Author name code: hirzberger
ADS astronomy entries on 2022-09-14
author:"Hirzberger, Johann"
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Title: The on-ground data reduction and calibration pipeline for
SO/PHI-HRT
Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez,
D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero,
A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero,
L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del
Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama,
J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez,
M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico,
G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.;
Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López
Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.;
Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub,
J.; Strecker, H.; Torralbo, I.; Valori, G.
Bibcode: 2022arXiv220814904S
Altcode:
The ESA/NASA Solar Orbiter space mission has been successfully launched
in February 2020. Onboard is the Polarimetric and Helioseismic Imager
(SO/PHI), which has two telescopes, a High Resolution Telescope
(HRT) and the Full Disc Telescope (FDT). The instrument is designed
to infer the photospheric magnetic field and line-of-sight velocity
through differential imaging of the polarised light emitted by the
Sun. It calculates the full Stokes vector at 6 wavelength positions
at the Fe I 617.3 nm absorption line. Due to telemetry constraints,
the instrument nominally processes these Stokes profiles onboard,
however when telemetry is available, the raw images are downlinked and
reduced on ground. Here the architecture of the on-ground pipeline
for HRT is presented, which also offers additional corrections not
currently available on board the instrument. The pipeline can reduce
raw images to the full Stokes vector with a polarimetric sensitivity
of $10^{-3}\cdot I_{c}$ or better.
Title: The essential role of Earth-Sun L4 in solar particle event
forecasting for Lunar and Mars exploration
Authors: Posner, Arik; Toit Strauss, Du; Solanki, Sami K.; Effenberger,
Frederic; Gandorfer, Achim; Hirzberger, Johann; Kühl, Patrick; Heber,
Bernd; Malandraki, Olga; Folta, David; Jones, Sarah; Arge, Charles;
Sterken, Veerle; Henney, Carl J.; Staub, Jan; Hatten, Noble; Stcyr,
O. Chris
Bibcode: 2022cosp...44.1157P
Altcode:
We learned from the STEREO mission that solar particle events
originating from behind the west limb of the Sun, i.e., out of view
from Earth, make up about 30 percent of those significantly affecting
Earth's vicinity and thus could endanger human exploration of the
Moon. The Earth-Sun Lagrangian point 4 is a meta-stable location at 1
au from the Sun, 60° ahead of Earth's orbit. L4 has an uninterrupted
view of the solar photosphere centered on W60, the Earth's nominal
magnetic field connection to the Sun. The role of L4 observations
for improving several existing short-term SEP forecasting techniques,
including protons, ESPERTA, UMASEP and pps, for Lunar exploration will
be highlighted. We can show that BFO dose savings from short-term
solar energetic particle forecasts are critically important in a
worst-case scenario. Placing a mission at L4 is even a precondition
for any SEP all-clear forecasting for Lunar exploration. Furthermore,
we analyzed example trajectories of short-term Mars round trips that
may be considered for future human exploration of Mars and find that
L4-based SWx observations would have relevance for protecting Mars
explorers from radiation exposure.
Title: The magnetic drivers of campfires seen by the Polarimetric
and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
Bibcode: 2022A&A...660A.143K
Altcode: 2022arXiv220213859K
Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
(SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
termed campfires, that have been proposed to be brightenings near the
apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
magnetic processes driving these campfires are not understood.
Aims: During the cruise phase of SO and at a distance of 0.523
AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
offering the possibility to investigate the surface magnetic field
dynamics underlying campfires at a spatial resolution of about 380
km.
Methods: We used co-spatial and co-temporal data of the
quiet-Sun network at disc centre acquired with the High Resolution
Imager of SO/EUI at 17.4 nm (HRIEUV, cadence 2 s) and the
High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
min). Campfires that are within the SO/PHI−SO/EUI common field
of view were isolated and categorised according to the underlying
magnetic activity.
Results: In 71% of the 38 isolated events,
campfires are confined between bipolar magnetic features, which seem to
exhibit signatures of magnetic flux cancellation. The flux cancellation
occurs either between the two main footpoints, or between one of the
footpoints of the loop housing the campfire and a nearby opposite
polarity patch. In one particularly clear-cut case, we detected the
emergence of a small-scale magnetic loop in the internetwork followed
soon afterwards by a campfire brightening adjacent to the location
of the linear polarisation signal in the photosphere, that is to
say near where the apex of the emerging loop lays. The rest of the
events were observed over small scattered magnetic features, which
could not be identified as magnetic footpoints of the campfire hosting
loops.
Conclusions: The majority of campfires could be driven
by magnetic reconnection triggered at the footpoints, similar to the
physical processes occurring in the burst-like EUV events discussed
in the literature. About a quarter of all analysed campfires, however,
are not associated to such magnetic activity in the photosphere, which
implies that other heating mechanisms are energising these small-scale
EUV brightenings.
Title: Disambiguation of Vector Magnetograms by Stereoscopic
Observations from the Solar Orbiter (SO)/Polarimetric and Helioseismic
Imager (PHI) and the Solar Dynamic Observatory (SDO)/Helioseismic
and Magnetic Imager (HMI)
Authors: Valori, Gherardo; Löschl, Philipp; Stansby, David; Pariat,
Etienne; Hirzberger, Johann; Chen, Feng
Bibcode: 2022SoPh..297...12V
Altcode: 2021arXiv211210650V
Spectropolarimetric reconstructions of the photospheric vector magnetic
field are intrinsically limited by the 180∘ ambiguity
in the orientation of the transverse component. The successful
launch and operation of Solar Orbiter have made the removal of
the 180∘ ambiguity possible using solely observations
obtained from two different vantage points. While the exploitation
of such a possibility is straightforward in principle, it is less so
in practice, and it is therefore important to assess the accuracy
and limitations as a function of both the spacecrafts' orbits and
measurement principles. In this work, we present a stereoscopic
disambiguation method (SDM) and discuss thorough testing of its
accuracy in applications to modeled active regions and quiet-Sun
observations. In the first series of tests, we employ magnetograms
extracted from three different numerical simulations as test fields
and model observations of the magnetograms from different angles and
distances. In these more idealized tests, SDM is proven to reach a 100%
disambiguation accuracy when applied to moderately-to-well resolved
fields. In such favorable conditions, the accuracy is almost independent
of the relative position of the spacecraft with the obvious exceptions
of configurations where the spacecraft are within a few degrees of
co-alignment or quadrature. Even in the case of disambiguation of
quiet-Sun magnetograms with significant under-resolved spatial scales,
SDM provides an accuracy between 82% and 98%, depending on the field
strength. The accuracy of SDM is found to be mostly sensitive to the
variable spatial resolution of Solar Orbiter in its highly elliptic
orbit, as well as to the intrinsic spatial scale of the observed
field. Additionally, we provide an example of the expected accuracy as
a function of time that can be used to optimally place remote-sensing
observing windows during Solar Orbiter observation planning. Finally,
as a more realistic test, we consider magnetograms that are obtained
using a radiative-transfer inversion code and the SO/PHI Software
siMulator (SOPHISM) applied to a 3D-simulation of a pore, and we
present a preliminary discussion of the effect of the viewing angle
on the observed field. In this more realistic test of the application
of SDM, the method is able to successfully remove the ambiguity in
strong-field areas.
Title: Solar Surface Stereoscopy with Solar Orbiter's Polarimetric
Helioseismic Imager (SO/PHI)
Authors: Romero Avila, Amanda; Inhester, Bernd; Hirzberger, Johann;
Solanki, Sami
Bibcode: 2021AGUFMSH25B2095R
Altcode:
A compound method for a stereoscopic analysis of the height variations
in the solar photosphere is presented. This method allows to estimate
relevant quantities (i.e. the Wilson depression) and to study structures
in the solar photosphere and within sunspots. We will demonstrate
the feasibility of the method using simulated Stokes I continuum
observations derived from a radiative transfer model using the plasma
properties of a MHD simulation of the solar surface. The large scale
variations in our method are estimated by shifting and correlating
two signals of the same region as observed from two different view
directions. This result is then introduced as an initial height estimate
in a least squares optimization algorithm in order to reproduce smaller
scale structures. This method has been developed to be applied to the
high resolution images of the PHI instrument on board Solar Orbiter or
similar instruments on other Sun-observing spacecraft. It will allow
to perform direct stereoscopic studies of solar surface observations
in different wavelengths of the solar spectrum. Preliminary results,
advantages and limitations, applications and particular considerations
for PHI data will be discussed.
Title: A Multi-Purpose Heliophysics L4 Mission
Authors: Posner, A.; Arge, C. N.; Staub, J.; StCyr, O. C.; Folta,
D.; Solanki, S. K.; Strauss, R. D. T.; Effenberger, F.; Gandorfer,
A.; Heber, B.; Henney, C. J.; Hirzberger, J.; Jones, S. I.; Kühl,
P.; Malandraki, O.; Sterken, V. J.
Bibcode: 2021SpWea..1902777P
Altcode:
The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from
the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of
the solar photosphere centered on W60, the Earth's nominal magnetic
field connection to the Sun. Such a mission on its own would serve
as a solar remote sensing observatory that would oversee the entire
solar radiation hemisphere with significant relevance for protecting
Moon and Mars explorers from radiation exposure. In combination with
appropriately planned observatories at L1 and L5, the three spacecraft
would provide 300° longitude coverage of photospheric magnetic field
structure, and allow continuous viewing of both solar poles, with
>3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun
with a 7.2° inclination out of the heliographic equator, 14.5° out of
the ecliptic plane. We discuss the impact of extending solar magnetic
field observations in both longitude and latitude to improve global
solar wind modeling and, with the development of local helioseismology,
the potential for long-term solar activity forecasting. Such a mission
would provide a unique opportunity for interplanetary and interstellar
dust science. It would significantly add to reliability of operational
observations on fast coronal mass ejections directed at Earth and
for human Mars explorers on their round-trip journey. The L4 mission
concept is technically feasible, and is scientifically compelling.
Title: The magnetic fine structure of the Sun's polar region as
revealed by Sunrise
Authors: Prabhu, A.; Lagg, A.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2020A&A...644A..86P
Altcode:
Context. Polar magnetic fields play a key role in the solar magnetic
cycle and they are the source of a significant portion of the
interplanetary magnetic field. However, observations of the poles
are challenging and hence our understanding of the polar magnetic
environment is incomplete.
Aims: We deduce properties of
small-scale magnetic features in the polar region using high-resolution
data and specifically aim to determine the flux per patch above which
one magnetic polarity starts to dominate over the other.
Methods:
We study the high spatial resolution, seeing-free observations of the
north solar polar region, obtained with the IMaX instrument on-board
the balloon-borne SUNRISE observatory during June 2009, at the solar
activity minimum. We performed inversions of the full Stokes vector
recorded by IMaX to retrieve atmospheric parameters of the Sun's
polar region, mainly the temperature stratification and the magnetic
field vector.
Results: We infer kilo-Gauss (kG) magnetic fields
in patches harbouring polar faculae, without resorting to a magnetic
filling factor. Within these patches we find the maxima of the magnetic
field to be near the dark narrow lanes, which are shifted towards the
disc centre side in comparison to the maxima in continuum intensity. In
contrast, we did not find any fields parallel to the solar surface
with kG strengths. In addition to the kG patches, we found the polar
region to be covered in patches of both polarities, which have a range
of sizes. We find the field strength of these patches to increase with
increasing size and flux, with the smaller patches showing a significant
dispersion in field strength. The dominating polarity of the north
pole during this phase of the solar cycle is found to be maintained
by the larger patches with fluxes above 2.3 × 1017 Mx.
Title: Multi-view magnetic synoptic maps with SO/PHI and SDO/HMI
Authors: Löschl, P.; Hirzberger, J.; Schou, J.; Solanki, S. K.
Bibcode: 2020AGUFMSH0360028L
Altcode:
With the recent launch of Solar Orbiter (SO) and the first data slowly
becoming available, it will soon be possible to simultaneously observe
the Sun from additional vantage points off the Earth-Sun line. One
of its instruments, the Polarimetric and Heliospheric Imager (PHI),
is the first spectro-polarimeter to operate outside of this line of
sight. This opens the possibility for joint observational campaigns
with similar instruments, such as the Heliospheric and Magnetic Imager
(HMI) on-board the Solar Dynamics Observatory (SDO). We utilise these
new observational possibilities to produce combined magnetic synoptic
maps from magnetograms of the PHI and HMI instruments. Building on the
existing software infrastructure for HMI synoptic maps, we extended
its current functionality to include PHI data and correct for the
different and varying relative orbital characteristics of the two
spacecraft. The result are joint magnetic synoptic maps, that can
be produced significantly faster than the approximately 27 days of
one solar rotation and therefore are less likely to suffer from the
evolution of the magnetic field over the observation period. Once Solar
Orbiter leaves the ecliptic plane, we will also be able to include
observations of the polar magnetic field into our synoptic maps,
which will give an unprecedented insight into the magnetic field of
the Sun. This work presents our preparatory modelling efforts and
gives an outlook for the future capabilities of this novel data product.
Title: First results from SO/PHI's on-board data reduction
Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge,
N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.;
Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.;
Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik,
H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G.
Bibcode: 2020AGUFMSH038..05A
Altcode:
The Polarimetric and Helioseismic Imager (PHI), on-board Solar
Orbiter (SO), is a spectropolarimeter imaging the solar photosphere
at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption
line. SO/PHI's aim is to provide data about the magnetic structures and
the line-of-sight (LOS) velocity in the solar atmosphere. For this, it
takes time series of data sets consisting of 2048 x 2048 pixel images of
the Sun at 6 wavelengths, each in 4 different polarisation states. With
the minimum necessary 17 bits pixel depth, one data set amounts to
approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast,
is only 50 GiB/orbit which would also need to contain any calibration
data obtained on-board, i.e. our flat and dark fields. To cope with
this discrepancy, SO/PHI is performing full data reduction on-board,
including the inversion of the radiative transfer equation. The
downloaded results are science ready data, containing 5 final images: a
total intensity image from nearby the spectral line, the magnetic field
strength, azimuth and inclination (describing the magnetic vector) and
the LOS velocity. This process maximises the science return by reducing
the number of necessary images in a data set, as well as rendering the
download of calibration data unessential. In the commissioning phase
of SO/PHI we used the on-board data reduction system successfully
for the first time. We have calibrated the instrument to its optimal
operational parameters (calculation of exposure time, focus, etc.),
acquired and processed calibration data (dark and flat fields),
removed the most significant instrumental artefacts from the data
(dark field, flat field, polarimetric modulation and polarimetric
cross-talk), and performed the inversion of the radiative transfer
equation. The data have then been compressed to further maximise the
use of our telemetry. This contribution presents and discusses the
final results from this process.
Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2020A&A...644A..44Y
Altcode: 2020arXiv201009037Y
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport
vary rapidly and a strongly superadiabatic region lies very closely
to a subadiabatic layer. Our tools for probing the turbulence are
high-resolution spectropolarimetric observations such as have recently
been obtained with the two balloon-borne SUNRISE missions, and numerical
simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations
and simulations. We also attempt to explain some properties of the
photospheric overshooting flow with the help of its governing equations
and simulations. We find that quiet-Sun observations and smeared
simulations are consistent with each other and exhibit a power-law
behavior in the subgranular range of their Doppler velocity power
spectra with a power-law index of ≈ - 2. The unsmeared simulations
exhibit a power law that extends over the full range between the
integral and Taylor scales with a power-law index of ≈ - 2.25. The
smearing, reminiscent of observational conditions, considerably reduces
the extent of the power-law-like portion of the power spectra. This
suggests that the limited spatial resolution in some observations
might eventually result in larger uncertainties in the estimation of
the power-law indices. The simulated vertical velocity power spectra
as a function of height show a rapid change in the power-law index
(at the subgranular range) from roughly the optical depth unity layer,
that is, the solar surface, to 300 km above it. We propose that the
cause of the steepening of the power-law index is the transition from
a super- to a subadiabatic region, in which the dominant source of
motions is overshooting convection. A scale-dependent transport of
the vertical momentum occurs. At smaller scales, the vertical momentum
is more efficiently transported sideways than at larger scales. This
results in less vertical velocity power transported upward at small
scales than at larger scales and produces a progressively steeper
vertical velocity power law below 180 km. Above this height, the
gravity work progressively gains importance at all relevant scales,
making the atmosphere progressively more hydrostatic and resulting
in a gradually less steep power law. Radiative heating and cooling of
the plasma is shown to play a dominant role in the plasma energetics
in this region, which is important in terms of nonadiabatic damping
of the convective motions.
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
Bibcode: 2020A&A...642A...6A
Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements.
Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together.
Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis.
Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
Bibcode: 2020A&A...642A...2R
Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk.
Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies.
Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter.
Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission.
Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
Title: Autonomous on-board data processing and instrument calibration
software for the Polarimetric and Helioseismic Imager on-board the
Solar Orbiter mission
Authors: Albert, Kinga; Hirzberger, Johann; Kolleck, Martin; Jorge,
Nestor Albelo; Busse, Dennis; Rodríguez, Julian Blanco; Carrascosa,
Juan Pedro Cobos; Fiethe, Björn; Gandorfer, Achim; Germerott, Dietmar;
Guan, Yejun; Guerrero, Lucas; Gutierrez-Marques, Pablo; Expósito,
David Hernández; Lange, Tobias; Michalik, Harald; Suárez, David
Orozco; Schou, Jesper; Solanki, Sami K.; del Toro Iniesta, José
Carlos; Woch, Joachim
Bibcode: 2020JATIS...6d8004A
Altcode:
A frequent problem arising for deep space missions is the discrepancy
between the amount of data desired to be transmitted to the ground
and the available telemetry bandwidth. A part of these data consists
of scientific observations, being complemented by calibration data
to help remove instrumental effects. We present our solution for this
discrepancy, implemented for the Polarimetric and Helioseismic Imager
on-board the Solar Orbiter mission, the first solar spectropolarimeter
in deep space. We implemented an on-board data reduction system that
processes calibration data, applies them to the raw science observables,
and derives science-ready physical parameters. This process reduces
the raw data for a single measurement from 24 images to five, thus
reducing the amount of downlinked data, and in addition, renders the
transmission of the calibration data unnecessary. Both these on-board
actions are completed autonomously.
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: PMI: The Photospheric Magnetic Field Imager
Authors: Staub, Jan; Fernandez-Rico, German; Gandorfer, Achim; Gizon,
Laurent; Hirzberger, Johann; Kraft, Stefan; Lagg, Andreas; Schou,
Jesper; Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Wiegelmann,
Thomas; Woch, Joachim
Bibcode: 2020JSWSC..10...54S
Altcode:
We describe the design and the capabilities of the Photospheric Magnetic
field Imager (PMI), a compact and lightweight vector magnetograph,
which is being developed for ESA's Lagrange mission to the Lagrange
L5 point. After listing the design requirements and give a scientific
justification for them, we describe the technical implementation and
the design solution capable of fulfilling these requirements. This is
followed by a description of the hardware architecture as well as the
operations principle. An outlook on the expected performance concludes
the paper.
Title: The SO/PHI instrument on Solar Orbiter and its data products
Authors: Solanki, Sami K.; Hirzberger, Johann; Wiegelmann, Thomas;
Gandorfer, Achim; Woch, Joachim; del Toro Iniesta, José Carlos
Bibcode: 2020EGUGA..2217904S
Altcode:
A central instrument of Solar Orbiter is the Polarimetric and
Helioseismic Imager, SO/PHI. It is a vector magnetograph that also
provides data for helioseismology. SO/PHI is composed of two telescopes,
a full-disk telescope (FDT) and a high-resolution telescope (HRT). The
HRT will observe at a resolution as high as 200 km on the solar
surface, while the FDT will obtain the magnetic field and velocity of
the full solar disc whenever it observes. SO/PHI will be the first
solar spectro-polarimeter to leave the Sun-Earth line, opening up
some unique perspectives, such as the first detailed view of the solar
poles. This will allow not just a more precise and exact mapping of the
polar magnetic field than possible so far, but will also enable us to
follow the dynamics of individual magnetic features at high latitudes
and to determine solar surface and sub-surface flows right up to the
poles. In addition to its standard data products (vector magnetograms,
continuum images and maps of the line-of-sight velocity), SO/PHI will
also provide higher-level data products. These will include synoptic
charts, local magnetic field extrapolations starting from HRT data and
global magnetic field extrapolations (from FDT data) with potential
field source-surface (PFSS) models and possibly also non-potential
models such as NLFFF (non-linear force-free fields), magnetostatics
and MHD. The SO/PHI data products will usefully complement the data
taken by other instruments on Solar Orbiter and on Solar Probe, as
well as instruments on the ground or in Earth orbit. Combining with
observations by Earth-based and near-Earth telescopes will enable
new types of investigations, such as stereoscopic polarimetry and
stereoscopic helioseismology.
Title: Metadata and Their Importance in SO/PHI's On-Board Data
Processing
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Castellanos Duran,
J. S.; Gutierrez–Marques, P.; Kolleck, M.
Bibcode: 2020ASPC..527..599A
Altcode: 2019arXiv191207919A; 2020adass..29..599A
To cope with the telemetry limitations, the Polarimetric and
Helioseismic Imager on Solar Orbiter does full on-board data
processing. Metadata are central to the autonomous processing flow,
crucial for providing science ready data sets to the community, as
well as important in the blind debugging process that will occur in
the commissioning phase. We designed a custom metadata logging system
for SO/PHI. This paper shows how the logged information is used in
the blind debugging scenario.
Title: Performance Analysis of the SO/PHI Software Framework for
On-board Data Reduction
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Rodríguez, J. Blanco;
Castellanos Duran, J. S.; Cobos Carrascosa, J. P.; Fiethe, B.;
Gandorfer, A.; Guan, Y.; Kolleck, M.; Lagg, A.; Lange, T.; Michalik,
H.; Solanki, S. K.; del Toro Iniesta, J. C.
Bibcode: 2019ASPC..523..151A
Altcode: 2019arXiv190508690A
The Polarimetric and Helioseismic Imager (PHI) is the first deep-space
solar spectropolarimeter, on-board the Solar Orbiter (SO) space
mission. It faces: stringent requirements on science data accuracy, a
dynamic environment, and severe limitations on telemetry volume. SO/PHI
overcomes these restrictions through on-board instrument calibration
and science data reduction, using dedicated firmware in FPGAs. This
contribution analyses the accuracy of a data processing pipeline by
comparing the results obtained with SO/PHI hardware to a reference
from a ground computer. The results show that for the analyzed pipeline
the error introduced by the firmware implementation is well below the
requirements of SO/PHI.
Title: A flexible and heterogeneous framework for scientific image
data processing on-board the Solar Orbiter PHI instrument
Authors: Lange, Tobias; Fiethe, Björn; Guan, Yejun; Michalik,
Harald; Albert, Kinga; Hirzberger, Johann; Orozco Suárez, David;
Rodríguez-Valido, Manuel
Bibcode: 2019SPIE11155E..06L
Altcode:
Present scientific space instruments generate a high amount of raw
data while deep-space missions only have a very limited telemetry
rate. Because the computation of the scientific relevant parameters
is usually accompanied with the reduction of the data, the processing
is desired to be carried out already on-board. To accomplish this,
the following paper presents a flexible image processing framework
which makes use of a heterogeneous data processing module consisting
of a space-grade General Purpose Processor (GPP) as well as two
dynamically reconfigurable Field-Programmable Gate Arrays used for
hardware acceleration. The flexibility and capabilities of the presented
framework are proven by means of three exemplary processing tasks of
the Polarimetric and Helioseismic Imager (PHI) on-board Solar Orbiter.
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: Image compression on reconfigurable FPGA for the SO/PHI
space instrument
Authors: Hernández Expósito, D.; Cobos Carrascosa, J. P.; Ramos
Mas, J. L.; Rodríguez Valido, M.; Orozco Suárez, D.; Hirzberger,
J.; Woch, J.; Solanki, S.; del Toro Iniesta, J. C.
Bibcode: 2018SPIE10707E..2FH
Altcode:
In this paper we present a novel FPGA implementation of the Consultative
Committee for Space Data Systems Image Data Compression (CCSDS-IDC
122.0-B-1) for performing image compression aboard the Polarimetric
Helioseismic Imager instrument of the ESA's Solar Orbiter mission. This
is a System-On-Chip solution based on a light multicore architecture
combined with an efficient ad-hoc Bit Plane Encoder core. This hardware
architecture performs an acceleration of 30 times with respect to a
software implementation running into space-qualified processors, like
LEON3. The system stands out over other FPGA implementations because
of the low resource usage, which does not use any external memory,
and of its configurability.
Title: Autonomous on-board data processing and instrument calibration
software for the SO/PHI
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.;
Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez,
J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández
Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H.
Bibcode: 2018SPIE10707E..0OA
Altcode: 2018arXiv181003493A
The extension of on-board data processing capabilities is an
attractive option to reduce telemetry for scientific instruments
on deep space missions. The challenges that this presents, however,
require a comprehensive software system, which operates on the limited
resources a data processing unit in space allows. We implemented such
a system for the Polarimetric and Helioseismic Imager (PHI) on-board
the Solar Orbiter (SO) spacecraft. It ensures autonomous operation
to handle long command-response times, easy changing of the processes
after new lessons have been learned and meticulous book-keeping of all
operations to ensure scientific accuracy. This contribution presents
the requirements and main aspects of the software implementation,
followed by an example of a task implemented in the software frame,
and results from running it on SO/PHI. The presented example shows
that the different parts of the software framework work well together,
and that the system processes data as we expect. The flexibility of
the framework makes it possible to use it as a baseline for future
applications with similar needs and limitations as SO/PHI.
Title: The High Resolution Telescope (HRT) of the Polarimetric and
Helioseismic Imager (PHI) onboard Solar Orbiter
Authors: Gandorfer, A.; Grauf, B.; Staub, J.; Bischoff, J.; Woch, J.;
Hirzberger, J.; Solanki, S. K.; Álvarez-Herrero, A.; García Parejo,
P.; Schmidt, W.; Volkmer, R.; Appourchaux, T.; del Toro Iniesta, J. C.
Bibcode: 2018SPIE10698E..4NG
Altcode:
Solar Orbiter is a joint mission of ESA and NASA scheduled for
launch in 2020. Solar Orbiter is a complete and unique heliophysics
mission, combining remote sensing and in-situ analysis; its special
elliptical orbit allows viewing the Sun from a distance of only 0.28
AU, and - leaving the ecliptic plane - to observe the solar poles from
a hitherto unexplored vantage point. One of the key instruments for
Solar Orbiter's science is the "Polarimetric and Helioseismic Imager"
(PHI), which will provide maps of the solar surface magnetic fields and
the gas flows on the visible solar surface. Two telescopes, a full disc
imager, and a high resolution channel feed a common Fabry-Perot based
tunable filter and thus allow sampling a single Fraunhofer line at 617.3
nm with high spectral resolution; a polarization modulation system
makes the system sensitive to the full state of polarization. From
the analysis of the Doppler shift and the magnetically induced Zeeman
polarization in this line, the magnetic field and the line-of-sight
gas motions can be detected for each point in the image. In this
paper we describe the opto-mechanical system design of the high
resolution telescope. It is based on a decentred Ritchey-Chrétien
two-mirror telescope. The telescope includes a Barlow type magnifier
lens group, which is used as in-orbit focus compensator, and a beam
splitter, which sends a small fraction of the collected light onto
a fast camera, which provides the error signals for the actively
controlled secondary mirror compensating for spacecraft jitter and other
disturbances. The elliptical orbit of the spacecraft poses high demands
on the thermo-mechanical stability. The varying size of the solar disk
image requires a special false-light suppression architecture, which is
briefly described. In combination with a heat-rejecting entrance window,
the optical energy impinging on the polarimetric and spectral analysis
system is efficiently reduced. We show how the design can preserve the
diffraction-limited imaging performance over the design temperature
range of -20°C to +60°C. The decentred hyperbolical mirrors require
special measures for the inter-alignment and their alignment with
respect to the mechanical structure. A system of alignment flats and
mechanical references is used for this purpose. We will describe the
steps of the alignment procedure, and the dedicated optical ground
support equipment, which are needed to reach the diffraction limited
performance of the telescope. We will also report on the verification
of the telescope performance, both - in ambient condition - and in
vacuum at different temperatures.
