roudier

explanation blue bibcodes open ADS page with paths to full text

Author name code: roudier
ADS astronomy entries on 2022-09-14
author:"Roudier, Thierry"

---------------------------------------------------------
Title: A Comparative Study of Measurements of the Suns Axisymmetric
Flows: A COFFIES Effort
Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant;
Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger;
Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber,
Shea; Hoeksema, J.
2021AGUFMSH55D1871U Altcode:
Consequence Of Fields and Flows in the Interior and Exterior of
the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC),
with the primary objective of developing a data driven model of
solar activity. One of COFFIES five primary science questions is
What drives varying large-scale motions in the Sun? To address this
question, we are developing a comprehensive catalog of the variable
differential rotation and meridional circulation flow patterns. This
catalog includes measurements of these flows as obtained by several
measurement techniques: Doppler imaging, granule tracking, magnetic
pattern tracking, magnetic feature tracking, as well as both time
distance and ring diagram helioseismology. We show a comparison of
these flows across these varied techniques, with a particular focus
on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We
investigate the uncertainties and attempt to reconcile any discrepancies
(e.g., due to flow depth or systematics associated with the different
measurement techniques). This analysis will pave the way toward
accurately determining the global patterns of axisymmetric flows and
their regular and irregular variations during the cycle.

---------------------------------------------------------
Title: One-sided arc averaging geometries in time-distance local
helioseismology
Authors: Korda, David; Švanda, Michal; Roudier, Thierry
2021A&A...654A..84K Altcode: 2021arXiv210800872K
Context. The study of solar oscillations (helioseismology) has been a
very successful method of researching the Sun. Helioseismology teaches
us about the structure and mean properties of the Sun. Together
with mid-resolution data, the local properties were uncovered in
quiet-Sun regions. However, magnetic fields affect the oscillations
and prevent us from studying the properties of magnetically active
regions with helioseismology. Aims: We aim to create a new
methodology to suppress the negative effects of magnetic fields on
solar oscillations and measure plasma properties close to active
regions. Methods: The methodology consists of new averaging
geometries, a non-linear approach to travel-time measurements, and a
consistent inversion method that combines plasma flows and sound-speed
perturbations. Results: We constructed the one-sided arc
averaging geometries and applied them to the non-linear approach
of travel-time measurements. Using the one-sided arc travel times,
we reconstructed the annulus travel times in a quiet-Sun region. We
tested the methodology against the validated helioseismic inversion
pipeline. We applied the new methodology for an inversion for surface
horizontal flows in a region with a circular H-type sunspot. The
inverted surface horizontal flows are comparable with the output of
the coherent structure tracking, which is not strongly affected by
the presence of the magnetic field. We show that the new methodology
suppresses the negative effects of magnetic fields up to outer
penumbra. We measure divergent flows with properties comparable to
the moat flow. Conclusions: The new methodology can teach us
about the depth structure of active regions and physical conditions
that contribute to the evolution of the active regions.

---------------------------------------------------------
Title: Changes in granulation scales over the solar cycle seen with
SDO/HMI and Hinode/SOT
Authors: Ballot, J.; Roudier, T.; Malherbe, J. M.; Frank, Z.
2021A&A...652A.103B Altcode: 2021arXiv210603556B
Context. The Sun is the only star where the superficial turbulent
convection can be observed at very high spatial resolution. The
Solar Dynamics Observatory (SDO) has continuously observed the full
Sun from space with multi-wavelength filters since July 2010. In
particular, the Helioseismic and Magnetic Imager (HMI) instrument
takes high-cadence frames (45 s) of continuum intensity in which
solar granulation is visible. Aims: We aimed to follow the
evolution of the solar granules over an activity cycle and look for
changes in their spatial properties. Methods: We investigated
the density of granules and their mean area derived directly from
the segmentation of deconvolved images from SDO/HMI. To perform the
segmentation, we define granules as convex elements of images. Results: We measured an approximately 2% variation in the density
and the mean area of granules over the cycle, the density of granules
being greater at solar maximum with a smaller granule mean area. The
maximum density appears to be delayed by about one year compared
to classical activity indicators, such as the sunspot number. We
complemented this study with high-spatial-resolution observations
obtained with Hinode/SOTBFI (Solar Optical Telescope Broadband Filter
Imager), which are consistent with our results. Conclusions:
The observed variations in solar granulation at the disc centre reveal
a direct insight into the change in the physical properties that occur
in the upper convective zone during a solar cycle. These variations
can be due to interactions between convection and magnetic fields,
either at the global scale or, locally, at the granulation scale.

---------------------------------------------------------
Title: Photospheric downflows observed with SDO/HMI, HINODE, and an
MHD simulation
Authors: Roudier, T.; Švanda, M.; Malherbe, J. M.; Ballot, J.; Korda,
D.; Frank, Z.
2021A&A...647A.178R Altcode: 2021arXiv210303077R
Downflows on the solar surface are suspected to play a major role in
the dynamics of the convection zone, at least in its outer part. We
investigate the existence of the long-lasting downflows whose effects
influence the interior of the Sun but also the outer layers. We study
the sets of Dopplergrams and magnetograms observed with Solar Dynamics
Observatory and Hinode spacecrafts and an magnetohydrodynamic (MHD)
simulation. All of the aligned sequences, which were corrected from
the satellite motions and tracked with the differential rotation,
were used to detect the long-lasting downflows in the quiet-Sun at
the disc centre. To learn about the structure of the flows below the
solar surface, the time-distance local helioseismology was used. The
inspection of the 3D data cube (x, y, t) of the 24 h Doppler sequence
allowed us to detect 13 persistent downflows. Their lifetimes lie in
the range between 3.5 and 20 h with a sizes between 2″ and 3″ and
speeds between −0.25 and −0.72 km s−1. These persistent
downflows are always filled with the magnetic field with an amplitude of
up to 600 Gauss. The helioseismic inversion allows us to describe the
persistent downflows and compare them to the other (non-persistent)
downflows in the field of view. The persistent downflows seem to
penetrate much deeper and, in the case of a well-formed vortex, the
vorticity keeps its integrity to the depth of about 5 Mm. In the MHD
simulation, only sub-arcsecond downflows are detected with no evidence
of a vortex comparable in size to observations at the surface of the
Sun. The long temporal sequences from the space-borne allows us to show
the existence of long-persistent downflows together with the magnetic
field. They penetrate inside the Sun but are also connected with the
anchoring of coronal loops in the photosphere, indicating a link between
downflows and the coronal activity. A links suggests that EUV cyclones
over the quiet Sun could be an effective way to heat the corona.

---------------------------------------------------------
Title: Pollux: A weak dynamo-driven dipolar magnetic field and
implications for its probable planet
Authors: Aurière, M.; Petit, P.; Mathias, P.; Konstantinova-Antova,
R.; Charbonnel, C.; Donati, J. -F.; Espagnet, O.; Folsom, C. P.;
Roudier, T.; Wade, G. A.
2021A&A...646A.130A Altcode: 2021arXiv210102016A
Context. Pollux is considered as an archetype of a giant star hosting a
planet since its radial velocity (RV) presents very stable sinusoidal
variations with a period of about 590 d. We then discovered a weak
magnetic field at its surface using spectropolarimetry, questioning the
planetary hypothesis. Aims: We followed up our investigations on
Pollux to characterize its magnetic field and to infer the effects of
magnetic activity on the RV variations. Methods: We first used
ESPaDOnS at CFHT and then Narval at TBL to obtain Stokes I and Stokes
V spectra of Pollux to study their variations for a duration of 4.25
years, that is, for more than two periods of the RV variations. We
used the least-squares deconvolution profiles to measure the
longitudinal magnetic field and to perform a Zeeman Doppler imaging
(ZDI) investigation. Results: The longitudinal magnetic field
of Pollux is found to vary with a sinusoidal behavior and a period
similar to that of the RV variations. From the ZDI investigation a
rotation period of Pollux is determined to be equal to 660 ± 15 days
and possibly different than the period of variations of the RV. As
to the magnetic topology, the poloidal component is dominant and
almost purely dipolar with an inclination of 10.5° of the dipole
with respect to the rotation axis. The mean strength of the surface
magnetic field is 0.44 G. Pollux is found approximately as active as
the Sun observed as a star and this activity could induce moderate
RV variations. Conclusions: As to the origin of the magnetic
field of Pollux, we favor the hypothesis that it is maintained through
contemporaneous dynamo action. Pollux appears as the representative
of a class of slowly rotating and weakly magnetic G-K red giants. To
explain the sinusoidal RV variations of Pollux, two scenarios are
proposed. If the RV period is different from the rotation period,
the observed periodic RV variations are due to the hosted planet and
the contribution of Pollux magnetic activity is not significantly
detected. In the peculiar case in which the two periods are equal,
we cannot discard the possibility that the activity of Pollux could
explain the total RV variations and that the planet hypothesis would
appear unnecessary. In any case magnetic activity could contribute
significantly to RV variations in some intermediate mass G-K red
giants hosting planets, particularly those with small amplitude RV
variations. Based on observations obtained at the Télescope
Bernard Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and
Université de Toulouse, 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.

---------------------------------------------------------
Title: Evolution of exploding granules from coordinated observations
by THEMIS, IRIS, SDO/HMI, and HINODE, and a simulation
Authors: Roudier, T.; Malherbe, J. M.; Gelly, B.; Douet, R.; Frank,
Z.; Dalmasse, K.
2020A&A...641A..50R Altcode: 2020arXiv200712438R
Exploding granules constitute the strongest horizontal flows on the
quiet Sun and contribute to the structure of the surface horizontal
velocity fields which build the large-scale organization of the discrete
magnetic field. In this work we explore exploding granule expansion
through the observations of the ground-based THEMIS telescope, IRIS,
SDO, and the Hinode space-borne instruments, and finally with the
magnetohydrodynamics simulation. We evaluate the detection and the
expansion of exploding granules at several wavelengths and at various
spatial and temporal resolutions. To analyze the different temporal
sequences, two methods of image segmentation are applied to select
the granules. The first allows us to follow individually the exploding
granules observed simultaneously by THEMIS, IRIS, and SDO. The second
uses long time independent sequences from THEMIS, IRIS, SDO, Hinode,
and a simulation. In the first method (called manual) the segmentation
isolates the cell of the granules (bright granules and intergranular
parts), while in the second method (called statistical) only the
bright part of the granules are isolated. The results obtained with
simultaneous or distinct temporal observations using the two methods
of segmentation are in good agreement. The granule area evolves
linearly with an expansion velocity that decreases with the radius. A
rapid decrease in the velocity expansion in the first two minutes is
observed. The detection and measurement of the dynamics of the explosive
granules can be performed from ground- and space-based instruments. Our
work reveals the usefulness of SDO data, with low spatial resolution, to
study the dynamics of the exploding granules all over the solar surface.

---------------------------------------------------------
Title: Evolution of photospheric flows under an erupting filament
in the quiet-Sun region
Authors: Wollmann, Jiří; Švanda, Michal; Korda, David; Roudier,
Thierry
2020A&A...636A.102W Altcode: 2020arXiv200312515W
Context. We studied the dynamics of the solar atmosphere in the region
of a large quiet-Sun filament, which erupted on 21 October 2010. The
filament eruption started at its northern end and disappeared from
the Hα line-core filtergrams line within a few hours. The very fast
motions of the northern leg were recorded in ultraviolet light by
the Atmospheric Imaging Assembly (AIA) imager. Aims: We aim to
study a wide range of available datasets describing the dynamics of
the solar atmosphere for five days around the filament eruption. This
interval covers three days of the filament evolution, one day before
the filament growth and one day after the eruption. We search for
possible triggers that lead to the eruption of the filament. 
Methods: The surface velocity field in the region of the filament
were measured by means of time-distance helioseismology and
coherent structure tracking. The apparent velocities in the higher
atmosphere were estimated by tracking the features in the 30.4 nm
AIA observations. To capture the evolution of the magnetic field,
we extrapolated the photospheric line-of-sight magnetograms and also
computed the decay index of the magnetic field. Results: We found
that photospheric velocity fields showed some peculiarities. Before the
filament activation, we observed a temporal increase of the converging
flows towards the filament's spine. In addition, the mean squared
velocity increased temporarily before the activation and peaked just
before it, followed by a steep decrease. We further see an increase
in the average shear of the zonal flow component in the filament's
region, followed by a steep decrease. The photospheric line-of-sight
magnetic field shows a persistent increase of induction eastward from
the filament spine. The decay index of the magnetic field at heights
around 10 Mm shows a value larger than critical one at the connecting
point of the northern filament end. The value of the decay index
increases monotonically there until the filament activation. Then,
it decreased sharply. AIA30.4 nm movie is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202037525/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Neural Network to Emulate Numerical Simulations of the Sun
and Infer Synthetic Observations for Data Assimilation
Authors: Tremblay, Benoit; Roudier, Thierry; Cossette, Jean-François;
Attié, Raphaël; Rieutord, Michel; Vincent, Alain
2019shin.confE..30T Altcode:
Satellites and ground-based observatories probe the Sun's photosphere
and atmosphere and are key in studying solar activity. Meanwhile,
numerical models have attempted to bridge the gap between the physics of
the solar interior and such observations. However, there are physical
quantities relevant to solar activity that can be modeled but that
cannot be directly measured and must be inferred. For example, direct
measurements of plasma motions at the photosphere are limited to the
line-of-sight component. Recently, neural network computing has been
used in conjunction with numerical models of the Sun to be able to
recover the full velocity vector in photospheric plasma of the Quiet
Sun. We used satellite observations as input in a fully convolutional
neural network to generate instantaneous synthetic plasma motions,
i.e. plasma motions that reflect the physics of a model but are made
to look as if they were observed by a specific instrument. A parallel
technique could then be invoked to eventually be able to derive the
plasma velocity vector maps of the Active Sun and, by extension, other
physical quantities of interest that can not yet be measured directly
at the photosphere or anywhere else in the solar atmosphere.

