explanation blue bibcodes open ADS page with paths to full text
Author name code: balthasar
ADS astronomy entries on 2022-09-14
author:"Balthasar, Horst"
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Title: An Interactive Virtual Hiking Map for the Mars 2020
Perseverance Landing Site, Jezero Crater
Authors: Walter, S. H. G.; Neu, D.; Gross, C.; Neesemann, A.;
Balthasar, H.; Jaumann, R.; Postberg, F.
2022LPICo2678.1921W Altcode:
We welcome you to explore the landing site of the Mars 2020 rover in
an interactive hiking map loaded with orbital imagery, terrain data,
and 3D panoramic views!
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Title: Observational evidence for two-component distributions
describing solar magnetic bright points
Authors: Berrios Saavedra, Gerardine; Utz, Dominik; Vargas Domínguez,
Santiago; Campos Rozo, José Iván; González Manrique, Sergio Javier;
Gömöry, Peter; Kuckein, Christoph; Balthasar, Horst; Zelina, Peter
2022A&A...657A..79B Altcode: 2021arXiv211012404B
Context. High-resolution observations of the solar photosphere reveal
the presence of fine structures, in particular the so-called Magnetic
Bright Points (MBPs), which are small-scale features associated with
strong magnetic field regions of the order of kilogauss (kG). It
is especially relevant to study these magnetic elements, which are
extensively detected in all moments during the solar cycle, in order to
establish their contribution to the behavior of the solar atmosphere,
and ultimately a plausible role within the coronal heating problem. <BR
/> Aims: Characterisation of size and velocity distributions of MBPs in
the solar photosphere in two different datasets of quiet Sun images
acquired with high-resolution solar instruments i.e. Solar Optical
Telescope SOT/Hinode and the High-resolution Fast Imager HiFI/GREGOR,
in the G-band (4308 Å). <BR /> Methods: In order to detect the
MBPs, an automatic segmentation and identification algorithm is
used. Next, the identified features were tracked to measure their
proper motions. Finally, a statistical analysis of hundreds of MBPs is
carried out, generating histograms for areas, diameters and horizontal
velocities. <BR /> Results: This work establishes that areas and
diameters of MBPs display log-normal distributions that are well-fitted
by two different components, whereas the velocity vector components
follow Gaussians and the vector magnitude a Rayleigh distribution
revealing again for all vector elements a two component composition. <BR
/> Conclusions: The results can be interpreted as due to the presence of
two different populations of MBPs in the solar photosphere one likely
related to stronger network magnetic flux elements and the other one
to weaker intranetwork flux elemens. In particular this work concludes
on the effect of the different spatial resolution of GREGOR and Hinode
telescopes, affecting detections and average values.
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Title: Velocity Difference of Ions and Neutrals in Solar Prominences
Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H.; Bianda, M.
2021ApJ...920...47W Altcode: 2021arXiv210813103W
Marked velocity excesses of ions relative to neutrals are obtained
from two time series of the neighboring emission lines He I 5015
Å and Fe II 5018 Å in a quiescent prominence. Their Doppler
shifts show time variations of quasi-periodic character where the
ions are faster than the neutrals, 1.0 ≤ V<SUB>macro</SUB>(Fe
II)/V<SUB>macro</SUB>(He I) ≤ 1.35 in series A and ≤1.25 in
series B. This "ratio excess" confirms our earlier findings of a 1.22
ion velocity excess, but the present study shows a restriction in
space and time of typically 5 Mm and 5 minutes. The ratio excess is
superposed by a time- and velocity-independent "difference excess"
of -0.3 ≤ V<SUB>macro</SUB>(Fe II)-V<SUB>macro</SUB>(He I) ≤
+0.7 km s<SUP>-1</SUP> in series A (also indicated in series B). The
high repetition rate of 3.9 s enables the detection of high-frequency
oscillations with several damped 22 s periods in series A. These show
a ratio excess with a maximum of 1.7. We confirm the absence of a
significant phase delay of He neutrals with respect to the Fe ions.
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Title: Multiple Stokes I inversions for inferring magnetic fields
in the spectral range around Cr I 5782 Å
Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.;
Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma,
M.; Kontogiannis, I.; Sobotka, M.
2021A&A...653A.165K Altcode: 2021arXiv210711116K
<BR /> Aims: In this work, we explore the spectral window containing
Fraunhofer lines formed in the solar photosphere, around the
magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0,
and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is
to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I,
Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer
the thermodynamic and magnetic properties in strongly magnetized
plasmas using an inversion code. <BR /> Methods: Our study is based
on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which
includes fast spectroscopic scans in the wavelength range around
the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all
spectral lines, as well as their response functions to temperature,
magnetic field, and Doppler velocity, were determined using the Stokes
Inversion based on Response functions (SIR) code. Snapshot 385 of the
enhanced network simulation from the Bifrost code serves to synthesize
all the lines, which are, in turn, inverted simultaneously with SIR to
establish the best inversion strategy. We applied this strategy to VTT
observations of a sunspot belonging to NOAA 12723 on 2018 September
30 and compared the results to full-disk vector field data obtained
with the Helioseismic and Magnetic Imager (HMI). <BR /> Results: The
15 simultaneously inverted intensity profiles (Stokes I) delivered
accurate temperatures and Doppler velocities when compared with the
simulations. The derived magnetic fields and inclinations achieve
the best level of accuracy when the fields are oriented along the
line-of-sight (LOS) and less accurate when the fields are transverse to
the LOS. In general, the results appear similar to what is reported in
the HMI vector-field data, although some discrepancies exist. <BR />
Conclusions: The analyzed spectral range has the potential to deliver
thermal, dynamic, and magnetic information for strongly magnetized
features on the Sun, such as pores and sunspots, even without the use
of polarimetry. The highest sensitivity of the lines is found in the
lower photosphere, on average, around log τ = −1. The multiple-line
inversions provide smooth results across the whole field of view
(FOV). The presented spectral range and inversion strategy will be
used for future VTT observing campaigns.
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Title: Properties of the inner penumbra boundary and temporal
evolution of a decaying sunspot (Corrigendum)
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
2021A&A...652C...7B Altcode:
No abstract at ADS
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Title: Evidence For Two-component Distributions Describing Magnetic
Bright Points In The Solar Photosphere
Authors: Vargas Domínguez, S.; Berrios Saavedra, G.; Utz, D.;
Campos Rozo, J. I.; González Manrique, S.; Gömöry, Peter; Kuckein,
Christoph; Balthasar, Horst; Zelina, Peter
2021AAS...23811310V Altcode:
High-resolution observations of the Sun reveal the presence of Magnetic
Bright Points (MBPs), which are small-scale features associated with
strong magnetic field regions, that are found all over the solar
photosphere. In this work, we characterize some physical properties
and dynamics of MBPs in a quiet Sun region by using time series of
images acquired with the High-resolution Fast Imager HiFI/GREGOR and
Solar Optical Telescope SOT/Hinode in the G-band (4308 Angstrom). An
automated segmentation algorithm is used to identify the MBPs and
track their evolution. The results show observational evidence for
two-component distributions of areas, diameters and velocities, that
can be interpreted as corresponding to different populations of MBPs.
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Title: High-Precision Topographic Map of the Mars 2020 Landing Site
as Part of the MC-13E Syrtis Major Quadrangle Digital Terrain Model.
Authors: Neesemann, A.; Walter, S. H. G.; Gross, C.; Jaumann, R.;
Gwinner, K.; Michael, G. G.; Schreiner, B. P.; Zuschneid, W.; Neu,
D.; Balthasar, H.; Rabethge, C.; Riedel, C.; Kersten, E.; Tirsch, D.
2021LPI....52.2509N Altcode:
For more than 17 years, the HRSC on board Mars Express has
acquired image data of the Red Planet on a global scale and at
high resolution. Here, we present the only recently finished MC-13E
Syrtis Major HRSC-based DTM covering the Mars 2020 Perseverance rover
landing site.
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Title: Looking Back to 17 Successful Years of High Resolution Stereo
Camera Image Release on ESA's Mars Express Mission
Authors: Gross, C.; Balthasar, H.; Dumke, A.; Neu, D.; Schreiner,
B.; Walter, S.; Jaumann, R.
2021LPI....52.1480G Altcode:
During the past 17 years, the experiment has collected image data
from more than 21.000 orbits, resulting in a steadily increasing set
of image, mosaic, and movie releases. Altogether more than 1.273 high
quality image PR products have been created.
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Title: Classification of High-resolution Solar Hα Spectra Using
t-distributed Stochastic Neighbor Embedding
Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke,
Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert;
Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S.
2021ApJ...907...54V Altcode: 2020arXiv201113214V
The Hα spectral line is a well-studied absorption line
revealing properties of the highly structured and dynamic solar
chromosphere. Typical features with distinct spectral signatures in
Hα include filaments and prominences, bright active-region plages,
superpenumbrae around sunspots, surges, flares, Ellerman bombs,
filigree, and mottles and rosettes, among others. This study is
based on high-spectral resolution Hα spectra obtained with the
Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at
Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic
neighbor embedding (t-SNE) is a machine-learning algorithm, which
is used for nonlinear dimensionality reduction. In this application,
it projects Hα spectra onto a two-dimensional map, where it becomes
possible to classify the spectra according to results of cloud model
(CM) inversions. The CM parameters optical depth, Doppler width,
line-of-sight velocity, and source function describe properties of
the cloud material. Initial results of t-SNE indicate its strong
discriminatory power to separate quiet-Sun and plage profiles from
those that are suitable for CM inversions. In addition, a detailed
study of various t-SNE parameters is conducted, the impact of seeing
conditions on the classification is assessed, results for various types
of input data are compared, and the identified clusters are linked
to chromospheric features. Although t-SNE proves to be efficient
in clustering high-dimensional data, human inference is required at
each step to interpret the results. This exploratory study provides
a framework and ideas on how to tailor a classification scheme toward
specific spectral data and science questions.
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Title: Observational study of chromospheric heating by acoustic waves
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.;
García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis,
I.; Koza, J.; Korda, D.; Kuckein, C.
2020A&A...642A..52A Altcode: 2020arXiv200802688A
<BR /> Aims: Our aim is to investigate the role of acoustic and
magneto-acoustic waves in heating the solar chromosphere. Observations
in strong chromospheric lines are analyzed by comparing the deposited
acoustic-energy flux with the total integrated radiative losses. <BR
/> Methods: Quiet-Sun and weak-plage regions were observed in the Ca
II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and
in the Hα and Hβ lines with the echelle spectrograph attached
to the Vacuum Tower Telescope on 2018 December 11 and 2019 June
6. The deposited acoustic energy flux at frequencies up to 20 mHz
was derived from Doppler velocities observed in line centers and
wings. Radiative losses were computed by means of a set of scaled
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models obtained by fitting synthetic to observed line profiles. <BR />
Results: In the middle chromosphere (h = 1000-1400 km), the radiative
losses can be fully balanced by the deposited acoustic energy flux in
a quiet-Sun region. In the upper chromosphere (h > 1400 km), the
deposited acoustic flux is small compared to the radiative losses in
quiet as well as in plage regions. The crucial parameter determining
the amount of deposited acoustic flux is the gas density at a given
height. <BR /> Conclusions: The acoustic energy flux is efficiently
deposited in the middle chromosphere, where the density of gas is
sufficiently high. About 90% of the available acoustic energy flux in
the quiet-Sun region is deposited in these layers, and thus it is a
major contributor to the radiative losses of the middle chromosphere. In
the upper chromosphere, the deposited acoustic flux is too low, so that
other heating mechanisms have to act to balance the radiative cooling.
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Title: High-resolution Spectroscopy of an Erupting Minifilament and
Its Impact on the Nearby Chromosphere
Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein,
C.; Balthasar, H.; Denker, C.
2020ApJ...898..144K Altcode: 2020arXiv200701564K
We study the evolution of a minifilament eruption in a quiet region
at the center of the solar disk and its impact on the ambient
atmosphere. We used high spectral resolution imaging spectroscopy in
Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope,
Tenerife, Spain; photospheric magnetic field observations from the
Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric
Imaging Assembly of the Solar Dynamics Observatory. The Hα line
profiles were noise-stripped using principal component analysis
and then inverted to produce physical and cloud model parameter
maps. The minifilament formed between small-scale, opposite-polarity
magnetic features through a series of small reconnection events, and
it erupted within an hour after its appearance in Hα. Its development
and eruption exhibited similarities to large-scale erupting filaments,
indicating the action of common mechanisms. Its eruption took place in
two phases, namely, a slow rise and a fast expansion, and it produced
a coronal dimming, before the minifilament disappeared. During its
eruption, we detected a complicated velocity pattern, indicative of
a twisted, thread-like structure. Part of its material returned to
the chromosphere, producing observable effects on nearby low-lying
magnetic structures. Cloud model analysis showed that the minifilament
was initially similar to other chromospheric fine structures, in terms
of optical depth, source function, and Doppler width, but it resembled a
large-scale filament on its course to eruption. High spectral resolution
observations of the chromosphere can provide a wealth of information
regarding the dynamics and properties of minifilaments and their
interactions with the surrounding atmosphere.
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Title: High-resolution spectroscopy of a surge in an emerging
flux region
Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar,
H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M.
2020A&A...639A..19V Altcode: 2020arXiv200503966V
<BR /> Aims: The regular pattern of quiet-Sun magnetic fields was
disturbed by newly emerging magnetic flux, which led a day later to
two homologous surges after renewed flux emergence, affecting all
atmospheric layers. Hence, simultaneous observations in different
atmospheric heights are needed to understand the interaction of
rising flux tubes with the surrounding plasma, in particular by
exploiting the important diagnostic capabilities provided by the
strong chromospheric Hα line regarding morphology and energetic
processes in active regions. <BR /> Methods: A newly emerged active
region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT)
at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High
spectral resolution observations using the echelle spectrograph in the
chromospheric Hαλ6562.8 Å line were obtained in the early growth
phase. Noise-stripped Hα line profiles yield maps of line-core and
bisector velocities, which were contrasted with velocities inferred
from Cloud Model inversions. A high-resolution imaging system recorded
simultaneously broad- and narrowband Hα context images. The Solar
Dynamics Observatory provided additional continuum images, line-of-sight
(LOS) magnetograms, and UV and extreme UV (EUV) images, which link the
different solar atmospheric layers. <BR /> Results: The active region
started as a bipolar region with continuous flux emergence when a new
flux system emerged in the leading part during the VTT observations,
resulting in two homologous surges. While flux cancellation at the
base of the surges provided the energy for ejecting the cool plasma,
strong proper motions of the leading pores changed the magnetic
field topology making the region susceptible to surging. Despite
the surge activity in the leading part, an arch filament system in
the trailing part of the old flux remained stable. Thus, stable
and violently expelled mass-loaded ascending magnetic structures
can coexist in close proximity. Investigating the height dependence
of LOS velocities revealed the existence of neighboring strong up-
and downflows. However, downflows occur with a time lag. The opacity
of the ejected cool plasma decreases with distance from the base of
the surge, while the speed of the ejecta increases. The location at
which the surge becomes invisible in Hα corresponds to the interface
where the surge brightens in He IIλ304 Å. Broad-shouldered and
dual-lobed Hα profiles suggests accelerated or decelerated and
highly structured LOS plasma flows. Significantly broadened Hα
profiles imply significant heating at the base of the surges, which
is also supported by bright kernels in UV and EUV images uncovered
by swaying motions of dark fibrils at the base of the surges. <BR />
Conclusions: The interaction of newly emerging flux with pre-existing
flux concentrations of a young, diffuse active region provided
suitable conditions for two homologous surges. High-resolution
spectroscopy revealed broadened and dual-lobed Hα profiles
tracing accelerated or decelerated flows of cool plasma along the
multi-threaded structure of the surge. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936762/olm">https://www.aanda.org</A>
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Title: HRSC on Mars Express - Imaging for Public Outreach: Global
Colour Mars View
Authors: Schreiner, B. P.; Neu, D.; Musiol, S.; Balthasar, H.; Dumke,
A.; Gross, C.; Michael, G. G.
2020LPI....51.2437S Altcode:
Based on HRSC colour data, a single orbit global Mars view is presented.
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Title: The magnetic structure and dynamics of a decaying active region
Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González
Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar,
Horst; Denker, Carsten
2020IAUS..354...53K Altcode:
We study the evolution of the decaying active region NOAA 12708, from
the photosphere up to the corona using high resolution, multi-wavelength
GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric
scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph
(GRIS), spectral imaging time-series in the Na ID<SUP>2</SUP> spectral
line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context
imaging in the Ca IIH and blue continuum by the High-resolution Fast
Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
complements our dataset. The region under study contains one pore with a
light-bridge, a few micro-pores and extended clusters of magnetic bright
points. We study the magnetic structure from the photosphere up to the
upper chromosphere through the spectropolarimetric observations in He
II and Si I and through the magnetograms provided by the Helioseismic
and Magnetic Imager (HMI). The high-resolution photospheric images
reveal the complex interaction between granular-scale convective
motions and a range of scales of magnetic field concentrations in
unprecedented detail. The pore itself shows a strong interaction with
the convective motions, which eventually leads to its decay, while,
under the influence of the photospheric flow field, micro-pores
appear and disappear. Compressible waves are generated, which are
guided towards the upper atmosphere along the magnetic field lines of
the various magnetic structures within the field-of-view. Modelling
of the He i absorption profiles reveals high velocity components,
mostly associated with magnetic bright points at the periphery
of the active region, many of which correspond to asymmetric Si I
Stokes-V profiles revealing a coupling between upper photospheric
and upper chromospheric dynamics. Time-series of Na ID<SUP>2</SUP>
spectral images reveal episodic high velocity components at the same
locations. State-of-the-art multi-wavelength GREGOR observations allow
us to track and understand the mechanisms at work during the decay
phase of the active region.
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Title: Coordinated observations between China and Europe to follow
active region 12709
Authors: González Manrique, S. J.; Kuckein, C.; Gömöry, P.; Yuan,
S.; Xu, Z.; Rybák, J.; Balthasar, H.; Schwartz, P.
2020IAUS..354...58G Altcode: 2020IAUS..354...58M; 2019arXiv191208611G
We present the first images of a coordinated campaign to follow active
region NOAA 12709 on 2018 May 13 as part of a joint effort between
three observatories (China-Europe). The active region was close to
disk center and enclosed a small pore, a tight polarity inversion line
and a filament in the chromosphere. The active region was observed
with the 1.5-meter GREGOR solar telescope on Tenerife (Spain) with
spectropolarimetry using GRIS in the He i 10830 Å spectral range
and with HiFI using two broad-band filter channels. In addition,
the Lomnicky Stit Observatory (LSO, Slovakia) recorded the same
active region with the new Solar Chromospheric Detector (SCD) in
spectroscopic mode at Hα 6562 Å. The third ground-based telescope
was located at the Fuxian Solar Observatory (China), where the active
region was observed with the 1-meter New Vacuum Solar Telescope
(NVST), using the Multi-Channel High Resolution Imaging System at
Hα 6562 Å. Overlapping images of the active region from all three
telescopes will be shown as well as preliminary Doppler line-of-sight
(LOS) velocities. The potential of such observations are discussed.
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Title: Revisiting the building blocks of solar magnetic fields
by GREGOR
Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván;
González Manrique, Sergio Javier; Balthasar, Horst; Gömöry,
Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu;
Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke,
Andrea
2020IAUS..354...38U Altcode:
The Sun is our dynamic host star due to its magnetic fields causing
plentiful of activity in its atmosphere. From high energetic flares
and coronal mass ejections (CMEs) to lower energetic phenomena such
as jets and fibrils. Thus, it is of crucial importance to learn about
formation and evolution of solar magnetic fields. These fields cover a
wide range of spatial and temporal scales, starting on the larger end
with active regions harbouring complex sunspots, via isolated pores,
down to the smallest yet resolved elements - so-called magnetic bright
points (MBPs). Here, we revisit the various manifestations of solar
magnetic fields by the largest European solar telescope in operation,
the 1.5-meter GREGOR telescope. We show images from the High-resolution
Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared
Spectrograph (GRIS). Besides, we outline resolved convective features
inside the larger structures - so-called light-bridges occurring on
large to mid-sized scales.
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Title: Polarimetry with the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Gisler, D.; González Manrique, S. J.; Kuckein,
C.; Verma, M.; Denker, C.
2019spw..confE...3B Altcode:
No abstract at ADS
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Title: Spectropolarimetric Observations of an Arch Filament System
with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
2019ASPC..526..217B Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s<SUP>-1</SUP> next
to the pores and to 4 km s<SUP>-1</SUP> at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.