Title: The Maximum Entropy Limit of Small-scale Magnetic Field
Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..233....5G
Altcode: 2017arXiv171008361G
The observed magnetic field on the solar surface is characterized by a
very complex spatial and temporal behavior. Although feature-tracking
algorithms have allowed us to deepen our understanding of this behavior,
subjectivity plays an important role in the identification and tracking
of such features. In this paper, we continue studies of the temporal
stochasticity of the magnetic field on the solar surface without relying
either on the concept of magnetic features or on subjective assumptions
about their identification and interaction. We propose a data analysis
method to quantify fluctuations of the line-of-sight magnetic field by
means of reducing the temporal field’s evolution to the regular Markov
process. We build a representative model of fluctuations converging to
the unique stationary (equilibrium) distribution in the long time limit
with maximum entropy. We obtained different rates of convergence to the
equilibrium at fixed noise cutoff for two sets of data. This indicates
a strong influence of the data spatial resolution and mixing-polarity
fluctuations on the relaxation process. The analysis is applied to
observations of magnetic fields of the relatively quiet areas around an
active region carried out during the second flight of the Sunrise/IMaX
and quiet Sun areas at the disk center from the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory satellite.
Title: Three-dimensional magnetic structure of a sunspot: Comparison
of the photosphere and upper chromosphere
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
Sami K.
Bibcode: 2017A&A...604A..98J
Altcode: 2017arXiv170508404J
Aims: We investigate the magnetic field of a sunspot in the
upper chromosphere and compare it to the photospheric properties
of the field.
Methods: We observed the main leading sunspot
of the active region NOAA 11124 during two days with the Tenerife
Infrared Polarimeter-2 (TIP-2) mounted at the German Vacuum Tower
Telescope (VTT). Through inversion of Stokes spectra of the He I
triplet at 10 830 Å, we obtained the magnetic field vector of the
upper chromosphere. For comparison with the photosphere, we applied
height-dependent inversions of the Si I 10 827.1 Å and Ca I 10 833.4 Å
lines.
Results: We found that the umbral magnetic field strength
in the upper chromosphere is lower by a factor of 1.30-1.65 compared
to the photosphere. The magnetic field strength of the umbra decreases
from the photosphere toward the upper chromosphere by an average rate of
0.5-0.9 G km-1. The difference in the magnetic field strength
between both atmospheric layers steadily decreases from the sunspot
center to the outer boundary of the sunspot; the field, in particular
its horizontal component, is stronger in the chromopshere outside the
spot and this is suggestive of a magnetic canopy. The sunspot displays
a twist that on average is similar in the two layers. However, the
differential twist between the photosphere and chromosphere increases
rapidly toward the outer penumbral boundary. The magnetic field
vector is more horizontal with respect to the solar surface by roughly
5-20° in the photosphere compared to the upper chromosphere. Above
a lightbridge, the chromospheric magnetic field is equally strong as
that in the umbra, whereas the field of the lightbridge is weaker than
its surroundings in the photosphere by roughly 1 kG. This suggests a
cusp-like magnetic field structure above the lightbridge.
Title: Erratum: Morphological Properties of
Slender CaII H Fibrils Observed by sunrise II (ApJS 229, 1, 6)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..230...11G
Altcode:
No abstract at ADS
Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Schmidt, W.
Bibcode: 2017ApJS..229...11J
Altcode: 2016arXiv161003104J
A dense forest of slender bright fibrils near a small solar active
region is seen in high-quality narrowband Ca II H images from the SuFI
instrument onboard the Sunrise balloon-borne solar observatory. The
orientation of these slender Ca II H fibrils (SCF) overlaps with the
magnetic field configuration in the low solar chromosphere derived
by magnetostatic extrapolation of the photospheric field observed
with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
qualitatively aligned with small-scale loops computed from a novel
inversion approach based on best-fit numerical MHD simulation. Such
loops are organized in canopy-like arches over quiet areas that differ
in height depending on the field strength near their roots.
Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...18W
Altcode: 2017arXiv170101458N; 2017arXiv170101458W
Magneto-static models may overcome some of the issues facing force-free
magnetic field extrapolations. So far they have seen limited use
and have faced problems when applied to quiet-Sun data. Here we
present a first application to an active region. We use solar vector
magnetic field measurements gathered by the IMaX polarimeter during
the flight of the Sunrise balloon-borne solar observatory in 2013
June as boundary conditions for a magneto-static model of the higher
solar atmosphere above an active region. The IMaX data are embedded
in active region vector magnetograms observed with SDO/HMI. This work
continues our magneto-static extrapolation approach, which was applied
earlier to a quiet-Sun region observed with Sunrise I. In an active
region the signal-to-noise-ratio in the measured Stokes parameters
is considerably higher than in the quiet-Sun and consequently the
IMaX measurements of the horizontal photospheric magnetic field allow
us to specify the free parameters of the model in a special class of
linear magneto-static equilibria. The high spatial resolution of IMaX
(110-130 km, pixel size 40 km) enables us to model the non-force-free
layer between the photosphere and the mid-chromosphere vertically
by about 50 grid points. In our approach we can incorporate some
aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
taking a finite Lorentz force into account, which was not possible with
lower-resolution photospheric measurements in the past. The linear model
does not, however, permit us to model intrinsic nonlinear structures
like strongly localized electric currents.
Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
Knölker, M.; Lecinski, A.
Bibcode: 2017ApJS..229....2S
Altcode: 2017arXiv170101555S
The Sunrise balloon-borne solar observatory, consisting of a 1 m
aperture telescope that provides a stabilized image to a UV filter
imager and an imaging vector polarimeter, carried out its second science
flight in 2013 June. It provided observations of parts of active regions
at high spatial resolution, including the first high-resolution images
in the Mg II k line. The obtained data are of very high quality, with
the best UV images reaching the diffraction limit of the telescope
at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
accounting for phase-diversity information. Here a brief update is
given of the instruments and the data reduction techniques, which
includes an inversion of the polarimetric data. Mainly those aspects
that evolved compared with the first flight are described. A tabular
overview of the observations is given. In addition, an example time
series of a part of the emerging active region NOAA AR 11768 observed
relatively close to disk center is described and discussed in some
detail. The observations cover the pores in the trailing polarity of
the active region, as well as the polarity inversion line where flux
emergence was ongoing and a small flare-like brightening occurred in
the course of the time series. The pores are found to contain magnetic
field strengths ranging up to 2500 G, and while large pores are clearly
darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed
those of the quiet Sun in the upper photosphere.
Title: Vertical magnetic field gradient in the photospheric layers
of sunspots
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
Sami K.; Tiwari, Sanjiv K.
Bibcode: 2017A&A...599A..35J
Altcode: 2016arXiv161000500J
Aims: We investigate the vertical gradient of the magnetic
field of sunspots in the photospheric layer.
Methods:
Independent observations were obtained with the Solar Optical
Telescope/Spectropolarimeter (SOT/SP) on board the Hinode spacecraft and
with the Tenrife Infrared Polarimeter-2 (TIP-2) mounted at the German
Vacuum Tower Telescope (VTT). We apply state-of-the-art inversion
techniques to both data sets to retrieve the magnetic field and the
corresponding vertical gradient along with other atmospheric parameters
in the solar photosphere.
Results: In the sunspot penumbrae we
detected patches of negative vertical gradients of the magnetic field
strength, I.e., the magnetic field strength decreases with optical depth
in the photosphere. The negative gradient patches are located in the
inner and partly in the middle penumbrae in both data sets. From the
SOT/SP observations we found that the negative gradient patches are
restricted mainly to the deep photospheric layers and are concentrated
near the edges of the penumbral filaments. Magnetohydrodynamic (MHD)
simulations also show negative gradients in the inner penumbrae, also
at the locations of filaments. In the observations and the simulation
negative gradients of the magnetic field vs. optical depth dominate
at some radial distances in the penumbra. The negative gradient with
respect to optical depth in the inner penumbrae persists even after
averaging in the azimuthal direction in the observations and, to a
lesser extent, in the MHD simulations. If the gradients in the MHD
simulations are determined with respect to geometrical height, then
the azimuthal averages are always positive within the sunspot (above
log τ = 0), corresponding to magnetic field increasing with depth,
as generally expected.
Conclusions: We interpret the observed
localized presence of negative vertical gradient of the magnetic
field strength in the observations as a consequence of stronger field
from spines expanding with height and closing above the weaker field
inter-spines. The presence of the negative gradients with respect
to optical depth after azimuthal averaging can be explained by two
different mechanisms: the high corrugation of equal optical depth
surfaces and the cancellation of polarized signal due to the presence
of unresolved opposite polarity patches in the deeper layers of the
penumbra.
Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....3C
Altcode: 2016arXiv161003531C
In 2013 June, the two scientific instruments on board the second Sunrise
mission witnessed, in detail, a small-scale magnetic flux emergence
event as part of the birth of an active region. The Imaging Magnetograph
Experiment (IMaX) recorded two small (∼ 5\prime\prime )
emerging flux patches in the polarized filtergrams of a photospheric Fe
I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
the highly dynamic chromospheric response to the magnetic fields pushing
their way through the lower solar atmosphere. The serendipitous capture
of this event offers a closer look at the inner workings of active
region emergence sites. In particular, it reveals in meticulous detail
how the rising magnetic fields interact with the granulation as they
push through the Sun’s surface, dragging photospheric plasma in
their upward travel. The plasma that is burdening the rising field
slides along the field lines, creating fast downflowing channels at
the footpoints. The weight of this material anchors this field to the
surface at semi-regular spatial intervals, shaping it in an undulatory
fashion. Finally, magnetic reconnection enables the field to release
itself from its photospheric anchors, allowing it to continue its
voyage up to higher layers. This process releases energy that lights
up the arch-filament systems and heats the surrounding chromosphere.
Title: Photospheric Response to an Ellerman Bomb-like Event—An
Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....5D
Altcode: 2016arXiv160903817D
Ellerman Bombs are signatures of magnetic reconnection, which is an
important physical process in the solar atmosphere. How and where they
occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
data, along with 3D MHD simulations that aim to reproduce the exact
scenario proposed for the formation of these features. Although
the observed event seems to be more dynamic and violent than the
simulated one, simulations clearly confirm the basic scenario for the
production of EBs. The simulations also reveal the full complexity of
the underlying process. The simulated observations show that the Fe I
525.02 nm line gives no information on the height where reconnection
takes place. It can only give clues about the heating in the aftermath
of the reconnection. However, the information on the magnetic field
vector and velocity at this spatial resolution is extremely valuable
because it shows what numerical models miss and how they can be
improved.
Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....9J
Altcode: 2016arXiv161007449J
We present observations of transverse oscillations in slender Ca II
H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
time series of high- (spatial and temporal-) resolution seeing-free
observations in a 1.1 Å wide passband covering the line core of Ca
II H 3969 Å from the second flight of the Sunrise balloon-borne solar
observatory. The entire field of view, spanning the polarity inversion
line of an active region close to the solar disk center, is covered with
bright, thin, and very dynamic fine structures. Our analysis reveals
the prevalence of transverse waves in SCFs with median amplitudes and
periods on the order of 2.4 ± 0.8 km s-1 and 83 ± 29 s,
respectively (with standard deviations given as uncertainties). We
find that the transverse waves often propagate along (parts of) the
SCFs with median phase speeds of 9 ± 14 km s-1. While the
propagation is only in one direction along the axis in some of the
SCFs, propagating waves in both directions, as well as standing waves
are also observed. The transverse oscillations are likely Alfvénic
and are thought to be representative of magnetohydrodynamic kink
waves. The wave propagation suggests that the rapid high-frequency
transverse waves, often produced in the lower photosphere, can
penetrate into the chromosphere with an estimated energy flux of ≈15
kW m-2. Characteristics of these waves differ from those
reported for other fibrillar structures, which, however, were observed
mainly in the upper solar chromosphere.
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
Bibcode: 2017ApJS..229....8J
Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km2 s-1, 80-90 km2 s-1,
and 25-70 km2 s-1, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.
Title: Spectropolarimetric Evidence for a Siphon Flow along an
Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...15R
Altcode: 2016arXiv161106732R
We study the dynamics and topology of an emerging magnetic flux
concentration using high spatial resolution spectropolarimetric data
acquired with the Imaging Magnetograph eXperiment on board the sunrise
balloon-borne solar observatory. We obtain the full vector magnetic
field and the line of sight (LOS) velocity through inversions of
the Fe I line at 525.02 nm with the SPINOR code. The derived vector
magnetic field is used to trace magnetic field lines. Two magnetic flux
concentrations with different polarities and LOS velocities are found
to be connected by a group of arch-shaped magnetic field lines. The
positive polarity footpoint is weaker (1100 G) and displays an upflow,
while the negative polarity footpoint is stronger (2200 G) and shows
a downflow. This configuration is naturally interpreted as a siphon
flow along an arched magnetic flux tube.
Title: Morphological Properties of Slender Ca II H Fibrils Observed
by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....6G
Altcode: 2016arXiv161200319G
We use seeing-free high spatial resolution Ca II H data obtained by
the SUNRISE observatory to determine properties of slender fibrils
in the lower solar chromosphere. In this work we use intensity images
taken with the SuFI instrument in the Ca II H line during the second
scientific flight of the SUNRISE observatory to identify and track
elongated bright structures. After identification, we analyze theses
structures to extract their morphological properties. We identify
598 slender Ca II H fibrils (SCFs) with an average width of around
180 km, length between 500 and 4000 km, average lifetime of ≈400
s, and average curvature of 0.002 arcsec-1. The maximum
lifetime of the SCFs within our time series of 57 minutes is ≈2000
s. We discuss similarities and differences of the SCFs with other
small-scale, chromospheric structures such as spicules of type I and
II, or Ca II K fibrils.
Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...16R
Altcode: 2016arXiv161105175R
We present a new method of Stokes inversion of spectropolarimetric
data and evaluate it by taking the example of a Sunrise/IMaX
observation. An archive of synthetic Stokes profiles is obtained
by the spectral synthesis of state-of-the-art magnetohydrodynamics
(MHD) simulations and a realistic degradation to the level of the
observed data. The definition of a merit function allows the archive
to be searched for the synthetic Stokes profiles that best match the
observed profiles. In contrast to traditional Stokes inversion codes,
which solve the Unno-Rachkovsky equations for the polarized radiative
transfer numerically and fit the Stokes profiles iteratively, the new
technique provides the full set of atmospheric parameters. This gives
us the ability to start an MHD simulation that takes the inversion
result as an initial condition. After a relaxation process of half an
hour solar time we obtain physically consistent MHD data sets with
a target similar to the observation. The new MHD simulation is used
to repeat the method in a second iteration, which further improves
the match between observation and simulation, resulting in a factor
of 2.2 lower mean {χ }2 value. One advantage of the new
technique is that it provides the physical parameters on a geometrical
height scale. It constitutes a first step toward inversions that give
results consistent with the MHD equations.
Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....7G
Altcode: 2017arXiv170102801G
We report the detection of oscillations in slender Ca II H fibrils
(SCFs) from high-resolution observations acquired with the Sunrise
balloon-borne solar observatory. The SCFs show obvious oscillations in
their intensity, but also their width. The oscillatory behaviors are
investigated at several positions along the axes of the SCFs. A large
majority of fibrils show signs of oscillations in intensity. Their
periods and phase speeds are analyzed using a wavelet analysis. The
width and intensity perturbations have overlapping distributions
of the wave period. The obtained distributions have median values
of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
find that the fluctuations of both parameters propagate in
the SCFs with speeds of {11}-11+49 km
s-1 and {15}-15+34 km s-1,
respectively. Furthermore, the width and intensity oscillations have a
strong tendency to be either in anti-phase or, to a smaller extent, in
phase. This suggests that the oscillations of both parameters are caused
by the same wave mode and that the waves are likely propagating. Taking
all the evidence together, the most likely wave mode to explain all
measurements and criteria is the fast sausage mode.
Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229....4C
Altcode: 2016arXiv161007484C
How and where are coronal loops rooted in the solar lower
atmosphere? The details of the magnetic environment and its evolution
at the footpoints of coronal loops are crucial to understanding the
processes of mass and energy supply to the solar corona. To address
the above question, we use high-resolution line-of-sight magnetic
field data from the Imaging Magnetograph eXperiment instrument on the
Sunrise balloon-borne observatory and coronal observations from the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
of an emerging active region. We find that the coronal loops are
often rooted at the locations with minor small-scale but persistent
opposite-polarity magnetic elements very close to the larger dominant
polarity. These opposite-polarity small-scale elements continually
interact with the dominant polarity underlying the coronal loop through
flux cancellation. At these locations we detect small inverse Y-shaped
jets in chromospheric Ca II H images obtained from the Sunrise Filter
Imager during the flux cancellation. Our results indicate that magnetic
flux cancellation and reconnection at the base of coronal loops due
to mixed polarity fields might be a crucial feature for the supply of
mass and energy into the corona.
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
Bibcode: 2017ApJS..229...13K
Altcode: 2016arXiv160905664K
Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
June, are used for a statistical analysis to determine the physical
properties of moving magnetic features (MMFs) observed near a pore. MMFs
of the same and opposite polarity, with respect to the pore, are found
to stream from its border at an average speed of 1.3 km s-1
and 1.2 km s-1, respectively, with mainly same-polarity MMFs
found further away from the pore. MMFs of both polarities are found to
harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
are blueshifted, whereas same-polarity MMFs do not show any preference
for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
size and carry a mean flux of ∼1.2 × 1017 Mx.
Title: Statistical evolution of quiet-Sun small-scale magnetic
features using Sunrise observations
Authors: Anusha, L. S.; Solanki, S. K.; Hirzberger, J.; Feller, A.
Bibcode: 2017A&A...598A..47A
Altcode: 2016arXiv160808499A
The evolution of small magnetic features in quiet regions of the Sun
provides a unique window for probing solar magneto-convection. Here
we analyze small-scale magnetic features in the quiet Sun, using the
high resolution, seeing-free observations from the Sunrise balloon
borne solar observatory. Our aim is to understand the contribution of
different physical processes, such as splitting, merging, emergence
and cancellation of magnetic fields to the rearrangement, addition
and removal of magnetic flux in the photosphere. We have employed a
statistical approach for the analysis and the evolution studies are
carried out using a feature-tracking technique. In this paper we provide
a detailed description of the feature-tracking algorithm that we have
newly developed and we present the results of a statistical study
of several physical quantities. The results on the fractions of the
flux in the emergence, appearance, splitting, merging, disappearance
and cancellation qualitatively agrees with other recent studies. To
summarize, the total flux gained in unipolar appearance is an order of
magnitude larger than the total flux gained in emergence. On the other
hand, the bipolar cancellation contributes nearly an equal amount to
the loss of magnetic flux as unipolar disappearance. The total flux
lost in cancellation is nearly six to eight times larger than the
total flux gained in emergence. One big difference between our study
and previous similar studies is that, thanks to the higher spatial
resolution of Sunrise, we can track features with fluxes as low as
9 × 1014 Mx. This flux is nearly an order of magnitude
lower than the smallest fluxes of the features tracked in the highest
resolution previous studies based on Hinode data. The area and flux
of the magnetic features follow power-law type distribution, while
the lifetimes show either power-law or exponential type distribution
depending on the exact definitions used to define various birth and
death events. We have also statistically determined the evolution
of the flux within the features in the course of their lifetime,
finding that this evolution depends very strongly on the birth and
death process that the features undergo.
Title: Lambda-shaped jets from a penumbral intrusion into a sunspot
umbra: a possibility for magnetic reconnection
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2017A&A...597A.127B
Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data were taken with the Swedish Solar Telescope
(SST) on the Canary Islands. Time series of Ca II H images show
a series of transient jets extending roughly 3000 km above a
penumbral intrusion into the umbra. For most of the time series,
jets were seen along the whole length of the intruding bright
filament. Some of these jets develop a clear λ-shaped structure,
with a small loop appearing at their footpoint and lasting for around
a minute. In the framework of earlier studies, the observed transient
λ shape of these jets suggests that they could be caused by magnetic
reconnection between a curved arcade-like or flux rope-like field in
the lower part of the penumbral intrusion and the more vertical umbral
magnetic field forming a cusp-shaped structure above the penumbral
intrusion. Movies associated to Figs. 1 and 2 are available at
http://www.aanda.org
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2017hdsi.book..257L
Altcode:
No abstract at ADS
Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
Bibcode: 2016AGUFMSH43A2554A
Altcode:
The Solar Orbiter mission, to be launched in October 2018, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit
of the Solar Orbiter spacecraft will reach a solar latitude up to
34 degrees by the end of the extended mission and thus will enable
the first local helioseismology studies of the polar regions. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. In this paper
we will review the helioseismic objectives achievable with PHI, and
will also give a short status report of the development of the Flight
Model of PHI.
Title: Radiated Emissions of the Power Converter Module of the
Polarimetric and Helioseismic Imager Instrument On Board of Solar
Orbiter: A Case Study
Authors: Sanchis Kilders, E.; Meller, R.; Lopez Jimenez, A.;
Hirzberger, J.; Laget, Ph.; Gasent Blesa, J. L.; Herranz de la Revila,
M.; Osorno Caudet, D.; Ferreres Sabater, A.; Balaguer Jimenez, M.;
Jordan Martinez, J.; Esteve Gomez, V.; Maset Sancho, E.; Ejea Marti,
J. B.
Bibcode: 2016ESASP.738E...2S
Altcode:
EMC requirements for scientific satellites are usually very stringent
and much more demanding than terrestrial standards, mainly because
ad-hoc scientific instruments developed for the mission require very
quiet electromagnetic environments to perform their science. These
requirements will assure the compatibility of all instruments on board
and with the platform.The electromagnetic noise generated by the DC/DC
converter of the PHI instrument, to be flown on board Solar Orbiter,
has been drastically reduced applying several different techniques.One
technique has been to change the grounding strategy from a single point
grounding to a distributed grounding. Two additional techniques were
needed to reach the required noise floor.Experimental measurements
show the improvements achieved with each technique.
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2015SSRv..196..251L
Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
The Solar Orbiter mission, to be launched in July 2017, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit of
the Solar Orbiter spacecraft will reach a solar latitude of up to
21∘ (up to 34∘ by the end of the extended
mission) and thus will enable the first local helioseismology studies of
the polar regions. Here we consider an array of science objectives to be
addressed by helioseismology within the baseline telemetry allocation
(51 Gbit per orbit, current baseline) and within the science observing
windows (baseline 3×10 days per orbit). A particularly important
objective is the measurement of large-scale flows at high latitudes
(rotation and meridional flow), which are largely unknown but play an
important role in flux transport dynamos. For both helioseismology
and feature tracking methods convection is a source of noise in
the measurement of longitudinally averaged large-scale flows, which
decreases as T -1/2 where T is the total duration of the
observations. Therefore, the detection of small amplitude signals (e.g.,
meridional circulation, flows in the deep solar interior) requires long
observation times. As an example, one hundred days of observations at
lower spatial resolution would provide a noise level of about three m/s
on the meridional flow at 80∘ latitude. Longer time-series
are also needed to study temporal variations with the solar cycle. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. We have used a
model of the PHI instrument to study its performance for helioseismology
applications. As input we used a 6 hr time-series of realistic solar
magneto-convection simulation (Stagger code) and the SPINOR radiative
transfer code to synthesize the observables. The simulated power
spectra of solar oscillations show that the instrument is suitable for
helioseismology. In particular, the specified point spread function,
image jitter, and photon noise are no obstacle to a successful mission.
Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
Zuccarello, Francesca
Bibcode: 2015JATIS...1d4006B
Altcode:
Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
for a small solar and space weather mission with a budget compatible
with an European Space Agency (ESA) S-class mission, including launch,
and a fast development cycle. ADAHELI was submitted to the European
Space Agency by a European-wide consortium of solar physics research
institutes in response to the "Call for a small mission opportunity
for a launch in 2017," of March 9, 2012. The ADAHELI project builds
on the heritage of the former ADAHELI mission, which had successfully
completed its phase-A study under the Italian Space Agency 2007 Small
Mission Programme, thus proving the soundness and feasibility of
its innovative low-budget design. ADAHELI is a solar space mission
with two main instruments: ISODY: an imager, based on Fabry-Pérot
interferometers, whose design is optimized to the acquisition of
highest cadence, long-duration, multiline spectropolarimetric images
in the visible/near-infrared region of the solar spectrum. XSPO: an
x-ray polarimeter for solar flares in x-rays with energies in the 15
to 35 keV range. ADAHELI is capable of performing observations that
cannot be addressed by other currently planned solar space missions,
due to their limited telemetry, or by ground-based facilities, due to
the problematic effect of the terrestrial atmosphere.
Title: The Polarimetric and Helioseismic Imager for Solar Orbiter:
SO/PHI
Authors: Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Woch,
Joachim; Gandorfer, Achim; Hirzberger, Johann; Schmidt, Wolfgang;
Appourchaux, Thierry; Alvarez-Herrero, Alberto
Bibcode: 2015IAUS..305..108S
Altcode: 2015arXiv150203368S
The Solar Orbiter is the next solar physics mission of the European
Space Agency, ESA, in collaboration with NASA, with a launch planned in
2018. The spacecraft is designed to approach the Sun to within 0.28 AU
at perihelion of a highly eccentric orbit. The proximity with the Sun
will also allow its observation at uniformly high resolution at EUV and
visible wavelengths. Such observations are central for learning more
about the magnetic coupling of the solar atmosphere. At a later phase
in the mission the spacecraft will leave the ecliptic and study the
enigmatic poles of the Sun from a heliographic latitude of up to 33°.
Title: Magnetic reconnection as a source of jets from a penumbral
intrusion into a sunspot umbra
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2015arXiv150902123B
Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data was taken with the Swedish Solar Telescope (SST)
on the Canary Islands. Time series of Ca\,II H images show a series of
transient jets extending roughly 3000 km above a penumbral intrusion
into the umbra. For most of the time series jets were seen along
the whole length of the intruding bright filament. Some of these jets
develop a clear $\lambda$-shaped structure, with a small loop appearing
at their footpoint and lasting for around a minute. In the framework
of earlier studies, the observed transient $\lambda$ shape of these
jets strongly suggests that they are caused by magnetic reconnection
between a curved arcade-like or flux-rope like field in the lower part
of the penumbral intrusion and the more vertical umbral magnetic field
forming a cusp-shaped structure above the penumbral intrusion.
Title: Evolution of Small Scale Magnetic Structures from Sunrise Data
Authors: Anusha, L. S.; Feller, A.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2014ASPC..489...83A
Altcode:
We present the results of an analysis of small scale magnetic features
in the quiet Sun, observed with the Sunrise balloon borne telescope. Our
aim is to understand the contribution of different physical processes
that drive the evolution of magnetic features in quiet regions of
the photosphere. To this end, we study the rearrangement, addition,
and removal of magnetic flux through splitting, merging, cancellation,
and emergence of magnetic fields.
Title: Discriminant analysis of solar bright points and faculae
II. Contrast and morphology analysis
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2014arXiv1410.5354K
Altcode:
Taken at a high spatial resolution of 0.1 arcsec, Bright Points (BPs)
are found to coexist with faculae in images and the latter are often
resolved as adjacent striations. Understanding the properties of these
different features is fundamental to carrying out proxy magnetometry. To
shed light on the relationship between BPs and faculae, we studied
them separately after the application of a classification method,
developed and described in a previous paper) on active region images
at various heliocentric angles. In this Paper, we explore different
aspects of the photometric properties of BPs and faculae, namely
their G-band contrast profiles, their peak contrast in G-band and
continuum, as well as morphological parameters. We find that: (1)
the width of the contrast profiles of the classified BPs and faculae
are consistent with studies of disk center BPs at and limb faculae,
which indirectly confirms the validity of our classification, (2) the
profiles of limb faculae are limbward skewed on average, while near
disk center they exhibit both centerward and limbward skewnesses due
to the distribution of orientations of the faculae, (3) the relation
between the peak contrasts of BPs and faculae and their apparent area
discloses a trend reminiscent of magnetogram studies. The skewness
of facular profiles provides a novel constraint for 3D MHD models of
faculae. As suggested by the asymmetry and orientation of their contrast
profiles, faculae near disk center could be induced by inclined fields,
while apparent BPs near the limb seem to be in fact small faculae
misidentified. The apparent area of BPs and faculae could be possibly
exploited for proxy magnetometry.
Title: Comparison of solar photospheric bright points between Sunrise
observations and MHD simulations
Authors: Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.;
Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.;
Hirzberger, J.