---------------------------------------------------------
Title: Link between trees of fragmenting granules and deep downflows
in MHD simulation
Authors: Roudier, T.; Malherbe, J. M.; Stein, R. F.; Frank, Z.
2019A&A...622A.112R Altcode: 2019arXiv190103255R
Context. Trees of fragmenting granules (TFG) and associated flows
are suspected to play a major role in the formation of the network in
the quiet Sun. We investigate the counterparts, in terms of dynamics,
of surface structures detectable by high resolution observations in
deeper layers up to 15 Mm, which are only available from numerical
simulations. Aims: The first aim is to demonstrate that TFG
can be evidenced either from surface intensitites, vertical (Vz),
or Doppler (Vdop) velocities. The second is to show that horizontal
flows, which are derived from intensities or Vz/Vdop flows, are in good
agreement, and that this is the case for observations and numerical
simulations. The third objective is to apply this new Vz-based method
to a 3D simulation to probe relationships between horizontal surface
flows, TFG, and deep vertical motions. Methods: The TFG were
detected after oscillation filtering of intensities or Vz/Vdop flows,
using a segmentation and labelling technique. Surface horizontal
flows were derived from local correlation tracking (LCT) and from
intensities or Vz/Vdop flows. These methods were applied to Hinode
observations, 2D surface results of a first simulation, and 3D Vz
data of a second simulation. Results: We find that TFG and
horizontal surface flows (provided by the LCT) can be detected either
from intensities or Vz/Vdop component, for high resolution observations
and numerical simulations. We apply this method to a 3D run providing
the Vz component in depth. This reveals a close relationship between
surface TFG (5 Mm mesoscale) and vertical downflows 5 Mm below the
surface. We suggest that the dynamics of TFG form larger scales
(the 15-20 Mm supergranulation) associated with 15 Mm downflowing
cells below the surface. Conclusions: The TFG and associated
surface flows seem to be essential to understanding the formation
and evolution of the network at the meso and supergranular scale. Movies associated to Figs. 3, 11, 12, and 14 are availabe at <A
href="https://www.aanda.org/10.1051/0004-6361/201834283/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Horizontal photospheric flows trigger a filament eruption
Authors: Roudier, T.; Schmieder, B.; Filippov, B.; Chandra, R.;
Malherbe, J. M.
2018A&A...618A..43R Altcode: 2018arXiv180802272R
Context. A large filament composed principally of two sections
erupted sequentially in the southern hemisphere on January 26,
2016. The central, thick part of the northern section was first
lifted up and lead to the eruption of the full filament. This event
was observed in Hα with the Global Oscillation Network Group (GONG)
and Christian Latouche IMageur Solaire (CLIMSO), and in ultraviolet
(UV) with the Atmospheric Imaging Assembly (AIA) imager on board
the Solar Dynamic Observatory (SDO). Aims: The aim of the
paper is to relate the photospheric motions below the filament and
its environment to the eruption of the filament. Methods: An
analysis of the photospheric motions using Solar Dynamic Observatory
Helioseismic and Magnetic Imager (SDO/HMI) continuum images with
the new version of the coherent structure tracking (CST) algorithm
developed to track granules, as well as large-scale photospheric flows,
has been performed. Following velocity vectors, corks migrate towards
converging areas. Results: The supergranule pattern is clearly
visible outside the filament channel but difficult to detect inside
because the modulus of the vector velocity is reduced in the filament
channel, mainly in the magnetized areas. The horizontal photospheric
flows are strong on the west side of the filament channel and oriented
towards the filament. The ends of the filament sections are found
in areas of concentration of corks. Whirled flows are found locally
around the feet. Conclusions: The strong horizontal flows with
an opposite direction to the differential rotation create strong shear
and convergence along the magnetic polarity inversion line (PIL) in the
filament channel. The filament has been destabilized by the converging
flows, which initiate an ascent of the middle section of the filament
until the filament reaches the critical height of the torus instability
inducing, consequently, the eruption. The n decay index indicated an
altitude of 60 Mm for the critical height. It is conjectured that
the convergence along the PIL is due to the large-scale size cells
of convection that transport the magnetic field to their borders. The movies associated to Figs. 1, 2, 4 and 5 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832937/olm">https://www.aanda.org</A>.

---------------------------------------------------------
Title: Reconstruction of Horizontal Plasma Motions at the Photosphere
from Intensitygrams: A Comparison Between DeepVel, LCT, FLCT, and CST
Authors: Tremblay, Benoit; Roudier, Thierry; Rieutord, Michel;
Vincent, Alain
2018SoPh..293...57T Altcode:
Direct measurements of plasma motions in the photosphere are limited
to the line-of-sight component of the velocity. Several algorithms have
therefore been developed to reconstruct the transverse components from
observed continuum images or magnetograms. We compare the space and time
averages of horizontal velocity fields in the photosphere inferred from
pairs of consecutive intensitygrams by the LCT, FLCT, and CST methods
and the DeepVel neural network in order to identify the method that
is best suited for generating synthetic observations to be used for
data assimilation. The Stein and Nordlund (Astrophys. J. Lett.753, L13,
2012) magnetoconvection simulation is used to generate synthetic SDO/HMI
intensitygrams and reference flows to train DeepVel. Inferred velocity
fields show that DeepVel performs best at subgranular and granular
scales and is second only to FLCT at mesogranular and supergranular
scales.

---------------------------------------------------------
Title: Dynamics of Trees of Fragmenting Granules in the Quiet Sun:
Hinode/SOT Observations Compared to Numerical Simulation
Authors: Malherbe, J. -M.; Roudier, T.; Stein, R.; Frank, Z.
2018SoPh..293....4M Altcode: 2018arXiv180401870M
We compare horizontal velocities, vertical magnetic fields, and the
evolution of trees of fragmenting granules (TFG, also named families of
granules) derived in the quiet Sun at disk center from observations
at solar minimum and maximum of the Solar Optical Telescope (SOT
on board Hinode) and results of a recent 3D numerical simulation
of the magneto-convection. We used 24-hour sequences of a 2D field
of view (FOV) with high spatial and temporal resolution recorded by
the SOT Broad band Filter Imager (BFI) and Narrow band Filter Imager
(NFI). TFG were evidenced by segmentation and labeling of continuum
intensities. Horizontal velocities were obtained from local correlation
tracking (LCT) of proper motions of granules. Stokes V provided a
proxy of the line-of-sight magnetic field (BLOS). The MHD simulation
(performed independently) produced granulation intensities, velocity,
and magnetic field vectors. We discovered that TFG also form in the
simulation and show that it is able to reproduce the main properties
of solar TFG: lifetime and size, associated horizontal motions, corks,
and diffusive index are close to observations. The largest (but not
numerous) families are related in both cases to the strongest flows
and could play a major role in supergranule and magnetic network
formation. We found that observations do not reveal any significant
variation in TFG between solar minimum and maximum.

---------------------------------------------------------
Title: Supergranulation and multiscale flows in the solar
photosphere. Global observations vs. a theory of anisotropic turbulent
convection
Authors: Rincon, F.; Roudier, T.; Schekochihin, A. A.; Rieutord, M.
2017A&A...599A..69R Altcode: 2016arXiv160905785R
The Sun provides us with the only spatially well-resolved astrophysical
example of turbulent thermal convection. While various aspects of solar
photospheric turbulence, such as granulation (one-Megameter horizontal
scale), are well understood, the questions of the physical origin and
dynamical organization of larger-scale flows, such as the 30-Megameters
supergranulation and flows deep in the solar convection zone,
remain largely open in spite of their importance for solar dynamics
and magnetism. Here, we present a new critical global observational
characterization of multiscale photospheric flows and subsequently
formulate an anisotropic extension of the Bolgiano-Obukhov theory of
hydrodynamic stratified turbulence that may explain several of their
distinctive dynamical properties. Our combined analysis suggests
that photospheric flows in the horizontal range of scales between
supergranulation and granulation have a typical vertical correlation
scale of 2.5 to 4 Megameters and operate in a strongly anisotropic,
self-similar, nonlinear, buoyant dynamical regime. While the theory
remains speculative at this stage, it lends itself to quantitative
comparisons with future high-resolution acoustic tomography of
subsurface layers and advanced numerical models. Such a validation
exercise may also lead to new insights into the asymptotic dynamical
regimes in which other, unresolved turbulent anisotropic astrophysical
fluid systems supporting waves or instabilities operate.

---------------------------------------------------------
Title: Polar cap magnetic field reversals during solar grand minima:
could pores play a role?
Authors: Švanda, Michal; Brun, Allan Sacha; Roudier, Thierry;
Jouve, Laurène
2016A&A...586A.123S Altcode: 2015arXiv151106894S
We study the magnetic flux carried by pores located outside active
regions with sunspots and investigate their possible contribution to
the reversal of the global magnetic field of the Sun. We find that they
contain a total flux of comparable amplitude to the total magnetic flux
contained in polar caps. The pores located at distances of 40-100 Mm
from the closest active region systematically have the correct polarity
of the magnetic field to contribute to the polar cap reversal. These
pores can be found predominantly in bipolar magnetic regions. We propose
that during grand minima of solar activity, such a systematic polarity
trend, which is akin to a weak magnetic (Babcock-Leighton-like) source
term, could still be operating but was missed by the contemporary
observers because of the limited resolving power of their telescopes.

---------------------------------------------------------
Title: Families of Granules, Flows, and Acoustic Events in the Solar
Atmosphere from Hinode Observations
Authors: Malherbe, J. -M.; Roudier, T.; Frank, Z.; Rieutord, M.
2015SoPh..290..321M Altcode: 2014SoPh..tmp..189M
We investigate the relationship between trees of fragmenting granules
(TFG), horizontal and vertical flows, and acoustic events (AE) in the
photospheric network. AE are spatially concentrated and short-duration
locations of acoustic energy flux. We performed observations at disk
center of a 2D field of view (FOV) with high spatial and temporal
resolutions provided by the Solar Optical Telescope onboard Hinode. Line
profiles of Fe I 557.6 nm were recorded by the Narrow-band Filter
Imager on an 80″×36″ FOV during five hours with a cadence of
22 seconds and 0.08″ pixel size. Vertical velocities were derived
at two atmospheric levels allowing the determination of the energy
flux at the acoustic frequency of 3.3 mHz. Families of granules and
horizontal velocities were obtained from local correlation tracking
(LCT) after segmentation and labeling of either continuum intensities
or granular Doppler shifts. AE exhibit durations in the range 0.25
to 1 hour compatible with the lifetime of families (80 % do not last
more than two hours). High-energy AE have the shortest lifetimes. We
found that most AE occur in intergranular lanes located in or close
to the boundaries between different families (called inter families)
in regions with predominantly downward vertical motions and horizontal
converging flows. In contrast, diverging flows are observed inside
families, with a few AE in the intergranules. At the beginning of the
sequence, when families are not yet detected, the distribution of AE
is not uniform and is already organized at spatial lengths related to
the mesogranular scale, with maximum contribution in the range 5″
to 10″, fully compatible with the scale of the maximum contribution
of families in the TFG space. Although all sizes and durations seem
to exist for families, their number decreases with increasing size
and lifetime.

---------------------------------------------------------
Title: The magnetic fields at the surface of active single G-K giants
Authors: Aurière, M.; Konstantinova-Antova, R.; Charbonnel, C.;
Wade, G. A.; Tsvetkova, S.; Petit, P.; Dintrans, B.; Drake, N. A.;
Decressin, T.; Lagarde, N.; Donati, J. -F.; Roudier, T.; Lignières,
F.; Schröder, K. -P.; Landstreet, J. D.; Lèbre, A.; Weiss, W. W.;
Zahn, J. -P.
2015A&A...574A..90A Altcode: 2014arXiv1411.6230A
 Aims: We investigate the magnetic field at the surface of 48
red giants selected as promising for detection of Stokes V Zeeman
signatures in their spectral lines. In our sample, 24 stars are
identified from the literature as presenting moderate to strong
signs of magnetic activity. An additional 7 stars are identified
as those in which thermohaline mixing appears not to have occured,
which could be due to hosting a strong magnetic field. Finally, we
observed 17 additional very bright stars which enable a sensitive
search to be performed with the spectropolarimetric technique. 
Methods: We use the spectropolarimeters Narval and ESPaDOnS to detect
circular polarization within the photospheric absorption lines of our
targets. We treat the spectropolarimetric data using the least-squares
deconvolution method to create high signal-to-noise ratio mean Stokes
V profiles. We also measure the classical S-index activity indicator
for the Ca ii H&amp;K lines, and the stellar radial velocity. To infer
the evolutionary status of our giants and to interpret our results,
we use state-of-the-art stellar evolutionary models with predictions
of convective turnover times. Results: We unambiguously
detect magnetic fields via Zeeman signatures in 29 of the 48 red
giants in our sample. Zeeman signatures are found in all but one of
the 24 red giants exhibiting signs of activity, as well as 6 out of
17 bright giant stars. However no detections were obtained in the 7
thermohaline deviant giants. The majority of the magnetically detected
giants are either in the first dredge up phase or at the beginning of
core He burning, i.e. phases when the convective turnover time is at a
maximum: this corresponds to a "magnetic strip" for red giants in the
Hertzsprung-Russell diagram. A close study of the 16 giants with known
rotational periods shows that the measured magnetic field strength
is tightly correlated with the rotational properties, namely to the
rotational period and to the Rossby number Ro. Our results show that
the magnetic fields of these giants are produced by a dynamo, possibly
of α-ω origin since Ro is in general smaller than unity. Four stars
for which the magnetic field is measured to be outstandingly strong
with respect to that expected from the rotational period/magnetic field
relation or their evolutionary status are interpreted as being probable
descendants of magnetic Ap stars. In addition to the weak-field giant
Pollux, 4 bright giants (Aldebaran, Alphard, Arcturus, η Psc) are
detected with magnetic field strength at the sub-Gauss level. Besides
Arcturus, these stars were not considered to be active giants before
this study and are very similar in other respects to ordinary giants,
with S-index indicating consistency with basal chromospheric
flux. Tables 6-8 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424579/olm">http://www.aanda.org</A>Based
on observations obtained at the Télescope Bernard Lyot (TBL) at
Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France, and at the Canada-France-Hawaii Telescope (CFHT) which is
operated by the National Research Council of Canada, CNRS/INSU and
the University of Hawaii.

