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Author name code: grossmann-doerth
ADS astronomy entries on 2022-09-14
author:"Grossmann-Doerth, Ulrich"
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Title: Strong Stokes V asymmetries of photospheric spectral lines:
What can they tell us about the magnetic field structure?
Authors: Grossmann-Doerth, U.; Schüssler, M.; Sigwarth, M.;
Steiner, O.
2000A&A...357..351G Altcode:
In an attempt to identify the mechanism responsible for the extremely
asymmetric Stokes V profiles which were recently observed we analyzed
several simple atmospheric configurations with separated layers of mass
flow and magnetic field. We found that under appropriate conditions
the models are capable of producing the observed one-lobe profiles.
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Title: Understanding Small Solar Magnetic Elements: Comparing Models
and Observations
Authors: Leka, K. D.; Steiner, O.; Grossmann-Doerth, U.
1999AAS...194.5507L Altcode: 1999BAAS...31R.911L
We perform direct comparisons of high-resolution spectropolarimetric
observations with a full MHD model of the magnetized solar
atmosphere. In this manner we investigate the evolution and dynamics of
small magnetic elements by fully utilizing the diagnostics available
with Stokes spectropolarimetry, both computed and observed. The model
is a 2-D time-dependent numerical simulation of a small (~ 600 km
diameter) magnetic feature embedded in a non-magnetized atmosphere
(Steiner et al., 1998). At select time-steps, synthetic emergent
Stokes I and V profiles are computed using a polarized radiation
transfer code. The data consist of Stokes I and V spectra from the
Advanced Stokes Polarimeter for seventeen small magnetic elements
located near disk-center. For both the observed and computed Stokes
spectra, diagnostics are computed including the emergent continuum
intensity, V-crossing shift, and amplitude and area asymmetries of
the V-profile. We find that it is possible to differentiate between
salient processes occurring in the magnetic atmosphere (strong flows,
gradients, etc.) by their spectropolarimetric signature; from this,
we determine the dominant processes present in the observed magnetic
structures. The results are extremely encouraging. We find good
qualitative agreement between the amplitude and area asymmetries
and their spatial variation. Quantitatively, the agreement is
surprisingly good in many cases. While limitations exist for both
the model and observations, this stringent test allows us to comment
on the dynamics and possible evolutionary differences present in the
observed magnetic features. This work is funded in part by NSF grant
ATM-9710782. Reference: - Steiner, O., Grossmann-Doerth, U., Knolker,
M., Schussler, M.: 1998, ApJ 495, 468
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Title: The formation of extremely asymmetric Stokes V profiles
Authors: Steiner, O.; Grossmann-Doerth, U.; Schüssler, M.; Sigwarth,
M.
1999AGAb...15R..10S Altcode: 1999AGM....15..A11S
Recent polarimetric observations at high spatial resolution (<
1 arcsec) and with high polarimetric accuracy (noise of Stokes V/I_c
< 3 cdot 10^{-4}) have revealed that about 10% of all Stokes V
profiles of a quiet Sun region have an abnormal shape that strongly
deviates from the more common, nearly antisymmetric profiles. 35% of the
abnormal Stokes V profiles are of one-wing type, where the profile shows
essentially one lobe only. We show, that a strongly asymmetric Stokes
V profile can be obtained when the atmosphere, in which the profile
is formed, is divided into two or more layers of different magnetic,
flow, and thermal properties. A simple configuration of that kind
(sometimes referred to as magnetic canopy) consists of a layer of
plasma at rest with a magnetic field component parallel to the line
of sight, located on top of a field-free layer with downdraft. The
Stokes V asymmetry in this case sensitively depends on the position
of the layers interface and may assume values up to about 80%. An
asymmetry of nearly 100% (corresponding to a one-wing profile) is
obtained when the plasma below the magnetic canopy is relatively cool,
giving rise to the formation of a strong, redshifted spectral line in
the field-free plasma beneath the canopy. If the core of this line is
formed at lower temperature than the temperature of the canopy layer,
the red wing of the resulting Stokes V profile is driven into emission,
leading to a “pathological” V profile.
