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Author name code: puschmann
ADS astronomy entries on 2022-09-14
author:"Puschmann, Klaus G."
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Title: Horizontal motions in sunspot penumbrae
Authors: Sobotka, Michal; Puschmann, Klaus G.
2022A&A...662A..13S Altcode: 2022arXiv220503171S
Context. A model of penumbral filaments represented by magnetoconvective
cells was derived recently from spectropolarimetric observations. This
model resolves many of the inconsistencies found in the relations
between intensity, magnetic, and velocity patterns in sunspot
penumbrae. <BR /> Aims: High-resolution observations of horizontal
motions in the penumbra are needed to complement the concept of
penumbrae obtained from spectropolarimetry. Time series of intensity
images of a large sunspot in AR 10634 acquired with the Swedish
Solar Telescope in the G band and red continuum are analysed. The
two simultaneous time series last six hours and five minutes. <BR />
Methods: Horizontal motions of penumbral grains (PGs), structures in
dark bodies of filaments, the outer penumbral border, and G-band bright
points are measured in time slices that cover the whole width of the
penumbra and the neighbouring granulation. The spatial and temporal
resolutions are 90 km and 20.1 s, respectively. <BR /> Results:
In the inner penumbra, PGs move towards the umbra (inwards) with
a mean speed of −0.7 km s<SUP>−1</SUP>. The direction of motion
changes from inwards to outwards at approximately 60% of the penumbral
width, and the mean speed increases gradually in the outer penumbra,
approaching 0.5 km s<SUP>−1</SUP>. This speed is also typical of
an expansion of the penumbra-granulation border during periods that
typically last one hour and are followed by a fast contraction. The
majority of the G-band bright points moves away from the sunspot,
with a typical speed of 0.6 km s<SUP>−1</SUP>. High outward speeds,
3.6 km s<SUP>−1</SUP> on average, are observed in dark bodies of
penumbral filaments. <BR /> Conclusions: According to the model
of penumbral filaments, it is suggested that the speeds detected
in the dark bodies of filaments are associated with the Evershed
flow and that the opposite directions of PG motions in the inner
and outer penumbrae may be explained by the interaction of rising
plasma in filament heads with a surrounding, differently inclined
magnetic field. <P />Movies associated to Fig. 1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243577/olm">https://www.aanda.org</A>
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Title: Magnetic Flux Density in 3D MHD Simulations and Observations
Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G.
2019ASPC..526..191B Altcode:
We compare the polarization signals induced in three-dimensional (3D)
magneto-hydrodynamical (MHD) simulations by the Zeeman effect in the
presence of photospheric magnetic fields to those in observations
at disc centre. We consider quantities determined from Stokes vector
profiles of observations of photospheric spectral lines in the visible
and near-infrared, and in corresponding synthetic spectra obtained
from numerical 3D MHD simulations with an average magnetic flux
density of 20-200 G. We match the spatial resolution of observations
by degrading the spectra of the simulations. We find that the total
unsigned vertical magnetic flux density in the simulation should
be less than 50 G to reproduce the observed polarization signals in
the quiet Sun internetwork. A value of ∼30 G best agrees with all
observations we employed.
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Title: Remote sensing optical instrumentation for enhanced space
weather monitoring from the L1 and L5 Lagrange points
Authors: Kraft, S.; Puschmann, K. G.; Luntama, J. P.
2017SPIE10562E..0FK Altcode:
As part of the Space Situational Awareness Programme (SSA), ESA
has initiated the assessment of two missions currently foreseen to
be implemented to enable enhanced space weather monitoring. These
missions utilize the positioning of satellites at the Lagrangian
L1 and L5 points. These Phase 0 or Pre-Phase A mission studies are
about to be completed and will thereby have soon passed the Mission
Definition Review. Phase A studies are planned to start in 2017. The
space weather monitoring system currently considers four remote sensing
optical instruments and several in-situ instruments to analyse the Sun
and the solar wind conditions, in order to provide early warnings of
increased solar activity and to identify and mitigate potential threats
to society and ground, airborne and space based infrastructure. The
suggested optical instruments take heritage from ESA and NASA science
missions like SOHO, STEREO and Solar Orbiter, but the instruments
are foreseen to be optimized for operational space weather monitoring
purposes with high reliability and robustness demands. The instruments
are required to provide high quality measurements particularly during
severe space weather events. The program intends to utilize the results
of the on-going ESA instrument prototyping and technology development
activities, and to initiate pre-developments of the operational space
weather instruments to ensure the required maturity before the mission
implementation.
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Title: The Polarization Signature of Photospheric Magnetic Fields
in 3D MHD Simulations and Observations at Disk Center
Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G.
2017ApJ...842...37B Altcode: 2017arXiv170506812B
Before using three-dimensional (3D) magnetohydrodynamical (MHD)
simulations of the solar photosphere in the determination of elemental
abundances, one has to ensure that the correct amount of magnetic
flux is present in the simulations. The presence of magnetic flux
modifies the thermal structure of the solar photosphere, which affects
abundance determinations and the solar spectral irradiance. The amount
of magnetic flux in the solar photosphere also constrains any possible
heating in the outer solar atmosphere through magnetic reconnection. We
compare the polarization signals in disk-center observations of the
solar photosphere in quiet-Sun regions with those in Stokes spectra
computed on the basis of 3D MHD simulations having average magnetic
flux densities of about 20, 56, 112, and 224 G. This approach allows
us to find the simulation run that best matches the observations. The
observations were taken with the Hinode SpectroPolarimeter (SP),
the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow
Spectrograph (POLIS), and the GREGOR Fabry-Pèrot Interferometer
(GFPI), respectively. We determine characteristic quantities of full
Stokes profiles in a few photospheric spectral lines in the visible
(630 nm) and near-infrared (1083 and 1565 nm). We find that the
appearance of abnormal granulation in intensity maps of degraded
simulations can be traced back to an initially regular granulation
pattern with numerous bright points in the intergranular lanes
before the spatial degradation. The linear polarization signals in
the simulations are almost exclusively related to canopies of strong
magnetic flux concentrations and not to transient events of magnetic
flux emergence. We find that the average vertical magnetic flux density
in the simulation should be less than 50 G to reproduce the observed
polarization signals in the quiet-Sun internetwork. A value of about 35
G gives the best match across the SP, TIP, POLIS, and GFPI observations.
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Title: Spectroscopy at the Solar Limb: II. Are Spicules Heated to
Coronal Temperatures?
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.; Fabbian, D.
2016SoPh..291.2281B Altcode: 2016arXiv160606132B; 2016SoPh..tmp..132B
Spicules of the so-called type II were suggested to be relevant for
coronal heating because of their ubiquity on the solar surface and
their eventual extension into the corona. We investigate whether solar
spicules are heated to transition-region or coronal temperatures and
reach coronal heights (≫6 Mm) using multiwavelength observations
of limb spicules in different chromospheric spectral lines (Ca II H,
Hε , Hα , Ca II IR at 854.2 nm, He I at 1083 nm) taken with slit
spectrographs and imaging spectrometers. We determine the line width
of spectrally resolved line profiles in individual spicules and
throughout the field of view, and estimate the maximal height that
different types of off-limb features reach. We derive estimates of
the kinetic temperature and the non-thermal velocity from the line
width of spectral lines from different chemical elements. We find that
most regular, i.e. thin and elongated, spicules reach a height of at
most about 6 Mm above the solar limb. The majority of features found
at larger heights are irregularly shaped with a significantly larger
lateral extension, of up to a few Mm, than spicules. Both individual and
average line profiles in all spectral lines show a decrease in their
line width with height above the limb with very few exceptions. The
kinetic temperature and the non-thermal velocity decrease with height
above the limb. We find no indications that the spicules in our data
reach coronal heights or transition-region or coronal temperatures.
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Title: Spicules and their on-disk counterparts, the main driver for
solar chromospheric heating?
Authors: Puschmann, Klaus Gerhard
2016arXiv160205185P Altcode:
The question how the outer solar atmosphere is heated from solar
photospheric temperatures of about 5800K up to solar chromospheric
and coronal temperatures of about 20.000K and millions of degrees
respectively, remained without any satisfying answer for centuries. On
4 May 2005, I recorded several time series of Halpha line scans with
the GREGOR Fabry-Perot Interferometer, still deployed at the German
Vacuum Tower Telescope (VTT), for different solar limb and on-disk
positions as well as for quiet sun at solar disk center. The spatially
and temporally highly resolved time series of Halpha line parameters
reveal the entire and detailed complexity as well as the overwhelming
dynamics of spicules covering the entire solar disk, thus apparently
confirming spicules as the potential driver of chromospheric heating
for both the Sun and sun-like stars, with an expected mass flux larger
than 100 times that of the solar wind. Spicules seem to be the result
of the interaction of the highly dynamic photospheric quiet-sun
or active-region small-scale magnetic field, which is dominated by
convective processes and is predominantly located in intergranular
lanes and at meso- or supergranular scales.
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Title: The GREGOR Fabry Perot Interferometer (GFPI), Technical
Innovations and Results achieved in 2013
Authors: Puschmann, Klaus Gerhard
2016arXiv160205783P Altcode:
This paper shall provide a summary of not yet published technical
innovations to the GREGOR Fabry-Perot Interferometer (GFPI) at the
1.5m GREGOR Solar Telescope (Europe's largest solar telescope) that
I implemented in 2013 as the Instrument Scientist of the GFPI. It
also represents an overview of important and not yet published
observational results that I achieved with the GFPI in 2013. The
results and achievements can be considered a milestone in the further
development, scientific verification and final acceptance of this
instrument. The instrument is now in operation and employed by the
international scientific community.
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Title: The association between sunspot magnetic fields and
superpenumbral fibrils
Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.;
Puschmann, K. G.; Denker, C.
2014AN....335..161L Altcode: 2013arXiv1312.1879L
Spectropolarimetric observations of a sunspot were carried out with
the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife,
Spain. Maps of the physical parameters were obtained from an inversion
of the Stokes profiles observed in the infrared Fe I line at 15 648
Å. The regular sunspot consisted of a light bridge which separated the
two umbral cores of the same polarity. One of the arms of the light
bridge formed an extension of a penumbral filament which comprised
weak and highly inclined magnetic fields. In addition, the Stokes V
profiles in this filament had an opposite sign as the sunspot and some
resembled Stokes Q or U. This penumbral filament terminated abruptly
into another at the edge of the sunspot, where the latter was relatively
vertical by about 30<SUP>o</SUP>. Chromospheric H\alpha and He II 304
Åfiltergrams revealed three superpenumbral fibrils on the limb-side
of the sunspot, in which one fibril extended into the sunspot and was
oriented along the highly inclined penumbral counterpart of the light
bridge. An intense, elongated brightening was observed along this fibril
that was co-spatial with the intersecting penumbral filaments in the
photosphere. Our results suggest that the disruption in the sunspot
magnetic field at the location of the light bridge could be the source
of reconnection that led to the intense chromospheric brightening and
facilitated the supply of cool material in maintaining the overlying
superpenumbral fibrils.
