explanation blue bibcodes open ADS page with paths to full text
Author name code: collados
ADS astronomy entries on 2022-09-14
author:"Collados, Manuel" OR author:"Collados Vera, Manuel"
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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
2022arXiv220710905Q Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.
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Title: Exploring dynamic, small-scale quiet Sun magnetism at high
S/N with the GREGOR/GRIS-IFU
Authors: Campbell, Ryan; Collados, Manuel; Quintero Noda, Carlos;
Mathioudakis, Mihalis; Gafeira, Ricardo
2022cosp...44.2510C Altcode:
We have taken advantage of the improvements to GREGOR (Kleint et
al. 2020, A&A, 641, A27), Europe's largest solar telescope,
to reveal small-scale magnetism at the solar internetwork (IN) in
unprecedented detail. The observations were carried out at solar disk
centre with the highly magnetically sensitive Fe I line at 1565nm. Our
observations suggest that GREGOR's overhaul has helped achieve a
higher effective spatial resolution while our synthetic profiles
produced from MHD simulations suggests this data have been obtained
at the telescope diffraction limit in the near infrared. By observing
with high signal-to-noise (S/N), and exceptional seeing conditions, we
reveal that as much as 35% of the IN shows linear polarisation signal
at the 5$\sigma$ level, the highest fraction of linear polarization
ever recorded in the quiet Sun IN, while as much as 70% shows circular
polarization. We use the Stokes inversion based on response functions
(SIR) inversion code to retrieve the thermodynamic, kinematic and
magnetic properties of the atmosphere. We statistically compare our
results to previous GRIS-IFU observations (Campbell et al. 2021,
647, A182) obtained in 2019, prior to GREGOR's overhaul, focusing on
controversies surrounding the impact of noise on the retrieval of the
magnetic inclination angle. We employ the new open-source SIR Explorer
(SIRE) application to easily and efficiently study several dynamic,
small-scale magnetic features. We see evidence for weak transverse
and complex small-scale 'loop-like' structures, with transverse fields
flanked between opposite polarity longitudinal fields. In the last part
of the presentation, SIRE will be demonstrated live for the audience.
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Title: Generalized Fluid Models of the Braginskii Type
Authors: Hunana, P.; Passot, T.; Khomenko, E.; Martínez-Gómez, D.;
Collados, M.; Tenerani, A.; Zank, G. P.; Maneva, Y.; Goldstein, M. L.;
Webb, G. M.
2022ApJS..260...26H Altcode: 2022arXiv220111561H
Several generalizations of the well-known fluid model of Braginskii
(1965) are considered. We use the Landau collisional operator and the
moment method of Grad. We focus on the 21-moment model that is analogous
to the Braginskii model, and we also consider a 22-moment model. Both
models are formulated for general multispecies plasmas with arbitrary
masses and temperatures, where all of the fluid moments are described
by their evolution equations. The 21-moment model contains two "heat
flux vectors" (third- and fifth-order moments) and two "viscosity
tensors" (second- and fourth-order moments). The Braginskii model
is then obtained as a particular case of a one ion-electron plasma
with similar temperatures, with decoupled heat fluxes and viscosity
tensors expressed in a quasistatic approximation. We provide all of
the numerical values of the Braginskii model in a fully analytic form
(together with the fourth- and fifth-order moments). For multispecies
plasmas, the model makes the calculation of the transport coefficients
straightforward. Formulation in fluid moments (instead of Hermite
moments) is also suitable for implementation into existing numerical
codes. It is emphasized that it is the quasistatic approximation that
makes some Braginskii coefficients divergent in a weakly collisional
regime. Importantly, we show that the heat fluxes and viscosity tensors
are coupled even in the linear approximation, and that the fully
contracted (scalar) perturbations of the fourth-order moment, which
are accounted for in the 22-moment model, modify the energy exchange
rates. We also provide several appendices, which can be useful as a
guide for deriving the Braginskii model with the moment method of Grad.
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Title: Polarimetric characterization of segmented mirrors
Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.;
Collados, M.
2022ApOpt..61.4908P Altcode: 2022arXiv220514640P
We study the impact of the loss of axial symmetry around the optical
axis on the polarimetric properties of a telescope with segmented
primary mirror when each segment is present in a different aging
stage. The different oxidation stage of each segment as they are
substituted in time leads to non-negligible crosstalk terms. This
effect is wavelength dependent and it is mainly determined by the
properties of the reflecting material. For an aluminum coating, the
worst polarimetric behavior due to oxidation is found for the blue
part of the visible. Contrarily, dust -- as modeled in this work --
does not significantly change the polarimetric behavior of the optical
system . Depending on the telescope, there might be segment substitution
sequences that strongly attenuate this instrumental polarization.
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Title: Optical design of an image-slicer integral field unit with
two output slits
Authors: Dominguez-Tagle, Carlos; Lopez, Roberto; Collados, Manuel;
Vaz Cedillo, Jacinto J.
2022JATIS...8a5002D Altcode:
The optical design of an integral field unit (IFU) based on
image-slicers represents an interesting design exercise because
of the small size of the components and the critical parameters
to reduce optical aberrations. When the IFU to be designed is also
intended to substitute an IFU prototype that is already integrated
into a spectropolarimeter, it becomes even more challenging. The main
reason to upgrade the IFU prototype is to cover a larger field of view
(FOV). One of the work packages of the European project "Getting Ready
for the European Solar Telescope" (GREST) had as its objective to find
the best option to design such an IFU. After analyzing the requirements
and the design considerations, the optical design pointed toward an IFU
that doubles the FOV, reaching a value of 40.5 arcsec<SUP>2</SUP>. The
designed IFU is composed of two image-slicers coupled together, each
one with eight mirrors of 1.8 mm × 100 μm that feed two slits to
the spectrograph.
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Title: First Light of the Integral Field Unit of GRIS on the GREGOR
Solar Telescope
Authors: Dominguez-Tagle, C.; Collados, M.; Lopez, R.; Cedillo,
J. J. Vaz; Esteves, M. A.; Grassin, O.; Vega, N.; Mato, A.; Quintero,
J.; Rodriguez, H.; Regalado, S.; Gonzalez, F.
2022JAI....1150014D Altcode: 2022arXiv220614294D
An Integral Field Unit (IFU) based on image slicers has been added
to the GREGOR Infrared Spectrograph (GRIS). This upgrade to the
instrument makes possible 2D spectropolarimetry in the near-infrared
by simultaneously recording the full Stokes profiles of spectral lines
(in a given spectral interval) at all the points in the field of view
(FOV). It provides high-cadence spectropolarimetric observations at
the instrument’s high spatial resolution and high polarization
sensitivity at the GREGOR solar telescope. The IFU is ideal for
observing the polarized spectrum of fast-evolving solar features at
high spatial and spectral resolutions. The high observing cadence
opens the possibility of time-series observations. The analysis of
observations to this level of accuracy is essential for understanding
the complex dynamics and interactions of solar plasma and magnetic
fields. The image slicer of the IFU has eight slices of width 100μm,
covering a total FOV of 6′′×3′′. It was designed and built
within the framework of the European projects SOLARNET and GREST,
as a prototype for future instruments of the European Solar Telescope
(EST) and was integrated into GRIS. After two commissioning campaigns
in 2017 and 2018, the IFU was finally installed at the end of September
2018 and offered to all observers who use the telescope.
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Title: 10th International Symposium on Advanced Optical Manufacturing
and Testing Technologies: Large Mirror and Telescopes
Authors: Rao, Chang-Hui; Veillet, Christian; Ma, Xiaoliang; Fan, Bin;
Liu, Fengchuan; Collados Vera, Manuel
2021SPIE12070E....R Altcode:
No abstract at ADS
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Title: Chromospheric Heating Mechanisms in a Plage Region Constrained
by Comparison of Magnetic Field and Mg II h & k Flux Measurements
with Theoretical Studies
Authors: Anan, Tetsu; Schad, Thomas; Kitai, Reizaburo; Dima, Gabriel;
Jaeggli, Sarah; Tarr, Lucas; Collados, Manuel; Dominguez-Tagle,
Carlos; Kleint, Lucia
2021AGUFMSH44A..05A Altcode:
The strongest quasi-steady heating in the solar atmosphere from the
photosphere through the corona occurs in plage regions. As many
chromospheric heating mechanisms have been proposed, important
discriminators of the possible mechanisms are the location of the
heating and the correlation between the magnetic field properties in
the chromosphere and the local heating rate. We observed a plage region
with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3
using the integral field unit mode of the GREGOR Infrared Spectrograph
(GRIS) installed at the GREGOR telescope. During the GRIS observation,
the Interface Region Imaging Spectrograph (IRIS) obtained spectra of the
ultraviolet Mg II h & k doublet emitted from the same region. In
the periphery of the plage region, within the limited field of view
seen by GRIS, we find that the Mg II radiative flux increases with the
magnetic field in the chromosphere. The positive correlation implies
that magnetic flux tubes can be heated by Alfvén wave turbulence
or by collisions between ions and neutral atoms relating to Alfvén
waves. Within the plage region itself, the radiative flux was large
between patches of strong magnetic field strength in the photosphere, or
at the edges of magnetic patches. On the other hand, we do not find any
significant spatial correlation between the enhanced radiative flux and
the chromospheric magnetic field strength or the electric current. In
addition to the Alfvén wave turbulence or collisions between ions
and neutral atoms relating to Alfvén waves, other heating mechanisms
related to magnetic field perturbations produced by interactions of
magnetic flux tubes could be at work in the plage chromosphere.
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Title: Measurements of Photospheric and Chromospheric Magnetic
Field Structures Associated with Chromospheric Heating over a Solar
Plage Region
Authors: Anan, Tetsu; Schad, Thomas A.; Kitai, Reizaburo; Dima,
Gabriel I.; Jaeggli, Sarah A.; Tarr, Lucas A.; Collados, Manuel;
Dominguez-Tagle, Carlos; Kleint, Lucia
2021ApJ...921...39A Altcode: 2021arXiv210807907A
In order to investigate the relation between magnetic structures and
the signatures of heating in plage regions, we observed a plage region
with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3
using the integral field unit mode of the GREGOR Infrared Spectrograph
(GRIS) installed at the GREGOR telescope. During the GRIS observation,
the Interface Region Imaging Spectrograph obtained spectra of the
ultraviolet Mg II doublet emitted from the same region. In the periphery
of the plage region, within the limited field of view seen by GRIS,
we find that the Mg II radiative flux increases with the magnetic
field in the chromosphere with a factor of proportionality of 2.38 ×
10<SUP>4</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> G<SUP>-1</SUP>. The
positive correlation implies that magnetic flux tubes can be heated
by Alfvén wave turbulence or by collisions between ions and neutral
atoms relating to Alfvén waves. Within the plage region itself,
the radiative flux was large between patches of strong magnetic field
strength in the photosphere or at the edges of magnetic patches. On
the other hand, we do not find any significant spatial correlation
between the enhanced radiative flux and the chromospheric magnetic
field strength or the electric current. In addition to the Alfvén
wave turbulence or collisions between ions and neutral atoms relating
to Alfvén waves, other heating mechanisms related to magnetic field
perturbations produced by interactions of magnetic flux tubes could
be at work in the plage chromosphere.
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Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere (Corrigendum)
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...652C...2C Altcode:
No abstract at ADS
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Title: Diagnostic capabilities of spectropolarimetric observations for
understanding solar phenomena. I. Zeeman-sensitive photospheric lines
Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo,
B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Uitenbroek, H.; Katsukawa, Y.
2021A&A...652A.161Q Altcode: 2021arXiv210605084Q
Future ground-based telescopes will expand our capabilities for
simultaneous multi-line polarimetric observations in a wide range of
wavelengths, from the near-ultraviolet to the near-infrared. This
creates a strong demand to compare candidate spectral lines to
establish a guideline of the lines that are most appropriate for each
observation target. We focused in this first work on Zeeman-sensitive
photospheric lines in the visible and infrared. We first examined their
polarisation signals and response functions using a 1D semi-empirical
atmosphere. Then we studied the spatial distribution of the line core
intensity and linear and circular polarisation signals using a realistic
3D numerical simulation. We ran inversions of synthetic profiles, and
we compared the heights at which we obtain a high correlation between
the input and the inferred atmosphere. We also used this opportunity
to revisit the atomic information we have on these lines and computed
the broadening cross-sections due to collisions with neutral hydrogen
atoms for all the studied spectral lines. The results reveal that
four spectral lines stand out from the rest for quiet-Sun and network
conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three
form higher in the atmosphere, and the last line is mainly sensitive to
the atmospheric parameters at the bottom of the photosphere. However,
as they reach different heights, we strongly recommend using at least
one of the first three candidates together with the Fe I 15 648 Å line
to optimise our capabilities for inferring the thermal and magnetic
properties of the lower atmosphere.
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Title: Magnetic field structures associated with chromospheric
heating in a plage region
Authors: Anan, T.; Schad, T.; Kitai, R.; Dima, G.; Jaeggli, S.;
Collados, M.; Dominguez-Tagle, C.; Kleint, L.
2021AAS...23821222A Altcode:
The strongest quasi-steady heating in the solar atmosphere occurs in
the active chromosphere and in particular within plage regions. Our
aim is to investigate the relation between magnetic structures and
the signatures of heating in the plage regions so as to clarify what
mechanisms are at work. We observed a plage region in NOAA active
region 12723 in the near infrared He I triplet and Si I 1082.7 nm
on 2018 October 3 using the Integral Field Unit mode of the GREGOR
Infrared Spectrograph (GRIS) installed at the GREGOR telescope. At the
same time, the Interface Region Imaging Spectrograph (IRIS) obtained
spectra in the ultra-violet Mg II h & k doublet emitted from the
same region. We applied the HAnle and ZEeman Light v2.0 inversion
code (HAZEL v2.0) to the GRIS data to infer the photospheric and
chromospheric magnetic field. We find that the radiative flux of the Mg
II was large between patches of strong magnetic field strength in the
photosphere, or at edges of the magnetic patches. On the other hand,
the spatial correspondences between the Mg II flux and the magnetic
field strength in the chromosphere and between the Mg II flux and the
electric current are not so clear. In conclusion, chromospheric heatings
in the plage region can be related to magnetic field perturbations
produced by interactions of magnetic flux tubes.
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Title: Modeling of 3d Atmospheres of Cool Stars with the Mancha Code
Authors: Perdomo, Andrea; Vitas, Nikola; Khomenko, Elena; Collados,
Manuel
2021csss.confE.129P Altcode:
The first results of the application of the MANCHA code to the case of
stars beyond the solar case are presented: hydrodynamical simulations
of stars of spectral type K0V and M0V compared with the solar case.
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Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...647A.182C Altcode: 2021arXiv210200942C
Context. While the longitudinal field that dominates in photospheric
network regions has been studied extensively, small-scale transverse
fields have recently been found to be ubiquitous in the quiet
internetwork photosphere and this merits further study. Furthermore,
few observations have been able to capture how this field evolves. <BR
/> Aims: We aim to statistically characterize the magnetic vector in
a quiet Sun internetwork region and observe the temporal evolution of
specific small-scale magnetic features. <BR /> Methods: We present
two high spatio-temporal resolution observations that reveal the
dynamics of two disk-centre internetwork regions taken by the new GREGOR
Infrared Spectrograph Integral Field Unit with the highly magnetically
sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87
Å. We record the full Stokes vector and apply inversions with the
Stokes inversions based on response functions code to retrieve the
parameters characterizing the atmosphere. We consider two inversion
schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in
a field free medium, and scheme 2 (S2), with two magnetic models
and a fixed 30% stray light component. <BR /> Results: The magnetic
properties produced from S1 inversions returned a median magnetic
field strength of 200 and 240 G for the two datasets, respectively. We
consider the median transverse (horizontal) component, among pixels
with Stokes Q or U, and the median unsigned longitudinal (vertical)
component, among pixels with Stokes V, above a noise threshold. We
determined the former to be 263 G and 267 G, and the latter to be 131
G and 145 G, for the two datasets, respectively. Finally, we present
three regions of interest, tracking the dynamics of small-scale magnetic
features. We apply S1 and S2 inversions to specific profiles of interest
and find that the latter produces better approximations when there is
evidence of mixed polarities. We find patches of linear polarization
with magnetic flux density of the order of 130−150 G and find that
linear polarization appears preferentially at granule-intergranular
lane boundaries. The weak magnetic field appears to be organized in
terms of complex `loop-like' structures, with transverse fields often
flanked by opposite polarity longitudinal fields.
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Title: Influence of ambipolar and Hall effects on vorticity in
three-dimensional simulations of magneto-convection
Authors: Khomenko, E.; Collados, M.; Vitas, N.; González-Morales,
P. A.
2021RSPTA.37900176K Altcode: 2020arXiv200909753K
This paper presents the results of the analysis of three-dimensional
simulations of solar magneto-convection that include the joint action of
the ambipolar diffusion and the Hall effect. Three simulation runs are
compared: one including both ambipolar diffusion and the Hall effect;
one including only ambipolar diffusion and one without any of these
two effects. The magnetic field is amplified from initial field to
saturation level by the action of turbulent local dynamo. In each of
these cases, we study 2 h of simulated solar time after the local
dynamo reaches the saturation regime. We analyse the power spectra
of vorticity, of magnetic field fluctuations and of the different
components of the magnetic Poynting flux responsible for the transport
of vertical or horizontal perturbations. Our preliminary results show
that the ambipolar diffusion produces a strong reduction of vorticity
in the upper chromospheric layers and that it dissipates the vortical
perturbations converting them into thermal energy. The Hall effect
acts in the opposite way, strongly enhancing the vorticity. When the
Hall effect is included, the magnetic field in the simulations becomes,
on average, more vertical and long-lived flux tube-like structures are
produced. We trace a single magnetic structure to study its evolution
pattern and the magnetic field intensification, and their possible
relation to the Hall effect. <P />This article is part of the Theo
Murphy meeting issue `High-resolution wave dynamics in the lower
solar atmosphere'.
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Title: Joint action of Hall and ambipolar effects in 3D
magneto-convection simulations of the quiet Sun. I. Dissipation and
generation of waves
Authors: González-Morales, P. A.; Khomenko, E.; Vitas, N.; Collados,
M.
2020A&A...642A.220G Altcode: 2020arXiv200810429G
The partial ionization of the solar plasma causes several nonideal
effects such as the ambipolar diffusion, the Hall effect, and the
Biermann battery effect. Here we report on the first three-dimensional
realistic simulations of solar local dynamo where all three effects
were taken into account. The simulations started with a snapshot of
already saturated battery-seeded dynamo, where two new series were
developed: one with solely ambipolar diffusion and another one also
taking into account the Hall term in the generalized Ohm's law. The
simulations were then run for about 4 h of solar time to reach the
stationary regime and improve the statistics. In parallel, a purely
MHD dynamo simulation was also run for the same amount of time. The
simulations are compared in a statistical way. We consider the average
properties of simulation dynamics, the generation and dissipation
of compressible and incompressible waves, and the magnetic Poynting
flux. The results show that, with the inclusion of the ambipolar
diffusion, the amplitudes of the incompressible perturbations related
to Alfvén waves are reduced, and the Poynting flux is absorbed, with
a frequency dependence. The Hall effect causes the opposite action:
significant excess of incompressible perturbations is generated and an
excess of the Poynting flux is observed in the chromospheric layers. The
model with ambipolar diffusion shows, on average, sharper current
sheets and slightly more abundant fast magneto-acoustic shocks in the
chromosphere. The model with the Hall effect has higher temperatures at
the lower chromosphere and stronger and more vertical magnetic field
concentrations all over the chromosphere. The study of high-frequency
waves reveals that significant power of incompressible perturbations
is associated with areas with intense and more vertical magnetic
fields and larger temperatures. This behavior explains the large
Poynting fluxes in the simulations with the Hall effect and provides
confirmation as to the role of Alfvén waves in chromospheric heating
in internetwork regions, under the action of both Hall and ambipolar
effects. We find a positive correlation between the magnitude of the
ambipolar heating and the temperature increase at the same location
after a characteristic time of 10<SUP>2</SUP> s.
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Title: The dynamics of a solar arch filament system from the
chromosphere to the photosphere
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C.
2020sea..confE.199G Altcode:
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s<SUP>-1</SUP>, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity patern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed in
models of AFSs. The observations and the nonlinear force-free field
(NLFFF) extrapolations demonstrate that the magnetic field loops of
the AFS rise with time.
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Title: Local dynamo in stars beyond the Sun: Study for a K0V star
Authors: Perdomo García, A.; Vitas, N.; Khomenko, E.; Collados Vera,
M. A.
2020sea..confE.206P Altcode:
We present the first results of application of the MANCHA3D code (Felipe
2010; Khomenko et al. 2017, 2018) to a K0V cool star. Initially we run
the code solving purely hydrodynamic equations until the stationary
convection is reached. Then we produce the magnetic field generation
and amplification by Biermann's battery seed and local dynamo. We find
values around 100 Gauss for the amplified saturated magnetic field,
similar to those found in Khomenko et al. (2017) for the solar case.
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Title: The European Solar Telescope (EST): Recent developments
Authors: Quintero Noda, C.; Collados, M.; EST Team
2020sea..confE.207Q Altcode:
The optical design has been updated to include an Adaptive Secondary
Mirror that becomes part of the Multi-Conjugated Adaptive Optics (MCAO)
system. This new concept allows simplifying the optical design reducing
the number of optical surfaces before the instrument suite. The project
has also announced a call for tenders for the Preliminary Design of
three EST main systems: the primary mirror assembly, the telescope
structure, pier and enclosure, and the adaptive secondary mirror. In
terms of science capabilities, the Science Advisory Group (SAG)
published an updated version of the Science Requirements Document
in December 2019. The EST Project Office elaborated a database of
instrument requirements based on that document. After discussing it
with the newly formed EST Review Panel, we developed a tentative
light distribution and instrument suite diagram. It was presented
and approved by the SAG in June. We are now starting to create the
instrument developers team to achieve the proposed performance. Our
goal is to deliver the community the construction proposal of the
telescope and the instruments by the end of 2022.
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Title: Photospheric magnetic topology of a north polar region
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2020A&A...635A.210P Altcode: 2020arXiv200304267P
<BR /> Aims: We aim to characterise the magnetism of a large fraction
of the north polar region close to a maximum of activity, when the
polar regions are reversing their dominant polarity. <BR /> Methods:
We make use of full spectropolarimetric data from the CRisp Imaging
Spectro-Polarimeter installed at the Swedish Solar Telescope. The data
consist of a photospheric spectral line, which is used to infer the
various physical parameters of different quiet Sun regions by means
of the solution of the radiative transfer equation. We focus our
analysis on the properties found for the north polar region and their
comparison to the same analysis applied to data taken at disc centre
and low-latitude quiet Sun regions for reference. We also analyse
the spatial distribution of magnetic structures throughout the north
polar region. <BR /> Results: We find that the physical properties
of the polar region (line-of-sight velocity, magnetic flux, magnetic
inclination and magnetic azimuth) are compatible with those found
for the quiet Sun at disc centre and are similar to the ones found
at low latitudes close to the limb. Specifically, the polar region
magnetism presents no specific features. The structures for which
the transformation from a line-of-sight to a local reference frame
was possible harbour large magnetic fluxes (>10<SUP>17</SUP> Mx)
and are in polarity imbalance with a dominant positive polarity, the
largest ones (>10<SUP>19</SUP> Mx) being located below 73° latitude.
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Title: Evolution of Stokes V area asymmetry related to a quiet Sun
cancellation observed with GRIS/IFU
Authors: Kaithakkal, A. J.; Borrero, J. M.; Fischer, C. E.;
Dominguez-Tagle, C.; Collados, M.
2020A&A...634A.131K Altcode: 2020arXiv200105465K
A quiet Sun magnetic flux cancellation event at the disk center was
recorded using the Integral Field Unit (IFU) mounted on the GREGOR
Infrared Spectrograph (GRIS). The GRIS instrument sampled the event
in the photospheric Si I 10827 Å spectral line. The cancellation was
preceded by a significant rise in line core intensity and excitation
temperature, which is inferred from Stokes inversions under local
thermodynamic equilibrium (LTE). The opposite polarity features
seem to undergo reconnection above the photosphere. We also found
that the border pixels neighboring the polarity inversion line
of one of the polarities exhibit a systematic variation of area
asymmetry. Area asymmetry peaks right after the line core intensity
enhancement and gradually declines thereafter. Analyzing Stokes
profiles recorded from either side of the polarity inversion line
could therefore potentially provide additional information on the
reconnection process related to magnetic flux cancellation. Further
analysis without assuming LTE will be required to fully characterize
this event. <P />Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936941/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Tracking Downflows from the Chromosphere to the Photosphere
in a Solar Arch Filament System
Authors: González Manrique, Sergio Javier; Kuckein, Christoph;
Pastor Yabar, Adur; Diercke, Andrea; Collados, Manuel; Gömöry,
Peter; Zhong, Sihui; Hou, Yijun; Denker, Carsten
2020ApJ...890...82G Altcode: 2020arXiv200107078G
We study the dynamics of plasma along the legs of an arch filament
system (AFS) from the chromosphere to the photosphere, observed with
high-cadence spectroscopic data from two ground-based solar telescopes:
the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph
in the He I 10830 Å range and the Swedish Solar Telescope (La Palma)
using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542
Å and Fe I 6173 Å spectral lines. The temporal evolution of the
draining of the plasma was followed along the legs of a single arch
filament from the chromosphere to the photosphere. The average Doppler
velocities inferred at the upper chromosphere from the He I 10830 Å
triplet reach velocities up to 20-24 km s<SUP>-1</SUP>, and in the lower
chromosphere and upper photosphere the Doppler velocities reach up to
11 km s<SUP>-1</SUP> and 1.5 km s<SUP>-1</SUP> in the case of the Ca II
8542 Å and Si I 10827 Å spectral lines, respectively. The evolution
of the Doppler velocities at different layers of the solar atmosphere
(chromosphere and upper photosphere) shows that they follow the same
line-of-sight (LOS) velocity pattern, which confirms the observational
evidence that the plasma drains toward the photosphere as proposed
in models of AFSs. The Doppler velocity maps inferred from the lower
photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not
show the same LOS velocity pattern. Thus, there is no evidence that
the plasma reaches the lower photosphere. The observations and the
nonlinear force-free field (NLFFF) extrapolations demonstrate that
the magnetic field loops of the AFS rise with time. We found flow
asymmetries at different footpoints of the AFS. The NLFFF values of
the magnetic field strength help us to explain these flow asymmetries.
---------------------------------------------------------
Title: Two-dimensional simulations of coronal rain dynamics. I. Model
consisting of a vertical magnetic field and an unbounded atmosphere
Authors: Martínez-Gómez, D.; Oliver, R.; Khomenko, E.; Collados, M.
2020A&A...634A..36M Altcode: 2019arXiv191106638M
Context. Coronal rain often comes about as the final product
of evaporation and condensation cycles that occur in active
regions. Observations show that the condensed plasma falls with an
acceleration that is less than that of free fall. <BR /> Aims: We aim
to improve the understanding of the physical mechanisms behind the
slower than free-fall motion and the two-stage evolution (an initial
phase of acceleration followed by an almost constant velocity phase)
detected in coronal rain events. <BR /> Methods: Using the MANCHA3D
code, we solve the 2D ideal magnetohydrodynamic equations. We
represent the solar corona as an isothermal vertically stratified
atmosphere with a uniform vertical magnetic field. We represent the
plasma condensation as a density enhancement described by a 2D Gaussian
profile. We analyse the temporal evolution of the descending plasma and
study its dependence on such parameters as density and magnetic field
strength. <BR /> Results: We confirm previous findings that indicate
that the pressure gradient is the main force that opposes the action
of gravity and slows down the blob descent, and that larger densities
require larger pressure gradients to reach the constant speed phase. We
find that the shape of a condensation with a horizontal variation of
density is distorted during its fall because the denser parts of the
blob fall faster than the lighter ones. This is explained by the fact
that the duration of the initial acceleration phase and, therefore,
the maximum falling speed attained by the plasma, increases with the
ratio of blob to coronal density. We also find that the magnetic
field plays a fundamental role in the evolution of the descending
condensations. A strong enough magnetic field (greater than 10 G
in our simulations) forces each plasma element to follow the path
given by a particular field line, which allows for the description
of the evolution of each vertical slice of the blob in terms of 1D
dynamics, without the influence of the adjacent slices. In addition,
under the typical conditions of the coronal rain events, the magnetic
field prevents the development of Kelvin-Helmholtz instability. <P
/>Movies associated to Figs. 1, 8 and 10 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201937078/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: An introductory guide to fluid models with anisotropic
temperatures. Part 1. CGL description and collisionless fluid
hierarchy
Authors: Hunana, P.; Tenerani, A.; Zank, G. P.; Khomenko, E.;
Goldstein, M. L.; Webb, G. M.; Cally, P. S.; Collados, M.; Velli,
M.; Adhikari, L.
2019JPlPh..85f2002H Altcode: 2019arXiv190109354H
We present a detailed guide to advanced collisionless fluid models
that incorporate kinetic effects into the fluid framework, and that are
much closer to the collisionless kinetic description than traditional
magnetohydrodynamics. Such fluid models are directly applicable to
modelling the turbulent evolution of a vast array of astrophysical
plasmas, such as the solar corona and the solar wind, the interstellar
medium, as well as accretion disks and galaxy clusters. The text
can be viewed as a detailed guide to Landau fluid models and it is
divided into two parts. Part 1 is dedicated to fluid models that
are obtained by closing the fluid hierarchy with simple (non-Landau
fluid) closures. Part 2 is dedicated to Landau fluid closures. Here
in Part 1, we discuss the fluid model of Chew-Goldberger-Low (CGL)
in great detail, together with fluid models that contain dispersive
effects introduced by the Hall term and by the finite Larmor radius
corrections to the pressure tensor. We consider dispersive effects
introduced by the non-gyrotropic heat flux vectors. We investigate
the parallel and oblique firehose instability, and show that the
non-gyrotropic heat flux strongly influences the maximum growth rate of
these instabilities. Furthermore, we discuss fluid models that contain
evolution equations for the gyrotropic heat flux fluctuations and that
are closed at the fourth-moment level by prescribing a specific form
for the distribution function. For the bi-Maxwellian distribution,
such a closure is known as the `normal' closure. We also discuss a
fluid closure for the bi-kappa distribution. Finally, by considering
one-dimensional Maxwellian fluid closures at higher-order moments,
we show that such fluid models are always unstable. The last possible
non Landau fluid closure is therefore the `normal' closure, and beyond
the fourth-order moment, Landau fluid closures are required.
---------------------------------------------------------
Title: An introductory guide to fluid models with anisotropic
temperatures. Part 2. Kinetic theory, Padé approximants and Landau
fluid closures
Authors: Hunana, P.; Tenerani, A.; Zank, G. P.; Goldstein, M. L.;
Webb, G. M.; Khomenko, E.; Collados, M.; Cally, P. S.; Adhikari, L.;
Velli, M.
2019JPlPh..85f2003H Altcode: 2019arXiv190109360H
In Part 2 of our guide to collisionless fluid models, we concentrate
on Landau fluid closures. These closures were pioneered by Hammett
and Perkins and allow for the rigorous incorporation of collisionless
Landau damping into a fluid framework. It is Landau damping that sharply
separates traditional fluid models and collisionless kinetic theory,
and is the main reason why the usual fluid models do not converge to the
kinetic description, even in the long-wavelength low-frequency limit. We
start with a brief introduction to kinetic theory, where we discuss in
detail the plasma dispersion function Z(ζ), and the associated plasma
response function R(ζ)=1+ζZ(ζ)=-Z^' }(ζ)/2. We then consider a
one-dimensional (1-D) (electrostatic) geometry and make a significant
effort to map all possible Landau fluid closures that can be constructed
at the fourth-order moment level. These closures for parallel moments
have general validity from the largest astrophysical scales down to
the Debye length, and we verify their validity by considering examples
of the (proton and electron) Landau damping of the ion-acoustic mode,
and the electron Landau damping of the Langmuir mode. We proceed by
considering 1-D closures at higher-order moments than the fourth order,
and as was concluded in Part 1, this is not possible without Landau
fluid closures. We show that it is possible to reproduce linear
Landau damping in the fluid framework to any desired precision,
thus showing the convergence of the fluid and collisionless kinetic
descriptions. We then consider a 3-D (electromagnetic) geometry in the
gyrotropic (long-wavelength low-frequency) limit and map all closures
that are available at the fourth-order moment level. In appendix Ae
provide comprehensive tables with Padé approximants of R(ζ) up to
the eighth-pole order, with many given in an analytic form.
---------------------------------------------------------
Title: Science Requirement Document (SRD) for the European Solar
Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S Altcode:
The European Solar Telescope (EST) is a research infrastructure
for solar physics. It is planned to be an on-axis solar telescope
with an aperture of 4 m and equipped with an innovative suite of
spectro-polarimetric and imaging post-focus instrumentation. The EST
project was initiated and is driven by EAST, the European Association
for Solar Telescopes. EAST was founded in 2006 as an association
of 14 European countries. Today, as of December 2019, EAST consists
of 26 European research institutes from 18 European countries. The
Preliminary Design Phase of EST was accomplished between 2008 and
2011. During this phase, in 2010, the first version of the EST Science
Requirement Document (SRD) was published. After EST became a project
on the ESFRI roadmap 2016, the preparatory phase started. The goal
of the preparatory phase is to accomplish a final design for the
telescope and the legal governance structure of EST. A major milestone
on this path is to revisit and update the Science Requirement Document
(SRD). The EST Science Advisory Group (SAG) has been constituted by
EAST and the Board of the PRE-EST EU project in November 2017 and has
been charged with the task of providing with a final statement on the
science requirements for EST. Based on the conceptual design, the SRD
update takes into account recent technical and scientific developments,
to ensure that EST provides significant advancement beyond the current
state-of-the-art. The present update of the EST SRD has been developed
and discussed during a series of EST SAG meetings. The SRD develops
the top-level science objectives of EST into individual science
cases. Identifying critical science requirements is one of its main
goals. Those requirements will define the capabilities of EST and the
post-focus instrument suite. The technical requirements for the final
design of EST will be derived from the SRD.
---------------------------------------------------------
Title: Spectropolarimetric Observations of an Arch Filament System
with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
2019ASPC..526..217B Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s<SUP>-1</SUP> next
to the pores and to 4 km s<SUP>-1</SUP> at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.
---------------------------------------------------------
Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
---------------------------------------------------------
Title: Recent advancements in the EST project
Authors: Jurčák, Jan; Collados, Manuel; Leenaarts, Jorrit; van Noort,
Michiel; Schlichenmaier, Rolf
2019AdSpR..63.1389J Altcode: 2018arXiv181100851J
The European Solar Telescope (EST) is a project of a new-generation
solar telescope. It has a large aperture of 4 m, which is necessary for
achieving high spatial and temporal resolution. The high polarimetric
sensitivity of the EST will allow to measure the magnetic field in the
solar atmosphere with unprecedented precision. Here, we summarise the
recent advancements in the realisation of the EST project regarding
the hardware development and the refinement of the science requirements.
---------------------------------------------------------
Title: Three-dimensional simulations of solar magneto-convection
including effects of partial ionization
Authors: Khomenko, E.; Vitas, N.; Collados, M.; de Vicente, A.
2018A&A...618A..87K Altcode: 2018arXiv180701061K
In recent decades, REALISTIC three-dimensional
radiative-magnetohydrodynamic simulations have become the dominant
theoretical tool for understanding the complex interactions between the
plasma and magnetic field on the Sun. Most of such simulations are based
on approximations of magnetohydrodynamics, without directly considering
the consequences of the very low degree of ionization of the solar
plasma in the photosphere and bottom chromosphere. The presence of a
large amount of neutrals leads to a partial decoupling of the plasma and
magnetic field. As a consequence, a series of non-ideal effects, i.e.,
the ambipolar diffusion, Hall effect, and battery effect, arise. The
ambipolar effect is the dominant in the solar chromosphere. We
report on the first three-dimensional realistic simulations
of magneto-convection including ambipolar diffusion and battery
effects. The simulations are carried out using the newly developed
MANCHA3Dcode. Our results reveal that ambipolar diffusion causes
measurable effects on the amplitudes of waves excited by convection
in the simulations, on the absorption of Poynting flux and heating,
and on the formation of chromospheric structures. We provide a low
limit on the chromospheric temperature increase owing to the ambipolar
effect using the simulations with battery-excited dynamo fields. <P
/>The movies associated to Figs. 16 and 17 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833048/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
A.; Diercke, A.