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Title: Convective intensification of solar surface magnetic fields:
results of numerical experiments
Authors: Grossmann-Doerth, U.; Schuessler, M.; Steiner, O.
1998A&A...337..928G Altcode:
The concentration of magnetic flux by convective flows in the solar
surface layers is studied by means of two-dimensional numerical
simulations with radiative transfer. We follow the evolution of an
initially homogeneous, vertical magnetic field, starting from an
evolved state of simulated solar granulation. The results of three
simulation runs with initial field strengths, B_0, of 100 G, 200 G,
and 400 G, respectively, are shown. In all cases, horizontal convective
flows rapidly sweep magnetic flux into the intergranular downflow
channels. The field is further amplified up to kilogauss values by
partial evacuation due to a strongly accelerated downflow within
the magnetic structure. The value of the field strength reached at
a given depth and the size of the flux concentrations grows with the
initial field strength (i.e., the amount of magnetic flux within the
computional box). In the case of B_0 = 400 G, the downflow within the
flux concentration becomes so strong that it `bounces' off the high
density plasma in the deeper layers; the resulting upflow leads to a
strong, upward moving shock and to the dispersal of the flux sheet after
a lifetime of about 200 s. In the cases with less magnetic flux (B_0 100
G, 200 G), the downflow is less vigorous and the flux concentrations
persist to the end of the simulation (about 5 minutes). Radiation
diagnostics in the continuum and in spectral lines predicts observable
signatures of the intensification process. The accelerated downflow
leads to a conspicuous Doppler shift and a negative area asymmetry of
Stokes V-profiles of spectral lines, while the intensification of the
magnetic field may be detectable through the `magnetic line ratio'
method in the visible and by direct Zeeman splitting of magnetically
sensitive lines in the infrared wavelength ranges.
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Title: Dynamical Interaction of Solar Magnetic Elements and Granular
Convection: Results of a Numerical Simulation
Authors: Steiner, O.; Grossmann-Doerth, U.; Knölker, M.; Schüssler,
M.
1998ApJ...495..468S Altcode:
Nonstationary convection in the solar photosphere and its
interaction with photospheric magnetic structures (flux sheets in
intergranular lanes) have been simulated using a numerical code
for two-dimensional MHD with radiative energy transfer. Dynamical
phenomena are identified in the simulations, which may contribute to
chromospheric and coronal heating. Among these are the bending and
horizontal displacement of a flux sheet by convective flows and the
excitation and propagation of shock waves both within and outside the
magnetic structure. Observational signatures of these phenomena are
derived from calculated Stokes profiles of Zeeman-sensitive spectral
lines. We suggest that the extended red wings of the observed Stokes
V profiles are due to downward coacceleration of magnetized material
in a turbulent boundary layer between the flux sheet and the strong
external downflow. Upward-propagating shocks in magnetic structures
should be detectable if a time resolution of about 10 s is achieved,
together with a spatial resolution that allows one to isolate individual
magnetic structures. Determination of the complicated internal dynamics
of magnetic elements requires observations with a spatial resolution
better than 100 km in the solar photosphere.
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Title: Observations of the quiet Sun's magnetic field.
Authors: Grossmann-Doerth, U.; Keller, C. U.; Schuessler, M.
1996A&A...315..610G Altcode:
The profiles of Stokes I and V of FeI 5247A, CrI 5247A, FeI 5250.2A and
Fe I 5250.6A have been measured in the quiet photosphere with ZIMPOL,
a new polarimeter, with very low noise level. The spatial resolution
element of about 1Mm was essentially determined by seeing. In about
15% of the observed area, the signal-to-noise ratio was sufficiently
large to determine the strength of the magnetic field and to derive
various properties of the Stokes V profiles (asymmetries, zero-crossing
shift and thermal line ratio). Our results show that, at least in this
fraction of area, the magnetic field in the quiet Sun is dominated by
strong flux concentrations which must be rather small. The data on the
Stokes V properties provide observational constraints for theoretical
models of flux concentrations.
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Title: Polarized Radiation Diagnostics of Magnetohydrodynamic Models
of the Solar Atmosphere
Authors: Steiner, O.; Grossmann-Doerth, U.; Schüssler, M.; Knölker,
M.