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Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).
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Title: 15 Years High Resolution Stereo Camera Observations with
ESA's Mars Express Mission
Authors: Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael,
G.; Neu, D.; Schreiner, B.; Jaumann, R.
2019LPI....50.1537M Altcode:
Within the last 15 years, HRSC has delivered a large quantity of images
that build the basis for mosaic generation.
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Title: HRSC on Mars Express - Image Mosaicking for Public Outreach:
Korolev Crater
Authors: Schreiner, B. P.; Neu, D.; Musiol, S.; Balthasar, H.; Dumke,
A.; Gross, C.; Michael, G. G.
2019LPI....50.2735S Altcode:
Public outreach image mosaic of Korolev Crater and volume estimation
of ice filling.
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Title: Properties of the inner penumbral boundary and temporal
evolution of a decaying sunspot
Authors: Benko, M.; González Manrique, S. J.; Balthasar, H.; Gömöry,
P.; Kuckein, C.; Jurčák, J.
2018A&A...620A.191B Altcode: 2018arXiv181013185B
Context. It has been empirically determined that the umbra-penumbra
boundaries of stable sunspots are characterized by a constant value of
the vertical magnetic field. <BR /> Aims: We analyzed the evolution
of the photospheric magnetic field properties of a decaying sunspot
belonging to NOAA 11277 between August 28-September 3, 2011. The
observations were acquired with the spectropolarimeter on-board of
the Hinode satellite. We aim to prove the validity of the constant
vertical magnetic-field boundary between the umbra and penumbra in
decaying sunspots. <BR /> Methods: A spectral-line inversion technique
was used to infer the magnetic field vector from the full-Stokes
profiles. In total, eight maps were inverted and the variation of
the magnetic properties in time were quantified using linear or
quadratic fits. <BR /> Results: We find a linear decay of the umbral
vertical magnetic field, magnetic flux, and area. The penumbra showed
a linear increase of the vertical magnetic field and a sharp decay
of the magnetic flux. In addition, the penumbral area quadratically
decayed. The vertical component of the magnetic field is weaker on the
umbra-penumbra boundary of the studied decaying sunspot compared to
stable sunspots. Its value seem to be steadily decreasing during the
decay phase. Moreover, at any time of the sunspot decay shown, the inner
penumbra boundary does not match with a constant value of the vertical
magnetic field, contrary to what is seen in stable sunspots. <BR />
Conclusions: During the decaying phase of the studied sunspot, the
umbra does not have a sufficiently strong vertical component of the
magnetic field and is thus unstable and prone to be disintegrated by
convection or magnetic diffusion. No constant value of the vertical
magnetic field is found for the inner penumbral boundary.
---------------------------------------------------------
Title: sTools - a software package for data reduction of GREGOR
instruments and general data analysis
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar,
Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva,
Ekaterina; Kontogiannis, Ioannis; Shen, Zili
2018csc..confE.105K Altcode:
The optical solar physics group at AIP is responsible for the GREGOR
Fabry-Perot Interferometer (GFPI) and the large-format facility cameras
(Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI))
at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since
the »Early Science Phase« of the telescope in 2014, the group
developed a data reduction pipeline for these two instruments. The
pipeline »sTools« is based on the Interactive Data Language
(IDL) and delivers reduced and image-restored data with a minimum
of user interaction. Furthermore, it creates quick-look data and
builds a webpage with an overview of the observations and their
statistics (http://gregor.aip.de). However, during the last years,
sTools continuously evolved and currently hosts many additional
routines for data analysis: (1) A local correlation tracking (LCT)
algorithm adapted for both high-resolution (GREGOR and Hinode) and
synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e.,
a Background-subtracted Solar Activity Map (BaSAM), to assess and
visualize the temporal variation of the photospheric magnetic field
and the EUV 160 nm intensity. This method utilizes SDO data and is
applicable to both full-disk observations and regions-of-interest. (3)
Calibration of synoptic full-disk data from the Chromospheric Telescope
(ChroTel) including extraction of Doppler velocities from He I 1083
nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy
for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle
Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed
under a creative commons license and is freely available, after
registration, at the abovementioned website.
---------------------------------------------------------
Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
A.; Diercke, A.
2018A&A...617A..55G Altcode: 2018arXiv180700728G
<BR /> Aims: We study the evolution of an arch filament system (AFS)
and of its individual arch filaments to learn about the processes
occurring in them. <BR /> Methods: We observed the AFS at the
GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
in the He I 10 830 Å spectral range. The He I triplet profiles
were fitted with analytic functions to infer line-of-sight (LOS)
velocities to follow plasma motions within the AFS. <BR /> Results:
We tracked the temporal evolution of an individual arch filament
over its entire lifetime, as seen in the He I 10 830 Å triplet. The
arch filament expanded in height and extended in length from 13″ to
21″. The lifetime of this arch filament is about 30 min. About 11
min after the arch filament is seen in He I, the loop top starts to
rise with an average Doppler velocity of 6 km s<SUP>-1</SUP>. Only two
minutes later, plasma drains down with supersonic velocities towards
the footpoints reaching a peak velocity of up to 40 km s<SUP>-1</SUP>
in the chromosphere. The temporal evolution of He I 10 830 Å profiles
near the leading pore showed almost ubiquitous dual red components of
the He I triplet, indicating strong downflows, along with material
nearly at rest within the same resolution element during the whole
observing time. <BR /> Conclusions: We followed the arch filament as it
carried plasma during its rise from the photosphere to the corona. The
material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational
results support theoretical AFS models and aids in improving future
models. <P />The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>
---------------------------------------------------------
Title: The Problem of the Height Dependence of Magnetic Fields
in Sunspots
Authors: Balthasar, Horst
2018SoPh..293..120B Altcode: 2018arXiv180806426B
To understand the physics of sunspots, it is important to know
the properties of their magnetic field, and especially its height
stratification plays a substantial role. There are mainly two methods
to assess this stratification, but they yield different magnetic
gradients in the photospheric layers. Determinations based on the
several spectral lines of different formation heights and the slope of
their profiles result in gradients of −2 to −3 G km<SUP>−1</SUP>,
or even steeper. This is similar for the total magnetic field strength
and for the vertical component of the magnetic field. The other option
is to determine the horizontal partial derivatives of the magnetic
field, and with the condition divB =0 also the vertical derivative is
known. With this method, gradients of −0.5 G km<SUP>−1</SUP> and
even shallower are obtained. Obviously, these results do not agree. If
chromospheric spectral lines are included, only shallow gradients around
−0.5 G km<SUP>−1</SUP> are obtained. Shallow gradients are also
found from gyro-resonance measurements in the radio wave range 300 -
2000 GHz.
---------------------------------------------------------
Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
2018A&A...614A...2V Altcode: 2018arXiv180103686V
<BR /> Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings. <BR /> Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines. <BR /> Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h. <BR /> Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.
---------------------------------------------------------
Title: High-cadence Imaging and Imaging Spectroscopy at the
GREGOR Solar Telescope—A Collaborative Research Environment for
High-resolution Solar Physics
Authors: Denker, Carsten; Kuckein, Christoph; Verma, Meetu; González
Manrique, Sergio J.; Diercke, Andrea; Enke, Harry; Klar, Jochen;
Balthasar, Horst; Louis, Rohan E.; Dineva, Ekaterina
2018ApJS..236....5D Altcode: 2018arXiv180210146D
In high-resolution solar physics, the volume and complexity
of photometric, spectroscopic, and polarimetric ground-based
data significantly increased in the last decade, reaching data
acquisition rates of terabytes per hour. This is driven by the
desire to capture fast processes on the Sun and the necessity
for short exposure times “freezing” the atmospheric seeing,
thus enabling ex post facto image restoration. Consequently,
large-format and high-cadence detectors are nowadays used in
solar observations to facilitate image restoration. Based on our
experience during the “early science” phase with the 1.5 m
GREGOR solar telescope (2014-2015) and the subsequent transition
to routine observations in 2016, we describe data collection and
data management tailored toward image restoration and imaging
spectroscopy. We outline our approaches regarding data processing,
analysis, and archiving for two of GREGOR’s post-focus instruments
(see <A href="http://gregor.aip.de">http://gregor.aip.de</A>), i.e.,
the GREGOR Fabry-Pérot Interferometer (GFPI) and the newly installed
High-Resolution Fast Imager (HiFI). The heterogeneous and complex
nature of multidimensional data arising from high-resolution solar
observations provides an intriguing but also a challenging example for
“big data” in astronomy. The big data challenge has two aspects: (1)
establishing a workflow for publishing the data for the whole community
and beyond and (2) creating a collaborative research environment
(CRE), where computationally intense data and postprocessing tools are
colocated and collaborative work is enabled for scientists of multiple
institutes. This requires either collaboration with a data center or
frameworks and databases capable of dealing with huge data sets based on
virtual observatory (VO) and other community standards and procedures.
---------------------------------------------------------
Title: Image Quality in High-resolution and High-cadence Solar Imaging
Authors: Denker, C.; Dineva, E.; Balthasar, H.; Verma, M.; Kuckein,
C.; Diercke, A.; González Manrique, S. J.
2018SoPh..293...44D Altcode: 2018arXiv180200760D
Broad-band imaging and even imaging with a moderate bandpass (about 1
nm) provides a photon-rich environment, where frame selection (lucky
imaging) becomes a helpful tool in image restoration, allowing us to
perform a cost-benefit analysis on how to design observing sequences
for imaging with high spatial resolution in combination with real-time
correction provided by an adaptive optics (AO) system. This study
presents high-cadence (160 Hz) G-band and blue continuum image sequences
obtained with the High-resolution Fast Imager (HiFI) at the 1.5-meter
GREGOR solar telescope, where the speckle-masking technique is used
to restore images with nearly diffraction-limited resolution. The
HiFI employs two synchronized large-format and high-cadence sCMOS
detectors. The median filter gradient similarity (MFGS) image-quality
metric is applied, among others, to AO-corrected image sequences of
a pore and a small sunspot observed on 2017 June 4 and 5. A small
region of interest, which was selected for fast-imaging performance,
covered these contrast-rich features and their neighborhood, which were
part of Active Region NOAA 12661. Modifications of the MFGS algorithm
uncover the field- and structure-dependency of this image-quality
metric. However, MFGS still remains a good choice for determining image
quality without a priori knowledge, which is an important characteristic
when classifying the huge number of high-resolution images contained in
data archives. In addition, this investigation demonstrates that a fast
cadence and millisecond exposure times are still insufficient to reach
the coherence time of daytime seeing. Nonetheless, the analysis shows
that data acquisition rates exceeding 50 Hz are required to capture a
substantial fraction of the best seeing moments, significantly boosting
the performance of post-facto image restoration.
---------------------------------------------------------
Title: Ca II 8542 Å brightenings induced by a solar microflare
Authors: Kuckein, C.; Diercke, A.; González Manrique, S. J.; Verma,
M.; Löhner-Böttcher, J.; Socas-Navarro, H.; Balthasar, H.; Sobotka,
M.; Denker, C.
2017A&A...608A.117K Altcode: 2017arXiv170906861K
<BR /> Aims: We study small-scale brightenings in Ca II 8542 Å
line-core images to determine their nature and effect on localized
heating and mass transfer in active regions. <BR /> Methods:
High-resolution two-dimensional spectroscopic observations of a solar
active region in the near-infrared Ca II 8542 Å line were acquired
with the GREGOR Fabry-Pérot Interferometer attached to the 1.5-m GREGOR
telescope. Inversions of the spectra were carried out using the NICOLE
code to infer temperatures and line-of-sight (LOS) velocities. Response
functions of the Ca II line were computed for temperature and LOS
velocity variations. Filtergrams of the Atmospheric Imaging Assembly
(AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI)
were coaligned to match the ground-based observations and to follow the
Ca II brightenings along all available layers of the atmosphere. <BR />
Results: We identified three brightenings of sizes up to 2” × 2”
that appeared in the Ca II 8542 Å line-core images. Their lifetimes
were at least 1.5 min. We found evidence that the brightenings belonged
to the footpoints of a microflare (MF). The properties of the observed
brightenings disqualified the scenarios of Ellerman bombs or Interface
Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some
common properties with flaring active-region fibrils or flaring arch
filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric
and coronal layers according to the AIA channels; and (2) both show
flaring arches with lifetimes of about 3.0-3.5 min and lengths of
20” next to the brightenings. The inversions revealed heating by
600 K at the footpoint location in the ambient chromosphere during
the impulsive phase. Connecting the footpoints, a dark filamentary
structure appeared in the Ca II line-core images. Before the
start of the MF, the spectra of this structure already indicated
average blueshifts, meaning upward motions of the plasma along the
LOS. During the impulsive phase, these velocities increased up to -
2.2 km s<SUP>-1</SUP>. The structure did not disappear during the
observations. Downflows dominated at the footpoints. However, in
the upper photosphere, slight upflows occurred during the impulsive
phase. Hence, bidirectional flows are present in the footpoints
of the MF. <BR /> Conclusions: We detected Ca II brightenings that
coincided with the footpoint location of an MF. The MF event led to
a rise of plasma in the upper photosphere, both before and during the
impulsive phase. Excess mass, previously raised to at most chromospheric
layers, slowly drained downward along arches toward the footpoints
of the MF. <P />The movie associated to Fig. 2 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201731319/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: sTools - a data reduction pipeline for the GREGOR Fabry-Pérot
Interferometer and the High-resolution Fast Imager at the GREGOR
solar telescope
Authors: Kuckein, C.; Denker, C.; Verma, M.; Balthasar, H.; González
Manrique, S. J.; Louis, R. E.; Diercke, A.
2017IAUS..327...20K Altcode: 2017arXiv170101670K
A huge amount of data has been acquired with the GREGOR Fabry-Pérot
Interferometer (GFPI), large-format facility cameras, and since 2016
with the High-resolution Fast Imager (HiFI). These data are processed
in standardized procedures with the aim of providing science-ready data
for the solar physics community. For this purpose, we have developed a
user-friendly data reduction pipeline called “sTools” based on the
Interactive Data Language (IDL) and licensed under creative commons
license. The pipeline delivers reduced and image-reconstructed data
with a minimum of user interaction. Furthermore, quick-look data are
generated as well as a webpage with an overview of the observations and
their statistics. All the processed data are stored online at the GREGOR
GFPI and HiFI data archive of the Leibniz Institute for Astrophysics
Potsdam (AIP). The principles of the pipeline are presented together
with selected high-resolution spectral scans and images processed
with sTools.
---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.
---------------------------------------------------------
Title: Flare-induced changes of the photospheric magnetic field in
a δ-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
Veronig, A. M.; González Manrique, S. J.; Kučera, A.; Schwartz,
P.; Hanslmeier, A.
2017A&A...602A..60G Altcode: 2017arXiv170406089G
<BR /> Aims: Changes of the magnetic field and the line-of-sight
velocities in the photosphere are being reported for an M-class
flare that originated at a δ-spot belonging to active region NOAA
11865. <BR /> Methods: High-resolution ground-based near-infrared
spectropolarimetric observations were acquired simultaneously in
two photospheric spectral lines, Fe I 10783 Å and Si I 10786 Å,
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
(VTT) in Tenerife on 2013 October 15. The observations covered several
stages of the M-class flare. Inversions of the full-Stokes vector of
both lines were carried out and the results were put into context using
(extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory
(SDO). <BR /> Results: The active region showed high flaring activity
during the whole observing period. After the M-class flare, the
longitudinal magnetic field did not show significant changes along
the polarity inversion line (PIL). However, an enhancement of the
transverse magnetic field of approximately 550 G was found that
bridges the PIL and connects umbrae of opposite polarities in the
δ-spot. At the same time, a newly formed system of loops appeared
co-spatially in the corona as seen in 171 Å filtergrams of the
Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot
exclude that the magnetic connection between the umbrae already existed
in the upper atmosphere before the M-class flare and became visible
only later when it was filled with hot plasma. The photospheric
Doppler velocities show a persistent upflow pattern along the PIL
without significant changes due to the flare. <BR /> Conclusions:
The increase of the transverse component of the magnetic field after
the flare together with the newly formed loop system in the corona
support recent predictions of flare models and flare observations. <P
/>The movie associated to Figs. 4 and 5 is available at <A
href="http://www.aanda.org/10.1051/0004-6361/201730644/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Center-to-limb variation of the velocity field in and around
a sunspot with light-bridges
Authors: Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke,
Andrea; González Manrique, S. J.; Löhner-Böttcher, Johannes;
Kuckein, Christoph; Sobotka, Michal
2017psio.confE.104D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Velocity fields in sunspots derived from observations with
the GREGOR Fabry-Pérot Interferometer
Authors: Balthasar, H.; Denker, C.; Diercke, A.; González Manrique,
S. J.; Kuckein, C.; Louis, R. E.; Verma, M., Löhner-Böttcher, J.;
Sobotka, M.
2017psio.confE.105B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare induced changes of the photospheric magnetic field in
a delta-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
Kuĉera, A.; González Manrique, S. J.; Schwartz, P.; Veronig, A. M.;
Hanslmeier, A.
2017psio.confE.107G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. <P />Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: NLTE modeling of a small active region filament observed with
the VTT
Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry,
P.; Rybák, J.; Heinzel, P.; Kučera, A.
2016AN....337.1045S Altcode:
An active region mini-discretionary-filament was observed with the
Vacuum Tower Telescope (VTT) in Tenerife simultaneously in the He
I infrared triplet using the Tenerife Infrared Polarimeter 1 (TIP
1), in Hα with the TESOS Fabry-Pérot interferometer, and in Ca II
8542 Å with the VTT spectrograph. The spectropolarimetric data were
inverted using the HAZEL code and Hα profiles were modelled by solving
a NLTE radiative transfer in a simple isobaric and isothermal 2D slab
irradiated both from its bottom and sides from the solar surface. It was
found that the mini-discretionary-filament is composed of horizontal
fluxtubes, along which the cool plasma of T∼10 000 K can flow with
very large, even supersonic, velocities.
---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. <BR /> Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. <BR /> Methods:
We investigated the magnetic field at log τ<SUB>5</SUB> = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. <BR /> Results: At log τ<SUB>5</SUB>
= 0 we find no evidence of regions with dynamically weak (B<
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.
---------------------------------------------------------
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s<SUP>-1</SUP> in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.
---------------------------------------------------------
Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F Altcode: 2016arXiv160800513F
Context. A significant part of the penumbral magnetic field returns
below the surface in the very deep photosphere. For lines in the
visible, a large portion of this return field can only be detected
indirectly by studying its imprints on strongly asymmetric and
three-lobed Stokes V profiles. Infrared lines probe a narrow layer
in the very deep photosphere, providing the possibility of directly
measuring the orientation of magnetic fields close to the solar
surface. <BR /> Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. <BR /> Methods: We analyzed 71 spectropolarimetric
datasets from Hinode and from the GREGOR infrared spectrograph. We
inferred the quality and polarimetric accuracy of the infrared data
after applying several reduction steps. Techniques of spectral
inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral
area covered by reversed-polarity and three-lobed Stokes V profiles for
sunspots at disk center. We determined the amount of reversed-polarity
and three-lobed Stokes V profiles in visible and infrared data of
sunspots at various heliocentric angles. From the results, we computed
center-to-limb variation curves, which were interpreted in the context
of existing penumbral models. <BR /> Results: Observations in visible
and near-infrared spectral lines yield a significant difference in the
penumbral area covered by magnetic fields of opposite polarity. In
the infrared, the number of reversed-polarity Stokes V profiles is
smaller by a factor of two than in the visible. For three-lobed Stokes
V profiles the numbers differ by up to an order of magnitude.
---------------------------------------------------------
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. <BR />
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. <BR /> Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. <BR />
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s<SUP>-1</SUP> is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.
---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
<BR /> Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. <BR /> Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. <BR /> Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. <BR /> Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.