2018A&A...617A..55G Altcode: 2018arXiv180700728G
<BR /> Aims: We study the evolution of an arch filament system (AFS)
and of its individual arch filaments to learn about the processes
occurring in them. <BR /> Methods: We observed the AFS at the
GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
in the He I 10 830 Å spectral range. The He I triplet profiles
were fitted with analytic functions to infer line-of-sight (LOS)
velocities to follow plasma motions within the AFS. <BR /> Results:
We tracked the temporal evolution of an individual arch filament
over its entire lifetime, as seen in the He I 10 830 Å triplet. The
arch filament expanded in height and extended in length from 13″ to
21″. The lifetime of this arch filament is about 30 min. About 11
min after the arch filament is seen in He I, the loop top starts to
rise with an average Doppler velocity of 6 km s<SUP>-1</SUP>. Only two
minutes later, plasma drains down with supersonic velocities towards
the footpoints reaching a peak velocity of up to 40 km s<SUP>-1</SUP>
in the chromosphere. The temporal evolution of He I 10 830 Å profiles
near the leading pore showed almost ubiquitous dual red components of
the He I triplet, indicating strong downflows, along with material
nearly at rest within the same resolution element during the whole
observing time. <BR /> Conclusions: We followed the arch filament as it
carried plasma during its rise from the photosphere to the corona. The
material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational
results support theoretical AFS models and aids in improving future
models. <P />The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>
---------------------------------------------------------
Title: Magnetic topology of the north solar pole
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2018A&A...616A..46P Altcode: 2018arXiv180409075P; 2018A&A...616A..46Y
The magnetism at the poles is similar to that of the quiet Sun in the
sense that no active regions are present there. However, the polar quiet
Sun is somewhat different from that at the activity belt as it has a
global polarity that is clearly modulated by the solar cycle. We study
the polar magnetism near an activity maximum when these regions change
their polarity, from which it is expected that its magnetism should be
less affected by the global field. To fully characterise the magnetic
field vector, we use deep full Stokes polarimetric observations of the
15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as
a quiet region at disc centre to compare their field distributions. In
order to calibrate the projection effects, we observe an additional
quiet region at the east limb. We find that the two limb datasets share
similar magnetic field vector distributions. This means that close to a
maximum, the poles look like typical limb, quiet-Sun regions. However,
the magnetic field distributions at the limbs are different from the
distribution inferred at disc centre. At the limbs, we infer a new
population of magnetic fields with relatively strong intensities (
600-800 G), inclined by 30° with respect to the line of sight, and
with an azimuth aligned with the solar disc radial direction. This
line-of-sight orientation interpreted as a single magnetic field gives
rise to non-vertical fields in the local reference frame and aligned
towards disc centre. This peculiar topology is very unlikely for such
strong fields according to theoretical considerations. We propose
that this new population at the limbs is due to the observation of
unresolved magnetic loops as seen close to the limb. These loops have
typical granular sizes as measured in the disc centre. At the limbs,
where the spatial resolution decreases, we observe them spatially
unresolved, which explains the new population of magnetic fields that is
inferred. This is the first (indirect) evidence of small-scale magnetic
loops outside the disc centre and would imply that these small-scale
structures are ubiquitous on the entire solar surface. This result has
profound implications for the energetics not only of the photosphere,
but also of the outer layers since these loops have been reported to
reach the chromosphere and the low corona.
---------------------------------------------------------
Title: Development of a field-of-view scanning system (FoV-SS):
test results and lessons learned
Authors: Esteves, Miguel A.; Dominguez-Tagle, Carlos; Vaz Cedillo,
Jacinto Javier; Grassin, Olivier; Vega Reyes, Nauzet; Gracia Temich,
Felix; Collados Vera, Manuel
2018SPIE10706E..6IE Altcode:
Here is presented the tests results and the lessons learnt concerning an
opto-mechanical device to scan the GREGOR telescope field of view. The
scanning is done by means of a set of mirrors and a mechanism which
allows to keep the optical path length constant, regardless the portion
of the field being scanned. This system is intended to feed a static
image slicer used for solar observations. The tight level of tolerances
required makes its design and tests a real challenging activity which
produces a lot of unexpected lessons to learn. The story after the
issues detection, the consequent root cause analysis, the additional
tests and tools developed to study the phenomena, and the construction
of the solutions and issue mitigation mechanisms provides a good
background to elaborate some recommendations for future developments.
---------------------------------------------------------
Title: The real time MCAO solar prototype for the EST
Authors: Montoya, Luzma M.; Velasco, Sergio; Sánchez Capuchino, Jorge;
Collados Vera, Manuel; Rodríguez Ramos, Luis Fernando; De Cos Juez,
Francisco J.; Asensio Ramos, Andrés.
2018SPIE10703E..48M Altcode:
The European Solar Telescope (EST) will be equipped with a MCAO
system to provide an excellent correction within one arcminute field
of view (FOV). A prototype of this system will be built with the same
requirements except for the frame rate. This prototype will allow to
test and verify new concepts for Solar MCAO, as, e.g., the integration
of neuronal networks in the reconstruction process. This prototype will
work as follows: a high-resolution image of the sun will be created and
perturbed by a turbulence simulator with different phase screens placed
at different heights. MCAO correction will be performed by one pupil DM
and four altitude DMs. Two wide field wavefront sensors will be used
to perform the tomography. The calibration and control strategies are
still to be defined in the lab for the future implementation on the
EST MCAO system. A scientific camera will evaluate the performance on
a 60" field. The prototype is currently under construction and it is
expected to be finished by 2019.
---------------------------------------------------------
Title: Commissioning tests of an Integral Field Unit (IFU) at GREGOR
solar telescope
Authors: Dominguez-Tagle, C.; Collados, M.; Esteves, M. A.; Vega
Reyes, N.; Vaz Cedillo, J. J.; López, R. L.; Paez, E.; Grassin, O.;
Gracia, F.
2018SPIE10702E..2ID Altcode:
We present the commissioning of an IFU based on image-slicers
and a 2D-Field-of-View Scanning System (FoV-SS) for the GREGOR
Infrared Spectrograph (GRIS). The prototype of the image-slicer has
eight slices of 1.8 mm x 0.1 mm in Zerodur, covering an area of 20
arcsec<SUP>2</SUP>. The FoV-SS, equipped with three Degrees of Freedom
(DoF), allows to scan a region of 1 arcmin<SUP>2</SUP>, feeding the
image-slicer with different portions of the field of view. A batch
of tests was done during the Assembly, Integration and Verification
(AIV) at GREGOR telescope.
---------------------------------------------------------
Title: Adaptive optics for high precision polarimetry: preliminary
tests of DM polarization
Authors: Stangalini, M.; Faccini, D.; Pedichini, F.; Piazzesi, R.;
Ermolli, I.; Giorgi, F.; Montoya, L. M.; Collados Vera, M.
2018SPIE10703E..4VS Altcode:
The European Solar Telescope (EST) will provide spectro-polarimetric
measurements of the solar atmosphere with unprecedented sensitivity
and accuracy. To this purpose, its optical scheme, as well as its MCAO
system, are designed to minimize the instrumental polarization. In the
framework of the EST design, we have started a series of laboratory
tests to characterize the effects of using deformable mirrors on
polarization measurements. In this contribution, we will show the
results of these tests. These results are not only relevant to solar
physics, but also to a number of other astrophysical research fields
where high precision polarimetry is becoming a fundamental tool, such as
for example exoplanets detection, and star formation characterization.
---------------------------------------------------------
Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
2018A&A...614A...2V Altcode: 2018arXiv180103686V
<BR /> Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings. <BR /> Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines. <BR /> Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h. <BR /> Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.
---------------------------------------------------------
Title: Partially Ionized Plasmas in Astrophysics
Authors: Ballester, José Luis; Alexeev, Igor; Collados, Manuel;
Downes, Turlough; Pfaff, Robert F.; Gilbert, Holly; Khodachenko,
Maxim; Khomenko, Elena; Shaikhislamov, Ildar F.; Soler, Roberto;
Vázquez-Semadeni, Enrique; Zaqarashvili, Teimuraz
2018SSRv..214...58B Altcode: 2017arXiv170707975B
Partially ionized plasmas are found across the Universe in many
different astrophysical environments. They constitute an essential
ingredient of the solar atmosphere, molecular clouds, planetary
ionospheres and protoplanetary disks, among other environments, and
display a richness of physical effects which are not present in fully
ionized plasmas. This review provides an overview of the physics of
partially ionized plasmas, including recent advances in different
astrophysical areas in which partial ionization plays a fundamental
role. We outline outstanding observational and theoretical questions
and discuss possible directions for future progress.
---------------------------------------------------------
Title: Rayleigh-Taylor instabilities with sheared magnetic fields
in partially ionised plasmas
Authors: Ruderman, M. S.; Ballai, I.; Khomenko, E.; Collados, M.
2018A&A...609A..23R Altcode: 2017A&A...609A..23R
<BR /> Aims: In the present study we investigate the nature of
the magnetic Rayleigh-Taylor instability appearing at a tangential
discontinuity in a partially ionised plasma when the effect of magnetic
shear is taken into account. <BR /> Methods: The partially ionised
character of the plasma is described by the ambipolar diffusion in
the induction equation. The dynamics of the plasma is investigated
in a single-fluid approximation. After matching the solutions on both
sides of the interface we derive a dispersion equation and calculate
the instability increment using analytical methods for particular
cases of parameters, and numerical investigation for a wide range
of parameters. <BR /> Results: We calculated the dependence of
the instability increment on the perturbation wavenumber. We also
calculated the dependence of the maximum instability increment on the
shear angle of the magnetic field for various values of the ionisation
degree. <BR /> Conclusions: Our results show that the Rayleigh-Taylor
instability becomes sensitive to the degree of plasma ionisation only
for plasmas with small values of plasma beta and in a very weakly
ionised state. Perturbations are unstable only for those wavenumbers
that are below a cut-off value.
---------------------------------------------------------
Title: Signatures of the impact of flare-ejected plasma on the
photosphere of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Rajaguru, S. P.;
Franz, M.; Kuckein, C.; Asensio Ramos, A.
2017A&A...608A..97F Altcode: 2017arXiv170806133F
<BR /> Aims: We investigate the properties of a sunspot light bridge,
focusing on the changes produced by the impact of a plasma blob ejected
from a C-class flare. <BR /> Methods: We observed a sunspot in active
region NOAA 12544 using spectropolarimetric raster maps of the four
Fe I lines around 15 655 Å with the GREGOR Infrared Spectrograph,
narrow-band intensity images sampling the Fe I 6173 Å line with
the GREGOR Fabry-Pérot Interferometer, and intensity broad-band
images in G-band and Ca II H-band with the High-resolution Fast
Imager. All these instruments are located at the GREGOR telescope at
the Observatorio del Teide, Tenerife, Spain. The data cover the time
before, during, and after the flare event. The analysis is complemented
with Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager
data from the Solar Dynamics Observatory. The physical parameters of
the atmosphere at differents heights were inferred using spectral-line
inversion techniques. <BR /> Results: We identify photospheric and
chromospheric brightenings, heating events, and changes in the Stokes
profiles associated with the flare eruption and the subsequent arrival
of the plasma blob to the light bridge, after traveling along an
active region loop. <BR /> Conclusions: The measurements suggest that
these phenomena are the result of reconnection events driven by the
interaction of the plasma blob with the magnetic field topology of the
light bridge. <P />Movies attached to Figs. 1 and 3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731374/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Detection of emission in the Si I 1082.7 nm line core in
sunspot umbrae
Authors: Orozco Suárez, D.; Quintero Noda, C.; Ruiz Cobo, B.;
Collados Vera, M.; Felipe, T.
2017A&A...607A.102O Altcode: 2017arXiv170906773O
Context. Determining empirical atmospheric models for the solar
chromosphere is difficult since it requires the observation and
analysis of spectral lines that are affected by non-local thermodynamic
equilibrium (NLTE) effects. This task is especially difficult in sunspot
umbrae because of lower continuum intensity values in these regions
with respect to the surrounding brighter granulation. Umbral data is
therefore more strongly affected by the noise and by the so-called
scattered light, among other effects. <BR /> Aims: The purpose of this
study is to analyze spectropolarimetric sunspot umbra observations
taken in the near-infrared Si I 1082.7 nm line taking NLTE effects into
account. Interestingly, we detected emission features at the line core
of the Si I 1082.7 nm line in the sunspot umbra. Here we analyze the
data in detail and offer a possible explanation for the Si I 1082.7 nm
line emission. <BR /> Methods: Full Stokes measurements of a sunspot
near disk center in the near-infrared spectral range were obtained
with the GRIS instrument installed at the German GREGOR telescope. A
point spread function (PSF) including the effects of the telescope,
the Earth's atmospheric seeing, and the scattered light was constructed
using prior Mercury observations with GRIS and the information provided
by the adaptive optics system of the GREGOR telescope during the
observations. The data were then deconvolved from the PSF using a
principal component analysis deconvolution method and were analyzed
via the NICOLE inversion code, which accounts for NLTE effects in the
Si I 1082.7 nm line. The information of the vector magnetic field was
included in the inversion process. <BR /> Results: The Si I 1082.7 nm
line seems to be in emission in the umbra of the observed sunspot after
the effects of scattered light (stray light coming from wide angles)
are removed. We show how the spectral line shape of umbral profiles
changes dramatically with the amount of scattered light. Indeed, the
continuum levels range, on average, from 44% of the quiet Sun continuum
intensity to about 20%. Although very low, the inferred levels are in
line with current model predictions and empirical umbral models. The Si
I 1082.7 nm line is in emission after adding more that 30% of scattered
light so that it is very sensitive to a proper determination of the
PSF. Additionally, we have thoroughly investigated whether the emission
is a byproduct of the particular deconvolution technique but have not
found any evidence to the contrary. Only the circular polarization
signals seem to be more sensitive to the deconvolution strategy
because of the larger amount of noise in the umbra. Interestingly,
current umbral empirical models are not able to reproduce the emission
in the deconvolved umbral Stokes profiles. The results of the NLTE
inversions suggests that to obtain the emission in the Si I 1082.7 nm
line, the temperature stratification should first have a hump located
at about log τ = -2 and start rising at lower heights when moving into
the transition region. <BR /> Conclusions: This is, to our knowledge,
the first time the Si I 1082.7 nm line is seen in emission in sunspot
umbrae. The results show that the temperature stratification of current
umbral models may be more complex than expected with the transition
region located at lower heights above sunspot umbrae. Our finding might
provide insights into understanding why the sunspot umbra emission in
the millimeter spectral range is less than that predicted by current
empirical umbral models.
---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
---------------------------------------------------------
Title: Numerical simulations of quiet Sun magnetic fields seeded by
the Biermann battery
Authors: Khomenko, E.; Vitas, N.; Collados, M.; de Vicente, A.
2017A&A...604A..66K Altcode: 2017arXiv170606037K
The magnetic fields of the quiet Sun cover at any time more than
90% of its surface and their magnetic energy budget is crucial to
explain the thermal structure of the solar atmosphere. One of the
possible origins of these fields is the action of the local dynamo
in the upper convection zone of the Sun. Existing simulations of the
local solar dynamo require an initial seed field and sufficiently
high spatial resolution in order to achieve the amplification of the
seed field to the observed values in the quiet Sun. Here we report
an alternative model of seeding based on the action of the Bierman
battery effect. This effect generates a magnetic field due to the
local imbalances in electron pressure in the partially ionized solar
plasma. We show that the battery effect self-consistently creates from
zero an initial seed field of a strength of the order of micro G, and
together with dynamo amplification allows the generation of quiet Sun
magnetic fields of a similar strength to those from solar observations.
---------------------------------------------------------
Title: High-frequency waves in the corona due to null points
Authors: Santamaria, I. C.; Khomenko, E.; Collados, M.; de Vicente, A.
2017A&A...602A..43S Altcode: 2017arXiv170406551S
This work aims to understand the behavior of non-linear waves in
the vicinity of a coronal null point. In previous works we have
shown that high-frequency waves are generated in such a magnetic
configuration. This paper studies those waves in detail in order to
provide a plausible explanation of their generation. We demonstrate
that slow magneto-acoustic shock waves generated in the chromosphere
propagate through the null point and produce a train of secondary shocks
that escape along the field lines. A particular combination of the
shock wave speeds generates waves at a frequency of 80 mHz. We speculate
that this frequency may be sensitive to the atmospheric parameters in
the corona and therefore can be used to probe the structure of this
solar layer. <P />Movies attached to Figs 2 and 4 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201629729/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Penumbral thermal structure below the visible surface
Authors: Borrero, J. M.; Franz, M.; Schlichenmaier, R.; Collados,
M.; Asensio Ramos, A.
2017A&A...601L...8B Altcode: 2017arXiv170502832B
Context. The thermal structure of the penumbra below its visible
surface (I.e., τ<SUB>5</SUB> ≥ 1) has important implications for
our present understanding of sunspots and their penumbrae: their
brightness and energy transport, mode conversion of magneto-acoustic
waves, sunspot seismology, and so forth. <BR /> Aims: We aim at
determining the thermal stratification in the layers immediately
beneath the visible surface of the penumbra: τ<SUB>5</SUB> ∈ [1,3]
(≈70-80 km below the visible continuum-forming layer) <BR /> Methods:
We analyzed spectropolarimetric data (I.e., Stokes profiles) in three Fe
I lines located at 1565 nm observed with the GRIS instrument attached
to the 1.5-m solar telescope GREGOR. The data are corrected for the
smearing effects of wide-angle scattered light and then subjected
to an inversion code for the radiative transfer equation in order
to retrieve, among others, the temperature as a function of optical
depth T(τ<SUB>5</SUB>). <BR /> Results: We find that the temperature
gradient below the visible surface of the penumbra is smaller than
in the quiet Sun. This implies that in the region τ<SUB>5</SUB> ≥
1 the penumbral temperature diverges from that of the quiet Sun. The
same result is obtained when focusing only on the thermal structure
below the surface of bright penumbral filaments. <BR /> Conclusions:
We interpret these results as evidence of a thick penumbra, whereby
the magnetopause is not located near its visible surface. In addition,
we find that the temperature gradient in bright penumbral filaments is
lower than in granules. This can be explained in terms of the limited
expansion of a hot upflow inside a penumbral filament relative to
a granular upflow, as magnetic pressure and tension forces from the
surrounding penumbral magnetic field hinder an expansion like this.
---------------------------------------------------------
Title: First tests on the Integral Field Unit for GRIS at GREGOR
Authors: Dominguez-Tagle, C.; Collados, M.; Lopez, R. L.; Vaz Cedillo,
J. J.; Esteves, M. A.; Paez, E.; Asensio Ramos, A.
2017sone.meetE..89D Altcode:
The observation of the highly dynamic events in the chromosphere with
current slit or filter spectropolarimeters is not adequate. With the
sake of incresing the time, spectral and spatial coherence of the
data, an integral field unit prototype has been developed for the
GRIS spectrograph on the GREGOR telescope. In this talk, we present
the first tests of the prototype.
---------------------------------------------------------
Title: Science with European Solar Telescope
Authors: Matthews, Sarah; Collados, Manuel
2017psio.confE..78M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The SOLARNET project
Authors: Collados, M.
2017psio.confE...1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Micro-meteorological contribution to the SHABAR seeing
retrieval
Authors: Hartogensis, Oscar; Hammerschlag, Robert; Sliepen, Guus;
Sprung, Detlev; von der Lühe, Oskar; Collados, Manuel
2017psio.confE.102H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SOLARNET WP70: Turbulence characterisation and correction
Authors: Collados, M.
2017psio.confE..98C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. <P />Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. <BR /> Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. <BR /> Methods:
We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
= 0 we find no evidence of regions with dynamically weak (B<
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.
---------------------------------------------------------
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
---------------------------------------------------------
Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F Altcode: 2016arXiv160800513F
Context. A significant part of the penumbral magnetic field returns
below the surface in the very deep photosphere. For lines in the
visible, a large portion of this return field can only be detected
indirectly by studying its imprints on strongly asymmetric and
three-lobed Stokes V profiles. Infrared lines probe a narrow layer
in the very deep photosphere, providing the possibility of directly
measuring the orientation of magnetic fields close to the solar
surface. <BR /> Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
datasets from Hinode and from the GREGOR infrared spectrograph. We
inferred the quality and polarimetric accuracy of the infrared data
after applying several reduction steps. Techniques of spectral
inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral
area covered by reversed-polarity and three-lobed Stokes V profiles for
sunspots at disk center. We determined the amount of reversed-polarity
and three-lobed Stokes V profiles in visible and infrared data of
sunspots at various heliocentric angles. From the results, we computed
center-to-limb variation curves, which were interpreted in the context
of existing penumbral models. <BR /> Results: Observations in visible
and near-infrared spectral lines yield a significant difference in the
penumbral area covered by magnetic fields of opposite polarity. In
the infrared, the number of reversed-polarity Stokes V profiles is
smaller by a factor of two than in the visible. For three-lobed Stokes
V profiles the numbers differ by up to an order of magnitude.
---------------------------------------------------------
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. <BR />
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. <BR /> Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. <BR />
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.
---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
<BR /> Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. <BR /> Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. <BR /> Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.
---------------------------------------------------------
Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
T.; Kneer, F.; Nicklas, H.; Sobotka, M.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. <BR />
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. <BR /> Methods: We present speckle-reconstructed images taken
with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
486 nm and 589 nm bands. We estimate the spatial resolution from the
noise characteristics of the image bursts and obtain 0.08″ at 589
nm. We describe structure details in individual best images as well
as the temporal evolution of selected features. <BR /> Results: We
find branched dark lanes extending along thin (≈1″) light bridges
in sunspots at various heliocentric angles. In thick (≳ 2″) light
bridges the branches are disconnected from the central lane and have a Y
shape with a bright grain toward the umbra. The images reveal that light
bridges exist on varying intensity levels and that their small-scale
features evolve on timescales of minutes. Faint light bridges show
dark lanes outlined by the surrounding bright features. Dark lanes are
very common and are also found in the boundary of pores. They have a
characteristic width of 0.1″ or smaller. Intergranular dark lanes of
that width are seen in active region granulation. <BR /> Conclusions: We
interpret our images in the context of magneto-convective simulations
and findings: while central dark lanes in thin light bridges are
elevated and associated with a density increase above upflows, the dark
lane branches correspond to locations of downflows and are depressed
relative to the adjacent bright plasma. Thick light bridges with central
dark lanes show no projection effect. They have a flat elevated plateau
that falls off steeply at the umbral boundary. There, Y-shaped filaments
form as they do in the inner penumbra. This indicates the presence of
inclined magnetic fields, meaning that the umbral magnetic field is
wrapped around the convective light bridge.
---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. <BR /> Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. <BR /> Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. <BR />
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. <BR /> Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. <BR /> Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. <BR /> Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. <BR /> Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: The European Solar Telescope (EST)
Authors: Matthews, Sarah A.; Collados, Manuel; Mathioudakis, Mihalis;
Erdelyi, Robertus
2016SPIE.9908E..09M Altcode:
The European Solar Telescope (EST) is being designed to optimize
studies of the magnetic coupling between the lower layers of the solar
atmosphere (the photosphere and chromosphere) in order to investigate
the origins and evolution of the solar magnetic field and its role
in driving solar activity. In order to achieve this, the thermal,
dynamic and magnetic properties of the solar plasma must be probed
over many scale heights and at intrinsic scales, requiring the use of
multi wavelength spectroscopy and spectropolarimetry at high spatial,
spectral and temporal resolution. In this paper we describe some of
the over-arching science questions that EST will address and briefly
outline the main features of the proposed telescope design and the
associated instrumentation package.
---------------------------------------------------------
Title: On the Magnetism and Dynamics of Prominence Legs Hosting
Tornadoes
Authors: Martínez González, M. J.; Asensio Ramos, A.; Arregui, I.;
Collados, M.; Beck, C.; de la Cruz Rodríguez, J.
2016ApJ...825..119M Altcode: 2016arXiv160501183M
Solar tornadoes are dark vertical filamentary structures observed
in the extreme ultraviolet associated with prominence legs and
filament barbs. Their true nature and relationship to prominences
requires an understanding of their magnetic structure and dynamic
properties. Recently, a controversy has arisen: is the magnetic field
organized forming vertical, helical structures or is it dominantly
horizontal? And concerning their dynamics, are tornadoes really rotating
or is it just a visual illusion? Here we analyze four consecutive
spectro-polarimetric scans of a prominence hosting tornadoes on its
legs, which helps us shed some light on their magnetic and dynamical
properties. We show that the magnetic field is very smooth in all the
prominence, which is probably an intrinsic property of the coronal
field. The prominence legs have vertical helical fields that show
slow temporal variation that is probably related to the motion of
the fibrils. Concerning the dynamics, we argue that (1) if rotation
exists, it is intermittent, lasting no more than one hour, and (2)
the observed velocity pattern is also consistent with an oscillatory
velocity pattern (waves).
---------------------------------------------------------
Title: Solar adaptive optics: specificities, lessons learned, and
open alternatives
Authors: Montilla, I.; Marino, J.; Asensio Ramos, A.; Collados, M.;
Montoya, L.; Tallon, M.
2016SPIE.9909E..1HM Altcode:
First on sky adaptive optics experiments were performed on the
Dunn Solar Telescope on 1979, with a shearing interferometer and
limited success. Those early solar adaptive optics efforts forced
to custom-develop many components, such as Deformable Mirrors and
WaveFront Sensors, which were not available at that time. Later on, the
development of the correlation Shack-Hartmann marked a breakthrough in
solar adaptive optics. Since then, successful Single Conjugate Adaptive
Optics instruments have been developed for many solar telescopes,
i.e. the National Solar Observatory, the Vacuum Tower Telescope and
the Swedish Solar Telescope. Success with the Multi Conjugate Adaptive
Optics systems for GREGOR and the New Solar Telescope has proved
to be more difficult to attain. Such systems have a complexity not
only related to the number of degrees of freedom, but also related
to the specificities of the Sun, used as reference, and the sensing
method. The wavefront sensing is performed using correlations on
images with a field of view of 10", averaging wavefront information
from different sky directions, affecting the sensing and sampling of
high altitude turbulence. Also due to the low elevation at which solar
observations are performed we have to include generalized fitting
error and anisoplanatism, as described by Ragazzoni and Rigaut, as
non-negligible error sources in the Multi Conjugate Adaptive Optics
error budget. For the development of the next generation Multi Conjugate
Adaptive Optics systems for the Daniel K. Inouye Solar Telescope and
the European Solar Telescope we still need to study and understand
these issues, to predict realistically the quality of the achievable
reconstruction. To improve their designs other open issues have to
be assessed, i.e. possible alternative sensing methods to avoid the
intrinsic anisoplanatism of the wide field correlation Shack-Hartmann,
new parameters to estimate the performance of an adaptive optics solar
system, alternatives to the Strehl and the Point Spread Function used
in night time adaptive optics but not really suitable to the solar
systems, and new control strategies more complex than the ones used in
nowadays solar Multi Conjugate Adaptive Optics systems. In this paper
we summarize the lessons learned with past and current solar adaptive
optics systems and focus on the discussion on the new alternatives to
solve present open issues limiting their performance.
---------------------------------------------------------
Title: Local seeing determination by thermal-CFD analysis to optimize
the European Solar Telescope image quality
Authors: Vega Reyes, N.; Cavaller, L.; Marco de la Rosa, J.; Baiges,
J.; Pont, A.; Pérez-Sánchez, D.; Codina, R.; Grivel, C.; Collados, M.
2016SPIE.9912E..1CV Altcode:
The European Solar Telescope, EST, ([1], [2]) is a 4-meter solar
telescope to be built in the Canary Islands in the near future. In
order to select the best configuration for the EST telescope facilities,
thermal and CFD analyses have been carried out to evaluate the seeing
degradation produced by the telescope environment. The aim of this
study is to calculate the values of optical parameters in different
configurations and to find out which one causes the lowest image quality
degradation. Starting from the determination of seeing degradation
along the optical path by CFD techniques, several configurations have
been compared making it possible to decide the future development line
for the EST.
---------------------------------------------------------
Title: Opto-mechanical design of an image slicer for the GRIS
spectrograph at GREGOR
Authors: Vega Reyes, N.; Esteves, M. A.; Sánchez-Capuchino, J.;
Salaun, Y.; López, R. L.; Gracia, F.; Estrada Herrera, P.; Grivel,
C.; Vaz Cedillo, J. J.; Collados, M.
2016SPIE.9912E..5PV Altcode:
An image slicer has been proposed for the Integral Field Spectrograph
[1] of the 4-m European Solar Telescope (EST) [2] The image
slicer for EST is called MuSICa (Multi-Slit Image slicer based on
collimator-Camera) [3] and it is a telecentric system with diffraction
limited optical quality offering the possibility to obtain high
resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by
coupling a polarimeter after the generated slit (or slits). Considering
the technical complexity of the proposed Integral Field Unit (IFU),
a prototype has been designed for the GRIS spectrograph at GREGOR
telescope at Teide Observatory (Tenerife), composed by the optical
elements of the image slicer itself, a scanning system (to cover
a larger field of view with sequential adjacent measurements) and
an appropriate re-imaging system. All these subsystems are placed
in a bench, specially designed to facilitate their alignment,
integration and verification, and their easy installation in front
of the spectrograph. This communication describes the opto-mechanical
solution adopted to upgrade GRIS while ensuring repeatability between
the observational modes, IFU and long-slit. Results from several tests
which have been performed to validate the opto-mechanical prototypes
are also presented.
---------------------------------------------------------
Title: Daytime turbulence profiling for EST and its impact in the
solar MCAO system design
Authors: Marco de la Rosa, J.; Montoya, L.; Collados, M.; Montilla,
I.; Vega Reyes, N.
2016SPIE.9909E..6XM Altcode:
The European Solar Telescope (EST) is a 4-meter facility to be built
in Canary Islands in the near future. Extensive daytime turbulence
observation campaigns with the long baseline SHABAR instrument has
been carried out in the two candidate sites from 2011 up to the end of
2014. The collected data together with nighttime turbulence data allow
the site characterization and the computation of average turbulence
profiles. These profiles can be used to feed numerical simulations
in order to take important design decisions for the multiconjugate
adaptive optics (MCAO) system in the telescope. This paper describes
the main tasks developed in this context up to date.
---------------------------------------------------------
Title: Observational Detection of Drift Velocity between Ionized
and Neutral Species in Solar Prominences
Authors: Khomenko, Elena; Collados, Manuel; Díaz, Antonio J.
2016ApJ...823..132K Altcode: 2016arXiv160401177K
We report the detection of differences in the ion and neutral velocities
in prominences using high-resolution spectral data obtained in 2012
September at the German Vacuum Tower Telescope (Observatorio del
Teide, Tenerife). A time series of scans of a small portion of a solar
prominence was obtained simultaneously with high cadence using the lines
of two elements with different ionization states, namely, Ca II 8542
Å and He I 10830 Å. The displacements, widths, and amplitudes of both
lines were carefully compared to extract dynamical information about the
plasma. Many dynamical features are detected, such as counterstreaming
flows, jets, and propagating waves. In all of the cases, we find a
very strong correlation between the parameters extracted from the
lines of both elements, confirming that both lines trace the same
plasma. Nevertheless, we also find short-lived transients where this
correlation is lost. These transients are associated with ion-neutral
drift velocities of the order of several hundred m s<SUP>-1</SUP>. The
patches of non-zero drift velocity show coherence in time-distance
diagrams.
---------------------------------------------------------
Title: Simulated interaction of magnetohydrodynamic shock waves with
a complex network-like region
Authors: Santamaria, I. C.; Khomenko, E.; Collados, M.; de Vicente, A.
2016A&A...590L...3S Altcode: 2016arXiv160408783S
We provide estimates of the wave energy reaching the solar chromosphere
and corona in a network-like magnetic field topology, including a
coronal null point. The waves are excited by an instantaneous strong
subphotospheric source and propagate through the subphotosphere,
photosphere, chromosphere, transition region, and corona with the
plasma beta and other atmospheric parameters varying by several
orders of magnitude. We compare two regimes of the wave propagation:
a linear and nonlinear regime. While the amount of energy reaching
the corona is similar in both regimes, this energy is transmitted at
different frequencies. In both cases the dominant periods of waves
at each height strongly depend on the local magnetic field topology,
but this distribution is only in accordance with observations in the
nonlinear case. <P />Movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201628515/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.
---------------------------------------------------------
Title: On the Robustness of the Pendulum Model for Large-amplitude
Longitudinal Oscillations in Prominences
Authors: Luna, M.; Terradas, J.; Khomenko, E.; Collados, M.; de
Vicente, A.
2016ApJ...817..157L Altcode: 2015arXiv151205125L
Large-amplitude longitudinal oscillations (LALOs) in prominences are
spectacular manifestations of solar activity. In such events nearby
energetic disturbances induce periodic motions on filaments with
displacements comparable to the size of the filaments themselves and
with velocities larger than 20 {km} {{{s}}}<SUP>-1</SUP>. The pendulum
model, in which the gravity projected along a rigid magnetic field is
the restoring force, was proposed to explain these events. However,
it can be objected that in a realistic situation where the magnetic
field reacts to the mass motion of the heavy prominence, the simplified
pendulum model could be no longer valid. We have performed nonlinear
time-dependent numerical simulations of LALOs considering a dipped
magnetic field line structure. In this work we demonstrate that for
even relatively weak magnetic fields the pendulum model works very
well. We therefore validate the pendulum model and show its robustness,
with important implications for prominence seismology purposes. With
this model it is possible to infer the geometry of the dipped field
lines that support the prominence.
---------------------------------------------------------
Title: Evershed flow observed in neutral and singly ionized iron lines
Authors: Khomenko, E.; Collados, M.; Shchukina, N.; Díaz, A.
2015A&A...584A..66K Altcode: 2015arXiv151000334K
The amplitudes of the Evershed flow are measured using pairs of
carefully selected Fe i and Fe ii spectral lines that are close in
wavelength and registered simultaneously. A sunspot belonging to the
NOAA 11582 group was scanned using the spectrograph of the German Vacuum
Tower Telescope (Observatorio del Teide, Tenerife). Velocities were
extracted from intensity profiles using the λ-meter technique. The
formation heights of the observed spectral lines were calculated using
semi-empirical models of a bright and dark penumbral filament taking
into account the sunspot location at the limb. Our objective is to
compare azimuthally averaged amplitudes of the Evershed flow extracted
from neutral and ion lines. We find measurable differences in the radial
component of the flow. All five pairs of lines show the same tendency;
the flow measured from the Fe i lines has an amplitude that is a few
hundred ms<SUP>-1</SUP> larger than that of the Fe ii lines. This
tendency is preserved at all photospheric heights and radial distances
in the penumbra. We discuss the possible origin of this effect.
---------------------------------------------------------
Title: Oscillations and Waves in Sunspots
Authors: Khomenko, Elena; Collados, Manuel
2015LRSP...12....6K Altcode:
A magnetic field modifies the properties of waves in a complex
way. Significant advances have been made recently in our understanding
of the physics of sunspot waves with the help of high-resolution
observations, analytical theories, as well as numerical simulations. We
review the current ideas in the field, providing the most coherent
picture of sunspot oscillations as by present understanding.
---------------------------------------------------------
Title: Where are the solar magnetic poles?
Authors: Pastor Yabar, A.; Martinez Gonzalez, M. J.; Collados, M.
2015MNRAS.453L..69P Altcode: 2018arXiv180409748P
Regardless of the physical origin of stellar magnetic fields -
fossil or dynamo induced - an inclination angle between the magnetic
and rotation axes is very often observed. Absence of observational
evidence in this direction in the solar case has led to generally assume
that its global magnetic field and rotation axes are well aligned. We
present the detection of a monthly periodic signal of the photospheric
solar magnetic field at all latitudes, and especially near the poles,
revealing that the main axis of the Sun's magnetic field is not aligned
with the surface rotation axis. This result reinforces the view of our
Sun as a common intermediate-mass star. Furthermore, this detection
challenges and imposes a strong observational constraint to modern
solar dynamo theories.
---------------------------------------------------------
Title: Full Stokes observations in the He i 1083 nm spectral region
covering an M3.2 flare
Authors: Kuckein, Christoph; Collados, Manuel; Sainz, Rafael Manso;
Ramos, Andrés Asensio
2015IAUS..305...73K Altcode: 2015arXiv150205505K
We present an exceptional data set acquired with the Vacuum Tower
Telescope (Tenerife, Spain) covering the pre-flare, flare, and
post-flare stages of an M3.2 flare. The full Stokes spectropolarimetric
observations were recorded with the Tenerife Infrared Polarimeter in
the He i 1083.0 nm spectral region. The object under study was active
region NOAA 11748 on 2013 May 17. During the flare the chomospheric
He i 1083.0 nm intensity goes strongly into emission. However, the
nearby photospheric Si i 1082.7 nm spectral line profile only gets
shallower and stays in absorption. Linear polarization (Stokes Q and U)
is detected in all lines of the He i triplet during the flare. Moreover,
the circular polarization (Stokes V) is dominant during the flare,
being the blue component of the He i triplet much stronger than the red
component, and both are stronger than the Si i Stokes V profile. The Si
i inversions reveal enormous changes of the photospheric magnetic field
during the flare. Before the flare magnetic field concentrations of up
to ~1500 G are inferred. During the flare the magnetic field strength
globally decreases and in some cases it is even absent. After the flare
the magnetic field recovers its strength and initial configuration.
