Author name code: bonet
ADS astronomy entries on 2022-09-14
author:"Bonet, Jose Antonio"
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Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
Aims: This paper describes the Polarimetric and Helioseismic
Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
helioseismology instrument to observe the Sun from outside the Sun-Earth
line. It is the key instrument meant to address the top-level science
question: How does the solar dynamo work and drive connections between
the Sun and the heliosphere? SO/PHI will also play an important role
in answering the other top-level science questions of Solar Orbiter,
while hosting the potential of a rich return in further science.
Methods: SO/PHI measures the Zeeman effect and the Doppler shift
in the Fe I 617.3 nm spectral line. To this end, the instrument
carries out narrow-band imaging spectro-polarimetry using a tunable
LiNbO3 Fabry-Perot etalon, while the polarisation modulation
is done with liquid crystal variable retarders. The line and the nearby
continuum are sampled at six wavelength points and the data are recorded
by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
are reduced on board, including being inverted under the assumption of
a Milne-Eddington atmosphere, although simpler reduction methods are
also available on board. SO/PHI is composed of two telescopes; one,
the Full Disc Telescope, covers the full solar disc at all phases of
the orbit, while the other, the High Resolution Telescope, can resolve
structures as small as 200 km on the Sun at closest perihelion. The high
heat load generated through proximity to the Sun is greatly reduced by
the multilayer-coated entrance windows to the two telescopes that allow
less than 4% of the total sunlight to enter the instrument, most of
it in a narrow wavelength band around the chosen spectral line.
Results: SO/PHI was designed and built by a consortium having partners
in Germany, Spain, and France. The flight model was delivered to
Airbus Defence and Space, Stevenage, and successfully integrated into
the Solar Orbiter spacecraft. A number of innovations were introduced
compared with earlier space-based spectropolarimeters, thus allowing
SO/PHI to fit into the tight mass, volume, power and telemetry budgets
provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
challenges posed by the mission's highly elliptical orbit.
Title: SOPHISM: Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
Bibcode: 2018ascl.soft10017B
Altcode:
SOPHISM models astronomical instrumentation from the entrance
of the telescope to data acquisition at the detector, along with
software blocks dealing with, for example, demodulation, inversion,
and compression. The code performs most analyses done with light
in astronomy, such as differential photometry, spectroscopy, and
polarimetry. The simulator offers flexibility and implementation of new
effects and subsystems, making it user-adaptable for a wide variety
of instruments. SOPHISM can be used for all stages of instrument
definition, design, operation, and lifetime tracking evaluation.
Title: SOPHISM: An End-to-end Software Instrument Simulator
Authors: Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Orozco
Suárez, D.; Martínez Pillet, V.; Bonet, J. A.; Feller, A.;
Hirzberger, J.; Lagg, A.; Piqueras, J.; Gasent Blesa, J. L.
Bibcode: 2018ApJS..237...35B
Altcode:
We present a software simulator for the modeling of astronomical
instrumentation, which includes platform effects and software
processing. It is an end-to-end simulator, from the entrance of
the telescope to the data acquisition at the detector, along with
software blocks dealing, e.g., with demodulation, inversion, and
compression. Developed following the Solar Orbiter/Polarimetric
and Helioseismic Imager (SO/PHI) instrument, it comprises elements
such as a filtergraph, polarimetric modulator, detector, vibrations,
and accumulations. Through these, the simulator performs most of the
analyses that can be done with light in astronomy, such as differential
photometry, spectroscopy, and polarimetry. The simulator is coded
with high flexibility and ease of implementation of new effects and
subsystems. Thus, it allows for the user to adapt it to a wide variety
of instruments, even not exclusively solar ones, as illustrated with
an example of application to a night-time observation. The simulator
can provide support in the phase of instrument design and help assess
tolerances and test solutions to underperformances arising during the
instrument operations. All this makes SOPHISM a very valuable tool
for all the stages of astronomical instrument definition, design,
operation, and lifetime tracking evaluation.
Title: The History of a Quiet-Sun Magnetic Element Revealed by
IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
Sami K.; Schmidt, Wolfgang
Bibcode: 2014ApJ...789....6R
Altcode: 2014arXiv1405.2837R
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
collapse mechanism. However, the small size of the magnetic elements in
quiet-Sun areas has prevented this scenario from being studied in fully
resolved structures. Here, we report on the formation and subsequent
evolution of one such photospheric magnetic flux tube, observed in
the quiet Sun with unprecedented spatial resolution (0.''15-0.''18)
and high temporal cadence (33 s). The observations were acquired by
the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
solar observatory. The equipartition field strength magnetic element
is the result of the merging of several same polarity magnetic flux
patches, including a footpoint of a previously emerged loop. The
magnetic structure is then further intensified to kG field strengths
by convective collapse. The fine structure found within the flux
concentration reveals that the scenario is more complex than can be
described by a thin flux tube model with bright points and downflow
plumes being established near the edges of the kG magnetic feature. We
also observe a daisy-like alignment of surrounding granules and a
long-lived inflow toward the magnetic feature. After a subsequent
weakening process, the field is again intensified to kG strengths. The
area of the magnetic feature is seen to change in anti-phase with the
field strength, while the brightness of the bright points and the speed
of the downflows varies in phase. We also find a relation between the
brightness of the bright point and the presence of upflows within it.
Title: The power spectrum of solar convection flows from
high-resolution observations and 3D simulations
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Bonet, J. A.
Bibcode: 2014A&A...563A..93Y
Altcode: 2014arXiv1402.2293Y
Context. Understanding solar surface magnetoconvection requires
the study of the Fourier spectra of the velocity fields. Nowadays,
observations are available that resolve very small spatial scales,
well into the subgranular range, almost reaching the scales routinely
resolved in numerical magnetoconvection simulations. Comparison of
numerical and observational data at present can provide an assessment
of the validity of the observational proxies.
Aims: Our aims are:
(1) to obtain Fourier spectra for the photospheric velocity fields using
the spectropolarimetric observations with the highest spatial resolution
so far (~120 km), thus reaching for the first time spatial scales well
into the subgranular range; (2) to calculate corresponding Fourier
spectra from realistic 3D numerical simulations of magnetoconvection
and carry out a proper comparison with their observational counterparts
considering the residual instrumental degradation in the observational
data; and (3) to test the observational proxies on the basis of
the numerical data alone, by comparing the actual velocity field
in the simulations with synthetic observations obtained from the
numerical boxes.
Methods: (a) For the observations, data from
the SUNRISE/IMaX spectropolarimeter are used. (b) For the simulations,
we use four series of runs obtained with the STAGGER code for different
average signed vertical magnetic field values (0, 50, 100, and 200
G). Spectral line profiles are synthesized from the numerical boxes for
the same line observed by IMaX (Fe I 5250.2 Å) and degraded to match
the performance of the IMaX instrument. Proxies for the velocity field
are obtained via Dopplergrams (vertical component) and local correlation
tracking (LCT, for the horizontal component). Fourier power spectra are
calculated and a comparison between the synthetic and observational data
sets carried out. (c) For the internal comparison of the numerical data,
velocity values on constant optical depth surfaces are used instead
of on horizontal planes.
Results: A very good match between
observational and simulated Fourier power spectra is obtained for the
vertical velocity data for scales between 200 km and 6 Mm. Instead,
a clear vertical shift is obtained when the synthetic observations are
not degraded to emulate the degradation in the IMaX data. The match
for the horizontal velocity data is much less impressive because
of the inaccuracies of the LCT procedure. Concerning the internal
comparison of the direct velocity values of the numerical boxes with
those from the synthetic observations, a high correlation (0.96) is
obtained for the vertical component when using the velocity values on
the log τ500 = -1 surface in the box. The corresponding
Fourier spectra are near each other. A lower maximum correlation (0.5)
is reached (at log τ500 = 0) for the horizontal velocities
as a result of the coarseness of the LCT procedure. Correspondingly,
the Fourier spectra for the LCT-determined velocities is well below that
from the actual velocity components.
Conclusions: As measured
by the Fourier spectra, realistic numerical simulations of surface
magnetoconvection provide a very good match to the observational
proxies for the photospheric velocity fields at least on scales from
several Mm down to around 200 km. Taking into account the spatial and
spectral instrumental blurring is essential for the comparison between
simulations and observations. Dopplergrams are an excellent proxy for
the vertical velocities on constant-τ isosurfaces, while LCT is a
much less reliable method of determining the horizontal velocities.
Title: Time evolution of a single, quiet-Sun magnetic structure
Authors: Requerey, Iker S.; Bonet, José Antonio; Solanki, Sami K.;
Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos
Bibcode: 2014cosp...40E2828R
Altcode:
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
instability mechanism. However, the small size of the magnetic elements
in quiet-Sun areas has prevented this scenario from being studied
in fully resolved structures. Here we report on the formation and
subsequent evolution of a photospheric magnetic flux tube, observed
in the quiet Sun with unprecedented spatial resolution (0. ('') 15 -
0. ('') 18) and high temporal cadence (33 s). The observations were
acquired by the Imaging Magnetograph Experiment (IMaX) aboard the
textsc{Sunrise} balloon-borne solar observatory. The equipartition
field strength magnetic element is reached from the merging of
several magnetic flux patches in a mesogranule-sized sink. The
magnetic structure is then further intensified to kG field strengths by
convective collapse and granular compression. The fine structure found
within the flux concentration reveal that the scenario is more complex
than a canonical flux tube model. After a subsequent weakening process,
the field is further intensified to kG strengths. Seen as a whole, the
evolution of the magnetic structure is compatible with oscillations in
all basic physical quantities. A discussion on whether this evolution
fits to the current theoretical descriptions is also presented.
Title: Is Magnetic Reconnection the Cause of Supersonic Upflows in
Granular Cells?
Authors: Borrero, J. M.; Martínez Pillet, V.; Schmidt, W.; Quintero
Noda, C.; Bonet, J. A.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.
Bibcode: 2013ApJ...768...69B
Altcode: 2013arXiv1303.2557B
In a previous work, we reported on the discovery of supersonic magnetic
upflows on granular cells in data from the SUNRISE/IMaX instrument. In
the present work, we investigate the physical origin of these events
employing data from the same instrument but with higher spectral
sampling. By means of the inversion of Stokes profiles we are able
to recover the physical parameters (temperature, magnetic field,
line-of-sight velocity, etc.) present in the solar photosphere at the
time of these events. The inversion is performed in a Monte-Carlo-like
fashion, that is, repeating it many times with different initializations
and retaining only the best result. We find that many of the events are
characterized by a reversal in the polarity of the magnetic field along
the vertical direction in the photosphere, accompanied by an enhancement
in the temperature and by supersonic line-of-sight velocities. In
about half of the studied events, large blueshifted and redshifted
line-of-sight velocities coexist above/below each other. These features
can be explained in terms of magnetic reconnection, where the energy
stored in the magnetic field is released in the form of kinetic
and thermal energy when magnetic field lines of opposite polarities
coalesce. However, the agreement with magnetic reconnection is not
perfect and, therefore, other possible physical mechanisms might also
play a role.
Title: Study of small magnetic structures in the solar photosphere
Authors: Cabello, I.; Domingo, V.; Bonet, J. A.; Blanco Rodríguez,
J.; Balmaceda, L. A.
Bibcode: 2013hsa7.conf..805C
Altcode:
The study of small scale magnetic structures in the solar photosphere
is of great relevance for the understanding of the global behaviour of
the Sun. Because of the small spatial and temporal scales involved, the
use of high resolution images and fast cadence is fundamental for their
study. In order to obtain such images, sophisticated computational
techniques that compensate for the atmospheric degradation and
telescope aberration have been developed, improving in this way the
spatial resolution. In this work, we use G-band images obtained with
the 1 m-Swedish Solar Telescope located at La Palma (Canary Islands,
Spain). The images have been restored with MOMFBD (Multi-Object
Multi-Frame Blind Deconvolution), a technique that combines multiple
images acquired in a short time interval. The resulting images have
a resolution close to the diffraction limit of the telescope (0.1
arcsec) allowing the study of very small bright structures present
in the inter-granular lanes in the solar photosphere, known as Bright
Points. It is highlighted the great presence of magnetic structures in
quiet Sun regions analyzed from different observational campaigns. The
density of BPs in the quiet Sun shows a decrease as we approach the
limb, with values of ≃q 1% at the centre (μ ≈ 1), and ≃q 0.2%
at μ ≈ 0.3. We also present the discovery of small vortexes detected
in the solar surface through the movement of BPs, with radii around 241
km and lifetimes longer than 5 minutes. Further analyses, comprising
longer time series and information from different solar layers, are
being performed aiming at a more in-depth knowledge of these phenomena.
Title: First Results from the SUNRISE Mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Jafarzadeh, S.; Lagg, A.; Riethmüller,
T. L.; Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; González,
M. J. M.; Pillet, V. M.; Khomenko, E.; Yelles Chaouche, L.; Iniesta,
J. C. d. T.; Domingo, V.; Palacios, J.; Knölker, M.; González,
N. B.; Borrero, J. M.; Berkefeld, T.; Franz, M.; Roth, M.; Schmidt,
W.; Steiner, O.; Title, A. M.
Bibcode: 2012ASPC..455..143S
Altcode:
The SUNRISE balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that reveal the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the SUNRISE data, which include a number of discoveries.