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Title: Sunspot splitting triggering an eruptive flare
Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard;
Balthasar, Horst; Denker, Carsten
2014A&A...562A.110L Altcode: 2013arXiv1311.5054L
<BR /> Aims: We investigate how the splitting of the leading sunspot
and associated flux emergence and cancellation in active region NOAA
11515 caused an eruptive M5.6 flare on 2012 July 2. <BR /> Methods:
Continuum intensity, line-of-sight magnetogram, and dopplergram data
of the Helioseismic and Magnetic Imager were employed to analyse
the photospheric evolution. Filtergrams in Hα and He I 10830 Å of
the Chromospheric Telescope at the Observatorio del Teide, Tenerife,
track the evolution of the flare. The corresponding coronal conditions
were derived from 171 Å and 304 Å images of the Atmospheric Imaging
Assembly. Local correlation tracking was utilized to determine
shear flows. <BR /> Results: Emerging flux formed a neutral line
ahead of the leading sunspot and new satellite spots. The sunspot
splitting caused a long-lasting flow towards this neutral line, where
a filament formed. Further flux emergence, partly of mixed polarity,
as well as episodes of flux cancellation occurred repeatedly at
the neutral line. Following a nearby C-class precursor flare with
signs of interaction with the filament, the filament erupted nearly
simultaneously with the onset of the M5.6 flare and evolved into a
coronal mass ejection. The sunspot stretched without forming a light
bridge, splitting unusually fast (within about a day, complete ≈6 h
after the eruption) in two nearly equal parts. The front part separated
strongly from the active region to approach the neighbouring active
region where all its coronal magnetic connections were rooted. It
also rotated rapidly (by 4.9° h<SUP>-1</SUP>) and caused significant
shear flows at its edge. <BR /> Conclusions: The eruption resulted
from a complex sequence of processes in the (sub-)photosphere and
corona. The persistent flows towards the neutral line likely caused
the formation of a flux rope that held the filament. These flows,
their associated flux cancellation, the emerging flux, and the
precursor flare all contributed to the destabilization of the flux
rope. We interpret the sunspot splitting as the separation of two
flux bundles differently rooted in the convection zone and only
temporarily joined in the spot. This explains the rotation as the
continued rise of the separating flux, and it implies that at least
this part of the sunspot was still connected to its roots deep in
the convection zone. <P />Movie available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201321106/olm">http://www.aanda.org</A>
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Title: Thermodynamic fluctuations in solar photospheric
three-dimensional convection simulations and observations
(Corrigendum)
Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.;
Rezaei, R.
2013A&A...559C...1B Altcode:
No abstract at ADS
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Title: Thermodynamic fluctuations in solar photospheric
three-dimensional convection simulations and observations
Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.;
Rezaei, R.
2013A&A...557A.109B Altcode: 2013arXiv1306.6093B
Context. Numerical three-dimensional (3D) radiative
(magneto-)hydrodynamical [(M)HD] simulations of solar convection
are nowadays used to understand the physical properties of the solar
photosphere and convective envelope, and, in particular, to determine
the Sun's photospheric chemical abundances. To validate this approach,
it is important to check that no excessive thermodynamic fluctuations
arise as a consequence of the partially incomplete treatment of
radiative transfer causing radiative damping that is too modest. <BR
/> Aims: We investigate the realism of the thermodynamics in recent
state-of-the-art 3D convection simulations of the solar atmosphere
carried out with the Stagger code. <BR /> Methods: We compared the
characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565
nm) and one Si i line at 1082.7 nm in solar disc-centre observations
of different spatial resolution with spectra synthesized from 3D
convection simulations. The observations were taken with ground-based
(Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI),
POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all
at the Vacuum Tower Telescope on Tenerife) and space-based instruments
(Hinode/Spectropolarimeter). We degraded the synthetic spectra to
the spatial resolution of the observations, based on the distribution
of the continuum intensity I<SUB>c</SUB>. We estimated the spectral
degradation to be applied to the simulation results by comparing atlas
spectra with averaged observed spectra. In addition to deriving a set
of line parameters directly from the intensity profiles, we used the
SIR (Stokes Inversion based on Response functions) code to invert
the spectra. <BR /> Results: The spatial degradation kernels yield
a similar generic spatial stray-light contamination of about 30%
for all instruments. The spectral stray light inside the different
spectrometers is found to be between 2% and 20%. Most of the line
parameters from the observational data are matched by the degraded
HD simulation spectra. The inversions predict a macroturbulent
velocity v<SUB>mac</SUB> below 10 m s<SUP>-1</SUP> for the HD
simulation spectra at full spatial resolution, whereas they yield
v<SUB>mac</SUB> ≲ 1000 m s<SUP>-1</SUP> at a spatial resolution of
0.″3. The temperature fluctuations in the inversion of the degraded
HD simulation spectra do not exceed those from the observational data
(of the order of 100-200 K rms for -2 ⪉ log τ<SUB>500 nm</SUB>
⪉ -0.5). The comparison of line parameters in spatially averaged
profiles with the averaged values of line parameters in spatially
resolved profiles indicates a significant change in (average) line
properties on a spatial scale between 0.″13 and 0.″3. <BR />
Conclusions: Up to a spatial resolution of 0.″3 (GFPI spectra),
we find no indications of excessive thermodynamic fluctuations
in the 3D HD simulation. To definitely confirm that simulations
without spatial degradation contain fully realistic thermodynamic
fluctuations requires observations at even higher spatial resolution
(i.e. <0.″13). <P />Appendices A and B are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: GREGOR Fabry-Pérot interferometer and its companion the blue
imaging solar spectrometer
Authors: Puschmann, Klaus G.; Denker, Carsten; Balthasar, Horst; Louis,
Rohan E.; Popow, Emil; Woche, Manfred; Beck, Christian; Seelemann,
Thomas; Volkmer, Reiner
2013OptEn..52h1606P Altcode: 2013arXiv1302.7157P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-m GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI allows
fast narrow-band imaging and postfactum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic sun and its magnetic field at spatial
scales down to ∼50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectrometric and spectropolarimetric observations between 530-860
nm and 580-660 nm, respectively, and possesses a theoretical spectral
resolution of R≈250,000. Large-format, high-cadence charged coupled
device detectors with sophisticated computer hard- and software enable
the scanning of spectral lines in time-spans equivalent to the evolution
time of solar features. The field-of-view (FOV) of 50″×38″ covers
a significant fraction of the typical area of active regions in the
spectroscopic mode. In case of Stokes-vector spectropolarimetry,
the FOV reduces to 25″×38″. The main characteristics of the GFPI
including advanced and automated calibration and observing procedures
are presented. Improvements in the optical design of the instrument
are discussed and first observational results are shown. Finally,
the first concrete ideas for the integration of a second FPI, the blue
imaging solar spectrometer, are laid out, which will explore the blue
spectral region below 530 nm.
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Title: Evidence of quiet-Sun chromospheric activity related to an
emerging small-scale magnetic loop
Authors: Gömöry, P.; Balthasar, H.; Puschmann, K. G.
2013A&A...556A...7G Altcode: 2013arXiv1306.3393G
<BR /> Aims: We investigate the temporal evolution of magnetic flux
emergence in the quiet-Sun atmosphere close to disk center. <BR />
Methods: We combined high-resolution SoHO/MDI magnetograms with TRACE
observations taken in the 1216 Å channel to analyze the temporal
evolution of an emerging small-scale magnetic loop and its traces
in the chromosphere. <BR /> Results: We find signatures of flux
emergence very close to the edge of a supergranular network boundary
located at disk center. The new emerging flux appeared first in the MDI
magnetograms in form of an asymmetric bipolar element, i.e., the patch
with negative polarity is roughly twice as weak as the corresponding
patch with opposite polarity. The average values of magnetic flux and
magnetic flux densities reached 1.6 × 10<SUP>18</SUP> Mx, - 8.5 ×
10<SUP>17</SUP> Mx, and 55 Mx cm<SUP>-2</SUP>, -30 Mx cm<SUP>-2</SUP>,
respectively. The spatial distance between the opposite polarity
patches of the emerged feature increased from about 2.″5 to 5.″0
during the lifetime of the loop, which was 36 min. A more precise
lifetime-estimate of the feature was not possible because of a gap
in the temporal sequence of the MDI magnetograms. The chromospheric
response to the emerged magnetic dipole occurred ~9 min later than in
the photospheric magnetograms. It consisted of a quasi-periodic sequence
of time-localized brightenings visible in the 1216 Å TRACE channel for
~14 min that were co-spatial with the axis connecting the two patches of
opposite magnetic polarity. <BR /> Conclusions: We identify the observed
event as a small-scale magnetic loop emerging at photospheric layers
that subsequently rose to the chromosphere. We discuss the possibility
that the fluctuations detected in the chromospheric emission probably
reflect magnetic-field oscillations which propagate to the chromosphere
in the form of waves.
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Title: Can spicules be detected at disc centre in broad-band Ca ii
H filter imaging data?
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.
2013A&A...556A.127B Altcode: 2013arXiv1306.5199B
Context. Recently, a possible identification of type II spicules
in broad-band (full-width at half-maximum (FWHM) of ~0.3 nm) filter
imaging data in Ca ii H on the solar disc was reported. <BR /> Aims:
We estimate the formation height range contributing to broad-band and
narrow-band filter imaging data in Ca ii H to investigate whether
spicules can be detected in such observations at the centre of the
solar disc. <BR /> Methods: We applied spectral filters of FWHMs
from 0.03 nm to 1 nm to observed Ca ii H line profiles to simulate
Ca imaging data. We used observations across the limb to estimate the
relative intensity contributions of off-limb and on-disc structures. We
compared the synthetic Ca filter imaging data with intensity maps of
Ca spectra at different wavelengths and temperature maps at different
optical depths obtained by an inversion of these spectra. In addition,
we determined the intensity response function for the wavelengths
covered by the filters of different FWHM. <BR /> Results: In broad-band
(FWHM = 0.3 nm) Ca imaging data, the intensity emitted off the solar
limb is about 5% of the intensity at disc centre. For a 0.3-nm-wide
filter centred at the Ca ii H line core, up to about one third of
the off-limb intensity comes from emission in Hɛ. On the disc, only
about 10 to 15% of the intensity transmitted through a broad-band
filter comes from the line-core region between the H<SUB>1</SUB>
minima (396.824 to 396.874 nm). No traces of elongated fibrillar
structures are visible in the synthetic Ca broad-band imaging data at
disc centre, in contrast to the line-core images of the Ca spectra. The
intensity-weighted response function for a 0.3-nm-wide filter centred at
the Ca ii H line core peaks at about log τ ~ -2 (z ~ 200 km). Relative
contributions from atmospheric layers above 800 km are about 10%. The
inversion results suggest that the slightly enhanced emission around
the photospheric magnetic network in broad-band Ca imaging data
is caused by a thermal canopy at a height of about 600 km. <BR />
Conclusions: Broad-band (~0.3 nm) Ca ii H imaging data do not trace
upper chromospheric structures such as spicules in observations at the
solar disc because of the too small relative contribution of the line
core to the total wavelength-integrated filter intensity. The faint haze
around network elements in broad-band Ca imaging observations at disc
centre presumably traces thermal canopies in the vicinity of magnetic
flux concentrations instead. <P />Appendix A is available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: The energy of waves in the photosphere and lower
chromosphere. IV. Inversion results of Ca II H spectra
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.