---------------------------------------------------------
Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
T.; Kneer, F.; Nicklas, H.; Sobotka, M.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. <BR />
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. <BR /> Methods: We present speckle-reconstructed images taken
with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
486 nm and 589 nm bands. We estimate the spatial resolution from the
noise characteristics of the image bursts and obtain 0.08″ at 589
nm. We describe structure details in individual best images as well
as the temporal evolution of selected features. <BR /> Results: We
find branched dark lanes extending along thin (≈1″) light bridges
in sunspots at various heliocentric angles. In thick (≳ 2″) light
bridges the branches are disconnected from the central lane and have a Y
shape with a bright grain toward the umbra. The images reveal that light
bridges exist on varying intensity levels and that their small-scale
features evolve on timescales of minutes. Faint light bridges show
dark lanes outlined by the surrounding bright features. Dark lanes are
very common and are also found in the boundary of pores. They have a
characteristic width of 0.1″ or smaller. Intergranular dark lanes of
that width are seen in active region granulation. <BR /> Conclusions: We
interpret our images in the context of magneto-convective simulations
and findings: while central dark lanes in thin light bridges are
elevated and associated with a density increase above upflows, the dark
lane branches correspond to locations of downflows and are depressed
relative to the adjacent bright plasma. Thick light bridges with central
dark lanes show no projection effect. They have a flat elevated plateau
that falls off steeply at the umbral boundary. There, Y-shaped filaments
form as they do in the inner penumbra. This indicates the presence of
inclined magnetic fields, meaning that the umbral magnetic field is
wrapped around the convective light bridge.
---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. <BR />
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. <BR /> Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. <BR /> Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. <P />Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (<500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. <BR /> Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. <BR /> Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. <BR /> Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.
---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s<SUP>-1</SUP> for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.
---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. <BR /> Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. <BR /> Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.
---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.
---------------------------------------------------------
Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.
---------------------------------------------------------
Title: Non-LTE Inversion of Spectropolarimetric and Spectroscopic
Observations of a Small Active-region Filament Observed at the VTT
Authors: Schwartz, P.; Balthasar, H.; Kuckein, C.; Koza, J.; Gömöry,
P.; Rybák, J.; Kučera, A.; Heinzel, P.
2016ASPC..504..205S Altcode:
An active region mini-filament was observed by VTT simultaneously
in the He<small>I</small> 10 830 Å triplet by the TIP 1
spectropolarimeter, in Hα by the TESOS Fabry-Pérot interferometer, and
in Ca <small>II</small> 8542 Å by the VTT spectrograph. The
spectropolarimetric data were inverted using the HAZEL code and Hα
profiles were modelled solving a NLTE radiative transfer in a simple
isobaric and isothermal 2D slab irradiated both from bottom and
sides. It was found that the mini-filament is composed of horizontal
fluxtubes, along which the cool plasma of T∼10 000 K can flow by
very large - even supersonic - velocities.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.
2016IAUS..320...68S Altcode:
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5-m GREGOR telescope, using a 0.1 nm Ca II H interference
filter. Context observations from SDO/AIA, Hinode/SOT, and IRIS show
that the ribbon is a part of a larger one that extends through the
neighboring positive polarities and also participates in several
other flares within the active region. A 140 second long time series
of Ca II H images was reconstructed by means of the Multi-Frame
Blind Deconvolution method, giving the respective spatial and
temporal resolutions of 0”.1 and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary but three move along the
ribbon with speeds of 7-11 km s<SUP>-1</SUP>. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
providing evidence for the presence of slipping reconnection at small
spatial scales.
---------------------------------------------------------
Title: GREGOR observations of a small flare above a sunspot
Authors: Sobotka, Michal; Dudik, Jaroslav; Denker, Carsten; Balthasar,
Horst; Jurcak, Jan; Liu, Wenjuan; GREGOR Team
2015IAUGA..2246841S Altcode:
A small flare ribbon above a sunspot with a light bridge was observed on
7 November 2014 around 12:00 UT in the blue imaging channel of GREGOR,
using a 0.1 nm Ca II H interference filter. Context observations from
SDO/AIA, Hinode/SOT and IRIS show that the ribbon is a part of a larger
ribbon extending through the neighbouring negative polarities that also
participates in several other flares within the active region. A 140
s long time series of Ca II H images was reconstructed by means of the
Multi Frame Blind Deconvolution method, giving the respective spatial
and temporal resolutions of 0.1" and 1 s. Light curves and horizontal
velocities of small-scale brightenings in the flare ribbon located
above an umbral core were measured. Some of them are stationary but
three brightenings move in opposite directions along the ribbon with
speeds of 7 - 11 km/s. Expecting that the brightenings correspond to
footpoints of flare loops, their motions can be interpreted in terms
of the slipping reconnection model.
---------------------------------------------------------
Title: The Magnetic Configuration of a δ-Spot
Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C.
2014ASPC..489...39B Altcode: 2013arXiv1312.5128B
Sunspots, which harbor both magnetic polarities within one penumbra, are
called δ-spots. They are often associated with flares. Nevertheless,
there are only very few detailed observations of the spatially resolved
magnetic field configuration. We present an investigation performed
with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
in Tenerife. We observed a sunspot with a main umbra and several
additional umbral cores, one of them with opposite magnetic polarity
(the δ-umbra). The δ-spot is divided into two parts by a line along
which central emissions of the spectral line Ca <font size=2>II
854.2 nm appear. The Evershed flow comming from the main umbra ends
at this line. In deep photospheric layers, we find an almost vertical
magnetic field for the δ-umbra, and the magnetic field decreases
rapidly with height, faster than in the main umbra. The horizontal
magnetic field in the direction connecting main and δ-umbra is rather
smooth, but in one location next to a bright penumbral feature at
some distance to the δ-umbra, we encounter a change of the magnetic
azimuth by 90° from one pixel to the next. Near the δ-umbra, but
just outside, we encounter a blue-shift of the spectral line profiles
which we interpret as Evershed flow away from the δ-umbra. Significant
electric current densities are observed at the dividing line of the
spot and inside the δ-umbra.
---------------------------------------------------------
Title: Overview of Outreach Activities of the Planetary Sciences
and Remote Sensing Group at Freie Universität Berlin
Authors: Musiol, S.; Balthasar, H.; Dumke, A.; Gross, C.; Michael, G.;
Neu, D.; Platz, T.; Rosenberg, H.; Schreiner, B.; Walter, S. H. G.;
van Gasselt, S.
2014EPSC....9..545M Altcode:
Planetary Sciences teach us how special our homeplanet is in the
solar system. Incorporating a broad variety of natural science
topics they count to the most fundamental branches of scientific
research with a strong interdisciplinary character. However, since
planetary sciences are not a school subject, children as well as
adults are often lacking an overall awareness and understanding of
that field. The mission of planetary education has to be fulfilled
by research institutions. With several platforms and activities our
group is engaged to address this topic. The Planetary Sciences and
Remote Sensing Group at Freie Universität Berlin (FUB) is involved in
space missions such as Mars Express with the High Resolution Stereo
Camera (HRSC), Cassini to Saturn, and Dawn to the asteroids Vesta
and Ceres. Moreover, we participate in developing a planetary X-ray
fluorescence spectrometer. Information of our planetary research
activities can be found on our institutes website [1]. Our outreach
activities include press releases, an image download hub, permanent and
special exhibition support, 3D-HD-animation production, science fairs,
workshops, hands-on courses, public talks at observatories and schools,
as well as media appearances in radio, press and TV.
---------------------------------------------------------
Title: High Resolution Stereo Camera (HRSC) on Mars Express — A
Decade of PR/EO Activities at Freie Universität Berlin
Authors: Balthasar, H.; Musiol, S.; van Gasselt, S.; PR Team
2014LPI....45.2099B Altcode:
The Planetary Sciences and Remote Sensing Group supports web-based
data access and educational outreach events for HRSC data dissemination.
---------------------------------------------------------
Title: The association between sunspot magnetic fields and
superpenumbral fibrils
Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.;
Puschmann, K. G.; Denker, C.
2014AN....335..161L Altcode: 2013arXiv1312.1879L
Spectropolarimetric observations of a sunspot were carried out with
the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife,
Spain. Maps of the physical parameters were obtained from an inversion
of the Stokes profiles observed in the infrared Fe I line at 15 648
Å. The regular sunspot consisted of a light bridge which separated the
two umbral cores of the same polarity. One of the arms of the light
bridge formed an extension of a penumbral filament which comprised
weak and highly inclined magnetic fields. In addition, the Stokes V
profiles in this filament had an opposite sign as the sunspot and some
resembled Stokes Q or U. This penumbral filament terminated abruptly
into another at the edge of the sunspot, where the latter was relatively
vertical by about 30<SUP>o</SUP>. Chromospheric H\alpha and He II 304
Åfiltergrams revealed three superpenumbral fibrils on the limb-side
of the sunspot, in which one fibril extended into the sunspot and was
oriented along the highly inclined penumbral counterpart of the light
bridge. An intense, elongated brightening was observed along this fibril
that was co-spatial with the intersecting penumbral filaments in the
photosphere. Our results suggest that the disruption in the sunspot
magnetic field at the location of the light bridge could be the source
of reconnection that led to the intense chromospheric brightening and
facilitated the supply of cool material in maintaining the overlying
superpenumbral fibrils.
---------------------------------------------------------
Title: Near-infrared spectropolarimetry of a δ-spot
Authors: Balthasar, H.; Beck, C.; Louis, R. E.; Verma, M.; Denker, C.
2014A&A...562L...6B Altcode: 2014arXiv1401.4386B
Sunspots harboring umbrae of both magnetic polarities within a common
penumbra (δ-spots) are often but not always related to flares. We
present first near-infrared observations (Fe i λ1078.3 nm and Si i
λ1078.6 nm spectra) obtained with the Tenerife Infrared Polarimeter at
the Vacuum Tower Telescope in Tenerife on 2012 June 17, which afford
accurate and sensitive diagnostics to scrutinize the complex fields
along the magnetic neutral line of a δ-spot within active region NOAA
11504. We examined the vector magnetic field, line-of-sight (LOS)
velocities, and horizontal proper motions of this rather inactive
δ-spot. We find a smooth transition of the magnetic vector field
from the main umbra to that of opposite polarity (δ-umbra), but a
discontinuity of the horizontal magnetic field at some distance from the
δ-umbra on the polarity inversion line. The magnetic field decreases
faster with height by a factor of two above the δ-umbra. The latter is
surrounded by its own Evershed flow. The Evershed flow coming from the
main umbra ends at a line dividing the spot into two parts. This line
is marked by the occurrence of central emission in the Ca iiλ854.2 nm
line. Along this line, high chromospheric LOS-velocities of both signs
appear. We detect a shear flow within the horizontal flux transport
velocities parallel to the dividing line.
---------------------------------------------------------
Title: Sunspot splitting triggering an eruptive flare
Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard;
Balthasar, Horst; Denker, Carsten
2014A&A...562A.110L Altcode: 2013arXiv1311.5054L
<BR /> Aims: We investigate how the splitting of the leading sunspot
and associated flux emergence and cancellation in active region NOAA
11515 caused an eruptive M5.6 flare on 2012 July 2. <BR /> Methods:
Continuum intensity, line-of-sight magnetogram, and dopplergram data
of the Helioseismic and Magnetic Imager were employed to analyse
the photospheric evolution. Filtergrams in Hα and He I 10830 Å of
the Chromospheric Telescope at the Observatorio del Teide, Tenerife,
track the evolution of the flare. The corresponding coronal conditions
were derived from 171 Å and 304 Å images of the Atmospheric Imaging
Assembly. Local correlation tracking was utilized to determine
shear flows. <BR /> Results: Emerging flux formed a neutral line
ahead of the leading sunspot and new satellite spots. The sunspot
splitting caused a long-lasting flow towards this neutral line, where
a filament formed. Further flux emergence, partly of mixed polarity,
as well as episodes of flux cancellation occurred repeatedly at
the neutral line. Following a nearby C-class precursor flare with
signs of interaction with the filament, the filament erupted nearly
simultaneously with the onset of the M5.6 flare and evolved into a
coronal mass ejection. The sunspot stretched without forming a light
bridge, splitting unusually fast (within about a day, complete ≈6 h
after the eruption) in two nearly equal parts. The front part separated
strongly from the active region to approach the neighbouring active
region where all its coronal magnetic connections were rooted. It
also rotated rapidly (by 4.9° h<SUP>-1</SUP>) and caused significant
shear flows at its edge. <BR /> Conclusions: The eruption resulted
from a complex sequence of processes in the (sub-)photosphere and
corona. The persistent flows towards the neutral line likely caused
the formation of a flux rope that held the filament. These flows,
their associated flux cancellation, the emerging flux, and the
precursor flare all contributed to the destabilization of the flux
rope. We interpret the sunspot splitting as the separation of two
flux bundles differently rooted in the convection zone and only
temporarily joined in the spot. This explains the rotation as the
continued rise of the separating flux, and it implies that at least
this part of the sunspot was still connected to its roots deep in
the convection zone. <P />Movie available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201321106/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: GREGOR Fabry-Pérot interferometer and its companion the blue
imaging solar spectrometer
Authors: Puschmann, Klaus G.; Denker, Carsten; Balthasar, Horst; Louis,
Rohan E.; Popow, Emil; Woche, Manfred; Beck, Christian; Seelemann,
Thomas; Volkmer, Reiner
2013OptEn..52h1606P Altcode: 2013arXiv1302.7157P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-m GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI allows
fast narrow-band imaging and postfactum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic sun and its magnetic field at spatial
scales down to ∼50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectrometric and spectropolarimetric observations between 530-860
nm and 580-660 nm, respectively, and possesses a theoretical spectral
resolution of R≈250,000. Large-format, high-cadence charged coupled
device detectors with sophisticated computer hard- and software enable
the scanning of spectral lines in time-spans equivalent to the evolution
time of solar features. The field-of-view (FOV) of 50″×38″ covers
a significant fraction of the typical area of active regions in the
spectroscopic mode. In case of Stokes-vector spectropolarimetry,
the FOV reduces to 25″×38″. The main characteristics of the GFPI
including advanced and automated calibration and observing procedures
are presented. Improvements in the optical design of the instrument
are discussed and first observational results are shown. Finally,
the first concrete ideas for the integration of a second FPI, the blue
imaging solar spectrometer, are laid out, which will explore the blue
spectral region below 530 nm.
---------------------------------------------------------
Title: Evidence of quiet-Sun chromospheric activity related to an
emerging small-scale magnetic loop
Authors: Gömöry, P.; Balthasar, H.; Puschmann, K. G.
2013A&A...556A...7G Altcode: 2013arXiv1306.3393G
<BR /> Aims: We investigate the temporal evolution of magnetic flux
emergence in the quiet-Sun atmosphere close to disk center. <BR />
Methods: We combined high-resolution SoHO/MDI magnetograms with TRACE
observations taken in the 1216 Å channel to analyze the temporal
evolution of an emerging small-scale magnetic loop and its traces
in the chromosphere. <BR /> Results: We find signatures of flux
emergence very close to the edge of a supergranular network boundary
located at disk center. The new emerging flux appeared first in the MDI
magnetograms in form of an asymmetric bipolar element, i.e., the patch
with negative polarity is roughly twice as weak as the corresponding
patch with opposite polarity. The average values of magnetic flux and
magnetic flux densities reached 1.6 × 10<SUP>18</SUP> Mx, - 8.5 ×
10<SUP>17</SUP> Mx, and 55 Mx cm<SUP>-2</SUP>, -30 Mx cm<SUP>-2</SUP>,
respectively. The spatial distance between the opposite polarity
patches of the emerged feature increased from about 2.″5 to 5.″0
during the lifetime of the loop, which was 36 min. A more precise
lifetime-estimate of the feature was not possible because of a gap
in the temporal sequence of the MDI magnetograms. The chromospheric
response to the emerged magnetic dipole occurred ~9 min later than in
the photospheric magnetograms. It consisted of a quasi-periodic sequence
of time-localized brightenings visible in the 1216 Å TRACE channel for
~14 min that were co-spatial with the axis connecting the two patches of
opposite magnetic polarity. <BR /> Conclusions: We identify the observed
event as a small-scale magnetic loop emerging at photospheric layers
that subsequently rose to the chromosphere. We discuss the possibility
that the fluctuations detected in the chromospheric emission probably
reflect magnetic-field oscillations which propagate to the chromosphere
in the form of waves.
---------------------------------------------------------
Title: Formation of a penumbra in a decaying sunspot
Authors: Louis, R. E.; Mathew, S. K.; Puschmann, K. G.; Beck, C.;
Balthasar, H.
2013A&A...552L...7L Altcode: 2013arXiv1303.3599L
Context. Penumbrae are an important characteristic of sunspots, whose
formation is intricately related to the nature of sub-photospheric
magnetic fields. <BR /> Aims: We study the formation of a penumbra in
a decaying sunspot and compare its properties with those seen during
the development of a proto-spot. <BR /> Methods: High-resolution
spectropolarimetric observations of active region NOAA 11283 were
obtained from the spectro-polarimeter on board Hinode. These were
complemented with full-disk filtergrams of continuum intensity,
line-of-sight magnetograms, and dopplergrams from the Helioseismic and
Magnetic Imager at high cadence. <BR /> Results: The formation of a
penumbra in the decaying sunspot occurs after the coalescence of the
sunspot with a magnetic fragment/pore, which initially formed in the
quiet Sun close to an emerging flux region. At first, a smaller set of
penumbral filaments develop near the location of the merger with very
bright penumbral grains with intensities of 1.2 I<SUB>QS</SUB>, upflows
of 4 km s<SUP>-1</SUP>, and a lifetime of 10 h. During the decay of
these filaments, a larger segment of a penumbra forms at the location
of the coalescence. These new filaments are characterized by nearly
supersonic downflows of 6.5 km s<SUP>-1</SUP> that change to a regular
Evershed flow nearly 3 h later. <BR /> Conclusions: The coalescence of
the pore with the decaying sunspot provided sufficient magnetic flux for
the penumbra to form in the sunspot. The emerging flux region could have
played a decisive role in this process because the formation occurred
at the location of the merger and not on the opposite side of the
sunspot. <P />An animation of the HMI data is available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Properties of a Decaying Sunspot
Authors: Balthasar, H.; Beck, C.; Gömöry, P.; Muglach, K.; Puschmann,
K. G.; Shimizu, T.; Verma, M.
2013CEAB...37..435B Altcode: 2013arXiv1301.1562B
A small decaying sunspot was observed with the Vacuum Tower Telescope
(VTT) on Tenerife and the Japanese Hinode satellite. We obtained
full Stokes scans in several wavelengths covering different heights
in the solar atmosphere. Imaging time series from Hinode and the
Solar Dynamics Observatory (SDO) complete our data sets. The spot is
surrounded by a moat flow, which persists also on that side of the
spot where the penumbra already had disappeared. Close to the spot,
we find a chromospheric location with downflows of more than 10 km
s^{-1} without photospheric counterpart. The height dependence of
the vertical component of the magnetic field strength is determined
in two different ways that yielded different results in previous
investigations. Such a difference still exists in our present data,
but it is not as pronounced as in the past.
---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.
---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer: A New Instrument for
High-Resolution Spectropolarimetric Solar Observations
Authors: Puschmann, K. G.; Balthasar, H.; Bauer, S. -M.; Hahn, T.;
Popow, E.; Seelemann, T.; Volkmer, R.; Woche, M.; Denker, C.
2012ASPC..463..423P Altcode: 2011arXiv1111.5509P
Fabry-Pérot interferometers have advantages over slit spectrographs
because they allow fast narrow-band imaging and post-factum image
reconstruction of the retrieved data. Temperature, plasma velocity,
and magnetic field maps can be derived from inversions of spectral
lines, thus, advancing our understanding of the dynamic Sun and its
magnetic fields at the smallest spatial scales. The GREGOR Fabry-Pérot
Interferometer (GFPI) is one of two first-light instruments of the
1.5-meter GREGOR solar telescope, which is currently being commissioned
at the Observatorio del Teide, Tenerife, Spain. The GFPI operates close
to the diffraction limit of GREGOR, thus, providing access to fine
structures as small as 60 km on the solar surface. The field-of-view
of 52″×40″ is sufficiently large to cover significant area
fraction of active regions. The GFPI is a tuneable dual-etalon system
in a collimated mounting. Equipped with a full-Stokes polarimeter,
it records spectropolarimetric data with a spectral resolution of R
≍ 250,000 over the wavelength range from 530-860 nm. Large-format,
high-cadence CCD detectors with powerful computer hard- and software
facilitate scanning of spectral lines in time spans corresponding
to the evolution time-scale of solar features. We present the main
characteristics of the GFPI including the latest developments in
software, mechanical mounts, and optics.
---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.
---------------------------------------------------------
Title: The GREGOR polarimetric calibration unit
Authors: Hofmann, A.; Arlt, K.; Balthasar, H.; Bauer, S. M.; Bittner,
W.; Paschke, J.; Popow, E.; Rendtel, J.; Soltau, D.; Waldmann, T.