Title: Detection of Vortex Tubes in Solar Granulation from
Observations SUNRISE
Authors: Steiner, O.; Franz, M.; González, N. B.; Nutto, C.; Rezaei,
R.; Pillet, V. M.; Bonet, J. A.; Iniesta, J. C. d. T.; Domingo, V.;
Solanki, S. K.; Knölker, M.; Schmidt, W.; Barthol, P.; Gandorfer, A.
Bibcode: 2012ASPC..455...35S
Altcode:
We investigated a time series of continuum intensity maps and
Dopplergrams of granulation in a very quiet solar region at the disk
center, recorded with the Imaging Magnetograph eXperiment (IMaX)
on board the balloon-borne solar observatory SUNRISE. We find that
granules frequently show substructure in the form of lanes composed of
a leading bright rim and a trailing dark edge, which move together
from the boundary of a granule into the granule itself. We find
strikingly similar events in synthesized intensity maps from an ab
initio numerical simulation of solar surface convection. We conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. This paper is a summary and
update of the results previously presented in Steiner et al. (2010).
Title: Supersonic Magnetic Flows in the Quiet Sun Observed with
SUNRISE/IMaX
Authors: Borrero, J. M.; Pillet, V. M.; Schlichenmaier, R.; Schmidt,
W.; Berkefeld, T.; Solanki, S. K.; Bonet, J. A.; Iniesta, J. C. d. T.;
Domingo, V.; Barthol, P.; Gandorfer, A.
Bibcode: 2012ASPC..455..155B
Altcode: 2012arXiv1202.4354B
In this contribution we describe some recent observations of high-speed
magnetized flows in the quiet Sun granulation. These observations
were carried out with the Imaging Magnetograph eXperiment (IMaX)
onboard the stratospheric balloon SUNRISE, and possess an unprecedented
spatial resolution and temporal cadence. These flows were identified as
highly shifted circular polarization (Stokes V) signals. We estimate
the LOS velocity responsible for these shifts to be larger than 6 km
s-1, and therefore we refer to them as supersonic magnetic
flows. The average lifetime of the detected events is 81.3 s and
they occupy an average area of about 23 000 km2. Most of
the events occur within granular cells and correspond therefore to
upflows. However some others occur in intergranular lanes or bear no
clear relation to the convective velocity pattern. We analyze a number
of representative examples and discuss them in terms of magnetic loops,
reconnection events, and convective collapse.
Title: Center-to-limb variation of the area covered by magnetic
bright points in the quiet Sun
Authors: Bonet, J. A.; Cabello, I.; Sánchez Almeida, J.
Bibcode: 2012A&A...539A...6B
Altcode: 2011arXiv1112.2513B
Context. The quiet Sun magnetic fields produce ubiquitous bright points
(BPs) that cover a significant fraction of the solar surface. Their
contribution to the total solar irradiance (TSI) is so-far unknown.
Aims: We aim at measuring the center-to-limb variation (CLV) of
the fraction of solar surface covered by quiet Sun magnetic bright
points. The fraction is referred to as the fraction of covered
surface (FCS).
Methods: We count the area covered by BPs in
G-band images obtained at various heliocentric angles with the 1-m
Swedish Solar Telescope on La Palma. We restore the images to bring
them close to the diffraction limit of the instrument (~0'.1).
Results: The FCS is largest at the disk center (≃1%), and then drops
down to become ≃0.2% at μ ≃ 0.3 (where μ is the cosine of the
heliocentric angle). The relationship has a large scatter, which we
evaluate by comparing different subfields within our FOVs. We develop
a toy-model to describe the observed CLV, which considers the BPs as
depressions in the mean solar photosphere characterized by a depth,
a width, and a spread in the inclinations. Although the model is
poorly constrained by observations, it shows the BPs to be shallow
structures (depth < width) with a large range of inclinations. We
also estimate how different parts of the solar disk may contribute to
the TSI variations, finding that 90% is contributed by BPs with μ >
0.5, and half of it is due to BPs with μ > 0.8.
Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibcode: 2012ApJ...745..160G
Altcode: 2011arXiv1110.1405G
We report on the photospheric evolution of an intermediate-scale (≈4
Mm footpoint separation) magnetic bipole, from emergence to decay,
observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
resolution. The observations were acquired by the Imaging Magnetograph
Experiment imaging magnetograph during the first science flight of the
SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
1017 Mx, representing a structure bridging the gap between
granular scale bipoles and the smaller ephemeral regions. Footpoints
separate at a speed of 3.5 km s-1 and reach a maximum
distance of 4.5 Mm before the field dissolves. The evolution of the
bipole is revealed to be very dynamic: we found a proper motion of
the bipole axis and detected a change of the azimuth angle of 90° in
300 s, which may indicate the presence of some writhe in the emerging
structure. The overall morphology and behavior are in agreement with
previous analyses of bipolar structures emerging at the granular scale,
but we also found several similarities with emerging flux structures
at larger scales. The flux growth rate is 2.6 × 1015 Mx
s-1, while the mean decay rate is one order of magnitude
smaller. We describe in some detail the decay phase of the bipole
footpoints that includes break up into smaller structures, and
interaction with preexisting fields leading to cancellation, but it
appears to be dominated by an as-yet unidentified diffusive process
that removes most of the flux with an exponential flux decay curve. The
diffusion constant (8 × 102 km2 s-1)
associated with this decay is similar to the values used to describe
the large-scale diffusion in flux transport models.
Title: Magnetic field emergence in mesogranular-sized exploding
granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Berkefeld, T.; Schmidt, W.; Knölker, M.
Bibcode: 2012A&A...537A..21P
Altcode: 2011arXiv1110.4555P
We report on magnetic field emergences covering significant
areas of exploding granules. The balloon-borne mission Sunrise
provided high spatial and temporal resolution images of the solar
photosphere. Continuum images, longitudinal and transverse magnetic
field maps and Dopplergrams obtained by IMaX onboard Sunrise are
analyzed by local correlation traking (LCT), divergence calculation
and time slices, Stokes inversions and numerical simulations are also
employed. We characterize two mesogranular-scale exploding granules
where ~1018 Mx of magnetic flux emerges. The emergence
of weak unipolar longitudinal fields (~100 G) start with a single
visible magnetic polarity, occupying their respective granules' top
and following the granular splitting. After a while, mixed polarities
start appearing, concentrated in downflow lanes. The events last around
20 min. LCT analyses confirm mesogranular scale expansion, displaying
a similar pattern for all the physical properties, and divergence
centers match between all of them. We found a similar behaviour
with the emergence events in a numerical MHD simulation. Granule
expansion velocities are around 1 kms-1 while magnetic
patches expand at 0.65 kms-1. One of the analyzed events
evidences the emergence of a loop-like structure. Advection of
the emerging magnetic flux features is dominated by convective
motion resulting from the exploding granule due to the magnetic
field frozen in the granular plasma. Intensification of the
magnetic field occurs in the intergranular lanes, probably
because of being directed by the downflowing plasma. Movies
associated to Figs. 2-4 are available in electronic form at http://www.aanda.org
Title: The Sun at high resolution: first results from the Sunrise
mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller,
A.; Gandorfer, A.; Hirzberger, J.; Lagg, A.; Riethmüller, T. L.;
Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; Pillet, V. Martínez;
Khomenko, E.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.;
Knölker, M.; González, N. Bello; Borrero, J. M.; Berkefeld, T.;
Franz, M.; Roth, M.; Schmidt, W.; Steiner, O.; Title, A. M.
Bibcode: 2011IAUS..273..226S
Altcode:
The Sunrise balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system and further infrastructure. The first
science flight of Sunrise yielded high-quality data that reveal the
structure, dynamics and evolution of solar convection, oscillations
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the Sunrise data, which include a number of discoveries.
Title: Mesogranulation and the Solar Surface Magnetic Field
Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
Solanki, S. K.
Bibcode: 2011ApJ...727L..30Y
Altcode: 2010arXiv1012.4481Y
The relation of the solar surface magnetic field with mesogranular
cells is studied using high spatial (≈100 km) and temporal (≈30
s) resolution data obtained with the IMaX instrument on board
SUNRISE. First, mesogranular cells are identified using Lagrange
tracers (corks) based on horizontal velocity fields obtained through
local correlation tracking. After ≈20 minutes of integration, the
tracers delineate a sharp mesogranular network with lanes of width
below about 280 km. The preferential location of magnetic elements in
mesogranular cells is tested quantitatively. Roughly 85% of pixels with
magnetic field higher than 100 G are located in the near neighborhood
of mesogranular lanes. Magnetic flux is therefore concentrated in
mesogranular lanes rather than intergranular ones. Second, magnetic
field extrapolations are performed to obtain field lines anchored in
the observed flux elements. This analysis, therefore, is independent
of the horizontal flows determined in the first part. A probability
density function (PDF) is calculated for the distribution of distances
between the footpoints of individual magnetic field lines. The PDF has
an exponential shape at scales between 1 and 10 Mm, with a constant
characteristic decay distance, indicating the absence of preferred
convection scales in the mesogranular range. Our results support
the view that mesogranulation is not an intrinsic convective scale
(in the sense that it is not a primary energy-injection scale of solar
convection), but also give quantitative confirmation that, nevertheless,
the magnetic elements are preferentially found along mesogranular lanes.
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.
Bibcode: 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 LiNbO3 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−1. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.
Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
Bibcode: 2011SoPh..268....1B
Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
The first science flight of the balloon-borne Sunrise telescope took
place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
Island in northern Canada. We describe the scientific aims and
mission concept of the project and give an overview and a description
of the various hardware components: the 1-m main telescope with its
postfocus science instruments (the UV filter imager SuFI and the imaging
vector magnetograph IMaX) and support instruments (image stabilizing
and light distribution system ISLiD and correlating wavefront sensor
CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry
systems, and the general electronics architecture. We also explain
the optimization of the structural and thermal design of the complete
payload. The preparations for the science flight are described,
including AIV and ground calibration of the instruments. The course
of events during the science flight is outlined, up to the recovery
activities. Finally, the in-flight performance of the instrumentation
is discussed.
Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
Bibcode: 2011SoPh..268...35G
Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
We describe the design of the Sunrise Filter Imager (SuFI) and the
Image Stabilization and Light Distribution (ISLiD) unit onboard the
Sunrise balloon borne solar observatory. This contribution provides the
necessary information which is relevant to understand the instruments'
working principles, the relevant technical data, and the necessary
information about calibration issues directly related to the science
data.
Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
Franz, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.127S
Altcode: 2010arXiv1008.3460S
The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that revealed the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. After a brief description of instruments and data, the first
qualitative results are presented. In contrast to earlier observations,
we clearly see granulation at 214 nm. Images in Ca II H display narrow,
short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields
are found to be highly dynamic. A significant increase in detectable
magnetic flux is found after phase-diversity-related reconstruction
of polarization maps, indicating that the polarities are mixed right
down to the spatial resolution limit and probably beyond.
Title: Supersonic Magnetic Upflows in Granular Cells Observed with
SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
Bibcode: 2010ApJ...723L.144B
Altcode: 2010arXiv1009.1227B
Using the IMaX instrument on board the SUNRISE stratospheric balloon
telescope, we have detected extremely shifted polarization signals
around the Fe I 5250.217 Å spectral line within granules in the solar
photosphere. We interpret the velocities associated with these events
as corresponding to supersonic and magnetic upflows. In addition, they
are also related to the appearance of opposite polarities and highly
inclined magnetic fields. This suggests that they are produced by the
reconnection of emerging magnetic loops through granular upflows. The
events occupy an average area of 0.046 arcsec2 and last for
about 80 s, with larger events having longer lifetimes. These supersonic
events occur at a rate of 1.3 × 10-5 occurrences per second
per arcsec2.
Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
W.; Barthol, P.; Knölker, M.
Bibcode: 2010ApJ...723L.159K
Altcode: 2010arXiv1008.0517K
Based on IMaX/SUNRISE data, we report on a previously undetected
phenomenon in solar granulation. We show that in a very narrow region
separating granules and intergranular lanes, the spectral line width
of the Fe I 5250.2 Å line becomes extremely small. We offer an
explanation of this observation with the help of magneto-convection
simulations. These regions with extremely small line widths correspond
to the places where the granular flows bend from upflow in granules
to downflow in intergranular lanes. We show that the resolution and
image stability achieved by IMaX/SUNRISE are important requisites to
detect this interesting phenomenon.
Title: Bright Points in the Quiet Sun as Observed in the Visible
and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
Bibcode: 2010ApJ...723L.169R
Altcode: 2010arXiv1009.1693R
Bright points (BPs) are manifestations of small magnetic elements
in the solar photosphere. Their brightness contrast not only gives
insight into the thermal state of the photosphere (and chromosphere) in
magnetic elements, but also plays an important role in modulating the
solar total and spectral irradiance. Here, we report on simultaneous
high-resolution imaging and spectropolarimetric observations of
BPs using SUNRISE balloon-borne observatory data of the quiet Sun
at the disk center. BP contrasts have been measured between 214 nm
and 525 nm, including the first measurements at wavelengths below
388 nm. The histograms of the BP peak brightness show a clear trend
toward broader contrast distributions and higher mean contrasts at
shorter wavelengths. At 214 nm, we observe a peak brightness of up to
five times the mean quiet-Sun value, the highest BP contrast so far
observed. All BPs are associated with a magnetic signal, although in
a number of cases it is surprisingly weak. Most of the BPs show only
weak downflows, the mean value being 240 m s-1, but some
display strong down- or upflows reaching a few km s-1.