2013A&A...553A..73B Altcode: 2013arXiv1302.6936B
Context. Most semi-empirical static one-dimensional (1D) models of
the solar atmosphere in the magnetically quiet Sun (QS) predict an
increase in temperature at chromospheric layers. Numerical simulations
of the solar chromosphere with a variable degree of sophistication,
i.e. from 1D to three-dimensional (3D) simulations; assuming local
thermal equilibrium (LTE) or non-LTE (NLTE), on the other hand,
only yielded an increase in the brightness temperature without any
stationary increase in the gas temperature. <BR /> Aims: We investigate
the thermal structure in the solar chromosphere as derived from an
LTE inversion of observed Ca ii H spectra in QS and active regions
(ARs). <BR /> Methods: We applied an inversion strategy based on the
SIR (Stokes inversion by response functions) code to Ca ii H spectra to
obtain 1D temperature stratifications. We investigated the temperature
stratifications on differences between magnetic and field-free regions
in the QS, and on differences between QS and ARs. We determined the
energy content of individual calcium bright grains (BGs) as specific
candidates of chromospheric heating events. We compared observed with
synthetic NLTE spectra to estimate the significance of the LTE inversion
results. <BR /> Results: The fluctuations of observed intensities yield
a variable temperature structure with spatio-temporal rms fluctuations
below 100 K in the photosphere and between 200 and 300 K in the QS
chromosphere. The average temperature stratification in the QS does not
exhibit a clear chromospheric temperature rise, unlike the AR case. We
find a characteristic energy content of about 7 × 10<SUP>18</SUP> J
for BGs that repeat with a cadence of about 160 s. The precursors of BGs
have a vertical extent of about 200 km and a horizontal extent of about
1 Mm. The comparison of observed with synthetic NLTE profiles partly
confirms the results of the LTE inversion that the solar chromosphere
in the QS oscillates between an atmosphere in radiative equilibrium and
one with a moderate chromospheric temperature rise. Two-dimensional x -
z temperature maps exhibit nearly horizontal canopy-like structures with
an extent of a few Mm around photospheric magnetic field concentrations
at a height of about 600 km. <BR /> Conclusions: The large difference
between QS regions and ARs and the better match of AR and NLTE reference
spectra suggest that magnetic heating processes are more important
than commonly assumed. The temperature fluctuations in QS derived by
the LTE inversion do not suffice on average to maintain a stationary
chromospheric temperature rise. The spatially and vertically resolved
information on the temperature structure allows one to investigate
in detail the topology and evolution of the thermal structure in the
lower solar atmosphere. <P />Appendix A is available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Formation of a penumbra in a decaying sunspot
Authors: Louis, R. E.; Mathew, S. K.; Puschmann, K. G.; Beck, C.;
Balthasar, H.
2013A&A...552L...7L Altcode: 2013arXiv1303.3599L
Context. Penumbrae are an important characteristic of sunspots, whose
formation is intricately related to the nature of sub-photospheric
magnetic fields. <BR /> Aims: We study the formation of a penumbra in
a decaying sunspot and compare its properties with those seen during
the development of a proto-spot. <BR /> Methods: High-resolution
spectropolarimetric observations of active region NOAA 11283 were
obtained from the spectro-polarimeter on board Hinode. These were
complemented with full-disk filtergrams of continuum intensity,
line-of-sight magnetograms, and dopplergrams from the Helioseismic and
Magnetic Imager at high cadence. <BR /> Results: The formation of a
penumbra in the decaying sunspot occurs after the coalescence of the
sunspot with a magnetic fragment/pore, which initially formed in the
quiet Sun close to an emerging flux region. At first, a smaller set of
penumbral filaments develop near the location of the merger with very
bright penumbral grains with intensities of 1.2 I<SUB>QS</SUB>, upflows
of 4 km s<SUP>-1</SUP>, and a lifetime of 10 h. During the decay of
these filaments, a larger segment of a penumbra forms at the location
of the coalescence. These new filaments are characterized by nearly
supersonic downflows of 6.5 km s<SUP>-1</SUP> that change to a regular
Evershed flow nearly 3 h later. <BR /> Conclusions: The coalescence of
the pore with the decaying sunspot provided sufficient magnetic flux for
the penumbra to form in the sunspot. The emerging flux region could have
played a decisive role in this process because the formation occurred
at the location of the merger and not on the opposite side of the
sunspot. <P />An animation of the HMI data is available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Properties of a Decaying Sunspot
Authors: Balthasar, H.; Beck, C.; Gömöry, P.; Muglach, K.; Puschmann,
K. G.; Shimizu, T.; Verma, M.
2013CEAB...37..435B Altcode: 2013arXiv1301.1562B
A small decaying sunspot was observed with the Vacuum Tower Telescope
(VTT) on Tenerife and the Japanese Hinode satellite. We obtained
full Stokes scans in several wavelengths covering different heights
in the solar atmosphere. Imaging time series from Hinode and the
Solar Dynamics Observatory (SDO) complete our data sets. The spot is
surrounded by a moat flow, which persists also on that side of the
spot where the penumbra already had disappeared. Close to the spot,
we find a chromospheric location with downflows of more than 10 km
s^{-1} without photospheric counterpart. The height dependence of
the vertical component of the magnetic field strength is determined
in two different ways that yielded different results in previous
investigations. Such a difference still exists in our present data,
but it is not as pronounced as in the past.
---------------------------------------------------------
Title: The energy of waves in the photosphere and lower
chromosphere. III. Inversion setup for Ca II H spectra in local
thermal equilibrium
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.
2013A&A...549A..24B Altcode: 2012arXiv1209.6194B
Context. The Ca II H line is one of the strongest lines in the solar
spectrum, and it provides continuous information on the solar atmosphere
from the photosphere to the lower chromosphere. <BR /> Aims: We describe
an inversion approach that reproduces observed Ca II H spectra by
assuming local thermal equilibrium (LTE). <BR /> Methods: We developed
an inversion strategy based on the SIR code that reproduces Ca II H
spectra in the LTE approximation. The approach uses a two-step procedure
with an archive of pre-calculated spectra to fit the line core and a
subsequent iterative modification to improve the fit mainly in the line
wing. Simultaneous spectra in the 630 nm range can optionally be used
to fix the continuum temperature. The method retrieves one-dimensional
(1D) temperature stratifications while neglecting lateral radiative
transport. Line-of-sight velocities are included post facto with
an empirical approach. <BR /> Results: An archive of about 300 000
pre-calculated spectra is more than sufficient to reproduce the line
core of observed Ca II H spectra both in the quiet Sun and in active
regions. The subsequent iterative adjustment of the thermodynamical
stratification matches observed and best-fit spectra to a level of about
0.5% of I<SUB>c</SUB> in the line wing and about 1% of I<SUB>c</SUB>
in the line core. <BR /> Conclusions: The successful application of
the LTE inversion strategy suggests that inversion schemes based on
pre-calculated spectra allow a reliable and relatively fast retrieval of
solar properties from observed chromospheric spectra. The approach can
be easily extended to a 1D non-LTE (NLTE) case by a simple exchange
of the pre-calculated archive spectra. Using synthetic NLTE spectra
from numerical three-dimensional (3D) simulations instead will
finally allow one to extend the approach from the static 1D-case
to dynamical atmosphere models, including the complete 3D radiative
transport. <P />The animation is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.
---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer: A New Instrument for
High-Resolution Spectropolarimetric Solar Observations
Authors: Puschmann, K. G.; Balthasar, H.; Bauer, S. -M.; Hahn, T.;
Popow, E.; Seelemann, T.; Volkmer, R.; Woche, M.; Denker, C.
2012ASPC..463..423P Altcode: 2011arXiv1111.5509P
Fabry-Pérot interferometers have advantages over slit spectrographs
because they allow fast narrow-band imaging and post-factum image
reconstruction of the retrieved data. Temperature, plasma velocity,
and magnetic field maps can be derived from inversions of spectral
lines, thus, advancing our understanding of the dynamic Sun and its
magnetic fields at the smallest spatial scales. The GREGOR Fabry-Pérot
Interferometer (GFPI) is one of two first-light instruments of the
1.5-meter GREGOR solar telescope, which is currently being commissioned
at the Observatorio del Teide, Tenerife, Spain. The GFPI operates close
to the diffraction limit of GREGOR, thus, providing access to fine
structures as small as 60 km on the solar surface. The field-of-view
of 52″×40″ is sufficiently large to cover significant area
fraction of active regions. The GFPI is a tuneable dual-etalon system
in a collimated mounting. Equipped with a full-Stokes polarimeter,
it records spectropolarimetric data with a spectral resolution of R
≍ 250,000 over the wavelength range from 530-860 nm. Large-format,
high-cadence CCD detectors with powerful computer hard- and software
facilitate scanning of spectral lines in time spans corresponding
to the evolution time-scale of solar features. We present the main
characteristics of the GFPI including the latest developments in
software, mechanical mounts, and optics.
---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
---------------------------------------------------------
Title: The GREGOR Fabry-Perot interferometer: status report and
prospects
Authors: Puschmann, Klaus G.; Balthasar, Horst; Beck, Christian;
Louis, Rohan E.; Popow, Emil; Seelemann, Thomas; Volkmer, Reiner;
Woche, Manfred; Denker, Carsten
2012SPIE.8446E..79P Altcode: 2012arXiv1207.2084P
The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI allows
fast narrow-band imaging and post-factum image restoration. The
retrieved physical parameters will be a fundamental building block
for understanding the dynamic Sun and its magnetic field at spatial
scales down to 50 km on the solar surface. The GFPI is a tunable
dual-etalon system in a collimated mounting. It is designed for
spectropolarimetric observations over the wavelength range from 530-860
nm with a theoretical spectral resolution of R ≍ 250,000. The GFPI is
equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD
detectors with powerful computer hard- and software enable the scanning
of spectral lines in time spans equivalent to the evolution time of
solar features. The field-of-view of 50”×38” covers a significant
fraction of the typical area of active regions. We present the main
characteristics of the GFPI including advanced and automated calibration
and observing procedures. We discuss improvements in the optical design
of the instrument and show first observational results. Finally, we
lay out first concrete ideas for the integration of a second FPI, the
Blue Imaging Solar Spectrometer, which will explore the blue spectral
region below 530 nm.
---------------------------------------------------------
Title: The energy of waves in the photosphere and lower
chromosphere. II. Intensity statistics
Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.