2012AN....333..854H Altcode:
The new Solar telescope GREGOR is designed to observe small-scale
dynamic magnetic structures below a size of 70 km on the Sun
with high spectral resolution and polarimetric accuracy. For
this purpose, the polarimetric concept of GREGOR is based on a
combination of post-focus polarimeters with pre-focus equipment for
high precision calibration. The Leibniz-Institute for Astrophysics
Potsdam developed the GREGOR calibration unit which is an integral
part of the telescope. We give an overview of the function and design
of the calibration unit and present the results of extensive testing
series done in the Solar Observatory “Einsteinturm” and at GREGOR.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
---------------------------------------------------------
Title: Spectral Inversion of Multiline Full-Disk Observations of
Quiet Sun Magnetic Fields
Authors: Balthasar, H.; Demidov, M. L.
2012SoPh..280..355B Altcode: 2012arXiv1203.4522B; 2012SoPh..tmp...80B
Spectral inversion codes are powerful tools for analyzing
spectropolarimetric observations, and they provide important
diagnostics of solar magnetic fields. Inversion codes differ according
to numerical procedure, approximation of the atmospheric model, and
description of radiative transfer. Stokes Inversion based on Response
functions (SIR) is an implementation widely used by the solar physics
community. It allows one to work with different atmospheric components,
where gradients of different physical parameters are possible, e.g.,
magnetic field strength and velocities. The spectropolarimetric
full-disk observations were carried out with the Stokesmeter of the
Solar Telescope for Operative Prediction (STOP) at the Sayan Observatory
on 3 February 2009, when neither an active region nor any other extended
flux concentration was present on the Sun. In this study of quiet Sun
magnetic fields, we apply the SIR code simultaneously to 15 spectral
lines. A tendency is found that weaker magnetic field strengths
occur closer to the limb. We explain this finding by the fact that,
close to the limb, we are more sensitive to higher altitudes in an
expanding flux tube, where the field strength should be smaller since
the magnetic flux is conserved with height. Typically, the inversions
deliver two populations of magnetic elements: i) high magnetic field
strengths (1500 - 2000 G) and high temperatures (5500 - 6500 K) and ii)
weak magnetic fields (50 - 150 G) and low temperatures (5000 - 5300 K).
---------------------------------------------------------
Title: The GREGOR Fabry-Perot interferometer: status report and
prospects
Authors: Puschmann, Klaus G.; Balthasar, Horst; Beck, Christian;
Louis, Rohan E.; Popow, Emil; Seelemann, Thomas; Volkmer, Reiner;
Woche, Manfred; Denker, Carsten
2012SPIE.8446E..79P Altcode: 2012arXiv1207.2084P
The GREGOR Fabry-Ṕerot 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 allows
fast narrow-band imaging and post-factum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic Sun and its magnetic field at spatial
scales down to 50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectropolarimetric observations over the wavelength range from 530-860
nm with a theoretical spectral resolution of R ≍ 250,000. The GFPI is
equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD
detectors with powerful computer hard- and software enable the scanning
of spectral lines in time spans equivalent to the evolution time of
solar features. The field-of-view of 50”×38” covers a significant
fraction of the typical area of active regions. We present the main
characteristics of the GFPI including advanced and automated calibration
and observing procedures. We discuss improvements in the optical design
of the instrument and show first observational results. Finally, we
lay out first concrete ideas for the integration of a second FPI, the
Blue Imaging Solar Spectrometer, which will explore the blue spectral
region below 530 nm.
---------------------------------------------------------
Title: On Multi-Line Spectro-Polarimetric Diagnostics of the Quiet
Sun's Magnetic Fields. Statistics, Inversion Results and Effects on
the SOHO/MDI Magnetogram Calibration
Authors: Demidov, M. L.; Balthasar, H.
2012SoPh..276...43D Altcode:
On the long way to establish reliable physical properties of the
solar atmosphere from different kinds of magnetic field measurement,
significant progress has been achieved, but many important issues are
still waiting for solution. This is essential for the investigation
of weak magnetic fields of the quiet Sun, which usually cover most
of the solar surface. Weak magnetic fields significantly contribute
to the formation of the interplanetary magnetic field. The problem of
reliable diagnostics of such fields hardly ever has a simple solution
using only single spectral line observations. A better chance is given
by multi-spectral line spectro-polarimetric observations, especially
with lines having very different properties. In the present study,
we use simultaneous high-precision Stokes-meter measurements of
the quiet solar magnetic fields in 15 lines in the vicinity of Fe I
525.0 nm. These measurements cover the whole range of heliocentric
distances. Magnetic field strength ratios of different spectral
lines with respect to Fe I 525.0 nm vary between 1.07 and 2.12. This
ratio depends also on the heliocentric position, moving closer to
the limb it decreases and approaches values of about unity in most
cases. To interpret the observations, different model approaches are
compared. SIR-inversions (Stokes Inversion based on Response functions)
with a two-component atmospheric model approach reproduce the basic
observables much better than with one-component atmospheres. Our best
fits are connected with field strengths of 1 - 2 kG and filling factors
of less than five percent. To check the justification for the recent
re-calibration of the data from the Michelson Doppler Imager (MDI)
onboard SOHO, we carried out a numerical experiment, and we confirm
our former conclusion that there is no need for such a re-calibration.
---------------------------------------------------------
Title: Horizontal flow fields observed in Hinode G-band
images. II. Flow fields in the final stages of sunspot decay
Authors: Verma, M.; Balthasar, H.; Deng, N.; Liu, C.; Shimizu, T.;
Wang, H.; Denker, C.
2012A&A...538A.109V Altcode: 2011arXiv1112.1589V
Context. Generation and dissipation of magnetic fields is a fundamental
physical process on the Sun. In comparison to flux emergence and the
initial stages of sunspot formation, the demise of sunspots still
lacks a comprehensive description. <BR /> Aims: The evolution of
sunspots is most commonly discussed in terms of their intensity and
magnetic field. Here, we present additional information about the
three-dimensional flow field in the vicinity of sunspots towards
the end of their existence. <BR /> Methods: We present a subset of
multi-wavelengths observations obtained with the Japanese Hinode
mission, the Solar Dynamics Observatory (SDO), and the Vacuum Tower
Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the
time period 2010 November 18-23. Horizontal proper motions were derived
from G-band and Ca ii H images, whereas line-of-sight velocities were
extracted from VTT echelle Hα λ656.28 nm spectra and Fe i λ630.25 nm
spectral data of the Hinode/Spectro-Polarimeter, which also provided
three-dimensional magnetic field information. The Helioseismic and
Magnetic Imager on board SDO provided continuum images and line-of-sight
magnetograms, in addition to the high-resolution observations for the
entire disk passage of the active region. <BR /> Results: We perform
a quantitative study of photospheric and chromospheric flow fields
in and around decaying sunspots. In one of the trailing sunspots of
active region NOAA 11126, we observe moat flow and moving magnetic
features (MMFs), even after its penumbra had decayed. We also detect
a superpenumbral structure around this pore. We find that MMFs follow
well-defined, radial paths from the spot all the way to the border of
a supergranular cell surrounding the spot. In contrast, flux emergence
near the other sunspot prevents the establishment of similar well
ordered flow patterns, which could be discerned around a tiny pore of
merely 2 Mm diameter. After the disappearance of the sunspots/pores,
a coherent patch of abnormal granulation remained at their location,
which was characterized by more uniform horizontal proper motions, low
divergence values, and smaller photospheric Doppler velocities. This
region, thus, differs significantly from granulation and other areas
covered by G-band bright points. We conclude that this peculiar flow
pattern is a signature of sunspot decay and the dispersal of magnetic
flux.
---------------------------------------------------------
Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
Soltau, D.; Volkmer, R.
2011ASPC..437..351B Altcode:
A brief description of the new 1.5-meter solar telescope GREGOR located
at the Observatorio del Teide in Tenerife will be given. GREGOR will
provide a spatial resolution of about 75 km on the Sun, and with its
light collecting capability we will be able to study the development
of small magnetic features with high cadence. From the beginning,
it will be equipped with the GREGOR Fabry-Pérot Interferometer
(GFPI) for the visible spectral range and with a GRating Infrared
Spectrograph (GRIS). Both postfocus instruments can be combined
with a polarimeter, and in both cases the light is modulated by two
ferro-electric liquid crystals. A calibration unit can be inserted to
determine the instrumental polarization. Because of the altazimuthal
mount, time-dependent rotation of the polarimetric reference plane
is introduced, and we have to develop a polarization model of the
telescope. Measurements to verify this model are in preparation.
---------------------------------------------------------
Title: On the Diagnostics of the Quiet Sun Magnetic Fields: Multi-Line
Spectro-Polarimetric Observations and Inversion Results
Authors: Demidov, M. L.; Balthasar, H.
2011ASPC..437..189D Altcode:
Sophisticated diagnostics of the quiet Sun magnetic fields are a very
important issue of modern solar physics because of the existence of
their deep genetic connections with active regions. For this aim, we
use high-precision spectro-polarimetric observations in about twenty
spectral lines in an almost 3 nm wide spectral domain around the
line Fe I 525.02 nm. These observations cover the whole solar disk. A
detailed statistical analysis of magnetic strength ratios in different
combinations of spectral lines is performed. For seven sufficiently
strong Fe I lines observed at disk center, we applied the SIR code
(Stokes Inversion based on Response functions). It was impossible
to reproduce the Stokes I and V profiles of these selected lines
simultaneously in the framework of models with only one atmospheric
component. But a very good agreement between observations and inversion
results was obtained for a model with two atmospheric components,
one with magnetic field and the other without. Reliable values were
found for the magnetic field strength and the filling factor.
---------------------------------------------------------
Title: On the diagnostics of the quiet Sun's magnetic fields:
application of the SIR inversion to the full-disk Stokes-meter
observations in 15 spectral lines
Authors: Demidov, M. L.; Balthasar, H.
2011ASInC...2..169D Altcode:
Although quiet solar magnetic fields are weak and they are difficult to
measure, they cover most of the solar disk, even the whole one during
epochs of minimal activity. They are basically responsible for the
formation of the open flux from the Sun, and, consequently, reliable
diagnostics of them are very important. In this study, we use a raster
scan covering the whole solar disk of high precision Stokes-meter
measurements of the quiet solar magnetic fields in 15 simultaneously
recorded lines in the vicinity of Fe I 525.02 nm. A two-component model
atmosphere and the SIR (Stokes Inversion based on Response functions)
approach were used for theoretical modeling. Two types of inversion
results were obtained for magnetic component: one with kG magnetic
field strength, high temperature and small filling factor, and the
other one with relatively weak magnetic field (no more then 200 G),
low temperature and big filling factor. A possible explanation of such
result is briefly discussed. An application of the obtained results
for the urgent issue to calibrate SOHO/MDI magnetograms is presented.
---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V
With the integration of a 1-meter Cesic primary mirror the GREGOR
telescope pre-commissioning started. This is the first time, that
the entire light path has seen sunlight. The pre-commissioning period
includes testing of the main optics, adaptive optics, cooling system,
and pointing system. This time was also used to install a near-infrared
grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5
meter primary mirror is installed, commissioning will be completed,
and an extended phase of science verification will follow. In the near
future, GREGOR will be equipped with a multi-conjugate adaptive optics
system that is presently under development at KIS.
---------------------------------------------------------
Title: The GREGOR Fabry-Perot interferometer: a new instrument for
high-resolution solar observations
Authors: Denker, Carsten; Balthasar, Horst; Hofmann, Axel; Bello
González, Nazaret; Volkmer, Reiner
2010SPIE.7735E..6MD Altcode: 2010SPIE.7735E.217D
The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of the first-light
instruments of the 1.5-meter GREGOR solar telescope currently being
commissioned at Observatorio del Teide (OT), Tenerife, Spain. A
spectral resolution of R ~ 250, 000 over the wavelength range from
530-860 nm can be achieved using a tunable dual etalon system. A high
spectral resolving power is needed to extract physical parameters
(e.g., temperature, plasma velocity and the magnetic field vector) from
inversions of photospheric and chromospheric spectral lines. The GFPI
is outfitted with a polarimeter, which accurately measures the full
Stokes vector. Precision polarimetry is facilitated by a calibration
unit in the immediate vicinity of GREGOR's secondary focus. The GFPI
operates close to the diffraction limit of GREGOR, thus providing
access to fine structures as small as 60 km on the solar surface. The
field-of-view (FOV) of 52" × 40" is sufficiently large to cover
significant portions of active regions. Large-format, high-cadence
CCD detectors are an integral part of the instrument to ensure that
scans of spectral lines can be obtained in time spans corresponding
to the evolution time scale of solar phenomena such as granulation,
evolving magnetic fields or dynamic chromospheric features. Besides
describing the technical features of the GFPI and providing a status
report on commissioning the instrument, we will use two-dimensional
spectropolarimetric data obtained with the Vacuum Tower Telescope
(VTT) at OT to illustrate GFPI's science capabilities.
---------------------------------------------------------
Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
D.; Strassmeier, K. G.
2010AN....331..624V Altcode:
The integration and verification phase of the GREGOR telescope
reached an important milestone with the installation of the
interim 1 m SolarLite primary mirror. This was the first time
that the entire light path had seen sunlight. Since then extensive
testing of the telescope and its subsystems has been carried out. The
integration and verification phase will culminate with the delivery and
installation of the final 1.5 m Zerodur primary mirror in the summer of
2010. Observatory level tests and science verification will commence in
the second half of 2010 and in 2011. This phase includes testing of the
main optics, adaptive optics, cooling and pointing systems. In addition,
assuming the viewpoint of a typical user, various observational modes
of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
Spectrograph (GRIS), and high-speed camera systems will be tested to
evaluate if they match the expectations and science requirements. This
ensures that GREGOR will provide high-quality observations with its
combination of (multi-conjugate) adaptive optics and advanced post-focus
instruments. Routine observations are expected for 2012.
---------------------------------------------------------
Title: Magnetic loop emergence within a granule
Authors: Gömöry, P.; Beck, C.; Balthasar, H.; Rybák, J.; Kučera,
A.; Koza, J.; Wöhl, H.
2010A&A...511A..14G Altcode: 2009arXiv0910.4449G
<BR /> Aims: We investigate the temporal evolution of magnetic
flux emerging within a granule in the quiet-Sun internetwork at
disk center. <BR /> Methods: We combined IR spectropolarimetry of
high angular resolution performed in two Fe i lines at 1565 nm with
speckle-reconstructed G-band imaging. We determined the magnetic
field parameters by a LTE inversion of the full Stokes vector using
the SIR code, and followed their evolution in time. To interpret
the observations, we created a geometrical model of a rising loop in
3D. The relevant parameters of the loop were matched to the observations
where possible. We then synthesized spectra from the 3D model for a
comparison to the observations. <BR /> Results: We found signatures of
magnetic flux emergence within a growing granule. In the early phases,
a horizontal magnetic field with a distinct linear polarization signal
dominated the emerging flux. Later on, two patches of opposite circular
polarization signal appeared symmetrically on either side of the linear
polarization patch, indicating a small loop-like structure. The mean
magnetic flux density of this loop was roughly 450 G, with a total
magnetic flux of around 3 × 10<SUP>17</SUP> Mx. During the ~12 min
episode of loop occurrence, the spatial extent of the loop increased
from about 1 to 2 arcsec. The middle part of the appearing feature
was blueshifted during its occurrence, supporting the scenario of an
emerging loop. There is also clear evidence for the interaction of
one loop footpoint with a preexisting magnetic structure of opposite
polarity. The temporal evolution of the observed spectra is reproduced
to first order by the spectra derived from the geometrical model. During
the phase of clearest visibility of the loop in the observations,
the observed and synthetic spectra match quantitatively. <BR />
Conclusions: The observed event can be explained as a case of flux
emergence in the shape of a small-scale loop. The fast disappearance
of the loop at the end could possibly be due to magnetic reconnection.
---------------------------------------------------------
Title: The three-dimensional structure of sunspots. II. The moat
flow at two different heights
Authors: Balthasar, H.; Muglach, K.
2010A&A...511A..67B Altcode: 2009arXiv0912.3661B
<BR /> Aims: Many sunspots are surrounded by a radial outflow called
the moat flow. We investigate the moat flow at two different heights
of the solar atmosphere for a sunspot whose magnetic properties were
reported in the first paper of this series. <BR /> Methods: We use
two simultaneous time series taken with the Transition Region And
Coronal Explorer (TRACE) in white light and in the UV at 170 nm. The
field-of-view is centered on the small sunspot NOAA 10886 located near
disk center. Horizontal velocities are derived by applying two different
local correlation tracking techniques. <BR /> Results: Outflows are
found everywhere in the moat. In the inner moat, the velocities from
the UV series are larger than those from white light, whereas in the
outer part of the moat we find the converse result. <BR /> Conclusions:
The results imply that the white light velocities represent a general
outflow of the quiet sun plasma in the moat, while UV velocities are
dominated by small bright points that move faster than the general
plasma flow.
---------------------------------------------------------
Title: Spectro-Polarimetric Observations of Solar Magnetic Fields
and the SOHO/MDI Calibration Issue
Authors: Demidov, M. L.; Balthasar, H.
2009SoPh..260..261D Altcode: 2009arXiv0908.2731D
Comparisons of solar magnetic-field measurements made in different
spectral lines are very important, especially in those lines
in which observations have a long history or (and) specific
diagnostic significance. The spectral lines Fe I 523.3 nm and Fe
I 525.0 nm belong to this class. Therefore, this study is devoted
to a comprehensive analysis using new high-precision Stokes-meter
full-disk observations. The disk-averaged magnetic-field strength ratio
R=B(523.3)/B(525.0) equals 1.97±0.02. The center-to-limb variation
(CLV) is R=1.74−2.43μ+3.43μ<SUP>2</SUP>, where μ is the cosine
of the center-to-limb angle. For the disk center, we find R=2.74, and
for near-limb areas with μ=0.3, R equals 1.32. There is only a small
dependence of R on the spatial resolution. Our results are rather close
to those published three decades ago, but differ significantly from
recent magnetographic observations. An application of our results to
the important SOHO/MDI magnetic data calibration issue is discussed. We
conclude that the revision of the SOHO/MDI data, based only on the
comparison of magnetic-field measurements in the line pair Fe I 523.3
nm and Fe I 525.0 nm (increasing by a factor of 1.7 or 1.6 on average
according to recent publications) is not obvious and new investigations
are urgently needed.
---------------------------------------------------------
Title: An Extended Line-Ratio Method Application: Comparison of
Large-Scale Solar Magnetic Field Observations in Different Spectral
Lines and Observatories
Authors: Demidov, M. L.; Golubeva, E. M.; Veretsky, R. M.; Balthasar,
H.
2009ASPC..405..241D Altcode:
We explore the distribution of the magnetic strength ratios (MSR)
across the solar disk in different combinations of spectral lines and
observatories. It was found that along with expected center-to-limb
variations (CLV) of MSRs, there are significant polar-equatorial
asymmetries of CLVs in some cases. The results of comparing the
experimental MSR CLVs with 3D multi-ray theoretical simulations in
the framework of two-component flux tubes models are presented.
---------------------------------------------------------
Title: The Height Dependence of the Magnetic Vector Field in Sunspots
Authors: Balthasar, H.; Bommier, V.
2009ASPC..405..229B Altcode:
A complex active region was observed simultaneously with the solar
telescopes VTT and THEMIS on Tenrife in May 2005. Spatial scans
across the sunspot group were performed at both telescopes. The
full Stokes-vector was recorded in several photospheric spectral
lines, i.~e. at the VTT in a group of iron and silicon lines in
the near infrared and at THEMIS in iron and chromium lines in the
visible. Inversions were carried out independently for the different
lines in order to derive the magnetic field strength, its inclination
and azimuth together with the temperature stratification. Thus we
obtained the three-dimensional structure of the magnetic field. Selected
locations in the penumbra and in light bridges were considered in
detail. We find a general tendency that the magnetic field is weaker
and less inclined in higher layers.
---------------------------------------------------------
Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot
interferometer
Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker,
C.; Hofmann, A.; Kneer, F.; Puschmann, K. G.
2009IAUS..259..665B Altcode:
One of the first post-focus instruments of the new solar telescope
GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the
Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope
(VTT) on Tenerife. This spectrometer is equipped with a full-Stokes
polarimeter. The modulation is performed with two ferroelectric liquid
crystals, one acting nominally as quarter-wave plate, and the other as
half-wave plate. A modified Savart plate serves as polarimetric beam
splitter. With the present liquid crystals, the optimum wavelength range
of this polarimeter is between 580 and 660 nm. The spectro-polarimeter
will benefit from the capabilities of the new telescope GREGOR which
will provide a spatial resolution of about 0″.1 (75 km on the solar
surface). Thus we will be able to investigate small magnetic features,
and we will study their development with high cadence.