Title: Transverse Component of the Magnetic Field in the Solar
Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.149D
Altcode: 2010arXiv1008.1535D
We present the first observations of the transverse component of
a photospheric magnetic field acquired by the imaging magnetograph
SUNRISE/IMaX. Using an automated detection method, we obtain statistical
properties of 4536 features with significant linear polarization
signal. We obtain a rate of occurrence of 7 × 10-4
s-1 arcsec-2, which is 1-2 orders of magnitude
larger than the values reported by previous studies. We show that
these features have no characteristic size or lifetime. They appear
preferentially at granule boundaries with most of them being caught
in downflow lanes at some point. Only a small percentage are entirely
and constantly embedded in upflows (16%) or downflows (8%).
Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
Bibcode: 2010ApJ...723L.134B
Altcode: 2010arXiv1009.4795B
We study the energy flux carried by acoustic waves excited by convective
motions at sub-photospheric levels. The analysis of high-resolution
spectropolarimetric data taken with IMaX/SUNRISE provides a total
energy flux of ~6400-7700 W m-2 at a height of ~250 km
in the 5.2-10 mHz range, i.e., at least twice the largest energy
flux found in previous works. Our estimate lies within a factor of
two of the energy flux needed to balance radiative losses from the
chromosphere according to the estimates of Anderson & Athay and
revives interest in acoustic waves for transporting energy to the
chromosphere. The acoustic flux is mainly found in the intergranular
lanes but also in small rapidly evolving granules and at the bright
borders, forming dark dots and lanes of splitting granules.
Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.185W
Altcode: 2010arXiv1009.4715W
We investigate the fine structure of magnetic fields in the atmosphere
of the quiet Sun. We use photospheric magnetic field measurements from
SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
the photospheric magnetic field into higher layers of the solar
atmosphere with the help of potential and force-free extrapolation
techniques. We find that most magnetic loops that reach into the
chromosphere or higher have one footpoint in relatively strong magnetic
field regions in the photosphere. Ninety-one percent of the magnetic
energy in the mid-chromosphere (at a height of 1 Mm) is in field
lines, whose stronger footpoint has a strength of more than 300 G,
i.e., above the equipartition field strength with convection. The
loops reaching into the chromosphere and corona are also found to be
asymmetric in the sense that the weaker footpoint has a strength B <
300 G and is located in the internetwork (IN). Such loops are expected
to be strongly dynamic and have short lifetimes, as dictated by the
properties of the IN fields.
Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
Knölker, M.
Bibcode: 2010ApJ...723L.139B
Altcode: 2010arXiv1009.1992B
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
telescope. By visual inspection of time series, we find some 3.1
× 10-3 vortices Mm-2 minute-1,
which is a factor of ~1.7 larger than previous estimates. The mean
duration of the individual events turns out to be 7.9 minutes, with
a standard deviation of 3.2 minutes. In addition, we find several
events appearing at the same locations along the duration of the time
series (31.6 minutes). Such recurrent vortices show up in the proper
motion flow field map averaged over the time series. The typical
vertical vorticities are lsim6 × 10-3 s-1,
which corresponds to a period of rotation of some 35 minutes. The
vortices show a preferred counterclockwise sense of rotation, which
we conjecture may have to do with the preferred vorticity impinged by
the solar differential rotation.
Title: Retrieval of solar magnetic fields from high-spatial resolution
filtergraph data: the Imaging Magnetograph eXperiment (IMaX)
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Martínez Pillet,
V.; Bonet, J. A.; Vargas Domínguez, S.; Del Toro Iniesta, J. C.
Bibcode: 2010A&A...522A.101O
Altcode: 2010arXiv1006.5510O
Context. The design of modern instruments does not only imply thorough
studies of instrumental effects but also a good understanding of the
scientific analysis planned for the data.
Aims: We investigate
the reliability of Milne-Eddington (ME) inversions of high-resolution
magnetograph measurements such as those to be obtained with the Imaging
Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also
provide arguments to choose either Fe I 525.02 or 525.06 nm as the
most suitable line for IMaX.
Methods: We reproduce an IMaX
observation using magnetoconvection simulations of the quiet Sun
and synthesizing the four Stokes profiles emerging from them. The
profiles are degraded by spatial and spectral resolution, noise,
and limited wavelength sampling, just as real IMaX measurements. We
invert these data and estimate the uncertainties in the retrieved
physical parameters caused by the ME approximation and the spectral
sampling.
Results: It is possible to infer the magnetic field
strength, inclination, azimuth, and line-of-sight velocity from
standard IMaX measurements (4 Stokes parameters, 5 wavelength points,
and a signal-to-noise ratio of 1000) applying ME inversions to any
of the Fe I lines at 525 nm. We also find that telescope diffraction
has important effects on the spectra coming from very high resolution
observations of inhomogeneous atmospheres. Diffration reduces the
amplitude of the polarization signals and changes the asymmetry of
the Stokes profiles.
Conclusions: The two Fe I lines at 525 nm
meet the scientific requirements of IMaX, but Fe I 525.02 nm is to be
preferred because it leads to smaller uncertainties in the retrieved
parameters and offers a better detectability of the weakest (linear)
polarization signals prevailing in the quiet Sun.
Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
Knölker, M.
Bibcode: 2010ApJ...723L.175R
Altcode: 2010arXiv1009.4790R
Solar oscillations are expected to be excited by turbulent flows in
the intergranular lanes near the solar surface. Time series recorded
by the IMaX instrument on board the SUNRISE observatory reveal solar
oscillations at high spatial resolution, which allow the study of
the properties of oscillations with short wavelengths. We analyze
two time series with synchronous recordings of Doppler velocity and
continuum intensity images with durations of 32 minutes and 23 minutes,
respectively, recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In
the Doppler velocity data, both the standing acoustic waves and the
short-lived, high-degree running waves are visible. The standing
waves are visible as temporary enhancements of the amplitudes of the
large-scale velocity field due to the stochastic superposition of
the acoustic waves. We focus on the high-degree small-scale waves by
suitable filtering in the Fourier domain. Investigating the propagation
and excitation of f- and p 1-modes with wavenumbers k>1.4
Mm-1, we also find that exploding granules contribute to
the excitation of solar p-modes in addition to the contribution of
intergranular lanes.
Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
Bibcode: 2010ApJ...723L.164L
Altcode: 2010arXiv1009.0996L
Until today, the small size of magnetic elements in quiet-Sun areas has
required the application of indirect methods, such as the line-ratio
technique or multi-component inversions, to infer their physical
properties. A consistent match to the observed Stokes profiles could
only be obtained by introducing a magnetic filling factor that specifies
the fraction of the observed pixel filled with magnetic field. Here,
we investigate the properties of a small magnetic patch in the quiet
Sun observed with the IMaX magnetograph on board the balloon-borne
telescope SUNRISE with unprecedented spatial resolution and low
instrumental stray light. We apply an inversion technique based on
the numerical solution of the radiative transfer equation to retrieve
the temperature stratification and the field strength in the magnetic
patch. The observations can be well reproduced with a one-component,
fully magnetized atmosphere with a field strength exceeding 1 kG and
a significantly enhanced temperature in the mid to upper photosphere
with respect to its surroundings, consistent with semi-empirical flux
tube models for plage regions. We therefore conclude that, within the
framework of a simple atmospheric model, the IMaX measurements resolve
the observed quiet-Sun flux tube.
Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
Bibcode: 2010ApJ...723L.154H
Altcode:
We present high-resolution images of the Sun in the near-ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1 m SUNRISE balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range are
among the highest values ever obtained for quiet-Sun solar surface
structures—up to 32.8% at a wavelength of 214 nm. We compare the
rms contrasts obtained from the observational data with theoretical
intensity contrasts obtained from numerical magnetohydrodynamic
simulations. For 388 nm and 312 nm the observations agree well with
the numerical simulations whereas at shorter wavelengths discrepancies
between observed and simulated contrasts remain.
Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
Bibcode: 2010arXiv1009.1050H
Altcode:
We present high-resolution images of the Sun in the near ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1-m Sunrise balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range
are among the highest values ever obtained for quiet-Sun solar
surface structures - up to 32.8% at a wavelength of 214 nm. We
compare with theoretical intensity contrasts obtained from numerical
magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
agree well with the numerical simulations whereas at shorter wavelengths
discrepancies between observed and simulated contrasts remain.
Title: Characterization of horizontal flows around solar pores from
high-resolution time series of images
Authors: Vargas Domínguez, S.; de Vicente, A.; Bonet, J. A.; Martínez
Pillet, V.
Bibcode: 2010A&A...516A..91V
Altcode: 2010arXiv1003.2134V
Context. Though there is increasing evidence linking the moat flow and
the Evershed flow along the penumbral filaments, there is not a clear
consensus regarding the existence of a moat flow around umbral cores
and pores, and the debate is still open. Solar pores appear to be a
suitable scenario to test the moat-penumbra relation as they correspond
to a direct interaction between the umbra and the convective plasma
in the surrounding photosphere without any intermediate structure in
between.
Aims: We study solar pores based on high-resolution
ground-based and satellite observations.
Methods: Local
correlation tracking techniques were applied to different-duration
time series to analyze the horizontal flows around several solar
pores.
Results: Our results establish that the flows calculated
from different solar pore observations are coherent among each other
and show the determining and overall influence of exploding events in
the granulation around the pores. We do not find any sign of moat-like
flows surrounding solar pores, but a clearly defined region of inflows
surrounding them.
Conclusions: The connection between moat
flows and flows associated to penumbral filaments is hereby reinforced.
Title: Magnetic Bright Points in the Quiet Sun
Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchié, B.; Del
Moro, D.
Bibcode: 2010ApJ...715L..26S
Altcode: 2010arXiv1004.1885S
We present a visual determination of the number of bright points
(BPs) existing in the quiet Sun, which are structures though to trace
intense kG magnetic concentrations. The measurement is based on a
0farcs1 angular resolution G-band movie obtained with the Swedish Solar
Telescope at the solar disk center. We find 0.97 BPs Mm-2,
which is a factor 3 larger than any previous estimate. It corresponds to
1.2 BPs per solar granule. Depending on the details of the segmentation,
the BPs cover between 0.9% and 2.2% of the solar surface. Assuming their
field strength to be 1.5 kG, the detected BPs contribute to the solar
magnetic flux with an unsigned flux density between 13 G and 33 G. If
network and inter-network regions are counted separately, they contain
2.2 BPs Mm-2 and 0.85 BPs Mm-2, respectively.
Title: Magnetic bright points in the quiet Sun
Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchie, B.; Del
Moro, D.
Bibcode: 2010iac..talk...95S
Altcode: 2010iac..talk..157S
No abstract at ADS
Title: Convectively Driven Vortex Flows in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello,
I.; Domingo, V.
Bibcode: 2008ApJ...687L.131B
Altcode: 2008arXiv0809.3885B
We have discovered small whirlpools in the Sun, with a size similar to
terrestrial hurricanes (lesssim0.5 Mm). The theory of solar convection
predicts them, but they had remained elusive so far. The vortex flows
are created at the downdrafts where the plasma returns to the solar
interior after cooling down, and we detect them because some magnetic
bright points (BPs) follow a logarithmic spiral on their way to being
engulfed by a downdraft. Our disk-center observations show 0.9 ×
10-2 vortexes per Mm2, with a lifetime of the
order of 5 minutes, and with no preferred sense of rotation. They are
not evenly spread out over the surface, but they seem to trace the
supergranulation and the mesogranulation. These observed properties are
strongly biased by our type of measurement, unable to detect vortexes
except when they are engulfing magnetic BPs.
Title: Convectively driven vortex flows in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello,
I.; Domingo, V.
Bibcode: 2008iac..talk..143B
Altcode: 2008iac..talk...26B
No abstract at ADS
Title: Moat Flow in the Vicinity of Sunspots for Various Penumbral
Configurations
Authors: Vargas Domínguez, S.; Rouppe van der Voort, L.; Bonet,
J. A.; Martínez Pillet, V.; Van Noort, M.; Katsukawa, Y.
Bibcode: 2008ApJ...679..900V
Altcode: 2008arXiv0802.1457V
High-resolution time series of sunspots have been obtained with
the Swedish 1 m Solar Telescope between 2003 and 2006 at different
locations on the solar disk. Proper motions in seven different active
regions have been studied. The analysis was performed by applying local
correlation tracking to every series of sunspots, each of them more than
40 minutes long. The sunspots' shapes include a different variety of
penumbral configurations. We report on the systematic behavior of the
large-scale outflows surrounding the sunspots, commonly known as moat
flows, that are essentially present only when preceded by a penumbra
not tangential but perpendicular to the sunspot border. We present
one case for which this rule appears not to be confirmed. We speculate
that the magnetic neutral line, which is located in the vicinity of the
anomalous region, might be responsible for blocking the outflow. These
new results confirm the systematic and strong relation between the
moat flows and the existence of penumbrae. A comparative statistical
study between moats and standard granulation is also performed.
Title: Small magnetic structures in the photosphere, radiative
properties
Authors: Palacios, Judith; Domingo, Vicente; Cabello, Iballa; Bonet,
José Antonio; Sánchez Almeida, Jorge
Bibcode: 2008cosp...37.2331P
Altcode: 2008cosp.meet.2331P
The three dimensional structure of small magnetic field features in the
photosphere, their dynamic behavior and their radiative properties are
studied. We analyze data obtained in simultaneous observations made on
Sept 29 and 30, 2007 with the HINODE spacecraft and the Swedish Solar
Telescope (SST) in La Palma in different wavelengths, such as CaII
(396.85 nm) and CN (388.35 nm) and other with Hinode data; and Gband
(430.56 nm) with SST. Tha analysis is completed with high resolution
Gband and Gcontinuum (436.39 nm) images from SST obtained on 2005 and
2006. Magnetograms have been obtained from both observatories. SST
images have been processed with MOMFB code. Ribbon-like structures and
"flowers" are studied in detail. Comparisons with solar atmospheric
models are presented.