2012A&A...544A..46B Altcode: 2012arXiv1206.1759B
Context. The energy source powering the solar chromosphere is still
undetermined, but leaves its traces in observed intensities. <BR />
Aims: We investigate the statistics of the intensity distributions
as a function of the wavelength for Ca ii H and the Ca ii IR line at
854.2 nm to estimate the energy content in the observed intensity
fluctuations. <BR /> Methods: We derived the intensity variations
at different heights of the solar atmosphere, as traced by the line
wings and line cores of the two spectral lines. We converted the
observed intensities to absolute energy units employing reference
profiles calculated in non-local thermal equilibrium (NLTE). We also
converted the intensity fluctuations to corresponding brightness
temperatures assuming LTE. <BR /> Results: The root-mean-square
(rms) fluctuations of the emitted intensity are about 0.6 (1.2)
W m<SUP>-2</SUP> ster<SUP>-1</SUP> pm<SUP>-1</SUP> near the core of
the Ca ii IR line at 854.2 nm (Ca ii H), corresponding to relative
intensity fluctuations of about 20% (30%). For the line wing,
we find rms values of about 0.3 W m<SUP>-2</SUP> ster<SUP>-1</SUP>
pm<SUP>-1</SUP> for both lines, corresponding to relative fluctuations
below 5%. The relative rms values show a local minimum for wavelengths
forming at a height of about 130 km, but otherwise increase smoothly
from the wing to the core, i.e., from photosphere to chromosphere. The
corresponding rms brightness temperature fluctuations are below 100 K
for the photosphere and up to 500 K in the chromosphere. The skewness
of the intensity distributions is close to zero in the outer line
wing and positive throughout the rest of the line spectrum, owing to
the frequent occurrence of high-intensity events. The skewness shows a
pronounced local maximum at locations with photospheric magnetic fields
for wavelengths in-between those of the line wing and the line core
(z ≈ 150-300 km), and a global maximum at the very core (z ≈ 1000
km) for both magnetic and field-free locations. <BR /> Conclusions:
The energy content of the intensity fluctuations is insufficient to
create a chromospheric temperature rise that would be similar to the
one in most reference models of the solar atmosphere. The increase in
the rms fluctuations with height indicates the presence of upwardly
propagating acoustic waves of increasing oscillation amplitude. The
intensity and temperature variations indicate that there is a
clear increase in dynamical activity from photosphere towards the
chromosphere, but the variations fall short of the magnitude predicted
by fully dynamical chromospheric models by a factor of about five. The
enhanced skewness between the photosphere and lower solar chromosphere
at magnetic locations is indicative of a mechanism that acts solely
on magnetized plasma. <P />Appendices are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Twist, Writhe, and Helicity in the Inner Penumbra of a Sunspot
Authors: Ruiz Cobo, B.; Puschmann, K. G.
2012ApJ...745..141R Altcode: 2011arXiv1111.3881R
The aim of this work is the determination of the twist, writhe, and
self-magnetic helicity of penumbral filaments located in an inner
sunspot penumbra. For this purpose, we inverted data taken with the
spectropolarimeter on board Hinode with the SIR (Stokes Inversion based
on Response function) code. For the construction of a three-dimensional
geometrical model we applied a genetic algorithm minimizing
the divergence of \vec{B} and the net magnetohydrodynamic force,
consequently a force-free solution would be reached if possible. We
estimated two proxies to the magnetic helicity frequently used in
literature: the force-free parameter α<SUB> z </SUB> and the current
helicity term h_{c_{z}}. We show that both proxies are only qualitative
indicators of the local twist as the magnetic field in the area under
study significantly departs from a force-free configuration. The
local twist shows significant values only at the borders of bright
penumbral filaments with opposite signs on each side. These locations
are precisely correlated to large electric currents. The average twist
(and writhe) of penumbral structures is very small. The spines (dark
filaments in the background) show a nearly zero writhe. The writhe
per unit length of the intraspines diminishes with increasing length
of the tube axes. Thus, the axes of tubes related to intraspines are
less wrung when the tubes are more horizontal. As the writhe of the
spines is very small, we can conclude that the writhe reaches only
significant values when the tube includes the border of an intraspine.
---------------------------------------------------------
Title: Application of speckle and (multi-object) multi-frame blind
deconvolution techniques on imaging and imaging spectropolarimetric
data
Authors: Puschmann, K. G.; Beck, C.
2011A&A...533A..21P Altcode: 2011arXiv1107.0703P
Context. Ground-based imaging and imaging spectropolarimetric data are
often subjected to post-facto reconstruction techniques to improve the
spatial resolution. <BR /> Aims: We test the effects of reconstruction
techniques on two-dimensional data to determine the best approach
to improve our data. <BR /> Methods: We obtained an 1-h time-series
of spectropolarimetric data in the Fe i line at 630.25 nm with the
Göttingen Fabry-Pérot Interferometer (FPI) that are accompanied
by imaging data in the blue continuum at 431.3 nm and Ca ii H at
396.85 nm. We apply both speckle and (multi-object) multi-frame blind
deconvolution ((MO)MFBD) techniques. We use the "Göttingen" speckle and
speckle deconvolution codes and the MOMFBD code in the implementation
of Van Noort et al. (2005). We compare the resulting spatial resolution
and investigate the impact of the image reconstruction on spectral
characteristics of the Göttingen FPI data. <BR /> Results: The speckle
reconstruction and MFBD perform similar for our imaging data with
nearly identical intensity contrasts. MFBD provides a better and more
homogeneous spatial resolution at the shortest wavelength when applied
to a series of image bursts. The MOMFBD and speckle deconvolution of the
intensity spectra lead to similar results, but our choice of settings
for the MOMFBD yields an intensity contrast smaller by about 2% at a
comparable spatial resolution. None of the reconstruction techniques
introduces significant artifacts in the intensity spectra. The
speckle deconvolution (MOMFBD) has a rms noise in Stokes V/I of 0.32%
(0.20%). The deconvolved spectra thus require a high significance
threshold of about 1.0% to separate noise peaks from true signal. A
comparison to spectra with a significantly higher signal-to-noise (S/N)
ratio and to spectra from a magneto-hydrodynamical simulation reveals
that the Göttingen FPI can only detect about 30% of the polarization
signal present in quiet Sun areas. The distribution of NCP values
for the speckle-deconvolved data matches that of observations with
higher S/N better than MOMFBD, but shows seemingly artificially sharp
boundaries and unexpected changes of the sign. <BR /> Conclusions: For
our imaging data, both MFBD and speckle reconstruction are equivalent,
with a slightly better and more stable performance of MFBD. For the
spectropolarimetric data, the higher intensity contrast of the speckle
deconvolution is balanced by the smaller amplification of the noise
level in the MOMFBD at a comparable spatial resolution. The noise level
prevents the detection of weak and diffuse magnetic fields. Future
efforts should be directed to improve the S/N of the Göttingen
FPI spectra for spectropolarimetric observations to lower the final
significance thresholds.
---------------------------------------------------------
Title: Polarimetry with GREGOR
Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker,
C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.;
Soltau, D.; Volkmer, R.
2011ASPC..437..351B Altcode:
A brief description of the new 1.5-meter solar telescope GREGOR located
at the Observatorio del Teide in Tenerife will be given. GREGOR will
provide a spatial resolution of about 75 km on the Sun, and with its
light collecting capability we will be able to study the development
of small magnetic features with high cadence. From the beginning,
it will be equipped with the GREGOR Fabry-Pérot Interferometer
(GFPI) for the visible spectral range and with a GRating Infrared
Spectrograph (GRIS). Both postfocus instruments can be combined
with a polarimeter, and in both cases the light is modulated by two
ferro-electric liquid crystals. A calibration unit can be inserted to
determine the instrumental polarization. Because of the altazimuthal
mount, time-dependent rotation of the polarimetric reference plane
is introduced, and we have to develop a polarization model of the
telescope. Measurements to verify this model are in preparation.
---------------------------------------------------------
Title: The Electrical Current Density Vector in the Inner Penumbra
of a Sunspot
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V.
2010ApJ...721L..58P Altcode: 2010arXiv1008.2131P
We determine the entire electrical current density vector in a
geometrical three-dimensional volume of the inner penumbra of a
sunspot from an inversion of spectropolarimetric data obtained with
Hinode/SP. Significant currents are seen to wrap around the hotter,
more elevated regions with lower and more horizontal magnetic fields
that harbor strong upflows and radial outflows (the intraspines). The
horizontal component of the current density vector is 3-4 times larger
than the vertical; nearly all previous studies only obtain the vertical
component J<SUB>z</SUB> , thus strongly underestimating the current
density. The current density \vec{J} and the magnetic field \vec{B}
form an angle of about 20°. The plasma β at the 0 km level is larger
than 1 in the intraspines and is one order of magnitude lower in the
background component of the penumbra (spines). At the 200 km level,
the plasma β is below 0.3, nearly everywhere. The plasma β surface
as well as the surface optical depth unity is very corrugated. At the
borders of intraspines and inside, \vec{B} is not force-free at deeper
layers and nearly force-free at the top layers. The magnetic field of
the spines is close to being potential everywhere. The dissipated ohmic
energy is five orders of magnitudes smaller than the solar energy flux
and thus negligible for the energy balance of the penumbra.
---------------------------------------------------------
Title: A Geometrical Height Scale for Sunspot Penumbrae
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V.
2010ApJ...720.1417P Altcode: 2010arXiv1007.2779P
Inversions of spectropolarimetric observations of penumbral filaments
deliver the stratification of different physical quantities in an
optical depth scale. However, without establishing a geometrical
height scale, their three-dimensional geometrical structure cannot
be derived. This is crucial in understanding the correct spatial
variation of physical properties in the penumbral atmosphere and to
provide insights into the mechanism capable of explaining the observed
penumbral brightness. The aim of this work is to determine a global
geometrical height scale in the penumbra by minimizing the divergence of
the magnetic field vector and the deviations from static equilibrium as
imposed by a force balance equation that includes pressure gradients,
gravity, and the Lorentz force. Optical depth models are derived from
the inversion of spectropolarimetric data of an active region observed
with the Solar Optical Telescope on board the Hinode satellite. We
use a genetic algorithm to determine the boundary condition for the
inference of geometrical heights. The retrieved geometrical height
scale permits the evaluation of the Wilson depression at each pixel and
the correlation of physical quantities at each height. Our results fit
into the uncombed penumbral scenario, i.e., a penumbra composed of flux
tubes with channeled mass flow and with a weaker and more horizontal
magnetic field as compared with the background field. The ascending
material is hotter and denser than their surroundings. We do not find
evidence of overturning convection or field-free regions in the inner
penumbral area analyzed. The penumbral brightness can be explained by
the energy transfer of the ascending mass carried by the Evershed flow,
if the physical quantities below z = -75 km are extrapolated from the
results of the inversion.
---------------------------------------------------------
Title: Three Dimensional Structure of Penumbral Filaments from
Hinode Observations
Authors: Puschmann, K. G.; Cobo, B. Ruiz; Pillet, V. Martínez
2010ASSP...14..457P Altcode: 2010hsa5.conf..457P; 2008arXiv0810.2432P
We analyze spectropolarimetric observations of the penumbra of the NOAA
AR 10953 at high spatial resolution (0.3<SUP> ″ </SUP>). The full
Stokes profiles of the Fe I lines at 630.1 nm and 630.2 nm have been
obtained with the Solar Optical Telescope (SOT) on board the Hinode
satellite. The data have been inverted by means of the SIR code,
deriving the stratifications of temperature, line-of-sight velocity,
and the components of the magnetic field vector in optical depth. In
order to evaluate the gas pressure and to obtain an adequate geometrical
height scale, the motion equation has been integrated for each pixel
taking into account the terms of the Lorentz force. To establish the
boundary condition, a genetic algorithm has been applied. The final
resulting magnetic field has a divergence compatible with 0 inside
its uncertainties. First analyzes of the correlation of the Wilson
depression with velocity, temperature, magnetic field strength,
and field inclination strongly support the uncombed penumbral model
proposed by Solanki & Montavon (1993, A&A, 275, 283).
