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Author name code: staude
ADS astronomy entries on 2022-09-14
author:"Staude, Juergen"
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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: 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.
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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>
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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.
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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.
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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.
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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.
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Title: Solar physics at the Einstein Tower
Authors: Denker, C.; Heibel, C.; Rendtel, J.; Arlt, K.; Balthasar,
Juergen H.; Diercke, A.; González Manrique, S. J.; Hofmann, A.;
Kuckein, C.; Önel, H.; Senthamizh Pavai, V.; Staude, J.; Verman, M.
2016AN....337.1105D Altcode: 2016arXiv160906949D
The solar observatory Einstein Tower ({Einsteinturm}) at the
Telegrafenberg in Potsdam is both a landmark of modern architecture
and an important place for solar physics. Originally built for
high-resolution spectroscopy and measuring the gravitational redshift,
research shifted over the years to understanding the active Sun and
its magnetic field. Nowadays, telescope and spectrographs are used for
research and development, i.e., testing instruments and in particular
polarization optics for advanced instrumentation deployed at major
European and international astronomical and solar telescopes. In
addition, the Einstein Tower is used for educating and training of the
next generation astrophysicists as well as for education and public
outreach activities directed at the general public. This article
comments on the observatory's unique architecture and the challenges
of maintaining and conserving the building. It describes in detail the
characteristics of telescope, spectrographs, and imagers; it portrays
some of the research and development activities.
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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.
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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.
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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.
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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.
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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: 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: 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: Wave Instabilities of a Collisionless Plasma in Fluid
Approximation
Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, Jürgen
2011CoPP...51..621D Altcode: 2009arXiv0911.2912D
Wave properties and instabilities in a magnetized, anisotropic,
collisionless, rarefied hot plasma in fluid approximation are studied,
using the 16-moments set of the transport equations obtained from
the Vlasov equations. These equations differ from the CGL-MHD fluid
model (single fluid equations by Chew, Goldberger, and Low, 1956)
by including two anisotropic heat flux evolution equations, where
the fluxes invalidate the double polytropic CGL laws. We derived the
general dispersion relation for linear compressible wave modes. Besides
the classic incompressible fire hose modes there appear four types of
compressible wave modes: two fast and slow mirror modes - strongly
modified compared to the CGL model - and two thermal modes. In the
presence of initial heat fluxes along the magnetic field the wave
properties become different for the waves running forward and backward
with respect to the magnetic field. The well known discrepancies between
the results of the CGL-MHD fluid model and the kinetic theory are
now removed: i) The mirror slow mode instability criterion is now the
same as that in the kinetic theory. ii) Similarly, in kinetic studies
there appear two kinds of fire hose instabilities - incompressible and
compressible ones. These two instabilities can arise for the same plasma
parameters, and the instability of the new compressible oblique fire
hose modes can become dominant. The compressible fire hose instability
is the result of the resonance coupling of three retrograde modes -
two thermal modes and a fast mirror mode. The results can be applied
to the theory of solar and stellar coronal and wind models.
---------------------------------------------------------
Title: The Haus der Astronomie in Heidelberg-A New Center for
Education and Outreach
Authors: Staude, J.
2011ASPC..441..471S Altcode:
Since October 2009, a unique facility is being erected on the grounds
of the Max Planck Institute for Astronomy on top of the Königstuhl
Mountain above Heidelberg, in the immediate vicinity of the State
Observatory. It will be dedicated to the communication between
scientists, to the development of educational material for junior and
high school students, to the training of teachers and student teachers
in physics, astronomy and natural sciences, and to the information of
the media and the general public about new developments and results
in astronomical research. The building will be donated by the Klaus
Tschira Foundation, while the Max Planck Society, the University and
the City of Heidelberg, and the State Departments of Research and of
Education will share the running costs of the new institution.
---------------------------------------------------------
Title: Observational evidences for multi-component magnetic field
structure in solar flares
Authors: Lozitsky, V. G.; Staude, J.
2009JApA...29..387L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wave instabilities in an anisotropic magnetized space plasma
Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J.
2008A&A...489..769D Altcode: 2008arXiv0805.2405D
Aims: We study wave instability in an collisionless, rarefied hot plasma
(e.g. solar wind or corona). We consider the anisotropy produced by
the magnetic field, when the thermal gas pressures across and along the
field become unequal. <BR />Methods: We apply the 16-moment transport
equations (obtained from the Boltzmann-Vlasov kinetic equation)
including the anisotropic thermal fluxes. The general dispersion
relation for the incompressible wave modes is derived. <BR />Results:
It is shown that a new, more complex wave spectrum with stable and
unstable behavior is possible, in contrast to the classic fire-hose
modes obtained in terms of the 13-moment integrated equations.
---------------------------------------------------------
Title: Instability of entropy waves in cosmic plasma
Authors: Somov, B. V.; Dzhalilov, N. S.; Staude, J.
2008CosRe..46..392S Altcode:
A dispersion equation is derived for small disturbances of the
magnetohydrodynamic type in optically transparent plasma with
cosmic abundance of elements. The electron heat conductivity along
the magnetic field and proton heat conductivity across the field
are taken into account. It is shown that entropy waves increase
exponentially in wide ranges of temperatures and densities of the
cosmic plasma. Manifestations of instability of the entropy waves in
the cosmic plasma are discussed.
---------------------------------------------------------
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: Magneto-Hydro-Dynamic Waves In The Collisionless Space Plasma
Authors: Dzhalilov, N. S.; Kuznetsov, V. D.; Staude, J.
2007SunGe...2...65D Altcode:
The instability of magneto-hydro-dynamic (MHD) waves in an anisotropic,
collisionless, rarefied hot plasma is studied. Anisotropy properties of
such a plasma are caused by a strong magnetic field, when the thermal
gas pressures across and along the field become unequal. Moreover,
there appears an anisotropy of the thermal fluxes. The study of the
anisotropy features of the plasma are motivated by observed solar
coronal data. The 16 moments equations derived from the Boltzmann-Vlasov
kinetic equation are used. These equations strongly differ from the
usual isotropic MHD case. For linear disturbances the wave equations
in homogenous anisotropic plasma are deduced. The general dispersion
relation for the incompressible wave modes is derived, solved and
analyzed. It is shown that a wide wave spectrum with stable and unstable
behavior is possible, in contrast to the usual isotropic MHD case. The
dependence of the instability on magnetic field, pressure anisotropy,
and heat fluxes is investigated. The general instability condition
is obtained. The results can be applied to the theory of solar and
stellar coronal heating, to wind models and in other modeling, where
the collisionless approximation is valid.
---------------------------------------------------------
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: Peculiarities of entropy and magnetosonic waves in optically
thin cosmic plasma
Authors: Somov, B. V.; Dzhalilov, N. S.; Staude, J.
2007AstL...33..309S Altcode: 2007PAZh...33..352S
The stability problem for small magnetohydrodynamic (MHD) perturbations
in an optically thin, perfectly conducting uniform plasma with a
cosmic abundance of elements is solved in the linear approximation. The
electron heat conduction along the magnetic field and the proton heat
conduction across the field are taken into account. We have shown
for the first time that the entropy waves can grow exponentially,
while the magnetosonic waves are damped in a wide range of physical
conditions closest to the conditions in stellar coronae with the proper
allowance for radiative losses. Slow magnetosonic waves are damped
particularly rapidly. For the solar corona, the calculated damping
decrement of slow magnetosonic waves agrees well with the averaged
one in 11 quasi-periodic events observed from the TRACE satellite in
extreme ultraviolet radiation. Other possible astrophysical applications
of the results obtained are briefly discussed.
---------------------------------------------------------
Title: The Characteristic Length Scale of the Magnetic Fluctuation in
a Sunspot Penumbra: A Stochastic Polarized Radiative Transfer Approach
Authors: Carroll, T. A.; Staude, J.
2007astro.ph..3327C Altcode:
The characteristic size of penumbral structures are still below the
current resolution limit of modern solar telescopes. Though we have
seen a significant progress in theoretical work over the last decades
no tight constraints can be placed on the size of penumbral structures
in order to favor models with relatively large and thick magnetic
flux elements, just at or below the current resolution limit, or on
the other hand, clusters of optically thin micro-structures. Based on
a macroscopic 2-component inversion and the approach of polarized
radiative transfer in stochastic media, we have estimated the
characteristic length scale of the magnetic fluctuation in a sunspot
penumbra from observed Stokes spectra. The results yield a coherent
picture for the entire magnetic neutral line of the penumbra and
indicate that the magnetic fluctuations have a typical length scale
between 30 km and 70 km.
---------------------------------------------------------
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: The Characteristic Length Scale of the Magnetic Fluctuation in
a Sunspot Penumbra: A Stochastic Polarized Radiative Transfer Approach
Authors: Carroll, T. A.; Staude, J.
2006ASPC..358..137C Altcode:
The characteristic size of penumbral structures are still below
the current resolution limit of modern solar telescopes. Though we
have seen a significant progress in theoretical work over the last
decades no tight constraints can be placed on the size of penumbral
structures in order to favor models with relatively large and thick
magnetic flux elements, just at or below the current resolution limit,
or on the other hand, clusters of optically thin micro-structures. <P
/>Based on a macroscopic 2-component inversion and the approach of
polarized radiative transfer in stochastic media, we have estimated the
characteristic length scale of the magnetic fluctuation in a sunspot
penumbra from observed Stokes spectra. The results yield a coherent
picture for the entire magnetic neutral line of the penumbra and
indicate that the magnetic fluctuations have a typical length scale
between 30 km and 70 km.
---------------------------------------------------------
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: Line Formation in Inhomogeneous Atmospheres and the Magnetic
Structure of the Internetwork
Authors: Carroll, T. A.; Staude, J.
2005ESASP.596E...9C Altcode: 2005ccmf.confE...9C
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: Dynamics of solar active regions. II. Oscillations observed
with MDI and their relation to the magnetic field topology
Authors: Muglach, K.; Hofmann, A.; Staude, J.
2005A&A...437.1055M Altcode:
We present new results of an international joint observing campaign,
which was carried out in September 2000 to study the oscillatory
behaviour of solar active regions. We concentrate on oscillations
in the lower layers of the solar atmosphere as observed with the
Michelson Doppler Imager (MDI, Scherrer et al. 1995, Sol. Phys., 162,
129). The resulting photospheric oscillation power maps are compared
with chromospheric maps from simultaneous UV continuum data (taken with
the TRACE instrument). From a magnetic field extrapolation of the MDI
magnetograms we infer that the reduction in chromospheric high frequency
power and enhancement of photospheric high frequency power may be
explained by the interaction of acoustic waves with the magnetic canopy.
---------------------------------------------------------
Title: Active Region Oscillations and Their Relation to the Magnetic
Field Topology
Authors: Muglach, K.; Hofmann, A.; Staude, J.
2005AGUSMSH13C..03M Altcode:
In this contribution we present an analysis of time sequences of MDI
intensity and Doppler velocity together with simultaneous filtergrams
taken by TRACE at 1700A in an active region. The high frequency
halos found in MDI velocity and the deficiency of high frequency
power sampled at the height of the TRACE UV filter around the active
region can be explained by an interaction of the acoustic wave field
with the magnetic field of the active region. From a magnetic field
extrapolation we calculate the plasma β for the complete TRACE FOV
up to the base of the corona. The contours giving the location of β
approximately 1 where h=500 km agree very well with the decrease in
1700A high frequency power.
---------------------------------------------------------
Title: Line formation in turbulent magnetic atmospheres
Authors: Carroll, T. A.; Staude, J.
2005AN....326..296C Altcode:
We present a stochastic formulation of the polarized radiative transfer
in an atmosphere permeated by a random magnetic field. On the basis
of a Markov process we describe the line formation as a stochastic
process which allows us to account for a finite correlation length of
the fluctuating structures. The resulting stochastic master equation
describes the evolution of the expectation value of the Stokes vector
(the macroscopic observable) through the atmosphere. As the correlation
length (mean structural length scale of the fluctuating or turbulent
elements) appears explicitly in the stochastic transport equation it
can be used as a diagnostic parameter from which an estimation of the
underlying structural length scale is possible.
---------------------------------------------------------
Title: The Helioseismological CORONAS-F DIFOS Experiment
Authors: Lebedev, N. I.; Kuznetsov, V. D.; Oraevskii, V. N.; Staude,
J.; Kostyk, R. I.