---------------------------------------------------------
Title: The Role of Subsurface Flows in Solar Surface Convection:
Modeling the Spectrum of Supergranular and Larger Scale Flows
Authors: Lord, J. W.; Cameron, R. H.; Rast, M. P.; Rempel, M.;
Roudier, T.
2014ApJ...793...24L Altcode: 2014arXiv1407.2209L
We model the solar horizontal velocity power spectrum at scales
larger than granulation using a two-component approximation to the
mass continuity equation. The model takes four times the density
scale height as the integral (driving) scale of the vertical motions
at each depth. Scales larger than this decay with height from the
deeper layers. Those smaller are assumed to follow a Kolmogorov
turbulent cascade, with the total power in the vertical convective
motions matching that required to transport the solar luminosity in a
mixing length formulation. These model components are validated using
large-scale radiative hydrodynamic simulations. We reach two primary
conclusions. (1) The model predicts significantly more power at low
wavenumbers than is observed in the solar photospheric horizontal
velocity spectrum. (2) Ionization plays a minor role in shaping the
observed solar velocity spectrum by reducing convective amplitudes in
the regions of partial helium ionization. The excess low wavenumber
power is also seen in the fully nonlinear three-dimensional radiative
hydrodynamic simulations employing a realistic equation of state. This
adds to other recent evidence suggesting that the amplitudes of
large-scale convective motions in the Sun are significantly lower
than expected. Employing the same feature tracking algorithm used
with observational data on the simulation output, we show that the
observed low wavenumber power can be reproduced in hydrodynamic
models if the amplitudes of large-scale modes in the deep layers
are artificially reduced. Since the large-scale modes have reduced
amplitudes, modes on the scale of supergranulation and smaller remain
important to convective heat flux even in the deep layers, suggesting
that small-scale convective correlations are maintained through the
bulk of the solar convection zone.

---------------------------------------------------------
Title: Pollux: a stable weak dipolar magnetic field but no planet?
Authors: Aurière, Michel; Konstantinova-Antova, Renada; Espagnet,
Olivier; Petit, Pascal; Roudier, Thierry; Charbonnel, Corinne; Donati,
Jean-François; Wade, Gregg A.
2014IAUS..302..359A Altcode: 2013arXiv1310.6907A
Pollux is considered as an archetype of a giant star hosting a planet:
its radial velocity (RV) presents sinusoidal variations with a period
of about 590 d, which have been stable for more than 25 years. Using
ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic
field at the surface of Pollux and followed up its variations with
Narval during 4.25 years, i.e. more than for two periods of the RV
variations. The longitudinal magnetic field is found to vary with a
sinusoidal behaviour with a period close to that of the RV variations
and with a small shift in phase. We then performed a Zeeman Doppler
imaging (ZDI) investigation from the Stokes V and Stokes I least-squares
deconvolution (LSD) profiles. A rotational period is determined, which
is consistent with the period of variations of the RV. The magnetic
topology is found to be mainly poloidal and this component almost
purely dipolar. The mean strength of the surface magnetic field is
about 0.7 G. As an alternative to the scenario in which Pollux hosts a
close-in exoplanet, we suggest that the magnetic dipole of Pollux can
be associated with two temperature and macroturbulent velocity spots
which could be sufficient to produce the RV variations. We finally
investigate the scenarii of the origin of the magnetic field which
could explain the observed properties of Pollux.

---------------------------------------------------------
Title: Proper horizontal photospheric flows in a filament channel
Authors: Schmieder, B.; Roudier, T.; Mein, N.; Mein, P.; Malherbe,
J. M.; Chandra, R.
2014A&A...564A.104S Altcode:
Context. An extended filament in the central part of the active
region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in
the southern hemisphere. It has been observed in Hα with the THEMIS
telescope in the Canary Islands and in 304 Å with the EUV imager (AIA)
onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the
Hα threads and bright moving blobs (jets) along the 304 Å filament
channel were observed during 10 h before the filament erupted at 17:03
UT. Aims: The aim of the paper is to understand the coupling
between magnetic field and convection in filament channels and relate
the horizontal photospheric motions to the activity of the filament. Methods: An analysis of the proper photospheric motions using SDO/HMI
continuum images with the new version of the coherent structure tracking
(CST) algorithm developed to track granules, as well as the large
scale photospheric flows, was performed for three hours. Using corks,
we derived the passive scalar points and produced a map of the cork
distribution in the filament channel. Averaging the velocity vectors
in the southern hemisphere in each latitude in steps of 3.5 arcsec,
we defined a profile of the differential rotation. Results:
Supergranules are clearly identified in the filament channel. Diverging
flows inside the supergranules are similar in and out of the filament
channel. Converging flows corresponding to the accumulation of corks
are identified well around the Hα filament feet and at the edges of
the EUV filament channel. At these convergence points, the horizontal
photospheric velocity may reach 1 km s-1, but with a mean
velocity of 0.35 km s-1. In some locations, horizontal
flows crossing the channel are detected, indicating eventually large
scale vorticity. Conclusions: The coupling between convection
and magnetic field in the photosphere is relatively strong. The
filament experienced the convection motions through its anchorage
points with the photosphere, which are magnetized areas (ends, feet,
lateral extensions of the EUV filament channel). From a large scale
point-of-view, the differential rotation induced a shear of 0.1 km
s-1 in the filament. From a small scale point-of-view,
any convective motions favored the interaction of the parasitic
polarities responsible for the anchorages of the filament to the
photosphere with the surrounding network and may explain the activity
of the filament. Two movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322861/olm">http://www.aanda.org
</A>

---------------------------------------------------------
Title: Dynamics in the filament of september 17 2010 and in its
channel
Authors: Mein, Nicole; Mein, Pierre; Schmieder, Brigitte; Malherbe,
Jean-Marie; Roudier, Thierry
2014IAUS..300..451M Altcode:
Dynamics of a filament is investigated in Hα. Counterstreaming flows
are observed along the filament. Photospheric horizontal motions have
been computed by using a Coherent Structure Tracking algorithm in the
filament environment.

---------------------------------------------------------
Title: Proper horizontal photospheric flows below an eruptive filament
Authors: Schmieder, Brigitte; Mein, Pierre; Mein, Nicole; Roudier,
Thierry; Chandra, Ramseh
2014cosp...40E2926S Altcode:
An analysis of the proper motions using SDO/HMI continuum images with
the new version of the coherent structure tracking (CST) algorithm
developed to track the granules as well as the large scale photospheric
flows, was perfomed during three hours in a region containing a large
filament channel on September 17, 2010. Supergranules were idenfied
in the filament channel. Diverging flows inside the supergranules are
similar in and out the filament channel. Using corks, we derived the
passive scalar points and produced maps of cork distribution. The
anchorage structures with the photosphere (feet) of the filament
are located in the areas of converging flows with accumulations of
corks. Averaging the velocity vectors for each latitude we defined a
profile of the differential rotation. We conclude that the coupling
between the convection and magnetic field in the photosphere is
relatively strong. The filament experienced the convection motions
through its feet. On a large scale point-of-view the differential
rotation induced a shear of 0.1 km/s in the filament. On a small scale
point-of-view convection motions favored the interaction/cancellation of
the parasitic polarities at the base of the feet with the surrounding
network explaining the brightenings,/jets and the eruption that were
observed in the EUV filament.

---------------------------------------------------------
Title: Comparison of Solar Surface Flows Inferred from Time-Distance
Helioseismology and Coherent Structure Tracking Using HMI/SDO
Observations
Authors: Švanda, Michal; Roudier, Thierry; Rieutord, Michel; Burston,
Raymond; Gizon, Laurent
2013ApJ...771...32S Altcode: 2013arXiv1305.0875S
We compare measurements of horizontal flows on the surface of the
Sun using helioseismic time-distance inversions and coherent structure
tracking of solar granules. Tracking provides two-dimensional horizontal
flows on the solar surface, whereas the time-distance inversions
estimate the full three-dimensional velocity flows in the shallow
near-surface layers. Both techniques use Helioseismic and Magnetic
Imager observations as input. We find good correlations between the
various measurements resulting from the two techniques. Further, we
find a good agreement between these measurements and the time-averaged
Doppler line-of-sight velocity, and also perform sanity checks on the
vertical flow that resulted from the three-dimensional time-distance
inversion.

---------------------------------------------------------
Title: Magnetic Fields and Convection in the Cool Supergiant
Betelgeuse
Authors: Petit, P.; Aurière, M.; Konstantinova-Antova, R.;
Morgenthaler, A.; Perrin, G.; Roudier, T.; Donati, J. -F.
2013LNP...857..231P Altcode: 2011arXiv1109.3979P
We present the outcome of a highly-sensitive search for magnetic fields
on the cool supergiant Betelgeuse. A time-series of six circularly
polarized spectra was obtained using the NARVAL spectropolarimeter
at Télescope Bernard Lyot (Pic du Midi Observatory (F)), between
March and April 2010. Zeeman signatures were repeatedly detected in
cross-correlation profiles, corresponding to a longitudinal component
of about 1 G. The time-series unveils a smooth increase of the
longitudinal field from 0.5 to 1.5 G, correlated with radial velocity
fluctuations. We observe a strong asymmetry of Stokes V signatures,
also varying in correlation with the radial velocity. The Stokes V line
profiles are red-shifted by about 9 km s-1 with respect to
the Stokes I profiles, suggesting that the observed magnetic elements
may be concentrated in the sinking components of the convective flows.

---------------------------------------------------------
Title: The Power Spectrum of the Solar Surface Flows from Hinode
Data and First Observations with MOF/CALAS Pic-du-Midi
Authors: Roudier, T.; Rieutord, M.; Rincon, F.; Malherbe, J. -M.;
Brito, D.; Berger, T.; Frank, Z.; Parés, L.; Bourrec, E.; Beigbeder,
F.
2012ASPC..454...47R Altcode:
Many features of solar surface turbulence, like the supergranulation,
are still poorly understood.We use long time series of images taken by
the Solar Optical Telescope on board the Hinode satellite to determine
the velocity fields. The dynamics in the subgranulation range can
be investigated with unprecedented precision thanks to the absence
of seeing effects and the use of the MTF of SOT for correcting the
spectra. The first MOF/CALAS/Pic-du-Midi results are also shown.

---------------------------------------------------------
Title: 14 Ceti: a probable Ap-star-descendant entering the Hertzsprung
gap
Authors: Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Charbonnel,
C.; Van Eck, S.; Donati, J. -F.; Lignières, F.; Roudier, T.
2012A&A...543A.118A Altcode: 2012arXiv1205.6962A
Context. 14 Ceti is a subgiant star of F spectral class that displays
variations in the S-index of its Ca ii H &amp; K lines and an X-ray
emission that is stronger than the mean observed for its spectral class,
which may be due to some magnetic activity. Aims: We attempt to
Zeeman-detect and study the magnetic field of 14 Ceti and to infer its
origin. Methods: We used the spectropolarimeter Narval at the
Telescope Bernard Lyot, Pic du Midi Observatory, and the least squares
deconvolution method to create high signal-to-noise ratio Stokes V
profiles. We derived the surface-averaged longitudinal magnetic field
Bl. We also measured the S-index, and the radial velocity for
each observation. Results: 14 Ceti is Zeeman-detected for the 30
observed dates spanning from August 2007 to January 2012. The average
longitudinal magnetic field does not reverse its sign, reaches about
-35 G, and shows some month-long-timescale variations in our 2008
and 2011-2012 observations. The S-index follows the same long-term
trend as Bl. 14 Ceti is confirmed as a single star without
H-K emission cores. The strength of the observed surface magnetic
field of 14 Ceti is one order of magnitude greater than the observed
one for late F main-sequence stars, and is comparable to the values
measured in the active late F pre-main-sequence star HR 1817. On the
other hand, taking into account the post-main-sequence evolution of
an Ap star, an oblique rotator model can explain the strength of the
magnetic field of 14 Ceti. The variations with a timescale of months
observed for both the Bl and S-index could be due to the
rotation. Conclusions: The most probable scenario to explain
our observations appears to be that 14 Ceti is the descendant of a cool
Ap star. Based on data obtained using the Télescope Bernard Lyot
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.