---------------------------------------------------------
Title: MCAO numerical simulations for EST: analysis and parameter
optimization
Authors: Montoya, Luzma; Montilla, Iciar; Collados, Manuel
2015aoel.confE..16M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analytical study of high altitude turbulence wide-field
wavefront sensing: impact on the design and reconstruction quality
of future solar AO systems
Authors: Montilla, Iciar; Collados, Manuel; Montoya, Luzma; Tallon,
Michel
2015aoel.confE..18M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the nature of transverse coronal waves revealed by wavefront
dislocations
Authors: López Ariste, A.; Luna, M.; Arregui, I.; Khomenko, E.;
Collados, M.
2015A&A...579A.127L Altcode: 2015arXiv150503348L
Context. Coronal waves are an important aspect of the dynamics of the
plasma in the corona. Wavefront dislocations are topological features
of most waves in nature and also of magnetohydrodynamic waves. Are there
dislocations in coronal waves? <BR /> Aims: The finding and explanation
of dislocations may shed light on the nature and characteristics of the
propagating waves, their interaction in the corona, and in general on
the plasma dynamics. <BR /> Methods: We positively identify dislocations
in coronal waves observed by the Coronal Multi-channel Polarimeter
(CoMP) as singularities in the Doppler shifts of emission coronal
lines. We study the possible singularities that can be expected in
coronal waves and try to reproduce the observed dislocations in terms of
localization and frequency of appearance. <BR /> Results: The observed
dislocations can only be explained by the interference of a kink and
sausage wave modes propagating with different frequencies along the
coronal magnetic field. In the plane transverse to the propagation,
the cross-section of the oscillating plasma must be smaller than the
spatial resolution, and the two waves result in net longitudinal and
transverse velocity components that are mixed through projection onto
the line of sight. Alfvén waves can be responsible for the kink mode,
but a magnetoacoustic sausage mode is necessary in all cases. Higher
(flute) modes are excluded. The kink mode has a pressure amplitude
that is less than the pressure amplitude of the sausage mode, though
its observed velocity is higher. This concentrates dislocations on
the top of the loop. <BR /> Conclusions: To explain dislocations,
any model of coronal waves must include the simultaneous propagation
and interference of kink and sausage wave modes of comparable but
different frequencies with a sausage wave amplitude much smaller than
the kink one. <P />Appendix A is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424340/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Variation in sunspot properties between 1999 and 2014
Authors: Rezaei, R.; Beck, C.; Lagg, A.; Borrero, J. M.; Schmidt,
W.; Collados, M.
2015A&A...578A..43R Altcode:
<BR /> Aims: We study the variation in the magnetic field strength,
area, and continuum intensity of umbrae in solar cycles 23 and 24. <BR
/> Methods: We analyzed a sample of 374 sunspots observed from 1999
until 2014 with the Tenerife Infrared Polarimeter at the German
Vacuum Tower Telescope and the Facility InfRared Spectropolarimeter
at the Dunn Solar Telescope. The sample of field strength, area,
and intensities was used to trace any long-term or cyclic trend of
umbral properties in the last 15 years. <BR /> Results: Sunspots
are systematically weaker, that is, have a weaker field strength and
stronger continuum intensity, toward the end of cycle 23 than they
had at the maximum of cycle 23. The linear trend reverses with the
onset of cycle 24. We find that the field strength decreases in the
declining phase of cycle 23 by about 112 (± 16) G yr<SUP>-1</SUP>,
while it increases in the rising phase of cycle 24 by about 138 (±
72) G yr<SUP>-1</SUP>. The umbral intensity shows the opposite trend:
the intensity increases with a rate of 0.7 (± 0.3)% of I<SUB>c</SUB>
yr<SUP>-1</SUP> toward the end of cycle 23 and decreases with a rate
of 3.8 (± 1.5)% of I<SUB>c</SUB> yr<SUP>-1</SUP> toward the maximum of
cycle 24. The distribution of the umbral maximum field strength in cycle
24 is similar to that of cycle 23, but is slightly shifted toward lower
values by about 80 G, corresponding to a possible long-term gradient in
umbral field strength of about 7 ± 4 G yr<SUP>-1</SUP>. If instead of
the maximum umbral field we consider the average value over the entire
umbra, the distribution shifts by about 44 Gauss. <BR /> Conclusions:
The umbral brightness decreases in the rising stage of a solar cycle,
but increases from maximum toward the end of the cycle. Our results
do not indicate a drastic change of the solar cycle toward a grand
minimum in the near future.
---------------------------------------------------------
Title: Magnetohydrodynamic wave propagation from the subphotosphere
to the corona in an arcade-shaped magnetic field with a null point
Authors: Santamaria, I. C.; Khomenko, E.; Collados, M.
2015A&A...577A..70S Altcode: 2015arXiv150303094S
<BR /> Aims: The aim of this work is to study the energy transport
by means of Magnetohydrodynamic (MHD) waves propagating in quiet-Sun
magnetic topology from layers below the surface to the corona. Upwardly
propagating waves find obstacles, such as the equipartition layer
with plasma β = 1, the transition region, and null points, and they
get transmitted, converted, reflected, and refracted. Understanding
the mechanisms by which MHD waves can reach the corona can give us
information about the solar atmosphere and the magnetic structures. <BR
/> Methods: We carried out two-dimensional numerical simulations of
wave propagation in a magnetic field structure that consists of two
vertical flux tubes with the same polarity separated by an arcade-shaped
magnetic field. This configuration contains a null point in the corona,
which significantly modifies the behavior of the waves as they pass
near it. <BR /> Results: We describe in detail the wave propagation
through the atmosphere under different driving conditions. We also
present the spatial distribution of the mean acoustic and magnetic
energy fluxes for the cases where these calculations are possible,
as well as the spatial distribution of the dominant frequencies in
the whole domain. <BR /> Conclusions: We conclude that the energy
reaches the corona preferably along almost vertical magnetic fields,
that is, inside the vertical flux tubes. This energy is acoustic
in nature. Most of the magnetic energy stays concentrated below the
transition region owing to the refraction of the magnetic waves and
the continuous conversion of acoustic-like waves into fast magnetic
waves in the equipartition layer located in the photosphere where
plasma β = 1. However, part of the magnetic energy reaches the low
corona when propagating in the region where the arcades are located,
but waves are sent back downward into the lower atmosphere at the
null-point surroundings. This phenomenon, together with the reflection
and refraction of waves in the TR and the lower turning point, act as
a re-feeding of the atmosphere, which keeps oscillating during all the
simulation time even if a driver with a single pulse was used as initial
perturbation. In the frequency distribution, we find that high frequency
waves can reach the corona outside the vertical flux tubes. <P />Movies
related to Figs. 3, 7, and 11 are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424701/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Magnetic and Dynamical Photospheric Disturbances Observed
During an M3.2 Solar Flare
Authors: Kuckein, C.; Collados, M.; Manso Sainz, R.
2015ApJ...799L..25K Altcode: 2015arXiv150104207K
This Letter reports on a set of full-Stokes spectropolarimetric
observations in the near-infrared He i 10830 Å spectral region
covering the pre-flare, flare, and post-flare phases of an M3.2 class
solar flare. The flare originated on 2013 May 17 and belonged to
active region NOAA 11748. We detected strong He i 10830 Å emission
in the flare. The red component of the He i triplet peaks at an
intensity ratio to the continuum of about 1.86. During the flare,
He i Stokes V is substantially larger and appears reversed compared
to the usually larger Si i Stokes V profile. The photospheric Si i
inversions of the four Stokes profiles reveal the following: (1) the
magnetic field strength in the photosphere decreases or is even absent
during the flare phase, as compared to the pre-flare phase. However,
this decrease is not permanent. After the flare, the magnetic field
recovers its pre-flare configuration in a short time (i.e., 30 minutes
after the flare). (2) In the photosphere, the line of sight velocities
show a regular granular up- and downflow pattern before the flare
erupts. During the flare, upflows (blueshifts) dominate the area where
the flare is produced. Evaporation rates of ∼ {{10}<SUP>-3</SUP>}
and ∼ {{10}<SUP>-4</SUP>} g cm<SUP>-2</SUP> s<SUP>-1</SUP> have been
derived in the deep and high photosphere, respectively, capable of
increasing the chromospheric density by a factor of two in about 400 s.
---------------------------------------------------------
Title: Fluid description of multi-component solar partially ionized
plasma
Authors: Khomenko, E.; Collados, M.; Díaz, A.; Vitas, N.
2014PhPl...21i2901K Altcode: 2014arXiv1408.1871K
We derive self-consistent formalism for the description of
multi-component partially ionized solar plasma, by means of the coupled
equations for the charged and neutral components for an arbitrary
number of chemical species, and the radiation field. All approximations
and assumptions are carefully considered. Generalized Ohm's law is
derived for the single-fluid and two-fluid formalism. Our approach is
analytical with some order-of-magnitude support calculations. After
general equations are developed, we particularize to some frequently
considered cases as for the interaction of matter and radiation.
---------------------------------------------------------
Title: Modeling the effect of high altitude turbulence in wide-field
correlating wavefront sensing and its impact on the performance of
solar AO systems
Authors: Montilla, I.; Tallon, M.; Langlois, M.; Béchet, C.; Collados
Vera, M.
2014SPIE.9148E..6DM Altcode:
Solar Adaptive Optics (AO) shares many issues with night-time AO,
but it also has its own particularities. The wavefront sensing
is performed using correlations to efficiently work on the solar
granulation as a reference. The field of view for that measurement
usually is around 10". A sensor collecting such a wide field of view
averages wavefront information from different sky directions, and
the anisoplanatism thus has a peculiar impact on the performance of
solar AO and MCAO systems. Since we are entering the era of large
solar telescopes (European Solar Telescope, Advanced Technology
Solar Telescope) understanding this issue is crucial to evaluate
its impact on the performance of future AO systems. In this paper we
model the correlating wide field sensor and the way it senses the high
altitude turbulence. Thanks to this improved modelling, we present an
analysis of the influence of this sensing on the performance of each AO
configuration, conventional AO and MCAO. In addition to the analytical
study, simulations similar to the case of the EST AO systems with
FRiM-3D (the Fractal Iterative Method for Atmospheric tomography)
are used in order to highlight the relative influence of design
parameters. In particular, results show the performance evolution
when increasing the telescope diameter. We analyse the effect of high
altitude turbulence correlation showing that increasing the diameter
of the telescope does not degrade the performance when correcting on
the same spatial and temporal scales.
---------------------------------------------------------
Title: MuSICa image slicer prototype at 1.5-m GREGOR solar telescope
Authors: Calcines, A.; López, R. L.; Collados, M.; Vega Reyes, N.
2014SPIE.9147E..3IC Altcode:
Integral Field Spectroscopy is an innovative technique that is being
implemented in the state-of-the-art instruments of the largest
night-time telescopes, however, it is still a novelty for solar
instrumentation. A new concept of image slicer, called MuSICa
(Multi-Slit Image slicer based on collimator-Camera), has been
designed for the integral field spectrograph of the 4-m European Solar
Telescope. This communication presents an image slicer prototype of
MuSICa for GRIS, the spectrograph of the 1.5-m GREGOR solar telescope
located at the Observatory of El Teide. MuSICa at GRIS reorganizes a
2-D field of view of 24.5 arcsec into a slit of 0.367 arcsec width by
66.76 arcsec length distributed horizontally. It will operate together
with the TIP-II polarimeter to offer high resolution integral field
spectropolarimetry. It will also have a bidimensional field of view
scanning system to cover a field of view up to 1 by 1 arcmin.
---------------------------------------------------------
Title: Rayleigh-Taylor instability in prominences from numerical
simulations including partial ionization effects
Authors: Khomenko, E.; Díaz, A.; de Vicente, A.; Collados, M.;
Luna, M.
2014A&A...565A..45K Altcode: 2014arXiv1403.4530K
We study the Rayleigh-Taylor instability (RTI) at a prominence-corona
transition region in a non-linear regime. Our aim is to understand how
the presence of neutral atoms in the prominence plasma influences the
instability growth rate, as well as the evolution of velocity, magnetic
field vector, and thermodynamic parameters of turbulent drops. We
perform 2.5D numerical simulations of the instability initiated by
a multi-mode perturbation at the corona-prominence interface using a
single-fluid magnetohydrodynamic (MHD) approach including a generalized
Ohm's law. The initial equilibrium configuration is purely hydrostatic
and contains a homogeneous horizontal magnetic field forming an
angle with the direction in which the plasma is perturbed. We analyze
simulations with two different orientations of the magnetic field. For
each field orientation we compare two simulations, one for the pure
MHD case, and one including the ambipolar diffusion in Ohm's law (AD
case). Other than that, both simulations for each field orientation are
identical. The numerical results in the initial stage of the instability
are compared with the analytical linear calculations. We find that the
configuration is always unstable in the AD case. The growth rate of
the small-scale modes in the non-linear regime is up to 50% larger in
the AD case than in the purely MHD case and the average velocities of
flows are a few percentage points higher. Significant drift momenta
are found at the interface between the coronal and the prominence
material at all stages of the instability, produced by the faster
downward motion of the neutral component with respect to the ionized
component. The differences in temperature of the bubbles between the
ideal and non-ideal case are also significant, reaching 30%. There is
an asymmetry between large rising bubbles and small-scale down flowing
fingers, favoring the detection of upward velocities in observations.
---------------------------------------------------------
Title: Rayleigh-Taylor instability in partially ionized compressible
plasmas: One fluid approach
Authors: Díaz, A. J.; Khomenko, E.; Collados, M.
2014A&A...564A..97D Altcode: 2014arXiv1401.5388D
<BR /> Aims: We study the modification of the classical criterion for
the linear onset and growth rate of the Rayleigh-Taylor instability
(RTI) in a partially ionized (PI) plasma in the one-fluid description
by considering a generalized induction equation. <BR /> Methods:
The governing linear equations and appropriate boundary conditions,
including gravitational terms, are derived and applied to the case of
the RTI in a single interface between two partially ionized plasmas. The
boundary conditions lead to an equation for the frequencies in which
some have positive complex parts, marking the appearance of the
RTI. We study the ambipolar term alone first, extending the result to
the full induction equation later. <BR /> Results: The configuration
is always unstable because of the presence of a neutral species. In
the classical stability regime, the growth rate is small, since the
collisions prevent the neutral fluid to fully develop the RTI. For
parameters in the classical instability regime, the growth rate is
lowered, but the differences with the compressible MHD case are small
for the considered theoretical values of the collision frequencies
and diffusion coefficients for solar prominences. <BR /> Conclusions:
The PI modifies some aspects of the linear RTI instability, since it
takes into account that neutrals do not feel the stabilizing effect
of the magnetic field. For the set of parameters representative for
solar prominences, our model gives the resulting timescale comparable
to observed lifetimes of RTI plumes.
---------------------------------------------------------
Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon
Flare
Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael;
Asensio Ramos, Andres
2014cosp...40E.568C Altcode:
On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar
atmosphere on the active region AR 11748. The flare evolution was
observed at the German VTT of the Observatorio del Teide using the
instrument TIP-II, with spectropolarimetric measurements of the
photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet
at 1083 nm). Simultaneous spectroscopic data of the chromospheric
spectral line of Ca II at 854.2 nm and filtergrams at Halpha were
also obtained. The flare evolution as observed from the ground can be
compared with the changes observed by AIA@SDO at different ultraviolet
wavelengths. The ground observations covered several hours, including
the pre-flare, impulsive, gradual and post-flare phases. We present
maps of the magnetic field, thermal and dynamical properties of the
region during its evolution from pre- to post-flare phase.
---------------------------------------------------------
Title: Rayleigh-Taylor instability in partially ionized prominence
plasma
Authors: Khomenko, E.; Díaz, A.; de Vicente, A.; Collados, M.;
Luna, M.
2014IAUS..300...90K Altcode: 2013arXiv1310.7016K
We study Rayleigh-Taylor instability (RTI) at the coronal-prominence
boundary by means of 2.5D numerical simulations in a single-fluid MHD
approach including a generalized Ohm's law. The initial configuration
includes a homogeneous magnetic field forming an angle with the
direction in which the plasma is perturbed. For each field inclination
we compare two simulations, one for the pure MHD case, and one including
the ambipolar diffusion in the Ohm's law, otherwise identical. We find
that the configuration containing neutral atoms is always unstable. The
growth rate of the small-scale modes in the non-linear regime is larger
than in the purely MHD case.
---------------------------------------------------------
Title: 3D simulations of Rayleigh-Taylor instability in prominences
including partial ionization effects
Authors: Khomenko, Elena; Collados, Manuel; De Vicente, Angel; Luna,
Manuel; Diaz, Antonio
2014cosp...40E1476K Altcode:
We study the Rayleigh-Taylor instability (RTI) at a prominence-corona
transition region in a non-linear regime. Our aim is to understand how
the presence of neutral atoms in the prominence plasma influences the
instability growth rate, and the evolution of velocity, magnetic field
vector and thermodynamic parameters of turbulent drops. We perform
3D numerical simulations of the instability initiated by a multi-mode
perturbation at the corona-prominence interface using a single-fluid
MHD approach including a generalized Ohm's law. Pairs of simulations
are compared, one of them done under ideal MHD conditions, and others
include ambipolar diffusion (AD) in the Ohm's law. Other than that,
the simulations of each pair are identical in their magnetic field
orientation and thermal parameters. The numerical results in the
initial stage of the instability are compared with the analytical
linear calculations. We find that the configuration is always
unstable in the AD case. The growth rate of the small-scale modes in
the non-linear regime is up to 50% larger in the AD case than in the
purely MHD case and the average velocities of flows are a few percent
larger. Significant drift momenta are found at the interface between the
coronal and the prominence material at all stages of the instability,
produced by the faster downward motion of the neutral component with
respect to the ionized component. The differences in temperature of
the bubbles between the ideal and non-ideal case are also significant.
---------------------------------------------------------
Title: Preliminary performance analysis of the Multi-Conjugate AO
system of the EST
Authors: Montilla, Icíar; Béchet, Clémentine; Langlois, Maud;
Tallon, Michel; Collados, Manuel
2013aoel.confE..44M Altcode:
The European Solar Telescope (EST), a 4-meter diameter world-class
facility, has been designed to measure the properties of the solar
magnetic field with great accuracy and high spatial resolution. For
that reason, it incorporates an innovative built-in Multi-Conjugate
Adaptive Optics system (MCAO), featuring 4 high altitude DM's. It
combines a narrow field high order wavefront sensor, providing the
information to correct the ground layer, and a wide field lower
order sensor to control the higher altitude mirrors. Using sensors
collecting wide field of view information has several implications,
i.e. it averages wavefront information from different sky directions,
making the Strehl ratio to drop for low elevation observations. So far
these effects have not been studied in MCAO. We analyze this effect
by using the Fractal Iterative Method (FrIM), which incorporates a
wide field Shack-Hartmann, and we performed end to end simulations
of the EST MCAO system to analyze the performance of this system
for a large range of elevations, as required in solar observations,
and depending on the asterism geometry and number and height of DM's,
in order to find the best system configuration.
---------------------------------------------------------
Title: MuSICa: the Multi-Slit Image Slicer for the est Spectrograph
Authors: Calcines, A.; López, R. L.; Collados, M.
2013JAI.....250009C Altcode:
Integral field spectroscopy (IFS) is a technique that allows one
to obtain the spectra of all the points of a bidimensional field of
view simultaneously. It is being applied to the new generation of the
largest night-time telescopes but it is also an innovative technique
for solar physics. This paper presents the design of a new image
slicer, MuSICa (Multi-Slit Image slicer based on collimator-Camera),
for the integral field spectrograph of the 4-m aperture European
Solar Telescope (EST). MuSICa is a multi-slit image slicer that
decomposes an 80 arcsec<SUP>2</SUP> field of view into slices of 50
μm and reorganizes it into eight slits of 0.05 arcsec width × 200
arcsec length. It is a telecentric system with an optical quality
at diffraction limit compatible with the two modes of operation of
the spectrograph: spectroscopic and spectro-polarimetric. This paper
shows the requirements, technical characteristics and layout of MuSICa,
as well as other studied design options.
---------------------------------------------------------
Title: a High Resolution Integral Field Spectrograph for the European
Solar Telescope
Authors: Calcines, A.; López, R. L.; Collados, M.
2013JAI.....250007C Altcode:
This paper presents the proposal of a high resolution, integral
field spectrograph that is currently being designed for the 4-meter
aperture European Solar Telescope that will be located in the Canary
Islands. This instrument is optimized to study the solar chromosphere
and photosphere to allow the investigation of several phenomena
concentrated within these two layers. It will be able to observe
simultaneously a bidimensional field of view of 80 arcsec<SUP>2</SUP>
that is reorganized, using an integral field unit, into 8 long slits
of 200 arcsec length by 0.05 arcsec width. It will have the capability
to observe different layers of the Sun at the same time due to its
multi-wavelength capability that allows the observation of 5 visible
and 3 near-infrared wavelength intervals from 3900 to 23,000 Å,
with a spectral resolution of about 300,000. The designed instrument
is telecentric and presents an optical quality limited by diffraction.
---------------------------------------------------------
Title: Dislocations in Magnetohydrodynamic Waves in a Stellar
Atmosphere
Authors: López Ariste, A.; Collados, M.; Khomenko, E.
2013PhRvL.111h1103L Altcode: 2013arXiv1308.0145L
We describe the presence of wave front dislocations in
magnetohydrodynamic waves in stratified stellar atmospheres. Scalar
dislocations such as edges and vortices can appear in Alfvén waves, as
well as in general magnetoacoustic waves. We detect those dislocations
in observations of magnetohydrodynamic waves in sunspots in the solar
chromosphere. Through the measured charge of all the dislocations
observed, we can give for the first time estimates of the modal
contribution in the waves propagating along magnetic fields in solar
sunspots.
---------------------------------------------------------
Title: MHD wave propagation in the solar network
Authors: Calvo Santamaria, I.; Khomenko, E.; Cally, P. S.; Collados, M.
2013hsa7.conf..806C Altcode:
Magneto-acoustic and Alfvénic waves are ubiquitous in solar coronal
loops, possibly being excited by photospheric motions. It is not
clear, though, how these waves get so high, having obstacles such as
the acoustic cut-off frequency, reflection and refraction of fast
MHD waves and also the strongly reflecting transition region. In
this contribution we report on 2D numerical modelling of waves in
magnetic arcade structures extending from photospheric layers through
the transition region to the corona. Waves in the arcade are excited
by sub-photospheric p-modes. We discuss the behaviour of waves, their
conversion and propagation properties and possible mechanisms allowing
their escape through the transition region.
---------------------------------------------------------
Title: MuSICa at GRIS: a prototype image slicer for EST at GREGOR
Authors: Calcines, A.; Collados, M.; López, R. L.
2013hsa7.conf..939C Altcode:
This communication presents a prototype image slicer for the 4-m
European Solar Telescope (EST) designed for the spectrograph of the
1.5-m GREGOR solar telescope (GRIS). The design of this integral
field unit has been called MuSICa (Multi-Slit Image slicer based on
collimator-Camera). It is a telecentric system developed specifically
for the integral field, high resolution spectrograph of EST and presents
multi-slit capability, reorganizing a bidimensional field of view of
80 arcsec^{2} into 8 slits, each one of them with 200 arcsec length
× 0.05 arcsec width. It minimizes the number of optical components
needed to fulfil this multi-slit capability, three arrays of mirrors:
slicer, collimator and camera mirror arrays (the first one flat
and the other two spherical). The symmetry of the layout makes it
possible to overlap the pupil images associated to each part of the
sliced entrance field of view. A mask with only one circular aperture
is placed at the pupil position. This symmetric characteristic
offers some advantages: facilitates the manufacturing process,
the alignment and reduces the costs. In addition, it is compatible
with two modes of operation: spectroscopic and spectro-polarimetric,
offering a great versatility. The optical quality of the system is
diffraction-limited. The prototype will improve the performances of
GRIS at GREGOR and is part of the feasibility study of the integral
field unit for the spectrographs of EST. Although MuSICa has been
designed as a solar image slicer, its concept can also be applied to
night-time astronomical instruments (Collados et al. 2010, Proc. SPIE,
Vol. 7733, 77330H; Collados et al. 2012, AN, 333, 901; Calcines et
al. 2010, Proc. SPIE, Vol. 7735, 77351X)
---------------------------------------------------------
Title: EST: the largest and most sensitive spectropolarimeter
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A. : Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2013hsa7.conf..808C Altcode:
Magnetic field plays a crucial role to understand most phenomena
happening in the solar atmosphere. Sunspots, flares, prominences,
coronal mass ejections are well known examples of its interaction
with the solar plasma. To study the properties of this interaction,
one needs to analyze the imprint it leaves in the radiation through
the polarization induced in spectral lines, via the Zeeman and Hanle
effects. Outside sunspots, the polarization degree of the emitted
light is usually well below one part in one thousand, which requires
sophisticated techniques to measure it accurately. To further complicate
the situation, telescopes use mirrors and these introduce undesired
polarization which is two or three orders of magnitude larger than
that caused by the magnetic field of solar structures. For this reason,
present telescopes doing polarimetry require an adequate modelling to
correct the measured data from these spurious effects. In addition,
most of the magnetic field interactions with the plasma take place
at small scales. The best achievable angular resolution is mandatory
to adequately study magnetic phenomena. The European solar Telescope
(EST) has been defined to overcome these difficulties. Here, some
aspects of the design are described.
---------------------------------------------------------
Title: The European Solar Telescope
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2013MmSAI..84..379C Altcode:
The European Solar Telescope (EST) is a project to design, build and
operate an European Solar 4-meter class telescope to be located in the
Canary Islands, with the participation of institutions from fifteen
European countries gathered around the consortium EAST (European
Association for Solar Telescopes). The project main objective up to the
present has been the development of the conceptual design study (DS)
of a large aperture Solar Telescope. The study has demonstrated the
scientific, technical and financial feasibility of EST. The DS has been
possible thanks to the co-financing allocated specifically by the EU
and the combined efforts of all the participant institutions. Different
existing alternatives have been analysed for all telescope systems and
subsystems, and decisions have been taken on the ones that are most
compatible with the scientific goals and the technical strategies. The
present status of some subsystems is reviewed in this paper.
---------------------------------------------------------
Title: An integral field spectrograph for the 4-m European Solar
Telescope
Authors: Calcines, A.; Collados, M.; López, R. L.
2013MmSAI..84..416C Altcode:
This paper presents the proposal of a high resolution, integral field
spectrograph that is currently being designed for the 4-meter aperture
European Solar Telescope. This instrument is optimized for the study
of the solar chromosphere and photosphere to allow the investigation
of magnetic phenomena concentrated within these two layers. It will
observe a bidimensional field of view of 80 arcsec<SUP>2</SUP> that
is reorganized, using an integral field unit, into eight long slits
of 200 arcsec length by 0.05 arcsec width. A new concept of image
slicer has been specifically designed for this instrument. It is a
telecentric system and, because of the symmetry of its layout, it
presents several advantages, which are presented in this paper. The
spectrograph will have capabilities to observe different layers of
the Sun at the same time due to its multi-wavelength capability that
allows the observation of 5 visible and 3 near-infrared wavelength
intervals from 3900 to 23000 Å{}, with a spectral resolution of about
300,000. In addition, it is designed to offer two modes of operation:
spectroscopic and spectro-polarimetric. The optical quality of the
instrument is diffraction limited.
---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.
---------------------------------------------------------
Title: Simulations of Chromospheric Heating by Ambipolar Diffusion
Authors: Khomenko, E.; Collados Vera, M.
2012ASPC..463..281K Altcode: 2012arXiv1202.2252K
We propose a mechanism for efficient heating of the solar chromosphere
based on non-ideal plasma effects. Three ingredients are needed for the
work of this mechanism: (1) presence of neutral atoms; (2) presence
of a non-potential magnetic field; (3) decrease of the collisional
coupling of the plasma. Due to the decrease of collisional coupling, a
net relative motion appears between the neutral and ionized components,
usually referred to as “ambipolar diffusion.” This results in
a significant enhancement of current dissipation as compared to the
classical MHD case. We propose that the current dissipation in this
situation is able to provide enough energy to heat the chromosphere
by several kK on the time scale of minutes, or even seconds. In this
paper, we show that this energy supply might be sufficient to balance
the radiative energy losses of the chromosphere.
---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.
---------------------------------------------------------
Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from
the Photosphere to the Corona
Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera,
M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.;
Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M.
2012ASPC..463.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Instrumental Capabilities of the EST
Authors: Collados Vera, M.; EST Team
2012ASPC..463..413C Altcode:
The EST has recently finished its conceptual design study. A number of
instruments have been devised to make possible the observation of the
solar photosphere and chromosphere with high spatial, spectral, and
temporal resolution, as well as with high polarimetric sensitivity. To
achieve these goals, the telescope is provided with a powerful MCAO
system and a polarimetrically compensated optical design. In this
paper, a summary of the present situation of the telescope and its
different subsystems is outlined. Especial emphasis is put in the
description of the instruments and of the flexible light distribution
system. The latter will allow scientists to perform observations
using all instruments at the same time or individually, to maximize
the efficiency of the system. With this expected performance, EST will
provide to the community with data of unprecedented quality to study
solar magnetic phenomena at its finest scales.
---------------------------------------------------------
Title: Gregor@night: The future high-resolution stellar spectrograph
for the GREGOR solar telescope
Authors: Strassmeier, K. G.; Ilyin, I. V.; Woche, M.; Granzer,
T.; Weber, M.; Weingrill, J.; Bauer, S. -M.; Popow, E.; Denker, C.;
Schmidt, W.; von der Lühe, O.; Berdyugina, S.; Collados, M.; Koubsky,
P.; Hackman, T.; Mantere, M. J.
2012AN....333..901S Altcode:
We describe the future night-time spectrograph for the GREGOR solar
telescope and present its science core projects. The spectrograph
provides a 3-pixel resolution of up to R=87 000 in 45 échelle orders
covering the wavelength range 390-900 nm with three grating settings. An
iodine cell can be used for high-precision radial velocity work in the
500-630 nm range. The operation of the spectrograph and the telescope
will be fully automated without the presence of humans during night-time
and will be based on the successful STELLA control system. Future
upgrades include a second optical camera for even higher spectral
resolution, a Stokes-V polarimeter and a link to the laser-frequency
comb at the Vacuum Tower Telescope. The night-time core projects are a
study of the angular-momentum evolution of “The Sun in Time” and a
continuation of our long-term Doppler imaging of active stars.
---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
---------------------------------------------------------
Title: GRIS: The GREGOR Infrared Spectrograph
Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes,
M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg,
A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier,
K. G.; von der Lühe, O.; Volkmer, R.
2012AN....333..872C Altcode:
This paper describes the main characteristics of GRIS (GREGOR Infrared
Spectrograph), the grating spectrograph installed in the recently
inaugurated (May 2012) 1.5-meter GREGOR telescope located at the
Observatorio del Teide in Tenerife. The spectrograph has a standard
Czerny-Turner configuration with parabolic collimator and camera mirrors
that belong to the same conic surface. Although nothing prevents its
use at visible wavelengths, the spectrograph will be initially used
in combination with the infrared detector of the Tenerife Infrared
Polarimeter (TIP-II) in standard spectroscopic mode as well as for
spectropolarimetric measurements.
---------------------------------------------------------
Title: Conceptual design of the data handling system for the European
Solar Telescope
Authors: Ermolli, Ilaria; Cauzzi, Gianna; Collados, Manuel; Paletou,
Frederic; Reardon, Kevin; Aboudarham, Jean; Cirami, Roberto; Cosentino,
Rosario; Del Moro, Dario; Di Marcantonio, Paolo; Giorgi, Fabrizio;
Lafon, Martine; Pietropaolo, Ermanno; Romano, Paolo
2012SPIE.8448E..1SE Altcode:
We present an overview of the conceptual design of the data handling
unit of the ECS, the Control System for the European Solar Telescope
(EST). We will focus on describing the critical requirements for this
unit resulting from the overall design of the telescope, together with
its architecture and the results of the feasibility analysis carried
out to date.
---------------------------------------------------------
Title: Preliminary design of a multi-slit image slicer for EST
Authors: Calcines, A.; López, R. L.; Collados, M.
2012SPIE.8446E..74C Altcode:
Integral field spectroscopy is a modern technique used in Astronomy
to obtain simultaneous spectral information of all points in a
bidimensional field of view. This communication presents the preliminary
design of a multi-slit image slicer to be coupled to the spectrographs
of the 4 meters aperture European Solar Telescope. This integral
field unit will provide the observation of an 80 arcsec<SUP>2</SUP>
field of view, rearranged into 8 slits of 200 arcsec length by 0.05
arcsec width. Different optical design alternatives with diffraction
limited optical quality, as well as the design of a prototype for the
GREGOR solar telescope, are presented.
---------------------------------------------------------
Title: Multi-purpose grating spectrograph for the 4-meter European
Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Gelly, B.; Grauf, B.;
Hirzberger, J.; López Ariste, A.; Lopez, R. L.; Mein, P.; Sayéde, F.
2012SPIE.8446E..6TC Altcode:
This communication presents a family of spectrographs designed for
the European Solar Telescope. They can operate in four different
configurations: a long slit standard spectrograph (LsSS), two devices
based on subtractive double pass (TUNIS and MSDP) and one based on
an integral field, multi-slit, multi-wavelength configuration. The
combination of them composes the multi-purpose grating spectrograph of
EST, focused on supporting the different science cases of the solar
photosphere and chromosphere in the spectral range from 3900 Å to
23000 Å. The different alternatives are made compatible by using
the same base spectrographs and different selectable optical elements
corresponding to specific subsystems of each configuration.
---------------------------------------------------------
Title: Multi-conjugate AO for the European Solar Telescope
Authors: Montilla, I.; Béchet, C.; Le Louarn, M.; Tallon, M.;
Sánchez-Capuchino, J.; Collados Vera, M.
2012SPIE.8447E..5HM Altcode:
The European Solar Telescope (EST) will be a 4-meter diameter
world-class facility, optimized for studies of the magnetic coupling
between the deep photosphere and upper chromosphere. It will specialize
in high spatial resolution observations and therefore it has been
designed to incorporate an innovative built-in Multi-Conjugate Adaptive
Optics system (MCAO). It combines a narrow field high order sensor that
will provide the information to correct the ground layer and a wide
field low order sensor for the high altitude mirrors used in the MCAO
mode. One of the challenging particularities of solar AO is that it
has to be able to correct the turbulence for a wide range of observing
elevations, from zenith to almost horizon. Also, seeing is usually worse
at day-time, and most science is done at visible wavelengths. Therefore,
the system has to include a large number of high altitude deformable
mirrors. In the case of the EST, an arrangement of 4 high altitude DMs
is used. Controlling such a number of mirrors makes it necessary to use
fast reconstruction algorithms to deal with such large amount of degrees
of freedom. For this reason, we have studied the performance of the
Fractal Iterative Method (FriM) and the Fourier Transform Reconstructor
(FTR), to the EST MCAO case. Using OCTOPUS, the end-to-end simulator of
the European Southern Observatory, we have performed several simulations
with both algorithms, being able to reach the science requirement of a
homogeneous Strehl higher that 50% all over the 1 arcmin field of view.
---------------------------------------------------------
Title: Heating of the Magnetized Solar Chromosphere by Partial
Ionization Effects
Authors: Khomenko, E.; Collados, M.
2012ApJ...747...87K Altcode: 2011arXiv1112.3374K
In this paper, we study the heating of the magnetized solar
chromosphere induced by the large fraction of neutral atoms present
in this layer. The presence of neutrals, together with the decrease
with height of the collisional coupling, leads to deviations from the
classical magnetohydrodynamic behavior of the chromospheric plasma. A
relative net motion appears between the neutral and ionized components,
usually referred to as ambipolar diffusion. The dissipation of currents
in the chromosphere is enhanced by orders of magnitude due to the
action of ambipolar diffusion, as compared with the standard ohmic
diffusion. We propose that a significant amount of magnetic energy
can be released to the chromosphere just by existing force-free
10-40 G magnetic fields there. As a consequence, we conclude that
ambipolar diffusion is an important process that should be included
in chromospheric heating models, as it has the potential to rapidly
heat the chromosphere. We perform analytical estimations and numerical
simulations to prove this idea.
---------------------------------------------------------
Title: Data handling and control of the European Solar Telescope
Authors: Ermolli, I.; Bettonvil, F.; Cauzzi, G.; Cavaller, L.;
Collados, M.; Di Marcantonio, P.; Grivel, C.; Paletou, F.; Romano,
P.; Aboudarham, J.; Cirami, R.; Cosentino, R.; Giorgi, F.; Lafon,
M.; Laforgue, D.; Reardon, K.; Sliepen, G.