2004ARep...48..871L Altcode:
The CORONAS-F DIFOS experiment continues the CORONAS-I studies
started in 1994, devoted to investigations of solar global
oscillations. CORONAS-F was launched July 31, 2001. Variations in
the intensity of the solar radiation are measured in the six spectral
intervals of the multi-channel photometer: 350, 500, 650, 850, 1100,
and 1500 nm, with the bandwidths being about 10% of the central
wavelength of each interval. The scientific goals of the experiment,
a brief description of the instrument, and observational conditions
are presented, as well as the data processing techniques. The first
observations of the low-order p eigenmodes of the solar oscillations
are presented for various wavelength ranges. A decrease in the relative
amplitudes with observing wavelength is indicated. The amplitude ratios
for various spectral ranges agree well with those detected earlier in
ground-and space-based experiments.
---------------------------------------------------------
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: Eigenoscillations of the differentially rotating
Sun. II. Generalization of the Laplace tidal equation
Authors: Dzhalilov, N. S.; Staude, J.
2004A&A...421..305D Altcode: 2002astro.ph..1170D
The general partial differential equation governing linear adiabatic
nonradial oscillations in a spherical, differentially and slowly
rotating non-magnetic star is derived. This equation describes
mainly low-frequency and high-degree g-modes, convective g-modes,
rotational Rossby-like vorticity modes, and their mutual interaction
for arbitrarily given radial and latitudinal gradients of the rotation
rate. Applying to this equation the “traditional approximation” of
geophysics results in a separation into radial- and angular-dependent
parts of the physical variables, each of which is described by an
ordinary differential equation. The angular parts of the eigenfunctions
are described by the Laplace tidal equation generalized here to
take into account differential rotation. It is shown that there
appears a critical latitude in the sphere where the frequencies of
eigenmodes coincide with the frequencies of inertial modes. The resonant
transformation of the modes into the inertial waves acts as a resonant
damping mechanism of the modes. Physically this mechanism is akin to
the Alfvén resonance damping mechanism for MHD waves. It applies even
if the rotation is rigid. The exact solutions of the Laplace equation
for low frequencies and rigid rotation are obtained. The eigenfunctions
are expressed by Jacobi polynomials which are polynomials of higher
order than the Legendre polynomials for spherical harmonics. In this
ideal case there exists only a retrograde wave spectrum. The modes are
subdivided into two branches: fast and slow modes. The long fast waves
carry energy opposite to the rotation direction, while the shorter
slow-mode group velocity is in the azimuthal plane along the direction
of rotation. It is shown that the slow modes are concentrated around the
equator, while the fast modes are concentrated around the poles. The
band of latitude where the mode energy is concentrated is narrow, and
the spatial location of these band depends on the wave numbers (l, m).
---------------------------------------------------------
Title: Observations of oscillations in the transition region above
sunspots
Authors: Rendtel, J.; Staude, J.; Curdt, W.
2003A&A...410..315R Altcode:
Observations during two campaigns of the SUMER spectrograph and the EIT
imager onboard SoHO were used to analyse oscillations in bright sunspot
plumes. We report variations of both intensity and velocity seen in
EUV emission lines originating in the sunspot upper chromosphere and
the transition region. The wavelet analysis reveals rapidly changing
conditions in the emitting volumes. Generally, oscillations in the 5
min range dominate in the chromosphere, while the transition region
lines show oscillations at shorter periods (2 to 3 min). A drift of the
oscillation period of the Doppler velocity from 5 min to 2.5 min within
about 30 min can be explained by a strongly non-stationary behaviour
of the upper chromosphere and transition region, probably related
to downstream of material within the plume region. Synchronous EIT
observations of the lower corona show no intensity oscillations. This
hints either at a strong damping or a downward reflection in the upper
transition region or lower corona.
---------------------------------------------------------
Title: Current Status of the 1.5m Solar Telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkfeld, Thomas; Schmidt, Wolfgang; Soltau, Dirk; Nicklas,
Harald; Wiehr, Eberhardt; Wittman, Axel; Hofmann, Axel; Sobotka,
Michal; Klvana, Miroslav
2003ANS...324..112V Altcode: 2003ANS...324..P19V
No abstract at ADS
---------------------------------------------------------
Title: GREGOR: the new 1.5m solar telescope on Tenerife
Authors: Volkmer, Reiner; von der Luehe, Oskar; Kneer, Franz; Staude,
Juergen; Hofmann, Axel; Schmidt, Wolfgang; Sobotka, Michal; Soltau,
Dirk; Wiehr, Eberhardt; Wittmann, Axel; Berkefeld, Thomas
2003SPIE.4853..360V Altcode:
The new 1.5 m high resolution telescope will be build up on the reused
solar tower of the German 45 cm Gregory Coudé Telescope at the Teide
Observatory, Izaña, Tenerife. The new telescope is a Gregory type
with open telescope structure, alt-azimuth mount, complete retractable
dome, and a pool of well established and new developed post focus
instruments. An adaptive optics system provides the capability for
diffraction limited observations at visible wavelengths and the
polarimetry device in the secondary focus reduces the perturbation
due to instrumental polarization in an efficient way. We describe the
main optical characteristics and the focal plane instrumentation with
respect to the latest status of the project.
---------------------------------------------------------
Title: Oscillations of velocity and magnetic fields in sunspot umbrae
Authors: Staude, J.
2003AN....324..391S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostics of Magnetic Field Mesostructuring
Authors: Carroll, T. A.; Staude, J.
2003ASPC..307..125C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Meso-structured magnetic atmospheres: Stochastic polarized
radiative transfer and Stokes profile inversion
Authors: Carroll, T. A.; Staude, J.
2003AN....324..392C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multi-Component Magnetic Field Structure in Solar Flares
Authors: Lozitsky, V. G.; Staude, J.
2003ASPC..307..378L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: GREGOR, a 1.5 m Gregory-type telescope for solar observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Soltau, W. Schmidt
D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2002NCimC..25..689K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Signature of differential rotation in solar disk-integrated
chromospheric line emission
Authors: Hasler, K. -H.; Rüdiger, G.; Staude, J.
2002AN....323..123H Altcode:
UARS SOLSTICE data have been subjected to Fourier and wavelet analyses
in order to search for the signature of the solar rotation law in
the disk-integrated irradiance of UV lines. Lyman-alpha, Mg II, and
Ca II data show a different behaviour. In the SOLSTICE data there
are significant temporal variations of the rotation rate of the UV
tracers over 5 - 6 years. Often several distinct rotation periods
appear almost simultaneously. Beside the basic period around 27 days
there are signals at 32 - 35 days corresponding to the rotation rate
at very high latitudes. For more than 5 years during another period of
the solar cycle the rotational behaviour is quite different; there is
an indication of differential rotation of active regions in these Ca
II ground-based data. The data contain a wealth of information about
the solar differential rotation, but it proves difficult to disentangle
the effects of the different emitting sources.
---------------------------------------------------------
Title: Magnetic field oscillations of sunspots?
Authors: Staude, J.
2002AN....323..317S Altcode:
For 3 decades it is known that sunspots show oscillations of velocity
and intensity, that is of thermodynamic quantities. Oscillatory power
is concentrated at periods around 2 \ldots 3 min, 5 min, and ga 20
min. Attempts to measure related magnetic field oscillations were
contradictory. Now there are hints of significant magnetic signals
in 2-D spectro-polarimetric data with power mainly in pores and at
the boundary between the umbra and the penumbra of larger spots. We
discuss these data and possibilities of their interpretation which
are still a matter of debate. The magnetic oscillations could be the
signature of a `whispering gallery' like mode of slow body waves in
a thick magnetic flux-tube. However, other interpretations such as
opacity oscillations or a crosstalk from velocity or compressive waves
cannot be ruled out as long as better observed data, measurements of
phase shifts in particular, and more realistic models are still missing.
---------------------------------------------------------
Title: On nonadiabatic waves in the photospheres of cool stars
Authors: Pregla, A. V.; Zhugzhda, Y. D.; Staude, J.
2002AN....323..465P Altcode:
The coupled set of equations of hydrodynamics and radiative transfer
is derived for small disturbances in a plane, grey atmosphere. Only
radiative transfer is taken into account in the energy equation;
dynamical effects of radiation are ignored. A mean stationary radiative
flux through the photosphere is taken into account. The radiative
transfer equation is used by assuming the Eddington approximation,
moreover, an exponential height profile of the temperature and an
analytical opacity formula are supposed. For this model we obtained an
asymptotic solution for plane nonadiabatic acoustic waves and radiation
waves. The approach provides a detailed discussion of the interaction
of nonadiabatic p-modes and radiation waves in a realistic model of
the photosphere of a solar-like star.
---------------------------------------------------------
Title: Long-period eigenoscillations of the solar interior: 1-3 yr,
20-40 yr, and 1500-20000 year modes
Authors: Staude, Jürgen; Dzhalilov, Namig S.
2002ESASP.477..167S Altcode: 2002scsw.conf..167S
Waves with periods much larger than the rotation period become trapped
in the solar radiative interior. The modelling considers compressible,
nonadiabatic, Rossby- like modes (ɛ-mechanism and radiative losses are
taken into account) for a very small latitudinal gradient of rotation,
without an arbitrary choice of other free parameters. We found global
vorticity modes in 3 separate period ranges of ≍1-3 yr, 20-40 yr,
and 1500-20000 yr which are maximum unstable. The discovered resonant
cavity modes (called R-modes) are different from the known r-modes. We
discuss some prospects to develop the theory of R-modes as a driver
of the dynamics in the convective zone which could explain e.g.,
observed short-term fluctuations of rotation, a control of the solar
magnetic cycle, and abrupt changes of terrestrial climate in the past
(Dansgaard-Oeschger events).
---------------------------------------------------------
Title: Eigenoscillations of the differentially rotating
Sun. I. 22-year, 4000-year, and quasi-biennial modes
Authors: Dzhalilov, N. S.; Staude, J.; Oraevsky, V. N.
2002A&A...384..282D Altcode: 2002astro.ph..1120D
Retrograde waves with frequencies much lower than the rotation frequency
become trapped in the solar radiative interior. The eigenfunctions of
the compressible, nonadiabatic (epsilon -mechanism and radiative losses
taken into account) Rossby-like modes are obtained by an asymptotic
method assuming a very small latitudinal gradient of the rotation
rate. An integral dispersion relation for the complex eigenfrequencies
is derived as a solution of the boundary value problem. The discovered
resonant cavity modes (called R-modes) are fundamentally different
from the known r-modes: their frequencies are functions of the solar
interior structure, and the reason for their existence is not related
to geometrical effects. The most unstable R-modes are those with
periods of ~1-3 yr, 18-30 yr, and 1500-20 000 yr; these three separate
period ranges are known from solar and geophysical data. The growing
times of those modes which are unstable with respect to the epsilon
-mechanism are ~10<SUP>2</SUP>, 10<SUP>3</SUP>, and 10<SUP>5</SUP>
years, respectively. The amplitudes of the R-modes are growing towards
the center of the Sun. We discuss some prospects to develop the theory
of R-modes as a driver of the dynamics in the convective zone which
could explain, e.g., observed short-term fluctuations of rotation, a
control of the solar magnetic cycle, and abrupt changes of terrestrial
climate in the past.
---------------------------------------------------------
Title: Global Oscillations of the Sun in a Wide Optical Spectral
Range: DIFOS Experiment Onboard CORONAS-F
Authors: Oraevsky, V.; Lebedev, N.; Kuznetsov, V.; Staude, J.;
Kostyk, R.
2002cosp...34E.345O Altcode: 2002cosp.meetE.345O
The DIFOS experiment onboard the CORONAS-F spacecraft continues the
investigation of solar global oscillations, which was started in 1994
during the CORONAS-I mission. The satellite was launched on July
31, 2001. It uses a multi-channel photometer to observe irradiance
fluctuations. The photometer measures fluctuations of the solar
flux in six optical spectral ranges: near 350, 500, 650, 850, 1100,
and 1500 nm with a bandwidth of about 10% of the central wavelength
for each. After a short description of the instrumentation and data
analyses, we present results of observations of low-degree p-modes of
global oscillations for different observational optical ranges. The
oscillation amplitudes were found to decrease with the growth of the
wavelength. The amplitude ratios for different wavelength are in a
good agreement with earlier observations and theoretical predictions.
---------------------------------------------------------
Title: GREGOR: a 1.5 m telescope for solar research
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Berkefeld, Th.;
Kneer, F.; Staude, J.
2001AN....322..353V Altcode:
GREGOR will be a new 1.5 meter solar telescope at the Teide Observatory,
Izaña, Tenerife. It will provide observations with high polarimetric
precision at visible and infra-red wavelengths from Earth in the
solar photosphere and chromosphere with a resolution of 70 km on the
Sun. GREGOR replaces the 45 cm Gregory Coudé telescope.
---------------------------------------------------------
Title: Introduction to Volume 322 (5/6) Proceedings of the
Joint-Discussion #1 and the Mini-Symposia #9 and #10 at the Joint
European and National Astronomical Meeting (JENAM) for 2001
Authors: Strassmeier, K. G.; Staude, J.; Dreizler, S.