---------------------------------------------------------
Title: The three-dimensional structure of the magnetic field of
a sunspot
Authors: Balthasar, Horst; Gömöry, Peter
2009IAUS..259..225B Altcode:
Spectro-polarimetric observations in several spectral lines allow
to determine the height variation of the magnetic field of a small
sunspot throughout the solar photosphere. The full Stokes-vector is
measured with high spatial resolution. From these data we derive the
magnetic field vector. The magnetic field strength decreases with
height everywhere in the spot, even in the outer penumbra where some
other authors have reported the opposite. The precise value of this
decrease depends on the exact position in the spot. Values vary between
0.5 and 2.2 G km<SUP>-1</SUP> when they are determined from an iron
and a silicon line in the near infrared. The magnetic field is less
inclined in the higher layers where the silicon line is formed. Once
the magnetic vector field is known, it is straight forward to determine
current densities and helicities. Current densities exhibit a radial
structure in the penumbra, although it is still difficult to correlate
this with the structure seen in the intensity continuum. In spite of
this, current densities have a potential to serve as diagnostic tools
to understand the penumbra, at least with the spatial resolution of
the upcoming telescopes. The mean infered helicity is negative, as
expected for a spot in the northern hemisphere. Nevertheless, there
are locations inside the spot with positive helicity.
---------------------------------------------------------
Title: The Moat Flow in Two Different Heights
Authors: Balthasar, H.; Muglach, K.
2008ESPM...12.2.26B Altcode:
We investigate time series obtained with the Transition Region And
Coronal Explorer (TRACE) simultaneously in two wavelength ranges, in
whitelight (WL) and in the ultraviolet at 170 nm (UV). In the quiet
sun, the UV is most sensitive to layers just below the temperature
minimum. The field-of-view was centered on a small sunspot passing
the central meridian. Horizontal velocities are determined by
local correlation techniques (LCT), and we compare two different
LCT-methods. We find an extended outflow in the moat. We detect the
outflow up to four times the radius of the spot. For both wavelength
ranges the outer boundary of the flow is located at the same distance
from the center of the spot. In the inner moat velocities are higher
in the UV, indicating higher velocities in the upper layers. In the
outer moat higher velocities are detected in WL.
---------------------------------------------------------
Title: GREGOR - The Calibration Unit
Authors: Hofmann, A.; Rendtel, J.; Arlt, K.; Balthasar, H.
2008ESPM...12..6.9H Altcode:
In 2010 we expect "first light" for GREGOR - a new solar telescope
with large aperture and modern scientific instruments. It is designed
to observe small-scale dynamic magnetic structures below a size
of 70 km on the Sun with high spectral resolution and polarimetric
accuracy. For this purpose, the polarimetric concept of GREGOR is based
on a combination of post-focus polarimeters with pre-focus equipment
for high precision calibration. The Astrophysical Institute Potsdam
developed the GREGOR calibration unit which is an integral part of the
telescope. We give an overview on function and design of the calibration
unit and present the results of extensive testing series in the Solar
Observatory "Einsteinturm".
---------------------------------------------------------
Title: The three-dimensional structure of sunspots. I. The height
dependence of the magnetic field
Authors: Balthasar, H.; Gömöry, P.
2008A&A...488.1085B Altcode:
Aims: We investigate the height dependence of the magnetic field
of a sunspot, which has been until now a controversial issue. <BR
/>Methods: Full-Stokes profiles of a sunspot, derived from infrared
spectro-polarimetric measurements, were investigated. The magnetic
field strength, inclination and azimuth were obtained using an inversion
code. The results from two different spectral lines deliver the height
dependence of the magnetic vector field. Vertical current densities
and helicities as well as the vertical derivative of the vertical
component of the magnetic field strength are calculated using Maxwell's
equations. <BR />Results: Inside the spot, the total magnetic field
strength decreases with height, even in the outer penumbra, where
the opposite trend was reported by other investigators. Outside the
spot, the field strength increases with height apart from at a few
small locations. This result is interpreted in terms of magnetic
canopies. Magnetic field lines are less inclined in higher layers
everywhere in the field of view. In the umbra, the vertical component
of the magnetic field decreases by values in the range 0.5-2.2
G km<SUP>-1</SUP>, depending on the applied method. Mean values
in the inner penumbra are smaller than in the umbra. In the outer
penumbra, the vertical magnetic component increases independently of
the local intensity distribution. A pore close to the spot exhibits
a more rapid decrease with height than the spot itself. The electric
current densities and helicities depend on the fine structure of the
sunspots. Typical values of the current densities vary in the range
±40 mA m<SUP>-2</SUP>. The mean values are -11 mA m<SUP>-1</SUP> for
the umbra and -2 mA m<SUP>-1</SUP> for the penumbra, respectively, but
the propagated errors are of the same order as the mean values. There
are indications that the radial structure of the penumbra is related
to enhanced current densities, but at the present resolution we are
unable to establish a correlation with local intensity fluctuations. <BR
/>Conclusions: If the spatial resolution is sufficiently high, electric
current densities and helicities could be applied as reliable diagnostic
tools for understanding penumbral fine structure.
---------------------------------------------------------
Title: First-Light Science Cases for the GREGOR Fabry-Perot
Interferometer
Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados,
M.; Kneer, H. F. Nicklas; Puschmann, K. G.
2008ESPM...12..6.8D Altcode:
The light-gathering capacity and resolving power of the 1.5-meter
aperture GREGOR telescope will provide solar observations of
the full Stokes vector with high temporal, spectral and spatial
resolution. As one of the first-light instruments, the GREGOR
Fabry-Perot Interferometer (GFPI) is well suited for observations
with adaptive optics (AO) correction. Post-facto image correction
(speckle masking imaging and deconvolution) will further enhance
the data quality to approach the diffraction-limited resolution of
the telescope. We will describe the GFPI optical design and its basic
operating procedures. Instruments characteristics such as field-of-view,
cadence, spectral resolution, and spectroscopic/polarimetric observing
modes will result in boundary conditions, which have to be carefully
considered in optimizing the scientific outcome of the first-light
observations. We will present two science cases for quiet Sun and
active region studies to illustrate the capabilities of this imaging
spectro-polarimeter.
---------------------------------------------------------
Title: Comparison of Solar Magnetic Fields Measured at Different
Observatories: Peculiar Strength Ratio Distributions Across the Disk
Authors: Demidov, M. L.; Golubeva, E. M.; Balthasar, H.; Staude, J.;
Grigoryev, V. M.
2008SoPh..250..279D Altcode: 2008SoPh..tmp..125D
In this paper we analyze the distribution of magnetic strength ratios
(MSR) across the solar disk using magnetograms in different spectral
lines from the same observatory (Mount Wilson Observatory (MWO)
and Sayan Observatory (SO)), magnetograms in the same line from
different observatories (MWO, SO, Wilcox Solar Observatory (WSO)),
and in different spectral lines from different observatories (the three
observatories mentioned above, the National Solar Observatory/Kitt Peak
(KP) and Michelson Doppler Imager (MDI) on board Solar and Heliospheric
Observatory (SoHO)). We find peculiarities in some combinations of data
sets. Besides the expected MSR center-to-limb variations, there is an
equator-to-pole asymmetry, especially in the near-limb areas. Therefore,
it is generally necessary to use 2D matrices of correction coefficients
to reduce one kind of observation into another one.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of sunspots. II. Search for
propagating waves and drifting velocity filaments in photospheric
layers
Authors: Balthasar, H.; Schleicher, H.
2008A&A...481..811B Altcode:
Aims: Running penumbral waves are often reported from observations in
chromospheric lines or lines formed in the upper photosphere. In this
work we investigate whether they can be detected in a line formed in
the mid to lower photosphere. <BR />Methods: We used time series of
two-dimensional spectra of an iron line that is insensitive to the
magnetic field and that is formed in the lower to mid photosphere. <BR
/>Results: No running penumbral waves are detected in this line formed
in the lower and mid photosphere. In the moat, outward moving velocity
features are detected. They are slightly faster than the plasma motions
but much slower than running penumbral waves. <BR />Conclusions:
Running penumbral waves are a phenomenon occurring in higher layers,
i.e. the lower chromosphere and the upper photosphere, but not in the
mid photosphere or below. In the moat, we found long-living filamentary
velocity features drifting outwards.
---------------------------------------------------------
Title: Propagating features in photospheric layers of sunspots
Authors: Schleicher, Helmold; Balthasar, Horst
2007AN....328..717S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotational periodicities in sunspot relative numbers
Authors: Balthasar, H.
2007A&A...471..281B Altcode:
Context: The search for active longitudes on the Sun has a long
history, and many controversial results have been published. Recently
the question became more important when active longitudes were found
on other stars. <BR />Aims: The aim of this paper is to investigate an
integral measure of solar activity available for a long time interval
and which allows enough frequency resolution for the investigation of
active longitudes. Such a measure is given by the daily sunspot relative
numbers. <BR />Methods: A search for periodicities is performed with
a classical Fast Fourier Transform (FFT), with a wavelet analysis
and with the tool of superimposed epochs. <BR />Results: The FFT
yields a hump of power peaks near the synodic rotation period of 27
days, but only a very weak and insignificant enhancement around 13.5
days, indicating that the mean rotational variation of the sunspot
numbers typically has one maximum and one minimum (overlaid by minor
fluctuations). The wavelet analysis shows that spectral power for
single periods varies for certain time intervals. A systematic drift
during the solar activity cycle is not detected. Similar results are
obtained from the superimposed epochs. Periodic “flip-flops” with
time scales of a few years as for some stars are not found for the Sun
in this investigation. <BR />Conclusions: Sunspots are not distributed
equally over the longitudes; there is a more active and a less active
hemisphere. The rotation period derived from the pattern varies over
long time scales. The results found in this work are not in favor
of an explanation of the variations due to a differential rotation
law. The rotation of the sunspot distribution pattern might reflect
the internal rotation of the Sun, but it better fits the range of
highest rotation rates in the upper convection zone than the rotation
near the tachocline. <P />Figure [see full text] is only available in
electronic form at http://www.aanda.org
---------------------------------------------------------
Title: GREGOR: the New German Solar Telescope
Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.;
Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.;
Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier,
K.; Wittmann, A.
2007ASPC..368..605B Altcode: 2007arXiv0704.2693B
GREGOR is a new open solar telescope with an aperture of 1.5 m. It
replaces the former 45-cm Gregory Coudé telescope on the Canary island
Tenerife. The optical concept is that of a double Gregory system. The
main and the elliptical mirrors are made from a silicon-carbide material
with high thermal conductivity. This is important to keep the mirrors
on the ambient temperature avoiding local turbulence. GREGOR will be
equipped with an adaptive optics system. The new telescope will be ready
for operation in 2008. Post-focus instruments in the first stage will be
a spectrograph for polarimetry in the near infrared and a 2-dimensional
spectrometer based on Fabry-Pérot interferometers for the visible.
---------------------------------------------------------
Title: Simultaneous polarimetric observations with VTT and THEMIS
Authors: Balthasar, H.; Bommier, V.
2007msfa.conf..229B Altcode:
Spectro-polarimetric observations of sunspot groups have been performed
simultaneously with the VTT and with THEMIS. At the VTT we observed a
group of iron and silicon lines at 1078 nm with the Tenerife Infrared
Polarimeter, and at THEMIS we observed in five spectral channels
(MTRmode): Fe 630 nm, Na D, Hα, Fe 557.6 nm and alternatively Cr 578
nm or Fe 525 nm. The inversion of the Stokes-profiles was done with
the SIR-code for the infrared lines and for Fe 630 nm, for the other
spectral ranges the inversion is still pending. So far we derived that
the magnetic field strength decreases with height at most locations
inside the spots, in contrast to some recently published results of
other investigations.
---------------------------------------------------------
Title: New high resolution solar telescope GREGOR
Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.;
Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier,
K.; Wittmann, A. D.
2007msfa.conf...39V Altcode:
The 1.5m solar telescope GREGOR is being constructed at Tenerife,
Spain. Its purpose is to observe with high spatial and spectral
resolution small-scale dynamic magnetic features on the Sun. The
telescope is completely open with retractable dome and actively cooled
primary mirror made of silicon carbide to minimize thermal effects
on the image quality. After completion it will be one of the most
powerful solar telescopes. This paper presents a general overview of
the telescope characteristics and the current status.
---------------------------------------------------------
Title: Magnetic vector field above a sunspot
Authors: Gömöry, P.; Balthasar, H.
2007msfa.conf..221G Altcode:
We present an analysis of the spectro-polarimetricmeasurements of the
active region NOAA 10886 taken with the Tenerife Infrared Polarimeter
in the Fe I 10783 Å spectral line. The magnetic field strength and
the magnetic inclination and azimuth were inferred from the data
using the inversion code SIR. The vertical current densities and
the vertical derivative of the vertical component of the magnetic
field were then calculated for the leading spot of the AR 10886. We
revealed that typical values of the vertical current densities vary in
the range ± 40mAm-2 inside the spot. Moreover, we found an extended
area of enhanced vertical current densities in the umbra (values up
to -80mAm-2). Our analysis also showed that the vertical component
of the magnetic field strength decreases by 0.6 - 1.6Gkm-1 and 0.5 -
0.8Gkm-1 in the umbra and inner penumbra; on the other hand we found
an increase of the vertical component of the magnetic field in the
outer penumbra (typical values varying between 0.1 - 0.5Gkm-1).
---------------------------------------------------------
Title: The new 1.5m solar telescope GREGOR: first light and start
of commissioning
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald;
Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus;
Sobotka, Michal; Klvana, Miroslav; Collados, Manuel
2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V
The integration of the three main silicon carbide mirrors into the new
1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
during 2006. We expect first light at the end of 2006. A progress
report about integration of the optics and mechanics and planning of
the commissioning phase of the telescope and post focus instruments
will be presented at the meeting. The GREGOR telescope is build by a
consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
Gottingen and additional national and international Partners.
---------------------------------------------------------
Title: Vertical current densities and magnetic gradients in sunspots
Authors: Balthasar, H.
2006A&A...449.1169B Altcode:
Aims.The vertical component of electric current densities and the
height dependence of the vertical component of the magnetic field in
sunspots were determined.Methods. Full-Stokes magnetograms of eight
sunspots obtained from infrared spectro-polarimetric measurements were
investigated. The magnetic field strength and the magnetic inclination
and azimuth were obtained from an inversion code. Vertical current
densities and the vertical derivative of the vertical component of the
magnetic field strength resulted from Maxwell equations.Results. It is
found that electric current densities and magnetic gradients depend on
the finestructure of the sunspots. Typical values for current densities
vary in the range ±40 mA m<SUP>-2</SUP>, but their errors are of the
same order. Disturbances in the radial structure of the penumbra are
related to enhanced current densities up to 149 mA m<SUP>-2</SUP>,
and a maximum value of 166 mA m<SUP>-2</SUP> was found in a light
bridge. There are indications that the radial structure of the
penumbra is related to current densities, but no correlation to the
local intensity fluctuations was found in the outer penumbra. The
vertical component of the magnetic field decreases by 0.5-1.5 G
km<SUP>-1</SUP> in the umbra. Mean values in the inner penumbra are
somewhat smaller than in the umbra, and locally dark structures exhibit
a faster decrease with height than bright ones. In the outer penumbra
the vertical magnetic component increases, independent of the local
intensity distribution. Conclusions. Electric current densities could
be a diagnostic tool for understanding the penumbral finestructure,
although the presently available spatial resolution is probably not
good enough to avoid artifacts. Magnetic extrapolations might depend
crucially on this problem.
---------------------------------------------------------
Title: The Vertical Component of Electric Current Densities in
Sunspots
Authors: Balthasar, H.
2005ESASP.600E..55B Altcode: 2005dysu.confE..55B; 2005ESPM...11...55B
No abstract at ADS
---------------------------------------------------------
Title: Influence of Instrumental Effects on High Frequency
Oscillations Observed with Trace
Authors: Muglach, K.; Balthasar, H.
2005ESASP.596E..76M Altcode: 2005ccmf.confE..76M
No abstract at ADS
---------------------------------------------------------
Title: The Vertical Component of Electric Current Densities in
Sunspots
Authors: Balthasar, H.
2005ESASP.596E...8B Altcode: 2005ccmf.confE...8B
No abstract at ADS
---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V Altcode:
The telescope structure including control system and the complete
retractable dome of the new 1.5 m solar telescope GREGOR were
assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
telescope is build by a consortium of the Kiepenheuer Institut fuer
Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
fuer Astrophysik Goettingen and additional national and international
Partners. Pointing, tracking and thermal tests were made to verify
the proposed performance. The results of these tests and a progress
report of the project will be presented.
---------------------------------------------------------
Title: Some properties of an isolated sunspot
Authors: Balthasar, H.; Collados, M.
2005A&A...429..705B Altcode:
We present an investigation of a single sunspot observed in the
neutral Fe line at 1089.6 nm with the Tenerife Infrared Polarimeter
at the Vacuum Tower Telescope on Tenerife. Using the SIR code, we
obtain maps of the magnetic field strength, inclination and azimuth,
and Doppler velocities. The magnetic field strength drops from 2800 G
in the umbra to about 700 G at the outer penumbral boundary, where we
encounter an average magnetic inclination of 72<SUP>o</SUP>. Comparing
the magnetic flux passing through different areas, we conclude that
the inner penumbra must be deep, while the outer penumbra could be
shallow. Assuming that the magnetic field strength encountered at the
outer penumbral boundary forms a smooth surface through which the total
flux of the spot passes, it would be approximately an ellipsoidal cap
with a top height of 5250 km. This scenario leads to an average vertical
magnetic gradient of 0.4 G km<SUP>-1</SUP>. Evershed Doppler velocities
are about 2 km s<SUP>-1</SUP>. Two penumbral locations related to dark
intensity features exhibit a steeper and slightly stronger magnetic
field than elsewhere in the penumbra, and one of them is connected to
an interruption of the Evershed effect.
---------------------------------------------------------
Title: Two magnetic components in sunspot penumbrae
Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.
2004A&A...427..319B Altcode:
The magnetic and kinematic configuration of sunspot penumbrae is
investigated by performing an inversion of the Stokes profiles of three
infrared lines at 1565 nm. We use a two-component model atmosphere
to describe, at least to first order, the unresolved structure of
the penumbra. The observed Stokes profiles are successfully fitted,
including those exhibiting abnormal shapes. The results of the inversion
are consistent with the idea that the penumbra is formed by almost
horizontal flux tubes embedded in a more vertical background magnetic
field, as proposed by Solanki & Montavon (\cite{Sol93}). The tubes
possess weaker fields than the background except in the very outer
penumbra, and carry most of the Evershed flow. We characterize the
radial variation of the magnetic field vector and the velocity vector
in these atmospheric components. In the middle penumbra and beyond,
the magnetic field and the flow in the tubes are seen to return to
the solar surface. Everywhere in the penumbra, there is a perfect
alignment of the magnetic field vector and the velocity vector in
the component describing the penumbral flux tubes. We find that the
Evershed flow is supercritical in many places of the outer penumbra,
and supersonic at some locations near the outer sunspot boundary. Based
on these inversions, we suggest that the azimuthal fluctuations in the
average magnetic field inclination and strength inferred from simple
one-component models are caused by fluctuations in the filling factor
(i.e., the fractional area of the resolution element occupied by
flux tubes), not by changes in the intrinsic magnetic and kinematic
properties of the background or the flux-tube atmospheres. Also,
we confirm the jump of magnetic field azimuth proposed by Müller et
al. (\cite{Mul02}) to explain the observed net circular polarization
of infrared lines.
---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V Altcode:
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
and other national and international Partners. The refurbishment of
the building is almost finished. The manufacturing of the telescope
structure and the optics is still in progress. After the integration of
the new complete retractable dome in July 2004 the telescope structure,
optic and post focus instruments will be assembled during the rest of
the year. First light is planned during May 2005.
---------------------------------------------------------
Title: Oscillations in Sunspots observed in the Near Infrared
Authors: Balthasar, H.
2003SoPh..218...85B Altcode:
Spectropolarimetric time series of two sunspots are investigated
to search for magnetic field oscillations. While the existence of
velocity oscillations in the five-minute band is clearly confirmed,
periodic variations of the magnetic field strength or the magnetic
angles inclination and azimuth are small and restricted to very
narrow areas. They occur in single frequency bins, but different for
magnetic field strength and angles. Small dark structures embedded
in one penumbra or in the near surroundings of the other spot exhibit
enhanced power for the magnetic variations at all frequencies. Phase
differences are rather unsure. The obtained values are in agreement with
intrinsic magnetic field variations produced by slow magnetoacoustic
modes as well as with an opacity mechanism connected with fast modes.