2012MSAIS..19..380E Altcode:
We describe some aspects of the facility operation that have been
considered for the design of the data handling and control of the
European Solar Telescope. The main sub-systems of the EST relevant for
the control are summarized, together with some information on current
solar data models.
---------------------------------------------------------
Title: Conceptual design of a high-resolution, integral field
spectrograph for the European Solar Telescope
Authors: Calcines, A.; Collados, M.; López, R. L.
2011hsa6.conf..660C Altcode:
This communication presents the current status of the conceptual design
of a high resolution, integral field spectrograph with multi-slit and
multi-wavelength capabilities, designed for the 4 meter European Solar
Telescope (EST).
---------------------------------------------------------
Title: Magneto-acoustic wave energy in sunspots: observations and
numerical simulations
Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.
2011hsa6.conf..630F Altcode:
We have reproduced some sunspot wave signatures obtained
from spectropolarimetric observations through 3D MHD
numericalsimulations. The results of the simulations arecompared with
the oscillations observed simultaneously at different heights from the
SiI lambda10827Å line, HeI lambda10830Å line, the CaII H core and
the FeI blends at the wings of the CaII H line. The simulations show
a remarkable agreement with the observations, and we have used them
to quantify the energy contribution of the magneto-acoustic waves to
the chromospheric heating in sunspots. Our findings indicate that the
energy supplied by these waves is 5-10 times lower than the amount
needed to balance the chromospheric radiative losses.
---------------------------------------------------------
Title: Venus transit 2004: Illustrating the capability of exoplanet
transmission spectroscopy
Authors: Hedelt, P.; Alonso, R.; Brown, T.; Collados Vera, M.; Rauer,
H.; Schleicher, H.; Schmidt, W.; Schreier, F.; Titz, R.
2011A&A...533A.136H Altcode: 2011arXiv1107.3700H
The transit of Venus in 2004 offered the rare possibility to remotely
sense a well-known planetary atmosphere using ground-based absorption
spectroscopy. Transmission spectra of Venus' atmosphere were obtained
in the near infrared using the Vacuum Tower Telescope (VTT) in
Tenerife. Since the instrument was designed to measure the very bright
photosphere of the Sun, extracting Venus' atmosphere was challenging. We
were able to identify CO<SUB>2</SUB> absorption lines in the upper
Venus atmosphere. Moreover, the relative abundance of the three
most abundant CO<SUB>2</SUB> isotopologues could be determined. The
observations resolved Venus' limb, showing Doppler-shifted absorption
lines that are probably caused by high-altitude winds. We demonstrate
the utility of ground-based measurements in analyzing the atmospheric
constituents of a terrestrial planet atmosphere using methods that
might be applied in future to terrestrial extrasolar planets.
---------------------------------------------------------
Title: Performance simulations for the conceptual design of the
European Solar Telescope (EST)
Authors: Cavaller, L.; Collados, M.; Castro, J.
2011SPIE.8336E..0GC Altcode: 2011SPIE.8336E..15C
The European Solar Telescope (EST) is a European collaborative
project promoted by the European Association for Solar Telescopes
(EAST) to build a high resolution 4m class solar telescope in the
Canary Islands. Since 2008 to 2011 a Design Study has been developed
to define the Conceptual Design of EST. During the Design Study,
several preliminary performance simulations have been developed in
order to demonstrate the feasibility of the proposed conceptual
design and provide preliminary feedback for the defined top-down
error budgets. Performance simulations developed during the Design
study include structural FE, servo-control of telescope main axes,
CFD analyses of wind load on the telescope, CFD analyses of local
seeing, transient thermal analysis of the telescope structure and
environment and AO performance. This paper presents a description of the
conceptual design of EST and the results of the preliminary performance
simulations, mainly focused to obtain the best telescope image quality.
---------------------------------------------------------
Title: Magnetoacoustic Wave Energy from Numerical Simulations of an
Observed Sunspot Umbra
Authors: Felipe, T.; Khomenko, E.; Collados, M.
2011ApJ...735...65F Altcode: 2011arXiv1104.4138F
We aim at reproducing the height dependence of sunspot wave signatures
obtained from spectropolarimetric observations through three-dimensional
MHD numerical simulations. A magnetostatic sunspot model based on
the properties of the observed sunspot is constructed and perturbed
at the photosphere, introducing the fluctuations measured with the Si
I λ10827 line. The results of the simulations are compared with the
oscillations observed simultaneously at different heights from the He
I λ10830 line, the Ca II H core, and the Fe I blends in the wings of
the Ca II H line. The simulations show a remarkable agreement with the
observations. They reproduce the velocity maps and power spectra at
the formation heights of the observed lines, as well as the phase and
amplification spectra between several pairs of lines. We find that the
stronger shocks at the chromosphere are accompanied with a delay between
the observed signal and the simulated one at the corresponding height,
indicating that shocks shift the formation height of the chromospheric
lines to higher layers. Since the simulated wave propagation matches
very well the properties of the observed one, we are able to use the
numerical calculations to quantify the energy contribution of the
magnetoacoustic waves to the chromospheric heating in sunspots. Our
findings indicate that the energy supplied by these waves is too low to
balance the chromospheric radiative losses. The energy contained at the
formation height of the lowermost Si I λ10827 line in the form of slow
magnetoacoustic waves is already insufficient to heat the higher layers,
and the acoustic energy which reaches the chromosphere is around 3-9
times lower than the required amount of energy. The contribution of
the magnetic energy is even lower.
---------------------------------------------------------
Title: The Polarization Optics for the European Solar Telescope
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2011ASPC..437..329B Altcode:
EST, the European Solar Telescope, is a 4-m class solar telescope,
which will be located at the Canary Islands. It is currently in the
conceptual design phase as a European funded project. In order to
fulfill the stringent requirements for polarimetric sensitivity
and accuracy, the polarimetry has been included in the design
work from the very beginning. The overall philosophy has been to
use a combination of techniques, which includes a telescope with
low (and stable) instrumental polarization, optimal full Stokes
polarimeters, differential measurement schemes, fast modulation
and demodulation, and accurate calibration, and at the same time not
giving up flexibility. The current baseline optical layout consists of a
14-mirror layout, which is polarimetrically compensated and non-varying
in time. In the polarization free F2 focus ample space is reserved for
calibration and modulators and a polarimetric switch. At instrument
level the s-, and p-planes of individual components are aligned,
resulting in a system in which eigenvectors can travel undisturbed
through the system.
---------------------------------------------------------
Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
Soltau, D.; Volkmer, R.
2011ASPC..437..351B Altcode:
A brief description of the new 1.5-meter solar telescope GREGOR located
at the Observatorio del Teide in Tenerife will be given. GREGOR will
provide a spatial resolution of about 75 km on the Sun, and with its
light collecting capability we will be able to study the development
of small magnetic features with high cadence. From the beginning,
it will be equipped with the GREGOR Fabry-Pérot Interferometer
(GFPI) for the visible spectral range and with a GRating Infrared
Spectrograph (GRIS). Both postfocus instruments can be combined
with a polarimeter, and in both cases the light is modulated by two
ferro-electric liquid crystals. A calibration unit can be inserted to
determine the instrumental polarization. Because of the altazimuthal
mount, time-dependent rotation of the polarimetric reference plane
is introduced, and we have to develop a polarization model of the
telescope. Measurements to verify this model are in preparation.
---------------------------------------------------------
Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
2011SoPh..268...57M Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
built by four institutions in Spain that flew on board the Sunrise
balloon-borne solar observatory in June 2009 for almost six days over
the Arctic Circle. As a polarimeter, IMaX uses fast polarization
modulation (based on the use of two liquid crystal retarders),
real-time image accumulation, and dual-beam polarimetry to reach
polarization sensitivities of 0.1%. As a spectrograph, the instrument
uses a LiNbO<SUB>3</SUB> etalon in double pass and a narrow band
pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
Stokes parameters at various points inside the spectral line. This
allows vector magnetograms, Dopplergrams, and intensity frames to be
produced that, after reconstruction, reach spatial resolutions in the
0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
cadences vary between 10 and 33 s, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in
various ways depending on the applied observing mode, from just two
points inside the line to 11 of them. All observing modes include
one extra wavelength point in the nearby continuum. Gauss equivalent
sensitivities are 4 G for longitudinal fields and 80 G for transverse
fields per wavelength sample. The line-of-sight velocities are estimated
with statistical errors of the order of 5 - 40 m s<SUP>−1</SUP>. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.
---------------------------------------------------------
Title: Magneto-acoustic waves in sunspots from observations and
numerical simulations
Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.
2011JPhCS.271a2040F Altcode: 2010arXiv1009.5512F
We study the propagation of waves from the photosphere to the
chromosphere of sunspots. From time series of cospatial Ca II H
(including its line blends) intensity spectra and polarimetric spectra
of Si I λ 1082.7 nm and He I λ 1083.0 nm we retrieve the line-of-sight
velocity at several heights. The analysis of the phase difference and
amplification spectra shows standing waves for frequencies below 4 mHz
and propagating waves for higher frequencies, and allows us to infer
the temperature and height where the lines are formed. Using these
observational data, we have constructed a model of sunspot, and we
have introduced the velocity measured with the photospheric Si I λ
1082.7 nm line as a driver. The numerically propagated wave pattern
fits reasonably well with the observed using the lines formed at higher
layers, and the simulations reproduce many of the observed features. The
observed waves are slow MHD waves propagating longitudinally along
field lines.
---------------------------------------------------------
Title: Numerical simulation of propagation of the MHD waves in
sunspots
Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky,
V.; Collados, M.
2010HiA....15..354P Altcode:
We present results of numerical 3D simulation of propagation of MHD
waves in sunspots. We used two self consistent magnetohydrostatic
background models of sunspots. There are two main differences
between these models: (i) the topology of the magnetic field and
(ii) dependence of the horizontal profile of the sound speed on
depth. The model with convex shape of the magnetic field lines near
the photosphere has non-zero horizorntal perturbations of the sound
speed up to the depth of 7.5 Mm (deep model). In the model with concave
shape of the magnetic field lines near the photosphere Δ c/c is close
to zero everywhere below 2 Mm (shallow model). Strong Alfven wave is
generated at the wave source location in the deep model. This wave is
almost unnoticeable in the shallow model. Using filtering technique
we separated magnetoacoustic and magnetogravity waves. It is shown,
that inside the sunspot magnetoacoustic and magnetogravity waves
are not spatially separated unlike the case of the horizontally
uniform background model. The sunspot causes anisotropy of the
amplitude distribution along the wavefront and changes the shape
of the wavefront. The amplitude of the waves is reduced inside the
sunspot. This effect is stronger for the magnetogravity waves than for
magnetoacoustic waves. The shape of the wavefront of the magnetogravity
waves is distorted stronger as well. The deep model causes bigger
anisotropy for both mgnetoacoustic and magneto gravity waves than the
shallow model.
---------------------------------------------------------
Title: Multi-layer Study of Wave Propagation in Sunspots
Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.
2010ApJ...722..131F Altcode: 2010arXiv1008.4004F
We analyze the propagation of waves in sunspots from the photosphere
to the chromosphere using time series of co-spatial Ca II H intensity
spectra (including its line blends) and polarimetric spectra of Si
I λ10,827 and the He I λ10,830 multiplet. From the Doppler shifts
of these lines we retrieve the variation of the velocity along the
line of sight at several heights. Phase spectra are used to obtain
the relation between the oscillatory signals. Our analysis reveals
standing waves at frequencies lower than 4 mHz and a continuous
propagation of waves at higher frequencies, which steepen into shocks
in the chromosphere when approaching the formation height of the Ca
II H core. The observed nonlinearities are weaker in Ca II H than in
He I lines. Our analysis suggests that the Ca II H core forms at a
lower height than the He I λ10,830 line: a time delay of about 20 s is
measured between the Doppler signal detected at both wavelengths. We fit
a model of linear slow magnetoacoustic wave propagation in a stratified
atmosphere with radiative losses according to Newton's cooling law to
the phase spectra and derive the difference in the formation height
of the spectral lines. We show that the linear model describes well
the wave propagation up to the formation height of Ca II H, where
nonlinearities start to become very important.
---------------------------------------------------------
Title: Magneto-acoustic Waves in Sunspots: First Results From a New
Three-dimensional Nonlinear Magnetohydrodynamic Code
Authors: Felipe, T.; Khomenko, E.; Collados, M.
2010ApJ...719..357F Altcode: 2010arXiv1006.2998F
Waves observed in the photosphere and chromosphere of sunspots
show complex dynamics and spatial patterns. The interpretation
of high-resolution sunspot wave observations requires modeling
of three-dimensional (3D) nonlinear wave propagation and mode
transformation in the sunspot upper layers in realistic spot model
atmospheres. Here, we present the first results of such modeling. We
have developed a 3D nonlinear numerical code specially designed to
calculate the response of magnetic structures in equilibrium to an
arbitrary perturbation. The code solves the 3D nonlinear MHD equations
for perturbations; it is stabilized by hyper-diffusivity terms and is
fully parallelized. The robustness of the code is demonstrated by a
number of standard tests. We analyze several simulations of a sunspot
perturbed by pulses of different periods at a subphotospheric level,
from short periods, introduced for academic purposes, to longer and
realistic periods of 3 and 5 minutes. We present a detailed description
of the 3D mode transformation in a non-trivial sunspot-like magnetic
field configuration, including the conversion between fast and slow
magneto-acoustic waves and the Alfvén wave, by calculation of the wave
energy fluxes. Our main findings are as follows: (1) the conversion from
acoustic to the Alfvén mode is only observed if the driving pulse is
located out of the sunspot axis, but this conversion is energetically
inefficient; (2) as a consequence of the cutoff effects and refraction
of the fast magneto-acoustic mode, the energy of the evanescent waves
with periods around 5 minutes remains almost completely below the level
β = 1; (3) waves with frequencies above the cutoff propagate field
aligned to the chromosphere and their power becomes dominating over that
of evanescent 5 minute oscillations, in agreement with observations.
---------------------------------------------------------
Title: Current concept for the 4m European Solar Telescope (EST)
optical design
Authors: Sánchez Capuchino, J.; Collados, M.; Soltau, D.; López,
R.; Rasilla, J. L.; Gelly, B.
2010SPIE.7652E..0SS Altcode: 2010SPIE.7652E..26S
The European Solar Telescope (EST) is a 4-m class solar telescope to
be located in the Canary Islands which is currently in its conceptual
design study. EST is a pan-european project (with 29 partners, plus 7
collaborating institutions, from 14 countries) promoted by the European
Association for Solar Telescopes (EAST). In the current concept,
the main telescope and its transfer optics assemblies 14 mirrors to
provide a Science Coudé Focus with an F/50 telecentric beam. It is
diffraction-limited in a FOV of 1 arcmin with an unvignetted FOV of
2'x2'. The whole system is being optimized in throughput for several
instruments observing simultaneously in a spectral range from 0.39
μm to 2.3 μm. Its innovative concept integrates an optical transfer
stage assembling multiconjugated adaptive optics with optical field
de-rotation and with a perfect balance of the whole system in terms
of polarization being also time and wavelength invariant.
---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V
With the integration of a 1-meter Cesic primary mirror the GREGOR
telescope pre-commissioning started. This is the first time, that
the entire light path has seen sunlight. The pre-commissioning period
includes testing of the main optics, adaptive optics, cooling system,
and pointing system. This time was also used to install a near-infrared
grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5
meter primary mirror is installed, commissioning will be completed,
and an extended phase of science verification will follow. In the near
future, GREGOR will be equipped with a multi-conjugate adaptive optics
system that is presently under development at KIS.
---------------------------------------------------------
Title: European Solar Telescope: project status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.;
Gelly, B.; Grivel-Gelly, C.; Pérez, A.; Socas-Navarro, H.; Soltau,
D.; Volkmer, R.
2010SPIE.7733E..0HC Altcode: 2010SPIE.7733E..15C
The European Solar Telescope is a project for a 4-meter class telescope
to be located in the Canary Islands. EST is promoted by the European
Association for Solar Telescopes (EAST). This is a consortium formed
by a number of research organizations from fifteen European countries
(Austria, Croatia, Czech Republic, France, Germany, Hungary, Italy,
the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden,
Switzerland, and United Kingdom). EST will specialize in high spatial
and temporal resolution using diverse instruments that can efficiently
produce two-dimensional spectropolarimetric information of the thermal,
dynamic and magnetic properties of the plasma over many scale heights
in the solar atmosphere. In this contribution, the status of the
development of the Design Study of EST is presented, emphasizing the
most important aspects of the optical design, mechanical structure, AO
and MCAO systems for wavefront correction, instruments and polarization
analysis.
---------------------------------------------------------
Title: Site-seeing measurements for the European Solar Telescope
Authors: Berkefeld, Th.; Bettonvil, F.; Collados, M.; López, R.;
Martín, Y.; Peñate, J.; Pérez, A.; Scharmer, G. B.; Sliepen, G.;
Soltau, D.; Waldmann, T. A.; van Werkhoven, T.
2010SPIE.7733E..4IB Altcode: 2010SPIE.7733E.141B
Seeing measurements are crucial for the optimum design of
(multi-conjugate) adaptive optics systems operating at solar
telescopes. For the design study of the 4-meter European Solar
Telescope, to be located in the Canary Islands, several instruments have
been constructed and operated, at the Observatorio del Roque de los
Muchachos (La Palma) and at the Observatorio del Teide (Tenerife),
to measure the properties of the ground layer and medium-high
altitude turbulence. Several units of short (42.34 cm) and two long
(323.06 cm) scintillometer bars are, or are to be, installed at
both observatories. In addition to them, two wide-field wavefront
sensors will be attached to the optical beams of the Swedish tower,
on La Palma, and of the German VTT, on Tenerife, simultaneously used
with the normal operation of the telescopes. These wavefront sensors
are of Shack-Hartmann type with ~1 arcminute field of view. In this
contribution, the instruments setup and their performance are described.
---------------------------------------------------------
Title: The heat stop for the 4-m European Solar Telescope EST
Authors: Berrilli, F.; Egidi, A.; Del Moro, D.; Manni, F.; Cocciolo,
M.; Scotto, A.; Volkmer, R.; Bettonvil, F. C. M.; Collados Vera, M.;
Cavaller Marquez, L.; Sanchez Capuchino, J.
2010SPIE.7733E..2ZB Altcode: 2010SPIE.7733E..92B
A study is presented for the realization of the heat stop for the
4-m European Solar Telescope EST, whose feasibility study will be
completed in 2011. EST is an on-axis Gregorian telescope, equipped
with a four-meter diameter primary mirror and primary focal length of
about six meters. The heat stop, positioned at the primary focus,
must be able to remove a heat load of 13 kW, while maintaining
its surfaces very close to room temperature, to avoid the onset of
seeing. In order to remove the heat, three configurations have been
taken into consideration: 1) a flat 45° inclined heat rejecter, 2)
a 45° conical heat rejecter and 3) a heat trap (made of a conical
heat rejecter and a cylindrical heat absorber). All devices include
an air removal system to avoid the formation of thermal plumes.
---------------------------------------------------------
Title: The polarization optics for the European Solar Telescope (EST)
Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.;
Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.;
Snik, F.; Socas-Navarro, H.
2010SPIE.7735E..6IB Altcode: 2010SPIE.7735E.214B
EST (European Solar Telescope) is a 4-m class solar telescope, which
is currently in the conceptual design phase. EST will be located at
the Canary Islands and aims at observations with the best possible
spectral, spatial and temporal resolution and best polarimetric
performance, of the solar photosphere and chromosphere, using a
suite of instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic
properties of the plasma over many scale heights, and ranging from
λ=350 until 2300 nm. In order to be able to fulfill the stringent
requirements for polarimetric sensitivity and accuracy, from the very
beginning the polarimetry has been included in the design work. The
overall philosophy has been to use a combination of techniques, which
includes a telescope with low (and stable) instrumental polarization,
optimal full Stokes polarimeters, differential measurement schemes,
fast modulation and demodulation, and accurate calibration. The
current baseline optical layout consists of a 14-mirror layout,
which is polarimetrically compensated and nonvarying in time. In the
polarization free F2 focus ample space is reserved for calibration and
modulators and a polarimetric switch. At instrument level the s-, and
p-planes of individual components are aligned, resulting in a system
in which eigenvectors can travel undisturbed through the system.
---------------------------------------------------------
Title: Data handling and control for the European Solar Telescope
Authors: Ermolli, Ilaria; Bettonvil, Felix; Cauzzi, Gianna; Cavaller,
Lluis; Collados, Manuel; Di Marcantonio, Paolo; Paletou, Frederic;
Romano, Paolo; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario;
Giorgi, Fabrizio; Lafon, Martine; Laforgue, Didier; Reardon, Kevin;
Sliepen, Guus
2010SPIE.7740E..0GE Altcode: 2010SPIE.7740E..13E
We introduce the concepts for the control and data handling systems of
the European Solar Telescope (EST), the main functional and technical
requirements for the definition of these systems, and the outcomes
from the trade-off analysis to date. Concerning the telescope control,
EST will have performance requirements similar to those of current
medium-sized night-time telescopes. On the other hand, the science
goals of EST require the simultaneous operation of three instruments
and of a large number of detectors. This leads to a projected data
flux that will be technologically challenging and exceeds that of
most other astronomical projects. We give an overview of the reference
design of the control and data handling systems for the EST to date,
focusing on the more critical and innovative aspects resulting from
the overall design of the telescope.
---------------------------------------------------------
Title: Adaptive optics and MCAO for the 4-m European Solar Telescope
EST
Authors: Soltau, D.; Berkefeld, T.; Sánchez Capuchino, J.; Collados
Vera, M.; Del Moro, D.; Löfdahl, M.; Scharmer, G.
2010SPIE.7736E..0US Altcode: 2010SPIE.7736E..27S
A consortium of more than 20 European solar physics institution from 15
different countries is conducting a design study for a 4 m class solar
telescope which shall be situated at the Canary Islands. In this paper
we introduce the AO and MCAO design concept for EST. A ground layer
deformable mirror is combined with an arrangement of four deformable
layer mirrors. A combination of Shack-Hartmann wave front sensors with
wide and narrow fields of view is used to control the system and to
achieve a corrected field of view of one arcmin.
---------------------------------------------------------
Title: Current concept for the 4m European Solar Telescope (EST)
optical design
Authors: Sánchez-Capuchino, J.; Collados, M.; Soltau, D.; López,
R.; Rasilla, J. L.; Gelly, B.
2010SPIE.7733E..36S Altcode: 2010SPIE.7733E..99S
The European Solar Telescope (EST) is a pan-european project (with 29
partners, plus 7 collaborating institutions, from 14 countries) for the
conceptual design study of a 4-meter class solar telescope promoted by
the European Association for Solar Telescopes (EAST) to be located in
the Canary Islands. The telescope, in the conceptual study, provides a
Coudé focus with an F/50 telecentric beam. It is diffraction-limited
in a FOV of 1 arcmin and it will be optimized in throughput for several
instruments observing simultaneously in a spectral range from 0.39
μm to 2.3 μm. Its innovative concept integrates an optical transfer
stage assembling multiconjugated adaptive optics with optical field
de-rotation and with a perfect balance of the whole system in terms
of polarization being time and wavelength invariant.
---------------------------------------------------------
Title: Feasibility study of high-resolution integral-field
spectrographs for EST with multislit and multi-wavelength capabilities
Authors: Calcines, Ariadna; Collados, Manuel; López, Roberto L.
2010SPIE.7735E..1XC Altcode: 2010SPIE.7735E..65C
This communication shows the feasibility study of a new instrument
designed for the 4 meter European Solar Telescope (EST) for high
resolution spectro-polarimetric observations. This paper is specifically
focused on the spectrographs that allow the simultaneous observation
of 5 visible and 4 near-infrared wavelengths (complying with the
science requirements), with 8 entrance slits of 200arcsec each fed by
an integral field unit covering an area on the solar surface of 9 x
9 arcsec<SUP>2</SUP>.
---------------------------------------------------------
Title: Spectrograph capabilities of the European Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Grauf, B.;
Grivel-Gelly, C.; Hirzberger, J.; López Ariste, A.; López López,
R.; Mein, P.; Sayède, F.
2010SPIE.7735E..20C Altcode: 2010SPIE.7735E..68C
EST is a project for a 4-meter class telescope to be located in the
Canary Islands. EST will be optimized for studies of the magnetic
coupling between the photosphere and the chromosphere. This requires
high spatial and temporal resolution diagnostics tools of properties of
the plasma, by using multiple wavelength spectropolarimetry. To achieve
these goals, visible and near-IR multi-purpose spectrographs are being
designed to be compatible with different modes of use: LsSS (Long-slit
Standard Spectrograph), multi-slit multi-wavelength spectrograph with
an integral field unit, TUNIS (Tunable Universal Narrow-band Imaging
Spectrograph), and new generation MSDP (Multi-channel Subtractive
Double-pass Spectrograph). In this contribution, these different
instrumental configurations are described.
---------------------------------------------------------
Title: European Solar Telescope: Progress status
Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly,
B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team
2010AN....331..615C Altcode:
In this paper, the present status of the development of the design of
the European Solar Telescope is described. The telescope is devised to
have the best possible angular resolution and polarimetric performance,
maximizing the throughput of the whole system. To that aim, adaptive
optics and multi-conjugate adaptive optics are integrated in the
optical path. The system will have the possibility to correct for the
diurnal variation of the distance to the turbulence layers, by using
several deformable mirrors, conjugated at different heights. The
present optical design of the telescope distributes the optical
elements along the optical path in such a way that the instrumental
polarization induced by the telescope is minimized and independent
of the solar elevation and azimuth. This property represents a large
advantage for polarimetric measurements. The ensemble of instruments
that are planned is also presented.
---------------------------------------------------------
Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
D.; Strassmeier, K. G.
2010AN....331..624V Altcode:
The integration and verification phase of the GREGOR telescope
reached an important milestone with the installation of the
interim 1 m SolarLite primary mirror. This was the first time
that the entire light path had seen sunlight. Since then extensive
testing of the telescope and its subsystems has been carried out. The
integration and verification phase will culminate with the delivery and
installation of the final 1.5 m Zerodur primary mirror in the summer of
2010. Observatory level tests and science verification will commence in
the second half of 2010 and in 2011. This phase includes testing of the
main optics, adaptive optics, cooling and pointing systems. In addition,
assuming the viewpoint of a typical user, various observational modes
of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
Spectrograph (GRIS), and high-speed camera systems will be tested to
evaluate if they match the expectations and science requirements. This
ensures that GREGOR will provide high-quality observations with its
combination of (multi-conjugate) adaptive optics and advanced post-focus
instruments. Routine observations are expected for 2012.
---------------------------------------------------------
Title: Mode transformation and frequency change with height in 3D
numerical simulations of magneto-acoustic wave propagation in sunspots
Authors: Felipe, T.; Khomenko, E.; Collados, M.
2010arXiv1005.3684F Altcode:
Three-dimensional numerical simulations of magnetoacoustic wave
propagation are performed in a sunspot atmosphere with a computational
domain covering from the photosphere to the chromosphere. The
wave source, with properties resembling the solar spectrum, is
located at different distances from the axis of the sunspot for
each simulation. These results are compared with the theory of mode
transformation and also with observational features. Simulations show
that the dominant oscillation frequency in the chromosphere decreases
with the radial distance from the sunspot axis. The energy flux of the
different wave modes involved, including de Alfvén mode, is evaluated
and discussed.
---------------------------------------------------------
Title: Numerical Simulation of Excitation and Propagation of
Helioseismic MHD Waves in Magnetostatic Models of Sunspots
Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky,
V.; Collados, M.
2010arXiv1002.1117P Altcode:
We present comparison of numerical simulations of propagation of
MHD waves,excited by subphotospheric perturbations, in two different
("deep" and "shallow") magnetostatic models of the sunspots. The "deep"
sunspot model distorts both the shape of the wavefront and its amplitude
stronger than the "shallow" model. For both sunspot models, the surface
gravity waves (f-mode) are affected by the sunspots stronger than
the acoustic p-modes. The wave amplitude inside the sunspot depends
on the photospheric strength of the magnetic field and the distance
of the source from the sunspot axis. For the source located at 9 Mm
from the center of the sunspot, the wave amplitude increases when
the wavefront passes through the central part of the sunspot. For
the source distance of 12 Mm, the wave amplitude inside the sunspot
is always smaller than outside. For the same source distance from
the sunspot center but for the models with different strength of the
magnetic field, the wave amplitude inside the sunspot increases with
the strength of the magnetic field. The simulations show that unlike
the case of the uniform inclined background magnetic field, the p-
and f-mode waves are not spatially separated inside the sunspot where
the magnetic field is strongly non-uniform. These properties have to
be taken into account for interpretation of observations of MHD waves
traveling through sunspot regions.
---------------------------------------------------------
Title: NUMERICAL SIMULATION OF PROPAGATION AND SCATTERING OF THE
MHD WAVES IN SUNSPOTS
Authors: Parchevsky, K.; Kosovichev, A. G.; Khomenko, E.; Collados, M.
2009AGUFMSH23B1535P Altcode:
We present comparison of numerical simulation results of MHD wave
propagation in two different magnitostatic models of sunspots
refferred to as "deep" and "shallow" models. The "deep" model has
convex shape of magnetic field lines near the photosphere and non-zero
horizorntal perturbations of the sound speed up to the bottom of the
model (7.5 Mm). The "shallow" model has concave shape of the magnetic
field lines near the photosphere and horizontally uniform sound speed
below 2 Mm. Common feature of MHD waves behaviour in these two models
is that for weak magnetic field (less than 1kG at the photosphere)
waves reduce their amplitude when they reach the center of the sunspot
and restore the amplitude when pass the center. For the "deep" model
this effect is bigger than for the "shallow" model. The wave amplitude
inside sunspots depends on the strength of the magnetic field. For the
"shallow" model with photospheric magnetic field of 2.2 kG the wave
amplitude inside the sunspot becomes bigger than outside (opposite to
the weak magnetic field). The wave amplitude depends on the distance
of the source from the sunspot center. For the "shallow" model and
source distance of 9 Mm from the sunspot center the wave amplitude at
some moment (when the wavefront passes the sunspot center) becomes
bigger inside the sunspot than outside. For the source distance
of 12 Mm the wave amplitude remains smaller inside the sunspot
than outside for all moments of time. Using filtering technique we
separated magnetoacoustic and magnetogravity waves. Simulations show
that the sunspot changes the shape of the wave front and amplitude
of the f-modes significantly stronger than the p-modes. It is shown,
that inside the sunspot magnetoacoustic and magnetogravity waves are
not spatially separated unlike the case of the horizontally uniform
background model. Strong Alfven wave is generated at the wave source
location in the "deep" model. This wave exists in the "shallow" model
as well, but with much smaller amplitude.
---------------------------------------------------------
Title: Sunspot seismic halos generated by fast MHD wave refraction
Authors: Khomenko, E.; Collados, M.
2009A&A...506L...5K Altcode: 2009arXiv0905.3060K
Aims: We suggest an explanation for the high-frequency power excess
surrounding active regions known as seismic halos. <BR />Methods:
We use numerical simulations of magneto-acoustic wave propagation in
a magnetostatic sunspot model. <BR />Results: We propose that seismic
halos can be caused by the additional energy injected by high-frequency
fast mode waves refracted in the higher atmosphere due to the rapid
increase of the Alfvén speed. Our model qualitatively explains the
magnitude of the halo and allows us to make predictions of its behavior
that can be checked in future observations.
---------------------------------------------------------
Title: The energy of waves in the photosphere and lower
chromosphere. I. Velocity statistics
Authors: Beck, C.; Khomenko, E.; Rezaei, R.; Collados, M.
2009A&A...507..453B Altcode: 2009arXiv0905.1011B
Context: Acoustic waves are one of the primary suspects besides magnetic
fields for the chromospheric heating process to temperatures above
radiative equilibrium (RE). <BR />Aims: We derived the mechanical
wave energy as seen in line-core velocities on disc centre to obtain
a measure of mechanical energy flux with height for a comparison
with the energy requirements in a semi-empirical atmosphere model,
the Harvard-Smithsonian reference atmosphere (HSRA). <BR />Methods: We
analyzed a 1-hour time series and a large-area map of Ca II H spectra
on the traces of propagating waves. We analyzed the velocity statistics
of several spectral lines in the wing of Ca II H, and the line-core
velocity of Ca II H. We converted the velocity amplitudes into volume
(∝ ρ v^2) and mass energy densities (∝ v^2). For comparison, we
used the increase of internal energy (∝ R ρ Δ T) necessary to lift
a RE atmosphere to the HSRA temperature stratification. <BR />Results:
We find that the velocity amplitude grows in agreement with linear
wave theory and thus slower with height than predicted from energy
conservation. The mechanical energy of the waves above around z ~ 500 km
is insufficient to maintain on a long-term average the chromospheric
temperature rise in the semi-empirical HSRA model. The intensity
variations of the Ca line core (z ~ 1000 km) can, however, be traced
back to the velocity variations of the lowermost forming spectral line
considered (z ~ 250 km). <BR />Conclusions: The chromospheric intensity,
and hence, (radiation) temperature variations are seen to be induced by
passing waves originating in the photosphere. The wave energy is found
to be insufficient to maintain the temperature stratification of the
semi-empirical HSRA model above 500 km. We will in a following paper of
this series investigate the energy contained in the intensity variations
to see if the semi-empirical model is appropriate for the spectra.
---------------------------------------------------------
Title: Flux Cancellation in the Solar Photosphere: a near-IR Line
of Mn I as a Diagnostic Tool
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2009ASPC..405..215A Altcode:
Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR
line of Mn I at 15262.702 Å provides a new diagnostic window for
exploring the magnetism of the quiet Sun. In contrast with previously
considered Mn I lines located at visible wavelengths this near-IR
line has the advantage that the shape of its intensity profile is very
sensitive to the presence of magnetic fields. This enhanced magnetic
sensitivity is produced by the coincidence of two favorable facts:
the enhanced Zeeman sensitivity of near-IR lines and because this line
is subjected to particularly strong Paschen-Back perturbations due to
the hyperfine structure of manganese. Of great diagnostic interest is
that the intensity profile itself give us information on the unsigned
magnetic flux, while the polarization profiles are sensitive to the
net flux. An application to spectropolarimetric observations with the
Tenerife Infrared Polarimeter has allowed us to obtain the first flux
cancellation map in an enhanced network region.
---------------------------------------------------------
Title: Observational Signatures of Numerically Simulated MHD Waves
in Small-scale Flux Sheets
Authors: Khomenko, E.; Collados, M.; Felipe, T.
2009ASPC..405..183K Altcode: 2008arXiv0801.3966K
We present some results obtained from the synthesis of Stokes profiles
in small-scale flux sheets with propagating MHD waves. To that aim,
2D flux sheets showing internal structure have been excited with 5
min period drivers, allowing non-linear waves to propagate inside the
magnetic structure. The observational signatures of these waves in
Stokes profiles of several spectral lines that are commonly used in
spectropolarimetric measurements are discussed.
---------------------------------------------------------
Title: Influence of Coronal EUV Irradiance on the Stokes Profiles
of the He I 10830 Å Multiplet
Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M.
2009ASPC..405..297C Altcode:
One of the most useful spectral windows for spectropolarimetric
investigations of the solar chromosphere is the one provided by the
spectral lines of the He I 10830 Å multiplet, whose polarization
signals are sensitive to the Hanle and Zeeman effects. However, in
order to be able to carry out reliable diagnostics of the dynamic
and magnetic properties of the solar outer atmosphere it is crucial
to have a good physical understanding of the sensitivity of the
observed spectral line radiation to the various competing triggering
mechanisms. Here we report a series of on-disk and off-the-limb
non-LTE calculations of the 10830 Å absorption and emission profiles,
focusing our investigation on their sensitivity to the EUV coronal
irradiation and the model atmosphere used in the calculations. We show
in what respects the on-disk case sensitivity of the polarization
signals induced by the Zeeman effect to the EUV coronal irradiance,
and investigate whether or not inversions based on the Milne-Eddington
model are reliable. Concerning the off-the-limb case we demonstrate
that the intensity ratio of the blue to the red components of the
He I 10830 Å multiplet is a sensitive function of the amount of EUV
coronal illumination. Therefore, measurements of this observable as
a function of the distance to the limb and its confrontation with
radiative transfer modeling might give us valuable information on the
physical properties of the solar atmosphere and on the amount of EUV
radiation penetrating the chromosphere from above.
---------------------------------------------------------
Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot
interferometer
Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker,
C.; Hofmann, A.; Kneer, F.; Puschmann, K. G.
2009IAUS..259..665B Altcode:
One of the first post-focus instruments of the new solar telescope
GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the
Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope
(VTT) on Tenerife. This spectrometer is equipped with a full-Stokes
polarimeter. The modulation is performed with two ferroelectric liquid
crystals, one acting nominally as quarter-wave plate, and the other as
half-wave plate. A modified Savart plate serves as polarimetric beam
splitter. With the present liquid crystals, the optimum wavelength range
of this polarimeter is between 580 and 660 nm. The spectro-polarimeter
will benefit from the capabilities of the new telescope GREGOR which
will provide a spatial resolution of about 0″.1 (75 km on the solar
surface). Thus we will be able to investigate small magnetic features,
and we will study their development with high cadence.