---------------------------------------------------------
Title: Acoustic Events in the Solar Atmosphere from Hinode/SOT
NFI Observations
Authors: Malherbe, J. -M.; Roudier, T.; Rieutord, M.; Berger, T.;
Franck, Z.
2012SoPh..278..241M Altcode: 2012arXiv1207.1170M
We investigate the properties of acoustic events (AEs), defined as
spatially concentrated and short duration energy flux, in the quiet
Sun, using observations of a 2D field of view (FOV) with high spatial
and temporal resolution provided by the Solar Optical Telescope (SOT)
onboard Hinode. Line profiles of Fe I 557.6 nm were recorded by the
Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with
a time step of 28.75 s and 0.08″ pixel size. Vertical velocities were
computed at three atmospheric levels (80, 130, and 180 km) using the
bisector technique, allowing the determination of energy flux to be
made in the range 3 - 10 mHz using two complementary methods (Hilbert
transform and Fourier power spectrum). Horizontal velocities were
computed using local correlation tracking (LCT) of continuum intensities
providing divergences. We found that the net energy flux is upward. In
the range 3 - 10 mHz, a full FOV space and time averaged flux of 2700 W
m−2 (lower layer 80 - 130 km) and 2000 W m−2
(upper layer 130 - 180 km) is concentrated in less than 1 % of the
solar surface in the form of narrow (0.3″) AE. Their total duration
(including rise and decay) is of the order of 103 s. Inside
each AE, the mean flux is 1.6×105 W m−2
(lower layer) and 1.2×105 W m−2 (upper). Each
event carries an average energy (flux integrated over space and time)
of 2.5×1019 J (lower layer) to 1.9×1019 J
(upper). More than 106 events could exist permanently on
the Sun, with a birth and decay rate of 3500 s−1. Most
events occur in intergranular lanes, downward velocity regions, and
areas of converging motions.

---------------------------------------------------------
Title: MHD simulations of the solar photosphere
Authors: Rieutord, M.; Rincon, F.; Roudier, T.
2012EAS....55....5R Altcode: 2012arXiv1206.6630R
We briefly review the observations of the solar photosphere and
pinpoint some open questions related to the magnetohydrodynamics of
this layer of the Sun. We then discuss the current modelling efforts,
addressing among other problems, that of the origin of supergranulation.

---------------------------------------------------------
Title: Some Dynamic Analysis of the Photosphere from Hinode/SOT and
SDO/HMI Observations
Authors: Roudier, T.; Malherbe, J.; Rieutord, M.; Berger, T.; Frank,
Z.; Prat, V.; Renon, N.; Gizon, L.; Svanda, M.
2012ASPC..456...65R Altcode:
We first present the important role played by the families of granule
(or Tree of Fragmenting granules) in the formation of the photospheric
network. Then, we describe the occurence and characteristics of
acoustic events (AE), defined as spatially concentrated energy flux,
in the quiet Sun. Finally, we present how horizontal velocities obtained
from SDO/HMI data are calibrated by using Hinode/SOT observations.

---------------------------------------------------------
Title: EK Eri: Magnetic Topology and Rotational Period
Authors: Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Roudier, T.
2011ASPC..448.1065A Altcode: 2011csss...16.1065A
We have observed during 3 seasons the slow rotating but active G8
giant EK Eri with the new generation spectropolarimeter NARVAL at
Telescope Bernard Lyot (Observatoire du Pic du Midi, France). We
got 21 observations between 20 September 2007 and 22 March 2010. For
all the spectra, we detected a significant Zeeman Stokes V signature
and the corresponding surface-averaged longitudinal magnetic field
varies between -13 G and -98 G, without reversing its sign. We fitted
the Stokes V profiles with a model of large-scale magnetic field
and obtained a Zeeman Doppler image of it. Our best fitted model
gives a rotational period of about 300 days. A strong magnetic spot
dominates the visible surface magnetic field and is phased with the
photometric spot given by the ephemeris of Dall et al. (2010). Whereas
a quadripolar component dominates for i greater than 80°, for i=
60°, we get a model almost purely dipolar. In the dipolar model,
the strong magnetic/photometric spot would correspond to the pole of
negative polarity of the dipole, which could be the remnant of that
of the Ap star progenitor of EK Eri.

---------------------------------------------------------
Title: Photospheric motions from an observational point of view:
HINODE and SDO satellite observations
Authors: Roudier, T.
2011sf2a.conf..241R Altcode:
Thanks to the Solar Optical Telescope onboard HINODE, we mainly aim at
the understanding of temporal evolution and spatial characterization
of solar granular and supergranular features and their relation with
magnetic field. We study the photospheric motions and the network
magnetic field interactions using the Tree of Fragmenting Granules
(TFGs). The mutual interactions of the TFGs tend to expulse corks
outside of them on 3h-4h and concentrate the corks on supergranular
scale in approximatively 6h-8h to form the magnetic network. Then,
the long living families contribute to form the magnetic network. The
measurement of the horizontal velocities by the proper motion of
granules over the full Sun with SDO data, allow us to determine,
for the first time, the solar differential rotation directly at the
central meridian. During the starting phase of the solar cycle 24,
the solar differential rotation seems to show some modification which
must be confirmed.

---------------------------------------------------------
Title: A dominant magnetic dipole for the evolved Ap star candidate
EK Eridani
Authors: Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Roudier,
T.; Donati, J. -F.; Charbonnel, C.; Dintrans, B.; Lignières, F.;
Wade, G. A.; Morgenthaler, A.; Tsvetkova, S.
2011A&A...534A.139A Altcode: 2011arXiv1109.5570A
Context. EK Eri is one of the most slowly rotating active giants known,
and has been proposed to be the descendant of a strongly magnetic
Ap star. Aims: We have performed a spectropolarimetric study
of EK Eri over 4 photometric periods with the aim of inferring the
topology of its magnetic field. Methods: We used the NARVAL
spectropolarimeter at the Bernard Lyot telescope at the Pic du Midi
Observatory, along with the least-squares deconvolution method, to
extract high signal-to-noise ratio Stokes V profiles from a timeseries
of 28 polarisation spectra. We have derived the surface-averaged
longitudinal magnetic field Bℓ. We fit the Stokes V
profiles with a model of the large-scale magnetic field and obtained
Zeeman Doppler images of the surface magnetic strength and geometry. We
studied the classical activity indicators, the Ca ii H and K lines,
the Ca ii infrared triplet, and Hα line, as well as the stellar
radial velocity. Results: Bℓ variations of up to
about 80 G are observed without any reversal of its sign, and which
are in phase with photometric ephemeris. The activity indicators are
shown to vary smoothly on a timescale compatible with the rotational
period inferred from photometry (308.8 d), however large deviations
can occur from one rotation to another. The surface magnetic field
variations of EK Eri appear to be dominated by a strong magnetic spot
(of negative polarity) which is phased with the dark (cool) photometric
spot. Our modeling shows that the large-scale magnetic field of EK Eri
is strongly poloidal. For a rotational axis inclination of i = 60°, we
obtain a model that is almost purely dipolar. Conclusions: In the
dipolar model, the strong magnetic/photometric spot corresponds to the
negative pole of the dipole, which could be the remnant of that of an Ap
star progenitor of EK Eri. Our observations and modeling conceptually
support this hypothesis, suggesting an explanation of the outstanding
magnetic properties of EK Eri as the result of interaction between deep
convection and the remnant of an Ap star magnetic dipole. Nevertheless,
the longitudinal magnetic field curve clearly shows changes from one
rotation to the next, indicating that the surface magnetic topology
is not static as in an Ap star. Based on data obtained using the
Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS/INSU and
Université de Toulouse, France.

---------------------------------------------------------
Title: Multiwavelength Investigations of Magnetic Bright Points
Authors: Kühner, O.; Utz, D.; Hanslmeier, A.; Veronig, A.; Roudier,
T.; Muller, R.; Muthsam, H.
2011CEAB...35...29K Altcode:
In this contribution we present our results regarding the study
of small scale magnetic fields as seen by magnetic bright points
(MBPs) in different wavelengths and hence different heights. By the
determination of the size distribution of these features we are able
to derive the value of the scale height parameter for the photosphere:
107 km ± 18.5 km. For the Fe I line at 630.25 nm we derived a formation
height of 225 km.

---------------------------------------------------------
Title: No detection of large-scale magnetic fields at the surfaces
of Am and HgMn stars
Authors: Aurière, M.; Wade, G. A.; Lignières, F.; Hui-Bon-Hoa, A.;
Landstreet, J. D.; Iliev, I. Kh.; Donati, J. -F.; Petit, P.; Roudier,
T.; Théado, S.
2010A&A...523A..40A Altcode: 2010arXiv1008.3086A
 Aims: We investigate the magnetic dichotomy between Ap/Bp and
other A-type stars by carrying out a deep spectropolarimetric study of
Am and HgMn stars. Methods: Using the NARVAL spectropolarimeter
at the Télescope Bernard Lyot (Observatoire du Pic du Midi, France),
we obtained high-resolution circular polarisation spectroscopy of
12 Am stars and 3 HgMn stars. Results: Using least squares
deconvolution (LSD), no magnetic field is detected in any of the 15
observed stars. Uncertaintiies as low as 0.3 G (respectively 1 G)
have been reached for surface-averaged longitudinal magnetic field
measurements for Am (respectively HgMn) stars. Conclusions:
Associated with the results obtained previously for Ap/Bp stars, our
study confirms the existence of a magnetic dichotomy among A-type
stars. Our data demonstrate that there is at least one order of
magnitude difference in field strength between Zeeman detected stars
(Ap/Bp stars) and non Zeeman detected stars (Am and HgMn stars). This
result confirms that the spectroscopically-defined Ap/Bp stars are the
only A-type stars harbouring detectable large-scale surface magnetic
fields. Based on data obtained using the Télescope Bernard Lyot
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.

---------------------------------------------------------
Title: The magnetic field of Betelgeuse: a local dynamo from giant
convection cells?
Authors: Aurière, M.; Donati, J. -F.; Konstantinova-Antova, R.;
Perrin, G.; Petit, P.; Roudier, T.
2010A&A...516L...2A Altcode: 2010arXiv1005.4845A
Context. Betelgeuse is an M supergiant with a complex and extended
atmosphere, which also harbors spots and giant granules at its
surface. A possible magnetic field could contribute to the mass loss
and to the heating of the outer atmosphere. Aims: We observed
Betelgeuse, to directly study and infer the nature of its magnetic
field. Methods: We used the new-generation spectropolarimeter
NARVAL and the least square deconvolution (LSD) method to detect
circular polarization within the photospheric absorption lines of
Betelgeuse. Results: We have unambiguously detected a weak Stokes
V signal in the spectral lines of Betelgeuse, and measured the related
surface-averaged longitudinal magnetic field B_ℓ at 6 different epochs
over one month. The detected longitudinal field is about one Gauss and
is apparently increasing on the time scale of our observations. Conclusions: This work presents the first direct detection of the
magnetic field of Betelgeuse. This magnetic field may be associated to
the giant convection cells that could enable a “local dynamo”. Based on observations obtained at the Télescope Bernard Lyot (TBL)
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.

---------------------------------------------------------
Title: On the power spectrum of solar surface flows
Authors: Rieutord, M.; Roudier, T.; Rincon, F.; Malherbe, J. -M.;
Meunier, N.; Berger, T.; Frank, Z.
2010A&A...512A...4R Altcode: 2009arXiv0911.3319R
Context. The surface of the Sun provides us with a unique and
very detailed view of turbulent stellar convection. Studying its
dynamics can therefore help us make significant progress in stellar
convection modelling. Many features of solar surface turbulence like
the supergranulation are still poorly understood. Aims: The aim
of this work is to give new observational constraints on these flows
by determining the horizontal scale dependence of the velocity and
intensity fields, as represented by their power spectra, and to offer
some theoretical guidelines to interpret these spectra. Methods:
We use long time-series of images taken by the Solar Optical Telescope
(SOT) on board the Hinode satellite; we reconstruct both horizontal
(by granule tracking) and vertical (by Doppler effect) velocity
fields in a field-of-view of ~ 75 × 75 Mm2. The dynamics
in the subgranulation range can be investigated with unprecedented
precision thanks to the absence of seeing effects and the use of the
modulation transfer function of SOT for correcting the spectra. 
Results: At small subgranulation scales down to 0.4 Mm the spectral
density of kinetic energy associated with vertical motions exhibits
a k-10/3-like power law, while the intensity fluctuation
spectrum follows either a k-17/3 or a k-3-like
power law at the two continuum levels investigated (525 and 450
nm respectively). We discuss the possible physical origin of these
scalings and interpret the combined presence of k-17/3 and
k-10/3 power laws for the intensity and vertical velocity
as a signature of buoyancy-driven turbulent dynamics in a strongly
thermally diffusive regime. In the mesogranulation range and up to a
scale of 25 Mm, we find that the amplitude of the vertical velocity
field decreases like λ-3/2 with the horizontal scale
λ. This behaviour corresponds to a k2 spectral power
law. Still in the 2.5-10 Mm mesoscale range, we find that intensity
fluctuations in the blue continuum also follow a k2
power law. In passing we show that granule tracking cannot sample
scales below 2.5 Mm. We finally further confirm the presence of a
significant supergranulation energy peak at 30 Mm in the horizontal
velocity power spectrum and show that the emergence of a pore erases
this spectral peak. We tentatively estimate the scale height of the
vertical velocity field in the supergranulation range and find 1 Mm;
this value suggests that supergranulation flows are shallow.

