also compiled T <SUB>eff</SUB>
and metallicity measurements available in the literature using the
VizieR database. We determine T <SUB>eff</SUB> for 441 stars with
previously unknown effective temperatures. We also identified 21 new
spectroscopic binaries and one triple system from our high-resolution
spectra. <P />Based on Gaia DR2 and Hipparcos parallax measurements.
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Title: Sliced Inverse Regression: application to fundamental stellar
parameters
Authors: Kassounian, Sarkis; Gebran, Marwan; Paletou, Frédéric;
Watson, Victor
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:
T<SUB>eff</SUB>., log g, [M/H] and v sin i. Different learning databases
were calculated using a range of sampling in T<SUB>eff</SUB>., 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.
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Title: Toulouse 2D numerical radiative transfer codes
Authors: Paletou, F.; Léger, L.; Chane-Yook, M.; Auer, L. H.
2019arXiv190305971P Altcode:
A tutorial associated with the distribution of 2D non-LTE multilevel
atom radiative transfer codes.
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Title: Deep learning determination of stellar atmospheric fundamental
parameters
Authors: Kou, R.; Petit, P.; Paletou, F.; Kulenthirarajah, L.; Glorian,
J. -M.
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.
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Title: On Milne-Barbier-Unsöld relationships
Authors: Paletou, Frédéric
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.
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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.
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). <P />(6 data files).
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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.
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). <P />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). <P />(7 data files).
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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.
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.
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Title: Sliced Inverse Regression for the inference of stellar
fundamental parameters
Authors: Watson, V.; Trouilhet, JF.; Paletou, F.; Gebran, M.
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.
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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.
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}<SUB>{HK</SUB>}<SUP>\prime </SUP>
as a function of the Rossby number R <SUB>0</SUB>. We find (I) for
dK4 stars, {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> as a function of R
<SUB>0</SUB> agrees well with previous results for F-G-K stars and
(II) in dK6, dM2, dM3, and dM4 stars, at a given R <SUB>0</SUB>, the
values of {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> 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 <SUB>X</SUB>/L <SUB>HK</SUB>
increases by a factor of 100 between dK4 and dM4 stars. <P />Based
on observations available at Observatoire de Haute Provence and the
European Southern Observatory databases and on Hipparcos parallax
measurements.
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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.
2016A&A...591A.119A Altcode: 2016arXiv160504702A
Context. <ASTROBJ>Betelgeuse</ASTROBJ> is an M supergiant that
harbors spots and giant granules at its surface and presents linear
polarization of its continuum. <BR /> 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 <ASTROBJ>Betelgeuse</ASTROBJ>. <BR /> 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. <BR /> Results: We have discovered the existence
of a linearly polarized spectrum for <ASTROBJ>Betelgeuse</ASTROBJ>,
detecting a rather strong signal (at a few times 10<SUP>-4</SUP>
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 <ASTROBJ>Betelgeuse</ASTROBJ>. 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 <ASTROBJ>Betelgeuse</ASTROBJ> obtained
over a period of 1.4 yr to study the evolution of the spots and of the
atmosphere. <BR /> Conclusions: Our study of the linearly polarized
spectrum of <ASTROBJ>Betelgeuse</ASTROBJ> 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. <P />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.
2016A&A...589A..83G Altcode: 2016arXiv160301146G
Context. We present an automated procedure that simultaneously derives
the effective temperature T<SUB>eff</SUB>, 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 . <BR /> 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. <BR /> Methods: Using three data sets
at resolving powers of R = 42 000, 65 000 and 76 000, about ~6.6 ×
10<SUP>6</SUP> 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. <BR /> 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 T<SUB>eff</SUB>, [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<SUP>-1</SUP> were found for T<SUB>eff</SUB>, log g, [Fe/H],
and vsini with respect to literature values for A-type stars. <BR />
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. <P
/>Based on data retrieved from the Polarbase, SOPHIE, and ELODIE
archives.Table 2 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A83">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A83</A>
---------------------------------------------------------
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.
2016ApJ...822...97H Altcode: 2016arXiv160407920H
The reliable determination of rotation-activity correlations (RACs)
depends on precise measurements of the following stellar parameters:
T <SUB>eff</SUB>, 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)<SUB> C </SUB> 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 <SUB>eff</SUB>, 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. <P />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.
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) <P />(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
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.
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.
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.
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. <P />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.
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. <BR />
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. <BR /> 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 T<SUB>eff</SUB> = 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). <BR /> 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<SUP>-4</SUP>. 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. <BR /> 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. <P />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.
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). <P />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. <P />(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.
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. <P />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.