Title: Relationships between magnetic foot points and G-band bright
structures
Authors: Ishikawa, R.; Tsuneta, S.; Kitakoshi, Y.; Katsukawa, Y.;
Bonet, J. A.; Vargas Domínguez, S.; Rouppe van der Voort, L. H. M.;
Sakamoto, Y.; Ebisuzaki, T.
Bibcode: 2007A&A...472..911I
Altcode: 2008arXiv0802.1765I
Aims:Magnetic elements are thought to be described by flux tube models,
and are well reproduced by MHD simulations. However, these simulations
are only partially constrained by observations. We observationally
investigate the relationship between G-band bright points and magnetic
structures to clarify conditions, which make magnetic structures
bright in G-band.
Methods: The G-band filtergrams together with
magnetograms and dopplergrams were taken for a plage region covered
by abnormal granules as well as ubiquitous G-band bright points,
using the Swedish 1-m Solar Telescope (SST) under very good seeing
conditions.
Results: High magnetic flux density regions are
not necessarily associated with G-band bright points. We refer to the
observed extended areas with high magnetic flux density as magnetic
islands to separate them from magnetic elements. We discover that G-band
bright points tend to be located near the boundary of such magnetic
islands. The concentration of G-band bright points decreases with inward
distance from the boundary of the magnetic islands. Moreover, G-band
bright points are preferentially located where magnetic flux density is
higher, given the same distance from the boundary. There are some bright
points located far inside the magnetic islands. Such bright points have
higher minimum magnetic flux density at the larger inward distance from
the boundary. Convective velocity is apparently reduced for such high
magnetic flux density regions regardless of whether they are populated
by G-band bright points or not. The magnetic islands are surrounded by
downflows.
Conclusions: These results suggest that high magnetic
flux density, as well as efficient heat transport from the sides or
beneath, are required to make magnetic elements bright in G-band.
Title: On the Moat-Penumbra Relation
Authors: Vargas Domínguez, S.; Bonet, J. A.; Martínez Pillet, V.;
Katsukawa, Y.; Kitakoshi, Y.; Rouppe van der Voort, L.
Bibcode: 2007ApJ...660L.165V
Altcode: 2007astro.ph..2713V
Proper motions in a sunspot group with a δ-configuration and close to
the solar disk center have been studied by employing local correlation
tracking techniques. The analysis is based on a more than 1 hr time
series of G-band images. Radial outflows with a mean speed of 0.67
km s-1 have been detected around the spots, the well-known
sunspots moats. However, these outflows are not found in those umbral
core sides without penumbra. Moreover, moat flows are only found
in those sides of penumbrae located in the direction marked by the
penumbral filaments. Penumbral sides perpendicular to them show no
moat flow. These results strongly suggest a relation between the
moat flow and the well-known, filament-aligned Evershed flow. The
standard picture of a moat flow originating from a blocking of the
upward propagation of heat is discussed in some detail.
Title: The Evershed Effect Observed with 0.2" Angular Resolution
Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez
Cerdeña, I.
Bibcode: 2007ApJ...658.1357S
Altcode: 2006astro.ph.11523S
We present an analysis of the Evershed effect observed with a resolution
of 0.2". Using the new Swedish 1 m Solar Telescope and its Littrow
spectrograph, we scan a significant part of a sunspot penumbra. Spectra
of the nonmagnetic line Fe I λ7090.4 allows us to measure Doppler
shifts without magnetic contamination. The observed line profiles are
asymmetric. The Doppler shift depends on the part of the line used for
measuring, indicating that the velocity structure of penumbrae remains
unresolved, even with our angular resolution. The observed line profiles
are properly reproduced if two components with velocities between zero
and several km s-1 coexist in the resolution elements. Using
Doppler shifts at fixed line depths, we find a local correlation
between upflows and bright structures and between downflows and dark
structures. This association is not specific to the outer penumbra,
but it also occurs in the inner penumbra. The existence of such a
correlation was originally reported in 1969 by Beckers and Schröter,
and it is suggestive of energy transport by convection in penumbrae.
Title: Evidence Of An Association Between The Presence Of Penumbrae
And Strong Radial Outflows In Sunspots
Authors: Santiago, Vargas Domínguez; Bonet, J. A.; Martinez Pillet,
V.; Katsukawa, Y.
Bibcode: 2007ESASP.641E..87S
Altcode:
Time series of high-resolution images of the complex ac-tive region NOAA
10786 are studied. The observations were performed in G-band (430.5 nm)
and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish
1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the
surroundings of the sunspots have been quantified. A large-scale radial
outflow in the velocity range 0.3 - 1 km s-1 has been measured around
the sunspots by using local correlation tracking techniques. However,
this outflow is not found in those regions around the sunspots with
no penumbral structure. This result evidences an association between
penumbrae and the existence of strong horizontal outflows (the moat)
in sunspots.
Title: S im ulation And Analysis Of VIM Measurements: Feedback On
Design Parameters
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; Vargas, S.; Bonet,
J. A.; Martíez Pillet, V.; del Toro Iniesta, J. C.
Bibcode: 2007ESASP.641E..49O
Altcode: 2006astro.ph.11443O
The Visible-light Imager and Magnetograph (VIM) proposed for the
ESA Solar Orbiter mission will observe a photo spheric spectral
line at high spatial resolution. Here we simulate and interpret VIM
measurements. Realistic MHD models are used to synthesize "observed"
Stokes profiles of the photospheric Fe I 617.3 nm line. The profiles are
degraded by telescope diffraction and detector pixel size to a spatial
resolution of 162 km on the solar surface. We stufy the influence
of spectral resolving power, noise, and limited wavelength sampling
on the vector magnetic fields and line-of-sight velocities derived
from Milne-Eddington inversions of the simulated measurements. VIM
will provide reasonably accurate values of the atmospheric parametes
even with the filter widths of 120 Å and 3 wavelength positions plus
continuum, as long as the noise level is kept below 10-3 Ic.
Title: Proper Motions in Sunspot Penumbrae: Signs of Convection
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.
Bibcode: 2006ASPC..358...80B
Altcode:
Proper motions in penumbra have been measured using local correlation
tracking techniques in a high spatial resolution series of images
(∼0.12 arcsec). Assuming these motions to trace true plasma motions,
we have detected converging flows that arrange the plasma in long
narrow filaments mostly placed along dark penumbral filaments. These
converging flows suggest downflows in the filaments of ∼ 200 m
s-1. We interpret the association between downflows and
dark features as a sign of convection that, once several observational
biases are considered, could transport enough energy to balance the
radiative losses of penumbra.
Title: The Evershed Effect with 0.2 arcsec Angular Resolution
Authors: Márquez, I.; Bonet, J. A.; Sánchez Almeida, J.; Domínguez
Cerdeña, I.
Bibcode: 2006ASPC..358...96M
Altcode:
We present a preliminary analysis of penumbral spectra observed with
unprecedented angular resolution (0.2 arcsec) using the new Swedish 1-m
Solar Telescope. The use of a non-magnetic line allows us to measure
Doppler shifts without magnetic contamination. The observed
Doppler shifts depend on the part of the line used for measuring,
indicating that the velocity structure of penumbrae remains unresolved
even with our resolution. We find a correlation between upflows
and bright filaments. This association is not specific of the outer
penumbra but it also occurs in the inner penumbra. The existence
of such correlation was originally reported by tet{m1 BS69}, and
it is suggestive of energy transport by convection in penumbrae.
Title: Evidence of an association between the presence of penumbrae
and strong radial outflows in sunspots
Authors: Vargas Domínguez, S.; Bonet, J. A.; Martinez Pillet, V.;
Katsukawa, Y.
Bibcode: 2006astro.ph.11500V
Altcode:
Time series of high-resolution images of the complex active region NOAA
10786 are studied. The observations were performed in G-band (430.5 nm)
and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish
1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the
surroundings of the sunspots have been quantified. A large-scale radial
outflow in the velocity range 0.3 - 1 km s^[-1] has been measured around
the sunspots by using local correlation tracking techniques. However,
this outflow is not found in those regions around the sunspots with
no penumbral structure. This result evidences an association between
penumbrae and the existence of strong horizontal outflows (the moat)
in sunspots.
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.
Bibcode: 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 3 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: High-Resolution Proper Motions in a Sunspot Penumbra
Authors: Márquez, I.; Sánchez Almeida, J.; Bonet, J. A.
Bibcode: 2006ApJ...638..553M
Altcode: 2005astro.ph.10220M
Local correlation tracking techniques are used to measure proper
motions in a series of high angular resolution (~0.1") penumbra
images. If these motions trace true plasma motions, then we have
detected converging flows that arrange the plasma in long narrow
filaments cospatial with dark penumbral filaments. Assuming that these
flows are stationary, the vertical stratification of the atmosphere
and the conservation of mass suggest downflows in the filaments on
the order of 200 m s-1. The association between downflows
and dark features may be a sign of convection, as it happens with the
nonmagnetic granulation. Insufficient spatial resolution may explain
why the estimated vertical velocities are not fast enough to supply
the radiative losses of penumbrae.
Title: Time series of high resolution photospheric spectra in a
quiet region of the Sun. II. Analysis of the variation of physical
quantities of granular structures
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.;
Hanslmeier, A.
Bibcode: 2005A&A...441.1157P
Altcode: 2012arXiv1205.1725P
From the inversion of a time series of high resolution slit spectrograms
obtained from the quiet sun, the spatial and temporal distribution
of the thermodynamical quantities and the vertical flow velocity is
derived as a function of optical depth (logτ) and geometrical height
(z). Spatial coherence and phase shift analyses between temperature
and vertical velocity depict the height variation of these physical
quantities for structures of different size. An average granular
cell model is presented, showing the granule-intergranular lane
stratification of temperature, vertical velocity, gas pressure and
density as a function of logτ and z. Studies of a specific small
and a specific large granular cell complement these results. A strong
decay of the temperature fluctuations with increasing height together
with a less efficient penetration of smaller cells is revealed. The
T-T coherence at all granular scales is broken already at logτ = -1
or z ~ 170 km. At the layers beyond, an inversion of the temperature
contrast at granular scales >1.5 arcsec is revealed, both in logτ
and z. At deeper layers the temperature sensitivity of the H-
opacity leeds to much smaller temperature fluctuations at equal logτ
than at equal z, in concordance with Stein & Nordlund (1998, ApJ,
499, 914). Vertical velocities are in phase throughout the photosphere
and penetrate into the highest layers under study. Velocities at the
largest granular scales (~ 4´´) are still found even at logτ ~ -2.8
or z ~ 370 km. Again a less efficient height penetration of smaller
cells concerning convective velocities is revealed, although still
at logτ ~ -2 or z ~ 280 km structures >1.4 arcsec are detected. A
similar size distribution of velocity and temperature structures with
height provides observational evidence for substantial overshoot into
the photosphere. At deep photospheric layers, the behaviour of the
vertical velocities reflected in simulations is for the first time
qualitatively reproduced by observations: intergranular velocities
are larger than the granular ones and, both reach extrema, where the
granular one is shifted towards higher layers.
Title: First Implementation Of Phase Diversity At Themis
Authors: Criscuoli, S.; Moro, D. Del; Bonet, J. A.; Márquez, I.
Bibcode: 2005SoPh..228..177C
Altcode:
Phase diversity techniques are robust post-processing tools for image
enhancement and correction of telescopic and atmospheric induced
aberrations. We present results obtained applying the Partitioned
Phase-Diverse Speckle (PPDS) technique to images acquired at THEMIS. We
also present an image quality estimator based on image power spectrum
content we developed in order to automatically evaluate the results
of large amount of data.
Title: Phase diversity restoration of sunspot images. II. Dynamics
around a decaying sunspot
Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.;
Roudier, Th.
Bibcode: 2005A&A...430.1089B
Altcode:
Two time series, taken simultaneously in the G-band and in white-light,
and corrected for telescope aberrations and turbulence perturbations
using the method of phase diversity, are employed to study the motions
of granules and G-band bright points (GBPs) in the moat of an old
regular sunspot. Local correlation tracking and feature tracking have
been utilized for this purpose. A large-scale radial outflow with
a mean velocity of 0.51 km s-1 has been measured in the
sunspot moat. Centres of diverging horizontal motions, identified
with families of granules formed by repeatedly splitting granules,
move away from the sunspot. Most of the GBPs in the moat also move
outwards through radially orientated ``channels'' (confined between
the borders of adjacent families) with velocities comparable to those
of the adjacent granules. However, 6% of the GBPs move faster (>1.4
km s-1) than the neighbouring granules. GBPs in the moat
are not regularly distributed but they are less frequent on its solar
centre side.
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.
Bibcode: 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 LiNbO3 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: Phase diversity restoration of sunspot images. I. Relations
between penumbral and photospheric features
Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.;
Tritschler, A.