---------------------------------------------------------
Title: Surface structure of the CoRoT CP2 target star HD 50773
Authors: Lüftinger, T.; Fröhlich, H. -E.; Weiss, W. W.; Petit, P.;
Aurière, M.; Nesvacil, N.; Gruberbauer, M.; Shulyak, D.; Alecian,
E.; Baglin, A.; Baudin, F.; Catala, C.; Donati, J. -F.; Kochukhov,
O.; Michel, E.; Piskunov, N.; Roudier, T.; Samadi, R.
2010A&A...509A..43L Altcode: 2009arXiv0911.3791L
 Aims: We compare surface maps of the chemically peculiar
star HD 50773 produced with a Bayesian technique and based on
high quality CoRoT photometry with those derived from rotation
phase resolved spectropolarimetry. The goal is to investigate the
correlation of surface brightness with surface chemical abundance
distribution and the stellar magnetic surface field. Methods:
The rotational period of the star was determined from a nearly 60
days long continuous light curve obtained during the initial run of
CoRoT. Using a Bayesian approach to star-spot modelling, which in this
work is applied for the first time for the photometric mapping of a CP
star, we derived longitudes, latitudes and radii of four different spot
areas. Additional parameters like stellar inclination and the spot's
intensities were also determined. The CoRoT observations triggered an
extensive ground-based spectroscopic and spectropolarimetric observing
campaign and enabled us to obtain 19 different high resolution spectra
in Stokes parameters I and V with NARVAL, ESPaDOnS, and SemelPol
spectropolarimeters. Doppler and Magnetic Doppler imaging techniques
allowed us to derive the magnetic field geometry of the star and the
surface abundance distributions of Mg, Si, Ca, Ti, Cr, Fe, Ni, Y, and
Cu. Results: We find a dominant dipolar structure of the surface
magnetic field. The CoRoT light curve variations and abundances of
most elements mapped are correlated with the aforementioned geometry:
Cr, Fe, and Si are enhanced around the magnetic poles and coincide
with the bright regions on the surface of HD 50773 as predicted by our
light curve synthesis and confirmed by photometric imaging. The
CoRoT space mission was developed and is operated by the French space
agency CNES, with participation of ESA's RSSD and Science Pograms,
Austria, Belgium, Brazil, Germany, and Spain.

---------------------------------------------------------
Title: Multiwavelength alignment of Hinode/SOT Data
Authors: Kuehner, O.; Utz, D.; Hanslmeier, A.; Veronig, A.; Roudier,
T.; Muller, R.; Muthsam, H.
2010CEAB...34...31K Altcode:
First results regarding the spatial alignment of observations taken at
different wavelengths are presented. An exceptionally long time series
(48 hours) of data, obtained by the Solar Optical Telescope (SOT)
of the Hinode satellite, has been analysed. Hinode delivers (among
other data) high resolution seeing free filtergrams in the magnetic
sensitive G-band, blue continuum, chromospheric Ca II H line and Fe I
line. For the study of the position and dynamics of small scale fields
(MBPs; Magnetic Bright Points) at different wavelengths (at different
heights in the photosphere and chromosphere) the alignment of these
data at pixel and subpixel level will be essential. Results concerning
the height dependence of MBPs will also be of vital importance for
questions regarding the coronal heating.

---------------------------------------------------------
Title: Hinode - Synoptic observations of convection dynamics
Authors: Hanslmeier, A.; Muller, R.; Utz, D.; Roudier, T.
2010CEAB...34...81H Altcode:
The variation of solar convection over the solar activity cycle is
still discussed with controversial results. In this paper we study
the solar granulation and its variation over the unusual long lasting
solar minimum between cycle 23 and 24. Spatially highly resolved Hinode
images were segmented and the mean value of the segmented granules as
well as their number was found to be practically constant.

---------------------------------------------------------
Title: Brightness profiles and size distributions of MBPs observed
in different heights by HINODE/SOT data
Authors: Kühner, Otmar; Veronig, Astrid; Utz, Dominik; Hanslmeier,
Arnold; Muthsam, Herbert; Muller, Richard; Roudier, Thierry
2010cosp...38.2948K Altcode: 2010cosp.meet.2948K
We study the characteristics of Magnetic Bright Points (MBPs)
observed at different wave-lenghts and hence different heights of
the photosphere and chromosphere. The data sets were obtained with
the Solar Optical Telescope (SOT) of the Hinode satellite. Hinode
delivers (among other data) high resolution seeing free filtergrams in
the blue continuum, the Fe I line, the magnetic sensitive G-band and
the chromospheric Ca II H line. Due to the small scale structure of
MBPs it was essential for our study to develop an algorithm for the
image co-alignment at subpixel level for the images taken at these
four wavelenghts. We studied an exceptionally long time series (48h)
and analyzed the brightness profiles and size distributions of MBPs
at different heights. The mean size of the features increases with
increasing height and shows an exponential behavior. We obtained the
scale height parameter of the photosphere to be 110 km.

---------------------------------------------------------
Title: Supergranulation, Network Formation, and TFGs Evolution from
Hinode Observations
Authors: Roudier, T.; Rincon, F.; Rieutord, M.; Brito, D.; Beigbeder,
F.; Parès, L.; Malherbe, J. -M.; Meunier, N.; Berger, T.; Frank, Z.
2009ASPC..415..203R Altcode:
In this paper, we analyse a a 48h high-resolution time sequence of the
quiet Sun photosphere obtained with the Solar Optical Telescope onboard
Hinode. Using floating corks advected by velocity fields inferred from
photometry measurements, we show that long-living Trees of Fragmenting
Granules play a crucial role in the advection of small-scale magnetic
fields and in the build-up of the magnetic network.

---------------------------------------------------------
Title: Discovery of a weak magnetic field in the photosphere of the
single giant Pollux
Authors: Aurière, M.; Wade, G. A.; Konstantinova-Antova, R.;
Charbonnel, C.; Catala, C.; Weiss, W. W.; Roudier, T.; Petit, P.;
Donati, J. -F.; Alecian, E.; Cabanac, R.; van Eck, S.; Folsom, C. P.;
Power, J.
2009A&A...504..231A Altcode: 2009arXiv0907.1423A
Aims: We observe the nearby, weakly-active single giant, Pollux,
in order to directly study and infer the nature of its magnetic
field. Methods: We used the new generation spectropolarimeters
ESPaDOnS and NARVAL to observe and detect circular polarization within
the photospheric absorption lines of Pollux. Our observations span 18
months from 2007-2009. We treated the spectropolarimetric data using
the Least-Squares Deconvolution method to create high signal-to-noise
ratio mean Stokes V profiles. We also measured the classical activity
indicator S-index for the Ca ii H and K lines, and the stellar
radial velocity (RV). Results: We have unambiguously detected
a weak Stokes V signal in the spectral lines of Pollux, and measured
the related surface-averaged longitudinal magnetic field B_l. The
longitudinal field averaged over the span of the observations is
below one gauss. Our data suggest variations of the longitudinal
magnetic field, but no significant variation of the S-index. We
observe variations of RV which are qualitatively consistent with the
published ephemeris for a proposed exoplanet orbiting Pollux. The
observed variations of Bl appear to mimic those of RV,
but additional data for this relationship to be established. Using
evolutionary models including the effects of rotation, we derive the
mass of Pollux and we discuss its evolutionary status and the origin
of its magnetic field. Conclusions: This work presents the first
direct detection of the magnetic field of Pollux, and demonstrates
that ESPaDOnS and NARVAL are capable of obtaining sub-G measurements
of the surface-averaged longitudinal magnetic field of giant stars,
and of directly studying the relationships between magnetic activity,
stellar evolution and planet hosting of these stars. Based on
observations obtained at the Canada-France-Hawaii Telescope (CFHT)
which is operated by the National Research Council of Canada, CNRS/INSU
and the University of Hawaii, and the Télescope Bernard Lyot (TBL)
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.

---------------------------------------------------------
Title: Direct detection of a magnetic field on the surface of slowly
rotating giant stars
Authors: Aurière, Michel; Konstantinova-Antova, R.; Petit, P.; Wade,
G.; Roudier, T.
2009IAUS..259..431A Altcode:
We present first results of the magnetic survey of a sample of slow
rotating giant stars for which an X-ray emission or variations of CaII
H &amp; K lines have been already detected.

---------------------------------------------------------
Title: Development of large and fast cmos aps cameras at latt
Authors: Beigbeder, F.; Bourrec, E.; Dupieux, M.; Delaigue, G.; Rondi,
S.; Rieutord, M.; Meunier, N.; Roudier, T.
2009EAS....37..301B Altcode:
Since 2004, at the Laboratoire d'Astrophysique de Toulouse Tarbes
(LATT), we work with CMOS APS detectors, firstly to develop a
large-field,high-resolution camera for the observation of the solar
supergranulation, secondly to develop a fast camera for an adaptive
optics test bench. In these two projects, we use detectors from
FillFactory, now continued by Cypress Semiconductor Corporation:
IBIS4-14000, IBIS-16000, LUPA-4000, 14 Mpixels, 16 Mpixels, 4 Mpixels
respectively. The last one just reads in a 240 × 240 pixels window to
obtain readout rate of 1000 Image/s. For these purposes we developed
dedicated controllers to follow the high pixel rate and multi-output
readout of this type of detectors. We also studied the characterization
methods and measured the main parameters of these CMOS detectors to
know their behaviour. Using these kinds of APS detectors in these
two particular projects proves that we can already find niches to
use CMOS detectors in astronomy taking advantage of their present
specificities. Recent improvements like back illumination, noise
reduction, should rapidly open news possibilities.

---------------------------------------------------------
Title: EK Eridani: the tip of the iceberg of giants which have
evolved from magnetic Ap stars
Authors: Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Charbonnel,
C.; Dintrans, B.; Lignières, F.; Roudier, T.; Alecian, E.; Donati,
J. F.; Landstreet, J. D.; Wade, G. A.
2008A&A...491..499A Altcode: 2008arXiv0810.2228A
Aims: We observe the slowly-rotating, active, single giant,
EK Eri, to study and infer the nature of its magnetic field
directly. Methods: We used the spectropolarimeter NARVAL at
the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least
Square Deconvolution method to create high signal-to-noise ratio
Stokes V profiles. We fitted the Stokes V profiles with a model of
the large-scale magnetic field. We studied the classical activity
indicators, the Ca ii H and K lines, the Ca ii infrared triplet, and
Hα line. Results: We detected the Stokes V signal of EK Eri
securely and measured the longitudinal magnetic field Bl
for seven individual dates spanning 60% of the rotational period. The
measured longitudinal magnetic field of EK Eri reached about 100 G
and was as strong as fields observed in RSCVn or FK Com type stars:
this was found to be extraordinary when compared with the weak fields
observed at the surfaces of slowly-rotating MS stars or any single red
giant previously observed with NARVAL. From our modeling, we infer that
the mean surface magnetic field is about 270 G, and that the large
scale magnetic field is dominated by a poloidal component. This is
compatible with expectations for the descendant of a strongly magnetic
Ap star. Based on data obtained using the Télescope Bernard Lyot
at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse,
France.

---------------------------------------------------------
Title: Supergranules over the solar cycle
Authors: Meunier, N.; Roudier, T.; Rieutord, M.
2008A&A...488.1109M Altcode:
Context: The origin of supergranulation has not been understood
yet. Contradictory results have been obtained in the past concerning
the relation between supergranule properties (mostly cell size) and
the solar cycle. Aims: We propose to study the variation in
supergranule cell sizes and velocity fields over the solar cycle, as
well as the intensity variation inside supergranules. Methods:
We define supergranule cells from maps of horizontal velocity field
divergences. The flow fields are derived from MDI/SOHO intensity
maps. The intensity variation in supergranules are compared to the
variation inside granules resulting from a numerical simulation. The
variation in these profiles with the cell size and over the solar cycle
is also analysed. Results: We find that cell sizes are smaller
on average at cycle maximum. We also find that the slope between Log
(V_rms) and Log (R) is weakly correlated with the spot number (i.e. the
global activity level) but anti-correlated with the local magnetic
field. We also confirm the decrease in the intensity variation from
cell centre to the boundary, which puts a lower limit on the temperature
variation of 0.57 ± 0.06 K. This temperature difference is of 1.03 ±
0.05 K when considering the areas of strongest divergence and strongest
convergence. We observe a strong similarity in the intensity variation
inside supergranules and granules. A significant variation with the
cell size is observed, also similar to that in granules, but the
variation over the solar cycle is not significant. Conclusions:
The sign of the variation in supergranule cell sizes over the solar
cycle is in agreement with what can be expected from the influence
of the magnetic field. The observed intensity variations show that a
common process could be the origin of both granules and supergranules.