---------------------------------------------------------
Title: Theoretical Modeling of Propagation of Magnetoacoustic Waves
in Magnetic Regions Below Sunspots
Authors: Khomenko, E.; Kosovichev, A.; Collados, M.; Parchevsky, K.;
Olshevsky, V.
2009ApJ...694..411K Altcode: 2008arXiv0809.0278K
We use two-dimensional numerical simulations and eikonal approximation
to study properties of magnetohydrodynamic (MHD) waves traveling below
the solar surface through the magnetic structure of sunspots. We
consider a series of magnetostatic models of sunspots of different
magnetic field strengths, from 10 Mm below the photosphere to the
low chromosphere. The purpose of these studies is to quantify the
effect of the magnetic field on local helioseismology measurements
by modeling waves excited by subphotospheric sources. Time-distance
propagation diagrams and wave travel times are calculated for models
of various field strengths and compared to the nonmagnetic case. The
results clearly indicate that the observed time-distance helioseismology
signals in sunspot regions correspond to fast MHD waves. The slow MHD
waves form a distinctly different pattern in the time-distance diagram,
which has not been detected in observations. The numerical results are
in good agreement with the solution in the short-wavelength (eikonal)
approximation, providing its validation. The frequency dependence of
the travel times is in good qualitative agreement with observations.
---------------------------------------------------------
Title: Wave Propagation and Shock Formation in Different Magnetic
Structures
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2009ApJ...692.1211C Altcode: 2008arXiv0810.3613C
Velocity oscillations "measured" simultaneously at the photosphere and
the chromosphere—from time series of spectropolarimetric data in the
10830 Å region—of different solar magnetic features allow us to study
the properties of wave propagation as a function of the magnetic flux
of the structure (i.e., two different-sized sunspots, a tiny pore,
and a facular region). While photospheric oscillations have similar
characteristics everywhere, oscillations measured at chromospheric
heights show different amplitudes, frequencies, and stages of shock
development depending on the observed magnetic feature. The analysis
of the power and the phase spectra, together with simple theoretical
modeling, lead to a series of results concerning wave propagation
within the range of heights of this study. We find that, while the
atmospheric cutoff frequency and the propagation properties of different
oscillating modes depend on the magnetic feature, in all the cases the
power that reaches the high chromosphere above the atmospheric cutoff
comes directly from the photosphere by means of linear vertical wave
propagation rather than from nonlinear interaction of modes.
---------------------------------------------------------
Title: Magnetohydrostatic Sunspot Models from Deep Subphotospheric
to Chromospheric Layers
Authors: Khomenko, E.; Collados, M.
2008ApJ...689.1379K Altcode: 2008arXiv0808.3571K
In order to understand the influence of magnetic fields on the
propagation properties of waves, as derived from different local
helioseismology techniques, forward modeling of waves is required. Such
calculations need a model in magnetohydrostatic equilibrium as an
initial atmosphere through which to propagate oscillations. We provide
a method to construct such a model in equilibrium for a wide range
of parameters, for use in simulations of artificial helioseismologic
data. The method combines the advantages of self-similar solutions and
current-distributed models. A set of models is developed by numerical
integration of magnetohydrostatic equations from the subphotospheric
to chromospheric layers.
---------------------------------------------------------
Title: High-resolution Ground-based European Solar Physics
Authors: Collados, M.
2008LNEA....3..113C Altcode:
This communication reviews some of the most challenging topics in
high-resolution ground-based Solar Physics. The most powerful European
facilities are described, together with their capabilities and skills
gained in Europe using them. The reasons for a large-aperture solar
telescope are outlined, based on present scientific needs, which have
led to the joint project EST (European Solar Telescope), in which
the most prestigious European Solar Physics research institutions
participate. Some technical challenges of a such a large telescope
are mentioned.
---------------------------------------------------------
Title: On the Possible Sources of Chromospheric Heating
Authors: Beck, C.; Collados, M. Vera; Khomenko, E.; Rezaei, R.
2008ESPM...12.2.14B Altcode:
The chromospheric temperature rise to values above the photospheric
temperature cannot be due to radiative energy transport alone. We will
outline different possibilities for the additional energy transport in
the solar atmosphere by processes that require (or exclude) the presence
of magnetic fields. We will discuss which of them could be identified
and studied in detail using current data. To find the signature of
the different heating processes and derive quantitative estimates
of their efficiency, we analyzed simultaneous spectropolarimetric
observations of photospheric magnetic fields (@630 nm) and intensity
spectra of the chromospheric Ca II H line (396 nm). The mechanical
energy flux at several height layers was derived from the velocity
amplitudes of propagating acoustic waves seen in different spectral
lines. The enhancement of chromospheric (radiation) temperature above
the radiative equilibrium values was taken from an inversion of the
Ca II H spectra with the SIR code assuming local thermal equilibrium
(LTE) and complete redistribution (CRD). We compare the obtained energy
values with each other and with the energy requirements demanded by
theoretical/semi-empirical atmospheric models. <P />We find that
the most important agent of chromospheric heating are propagating
(magneto-)acoustic waves, which suffice to explain the brightenings in
Ca II H spectra and their corresponding temperature enhancements. The
energy contained in these intensity variations of the Ca II H line,
however, is found to be insufficient to maintain a full-time and
full-volume "hot" chromosphere. Additional energy transport mechanisms
without a signature in the Ca II H spectra are thus necessary. Finally,
we will outline which improvements are to be expected with future
observations of higher quality (spatial resolution, enhanced
polarimetric sensitivity, temporal cadence, other spectral lines)
to be achieved with new ground-based telescopes like GREGOR or EST.
---------------------------------------------------------
Title: EST: The European Solar Telescope
Authors: Collados, M.
2008ESPM...12..6.3C Altcode:
The European Solar Telescope (EST) is a project for a 4 meter-class
ground-based telescope, to be located in the Canary Islands. The
project is promoted by the European Association for Solar Telescopes
(EAST), a consortium formed by research organizations from 15 European
countries. EST will be optimized for studies of magnetic coupling
between the deep photosphere and upper chromosphere. The project
has been approved for funds by the European Union, within the FP-7
framework, to produce the design of all systems and subsystems of the
telescope during the next three years. This includes the optical and
optomechanical design of the telescope itself and of the instruments
and their control. MCAO will be included in the optical path in a
natural way to compensate for atmospheric disturbances in an optimum
way. The design of EST will strongly emphasize the use of a large
number of visible and near-infrared instruments simultaneously which
will influence the telescope design from the very beginning. This
communication will center mainly on the scientific objectives that
EST will address. Generally speaking, they involve understanding how
the magnetic field emerges through the solar surface, interacts with
the plasma dynamics to transfer energy between different regions,
and finally releases it in the form of heat or as violent events in
the solar chromosphere and corona. Among the many topics of interest,
one may cite, as described in the EST Science Requirements Document:
small-scale flux emergence in quiet sun regions, large-scale magnetic
structures, magnetic flux cancellation processes, polar magnetic fields,
magnetic topology of the photosphere and chromosphere, conversion of
mechanical to magnetic energy in the photosphere, wave propagation from
photosphere to chromosphere, energy dissipation in the chromosphere at
small and large scales, etc. The present status and future perspectives
of the project will also be outlined.
---------------------------------------------------------
Title: Multi-layer Study of Wave Propagation in Sunspots
Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C.
2008ESPM...12.2.12F Altcode:
Observations in different spectral lines give us information about
the different layers of the solar atmosphere. Here we analyze
the propagation of waves in sunspots from the photosphere to the
chromosphere using time series of cospatial Ca II H intensity
spectra and polarimetric spectra of Si I 10827 A and He I 10830
A multiplet. From the Doppler shifts of these lines we retrieve
the temporal variations of the velocity along the line-of-sight
at several heights. Phase spectra are used to get the relation
between oscillatory signals measured at each spectral signature. Our
analysis reveals standing waves for frequencies lower than 3.5 mHz and
propagating waves for higher frequencies, which steepen into shocks
in the chromosphere. Oscillations are detectable in Ca II H wings and
they are propagated along line wing layers to the line core. Ca II H
core forms at a lower height than the He I 10830 A line. A time delay
of about 30 s is measured between the Doppler signals detected at both
wavelengths. We also find that in "cold" sunspots the Si I 10827 A forms
deeper than in the quiet sun. This type of measurements demonstrate
the importance of simultaneous co-spatial observations at different
wavelengths. Future infrastructures, such as GREGOR and EST, should
include multi-wavelength capabilities to make possible the study of
the photosphere-chromosphere connection with the highest spatial and
temporal resolution.
---------------------------------------------------------
Title: Nonlinear Numerical Simulations of Magneto-Acoustic Wave
Propagation in Small-Scale Flux Tubes
Authors: Khomenko, E.; Collados, M.; Felipe, T.
2008SoPh..251..589K Altcode: 2008SoPh..tmp...32K; 2007arXiv0710.3335K
We present results of nonlinear, two-dimensional, numerical simulations
of magneto-acoustic wave propagation in the photosphere and chromosphere
of small-scale flux tubes with internal structure. Waves with realistic
periods of three to five minutes are studied, after horizontal and
vertical oscillatory perturbations are applied to the equilibrium
model. Spurious reflections of shock waves from the upper boundary
are minimized by a special boundary condition. This has allowed us to
increase the duration of the simulations and to make it long enough to
perform a statistical analysis of oscillations. The simulations show
that deep horizontal motions of the flux tube generate a slow (magnetic)
mode and a surface mode. These modes are efficiently transformed
into a slow (acoustic) mode in the v<SUB>A</SUB><c<SUB>S</SUB>
atmosphere. The slow (acoustic) mode propagates vertically along
the field lines, forms shocks, and remains always within the flux
tube. It might effectively deposit the energy of the driver into the
chromosphere. When the driver oscillates with a high frequency, above
the cutoff, nonlinear wave propagation occurs with the same dominant
driver period at all heights. At low frequencies, below the cutoff,
the dominant period of oscillations changes with height from that
of the driver in the photosphere to its first harmonic (half period)
in the chromosphere. Depending on the period and on the type of the
driver, different shock patterns are observed.
---------------------------------------------------------
Title: First-Light Science Cases for the GREGOR Fabry-Perot
Interferometer
Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados,
M.; Kneer, H. F. Nicklas; Puschmann, K. G.
2008ESPM...12..6.8D Altcode:
The light-gathering capacity and resolving power of the 1.5-meter
aperture GREGOR telescope will provide solar observations of
the full Stokes vector with high temporal, spectral and spatial
resolution. As one of the first-light instruments, the GREGOR
Fabry-Perot Interferometer (GFPI) is well suited for observations
with adaptive optics (AO) correction. Post-facto image correction
(speckle masking imaging and deconvolution) will further enhance
the data quality to approach the diffraction-limited resolution of
the telescope. We will describe the GFPI optical design and its basic
operating procedures. Instruments characteristics such as field-of-view,
cadence, spectral resolution, and spectroscopic/polarimetric observing
modes will result in boundary conditions, which have to be carefully
considered in optimizing the scientific outcome of the first-light
observations. We will present two science cases for quiet Sun and
active region studies to illustrate the capabilities of this imaging
spectro-polarimeter.
---------------------------------------------------------
Title: Seismology of Sunspots: An Interplay between Temperature and
Magnetic Field Structures
Authors: Olshevsky, V.; Khomenko, E.; Collados, M.
2008ESPM...12..3.2O Altcode:
Using a numerical three-dimensional MHD modelling of magneto-acoustic
wave propagation in a realistic magnetostatic sunspot model we
investigate the influence of the magnetic field on the parameters
measured by local helioseismology. We find that the variations of
temperature as well as the presence of the magnetic field cause
important changes to the wave travel times. Magnetic field speeds up
the waves to considerable amount, while the temperature depression
within a sunspot causes the opposite action. The calculated travel time
differences between the unmagnetized and magnetized atmospheres lie in
the range typically obtained from local helioseismology correlation
analysis. Our numerical results are also in agreement with the
analytical calculations of the travel times applying WKB technique.
---------------------------------------------------------
Title: European Solar Telescope (EST): project status
Authors: Collados, Manuel
2008SPIE.7012E..0JC Altcode: 2008SPIE.7012E..17C
The European Solar Telescope (EST) is a project for a large aperture
(3-5 meters) ground-based telescope, to be located in the Canary
Islands. EST will be optimized for studies of magnetic coupling
between the deep photosphere and upper chromosphere. This will require
diagnostics of the thermal, dynamic and magnetic properties of the
plasma over many scale heights, by using multiple wavelength imaging,
spectroscopy and spectropolarimetry. The design of EST will strongly
emphasize the use of a large number of visible and near-infrared
instruments simultaneously. To achieve these goals, EST will specialize
in high spatial and temporal resolution using instruments that can
efficiently produce twodimensional spectral information. In this
communication, the present situation of the design is outlined, as
well as the expected future phases and scheduling.
---------------------------------------------------------
Title: The participation of the Instituto de Astrofísica de Canarias
in the European Solar Telescope
Authors: Collados, M.; Calcines, A.; Diaz, J. J.; Gracia, F.;
Grivel-Gelly, C.; López, R.; Mangharam, H.; Páez, E.; Perez,
A.; Rasilla, J. L.; Rodríguez, L. F.; Sánchez-Capuchino, J.;
Socas-Navarro, H.
2008SPIE.7012E..32C Altcode: 2008SPIE.7012E.105C
This communication reviews the participation of the Instituto
de Astrofísica de Canarias (IAC) in the design of the European
Solar Telescope. Apart of being the coordinator institution of the
whole project, and, as such, responsible for the project managing,
the IAC leads several tasks like overall instrument definition or
characterization of the atmospheric turbulence profile with height or
the definition of adequate detectors. More in particular, the IAC will
design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments
to measure medium-altitude seeing. The IAC is also responsible for the
design, together with other institutions, of the design of grating
spectropolarimeters suitable for multiwavelength high spatial and
spectral resolution.
---------------------------------------------------------
Title: A high-resolution spectrograph for the solar telescope GREGOR
Authors: Collados, Manuel; Calcines, A.; Díaz, J. J.; Hernnádez,
E.; López, R.; Páez, E.
2008SPIE.7014E..5ZC Altcode: 2008SPIE.7014E.198C
This communication shows the design, layout, mounting and start-up
of a high-resolution grating spectrograph for VIS-NIR at GREGOR 1.5m
Solar Telescope (Observatorio del Teide, Tenerife, Canary Islands). The
instrument will be used together with the Tenerife Infrared Polarimeter
(TIP-II). As special characteristics of the design, the following
can be mentioned: The first folding mirror of the spectrograph can be
placed in two positions to take into account the change of the optical
axis introduced by the polarizing beamsplitter of TIP-II. This way
the instrument is optimally aligned when used in situations with and
without polarimeter. The second and third mirrors rotate the image
of the entrance slit, making it parallel to the grating grooves. A
system of prisms are used to adequately fit onto the detector the
two orthogonal polarized beams generated by the polarimeter. Two
output beams are possible, to make feasible simultaneous visible and
near-infrared observations.
---------------------------------------------------------
Title: Error propagation in polarimetric demodulation
Authors: Asensio Ramos, A.; Collados, M.
2008ApOpt..47.2541A Altcode: 2008arXiv0804.4708A
The polarization analysis of light is typically carried out using
modulation schemes. The light of an unknown polarization state is passed
through a set of known modulation optics, and a detector is used to
measure the total intensity passing the system. The modulation optics is
modified several times, and, with the aid of several such measurements,
the unknown polarization state of the light can be inferred. How to
find the optimal demodulation process has been investigated in the
past. However, since the modulation matrix has to be measured for a
given instrument and the optical elements can present problems of
repeatability, some uncertainty is present in the elements of the
modulation matrix or covariances between these elements. We analyze in
detail this issue, presenting analytical formulas for calculating the
covariance matrix produced by the propagation of such uncertainties on
the demodulation matrix, on the inferred Stokes parameters, and on the
efficiency of the modulation process. We demonstrate that even if the
covariance matrix of the modulation matrix is diagonal, the covariance
matrix of the demodulation matrix is in general nondiagonal because
matrix inversion is a nonlinear operation. This propagates through
the demodulation process and induces correlations on the inferred
Stokes parameters.
---------------------------------------------------------
Title: The Influence of Coronal EUV Irradiance on the Emission in
the He I 10830 Å and D<SUB>3</SUB> Multiplets
Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M.
2008ApJ...677..742C Altcode: 2007arXiv0712.2203C
Two of the most attractive spectral windows for spectropolarimetric
investigations of the physical properties of the plasma structures
in the solar chromosphere and corona are the ones provided by the
spectral lines of the He I 10830 and 5876 Å (or D<SUB>3</SUB>)
multiplets, whose polarization signals are sensitive to the Hanle and
Zeeman effects. However, in order to be able to carry out reliable
diagnostics, it is crucial to have a good physical understanding
of the sensitivity of the observed spectral line radiation to the
various competing driving mechanisms. Here we report a series of
off-the-limb non-LTE calculations of the He I D<SUB>3</SUB> and 10830
Å emission profiles, focusing our investigation on their sensitivity
to the EUV coronal irradiation and the model atmosphere used in the
calculations. We show in particular that the intensity ratio of the
blue to the red components in the emission profiles of the He I 10830
Å multiplet turns out to be a good candidate as a diagnostic tool for
the coronal irradiance. Measurements of this observable as a function of
the distance to the limb and its confrontation with radiative transfer
modeling might give us valuable information on the physical properties
of the solar atmosphere and on the amount of EUV radiation at relevant
wavelengths penetrating the chromosphere from above.
---------------------------------------------------------
Title: Channeling 5 Minute Photospheric Oscillations into the Solar
Outer Atmosphere through Small-Scale Vertical Magnetic Flux Tubes
Authors: Khomenko, E.; Centeno, R.; Collados, M.; Trujillo Bueno, J.
2008ApJ...676L..85K Altcode: 2008arXiv0802.0938K
We report two-dimensional MHD simulations which demonstrate that
photospheric 5 minute oscillations can leak into the chromosphere
inside small-scale vertical magnetic flux tubes. The results of
our numerical experiments are compatible with those inferred from
simultaneous spectropolarimetric observations of the photosphere and
chromosphere obtained with the Tenerife Infrared Polarimeter (TIP)
at 10830 Å. We conclude that the efficiency of energy exchange by
radiation in the solar photosphere can lead to a significant reduction
of the cutoff frequency and may allow for the propagation of the 5
minute waves vertically into the chromosphere.
---------------------------------------------------------
Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and
6302 Å
Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.;
Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez
González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez
Almeida, J.
2008ApJ...674..596S Altcode:
The reliability of quiet-Sun magnetic field diagnostics based on the
Fe I lines at 6302 Å has been questioned by recent work. Here we
present the results of a thorough study of high-resolution multiline
observations taken with the new spectropolarimeter SPINOR, comprising
the 5250 and 6302 Å spectral domains. The observations were analyzed
using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Å lines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magnetohydrodynamic constrains. When this is done, the 5250 Å lines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point toward a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic
field strengths. Instead, we advocate for a combined analysis of both
spectral ranges, which yields a better determination of the quiet-Sun
magnetic properties. Finally, we propose the use of two other Fe I
lines (at 4122 and 9000 Å) with identical line opacities that seem
to work much better than the others.
---------------------------------------------------------
Title: Internetwork magnetic field distribution from simultaneous
1.56 μm and 630 nm observations
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
Beck, C.
2008A&A...477..953M Altcode: 2007arXiv0711.0267M
Aims:We study the contradictory magnetic field strength distributions
retrieved from independent analyses of spectropolarimetric observations
in the near-infrared (1.56 μm) and in the visible (630 nm) spectral
ranges in internetwork regions. <BR />Methods: To solve this apparent
controversy, we present simultaneous and co-spatial 1.56 μm and 630 nm
observations of an internetwork area. The properties of the circular
and linear polarization signals, as well as the Stokes V area and
amplitude asymmetries, are discussed. As a complement, we also used
inversion techniques to infer the physical parameters of the solar
atmosphere. As a first step, the infrared and visible observations
are analysed separately to check their compatibility. Finally, the
simultaneous inversion of the two data sets is performed. <BR />Results:
The magnetic flux densities retrieved from the individual analysis
of the infrared and visible data sets are strongly correlated. The
polarity of the Stokes V profiles is the same at co-spatial pixels
in both wavelength ranges. This indicates that both 1.56 μm and
630 nm observations trace the same magnetic structures on the solar
surface. The simultaneous inversion of the two pairs of lines reveals
an internetwork full of sub-kG structures that fill only 2% of the
resolution element. A correlation is found between the magnetic field
strength and the continuum intensity: equipartition fields (B∼ 500
G) tend to be located in dark intergranular lanes, whereas weaker
field structures are found inside granules. The most probable unsigned
magnetic flux density is 10 Mx/cm^2. The net magnetic flux density in
the whole field of view is nearly zero. This means that both polarities
cancel out almost exactly in our observed internetwork area.
---------------------------------------------------------
Title: Supersonic Downflows in the Photosphere Discovered in Sunspot
Moat Regions
Authors: Shimizu, T.; Martinez-Pillet, V.; Collados, M.; Ruiz-Cobo,
B.; Centeno, R.; Beck, C.; Katsukawa, Y.
2007ASPC..369..113S Altcode:
This paper reports on our new findings from the International
Time Program observations at the Canaries islands, Spain, in July
2005. We have found small-scale photospheric events with extremely
red-shifted Stokes V signals in sunspot moat regions. A preliminary
estimate of the physical conditions for an observed Stokes V profile
indicates the presence of a downward motion with a supersonic speed
in the order of 10 km/s. With the currently evaluated observational
information, we interprete the supersonic flows as downward motion from
magnetic reconnection occurring at the upper chromosphere or lower
photosphere. With coordinated observations of the Solar-B onboard
telescopes, Stokes measurements by the SOT spectro-polarimeter would
give new information for further understanding the nature of these
events with strongly red-shifted Stokes V, and for discussing the
physical conditions involving in possible magnetic reconnections in
the lower solar atmosphere.
---------------------------------------------------------
Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å
Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados,
M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González,
M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J.
2007arXiv0710.1099S Altcode:
The reliability of quiet Sun magnetic field diagnostics based on the
\ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We
present here the results of a thorough study of high-resolution
multi-line observations taken with the new spectro-polarimeter SPINOR,
comprising the 5250 and 6302 Åspectral domains. The observations were
analyzed using several inversion algorithms, including Milne-Eddington,
LTE with 1 and 2 components, and MISMA codes. We find that the
line-ratio technique applied to the 5250 Ålines is not sufficiently
reliable to provide a direct magnetic diagnostic in the presence
of thermal fluctuations and variable line broadening. In general,
one needs to resort to inversion algorithms, ideally with realistic
magneto-hydrodynamical constrains. When this is done, the 5250 Ålines
do not seem to provide any significant advantage over those at 6302
Å. In fact, our results point towards a better performance with the
latter (in the presence of turbulent line broadening). In any case,
for very weak flux concentrations, neither spectral region alone
provides sufficient constraints to fully disentangle the intrinsic field
strengths. Instead, we advocate for a combined analysis of both spectral
ranges, which yields a better determination of the quiet Sun magnetic
properties. Finally, we propose the use of two other \ion{Fe}{1} lines
(at 4122 and 9000 Å) with identical line opacities that seem to work
much better than the others.
---------------------------------------------------------
Title: Low-lying magnetic loops in the solar internetwork
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
Solanki, S. K.
2007A&A...469L..39M Altcode: 2007arXiv0705.1319M
Aims:We study the structure of the magnetic field vector in the
internetwork and search for the presence of small-scale loops. <BR
/>Methods: We invert 1.56 μm spectropolarimetric observations of
internetwork regions at disc centre by applying the SIR code. This
allows us to recover the atmospheric parameters that play a role in
the formation of these spectral lines. We are mainly interested in the
structure of the magnetic field vector. <BR />Results: We find that
many opposite polarity elements of the internetwork are connected by
short (2-6´´), low-lying (photospheric) loops. These loops connect
at least the 10-20% of the internetwork flux visible in our data. Also
we have some evidence that points towards a dynamic scenario that can
be produced by the emergence of internetwork magnetic flux.
---------------------------------------------------------
Title: A Magnetic Map of a Solar Filament
Authors: Merenda, L.; Trujillo Bueno, J.; Collados, M.
2007ASPC..368..347M Altcode:
One of the most useful diagnostic tools for the detection of inclined
magnetic fields in solar chromospheric and coronal structures is
that based on the fact that the Hanle effect in forward scattering
at the solar disk center creates linear polarization in some spectral
lines, such as those of the He I 10830 Å multiplet. Here we show the
preliminary results of an ongoing investigation on the magnetic field
of a solar filament, based on the inversion of spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter.
---------------------------------------------------------
Title: GREGOR: the New German Solar Telescope
Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.;
Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.;
Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier,
K.; Wittmann, A.
2007ASPC..368..605B Altcode: 2007arXiv0704.2693B
GREGOR is a new open solar telescope with an aperture of 1.5 m. It
replaces the former 45-cm Gregory Coudé telescope on the Canary island
Tenerife. The optical concept is that of a double Gregory system. The
main and the elliptical mirrors are made from a silicon-carbide material
with high thermal conductivity. This is important to keep the mirrors
on the ambient temperature avoiding local turbulence. GREGOR will be
equipped with an adaptive optics system. The new telescope will be ready
for operation in 2008. Post-focus instruments in the first stage will be
a spectrograph for polarimetry in the near infrared and a 2-dimensional
spectrometer based on Fabry-Pérot interferometers for the visible.
---------------------------------------------------------
Title: Tenerife Infrared Polarimeter II
Authors: Collados, M.; Lagg, A.; Díaz Garcí A, J. J.; Hernández
Suárez, E.; López López, R.; Páez Mañá, E.; Solanki, S. K.
2007ASPC..368..611C Altcode:
Since May 2005 the Tenerife Infrared Polarimeter II (TIP-II) has been
operational at the Vacuum Tower Telescope on Tenerife. The core of the
polarimeter is a 1024×1020 pixel infrared camera allowing for high
precision measurements of the full Stokes vector with a pixel size of
0.18 arcsec, corresponding to the diffraction limit of the telescope at
1 μm. The polarimeter is able to reach a polarimetric accuracy of a few
times 10<SUP>-4</SUP>, covering a wavelength range of 1 to 1.8 μm. With
an upgrade in July 2006, the slit size has been increased to 77 arcsec
allowing most active regions to be covered with a single scan. Here
we present the technical details of the polarimeter and the camera. We
also show some data illustrating the power of this new instrumentation.
---------------------------------------------------------
Title: Full-Stokes Observations and Analysis of He I 10830 Å in a
Flaring Region
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Aznar Cuadrado, R.;
Collados, M.
2007ASPC..368..467S Altcode:
We present observations of the full Stokes vector in a flaring
region, taken in the chromospheric He I 10830 Å multiplet. The data
were recorded with the new Tenerife Infrared Polarimeter (TIP 2)
at the German Vacuum Tower Telescope (VTT) during May 2005. The He
profiles during the flare are extraordinary, showing extremely broad
Stokes I absorption and very complex and spatially variable Stokes V
signatures. We give first results on the line-of-sight velocities and
the magnetic field vector values in the chromosphere for one observed
Stokes profile by applying an inversion code to the He I lines.
---------------------------------------------------------
Title: On the Stokes V Amplitude Ratio as an Indicator of the Field
Strength in the Solar Internetwork
Authors: Khomenko, E.; Collados, M.
2007ApJ...659.1726K Altcode:
The results of the determination of magnetic field strength from weak
polarimetric signals in solar internetwork regions are contradictory. We
investigate the origin of this contradiction with the help of MHD
simulations. It is shown that the Stokes V amplitude ratio of the
Fe I λλ15652-15648 lines is a good indicator of kG magnetic field
concentrations, even for magnetic fields with a complex internal
structure like those in MHD simulations. The Stokes V amplitude ratio
of the Fe I λλ5247-5250 lines also shows a good correlation with
magnetic field strength. However, in simulations with a flux level
appropriate for the internetwork, it gives values corresponding to
sub-kG fields. The reason is the rapid decrease of the field strength
with height in kG magnetic field concentrations. These lines sample
high regions of the atmosphere, where the field is already below
kG levels. We also find that the Stokes V amplitude ratio of the Fe
I λλ6301-6302 lines shows no correlation with the magnetic field
strength. The reason lies in the large difference in the heights of
formation of these two lines. The value of the magnetic field strength
obtained from the Fe I λλ6301 and 6302 lines depends crucially on the
treatment of gradients of the magnetic field, line-of-sight velocity,
and temperature, even at a numerical spatial resolution of 20 km.
---------------------------------------------------------
Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the
Average Magnetic Energy in the Solar Photosphere
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
A.; Trujillo Bueno, J.; Collados, M.
2007ApJ...659..829A Altcode: 2006astro.ph.12389A
We report on spectropolarimetric observations of a near-IR line of Mn I
located at 15262.702 Å whose intensity and polarization profiles are
very sensitive to the presence of hyperfine structure. A theoretical
investigation of the magnetic sensitivity of this line uncovers several
interesting properties. The most important one is that the presence
of strong Paschen-Back perturbations due to the hyperfine structure
produces an intensity line profile whose shape changes according to the
absolute value of the magnetic field strength. A line ratio technique is
developed from the intrinsic variations of the line profile. This line
ratio technique is applied to spectropolarimetric observations of the
quiet solar photosphere in order to explore the probability distribution
function of the magnetic field strength. Particular attention is given
to the quietest area of the observed field of view, which was encircled
by an enhanced network region. A detailed theoretical investigation
shows that the inferred distribution yields information on the average
magnetic field strength and on the spatial scale at which the magnetic
field is organized. A first estimation gives ~250 G for the mean field
strength and a tentative value of ~0.4" for the spatial scale at which
the observed magnetic field is horizontally organized.
---------------------------------------------------------
Title: Multi-wavelength observations at the German VTT on Tenerife
Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Kentischer, T.;
Collados, M.
2007msfa.conf...55B Altcode:
To study the small-scale dynamic processes of magneto-convection in the
solar photosphere in more detail than currently achieveable, not only
the spatial resolution has to be increased, but also the information
content of observations. In order to do so, several wavelengths and
spectral lines must be observed simultaneously. This is often achieved
by coordinated campaigns at several telescopes with different post-focus
instrumentation. The German Vacuum Tower Telescope (VTT) on Tenerife
offers the possibility to operate several dedicated instruments
spectrometers, polarimeters, imaging systems at the same time. We
describe some of the possible combinations of post-focus instruments,
and present examples of multi-wavelength data obtained recently.
---------------------------------------------------------
Title: Line ratio method applied to inter-network magnetic fields
Authors: Khomenko, E.; Collados, M.
2007msfa.conf..303K Altcode:
We investigate the validity of the Stokes V amplitude ratio as an
indicator of the magnetic field strength in solar inter-network
regions with the help ofMHD simulations. We show that the Stokes V
amplitude ratio of the Fe I 15652-15648 Å lines and Fe I 5247-5250 Å
lines show a good correlation with the magnetic field strength even
for magnetic fields with a complex internal structure like those in
MHD simulations. However, in the latter case, the amplitude ratio
sub-estimates the magnetic field strength, always revealing sub-kG
values. The Stokes V amplitude ratio of the Fe I 6301-6302 Å lines
shows no correlation with the magnetic field strength. The reasons of
this behaviour are explained.
---------------------------------------------------------
Title: Numerical modeling of MHD wave propagation in sunspots:
a 3D case
Authors: Olshevsky, V.; Khomenko, E.; Collados, M.
2007msfa.conf..347O Altcode:
We present the first results of a 3D numerical modeling of linear MHD
wave propagation in a realistic sunspot model. In our simulations,
a piston located at the base of the photosphere generates waves with
a certain period. The ratio between the acoustic and the Alfven speed,
cS /vA, decreases from much larger than one at the photosphere to much
lower than one in the chromosphere in our simulation domain. Waves
propagate through the region where cS << vA, where mode
transformation is observed. At a somewhat higher region, where cS =
vA, the fast (magnetic) mode reflects back to the photosphere due
to the vertical and horizontal gradients of vA. The slow (acoustic)
mode propagates to the upper layers and increases its velocity
amplitude. Unlike the 2D simulations, the Alfven mode is also generated
by the piston and experiences transformations at the cS = vA layer. The
behaviour of this mode requires further study.
---------------------------------------------------------
Title: New high resolution solar telescope GREGOR
Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.;
Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier,
K.; Wittmann, A. D.
2007msfa.conf...39V Altcode:
The 1.5m solar telescope GREGOR is being constructed at Tenerife,
Spain. Its purpose is to observe with high spatial and spectral
resolution small-scale dynamic magnetic features on the Sun. The
telescope is completely open with retractable dome and actively cooled
primary mirror made of silicon carbide to minimize thermal effects
on the image quality. After completion it will be one of the most
powerful solar telescopes. This paper presents a general overview of
the telescope characteristics and the current status.
---------------------------------------------------------
Title: Wave propagation and shock formation in diverse magnetic
structures
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2007msfa.conf..245C Altcode:
Velocity oscillations measured simultaneously at the photosphere
and the chromosphere of different solar magnetic features (sunspots,
pores and facular regions) allow us to study the properties of wave
propagation as a function of the magnetic flux of the structure. While
photospheric oscillations are similar everywhere, oscillations measured
at chromospheric heights show different amplitudes, frequencies
and stages of shock development depending on the observed magnetic
feature. The analysis via power and phase spectra, together with simple
theoretical modeling, lead to a series of results concerning wave
propagation within the range of heights of this study. We find that,
while the atmospheric cut-off frequency and the propagation properties
of the different oscillating modes depend on the magnetic feature,
in all the cases the power that reaches the high chromosphere comes
directly from the photosphere by means of linear wave propagation
rather than from non-linear interaction of modes.
---------------------------------------------------------
Title: Magnetic field inversions from Stokes profiles generated by
MHD simulations
Authors: Khomenko, E.; Collados, M.
2007MmSAI..78..166K Altcode:
We report tests of inversion methods applied to complex Stokes spectra
generated by realistic MHD simulations. The average magnetic field
strength of the simulations used is of 30 and 140 G, which we believe
is representative of quiet solar regions. The behaviour of the Fe I at
1.56 mu m and 630 nm lines is analyzed. The tests have been done with
the original resolution of simulations (20 km) and also with resolution
of 0.6” and 1.4” (after having conveniently degraded the images).
---------------------------------------------------------
Title: Polarimetry in the visible and near infrared
Authors: Collados, M.
2007msfa.conf..143C Altcode:
The various techniques used in the visible and near-infrared for
the measurement of intrinsic polarization coming from solar regions
are described. Their performance to allow for the acquisition of
simultaneous spectropolarimetric data at several wavelengths is
discussed. Any development of a future facility should take advantage of
these capabilities to measure simultaneously different solar atmospheric
layers with high spatial resolution.
---------------------------------------------------------
Title: Internetwork magnetic fields
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2007msfa.conf..157M Altcode:
Spectropolarimetric observations of the internetwork obtained in the
1.56 [mμ]m Fe I doublet are used to calculate the distributions of
magnetic field strength, filling factor and magnetic flux density
at different positions on the solar surface. We go one step further
and describe what the observations show about the three-dimensional
structure of the magnetic fields at the internetwork quiet Sun.
---------------------------------------------------------
Title: Oscillations and Wave Propagation in Different Solar Magnetic
Features
Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J.
2006ASPC..358..465C Altcode:
We present the results of the analysis of temporal series of
spectro-polarimetric data measured simultaneously in the photospheric
Si I 10827 Å line and the chromospheric He I 10830 Å triplet, on
top of two different targets: a facular region and the umbra of a
sunspot. The full Stokes inversion of both spectral features gives us
the temporal variability of the physical conditions at two different
regions in the solar atmosphere, allowing us to compare the LOS velocity
oscillations at the photosphere and the chromosphere, and infer the
main characteristics of wave propagation in both magnetic structures.
---------------------------------------------------------
Title: Measuring the Magnetic Vector with the He I 10830 Å Line:
A Rich New World
Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez,
D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N.
2006ASPC..358..431S Altcode:
The triplet of the He I transitions around 10830 Å not only shows a
rich variety of Stokes profiles, but also allows the full magnetic
vector in the upper chromosphere to be probed, thus revealing
the magnetic structure of loops, current sheets, finely structured
supersonic downflows, the chromospheric layers of sunspots (supporting
the presence of uncombed fields in the penumbra), flares, and the
quiet Sun. A very brief overview of some of the observations and
results obtained so far is given.
---------------------------------------------------------
Title: Numerical Modeling of Magnetohydrodynamic Wave Propagation
and Refraction in Sunspots
Authors: Khomenko, E.; Collados, M.