Bibcode: 2004A&A...423..737B
Altcode: 2004astro.ph..5542B
We investigate the dynamics of and the relations between small-scale
penumbral and photospheric features near the outer penumbral
boundary: penumbral grains (PGs), dark penumbral fibrils, granules,
and photospheric G-band bright points. The analysis is based on a 2 h
time sequence of a sunspot close to disc center, taken simultaneously
in the G-band and in the blue continuum at 450.7 nm. Observations
were performed at the Swedish Vacuum Solar Telescope (La Palma)
in July 1999. A total of 2564 images (46 arcsec × 75 arcsec) were
corrected for telescope aberrations and turbulence perturbations by
applying the inversion method of phase diversity. Our findings can by
summarized as follows: (a) one third of the outward-moving PGs pass
through the outer penumbral boundary and then either continue moving
as small bright features or expand and develop into granules. (b)
Former PGs and G-band bright points next to the spot reveal a different
nature. The latter have not been identified as a continuation of PGs
escaping from the penumbra. The G-band bright points are mostly born
close to dark penumbral fibrils where the magnetic field is strong,
whereas PGs stem from the less-magnetized penumbral component and
evolve presumably to non-magnetic granules or small bright features.
Title: Bright Points in the Internetwork Quiet Sun
Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez
Cerdeña, I.; Muller, R.
Bibcode: 2004ApJ...609L..91S
Altcode: 2004astro.ph..5515S; 2004astro.ph..5515A
High-resolution G-band images of the interior of a supergranulation
cell show ubiquitous bright points (BPs; some 0.3 BPs per
Mm2). They are located in intergranular lanes and often
form chains of elongated blobs whose smallest dimension is at
the resolution limit (135 km on the Sun). Most of them live for a
few minutes, having peak intensities from 0.8 to 1.8 times the mean
photospheric intensity. These BPs are probably tracing intense magnetic
concentrations, whose existence has been inferred in spectropolarimetric
measurements. Our finding provides a new convenient tool for the study
of the internetwork magnetism, so far restricted to the interpretation
of weak polarimetric signals.
Title: Motions of photospheric features in a sunspot moat
Authors: Sobotka, M.; Bonet, J. A.; Márquez, I.; Muller R.;
Roudier, Th.
Bibcode: 2004HvaOB..28...27S
Altcode:
Two time series, taken simultaneously in the G-band and the blue
continuum, corrected for instrumental and atmospheric degradation
using the method of phase diversity, are employed to study the motions
of granules and G-band bright points (GBPs) in the moat of an old
regular sunspot. Centres of diverging horizontal motions, identified
with families of granules formed by recurrently splitting granules,
move away from the sunspot. Most of GBPs show radially oriented motions
in the same direction, with velocities comparable to those of adjacent
granules. However, 7 % of GBPs move faster (>1.4 km s-1)
than the neighbouring granules.
Title: Time series of high resolution photospheric spectra in a quiet
region of the sun. I. Analysis of global and spatial variations of
line parameters
Authors: Puschmann, K.; Vázquez, M.; Bonet, J. A.; Ruiz Cobo, B.;
Hanslmeier, A.
Bibcode: 2003A&A...408..363P
Altcode: 2012arXiv1205.1723P
A 50 min time series of one-dimensional slit-spectrograms, taken in
quiet sun at disk centre, observed at the German Vacuum Tower Telescope
(Observatorio del Teide), was used to study the global and spatial
variations of different line parameters. In order to determine the
vertical structure of the photosphere two lines with well separated
formation heights have been considered. The data have been filtered of
p-modes to isolate the pure convective phenomenon. From our studies
of global correlation coefficients and coherence and phase shift
analyses between the several line parameters, the following results
can be reported. The convective velocity pattern preserves structures
larger than 1.0 arcs to the highest layers of the photosphere (
~ 435 km). However, at these layers, in the intensity pattern only
structures larger than 2.0 arcs are still connected with those at the
continuum level although showing inverted brightness contrast. This
confirms an inversion of temperature that we have found at a height
of ~ 140 km. A possible evidence of gravity waves superimposed to
the convective motions is derived from the phase shift analysis. We
interprete the behaviour of the full width at half maximum and the
equivalent width as a function of the distance to the granular borders,
as a consequence of enhanced turbulence and/or strong velocity gradients
in the intergranular lanes.
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
Bibcode: 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: Granule and Supergranule properties derived from solar
timeseries
Authors: Del Moro, D.; Berrilli, F.; Bonet, J. A.; Consolini, G.;
Kosovichev, A.; Pietropaolo, E.
Bibcode: 2003MmSAI..74..584D
Altcode:
In this paper we mainly aim at the understanding of temporal evolution
and spatial characterization of solar granular and supergranular
features. For this purpose we apply an automatic feature-tracking
algorithm to three different solar granulation timeseries and to a
supergranular timeseries of near-surface divergence fields. The single
lifetimes are calculated measuring the time elapsing between the birth
and death of each target. In addition, we investigate spatial order of
surface flows studying the g2(r) function of time-averaged
supergranular fields.
Title: Phase diversity at THEMIS : first implementation
Authors: Del Moro, D.; Criscuoli, S.; Bonet, J. A.; Márquez, I.;
Lemen, C.; Briand, C.
Bibcode: 2003MmSAI..74..811D
Altcode:
Phase diversity techniques actually provide robust post-processing
methods to restore solar images degraded by seeing-optical
aberrations. We present preliminary results of the application of a
Partitioned Phase-Diverse Speckle (PPDS) technique at THEMIS. The images
have been acquired using the IPM broad-band CCD camera and reduced
using a suitable IDL code. The spectral analysis of unrestored/restored
images shows a significant improvement of image quality, achieving
diffraction limited resolution.
Title: Infrared photometry of a sunspot near the disk center
Authors: Stangl, S.; Sobotka, M.; Bonet, J. A.; Vázquez, M.;
Hanslmeier, A.
Bibcode: 2003AN....324..376S
Altcode:
A time series of broadband images of a sunspot near the disk center
was obtained simultaneously in two wavelength bands at 0.56 mu m and
1.55 mu m at the German VTT on June 17, 1998. We computed intensity
difference images of the best frame pairs which reveal information
about the facular distribution in the present field of view. Faculae
are found around pores, in the quiet granulation and as well around
the sunspot penumbra.
Title: Phase diversity at THEMIS : first implementation
Authors: Del Moro, D.; Lemen, C.; Bonet, J. A.; Márquez, I.;
Criscuoli, S.; Briand, C.
Bibcode: 2003AN....324..299D
Altcode:
No abstract at ADS
Title: Models of a mean granular cell
Authors: Puschmann, K.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.;
Hanslmeier, A.
Bibcode: 2003AN....324..352P
Altcode:
From inversion of a time series of slit spectra, observed in a quiet
region of the solar photosphere, averaged models of a granular cell
have been obtained showing the stratification of physical quantities
versus optical depth and geometrical height. Furthermore a semi-empiric
dynamic model of a mean granular cell has been derived and the results
are presented.
Title: Centre-to-limb variation of solar granulation in the infrared
Authors: Sánchez Cuberes, M.; Vázquez, M.; Bonet, J. A.; Sobotka, M.
Bibcode: 2003A&A...397.1075S
Altcode:
Broad-band images have been obtained at the extremes of the continuum
absorption coefficient of the solar atmosphere, at lambda 0.8 mu m
and lambda 1.55 mu m. Quiet regions have been observed for different
heliocentric angles. The centre-to-limb variation of granulation
contrast has been computed in both wavelength ranges and a steeper
decrease in the contrast is obtained for lambda 0.8 mu m than for
lambda 1.55 mu m. For positions near the solar limb the granulation
contrast shows a tendency to increase at both wavelengths. Mean
granular sizes vary from 1.25 arcsec2 at the disc centre
to 2 arcsec2 at mu =0.6 in the lambda 0.8 mu m images and
from 1.24 arcsec2 to 1.85 arcsec2 at lambda
1.55 mu m. Observations close to the limb detect granular structures
of 0.\arcsec 96 or even smaller at a distance from the limb of d=
0.\arcsec 32, equal to the diffraction limit of the telescope at
lambda 8000 Å. Using an Eddington-Barbier approximation this implies a
penetration of the temperature fluctuations associated with granulation
up to approximately z ~ 220 km, although the calculation of response
functions defines a broader interval.
Title: Phase Diversity Reconstruction of Long Time Series Observations
at the SVST
Authors: Bonet, J. A.; Márquez, I.
Bibcode: 2003ASPC..307..137B
Altcode:
No abstract at ADS
Title: Infrared photometric results of a sunspot
Authors: Stangl, S.; Hanslmeier, A.; Sobotka, M.; Bonet, J. A.;
Vázquez, M.
Bibcode: 2002ESASP.506..473S
Altcode: 2002ESPM...10..473S; 2002svco.conf..473S
We obtained simultaneously recorded time series of broadband
images of a sunspot close to the disk center at the German Vacuum
Tower Telescope, Tenerife, in two wavelength bands at 0.56 μm and
1.55 μm. Maps of brightness difference images Tb(1.55
μm) and Tb(0.56 μm) were computed for the best image
pairs. Furthermore, a scatter plot of the brightness temperatures
was made where five different magnetic and nonmagnetic regions -
quiet region (QR), faculae, pores, penumbra, and umbra - in the
field of view can be clearly distinguished. Pores as well as the
penumbra are surrounded by the facular regions consisting of several
single facular elements. However, facular regions are also found in
non-magnetic vicinity.
Title: Properties of horizontal flows inside and outside a solar pore
Authors: Roudier, Th.; Bonet, J. A.; Sobotka, M.
Bibcode: 2002A&A...395..249R
Altcode:
Horizontal velocities and their temporal variations inside a large pore
and in the surrounding granulation are studied from a 73 min sequence
of white light frames, acquired at the Swedish Vacuum Solar Telescope
(La Palma). The local correlation tracking technique with high spatial
(0\farcs 31) and temporal (5 min) resolution was applied to binarized
images, yielding 14 independent velocity maps. A ring of divergence
centres around the pore was observed in all the maps. Motions directed
into the pore, deposited by the divergence centres, continue also within
the pore but with magnitudes smaller by factor of 2-3. A link between
the variations of large velocity amplitudes around the pore and the
brightness fluctuations of umbral dots is suggested. A phase delay
between velocity and intensity changes at the periphery of the pore,
probably related to the penetration of bright features inwards across
the pore's border, was observed.
Title: Evolution of small-scale features at the penumbra-photosphere
border
Authors: Sobotka, M.; Muller, R.; Bonet, J. A.; Márquez, I.
Bibcode: 2002ESASP.505..579S
Altcode: 2002IAUCo.188..579S; 2002solm.conf..579S
Time series of images of a sunspot, acquired simultaneously
in blue light and in G-band at the SVST, La Palma, are used to
study horizontal motions of granules in the vicinity of the spot
and evolution of penumbral grains (PGs) near the outer penumbral
border. Local correlation tracking and feature tracking algorithms
have been utilized for this purpose. Around sunspots and pores we
can observe numerous centers of diverging local horizontal motions,
caused mostly by exploding granules. Around developed spots we find an
organized motion directed out from the penumbra. The divergence centers
are carried away from the spot by this motion. In the outer penumbra,
PGs move mostly outwards, toward the surrounding granulation. About 2/3
of PGs disappear near the penumbra-granulation border. The remaining
PGs move across the border, they transform either to granules or to
small bright features, and continue moving away from the sunspot.
Title: Infrared Photometry of Solar Photospheric
Structures. II. Center-to-Limb Variation of Active Regions
Authors: Sánchez Cuberes, M.; Vázquez, M.; Bonet, J. A.; Sobotka, M.
Bibcode: 2002ApJ...570..886S
Altcode:
Simultaneous broadband single images and time series of images have
been obtained at λ0.8 and λ1.55 μm, which are at the extremes of
the continuum absorption coefficient of the solar atmosphere. Active
regions have been observed for different heliocentric angles. Weighted
difference images between the two wavelength bands have been used
to identify faculae. Center-to-limb variations of facular relative
intensity distribution, facular size distribution, and facular
size-intensity relations have been obtained. At the spatial resolution
of the observations, faculae show no contrast at the disk center
at λ0.8 μm, while dark faculae are observed at λ1.55 μm. The
transition from dark to bright faculae occurs between μ=0.6 and
0.5 in λ1.55 μm images. The maximum of the mean facular relative
intensity is found at μ=0.3 for both wavelengths. However, the peak
of the facular relative intensity is greater and appears closer to
the limb the larger the faculae are. Brightness temperature maps
have been computed for the best pairs of images, and temperature
difference images have been derived. The temperature difference
Tb(1.55μm)-Tb(0.8μm) in pores is larger than
that in the quiet photosphere at the disk center, but smaller near
the limb. Faculae show smaller temperature differences than the quiet
photosphere at the disk center, but the temperature differences near
the limb are almost equal. Pores are surrounded by ringlike structures
of low temperature difference at the disk center. Near the limb these
ringlike structures appear bright in the brightness temperature maps and
show a temperature difference similar to that of the quiet photosphere.
Title: Fine structure and dynamics in a light bridge inside a
solar pore
Authors: Hirzberger, J.; Bonet, J. A.; Sobotka, M.; Vázquez, M.;
Hanslmeier, A.
Bibcode: 2002A&A...383..275H
Altcode:
A photometric analysis of the sub-structure of a granular light
bridge in a large solar pore is performed. The data consist of a
66 min time series of white light images (lambda = 5425 Å,+/- 50
Å) of an active region NOAA 7886 obtained at the Swedish Vacuum
Solar Telescope on La Palma, Canary Islands. The light bridge can
be resolved into an assembly of small grains embedded in a diffuse
background with an intensity of about 85% of the mean photospheric
intensity (Iphot). Following the temporal evolution of these
sub-structures in their irregular motions inside the light bridge,
proper motions with velocities up to 1.5 km s-1 can be
detected. Their lifetime distribution shows a maximum at 5 min and a
second peak at approximately 20 min. The origin and the decay of these
sub-structures is very similar to those of granules, i.e. fragmentation,
merging and spontaneous origination from, and dissolution into, the
background can be observed. Some of them are able to escape from the
light bridge into the umbra where they cannot be distinguished from
adjacent umbral dots. Generally, this study presents evidence that
the observed phenomenon represents convective motions.