---------------------------------------------------------
Title: Dynamics of the Solar Surface Reavealed by Granule Tracking
Authors: Rieutord, M.; Roudier, T.
2008ESPM...12..2.9R Altcode:
We present the recent results obtained by the Toulouse-Tarbes group
on the dynamics of the solar surface at meso and supergranular scale,
and their interactions with the magnetic field. First, using the
14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained
a 7.5h-long sequence of high resolution images with unprecedented
field size (524"x350"). Tracking granules, we have determined the
velocity field at the Sun's surface in great detail from a scale of
2.5 Mm up to 250 Mm. The kinetic energy density spectrum shows that
supergranulation peaks at 36Mm and spans on scales ranging between 20Mm
and 75Mm. The decrease of supergranular flows in the small scales is
close to a 1/k^2-power law, steeper than the equipartition Kolmogorov
one. The probability distribution function of the divergence field shows
the signature of intermittency of the supergranulation and thus its
turbulent nature. Second, using a 48hours-long sequence of white
light images from the HINODE satellite, we determined the evolution of
granule families, which give birth to correlated motion at mesogranular
scale. Using passive cork and magnetic field observations, we show
that the surface velocity field via family organization is sufficient
to explain the magnetic field concentrations at the Sun's surface,
namely the magnetic network. We also find robust scaling laws for the
life time of granule families.

---------------------------------------------------------
Title: Weak magnetic fields in CP stars
Authors: Aurière, M.; Wade, G. A.; Lignières, F.; Landstreet, J. D.;
Donati, J. -F.; Hui Bon Hoa, A.; Iliev, I.; Petit, P.; Roudier, T.;
Silvester, J.; Theado, S.
2008CoSka..38..211A Altcode:
We present the first results of a magnetic survey of main sequence A
and late B stars with NARVAL, the new generation spectropolarimeter
available at Telescope Bernard Lyot at Pic du Midi Observatory. We
observed 3 HgMn stars, 12 Am stars and the only Ap star for which
no Zeeman detection was obtained with MuSiCoS. If we combine our
results with those of our previous survey of weak magnetic fields in
spectroscopically selected Ap/Bp stars we get the following situation:
- Ap/Bp stars: all these stars appear to host a detectable magnetic
field. A threshold dipolar magnetic field of 300 G appears to exist,
below which fields are very rare and perhaps altogether absent. -
Am and HgMn stars: no magnetic field is detected up to now for the 15
observed stars. An accuracy down to 0.3 G (respectively 1 G) is reached
on longitudinal magnetic field measurements for Am (respectively HgMn)
stars. We propose a possible interpretation of the observed threshold
field which naturally explains the magnetic dichotomy: there exists
a critical field strength above which stable magnetic configurations
exist and below which any large scale field configuration is destroyed
by some instability.

---------------------------------------------------------
Title: Topological Departures from Translational Invariance along
a Filament Observed by THEMIS
Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Bommier, V.;
Roudier, T.
2008SoPh..248...29D Altcode: 2008SoPh..tmp...53D
We study the topology of the 3D magnetic field in a filament channel
to address the following questions: Is a filament always formed in a
single flux tube? How does the photospheric magnetic field lead to
filament interruptions and to feet formation? What is the relation
between feet-related field lines and the parasitic polarities? What
can topological analyses teach us about EUV filament channels? To do
so, we consider a filament observed on 6 October 2004 with THEMIS/MTR,
in Hα with the full line profile simultaneously and cospatially with
its photospheric vector magnetic field. The coronal magnetic field
was calculated from a "linear magnetohydrostatic" extrapolation of a
composite THEMIS-MDI magnetogram. Its free parameters were adjusted
to get the best match possible between the distribution of modeled
plasma-supporting dips and the Hα filament morphology. The model
results in moderate plasma β≤1 at low altitudes in the filament,
in conjunction with non-negligible departures from force-freeness
measured by various metrics. The filament here is formed by a split
flux tube. One part of the flux tube is rooted in the photosphere aside
an observed interruption in the filament. This splitted topology is
due to strong network polarities on the edge of the filament channel,
not to flux concentrations closer to the filament. We focus our study
to the northwest portion of the filament. The related flux tube is
highly fragmented at low altitudes. This fragmentation is due to small
flux concentrations of two types. First, some locally distort the
tube, leading to noticeable thickness variations along the filament
body. Second, parasitic polarities, associated with filament feet,
result in secondary dips above the related local inversion line. These
dips belong to long field lines that pass below the flux tube. Many
of these field lines are not rooted near the related foot. Finally,
the present model shows that the coronal void interpretation cannot
be ruled out to interpret the wideness of EUV filament channels.

---------------------------------------------------------
Title: Large-scale horizontal flows in the solar
photosphere. III. Effects on filament destabilization
Authors: Roudier, T.; Švanda, M.; Meunier, N.; Keil, S.; Rieutord,
M.; Malherbe, J. M.; Rondi, S.; Molodij, G.; Bommier, V.; Schmieder, B.
2008A&A...480..255R Altcode: 2007arXiv0711.3112R
Aims:We study the influence of large-scale photospheric motions on
the destabilization of an eruptive filament, observed on October 6,
7, and 8, 2004, as part of an international observing campaign (JOP
178). Methods: Large-scale horizontal flows were investigated
from a series of MDI full-disc Dopplergrams and magnetograms. From
the Dopplergrams, we tracked supergranular flow patterns using the
local correlation tracking (LCT) technique. We used both LCT and manual
tracking of isolated magnetic elements to obtain horizontal velocities
from magnetograms. Results: We find that the measured flow
fields obtained by the different methods are well-correlated on large
scales. The topology of the flow field changed significantly during
the filament eruptive phase, suggesting a possible coupling between
the surface flow field and the coronal magnetic field. We measured
an increase in the shear below the point where the eruption starts
and a decrease in shear after the eruption. We find a pattern in the
large-scale horizontal flows at the solar surface that interact with
differential rotation. Conclusions: We conclude that there is
probably a link between changes in surface flow and the disappearance
of the eruptive filament.

---------------------------------------------------------
Title: Solar supergranulation revealed by granule tracking
Authors: Rieutord, M.; Meunier, N.; Roudier, T.; Rondi, S.; Beigbeder,
F.; Parès, L.
2008A&A...479L..17R Altcode: 2008arXiv0801.1369R
Context: Supergranulation is a pattern of the velocity field at the
surface of the Sun, which has been known about for more than fifty
years, however, no satisfactory explanation of its origin has been
proposed. Aims: New observational constraints are therefore
needed to guide theoretical approaches which hesitate between scenarios
that either invoke a large-scale instability of the surface turbulent
convection or a direct forcing by buoyancy. Methods: Using the
14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained
a 7.5 h-long sequence of high resolution images with unprecedented
field size. Tracking granules, we have determined the velocity field
at the Sun's surface in great detail from a scale of 2.5 Mm up to
250 Mm. Results: The kinetic energy density spectrum shows that
supergranulation peaks at 36 Mm and spans on scales ranging between 20
Mm and 75 Mm. The decrease of supergranular flows in the small scales
is close to a k-2-power law, steeper than the equipartition
Kolmogorov one. The probability distribution function of the divergence
field shows the signature of intermittency of the supergranulation
and thus its turbulent nature. Conclusions:

---------------------------------------------------------
Title: Properties of sunspot moats derived from horizontal motions
Authors: Sobotka, M.; Roudier, T.
2007A&A...472..277S Altcode:
Context: Sunspots in late phases of evolution are usually surrounded by
annular moats, regions where systematic horizontal flows are observed
to be directed radially away from the spot. These flows are considered
to be a manifestation of the sub-photospheric convection. Aims:
The characteristics of moats are derived at two different heights
in the solar atmosphere from horizontal motions around sunspots of
different sizes, shapes, and phases of evolution. We also study the
temporal evolution of moats. Methods: Local correlation tracking
is applied to approximately 70-min long time series of white-light
and 1600 Å images, acquired by the satellite TRACE, to analyse the
horizontal motions of photospheric granules and C IV emission structures
in the vicinity of 32 sunspots. Moat regions are defined by means of
radially-oriented, outward velocities. Results: Relations between
sunspot types and the occurrence, areas, and horizontal velocities of
moats in the photosphere and transition region are described. Moats do
not show substantial changes during the period of about 12 h. Observed
asymmetries in moat shapes and velocities are related to the height in
the atmosphere, to sunspot age, and to proper motion. It is suggested
that the sub-photospheric convective flows around sunspots may be
influenced by the spots' proper motion through the convection zone.

---------------------------------------------------------
Title: Tracking granules on the Sun's surface and reconstructing
velocity fields. I. The CST algorithm
Authors: Rieutord, M.; Roudier, T.; Roques, S.; Ducottet, C.
2007A&A...471..687R Altcode: 2007arXiv0707.1991R
Aims:Determination of horizontal velocity fields on the solar
surface is crucial for understanding the dynamics of structures like
mesogranulation or supergranulation or simply the distribution of
magnetic fields. Methods: We pursue here the development of a
method called CST for coherent structure tracking, which determines the
horizontal motion of granules in the field of view. Results: We
first devise a generalization of Strous method for the segmentation of
images and show that when segmentation follows the shape of granules
more closely, granule tracking is less effective for large granules
because of increased sensitivity to granule fragmentation. We then
introduce the multi-resolution analysis on the velocity field, based on
Daubechies wavelets, which provides a view of this field on different
scales. An algorithm for computing the field derivatives, like the
horizontal divergence and the vertical vorticity, is also devised. The
effects from the lack of data or from terrestrial atmospheric distortion
of the images are also briefly discussed.

---------------------------------------------------------
Title: Tracking granules on the Sun's surface and reconstructing
velocity fields. II. Error analysis
Authors: Tkaczuk, R.; Rieutord, M.; Meunier, N.; Roudier, T.
2007A&A...471..695T Altcode: 2007arXiv0707.1994T
Context: The determination of horizontal velocity fields at the solar
surface is crucial to understanding the dynamics and magnetism of the
convection zone of the sun. These measurements can be done by tracking
granules. Aims: Tracking granules from ground-based observations,
however, suffers from the Earth's atmospheric turbulence, which
induces image distortion. The focus of this paper is to evaluate the
influence of this noise on the maps of velocity fields. Methods:
We use the coherent structure tracking algorithm developed recently
and apply it to two independent series of images that contain the same
solar signal. Results: We first show that a k-ω filtering of
the times series of images is highly recommended as a pre-processing
to decrease the noise, while, in contrast, using destretching should
be avoided. We also demonstrate that the lifetime of granules has a
strong influence on the error bars of velocities and that a threshold
on the lifetime should be imposed to minimize errors. Finally, although
solar flow patterns are easily recognizable and image quality is very
good, it turns out that a time sampling of two images every 21 s is
not frequent enough, since image distortion still pollutes velocity
fields at a 30% level on the 2500 km scale, i.e. the scale on which
granules start to behave like passive scalars. Conclusions:
The coherent structure tracking algorithm is a useful tool for noise
control on the measurement of surface horizontal solar velocity fields
when at least two independent series are available.

---------------------------------------------------------
Title: Are supergranule sizes anti-correlated with magnetic activity?
Authors: Meunier, N.; Roudier, T.; Tkaczuk, R.
2007A&A...466.1123M Altcode:
Context: The variation of supergranule cell sizes with the magnetic
environment is still controversial. Aims: We study this relation
in detail to understand the discrepancies observed between previous
results. Methods: We determine the cell size using divergence of
horizontal flows derived from local correlation tracking of intensity
maps (MDI/SOHO). We study the variation of the cell size as a function
of the magnetic field inside the cell. We also consider which component
of the magnetic field most influences the cell size. Results: Our
main conclusion is that there are no large cells when the magnetic field
(in absolute value) averaged over the cell is large. This is mostly
due to the magnetic field inside the cell (intranetwork fields), while
strong network magnetic fields (at the cell boundary) are associated
with larger cells. Further studies of the evolution of the cells and of
the flux imbalance suggest that a high level of weak fields may prevent
the formation of large cells. This is compatible with the expectation
that strong magnetic fields should prevent large-scale flows. Conclusions: The relation between the local activity level determined
by the average magnetic field inside the cells and the supergranule size
is not linear. Furthermore, it strongly depends on the definition of
the activity level (magnetic field inside the cell or magnetic network)
and on the magnetic sensitivity of the data. This last point probably
explains at least partially the conflicting results obtained up to now.

---------------------------------------------------------
Title: The superrotation of solar supergranules
Authors: Meunier, N.; Roudier, T.
2007A&A...466..691M Altcode:
Context: Supergranules have long been believed to rotate faster
than plasma and than magnetic structures. However, it has recently
been shown that this could be due to a bias appearing when using
Dopplergrams, which are strongly affected by projection effets. Aims: Our purpose is to perform new measurements of supergranule
angular velocities using a technique that would not be significantly
influenced by projection effets. Methods: We are therefore
tracking horizontal divergence maps smoothed on the supergranular scale,
either globally or on the scale of cells. Tracking the magnetic field
using the same technique allows them to be used as a reference. Doppler
tracking is performed for a direct comparison. Results: We
confirm that the tracking of Doppler features is not reliable when
computing the dynamics on the supergranular scale. However, we find
that divergence features are still rotating faster than the magnetic
field, when using two independent time series. Conclusions: We
conclude that the long-standing puzzle of supergranular superrotation
persists, and that interpreting it in terms of anchorage depth inside
the convective zone may not be sufficient to explain it.

---------------------------------------------------------
Title: Horizontal Motions in the Vicinity of Sunspots
Authors: Sobotka, M.; Roudier, T.
2007ASPC..368..259S Altcode:
Many sunspots in late phases of evolution are surrounded by an annular
“moat”, where systematic horizontal flows radially away from the
sunspot are observed. Applying the local correlation tracking technique
to series of white-light and 1600 Å images acquired by the satellite
TRACE, we use photospheric granules and C IV emission structures to
track horizontal motions in the vicinity of sunspots of different
sizes, shapes, and phases of evolution. We define the moat regions on
the basis of horizontal motions. We present preliminary results about
the relations between the sunspot types and the occurrence, areas, and
velocities of the moats in the photosphere and chromosphere. Further
we analyze observed asymmetries in moat shapes and velocities and
their relation to the sunspot age and proper motion.