2001AN....322..271S Altcode:
This volume of AN contains the proceedings of the Joint Discussion
#1 (JD-1) “Astronomy with Robotic Telescopes: Present and Future
Projects” and of the Mini Symposia #9 (MS-9) “Hot subdwarfs,
white dwarfs, and low-mass star evolution”, and #10 (MS-10) “Large
Telescopes for Solar Physics”. The meetings were held as part of the
JENAM 2001 conference “Five Days of Creation. Astronomy with Large
Telescopes from Ground and Space” in Munich, Germany, from September
10 through 15, 2001.
---------------------------------------------------------
Title: Post-focus instrumentation for GREGOR
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2001AN....322..361K Altcode:
GREGOR is a high-resolution solar telescope with an aperture of 1.5
m. It will be equipped with an Adaptive Optics system and is designed
for high-precision measurements of magnetic fields and plasma motions
in the solar photosphere and chromosphere with a resolution of 70
km on the Sun. GREGOR will replace the Gregory Coudé Telescope at
the Observatorio del Teide on Tenerife. In concert with the other
solar telescopes at Teide Observatory it will be useful for studying
the dynamics of the solar atmosphere and the underlying physical
processes. GREGOR will also serve as a test bed for next generation
solar telescopes. We discuss briefly the postfocus instrumentation
of GREGOR.
---------------------------------------------------------
Title: The inversion of Stokes profiles with artificial neural
networks
Authors: Carroll, T. A.; Staude, J.
2001A&A...378..316C Altcode:
We investigate the application of artificial neural networks (ANNs)
for the interpretation of Stokes profiles. We have employed ANNs to
approximate the nonlinear inverse mapping between the Stokes profiles
and some of the underlying atmospheric parameters. This approximate
model is used in the following to carry out a fast non-iterative
inversion of synthetic Stokes profiles. We have used synthetic Stokes
profiles of the photospheric infrared line Fe I lambda 15648 to
demonstrate that the ANNs are capable to yield accurate single valued
estimates of the complete magnetic field vector, line-of-sight (LOS)
velocity, microturbulence, macroturbulence and the filling factor with
exceptional speed. For a stratified atmosphere we also demonstrate
that these single valued parameters do represent very good averaged
values of the input stratification. To retrieve some of the temperature
information encoded in the Stokes profiles we modeled a neural network
classifier on the basis of several semi-empirical model atmospheres
(i.e. temperature and pressure stratification). With this classifier
we are able to determine the probability that a given Stokes profile
has its origin from a particular temperature stratification of a
semi-empirical model.
---------------------------------------------------------
Title: GREGOR: high resolution solar observations from 1 AU
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
Staude, J.; Pailer, N.
2001ESASP.493..417V Altcode: 2001sefs.work..417V
No abstract at ADS
---------------------------------------------------------
Title: Waves in Sunspots: Resonant Transmission and the Adiabatic
Coefficient
Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D.
2001SoPh..202..281S Altcode:
We investigate linear acoustic-gravity waves in three different
semi-empirical model atmospheres of large sunspot umbrae. The sunspot
filter theory is applied, that is, the resonant transmission of
vertically propagating waves is modelled. The results are compared
with observed linear sunspot oscillations. For three umbral models we
present the transmission coefficients and the energy density of the
oscillations with the maxima of transmission. The height dependence of
the adiabatic coefficient (the ratio of specific heats) γ strongly
influences the calculated resonance frequencies. The variable γ can
explain the observed closely spaced resonance period peaks. The first
resonance in the 3 min range is interpreted as a resonance of the upper
chromosphere only, while the higher order peaks are resonances of the
whole chromosphere.
---------------------------------------------------------
Title: Observations of oscillations above sunspots
Authors: Rendtel, Jürgen; Staude, Jürgen
2001ESASP.493..337R Altcode: 2001sefs.work..337R
No abstract at ADS
---------------------------------------------------------
Title: Analysis and interpretation of Stokes profiles with artificial
neural networks
Authors: Carroll, T. A.; Staude, J.
2001ESASP.493..183C Altcode: 2001sefs.work..183C
No abstract at ADS
---------------------------------------------------------
Title: Shifts of p-mode frequencies by wave tunneling through the
solar atmosphere
Authors: Dzhalilov, Namig S.; Staude, Jürgen
2001ESASP.464..625D Altcode: 2001soho...10..625D
Global adiabatic p-modes are modelled by an asymptotic theory, taking
into account the influence of the solar atmosphere on the formation of
the eigenoscillations: waves of the whole frequency range 2-10 mHz are
now reaching the chromosphere-corona transition region (CCTR) by the
tunneling of acoustic waves through the atmospheric barriers. The main
acoustic cavity inside the Sun becomes considerably extended in this
way, leading to a change of frequencies: low frequencies are increased,
while high frequencies are decreased. The transition from low p-mode
frequencies to high peak frequencies >6mHz is smooth. The imaginary
parts of the frequencies indicate a decay of the amplitudes, resulting
from considerable energy losses by tunneling from the main cavity. A
penetration of linear p-modes to the corona is impossible. The behavior
of the CCTR is that of a free surface: the p-modes may drive forced
surface gravity waves of this free surface.
---------------------------------------------------------
Title: Problems in the interpretation of sunspot oscillation
measurements
Authors: Settele, A.; Staude, J.; Zhugzhda, Y. D.
2001ESASP.464..247S Altcode: 2001soho...10..247S
Sunspot oscillations are observed in spectral lines formed at different
depths in the sunspot atmosphere. The interpretation of measurements in
chromospheric lines is problematic as the lines are formed in NLTE. So
the measured power spectra do not originate from one specific depth in
the atmosphere but are smoothed out over a larger region. This will also
influence the phase shifts of the waves measured in different spectral
lines and might cause some misinterpretation. These complications
are illustrated by our model calculations: Modelling the transmission
of magneto-atmospheric waves through the sunspot atmosphere by means
of the sunspot filter approach, we show the "real" power spectra at
different atmospheric depths. These results are compared with Ca II-H/K
power spectra gained from the NLTE calculations of the Ca II-H/K lines
in an atmosphere perturbed by our waves. All results are preliminary.
---------------------------------------------------------
Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2001AGM....18.P223K Altcode:
GREGOR is a high-resolution solar telescope with an aperture of 1.5
m. It will be equipped with an Adaptive Optics system and is designed
for high-precision measurements of magnetic fields and plasma motions
in the solar atmosphere and chromosphere with a resolution of 70 km
on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the
Observatorio del Teide on Tenerife. We describe the optical design
and the focal plane instrumentation. In concert with the other solar
telescopes at Teide Observatory it will be useful for studying the
dynamics of the solar atmosphere and the underlying processes. GREGOR
will also serve as a test bed for next generation solar telescopes.
---------------------------------------------------------
Title: Sunspot transition region oscillations
Authors: Rendtel, J.; Staude, J.; Wilhelm, K.; Gurman, J. P.
2001ESASP.464..235R Altcode: 2001soho...10..235R
Intensity and velocity oscillations have been observed over a period
of 4.3 hours in lines of Ne VIII and C IV with the SUMER spectrograph
aboard SOHO. These lines are formed in the EUV plume above a
sunspot. Applying a wavelet analysis, we find oscillations mainly close
to 3 mHz. The temporal behaviour is strongly intermittent, particularly
for the velocity oscillations. This non-stationary behaviour may be
related with occurrence of blinkers in the umbral transition region.
---------------------------------------------------------
Title: Resonant Transmission of Magneto-atmospheric Waves in Sunspot
Umbrae
Authors: Staude, J.; Rendtel, J.; Settele, A.
2001IAUS..203..320S Altcode:
Oscillations of velocity and intensity, of the magnetic field in
the photosphere as well, have been observed at all height levels of
the atmosphere above sunspots from the photosphere up to the lower
corona. We discuss the nonstationary behavior of intensity and velocity
oscillations; they have been observed by SOHO in transition region lines
formed in the EUV plume of a sunspot during a continuous time series
of 4.3 hours. Applying a wavelet analysis, we find periods around 3 mHz
with different periods in the observed EUV lines. Moreover, we discuss
the observed oscillations within the frame of model calculations
for the resonant transmission of magneto-atmospheric waves through
realistic models of the sunspot subphotosphere and atmosphere.
---------------------------------------------------------
Title: Long-period Eigenoscillations of the Solar Interior: 22-year,
4500-year, and Quasi-biennial Modes
Authors: Staude, J.; Dzhalilov, N. S.
2001AGM....18..P04S Altcode:
Waves with periods much larger than the rotation period become trapped
in the solar radiative interior. Our modelling considers compressible,
nonadiabatic, Rossby-like modes (ɛ-mechanism and radiative losses are
taken into account) for a very small latitudinal gradient of rotation,
without an arbitrary choice of further free parameters. These `R-modes'
are fundamentally different from the known `r-modes': their frequencies
are functions of the solar interior structure, and the reason for
their existence is not related to geometrical effects. The amplitudes
of the R-modes are growing towards the center of the Sun. We found
global vorticity modes in 3 separate period ranges around 1.3-2.0,
22, and 4500 years (with an onset at 1500 years) which are maximum
unstable. They could possibly control the solar activity cycle, cause
the 1.3 year period variation of solar rotation which was recently
found in the deeper convective zone and produce the quasi-biennial
oscillations in solar activity and geophysical data. Moreover, they
could be related to the abrupt changes of terrestrial climate in the
past (Dansgaard-Oeschger events).
---------------------------------------------------------
Title: Low-Frequency Eigenoscillations of the Differentially Rotating
Solar Interior
Authors: Dzhalilov, N. S.; Staude, J.
2001ASPC..248..173D Altcode: 2001mfah.conf..173D
No abstract at ADS
---------------------------------------------------------
Title: Influence of the solar atmosphere on the p-mode
eigenoscillations
Authors: Dzhalilov, N. S.; Staude, J.; Arlt, K.
2000A&A...361.1127D Altcode:
An asymptotic theory of global adiabatic p-modes is developed,
taking into account the influence of the solar atmosphere. It is
shown that waves of the whole frequency range nu ~ 2-10 mHz may
reach the chromosphere-corona transition region (CCTR) by means of
a tunneling through the atmospheric barriers. The primary acoustic
cavity inside the Sun becomes considerably extended by this way,
leading to a change of frequencies: low frequencies are increased,
while high frequencies are decreased. The transition from low p-mode
frequencies to high peak frequencies (nu >~ 6;mHz) is smooth. The
locations of the turning points are determined from the wave equation
for {div}*/rightarrow{v}. It is shown that the internal turning point
of the acoustic cavity is strongly shifted toward the center of the Sun,
while the upper turning point is shifted from the surface to CCTR. That
means, the turning points cannot be located in the convective zone. A
new complex integral dispersion relation for the eigenfrequencies is
derived. The imaginary parts of the frequencies indicate a decay of
the amplitudes, resulting from considerable energy losses by tunneling
from the main cavity. It is shown that waves with a decaying amplitude
(complex frequency) may exist in a limited area only, penetration of
linear p-modes to the corona is impossible. The CCTR acts as a free
surface. We conclude that the p-modes may drive forced surface gravity
waves at this surface.
---------------------------------------------------------
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: Helioseismologie - ein neues Fenster der Sonnenforschung.
Authors: Staude, J.
2000A&R....37....4S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Friedrich Wilhelm Jäger (1914 - 14. Februar 2000).
Authors: Staude, J.
2000MitAG..83...13S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenphysik in Potsdam
---------------------------------------------------------
Title: Sonnenphysik in Potsdam Title:
Solar physics in Potsdam.
Authors: Staude, Jürgen
2000AcHA...11...81S Altcode:
Solar research initiated the establishment of the Astrophysical
Observatory Potsdam (AOP) in 1874. The present contribution outlines the
development of solar physics in Potsdam from the early history of the
AOP to this day. The main topics are the work of Karl Schwarzschild,
the investigations related to the general theory of relativity, the
foundation of the Einstein tower, Walter Grotrian's founding of modern
coronal physics, and the investigations of sunspot magnetic fields.
---------------------------------------------------------
Title: Sonnenforschung in Potsdam - Streiflichter aus der Geschichte
---------------------------------------------------------
Title: Sonnenforschung in Potsdam - Streiflichter aus der Geschichte
---------------------------------------------------------
Title: Solar research in Potsdam - sidelights on its history.
Authors: Staude, Jürgen; Hofmann, Axel
2000AcHA....8..107S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: GREGOR: A 1.5m Telescope for Solar Research
Authors: von der Lühe, O.; Schmidt, Wolfgang; Soltau, Dirk; Kneer,
Franz; Staude, Jurgen
2000ESASP.463..629V Altcode: 2000sctc.proc..629V
No abstract at ADS
---------------------------------------------------------
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: The Influence of the Adiabatic Coefficient and the Magnetic
Field on Sunspot Oscillations
Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J.