1996SoPh..164..223S Altcode:
Solar magnetic elements and their dynamical interaction with
the convective surface layers of the Sun are numerically
simulated. Radiation transfer in the photosphere is taken into
account. A simulation run over 18.5 minutes real time shows that the
granular flow is capable of moving and bending a magnetic flux sheet
(the magnetic element). At times it becomes inclined by up to 30°
with respect to the vertical around the level τ<SUB>5000</SUB> =
1 and it moves horizontally with a maximal velocity of 4 km/s. Shock
waves form outside and within the magnetic flux sheet. The latter
cause a distinctive signature in a time series of synthetic Stokes
V-profiles. Such shock events occur with a mean frequency of about
2.5 minutes. A time resolution of at least 10 seconds in Stokes V
recordings is needed to reveal an individual shock event by observation.
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Title: Convective intensification of photospheric magnetic fields.
Authors: Schüssler, M.; Grossmann-Doerth, U.; Steiner, O.; Knölker,
M.
1996AGAb...12...89S Altcode:
No abstract at ADS
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Title: Simulation of the Interaction of Convective Flow with Magnetic
Elements in the Solar Atmosphere.
Authors: Steiner, O.; Grossmann-Doerth, U.; Knoelker, M.; Schuessler,
M.
1995RvMA....8...81S Altcode:
No abstract at ADS
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Title: The deep layers of solar magnetic elements
Authors: Grossmann-Doerth, U.; Knoelker, M.; Schuessler, M.; Solanki,
S. K.
1994A&A...285..648G Altcode:
We compare self-consistent theoretical models of solar magnetic
flux sheets with spectropolarimetric observations of a solar plage
and a network region. Our observational diagnostics mainly provide
information on temperature and magnetic field of the deep photospheric
layers. They are used to constrain the two free parameters of the
models, viz. width and initial evacuation of the flux sheets. We find
that the width of flux sheets in the network is approximately 200 km,
while it is 300-350 km in an active plage. The flux sheets turn out
to be less evacuated than previously thought, so they have continuum
intensities close to unity. Since these are average values, however,
our results do not exclude the presence of either smaller and brighter
or larger and darker magnetic structures.
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Title: Height of formation of solar photospheric spectral lines
Authors: Grossmann-Doerth, U.
1994A&A...285.1012G Altcode:
The dependence of the line depression contribution functions of spectral
lines on the relevant line parameters in the solar photosphere is
investigated. It is shown how the formation height range varies
as function of excitation and ionization potential, line strength,
central wavelength and wavelength offset. Furthermore it is shown that
the type of contribution function used provides reliable information
on the depth where a given line - or part of the line - is sensitive
to atmospheric field quantities like, for example, the bulk velocity.
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Title: Solar Magnetic Elements: Models Compared with Observations
Authors: Grossmann-Doerth, U.; Knolker, M.; Schussler, M.; Solanki,
S. K.
1994ASPC...68...96G Altcode: 1994sare.conf...96G
No abstract at ADS
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Title: MHD simulations with adaptive mesh refinement
Authors: Steiner, O.; Grossmann-Doerth, U.; Knölker, M.; Schüssler,
M.
1994smf..conf..282S Altcode:
No abstract at ADS
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Title: Simulation of magneto-convection with radiative transfer
Authors: Steiner, O.; Grossmann-Doerth, U.; Knölker, M.; Schüssler,
M.
1994smf..conf..286S Altcode:
No abstract at ADS
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Title: Chromospheric fine structure revisited
Authors: Grossmann-Doerth, U.; Schmidt, W.
1992A&A...264..236G Altcode:
We obtained H-alpha spectra from both spicules at the limb and mottles
at disk center. We compare our results with data obtained by other
groups and derive two distributions of axial spicule velocity, one
based on limb, the other on disk observations. The two distributions
disagree. We conclude that our knowledge on the basic properties of
the chromospheric fine structure has not much improved in the last
two decades; it is still rather scanty.
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Title: Stokes Inversion in the Presence of Canopy-Like Structures
and Unresolved Flux-Tubes
Authors: Skumanich, A.; Grossmann-Doerth, U.; Lites, B. W.
