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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 &lt;= 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 &lt;= 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.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Die Struktur der solaren Chromosphäre
Authors: Grossmann-Doerth, U.; von Uexküll, M.
1973MitAG..32..187G    Altcode:
  No abstract at ADS

---------------------------------------------------------
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.

---------------------------------------------------------
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.