1999ESASP.448..367S Altcode: 1999ESPM....9..367S; 1999mfsp.conf..367S
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: Determination of the Velocity Vector Field in an Asymmetric
Sunspot Based on Vector Magnetograph Measurements
Authors: Krivtsov, A. M.; Hofmann, A.; Staude, J.; Klvaña, M.;
Bumba, V.
1999ASPC..184..108K Altcode:
A new method to determine the distribution of the full velocity
vector in an asymmetric sunspot is presented. Measurements of the
Doppler velocity and of the vector of the magnetic field are used as
initial data for these calculations. The determination is subdivided
into two stages: in a first step we obtain the distribution of the
velocity projection onto the solar surface, and in the second step
the orthogonal component of the velocity field is calculated. The
resulting vector velocity field is in good agreement with the basic
features of the siphon flow model of penumbral flux tubes.
---------------------------------------------------------
Title: SUMER Observations of Intensity Oscillations in the Transition
Region of a Sunspot
Authors: Rendtel, J.; Staude, J.; Innes, D. E.; Wilhelm, K.
1999ASPC..184..271R Altcode:
UV spectroscopic data obtained with the SUMER spectrograph aboard SOHO
have been analysed to detect oscillations in the chromosphere-corona
transition region (TR) above sunspots. We observed the active region
NOAA 7986 in the wavelength bands around the Ne VIII line at 770.4 Å
and the C IV line at 1548.1 Å on August 29, 1996, between 09:08 UT
and 13:31 UT. Simultaneous observations with the Normal Incidence
Spectrometer of CDS aboard SOHO have shown, that the spot had a
bright EUV plume at TR temperatures. A preliminary data analysis
indicates intensity oscillations in the 2-minute range (7.3...7.9
mHz) in both spectral lines. The temporal variation of oscillatory
power in the two spectral lines is generally in opposite directions,
i.e. during an increase of oscillatory power in the Ne VIII line we
find a decrease in the C IV line. A similar but smaller tendency is
observed in the average intensity of the line profiles. This hints at
a non-adiabatic behaviour of the oscillations and a slow cooling of
the emitting sunspot plume region.
---------------------------------------------------------
Title: Sunspot Oscillations
Authors: Staude, J.
1999ASPC..184..113S Altcode:
Sunspots show oscillations of velocity, of intensity, and probably
of the magnetic field; the oscillations are observed at different
periods (2-3 min, 5 min, <= 20 min), at all height levels of the
sunspot atmosphere, and with different spatial distributions and
characteristic phase relations. In the present paper a short review
on the various phenomena is given, with focusing on oscillations of
the magnetic field at photospheric levels and on oscillations in the
transition region to the corona above sunspots, derived from recent
2-D observations with high spatial resolution. The observed data are
compared with the predictions from theory and modelling.
---------------------------------------------------------
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: Third Advances in Solar Physics Euroconference: Magnetic
Fields and Oscillations
Authors: Schmieder, B.; Hofmann, A.; Staude, J.
1999ASPC..184.....S Altcode:
The third Advances in Solar Physics Euroconference (ASPE) "Magnetic
Fields and Oscillations"concluded a series of three Euroconferences
sponsored by the European Union. The meeting took place in Caputh
near Potsdam, Germany, on September 22-25, 1998, followed by the JOSO
(Joint Organization for Solar Observations) 30th Annual Board Meeting
on September 26, 1998. The ASPE formula is attractive and compares well
with other meetings with "show-and-tell" character. This meeting had
122 participants coming from 26 countries; 36 participants came from
countries formerly behind the Iron Curtain; a "politically incorrect"
estimate says that 48 participants were below 35 years of age,
with an unusually large female-to-male ratio. This characteristic of
youngness is the more striking since solar physics is a perhaps overly
established field exhibiting an overly senior age profile. It was a
good opportunity to train this young generation in Solar Physics. The
conference topic "Magnetic Fields and Oscillations" obviously was
wide enough to cater to many an interest. These proceedings are
organized according to the structure of the meeting. They include
the topics 'High resolution spectropolarimetry and magnetometry',
'Flux-tube dynamics', 'Modelling of the 3-D magnetic field structure',
'Mass motions and magnetic fields in sunspot penumbral structures',
'Sunspot oscillations', 'Oscillations in active regions - diagnostics
and seismology', 'Network and intranetwork structure and dynamics',
and 'Waves in magnetic structures'. These topics covered the first
2.5 days of the conference. The reviews, oral contributions, and
poster presentations were by no means all of the meeting. The ASPE
formula also adds extensive plenary sessions of JOSO Working groups
on topics that involve planning of Europe-wide collaboration. At this
meeting these concerned solar observing techniques, solar data bases,
coordination between SOHO and ground-based observing, and preparations
for August 11, 1999 when more Europeans will be eclipsed than ever
before. The contributions to these sessions have been included into
the present volume as well. The participants of the EU-TMR Research
Network 'Solar Magnetometry Network' came together to discuss in a
special working group session questions of their future collaboration.
---------------------------------------------------------
Title: An attempt to estimate nonideal effects on the electron
partial pressure in the solar interior up to density order 5/2
Authors: Meister, C. -V.; Staude, J.; Pregla, A. V.
1999AN....320...43M Altcode:
Helioseismology is probing the equation of state of the solar interior
with ever increasing precision. Recently, even nonideal pressure
modifications below 1 % are being considered, mainly due to the use of
different partition functions. In the present paper only the electron
partial pressure has been studied, and thus no partition function was
taken into account. Instead, the pressure was calculated beyond the
usually applied Debye-Huckel theory, and quantum-mechanical electron
exchange was taken into account very carefully. If the total electron
pressure at distances from the solar centre larger than 0.83 solar radii
could be described by equilibrium thermodynamics, it proved smaller
than the value for an ideal gas due to the dominating Debye-Huckel
screening. On the contrary, at distances smaller than 0.83 solar radii
electron exchange increases the total pressure up to values above the
ideal pressure. Pressure modifications up to one per cent are caused
by the higher-order interactions beyond the Debye-Huckel screening.
---------------------------------------------------------
Title: Measurements of magnetic field strength on T Tauri stars
Authors: Guenther, Eike W.; Lehmann, Holger; Emerson, James P.;
Staude, Jürgen
1999A&A...341..768G Altcode:
We have investigated the magnetic field strength of one weak-line and
four classical T Tauri stars. The magnetic field strength is derived
from the differential change of the equivalent width of photospheric
Fe I lines in the presence of a magnetic field, calculated using a
full radiative transfer code. The method was successfully tested by
applying it to a non-magnetic solar-type star, and to <ASTROBJ>VY
Ari</ASTROBJ> which is believed to have a strong magnetic field. For
two of the classical T Tauri stars, we find a product of magnetic
field strength and filling factor B * f = (2.35+/- 0.15) kG for
<ASTROBJ>T Tau</ASTROBJ>, and B * f = (1.1+/- 0.2) kG for <ASTROBJ>LkCa
15</ASTROBJ>. For the classical T Tauri star <ASTROBJ>UX Tau A</ASTROBJ>
and the weak-line T Tauri star <ASTROBJ>LkCa 16</ASTROBJ> the detection
is only marginal, indicating magnetic field strengths of the order of
1 kG and possibly of more than 2 kG, respectively. No field could be
detected for the classical T Tauri star <ASTROBJ>GW Ori</ASTROBJ>. For
the two classical T Tauri stars for which we have detected a field, we
find the filling factors to be larger than ~ 0.5, which indicates that
the magnetic field covers most of the photosphere. We also show that
ignoring a magnetic field can, depending on the lines used, result in
errors in effective temperature and underestimates of veiling. Based
on observations made with the William Herschel Telescope operated
on the island of La Palma by the Royal Greenwich Observatory in the
Spanish Observatorio de los Roque de los Muchachos of the Instituto
de Astrofisica de Canarias
---------------------------------------------------------
Title: GREGOR, a 1.5 M Solar Telescope
Authors: von der Lühe, O.; Schmidt, W.; Soltau, D.; Kneer, F.;
Staude, J.
1999AGAb...15....5V Altcode: 1999AGM....15..A01V
We present the design of a new large solar telescope which is going to
be installed at the Observatorio del Teide, in the tower that presently
houses the 45cm Gregory-Coudé-Telescope. The new telescope has an
aperture of 1.5 meters and its optical design is basically a Gregorian
configuration. It will be an open telescope in an azimuthal mount. An
adaptive optics system is incorporated in the optical design as well as
a polarimetry package. The feasibility of lightweight optics for the
primary mirror has been investigated in an industrial pre-study. The
focal plane instrumentation will include a high resolution filter
spectrometer similar to the existing TESOS instrument at the VTT and
a new spectro-polarimeter for the visible and the near UV. The latter
instrument is presently being developed jointly by the KIS and the
High Altitude Observatory in Boulder, USA. Budget permitting, detailed
(Phase-B) planning will start in 2000, and the telescope will be
developed and built in 2002 and 2003 with first light in spring of 2004.
---------------------------------------------------------
Title: Max-Planck-Institut für Astronomie,
Heidelberg-Königstuhl. Jahresbericht 1997.
Authors: Staude, J.; Appenzeller, I.; Bührke, T.
1999mfah.bookQ....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A new method to calculate the resonant response of a sunspot
model atmosphere to magneto-atmospheric waves
Authors: Settele, A.; Zhugzhda, Y. D.; Staude, J.
1999AN....320..147S Altcode:
In order to understand the observed oscillations in sunspots we
present a new method for calculating the resonant response of a
realistic semi-empirical model of the sunspot umbral atmosphere and
subphotosphere to magneto-atmospheric waves in a vertical magnetic
field. The depth dependence of both the adiabatic coefficient and the
turbulent pressure is taken into account. This requires an extension
of the wave equations by Ferraro & Plumpton (1958). We compare
the coefficients of wave transmission, reflection, and conversion
between fast mode and slow mode waves for different assumptions,
compare the results with those from earlier modelling efforts, and
point out possible sources of mistakes. The depth dependence of the
adiabatic coefficient strongly influences the resulting spectrum of
resonance frequencies. The condition of a conservation of wave flux
is violated if the depth dependence of the turbulent pressure is not
properly considered.
---------------------------------------------------------
Title: High resolution spectro-polarimetric observations of sunspot
penumbrae.
Authors: Maleki, D.; Staude, J.
1999joso.proc...85M Altcode:
Spectro-polarimetric observations with high spatial resolution have
been obtained in sunspot penumbrae and used to derive the magnetic
field structure in different filamentary fine structures. Some results
from a preliminary data analysis are listed.
---------------------------------------------------------
Title: Magnetic fields and oscillations. 3rd Euroconference ASPE98
(Advances in Solar Physics Euroconference 1998), Potsdam/Caputh
(Germany), 22 - 25 Sep 1998. Poster contributions.
Authors: Schmieder, B.; Staude, J.
1999joso.proc...74S Altcode:
All of the oral presentations of ASPE98 will be published in a separate
volume of the ASP Conference Series, while this volume contains the
poster presentations.
---------------------------------------------------------
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: Max-Planck-Institut für Astronomie,
Heidelberg-Königstuhl. Jahresbericht 1998.
Authors: Staude, J.; Appenzeller, I.; Bührke, T.
1999mfah.bookR....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of the full velocity vector based on vector
magnetograph measurements in an asymmetric sunspot
Authors: Krivtsov, A. M.; Hofmann, A.; Staude, J.; Klvana, M.;
Bumba, V.
1998A&A...335.1077K Altcode:
A new method to determine the distribution of the full velocity
vector in an asymmetric sunspot is presented. Measurements of the
Doppler velocity and of the vector of the magnetic field are used as
initial data for these calculations. The determination is subdivided
into two stages: in a first step we obtain the distribution of the
velocity projection onto the solar surface, and in the second step
the orthogonal component of the velocity field is calculated. The
method has been applied to a sunspot observed from two observatories
over 7 days, that is at different positions on the solar disk and in
different phases of its development. The resulting vector velocity
field is in good agreement with the basic features of the siphon flow
model of penumbral flux tubes. The velocities are directed outwards
from the sunspot, and they have small values in the umbra and maximum
values in the central part of the penumbra, while in the outer penumbra
the velocities decrease rapidly. The vertical velocities are mainly
localized at the umbral boundary (upflows) and at the outer parts of
the penumbra (downflows).