---------------------------------------------------------
Title: Velocity Field of a Complex Sunspot with Light Bridges
Authors: Schleicher, H.; Balthasar, H.; Wöhl, H.
2003SoPh..215..261S Altcode:
For the leading part of sunspot group NOAA 8323, which rapidly changed
its complex structure, a time series of the line-of-sight (LOS)
component of the velocity field was obtained. With a two-dimensional
Fabry-Pérot spectrometer, the magnetically insensitive line Fe i
557.6 nm was scanned. The inclination of the LOS (heliographic angle)
to the vertical was θ=28.5°. The umbra of the observed spot was
divided by a system of light bridges into several parts. The spatial and
temporal velocity field also exhibits a considerable complexity: in one
extended umbral area there is a downward flow of 1 km s<SUP>−1</SUP>
relative to other dark sub-umbrae. At the center-side penumbra,
with a line-of-sight Evershed outflow of 1.5 km s<SUP>−1</SUP>,
a persistent patch, somewhat darker than the average penumbra, has
a LOS velocity of 1.3 km s<SUP>−1</SUP> in opposite direction,
probably a downflow. At the limb-side penumbra, a photosphere-like
area is interspersed, interrupting the Evershed flow which resumes
with typical strength beyond this feature towards the outer penumbral
boundary. Most interesting is the behavior of the light bridges, which
have a slight blue shift, interrupted by short events of strong blue
or red shifts which - within the time resolution of 35 s - instantly
affect a considerable part of a light bridge.
---------------------------------------------------------
Title: Mercury Transit Observed with TESOS at the VTT on Tenerife
Authors: Schleicher, Helmold; Wöhl, Hubertus; Balthasar, Horst
2003ANS...324..114S Altcode: 2003ANS...324..P21S
No abstract at ADS
---------------------------------------------------------
Title: Properties of a Simple Sunspot Observed in the Near Infrared
Authors: Balthasar, Horst
2003ANS...324...30B Altcode: 2003ANS...324..D05B
No abstract at ADS
---------------------------------------------------------
Title: Field-aligned Evershed flows in the photosphere of a sunspot
penumbra
Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.;
Schlichenmaier, R.
2003A&A...403L..47B Altcode:
We determine the inclinations of the vector magnetic field and flow
velocity in a sunspot penumbra by interpreting full Stokes profiles of
three infrared lines observed with the Tenerife Infrared Polarimeter. It
is shown that analyses based on one-component atmospheres deliver flow
velocities which are more horizontal than the average magnetic field
by up to 10 deg. This apparent violation of the concept of frozen-in
magnetic fields is solved as soon as two magnetic atmospheres are
allowed to coexist in the resolution element. The magnetic field and
velocity in the atmospheric component carrying the Evershed flow are
found to be aligned to within +/- 2 deg all the way from the inner
to the outer penumbra. This is the first observational confirmation
of magnetic fields being frozen into the plasma in sunspots. Our
results indicate that sunspot penumbrae can be understood in terms of
inclined flux tubes embedded in a more vertical background field. The
flux tubes carry most of the Evershed flows and return to the solar
surface in the middle penumbra and beyond. The background atmosphere
is essentially at rest in the inner penumbra, and harbors small flows
in the outer penumbra.
---------------------------------------------------------
Title: The structure of the penumbra
Authors: Balthasar, H.; Bellot Rubio, L.; Collados, M.
2003AN....324..390B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: IR-Observations of the Magnetic Field in Sunspots-Oscillations
in a Sunspot
Authors: Balthasar, H.
2003ASPC..307..364B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Two-dimensional distribution of oscillations in a quiescent
solar prominence
Authors: Terradas, J.; Molowny-Horas, R.; Wiehr, E.; Balthasar, H.;
Oliver, R.; Ballester, J. L.
2002A&A...393..637T Altcode:
Using time series of two-dimensional Dopplergrams, a temporal and
spatial analysis of oscillations in a quiescent prominence has been
performed. The presence of an outstanding oscillatory signal in the
acquired data has allowed us to study the two-dimensional distribution
of wave motions and, in particular, to detect the location of wave
generation and the anisotropic propagation of perturbations from that
place. Moreover, a strong damping of oscillations has been observed,
with damping times between two and three times the wave period. The
direction of propagation, wavelength and phase speed, together with
the damping time and wave period, have been quantified and their
spatial arrangement has been analysed. Thanks to the goodness of the
observational data, the image alignment procedure applied during
the data reduction stage and the analysis tools employed, it has
been possible to carry out a novel and far-reaching observational
study of prominence oscillations. The five movies are available at
http://www.edpsciences.org
---------------------------------------------------------
Title: Penumbral finestructure: need for larger telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AN....322..367B Altcode:
We obtained at the same time G-band images at the Dutch Open Telescope
(DOT) on La Palma and spectropolarimetric data in the near infrared
at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright
filaments have a smaller magnetic field s trength, and higher
Evershed velocities occur in dark structures. This result is in
agreement with some previous observations, but also in contradiction
to others. However, we suffer from the fact that the resolution limit
of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial
power spectra derived from the DOT data indicate a typical width of
250 km for penumbral filaments. Obviously a solar telescope with an
aperture of at least 1.5~m is needed to obtain sophisticated results
for penumbral structures.
---------------------------------------------------------
Title: Penumbral Finestructure: Need for Larger Telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AGM....18S1003B Altcode:
We obtained at the same time G-band images at the Dutch Open
Telescope (DOT) on La Palma and spectropolarimetric data in the near
infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright filaments
have a smaller magnetic field strength, and higher Evershed velocities
occur in dark structures. This result is in agreement with some previous
observations, but also in contradiction to others. However, we suffer
from the fact that the resolution limit of the VTT at a wavelength
of 1.565 μm corresponding to 400 km. Spatial power spectra derived
from the DOT data indicate a typical width of 250 km for the penumbral
filaments. Obviously a solar telescope with an aperture of at least 1.5
m is needed to obtain sophisticated results for penumbral structures.
---------------------------------------------------------
Title: Magnetic field oscillations in sunspots and active regions
Authors: Balthasar, Horst; Collados, Manuel; Muglach, Karin
2001ESASP.464..163B Altcode: 2001soho...10..163B
In order to investigate the oscillatory behaviour of the magnetic
field in sunspots and pores, full Stokes measurements of 1.56 μm
iron lines have been performed using the Tenerife Infrared Polarimeter
(TIP) at the German Vacuum Tower Telescope on Tenerife. As expected,
velocity oscillations have power peaks at five minutes. First results
for temporal variations of the magnetic field show that they occur in
locally restricted areas in sunspots. Periods in the five minute range
are preferred. In addition, we investigate magnetograms taken with
the Michelson Doppler Imager (MDI) on SOHO. Intensity images in white
light and around 160 nm were obtained with TRACE as well. Intensity
power is strongly with TRACE as well. Intensity power is strongly
suppressed in the sunspot area, although we find powerpeaks in the
five and three minute ranges.
---------------------------------------------------------
Title: Inversion of Stokes Profiles with Artificial Neural Networks
Authors: Carroll, T. A.; Balthasar, H.; Muglach, K.; Nickelt, I.
2001ASPC..236..511C Altcode: 2001aspt.conf..511C
No abstract at ADS
---------------------------------------------------------
Title: Wave modulation and wave sources in the solar convection zone
Authors: Kiefer, M.; Stix, M.; Balthasar, H.
2000A&A...359.1175K Altcode:
We investigate the behavior of upward running sound waves in the lower
photosphere by means of a 2-hour time series of FPI-filtergrams and a
corresponding series of white-light images. From the FPI-filtergrams
we obtain velocities in two heights in the solar photosphere. Using
specific filters in the k_h-nu -space, we extract running sound waves
from the velocity time series and the granulation from the white-light
series. The relation between granular structure and wave amplitude
is examined. To this end the granulation images are subdivided into
intensity classes. The amplitudes of the waves are extracted on the
pixel maps corresponding to these classes. We find hints for wave
modulation due to the inhomogeneities in the solar convection zone:
The behavior of the wave amplitudes meets theoretical predictions
with respect to frequency- and height-dependence. The dependence
on the horizontal wave number meets the predictions too, but due
to low wave coherence at high wave numbers no definitive statement
is possible. Further the darkest locations in the granulation are
preferred by waves of increased amplitudes. There also seems to
be a preference for the brightest granular regions. In both cases
the behavior of the waves can be well described by subsurface sound
sources. This is confirmed by comparison of the data with a simple
model of a subsurface sound source.
---------------------------------------------------------
Title: Multi-mode oscillations of sunspots
Authors: Zhugzhda, Y. D.; Balthasar, H.; Staude, J.
2000A&A...355..347Z Altcode:
Oscillations of the magnetic field in the sunspot photosphere have been
detected by recent high-resolution, two-dimensional observations. Their
power is concentrated in isolated small flux bundles (pores) outside of
larger umbrae and at the boundary between umbra and penumbra of larger
spots. The slow body mode provides an explanation of the appearance
of magnetic oscillations in small sunspots if the azimuth number m=0,
but also of the small features piling up in rings in large sunspots. In
the latter model the magnetic oscillations are the signature of the
slow body mode with m>> 1, which bears a resemblance to the
well-known whispering gallery mode in acoustics. The slow surface
modes and fast body modes are also discussed.
---------------------------------------------------------
Title: Oscillations in a solar pore
Authors: Balthasar, H.; Collados, M.; Muglach, K.
2000AN....321..121B Altcode:
Temporal variations of a solar pore were observed at the ground based
Vacuum Tower Telescope (VTT) on Tenerife and with the satellite
TRACE. At the VTT Stokes I and V of the iron line at 1.56 mu m,
originating in the deep photosphere, was measured. TRACE delivered
UV images at 170 nm which show chromospheric continuum. In a part of
the pore we find oscillations of the magnetic field in the 5 minute
range. Velocities derived from shifts of the Stokes V profiles show
5 minutes everywhere in the pore, but the coherence of magnetic field
and velocities is low. The intensity at 170 nm varies with 3 minutes,
and for a part of the whole time series additionally with 4 minutes.
---------------------------------------------------------
Title: Multi-mode Magnetic Oscillations in Sunspots
Authors: Zhugzhda, Y.; Balthasar, H.; Staude, J.
1999ESASP.448..417Z Altcode: 1999mfsp.conf..417Z; 1999ESPM....9..417Z
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Sunspots: Observations and Modelling
Authors: Staude, J.; Rendtel, J.; Balthasar, H.; Zhugzhda, Y.
1999ESASP.448..373S Altcode: 1999ESPM....9..373S; 1999mfsp.conf..373S
No abstract at ADS
---------------------------------------------------------
Title: New Results of 2D-Spectroscopy of Sunspots - Temporal
Variations of the Magnetic Field
Authors: Balthasar, H.
1999ASPC..184..141B Altcode:
Two-dimensional spectra of a sunspot were obtained at the German Vacuum
Tower Telescope (VTT) on Tenerife using the 2D-spectrometer of the
Göttingen observatory. The magnetic field strength is derived from
the I-profiles of the Fe I line at 684.3 nm. Temporal variations of
the magnetic field occur at the umbra-penumbra transition of larger
spots and in the central part of some small spots and pores. A clear
coherence between the variations of the magnetic field and those of
intensities or Doppler shifts is not detected.
---------------------------------------------------------
Title: Temporal fluctuations of the magnetic field in sunspots
Authors: Balthasar, H.
1999SoPh..187..389B Altcode:
The magnetic field strength in sunspots was derived from time series
of two-dimensional spectra taken with the Göttingen 2D-spectrometer
at the Vacuum Tower Telescope on Tenerife in August 1997. For the
present measurements the magnetically sensitive line Fe i 684.3 nm
was selected. The main spot of the investigated sunspot group has
a maximum magnetic field strength of 2270 G. Enhanced power of the
magnetic field variations was found at the boundary between umbra and
penumbra for all frequency ranges. These fluctuations are not well
correlated with those of intensity variations or line shifts. Other
spatial power peaks occur in a dark patch inside the centreside penumbra
and at the centres of some accompanying small spots. Since no clear
peaks at certain frequencies are found, the variations are not harmonic
oscillations. A possible relation to Hα flares is investigated. There
are several cases of published observations of magnetic field variations
where flares occurred soon after the measurements, but very little
before. Therefore it is not very probable that flares act as exciters
of magnetic field variations.
---------------------------------------------------------
Title: On the Relation Between Solar Oscillations and Granulation
Authors: Kiefer, M.; Balthasar, H.
1999ASPC..183..465K Altcode: 1999hrsp.conf..465K
No abstract at ADS
---------------------------------------------------------
Title: New Results of 2D-Spectroscopy of Sunspots
Authors: Balthasar, H.
1999ASPC..183..100B Altcode: 1999hrsp.conf..100B
No abstract at ADS
---------------------------------------------------------
Title: Magnetic field oscillations in sunspots - - a `whispering
gallery' mode?
Authors: Staude, J.; Balthasar, H.; Zhugzhda, Y. D.
1999AGAb...15....9S Altcode: 1999AGM....15..A08S
Oscillations of the magnetic field in the sunspot photosphere have been
detected by recent high-resolution, two-dimensional, spectro-poarimetric
observations at Tenerife and aboard the SOHO satellite. Their power is
concentrated in isolated small flux bundles (pores) outside of larger
umbrae and in patches at the boundary between umbra and penumbra of
larger spots. The slow body mode of magneto-acoustic waves in an intense
magnetic fluxtube provides an explanation of the strange appearance
of such magnetic oscillations. This applies to small sunspots if the
azimuth number m=0, but also to the small features piling up in rings
at the border of the umbrae of larger sunspots. In the latter model
the magnetic oscillations are the signature of the slow body mode with
m >> 1, which bears a resemblance to the well-known whispering
gallery mode in acoustics. The slow surface modes and fast body modes
are also discussed.
---------------------------------------------------------
Title: Velocity Pulses in a Sunspot with Lightbridges
Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.
1999AGAb...15....7B Altcode: 1999AGM....15..A05B
See splinter meeting SOLAR OBSERVATION WITH HIGH RESOLUTION
---------------------------------------------------------
Title: Magnetic Field Oscillations in Sunspots?
Authors: Staude, Juergen; Balthasar, Horst; Zhugzhda, Yuzef
1999soho....9E..25S Altcode:
Oscillations of velocity and intensity are known for more than 2
decades; they are observed in spectral lines formed at different height
levels of the sunspot atmosphere. The interpretation of measurements
of magnetic field oscillations, however, is still contradictory. We
give evidence of the presence of such oscillations and describe the
observed properties. The basic features of their spatial structure
can be explained by slow body waves in intense magnetic flux tubes. In
particular, a `whispering gallery'-like mode could be an appropriate
model.
---------------------------------------------------------
Title: Prominence Doppler oscillations.
Authors: Molowny-Horas, R.; Wiehr, E.; Balthasar, H.; Oliver, R.;
Ballester, J. L.
1999joso.proc..126M Altcode:
Longitudinal velocity maps have been constructed from time series
of Hβ filtergrams, obtained at three positions along the emission
line profile. Several examples of velocity perturbations with a
periodic behaviour have been found at different spatial locations in
the prominence. Periods have been determined to vary approximately
between 28 and 95 minutes. The presence of damping (and in one case,
of excitation) in those oscillatory motions is discussed.
---------------------------------------------------------
Title: Velocity Oscillations in Active Sunspot Groups
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
1998SoPh..182...65B Altcode:
Time series of two-dimensional spectra were taken with the Göttingen
2D spectrometer at the VTT on Tenerife in 1996. They were investigated
for Doppler velocities and velocity oscillations in small spots and
pores of rapidly evolving sunspot groups. For the present measurements
the magnetically insensitive lines Fe i 557.6 nm and Fe i 709.0 nm
were selected.
---------------------------------------------------------
Title: The role of the f-mode in the relation between solar intensity
oscillations and granulation
Authors: Kiefer, M.; Balthasar, H.
1998A&A...335L..73K Altcode:
A series of white-light images is used to examine the relation of
solar intensity oscillations and the granulation structure. Much
of the oscillation power lies on the f-mode ridge in the diagnostic
diagram. Filters are constructed to separate granulation, p-modes, and
the f-mode. The filtered data are used to investigate the relation
between rms-amplitudes of the oscillations and the granulation
structure. Both p-modes and f-mode show a tendency to increased
amplitudes in the darkest features of the granulation structure, with
the f-mode showing this preference for dark regions much clearer. We
emphasize that due to the different propagation characteristics of
p-modes and the f-mode a separation like ours is mandatory to draw
conclusions about wave excitation and diffraction.
---------------------------------------------------------
Title: Heights of formation of FeI photospheric lines
Authors: Kucera, A.; Balthasar, H.; Rybak, J.; Woehl, H.
1998A&A...332.1069K Altcode:
The determination of the location of spectral line-forming layers
by means of line-depression contribution functions is checked by
observational tests. The method is based on the assumption that the
Doppler velocities derived from line bisectors at a given position in
the profile of a spectral line are related to the actual bulk velocity
at a particular height in the atmosphere. For a set of six magnetically
sensitive and non-sensitive Fe I lines (543.45, 557.61, 630.15, 630.25,
649.50, 649.45 nm) the fluctuations of Doppler velocities along the slit
of the spectrograph were determined at various Delta lambda from the
line centers i.e. at various heights in the photosphere. Correlations
of fluctuations allow us to find those parts in line profiles which
are formed at identical heights in the photosphere. These experimental
results are compared with theoretical estimates based on line depression
contribution functions. The agreement is good and best results are found
for nonmagnetic strong, but still unsaturated lines. The results support
the hypothesis that it is possible to ascribe a single height point
in the solar atmosphere to a given position in a spectral line profile.
---------------------------------------------------------
Title: The solar granulation in different heights.
Authors: Balthasar, H.
1998AN....319..387B Altcode:
Intensity images and Doppler-velocity maps of the quiet Sun in different
heights are obtained from simultaneously recorded spectra of different
lines. A relation between the intensity images is recognizable up
to formation heights of 900 km above continuum, but the correlation
coefficient changes sign above 400 km. The core of Hα shows a different
pattern without any correlation to the continuum layer. Extreme Doppler
velocities as well as the rms-velocities have minima at a height of
400 km, values of about 2 km/s occur in deep photospheric layers and
2.5 km/s in a height of 900 km. The velocities in the lower and in the
upper photosphere are well correlated indicating that the pattern of
the velocity field is preserved up to higher layers than the intensity
pattern. Hα-velocities reach values up to 10 km/s and more, they show
no correlation with the continuum intensities and almost no correlation
with the line core intensities.
---------------------------------------------------------
Title: The Depth Dependence of Penumbral Absolute Velocities
Authors: Balthasar, H.; Schmidt, W.; Wiehr, E.
1997SoPh..171..331B Altcode:
Penumbral line-core shifts at different heights are determined from
the lines Fei 5434.5 Å, Fei 5435.2 Å, and Nii 5435.8 Å using two
adjacent water vapor lines for an absolute wavelength scale. The large
granular blue shift of 0.6 km s<SUP>-1</SUP> for the faint Fe 5435
line from deep layers yields for the centre-side penumbra absolute
velocities up to 3 km s<SUP>-1</SUP>. This value is much larger than
velocities deduced from the bisectors of the line wings of Ni 5436 and
Fe 5434, thus supporting the concern against an interpretation of the
line asymmetries in term of a velocity gradient with depth.
---------------------------------------------------------
Title: Velocity oscillations in active sunspot groups.
Authors: Balthasar, H.; Martínez Pillet, V.; Schleicher, H.; Wöhl, H.
1997AGAb...13...12B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: First Observations SUMER - VTT, SI IV - CA II K
Authors: Balthasar, H.; von Uexkull, M.; Innes, D.; Gigas, D.;
Wilhelm, K.
1997ASPC..118..315B Altcode: 1997fasp.conf..315B
We tried to do a comparison of Ca II K (393.3 nm) filtergrams obtained
at the Vacuum Tower Telescope on Tenerife with spectra in the line Si
IV 139.4 nm obtained simultaneously with the SUMER telescope on the
SOHO-spacecraft. Some bright features can be well identified in both
observations. We compare temporal changes of the brightness for these
common features.