Bibcode: 2014A&A...568A..13R
Altcode: 2014arXiv1406.1387R
Bright points (BPs) in the solar photosphere are thought to be the
radiative signatures (small-scale brightness enhancements) of magnetic
elements described by slender flux tubes or sheets located in the darker
intergranular lanes in the solar photosphere. They contribute to the
ultraviolet (UV) flux variations over the solar cycle and hence may
play a role in influencing the Earth's climate. Here we aim to obtain
a better insight into their properties by combining high-resolution
UV and spectro-polarimetric observations of BPs by the Sunrise
Observatory with 3D compressible radiation magnetohydrodynamical
(MHD) simulations. To this end, full spectral line syntheses are
performed with the MHD data and a careful degradation is applied
to take into account all relevant instrumental effects of the
observations. In a first step it is demonstrated that the selected
MHD simulations reproduce the measured distributions of intensity at
multiple wavelengths, line-of-sight velocity, spectral line width,
and polarization degree rather well. The simulated line width also
displays the correct mean, but a scatter that is too small. In
the second step, the properties of observed BPs are compared with
synthetic ones. Again, these are found to match relatively well,
except that the observations display a tail of large BPs with strong
polarization signals (most likely network elements) not found in the
simulations, possibly due to the small size of the simulation box. The
higher spatial resolution of the simulations has a significant effect,
leading to smaller and more numerous BPs. The observation that most BPs
are weakly polarized is explained mainly by the spatial degradation,
the stray light contamination, and the temperature sensitivity of the Fe
i line at 5250.2 Å. Finally, given that the MHD simulations are highly
consistent with the observations, we used the simulations to explore
the properties of BPs further. The Stokes V asymmetries increase with
the distance to the center of the mean BP in both observations and
simulations, consistent with the classical picture of a production
of the asymmetry in the canopy. This is the first time that this has
been found also in the internetwork. More or less vertical kilogauss
magnetic fields are found for 98% of the synthetic BPs underlining
that basically every BP is associated with kilogauss fields. At the
continuum formation height, the simulated BPs are on average 190 K
hotter than the mean quiet Sun, the mean BP field strength is found to
be 1750 G, and the mean inclination is 17°, supporting the physical
flux-tube paradigm to describe BPs. On average, the synthetic BPs
harbor downflows increasing with depth. The origin of these downflows
is not yet understood very well and needs further investigation.
Title: Comparison between Mg II k and Ca II H Images Recorded by
SUNRISE/SuFI
Authors: Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.; Knölker,
M.; Schmidt, W.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.
Bibcode: 2014ApJ...784...20D
Altcode:
We present a comparison of high-resolution images of the solar surface
taken in the Mg II k and Ca II H channels of the Filter Imager on the
balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled
with 0.48 nm and 0.11 nm wide filters, respectively. The two channels
show remarkable qualitative and quantitative similarities in the quiet
Sun, in an active region plage and during a small flare. However, the Mg
filtergrams display 1.4-1.7 times higher intensity contrast and appear
more smeared and smoothed in the quiet Sun. In addition, the fibrils
in a plage are wider. Although the exposure time is 100 times longer
for Mg images, the evidence suggests that these differences cannot be
explained only with instrumental effects or the evolution of the solar
scene. The differences at least partially arise because of different
line-formation heights, the stronger response of Mg k emission peaks
to the higher temperatures, and the larger height range sampled by
the broad Mg filter used here. This is evidently manifested during
the flare when a surge in Mg evolves differently than in Ca.
Title: First High-resolution Images of the Sun in the 2796 Å Mg II
k Line
Authors: Riethmüller, T. L.; Solanki, S. K.; Hirzberger, J.;
Danilovic, S.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.;
Knölker, M.; Schmidt, W.; Del Toro Iniesta, J. C.
Bibcode: 2013ApJ...776L..13R
Altcode: 2013arXiv1309.5213R
We present the first high-resolution solar images in the Mg II k 2796
Å line. The images, taken through a 4.8 Å broad interference filter,
were obtained during the second science flight of Sunrise in 2013 June
by the Sunrise Filter Imager (SuFI) instrument. The Mg II k images
display structures that look qualitatively very similar to images taken
in the core of Ca II H. The Mg II images exhibit reversed granulation
(or shock waves) in the internetwork regions of the quiet Sun, at
intensity contrasts that are similar to those found in Ca II H. Very
prominent in Mg II are bright points, both in the quiet Sun and in plage
regions, particularly near the disk center. These are much brighter than
at other wavelengths sampled at similar resolution. Furthermore, Mg II k
images also show fibril structures associated with plage regions. Again,
the fibrils are similar to those seen in Ca II H images, but tend to
be more pronounced, particularly in weak plage.
Title: Fine structures in the atmosphere above a sunspot umbra
Authors: Bharti, L.; Hirzberger, J.; Solanki, S. K.
Bibcode: 2013A&A...552L...1B
Altcode: 2013arXiv1302.2772B
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904, obtained with the Swedish
Solar Telescope (SST) La Palma, Canary Islands. Time series of high
resolution Ca ii H images show transient jet-like structures in sunspot
umbrae are elongated, which we call umbral microjets. These jets are
directed roughly parallel to nearby penumbral microjets, suggesting
that they are aligned with the background magnetic field. In general,
first a bright dot-like structure appears, from which a jet later
emerges, although some jets appear without an associated chromospheric
dot. Bright photospheric umbral dots are associated with umbral
microjets arising in the outer umbra. Nevertheless, a one-to-one
correspondence between jet-like events and underlying umbral dots
is not seen. They are typically less than 1'' long and less than 0.3
arcsec wide. The typical lifetime of umbral microjets is around one
minute. The brightness of these structures increases from the center of
the umbra toward the umbra-penumbra boundary along with the brightness
of the local background.
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
Bibcode: 2012AN....333..880P
Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
Title: Reflectivity, polarization properties, and durability of
metallic mirror coatings for the European Solar Telescope
Authors: Feller, A.; Krishnappa, N.; Pleier, O.; Hirzberger, J.;
Jobst, P. J.; Schürmann, M.
Bibcode: 2012SPIE.8450E..3UF
Altcode:
In the context of the conceptual design study for the European Solar
Telescope (EST) we have investigated different metallic mirror
coatings in terms of reflectivity, polarization properties and
durability. Samples of the following coating types have been studied:
bare aluminum, silver with different dielectric layers for protection
and UV enhancement, and an aluminum-silver combination. From 2009 to
2011 we have carried out a long-term durability test under realistic
observing conditions at the VTT solar telescope of the Observatorio
del Teide (Tenerife, Spain), accompanied by repeated reflectivity
measurements in the EST spectral working range (0.3 - 20 μm), and
by polarization measurements in the visible range. The test results
allow us to find the optimum coatings for the different mirrors in the
EST beampath and to eventually assess aging effects and re-coating
cycles. The results of the polarization measurements are a valuable
input for an EST telescope polarization model, helping to meet the
stringent requirements on polarimetric accuracy.
Title: Multi-purpose grating spectrograph for the 4-meter European
Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Gelly, B.; Grauf, B.;
Hirzberger, J.; López Ariste, A.; Lopez, R. L.; Mein, P.; Sayéde, F.
Bibcode: 2012SPIE.8446E..6TC
Altcode:
This communication presents a family of spectrographs designed for
the European Solar Telescope. They can operate in four different
configurations: a long slit standard spectrograph (LsSS), two devices
based on subtractive double pass (TUNIS and MSDP) and one based on
an integral field, multi-slit, multi-wavelength configuration. The
combination of them composes the multi-purpose grating spectrograph of
EST, focused on supporting the different science cases of the solar
photosphere and chromosphere in the spectral range from 3900 Å to
23000 Å. The different alternatives are made compatible by using
the same base spectrographs and different selectable optical elements
corresponding to specific subsystems of each configuration.
Title: Waves as the Source of Apparent Twisting Motions in Sunspot
Penumbrae
Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.;
Solanki, S. K.
Bibcode: 2012ApJ...752..128B
Altcode: 2012arXiv1204.2221B
The motion of dark striations across bright filaments in a sunspot
penumbra has become an important new diagnostic of convective gas
flows in penumbral filaments. The nature of these striations has,
however, remained unclear. Here, we present an analysis of small-scale
motions in penumbral filaments in both simulations and observations. The
simulations, when viewed from above, show fine structure with dark lanes
running outward from the dark core of the penumbral filaments. The
dark lanes either occur preferentially on one side or alternate
between both sides of the filament. We identify this fine structure
with transverse (kink) oscillations of the filament, corresponding to
a sideways swaying of the filament. These oscillations have periods in
the range of 5-7 minutes and propagate outward and downward along the
filament. Similar features are found in observed G-band intensity time
series of penumbral filaments in a sunspot located near disk center
obtained by the Broadband Filter Imager on board the Hinode. We also
find that some filaments show dark striations moving to both sides
of the filaments. Based on the agreement between simulations and
observations we conclude that the motions of these striations are
caused by transverse oscillations of the underlying bright filaments.
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: Fast Up-flows Observed on Granules with Sunrise
Authors: Macdonald, G. A.; Hirzberger, J.; Solanki, S.; Choudhary,
D. P.
Bibcode: 2011AGUFMSH13B1985M
Altcode:
We present results from a rigorous study of fast granular up flows
observed with the Imaging Magnetograph eXperiment (IMaX) aboard
the SUNRISE balloon-borne observatory. A time series ∼ 23 minutes
long made June 9, 2009 with a cadence of ∼ 33sec and resolution
of 0.15--0.18'' was used. Our study concentrates on up
flows with a LOS speeds in excess of 2km/s. These flows occur most
frequently on the bright areas of the smallest granules, and less
so on the bright edges of larger granules. The maximum up flow speed
tends to scale with its area which scales with the size of the host
granule. The longest-lived up flows are located on larger granules,
while shorter-lived ones tend to be located on smaller granules. Results
from simulations carried out in other studies suggest that the fastest
granular up flows occur chiefly during two scenarios: 1) on the edges
of granules when their centers cool, before the granules subsequently
split and 2) when a granule is forced under the surface by powerful
down flows from adjacent granules. Our observations provide evidence
for these results.
Title: Chromospheric Observations of a Kink Wave in an On-disk Active
Region Fibril
Authors: Pietarila, A. M.; Aznar Cuadrado, R.; Hirzberger, J.;
Solanki, S.
Bibcode: 2011AGUFMSH13B1951P
Altcode:
Most observations of kink and Alfven waves in the chromosphere are
made in off-limb spicules. Here we present observations of a kink wave
in high spatial and temporal resolution Ca II 8542 data of an active
region fibril on the solar disk. The properties of the observed wave
are similar to kink waves in spicules. From the inferred wave phase
and period we estimate the lower limit for the field strength in the
chromospheric fibril to be a few hundred Gauss. The observations
indicate that the event may have been triggered by a small-scale
reconnection event higher up in the atmosphere.
Title: Erratum:"Convective Nature of Sunspot Penumbral
Filaments: Discovery of Downflows in the Deep Photosphere" (2011, ApJ, 734, L18)
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
Bibcode: 2011ApJ...740L..55J
Altcode:
No abstract at ADS
Title: Kink Waves in an Active Region Dynamic Fibril
Authors: Pietarila, A.; Aznar Cuadrado, R.; Hirzberger, J.; Solanki,
S. K.
Bibcode: 2011ApJ...739...92P
Altcode: 2011arXiv1107.3113P
We present high spatial and temporal resolution Ca II 8542 Å
observations of a kink wave in an on-disk chromospheric active region
fibril. The properties of the wave are similar to those observed in
off-limb spicules. From the observed phase and period of the wave we
determine a lower limit for the field strength in the chromospheric
active region fibril located at the edge of a sunspot to be a few
hundred gauss. We find indications that the event was triggered by a
small-scale reconnection event higher up in the atmosphere.
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: Convective Nature of Sunspot Penumbral Filaments: Discovery
of Downflows in the Deep Photosphere
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
Bibcode: 2011ApJ...734L..18J
Altcode: 2011arXiv1105.1877J
We study the velocity structure of penumbral filaments in the deep
photosphere to obtain direct evidence for the convective nature of
sunspot penumbrae. A sunspot was observed at high spatial resolution
with the 1 m Swedish Solar Telescope in the deep photospheric C I 5380
Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution
method is used for image restoration and straylight is filtered out. We
report here the discovery of clear redshifts in the C I 5380 Å line
at multiple locations in sunspot penumbral filaments. For example,
bright head of filaments show larger concentrated blueshift and are
surrounded by darker, redshifted regions, suggestive of overturning
convection. Elongated downflow lanes are also located beside bright
penumbral fibrils. Our results provide the strongest evidence yet
for the presence of overturning convection in penumbral filaments and
highlight the need to observe the deepest layers of the penumbra in
order to uncover the energy transport processes taking place there.
Title: Performance validation of phase diversity image reconstruction
techniques
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Gandorfer,
A.; Solanki, S. K.
Bibcode: 2011A&A...529A.132H
Altcode:
We present a performance study of a phase diversity (PD) image
reconstruction algorithm based on artificial solar images obtained
from MHD simulations and on seeing-free data obtained with the SuFI
instrument on the Sunrise balloon borne observatory. The artificial
data were altered by applying different levels of degradation with
synthesised wavefront errors and noise. The PD algorithm was modified
by changing the number of fitted polynomials, the shape of the pupil and
the applied noise filter. The obtained reconstructions are evaluated by
means of the resulting rms intensity contrast and by the conspicuousness
of appearing artifacts. The results show that PD is a robust method
which consistently recovers the initial unaffected image contents. The
efficiency of the reconstruction is, however, strongly dependent on the
number of used fitting polynomials and the noise level of the images. If
the maximum number of fitted polynomials is higher than 21, artifacts
have to be accepted and for noise levels higher than 10-3
the commonly used noise filtering techniques are not able to avoid
amplification of spurious structures.
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: 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: 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: Evidence for Convection in Sunspot Penumbrae
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
Bibcode: 2010ApJ...722L.194B
Altcode: 2010arXiv1009.2919B
We present an analysis of twisting motions in penumbral filaments in
sunspots located at heliocentric angles from 30° to 48° using three
time series of blue continuum images obtained by the Broadband Filter
Imager (BFI) on board Hinode. The relations of the twisting motions to
the filament brightness and the position within the filament and within
the penumbra, respectively, are investigated. Only certain portions
of the filaments show twisting motions. In a statistical sense, the
part of the twisting portion of a filament located closest to the
umbra is brightest and possesses the fastest twisting motion, with a
mean twisting velocity of 2.1 km s-1. The middle and outer
sections of the twisting portion of the filament (lying increasingly
further from the umbra), which are less bright, have mean velocities
of 1.7 km s-1 and 1.35 km s-1, respectively. The
observed reduction of brightness and twisting velocity toward the
outer section of the filaments may be due to reducing upflow along the
filament's long axis. No significant variation of twisting velocity as
a function of viewing angles was found. The obtained correlation of
brightness and velocity suggests that overturning convection causes
the twisting motions observed in penumbral filament and may be the
source of the energy needed to maintain the brightness of the filaments.
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: Spectrograph capabilities of the European Solar Telescope
Authors: Calcines, A.; Collados, M.; Feller, A.; Grauf, B.;
Grivel-Gelly, C.; Hirzberger, J.; López Ariste, A.; López López,
R.; Mein, P.; Sayède, F.