---------------------------------------------------------
Title: German-Russian Cooperation in Helioseismology
Authors: Horn, T.; Hasler, K. -H.; Arlt, K.; Staude, J.; Oraevsky,
V. N.; Zhugzhda, Y. D.
1998ESASP.417..243H Altcode: 1998cesh.conf..243H
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Oscillations from SUMER Spectra
Authors: Rendtel, J.; Staude, J.; Innes, D.; Wilhelm, K.; Gurman, J. B.
1998ESASP.417..277R Altcode: 1998cesh.conf..277R
No abstract at ADS
---------------------------------------------------------
Title: Oscillations in a Sunspot Transition Region Observed with SOHO
Authors: Staude, J.; Rendtel, J.; Innes, D.; Wilhelm, K.; Gurman, J. B.
1998ESASP.418..651S Altcode: 1998soho....6..651S
Measurements of oscillations in the chromosphere-corona transition
region (TR) above sunspots are of fundamental importance for
investigating sunspot structure and dynamics; for instance, resonator
models of magneto-atmospheric waves and their non-adiabatic behavior
can be tested in this way (Staude et al., 1985). UV spectroscopic
data obtained with the SUMER spectrograph aboard SOHO have been
analyzed to detect such oscillations. The longest time series was
obtained on August 29, 1996, between 09:08 UT and 13:31 UT. During
this period, scans were made over the active region NOAA 7986 in the
wavelength bands around 770.4 AA (Ne VIII line, formed at T ~6 times
10<SUP>5</SUP> K) and 1548.1 AA (C IV line, T ~7 times 10<SUP>4</SUP>
dots 1.3 times 10<SUP>5</SUP> K). The large dominating sunspot of this
active region was close to the disk centre. Simultaneous observations
with the Normal Incidence Spectrometer of CDS aboard SOHO have shown,
that the spot had a bright EUV plume at TR temperatures (Maltby et al.,
1998). For compensating possible instrumental and exposure effects,
we extract background information from each image. A preliminary
data analysis indicates intensity oscillations in the 2-minute range
(at 7.4 dots 7.7 mHz) in both spectral lines and a slow temporal
decrease of oscillatory power in the Ne VIII line, but an increase
in the C IV line. These results hint at a non-adiabatic behavior of
the oscillations and a slow cooling of the emitting sunspot plume
region. Further supplementary observations of the active region NOAA
7986 are from EIT aboard SOHO (in the Fe IX/X lines at 171 AA ---
T ~1.3 times 10<SUP>6</SUP> K --- a time series of 2 hours has been
obtained simultaneous to the first part of the SUMER series, moreover,
single high-resolution pictures in 4 UV lines exist) as well as from
the magnetograph of the Einsteinturm observatory at Potsdam showing
a rather complex polarity distribution. It is planned to extend the
study towards velocity variations and to correlations between the
oscillations in the two SUMER lines. Furthermore, correlations will
be investigated towards the EIT time series.
---------------------------------------------------------
Title: Oscillations of the magnetic field in an active region
Authors: Horn, T.; Staude, J.
1998IAUS..185..449H Altcode:
In 1994 we performed observations at the German Vacuum Tower Telescope
at the Observatorio del Teide (Tenerife) using a polarimeter in front
of a two-dimensional imaging spectrometer with a tunable narrow-band
Fabry-Perot interferometer. We observed the main sunspot of the active
region NOAA 7577 and measured the Doppler line shift and the Zeeman
splitting of the line Fe I 6173 AA. The data show significant power of
velocity and magnetic field oscillations in period bands at 3 min and 5
min, a strong coherence of the velocity and magnetic field oscillations,
and a clear dependence of the phase difference on the period and on
the position, pointing out a longitudinal character of the oscillations.
---------------------------------------------------------
Title: Oscillation of the magnetic field in an active region.
Authors: Horn, T.; Staude, J.
1998joso.proc...79H Altcode:
The solar vacuum telescope VTT at Tenerife has been used to obtain
high-resolution two-dimensional spectro-polarimetric observations
of oscillations in the photospheric layers of sunspots. The spectra
of velocity oscillations show the known features of closely packed
power peaks in bands of periods around 3 min (strengthened) and 5
min (weakened with respect to the quiet Sun). In the same frequency
bands the VTT data show significant oscillations of the magnetic
field strength as well, which could not be attributed to disturbing
influences. Maximum power of both velocity and magnetic oscillations and
a strong correlation between them, in the 3-min band in particular,
is found to occur in those parts of the umbra where the magnetic
lines of force are parallel to the line-of-sight. The oscillations are
characterized by a marked spatial fine structure and a non-stationary
behaviour.
---------------------------------------------------------
Title: Two-dimensional measurements of sunspot oscillations
Authors: Staude, J.; Horn, T.
1997ASSL..225..235S Altcode: 1997scor.proc..235S
High-resolution two-dimensional spectro-polarimetric observations
of oscillations in the photospheric layers of a sunspot have been
obtained using the Vacuum Tower Telescope at Tenerife. A Fabry-Perot
interferometer has been applied to get narrow-band filtergrams directly
and to scan through the line profile. The spectra show significant power
of oscillations of velocity $v$ and of the magnetic field strength
as well. Both are concentrated in bands of peaks at periods around
3 min ($v$ strengthened) and 5 min ($v$ weakened with respect to the
quiet Sun), with maxima occuring in those parts of the umbra where the
magnetic lines of force are parallel to the line-of-sight. Coherence
and the phase difference between both types of oscillations show a
clear dependence on the magnetic field direction as well.
---------------------------------------------------------
Title: Observations of Sunspot Umbral Oscillations
Authors: Horn, T.; Staude, J.; Landgraf, V.
1997SoPh..172...69H Altcode: 1997ESPM....8...69H
The solar vacuum telescopes VTT and GCT at Tenerife have been used to
obtain high-resolution two-dimensional spectro-polarimetric observations
of oscillations in the photospheric layers of sunspots. At the GCT
the area of the sunspot has been scanned by shifting the spectrograph
slit; at the VTT a Fabry-Pérot interferometer has been applied to get
narrow-band filtergrams directly and to scan through the line profile.
---------------------------------------------------------
Title: Contribution Functions for Polarized Radiative Transfer
Authors: Staude, J.
1996SoPh..164..183S Altcode:
The concepts of contribution functions (CF) and of mean depths of line
formation of unpolarized light as well as of Stokes profiles will be
critically discussed. After having outlined the historical development
arguments are given in favour of the use of directly observable
quantities such as the emergent line intensity or the polarized
components seen through polarization optics only. The arguments are
provided by a probability interpretation of the CF; the ambiguities
of line depression CF as well as some physically strange features in
Stokes profiles are avoided if the rules based on this interpretation
are observed. Some problems of the interpretation of measurements in
chromospheric lines will be discussed as well.
---------------------------------------------------------
Title: Two-dimensional measurements of sunspot oscillations.
Authors: Staude, J.; Horn, T.; Landgraf, V.
1996AGAb...12...91S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectral darkening functions of solar p-modes - an effective
tool for helioseismology.
Authors: Zhugzhda, Y. D.; Staude, J.; Bartling, G.
1996A&A...305L..33Z Altcode:
Darkening functions (contrasts) of intensity fluctuations due to waves
in a nongrey LTE model of the solar atmosphere are calculated for
different wavelengths λ in the optical continuum spectrum. Adiabatic
and isothermal acoustic waves as well as temperature waves are
considered. A change of the sign of the darkening function for certain
ranges of λ is revealed for adiabatic waves. This effect makes it
possible to observe modes with l>=3 even in stars. Observations of
the darkening function of p-modes at different λ are proposed as a
new tool, making it possible to check numerical models of p-modes, to
impose restraints to the choice of the boundary conditions, to reduce
the arbitrariness in the calculation of nonadiabatic corrections
to eigenfrequencies, and to improve the accuracy of solar interior
sounding in this way.
---------------------------------------------------------
Title: On the possibility of detection of p-modes with L> 3 in
the sun-like stars
Authors: Staude, J.; Zhugzhda, Y. D.
1996ASPC..109..161S Altcode: 1996csss....9..161S
No abstract at ADS
---------------------------------------------------------
Title: An analytic theory of adiabatic p-modes in the atmospheres
of the Sun and Sun-like stars.
Authors: Dzhalilov, N. S.; Staude, J.
1995A&A...303..561D Altcode:
The height profile of temperature T of the solar or a stellar model,
extending from the subphotosphere through the atmosphere up to the
corona, has been piecewise approximated by various nonlinear and linear
functions for the different regions. Solving the basic equations of
adiabatic, nonvertical oscillations for these regions in the Cowling
approximation we obtained the eigenfunctions for the p-modes in
analytic form. Using these exact solutions it has been demonstrated,
that the mechanism of resonant transmission of acoustic waves through
the considered layers is sufficient to explain the main features of
the observed frequency spectrum of the solar p-modes, including the
5-min oscillations and the peaks in the high-frequency tail. It has
been shown that the upper turning point of the resonator for low
frequencies ν<~4mHz does not coincide with the boundary of the
acoustic potential barrier, the latter extending from the steep gradient
of T at the upper subphotosphere up to that above the minimum of T. The
wakes of the waves penetrate deep into the barrier (up to a height
of 500km in the solar atmosphere) and are reflected from there. High
frequencies are reflected from the chromosphere-corona transition
region. For not any frequency there exists a total reflection; with
increasing frequency there is an increasing leakage of wave energy
into the corona. It has been shown that all observable characteristics
of oscillations depend directly on the phase shift {DELTA}φ between
upward and downward running waves. The resonance peaks in the spectrum
arise at {DELTA}φ=0, where {DELTA}φ has been defined in the limits
[-π, +π]. The dependence of the power spectrum on the height, on
the frequency, and on the degree l has been demonstrated. The first
resonant frequencies always correspond to the 5-min oscillations.
---------------------------------------------------------
Title: Solar Irradiance Oscillations: Preliminary Results of the
Coronas-Difos Experiment
Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev,
I. M.; Kostyk, R. I.; Pflug, K.; Rüdiger, G.; Staude, J.; Bettac,
H. -D.
1995ESASP.376b.353L Altcode: 1995soho....2..353L; 1995help.confP.353L
No abstract at ADS
---------------------------------------------------------
Title: An Analytical Model of Adiabatic P-Modes Resonant Transmission
Through the Solar Atmosphere
Authors: Dzhalilov, N. S.; Staude, J.
1995ESASP.376b.441D Altcode: 1995soho....2..441D; 1995help.confP.441D
No abstract at ADS
---------------------------------------------------------
Title: First results of the CORONAS-DIFOS experiment. Space
observations of solar irradiance oscillations.
Authors: Lebedev, N. I.; Oraevsky, V. N.; Zhugzhda, Y. D.; Kopaev,
I. M.; Kostyk, R. I.; Pflug, K.; Ruediger, G.; Staude, J.; Bettac,
H. -D.
1995A&A...296L..25L Altcode:
The DIFOS experiment aboard the satellite CORONAS has been designed to
observe irradiance fluctuations due to global solar oscillations. The
satellite was launched on March 2, 1994. It uses a photometer measuring
fluctuations of the solar flux in three channels: near 550nm, 750nm,
and from 400nm through 1.1μm. After a short description of the
instrumentation and the data analysis we present first, preliminary
results of observations of low-degree p-modes including their variation
in time.
---------------------------------------------------------
Title: Book-Review - Robotic Telescopes in the 1990S
Authors: Filippenko, A. V.; Staude, J.
1995AN....316..154F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Visibility Functions of Solar and Stellar Irradiance Variations
Authors: Staude, J.; Bartling, G.; Zhugzhda, Y. D.; Dzhalilov, N. S.
1995ASPC...83..451S Altcode: 1995IAUCo.155..451S; 1995aasp.conf..451S
No abstract at ADS
---------------------------------------------------------
Title: An Analytic Theory of Adiabatic p-modes in the Atmospheres
of the Sun and Sun-like Stars
Authors: Dzhalilov, N. S.; Staude, J.
1995ASPC...83..449D Altcode: 1995IAUCo.155..449D; 1995aasp.conf..449D
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung am Sonnenobservatorium Einsteinturm des
Astrophysikalischen Instituts Potsdam.
Authors: Staude, J.
1995epaa.book...98S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung am Einsteinturm.
Authors: Staude, J.
1995Stern..71..142S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiation-Hydrodynamic Waves and Solar P Modes: Visibility
Functions
Authors: Staude, J.; Zhugzhda, Y. D.; Dzhalilov, N. S.
1995ASPC...76..338S Altcode: 1995gong.conf..338S
No abstract at ADS
---------------------------------------------------------
Title: Radiation-hydrodynamic waves in an optically grey
atmosphere. II. Analysis of wave properties and effects of thermal
conductivity in a homogeneous model.
Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J.