---------------------------------------------------------
Title: Morphology and evolution of umbral dots and their substructures
Authors: Sobotka, M.; Puschmann, K. G.
2009A&A...504..575S Altcode: 2009arXiv0907.4236S
Context: Substructures - dark lanes and tails - of umbral dots (UDs)
were predicted by numerical simulations of magnetoconvection and have
been detected later in some observations. <BR />Aims: To provide
constraints for realistic theoretical models of sunspot umbrae, we
describe the observed properties and evolutionary characteristics of
UDs (including their substructure) and of other umbral structures. <BR
/>Methods: We analyse a 6 h 23 min time series of broadband images
of a large umbra in the active region NOAA 10634, acquired with the
1-m Swedish Solar Telescope, in the wavelength band around 602 nm. A
43 min part of this series was reconstructed with the MFBD method,
reaching a spatial resolution of 0.14 arcsec. With the help of image
segmentation, feature tracking, and local correlation tracking,
we measured brightness, size, lifetime, and horizontal velocities
of various umbral structures. <BR />Results: Large structures in the
umbra - strong and faint light bridges (LBs) and an extended penumbral
filament - evolve on time scales of hours. Most (90%) of UDs and bright
point-like features in faint LBs split and merge, and their median
lifetimes are 3.5 or 5.7 min, depending on whether the split or merge
event is considered as the end of their life. Both UDs and features in
faint LBs that do not split or merge are clearly smaller (0.15 arcsec)
than the average size (0.17 arcsec) of all features. Horizontal motions
of umbral bright small-scale features are directed either into the
umbra or along faint LBs with mean horizontal velocities of 0.34 km
s<SUP>-1</SUP>. Features faster than 0.4 km s<SUP>-1</SUP> appear
mostly at the periphery of the umbra. The motion of peripheral UDs
(PUDs) seems to be the continuation of the motion of penumbral grains
(PGs). The intensity of dark lanes, measured in four bright central UDs
(CUDs), is by a factor 0.8 lower than the peak intensity of CUDs. The
width of dark lanes is probably less than the resolution limit 0.14
arcsec. The characteristic time of substructure changes of UDs is ~4
min. We observe narrow (0.14 arcsec) bright and dark filaments connected
with PUDs. The bright filaments are 0.06 I_ph brighter than the dark
ones. Usually one dark and two bright filaments form a 0.4 arcsec
wide tail attached to one PUD, resembling a short dark-cored penumbral
filament. <BR />Conclusions: Our results indicate the similarity between
PUDs and PGs located at the tips of bright penumbral filaments. The
features seen in numerical MHD simulations are consistent with our
observations of dark lanes in CUDs and tails attached to PUDs.
---------------------------------------------------------
Title: Supersonic Continuation of the Evershed Flow Outside a Sunspot
as Observed with Hinode
Authors: Martínez Pillet, V.; Katsukawa, Y.; Puschmann, K. G.;
Ruiz Cobo, B.
2009ApJ...701L..79M Altcode: 2009arXiv0907.3835M
We report on the discovery of mostly horizontal field channels just
outside sunspot penumbrae (in the so-called "moat" region) that are
seen to sustain supersonic flows (line-of-sight component of 6 km
s<SUP>-1</SUP>). The spectral signature of these supersonic flows
corresponds to circular polarization profiles with an additional,
satellite, third lobe of the same sign as the parent sunspot' Stokes
V blue lobe, for both downflows and upflows. This is consistent with
an outward directed flow that we interpret as the continuation of the
magnetized Evershed flow outside sunspots at supersonic speeds. In
Stokes Q and U, a clear signature of a transverse field connecting
the two flow streams is observed. Such an easily detectable spectral
signature should allow for a clear identification of these horizontal
field channels in other spectropolarimetric sunspot data. For the spot
analyzed in this paper, a total of five channels with this spectral
signature have been unambiguously found.
---------------------------------------------------------
Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot
interferometer
Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker,
C.; Hofmann, A.; Kneer, F.; Puschmann, K. G.
2009IAUS..259..665B Altcode:
One of the first post-focus instruments of the new solar telescope
GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the
Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope
(VTT) on Tenerife. This spectrometer is equipped with a full-Stokes
polarimeter. The modulation is performed with two ferroelectric liquid
crystals, one acting nominally as quarter-wave plate, and the other as
half-wave plate. A modified Savart plate serves as polarimetric beam
splitter. With the present liquid crystals, the optimum wavelength range
of this polarimeter is between 580 and 660 nm. The spectro-polarimeter
will benefit from the capabilities of the new telescope GREGOR which
will provide a spatial resolution of about 0″.1 (75 km on the solar
surface). Thus we will be able to investigate small magnetic features,
and we will study their development with high cadence.
---------------------------------------------------------
Title: Local Helioseismology with GFPI at the Vacuum Tower Telescope,
Tenerife
Authors: Staiger, J.; Roth, M.; Wöhl, H.; Schleicher, H.; Puschmann,
K.
2008ESPM...12..2.3S Altcode:
Local Helioseimology has recently become an important tool to
investigate the Solar Interior in the vicinity of localized
phenomena like sunspots. It possibly holds the promise to give
informations about subsurface magnetic fields and material flows. We
are currently modifying the GFPI Instrument at the VTT which will
also be a First Light Instrument at GREGOR Telescope to the needs of
ground-based helioseismologic observations (GFPI: Göttingen Fabry
Perot Interferomer). <P />The upgrade consists of a CCD-camera with a
larger Field-of-View (100"-by-100"), a modified Interfacing Hardware and
dedicated Control- and Recording-Software. Direct Interfacing to the
VTT's telescope control system allows for mosaic type patching of the
observations field. Cadence times of below 1 Minute for a 300"-by-300"
field at the telescope's resolution limit of 0.2" are possible. Data
are stored to USB-based external harddisks. An of-the-shelf beamer
allows for optical adjustments with an artificial light source. <P
/>Available Preprocessing Tools allow to immediately visualize the
quality of the observational data. This includes a prelimary Ringdiagram
Analysis. Future Online Preprocessing Capabilities are to further
reduce the achievable cycle times. <P />We will present some details
of the instrumental setup and some prelimiary observational results.
---------------------------------------------------------
Title: First-Light Science Cases for the GREGOR Fabry-Perot
Interferometer
Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados,
M.; Kneer, H. F. Nicklas; Puschmann, K. G.
2008ESPM...12..6.8D Altcode:
The light-gathering capacity and resolving power of the 1.5-meter
aperture GREGOR telescope will provide solar observations of
the full Stokes vector with high temporal, spectral and spatial
resolution. As one of the first-light instruments, the GREGOR
Fabry-Perot Interferometer (GFPI) is well suited for observations
with adaptive optics (AO) correction. Post-facto image correction
(speckle masking imaging and deconvolution) will further enhance
the data quality to approach the diffraction-limited resolution of
the telescope. We will describe the GFPI optical design and its basic
operating procedures. Instruments characteristics such as field-of-view,
cadence, spectral resolution, and spectroscopic/polarimetric observing
modes will result in boundary conditions, which have to be carefully
considered in optimizing the scientific outcome of the first-light
observations. We will present two science cases for quiet Sun and
active region studies to illustrate the capabilities of this imaging
spectro-polarimeter.
---------------------------------------------------------
Title: Fast events and waves in an active region of the Sun observed
in Hα with high spatial resolution
Authors: Sánchez-Andrade Nuño, B.; Bello González, N.; Blanco
Rodríguez, J.; Kneer, F.; Puschmann, K. G.
2008A&A...486..577S Altcode:
Context: We study the chromosphere of an active region of the Sun in
the Hα line. <BR />Aims: The development of new instrumentation and new
methods of data analysis allows to scrutinize the dynamics of the solar
chromosphere with high spatial, spectral, and temporal resolution. The
observations we present shed light on some magneto-dynamic processes
occurring above an active region in the chromosphere. <BR />Methods:
We took a time series of 55 min in Hα from AR 10875 at θ≈36°. We
used the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower
Telescope, Observatorio del Teide/Tenerife, to obtain two-dimensional
spectrograms in Hα. Adaptive optics and image reconstruction yielded
a spatial resolution better than 0.5 arcsec throughout the time
sequence. From the wealth of structures, we selected areas of interest
to study further, in detail, some ongoing processes. <BR />Results:
A small straight surge developed aside of a pore with upward phase
speed of 100 km s<SUP>-1</SUP> and line-of-sight (LOS) velocity of 15
km s<SUP>-1</SUP>. The surge retreated rapidly with LOS velocity of
45 km s<SUP>-1</SUP> at its mouth. It underwent a rebound and fell
back again. Two sympathetic mini-flares were observed that lasted
only approximately 40 s, but showed strong Hα emission. We found
magnetoacoustic waves in long fibrils as mainly short wave trains,
short packets or pulses, i.e., solitary waves consisting of small
(1´´-2´´) blobs. They start at either end of the fibrils and travel
with phase speeds of 12-14 km s<SUP>-1</SUP>, i.e., close to the tube
speed and approximately the sound velocity for sufficiently large
magnetic field strengths. Some waves speed up to reach velocities of
the order of 30 km s<SUP>-1</SUP>. This is much lower than the expected
Alfvén velocity of ≥200 km s<SUP>-1</SUP> for reasonable magnetic
field strengths and mass densities. We suggest that slow waves are not
purely longitudinal, but possess gas velocities perpendicular to the
direction of propagation of few km s<SUP>-1</SUP>. Also, fast waves
travel along sinuous lines suggesting entangled magnetic fields. They
spread out along the direction of propagation in the course of their
evolution and often vanish. We discuss the implications.
---------------------------------------------------------
Title: Kinematics of Umbral Fine Structure
Authors: Sobotka, M.; Puschmann, K. G.; Hamedivafa, H.
2008CEAB...32..125S Altcode:
A 2-hour long series of white-light images of a large sunspot acquired
in June 2004 with the 1-m Swedish Solar Telescope at La Palma is
utilized to study the evolution and motions of small-scale umbral
structures - umbral dots and features in faint light bridges. For
this purpose, a newly improved feature-tracking code is applied. The
small-scale structures move with average speeds of 0.34 km s^{-1} either
into the umbra or along the faint light bridges. Structures that do not
split or merge are smaller (0.15 arcsec) than the average size (0.17
arcsec). Brightness and size variations of individual non-split/merge
structures are positively correlated during their evolution.
---------------------------------------------------------
Title: On the properties of faculae at the poles of the Sun
Authors: Blanco Rodríguez, J.; Okunev, O. V.; Puschmann, K. G.;
Kneer, F.; Sánchez-Andrade Nuño, B.