2006ApJ...653..739K Altcode:
We present numerical simulations of magnetoacoustic wave propagation
from the photosphere to the low chromosphere in a magnetic sunspot-like
structure. A thick flux tube, with dimensions typical of a small
sunspot, is perturbed by a vertical or horizontal velocity pulse
at the photospheric level. The type of mode generated by the pulse
depends on the ratio between the sound speed c<SUB>S</SUB> and the
Alfvén speed v<SUB>A</SUB>, on the magnetic field inclination at the
location of the driver, and on the shape of the pulse in the horizontal
direction. Mode conversion is observed to occur in the region in which
both characteristic speeds have similar values. The fast (magnetic)
mode in the region c<SUB>S</SUB><v<SUB>A</SUB> does not reach the
chromosphere and reflects back to the photosphere at a somewhat higher
layer than the c<SUB>S</SUB>=v<SUB>A</SUB> line. This behavior is due
to wave refraction, caused primarily by the vertical and horizontal
gradients of the Alfvén speed. The slow (acoustic) mode continues up
to the chromosphere along the magnetic field lines with increasing
amplitude. We show that this behavior is characteristic for waves
in a wide range of periods generated at different distances from the
sunspot axis. Since an important part of the energy of the pulse is
returned back to the photosphere by the fast mode, the mechanism of
energy transport from the photosphere to the chromosphere by waves in
sunspots is rather ineffective.
---------------------------------------------------------
Title: Internetwork Magnetic Field Distribution from Simultaneous
Fe I 1.5 µ and Fe I 630 nm Observations
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2006ASPC..358...36M Altcode:
We took simultaneous observations in Fe I 1.5 µ and Fe I 630 nm of
an internetwork region. We discuss the compatibility of the data in
the two spectral ranges, and present results for the magnetic field
distribution. We show that the larger contribution comes from hG
field strengths.
---------------------------------------------------------
Title: On the validity of the 630 nm Fe I lines for magnetometry of
the internetwork quiet Sun
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2006A&A...456.1159M Altcode: 2006astro.ph..5446M
Aims.The purpose of this work is to analyze the reliability of the
magnetic field strengths inferred from the 630 nm pair of Fe i lines
in internetwork quiet Sun regions.<BR /> Methods: .Some numerical
experiments have been performed that demonstrate the inability
of these lines to recover the magnetic field strength in such low
flux solar regions.<BR /> Results: .It is shown how different model
atmospheres, with magnetic field strengths ranging from a few hundred
Gauss to kiloGauss, give rise to Stokes profiles that cannot be
distinguished. The reasons for this degeneracy are discussed.<BR />
---------------------------------------------------------
Title: Detailed design of the imaging magnetograph experiment (IMaX):
a visible imager magnetograph for the Sunrise mission
Authors: Álvarez-Herrero, A.; Belenguer, T.; Pastor, C.; González,
L.; Heredero, R. L.; Ramos, G.; Reina, M.; Sánchez, A.; Villanueva,
J.; Sabau, L.; Martínez Pillet, V.; Bonet, J. A.; Collados, M.;
Jochum, L.; Ballesteros, E.; Medina Trujillo, J. L.; Ruiz, Cobo B.;
González, J. C.; del Toro Iniesta, J. C.; López Jiménez, A. C.;
Castillo Lorenzo, J.; Herranz, M.; Jerónimo, J. M.; Mellado, P.;
Morales, R.; Rodríguez, J.; Domingo, V.; Gasent, J. L.; Rodríquez, P.
2006SPIE.6265E..4CA Altcode: 2006SPIE.6265E.132A
In this work, it is described the Imaging Magnetograph eXperiment,
IMaX, one of the three postfocal instruments of the Sunrise mission. The
Sunrise project consists on a stratospheric balloon with a 1 m aperture
telescope, which will fly from the Antarctica within the NASA Long
Duration Balloon Program. IMaX will provide vector magnetograms
of the solar surface with a spatial resolution of 70 m. This data
is relevant for understanding how the magnetic fields emerge in
the solar surface, how they couple the photospheric base with the
million degrees of temperature of the solar corona and which are the
processes that are responsible of the generation of such an immense
temperatures. To meet this goal IMaX should work as a high sensitivity
polarimeter, high resolution spectrometer and a near diffraction
limited imager. Liquid Crystal Variable Retarders will be used as
polarization modulators taking advantage of the optical retardation
induced by application of low electric fields and avoiding mechanical
mechanisms. Therefore, the interest of these devices for aerospace
applications is envisaged. The spectral resolution required will be
achieved by using a LiNbO <SUB>3</SUB> Fabry-Perot etalon in double
pass configuration as spectral filter before the two CCDs detectors. As
well phase-diversity techniques will be implemented in order to improve
the image quality. Nowadays, IMaX project is in the detailed design
phase before fabrication, integration, assembly and verification. This
paper briefly describes the current status of the instrument and the
technical solutions developed to fulfil the scientific requirements.
---------------------------------------------------------
Title: The new 1.5m solar telescope GREGOR: first light and start
of commissioning
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald;
Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus;
Sobotka, Michal; Klvana, Miroslav; Collados, Manuel
2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V
The integration of the three main silicon carbide mirrors into the new
1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
during 2006. We expect first light at the end of 2006. A progress
report about integration of the optics and mechanics and planning of
the commissioning phase of the telescope and post focus instruments
will be presented at the meeting. The GREGOR telescope is build by a
consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
Gottingen and additional national and international Partners.
---------------------------------------------------------
Title: Site testing for the Advanced Technology Solar Telescope
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn,
M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K.
2006SPIE.6267E..1TH Altcode: 2006SPIE.6267E..59H
The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
being designed for high spatial, spectral and temporal resolution,
as well as IR and low-scattered light observations. The overall
limit of performance of the telescope is strongly influenced by the
qualities of the site at which it is located. Six sites were tested
with a seeing monitor and a sky brightness instrument for 1.5 to 2
years. The sites were Big Bear (California), Haleakala (Hawaii), La
Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak
(New Mexico), and San Pedro Martir (Baja California, Mexico). In this
paper we will describe the methods and results of the site survey,
which chose Haleakala as the location of the ATST.
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector via the Hanle and
Zeeman Effects in the He I λ10830 Multiplet: Evidence for Nearly
Vertical Magnetic Fields in a Polar Crown Prominence
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2006ApJ...642..554M Altcode:
The magnetic field is the key physical quantity responsible for the
formation, stability, and evolution of solar prominences (ribbons of
cool dense gas embedded in the hot tenuous corona). Therefore, it is
important to obtain good empirical knowledge of the three-dimensional
structure of prominence magnetic fields. Here we show how the magnetic
field vector can be inferred via the physical interpretation of
spectropolarimetric observations in the He I λ10830 multiplet. To this
end, we have developed an inversion code based on the quantum theory
of the Hanle and Zeeman effects and on a few modeling assumptions. We
show an application to full Stokes vector observations of a polar crown
prominence that, in the slit-jaw Hα image, showed nearly vertical
plasma structures. Our results provide evidence for magnetic fields
on the order of 30 G inclined by about 25° with respect to the local
solar vertical direction. Of additional interest is that the inferred
nearly vertical magnetic field vector appears to be slightly rotating
around a fixed direction in space as one proceeds along the direction
of the spectrograph's slit. While these results provide new light on
the three-dimensional geometry of the magnetic fields that confine the
plasma of polar crown prominences, they also urge us to develop improved
solar prominence models and to pursue new diagnostic investigations.
---------------------------------------------------------
Title: Spectropolarimetric Investigation of the Propagation of
Magnetoacoustic Waves and Shock Formation in Sunspot Atmospheres
Authors: Centeno, Rebecca; Collados, Manuel; Trujillo Bueno, Javier
2006ApJ...640.1153C Altcode: 2005astro.ph.12096C
Velocity oscillations in sunspot umbrae have been measured
simultaneously in two spectral lines: the photospheric Si I λ10827
line and the chromospheric He I λ10830 multiplet. From the full Stokes
inversion of temporal series of spectropolarimetric observations, we
retrieved, among other parameters, the line-of-sight velocity temporal
variations at photospheric and chromospheric heights. Chromospheric
velocity oscillations show a 3 minute period with a clear sawtooth
shape typical of propagating shock wave fronts. Photospheric velocity
oscillations have basically a 5 minute period, although the power
spectrum also shows a secondary peak in the 3 minute band that has
been proven to be a predecessor for its chromospheric counterpart. The
derived phase spectra yield a value of the atmospheric cutoff frequency
around 4 mHz and give evidence for the upward propagation of higher
frequency oscillation modes. The phase spectrum has been reproduced with
a simple model of linear vertical propagation of slow magnetoacoustic
waves in a stratified magnetized atmosphere that accounts for radiative
losses through Newton's cooling law. The model explains the main
features in the phase spectrum and allows us to compute the theoretical
time delay between the photospheric and chromospheric signals, which
happens to have a strong dependence on frequency. We find a very good
agreement between this and the time delay obtained directly from the
cross-correlation of photospheric and chromospheric velocity maps
filtered around the 6 mHz band. This allows us to infer that the 3
minute power observed at chromospheric heights comes directly from
the photosphere by means of linear wave propagation, rather than from
nonlinear interaction of 5 minute (and/or higher frequency) modes.
---------------------------------------------------------
Title: A polarization model for the German Vacuum Tower Telescope
from in situ and laboratory measurements
Authors: Beck, C.; Schlichenmaier, R.; Collados, M.; Bellot Rubio,
L.; Kentischer, T.
2005A&A...443.1047B Altcode:
It is essential to properly calibrate the polarimetric properties of
telescopes, if one wants to take advantage of the capabilities of high
precision spectro-polarimeters. We have constructed a model for the
German Vacuum Tower Telescope (VTT) that describes its time-dependent
polarization properties. Since the coelostat of the telescope changes
the polarization state of the light by introducing cross talk among
different polarization states, such a model is necessary to correct the
measurements, in order to retrieve the true polarization as emitted
from the Sun. The telescope model is quantified by a time-dependent
Mueller matrix that depends on the geometry of the light beam through
the telescope, and on material properties: the refractive indices of the
coelostat mirrors, and the birefringence of the entrance window to the
vacuum tube. These material properties were determined experimentally
in-situ by feeding the telescope with known states of polarization
(including unpolarized light) and by measuring its response, and from
measurements of an aluminum-coated sample in the laboratory. Accuracy
can in our case be determined only for the combination of telescope
and spectro-polarimeter used; for the instrument POLIS at the VTT,
we estimate an accuracy of ±4-5× 10<SUP>-3</SUP> for the cross talk
correction coefficients.
---------------------------------------------------------
Title: Evidence for Fine Structure in the Chromospheric Umbral
Oscillation
Authors: Centeno, R.; Socas-Navarro, H.; Collados, M.; Trujillo
Bueno, J.
2005ApJ...635..670C Altcode: 2005astro.ph.10740C
Novel spectropolarimetric observations of the He I multiplet are
used to explore the dynamics of the chromospheric oscillation above
sunspot umbrae. The results presented here provide strong evidence
in support of the two-component model proposed by Socas-Navarro
and coauthors. According to this model, the waves propagate only
inside channels of subarcsecond width (the “active” component),
whereas the rest of the umbra remains nearly at rest (the “quiet”
component). Although the observations support the fundamental elements
of that model, there is one particular aspect that is not compatible
with our data. We find that, contrary to the scenario as originally
proposed, the active component remains through the entire oscillation
cycle and harbors both the upflowing and the downflowing phase of
the oscillation.
---------------------------------------------------------
Title: Determination of the Magnetic Field Vector in a Polar Crown
Prominence via the Hanle and Zeeman Effects in the He I 10830 Å
Multiplet.
Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.;
Collados, M.
2005ESASP.596E..18M Altcode: 2005ccmf.confE..18M
No abstract at ADS
---------------------------------------------------------
Title: Simulations of - Acoustic Waves in Sunspots
Authors: Khomenko, E. V.; Collados, M.
2005ESASP.596E..40K Altcode: 2005ccmf.confE..40K
No abstract at ADS
---------------------------------------------------------
Title: Solar Site Survey for the Advanced Technology Solar
Telescope. I. Analysis of the Seeing Data
Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.;
Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer,
S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.;
Oncley, S.; Penn, M.; Rimmele, T.; Streander, K.
2005PASP..117.1296S Altcode: 2005astro.ph..8690S
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than 2 years of data gathering and analysis. Six
locations, including lake, island, and continental sites, were
thoroughly probed for image quality and sky brightness. The present
paper describes the analysis methodology employed to determine the
height stratification of the atmospheric turbulence. This information
is crucial, because daytime seeing is often very different between the
actual telescope aperture (~30 m) and the ground. Two independent
inversion codes have been developed to simultaneously analyze
data from a scintillometer array and a solar differential image
monitor. We show here the results of applying them to a sample subset
of data from 2003 May that was used for testing. Both codes retrieve a
similar seeing stratification through the height range of interest. A
quantitative comparison between our analysis procedure and actual in
situ measurements confirms the validity of the inversions. The sample
data presented in this paper reveal a qualitatively different behavior
for the lake sites (dominated by high-altitude seeing) and the rest
(dominated by near-ground turbulence).
---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V Altcode:
The telescope structure including control system and the complete
retractable dome of the new 1.5 m solar telescope GREGOR were
assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
telescope is build by a consortium of the Kiepenheuer Institut fuer
Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
fuer Astrophysik Goettingen and additional national and international
Partners. Pointing, tracking and thermal tests were made to verify
the proposed performance. The results of these tests and a progress
report of the project will be presented.
---------------------------------------------------------
Title: Magnetic flux in the internetwork quiet Sun
Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.;
Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C.
2005A&A...436L..27K Altcode:
We report a direct comparison of the amplitudes of Stokes spectra of the
Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations
with simultaneous observations in the same spectral regions. The
Stokes spectra were synthesized in snapshots with a mixed polarity
magnetic field having a spatially averaged strength, < B >,
between 10 and 30 G. The distribution of Stokes V amplitudes depends
sensitively on < B >. A quiet inter-network region was observed
at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630
nm). We find that the Stokes V amplitudes of both infrared and visible
observations are best reproduced by the simulation snapshot with <
B > = 20 G. In observations with 1 resolution, up to 2/3 of the
magnetic flux can remain undetected.
---------------------------------------------------------
Title: On the fine structure of sunspot penumbrae. II. The nature
of the Evershed flow
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Collados, M.
2005A&A...436..333B Altcode: 2005astro.ph..3677B
We investigate the fine structure of the sunspot penumbra by means of
a model that allows for a flux tube in horizontal pressure balance
with the magnetic background atmosphere in which it is embedded. We
apply this model to spectropolarimetric observations of two neutral
iron lines at 1.56 μm and invert several radial cuts in the penumbra
of the same sunspot at two different heliocentric angles. In the inner
part of the penumbra we find hot flux tubes that are somewhat inclined
to the horizontal. They become gradually more horizontal and cooler
with increasing radial distance. This is accompanied by an increase
in the velocity of the plasma and a decrease of the gas pressure
difference between flux tube and the background component. At large
radial distances the flow speed exceeds the critical speed and evidence
is found for the formation of a shock front. These results are in good
agreement with simulations of the penumbral fine structure and provide
strong support for the siphon flow as the physical mechanism driving
the Evershed flow.
---------------------------------------------------------
Title: The ATST Site Survey
Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.;
Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst,
T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.;
Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K.
2005AGUSMSP34A..04H Altcode:
The Advanced Technology Solar Telescope (ATST) will be the world's
largest aperture solar telescope, and is being designed for high
resolution, IR, and coronal research. It must be located at a site that
maximizes the scientific return of this substantial investment. We
present the instrumentation, analysis and results of the ATST site
survey. Two instrumentation sets were deployed at each of six sites to
measure seeing as a function of height, and sky brightness as a function
of wavelength and off-limb position. Analysis software was developed
to estimate the structure function Cn2 as a function of height near
the ground, and the results were verified by comparison with in-situ
measurements. Additional software was developed to estimate the sky
brightness. The statistics of the conditions at the sites were corrected
for observing habits and the annualized hours of specific observing
conditions were estimated. These results were used to identify three
excellent sites suitable to host the ATST: Haleakala, Big Bear and La
Palma. Among them, Haleakala is proposed as the optimal location of
the ATST, La Palma and Big Bear being viable alternative sites.
---------------------------------------------------------
Title: Observation and Modeling of Anomalous CN Polarization Profiles
Produced by the Molecular Paschen-Back Effect in Sunspots
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2005ApJ...623L..57A Altcode: 2005astro.ph..5076A
We report novel spectropolarimetric observations of sunspots carried
out with the Tenerife Infrared Polarimeter in a near-IR spectral
region around 15410 Å, which is known to contain two groups of
prominent OH lines that show circular polarization signals of
opposite polarity. Surrounding these well-known OH lines, we have
discovered the presence of CN lines of the Δv=1 band that show
anomalous polarization profiles. Although the Stokes V signals of
the OH lines are antisymmetric and of a sizable amplitude, the CN
lines show almost negligible circular polarization. On the contrary,
the linear polarization signals turn out to be much stronger in the
CN lines than in the OH lines. Interestingly, these CN lines present
striking antisymmetric linear polarization profiles, which we are able
to explain and model via the Paschen-Back effect theory for diatomic
molecules. The presence of such peculiar CN lines in the same spectral
region of the OH lines may be useful to improve our empirical knowledge
of solar magnetic fields via the simultaneous observation and modeling
of the transverse and longitudinal Zeeman effects in two different
molecular species.
---------------------------------------------------------
Title: The Hanle and Zeeman Effects in Solar Spicules: A Novel
Diagnostic Window on Chromospheric Magnetism
Authors: Trujillo Bueno, J.; Merenda, L.; Centeno, R.; Collados, M.;
Landi Degl'Innocenti, E.
2005ApJ...619L.191T Altcode: 2005astro.ph..1533T; 2005astro.ph..1533B
An attractive diagnostic tool for investigating the magnetism of the
solar chromosphere is the observation and theoretical modeling of
the Hanle and Zeeman effects in spicules, as shown in this Letter for
the first time. Here we report on spectropolarimetric observations of
solar chromospheric spicules in the He I λ10830 multiplet and on their
theoretical modeling accounting for radiative transfer effects. We find
that the magnetic field in the observed (quiet-Sun) spicular material at
a height of about 2000 km above the visible solar surface has a strength
of the order of 10 G and is inclined by approximately 35<SUP>deg</SUP>
with respect to the local vertical direction. Our empirical finding
based on full Stokes vector spectropolarimetry should be taken into
account in future magnetohydrodynamical simulations of spicules.
---------------------------------------------------------
Title: Some properties of an isolated sunspot
Authors: Balthasar, H.; Collados, M.
2005A&A...429..705B Altcode:
We present an investigation of a single sunspot observed in the
neutral Fe line at 1089.6 nm with the Tenerife Infrared Polarimeter
at the Vacuum Tower Telescope on Tenerife. Using the SIR code, we
obtain maps of the magnetic field strength, inclination and azimuth,
and Doppler velocities. The magnetic field strength drops from 2800 G
in the umbra to about 700 G at the outer penumbral boundary, where we
encounter an average magnetic inclination of 72<SUP>o</SUP>. Comparing
the magnetic flux passing through different areas, we conclude that
the inner penumbra must be deep, while the outer penumbra could be
shallow. Assuming that the magnetic field strength encountered at the
outer penumbral boundary forms a smooth surface through which the total
flux of the spot passes, it would be approximately an ellipsoidal cap
with a top height of 5250 km. This scenario leads to an average vertical
magnetic gradient of 0.4 G km<SUP>-1</SUP>. Evershed Doppler velocities
are about 2 km s<SUP>-1</SUP>. Two penumbral locations related to dark
intensity features exhibit a steeper and slightly stronger magnetic
field than elsewhere in the penumbra, and one of them is connected to
an interruption of the Evershed effect.
---------------------------------------------------------
Title: Two magnetic components in sunspot penumbrae
Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.
2004A&A...427..319B Altcode:
The magnetic and kinematic configuration of sunspot penumbrae is
investigated by performing an inversion of the Stokes profiles of three
infrared lines at 1565 nm. We use a two-component model atmosphere
to describe, at least to first order, the unresolved structure of
the penumbra. The observed Stokes profiles are successfully fitted,
including those exhibiting abnormal shapes. The results of the inversion
are consistent with the idea that the penumbra is formed by almost
horizontal flux tubes embedded in a more vertical background magnetic
field, as proposed by Solanki & Montavon (\cite{Sol93}). The tubes
possess weaker fields than the background except in the very outer
penumbra, and carry most of the Evershed flow. We characterize the
radial variation of the magnetic field vector and the velocity vector
in these atmospheric components. In the middle penumbra and beyond,
the magnetic field and the flow in the tubes are seen to return to
the solar surface. Everywhere in the penumbra, there is a perfect
alignment of the magnetic field vector and the velocity vector in
the component describing the penumbral flux tubes. We find that the
Evershed flow is supercritical in many places of the outer penumbra,
and supersonic at some locations near the outer sunspot boundary. Based
on these inversions, we suggest that the azimuthal fluctuations in the
average magnetic field inclination and strength inferred from simple
one-component models are caused by fluctuations in the filling factor
(i.e., the fractional area of the resolution element occupied by
flux tubes), not by changes in the intrinsic magnetic and kinematic
properties of the background or the flux-tube atmospheres. Also,
we confirm the jump of magnetic field azimuth proposed by Müller et
al. (\cite{Mul02}) to explain the observed net circular polarization
of infrared lines.
---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V Altcode:
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
and other national and international Partners. The refurbishment of
the building is almost finished. The manufacturing of the telescope
structure and the optics is still in progress. After the integration of
the new complete retractable dome in July 2004 the telescope structure,
optic and post focus instruments will be assembled during the rest of
the year. First light is planned during May 2005.
---------------------------------------------------------
Title: Solar site testing for the Advanced Technology Solar Telescope
Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John;
Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher,
Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski,
Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas
R.; Socas-Navarro, Hector; Streander, Kim
2004SPIE.5489..122H Altcode:
The location of the Advanced Technology Solar Telescope (ATST) is a
critical factor in the overall performance of the telescope. We have
developed a set of instrumentation to measure daytime seeing, sky
brightness, cloud cover, water vapor, dust levels, and weather. The
instruments have been located at six sites for periods of one to two
years. Here we describe the sites and instrumentation, discuss the
data reduction, and present some preliminary results. We demonstrate
that it is possible to estimate seeing as a function of height near the
ground with an array of scintillometers, and that there is a distinct
qualitative difference in daytime seeing between sites with or without
a nearby lake.
---------------------------------------------------------
Title: The imaging magnetograph eXperiment for the SUNRISE balloon
Antarctica project
Authors: Martinez Pillet, Valentin; Bonet, Jose A.; Collados, Manuel
V.; Jochum, Lieselotte; Mathew, S.; Medina Trujillo, J. L.; Ruiz Cobo,
B.; del Toro Iniesta, Jose Carlos; Lopez Jimenez, A. C.; Castillo
Lorenzo, J.; Herranz, M.; Jeronimo, J. M.; Mellado, P.; Morales, R.;
Rodriguez, J.; Alvarez-Herrero, Alberto; Belenguer, Tomas; Heredero,
R. L.; Menendez, M.; Ramos, G.; Reina, Manuel; Pastor, C.; Sanchez,
A.; Villanueva, J.; Domingo, Vicente; Gasent, J. L.; Rodriguez, P.
2004SPIE.5487.1152M Altcode:
The SUNRISE balloon project is a high-resolution mission to study solar
magnetic fields able to resolve the critical scale of 100 km in the
solar photosphere, or about one photon mean free path. The Imaging
Magnetograph eXperiment (IMaX) is one of the three instruments that
will fly in the balloon and will receive light from the 1m aperture
telescope of the mission. IMaX should take advantage of the 15 days
of uninterrupted solar observations and the exceptional resolution
to help clarifying our understanding of the small-scale magnetic
concentrations that pervade the solar surface. For this, IMaX should
act as a diffraction limited imager able to carry out spectroscopic
analysis with resolutions in the 50.000-100.000 range and capable
to perform polarization measurements. The solutions adopted by the
project to achieve all these three demanding goals are explained in this
article. They include the use of Liquid Crystal Variable Retarders for
the polarization modulation, one LiNbO<SUB>3</SUB> etalon in double pass
and two modern CCD detectors that allow for the application of phase
diversity techniques by slightly changing the focus of one of the CCDs.
---------------------------------------------------------
Title: Thermal-magnetic relation in a sunspot and a map of its
Wilson depression
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
Borrero, J. M.; Berdyugina, S.
2004A&A...422..693M Altcode:
We present relations between thermal and magnetic quantities in a
simple, isolated sunspot, as deduced from the inversion of 1.56 μm
spectropolarimetric data. We used a combination of two infrared Fe I
lines at 15 648.5 Å and 15 652.8 Å/ in the inversions. Due to the
high Zeeman sensitivity of these lines, we can study this relationship
in the entire sunspot. The relevant parameters were derived both as a
function of location within the sunspot and of height in the atmosphere
using an inversion technique based on response functions. In this paper
we relate the magnetic vector with temperature. We find a non-linear
relationship between the various components of the magnetic vector and
temperature, which confirm the results from earlier investigations. We
also computed the Wilson depression and the plasma β for the observed
sunspot and compare our results with earlier findings.
---------------------------------------------------------
Title: Latest Results from the ATST Site Survey
Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt,
P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa,
M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau,
D.; Streander, K.
2004AAS...204.6909H Altcode: 2004BAAS...36..795H
We present the latest results and current status of the site survey
portion of the Advanced Technology Solar Telescope (ATST) project. The
ATST will provide high resolution solar data in the visible and IR. The
site is a major factor determining the performance of the telescope. The
most critical site characteristics are the statistics of daytime seeing
quality and sky clarity. These conditions are being measured by a suite
of instruments at three sites (Big Bear, Haleakala, La Palma). These
sites were chosen from a set of six that have been tested starting in
November 2001. The instrumentation includes a solar differential image
motion monitor, an array of scintillometers, a miniature coronagraph,
a dust monitor, and a weather station. The analysis of the data provides
an estimate of the seeing as a function of height near the ground. We
will present the latest results of the analysis of the survey data set.
---------------------------------------------------------
Title: Detection of Polarization from the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π System of FeH in Sunspot Spectra
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M.
2004ApJ...603L.125A Altcode: 2004astro.ph..1597A; 2004astro.ph..1597R
Here we report the first detection of polarization signals
induced by the Zeeman effect in spectral lines of the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π system of FeH located around 1.6
μm. Motivated by the tentative detection of this band in the
intensity spectrum of late-type dwarfs, we have investigated the
full Stokes sunspot spectrum and have found circular and linear
polarization signatures that we associate with the FeH lines of the
E<SUP>4</SUP>Π-A<SUP>4</SUP>Π band system. We investigate the Zeeman
effect in these molecular transitions and point out that in Hund's case
(a) coupling, the effective Landé factors are never negative. For this
reason, the fact that our spectropolarimetric observations indicate that
the Landé factors of pairs of FeH lines have opposite signs prompts
us to conclude that the E<SUP>4</SUP>Π-A<SUP>4</SUP>Π system must be
in intermediate angular momentum coupling between Hund's cases (a) and
(b). We emphasize that theoretical and/or laboratory investigations of
this molecular system are urgently needed for exploiting its promising
diagnostic capabilities.
---------------------------------------------------------
Title: Successful Measurement of the Full Magnetic Vector Near the
Base of the Solar Corona
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Landi
Degl'Innocenti, E.; Collados, M.
2003AGUFMSH41D..05S Altcode:
The measurement of coronal fields has in the past generally been
restricted to the field strength or to only some of the components of
the magnetic vector. We present here a technique for measuring the full
magnetic vector near the base of the solar corona. As an application
we report on observations of a developing active region with ongoing
magnetic flux emergence. The data allow the first measurement of the 3-D
structure of magnetic loops. They also provide the first detection of an
electric current sheet located near the base of the solar corona. Such
current sheets or tangential discontinuities of the coronal magnetic
field have long been thought to be a major source of coronal heating.
---------------------------------------------------------
Title: Three dimensional structure of a regular sunspot from the
inversion of IR Stokes profiles
Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.;
Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C.
2003A&A...410..695M Altcode:
The magnetic, thermal and velocity structure of a regular sunspot,
observed close to solar disk center is presented. Spectropolarimetric
data obtained with the Tenerife Infrared Polarimeter (TIP) in two
infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted
employing a technique based on response functions to retrieve the
atmospheric stratification at every point in the sunspot. In order
to improve the results for the umbra, profiles of Zeeman split OH
lines blending the FeI 15 652.8 Å are also consistently fit. Thus
we obtain maps of temperature, line-of-sight velocity, magnetic
field strength, inclination, and azimuth, as a function of both
location within the sunspot and height in the atmosphere. We present
these maps for an optical depth range between log tau<SUB>5</SUB> =
0 and log tau<SUB>5</SUB> = -1.5, where these lines provide accurate
results. We find decreasing magnetic field strength with increasing
height all over the sunspot, with a particularly large vertical field
gradient of ~ -4 G km<SUP>-1</SUP> in the umbra. We also observe the
so called “spine” structures in the penumbra, i.e. extended radial
features with a stronger and more vertical magnetic field than the
surroundings. Also we found that the magnetic field zenith angle
increases with height. From the velocity map it is clear that the
Evershed flow avoids the spines and mostly concentrates in the more
inclined intervening field. The field inclination at a few locations
in the outer penumbra in lower layers goes beyond 90<SUP>o</SUP>. These
locations coincide with the strongest flows in the velocity map.
---------------------------------------------------------
Title: Three-dimensional magnetic field topology in a region of
solar coronal heating
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Collados, M.
2003Natur.425..692S Altcode:
Flares and X-ray jets on the Sun arise in active regions where magnetic
flux emerges from the solar interior amd interacts with the ambient
magnetic field. The interactions are believed to occur in electric
current sheets separating regions of opposite magnetic polarity. The
current sheets located in the corona or upper chromosphere have long
been thought to act as an important source of coronal heating, requiring
their location in the corona or upper chromosphere. The dynamics and
energetics of these sheets are governed by a complex magnetic field
structure that, until now, has been difficult to measure. Here we report
the determination of the full magnetic vector in an interaction region
near the base of the solar corona. The observations reveal two magnetic
features that characterize young active regions on the Sun: a set of
rising magnetic loops and a tangential discontinuity of the magnetic
field direction, the latter being the observational signature of an
electric current sheet. This provides strong support for coronal heating
models based on the dissipation of magnetic energy at current sheets.
---------------------------------------------------------
Title: Quiet-Sun inter-network magnetic fields observed in the
infrared
Authors: Khomenko, E. V.; Collados, M.; Solanki, S. K.; Lagg, A.;
Trujillo Bueno, J.
2003A&A...408.1115K Altcode:
This paper presents the results of an investigation of the quiet Sun's
magnetic field based on high-resolution infrared spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter (TIP)
at the German VTT of the Observatorio del Teide. We observed two very
quiet regions at disc centre. The seeing was exceptionally good during
both observing runs, being excellent during one of them. In both cases
the network was intentionally avoided to the extent possible, to focus
the analysis on the characteristics of the weak polarization signals
of the inter-network regions. We find that the Stokes V profile of
Fe I 15648 Å line in almost 50% of the pixels and Stokes Q and/or
U in 20% of the pixels have a signal above 10<SUP>-3</SUP> (in units
of continuum intensity I<SUB>c</SUB>), which is significantly above
the noise level of 2-3 x 10<SUP>-4</SUP>. This implies that we detect
fluxes as low as 2 x 10<SUP>15</SUP> Mx/px. We find evidence that we
have detected most of the net flux that is in principle detectable at
1<SUP>”</SUP> resolution with the Zeeman effect. The observed linear
polarization resulting from the transverse Zeeman effect indicates that
the magnetic fields have a broad range of inclinations, although most
of the pixels show polarization signatures which imply an inclination
of about 20<SUP>o</SUP>. Nearly 30% of the selected V-profiles have
irregular shapes with 3 or more lobes, suggesting mixed polarities with
different LOS velocity within the resolution element. The profiles are
classified using a single value decomposition approach. The spatial
distribution of the magnetic signal shows that profiles of different
classes (having different velocities, splitting, asymmetries) are
clustered together and form patches, close to the spatial resolution
in size. Most of the field is found to be located in intergranular
lanes. The statistical properties of the mainly inter-network field
sampled by these observations are presented, showing that most of
the observed fields are weak with relatively few kG features. The
field strength distribution peaks at 350 G and has a FWHM of 300
G. Other parameters, such as profile asymmetries, filling factors and
line-of-sight velocities are also determined and discussed. <P />Based
on observations with the German Vacuum Tower Telescope (VTT) operated by
the Kiepenheuer-Institut für Sonnenphysik at the Spanish Observatorio
del Teide of the Instituto de Astrofísica de Canarias (IAC).
---------------------------------------------------------
Title: Understanding internetwork magnetic fields as determined
from visible and infrared spectral lines
Authors: Bellot Rubio, L. R.; Collados, M.
2003A&A...406..357B Altcode:
We present numerical experiments aimed at understanding why
near-infrared observations systematically deliver weak magnetic fields
in the internetwork, whereas analyses based on visible lines indicate
that kG fields are ubiquitous. Synthetic noisy Stokes V profiles of the
iron lines at 6302 Å and 1.565 mu m have been produced under varying
conditions in an effort to simulate polarized spectra coming from the
internetwork. An inversion technique has been applied to the profiles,
as it is usually done with real observations, in order to derive the
distribution of magnetic fields in the simulated region. Our results
show that infrared lines yield distributions which are very similar to
those used as input for the simulation, while visible lines are to a
large extent affected by noise. Analyses based on the Fe I lines at 6302
Å may lead to an overabundance of kG fields if the signal-to-noise
ratio in Stokes V is poorer than about 10. A particular example is
shown where strong fields are retrieved in nearly 30% of the pixels
of a simulated internetwork region in which only fields of 200 G exist.
---------------------------------------------------------
Title: Magnetoacoustic Waves in Sunspots
Authors: Khomenko, E. V.; Collados, M.; Bellot Rubio, L. R.
2003ApJ...588..606K Altcode:
Observed variations of the magnetic field strength in sunspot umbrae
consist of intrinsic oscillations and “false” oscillations due to
time-dependent opacity effects. Here we present an approach intended for
the separation of these components. We develop a mathematical formalism
based on the analytical solution of the MHD equations including gravity,
inclination of the magnetic field, and effects of nonadiabaticity. The
theoretical results are compared with observations in the near-infrared
at 1.56 μm by Bellot Rubio and coworkers using the Tenerife Infrared
Polarimeter. It is shown that part of the detected field strength
variations can be intrinsic magnetic field oscillations caused by
magnetoacoustic waves.
---------------------------------------------------------
Title: Field-aligned Evershed flows in the photosphere of a sunspot
penumbra
Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.;
Schlichenmaier, R.
2003A&A...403L..47B Altcode:
We determine the inclinations of the vector magnetic field and flow
velocity in a sunspot penumbra by interpreting full Stokes profiles of
three infrared lines observed with the Tenerife Infrared Polarimeter. It
is shown that analyses based on one-component atmospheres deliver flow
velocities which are more horizontal than the average magnetic field
by up to 10 deg. This apparent violation of the concept of frozen-in
magnetic fields is solved as soon as two magnetic atmospheres are
allowed to coexist in the resolution element. The magnetic field and
velocity in the atmospheric component carrying the Evershed flow are
found to be aligned to within +/- 2 deg all the way from the inner
to the outer penumbra. This is the first observational confirmation
of magnetic fields being frozen into the plasma in sunspots. Our
results indicate that sunspot penumbrae can be understood in terms of
inclined flux tubes embedded in a more vertical background field. The
flux tubes carry most of the Evershed flows and return to the solar
surface in the middle penumbra and beyond. The background atmosphere
is essentially at rest in the inner penumbra, and harbors small flows
in the outer penumbra.
---------------------------------------------------------
Title: Inverting Scintillometer Array Data to Estimate
C<SUB>n<SUP>2(h)</SUP></SUB> for the ATST Site Survey
Authors: Hill, F.; Collados, M.
2003SPD....34.2020H Altcode: 2003BAAS...35..848H
One of the instruments developed for the Advanced Technology
Solar Telescope (ATST) site survey is a non-redundant array
of six scintillometers known as a ShaBaR (SHAdow BAnd Ranging)
system, developed by J. Beckers. The ShaBaR provides an estimate
of C<SUB>n<SUP>2(h)</SUP></SUB>, the turbulence structure
function, in the Earth's atmosphere. We can use the estimate of
C<SUB>n<SUP>2(h)</SUP></SUB> to infer the value of r<SUB>0</SUB>, the
Fried parameter, at any height above the ground up to the maximum range
of the ShaBaR. In this poster, we present two methods of extracting
the estimates by 1) inverting the data via a kernel function derived
from the theory of atmospheric turbulence, and 2) assuming a modified
Hufnagel-Valley model of C<SUB>n<SUP>2(h)</SUP></SUB>. We also show
a series of simulations that has been produced and used to test the
accuracy and precision of the methods.