1994A&A...291.1001D Altcode:
The properties of radiation-hydrodynamic waves in a radiative,
thermally conducting, uniform atmosphere are investigated, avoiding the
Eddington approximation and considering a temporal as well as a spatial
analysis. The analysis of the dispersion equation shows the existence
of acoustic, radiation, and thermal wave modes and a relaxation mode
as well. The generalized Spiegel formula is discussed and the accuracy
of the Eddington approximation for the radiation-hydrodynamic waves
is considered. The amplitudes and phases of disturbances of gas
and radiation pressure, intensity, and temperature are obtained for
standing and travelling waves and for the relaxation mode too. The
polar angle dependence of the phase shift between velocity and intensity
is investigated. The predictions for full-disk intensity observations
and the deficiencies of earlier, less complete approaches are discussed.
---------------------------------------------------------
Title: Radiation Hydrodynamic Waves and Global Solar Oscillations
Authors: Staude, J.; Dzhalilov, N. S.; Zhugzhda, Y. D.
1994SoPh..152..227S Altcode: 1994IAUCo.143..227S; 1994svs..coll..227S
We investigate nonadiabatic hydrodynamic waves in a nongrey, radiating,
thermally conducting, homogeneous atmosphere in LTE with a finite mean
free path of photons. Avoiding the Eddington approximation the remaining
simplifications in the basic equations are discussed, the generalized
dispersion relation is analysed, and some wave properties in a grey
model are studied. The properties of waves in a stratified atmosphere
are analysed as well. In connection with the predicted properties of
the nonadiabatic waves we discuss observations ofp-modes by measuring
brightness fluctuations.
---------------------------------------------------------
Title: Sunspot umbral oscillations
Authors: Staude, J.
1994smf..conf..248S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interpretation of sunspot oscillations
Authors: Staude, J.
1994ASIC..433..189S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Visibility functions of solar and stellar luminosity
oscillations.
Authors: Staude, J.; Bartling, G.; Dzhalilov, N. S.; Zhugzhda, Y. D.
1994AGAb...10..116S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung in Potsdam - Das Sonnenobservatorium
Einsteinturm des Astrophysikalischen Instituts Potsdam.
Authors: Staude, J.
1994ABLD....5.....S Altcode:
Contents: 1. Das Astrophysikalische Observatorium
Potsdam. 2. Die Relativitätstheorie. 3. Instrumentarium des
Einsteinturms. 4. Forschungsprogramm. 5. Das Astrophysikalische
Institut Potsdam.
---------------------------------------------------------
Title: Radiation-Hydrodynamic Waves in the Solar Atmoshere
Authors: Zhugzhda, Y. D.; Staude, J.; Dzhalilov, N. S.
1994emsp.conf....9Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiation-hydrodynamic waves in an optically non-grey
atmosphere
Authors: Zhugzhda, Y. D.; Dzhalilov, N. S.; Staude, J.
1993A&A...278L...9Z Altcode:
We derive the dispersion equation of radiation-hydrodynamic waves for
a nongrey atmosphere in Local Thermodynamic Equilibrium (LTE) avoiding
the Eddington approximation. It is shown that the Rosseland mean opacity
doesn't describe the relaxation processes in the atmosphere except the
opaque limit. For the transparent limit the relaxation time depends on
the so-called Newton mean opacity. The grey and nongrey approximations
are compared for a model of the solar photosphere.
---------------------------------------------------------
Title: Planeten - Wanderer im All
Authors: Lang, Kenneth R.; Whitney, Charles A.; Staude, J.; Bührke, T.
1993pwia.book.....L Altcode:
In allgemeinverständlicher Form und ohne fachliche Vorkenntnisse
beim Leser vorauszusetzen stellen die Autoren unser Planetensystem
vor. Der klar geschriebene Text wird durch eine Fülle
z.T. bisher unveröffentlichter Fotos aufgelockert, und die
Ergebnisse von Raumsonden- und Satellitenmissionen bis 1992 sind
berücksichtigt. "...besticht durch exzellentes Bildmaterial und
Stilsicherheit in der Formulierung. Die Autoren erklären astronomische
Sachverhalte umfassend und leichtverständlich. Der Leser erlebt
einen faszinierenden Raumflug durch unser Sonnensystem...Mit sinnvoll
eingeschobenen Zusammenfassungen und Kurzinformationen, umfassendem
Anhang, Register und Bilbliographie. Ein ideales Buch für interessierte
Laien und angehende Astronomen." (Westdeutsche Zeitung)
---------------------------------------------------------
Title: Book-Review - the Sun - a Laboratory for Astrophysics
Authors: Schmelz, J. T.; Brown, J. C.; Staude, J.
1992AN....313..348S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - the Sun and Cool Stars - Activity Magnetism
Dynamos - I.A.U.COLL - Helsinki 1990JUL17-20
Authors: Tuominen, I.; Moss, D.; Rudiger, G.; Staude, J.
1992AN....313..318T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Solar Observations - Techniques and
Interpretation - First Canary Islands Winter School of Astrophysics
Authors: Sanchez, F.; Collados, M.; Vazquez, M.; Staude, J.
1992AN....313Q.302S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiation-hydrodynamic waves in an optically gray atmosphere. I
- Homogeneous model
Authors: Dzhalilov, N. S.; Zhugzhda, Y. D.; Staude, J.
1992A&A...257..359D Altcode:
We consider the coupled set of equations of hydrodynamics and
radiative transfer. Only radiative transfer is taken into account
in the energy equation, while other mechanisms of heat transfer
are ignored. Disturbances of the tensor of radiative pressure are
included in the linearized momentum equation. This term proves to be
of great importance for radiation-acoustic waves. LTE as well as a
gray approximation and homogeneity of the atmosphere are assumed. The
hydrodynamic equations are solved by using an exact solution of the
radiative transfer equation (no Eddington approximation is made). The
dispersion equation for the nonadiabatic oscillations is derived. This
equation is valid for arbitrary optical thickness and generalizes all
hitherto known results.
---------------------------------------------------------
Title: Oscillations &Seismological Diagnostics of Sunspots
(Invited)
Authors: Staude, J.
1992LNP...397..181S Altcode: 1992sils.conf..181S
Comparisons between recent observations of umbrae and detailed numerical
model calculations have achieved a substantial agreement. This implies
that the hitherto developed models for the structure and dynamics of
sunspot umbrae seem to reflect essential features of the nature of
sunspots, notwithstanding the various simplifying assumptions. Recent
analytic calculations for simplified umbral models also confirmed
our model of a system of umbral resonators (Campos, 1989; Evans and
Roberts, 1990); Campos (1989) only argued in favour of an additional
resonator for pure Alfvén waves. The model provides an important tool
for sounding subphotospheric and atmospheric layers of sunspots and
possibly of other magnetized stellar atmospheres. Further observations
of oscillations should try to improve the spatial resolution on the
sun and the coverage of the data in space and time. Model calculations
should abandon the restrictive assumptions by considering nonlinear
and nonadiabatic processes such as radiative dissipations of waves and,
moreover, self-consistent calculations of wave propagation and non-LTE
line formation are needed to improve the diagnostics.
---------------------------------------------------------
Title: Das Sonnenobservatorium Einsteinturm in Potsdam. Erforschung
solarer Magnetfelder und der Physik von Sonnenflecken.
Authors: Staude, J.
1991S&W....30..505S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Dynamics of Quiescent Prominences -
I.A.U. COLL.117 - Hvar - Croatia
Authors: Ruzdjak, V.; Tandberg-Hanssen, E.; Staude, J.
1991AN....312..326R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Potsdam vector magnetograph: methodical experiences
and results.
Authors: Staude, J.; Hofmann, A.; Bachmann, G.
1991sopo.work...49S Altcode:
After a short historical introduction the instrumentation of the double
line vector magnetograph is described as it is working in connection
with the tower telescope of the Solar Observatory "Einsteinturm"
at Potsdam. Subsequently the authors outline the calibration of the
instrumental response to incident polarised light. The theoretical
calibration of deriving the magnetic field components from the
observed Stokes profiles is the next step. Finally the authors give a
few examples of vector magnetograms and outline some of their methods
for deriving further information from the magnetograms.
---------------------------------------------------------
Title: Solar Research at Potsdam: Papers on the Structure and Dynamics
of Sunspots.
Authors: Staude, J.
1991RvMA....4...69S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Energetic Phenomena on the Sun
Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.; Staude, J.
1990AN....311..416K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Asymptotics of High Order Differential Equations
Authors: Paris, R. B.; Wood, A. D.; Staude, J.
1990AN....311..425P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - the Physics of Solar Flares
Authors: Tandberg-Hanssen, E.; Emslie, A. G.; Staude, J.
1990AN....311..106T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Seismological diagnostics of sunspot umbral structure.
Authors: Staude, J.
1990PDHO....7..302S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Advances in - and Asteroseismology -
I.A.U. SYMP.123
Authors: Christensen-Dalsgaard, J.; Frandsen, S.; Staude, J.
1989AN....310..280C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Probing of Sunspot Umbral Structure by Oscillations
Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V.
1989ASIC..263..601Z Altcode: 1989ssg..conf..601Z
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Solar and Stellar Physics - 5TH European Solar
Meeting - Titisee / Schwarzwald - Germany - 1987APR27-30
Authors: Schroter, E. H.; Schussler, M.; Staude, J.
1989AN....310...66S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Possibilities and Problems of the Interpretation of Solar
Magnetograph Measurements and Applications to Flare-Active Regions
Authors: Staude, J.; Hofmann, A.
1989ESASP.285..123S Altcode: 1989rsp..conf..123S
The basic uncertainties encountered in the interpretation of
magnetograph data, and possibilities for deriving more reliable
information are reviewed. The problems are illustrated by describing
the data handling of a vector magnetograph. Examples of observed
flare-active regions demonstrate the state of information which can
be obtained.
---------------------------------------------------------
Title: Oscillations and the temperature minimum in sunspot umbrae
Authors: Locans, V.; Skerse, D.; Staude, J.; Zhugzhda, Iu. D.
1988A&A...204..263L Altcode:
Observed umbral oscillation with periods of 2 - 3 min can be explained
by slow-mode longitudinal magnetoatmospheric waves which are partly
trapped in the umbral photosphere and chromosphere. Detailed numerical
calculations for such a resonator in semi-empirical model atmospheres
predict details of umbral oscillations which, after comparison with
observed data, provide new information on the atmospheric structure. The
results support arguments in favour of a low value of the temperature
minimum (≤3000K) in the dark parts of umbrae, while the oscillations
are deteriorated in bright umbral structures such as dots or light
bridges.
---------------------------------------------------------
Title: A two-component working model for the atmosphere of a large
sunspot umbra
Authors: Obridko, V. N.; Staude, J.
1988A&A...189..232O Altcode:
A two-component working model for the atmosphere of the umbra of a
typical large sunspot is proposed which represents an improvement
over the earlier Wroclaw-Ondrejov sunspot model. The main component
is assumed to consist of cold matter at photospheric levels, a thin
chromosphere, a shallow transition region, and a deep-set corona. The
secondary component in the model has a volume filling factor of
5-10 percent at all heights and is suggested to consist of thin
fine-structure elements which are elongated parallel to the magnetic
field. The present model is able to account for the basic features of
sunspot observations at frequencies from X-rays up to microwaves.
---------------------------------------------------------
Title: Oscillations and waves in sunspots.
Authors: Staude, J.; Zhugzhda, Iu. D.; Locans, V.
1987PAICz..66..161S Altcode: 1987eram....1..161S
The authors review the basic features of oscillations observed at
different height levels in the sunspot atmosphere, moreover, various
possibilities for a theoretical interpretation are discussed.
---------------------------------------------------------
Title: The interpretation of oscillations in sunspot umbrae
Authors: Zhugzhda, Iu. D.; Locans, V.; Staude, J.
1987AN....308..257Z Altcode:
Possibilities for an interpretation of oscillations observed
in several period bands (3 min, 5 min, 20 min) and at different
heights in sunspot umbrae are reviewed. At subphotospheric depths
two independent resonators are acting: a resonator for slow,
quasi-transverse waves which can explain the lifetimes of bright
umbral dots (greater than or equal to 20 sec), and a resonator for fast
(acoustic), quasi-longitudinal waves which could result in the 5-min
oscillations. The acoustic resonator strongly couples with the slow-mode
longitudinal resonator at photospheric and chromospheric heights, the
latter producing the resonance peaks in the 3-min period band. The whole
scheme of resonance levels generalizes and corroborates a chromospheric
resonator model earlier proposed by the present authors. Comparisons
with alternative models and recent measurements show that the present
model most naturally explains the majority of observed data.
---------------------------------------------------------
Title: Electric current density in the sunspot photosphere derived
from vector magnetograms.
Authors: Hofmann, A.; Staude, J.