2007A&A...474..251B Altcode:
Context: Faculae at the poles of the Sun, or polar faculae (PFe),
take part in the solar magnetic cycle. Their occurrence maximum is
shifted by 5-6 years with respect to the sunspot cycle. PFe are stable
phenomena, with lifetimes of several hours to days, and harbour magnetic
fields of kilo-Gauss strength. Yet their role for the global magnetic
field at the solar poles is unknown. <BR />Aims: To contribute to the
knowledge of the physical properties of PFe and to the understanding of
their role in the global magnetism of the Sun. <BR />Methods: PFe were
observed on 21-24 August 2005 with the Vacuum Tower Telescope at the
Observatorio del Teide. The “Göttingen” Fabry-Perot spectrometer
was used with a Stokes V polarimeter to scan the Fe i 6173 Å line
(Landé factor g = 2.5) and the Hα line in two-dimensional fields
of view (FOVs). A large observational coverage of the polar caps was
obtained. The data were analysed with speckle methods. Magnetic field
strengths were determined with the weak field approximation, with the
approximation of the strong field regime, and with the centre of gravity
(COG) method. Velocities were measured with the COG method and from
the zero-crossing of the Stokes V profiles. <BR />Results: PFe show
a decrease of the continuum and broadband intensity contrast towards
the disc centre and no decrease of contrast towards the limb, similar
to as faculae in active regions near the equator. Extrapolating from
the observed FOVs to the total areas of PF occurrence around the solar
poles, we find 4 120 PFe in the northern polar cap and, asymmetrically
to this number, 1 250 PFe near the south pole. The total area coverages
by PFe are ~7.6×10<SUP>8</SUP> km<SUP>2</SUP> and ~3.4×10<SUP>8</SUP>
km<SUP>2</SUP> near the solar north and south poles, respectively. Some
of the PFe exhibit magnetic polarities opposite to the global polarity
at the time of observation. The resulting total magnetic fluxes in PFe
fall short by an order of magnitude from those found in the literature
for the fluxes at the polar caps. This also holds if we include magnetic
structures which are not related to brightenings. We conclude that
with the present spatial resolution of 0.4 arcsec-0.5 arcsec (FWHM),
PFe represent the “large-scale” end of a distribution of unipolar
strands near the solar poles. The velocities in PFe show amplitudes of
2 km s<SUP>-1</SUP>, with systematic up-flows in the Stokes I profile,
but no average velocity measured in the V zero-crossings.
---------------------------------------------------------
Title: Spicule emission profiles observed in He i 10 830 Å
Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.;
Trujillo Bueno, J.; Blanco Rodríguez, J.; Kneer, F.
2007A&A...472L..51S Altcode: 2007arXiv0707.4421S
Aims:Off-the-limb observations with high spatial and spectral resolution
will help us understand the physical properties of spicules in the
solar chromosphere. <BR />Methods: Spectropolarimetric observations
of spicules in the He i 10 830 Å multiplet were obtained with the
Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope
at the Observatorio del Teide (Tenerife, Spain). The analysis shows
the variation of the off-limb emission profiles as a function of the
distance to the visible solar limb. The ratio between the intensities
of the blue and the red components of this triplet (R=I_blue/I_red)
is an observational signature of the optical thickness along the light
path, which is related to the intensity of the coronal irradiation. <BR
/>Results: We present observations of the intensity profiles of spicules
above a quiet Sun region. The observable R as a function of the distance
to the visible limb is also given. We have compared our observational
results to the intensity ratio obtained from detailed radiative transfer
calculations in semi-empirical models of the solar atmosphere assuming
spherical geometry. The agreement is purely qualitative. We argue that
future models of the solar chromosphere and transition region should
account for the observational constraints presented here.
---------------------------------------------------------
Title: Modern Solar Facilities - Advanced Solar Science
Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D.
2007msfa.conf.....K Altcode:
An international workshop entitled: Modern Solar Facilities - Advanced
Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop,
which was attended by 88 participants from 24 different countries, gave
a broad overview of the current state of solar research, with emphasis
on telescopes and instrumentation, high-resolution and high-precision
observations, and theory and interpretation. The book collects written
versions of 71 papers presented at the conference.
---------------------------------------------------------
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: Temporal evolution of intensity, velocity and magnetic field
of sunspots at high spatial resolution
Authors: Bello González, N.; Kneer, F.; Puschmann, K. G.
2007msfa.conf..217B Altcode:
We present results of sunspot observations obtained in April 2006
with the new "Göttingen" Fabry-Perot spectrometer. Thanks to the
large field of view (77"x58") of the new optical setup it has been
possible to perform 2D-spectropolarimetric observations of a small
sunspot and ist surroundings at a heliocentric angle [Theta] ~ 40Å. A
long time series of about one hour has been taken scanning along the
magnetic Fe I 6173 Å and the non-magnetic Fe I 5576 Å spectral lines
quasi-simultaneously. Hence, with the help of image reconstruction
techniques, the temporal evolution of the sunspot fine-structure in
intensity as well as in velocity and magnetic field is analysed at
high spatial resolution.
---------------------------------------------------------
Title: Off-limb spectroscopy of the He I 10830 Å multiplet:
observations vs. modelling
Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.;
Trujillo Bueno, J.; Kneer, F.
2007msfa.conf..177S Altcode:
Spectropolarimetric observations of spicules were carried out with
the new optical setup of the Tenerife Infrared Polarimeter (TIP 2)
at the VTT, showing the variation of the He I 10830Å multiplet
off-limb emission profiles with increasing distance to the solar
visible limb. The ratio between the intensities of the blue and the
red components of this triplet (R = Iblue/Ired) is an observational
signature of the optical thickness along the light path, which, at the
same time, is proportional to the population of the lower (metastable)
level that takes part in these transitions. Our observational results
show a variation of R as a function of the distance to the limb. In
agreement with recent theoretical results we conclude that R could be
used as a diagnostic tool for downward UV coronal irradiance, which is
believed to be responsible for the population of the metastable level of
the He I 10830 Å triplet. We have compared our observational results
with the ratio obtained from detailed radiative transfer calculations
in semi-empirical models of the solar atmosphere (assuming spherical
geometry) finding a fairly poor agreement. We argue that future models
of the solar chromosphere and transition region should account for
the observational constraints presented here.
---------------------------------------------------------
Title: From the "Göttingen" Fabry-Perot Interferometer to the
GREGOR FPI
Authors: Puschmann, K. G.; Kneer, F.; Nicklas, H.; Wittmann, A. D.
2007msfa.conf...45P Altcode:
Fabry-Perot Interferometers (FPIs) have advantages over slit
spectrographs, allowing fast two-dimensional, narrowband imaging
and post factum image reconstruction of the spectropolarimetric data
obtained. The resulting intensity, velocity and magnetic field maps
are a fundamental base for the understanding of the dynamics of
the solar atmosphere and its magnetic fields at smallest spatial
scales. Efforts are undertaken to provide, with the Göttingen
Fabry-Perot interferometer, an up-todate post-focus instrument for
the German 1.5 m GREGOR solar telescope. Therefore a renewal of the
spectrometer has been achieved during the first half of 2005. First
observations at the German Vacuum Tower Telescope (VTT) reveal new
scientific aspects and a very promising outlook for the future at
GREGOR. In this contribution a general description of the upgraded
spectrometer is given. Its final optical design at GREGOR is described
and an optical analysis of the GREGOR FPI is outlined. Latest results
with the new instrument obtained at the VTT are presented.
---------------------------------------------------------
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: Modern solar facilities - advanced solar science
Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D.
2007msfa.conf....0K Altcode:
An international workshop entitled: Modern Solar Facilities - Advanced
Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop,
which was attended by 88 participants from 24 different countries, gave
a broad overview of the current state of solar research, with emphasis
on telescopes and instrumentation, high-resolution and high-precision
observations, and theory and interpretation. The book collects written
versions of 71 papers presented at the conference.
---------------------------------------------------------
Title: Observations of a flaring active region in H[alpha]
Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F.
2007msfa.conf..273S Altcode:
A 40 min time series of the active region NOAA AR10875 was obtained
on April 26th, 2006 under very good seeing conditions using the new
"Göttingen" - Fabry-Perot interferometer at the German Vacuum Tower
Telescope, Observatorio del Teide, Tenerife. The Hα line was scanned
giving two-dimensional images at 21 different wavelength positions
with a cadence of ~ 20 s per scan. After speckle reconstruction the
spatial resolution achieved was better than 0".35. The data provide a
unique possibility to study the temporal evolution of a pre-flaring,
flaring and post-flaring solar active region in Hα. From the analysis
of the present spectrometric data set we expect important advances in
the understanding of Alfén waves, dynamics of fibrils and filaments
and the physical nature of the sigmoid structure seen in the core of
Hα. Here we present first results from this data set.
---------------------------------------------------------
Title: Dynamics of the quiet photosphere and its magnetic field
under high spatial resolution
Authors: Puschmann, K. G.; Kneer, F.; Domínguez Cerdeña, I.
2007msfa.conf..151P Altcode:
An excellent 1 h 10 min time series of a quiet solar region near
disk centre was acquired on 4th of May 2006 at the German Vacuum
Tower Telescope. Using the new "Göttingen" Fabry-Perot interferometer
together with the Kiepenheuer Adaptive Optics system spectropolarimetric
images were obtained, scanning the Fe I 5247Å and Fe I 5250Å lines
with a temporal cadence of 17 s each. Thanks to speckle reconstruction
methods the achieved spatial resolution of the obtained intensity,
velocity and magnetic field maps is ~ 0."3. First results on
the dynamics of the quiet photosphere and magnetic fields reveal
strengthening and weakening of the polarisation signal in interaction
to granular convection processes indicating advection and diffusion
of magnetic flux at smallest scales. Field structures, very elongated
along intergranular lanes, show high dynamics, combine and split, and
leave strong fingerprints at high photospheric layers where related
temperatures fluctuate. Recent numerical MHD simulations come close
to our findings. Possible indications of magnetic flux annihilation,
flux tube evacuation or signs of upward-propagating shock fronts
are illustrated.
---------------------------------------------------------
Title: Fine structure in a dark umbra
Authors: Sobotka, M.; Puschmann, K. G.
2007msfa.conf..205S Altcode:
An excellent-quality time series of images of a large dark umbra of
the leading sunspot of NOAA 10634 was acquired on 18 June 2004 with the
1-m Swedish Solar Telescope at La Palma, simultaneously in blue, red,
and G-band channels. The temporal and spatial resolutions are 20 s and
0".14. A 2-hour long series of the red continuum images is analysed,
showing the faintest umbral fine structures. In addition to umbral dots,
often clustered to more stable "granules" or aligned to short chains,
we observe large, low-intensity elongated structures with dark central
channels, resembling extremely faint light bridges. At the periphery
of the umbra, bright umbral dots move inwards, showing a similarity
to penumbral grains. Kinematic properties of umbral fine structures
are studied.
---------------------------------------------------------
Title: Study of polar faculae with north pole coverage of the Sun
Authors: Blanco Rodríguez, J.; Okunev, O.; Puschmann, K. G.; Kneer, F.
2007msfa.conf..181B Altcode:
We present here a description of the main characteristics of faculae
at the poles of the Sun (polar faculae PFe) observed in a series of
observations covering the north solar pole. Statistics of a group
of these PFe are used to estimate the contrast behaviour from [mμ]
= 0.6 towards the limb as well as their magnetic field. Hα is also
observed to analyse the behaviour of PFe in the chromosphere.