Title: High Resolution Observations of a Photospheric Light Bridge
Authors: Hirzberger, J.; Hanslmeier, A.; Bonet, J. A.; Vázquez, M.
Bibcode: 2001ASSL..259..271H
Altcode: 2001dysu.conf..271H
We analyzed a 66 min time series of spatially highly resolved white
light images to study the dynamics of photospheric light bridges
which we assumed to be a restoration of the quiet surface inside
sunspots. Similar decaying mechanisms were found as for normal
photospheric dynamics for granulation.
Title: A Photometric and Magnetic Analysis of the Wilson Effect
Authors: Steinegger, M.; Bonet, J. A.; Vázquez, M.; Martinez
Pillet, V.
Bibcode: 2001ASSL..259..279S
Altcode: 2001dysu.conf..279S
For two sunspot groups observed in June 1992 we analyze the
center-to-limb variation and height dependence of various geometrical
parameters describing the Wilson effect by using continuum observations
and simultaneously obtained images of the degree of polarization.
Title: Infrared Photometry of Solar Photospheric Structures. I. Active
Regions at the Center of the Disk
Authors: Sobotka, M.; Vázquez, M.; Sánchez Cuberes, M.; Bonet,
J. A.; Hanslmeier, A.
Bibcode: 2000ApJ...544.1155S
Altcode:
Simultaneous time series of broadband images of two active regions
close to the disk center were acquired at the Swedish Vacuum
Solar Telescope, La Palma, in the infrared bands at 1.55 and 0.80
μm, corresponding to the minimum and maximum continuum opacities,
respectively. Dark faculae are detected in images obtained as weighted
intensity differences between both wavelength bands. Maps of brightness
temperatures Tb (1.55 μm) and Tb (0.80 μm)
were computed for the best pairs of images. In the scatter plots
Tb (1.55) versus Tb (0.80), the elements of
quiet regions can be clearly distinguished from those of faculae and
pores, while the transition between faculae and pores is smooth. The
temperature difference Tb(1.55)-Tb(0.80) in
faculae is lower than that in the quiet photosphere but increases with
decreasing Tb and is higher inside pores. Most of the pores
are surrounded by ringlike regions of low temperature difference. The
minimum intensity of pores at both wavelengths decreases with increasing
diameter. Maps of horizontal motions of dark faculae and pores were
derived from time series of intensity-difference images, using the
local correlation tracking technique. Velocities corresponding to
large-scale separation of polarities, an emergence of magnetic flux,
twist and contraction related to a pore formation, shear motions,
and a twist in dark faculae were measured.
Title: Center-to-Limb Variation of Solar Granulation from Partial
Eclipse Observations
Authors: Sánchez Cuberes, M.; Bonet, J. A.; Vázquez, M.; Wittmann,
A. D.
Bibcode: 2000ApJ...538..940S
Altcode:
We have measured the center-to-limb variation (CLV) of parameters
describing geometric and photometric statistical properties of the
solar granulation at 6708 Å. This work is based on an excellent
series of white-light images obtained with the Swedish Vacuum Solar
Telescope at Roque de los Muchachos Observatory, La Palma, during the
partial solar eclipse of 1994 May 10. The lunar limb profile, which is
visible in each frame, was used as a calibration tool for estimating
the point-spread function of the combined optical system formed by the
atmosphere and the telescope. Before restoration, noise was removed
from the images by a novel application of the so-called optimum filter
for two-dimensional objects. The latter was optimized in terms of
rms error and was constructed from very precise smoothed models of the
specific power spectrum of the granulation at each position on the solar
disk. The determination of the positions on the solar disk was achieved
with high accuracy by matching the position of the Moon's limb in our
images to a numerical simulation of the eclipse geometry. The CLV curve
of the ΔIrms granular contrast shows one of the steepest
gradients among those reported in the literature and quite a high value
(9.6%) at the disk center considering that our working wavelength is
in the far-red range of the solar spectrum. The elliptical shape of
the restored power spectra with ellipticities equal to those expected
just from foreshortening proves that radiative transfer effects do not
alter the isotropy of the horizontal intensity pattern of the solar
granulation, at least up to μ=0.4. The mean wavenumber, k, derived
from the two-dimensional power spectra azimuthally integrated along
the ellipses amounts to a value of 6.15 Mm-1 at the center
of the solar disk and then shows a decrease toward the limb. Apart
from the power spectra analysis, a direct statistical study of the
granulation size and brightness, based on the image segmentation for
defining granular contours, has also been performed. A general increase
in both granular and intergranular areas is found as we move toward the
solar limb. The mean granular cell area varies from 1.36 Mm2
at μ=1 up to 2.06 Mm2 at μ=0.6, and in parallel, the
granular filling factor (the percentage of area of the image covered
by granules) decreases from 44.2% to 42.8%. In the small area range,
the granular brightness increases linearly with the granular cell size
and is preserved constant, on average, for granular cells larger than
~2.0". No slope variation is found for the intergranular intensities
versus granular cell areas. Observations close to the solar limb detect
granular structures as small as 0.53" or even smaller up to a distance
of at least ~0.5" from the limb, showing that the ΔT associated
with the granulation persist at least until z~200 km. However, this
penetration could be different for small and large granules because we
find several hints indicating the progressive disappearance of small
structures toward the limb.
Title: Infrared Photometry of Solar Active Regions
Authors: Sobotka, M.; Vázquez, M.; Cuberes, M. S.; Bonet, J. A.;
Hanslmeier, P.
Bibcode: 2000JApA...21..289S
Altcode:
No abstract at ADS
Title: Long-Term Observations of Solar Active Regions at the VNT
Authors: Bonet, J. A.; Casas, R.; Giammanco, C.; Martinez Pillet,
V.; Vazquez
Bibcode: 2000ESASP.463..635B
Altcode: 2000sctc.proc..635B
No abstract at ADS
Title: Time Series of Solar Granulation Images. III. Dynamics of
Exploding Granules and Related Phenomena
Authors: Hirzberger, J.; Bonet, J. A.; Vázquez, M.; Hanslmeier, A.
Bibcode: 1999ApJ...527..405H
Altcode:
The evolution of exploding granules is studied by using a spatially as
well as temporally highly resolved time series of white-light images of
80 minute duration. The results of this study show that the dynamics
of exploding granules is strongly affected by their surroundings and
that their appearance is closely related to the mesogranular flow
field. Comparing the behavior of exploding granules with that of
smaller dark structures--so-called dark dots--and with the results of
model simulations leads to the conclusion that both phenomena, as well
as a third newly found phenomenon (dark structures occurring in the
centers of granules that are approximately twice as large as dark dots
but smaller than typical centers of exploding granules) are different
types of strong downflows developing in the centers of granules. The
motions of all these three phenomena--the expansion of exploding
granules and the proper motions of the smaller dark structures,
respectively--can reach velocities close to the sound speed in the solar
photosphere. Another type of structure--narrow intergranular connections
between granules--has also been studied. Our results show that these
structures are real solar phenomena and are not caused by a variation
of the image quality. Therefore, in following and describing their
evolution, we try to find an explanation for their frequent occurrence.
Title: Interaction of Convective Structures with the Magnetic Field
of Solar Pores
Authors: Sobotka, M.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A.
Bibcode: 1999ASPC..184...60S
Altcode:
Time series of high-resolution white-light images of solar pores are
analyzed. Granular motions in the vicinity of pores are driven by
mesogranular flows: Motions toward the pore dominate in the 2 arcsec
zone around the pore boundary, while at larger distances the granules
move away from the pore. Triggered by these motions, small granules
and granular fragments located close to the pore border penetrate into
the pore, where they move inwards as short-lived bright features very
similar to umbral dots. The formation of a transitory penumbra-like
structure at the border of a large pore was observed simultaneously
with a temporary reorganization of adjacent granular field to expanding
elongated granules separated by dark filaments.
Title: Time Series of Solar Granulation Images. II. Evolution of
Individual Granules
Authors: Hirzberger, J.; Bonet, J. A.; Vázquez, M.; Hanslmeier, A.
Bibcode: 1999ApJ...515..441H
Altcode:
The properties of the evolution of solar granulation have been
studied using an 80 minute time series of high spatial resolution
white-light images obtained with the Swedish Vacuum Solar Telescope at
the Observatorio del Roque de los Muchachos, La Palma. An automatic
tracking algorithm has been developed to follow the evolution of
individual granules, and a sample of 2643 granules has been analyzed. To
check the reliability of this automatic procedure, we have manually
tracked a sample of 481 solar granules and compared the results of both
procedures. An exponential law gives a good fit to the distribution of
granular lifetimes, T. Our estimated mean lifetime is about 6 minutes,
which is at the lower limit of the ample range of values reported
in the literature. We note a linear increase in the time-averaged
granular sizes and intensities with the lifetime. T=12 minutes marks
a sizeable change in the slopes of these linear trends. Regarding
the location of granules with respect to the meso- and supergranular
flow field, we find only a small excess of long-lived granules in the
upflows. Fragmentation, merging, and emergence from (or dissolution
into) the background are the birth and death mechanisms detected,
resulting in nine granular families from the combination of these
six possibilities. A comparative study of these families leads to
the following conclusions: (1) fragmentation is the most frequent
birth mechanism, while merging is the most frequent death mechanism;
(2) spontaneous emergence from the background occurs very rarely,
but dissolution into the background is much more frequent; and (3)
different granular mean lifetimes are determined for each of these
families; the granules that are born and die by fragmentation have
the longest mean lifetime (9.23 minutes). From a comparison of the
evolution of granules belonging to the most populated families, two
critical values appear for the initial area in a granular evolution:
0.8 Mm2 (dg=1.39") and 1.3 Mm2
(dg=1.77"). These values mark limits characterizing the birth
mechanism of a granule, and predict its evolution to some extent. The
findings of the present work complement the earlier results presented
in this series of papers and reinforce with new inputs, as far as
the evolutionary aspects are concerned, the conclusion stated there
that granules can be classified into two populations with different
underlying physics. The boundary between these two classes could be
established at the scale of dg=1.4".
Title: Implementation of a Filter for the Restoration of Solar
Granulation Images
Authors: Sánchez Cuberes, M.; Bonet, J.; Vázquez, M.; Wittmann, A.
Bibcode: 1999ASPC..183..515S
Altcode: 1999hrsp.conf..515S
No abstract at ADS
Title: The Spectrum of Intensity Fluctuations Across Penumbral
Filaments
Authors: Sánchez Almeida, J.; Bonet, J.
Bibcode: 1999ASPC..183...87S
Altcode: 1999hrsp.conf...87S
No abstract at ADS
Title: Temporal Evolution of Fine Structures in and around Solar Pores
Authors: Sobotka, Michal; Vázquez, Manuel; Bonet, José Antonio;
Hanslmeier, Arnold; Hirzberger, Johann
Bibcode: 1999ApJ...511..436S
Altcode:
Time series of high-resolution white-light images of six solar pores,
observed in 1993 and 1995 at the Swedish Vacuum Solar Telescope (La
Palma), are analyzed. The pores constitute an almost ideal laboratory
in which to study the interaction of a vertical magnetic field with
surrounding convective motions, without the perturbation of the inclined
magnetic field in the penumbra. Umbral dots observed in a large (D=8.9")
pore are similar to those in mature umbrae, but they live longer, are
brighter, and have a higher filling factor. Granular motions in the
vicinity of pores are driven by mesogranular flows. Motions toward the
pore dominate in the 2" zone around the pore boundary, while at larger
distances the granules move away from the pore. Pushed by these motions,
small granules and granular fragments located close to the pore border
sometimes penetrate into the pore, where they move inward as bright
short-lived features very similar to umbral dots. The capture of bright
features by the pore is probably a microscale manifestation of the
``turbulent erosion,'' which results in the decay of the pore. Formation
of a transitory penumbra-like structure at the border of the large
pore was observed simultaneously with the appearance of expanding
elongated granules, separated by dark filaments, in an adjacent
granular field. These effects can be interpreted as a consequence of
emerging bipolar magnetic ``loops'' caused by a temporary protrusion
of opposite magnetic polarity.
Title: Time Evolution of Solar Granulation
Authors: Hirzberger, J.; Hanslmeier, A.; Bonet, J.; Vázquez, M.
Bibcode: 1999ASPC..183..507H
Altcode: 1999hrsp.conf..507H
No abstract at ADS
Title: Time Series of Solar Photospheric Spectrograms Bisector
Analysis
Authors: Hanslmeier, A.; Bonet, J.; Vázquez, M.
Bibcode: 1999ASPC..183..479H
Altcode: 1999hrsp.conf..479H
No abstract at ADS
Title: Granulation in active regions as compared to quiet regions
Authors: Hirzberger, J.; Bonet, J. A.; Vázquez, M.; Hanslmeier, A.;
Sobotka, M.