Bibcode: 2010SPIE.7735E..20C
Altcode: 2010SPIE.7735E..68C
EST is a project for a 4-meter class telescope to be located in the
Canary Islands. EST will be optimized for studies of the magnetic
coupling between the photosphere and the chromosphere. This requires
high spatial and temporal resolution diagnostics tools of properties of
the plasma, by using multiple wavelength spectropolarimetry. To achieve
these goals, visible and near-IR multi-purpose spectrographs are being
designed to be compatible with different modes of use: LsSS (Long-slit
Standard Spectrograph), multi-slit multi-wavelength spectrograph with
an integral field unit, TUNIS (Tunable Universal Narrow-band Imaging
Spectrograph), and new generation MSDP (Multi-channel Subtractive
Double-pass Spectrograph). In this contribution, these different
instrumental configurations are described.
Title: High resolution imaging and polarimetry with SUNRISE, a
balloon-borne stratospheric solar observatory
Authors: Barthol, Peter; Chares, Bernd; Deutsch, Werner; Feller, Alex;
Gandorfer, Achim; Grauf, Bianca; Hirzberger, Johann; Meller, Reinhard;
Riethmueller, Tino; Schuessler, Manfred; Solanki, Sami K.; Knoelker,
Michael; Martinez Pillet, Valentin; Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4063B
Altcode: 2010cosp.meet.4063B
SUNRISE is an international collaboration for the development
and operation of a meter-class balloon-borne stratospheric solar
observatory. Prime science goal is the study of structure and dynamics
of the magnetic field in the solar atmosphere and the interaction of
the magnetic field with convective plasma flows. These processes are
studied by high resolution imaging in the UV and polarimetry at visible
wavelengths. The instrument has been successfully launched on June 8,
2009 from ESRANGE, Kiruna, Northern Sweden. During the more than 5
days flight about 1.5 TByte of scientific data were collected. The
paper gives an overview of the instrument and mission, examples of
the scientific output will also be presented. SUNRISE is a joint
project of the Max-Planck-Institut fuer Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik
(KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the
Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and
the Spanish IMaX consortium.
Title: The Ultraviolet Filter Imager (SuFI) onboard the Sunrise
balloon-borne solar observatory: Instrument description and first
results
Authors: Gandorfer, Achim; Barthol, Peter; Feller, Alex; Grauf,
Bianca; Hirzberger, Johann; Riethmueller, Tino; Solanki, Sami K.;
Berkefeld, Thomas; Knoelker, Michael; Martinez Pillet, Valentin;
Schmidt, Wolfgang; Title, Alan
Bibcode: 2010cosp...38.4064G
Altcode: 2010cosp.meet.4064G
We describe the design of the near UV filter imager SuFi onboard
Sunrise, which was successfully flown in the stratosphere in June
2009. During its five days flight SuFI captured the highest contrast
images of solar granulation ever. SuFI is a diffraction limited filter
imager with an effective focal length of 121m, working in 5 distinct
wavelength bands between 210nm and 397nm. It is based on a two mirror
modified Schwarzschild microscope, which is integral part of the central
Image stabilization and light Distribution unit (ISLiD) of Sunrise,
which acts as the reimaging optics between the 1m telescope and the
science instruments. The key technical features of the instrument are
presented under the view of the specific demands of balloon-borne
optical systems. First results obtained with the instrument are
presented to demonstrate the capabilities of the instrument.
Title: UV intensity distributions of the quiet Sun observed with
Sunrise
Authors: Hirzberger, Johann; Feller, A.; Riethmueller, T.; Borrero,
J. M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martínez Pillet, V.; Schmidt, W.; Solanki, S.; Title, A.
Bibcode: 2010cosp...38.1735H
Altcode: 2010cosp.meet.1735H
High resolution solar images in the near UV have been obtained with
the Solar UV Filtergraph (SUFI) onboard the Sunrise balloon borne
observatory, amongst others in wavelength regions not accessible
from the ground. We present intensity distributions of the quiet
Sun at different heliocentric angles, from disk center to the solar
limb. These results, obtained in spectral windows at 214 nm, 313 nm
(OH band), 388 nm (CN band) and 396.7 nm (CaIIH), represent an important
validation of numerical models of the solar photosphere and are, thus,
fundamental ingredients for our understanding of the thermal processes
in the solar surface region.
Title: Relation between the Sunrise photospheric magnetic field and
the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
Bibcode: 2010cosp...38.2856J
Altcode: 2010cosp.meet.2856J
Recent observations from the Sunrise balloon-borne solar telescope
have enabled us to reach an unprecedented high spatial resolution
on the solar surface with the near-ultraviolet photo-spheric and
chromospheric images as well as the magnetograms. We use these high
resolution observations to investigate the structure of the solar
upper photosphere and lower chromosphere as well as their temporal
evolutions. We study the relation between the inter-granular Ca II
397 nm bright structures in images obtained by the Sunrise Filter
Imager (SuFI) and their corresponding photospheric vector magnetic
field computed from the Imaging Magnetogram eXperiment (IMaX)
observations. The targets under study are in a quiet Sun region and
close to disc-centre.
Title: High-resolution spectro-polarimetry of a flaring sunspot
penumbra
Authors: Hirzberger, J.; Riethmüller, T.; Lagg, A.; Solanki, S. K.;
Kobel, P.
Bibcode: 2009A&A...505..771H
Altcode: 2009arXiv0908.3803H
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904 during a weak flare eruption
(GOES magnitude B7.8), obtained with the Swedish Solar Telescope
(SST) in La Palma, Canary Islands. High-resolution Ca II H images
show a typical two-ribbon structure that has been hitherto only
known for larger flares, and the flare appears in a confined region
that is discernible by a bright border. The underlying photosphere
shows a disturbed penumbral structure with intersecting branches of
penumbral filaments. High-resolution Doppler- and vector-magnetograms
exhibit oppositely directed Evershed flows and magnetic field vectors
in the individual penumbral branches, resulting in several regions
of magnetic azimuth discontinuity and several islands where the
vertical magnetic field is reversed. The discontinuity regions are
co-spatial with the locations of the onset of the flare ribbons. From
the results, we conclude that the confined flare region is detached
from the global magnetic field structure by a separatrix marked by the
bright border visible in C II H. We further conclude that the islands
of reversed vertical field appear because of flux emergence and that
the strong magnetic shear appearing in the regions of magnetic azimuth
discontinuity triggers the flare. Movies are only available in
electronic form at http://www.aanda.org
Title: Bright fibrils in Ca II K
Authors: Pietarila, A.; Hirzberger, J.; Zakharov, V.; Solanki, S. K.
Bibcode: 2009A&A...502..647P
Altcode: 2009arXiv0905.3124P
Context: Except for the Ca II resonance lines, fibrils are ubiquitously
present in most high-resolution observations of chromospheric lines.
Aims: We show that fibrils are also a prevailing feature in Ca II K,
provided the spatial-resolution is sufficiently high.
Methods:
We present high spatial resolution observations of an active region in
the Ca II K line from the Swedish Solar Telescope. Through a comparison
between photospheric intensity and magnetic field data, we study the
connection between bright chromospheric fibrils and photospheric
structures. Additionally, using Fourier analysis we study how the
fibrils are linked to the observed dynamics.
Results: We find
that very narrow, bright fibrils are a prevailing feature over large
portions of the observed field. We also find a clear connection between
the fibril footpoints and photospheric magnetic features. We show that
the fibrils play two distinct roles in the observed dynamics: depending
on their location they can act as a canopy suppressing oscillations or
they can channel low-frequency oscillations into the chromosphere.
Conclusions: The Ca II K fibrils share many characteristics with
fibrils observed in other chromospheric lines, but some features,
such as the very small widths, are unique to these observations.
Title: Discriminant analysis of solar bright points and
faculae. I. Classification method and center-to-limb distribution
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.; Gandorfer, A.;
Zakharov, V.
Bibcode: 2009A&A...502..303K
Altcode: 2010arXiv1001.5143K
Context: While photospheric magnetic elements appear mainly as
Bright Points (BPs) at the disk center and as faculae near the limb,
high-resolution images reveal the coexistence of BPs and faculae over a
range of heliocentric angles. This is not explained by a “hot wall”
effect through vertical flux tubes, and suggests that the transition
from BPs to faculae needs to be quantitatively investigated.
Aims:
To achieve this, we made the first recorded attempt to discriminate
BPs and faculae, using a statistical classification approach based
on Linear Discriminant Analysis (LDA). This paper gives a detailed
description of our method, and shows its application on high-resolution
images of active regions to retrieve a center-to-limb distribution of
BPs and faculae.
Methods: Bright “magnetic” features were
detected at various disk positions by a segmentation algorithm using
simultaneous G-band and continuum information. By using a selected
sample of those features to represent BPs and faculae, suitable
photometric parameters were identified for their discrimination. We
then carried out LDA to find a unique discriminant variable, defined
as the linear combination of the parameters that best separates the
BPs and faculae samples. By choosing an adequate threshold on that
variable, the segmented features were finally classified as BPs and
faculae at all the disk positions.
Results: We thus obtained
a Center-to-Limb Variation (CLV) of the relative number of BPs and
faculae, revealing the predominance of faculae at all disk positions
except close to disk center (μ ≥ 0.9).
Conclusions: Although
the present dataset suffers from limited statistics, our results are
consistent with other observations of BPs and faculae at various disk
positions. The retrieved CLV indicates that at high resolution, faculae
are an essential constituent of active regions all across the solar
disk. We speculate that the faculae near disk center as well as the BPs
away from disk center are associated with inclined fields. Figures
11-14 are only available in electronic form at http://www.aanda.org
Title: Center to Limb Distribution of Bright Points and Faculae:
First Results of an Automated Detection Algorithm
Authors: Kobel, P.; Hirzberger, J.; Zakharov, V.; Gandorfer, A.;
Solanki, S. K.
Bibcode: 2009ASPC..405..211K
Altcode:
Center to limb variations (CLV) of photospheric Bright Points (BPs)
and faculae are important to understand the fundamental relationship
between these magnetic features. In this context, we present a
statistical study of the center to limb distribution of BPs and faculae
in active regions. Magnetic brightenings were detected at various disk
positions by an automated segmentation algorithm based on joint G-band
and continuum information. They were then classified as BPs or faculae
according to a linear discriminant analysis, which allowed to determine
the relative fraction of the two classes at each disk position.
Title: Multi-Channel Observations of a Solar Flare
Authors: Hirzberger, J.; Riethmüller, T.; Solanki, S. K.; Kobel, P.
Bibcode: 2009ASPC..405..125H
Altcode:
On August 13, 2006 we performed simultaneous observations in Ca IIH,
G-band and Fe I 6303 Å of a complex sunspot in NOAA~10904 with
the Swedish Solar Telescope (SST) on La Palma, Canary Islands. From
spectro-polarimetric scans through the Fe I line with the tunable
SOUP filter we computed the full Stokes vectors at each pixel of the
field of view. At 8:47 UT a weak flare eruption (GOES class B7.8) was
registered in the line core of Ca IIH. We present the changing magnetic
field and flow topologies in the underneath penumbral photosphere
during the flaring phase. The unmatched spatial resolution of SST
observations allows detailed simultaneous mapping of chromospheric
and photospheric events.
Title: Fibrils in Ca II K
Authors: Pietarila, A.; Solanki, S.; Hirzberger, J.; Zakharov, V.
Bibcode: 2008ESPM...12.2.51P
Altcode:
High spatial resolution observations have revealed that fibril-like
structures are a ubiquitous feature of the solar chromosphere. They are
observed in most chromospheric lines, e.g., H-? and Ca II IRT. Until
recently, there have been no reports of these structures in the Ca
II H and K lines. Instead, these lines have revealed a hazy, uniform
chromosphere and only in the highest resolution images have there been
any indications of fibril structures. We present high spatial
resolution Ca II K observations from the Swedish Solar Telescope
which show that fibrils are a prevailing feature in regions where
the bulk of the signal is chromospheric. Based on the cotemporal
continuum and nearly cotemporal magnetic field observations it is
clear that the fibril foot points originate from photospheric magnetic
concentrations. The fibrils share many characteristics, e.g. lifetime
and dynamics, with fibrils observed in other spectral lines. They are
also found to play an important role in the dynamics: in the plage
they channel low frequency waves into the chromosphere while in the
more quiet regions the highly inclined fibrils form a multi-layer
canopy that suppresses oscillations from below.
Title: Structure and Evolution of Supergranulation from Local
Helioseismology
Authors: Hirzberger, Johann; Gizon, Laurent; Solanki, Sami K.; Duvall,
Thomas L.
Bibcode: 2008SoPh..251..417H
Altcode: 2008SoPh..tmp..106H
Supergranulation is visible at the solar surface as a cellular
pattern of horizontal outflows. Although it does not show a distinct
intensity pattern, it manifests itself indirectly in, for example,
the chromospheric network. Previous studies have reported significant
differences in the inferred basic parameters of the supergranulation
phenomenon. Here we study the structure and temporal evolution of a
large sample of supergranules, measured by using local helioseismology
and SOHO/MDI data from the year 2000 at solar activity minimum. Local
helioseismology with f modes provides maps of the horizontal divergence
of the flow velocity at a depth of about 1 Mm. From these divergence
maps supergranular cells were identified by using Fourier segmentation
procedures in two dimensions and in three dimensions (two spatial
dimensions plus time). The maps that we analyzed contain more than
105 supergranular cells and more than 103
lifetime histories, which makes possible a detailed analysis with high
statistical significance. We find that the supergranular cells have
a mean diameter of 27.1 Mm. The mean lifetime is estimated to be 1.6
days from the measured distribution of lifetimes (three-dimensional
segmentation), with a clear tendency for larger cells to live longer
than smaller ones. The pair and mark correlation functions do not
show pronounced features on scales larger than the typical cell size,
which suggests purely random cell positions. The temporal histories of
supergranular cells indicate a smooth evolution from their emergence
and growth in the first half of their lives to their decay in the
second half of their lives (unlike exploding granules, which reach
their maximum size just before they fragment).
Title: Evidence of convective rolls in a sunspot penumbra
Authors: Zakharov, V.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Kobel, P.
Bibcode: 2008A&A...488L..17Z
Altcode: 2008arXiv0808.2317Z
Aims: We study the recently discovered twisting motion of bright
penumbral filaments with the aim of constraining their geometry and
the associated magnetic field.