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.
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. <P />(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.
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.
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
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.
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
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<SUP>-1</SUP>. Several spectra have been taken for lines of the
R branches of the F ^4Δ<SUB>7/2</SUB>←X ^4Δ<SUB>7/2</SUB> and F
^4Δ<SUB>5/2</SUB>←X ^4Δ<SUB>5/2</SUB> 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. <P />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. <P />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.
2012A&A...540A.138M Altcode: 2011arXiv1109.5066M
<BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP>. <P />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 <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Laboratory determination of Landé factors for the molecular
radical FeH
Authors: Crozet, P.; Tourasse, G.; Ross, A.; Paletou, F.; López
Ariste, A.
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.
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.
2011A&A...532L..13P Altcode: 2011arXiv1106.5363P
<BR /> 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. <BR /> 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. <BR /> 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. <BR />
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. <P />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.
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. <P />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.
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.
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
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.
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). <P />(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.
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. <P />(2 data files).
---------------------------------------------------------
Title: A conjugate gradient method for solving the non-LTE line
radiation transfer problem
Authors: Paletou, F.; Anterrieu, E.
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.
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.
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 (D<SUB>3</SUB>) 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<SUP>-3</SUP> 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.
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.
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.
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.
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.
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. <BR />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. <BR />Methods: We apply our 2D non-LTE radiative transfer
code, which is based on the multi-grid Gauss-Seidel/SOR iterative
schemes. <BR />Results: It allows us to compute realistic emergent
intensity profiles for the He i λ 10 830 Å and D<SUB>3</SUB>
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.
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.
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.
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.
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). <P
/>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. <P />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. <P
/>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. <P
/>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.
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. <P />This paper
focuses on five stars of spectral type ~M4, i.e. with masses close
to the full convection threshold (~=0.35M<SUB>solar</SUB>), 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. <P
/>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. <P />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. <P
/>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.
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. <P />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.
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. <P />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. <P />Preliminary modelling
suggests that the magnetosphere of BP Tau extends to distances of at
least 4R<SUB>*</SUB> 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. <P />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. <P
/>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.
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.
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. <BR />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). <BR />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. <P />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.
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.
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.
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.
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.
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. <P />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. <P
/>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<SUB>*</SUB> 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. <P />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. <P />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.
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). <P
/>(2 data files).
---------------------------------------------------------
Title: Multidimensional NLTE Radiative Transfer
Authors: Léger, L.; Paletou, F.; Navarre, F.
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.
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. <BR />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. <BR />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. <BR />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.
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. <BR />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. <BR />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. <BR />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. <P />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
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.
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.
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.
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. <P />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. <P />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. <P />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. <P />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.
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.<BR /> Aims: .With this work, we have conducted an
extensive search for magnetic fields in the photosphere of α And.<BR />
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.<BR /> 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.<BR />
---------------------------------------------------------
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
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.
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. <P
/>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.
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.
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
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.
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 (P<SUB>rot</SUB> = 12.45877 ±
0.00016 d, crucial for interpretation of upcoming MOST observations
of this star), new rotational periods for HD 12098 and HD 122970
(P<SUB>rot</SUB>=5.460 ± 0.001 d and P<SUB>rot</SUB>=3.877 ± 0.001
d, respectively) and evidence for an extremely long period for HD
176232. <P />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.
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.
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
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.
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.
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 τ<SUB>5000</SUB> =
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.
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.
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.
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
<SUP>*</SUP>, 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 <SUP>*</SUP> 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.
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.
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. <P />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.
2003ASPC..307..458P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Need of High-Resolution Spectropolarimetric Observations
of Prominences
Authors: Paletou, F.; Aulanier, G.
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.
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.
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.
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.
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 D<SUB>3</SUB> 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.
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.
2001ASPC..248...93A Altcode: 2001mfah.conf...93A
No abstract at ADS
---------------------------------------------------------
Title: Transfert de rayonnement : méthodes itératives
Authors: Paletou, F.
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.
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.
2001ASPC..236..151A Altcode: 2001aspt.conf..151A
No abstract at ADS
---------------------------------------------------------
Title: Multi-line Spectropolarimetry at THÉMIS
Authors: Paletou, F.; Molodij, G.
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.
2000JApA...21..255N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations à haute sensibilité polarimétrique à THEMIS
Authors: Paletou, F.; Molodij, G.
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.
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.
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.
1999ASSL..243..115F Altcode: 1999sopo.conf..115F
No abstract at ADS
---------------------------------------------------------
Title: On the Bright Rims of H-alpha Filaments
Authors: Paletou, F.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