1992AAS...180.1203S Altcode: 1992BAAS...24Q.748S
The issue of the Stokes polarization signature of canopy-like structures
and the inversion of the resulting Stokes profiles is considered for
a self-consistent flux tube (sheet) model. It is found that when the
`canopy' and its attendant current sheet have an optical thickness at
line center tau_0 <= 5, the intensity and net polarization profiles
become decoupled. An effective inversion strategy is to reduce or
eliminate the role of the intensity parameter. The Milne-Eddington
(ME) analytic inversion in current use is easily adapted for this
purpose. It is found that the use of a magnetic fill factor allows for
an approximate compensation for the presence of a field discontinuity
along the line of sight but a more accurate procedure is to restrict the
inversion to the net polarization profiles. In the case of sufficiently
thin canopies the ME inversion, when reduced to the Sears form, yields
fields within ~ 100 G of the true field. When the Stokes profiles
are averaged over the flux sheet to simulate the effects of limited
angular resolution, the fill factor strategy yields an accurate measure
of both the axial field and the width of the flux sheet at tau_0 =~
1 for observing angles <= 35(deg) to the normal. For larger angles,
opacity shielding occurs and reduced fields are derived.
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Title: MHD simulations with adaptive mesh refinement.
Authors: Steiner, O.; Grossmann-Doerth, U.; Knölker, M.; Schüssler,
M.
1992AGAb....7..213S Altcode:
No abstract at ADS
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Title: The effect of non-linear oscillations in magnetic flux tubes
on Stokes V asymmetry
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1991A&A...249..239G Altcode:
The present knowledge on, and interpretation of, the asymmetry of
Stokes V of spectral lines thought to be formed in and around magnetic
flux tubes is reviewed. Crude models of nonlinear oscillations in the
flux tube were investigated in order to explain the observed values
of Stokes V amplitude and area asymmetry. It was found that flux tube
models with quasi-oscillatory motions, consisting of a slow upflow
and a rapid downflow in the magnetic region, as well as a downflow
in the nonmagnetic surroundings, may reproduce the observations,
both asymmetries and zero-crossing shift of Stokes V.
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Title: Solar magnetic elements: results of MHD simulations.
Authors: Grossmann-Doerth, U.; Knölker, M.; Schüssler, M.;
Weisshaar, E.
1991AGAb....6...31G Altcode:
No abstract at ADS
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Title: Stokes profile formation heights in solar magnetic flux tubes.
Authors: Larson, B.; Solanki, S. K.; Grossmann-Doerth, U.
1991sopo.work..479L Altcode:
The formation heights of magnetically split lines in small solar
magnetic flux tubes are investigated. In particular, the authors
are interested in how the heights of formation depend on different
flux tube parameters, like magnetic field strength, temperature and
temperature gradient, as well as on line parameters, such as line
strength, excitation potential and ionization stage.
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Title: Some developments in the theory of magnetic flux concentrations
in the solar atmosphere
Authors: Knoelker, M.; Grossmann-Doerth, U.; Schuessler, M.;
Weisshaar, E.
1991AdSpR..11e.285K Altcode: 1991AdSpR..11..285K
Most of the magnetic flux in the solar photosphere is concentrated
in small-scale structures of large field strength, called magnetic
elements. We discuss briefly the observationally determined properties
of magnetic elements and the theoretical concepts for the origin of
magnetic flux filamentation and concentration. New results of model
calculations for 2D magnetic flux sheets on the basis of numerical
simulation of the compressible MHD equations including a full (grey)
radiative transfer are presented. Synthetic Stokes profiles of spectral
lines and continuum intensity distributions serve to compare the
theoretical models with observational data. Among the key results are:
(1) The upper layers of the magnetic structure become hotter than
the environment due to radiative illumination effects; (2) a strong
convective flow evolves with horizontal velocity of 2 km/s towards the
flux sheet and a narrow “downflow jet” with velocity up to 6 km/s
adjacent to the magnetic structure; (3) both flux sheet and non-magnetic
environment oscillate with a period around 5 minutes. Comparison with
observed properties of solar magnetic elements reveals: (4) Calculated
and semi-empirical temperature profiles as function of height in the
photosphere are in reasonable agreement; (5) the calculated velocity
field around flux concentrations explains the area asymmetry of the
observed Stokes V-profiles including their center-limb variation; (6)
the calculated continuum intensity of a flux sheet model is compatible
with the values inferred from high spatial resolution observations
of bright points at solar disk center; (7) the observed center-limb
variation of facular contrast at low or medium spatial resolution is
reproduced by arranging calculated flux sheets in arrays. We stress the
importance of MHD simulation models for the analysis and interpretation
of data from future facilities for high spatial resolution observations
like OSL and LEST.