Methods: A large sunspot located
40° from disk center was observed at high resolution with the 1-m
Swedish Solar Telescope. Inversions of multi-wavelength polarimetric
data and speckle reconstructed time series of continuum images were
used to determine proper motions, as well as the velocity and magnetic
structure in penumbral filaments.
Results: The continuum movie
reveals apparent lateral motions of bright and dark structures inside
bright filaments oriented parallel to the limb, confirming recent
Hinode results. In these filaments we measure upflows of ≈1.1
km s-1 on their limbward side and weak downflows on
their centerward side. The magnetic field in them is significantly
weaker and more horizontal than in the adjacent dark filaments.
Conclusions: The data indicate the presence of vigorous convective
rolls in filaments with a nearly horizontal magnetic field. These
are separated by filaments harbouring stronger, more vertical
fields. Because of reduced gas pressure, we see deeper into the
latter. When observed near the limb, the disk-centerward side of the
horizontal-field filaments appear bright due to the hot wall effect
known from faculae. We estimate that the convective rolls transport
most of the energy needed to explain the penumbral radiative flux.
Title: Discriminant Analysis of Bright Points and Faculae:
Center-to-Limb Distribution, Contrast and Morphology
Authors: Kobel, P.; Hirzberger, J.; Gandorfer, A.; Solanki, S. K.;
Zakharov, V.
Bibcode: 2008ESPM...12.2.60K
Altcode:
High-resolution images of the solar photosphere reveal an intriguing
mixture of Brights Points (BPs) and faculae at several disk positions,
which is not explained by the conventional "hot wall'' model. Together
with quantitative discrepancies between observations and simulations
of faculae, it stresses that the fundamental relationship between BPs
and faculae is not yet clear: How are BPs and faculae distributed on
the solar disk? How do the photometric properties of BPs and faculae
differ and vary with disk position? To tackle these issues, a
necessary step is to sort the BPs and faculae at various disk positions,
in order to treat them separately. We present here the first attempt
to discriminate BPs and faculae, using a statistical classification
approach based on Linear Discriminant Analysis (LDA). This has never
been done so far, presumably due to the lack of known automated methods
to distinguish such features, and to the difficulty to obtain a coherent
dataset of high-resolution images recorded in the same conditions. We
applied our method to high-resolution G-band and continuum images
of active regions recorded at the Swedish Solar Telescope, covering
several disk positions where the transition from BPs to faculae
is expected. This allowed us to retrieve a first estimate of
the center-to-limb variation of the relative distribution of both
species. The center-to-limb distribution of BPs and faculae reveals
the predominance of faculae at all disk positions except close to disk
center. We argue that these ubiquitous faculae could be the transient
signatures of swaying flux tubes with a wide range of inclination
angles. Moreover, we statistically compared the G-band and continuum
contrast of BPs and faculae, and characterized their morphology. Both
the G-band and continuum contrast of BPs and faculae are found to
similarly increase from center to limb. But when comparing G-band
to continuum, BPs and faculae exhibit slightly different behaviours,
which are related to radiative transfer processes. By orienting the
features in local coordinate frames corresponding to the principal axes
of their contrast moment of inertia, we could retrieve characteristic
G-band contrast profiles exhibiting the typical predicted asymmetry
for faculae. Finally, our BPs and faculae were found to have very
similar morphological properties. Although our study is essentially
descriptive and based on purely photometric information, we hope that it
will provide novel useful constraints for future BPs/faculae MHD models.
Title: Imaging of the He D3/Hβ Emission Ratio in Quiescent
Solar Prominences
Authors: Hirzberger, J.; Wiehr, E.; Stellmacher, G.
Bibcode: 2007ASPC..368..321H
Altcode:
Quiescent solar prominences have been observed simultaneously in
profile-integrated He D3 and Hβ emission with the SST on
La Palma. The two-dimensional ratio maps of the He D3 and
Hβ intensities are used to study temporal variations of intrinsic
prominence parameters. Sub-areas with substantial variation of
the intensity distribution indicate the evolution of prominence
structures. When the emission ratio remains unchanged, the evolving
threads are of largely equal physical state. Other regions which show
a temporal varying emission ratio indicate substancial evolution of
the intrinsic physical conditions. We propose that distance variation
between the threads affects different penetration of the EUV irradiation
required for populating of the He triplet system.
Title: Two-dimensional imaging of the He D_3/Hbeta emission ratio
in quiescent solar prominences .
Authors: Stellmacher, G.; Wiehr, E.; Hirzberger, J.
Bibcode: 2007MmSAI..78..108S
Altcode:
Simultaneous prominences spectroscopy with THEMIS in the emission
lines H-alpha, H-beta, HeD3, NaD2, Mgb2 and He(singlet)5015 lead to
an extended study of two-dimensional images simultaneously in H-beta
and HeD3. The spatial variation of the integrated line intensities and
their ratio shows mainly two characteristics: (a) A constant emission
ratio (even) in regions with substantial intensity variations; this
can be explained by a varying number of superposing threads with equal
physical states. (b) A varying emission ratio (often) tightly related
to intensity changes; this indicates a superposition of threads with
different physical states (most likely the gas-pressure). We also
observe temporal changes of the emission ratio which seem to be too
fast for a variation of the gas-pressure; here, we suppose a change of
the packing density of threads along the line-of-sight which affects
the penetration of ionizing UV radiation required for the He triplet
excitation.
Title: Two-Dimensional Mapping of the He D3/Hβ Emission
Ratio in Solar Prominences
Authors: Wiehr, Eberhard; Stellmacher, Goetz; Hirzberger, Johann
Bibcode: 2007SoPh..240...25W
Altcode:
Solar prominences have been simultaneously observed in the integrated
light of the He D3 and the Hβ emissions on two successive
days, using the SST on La Palma with its tip-tilt mirror locked on a
nearby white-light limb facular grain. The spatial and the temporal
variation of the integrated line intensities and their ratio shows
mainly two characteristics: (A) Constant emission ratio (even)
in regions with substantial intensity variations and (B) varying
emission ratio (often) tightly related to intensity structures of the
prominence. (A) May be explained by a different number of superposing
threads along the line of sight having very similar physical state. (B)
Indicates threads with different intrinsic physical states; these
may depend on the gas pressure or the inner structure of each thread,
i.e., the "packing density," affecting the penetration of ionizing EUV
radiation, which affects the He I level populations and thus the rate
of the triplet excitation.
Title: Structure and evolution of supergranulation from local
helioseismology
Authors: Hirzberger, J.; Gizon, L.; Solanki, S. K.; Duvall, T. L.
Bibcode: 2007msfa.conf..103H
Altcode:
Maps of the horizontal divergence of the near-surface velocity field
have been calculated using local helioseismology and SOHO/MDI full-disk
Dopplergrams. These maps provide a continuous coverage for two to
three months each year with a cadence of 12 hours. Geometrical and
evolutional properties of individual supergranular cells have been
studied. Supergranular cells have sizes in a range around 650Mm2
(circular diameter of 28.77 Mm) with lifetimes of up to 4.5 days. We
also observe a clear trend for larger cells to have stronger divergence
values and larger lifetimes than smaller ones.
Title: T he Performance Of The SOLO-VIM Instrument: Effects Of
Instrumental Noise And Lossy Data Compression
Authors: Lagg, A.; Yelles, L.; Hirzberger, J.; Woch, J.; Solanki, S. K.
Bibcode: 2007ESASP.641E..69L
Altcode:
Spectropolarimetric observations in photospheric lines reveal a
wealth of information on physical parameters of the solar atmosphere
like magnetic field strength and di rection or the line-of sight
velocity. These observations require the measurement of the four Stokes
parameters at a sample of N wavelength positions around the core of the
spectral line, resulting in 4N images for one observation. The Visible
light Imager and Magnetograph (VIM) instrument on board Solar Orbiter
is capable of performing these measurements. However, the data rate
required to transfer all 4N images with the required cadence is well
beyond the telemetry limit. Here we use realistic, three-dimensional
MHD simulations in order to simulate science data provided by VIM which
are then used to test various compression techniques. We conclude that
lossy data compression and instrumental noise have similar effects on
the output data.
Title: S imulations Of Science Data Of The Solo-VIM Instrument
Authors: Yelles, L.; Hirzberger, J.; Lagg, A.; Woch, J.; Solanki,
S. K.; Vögler, A.
Bibcode: 2007ESASP.641E..34Y
Altcode:
The SolO-VIM instrument will be a two-dimensional full-Stokes
spectro-polarimeter which will provide diffraction-limited
vector-magnetograms, Dopplergrams, and continuum images of the solar
photosphere. The instrument's performance depends on various parameters
such as aperture diameter, filter characteristics, spectral- line
sampling, and orbital position. Here we compute Stokes profiles in
realistic 3D MHD simulations. These synthetic data are then degraded to
match the output ex- pected from the VIM instrument, and subsequently
inverted using a Milne-Eddington atmosphere. We present parameter
studies in order to set up minimum require- ments on limitations of
VIM's capabilities.
Title: Two-dimensional imaging of the HeD3/H[Beta] emission ratio
in quiescent solar prominences
Authors: Wiehr, E.; Stellmacher, G.; Hirzberger, J.
Bibcode: 2007msfa.conf..261W
Altcode:
We extend our earlier studies of two-dimensional prominence imaging
by simultaneous observations of the HeD3 and H[Beta] emissions at
the 1m SST on La Palma. The observed small spatial variations of the
HeD3/H[Beta] ratio indicate rather homogeneous physical conditions
within prominences. Sub-regions do exist which show a largely uniform
ratio in spite of substantial spatial intensity variations. Here, the
fine-structures will exhibit almost uniform physical conditions. In
other regions with variations of the ratio parallel to the emissions,
the structures will have different intrinsic physical state.
Title: Dynamics of solar mesogranulation
Authors: Leitzinger, M.; Brandt, P. N.; Hanslmeier, A.; Pötzi, W.;
Hirzberger, J.
Bibcode: 2005A&A...444..245L
Altcode:
Using a 45.5-h time series of photospheric flow fields generated
from a set of high-resolution continuum images (SOHO/MDI) we analyze
the dynamics of solar mesogranule features. The series was prepared
applying a local correlation tracking algorithm with a 4.8´´ FWHM
window. By computing 1-h running means in time steps of 10 min we
generate 267 averaged divergence maps that are segmented to obtain
binary maps. A tracking algorithm determines lifetimes and barycenter
coordinates of regions of positive divergence defined as mesogranules
(MGs). If we analyze features of lifetimes ≥1 h and of areas ≥5
Mm{2 we find a mean drift velocity of 304 m s-1
(with ± 1σ variation of 180 m s-1), a mean travel distance
of 2.5 ± 1.8 Mm, a mean lifetime of 2.6 ± 1.8 h, and a 1/e decay time
of 1.6 h for a total of 2022 MGs. The advective motion of MGs within
supergranules is seen for 50 to 70% of the long-lived (≥4 h) MGs while
the short-lived ones move irregularly. If only the long-lived MGs are
further analyzed the drift velocities reduce to 207 m s-1
and the travel distances increase to 4.1 Mm on average, which is an
appreciable fraction of the supergranular radius. The results are
largely independent of the divergence segmentation level.
Title: The structure of a penumbral connection between solar pores
Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.;
Puschmann, K. G.; Sobotka, M.
Bibcode: 2005A&A...442.1079H
Altcode:
High resolution 2D-spectro-polarimetric observations have been used
to analyse the magnetic field and flow topologies of a penumbral
connection between two opposite polarity solar pores. A filamentary
structured Evershed-like material flow from one pore to the other
along the magnetic field lines has been detected. The flow channels
are co-spatial with bright penumbral filaments close to the pore which
feeds the flow and the clear brightness-velocity relation vanishes close
to the pore which represents the sink of the flow. The boundary between
umbra and penumbra of the two pores show significant differences: bright
comet-like penumbral grains represent endings of penumbral filaments
at the flow sources whereas no such grains were found at the sinks of
the flow. Furthermore, a systematic variation of the asymmetries of
measured Stokes V profiles across the penumbral connection have been
found. The obtained results are in accordance with the widely-accepted
uncombed penumbra hypothesis and the moving flux tube model.
Title: Solar limb faculae
Authors: Hirzberger, J.; Wiehr, E.
Bibcode: 2005A&A...438.1059H
Altcode:
We observe solar limb faculae at an unprecedented spatial
resolution with the new 1 m Swedish Solar Telescope SST on La
Palma. Speckle-reconstructed images are used to study 4475 limb
facular grains simultaneously in the 430 nm G-band and the 587.5±1.5
continuum up to only 1'' from the limb (cos θ=0.05). No systematic
contrast decrease is found even a few arcsec from the solar limb. The
facular grains appear to be “projected” on the limb-side neighboring
granules; approaching the disc center, the corresponding features occur
as inter-granular G-band bright points. Independently, we took spectra
with the French-Italian THEMIS telescope on Tenerife and find that
the known “line-gap effect” from disc center disappears near the
limb. Here, the facular continuum is enhanced whereas the normalized
profiles are unchanged with respect to the undisturbed neighborhood.
Title: On small scale magnetic structures in the solar photosphere
Authors: Stangl, S.; Hirzberger, J.
Bibcode: 2005A&A...432..319S
Altcode:
The distribution of the magnetic field on the solar surface is as
yet unknown in detail, but of considerable importance for solar
physics in general. We have observed two different solar regions,
one containing a small pore, the other region comprising a network in
the light of the Fe I λ6301.5 Å and Fe I λ6302.5 Å lines at the
German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife,
Spain) with the “Göttingen” Fabry-Pérot Interferometer. By
applying image reconstruction techniques to broad- and narrowband
filtergrams we obtained continuum images, line core images, as well
as line-of-sight velocity and magnetic field maps. We present scatter
plots of the line core intensity vs. the Doppler velocity and the
vertical component of the magnetic field, which reveal that the line
core brightness is not a clear indicator for magnetic fields in the
solar atmosphere. Furthermore, we estimate the swaying motion of flux
tubes to be mostly smaller than 0.3 arcsec and thus in good agreement
with the predictions of theoretical dynamic models. Finally, we show
how the choice of the observed solar target influences the results
and their interpretation. We claim that generalizations can mislead,
and strongly depend on the presence or absence of solar (magnetic)
features in the analyzed data.
Title: Dynamics of Solar Mesogranulation
Authors: Leitzinger, M.; Brandt, P. N.; Hanslmeier, A.; Pötzi, W.;
Hirzberger, J. K.