Bibcode: 1999AGAb...15...88H
Altcode: 1999AGM....15..P09H
A comparative study of the statistical properties of granulation
in active and quiet regions is performed. The analysis is based on a
high-resolution time series of simultaneous white light (lambda5425 Å)
and G-band (lambda 4308 Å) images obtained at the Swedish Vacuum Solar
Telescope, La Palma, Canary Islands. The G-band images have been used
to discern quiet and active regions in the field of view, whereas the
white-light images were taken to analyze the photometry, size and time
evolution of granules in regions of different magnetic activity. Power
spectra confirm that the granular size decreases with increasing G-band
brightness. Granules with diameters below 0''.8 are systematically
brighter in the abnormal granulation than in quiet regions. These
small and bright elements are embedded in a diffuse background of
approximately mean photospheric brightness covering all the fields of
abnormal granulation. The granular lifetime decreases with increasing
G-band brighness. The conclusions about the behaviour of the granulation
have been decontaminated of the influence of magnetic elements (the
so-called Bright Points), that have been separated using criteria
of size (d < 0''.5) and lifetime (T > 6 min). A significant
fraction of them are concentrated in regions of high G-band activity,
an emerging flux region, and the rest are m ainly aligned outlining a
cellular pattern (the magnetic network formed by supergranular motions).
Title: High Spatial Resolution Imaging in Solar Physics
Authors: Bonet, J. A.
Bibcode: 1999ASSL..239....1B
Altcode: 1999msa..proc....1B
Physical processes in the Sun give rise to an ample variety of
structures on different spatial scales that in many cases are very
small, with sizes probably below the resolution limit of existing
solar telescopes (see Sánchez Almeida, 1997; Sánchez Almeida and
Bonet, 1997). Thus, the interpretation of solar phenomena requires
the study of these structures, and consequently high spatial
resolution observations are necessary to understand the physics
of the Sun. These observations must be complemented by an equally
important high-resolution spectroscopic analysis, including polarimetric
measurements to determine the magnetic field strength (magnetic fields
have a pervasive influence on the physical events in the Sun). However,
in the present study we shall concentrate on the first aspect of the
observational process, i.e. we shall describe some of the tools and
resources available for producing high spatial resolution images.
Title: The Spectrum of Fluctuations across Penumbral Filaments
Authors: Sánchez Almeida, J.; Bonet, J. A.
Bibcode: 1998ApJ...505.1010S
Altcode:
We estimate the typical spectrum of spatial fluctuations of intensity
due to the penumbral filaments. High angular resolution continuum
images are used (cut-off frequencies equivalent to 0.28" wavelength
of about 5257 Å). The amplitude of the observed spectra follows the
modulation transfer function of our optical system. In other words,
the spectrum of real penumbral fluctuations seems to be flat up to the
higher observable spatial frequency. We expect it to continue far beyond
the artificial instrumental cutoff, which implies that the structure
of the penumbra remains unresolved to the present solar observations.
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.
Bibcode: 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: Centre-To-Limb Variation of the Solar Granulation
Authors: Sánchez Cuberes, M.; Bonet, J. A.; Vázquez, M.; Wittmann,
A. D.
Bibcode: 1998Ap&SS.263..343S
Altcode: 1999Ap&SS.263..343S
An excellent series of images of solar granulation was taken during
the partial solar eclipse of 1994 May 10 at the Swedish Vacuum Solar
Telescope at Roque de los Muchachos Observatory. Making use of the
lunar limb profile, images at different heliocentric positions were
corrected for instrumental and atmospheric effects. The centre-to-limb
variation of the granulation contrast was calculated and compared with
previous determinations.
Title: On the Intensity Thresholds of the Network and Plage Regions
Authors: Steinegger, Michael; Bonet, Jose A.; Vázquez, Manuel;
Jiménez, Antonio
Bibcode: 1998SoPh..177..279S
Altcode:
A period of minimum solar activity in April and May 1996 was used to
analyze full-disk CaK spectroheliograms with the aim of deriving the
intensity thresholds of the quiet network and the plages by applying
the so-called inflexion point method. The average network intensity
threshold is found to be influenced mainly by the seeing, whereas the
average plage threshold shows an increasing trend from disk center
towards the solar limb. Both parameters are compared with the results
of other authors.
Title: On the Intensity Thresholds of the Network and Plage Regions
Authors: Steinegger, Michael; Bonet, Jose A.; Vázquez, Manuel;
Jiménez, Antonio
Bibcode: 1998sers.conf..279S
Altcode:
No abstract at ADS
Title: Time Series of Solar Granulation Images. I. Differences
between Small and Large Granules in Quiet Regions
Authors: Hirzberger, J.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A.;
Sobotka, M.
Bibcode: 1997ApJ...480..406H
Altcode:
A 90 minute time series of high spatial resolution white-light images
of solar granulation, obtained at the Swedish Vacuum Solar Tower
(Observatorio del Roque de los Muchachos, La Palma), was analyzed
to study how the physical properties of the granules changed with
size. The observational material was corrected for global motions and
for the instrumental profile, and a subsonic filter was applied. A
definition of granular border was adopted using the inflection points
of the intensity of the images, and the granular cells were defined
as areas including, in addition to the granules, one-half of their
surrounding intergranular lanes. Using time series to investigate the
average behavior of solar granulation has three strong advantages:
the first is the possibility of removing the acoustic waves; second,
the possibility of estimating the effect of the variability of
seeing on our results; and, third, the opportunity to attain high
statistical significance in the analysis as a result of the large
number of extracted granules (61,138). It is shown that the
granules of the sample can be classified according to their mean
and maximum intensities and their fractal dimension into two regimes,
with diameters smaller than and larger than 1.4", respectively. A broad
transition region in which both regimes coexist was found. The resolved
internal brightness structure of both the granules and the intergranular
lanes shows a linear increase of the number of substructures with the
granular and intergranular areas. The diameters of these substructures
range between our effective resolution limit (~0.3") and ~1.5",
with preferential sizes at 0.65" and 0.55", respectively. Moreover,
it seems that large and small granules are unevenly distributed with
respect to the large-scale vertical flows. Thus smaller granules are
more concentrated along downdrafts whereas larger ones preferentially
occupy the updrafts. Finally, a physical scenario compatible with the
existence of these two granular populations is discussed.
Title: Simulation of Seeing Influences on the Photometric
Determination of Sunspot Areas
Authors: Steinegger, Michael; Bonet, José A.; Vázquez, Manuel
Bibcode: 1997SoPh..171..303S
Altcode:
Various methods for measuring areas of sunspots and umbrae are compared
to test their robustness against changing seeing conditions. The
influence of the seeing is simulated by artificially degrading
high-resolution sunspot images. A new procedure - the so-called
inflexion point method - for area determinations is described. It
is based on the calculation of the inflexion point contours of the
two-dimensional sunspot intensity distribution. The areas derived with
this method are much more stable against seeing influences than those
obtained by the other procedures tested. The effect of the seeing on
the measurements of the bolometric sunspot contrast and irradiance
deficit produced by a sunspot is also studied.
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.
Bibcode: 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: A new method for the photometric determination of umbral and
total sunspot areas.
Authors: Steinegger, M.; Bonet, J. A.; Vázquez, M.
Bibcode: 1997joso.proc...89S
Altcode:
No abstract at ADS
Title: Time evolution of solar granulation phenomena.
Authors: Hirzberger, J.; Bonet, J. A.; Hanslmeier, A.; Vázquez, M.;
Sobotka, M.
Bibcode: 1996AGAb...12..160H
Altcode:
No abstract at ADS
Title: On the Energy Balance of Solar Active Regions
Authors: Steinegger, Michael; Vazquez, Manuel; Bonet, Jose A.; Brandt,
Peter N.
Bibcode: 1996ApJ...461..478S
Altcode:
Ground-based observations of the sunspot irradiance deficit Ψ
and the excess by facular regions in the period 1989 June 3-15 are
analyzed using photometric techniques. The results are compared with
solar irradiance measurements taken by the Nimbus 7 satellite. The
photographic sunspot data were obtained at the Vakuum Newton
Teleskop, Observatorio del Teide (Tenerife), and the information on
facular emission was derived by means of a "proxy" method from the
analysis of full-disk Ca II K spectroheliograms taken at Sacramento
Peak Observatory. The first part of the observing period was
characterized by a rather constant activity with sunspot groups of
small and medium size, whereas the second part (from June 8 onward)
exhibited a drastic increase of activity, dominated by the appearance
of the large group NOAA 5528. By increasing the pixel size of
the digitized photographic data, the influence of the variable spatial
resolution on the measurements is simulated. Above a certain threshold,
the bolometric sunspot contrast falls and the spot area grows; however,
the resulting influence on the sunspot deficit Ψ and the corresponding
umbral parameters (area, contrast, and deficit) is negligible. Data of areas of sunspot groups (total and umbral) from different
observatories are compared with our measurements. Total areas show
similar values, but umbral areas from our measurements are clearly
larger than those estimated from full-disk images, like those from the
Debrecen and San Fernando Observatories. Analyzing the data of
single spots, we confirm earlier findings, namely, that the bolometric
contrast is lower than 0.32, the standard value used in the calculation
of the photometric sunspot index, and we report that small spots exhibit
smaller bolometric contrasts than larger ones. The intensity minimum
of the spots is a very appropriate parameter to describe their global
thermal properties; it is linearly proportional to the total (α) and
umbral (αμ) bolometric contrasts and also correlates with
the maximum strength of the magnetic field of the spots and with the
spot's size. The energy balance of individual active regions seems
to depend mainly on the area ratio of the plage and the corresponding
sunspot group. The different rates at which these areas change produces
the temporal evolution of the energy balance. The daily variations
of the global activity indices radio flux at 10.7 cm, Mg II core-to-wing
ratio, and the average magnetic field are well correlated with the
fluctuations of irradiance and the spot deficit Ψ. But on the other
hand, the equivalent width of the He I λ10830 line and the coronal
index do not follow this behavior. The irradiance fluctuations,
as measured by Nimbus 7, can be modeled to within 60 parts per million
(ppm) using only our ground-based determination of Ψ and Φ. By adding
the sunspot deficit Ψ to the irradiance fluctuations, the result
is modeled to within 25 ppm using an empirical law that combines our
Φ with a set of global activity indices. After correcting the
irradiance measurements for the facular Φ and spot Ψ contributions,
a residual remains with an apparent periodicity of 6 days. Different
sources to explain this variability are discussed and the importance
of an adequate determination of the threshold of Ca II K brightness
for the calculation of Φ is explained.
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.
Bibcode: 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: Numerical modelling of spectral line asymmetries in
photospheric structures. II. Plage regions.
Authors: Marquez, I.; Bonet, J. A.; Vazquez, M.
Bibcode: 1996A&A...306..305M
Altcode:
A numerical code has been developed for modelling the asymmetries in
three spectral lines (K I 7699, Fe I 5576 and Fe I 5635A) formed at
different photospheric heights and observed in plage regions near the
solar disk center. The aim of this work was to reproduce the absolute
line bisectors obtained from low resolution observations. The mere
insertion of a flux tube in a model of quiet granulation, without
mutual interaction, has proved insufficient to explain many of
the observational results. Therefore, several models of abnormal
granulation close to the tube, representing the influence of the
magnetic field, are considered. The code consists of two computation
modules, one representing a model of the unperturbed photosphere,
and the other including a flux tube inserted in a model of altered
granulation; various combinations of both computation modules allow
different values of the magnetic filling factor to be simulated. The
influence of other physical parameters and observational aspects
on the bisector is also discussed, e.g. waves, microturbulence,
defective time or spatial averages, etc. The proposed model reproduces
the observed variation in the shape and in the absolute shift of the
bisector when the filling factor increases. Likewise, the computed
spatial distribution of intensity in the continuum fits many of the
photometric results reported in the literature for plage regions.
Title: Numerical modelling of spectral line asymmetries in
photospheric structures. I. Quiet Sun.
Authors: Marquez, I.; Bonet, J. A.; Vazquez, M.; Woehl, H.
Bibcode: 1996A&A...305..316M
Altcode:
Modelling of asymmetries in spectral lines with different formation
heights (K I 7699, Fe I 5576 and Fe I 5635A), observed in the quiet Sun
at the disk center, has been performed with the aim of reproducing the
absolute line bisectors obtained from low resolution observations. The
influence of a number of physical and observational factors on the
bisector shape and line shifts, acting together or separately, is
discussed, e.g. mesogranular flows, waves, microturbulence, defective
temporal and spatial averages, etc. The simulations are based on the
VAL-C model (Vernazza et al. 1981) representing the mean photosphere,
and the granular model by Nelson (1978). Following evidence in the
literature, the best match to the observed absolute mean bisectors
is obtained by including in the numerical code a gravity wave and
a strengthening of the microturbulence in the lower layers of the
intergranule.
Title: On the Dynamics of Bright Features in Sunspot Umbrae
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel; Hanslmeier,
Arnold
Bibcode: 1995ApJ...447L.133S
Altcode:
Time series of white-light pictures of the sunspot NOAA 7522, obtained
at the Swedish Vacuum Solar Telescope (La Palma), were analyzed
to study the proper motion of bright features in sunspots. For the
first time, its relation with the dark nuclei present in the umbra is
investigated. The bright features are visible in the penumbra as bright
grains moving into the umbra. A few of them cross the penumbra/umbra
boundary, becoming peripheral umbral dots, which move farther into
the umbra until they meet dark nuclei, braking their motion and
disappearing. In some cases the encounter with a dark nucleus produces
a brightening of the central umbral dots placed on the opposite side
of the nucleus. A similar phenomenon is observed in the grains of a
faint light bridge, when bright penumbral grains collide with one of
the edges of the bridge.