1987PAICz..66..105H Altcode: 1987eram....1..105H
The authors present observational results from which they determine
azimuthal currents flowing across the magnetic field.
---------------------------------------------------------
Title: Models of the solar atmosphere above sunspots
Authors: Staude, J.
1986CoSka..15..299S Altcode:
The "Wroclaw-Ondřejov sunspot model", together with its recent
improvements, provides a unified working model based on self-consistent
physical assumptions for a large of heights from the deepest
photospheric levels up to the lower corona. Using the WOSM together
with emission models developed for various wavelength regions, the
theoretically predicted emissions have been beautifully checked by
comparison with new observed data.
---------------------------------------------------------
Title: Spektroskopische Untersuchungen am Einsteinturm: Zur Physik
der Korona und der Sonnenflecken.
Authors: Staude, J.
1986Stern..62..109S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Investigation of the large preceding spot of AR 2779 from
SMM data
Authors: Siarkowski, M.; Jakimiec, J.; Staude, J.
1986CoSka..15..111S Altcode:
Complex data from the SMM spacecraft (UVSP and XRP/FCS) have been
used to investigate the structure and dynamics of the large p spot
of the active region NOAA 2779 from November 1980. The spot shows an
inhomogeneous structure characterized by a light bridge. In comparison
with the darkest photospheric umbral cores the light bridge is
bright in the photosphere and the transition region, but darker in the
chromosphere. In the transition region the authors found upward motions
above the umbra, but downward motions in the light bridge. Compared to
the spot's surroundings the Ly-α emission is stronger above the umbra
up to a factor of 3, but its spatial distribution is more inhomogeneous
than the photospheric emission.
---------------------------------------------------------
Title: Oscillations in the chromosphere and transition region above
sunspot umbrae - A photospheric or a chromospheric resonator?
Authors: Zhugzhda, Ia. D.; Locans, V.; Staude, J.
1985A&A...143..201Z Altcode:
A model for a chromospheric resonator for slow waves is proposed,
and its basic features are compared with those of the model for a
photospheric resonator for fast waves, proposed by Thomas and Scheuer
(1982), (TS). Moreover, the model predictions are tested for agreement
with recent observations of umbral oscillations. The observations in
the umbral chromosphere and transition region are in agreement with the
model presented but are difficult to reconcile with the TS model. This
conclusion does not exclude the possibility that a TS-type photospheric
resonator is excited as well. Finally, necessary improvements in the
existing simplified theories are outlined.
---------------------------------------------------------
Title: On the inhomogeneous structure of the chromosphere-corona
transition region above sunspot umbrae
Authors: Staude, J.
1985AN....306..197S Altcode:
Recent multiple wavelength observations of sunspot umbrae are
explained within the framework of an inhomogeneous, two-component
model of the structure of the umbral transition region, the
Wroclaw-Ondrejov model. Simple analytical expressions for the
atmospheric structure in each component, and in the lower corona,
are derived and the free parameters were fitted to observations of
EUV emission line intensities. It is shown that the main component of
the umbral transition has a shallow transition region and a deep set
corona. The second 'active' component displayed a large transition
region embedded in the main coronal component.The spatial filling
factor of the active component was about 5-10 percent in sunspots having
bright EUV plumes. For sunspots without bright EUV plumes, the spatial
filling factor was more than ten times smaller. The EUV emission line
intensities are compared to temperature measurements in both quiet
and active sunspot regions and the results are discussed in detail.
---------------------------------------------------------
Title: Interpretation of Oscillations in Ultraviolet Lines Observed
above Sunspot Umbrae
Authors: Staude, J.; Zhugzhda, Iu. D.; Locans, V.
1985SoPh...95...37S Altcode:
Our theory of a resonator for slow magneto-atmospheric waves in the
chromosphere of a sunspot umbra has been used to check different models
of the structure of the chromosphere and transition region. Oscillations
of velocity and intensity in CIV, SiIV, and OIV lines observed by
Gurman et al. (1982) on the SMM spacecraft have been compared with
the calculated oscillations. The observed spectrum of resonant
peaks could well be explained by a gradient model of the umbral
chromosphere. Different assumptions concerning the structure of the
transition region do not influence the calculated resonance periods, but
the amplitudes and phases of oscillations are modified. There is strong
evidence for a concentration of the observed oscillations in cold fine
structure elements of the transition region, even if the filling factor
of such elements is very small (some few percent). Isothermal rather
than adiabatic oscillations in the cold elements should be assumed
in order to explain the observed fluctuations of line intensity; the
relative amplitudes of pressure oscillations in the hot main component
with a steep gradient of temperature are too small to explain the
observed intensity fluctuations.
---------------------------------------------------------
Title: The Atmosphere of a Sunspot Based on Observations in the
X-Ray Extreme Ultraviolet Optical and Radio Ranges
Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
1984SvA....28..557S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The atmosphere of a sunspot based on observations in the X-ray,
extreme ultraviolet, optical, and radio ranges
Authors: Staude, J.; Furstenberg, F.; Hildebrandt, J.; Kruger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
1984AZh....61..956S Altcode:
A model of the solar atmosphere above a sunspot umbra is developed on
the basis of published X-ray, EUV, optical, and radio observations,
summarizing the findings of working conferences held at Wroclaw in
November-December 1979 (Bromboszcz et al. 1981) and at Ondrejov in
September-October 1981 (Bromboszcz et al., 1982). A lower-chromosphere
model like that of Teplitskaya et al. (1977 and 1978) is extended
upward by applying a strong temperature gradient, with T = 40,000 K
and n(e) = 4 x 10 to the 10th/cu cm at z = 2000 km above the umbral
chromosphere. At z = 3000-5000 km, cool loops with T = (1-100) x 10
to the 4th k are surrounded by hot (1.8 x 10 to the 6th K) coronal
matter with a narrow transition layer and n(e) = 5 x 10 to the 8th/cu
cm which occupies 0.8-0.9 of the total volume.
---------------------------------------------------------
Title: A Model of the Oscillations in the Chromosphere and Transition
Region above Sunspot Umbrae
Authors: Zhugzhda, Iu. D.; Staude, J.; Locans, V.
1984SoPh...91..219Z Altcode:
In an earlier paper (Solar Phys.82, 369) the present authors proposed
a model for the interpretation of velocity and intensity oscillations
with periods between 2 and 3 minutes observed above umbrae. The model
explains the oscillations by the resonant transmission of slow-mode
magnetic-acoustic waves which are semi-trapped in a chromospheric
cavity. In this way we get an independent method of checking
semi-empirical models of umbral atmospheres.
---------------------------------------------------------
Title: A Model of the Oscillations in the Chromosphere and Transition
Region above Sunspot Umbrae
Authors: Zugzda, Y. D.; Staude, J.; Locans, V.
1984AN....305..236Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ein Modell der Oszillationen der Chromosphäre und
Übergangsregioh über Sonnenfleckenumbrae
Authors: Žugžda, Y. D.; Staude, J.; Locans, V.
1984AN....305Q.236Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Model of the Oscillations in the Chromosphere and
Authors: Žugžda, Y. D.; Staude, J.; Locans, V.
1984AN....305R.236Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A working model of sunspot structure in photosphere,
chromosphere and corona, derived from X-ray, EUV, optical and radio
observations
Authors: Staude, J.; Hildebrandt, J.; Fuerstenberg, F.; Krueger,
A.; Jakimiec, J.; Obridko, V. N.; Siarkowski, M.; Sylwester, B.;
Sylwester, J.
1983AcA....33..441S Altcode:
The presented sunspot model consists of several parts which have been
consistently put together: the umbral model describing the spatial
distribution of thermodynamic quantities up to the transition region as
derived from EUV and optical observations, the magnetic field model,
the model of X-ray emission, and the S-component emission model. The
model assumptions have been tested and corroborated by recently
published observations with high spatial resolution obtained in the
X-ray and EUV spectral range from Skylab, HRTS, and SMM, at centimeter
wavelengths from RATAN, VLA, and WSRT, and by ground-based magnetograms.
---------------------------------------------------------
Title: A Model of the Oscillations in the Chromosphere and Transition
Region Above Sunspot Umbrae
Authors: Zhugzhda, Y. D.; Staude, J.; Locans, V.
1983PDHO....5..451Z Altcode: 1984PDHO....5..451Z
In an earlier paper the authors proposed a model for the interpretation
of velocity and intensity oscillations with periods between 2 and 3
minutes observed above umbrae. The oscillations are explained by the
resonant transmission of slow mode magneto-acoustic waves which are
semi-trapped in a chromospheric cavity. The model has now been improved
by more detailed calculations and corroborated by recently published
observations: The calculations are in good agreement with (1) the
height dependence of the observed phase difference between velocity
and intensity oscillations, and with (2) the frequency spectrum of
oscillations in the transition region above sunspots observed on the
SMM spacecraft during the SMY.
---------------------------------------------------------
Title: Results of vector magnetographic measurements in the active
region SD 228/229 on 15 July 1982.
Authors: Bachmann, G.; Hofmann, A.; Staude, J.
1983PDHO....5..369B Altcode: 1984PDHO....5..369B
The authors present measurements of vector magnetic fields in an active
region of 15 July 1982 obtained with the new code-impulse magnetograph
working in the wing of Fe I 5250 line. Linear polarization down to
0.004 corresponding to transverse magnetic fields of about 150 G has
been taken into account. The direction of the transverse magnetic
fields is compared with dark chromospheric structure elements in Hα
filtergrams and with the contours of sunspots obtained by means of
a heliogram. For long-lived stable structures, such as the central
part of the zero-line filament or systems of fibrils and threads,
the correspondence is good, in contrast to short-lived. In regions
with weak magnetic fields no correspondence is found.
---------------------------------------------------------
Title: Seismology of Sunspot Atmospheres
Authors: Zhugzhda, Iu. D.; Locans, V.; Staude, J.
1983SoPh...82..369Z Altcode: 1983IAUCo..66..369Z
The present work deals with the theory of oscillations with periods
of about 3 min observed in the chromosphere above sunspot umbrae. The
model of these oscillations (slow mode magneto-acoustic waves trapped
in a chromospheric resonant cavity) provides an independent method of
checking empirical models of the chromosphere above sunspots.
---------------------------------------------------------
Title: Beobachtungen an neuen bipolaren Nebeln
Authors: Staude, J.; Neckel, Th.
1983MitAG..60..322S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A unified working model for the atmospheric structure of
large sunspot umbrae
Authors: Staude, J.
1981A&A...100..284S Altcode:
Horizontally averaged working models are derived for both the umbra
of a large stable sunspot and the mean undisturbed environment
for reference. It is noted that these models extend on a common
geometrical height scale from subphotospheric layers to the base of
the transition layer between chromosphere and corona; they are based
on uniform and self-consistent physical assumptions for all layers
and are able to explain the basic features of many observations at
different wavelengths, including recent data from space. The present
sunspot model furnishes the lower boundary condition for an attempt
to model the transition layer and lower corona above large umbrae.
---------------------------------------------------------
Title: Evidence for an X-Type Neutral Sheet Producing Chromospheric
Activity
Authors: Seehafer, N.; Staude, J.
1980SoPh...67..121S Altcode:
Force-free magnetic field extrapolation for region McMath 12417 on 4
July 1973 corroborates a suggestion by Roy and Michalitsanos (1974):
A large moving magnetic feature presses together opposite fluxes to
form an X-type neutral sheet; the supposed geometry of the field as
derived from chromospheric activity (subflares, ejections) is confirmed
by the calculated lines of force.
---------------------------------------------------------
Title: Problems concerning the calibration and interpretation of
magnetograph observations in the solar photosphere and chromosphere
Authors: Staude, J.
1980tpmb.meet...58S Altcode:
The paper presents procedures for the calibration of solar photoelectric
magnetographs, which relate to the practical calibration of the
primarily measured state of polarization in a magneto-sensitive line
and to the theoretical derivation of magnetic field parameters from
the polarization measurements. Disturbing influences are discussed
including external disturbances such as stray light and instrumental
polarization, saturation effects, and fine structures of the solar
atmosphere, of velocity and magnetic fields. Problems in line formation
theory are also discussed.
---------------------------------------------------------
Title: Force-free Magnetic Field Extrapolation for the Complex
Sunspot Group of August 1972
Authors: Seehafer, N.; Staude, J.
1979AN....300..151S Altcode:
A method for theoretical extrapolation of photospheric longitudinal
magnetograms to higher levels for force-free magnetic fields is
presented. The method has been used to calculate the magnetic field
vector and lines of force in the flare active region of August
1972. Calculated fields are compared with other observations such
as structures in H-alpha. Results of August 3 show that the loop
prominence systems observed during the flares of August 2 and 4
are represented by a force field with a positive value of alpha,
rather than a current-free field. The extractable energy supply of
this force-free field is of the order of maximum flare demand (10 to
the 32nd erg); the height dependence of the magnetic field strengths
agrees with that from radio and X-ray estimates. Similar results are
obtained for the August 7 magnetic field structure. It is suggested
that the mean magnetic field structure of the active region may be
represented by a force-free field much better than by a potential field.