---------------------------------------------------------
Title: The Velocity Field in and around Sunspots. Results from
2D-Spectroscopy
Authors: Balthasar, H.; Schleicher, H.
1997ASPC..118..111B Altcode: 1997fasp.conf..111B
A sunspot was observed on June 11, 1995 with the Gottingen
2D-spectrometer at the Vacuum Tower Telescope on Tenerife using the
line Fe 709 nm. The data show an radial outflow of 500 m/s outside
the penumbra for about 15000 km. This flow is separated from the
Evershed flow of 1.6 km/s by a sharp decrease at the boundary of the
visible penumbra. The Evershed flow is associated to dark penumbral
filaments, but we do not find a correlation between intensities and
line asymmetries. No relation between the power distribution and the
filaments is found for the 5 minute oscillations. Small spots and
pores in the vicinity of the main spot show 3 minute oscillations.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of sunspots. I. Intensity,
velocity, and velocity power maps of a sunspot.
Authors: Balthasar, H.; Schleicher, H.; Bendlin, C.; Volkmer, R.
1996A&A...315..603B Altcode:
A time series of two-dimensional spectra of a sunspot at θ=~45°
has been obtained with a spectrometer based on a Fabry-Perot
interferometer. From our observations in the FeI line at 709.04nm we
find that the gas plasma in the vicinity of the sunspot (the moat)
has a velocity of about 500m/s directed outwards. Nevertheless,
the Evershed flow shows a sharp decrease by about 1000m/s at the
outer boundary of the visible penumbra. The mean white-light image
averaged over 1^h^52^m^ still shows radial structures in the penumbra,
indicating their long lifetime. Spatial variations of the velocities
and continuum intensities have correlation coefficients of +0.66
for the centre-side penumbra and -0.57 for the limb-side one. The
correlation coefficients increase to +/-0.75 for the line-centre
intensities. This correlation confirms that the Evershed effect is
related to the dark filaments. Outside the spot, the long-time average
images of the continuum and the line-centre intensities show a chain of
bright dots with a size of about one arcsec and intensities up to 4.5%
higher than their surroundings. These dots are related to the outer
boundary of the velocity field in the moat. In the five-minute range,
velocity power spectra show a decrease in the umbra and in the penumbra,
but no dependence on the radial structure. In the range between eight
and twenty minutes, power is present in the centre-side penumbra; it
resembles that of granular areas, but it has a radial structure. In
the umbra or the limb-side penumbra, the power values are much lower.
---------------------------------------------------------
Title: A search for formation-height oscillations in umbrae.
Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wiehr, E.;
Woehl, H.
1996A&A...310..328B Altcode:
The formation heights of spectral lines and continua in sunspots can be
determined by measuring the apparent distance of the spot relative to
the nearby solar limb. In order to confirm the existence of oscillatory
variations of such limb distances and to exclude possible influences
of differential image motion between the spot and the nearby limb, we
have obtained time series observations of the lines Ca^+^ 8542, Mg b,
and the non-magnetic line Fe 5576 simultaneously on two telescopes. No
indication is found for periodic fluctuations of the spot's apparent
limb distance. Only one of the seven time series shows a significant
40 min period of the line core but not of the continuum in the data
from both telescopes. This variation of the line formation height,
however, may be attributed to parallel guiding corrections of a
spatially inhomogenous umbral chromosphere. The other time series
show different periods for the two telescopes, which must be caused
by unrelated guiding corrections.
---------------------------------------------------------
Title: High Resolution Polarimetric Measurements in a Sunspot
Authors: Horn, T.; Hofmann, A.; Balthasar, H.
1996SoPh..164..321H Altcode:
A Fabry-Perot interferometer is being used for two-dimensional
spectropolarimetric measurements. We demonstrate the suitability of
the setup for the measurement of the magnetic field and present some
preliminary results from first observations.
---------------------------------------------------------
Title: Observation at 892 nm of impact "L" with the solar Vacuum
Tower Telescope at Tenerife.
Authors: Schleicher, H.; Balthasar, H.; Jockers, K.; Knölker, M.;
Schmidt, W.
1995ESOC...52..171S Altcode: 1995eslj.work..171S; 1995esl9.conf..171S
During the period of SL-9 impacting Jupiter, the authors observed
Jupiter with the solar VTT. The impact of fragment "L" was monitored
with a time series of filtergrams in the CH<SUB>4</SUB>-band at 892 nm.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of a sunspot.
Authors: Balthasar, H.; Schleicher, H.; Bendlin, C.; Volkmer, R.
1995AGAb...11..143B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot limb distance variations measured simultaneously with
two telescopes.
Authors: Berger, B.; Balthasar, H.; Schleicher, H.; Wöhl, H.;
Wiehr, E.
1995AGAb...11..142B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric Magnetic Field Measurements in He I 10830Å
Authors: Rüedi, I.; Solanski, S. K.; Balthasar, H.; Livingston, W.;
Schmidt, W.
1995itsa.conf..431R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Umbral Structures Observed in FE I 1027 NM
Authors: Schmidt, W.; Balthasar, H.
1995itsa.conf..357S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impact L observed at a wavelength of 892 nm with the solar
vacuum telescope on Tenerife
Authors: Schleicher, H.; Balthasar, H.; Knölker, M.; Schmidt, W.;
Jockers, K.
1995HiA....10..632S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polarimetry and spectroscopy of a simple sunspot. IV. Umbral
structures observed in FeI 1027nm
Authors: Balthasar, H.; Schmidt, W.
1994A&A...290..649B Altcode:
Magnetic fields and velocities in bright umbral structures have been
determined from long time sequences of high resolution Stokes-I
spectra obtained with the near infrared FeI 1026.52nm line. This
weak line is unblended in the umbra and has a triplet-like Zeeman
pattern similar to a g_eff_=2.5 line. The umbral bright structures
show velocity oscillations identical to those of the surrounding
umbra. A bright structure with a size of 2 arcsec close to the center
of the umbra shows a slightly lower magnetic field strength than its
surroundings. This difference decreases whereas the structure becomes
brighter during several hours of observations.
---------------------------------------------------------
Title: Temporal and spatial variation of physical parameters in a
quiescent prominence.
Authors: Balthasar, H.; Wiehr, E.
1994A&A...286..639B Altcode:
The emission lines He 3889 A, H_8_ and Ca^+^IR_3_ are observed
simultaneously in a prominence over a total of 4 hours. The time
variations of the He 3889 / H_8_ emission ratio R, the thermal and the
non-thermal line broadenings T_kin_ and ξ, respectively, are compared
with those of the Doppler shift, v_D_, for 10 spatial locations along
the slit. The time-averaged spatial variations along the slit show
an increase of R, T_kin_, and ξ with height related to a decrease of
the H_8_ emission, E_tot_(H_8_), in agreement with other authors. The
short-time fluctuations show that quasi-oscillations, known from
Doppler shifts, also exist for other physical parameters. The long-term
variations over the total of 4 hours indicate a smooth increase of R,
T_kin_, and ξ at the upper parts of the prominence, resembling the
known spatial behaviour of these parameters at prominence edges. Also
the well known anti-correlation of the emission ratio R and the
E_tot_(H_8_) occurs in the long-term behaviour. We suggest that the
decrease of E_tot_(H_8_) parallel with the increase of R might be
related to a dissolution of the prominence yielding a smaller density
of fine-structures.
---------------------------------------------------------
Title: Polarimetry and spectroscopy of a simple sunspot. 3: Velocity
and magnetic field of sunspot umbral dots
Authors: Schmidt, W.; Balthasar, H.
1994A&A...283..241S Altcode:
Velocities and magnetic fields in sunspot umbrae and in umbral dots
have been determined from high resolution Stokes-I spectra obtained at
the Vacuum Tower Telescope (VTT) on Tenerife. Except for oscillatory
motions the umbra is at rest and flow velocities in umbral dots,
measured at an optical depth of about 0.01, are smaller than 25
m/s. The magnetic field strength is weakened in the dots by 10-20%
for a central umbral dot and by 5-10% for a peripheral umbral dot. The
line of sight decrease of magnetic field in a peripheral dot shows no
difference to the surrounding umbra and amounts to 2.5-3 G/km.
---------------------------------------------------------
Title: Observations at 891 nm of the impact "L" of SL-9 on Jupiter.
Authors: Balthasar, H.; Jockers, K.; Knölker, M.; Schleicher, H.;
Schmidt, W.
1994AGAb...10..122B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Fe I 10265 Å line as an excellent tool for magnetic
field measurements
Authors: Schmidt, W.; Balthasar, H.; Wiehr, E.
1994ASIC..433...49S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Impact of Fragment “L” of Comet SL-9 on Jupiter
Authors: Schleicher, H.; Balthasar, H.; Knolker, M.; Schmidt, W.;
Jockers, K.
1994EM&P...66...13S Altcode:
Filtergrams of high spatial and temporal resolution were obtained in
the methane band centred at 892 nm during the impact of fragment L of
comet Shoemaker-Levy 9 on Jupiter. The light curve shows two maxima of
an emission ball observed above the limb shortly after the impact. The
second maximum was the brightest and had a short life time of about 90
seconds. During it's life, the apparent height of the emission ball
declined towards the surface of Jupiter; the amount of displacement
is larger than the expected effect caused by Jupiter's rotation. About
half an hour after the impact, a domelike feature became visible when
the location of the impact rotated into the illuminated hemisphere
of Jupiter.
---------------------------------------------------------
Title: On the magnetic field and the velocities in simple sunspots
Authors: Balthasar, H.; Schmidt, W.
1994smf..conf..207B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time saeries of the penumbral Evershed effect.
Authors: Schleicher, H.; Wiehr, E.; Balthasar, H.; Wöhl, H.
1994AGAb...10..113S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Vector-Stokes polarimetry in a sunspot
Authors: Hofmann, A.; Shine, R. A.; Frank, Z. A.; Schmidt, W.;
Balthasar, H.
1994smf..conf..204H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High resolution vector polarimetry of sunspot magnetic fields.
Authors: Balthasar, H.; Hofmann, A.; Schmidt, W.; Shine, R. A.; Frank,
Z. A.
1994AGAb...10..112B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Polarimetry and spectroscopy of a simple sunspot. 2: On the
height and temperature dependence of the magnetic field
Authors: Balthasar, H.; Schmidt, W.
1993A&A...279..243B Altcode:
We have observed a fairly regular sunspot located near disk center
and have taken series of spectrograms in three different photospheric
lines. The magnetic field strength across the spot has been measured
in different heights of the sunspot photosphere and shows a change in
slope at the umbra-penumbra boundary. The line depression contribution
functions have been computed in order to obtain the height of formation
of the spectral lines used in this analysis. Along the line-of-sight,
we find an upward decrease of the field strength of 2.5 to 3 G/km in
the penumbra and the adjacent outer part of the umbra. A relation has
been deduced between the magnetic field and the brightness temperature
measured across the sunspot which is strongly nonlinear and shows
pronounced differences between the umbra and the penumbra.
---------------------------------------------------------
Title: Doppler oscillations in solar prominences simultaneously
observed with two telescopes. Discovery of a 30 S oscillation
Authors: Balthasar, H.; Wiehr, E.; Schleicher, H.; Wohl, H.
1993A&A...277..635B Altcode:
Time series of Doppler shifts are observed simultaneously with two
telescopes in order to separate actual solar velocities from influences
of image motion or unperfect guiding. Several maxima of the power
contours occur only in the data set from one of the two telescopes
and may thus originate from non-solar sources. Considering only those
power maxima which are observed with both telescopes we establish the
solar origin of periods near 20 and 12 min, which may be identified
with `hybrid fast modes' from model calculations. For one prominence a
significant period of 30 5 is detected which theory predicts as a wave
guided by the prominence fine-structures. Our prominence oscillations
are restricted to spatially small areas of a few arc see diameter.
---------------------------------------------------------
Title: High Resolution Magnetic Field Measurements in the Sunspot
Photosphere (Invited)
Authors: Hofmann, A.; Schmidt, W.; Balthasar, H.; Tarbell, T. T.;
Frank, Z. A.
1993ASPC...46...11H Altcode: 1993IAUCo.141...11H; 1993mvfs.conf...11H
No abstract at ADS
---------------------------------------------------------
Title: Polarimetry and spectroscopy of a simple sunspot. I - On the
magnetic field of a sunspot penumbra
Authors: Schmidt, W.; Hofmann, A.; Balthasar, H.; Tarbell, T. D.;
Frank, Z. A.
1992A&A...264L..27S Altcode:
We investigate the magnetic field structure of a medium sized sunspot
using high resolution magnetograms and spectrograms and derive a
relationship between the brightness of penumbral structures and the
inclination of the magnetic field. The field inclination to the spot
normal is larger in the dark structures than in the bright ones. We
show that the field strength does not vary between dark and bright
structures. At the inner penumbral boundary the field strength is 2000
Gauss and about 1000 Gauss at the outer penumbral edge. The line-of
sight component of the material flow decreases rapidly within one
arcsecond at the photospheric boundary of the spot.
---------------------------------------------------------
Title: Doppler-Oszillationen unter dem Einfluss solarer Magnetfelder.
Authors: Balthasar, H.
1992S&W....31..304B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time series of Doppler velocities in prominences.
Authors: Balthasar, H.; Schleicher, H.; Wöhl, H.; Wiehr, E.
1992AGAb....7..151B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the magnetic field of a sunspot penumbra.
Authors: Balthasar, H.; Schmidt, W.; Hofmann, A.; Tarbell, T. D.;
Frank, Z. A.
1992AGAb....7..153B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations of Evershed velocities and asymmetries
Authors: Balthasar, H.; Wiehr, E.
1990A&A...237..243B Altcode:
Four sunspots at different heliocentric angles have been observed to
study the oscillatory behavior of line asymmetries and velocities due
to the Evershed effect. For two spots the power maxima of the line core
velocities and of the line asymmetries are spatially anticorrelated. The
central part of the penumbra as intersected by the spectrograph slit
is the location of a velocity power maximum for the one spot, however,
of an asymmetry power maximum for the other spot. In contrast, for two
other spots several local power maxima are spatially coincident for
the line asymmetry and the line core velocity. These variable spatial
relations of line core velocities and line asymmetries support the
idea that the Evershed effect may be a result of the superposition of
penumbral fine structures affected by the underlying oscillating layers.
---------------------------------------------------------
Title: Intensity correlations in granular spectra
Authors: Balthasar, H.; Grosser, H.; Schroeter, C.; Wiehr, E.
1990A&A...235..437B Altcode:
Spectra of high spatial resolution were taken at the Gregory-Coude
Telescope on Tenerife to investigate the relation between the
line core intensities and the adjacent continuum for selected iron
lines. Anti-correlations of these two quantities are found for the four
lines with low excitation potential Fe5079, Fe5434, Fe5501, and Fe5506
which are known to show a limb effect although they have no blue shift
at the disk center. An anti-correlation is also found for the line
with high excitation potential, Fe5074, which shows a very small limb
effect. This result is compatible with a granular intensity pattern
which reverses in high layers, as suggested by numerical simulations
of the granulation.
---------------------------------------------------------
Title: The Oscillatory Behaviour of Solar Faculae
Authors: Balthasar, H.
1990SoPh..127..289B Altcode:
The oscillatory behaviour of some faculae has been observed. In some
cases power values in the faculae are larger than in the photosphere,
but in other faculae power minima are found.
---------------------------------------------------------
Title: Die Sonnenrotation vor 100 Jahren.
Authors: Balthasar, H.; Wöhl, H.
1990S&W....29..296B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Penumbral Velocity Oscillations
Authors: Balthasar, Horst
1990SoPh..125...31B Altcode:
Doppler velocity variations of four sunspot penumbrae were observed
in November 1988 at the Observatorio del Teide, Tenerife, using the
spectral line Fe I 5576 Å. All of the penumbrae show local power
maxima in the five-minute range, while no power is found around three
minutes. This indicates that the five-minute oscillations are still
present in the penumbrae, but the direction of the velocities might be
tilted by the magnetic field. On the other hand, the maxima of the power
and of the Evershed flow do not always occur at the same locations.
---------------------------------------------------------
Title: Doppler Velocity Oscillations in Quiescent Prominences
Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G.
1990LNP...363..255W Altcode: 1990IAUCo.117..255W; 1990doqp.coll..255W
No abstract at ADS
---------------------------------------------------------
Title: Combination of a 256 x 256 pixel matrix detector and an
image intensifier
Authors: Balthasar, H.; Wiehr, E.
1989hsrs.conf..345B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar rotation 1883 until 1893 as inferred from the
Greenwich Photoheliographic Results and observations published by
G. Spoerer
Authors: Woehl, H.; Balthasar, H.
1989A&A...219..313W Altcode:
The finding that the solar rotation velocity inferred from the
Greenwich Photoheliographic Results (GPR) as compared to that from
observations published by G. Spoerer for the years 1883 until 1893
shows a difference of the order of 0.1 deg/day is investigated in
some details. An analysis of rotation velocities of stable sunspots,
which are covered sufficiently by observations in both sets of data,
yields no significant differences. The mean difference is nearly two
orders of magnitude below the above cited value. The explanation of the
difference is the presence of more short-living sunspots in the GPR,
which show a more rapid rotation velocity. There are about twice as
many days without any spot observations in the publications of Spoerer
as compared to the GPR. Some indications are presented, that the solar
behavior changed after the begining of our century.
---------------------------------------------------------
Title: The decrease of penumbral velocity and magnetic field at the
outer sunspot boundary
Authors: Wiehr, E.; Balthasar, H.
1989A&A...208..303W Altcode:
Numerical simulation of atmospheric and instrumental smearing
indicates that velocity and magnetic field disappear at the outer
spot border within a length of maximally 1650 km and 2200 km,
respectively. Accepting the (known) inclination of 84 deg, the
corresponding height ranges of 165 and 220 km, respectively, are not
compatible with the picture of a disappearance of both fields due to
a kind of 'optical dilution' with height. Indication is given for a
disappearance of the fields beyond an iso-tau discontinuity.
---------------------------------------------------------
Title: Doppler Velocity Oscillations in Quiescent Prominences
Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G.
1989HvaOB..13..131W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intensity Correlations in the Continuum and the Cores of
Lines in Spectra of the Solar Granulation
Authors: Schröter, C.; Balthasar, H.
1989AGAb....3...10S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in presence of local magnetic fields.
Authors: Wiehr, E.; Balthasar, H.; Stellmacher, G.
1988ESASP.286..269W Altcode: 1988ssls.rept..269W
Oscillatory Doppler shifts in sunspots and in small fluxtubes are
observed using either the intensity profile of lines with negligible
magnetic splitting or the circular Zeeman profile (Stokes-V inversion
point) of lines with strong Zeeman splitting. Sunspot umbrae
show local 5 min oscillations of reduced amplitude as compared to
the neighbouring photosphere. Occasionally the authors find 5 min
oscillations of opposite phase at both outer penumbral borders. This
could be interpreted as tilting and bobbing of the spot as a whole
on the oscillating solar surface. In contrast to these larger scale
sunspot fluxtubes the gas in the small fluxtubes of a few hundred km
diameter seems to fully participate in the photospheric oscillations
without any interaction with the magnetic field. Prominence magnetic
fields show sometimes a reaction to the photospheric 5 min and to the
chromospheric 3 min oscillations, in addition several other periods
are found. Indication is found for eigenmodes of Alfvén waves.
---------------------------------------------------------
Title: Periodic and quasiperiodic Doppler velocity variations in
solar prominences along one spatial direction
Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G.
1988A&A...204..286B Altcode:
Temporal variations of the Doppler displacement of the Hα-emission
line were measured in four quiescent prominences in autumn 1986 at
the recently installed Gregory telescope on Tenerife. As detector,
a 100×100 pixel diode array was used. The length of the time series
was up to seven hours. The slit was oriented parallel to the solar
limb in the first case and perpendicular in the others. In November
1987 another prominence was observed with a 256×256 pixel camera
simultaneously in Ca<SUP>+</SUP>H and Hɛ over five hours. In this case,
the slit was oriented parallel to the solar limb. The result for the
two lines are in good agreement. The authors earlier result of periods
near one hour is confirmed. Short periods near five and three minutes
are found in some parts of the prominences. They might be interpreted
as a reaction of the prominence on the photospheric and chromospheric
oscillations. For the time series of more than five hours indications
of eigenmodes of the prominences are found.
---------------------------------------------------------
Title: Comparison of the differential rotation laws and meridional
motions determined from sunspot positions taken from the Greenwich
Photoheliographic Results, the drawings of G. Spoerer, and the
Kanzelhoehe data
Authors: Balthasar, H.; Fangmeier, E.