---------------------------------------------------------
Title: Solar Spectro-Polarimetry at Pic-du-Midi/LJR
Authors: Arnaud, J.; Roudier, T.; Malherbe, M.; Moity, J.
2006ASPC..358..167A Altcode:
A modern polarization analysis package was installed in 2004 at the
50 cm Pic-du-Midi solar telescope (Lunette Jean Rösch-LJR) by one
of us (JMM) to complement LJR instrumentation which already included
a spectrograph built by Z. Mouradian (LESIA), an MSDP device built by
P. Mein (LESIA), and one La Vision CCD camera bought by R. Muller (LATT)
and installed by one of us (JMM). We describe hereafter characteristics
of the telescope and of its instrumentation and present some of the
first Zeeman and Hanle effects measurements obtained using LJR new
polarimeter.

---------------------------------------------------------
Title: The DynaMICS perspective
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.624E..24T Altcode: 2006soho...18E..24T
No abstract at ADS

---------------------------------------------------------
Title: Scientific Objectives of the Novel Formation Flying Mission
Aspiics
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.164L Altcode: 2006soho...17E.164L
No abstract at ADS

---------------------------------------------------------
Title: The EUV Variability Experiment (EVE) on the Solar Dynamics
Observatory (SDO): Science Plan and Instrument Overview
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.165W Altcode: 2006soho...17E.165W
No abstract at ADS

---------------------------------------------------------
Title: The Dynamics Project
Authors: Turck-Chièze, S.; Schmutz, W.; Thuillier, G.; Jefferies,
S.; Pallé; Dewitt, S.; Ballot, J.; Berthomieu, G.; Bonanno, A.;
Brun, A. S.; Christensen-Dalsgaard, J.; Corbard, T.; Couvidat, S.;
Darwich, A. M.; Dintrans, B.; Domingo, V.; Finsterle, W.; Fossat,
E.; Garcia, R. A.; Gelly, B.; Gough, D.; Guzik, J.; Jiménez, A. J.;
Jiménez-Reyes, S.; Kosovichev, A.; Lambert, P.; Lefebvre, S.; Lopes,
I.; Martic, M.; Mathis, S.; Mathur, S.; Nghiem, P. A. P.; Piau, L.;
Provost, J.; Rieutord, M.; Robillot, J. M.; Rogers, T.; Roudier, T.;
Roxburgh, I.; Rozelot, J. P.; Straka, C.; Talon, S.; Théado, S.;
Thompson, M.; Vauclair, S.; Zahn, J. P.
2006ESASP.617E.162T Altcode: 2006soho...17E.162T
No abstract at ADS

---------------------------------------------------------
Title: Photospheric flows measured with TRACE II. Network formation
Authors: Krijger, J. M.; Roudier, T.
2003A&A...403..715K Altcode:
We analyse a 7 d (167 h) sequence of TRACE white-light images with 1
arcsec angular resolution taken at 1 min cadence. The TRACE resolution
and the fast cadence allows us to produce maps of the horizontal
flow fields with high angular (1 arcsec) and temporal resolution (5
min). The field of view of 128arcsec x 128arcsec (~93 Mm x 93 Mm)
covers approximately an area of 10 to 30 supergranules. This area
was followed during solar rotation. Magnetic flux was artificially
inserted into the successive flow maps in the form of ephemeral
regions with positive and negative polarity. The emergence rate of 2
x 1022 Mx h-1 with an average flux per region
of about 1.1 x 1019 Mx produces a good reproduction of the
chromospheric network as observed in images taken simultaneously at
1600 Å. In addition, we show that the quiet network can be maintained
only if field elements of both polarities are inserted into the flow
fields. Our analysis suggests that the network is fully replenished
on a time scale of a day and the lifetimes of the magnetic elements
are of a similar duration.

---------------------------------------------------------
Title: A simulation of solar convection at supergranulation scale
Authors: Rieutord, M.; Ludwig, H. -G.; Roudier, T.; Nordlund, .;
Stein, R.
2002NCimC..25..523R Altcode: 2001astro.ph.10208R
We present here numerical simulations of surface solar convection
which cover a box of 30$\times30\times$3.2 Mm$^3$ with a resolution of
315$\times315\times$82, which is used to investigate the dynamics of
scales larger than granulation. No structure resembling supergranulation
is present; possibly higher Reynolds numbers (i.e. higher numerical
resolution), or magnetic fields, or greater depth are necessary. The
results also show interesting aspects of granular dynamics which are
briefly presented, like extensive p-mode ridges in the k-$\omega$
diagram and a ringlike distribution of horizontal vorticity around
granules. At large scales, the horizontal velocity is much larger
than the vertical velocity and the vertical motion is dominated by
p-mode oscillations.

---------------------------------------------------------
Title: Photospheric flows measured with TRACE
Authors: Krijger, J. M.; Roudier, T.; Rieutord, M.
2002A&A...387..672K Altcode:
We analyse white-light image sequences taken with the Transition
Region and Coronal Explorer (TRACE) using an optimised local
correlation tracking (LCT) method to measure the horizontal flows
in the quiet solar photosphere with high spatial (1 arcsec) and
temporal (5 min) resolution. Simultaneously taken near-ultraviolet
images from TRACE confirm that our LCT-determined flows recover the
actual supergranulation pattern, thus proving that the topology of the
horizontal flow distribution and network assembly may be studied from
long-duration TRACE white-light sequences with our method.

---------------------------------------------------------
Title: Are granules good tracers of solar surface velocity fields?
Authors: Rieutord, M.; Roudier, T.; Ludwig, H. -G.; Nordlund, Å.;
Stein, R.
2001A&A...377L..14R Altcode: 2001astro.ph..8284R
Using a numerical simulation of compressible convection with radiative
transfer mimicking the solar photosphere, we compare the velocity
field derived from granule motions to the actual velocity field of
the plasma. We thus test the idea that granules may be used to trace
large-scale velocity fields at the sun's surface. Our results show that
this is indeed the case provided the scale separation is sufficient. We
thus estimate that neither velocity fields at scales less than 2500
km nor time evolution at scales shorter than 0.5 hr can be faithfully
described by granules. At larger scales the granular motions correlate
linearly with the underlying fluid motions with a slope of ≲2 reaching
correlation coefficients up to ~ 0.9.

---------------------------------------------------------
Title: On mesogranulation, network formation and supergranulation
Authors: Rieutord, M.; Roudier, T.; Malherbe, J. M.; Rincon, F.
2000A&A...357.1063R Altcode:
We present arguments which show that in all likelihood mesogranulation
is not a true scale of solar convection but the combination of
the effects of both highly energetic granules, which give birth to
strong positive divergences (SPDs) among which we find exploders, and
averaging effects of data processing. The important role played by SPDs
in horizontal velocity fields appears in the spectra of these fields
where the scale ~ 4 Mm is most energetic; we illustrate the effect
of averaging with a one-dimensional toy model which shows how two
independent non-moving (but evolving) structures can be transformed
into a single moving structure when time and space resolution are
degraded. The role of SPDs in the formation of the photospheric network
is shown by computing the advection of floating corks by the granular
flow. The coincidence of the network bright points distribution and
that of the corks is remarkable. We conclude with the possibility that
supergranulation is not a proper scale of convection but the result
of a large-scale instability of the granular flow, which manifests
itself through a correlation of the flows generated by SPDs.

---------------------------------------------------------
Title: Internal intermittency on the Sun surface?
Authors: Roudier, T.; Rieutord, M.; Malherbe, J. M.; Vigneau, J.
1999joso.proc..197R Altcode:
An improved version of LCT and FT is presented and used to determine
high spatial and temporal resolution horizontal flow fields at the
Sun's surface. The granule diplacements and group evolution can be
followed. The horizontal flow fields calculated by these methods show
a structured flow at mean scale (4 to 8 arcsec) by a group of granules
which is probably related to the local intermittency.

---------------------------------------------------------
Title: Magnetic reconnection driven by emergence of sheared magnetic
field.
Authors: Schmieder, B.; Aulanier, G.; Demoulin, P.; van
Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Cauzzi, G.
1997A&A...325.1213S Altcode:
Recurrent subflares (Class C) were observed in the NOAA 7608 active
region on 27 October 1993. From multi-wavelength observations
(white-light, magnetic field, H-alpha, X-ray), obtained during a
coordinated campaign between Pic du Midi and Yohkoh, it appears that
these flares were double ribbon flares caused by new flux emergence. As
the flare begins, the X-ray emission observed with Yohkoh/SXT is
loop-shaped with the axis almost parallel to the magnetic inversion
line, while during the flare development, X-ray loops appear at the
location of the emerging flux. The extrapolation of the photospheric
magnetic field in a linear force-free field configuration allows
identification of the magnetic configuration given by the flares. The
Hα flare ribbons are located at the intersections of the computed
quasi-separatrice layers (QSLs) with the chromosphere. We show that
the initial loop-shaped X-ray emission region is in fact formed by
several smaller loops directed in a nearly orthogonal direction with
their feet anchored close to or in the Hα ribbons. During the flare
development there are X-ray loops which represent only one foot of
open or largescale magnetic loops. For the studied flares the puzzling
soft X-rays observations could only be understood with the help of Hα
and magnetic data combined with a modeling of the coronal magnetic
field. Further, from the deduced magnetic field topology, the width
of the QSLs and our present knowledge of 3-D magnetic reconnection,
we conclude that the flare was due to magnetic reconnection driven
by emergence of sheared magnetic field impacting in the pre-existing
coronal field.

---------------------------------------------------------
Title: Intergranular plumes and formation of network bright points.
Authors: Roudier, T.; Malherbe, J. M.; November, L.; Vigneau, J.;
Coupinot, G.; Lafon, M.; Muller, R.
1997A&A...320..605R Altcode:
We discuss the temporal evolution of the photospheric intergranular
lanes using a 1 hour time sequence of white-light images of solar
granulation. The time series was obtained with the 50 cm refractor at
the turret dome of the Pic du Midi Observatory. Analysis reveals the
existence of singularities in the intergranular lanes that we call
“intergranular holes”. Intergranular holes, which have diameters
between 0.24arcsec and 0.45arcsec, are continuously visible for more
than 45 minutes. The holes appear to be systematically distributed at
the periphery of mesogranular and supergranular cells. Our study reveals
the formation of bright points (BPs) in 4 out of 14 cases studied very
close to the intergranular holes, suggesting that intergranular holes
may be the locations where magnetic flux tubes are formed.

---------------------------------------------------------
Title: 3-D reconnection related to new emerging flux
Authors: Schmeider, B.; Démoulin, P.; Aulanier, G.; Malherbe, J. M.;
van Driel-Gesztelyi, L.; Mandrini, C. H.; Roudier, T.; Nitta, N.;
Harra-Murnion, L. K.
1997AdSpR..19.1871S Altcode:
We present evidences that emergence of new flux in the lower
atmosphere leads to magnetic reconnection of field lines. In a
first phase the phenomenon is observed in the chromosphere by the
formation of dark filaments (arch filament system) which are overlaid
by bright loops visible in soft X-rays. Different types of event appear
according to the magnetic field configuration and the amount of energy
involved. 3-D modelling of the photospheric magnetic field provides a
new tool for understanding reconnection in real configurations. The
observed chromospheric and coronal loops are good diagnostics for
the modelling. We document our statement by examples obtained during
coordinated campaigns with the Hα Multichannel Subtractive Double
Pass spectrographs-MSDP (Pic du Midi and Tenerife) and the Yohkoh
instruments.

---------------------------------------------------------
Title: Magnetic reconnection driven by an emerging flux.
Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Malherbe, J. M.;
van Driel-Gesztelyi, L.; Roudier, T.
1997joso.proc...51A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Spatial relation between the 5-minute oscillations and
granulation patterns.
Authors: Espagnet, O.; Muller, R.; Roudier, T.; Mein, P.; Mein, N.;
Malherbe, J. M.
1996A&A...313..297E Altcode:
A white light, high resolution movie of the quiet photosphere has been
used to study the spatial relation between the solar granulation and
the 5-min oscillations of high degree mode (small spatial scale). The
granular and oscillatory brightness components have been separated with
the help of a specific filter, in the k-ω diagram. The surface of the
Sun appears to be covered with adjacent oscillating cells of apparent
size 2" (1500km) to 3" (2000km). Some cells are noticeable by their
amplitude which is much larger than average. These strong oscillations
usually appear in expanding intergranular spaces. Our observations
suggest that the 5-min oscillations are stochastically generated by
turbulent convection. However, the most energetic oscillations occur
in downflows only, well separated of each other in time and space.

---------------------------------------------------------
Title: Post-Flare Loops of 26 June 1992, III
Authors: Wiik, J. E.; Schmieder, B.; Heinzel, P.; Roudier, T.
1996SoPh..166...89W Altcode:
Post-flare loops were observed on June 26, 1992 in the Hα line
with the Multichannel Subtractive Double-Pass spectrograph (MSDP)
on Pic-du-Midi and with the Swedish telescope on La Palma. The highly
dynamic loops are inhomogeneous (blobs). The cool loops were observed
10-12 hours after the X 3.9 class flare which had a maximum on June
25 at 20∶11 UT. From 2D images obtained with the MSDP on June 26 we
derive Hα intensities and Doppler velocities of the loop plasma. Using
a geometrical reconstruction technique we show that these loops are
mainly perpendicular to the solar surface and have the shape of a
dipole magnetic configuration. We derive the bulk-flow velocities along
the loop as a function of height using the Doppler velocities and the
results from the loop reconstruction. Where the Doppler velocities are
too small, we derive the bulk-flow velocities from the displacements
of the falling blobs. We discuss existing deviations from free-fall
velocity in the lower parts of the loops.