---------------------------------------------------------
Title: Magnetfelder der Sonne und der Sterne. I.
Authors: Scholz, G.; Staude, J.
1979Stern..55...65S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetfelder der Sonne und der Sterne. II.
Authors: Scholz, G.; Staude, J.
1979Stern..55..206S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Models of Heat Flux in the Subphotospheric Layers of Sunspots
and the Interpretation of Umbral Granulation
Authors: Staude, J.
1978BAICz..29...71S Altcode:
Different models of heat flux in the normal convective zone (deep and
shallow reference models) and in an umbral flux tube in magnetostatic
equilibrium are investigated by numerical calculations. Recent
observations of umbral granulation are explained by residual cellular
convection which still transfers a small fraction of energy to the
subphotospheric flux tube. The models deduced from special assumptions
concerning the reduced convective heat flux are also compatible
with other recent observations such as superadiabatic temperature
gradients in the deep umbral photosphere, and with results from
nonlinear calculations considering effects of interaction between
the magnetic field and turbulent convection. Some criteria for the
inhibiting effect of the magnetic field on convection, derived from
linear theories seem to be too strong.
---------------------------------------------------------
Title: Influence of scintillation and scattering of light on
magnetographic measurements.
Authors: Bachmann, G.; Staude, J.
1977IzKry..56..148B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Influence of the instrumental polarization on magnetographic
observations.
Authors: Eger, F. W.; Staude, J.
1977IzKry..56..149E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Investigations in the field of magnetographic observations
at the Einstein Solar Observatory in Potsdam.
Authors: Staude, J.
1977IzKry..56R.205S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Force-free magnetic field extrapolation for the complex
sunspot group of August 1972.
Authors: Seehafer, N.; Staude, J.
1977PDHO....3..137S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Light Variations of AP Stars: 10-COLOUR Photometry and its
Interpretation by a Magnetic SPOT Model
Authors: Schöneich, W.; Staude, J.
1976paps.coll..387S Altcode: 1976IAUCo..32..387S
No abstract at ADS
---------------------------------------------------------
Title: Models of the Solar Convective Zone: The Influence of Free
Parameters in Mixing Length Theories
Authors: Staude, J.
1976BAICz..27..365S Altcode:
Using Opik's (1950) mixing-length theory of convection, Mullan (1971)
obtained extremely shallow models of the solar convection zone whose
structure is incompatible with current conceptions of solar physics
in general and with the deep models resulting from the Boehm-Vitense
theory (1958) in particular. In the present paper, the Opik theory
is generalized to take into account an anisotropy of small-scale
turbulence; this version is then compared with the Boehm-Vitense
theory. Neglecting a thin surface layer where radiative losses are
important, a simple analytic comparison alone shows that both theories
yield the same results, if the free parameters are chosen consistent
with each other. To study the influence of the different parameters, a
series of solar convection-zone models has been calculated numerically,
assuming an empirical photospheric model as the upper boundary condition
and various values of the parameters in both theories.
---------------------------------------------------------
Title: Einige Methoden und Ergebnisse der modernen Sonnenforschung.
Authors: Staude, J.
1976AsSch..13..101S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Methodical improvements of magnetographic measurements
Authors: Bachmann, G.; Künzel, H.; Pflug, K.; Staude, J.
1976CoSka...6..395B Altcode:
No abstract at ADS
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Title: Model calculations concerning the subphotospheric layers of
stable sunspots.
Authors: Staude, J.
1976fsp..conf...63S Altcode:
No abstract at ADS
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Title: Methodical improvement of magnetographic measurements.
Authors: Bachmann, G.; Künzel, H.; Pflug, K.; Staude, J.
1976str..book..395B Altcode:
No abstract at ADS
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Title: The Anomalous Splitting of the π-component of a ZEEMAN
Triplet in Sunspot Umbrae and Suggestions for its Interpretation
Authors: Kuenzel, H.; Staude, J.
1975AN....296..171K Altcode:
An investigation of the anomalous splitting of the pi-component
of the line Fe I at 6302.5 A in umbrae is conducted, taking into
account Zeeman spectrograms from 1200 sunspots of the maximum year
1957. Disturbing effects are examined, giving attention to blends,
stray light, and instrumental polarization. The observations appear to
show a preponderance of left-hand screws of the magnetic field vector
H in most umbrae independent of the polarity and the solar hemisphere.
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Title: Mie- und Rayleigh-Streuung in der Erdatmosphäre
Authors: Staude, J.
1974MitAG..35Q.267S Altcode:
No abstract at ADS
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Title: Possibilities regarding the determination of the structure
of solar magnetic fields outside the photosphere
Authors: Staude, J.
1974ZMete..24..214S Altcode:
Physically well founded predictions of the solar activity and
associated terrestrial effects require better, i.e. more detailed,
knowledge of magnetic fields in the solar atmosphere, the chromosphere
in particular. A critical review on methods of observing the solar
magnetic fields is followed by a discussion of approaches of how to
extrapolate, theoretically, into higher layers of the solar atmosphere
the magnetic fields measured rather precisely in the photosphere. The
force-free magnetic fields are given particular consideration;
possibilities of testing by observations the theoretically calculated
fields are described. Finally, the review contains proposals for
further investigations.
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Title: Die Frühjahrstagung in Garching.
Authors: Staude, J.
1974S&W....13..111S Altcode:
No abstract at ADS
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Title: On the interpretation of some peculiarities observed in
zeeman-split line contours in sunspots
Authors: Staude, Jürgen
1973SoPh...32..403S Altcode:
Strong line wings and the V-reversal in umbral countours of Fe I 6302.5
Å and similar lines have been explained earlier by inhomogeneous
magnetic models. It is shown that both effects may also be explained
assuming a homogeneous magnetic field and homogeneous umbral model
atmospheres.
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Title: Non-LTE Line Formation in a Magnetic Field. II: The Influence
of Non-Coherent Scattering on Line Contours
Authors: Domke, H.; Staude, J.
1973SoPh...31..291D Altcode:
Theoretical line contours calculated for fixed values of the line
constants and a given model atmosphere show an increase of the
Stokes parameters Q, U, and V but a decrease of I if the portion of
non-coherent scattering increases. These effects increase from the
centre of the solar disk to the limb. The action of scattering may be
approximately simulated in LTE contours by increasing the gradient
of the source function and fitting in this way theoretical contours
to observed ones. There remains, however, the effect of V-reversal
near the line core, which is caused by anomalous dispersion and is
abnormally increased by scattering.
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Title: Non-LTE Line Formation in a Magnetic Field. I: Non-Coherent
Scattering and True Absorption
Authors: Domke, H.; Staude, J.
1973SoPh...31..279D Altcode:
The formation of a Zeeman-multiplet by noncoherent scattering and true
absorption in a Milne-Eddington atmosphere is considered assuming a
homogeneous magnetic field and complete depolarization of the atomic
line levels. The transfer equation for the Stokes parameters is
transformed into a scalar integral equation of the Wiener-Hopf type
which is solved by Sobolev's method in closed form. The influence of
the magnetic field on the mean scattering number in an infinite medium
is discussed.
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Title: Flächenpolarimetrie der südlichen Milchstraße
Authors: Staude, J.; Wolf, K.; Schmidt, Th.
1973MitAG..34...95S Altcode:
No abstract at ADS
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Title: A Surface Polarization Survey of the Milky way and the Zodiacal
Light (presented by th. Schmidt)
Authors: Staude, J.; Wolf, K.; Schmidt, Th.
1973IAUS...52..139S Altcode:
No abstract at ADS
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Title: About the influence of a magnetic field on the model atmosphere
of a magnetic star.
Authors: Staude, J.
1973AN....294..113S Altcode:
No abstract at ADS
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Title: About the Influence of a Magnetic Field on the Model Atmosphere
of a Magnetic Star
Authors: Staude, J.
1972AN....294..113S Altcode:
No abstract at ADS
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Title: Circular Polarisation Measurements of the Zodiacal Light
Authors: Staude, J.; Schmidt, Th.
1972A&A....20..163S Altcode:
Key words: circular polarisation - zodiacal light Summary. The circular
polarisation component of the zodiacal light is shown to be zero within
the accuracy of l 10/00 (p. p. thousands).
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Title: On the Mean Depth of Line Formation in a Magnetic Field
Authors: Staude, Jürgen
1972SoPh...24..255S Altcode:
Probability interpretation of radiative transfer is used to calculate
the contribution of different layers of the solar atmosphere to the
emergent intensity. Generally the mean depths of line formation increase
with increasing intensity; this is valid also for arbitrarily polarized
constituents of a line formed in a magnetic field.
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Title: Flächenpolarimetrie des südlichen Gesamthimmels
Authors: Wolf, K.; Staude, J.
1972MitAG..31..167W Altcode:
No abstract at ADS
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Title: Einige Methoden und Ergebnisse der modernen Sonnenforschung.
Authors: Staude, J.
1972AsSch...9...90S Altcode:
No abstract at ADS
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Title: A Generalized Analytic Solution to the Equations of Transfer
in a Magnetic Field
Authors: Staude, Jürgen
1971SoPh...18...22S Altcode:
No abstract at ADS
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Title: Remarks on Some Recent Papers Concerning Line Formation in
a Magnetic Field
Authors: Staude, Jürgen
1971SoPh...18...24S Altcode:
No abstract at ADS
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Title: On apparent differences in magnetic field strengths measured
from Zeeman splittings of molecular lines and Fe i λ 5250.2 Å
Authors: Staude, Jürgen
1971SoPh...17..331S Altcode:
No abstract at ADS
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Title: Line Formation in a Magnetic Field and the Interpretation of
Magnetographic Measurements. III: Calculations for Different Spot
Models and Arbitrary Depth Dependence of the Magnetic Field Vector
Authors: Staude, J.
1970SoPh...15..102S Altcode:
The strong temperature dependence of the line FeIλ 5250.2 Ā has been
studied by calculating line contours and magnetographic calibration
curves for different spot models and the BCA. Line contours calculated
for arbitrary depth dependence of the magnetic field vector show
depolarization effects within the Zeeman components for transversal
fields with variable direction and changes of the observed plane of
polarization if anomalous dispersion is taken into account.
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Title: Europium and Lanthanum in Sunspot and in the Undisturbed
Photosphere
Authors: Bachmann, G.; Pflug, K.; Staude, J.
1970SoPh...15..113B Altcode:
Line profiles of EUIIλ4129.7 Å and LaIIλ4086.7 Å were observed
photoelectrically and photographically in the photosphere and
within sunspots and after correction were compared with calculated
profiles. The observed large hyperfine structure broadening and
isotope shift of λ4129.7 Å confirm the Eu origin of this line and
suggest a larger Eu abundance than that recently published by Grevesse
and Blanquet (1969). The line profiles within the spot may be well
represented by means of the spot model of Hénoux (1969), while older
spot models are not able to do it. An abundance difference between
spot and photosphere has not been observed.
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Title: Line Formation in a Magnetic Field and the Interpretation of
Magnetographic Measurements. II: The Influence of Different Atmosphere
Models and of a Magnetic Field Gradient
Authors: Staude, J.
1970SoPh...12...84S Altcode:
The solution of the equations of transfer for the Stokes parameters
in a magnetic field given by Unno (1956) has been generalized for a
non-linear source function. Model calculations have been carried out
for empiric atmosphere models of the photosphere and spots both for
homogeneous magnetic fields and for a field strength gradient. Their
influence on line contours and magnetographic calibration curves had
been studied for the line FeI λ5250.2 Å.
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Title: About the Influence of Inhomogeneities of Magnetic Fields on
Line Contours and Magnetographic Measurements
Authors: Staude, J.
1969SoPh....8..264S Altcode:
The discrepancies between theoretical and experimental calibration
curves for solar magnetographs (Severny, 1967) may be explained by
horizontal inhomogeneities of the observed but not resolved magnetic
field region. Using the Unno solution of the equations of transfer
simple two-stream models have been constructed. For the more complicated
case of a depth dependence of the magnetic field vector it is shown
assuming pure absorption and permitting arbitrary variations of the
magnetic field vector and the atmosphere model with depth that a
solution of the equations of transfer may be found by iteration.
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Title: Influence of inhomogeneities of magnetic fields on line
contours and magnetographic measurements.
Authors: Staude, J.
1969VeGG...13..123S Altcode:
No abstract at ADS