---------------------------------------------------------
Title: Stokes polarimeters in the near-infrared
Authors: Collados, Manuel V.
2003SPIE.4843...55C Altcode:
In this contribution, the main characteristics of near infrared
spectropolarimetric measurements are described, putting especial
emphasis on the techniques to minimize the crosstalk between the
Stokes parameters.
---------------------------------------------------------
Title: Liquid crystal optical retarders for IMaX to fly with SUNRISE
Authors: Jochum, Lieselotte; Herrero, Pilar; Collados, Manuel;
Martinez Pillet, Valentin; Rodriguez, Javier; Lopez, Manuel
2003SPIE.4843...30J Altcode:
The Instituto de Astrofísica de Canarias (IAC), Spain, together with
the Spanish company Tecdis Displays Ibérica, S.A., are developing
voltage tunable optical retarders using liquid crystals as phase
retarding medium. The ROCLIs are built for being used in the Imaging
Magnetograph eXperiment (IMaX), which is one of the instruments aboard
of the SUNRISE balloon mission (details about IMaX are described
in a different paper in this session). A big advantage of using
voltage tuned retarder plates is that no mechanisms are needed, which
reduces significantly failure risk, weight, power and cost, aspects
of particular importance in the SUNRISE balloon mission and for many
future space borne applications. A set of prototypes has already
been fabricated by Tecdis S.A. and is being characterized in the
IAC laboratories. The purpose of these prototypes is to evaluate and
demonstrate conceptually the suitability of the chosen liquid crystal
for our use in IMaX. First results are very promising. In this paper
we will present a full technical description of the ROCLIs for IMaX
together with the laboratory test and verification results.
---------------------------------------------------------
Title: IMax: a visible magnetograph for SUNRISE
Authors: Jochum, Lieselotte; Collados, Manuel; Martínez Pillet,
Valentin; Bonet, Jose A.; del Toro Iniesta, Jose Carlos; Lopez,
Antonio; Alvarez-Herrero, Alberto; Reina, Manuel; Fabregat, Juan;
Domingo, Vicente
2003SPIE.4843...20J Altcode:
The description of the Imaging Magnetograph eXperiment (IMaX) is
presented in this contribution. This is a magnetograph which will
fly by the end of 2006 on a stratospheric balloon, together with
other instruments (to be described elsewhere). Especial emphasis
is put on the scientific requirements to obtain diffraction-limited
visible magnetograms, on the optical design and several constraining
characteristics, such as the wavelength tuning or the crosstalk between
the Stokes parameters.
---------------------------------------------------------
Title: The structure of the penumbra
Authors: Balthasar, H.; Bellot Rubio, L.; Collados, M.
2003AN....324..390B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Structure of a simple sunspot from the inversion of IR
spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J.
2003AN....324..388M Altcode:
Analysis of spectral data of two neighboring infrared lines, Fe i
15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out
for a simple sunspot when it was near the solar disk center (mu = 0.92),
to understand the basic structure of sunspot magnetic field. Inversions
of Stokes profiles are carried out to derive different atmospheric
parameters both as a function of location within the sunspot and height
in the atmosphere. As a result of the inversion we have obtained maps
of magnetic field strength, temperature, line-of-sight velocity, field
inclination and azimuth for different optical depth layers between log
(tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present
few results from our inversion for a layer averaged between log (tau_
{5}) from 0.0 to -0.5.
---------------------------------------------------------
Title: Modeling the Fine Structure of a Sunspot Penumbra through
the Inversion of Stokes Profiles
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.;
Collados, M.; Bellot Rubio, L. R.
2003ASPC..286..235B Altcode: 2003ctmf.conf..235B
No abstract at ADS
---------------------------------------------------------
Title: New Spectropolarimetric Observations of Solar Coronal Filaments
in the He I 10830 Å Multiplet
Authors: Collados, M.; Trujillo Bueno, J.; Asensio Ramos, A.
2003ASPC..307..468C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermal-magnetic relation of a sunspot as inferred from the
inversion of 1.5 μm spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch,
J.; Collados, M.; Berdyugina, S.; Frutiger, C.
2002ESASP.505..501M Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M
We present the thermal-magnetic relation in a simple, isolated sunspot
deduced from the inversion of 1.56 μm spectropolarimetric data. Due to
the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can
study this relationship in the entire sunspot. An inversion technique
based on response functions is used to derive various parameters,
both as a function of location within the sunspot and of height in the
atmosphere. In this paper we attempt to relate field strength, vertical
and radial field components and the field inclination with temperature.
---------------------------------------------------------
Title: THEMIS and DOT joint observations on NOAA 9716
Authors: Briand, C.; Collados, M.; Sütterlin, P.
2002ESASP.505..361B Altcode: 2002IAUCo.188..361B; 2002solm.conf..361B
Ephemeral magnetic emergence has been detected in a decaying β region
observed in December 2001 simultaneously with the DOT and THEMIS. We
present here the main characteristics of this phenomenon. Also the
time evolution of a small group of pores is shown together with the
time evolution of an horizontal magnetic field overlying them.
---------------------------------------------------------
Title: Statistical properties of magnetic fields in intranetwork
Authors: Khomenko, E. V.; Collados, M.; Lagg, A.; Solanki, S. K.;
Trujillo Bueno, J.
2002ESASP.505..445K Altcode: 2002IAUCo.188..445K; 2002solm.conf..445K
We report a study of the quiet sun's magnetic field based
on high-resolution infrared spectropolarimetric observations
(TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15%
the Stokes Q and/or U profiles have a signal above 10<SUP>-3</SUP>. The
statistical properties of the mainly intranetwork field sampled by these
observations are presented, showing that most of the observed fields
are weak (the field strength distribution peaks at 350 G and has a FWHM
of 300 G) with very few kG features. The magnetized regions occupy a
very small fill fractions (about 2%). The field changes properties on
granular spatial scales and the size of the patches formed by similar
profiles is close to 1". Most of the parameters of the observed
polarization profiles show correlations with granulation parameters.
---------------------------------------------------------
Title: Infrared spectropolarimetry of sunspots
Authors: Collados, M.
2002AN....323..254C Altcode:
Recently a number of works have given interesting results on the
penumbral fine structure of sunpots (del Toro Iniesta, Bellot Rubio
& Collados 2001; Schlichenmaier & Collados 2002), where,
for instance, cold supersonic Evershed downflows were observed. In
addition, there are recent results that show the existence of shock
wave trains propagating in umbral chromospheres with a 3-min period,
where the photospheric driving signal has also been detected. The phase
difference between the photospheric and chromospheric signals in the
5.5-6.5 mHz band (3 minute) allows to infer that an upward propagation
of the slow magnetoacoustic mode, with an increasing velocity amplitude
(due to the rapid decrease of density) and reaching the non-linear
regime, is giving rise to shock fronts. All these results show that
the umbra and the penumbra have a dynamical behaviour which is far
from being near an equilibrium situation.
---------------------------------------------------------
Title: Spectropolarimetry in a sunspot penumbra. Spatial dependence
of Stokes asymmetries in Fe I 1564.8 nm
Authors: Schlichenmaier, R.; Collados, M.
2002A&A...381..668S Altcode:
Stokes profiles of sunspot penumbrae show distinct asymmetries, which
point to gradients in the velocity field and in the magnetic field. We
present spectropolarimetric measurements of the Stokes vector in the
neutral iron triplet at 1564.8 nm taken with the Tenerife Infrared
Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT) in
Tenerife. We report on the peculiarities of the profiles of circularly
and linearly polarized light for spots at different heliocentric
angles. We elaborate on the spatial dependence of Stokes asymmetries
within the penumbra and find for profiles of circularly polarized light:
(1) In the center-side penumbra the amplitude difference of Stokes-V
exhibits a sign reversal on a radial cut, i.e., in the inner (outer)
penumbra the red (blue) lobe is broader and shows a smaller amplitude
than the blue (red) lobe. (2) In the outer limb-side penumbra (beyond
the magnetic neutral line) the red lobe is broader and of less amplitude
than the blue lobe. (3) Along the magnetic neutral line we find abnormal
Stokes-V profiles, which consist of more than 2 lobes. This indicates
the presence of two polarities. For small heliocentric angles abnormal
profiles are also seen beyond the magnetic neutral line in the outer
penumbra. (4) Maps of the net circular polarization have the tendency to
be antisymmetric with respect to the axis that connects disk center with
spot center. This finding is striking, because corresponding maps for Fe
I 630.25 are symmetric. For linearly polarized profiles we extract the
following features: (5) On the center-side penumbra at a heliocentric
angle of 56<SUP>o</SUP> a Doppler-shift as high as 5 km s<SUP>-1</SUP>
can be directly measured by the splitting of the pi -component of
the linearly polarized component. (6) In limb-side penumbrae, the
profiles of the pi -component show the typical asymmetry properties of
the Evershed flow as observed in Stokes-I of magnetically insensitive
lines. (7) In the outer center- and limb-side penumbrae the center of
the pi -component is blue-shifted relative to the zero-crossing of
the V-profile. Motivated by the moving tube model of Schlichenmaier
et al. (\cite{schlichenmaier+jahn+schmidt1998b}), we construct simple
model atmospheres featuring hot upflows and cool outflows and calculate
corresponding synthetic V-profiles. These profiles are compared with
our measured ones and with observed V-profiles in Fe I 630.25 from
other authors. We find that the synthetic V-profiles can reproduce
all essential characteristics of observed V-profiles for both lines.
---------------------------------------------------------
Title: Selective absorption processes as the origin of puzzling
spectral line polarization from the Sun
Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.;
Merenda, L.; Manso Sainz, R.
2002Natur.415..403T Altcode: 2002astro.ph..1409T
Magnetic fields play a key role in most astrophysical systems, from
the Sun to active galactic nuclei. They can be studied through their
effects on atomic energy levels, which produce polarized spectral
lines. In particular, anisotropic radiation `pumping' processes (which
send electrons to higher atomic levels) induce population imbalances
that are modified by weak magnetic fields. Here we report peculiarly
polarized light in the HeI 10,830-Å multiplet observed in a coronal
filament located at the centre of the solar disk. We show that the
polarized light arises from selective absorption from the ground level
of the triplet system of helium, and that it implies the presence of
magnetic fields of the order of a few gauss that are highly inclined
with respect to the solar radius vector. This disproves the common
belief that population imbalances in long-lived atomic levels are
insignificant in the presence of inclined fields of the order of a few
gauss, and opens up a new diagnostic window for the investigation of
solar magnetic fields.
---------------------------------------------------------
Title: Penumbral finestructure: need for larger telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AN....322..367B Altcode:
We obtained at the same time G-band images at the Dutch Open Telescope
(DOT) on La Palma and spectropolarimetric data in the near infrared
at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright
filaments have a smaller magnetic field s trength, and higher
Evershed velocities occur in dark structures. This result is in
agreement with some previous observations, but also in contradiction
to others. However, we suffer from the fact that the resolution limit
of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial
power spectra derived from the DOT data indicate a typical width of
250 km for penumbral filaments. Obviously a solar telescope with an
aperture of at least 1.5~m is needed to obtain sophisticated results
for penumbral structures.
---------------------------------------------------------
Title: Observation of Convective Collapse and Upward-moving Shocks
in the Quiet Sun
Authors: Bellot Rubio, Luis R.; Rodríguez Hidalgo, Inés; Collados,
Manuel; Khomenko, Elena; Ruiz Cobo, Basilio
2001ApJ...560.1010B Altcode:
We present spectropolarimetric evidence of convective collapse
and destruction of magnetic flux by upward-moving fronts in the
quiet Sun. The observational material consists of time series of
the full Stokes vector of two infrared spectral lines emerging from
regions associated with Ca II K network points. The amplitude of the
circular polarization profiles of a particular spatial point is seen to
increase while the profiles are redshifted. It then decreases during
a much shorter phase characterized by large blueshifts. Inspection
of the data indicates that the blueshift occurs because of the sudden
appearance of a new, strongly displaced Stokes V profile of the same
polarity. The amplification of the magnetic signal takes place in a
time interval of about 13 minutes, while blueshifts and the concomitant
decreasing Stokes V amplitudes last for only 2 minutes. An inversion
code based on the thin flux-tube scenario has been applied to the data
in order to derive the thermal, magnetic, and dynamic structures of
the atmosphere. According to our results, the field strength undergoes
a moderate increase from 400 to 600 G at z=0 km during the phase in
which redshifts are present. The observed redshifts are produced by
internal downflows of up to 6 km s<SUP>-1</SUP> at z=0 km. After ~13
minutes, the material falling down inside the tube appears to bounce
off in the deeper layers, originating an upward-propagating front whose
manifestation on the Stokes V profiles is a large blueshift. The front
moves with a speed of 2.3 km s<SUP>-1</SUP> and has a downflow-to-upflow
velocity difference of about 7 km s<SUP>-1</SUP> initially and some
4 km s<SUP>-1</SUP> after 2 minutes. It strongly weakens the magnetic
field strength and may be responsible for the complete destruction of
the magnetic feature. The observed behavior is in general agreement
with theoretical predictions of flux expulsion, convective collapse,
and development of shocks within magnetic flux tubes.
---------------------------------------------------------
Title: A proposal for the visible-light imager magnetograph
Authors: von der Lühe, O.; Martinez Pillet, V.; Schmidt, W.;
Collados, M.
2001ESASP.493..421V Altcode: 2001sefs.work..421V
No abstract at ADS
---------------------------------------------------------
Title: Cold, Supersonic Evershed Downflows in a Sunspot
Authors: del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.;
Collados, Manuel
2001ApJ...549L.139D Altcode:
We report here on the discovery of supersonic Evershed downflows
in the penumbra of a sunspot. These flows are shown to occur along
spatially unresolved, very cold magnetic flux tubes whose downflowing
footpoints are found from the middle penumbra outward. Evershed
flows along magnetic field lines returning to the solar surface were
discovered by Westendorp Plaza and coworkers, but only in the outer
parts of the penumbra and beyond its visible boundary; on the other
hand, no supersonic flows of any type have ever been reported in the
photosphere of sunspots, except for the very different case of the
delta spot analyzed by Martínez Pillet and coworkers. We present
unequivocal evidence of such supersonic motions, already predicted
theoretically by the siphon-flow model, from the interpretation
of infrared spectropolarimetric observations of a sunspot with
unprecedented spatial resolution.
---------------------------------------------------------
Title: Penumbral Finestructure: Need for Larger Telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AGM....18S1003B Altcode:
We obtained at the same time G-band images at the Dutch Open
Telescope (DOT) on La Palma and spectropolarimetric data in the near
infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright filaments
have a smaller magnetic field strength, and higher Evershed velocities
occur in dark structures. This result is in agreement with some previous
observations, but also in contradiction to others. However, we suffer
from the fact that the resolution limit of the VTT at a wavelength
of 1.565 μm corresponding to 400 km. Spatial power spectra derived
from the DOT data indicate a typical width of 250 km for the penumbral
filaments. Obviously a solar telescope with an aperture of at least 1.5
m is needed to obtain sophisticated results for penumbral structures.
---------------------------------------------------------
Title: Full Stokes LPSP Observations of the Na D<SUB>1</SUB> and
D<SUB>2</SUB> Lines in Magnetized Regions close to the Solar Limb
Authors: Martínez Pillet, V.; Trujillo Bueno, J.; Collados, M.
2001ASPC..236..133M Altcode: 2001aspt.conf..133M
No abstract at ADS
---------------------------------------------------------
Title: Spectropolarimetric Signatures of Convective Collapse
Authors: Rodrígues Hidalgo, I.; Bellot Rubio, L. R.; Collados, M.;
Ruiz Cobo, B.
2001ASPC..236..415R Altcode: 2001aspt.conf..415R
No abstract at ADS
---------------------------------------------------------
Title: Infrared Polarimetry
Authors: Collados, M.
2001ASPC..236..255C Altcode: 2001aspt.conf..255C
No abstract at ADS
---------------------------------------------------------
Title: THÉMIS Observations of the Second Solar Spectrum
Authors: Trujillo Bueno, J.; Collados, M.; Paletou, F.; Molodij, G.
2001ASPC..236..141T Altcode: 2001aspt.conf..141T
No abstract at ADS
---------------------------------------------------------
Title: Magnetic field oscillations in sunspots and active regions
Authors: Balthasar, Horst; Collados, Manuel; Muglach, Karin
2001ESASP.464..163B Altcode: 2001soho...10..163B
In order to investigate the oscillatory behaviour of the magnetic
field in sunspots and pores, full Stokes measurements of 1.56 μm
iron lines have been performed using the Tenerife Infrared Polarimeter
(TIP) at the German Vacuum Tower Telescope on Tenerife. As expected,
velocity oscillations have power peaks at five minutes. First results
for temporal variations of the magnetic field show that they occur in
locally restricted areas in sunspots. Periods in the five minute range
are preferred. In addition, we investigate magnetograms taken with
the Michelson Doppler Imager (MDI) on SOHO. Intensity images in white
light and around 160 nm were obtained with TRACE as well. Intensity
power is strongly with TRACE as well. Intensity power is strongly
suppressed in the sunspot area, although we find powerpeaks in the
five and three minute ranges.
---------------------------------------------------------
Title: Penumbral Stokes-V Asymmetries of Fe I 1564.8 nm
Authors: Schlichenmaier, R.; Soltau, D.; Lühe, O. V. D.; Collados, M.
2001ASPC..236..579S Altcode: 2001aspt.conf..579S
No abstract at ADS
---------------------------------------------------------
Title: Lagrangian and Eulerian Stratifications of Acoustic
Oscillations through the Solar Photosphere
Authors: Rodríguez Hidalgo, Inés; Ruiz Cobo, Basilio; Collados,
Manuel; Bellot Rubio, Luis R.
2001ApJ...547..491R Altcode:
We evaluate the stratification of acoustic oscillations in the solar
photosphere in both the Lagrangian (comoving) frame of reference and
the Eulerian (inertial) frame of reference, from a temporal sequence
of model atmospheres in an optical depth scale obtained after a
quasi-non-LTE inversion of the radiative transfer equation applied to
spectral observations of the K I 7699 Å line. Our results suggest
that, to first order, the photosphere moves up and down as a whole
with amplitudes ranging from ~8 km in deep layers (around 0 km) to ~19
km in the upper layers (around 640 km). In Lagrangian coordinates, we
observe numerous short-lived, local temperature and velocity amplitude
enhancements in medium-high layers, together with asymmetric waveforms
in the oscillation of these two physical quantities. The Lagrangian
temperature oscillation clearly shows two nodes associated with sharp
phase jumps of about 180°, whereas the velocity amplitude shows
the well-known increase with geometrical height, at nearly constant
phase. In Eulerian coordinates, the perturbations are dominated by
the coherent oscillation of the entire photosphere.
---------------------------------------------------------
Title: Photospheric acoustic oscillations in a Langrangian reference
system
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados Vera, M.;
Bellot Rubio, L. R.
2001ESASP.464..239R Altcode: 2001soho...10..239R
The stratification of acoustic oscillations through the solar
photosphere in Lagrangian (comoving) coordinates has been evaluated from
a quasi-NLTE inversion of the radiative transfer equation (RTE) applied
to a temporal sequence of K I 7699 Å line spectra. The stratifications
of amplitude and phase of the temperature and line-of-sight (LOS)
velocity Lagrangian oscillations have been evaluated. Our results
suggest that, to first order, the photosphere moves up and down as a
whole with amplitudes ranging from ~8 km in deep layers (around 0 km)
to ~19 km in the upper layers (around 640 km). Numerous short-lived,
local temperature and velocity amplitude enhancements in medium-high
layers are observed, together with an asymmetric waveform in the
oscillation of these two physical quantities. Two nodes are clearly seen
in the Lagrangian temperature oscillation run, which are associated with
sharp phase jumps of about 180°. The velocity amplitude shows the well
known increase with geometrical height, keeping practically in phase.
---------------------------------------------------------
Title: Structure of Plage Flux Tubes from the Inversion of Stokes
Spectra. I. Spatially Averaged Stokes I and V Profiles
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
2000ApJ...535..489B Altcode:
We present results of the inversion of spatially averaged Stokes
I and V profiles emerging from plage regions near disk center. The
observations analyzed in this work were recorded with the Advanced
Stokes Polarimeter. All atmospheric quantities determining the
radiative transfer in the thin flux-tube approximation are inferred
self-consistently with the help of the inversion code described by
Bellot Rubio et al. With regard to thermodynamics, the retrieved
model atmospheres are found to behave as expected on theoretical
grounds. For the first time, velocities inside and outside the tubes
have been derived empirically. The magnetic atmospheres resulting from
the inversion are characterized by the absence of significant motions in
high layers but show strong velocity gradients in deeper layers. These
gradients turn out to be essential for reproducing the whole shape
of the observed profiles and, in particular, the asymmetries and the
extended red tail of Stokes V. Our scenario predicts that the Stokes
V zero-crossing wavelengths of Fe I and Fe II lines are redshifted
by small but nonnegligible amounts, which is indeed confirmed by
observations made with the Fourier Transform Spectrometer. According
to recent numerical simulations, the internal downflows derived from
the inversion could be produced by the strong shear that takes place
in the intermediate layer between the magnetized interior and the
ambient medium. Another possible origin is magnetic flux undergoing
convective collapse within the resolution element.
---------------------------------------------------------
Title: Oscillations in the Photosphere of a Sunspot Umbra from the
Inversion of Infrared Stokes Profiles
Authors: Bellot Rubio, L. R.; Collados, M.; Ruiz Cobo, B.; Rodríguez
Hidalgo, I.
2000ApJ...534..989B Altcode:
We report on the detection of magnetic field strength and velocity
oscillations in the photosphere of a sunspot umbra. Our analysis is
based on the inversion of the full Stokes vector of three Fe I lines
at 15650 Å, from which the stratification with optical depth of the
different atmospheric parameters has been derived. This allows us to
estimate the amplitude of the oscillations and the phase lag between
the fluctuations in the line-of-sight velocity and field strength. Our
results suggest that the inferred magnetic field oscillations are caused
by opacity fluctuations that move upward and downward the region where
the spectral lines are sensitive to magnetic fields.
---------------------------------------------------------
Title: Inversion of Stokes Profiles from Solar Magnetic Elements
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
2000ApJ...535..475B Altcode:
We describe a new LTE inversion code for the analysis of Stokes
profiles emerging from unresolved magnetic elements. It has been
specifically designed to obtain the thermal, dynamic, and magnetic
properties of these structures in a self-consistent manner by fitting
the whole shape of the observed spectra. The inversion code is based on
a previous scheme by Ruiz Cobo & del Toro Iniesta and implements
the thin flux-tube model as a reasonable description of reality. All
physical parameters considered relevant for the problem (including
velocity fields) are retrieved by means of a Marquardt nonlinear
least-squares algorithm. We present the results of extensive tests
aimed at characterizing the behavior of the code so as to understand
its limitations for the analysis of real observations. The code is
found to produce accurate results even with only two spectral lines and
noisy Stokes I and V profiles. A detailed error treatment, in which
the covariances between parameters are explicitly included, is also
carried out in order to investigate the uniqueness and reliability of
the inferred model atmospheres.
---------------------------------------------------------
Title: Optimum Modulation and Demodulation Matrices for Solar
Polarimetry
Authors: del Toro Iniesta, Jose Carlos; Collados, Manuel
2000ApOpt..39.1637D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in a solar pore
Authors: Balthasar, H.; Collados, M.; Muglach, K.
2000AN....321..121B Altcode:
Temporal variations of a solar pore were observed at the ground based
Vacuum Tower Telescope (VTT) on Tenerife and with the satellite
TRACE. At the VTT Stokes I and V of the iron line at 1.56 mu m,
originating in the deep photosphere, was measured. TRACE delivered
UV images at 170 nm which show chromospheric continuum. In a part of
the pore we find oscillations of the magnetic field in the 5 minute
range. Velocities derived from shifts of the Stokes V profiles show
5 minutes everywhere in the pore, but the coherence of magnetic field
and velocities is low. The intensity at 170 nm varies with 3 minutes,
and for a part of the whole time series additionally with 4 minutes.
---------------------------------------------------------
Title: Formation and Destruction of a Weak Magnetic Feature in the
Solar Photosphere
Authors: Khomenko, E.; Collados, M.; Bellot Rubio, L. R.; Rodríguez
Hidalgo, I.; Ruiz Cobo, B.
1999ESASP.448..307K Altcode: 1999mfsp.conf..307K; 1999ESPM....9..307K
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Spectropolarimetry and Magnetography
Authors: Collados, M.
1999ASPC..184....3C Altcode:
From an observational point of view, magnetic field leaves its imprint,
via Zeeman effect, on spectral line splitting and the induced
wavelength dependence of the polarization state of the observed
photons. The characteristics of the most recent polarimetric analyzers
are described, together with their limitations. Next, inversion
techniques are presented as the most accurate diagnostic tools
available at present to determine the properties of magnetic field,
derived from its polarization signature. Finally, the importance of
feeding inversion codes with the adequate physics are stressed.
---------------------------------------------------------
Title: Velocity and Temperature 5 Minute Oscillations as Functions
of Geometrical Height in the Photosphere
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.
1999ASPC..184..176R Altcode:
The stratification with geometrical height of the velocity and
temperature 5 minute oscillation through the solar photosphere is
obtained after the inversion of a time series of KI 7699 Å line
spectra taken at disk center.
---------------------------------------------------------
Title: TIP: The Tenerife Infrared Polarimeter
Authors: Martínez Pillet, V.; Collados, M.; Bellot Rubio, L. R.;
Rodríiguez Hidalgo, I.; Ruiz Cobo, B.; Soltau, D.
1999AGAb...15...89M Altcode: 1999AGM....15..P05M
The aim of the IAC Tenerife Infrared Polarimeter is to obtain
quantitative measurements of the polarization state of the solar
radiation collected in near-infrared wavelengths by the Gregory Coudé
Telescope and the Vacuum Tower Telescope of the Observatorio del Teide
(Spain). In this contribution we describe the analyzer, instrumental
calibration, and detector subsystems of TIP, and give details concerning
the specifications of the instrument.
---------------------------------------------------------
Title: Quiet and Active Granulation Properties
Authors: Manso Sainz, R.; Rodríguez Hidalgo, I.; Collados, M.
1999ASSL..239..197M Altcode: 1999msa..proc..197M
The preliminary results of a classical spectroscopic analysis of a
facular region at mu=0.78 of ~100 arcsec x 50 arcsec are presented. The
variation with magnetic activity of several spectroscopic parameters
has been studied, showing clear evidence that granulation properties
are modified.
---------------------------------------------------------
Title: Granular and Intergranular Model Atmospheres from Inversion
of Solar Two-Dimensional Spectroscopic Data
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.; del
Toro Iniesta, J. C.
1999ASPC..173..313R Altcode: 1999sstt.conf..313R
No abstract at ADS
---------------------------------------------------------
Title: Structure of a Facular Region From the Inversion of High
Spatial and Temporal Resolution Stokes Spectra
Authors: Bellot Rubio, L.; Ruiz Cobo, B.; Collados, M.
1999ASPC..183...61B Altcode: 1999hrsp.conf...61B
No abstract at ADS
---------------------------------------------------------
Title: An LTE code for the inversion of Stokes spectra from solar
magnetic elements
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1999ASSL..243..271B Altcode: 1999sopo.conf..271B
No abstract at ADS
---------------------------------------------------------
Title: TIP (Tenerife Infrared Polarimeter): a near IR full Stokes
Polarimeter for the German Solar Telescopes at Observatorio del Teide
Authors: Collados, M.; Rodríguez Hidalgo, I.; Bellot Rubio, L.;
Ruiz Cobo, B.; Soltau, D.
1999AGAb...15Q..11C Altcode: 1999AGM....15..A13C
In this contribution, the main characteristics of the=20 Tenerife
Infrared Polarimeter (TIP), recently built at the Instituto de
Astrofísica de Canarias, to be operated at the German Solar
Telescopes (GCT and VTT) of the Observatorio del Teide (Tenerife)
are presented. Especial emphasis is put on the modulation scheme,
polarisation efficiencies, signal-to-noise ratio, spatial and spectral
resolution, and instrumental polarisation cross-talk. Some examples
of data recently obtained are presented, which give an idea of the
performance and capabilities of this instrument.
---------------------------------------------------------
Title: The Hermitian solution of the radiative transfer equation
for non-LTE problems
Authors: Ruiz Cobo, B.; Bellot Rubio, L. R.; Collados, M.
1999ASSL..243..231R Altcode: 1999sopo.conf..231R
No abstract at ADS
---------------------------------------------------------
Title: Probing downflows in solar magnetic elements: the Fe II test
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1999A&A...341L..31B Altcode:
In an attempt to assess the physical realism of the plage flux tube
model derived by Bellot Rubio, Ruiz Cobo & Collados (\cite{brc},
\cite{bellot}) we extend its predictions to the Stokes V zero-crossing
shifts of a number of Fe ii lines. For this analysis, accurate Fe
ii central wavelengths are required. We have devised a procedure for
bringing the available Fe ii laboratory wavelengths to the system of
accurate Fe i wavelengths of Nave et al. (\cite{nav}). It is shown that,
relative to this system, the Fe ii system of Kurucz (\cite{kur}) is
shifted by 6.4 m Angstroms/ towards longer wavelengths. Some lines,
however, are displaced by more than 10 m Angstroms/. Corrected
central wavelengths have been used to extract the observed Stokes
V zero-crossing shifts of 16 Fe ii lines. Comparison with the
values resulting from the model of Bellot Rubio et al. (\cite{brc},
\cite{bellot}) suggests that the velocity gradients derived by these
authors are esentially correct.
---------------------------------------------------------
Title: Thermodynamical properties of granulation in active regions.
Authors: Rodríguez Hidalgo, I.; Collados, M.; Manso Sainz, R.;
Barkler, J.
1999joso.proc..195R Altcode:
A two-dimensional spectroscopic study of two solar active regions
is presented. A magnetic filling factor has been defined, and a new
technique to separate large and small spatial scale motions has been
used. Different types of features in the fields of view have been
classified according to their magnetic and convective properties,
and have been analysed with varying magnetic activity.
---------------------------------------------------------
Title: LPSP & TIP: Full Stokes Polarimeters for the Canary
Islands Observatories
Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.;
González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.;
Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D.
1999ASPC..183..264M Altcode: 1999hrsp.conf..264M
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in a sunspot umbra from the inversion of infrared
Stokes profiles
Authors: Bellot Rubio, Luis R.; Collados, Manuel; Ruiz Cobo, Basilio;
Rodríguez Hidalgo, Inés; Bogdan, Thomas J.
1999AGM....15..A07B Altcode:
We report on the detection of magnetic field strength and velocity
oscillations in the photosphere of a sunspot umbra. Our analysis is
based on the inversion of the full Stokes profiles of three Fe I lines
at 15650 Å, from which the stratification with optical depth of the
different atmospheric parameters has been derived. This allows us to
estimate the amplitude of the oscillations and the phase lag between
the fluctuations in the line-of-sight velocity and field strength. Our
results suggest that the inferred magnetic field oscillations are caused
by opacity fluctuations that move upward and donward the region where
the spectral lines are sensitive to magnetic fields.
---------------------------------------------------------
Title: An Hermitian Method for the Solution of Polarized Radiative
Transfer Problems
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1998ApJ...506..805B Altcode:
Spectral synthesis calculations in stellar (magnetized) atmospheres
are based on the solution of the radiative transfer equation (RTE)
for polarized light. The thermodynamic and magnetic properties of the
atmospheres, along with the radiation field, completely specify the
basic ingredients of the RTE, after which numerical methods have to
be employed to calculate the emergent Stokes spectra. The advent of
powerful analysis techniques for the inversion of Stokes spectra has
evidenced the need for accurate and fast solutions of the RTE. In
this paper we describe a novel Hermitian strategy to integrate the
polarized RTE that is based on the Taylor expansion of the Stokes
parameter vector to fourth order in depth. Our technique makes use
of the first derivatives of the absorption matrix and source vector
with respect to the coordinate measured along the ray path. Both
analytical and numerical results indicate that the new strategy is
superior to other methods in terms of speed and accuracy. It also gives
an approximation to the evolution operator at no extra cost, which is
of interest for inversion algorithms based on response functions. The
Hermitian technique can be straightforwardly particularized to the
scalar case, providing a very efficient solution of the RTE in the
absence of magnetic fields. We investigate in detail the consequences
of the oscillations that appear in the evolution operator for large
values of line strength η<SUB>0</SUB>. The problems they pose are
shared by all integration schemes, but can be minimized by adopting
nonequally spaced grids.
---------------------------------------------------------
Title: Near-infrared camera for solar research: a photometric
application
Authors: Reyes, Marcos; Joven-Alvarez, Enrique; Collados, Manuel;
Bonet, Jose A.; Vazquez, Manuel; Diaz, Jose J.; Fuentes, F. Javier;
Escalera, Victor G.; Rodriguez, Luis F.; Garcia-Herrero, Jose L.
1998SPIE.3410..233R Altcode:
We report here the main characteristics of a near IR camera devoted to
astrophysical solar research, which has been developed by the Instituto
de Astrofisica de Canarias (IAC). The system is now being used for
photometric and spectroscopic applications, and it will also be used
for spectropolarimetry in the near future. The first application is
described below in detail. The IACs IR camera is based on a Rockwell
256 X 256 HgCdTe NICMOS3 array, sensitive from 1 to 2.5 microns. The
necessary cooling system is a LN2- cryostat, designed and built by IR
labs under out requirements. The main electronics are the standard VME-
based, FPGA programmable MCE-3 system, also developed by IR labs. We
have implemented different readout schemes to improve sped, reduce
noise and avoid seeing effects, taking into account each specific
application. Data are transferred via fiber optics to a control unit,
which re-send them to the main data acquisition system. Several
acquisition modes to select the best images have been implemented,
and a real- time data processing is available, the entire camera has
been characterized and calibrated, and the main radiometric parameters
given. Preliminary test in spectroscopic observations have been made
in the German Towers at the Observatorio del Teide in Tenerife, Spain,
and a series of photometric measurements performed in the Swedish Solar
Telescope, at the Observatorio del Roque de los Muchachos in La Palma,
Spain. As examples, some scientific results are also presented.
---------------------------------------------------------
Title: Stratification with Optical Depth of the 5 Minute Oscillation
through the Solar Photosphere
Authors: Ruiz Cobo, Basilio; Rodríguez Hidalgo, Inés; Collados,
Manuel
1997ApJ...488..462R Altcode:
An analysis of the 5 minute oscillation in the solar photosphere
has been carried out using an inversion of the radiative transfer
equation applied to a time-series of K I λ7699 line spectra with
a 5" × 5" window at disk center. A thorough discussion of the
inversion conditions, with special emphasis on the LTE approach
and a careful error treatment, is offered. The inversion has been
performed introducing fixed non-LTE departure coefficients taken from
the literature. A sequence of instantaneous model atmospheres has been
obtained, reliable from log τ ~= 0 to log τ ~= -3.5. From the temporal
power spectra of line-of-sight velocity and temperature fluctuations,
the amplitude and phase stratifications of the oscillations of these
magnitudes have been obtained as functions of the optical depth. The
amplitude accuracies are better than 4 m s<SUP>-1</SUP> and 2 K in
most of the photosphere. The increase of the velocity oscillation
amplitude toward higher photospheric layers has been confirmed and
quantified. Its phase angle remains constant through the photosphere,
and significant power is obtained in temperature.
---------------------------------------------------------
Title: Stratification of the 5-min oscillation through the solar
photosphere
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.
1997SoPh..172...77R Altcode: 1997ESPM....8...77R
The inversion of the radiative transfer equation has been applied to a
time series of low spatial resolution Ki 7699 Å line spectra, allowing
us to obtain a sequence of instantaneous models which are compared
to the mean one to derive the 5-min oscillation stratification. The
resulting models are reliable from log τ ≃ 0 to log τ ≃
-3.5. The increase of the velocity oscillation amplitude towards higher
photospheric layers has been confirmed and quantified. Significant
oscillation is observed in temperature.
---------------------------------------------------------
Title: Flux-Tube Model Atmospheres and Stokes V Zero-crossing
Wavelengths
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1997ApJ...478L..45B Altcode: 1997astro.ph..1059B; 1997astro.ph..1059R
First results of the inversion of Stokes I and V profiles from plage
regions near disk center are presented. Both low and high spatial
resolution spectra of Fe I 6301.5 and Fe I 6302.5 Å obtained with the
Advanced Stokes Polarimeter (ASP) have been considered for analysis. The
thin flux-tube approximation, implemented in an LTE inversion code
based on response functions, is used to describe unresolved magnetic
elements. The code allows the simultaneous and consistent inference of
all atmospheric quantities determining the radiative transfer with the
sole assumption of hydrostatic equilibrium. By considering velocity
gradients within the tubes, we are able to match the full ASP Stokes
profiles. The magnetic atmospheres derived from the inversion are
characterized by the absence of significant motions in high layers
and strong velocity gradients in deeper layers. These are essential
to reproduce the asymmetries of the observed profiles. Our scenario
predicts a shift of the Stokes V zero-crossing wavelengths, which
is indeed present in observations made with the Fourier Transform
Spectrometer.