---------------------------------------------------------
Title: Dynamics of Magnetic Bright Points in an Active Region
Authors: Möstl, C.; Hanslmeier, A.; Sobotka, M.; Puschmann, K.;
Muthsam, H. J.
2006SoPh..237...13M Altcode: 2006SoPh..tmp....2M
A high-quality 80-minute time series of a part of a sunspots moat
(18 ″ × 23 ″) in the G-band (4308.64 Å) has been analysed
to measure the horizontal velocities of Magnetic Bright Points
(MBPs). The observations were carried out in June 2004 at the new
1-meter Swedish Solar Telescope in La Palma. Spatial resolution was
estimated to be 0.17 ″ or 125 km on the Sun, and images were taken
in a frame selection mode in a 20-seconds interval. Individual feature
tracking of MBPs with manual selection and automated tracking has been
performed. The intensity of MBPs increases with size. The mean value
in a MBP-velocity histogram was found to be 1.11 km s <SUP>−1</SUP>
and it shows good accordance with an abnormal granulation-velocity
histogram. MBP velocity histograms as presented here can be taken
as an input for coronal heating models in an active region. However,
MBPs move slower in an active region than in the network (presumably
because of the higher active region magnetic flux) and hence, a process
that includes dissipation of MHD waves through fast MBP motions (>2
km s <SUP>−1</SUP>) may not alone explain the observed properties
of the corona.
---------------------------------------------------------
Title: Speckle reconstruction of photometric data observed with
adaptive optics
Authors: Puschmann, K. G.; Sailer, M.
2006A&A...454.1011P Altcode:
To achieve the highest spatial resolution for ground-based observations
one has to correct for degradations by the Earth's atmosphere. This
can be done by on-line and post-facto techniques. Here we combine
observations with Adaptive Optics (AO) and speckle reconstruction. As
possible techniques we present two modified versions (methods B and C)
of the Göttingen speckle masking code and describe their application
to observations of a solar active region obtained with the Swedish 1-m
Solar Telescope (La Palma) by means of AO. By comparing the results with
those obtained from the conventional method (method A), the influence
of AO on the post-facto reconstruction is revealed. One has to account
for the field dependence of the AO correction and the fitting errors
of the calculated surface of the deformable mirror with respect to
the according wave fronts. Both new approaches enhance the contrast in
the lockpoint region less than the conventional method. Method C uses
simulated AO corrected speckle transfer functions (STFs). This method
shows the most uniform image quality over the whole field of view
and indicates the importance of the atmospheric model assumptions and
the partial character of the WF correction by AO with appropriate WF
error statistics. However, the consideration of field dependent speckle
transfer functions in the classical speckle reconstruction (Method B)
can serve as a first approach to avoid an intensity over-amplification
around the AO-lockpoint region, although the rms of the contrast in the
reconstructed images tends to rise slightly towards the outer parts
of the field of view. Even the apparently small differences between
the speckle transfer functions, used in the different reconstruction
methods, cause the modulus of the estimated intensity differences to
vary by up to 22%.
---------------------------------------------------------
Title: The new Göttingen Fabry-Pérot spectrometer for
two-dimensional observations of the Sun
Authors: Puschmann, K. G.; Kneer, F.; Seelemann, T.; Wittmann, A. D.
2006A&A...451.1151P Altcode:
Studies of small-scale dynamics and magnetic fields in the solar
atmosphere require spectroscopy and polarimetry with high spatial
resolution. For this purpose, spectrometers based on Fabry-Pérot
interferometers (FPIs) have advantages over slit spectrographs. They
possess a high throughput and allow fast two-dimensional,
narrow-band imaging and image reconstruction of the data. In the
present contribution we describe an upgrade, essentially renewal,
of the Göttingen FPI spectrometer achieved during the first half of
2005. A new etalon from IC Optical Systems Ltd. (formerly Queensgate),
England, with 70 mm free aperture for high spectral resolution has
been mounted. New CCD detectors from LaVision GmbH (Göttingen) with
powerful computer hard- and software were implemented. We consider the
product of signal-to-noise ratio, frame rate, and field of view as a
measure of the efficiency. At low light levels, e.g. in narrow-band
speckle applications, this product has increased by a factor ~60
compared to the old system. In addition, several spectral regions can
now be scanned quasi-simultaneously. We present first results obtained
with the upgraded spectrometer. The efforts are undertaken to provide
an up-to-date post-focus instrument for the new German 1.5 m GREGOR
solar telescope presently under construction at the Observatorio del
Teide on Tenerife.
---------------------------------------------------------
Title: The flux-gap between bright and dark solar magnetic structures
Authors: Puschmann, K. G.; Wiehr, E.
2006A&A...445..337P Altcode:
The upper size limit of solar small-scale magnetic flux concentrations
("G-band bright points", BP) is reconsidered from speckle-reconstructed
images taken at the 1-m SST on La Palma. The size-histogram shows
a sharp drop towards 250 km diameter, variation of the noise filter
threshold diminishes that value due to segmentation of the elongated
structures. A further artificial segmentation of still elongated
(i.e. not round) BP indicates that the upper limit may well be below 200
km diameter, corresponding to a flux smaller than 2.5×10<SUP>17</SUP>
Mx which is more than 40 times smaller than that of smallest dark
(mini-) pores. BP with diameters of 130 km would already yield to a
flux gap of two orders of magnitude. The drop of BP numbers between the
histogram maximum and the 90 km resolution limit achieved is found to
depend on the low-pass filtering and is thus probably virtual. Higher
spatial resolution data will still increase the flux gap between bright
and dark solar magnetic flux concentrations which might be a signature
of differently deep rooting in the solar atmosphere.
---------------------------------------------------------
Title: Chromospheric Dynamics of a Solar Active Region
Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez
Cuberes, M.; Blanco Rodríguez, J.; Kneer, F.
2005ESASP.600E..70S Altcode: 2005dysu.confE..70S; 2005ESPM...11...70S
No abstract at ADS
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Title: Study of Polar Faculae
Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann,
K. G.; Kneer, F.
2005ESASP.600E..59B Altcode: 2005dysu.confE..59B; 2005ESPM...11...59B
No abstract at ADS
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Title: Analysis of a Wide Chromospheric Active Region
Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez
Cuberes, M.; Blanco Rodríguez, J.; Kneer, F.
2005ESASP.596E..62S Altcode: 2005ccmf.confE..62S
No abstract at ADS
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Title: Magnetic Structures on the Sun: Osbervations with the New
"GÖTTINGEN" Two-Dimensional Spectrometer on Tenerife
Authors: Kneer, F.; Puschmann, K. G.; Blanco Rodríguez, J.;
Sánchez-Andrade Nuño, B.; Wittmann, A. D.
2005ESASP.596E..71K Altcode: 2005ccmf.confE..71K
No abstract at ADS
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Title: Study of Polar Faculae
Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann,
K. G.; Kneer, F.
2005ESASP.596E..52B Altcode: 2005ccmf.confE..52B
No abstract at ADS
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Title: Analysis of Polarimetric Sunspot Data from Tesos/vtt/tenerife
Authors: Valdivielso Casas, L.; Bello González, N.; Puschmann, K. G.;
Sánchez-Andrade Nuño, B.; Kneer, F.
2005ESASP.596E..67V Altcode: 2005ccmf.confE..67V
No abstract at ADS
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Title: The structure of a penumbral connection between solar pores
Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.;
Puschmann, K. G.; Sobotka, M.
2005A&A...442.1079H Altcode:
High resolution 2D-spectro-polarimetric observations have been used
to analyse the magnetic field and flow topologies of a penumbral
connection between two opposite polarity solar pores. A filamentary
structured Evershed-like material flow from one pore to the other
along the magnetic field lines has been detected. The flow channels
are co-spatial with bright penumbral filaments close to the pore which
feeds the flow and the clear brightness-velocity relation vanishes close
to the pore which represents the sink of the flow. The boundary between
umbra and penumbra of the two pores show significant differences: bright
comet-like penumbral grains represent endings of penumbral filaments
at the flow sources whereas no such grains were found at the sinks of
the flow. Furthermore, a systematic variation of the asymmetries of
measured Stokes V profiles across the penumbral connection have been
found. The obtained results are in accordance with the widely-accepted
uncombed penumbra hypothesis and the moving flux tube model.
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Title: The Size of Small-Scale Solar Magnetic Regions
Authors: Wiehr, E.; Puschmann, K. G.
2005ESASP.596E..20W Altcode: 2005ccmf.confE..20W
No abstract at ADS
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Title: Time series of high resolution photospheric spectra in a
quiet region of the Sun. II. Analysis of the variation of physical
quantities of granular structures
Authors: Puschmann, K. G.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.;
Hanslmeier, A.
2005A&A...441.1157P Altcode: 2012arXiv1205.1725P
From the inversion of a time series of high resolution slit spectrograms
obtained from the quiet sun, the spatial and temporal distribution
of the thermodynamical quantities and the vertical flow velocity is
derived as a function of optical depth (logτ) and geometrical height
(z). Spatial coherence and phase shift analyses between temperature
and vertical velocity depict the height variation of these physical
quantities for structures of different size. An average granular
cell model is presented, showing the granule-intergranular lane
stratification of temperature, vertical velocity, gas pressure and
density as a function of logτ and z. Studies of a specific small
and a specific large granular cell complement these results. A strong
decay of the temperature fluctuations with increasing height together
with a less efficient penetration of smaller cells is revealed. The
T-T coherence at all granular scales is broken already at logτ = -1
or z ~ 170 km. At the layers beyond, an inversion of the temperature
contrast at granular scales >1.5 arcsec is revealed, both in logτ
and z. At deeper layers the temperature sensitivity of the H<SUP>-</SUP>
opacity leeds to much smaller temperature fluctuations at equal logτ
than at equal z, in concordance with Stein & Nordlund (1998, ApJ,
499, 914). Vertical velocities are in phase throughout the photosphere
and penetrate into the highest layers under study. Velocities at the
largest granular scales (~ 4´´) are still found even at logτ ~ -2.8
or z ~ 370 km. Again a less efficient height penetration of smaller
cells concerning convective velocities is revealed, although still
at logτ ~ -2 or z ~ 280 km structures >1.4 arcsec are detected. A
similar size distribution of velocity and temperature structures with
height provides observational evidence for substantial overshoot into
the photosphere. At deep photospheric layers, the behaviour of the
vertical velocities reflected in simulations is for the first time
qualitatively reproduced by observations: intergranular velocities
are larger than the granular ones and, both reach extrema, where the
granular one is shifted towards higher layers.
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Title: Spectropolarimetry of a sunspot at disk centre
Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E.