Title: Photometry of sunspot pores from partial eclipse observations.
Authors: Bonet, J. A.; Sobotka, M.; Vazquez, M.
Bibcode: 1995A&A...296..241B
Altcode:
White-light images, centered at λ6708A, were obtained at the Swedish
Solar Telescope, La Palma, on occasion of the 1994 May 10 partial solar
eclipse. From the recorded information, 5 frames showing several pores
together with the moon's limb were selected for detailed photometric
analysis. The observed intensity profile of the moon's limb projected
against the solar disk was used to derive, from each frame, the
Point Spread Function of the atmosphere + instrument to restore the
images. The characteristics of the obtained PSFs -low noise and precise
determination of the wings far away from the core- enabled us to avoid
arbitrary assumptions about analytical approximations. The FWHM of these
functions was typically 0.47". Several bright features were identified
in one of the pores. After determining the photometric parameters of
these fine umbral structures their link with the population of the
bright features in the umbra of evolved spots is discussed in the
framework of the dependence of sunspot properties on the spot size.
Title: Area and intensity distribution in solar granulation
Authors: Hirzberger, J.; Hanslmeier, A.; Bonet, J. A.; Vázquez, M.
Bibcode: 1995IAUS..176P.114H
Altcode:
No abstract at ADS
Title: A High-Resolution Study of the Structure of Sunspot Light
Bridges and Abnormal Granulation
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel
Bibcode: 1994ApJ...426..404S
Altcode:
Strong light bridges (SLBs) represent an abrupt change in the physical
conditions of sunspot umbrae. They divide the umbra into separate units
(fragments, umbral cores) and very often show a granular structure. A
photometric and spectroscopic study of SLBs, and also of abnormal
granulation (AG) in a region of pores, is presented. Slit-jaw images
(bandpass 5425 +/- 50 A) and spectra (line Fe I 5434.5 A), with a
spatial resolution of 0.3 sec, were acquired during the period 1991 July
1-10 at the Swedish Solar Telescope at the Observatorio del Roque de
los Muchachos (La Palma). The power spectra of intensity fluctuations
in the slit-jaw images, were used as the primary diagnostic tool,
complemented by the analysis of line profiles. The following results
were obtained. 1. The structures present in SLBs and AG are generally
smaller than the granules in the quiet photosphere. The typical size
of SLB granules is 1.2 sec (in quiet granulation, 1.5 sec). In AG, the
distribution of power is more complex and is characterized by peaks
corresponding to scales of 2.5 sec, 1.3 sec, and 0.64 sec. 2. SLB
and AG power spectra show an excess of power (compared to quiet
granulation) at scales of 0.5 sec. This power enhancement reflects
the presence of small bright grains, clearly visible in SLBs and AG,
with a mean nearest neighbor distance of 0.5 sec. 3. Two of these small
bright grains, together with a dark lane between them, were resolved
spectroscopically in a SLB. The line shifts and bisector shapes suggest
a convective origin of these structures. 4. The SLB power spectra in
the log P/log k scale indicate the presence of a Kolmogorov turbulent
cascade in the structures between 1.7 sec and 0.64 sec. However, the
small bright grains do not pertain to the turbulent cascade. They
are particular phenomena, probably with a convective origin. The
power spectrum of AG does not give any indication of the presence of
a turbulent cascade. 5. Small bright features (umbral dots or bright
grains) can be found in unbral cores, light bridges, and AG regions as
well. <Their mean nearest neighbor distance, in the observed areas,
decreases with increasing brightness and decreasing magnetic field
strength. &We thus propose that they are a manifestation of altered
convection, which is modulated and maintained by the magnetic field.
Title: Spatially highly resolved time series of solar granulation
spectra.
Authors: Hanslmeier, A.; Bonet, J. A.; Vazquez, M.
Bibcode: 1994AGAb...10..114H
Altcode:
No abstract at ADS
Title: Active Compensation of Global Wavefront Tilts at Solar
Telescopes: Present Status of an Electronic Development
Authors: Ballesteros, E.; Viera, T.; Lorenzo, F.; Reyes, M.; Bonet,
J. A.; Martin, C.
Bibcode: 1994ASIC..423..249B
Altcode: 1994aoa..conf..249B
No abstract at ADS
Title: Strong light bridges and abnormal granulation
Authors: Sobotka, M.; Bonet, J. A.; Vázquez, M.
Bibcode: 1994smf..conf..197S
Altcode:
No abstract at ADS
Title: A Solar Correlation Tracker Using a Video Motion Estimation
Processor
Authors: Ballesteros, E.; Bonet, J. A.; Martin, C.; Fuentes, F. J.;
Lorenzo, F.; Manescau, A.; Viera, T.; Diaz, J. J.; Joven, E.
Bibcode: 1993rtpf.conf...44B
Altcode:
No abstract at ADS
Title: A High-Resolution Study of Inhomogeneities in Sunspot Umbrae
Authors: Sobotka, Michal; Bonet, Jose A.; Vazquez, Manuel
Bibcode: 1993ApJ...415..832S
Altcode:
A detailed study of the brightness, size, spatial distribution,
and filling factor of the different umbral inhomogeneities is
presented. Many sunspots show multiple umbrae (separated by strong
light bridges, SLBs), which behave like independent units. These are
termed umbral cores (UCs). From the phenomenological point of view, UCs
show two components: (1) a dark area, formed by a diffuse background
(DB), with local intensity minima called dark nuclei (DNs), and (2)
bright features including umbral dots (UDs) and faint light bridges
(FLBs). Slit-jaw images (bandpass 5425±50 Å) and spectra
(line Fe I 5434.5 Å) of seven sunspots with 13 separate UCs were
acquired using the Swedish Solar Telescope at the Observatorio
del Roque de los Muchachos (La Palma) with a spatial resolution of
0".3. Image restoration and inversion of the spectral line profile
were applied, with the following results: The most important
photometric parameter of the UCs is the mean intensity of their DB
(mean background intensity ‾Iback). It is well correlated
to the intensity minimum of the diffuse background and to the mean
brightness of UDs. The relation between the size of the UCs and their
‾Iback is not straightforward, but UCs with radii <5"
are in general brighter than the larger ones. The differences in the
brightness of individual umbrae can be explained mainly by variations
of ‾Iback rather than in terms of variations of UD filling
factor. The linear relation between the peak intensity of UDs
and the intensity of the adjacent DB (local background intensity)
was confirmed in a sample of more than 1500 elements, and the
"true" peak-to-background ratio was estimated as 3. The spatial
distribution of UDs is nonuniform. In DNs (whose size is comparable to
that of photospheric granules) UDs appear very rarely; they prefer to
form clusters and alignments outside the DNs. The mean nearest neighbor
distance decreases, and the density of UDs increases with increasing
‾Iback. The filling factor of UDs is in the range 3%-10%,
and the size of UDs is similar in all UCs. The typical "true" size is
180-300 km, and it is uncorrelated to the peak brightness of UDs. FLBs are composed of bright grains and dark spaces between them. The
bright grains are darker than photospheric granules. The size of the
bright grains is similar to that of UDs, and their relative area in
FLBs is very close to the fractional area granulum-intergranulum in the
quiet photosphere. On the basis of the obtained spectral profiles,
working models of temperature stratification are presented for UDs,
their adjacent DB, and DNs. On the basis of observational facts
the following is proposed: UDs and FLBs are probably demonstrations
of some kind of altered convection, with a cell size of about 0".5,
modulated by a smoothly varying magnetic field.
Title: High Resolution Observations of Umbral Fine Structure
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
Bibcode: 1993ASPC...46...20S
Altcode: 1993mvfs.conf...20S; 1993IAUCo.141...20S
No abstract at ADS
Title: Spectroscopic determination of intensities of umbral bright
features and adjacent background
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
Bibcode: 1992A&A...260..437S
Altcode:
Profiles of the Na I D doublet in three bright features (clusters
of umbral dots), located in a relatively dark umbra, were analyzed
by means of the 'local two-component modeling' to obtain the 'true'
continuum intensities and temperatures of the bright features and
their dark surroundings (background). The intensities of two central
and one peripheral bright feature were 0.31 (background 0.11), 0.33
(0.13), and 0.40 (0.17), respectively. For the ratio of the object and
background intensity (assumed to be constant, but unknown until now)
the value of 2.6 +/- 0.2 was obtained.
Title: On the relation between the intensities of bright features
and the local background in sunspot umbrae
Authors: Sobotka, M.; Bonet, J. A.; Vazquez, M.
Bibcode: 1992A&A...257..757S
Altcode:
A photometric study of umbral bright features (umbral dots, clusters
of umbral dots, bright grains of light bridges) in sunspots is
presented. It is based on white-light images taken with a CCD video
camera driven by an automatic image selection system. A direct linear
relation between the observed brightness of the features and that
of the surrounding background areas has been found. To eliminate the
influence of the seeing on this result, the radiative fluxes, which
are much less sensitive to the image degradation, have been examined
and an analogous relation has been found. Finally, a possible physical
explanation is suggested.
Title: A possible correlation tracker for LEST.
Authors: Bonet, J. A.; Martin, C.; Ballesteros, E.; Fuentes, F. J.;
Lorenzo, F.; Manescau, A.; Rodriguez, L. F.; Zadrozny, A.
Bibcode: 1992LFTR...51.....B
Altcode:
This document presents a proposal for the design of the LEST correlation
tracker prototype. The proposed correlator, based on the absolute
differences algorithm, is built around the LSI L64720 (Video Motion
Estimation Processor) chip. The performances of the tracker system are
established according to the LEST specifications and the experience
derived from similar programmes. The design for the optomechanical
support system to test the correlation tracker is also included.
Title: A Possible Correlation Tracker for lest
Authors: Bonet, J. A.; Martin, C.; Ballesteros, E.; Fuentes, F. J.;
Lorenzo, F.; Manescau, A.; Rodriguez, L. F.; Zadrozny, A.
Bibcode: 1992lest.rept....1B
Altcode:
No abstract at ADS
Title: Asymmetries and shifts of the solar K I 7699 A line and
possible evidence for gravity waves in the quiet photosphere
Authors: Bonet, J. A.; Marquez, I.; Vazquez, M.; Woehl, H.
Bibcode: 1991A&A...244..492B
Altcode:
A computing code has been developed to simulate the center-to-limb
variation (CLV) of the bisector's shape, and absolute wavelength
shift of the core in strong photospheric lines. Observational results
concerning these aspects are also reported for the K I 7699 line. In
the numerical simulation, granulation is represented, as a first
approximation, by means of the granular model by Nelson (1978). It
appears that granulation alone does not reproduce the observations and
thus some modification has to be implemented in the dynamical model
employed. A good match to the observed CLV of the wavelength shift
of the line core is achieved by adding two 8-min period gravity waves
with horizontal wavelength of the granular scale, the only difference
between them being the sign of their horizontal wavenumber. Changes
in the phase difference between the oscillating parameters have a
decisive influence on the result.
Title: The Limb Effect of the KI 769. 9 nm Line in Quiet Regions
Authors: Bonet, J. A.; Marquez, I.; Vázquez, M.
Bibcode: 1989ASIC..263..299B
Altcode: 1989ssg..conf..299B
No abstract at ADS
Title: Temporal and center-to-limb variations of the K I 769.9 NM
line profiles in quiet and active solar regions
Authors: Bonet, J. A.; Marquez, I.; Vazquez, M.; Woehl, H.
Bibcode: 1988A&A...198..322B
Altcode:
The temporal and spatial behaviour of the K I 769.9 nm solar line are
investigated using several series of high spectral resolution low-noise
photoelectric scans obtained at Kitt Peak National Observatory in
quiet and active (plages and sunspots) regions. Corrections due
to the instrumental profile were applied to yield the best line
shape. A systematic center-to-limb investigation of the behaviour
of the line shape was performed in quiet regions. Power and phase
spectra of the main parameters defining the line shape have also
been determined. Within several umbrae at different cos θ positions,
an inverse C-shape or even an "S"-shape of the bisectors was found.
Title: Center-to-Limb Variation of the Asymmetries of the K 7699 Å
line in Solar Quiet and Active Regions
Authors: Bonet, J. A.; Marquez, I.; Vázquez, M.; Wöhl, H.
Bibcode: 1987rfsm.conf...32B
Altcode:
No abstract at ADS
Title: On the Width Distribution of Penumbral Filaments in Sunspots
Authors: Bonet, J. A.; Ponz, J. D.; Vazquez, M.
Bibcode: 1982SoPh...77...69B
Altcode:
The mean width and distribution of penumbral filaments of a sunspot have
been estimated, using white light photographs obtained with a vacuum,
Newtonian type, telescope. Three areas corresponding to the penumbra
of a sunspot have been analysed. Data were collected during the solar
eclipse of June 1973. The photometric profiles of the Moon limb over the
photosphere have been analysed to obtain useful information on both,
atmospheric and instrumental perturbation on each exposure. The mean
value of the width of penumbral filaments is 0.37 arc sec.
Title: Aspectos magneticos de la evolucion de las manchas solares.
Authors: Casanovas, J.; Vazquez, M.; Bonet, J. A.
Bibcode: 1974UrBar..59...79C
Altcode:
The spectroscopic determinations of the solar magnetic fields are based
on the Zeeman effect observed in relation to a number of absorption
lines of the solar spectrum. It is attempted to deduce indirectly
certain characteristics of the magnetic field in a sunspot, giving
attention to morphological aspects and the magnetic polarities. The
results of the investigation are illustrated with the aid of a number
of pictures.