---------------------------------------------------------
Title: Signatures of New Emerging Flux in the Solar Atmosphere
Authors: Schmieder, B.; Malherbe, J. M.; Mein, P.; Mein, N.; van
Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Harra-Murnion, L. K.
1996ASPC..111...43S Altcode: 1997ASPC..111...43S
The emergence of new flux in the low atmosphere leads to magnetic
reconnection of field lines. In a stable phase the phenomenon is
observed in the chromosphere by the formation of dark filaments (arch
filament system, AFS). The authors show how bright loops visible in soft
X-rays are co-aligned with the AFS. Different types of events appear
as the released energy increases. With less energetic phenomena than
flares one observes surges, jets or X-ray bright points, according
to the configuration of the field lines (open/closed). A low-level
reconnection process is detectable as an X-ray bright point. If
the energy is ≡1028ergs cm-3, one observes
subflares. The authors document their statement by showing examples
observed in coordinated observations obtained with the MSDP (Pic du
Midi and Tenerife) and Yohkoh/SXT and BCS for the events occurring on
Oct 5, 1994, Oct 27, 1993, and May 1, 1993.

---------------------------------------------------------
Title: Penetration of the solar granulation into the photosphere:
height dependence of intensity and velocity fluctuations.
Authors: Espagnet, O.; Muller, R.; Roudier, T.; Mein, N.; Mein, P.
1995A&AS..109...79E Altcode:
A 16-min time series of two-dimensional "Multichanel Subtractive Double
Pass" spectrograms, recorded in the NaD_2_ 5690 line, has been used to
study the vertical structure of the photosphere and, in particular,
the penetration of granules. A statistical and a morphological
investigations have been made. The 5-min oscillations have been
carefully filtered in the k-ω space. Intensity fluctuations associated
to granules disappear in a very short distance, about 60 to 90km above
the continuum level. The intensity features in the upper photosphere
are not related to the granules. The velocity fluctuations associated
to the granulation, cross the whole thickness of the photosphere. The
photosphere can thus be separated into two distinct layers, but only
for the intensity features, not for the velocity features which are
the same from the bottom to the top of the stable atmosphere. In the
lower photosphere, below 90km, only granules are detected. In the upper
photosphere, our observations suggest that the weak pattern visible
there, is turbulent in origin. In addition to this weak pattern,
bright sinking plumes have been discovered; they are associated with
strong downflows, often adjacent to strong upflows. The size of most
plumes is 1" to 2"; however the most outstanding of them may be as
large as 4". Their origin, which may be photospheric or chromospheric,
is still unknown.

---------------------------------------------------------
Title: THEMIS IR Capabilities
Authors: Roudier, T.; Mein, P.; Rayrole, J.
1995itsa.conf..195R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: BASS 2000: Base solaire 'sol' 2000 (solar 'ground-based'
database 2000)
Authors: Roudier, T.
1995VA.....39..115R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of post-flare loops observed on June 26, 1992
Authors: Wiik, J. E.; Schmieder, B.; Heinzel, P.; Roudier, T.
1994ESASP.373..207W Altcode: 1994soho....3..207W
No abstract at ADS

---------------------------------------------------------
Title: Peculiar interactions between granules and network bright
points in the solar photosphere
Authors: Roudier, T.; Espagnet, O.; Muller, R.; Vigneau, J.
1994A&A...287..982R Altcode:
The magnetic elements which form the photospheric network, outside
active regions, are visible as tiny bright features, smaller than 0.5",
called network bright points (NBPs). 15 to 20% of them elongate during
their life, when they are squeezed between two expanding granules,
or simply pushed by an expanding or a moving granule. Some statistical
properties are reported. The most interesting property is that their
size and brightness increases simultaneously indicating a strong
increase of radiative flux as they grow. They can become as large as
1000 km x 400 km and as bright as 1.25 the brightness of the average
photosphere. As theoretical models predict that magnetic flux tubes of
size larger than 300 km should be darker than the mean photosphere, our
observations suggest that during the elongation, some mechanical energy
should contribute in the heating of the tubes. This additional energy
may heat some features in the upper photosphere like chromospheric
spicules and transition zone jets or microflares, whose production
rates and lifetimes are about the same as those of elongation of
NBPS. Elongated NBPs are shaked by the turbulent granules, similarly
to the normal NBPs and thus should contribute to the heating of the
solar corona too.

---------------------------------------------------------
Title: Turbulent power spectra of solar granulation.
Authors: Espagnet, O.; Muller, R.; Roudier, T.; Mein, N.
1993A&A...271..589E Altcode:
High resolution "Multichannel Subtractive Double Pass" spectrograms
and white light photographs have been used to compute power spectra
of the solar granulation. The 5 min oscillations have been carefully
filtered, and the influence of the variation of the mean size of
granules at the mesogranulation scale has been taken into account. It results that both the power spectra of velocity and intensity
fluctuations, displayed in a log P - log k scale, are characteristic
of a turbulent atmosphere: they present a discontinuity at 3" =
2000 km (which corresponds to the size of a large granules) and an
energy which decreases according to the Kolmogorov -5/3 power law
in the granulation range; another discontinuity, at 1".4 = 1000 km
(which corresponds approximately to a Peclet number Pe = 1, for which
thermal diffusion and advection are of equal importance) is present in
the intensity power spectrum, which decreases with a -17/3 power law,
in the range of sizes smaller than 1".4. These results indicate
that granules are turbulent eddies. They have some convective characters
(like the correlation between velocities and brightness) because they
are formed in a strongly superadiabatic atmosphere.

---------------------------------------------------------
Title: Turbulence et granulation solaire.
Authors: Espagnet, O.; Muller, R.; Roudier, T.
1992JAF....43...35E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamique de la photosphère solaire: granulation,
mésogranulation, oscillations.
Authors: Espagnet, O.; Muller, R.; Roudier, T.; Mein, N.; Mein, P.
1992JAF....43...36E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Evolution and advection of solar mesogranulation
Authors: Muller, Richard; Auffret, Herve; Roudier, Thierry; Vigneau,
Jean; Simon, George W.; Frank, Zoe; Shine, Richard A.; Title, Alan M.
1992Natur.356..322M Altcode:
GRANULAR structure on the Sun's surface, with a typical scale
of 1-2 Mm, has been known since 1800, and one hundred years ago,
with the first observations by spectroheliograph1,2,
a mesh-like bright network was found with a characteristic scale
of 30 Mm (40”). This pattern was found, thirty years ago, to be
coincident with close-packed convective cells ('supergranulation')
revealed by Doppler observations3-5 to be nestling inside
the bright network. More recently6,7 an intermediate
'mesogranular' structure was found, with a characteristic scale of
3-10 Mm. We have obtained a three-hour sequence of observations at
the Pic du Midi observatory which shows the evolution of mesogranules
from appearance to disappearance with unprecedented clarity. We see
that the supergranules, which are known to carry along (advect) the
granules with their convective motion, also advect the mesogranules to
their boundaries. This process controls the evolution and disappearance
of mesogranules.

---------------------------------------------------------
Title: La fondation de l'observatoire et les débuts de l'astronomie
au Pic du Midi (1852 - 1947). Dernière partie: Le règne de la
coupole Baillaud.
Authors: Malherbe, J. -M.; Coutard, C.; Roudier, T.
1991LAstr.105R...1M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: La fondation de l'observatoire et les débuts de l'astronomie
au Pic du Midi (1852 - 1947). Deuxième partie: L'introduction
de l'astronomie.
Authors: Malherbe, J. -M.; Coutard, C.; Roudier, T.
1991LAstr.105Q...1M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: La fondation de l'observatoire et les débuts de l'astronomie
au Pic du Midi (1852 - 1947). Introduction. Première partie: La
fondation de l'observatoire.
Authors: Malherbe, J. -M.; Coutard, C.; Roudier, T.
1991LAstr.105....6M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of the solar granulation. II - Statistical analysis:
Power spectra, coherence, phase
Authors: Roudier, T.; Vigneau, J.; Espagnet, O.; Muller, R.; Mein,
P.; Malherbe, J. M.
1991A&A...248..245R Altcode:
The solar granulation is analyzed statistically by the computation
of coherence, phase, and power spectra using data provided by the
Multichannel Subtractive Double Pass spectrograph of the Pic du Midi
Observatory. The main result of the analysis is that the velocity
power spectrum of the granulation changes in shape at 3 arcsec: the raw
spectrum features a slope discontinuity; the corrected spectra have a
power maximum at 3 arcsec. Between 3 arcsec and the resolution limit
(0.8 arcsec), the power decreases almost linearly, with a slope close
to -5/3, consistent with the Kolmogorov power law for a turbulent
energy cascade.

---------------------------------------------------------
Title: Dynamics of solar granulation. I - Processing of MSDP spectra
Authors: Roudier, T.; Vigneau, J.; Mein, P.; Malherbe, J. M.; Coutard,
C.; Hellier, R.; Muller, R.
1991A&A...248..237R Altcode:
High resolution (about 0.5 arcsec) 2D spectra have been obtained
with the Multichannel Subtractive Double Pass spectrograph of the Pic
du Midi Observatory in a quiet region at the solar disk center. The
adapted image processing which provides 2D intensity and velocity maps
of the solar granulation, at two intensity levels of the line NaD2,
is described. A quantitative evaluation of the spatial resolution is
determined both for the intensity and velocity granulation fields.

---------------------------------------------------------
Title: La granulation solaire dans les régions calmes et actives.
Authors: Roudier, Thierry
1990LAstr.104..345R Altcode:
The current understanding of solar granulation in quiet and active
regions is examined. Recent observations are discussed in relation to
current theory. The origin of granulation is considered with reference
to turbulent convection processes which concentrate and disperse the
magnetic field in the photosphere. It is concluded that, despite recent
hypotheses on the turbulent orgin of small granules (fractal analysis),
convective penetration into stable layers of the photosphere is still
the most likely scenario.

---------------------------------------------------------
Title: Proper Motion and Lifetime of Mesogranules
Authors: Frank, Z.; Muller, R.; Roudier, T.; Vigneau, J.; Shine, R.;
Tarbell, T.; Title, A.; Topka, K.; Simon, G.
1989BAAS...21..841F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Amateur/professional Cooperation in 2 Solar Studies
Authors: Roudier, T.; Muller, R.; Hulot, J. C.; Vaissière, F.
1988scaa.conf..168R Altcode: 1988IAUCo..98..168R
No abstract at ADS

---------------------------------------------------------
Title: Structures fines de la photosphère solaire.
Authors: Roudier, T.
1987JAF....29...14R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Digital filtering of low-contrast images with the possibility
of structural analysis by segmentation in connected domains
Authors: Roudier, T.; Coupinot, G.; Hecquet, J.; Muller, R.
1985JOpt...16..107R Altcode:
A digital filtering technique is developed by analogy to the optical
blurred-mask procedure and applied to astronomical images, demonstrating
its usefulness in cases where the image is to be segmented by intensity
levels into connected domains after processing. Images of granules
on the solar surface, globular clusters, Venus and its atmosphere,
and a solar prominence are treated; and the physiological implications
of the blurred-mask filter are discussed.

---------------------------------------------------------
Title: Variability of the quiet photospheric network.
Authors: Muller, R.; Roudier, T.
1984ESASP.220..239M Altcode: 1984ESPM....4..239M
High resolution photographs of the photospheric network taken in the
Ca II K 3933 Å line and λ4308 Å are analysed in order to study the
variation, in latitude and over the solar cycle, of its density.

---------------------------------------------------------
Title: Variability of the structure of the granulation over the
solar activity cycle.
Authors: Muller, R.; Roudier, T.
1984ESASP.220...51M Altcode: 1984ESPM....4...51M
High resolution photographs of solar granulation, obtained between
1976 and 1983, have been computer processed, in order to study the
structure of the granulation and its variation over the solar cycle.

---------------------------------------------------------
Title: Variation of the Mesh of the Granular Network Along the
Solar Cycle
Authors: Macris, C. J.; Mueller, R.; Rosch, J.; Roudier, T.
1984ssdp.conf..265M Altcode:
Using high resolution photographs of the granular field in the center
of the disk obtained since 1966 at the Pic-du-Midi Observatory, it
is shown, either by measuring the center-to-center distances or by
counting granules, that a substantial change in these parameters does
occur along the undecennal cycle, the number of granules per 10×10
arc seconds being around 35 at minimum and 45 at maximum. Automatic
counting of features displaying closed isophotal curves is under way.

---------------------------------------------------------
Title: Lists of minima of eclipsing binaries.
Authors: Carnevali, P.; Diethelm, R.; Figer, A.; Germann, R.;
Le Borgne, J. -F.; Locher, K.; Mauron, N.; Marot, A.; Peter, H.;
Ralincourt, P.; Remis, J.; Sanchez, C.; Domec, C.; Hevesi, Z.; Rolland,
R.; Roudier, T.; Behagle, M.; Royer, A.; Dumarchi, G.
1975BBSAG..19....1C Altcode:
No abstract at ADS