2005A&A...440..345S Altcode:
The magnetic, thermal and velocity structure of a sunspot at
the solar disk centre (θ=2°) is investigated by inverting the
full Stokes profiles of three infrared lines. A single magnetic
component atmosphere is assumed with height gradients of the physical
quantities. Since the line-of-sight (LOS) is perpendicular to the solar
surface, differential optical or projection effects do not interfere,
as often is the case for the usual observations at oblique LOS. We find
a symmetric configuration of the field and flow and the downward motion
that increases with radial distance by up to 3 km s<SUP>-1</SUP> near
the outer penumbral border. The magnetic field is found to be highly
axially symmetric without any indication of azimuthal vortices. A
tight relation between field strength and inclination is obtained
with a gradient of 35°/1000 G independent of height. The penumbra
shows "spines" hosting a pronounced negative correlation between
field strength and inclination in the sense that steeper and stronger
magnetic fields are related to brightenings in the line cores but not
in the continuum. We discuss the dependence of the obtained results
on different assumptions of parasitic light, and present indications
of its overestimation by the inversion code.
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Title: On super-resolution in astronomical imaging
Authors: Puschmann, K. G.; Kneer, F.
2005A&A...436..373P Altcode:
Our work is an attempt to fulfil one of the aims of astronomical
imaging, that is, to obtain information at high angular
resolution. Stars as point sources can be represented by
Dirac δ-functions whose Fourier transforms contain information
about the position and the (integrated) intensity at all angular
frequencies. Thus, we can deconvolve unresolved images of star fields
even at angular distances smaller than the diffraction limit of
the telescope with which the observations are performed. We give an
example of reconstruction of the image of two stars with an angular
separation of a factor 2.5 less than α_Ra=1.22×λ/D. However, we
find that super-resolution is feasible only for point sources. For
extended objects the information about intensity fluctuations at angular
frequencies u>u_max=D/λ=1/α_min is irretrievably lost. We discuss
the impossibility of super-resolution for the Sun using a numerically
simulated image of solar granulation. However, one can enhance the
contrast of solar images, though without increasing angular resolution
beyond the diffraction limit.
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Title: Polarimetry of sunspot penumbrae with high spatial resolution
Authors: Bello González, N.; Okunev, O. V.; Domínguez Cerdeña,
I.; Kneer, F.; Puschmann, K. G.
2005A&A...434..317B Altcode:
We present two-dimensional high-spatial-resolution spectropolarimetric
observations of sunspot penumbrae. They were obtained in April 2002 and
May 2003 with the "Göttingen" Fabry-Pérot spectrometer at the Vacuum
Tower Telescope at the Observatorio del Teide (Tenerife). Speckle
methods were applied for image reconstruction which resulted
in a spatial resolution of 0.5 arcsec in the magnetograms of the
penumbrae. We analysed Stokes I and V profiles of the Fe II 6149 Å
line, which exhibits no instrumental Stokes Q/U→ V crosstalk, and of
the Fe I line pair at 6302 Å. The main results are the following: 1)
on scales larger than 0.5 arcsec, the intensity pattern of penumbrae
stays the same in the continuum and core images of the 6301.5 Å line,
which stem from 0 km and 300 km (above τ_5=1), respectively. Yet
at scales of 0.5 arcsec and smaller the pattern in the two spectral
features is clearly different. 2) On the limb side of sunspots the
Evershed flow is carried by dark filaments and on the centre side by
bright features and their somewhat weakened tails. We explain this with
a picture in which the velocity of hot rising gas is best seen on the
centre side, while on the limb side the horizontal outward and possibly
downward flows are seen when the gas has cooled down. 3) The un-combed
structure of the magnetic field is confirmed. On the limb side, the more
horizontal fields coincide with dark fibrils or with diffuse intensity
structures. Generally, the more horizontal fields are located at the
positions of strong outflows. 4) Strong line-of-sight components of
the magnetic fields are not found in bright filaments but in dark
structures, somewhat displaced from the darkest parts. Their positions
do not coincide with those of the strongest velocity fields. In general,
our results are compatible with the picture of low lying flow channels
coincident with the horizontal magnetic field, or possibly emerging and
diving down into sub-photospheric layers, like a "sea serpent". Some
further dynamic phenomena are discussed, which demonstrate the richness
of processes in penumbrae, and reveal unexpected properties.
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Title: Quiet sun magnetic fields vs. polar faculae - local vs. global
dynamo?
Authors: Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.;
Kneer, F.; Sánchez Almeida, J.
2005AN....326..205O Altcode:
Quiet Sun magnetic fields in the internetwork are almost
ubiquitous. Simultaneous observations in infra-red and visible lines
and high spatial resolution (< 0.5<SUP>”</SUP>) data in visible
lines show that their field strengths range from below few hundred
Gauss to kilo-Gauss. Most of the flux is contained in small-scale,
strong-field features located mainly in intergranular lanes. The
average unsigned flux density exceeds 20 Gauss. The new detections
are confirmed by recent quiet Sun observations in the G band. The
generation of the strong fields in the internetwork, which may be due
to a local dynamo, poses a challenging problem. - Polar faculae (PFe)
are small-scale magnetic features at the polar caps of the Sun. They
take part in the solar cycle and are thus likely to be rooted deeply
in the solar interior. They are the result of the global dynamo at
the solar poles. PFe also possess kilo-Gauss magnetic fields which
have the same polarity as the global magnetic field. The rôle of
quiet Sun magnetic field structures and of PFe for the dynamics of
the corona and for the solar wind are addressed.
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Title: Polarimetry of a sunspot at disk centre
Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E.
2004IAUS..223..237S Altcode: 2005IAUS..223..237S
No abstract at ADS
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Title: Time series of high resolution photospheric spectra in a quiet
region of the sun. I. Analysis of global and spatial variations of
line parameters
Authors: Puschmann, K.; Vázquez, M.; Bonet, J. A.; Ruiz Cobo, B.;
Hanslmeier, A.
2003A&A...408..363P Altcode: 2012arXiv1205.1723P
A 50 min time series of one-dimensional slit-spectrograms, taken in
quiet sun at disk centre, observed at the German Vacuum Tower Telescope
(Observatorio del Teide), was used to study the global and spatial
variations of different line parameters. In order to determine the
vertical structure of the photosphere two lines with well separated
formation heights have been considered. The data have been filtered of
p-modes to isolate the pure convective phenomenon. From our studies
of global correlation coefficients and coherence and phase shift
analyses between the several line parameters, the following results
can be reported. The convective velocity pattern preserves structures
larger than 1.0 arcs to the highest layers of the photosphere (
~ 435 km). However, at these layers, in the intensity pattern only
structures larger than 2.0 arcs are still connected with those at the
continuum level although showing inverted brightness contrast. This
confirms an inversion of temperature that we have found at a height
of ~ 140 km. A possible evidence of gravity waves superimposed to
the convective motions is derived from the phase shift analysis. We
interprete the behaviour of the full width at half maximum and the
equivalent width as a function of the distance to the granular borders,
as a consequence of enhanced turbulence and/or strong velocity gradients
in the intergranular lanes.
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Title: Models of a Small and a Large Mean Granular Cell Obtained
from Inversion of Spectrometric Data Observed with Adaptive Optics
Authors: Puschmann, K.; Ruiz Cobo, B.
2003ANS...324...21P Altcode: 2003ANS...324..C01P
No abstract at ADS
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Title: Models of a mean granular cell
Authors: Puschmann, K.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.;
Hanslmeier, A.
2003AN....324..352P Altcode:
From inversion of a time series of slit spectra, observed in a quiet
region of the solar photosphere, averaged models of a granular cell
have been obtained showing the stratification of physical quantities
versus optical depth and geometrical height. Furthermore a semi-empiric
dynamic model of a mean granular cell has been derived and the results
are presented.
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Title: A Fabry-Perot spectrometer for high-resolution observation
of the Sun
Authors: Kneer, F.; Al, N.; Hirzberger, J.; Nicklas, H.; Puschmann,
K. G.
2003AN....324..302K Altcode:
No abstract at ADS
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Title: Size-dependent properties of simulated 2-D solar granulation
Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.; Ploner,
S. R. O.; Puschmann, K. G.; Solanki, S. K.
2000A&AS..146..267G Altcode:
Two time-dependent sets of two-dimensional hydrodynamic models of solar
granulation have been analyzed to obtain dependence of simulated thermal
convection on the horizontal size of the convection cells. The two
sets of models treat thermal convection either as fully non-stationary,
multiscale convection (granular convection is a surface phenomenon) or
as quasi-steady-state convection cells (they treat granular convection
as a collection of deep-formed cells). The following results were
obtained: 1) quasi-steady convection cells can be divided into 3
groups according to their properties and evolution, namely small-scale
(up to L ~ 900 km), intermediate-scale (1000-1500 km) and large-scale
(larger 1500 km) convection cells. For the first group thermal damping
due to radiative exchange of energy, mostly in the horizontal direction,
is very important. Large-scale cells build up a pressure excess, which
can lead to their total fragmentation. Similar processes also acts on
the fully non-stationary convection. 2) The largest horizontal size
of convection cells for which steady-state solutions can be obtained
is about 1500 km. This corresponds to granules, i.e. the bright
parts of the convection cells, with a diameter of about 1000 km. 3)
In addition to the zone of high convective instability associated
with the partial ionization of hydrogen, we identify another layer
harboring important dynamic processes in steady-state models. Just
below the hydrogen-ionization layer pressure fluctuations and the
acoustic flux are reduced. Steady-state models with reflecting lateral
boundaries even exhibit an inversion of pressure fluctuations there. 4)
From observational point of view the surface convection differs from
steady-state deep treatment of thermal convection in the dependence
of vertical granular velocities on their sizes for small-scale
inhomogeneous. However, they cannot be distinguished by the dependence
of temperature or emergent intensity of brightness structures. 5) Both
kinds of models demonstrate the inversion of density in subphotospheric
layers. It is more pronounced in small-scale cells and inside hot
upflows. 6) The brightness of simulated granules linearly increases
with their size for small granules and is approximately constant or
even decreases slightly for larger granules. For intergranular lanes
the simulations predict a decrease of their brightness with increasing
size. It falls very rapidly for narrow lanes and remains unchanged
for broader lanes. 7) A quantitative comparison of the brightness
properties of simulated granulation with real observations shows
that the strong size-dependence of the properties of the smallest
simulated granules is not accessible to current observations due to
their limited spatial resolution. The observed size dependences result
rather from spatial smoothing and the granule-finding algorithm. We
do not exclude, however, an influence of the limitations of the 2-D
treatment of thermal convection on the present results.
---------------------------------------------------------
Title: Solar Line Bisectors in the Infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
1999ASSL..239..227P Altcode: 1999msa..proc..227P
In the present work we made some analysis with respect to shifts
and asymmetries of infrared solar spectral lines to get information
about vertical velocity fields in the deep layers of the Solar
Photosphere. For the analysis of shifts and asymmetries of bisectors
were used. We averaged bisectors belonging to a group of similar line
parameter. Therefore it was possible, to analyse correlations between
asymmetries and line shifts and corresponding vertical velocities with
line parameters and to discuss the results with other literature.
---------------------------------------------------------
Title: Solar line bisectors in the infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
1995IAUS..176P.117P Altcode:
No abstract at ADS
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Title: Solar line bisectors in the infrared.
Authors: Puschmann, K.; Anslmeier, A.; Solanki, S.
1994AGAb...10..117P Altcode:
No abstract at ADS