---------------------------------------------------------
Title: (Erratum) Response functions for the inversion of data from
unresolved solar magnetic elements.
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1997A&A...319.1036B Altcode:
Erratum to Astron. Astrophys. 306, 960 (1996).
---------------------------------------------------------
Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing
Projects
Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.;
Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven,
E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum,
L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I.
1997ASPC..118..366S Altcode: 1997fasp.conf..366S
The IAC is currently developing two similar polarimeters, one for
optical wavelengths and one for near infra-red wavelengths (1.5
mu m). Both instruments will provide spectra of the four Stokes
parameters over 2D solar regions. The visible spectro-polarimeter will
be operated at the Swedish Tower (La Palma), and it is being developed
in collaboration with the Royal Swedish Academy of Sciences. We intend
to take advantage of the excellent seeing conditions at this telescope,
while maintaining high polarimetric precision. The IR polarimeter
is being designed for the German VTT (Tenerife) which has better
angular resolution in the near infra-red. This report describes the
goals and technical solutions. It also briefs on the current status
of the projects.
---------------------------------------------------------
Title: The IAC's Near Infrared Camera
Authors: Collados, M.; Joven, E.; Fuentes, F. J.; Diaz, J. J.;
Gonzalez Escalera, V.; Bonet, J. A.; Vazquez, M.
1997ASPC..118..361C Altcode: 1997fasp.conf..361C
Here we report the main characteristics of the recently acquired near
infrared camera. It is based on a 256x256 HgCdTe Nicmos-3 array,
sensitive from 1 mu m to 2.5mu m. The pixel size is 40mu mx40mu
m, adequate for the spatial and spectral scales at the different
telescopes operating at the observatories of La Palma and Tenerife. The
cooling system operates with LN2 with a hold time larger than 20
hours. The camera will be used for photometric, spectroscopic and
spectropolarimetric observations.
---------------------------------------------------------
Title: Two-dimensional, high spatial resolution, solar spectroscopy
using a correlation tracker. I. Correlation tracker description.
Authors: Ballesteros, E.; Collados, M.; Bonet, J. A.; Lorenzo, F.;
Viera, T.; Reyes, M.; Rodriguez Hidalgo, I.
1996A&AS..115..353B Altcode:
In this paper the description of the Solar Correlation Tracker prototype
built by the Instituto de Astrof isica de Canarias is presented. The
system is mainly conceived as a solar image tranquilizer, although a
scanning utility has also been included in order to displace the image
on the final focal plane with sub-arcsecond steps, thus allowing to
perform two-dimensional high spatial resolution spectroscopy. The
behaviour of the different elements of the tracker is shown,
as well as their influence in the performance of the system. The
restrictions of the Absolute Differences algorithm, used to detect
image motion when granulation fields are considered, are extensively
discussed. Laboratory and telescope tests have demonstrated the
capabilities of the system. The electronic components have been adapted
to new optics and mechanics developed at the Kiepenheuer Institut to
build an Advanced Solar Correlation Tracker. The final version of the
system has been installed at the German VTT of the Spanish Observatorio
del Teide. The tests carried out have demonstrated that a bandwidth
of about 60Hz (for an attenuation factor of two) is achieved, which
is approximately four times larger than that of previous Correlation
Trackers, at the same level of attenuation.
---------------------------------------------------------
Title: Two-dimensional, high spatial resolution, solar spectroscopy
using a Correlation Tracker. II. Maps of spectral quantities.
Authors: Collados, M.; Rodriguez Hidalgo, I.; Ballesteros, E.; Ruiz
Cobo, B.; Sanchez Almeida, J.; del Toro Iniesta, J. C.
1996A&AS..115..367C Altcode:
In this paper we illustrate some of the capabilities of the Correlation
Tracker prototype developed at the Instituto de Astrofisica de
Canarias used for two-dimensional, high spatial resolution, solar
spectroscopy. Slit spectra have been taken, using the Correlation
Tracker as a stabilizer (minimizing image motion during exposures) and
as an accurate positioning device (allowing to precisely locate the
entrance slit of the spectrograph at adjacent positions on the solar
disc). Spectral information is obtained from several solar regions
of different sizes. Granules (including some exploding ones) and
intergranules are clearly resolved. Several sub-arcsecond structures
are undoubtedly distinguished as well. The two-dimensional variation
of several spectral quantities in the solar atmosphere is shown,
demonstrating the power of this technique and its future possibilities.
---------------------------------------------------------
Title: Response functions for the inversion of data from unresolved
solar magnetic elements.
Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M.
1996A&A...306..960B Altcode:
By adopting the thin flux tube model as representative of spatially
unresolved magnetic elements in the photosphere of the Sun, we
identify an adequate set of parameters for the model and derive
the corresponding response functions (RFs) which inform about the
variation of the emergent Stokes spectrum when such parameters are
perturbed. We numerically compute these RFs for reasonable values of
the parameters and explore their main properties. It turns out that
the RFs at a given height often depend on the state of layers above as
a result of the constraints imposed by flux tube geometry. As a whole,
RFs can be classified into two well defined groups: one containing RFs
dominated by local effects and another which contains RFs governed by
non-local effects (i.e., contributions coming from layers other than
that where the perturbation takes place). In particular, the RFs to
the temperature, line of sight velocity and microturbulence of both
the internal and the external atmospheres belong to the first group,
while the RFs to the magnetic field strength, external gas pressure and
radius of the tube at the base of the atmosphere must be ascribed to
the second group. The RFs presented in this paper constitute a first
step for the inversion of Stokes spectra from faculae and the network.
---------------------------------------------------------
Title: Book-Review : Observational and Physical Cosmology
Authors: Sanchez, R.; Collados, M.; Rebolo, R.; Andrews, A. D.
1996IrAJ...23R.127S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Amplitude and phase stratification of the solar 5-minute
temperature and velocity oscillations through the photosphere
Authors: Rodriguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.
1996ASPC..109..151R Altcode: 1996csss....9..151R
No abstract at ADS
---------------------------------------------------------
Title: Empirical granular/intergranular average model atmospheres.
Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Del Toro Iniesta,
J. C.; Collados, M.; Sánchez Almeida, J.
1996joso.proc..162R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Empirical model of an average solar granule
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Rodriguez Hidalgo,
I.; Collados, M.; Sanchez Almeida, J.
1996ASPC..109..155R Altcode: 1996csss....9..155R
No abstract at ADS
---------------------------------------------------------
Title: LTE polarized radiative transfer through interlaced
atmospheres.
Authors: del Toro Iniesta, J. C.; Ruiz Cobo, B.; Bellot Rubio, L. R.;
Collados, M.
1995A&A...294..855D Altcode:
We show that the solution of the radiative transfer equation (RTE)
through a line of sight that pierces several times two alternate
atmospheres can be obtained in terms of the solutions of the RTE
through both single atmospheres separately considered. This also
applies to the response functions of the observed Stokes spectrum
to perturbations of the physical quantities. The analytic solution
of the RTE in case that the single atmospheres are Milne-Eddington
is presented. The simplification of the solution in the case of a
longitudinal or transversal (with constant azimuth) magnetic field
is presented as well. Finally, as a numerical example, we synthesize
the Stokes I- and V-spectrum emerging from a thin magnetic flux tube,
achieving a considerable decrease in computation time with respect to
conventional integrations and without loss of accuracy.
---------------------------------------------------------
Title: A morphological description of the Sun observed in Honduras
during the total solar eclipse of 11 July 1991
Authors: Pineda de Carías, María Cristina; Zamorano, Jaime;
Collados, Manuel
1995AIPC..320..144P Altcode: 1995bss..conf..144P; 1995ESAC....4..144P
A morphological description of the solar photosphere, chromosphere,
and the corona is presented from a complete sequence of visual and
spectroscopic observations made in Honduras (Amapala), during the total
solar eclipse of 11 July 1991 and from the analysis of some emission
and absorption lines at all the eclipse phases.
---------------------------------------------------------
Title: Lest Detector and Data Acquisition System - Part One -
Specifications
Authors: Collados, M.; Keller, C. U.; Steiner, P.
1995lest.rept....1C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: LEST detector and data acquisition systems.
Authors: Collados, M.; Keller, C. U.; Steiner, P.
1995LFTR...61.....C Altcode:
Contents: 1. Specifications (M. Collados, C. U. Keller,
P. Steiner). 2. Design considerations for the data acquisition system
(P. Steiner).
---------------------------------------------------------
Title: Observed differences between large and small sunspots.
Authors: Collados, M.; Martinez Pillet, V.; Ruiz Cobo, B.; del Toro
Iniesta, J. C.; Vazquez, M.
1994A&A...291..622C Altcode:
We confirm recent results about the differences in temperature
and magnetic field strength between the umbra of large and small
sunspots. Five Stokes I- and V-spectra from the darkest cores of
three different umbrae have been analysed with the inversion code
of the radiative transfer equation by Ruiz Cobo & del Toro
Iniesta (1992). The run with depth of temperature, magnetic field
(strength and inclination) and velocity along the line of sight are
obtained. The larger sunspots turn out to be cooler and possesing
a larger magnetic field strength, practically throughout the whole
atmosphere. Neither significant gradients of the line-of-sight velocity,
nor of the magnetic field inclination, are detected in any of the
spots analysed. Two model atmospheres are given corresponding to hot
(small) and cool (large) sunspots. The models are, to a large extent,
free from effects of penumbral/photospheric stray-light because it is
nearly absent in the large spots and because in the small one, where
it is important for the Stokes I-profile, only Stokes V is considered
to obtain the model atmosphere. These are the first umbral models in
the literature for which a simultaneous determination of the magnetic
field and thermodynamic stratifications is presented. The implications
of these stratifications for the energy transport in sunspot umbrae
are discussed.
---------------------------------------------------------
Title: Variations of properties of the quiet photosphere along the
equator and the central meridian: Spectroscopic results
Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M.
1994A&A...283..263R Altcode:
Spectra of four lines (CI5380.3 A, MnI 5394.7 A, FeI 5930.2 A and
SiI 5948.5 A) have been obtained in the quiet photosphere, at regular
intervals along the polar axis and the equator. The spatially averaged
spectra have been analyzed, studying the center-to-limb variation (CLV)
and possible changes with the heliographic latitude of the residual
intensity (RI), equivalent width (EW), full width at half line minimum
(FWHM), and bisector of the line profiles. The aim of this spectroscopic
study is to complete the photometric work carried out and recently
published by the authors (Rodriguez Hildago et al. 1992, hereafter Paper
I). It allows us to test some conclusions of Paper I and to extend our
analysis to higher photospheric layers. Firstly the general behavior
of the CLV is shown and discussed. From the comparison betwen the CLV
along the North-South and East-West diameters, it is observed that the
Cl line, formed very deep in the photosphere, broadens and shows raised
minima with latitude, not showing variations in its EW, except at very
high latitudes. The other three lines, which inform about the physical
conditions in the middle photosphere, become deeper and stronger, and
the FeI one seems broader, with latitude. The observational results
are discussed in terms of physical scenarios based on changes in the
velocity fields present in the photosphere (mainly of the granulation),
possible spatial anisotropies in the distribution of network bright
points (which would be related to differences in the mean temperature
gradient) and the latitudinal variation of the granulation contrast
found in Paper I.
---------------------------------------------------------
Title: A multiline method to determine stellar magnetic fields
Authors: Ripodas, P.; Collados, M.; Sanchez Almeida, J.; Garcia Lopez,
R. J.
1993ASPC...40..196R Altcode: 1993IAUCo.137..196R; 1993ist..proc..196R
No abstract at ADS
---------------------------------------------------------
Title: Variation of properties of the quiet photosphere with
heliographic latitude.
Authors: Hidalgo, I. R.; Collados, M.; Vázquez, M.
1993sova.conf...96H Altcode:
Spectra of four selected lines (CI 5380.3 Å, MnI 5394.7 Å, FeI 5930.2
Å and SiI 5948.5 Å) have been obtained in the quiet photosphere, at
regular intervals along the polar axis and the equator. The spatially
averaged spectra have been analysed, studying the centre-to-limb
variation and possible changes with heliographic latitude of the
residual intensity equivalent width, full width at half line minimum
and bisector of the lines.
---------------------------------------------------------
Title: Centre-to-limb variation of solar granulation along the
equator and the central meridian
Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M.
1992A&A...264..661R Altcode:
The paper analyzes white-light images of solar granulation taken
outside active regions, at regular intervals along the polar axis
and the equator, in order to study its center-to-limb variation
and possible changes with the solar latitude. The 2D spatial
power spectra of the brightness distribution are calculated and
corrected for the distortions produced by the atmosphere and the
telescope. One-dimensional integrated spectra are obtained for each
position, with the geometrical foreshortening effect taken into
account. A lower contrast, a smaller mean wavenumber, and a steeper
center-to-limb variation of the contrast are found in the central
meridian as compared to the equator. Sources of error are discussed,
and different scenarios are presented in order to interpret these
observational facts. Intensity fluctuations were detected until the
extreme limb, with a spatial scale of about 10 arcsec.
---------------------------------------------------------
Title: Book-Review - Solar Observations - Techniques and
Interpretation - First Canary Islands Winter School of Astrophysics
Authors: Sanchez, F.; Collados, M.; Vazquez, M.; Staude, J.
1992AN....313Q.302S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Observational and Physical Cosmology - 2ND
Canary Islands Winter School of Astrophysics
Authors: Sanchez, F.; Collados, M.; Rebolo, R.; Gottlober, S.
1992AN....313R.302S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Observational and Physical Cosmology
Authors: Sanchez, F.; Collados, M.; Rebolo, R.
1992Sci...257R.278S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Observational and Physical Cosmology
Authors: Sanchez, F.; Collados, M.; Rebolo, R.
1992Sci...257Q.278S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Observational and Physical Cosmology
Authors: Sanches, F.; Collados, M.; Rebolo, R.
1992JBAA..102R.175S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Solar Observations - Techniques and
Interpretations
Authors: Sanchez, F.; Collados, M.; Vazquez, M.
1992Sci...255.1757S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Estimating the Degradation of Brightness Power Spectra of
Solar Granulation from Images Outside the Disk Centre
Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M.
1992A&A...254..371R Altcode:
A method is presented to estimate the influence of the atmospheric
turbulence and the telescope on the mean power spectra of the
granulation brightness distribution at positions outside the disk
centre, derived using the determination of Fried's parameter. <P />The
procedure is based on the differential degradation suffered by the
directions perpendicular and parallel to the solar limb; the former one
is more affected because it contains more power at high frequencies,
due to the geometrical foreshortening effect. A certain spectral ratio
is defined, which can be evaluated after the observed power spectra
and can be described directly by a Korff's function for a given value
of the Fried parameter r<SUB>0</SUB>. The best fit of the measured
attenuation to the theoretical one is calculated, allowing to obtain
the adequate Modulation Transfer Function to reconstruct the original
power spectra. A test has been performed by evaluating the mentioned
ratio after restored spectra showing that these present the required
elongation up to a resolution of about 0".4.
---------------------------------------------------------
Title: Book-Review - Solar Observations - Techniques and
Interpretation
Authors: Sanches, F.; Collados, M.; Vazques, M.
1992JBAA..102T..62S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational and Physical Cosmology
Authors: Sanchez, F.; Collados, M.; Reboldo, R.
1992opc..book.....S Altcode:
1. Lectures on the very early universe V. N. Lukash and I. D. Novikov;
2. Primordial nucleosynthesis Hubert Reeves; 3. Big Bang nucleosynthesis
and abundances of light elements Bernard E. J. Pagel; 4. The microwave
sky Jose Luis Sanz; 5. The large scale structure of the universe Bernard
J. T. Jones; 6. Large-scale structure of the universe Jaan Einasto.
---------------------------------------------------------
Title: Solar observations : techniques and interpretation
Authors: Sanchez, F.; Collados, M.; Vazquez, M.
1992soti.book.....S Altcode:
This book includes four chapters devoted to techniques and
interpretation of solar observations. The chapter on high spatial
resolution techniques considers basic concepts, single frame analysis,
interferometry techniques, and other methods. The magnetic field
measurements chapter discusses a prototype polarimeter, physical
components of polarimeters, radiative transfer for polarized radiation,
transfer equations for the Stokes parameters in a magnetized atmosphere,
and magnetic field measurements in unresolved structures and in
prominences. The chapter on solar postfocus instrumentation gives
particular attention on the locations of postfocus instrumentation,
postfocus imaging, spectrometers, detectors for spectrometers, and
special instruments at spectrometer foci. The chapter on the dynamics
of the solar atmosphere focuses on the features of the solar structure,
diagnostic methods for velocity measurements, rotation and convection,
motions in magnetic flux tubes and spots, and velocity fields in
prominences and filaments.
---------------------------------------------------------
Title: Observational and physical cosmology. Lectures.
Authors: Sánchez, F.; Collados, M.; Rebolo, R.
1992opcl.book.....S Altcode:
The lectures presented deal with theories on the very early universe,
capable of providing the initial conditions of the Friedmann model and
of generating inhomogeneities in the inflationary period; modelling of
the epoch of primordial nucleosynthesis. The properties of the cosmic
microwave background are examined both its spectrum and the anisotropy
at different angular scales. The book includes a state-of-the-art
review of the large scale structure of statistical measurements of the
distribution of galaxies, large-scale flows, the origin and distribution
of voids and superclusters.
---------------------------------------------------------
Title: Solar Observations
Authors: Sánchez, F.; Collados, M.; Vazquez, M.
1991soob.book.....S Altcode:
This book is a collection of papers by four internationally known
speakers who explore some key areas in solar physics. O. von der Lühe
discusses new techniques that are being developed for observing the sun
at high spatial resolution and which have played a key role in most
of the recent discoveries about the Sun. Egidio Landi Degl'Innocenti
describes the magnetic field that dominates much of the structure we
see and many of the active phenomena on the Sun. An understanding of
how to measure the field is important. New solar telescopes in Europe
and the United States have led the way in the present revolution
in the understanding of the sun and important new breakthroughs are
expected from LEST. In particular, the post-focus instrumentation has
been crucial, and this is detailed by Hubertus Wohl; finally Pierre
Mein writes about the solar atmosphere, which is now known to be a
dynamic atmosphere with many puzzling features.
---------------------------------------------------------
Title: Magnetic Flux Determination in Late-Type Dwarfs
Authors: Rípodas, P.; Sánchez Almeida, J.; García López, R. J.;
Collados, M.
1991LNP...380..417R Altcode: 1991IAUCo.130..417R; 1991sacs.coll..417R
We present a very preliminary and simplified analysis designed to
measure photospheric magnetic fields in late-type stars, using the FeI
5247.06 Å and 5250.22 Å lines. We show how the use of the equivalent
widths of the lines and differences in their depth can give a rapid
estimation of the magnetic flux.
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Title: Numerical Test of a New V-Profile Inversion Technique
Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Collados, M.;
Sanchez Almeida, J.
1990Ap&SS.170..113R Altcode:
The diagnostic method proposed by Landi Degl'Innocenti and Landolfi
(1982), based on the observation of circular polarization, has been
generalized to derive the thermodynamic properties of unresolved
magnetic elements in the solar atmosphere. The final aim is to derive
the height dependence of several parameters of the flux tube atmosphere
(such as temperature, magnetic field and velocity distributions,
macroturbulence and filling factor). We have used a perturbation
method based on the concept of response functions for the Stokes
profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti
(1977). We present here the preliminary results of invertingV-profiles
by an iterative standard least-squares technique, which allows to find
the magnetic 1-D atmosphere consistent with simulated data.
---------------------------------------------------------
Title: Fried's Parameter Derived from Observations of Granulation
Outside the Disk Centre
Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M.
1990Ap&SS.170..155R Altcode:
A new method has recently been developed to obtain the Fried's parameter
from observations of granulation outsude the disk centre, based on
the different degradation suffered by the images on the directions
parallel and perpendicular to the solar limb, due to the geometrical
foreshortening. This procedure has been applied to CCD images obtained
at the Swedish Solar Tower of the Observatorio del Roque de los
Muchachos, with satisfactory results which are presented and discussed.
---------------------------------------------------------
Title: Facular points and small-scale magnetic elements
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
1990Ap&SS.170....9D Altcode:
We present spectroscopic observations, with high spatial resolution, of
Ca ii K bright points very near the disc centre. Magnetic concentrations
have been detected in these network (facular) points by only using
intensity profiles of the well-known pair of lines Fe i5250.22 Å and
5247.06 Å. No brightening of these structures with respect to the quiet
photosphere can be ascertained within an accuracy threshold of 1.2%.
---------------------------------------------------------
Title: Velocity Fields Associated with the Magnetic Component of
Solar Faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1990Ap&SS.170...31S Altcode:
The StokesV asymmetries observed in solar faculae can be interpreted
by invoking the presence of magnetic and velocity fields variations
along the line-of-sight. By means of a perturbative approach, we
develop the theoretical dependence on magnetic and velocity fields
of the StokesV profile around its zero-crossing point. We find that
the empirical curves of growth for theV zero-crossing point and the
slope, as well as the curve of growth for the integral (previously
derived by Sánchez Almeidaet al., 1989, through the same approach),
are reproduced quite well with a single atmosphere which assumes such
simultaneous variations. The depth dependence of the fields that give
the best fit in our model presents several striking properties which
cannot be released without totally compromising the goodness of the
fit. Namely, the magnetic field strength increases towards the observer
while the downflowing velocity field decreases. Both variations must
occur co-spatially, in the same atmospheric layers. This fact seems to
contradict theoretical models for the fanning out parts of magnetic
concentrations which foresee a sharp separation between a static
magnetic layer and a deep zone with velocity fields. We discuss a
possible solution of such contradiction in terms of a finite optical
thickness of the boundary layer between zones with and without magnetic
field in faculae.
---------------------------------------------------------
Title: Photometry and Spectroscopy of the Solar Granulation Along
the Polar Axis and Equator
Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M.
1990Ap&SS.170...23R Altcode:
From high-resolution CCD images of granulation obtained at the Swedish
Solar Tower of the Observatorio del Roque de los Muchachos at different
positions on the solar disk, mean bi-dimensional spatial power spectra
have been obtained at each position and restored following the method
proposed by Rodríguez Hidalgoet al. (1990). The variation with latitude
of the power spectrum, of the granular brightness contrast and of the
mean wave number of the power spectrum are presented. The analysis
is completed with spectroscopic observations obtained at the Gregory
Coudé Telescope of the Observatorio del Teide. The centre-to-limb
and latitudinal variation of the bisectors, residual intensities and
equivalent widths are shown for several photometric lines.
---------------------------------------------------------
Title: Are small-scale magnetic concentrations spatially coincident
with bright facular points?
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Martinez Pillet, V.; Ruiz Cobo, B.
1990A&A...233..570D Altcode:
The usually assumed identification of small-scale magnetic
concentrations with bright facular or network points on the photosphere
is observationally checked by using high spatial resolution spectra
of Ca II K bright points very near the disk center. The detection of
spatially unresolved magnetic structures is made via a new differential
analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22
A; these concentrations are present in the central part of a line
weakening zone, which is of some 2 arcsec wide. No continuum intensity
enhancement with respect to the quiet photosphere can be ascertained of
these structures, within an accuracy threshold of 1.2 percent. In spite
of this, magnetic concentrations brighter than the quiet photosphere
are compatible with the observations, but if so, they must be narrower
than 0.2 arcsec.
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Title: CCD Photometry of Stars in the Old Open Cluster NGC 188
Authors: Caputo, F.; Chieffi, A.; Castellani, V.; Collados, M.;
Martinez Roger, C.; Paez, E.
1990AJ.....99..261C Altcode:
CCD photometry for stars in three fields centered on the old open
cluster NGC 188 is presented, with the aim of investigating the HR
diagram distribution of cluster main-sequence stars. A sequence of
subgiant, turnoff, and main-sequence stars has been detected, extending
the observed lower main sequence down to about m(v) = 20 mag. It is
found that the observed color-magnitude diagram appears well fitted by
a theoretical isochrone for an age of about 6-billion yr, provided that
Yale transformations from the theoretical into the observational plane
are assumed. From the distribution of the stellar luminosities, it is
found that the turnoff stars should have masses of about 1.3 solar
mass. The cluster evolutionary scenario is discussed in connection
with the reported luminosity of the clump of He-burning giants.
---------------------------------------------------------
Title: Spectropolarimetry of solar faculae - High spatial resolution
results
Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.;
Semel, M.
1990A&A...227..591D Altcode:
A new method to measure the magnetic field strength of small-scale
solar magnetic concentrations is presented. It is based on the center
of gravity method (Semel, 1967), is independent of radiative transfer
calculations and only observable parameters are needed. This method
also provides parameters like filling factor (area fraction occupied by
the tubes), continuum intensity contrast between flux tubes and their
surroundings, in a two-component model scheme. The method is applied
to spectropolarimetric high spatial resolution data. Local variations
of the above parameters inside single faculae are found. This result
suggests some indications about flux tube evolution. A comparison with
low spatial resolution results is also made.
---------------------------------------------------------
Title: An example of the cancellation of magnetic fields during the
decay of an active region
Authors: De La Rosa, J. I. García; Aballe, M. A.; Collados, M.
1989SoPh..124..219D Altcode:
A case of cancellation of magnetic fields is observed during the decay
of a small active region. Three different sources of information were
simultaneously used: high resolution magnetograms, chromospheric CaII
filtergrams and transverse velocity fields.
---------------------------------------------------------
Title: On the generation of the net circular polarization observed
in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1989A&A...222..311S Altcode:
The net circular polarization observed in solar faculae (Stenflo et
al., 1984) follows a law expected from the combination of velocity
and magnetic field gradients in the photosphere. To show this, the
theoretical curve of growth (net circular polarization produced by
a single line versus its absorption coefficient) predicted by this
mechanism is developed. An empirical curve of growth with more than
80 Fe I lines is also constructed. The agreement between theory and
observation seems to point toward this mechanism as responsible for
circular polarization in faculae at the disk center.
---------------------------------------------------------
Title: An example of the cancellation of magnetic fields during the
decay of an active region
Authors: Garcia de La Rosa, J. I.; Aballe, M. A.; Collados, M.
1989SoPh..124..219G Altcode: 1989SoPh..124..219D
A case of cancellation of magnetic fields is observed during the decay
of a small active region. Three different sources of information were
simultaneously used: high resolution magnetograms, chromospheric Ca
ii filtergrams and transverse velocity fields. A magnetic structure
is apparently dragged to the network by the supergranular velocity
field while it splits into two. There, they meet another structure
with opposite magnetic polarity. After a period of coexistence,
the magnetic pairs vanish, leaving no trace of either magnetic or
chromospheric structures.
---------------------------------------------------------
Title: Numerical determination of the modulation transfer function
from observations of granulation outside the disk centre
Authors: Rodriguez Hidalgo, I.; Collados, M.
1989hsrs.conf..203R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Numerical determination of the modulation transfer function
from observations of granulation outside the disk centre.
Authors: Hidalgo, I. R.; Collados, M.
1989hsrs.conf..203H Altcode:
A spectral ratio, similar to that of von der Lühe (1984), is proposed
to derive information on the degradation of the mean granular power
spectrum at a position outside the disk centre. It has the advantage
that the modulation transfer function is obtained directly from the
data, without making any assumption on turbulence theory to describe
the atmospheric behaviour.
---------------------------------------------------------
Title: Les facules solaires ou comment observer l'invisible.
Authors: Sanchez Almeida, J.; Collados, M.; Del Toro Iniesta, J. C.
1989Rech...20..810S Altcode: 1989Rech...20..810A
No abstract at ADS
---------------------------------------------------------
Title: An explanation for the Stokes V asymmetry in solar faculae
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.
1988A&A...201L..37S Altcode:
The asymmetry in the Stokes V profile observed in solar faculae
can be explained by assuming that the magnetic field increases with
height while downflow speed decreases. The MHD compatibility of such
solution is briefly discussed together with an observational test for
that possibility.
---------------------------------------------------------
Title: Magnetic field strength in solar flux tubes - A model
atmosphere independent determination
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
1988A&A...196..266S Altcode:
The "line ratio method" (Stenflo, 1973) has been extensively used in
the past to carry out measurements of the magnetic field strength in
spatially unresolved magnetic flux concentrations. The authors present
here a new variant of this technique, which is particularly simple as
it does not depend on any radiative transfer calculations and thus the
assumption of a model atmosphere is not required. General properties
of the transfer equation lead to a relationship between the circular
polarization generated by two lines which are identical except for
their Landé factors. This can be used to directly determine the field
strength from the measured line profiles. In order to test the method
the authors have applied it to experimental data. A comparison with
the traditional line ratio method is shown.
---------------------------------------------------------
Title: Photometry of sunspot penumbrae
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.
1988A&A...195..315C Altcode:
The authors present the results of a statistical analysis of the
penumbra of sunspots. The intensity distribution, and several
parameters derived from it, is analysed at different heliocentric
angles and positions on the spot. It has revealed, on the one hand,
that a two-component model is compatible with the observations and
that both components lie at the same height, and on the other, that
the penumbral asymmetry found by Collados et al. (1987) is confirmed
under a photometrical point of view, the western penumbra being slightly
shorter than the eastern one.
---------------------------------------------------------
Title: On the Age Dependence of the Asymmetry of Penumbrae of Sunspots
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.; Woehl, H.
1988SoPh..117..199C Altcode:
The age dependence of the recently described asymmetry of penumbrae
of large stable sunspots was analyzed. Young sunspots showed shorter
eastern penumbrae, which differed by a maximum of ± 10 % from their
mean width. For older sunspots the western penumbrae became smaller
than the mean penumbra reaching differences of 20 % for spots of two
months age.
---------------------------------------------------------
Title: A Statistical Study of the Geometrical Wilson Effect
Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.
1987SoPh..112..281C Altcode:
An analysis has been carried out of the centre-to-limb variation of the
apparent sizes of the umbra, penumbra and whole spot. It has revealed
that the umbral size decreases with height. We have interpreted this
result in terms of the penumbral geometrical height scale. A value
of 230 km, which is larger than that of the photosphere or the umbra,
explains the observed decrease. An intrinsic asymmetry in the penumbra
of old sunspots has also been found, the western penumbra being slightly
shorter that the rest of the penumbra. This explains why the inverse
Wilson effect is present, preferentially, in the western hemisphere,
as found in previous investigations. A comparison with other works is
also made.
---------------------------------------------------------
Title: A new determination of the solar granulation contrast
Authors: Collados, M.; Vazquez, M.
1987A&A...180..223C Altcode:
The contrast of the photospheric granulation in the centre of the
disk at a wavelength of 500 nm has been determined by means of
photographs taken during the solar eclipse of May 30<SUP>th</SUP>
1984. After restoration, values of 17.3% and 20.4%, using the sum of
two lorentzians to define the instrumental profile, and of 11.7% and
14.3%, using the sum of two gaussians, have been obtained. This suggests
that the results are quite sensitive to the particular choice which is
made of the analytical approximation to the point spread function. The
corrected power spectrum does not show significant differences to those
of previous works. A comparison between the method for correcting the
image degradation which the authors propose with those used by other
investigators is also made.
---------------------------------------------------------
Title: Detailed processes accompanying the decay of an active region.
Authors: Garcia de La Rosa, J. I.; Collados, M.
1987PAICz..66...55G Altcode: 1987eram....1...55G
High resolution (better than 1arcsec) magnetograms obtained at the
Sacramento Peak Vacuum Tower Telescope were used to study the decay
of a small active region. The reduction process allows one to match
intensity and magnetic pictures exactly.
---------------------------------------------------------
Title: Observations of the Magnetic Fine Structure of a Facula
Authors: del Toro Iniesta, J. C.; Semel, M.; Collados, M.
1987rfsm.conf..122D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Continuum intensity and magnetic flux of solar fluxtubes.
Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.; Sánchez
Almeida, J.
1987PAICz..66..265D Altcode: 1987eram....1..265D
The continuum contrast between fluxtubes and their quiet background,
and the magnetic flux carried by these magnetic elements, have been
determined at different points of a solar facula, in the frame of a
two-component model from spectropolarimetric observations of 1arcsec
spatial resolution. Local spatial variations of these two parameters
have been obtained.
---------------------------------------------------------
Title: The Wilson Effect in Sunspots
Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M.
1987rfsm.conf..183C Altcode:
An analysis of the center to limb variation of the geometrical
properties of spots has been carried out. It has revealed that spots do
not have a symmetrical behaviour with respect to the centre of solar
disk. Thus, the Wilson effect is not zero at δ = 0°, but at δ ≡
45°W. Moreover, the inverse Wilson effect is the general rule in that
interval, while the normal phenomenon is maximum at a heliocentric
angle of 40° - 50°E.
---------------------------------------------------------
Title: Intensity profiles in fluxtubes.
Authors: Sanches Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
1987PAICz..66..261S Altcode: 1987eram....1..261S
Spectroscopic analysis of the light coming from an atmosphere is a
powerful tool for revealing its properties. The problem when using
conventional spectroscopy for solar fluxtubes is their unresolved
character: magnetic and non-magnetic regions of a plage have to be
observed as a whole. With the aim of obtaining the true intensity
spectrum of an unresolved tube, the authors have developed a simple
method which can reconstruct the intensity generated in the magnetic
component. Only observed parameters are used: intensity and circular
polarization in the plage and intensity in the quiet photosphere.
---------------------------------------------------------
Title: The Intensity Distribution in Sunspot Penumbras
Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M.
1987rfsm.conf..214C Altcode:
The intensity distribution of the penumbra at different stages of
evolution has been analyzed. The results have been different for both
evolved and primitive penumbras. While the former present almost
symmetrical, single-peaked histograms, the same does not occur for
the latter, their distributions being, preferentially, asymmetrical
or double-peaked. These results are interpreted in terms of bright
and dark elements. Thus, an evolutionary process has been proposed to
explain the diverse characteristics found at the different stages.
---------------------------------------------------------
Title: Observations of the magnetic fine structure of a facula.
Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.
1987rfsm.conf..127D Altcode:
Simultaneous spectropolarimetric observations of a facula have
been carried out in 10 spectral lines with a spatial resolution of
1arcsec. Local variations of the magnetic field strength and the filling
factor of fluxtubes were obtained. The analysis of the velocities inside
fluxtubes shows that positive and negative Doppler shifts are present,
at the same time, at different points of the facula.
---------------------------------------------------------
Title: Variation of the granulation with the solar latitude.
Authors: Collados, M.; Rodriguez Hidalgo, I.; Vazquez, M.
1987PAICz..66...41C Altcode: 1987eram....1...41C
Preliminary results of a search for the variation of the
solar granulation properties with the heliographic latitude are
presented. Within errors, no changes are found in the power spectra
and sizes between N-S and E-W scans.
---------------------------------------------------------
Title: Granulation Deformation Near and in Sunspot Regions
Authors: Collados, M.; Marco, E.; del Toro, J. C.; Vazquez, M.
1986SoPh..105...17C Altcode:
High-resolution white-light pictures are analyzed to study the
differences between the granular size near sunspot penumbrae and in
light-bridges presenting granular structure and that of the quiet
photosphere. No difference is found between the mean granular diameter
in light-bridges and the quiet photosphere. The dispersion found in the
results corresponding to different zones around the sunspots indicates
that the size of the granulation may vary from place to place near the
sunspots, its mean value not differing significantly from that of the
quiet photosphere. A possible systematic bias in the selection of the
granules by Macris (1979) is found.
---------------------------------------------------------
Title: Estudio fotométrico de estructuras fotosféricas solares
---------------------------------------------------------
Title: Estudio fotométrico de estructuras fotosféricas solares
---------------------------------------------------------
Title: Photometric study of solar photosphere structures;
Authors: Collados Vera, Manuel Arturo
1986PhDT.......146C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of the Birth and Fine Structure of Sunspot
Penumbrae
Authors: Collados, M.; Garcia de La Rosa, J. I.; Moreno-Insertis,
F.; Vazquez, M.
1985LNP...233..133C Altcode: 1985hrsp.proc..133C
High resolution white-light pictures of sunspot penumbrae are
presented. These include pictures showing details of their filamentary
structure and some instances of the birth of a penumbra. The
observations are discussed in the framework of current penumbra
theories.
---------------------------------------------------------
Title: Photometry of Light-Bridges in Sunspots
Authors: Collados, M.; Marco, E.; Vazquez, M.
1985LNP...233..299C Altcode: 1985hrsp.proc..299C
The decay of a sunspot region was studied using high resolution
white-light pictures. The photometric and geometric parameters of a
light-bridge showing granular structure were determined. No difference
is found comparing it with the quiet photosphere.