1988A&A...203..381B Altcode:
A comparison of the solar rotation velocities derived from the Greenwich
Photoheliographic Results (GPR) and from Sporer's observations for
the period 1883-1893 and from the Kanzelhohe data for 1948-1976 is
presented. Although there is a good agreement of the results from
Sporer's data with those from the modern GPR, it cannot be surely
excluded that the decrease of the rotation velocity of the GPR during
the early 20<SUP>th</SUP> century is of solar origin. But the comparison
of the rotation velocities of recurrent groups determined from the
individual positions during two passages and from the central meridian
transits yield hints that systematical effects are present in the old
GPR and in the Kanzelhohe data. A comparison of the meridional motions
determined from Sporer's data and from the GPR yields no significant
difference.
---------------------------------------------------------
Title: The center-to-limb variation of solar spectral lines
Authors: Balthasar, H.
1988A&AS...72..473B Altcode:
A listing of the center-to-limb variation of 143 solar lines
from different elements measured simultaneously with the Fourier
transform-spectrometer of the McMath-telescope at the Kitt Peak National
Observatory is presented. The listing includes different asymmetry
parameters, the limb effect, the intensity of the line core and the
equivalent width.
---------------------------------------------------------
Title: Velocity variations of prominences.
Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G.
1988AGAb....1R..12B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in Sunspot Umbra Penumbra and the Surrounding
Photosphere
Authors: Balthasar, H.; Fangmeier, E.; Kuveler, G.; Wiehr, E.
1988IAUS..123..183B Altcode:
Doppler shifts of the nonsplit line Fe I 7090 Å have been measured
simultaneously in the sunspot umbra, penumbra and the photosphere
using a 100×100 diode array. The power in the range 2.5 - 4.5 mHz is
found to decrease from the photosphere towards the umbra. Besides the
minimum at the center of the umbra, further power minima occur at the
transition region between umbra and penumbra. No significant power is
found in the range 5.0 - 6.0 mHz.
---------------------------------------------------------
Title: Oscillatory motions of the H<SUB>α</SUB>-emission line in
quiescent prominences.
Authors: Balthasar, H.; Wiehr, E.; Stellmacher, G.
1988dssp.conf...63B Altcode:
Temporal variations of the Doppler displacement of the
H<SUB>α</SUB>-emission were measured in 4 prominences (September 28
through October 5, 1986) at the recently installed Gregory telescope at
Tenerife, using a 100×100 pixel diode array. Long periods near one hour
confirm former results. The amplitude of these long periods vary with
height and also in the direction parallel to the limb. Short periods
near 5 minutes and near 3 minutes are found which might be interpreted
as perturbations by the photospheric and chromospheric oscillations.
---------------------------------------------------------
Title: Oscillations of sunspots in the Stokes-V-inversion point.
Authors: Balthasar, H.; Wiehr, E.
1988AGAb....1Q..12B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The solar rotation elements i and Omega derived from recurrent
single sunspots
Authors: Balthasar, H.; Woehl, H.; Stark, D.
1987A&A...174..359B Altcode:
Using the data of recurrent single sunspot observations obtained at
Greenwich 1874 to 1976 the solar rotation elements were determined. The
results confirm earlier results, where a smaller i-value and a slightly
bigger Ω-value as compared to the well known Carrington rotation
elements was found. No indication was found for a systematic difference
between solar rotation elements determined from recurrent single
sunspots as compared with results using all sunspot group positions.
---------------------------------------------------------
Title: A comparison of the oscillations in sunspot umbrae, penumbrae,
and the surrounding photosphere
Authors: Balthasar, H.; Wiehr, E.; Kueveler, G.
1987SoPh..112...37B Altcode:
Time series of the nonsplit FeI 7090 Å line have been observed in
several sunspots with a 100 x 100 diode array corresponding to 48
arc sec times 1.39 Å. The spatial behaviour of Doppler motions
along one fixed slit position has been studied as a function of
time. Former results are confirmed, that the power in the five minute
range decreases from the photosphere to the umbra, where, however,
values still well above the noise level are measured. Regarding the
penumbra, the power tends to exhibit a maximum at locations where
the line-of-sight component of a radial horizontal field should
be maximal. This indicates that the direction of the oscillatory
velocities might be influenced by the magnetic field or the Evershed
flow. No significant power is found in the 3 min range. An exception
might be seen in a small patch at the limb of the umbra of one spot.
---------------------------------------------------------
Title: Oscillatory Motions of the H Emission Line in Quiescent
Prominences
Authors: Balthasar, H.; Wiehr, E.
1987dssp.work...63B Altcode: 1987ASSL..150...63B
No abstract at ADS
---------------------------------------------------------
Title: Evidence for quasi-periodic Doppler motions in solar
prominences
Authors: Balthasar, H.; Knoelker, M.; Wiehr, E.; Stellmacher, G.
1986A&A...163..343B Altcode:
Observations of Doppler displacements in solar prominences have been
performed using the Hα emission line. Evidence is found for the
existence of quasi-periodic line-of-sight velocities in the range of
2.5 - 4.7 mHz. Former findings of long time variations near one hour
are confirmed. Possible influences by misguiding and by image motion
can be excluded. Scattered light from the solar aureola cannot produce
the observed amplitudes.
---------------------------------------------------------
Title: The solar rotation elements i and omega derived from sunspot
groups
Authors: Balthasar, H.; Lustig, G.; Woehl, H.; Stark, D.
1986A&A...160..277B Altcode:
Greenwich Photoheliographic results from 1874 to 1976 are completed
to reduce the mean value errors of the i and Omega determination, and
results are verified with independent data obtained between 1947 and
1984 at the Kanzelhohe observatory. The data-reduced i value of 7.137 +
or - 0.017 deg is much less than the Carrington (1863) value, while
the Omega(1850) vlkue of 73.75 + or - 0.15 deg is not significantly
different than the Carrington Value.
---------------------------------------------------------
Title: Oszillationen in Sonnenflecken-Umbren, -penumbren und der
benachbarten Photosphäre
Authors: Balthasar, H.; Fangmeier, E.; Küveler, G.; Wiehr, E.
1986MitAG..65..155B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differential rotation of sunspot groups in the period from
1874 through 1976 and changes of the rotation velocity within the
solar cycle
Authors: Balthasar, H.; Vazquez, M.; Woehl, H.
1986A&A...155...87B Altcode:
An effort is made to determine the differential rotation of the sun
on the basis of the complete sample (1874-1976) of the Greenwich
Photoheliographic Results. In order to improve the representation
of differential rotation, a modified fit formula whose constant
lies at 15 deg latitude (where sunspots nearly always occur) is
introduced. Rotation is noted to strongly depend on sunspot type,
with C-groups exhibiting high velocities and H- and J-spots the lowest
ones. The new fit formula indicates that the highest velocity is found
around the minima; at the beginning of an activity maximum, there
is a secondary velocity maximum. The lowest velocities lie between
the activity maximum and minimum. The braking of recurrent sunspots
is confirmed.
---------------------------------------------------------
Title: Eine Jahrhundertarbeit über Sonnenfleckengruppen.
Authors: Balthasar, H.; Vázquez, M.; Wöhl, H.
1985S&W....24..634B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Contribution of Horizontal Granular Motions to Observed
Limb-Effect Curves
Authors: Balthasar, H.
1985SoPh...99...31B Altcode:
From the comparison of 59 iron lines at the center of the solar disk
with laboratory wavelenghts, the mean vertical velocity of solar
granulation and its depth dependence is determined. These values are
used to calculate limb-effect curves. The differences to observed
curves are interpreted as mean horizontal motions. These motions yield
again a depth dependence showing Doppler shifts toward the observer in
deep layers and away from the observer in high layers for regions away
from the disk center. Values from - 400 m s<SUP>−1</SUP> through +
500 m s<SUP>−1</SUP> are obtained.
---------------------------------------------------------
Title: Oscillations of the Hα Emission in Solar Prominences
Authors: Wiehr, E.; Stellmacher, G.; Balthasar, H.
1984SoPh...94..285W Altcode:
The time dependence of Doppler shift and line-center intensity
is simultaneously observed for the Hα emission of three solar
prominences, each one during about two hours. Doppler oscillations
with periods near one hour and amplitudes between 1 and 2 km
s<SUP>−1</SUP> are conspicuously visible in the recordings of all
three prominences. Fourier analysis yields periods of 50, 60, and
64 min, as well as slight indications of short periods near 3 and 5
min. No oscillations are found in the line-center brightness.
---------------------------------------------------------
Title: Umbral Oscillations Measured in the Stokes-V Inversion Point
Authors: Balthasar, H.; Wiehr, E.
1984SoPh...94...99B Altcode:
The inversion point of the circular Zeeman polarization profile
(V-Stokes) parameter is used to observe umbral Doppler oscillations
free from disturbing influences of parasitic light. In a second step,
purely umbral lines are used to avoid remaining influences from the
V-profile of the (oscillating) penumbra. Among a total of nine sunspot
umbrae, three exhibit oscillations within the various 1.5 to 2.5 hr
samples. The periods differ significantly from 300 s, vary with time,
and occur within time intervals of high tranquility thus explaining
the lack of oscillations in the remaining sunspots.
---------------------------------------------------------
Title: Asymmetries and Wavelengths of Solar Spectral Lines and the
Solar Rotation Determined from Fourier-Transform Spectra
Authors: Balthasar, H.
1984SoPh...93..219B Altcode:
Wavelength shifts and asymmetries of solar spectral lines and of the
solar rotation are determined on the basis of 143 selected lines from
Fourier-transform spectra obtained in 1980 and 1981. The asymmetries are
noted to strongly depend on the formation layer of the line cores; lines
with cores formed at higher layers have larger asymmetries. Wavelength
shifts at the solar disk center show a depth dependence similar to
that found by Keil (1980), but exhibit an exponential line. Lines with
cores formed at higher layers of the solar atmosphere show wavelength
shifts of approximately the gravitational redshift. Ionized element line
redshifts are larger than those from neutral elements. An equatorial
rotation velocity of 1.971 km/sec is found.
---------------------------------------------------------
Title: Evidence for the 22-YEAR-CYCLE in the Longitudinal Distribution
of Sunspots
Authors: Balthasar, Horst; Schüssler, Manfred
1984SoPh...93..177B Altcode:
It was shown in an earlier paper that preferred hemispheres of solar
activity alternate with the 22-year magnetic cycle, when analyzed in
the 27.0 day Bartels rotation. Using data which cover the time between
1818 and 1983 we trace back this result to 1880 (cycle 12). Before
1880 no significant correlations are found.
---------------------------------------------------------
Title: On the Determination of Heliographic Positions and Rotation
Velocities of Sunspots - Part Three - Effects Caused by Wrong Solar
Image Radii and Their Corrections
Authors: Balthasar, H.; Lustig, G.; Woehl, H.
1984SoPh...91...55B Altcode:
In an earlier paper of this series it was shown how the Wilson
depression influences the determination of sunspot rotation
velocities. Using this finding and the fact that stable recurrent
sunspots show a very constant rotation velocity it is possible to
determine the effect of wrong solar image radii on the determination
of sunspot rotation velocities and correct them.
---------------------------------------------------------
Title: New information about solar rotation
Authors: Woehl, H.; Balthasar, H.; Koch, A.; Kueveler, G.; Roca-Cortes,
T.; Schmidt, W.; Vazquez, M.
1984S&W....23...73W Altcode:
It is pointed out that the phenomenon of solar rotation is known
since the introduction of the telescope into astronomy by Galilei in
1610. Regular measurements concerning the positions of sunspots were
conducted with the aid of photographic plates at the Royal Greenwich
Observatory during the time from 1874 to 1976. The obtained data
provide an excellent basis for statistical analysis. Information
obtained as a result of such analyses is discussed. Attention is given
to the determination of the Wilson depression, details regarding
solar differential rotation, plans for an evaluation of data with
the aid of a computer, the rotation of the solar plasma, a comparison
of sunspots and plasma, the theory of differential rotation, and new
information concerning solar rotation partly obtained with the aid of
solar telescopes in a Spanish observatory on the island of Tenerife.
---------------------------------------------------------
Title: Asymmetrien und Wellenlängen solarer Spektrallinien
aus Fourier-Transform-Spektren in Abhängigkeit von der
Beobachtungsposition auf der Sonne
---------------------------------------------------------
Title: Asymmetrien und
Wellenlängen solarer Spektrallinien aus Fourier-Transform-Spektren
in Abhängigkeit von der Beobachtungsposition auf der Sonne Title:
Asymmetries and wavelengths of solar spectral lines from Fourier
transform spectra depending on the observed position on the Sun;
Authors: Balthasar, Horst
1984PhDT.......213B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Atlas of Spectral Line Asymmetries and Their CLV From
Solar FTS Spectra
Authors: Balthasar, H.; Wohl, H.
1984ssdp.conf..317B Altcode:
Preliminary informations are given on the CLV of solar spectral line
asymmetries in quiet regions. The results are based on FTS spectra with
high spectral resolution and a S/N of about 3000. Three main classes of
the CLVs of solar spectral lines are introduced and their dependences on
the excitation potentials of the lines and their heights of formation
are given. In addition shifts of lines depending on their formation
depths, equatorial rotation velocities and limb-effect results are
given.
---------------------------------------------------------
Title: Neues über die Sonnenrotation.
Authors: Balthasar, H.; Koch, A.; Küveler, G.; Roca-Cortes, T.;
Schmidt, W.; Vázquez, M.; Wöhl, H.
1984S&W....23...73B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Determination of Heliographic Positions and Rotation
Velocities of Sunspots - Part Two - Systematic Effects Caused by
the Wilson Depression
Authors: Balthasar, H.; Woehl, H.
1983SoPh...88...71B Altcode:
Using sunspot positions of small sunspots observed at Debrecen and
Locarno as well as positions of recurrent sunspots taken from the
Greenwich Photoheliographic Results (1940-1976) the influence of the
Wilson depression on the rotation velocities was investigated. It
was found that the Wilson depression can be determined by minimizing
errors of the rotation velocities or minimizing the differences of
rotation velocities determined from disk passages and central meridian
passages. The Wilson depressions found were between 765 km and 2500
km for the first sample while they were between 0 km and several
1000 km for the second sample. The averaged Wilson depression for the
second sample is between 500 km and 965 km depending on the reduction
method. A dependence of the Wilson depression on the age of the spots
investigated seems not to exist.
---------------------------------------------------------
Title: Preferred longitudes of sunspot groups and high-speed solar
wind streams: evidence for a "solar memory".
Authors: Balthasar, H.; Schuessler, M.
1983SoPh...87...23B Altcode:
Correlation analysis of the mean longitude distribution of sunspot
groups (taken from the Greenwich Photoheliographic Results)
and high-speed solar wind streams (inferred from the C9 index for
geomagnetic disturbances) with the Bartels rotation period P = 27.0
days shows anti-correlation for individual cycles.
---------------------------------------------------------
Title: On the Depth Dependence of the Solar Rotation Velocity
Determined from Fraunhofer Lines
Authors: Balthasar, H.
1983SoPh...84..371B Altcode:
From 63 mostly unblended Fraunhofer lines measured along the solar
east-west diameter the rotation velocity has been determined. The mean
value is 1986 km s<SUP>#X2212;1</SUP>. The velocity decreases with the
optical depth in the photosphere. Over a range of 700 km the difference
of the velocities is 41 m s<SUP>#X2212;1</SUP> for the Holweger-Müller
atmosphere or 34 m s<SUP>#X2212;1</SUP> for the Harvard Smithsonian
reference atmosphere.
---------------------------------------------------------
Title: Erratum - Differential Rotation and Meridional Motions of
Sunspots from 1874 TO 1902
Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.;
Wohl, H.
1983A&A...117..170A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Asymmetrien solarer Spektrallinien
Authors: Balthasar, H.
1983MitAG..60..278B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Oszillationen in Flecken-Umbren
Authors: Soltau, D.; Balthasar, H.; Koch, A.; Küveler, G.; Wiehr, E.
1983MitAG..60..225S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotationsgeschwindigkeiten von Sonnenflecken - mögliche
Fehler und ihre Korrektion
Authors: Balthasar, H.; Lustig, G.; Wöhl, H.
1983MitAG..60..236B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Terrestrial O2 lines used as wavelength references - Comparison
of measurements and model computations
Authors: Balthasar, H.; Thiele, U.; Woehl, H.
1982A&A...114..357B Altcode:
High precision spectral measurements of the wavelength of terrestrial
O2 lines within solar spectra using the Kitt Peak 1-m Vacuum Fourier
Transform Spectrometer are compared with model computations of the
shifts of these lines due to wind up to 20 km. Although the wind data
available existed only from radio sonde measurements about 65 km away
and only from two launches per day, the shifts observed during two days
could be explained well. Maximum shifts of terrestrial O2 lines of +
or - 0.3 mA at about 6300 A were observed. It is shown that it may
be possible to correct a general trend of the observed shifts with a
precision of + or - 3 m/sec during a day.
---------------------------------------------------------
Title: Differential rotation and meridional motions of sunspots from
1874 to 1902
Authors: Arevalo, M. J.; Gomez, R.; Vazquez, M.; Balthasar, H.;
Woehl, H.
1982A&A...111..266A Altcode:
Position data of sunspot groups from the period 1874-1902 are used to
investigate the differential rotation of the Sun and the meridional
motions of the sunspots. The equatorial velocity is higher than in
the period 1940-1968 investigated by Balthasar and Wöhl (1980), while
differences between the northern and southern hemispheres are less. For
cycle 12 we find meridional motions towards north while in cycle 13 the
motions are directed towards south like in the period 1940-1968. Our
other results are comparable to those of Balthasar and Wöhl (1980)
for the period 1940-1968.
---------------------------------------------------------
Title: On changes of the rotation velocities of stable, recurrent
sunspots and their interpretation with a flux tube model
Authors: Balthasar, H.; Schuessler, M.; Woehl, H.
1982SoPh...76...21B Altcode:
The angular rotation velocities of stable, recurrent sunspots
were investigated using data from the Greenwich Photoheliographic
Results 1940 until 1968. We found constant rotation velocities
during the passages on the solar disk with errors of about ±4 m
s<SUP>−1</SUP>. During their lifetime these spots show a decreasing
braking of their rotation velocities from 0.8 to 0.3 m s<SUP>−1</SUP>
per day. A plausible interpretation is found by assuming the spots
to be coupled to a slowly rising subsurface flux tube and a rotation
velocity which increases with depth.
---------------------------------------------------------
Title: Limb-Effekte und Asymmetrien solarer Spektrallinien zwischen
4800 und 6500 Angström in Fouriertransformspektren
Authors: Balthasar, H.; Wöhl, H.
1982MitAG..55...71B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum - Differential Rotation and Meridional Motions of
Sunspots in the Years 1940-1968
Authors: Balthasar, H.; Wohl, H.
1981A&A....98..422B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differentielle Rotation und meridionale Bewegungen von
Sonnenflecken in den Jahren 1940 bis 1968
Authors: Balthasar, H.; Wöhl, H.
1981MitAG..52...26B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Differential rotation and meridional motions of sunspots in
the years 1940-1968
Authors: Balthasar, H.; Woehl, H.
1980A&A....92..111B Altcode:
Using positions of sunspots from the Greenwich Photoheliographic
Results from 1940 to 1968 equations for the differential rotation and
meridional motions of sunspot groups are determined. The differential
rotation depends on the phase in the solar cycle and on the type of the
groups. The meridional motions show a general southdrift of the spots,
but they are not significantly different from zero. The significance
of the equatorward motion near the equator found by Ward (1965) seems
to be due to an effect of selection. Changes of the meridional motions
with time are not in good agreement with former publications, but they
are also not significant. A dependence of the meridional motions on
the local activity is not detectable.
---------------------------------------------------------
Title: Änderungen der differentiellen Rotation und meridionale
Bewegungen von Sonnenflecken 1940 bis 1968.
Authors: Balthasar, H.; Woehl, H.
1980S&W....19..385B Altcode:
Various methods of measuring solar activity are discussed with
emphasis given to following identifiable objects such as sunspots over
a period of time. A formula describes the rotation of sunspots for the
period between 1940 and 1968, and the data for each year are divided
within a seven year cycle. Mathematical formulas of rotation are also
presented for the northern and southern hemispheres. Latitudinal
movement of sunspots is investigated and compared to the method of
Ward (1965). Differences in northern and southern hemisphere movement
are considered.