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Title: The influence of vertical magnetic field gradients on the
measured field strength and filling factor in late-type stars.
Authors: Grossmann-Doerth, U.; Solanki, S. K.
1990A&A...238..279G Altcode:
The influence of a vertical gradient of the magnetic field in late type
stars on the measurement of magnetic field strengths and filling factors
is studied. Line profiles and contribution functions of spectral lines
with large Lande factors are calculated in model stellar atmospheres in
the presence of a magnetic field with a vertical gradient. It is found
that the four lines, which have often been used to measure solar and
stellar magnetic fields in the past, are formed at heights sufficiently
different to account for differences in apparent field strength of up
to 1000 G if the fields are assumed to be similarly structured as in
the sun. Thus it is concluded that the vertical gradient of the field
may contribute to a good part of the discrepancy between different
published measurements of field strength and filling factor in the K2
dwarf Epsilon-Eri.
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Title: Model calculations of magnetic flux concentrations in the
solar photosphere.
Authors: Grossmann-Doerth, U.; Knölker, M.; Schüssler, M.;
Weisshaar, E.
1990AGAb....5...44G Altcode:
No abstract at ADS
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Title: At what heights are spectral lines formed in solar magnetic
flux tubes?
Authors: Larsson, B.; Solanki, S.; Grossmann-Doerth, U.
1990nba..meet..169L Altcode: 1990taco.conf..169L
Illustrative examples, taken from a study of the formation of
magnetically split lines in solar magnetic flux tubes, are presented. A
particular interest is: in how the heights of formation depend on
different flux tube parameters, like the magnetic field strength, the
temperature and temperature gradient, as well as on line parameters,
such as line strength, excitation potential and ionization stage. The
result should help to improve the construction of empirical models
of magnetic features and provide a new understanding of the spectral
diagnostics used in the study of the solar magnetic field.
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Title: Stokes V asymmetry and shift of spectral lines
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1989A&A...221..338G Altcode:
Further evidence is given for the interpretation of the observed
unshifted and asymmetric Stokes V profiles in the solar atmosphere
in terms of a magnetic flux concentration expanding with height and
surrounded by a downflow. A general proof is given that a V profile
originating in an atmosphere in which magnetic field and flow are
spatially separated along the line of sight has a zero-crossing
wavelength which is unshifted with respect to the rest wavelength of
the line center. Heuristic considerations for the dependence of the
asymmetry of Stokes V on Zeeman shift, Doppler shift, line width,
and strength are described and confirmed by exploratory calculations.
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Title: Observational aspects of magnetic flux sheet models
Authors: Grossmann-Doerth, U.; Knölker, M.; Schüssler, M.;
Weisshaar, E.
1989hsrs.conf..427G Altcode:
No abstract at ADS
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Title: Models of Magnetic Flux Sheets
Authors: Grossmann-Doerth, U.; Knölker, M.; Schüssler, M.;
Weisshaar, E.
1989ASIC..263..481G Altcode: 1989ssg..conf..481G
No abstract at ADS
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Title: Unshifted, asymmetric Stokes V-profiles - Possible solution
of a riddle
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1988A&A...206L..37G Altcode:
We show that Stokes V-profiles originating in an atmosphere
in which a magnetic field and a systematic velocity field are
spatially separated along the line of sight are asymmetric with
unshifted zero-crossings. Such a configuration is probably realized
in the peripheral parts of magnetic flux concentrations in the solar
photosphere: Since the magnetic field flares out with height, the line
of sight traverses both a static magnetic region and a downdraft in
the non-magnetic surroundings. V-profiles formed in these parts of the
flux concentation will be strongly asymmetric but unshifted while the
V-profiles from the central parts are symmetric and unshifted. The
resulting mean V-profiles show the characteristics of the observed
profiles, i.e. they are unshifted and asymmetric.