Bibcode: 2005HvaOB..29...49L
Altcode:
Using a 45.5-h time series of photospheric flow fields generated from
a set of high-resolution continuum images (SOHO/MDI) we analyse the
dynamics of solar mesogranule features. The series was prepared by
Shine et al. (2000) applying a local correlation tracking algorithm
with a 4.8 arcsec FWHM window. By computing 1-h running means in time
steps of 10 minutes we generate 267 averaged divergence maps which
are then segmented to obtain binary maps. A tracking algorithm then
determines lifetimes and barycentre coordinates of regions of positive
divergence defined as mesogranules (MGs). If we analyse features of
lifetimes ≥1 h and areas ≥5 Mm2 we find a mean drift velocity of
304 ms, a mean travel distance of 2.5 Mm, a mean lifetime of 2.6 h,
and a 1/e decay time of 1.6 h for a total of 2022 MGs. The advective
motion of MGs within supergranules, which was found by Muller et
al. (1992) and confirmed by Shine et al. (2000), is seen for half to
two-thirds of the long-lived (≥4 h) MGs while the short-lived ones
move irregularly. The results prove to be nearly independent of the
divergence segmentation level.
Title: Properties of a Small Active Region in the Solar Photosphere
Authors: Stangl, S.; Hirzberger, J.
Bibcode: 2005ASSL..320..251S
Altcode: 2005smp..conf..251S
No abstract at ADS
Title: Brightness and size of small-scale solar magnetic flux
concentrations
Authors: Wiehr, E.; Bovelet, B.; Hirzberger, J.
Bibcode: 2004A&A...422L..63W
Altcode:
The new 1 m Swedish Solar Telescope SST on La Palma allows to observe
inter-granular G-band bright points (igBP) in solar active regions at
an unprecedented spatial resolution. The igBP are reasonably assumed
to be small-scale magnetic flux-concentrations. A sample of more than
1500 igBP shows tight relations of diameter and brightness in the
G-band and in the continuum; it covers a diameter range of 100 km to
300 km, with a most frequent value near 160 km. Features larger than
300 km formerly reported, evidently result from insufficient spatial
resolution; that upper diameter limit is close to the typical width
of inter-granular lanes, and suggests a ``gap'' to small pores. The
lack of igBP with sizes below 130 km is discussed not to arise from
the finite spatial resolution of the 1 m telescope.
Title: Dynamics of an enhanced network region observed in Hα
Authors: Al, N.; Bendlin, C.; Hirzberger, J.; Kneer, F.; Trujillo
Bueno, J.
Bibcode: 2004A&A...418.1131A
Altcode:
This investigation is based on Hα observations of high spatial
resolution. They stem from an enhanced network region near disk centre
of the sun and consist of broad-band and narrow-band images taken with
the two-dimensional ``Göttingen'' Fabry-Perot spectrometer mounted in
the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The
``lambdameter method'' was applied to derive intensity and velocity
maps over the two-dimensional field of view reflecting the behaviour
of these parameters in the solar chromosphere. The determination of
the source function, the line-of-sight (LOS) velocity, the Doppler
width and the optical depth was based on Beckers' cloud model
(Beckers \cite{beckers}). From the LOS velocity distribution along
the Hα structures we conclude that ballistic motions are unlikely to
prevail. Especially the bright Hα features cannot be explained by the
cloud model. It is shown how, instead, two-dimensional non-LTE radiative
transfer calculations of embedded chromospheric structures lead to
reasonable agreement with the observed line profiles from these bright
features. It is found that many of the bright fibril-like structures
near dark fibrils can be explained by radiation which is blocked by
absorbing material at large heights and escapes through less opaque
regions. We estimate the number densities and the temperature. With
these and with the measured velocities, the kinetic energy flux and
the enthalpy flux related to the motions of the fine structures can
be calculated. Both fall short by at least an order of magnitude of
covering energy losses by radiation of active chromospheric regions.
Title: Imaging spectroscopy of solar pores
Authors: Hirzberger, J.
Bibcode: 2003A&A...405..331H
Altcode:
Time series of two-dimensional spectra and corresponding broad band
images of solar pore regions have been obtained with the ``Göttingen''
Fabry-Perot Interferometer at the Vacuum Tower Telescope in Izaña,
Tenerife. Line bisector shifts have been used for the computation
of line-of-sight velocities in the studied regions. Additionally,
a local correlation tracking (LCT) algorithm has been applied to
obtain horizontal flow velocities from the time series of broad band
images. Resulting velocity maps show that within the pore umbrae the
flows are almost completely inhibited by the magnetic fields. This also
holds for umbral dots and light bridges. On the boundaries of several
pore umbrae persistent downflow channels are visible. The structure
and temporal evolution of these phenomena have been studied. Finally,
the formation of a protopore out of magnetic bright points has been
analyzed. The obtained observational results are in good agreement
with numerical models and common theoretical scenarios explaining the
behaviour and formation of solar pores.
Title: Dynamics of Solar Chromospheric Finestructures in H-alpha
observed with High Spatial Resolution
Authors: Al, Nurol; Kneer, Franz; Hirzberger, Johann
Bibcode: 2003ANS...324..111A
Altcode: 2003ANS...324..P17A
No abstract at ADS
Title: Two-dimensional speckle spectroscopy of Hα features
Authors: Al, N.; Hirzberger, J.; Kneer, F.
Bibcode: 2003AN....324..364A
Altcode:
In May 2002, the solar chromosphere was observed with a two-dimensional
spectrometer which is mounted in the German Vacuum Tower Telescope (VTT)
at the Observatorio del Teide/Tenerife. The aim of this observation was
to investigate the fine structure of the solar chromosphere seen in Hα
. We took narrow-band filtergrams (Delta lambda ~ 72 mÅ) by scanning
through this line. Broad-band images taken strictly simultaneously
with the narrow-band filtergrams were restored by speckle methods. The
instantaneous optical transfer function from this restoration procedure
was used for the reconstruction of the narrow-band images. Some results
of this high spatial resolution observation are presented below.
Title: Granulation and waves
Authors: Hirzberger, J.
Bibcode: 2003AN....324..344H
Altcode:
A summary of the most recent observational results on the solar
granulation phenomenon is given and its physical interpretation
with respect to theoretical and numerical models is briefly
discussed. Special attention is paid to unsolved questions concerning
the relation between convective motions and related solar features.
Title: A Fabry-Perot spectrometer for high-resolution observation
of the Sun
Authors: Kneer, F.; Al, N.; Hirzberger, J.; Nicklas, H.; Puschmann,
K. G.
Bibcode: 2003AN....324..302K
Altcode:
No abstract at ADS
Title: Evidence for short-period acoustic waves in the solar
atmosphere
Authors: Wunnenberg, M.; Kneer, F.; Hirzberger, J.
Bibcode: 2002A&A...395L..51W
Altcode:
Short-period acoustic waves are thought to supply the energy for the
radiative losses of the non-magnetic chromosphere of the Sun and,
in general, of late-type stars. Here, we present evidence for the
existence of waves in the solar atmosphere with periods in the range
of 50 s <P< 100 s. Two-dimensional time sequences with a cadence
of 25 s were obtained from quiet Sun disk center in Fe I 5434 Å. The
observations were performed with the ``Göttingen'' Fabry-Perot
spectrometer in the Vacuum Tower Telescope at the Observatorio del
Teide/Tenerife. They are subjected to speckle reconstruction and to a
wavelet analysis. The atmospheric ranges forming the velocity signals
are narrowed by linear combinations of Doppler maps from wavelengths
near line center. The power in the short-period range is concentrated
above intergranular spaces. We estimate an acoustic flux into the
chromosphere of approximately 3*E6 erg cm-2
s-1, as needed for the chromospheric radiative losses.
Title: On the brightness and velocity structure of solar granulation
Authors: Hirzberger, J.
Bibcode: 2002A&A...392.1105H
Altcode:
A 45 min time series of two-dimensional spectra has been obtained with
the Vacuum Tower Telescope at the Observatorio del Teide in Iza\~
na, Tenerife. Scans over the non-magnetic ion {Fe}i 5576 Å line of
a quiet granular field at disk center were taken simultaneously with
a time series of broad band images. From the spectra intensity and
velocity maps have been calculated at different line-depths. From the
white light images granular shapes have been computed by means of an
automatic image segmentation algorithm. A statistical analysis of the
intensity and velocity distribution in the detected granular shapes has
been carried out. Intensities and velocities are well correlated at low
photospheric levels. In the higher photosphere the intensity pattern
dissolves whereas the velocities show almost no variation within
the probed height interval. The intensity excess of small granules
dissolves at lower heights than that of larger ones. The intensity
and velocity distribution within the granules depends on the granular
size. In smaller structures the maximum intensities and velocities are
located close to the granular barycenters whereas for larger granules
the maxima are shifted towards the granular boundaries. The width of the
transition zone between granules and intergranular lanes is independent
on the granular intensity and is constant at approximately 0farcs 5. The
time evolution of the granular pattern shows a clear dependence of the
lifetime of structures on the spatial wavenumber. The e-folding times
of the temporal coherences decrease according to a power law with an
exponent of beta = 3/2 which is incompatible with the Kolmogorov energy
spectrum of homogeneous and isotropic turbulence and might be taken
as a hint against the overall turbulent character of granular motions.
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: 2D-spectroscopy of the Evershed flow in sunspots
Authors: Hirzberger, J.; Kneer, F.
Bibcode: 2001A&A...378.1078H
Altcode:
The radial variation of the Evershed flow in two small sunspots (NOAA
8737 and NOAA 9145) is studied by means of two-dimensional spectrograms
of high spatial resolution. We find a systematic decrease of the
flow velocity with photospheric height and a shift of the velocity
maximum towards larger penumbral radii in higher layers but no clear
correlation between flow velocity and continuum intensity. At the
outer penumbral boundaries the Evershed flow ceases abruptly and even
downward directed flow velocities in the deepest probed photospheric
layers were found. Furthermore, granules adjacent to the penumbral
boundary show a systematic redshift of their spot-side parts which is
attributed to fast, eventually supersonic, downflows between them and
the penumbral boundary.
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: High resolution 2D-spectroscopy of granular dynamics
Authors: Hirzberger, J.; Koschinsky, M.; Kneer, F.; Ritter, C.
Bibcode: 2001A&A...367.1011H
Altcode:
Spectroscopic data with high spatial resolution are used to study the
granular dynamics of the Sun. The observations were obtained with the
``Göttingen'' two-dimensional (2D) Fabry-Perot interferometer in the
Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Time
sequences of spectral scans across the non-magnetic Fe I 5576 Å
line were taken from disc center. The 2D spectroscopic images were
reconstructed with speckle methods, from which a spatial resolution
of 0\farcs4-0\farcs5 was achieved. A power and coherence analysis of
intensity and velocity maps from different photospheric heights has been
carried out. The coherence between intensity and velocity fluctuations
stays high for structural scales >0\farcs5, which underlines the
high spatial resolution of the data. Furthermore, the vertical flow
field and its time evolution within exploding granules have been
analyzed. We find fast downflows in the dark centers of exploding
granules with velocities up to 1.2 km s-1. Additionally, we
estimated the flow velocities of so-called ``dark dots''. We discuss
indications that these structures represent a new type of downflow
within the centers of bright granules.
Title: A Fabry-Perot Spectrometer for High-Resolution Observation
of the Sun
Authors: Kneer, F.; Hirzberger, J.
Bibcode: 2001AGM....18S1005K
Altcode:
Fabry-Perot interferometers (FPIs) are powerful instruments for
spectro-polarimetry of the Sun with high spatial resolution. They
allow easy image reconstruction of two-dimensional narrow-band fields
of view. Some examples of high quality results obtained with the
``Göttingen'' FPI spectrometer, mounted in the Vacuum Tower Telescope
at the Observatorio del Teide/Tenerife, are presented in a poster to
this workshop. We thus concentrate on the design of a new instrument
for the 1.5 m GREGOR solar telescope. We discuss the pros and cons
of telecentric and collimated mounting and describe the expected
performance, especially the spectral resolution, of our design.
Title: Speckle spectro-polarimetry of solar magnetic structures
Authors: Koschinsky, M.; Kneer, F.; Hirzberger, J.
Bibcode: 2001A&A...365..588K
Altcode:
We present speckle observations of small-scale magnetic structures
on the Sun. They were obtained with the ``Göttingen'' Fabry-Perot
interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio
del Teide, Tenerife, from quiet and active regions close to disc
center. A Stokes V polarimeter was added to the FPI to measure
V profiles in the Fe I 6302.5 Å line. The setup allows image
reconstruction with speckle methods. The achieved spatial resolution
in the magnetograms is 0farcs4 -0farcs5 . We describe the observational
technique and the data reduction. The results from small-scale magnetic
flux elements in a very quiet region, in an active region with pores
and abnormal granulation, and in a sunspot with its surroundings
are discussed. In the quiet Sun, granular dynamics dominate the
time evolution of the magnetic elements. Flux occurs in both bright
intergranular points and in dark intergranular spaces. Likewise,
with the present spatial resolution, no preference of magnetic flux in
abnormal granulation in an active region can be found. Flux occurs in
both bright (abnormal) small-scale granules and in the darker spaces
in between them. The small sunspot studied has very little magnetic
flux in its ambient quiet regions, especially no strong, conspicuous
concentrations of returned flux, i.e. of flux with polarity opposite
to that in the sunspot.
Title: High Resolution 2D-Spectroscopy of the Sun
Authors: Hirzberger, J.; Kneer, F.
Bibcode: 2000HvaOB..24...89H
Altcode:
With the "Goettingen" Fabry-Perot interferometer which is installed
at the Vacuum Tower Telescope in Izana, Tenerife the non-magnetic
FeI 5576 A line was scanned in a field of quiet granulation at solar
disk center. From the simultaneously obtained broad band images an
instantaneous optical transfer function (OTF) of the Earth's atmosphere
was computed with speckle interferometric methods. Restoring the narrow
band data from this OTF the spatial resolution of the two-dimensional
spectra was successfully enhanced by a factor of two.
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: 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: 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: 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: Analyse von Zeitserien räumlich hochaufgelöster Aufnahmen
der Sonnengranulation Title: Analyse von Zeitserien räumlich
hochaufgelöster Aufnahmen der Sonnengranulation Title: Analysis of
time series of spatially high-resolution images of solar granulation;
Authors: Hirzberger, Johann
Bibcode: 1998PhDT.......409H
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: 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: 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: Solar granulation models - comparison with observations.
Authors: Hirzberger, J.; Hanslmeier, A.
Bibcode: 1994AGAb...10..115H
Altcode:
No abstract at ADS