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Title: Contribution and response functions for Stokes line profiles
formed in a magnetic field
Authors: Grossmann-Doerth, U.; Larsson, B.; Solanki, S. K.
1988A&A...204..266G Altcode:
Expressions defining the contribution functions of the 'line depression'
Stokes profiles formed in a general magnetic field are derived. Such
contribution functions are better suited to determining the heights at
which the bound-bound transitions responsible for spectral lines are
important than the contribution functions to the 'intensity' Stokes
parameters defined by Van Ballegooijen (1985). Expressions defining
response functions for both 'intensity' and 'line depression' Stokes
parameters are also derived for an arbitrary atmosphere and magnetic
field. A code for calculating the various Stokes contribution functions
is described and some example calculations are presented. These clearly
demonstrate the superior diagnostic value of the contribution functions
to the 'line depression' Stokes profiles.
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Title: The solar granulation in the vicinity of sunspots
Authors: Schmidt, W.; Grossmann-Doerth, U.; Schroeter, E. H.
1988A&A...197..306S Altcode:
The mean size of the granulation close to sunspots is about 10 percent
smaller than the corresponding value in the normal photosphere. The
percentage of small granules increases steadily over a distance of
about 30 arcsedc, as one approaches the sunspots. The observed rms
intensity-contrast of the granulation at distances of less than 10
arcse to the penumbra is lower than in the quiet photosphere. This is
the result of a power spectrum analysis of 11 white light pictures of
different sunspots taken in 1980 with the 40 cm Newtonian Telescope
of the Kiepenheuer-Institut operated at the Observatorio del Teide,
Tenerife.
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Title: Models of small magnetic flux concentrations in the solar
photosphere.
Authors: Grossmann-Doerth, U.; Knölker, M.; Schüssler, M.
1988AGAb....1...11G Altcode:
No abstract at ADS
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Title: Spurious variation of photospheric magnetic flux
Authors: Grossmann-Doerth, U.; Pahlke, K. -D.; Schuessler, M.
1987A&A...176..139G Altcode:
The response of a Babcock-type magnetograph to emission from different
stages in the evolution of a solar active region is simulated by
computing the Stokes I and V profiles of the 525.02-nm and 630.25-nm
lines of Fe I in model atmospheres representing sunspot umbrae,
magnetic knots, and magnetic elements. The results are presented in
tables and graphs and characterized. Breakup of a single sunspot into
small hot elements with the same total magnetic flux is shown to produce
a significant (as much as factor of 10) spurious loss of signal in the
magnetograph. It is suggested that recent observations of flux-loss
events (in unipolar regions of the solar photosphere without magnetic
neutral lines) be carefully reexamined and analyzed.
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Title: Size and temperature of umbral dots
Authors: Grossmann-Doerth, U.; Schmidt, W.; Schroeter, E. H.
1986A&A...156..347G Altcode:
In 12 white light broad band pictures of 6 different sunspots, taken
in 1980 and 1981 with the 40 cm Newtonian Vacuum Telescope operated at
the Observatorio del Teide (Iazaña), the authors identified nearly 100
umbral dots and attempted to derive their temperature and diameter. They
found strong evidence that the diameter of the dots is in the range
0arcsec.4 to 0arcsec.9 and the temperature is several 100K up to more
than 1000K cooler than the photosphere.
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Title: Bericht und Programm
Authors: Grossmann-Doerth, U.
1984MitAG..62..184G Altcode:
No abstract at ADS
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Title: The brightness distribution in sunspot penumbrae
Authors: Grossmann-Doerth, U.; Schmidt, W.
1981A&A....95..366G Altcode:
From a set of high quality sunspot photographs the intensity
distribution in the penumbrae as well as mean intensities and rms
contrast were derived. For image restoration a Fourier technique was
employed. The intensity distribution was found to be almost symmetrical
and singly peaked.
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Title: Observations of Chromospheric Lines from OSO-8
Authors: Grossmann-Doerth, U.; Kneer, F.; Uexkuell, M.; Artzner,
G. E.; Vial, J. C.
1980SoPh...66....3G Altcode:
The line profiles of Lα, Ca II K and Mg IIk were measured with the
spectrometer of the `Laboratoire de Physique Stellaire et Planétaire'
on board of OSO-8. The results of these measurements are presented.
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Title: Some comments on Suemoto's paper "An empirical, statistical
model for the formation of the cores of chromospheric Fraunhofer
lines".
Authors: Cram, L. E.; Durrant, C. J.; Grossmann-Doerth, U.
1978SoPh...58..279C Altcode:
We discuss a recent model for the solar chromosphere proposed by Suemoto
(Solar Phys.54, 3). We conclude that the model is incompatible with the
basic constraints imposed by high resolution observations and by line
formation theory, and that consequently the model does not adequately
describe the solar chromosphere.
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Title: Spectral investigation of the chromosphere. VI: Observations
of Halpha close to the limb.
Authors: Grossmann-Doerth, U.; von Uexkuell, M.
1977SoPh...55..321G Altcode:
Several hundred Hα spectrograms from areas close to the solar
limb were taken with the 35 cm Coudé refractor at Anacapri. The
41 spectra with the greatest spatial resolution were selected and
analysed. At the supergranular boundaries a considerable fraction of
the line profiles were found to correspond to Beckers' Cloud Model
(BCM). Moreover, the BCM parameters of the dark mottles at the limb
appear to be approximately equal to those from the center of the
disk. On the other hand, we also obtained evidence in disagreement
with the general applicability of the BCM to all features of the
chromospheric fine structure.
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Title: The sun's chromospheric velocity field as inferred from the
Ca II K line.
Authors: Durrant, C. J.; Grossmann-Doerth, U.; Kneer, F. J.
1976A&A....51...95D Altcode:
Theory and observation of the solar Ca II K line under high spatial
resolution are briefly reviewed. It is shown that contrary to popular
belief, present theory is not capable of explaining the observed
features of the K line. An attempt is made to develop a schematic model
of the temporal behavior of the spatially resolved K line, based on
Leibacher's (1971) investigation of waves in the solar atmosphere
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Title: Solar activity (Activité solaire).
Authors: Newkirk, G.; Dunn, R. B.; Mehltretter, P.; MacQueen, R.;
Bonnet, R. M.; White, O. R.; Fokker, A. D.; Zwaan, C.; Bruzek, A.;
Durrant, C.; Grossmann-Doerth, U.; Mehltretter, J. P.; Svestka, Z.;
de Feiter, L. D.; Tandberg-Hanssen, E.; Howard, R.; Stix, M.; Pneuman,
G. W.; Hundhausen, A. J.; Sawyer, C.; Simon, P.
1976IAUTA..16b..13N Altcode:
No abstract at ADS
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Title: Spectral Investigation of the Chromosphere. V: Observation
and Analysis of Hβ
Authors: Grossmann-Doerth, U.; Uexkuell, M. V.
1975SoPh...42..303G Altcode:
The results of the analysis of 16 Hβ spectra taken with high spatial
resolution are presented. The properties of the line profile in
the boundary regions of supergranular cells (SGB) are described by
the statistical distribution functions and correlation coefficients
of four parameters which determine the shape of a suitable fitting
curve. Although some of the line profile properties of both Hβ and Hα
in the SGB can be interpreted in terms of a model which was recently
proposed by Durrant (1975) the agreement between that theory and our
observations is not entirely satisfactory.
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Title: Properties of the solar Ca ii K-Line at high spatial
resolution
Authors: Grossmann-Doerth, U.; Kneer, F.; Uexküll, M. v.
1974SoPh...37...85G Altcode:
The analysis of three Ca II K-spectra with spatial resolution of
∼1″ is described and its results presented. The comparison of
the observed single peak line profiles with model computation leads
to some conclusions regarding the non-uniform large-scale velocity
fields in the chromosphere.
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Title: On the Design of Chromospheric Models
Authors: Grossmann-Doerth, U.
1974IAUS...56...93G Altcode:
No abstract at ADS
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Title: Spectroscopic Investigation of the Chromosphere. III: Hα
Line Profile from the Interior Supergranular Cells
Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina
1973SoPh...30...71G Altcode:
The line profile of H⇓ as emanating from the interior of supergranular
cells was measured at sin θ = 0, 0.6, 0.8 and 0.9. The measurements
are described and the results presented.
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Title: Spectral Investigation of the Chromosphere. II. The Nature
of the Mottles and a Model of the Overall Structure
Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina
1973SoPh...28..319G Altcode:
Highly resolved Hα spectra and filtergrams obtained at the Fraunhofer
Observatory on Capri were analysed by a method whose principles have
been described before. As a result the tentative conclusion of our
previous work has been confirmed: The mottles of the chromospheric fine
structure are clouds superimposed on the low chromosphere. Furthermore,
it is proposed that the latter is identical with the interior of
the supergranular cells whose spatial averages lend themselves to an
interpretation in terms of a spherically symmetric model. On the other
hand, we present evidence that the boundary regions which are formed
by the mottles of the fine structure pattern and which constitute
the upper chromosphere are not adequately described by spatial
averages. Instead, the properties of the individual structural elements
should be taken into account by an appropriate theory, if only in a
statistical fashion. Some of these properties, viz. source function,
optical thickness, Doppler width and velocity, were measured for a
large number of elements. On the basis of indirect evidence we suggest
that the spicules seen on limb photographs of chromospheric lines are
identical with the elements of the supergranule boundary structure.
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Title: Die Struktur der solaren Chromosphäre
Authors: Grossmann-Doerth, U.; von Uexküll, M.
1973MitAG..32..187G Altcode:
No abstract at ADS
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Title: Spectral Investigation of Chromospheric Fine Structure
Authors: Grossmann-Doerth, Ulrich; Von Uexküll, Marina
1971SoPh...20...31G Altcode:
Hα spectra and effectively simultaneous filtergrams were taken at the
Fraunhofer Observatory on Capri with the 35 cm domeless Coudé. The
spatial resolution of the 19 best spectra selected for analysis was
estimated to be 1-2 arc sec. The comparison of several hundred Hα
line profiles emitted by typical chromospheric structure elements
with theoretical prediction yielded strong evidence to suggest that
the chromosphere consists of two parts: A lower, rather uniform
layer at rest superposed by `clouds' (condensations of great spatial
variability) which constitute the well-known structure pattern of
Hα filtergrams. For most image points the line-of-sight velocity,
optical thickness, source function and Doppler broadening of these
clouds could be determined. While the values of the latter three
quantities were found to be similar to what Beckers (1968) has found
for limb spicules the velocity of the bright and of the dark mottles
is considerably smaller than to be expected if these features were
the spicules as seen on the disk. However, our results do not rule
out the possibility that the spicules rise at the centers of rosettes
where they are difficult to detect.
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Title: On Temperature in Line-Gap Regions
Authors: Grossmann-Doerth, U.
1970SoPh...13..287G Altcode:
The small regions in the photosphere where many absorption lines weaken
have been investigated by several authors. Sheeley attempted to explain
the weakening of neutral lines in terms of a temperature increase on
the basis of a simple theoretical model. It is shown that this model
is not applicable but that a modified theory is able to interpret the
observed behaviour of both neutral and ionized lines in terms of a
temperature increase of a few percent.
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Title: On Astronomical Seeing: The Single Schlieren Model
Authors: Grossmann-Doerth, Ulrich
1969SoPh....9..210G Altcode:
A model of astronomical seeing with particular view to solar
observations is developed which assumes the atmospheric disturbances
to consist of individual turbulence elements called Schlieren. A
quantitative account is given of each image motion, image blurring
and scintillation as function of Schlieren properties and telescope
parameters. The theory permits to explain the observational results
under conditions of good seeing; furthermore, it provides a basis
for the discussion of the physical phenomena in the atmosphere that
cause image deterioration. As an illustration it is shown how the
theory could be applied to a problem of interest to solar astronomers
searching for a suitable observatory site.