explanation blue bibcodes open ADS page with paths to full text
Author name code: suetterlin
ADS astronomy entries on 2022-09-14
author:"Suetterlin, Peter"
---------------------------------------------------------
Title: Design and Performance Analysis of a Highly Efficient
Polychromatic Full Stokes Polarization Modulator for the CRISP
Imaging Spectrometer
Authors: de Wijn, A. G.; de la Cruz Rodríguez, J.; Scharmer, G. B.;
Sliepen, G.; Sütterlin, P.
2021AJ....161...89D Altcode: 2021arXiv210201231D
We present the design and performance of a polychromatic polarization
modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry-Perot
tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar
Telescope (SST). We discuss the design process in depth, compare
two possible modulator designs through a tolerance analysis, and
investigate thermal sensitivity of the selected design. The trade-offs
and procedures described in this paper are generally applicable in the
development of broadband polarization modulators. The modulator was
built and has been operational since 2015. Its measured performance
is close to optimal between 500 and 900 nm, and differences between
the design and as-built modulator are largely understood. We show some
example data, and briefly review scientific work that used data from
SST/CRISP and this modulator.
---------------------------------------------------------
Title: CRISPRED: CRISP imaging spectropolarimeter data reduction
pipeline
Authors: de la Cruz Rodríguez, J.; Löfdahl, M. G.; Sütterlin, P.;
Hillberg, T.; Rouppe van der Voort, L.
2017ascl.soft08003D Altcode:
CRISPRED reduces data from the CRISP imaging spectropolarimeter at
the Swedish 1 m Solar Telescope (SST). It performs fitting routines,
corrects optical aberrations from atmospheric turbulence as well as
from the optics, and compensates for inter-camera misalignments,
field-dependent and time-varying instrumental polarization, and
spatial variation in the detector gain and in the zero level offset
(bias). It has an object-oriented IDL structure with computationally
demanding routines performed in C subprograms called as dynamically
loadable modules (DLMs).
---------------------------------------------------------
Title: CRISPRED: A data pipeline for the CRISP imaging
spectropolarimeter
Authors: de la Cruz Rodríguez, J.; Löfdahl, M. G.; Sütterlin, P.;
Hillberg, T.; Rouppe van der Voort, L.
2015A&A...573A..40D Altcode: 2014arXiv1406.0202D
The production of science-ready data from major solar telescopes
requires expertise beyond that of the typical observer. This is
a consequence of the increasing complexity of instruments and
observing sequences, which require calibrations and corrections
for instrumental and seeing effects that are not only difficult to
measure, but are also coupled in ways that require careful analysis
in the design of the correction procedures. Modern space-based
telescopes have data-processing pipelines capable of routinely
producing well-characterized data products. High resolution imaging
spectropolarimeters at ground-based telescopes need similar data
pipelines.We present new methods for flat-fielding spectropolarimetric
data acquired with telecentric Fabry-Perot instruments and a new
approach for accurate camera co-alignment for image restoration. We
document a procedure that forms the basis of current state-of-the-art
processing of data from the CRISP imaging spectropolarimeter at the
Swedish 1 m Solar Telescope (SST). By collecting, implementing, and
testing a suite of computer programs, we have defined a data reduction
pipeline for this instrument. This pipeline, CRISPRED, streamlines the
process of making science-ready data.It is implemented and operated
in IDL, with time-consuming steps delegated to C.CRISPRED will also be
the basis for the data pipeline of the forthcoming CHROMIS instrument.
---------------------------------------------------------
Title: Ellerman bombs: fallacies, fads, usage
Authors: Rutten, Robert J.; Vissers, Gregal J. M.; Rouppe van der
Voort, Luc H. M.; Sütterlin, Peter; Vitas, Nikola
2013JPhCS.440a2007R Altcode: 2013arXiv1304.1364R
Ellerman bombs are short-lived brightenings of the outer wings of Hα
that occur in active regions with much flux emergence. We point out
fads and fallacies in the extensive Ellerman bomb literature, discuss
their appearance in various spectral diagnostics, and advocate their
use as indicators of field reconfiguration in active-region topography
using AIA 1700 Å images.
---------------------------------------------------------
Title: Opposite polarity field with convective downflow and its
relation to magnetic spines in a sunspot penumbra
Authors: Scharmer, G. B.; de la Cruz Rodriguez, J.; Sütterlin, P.;
Henriques, V. M. J.
2013A&A...553A..63S Altcode: 2012arXiv1211.5776S
We discuss NICOLE inversions of Fe i 630.15 nm and 630.25 nm Stokes
spectra from a sunspot penumbra recorded with the CRISP imaging
spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial
resolution close to 0.15 arcsec. We report on narrow, radially extended
lanes of opposite polarity field, located at the boundaries between
areas of relatively horizontal magnetic field (the intra-spines) and
much more vertical field (the spines). These lanes harbor convective
downflows of about 1 km s<SUP>-1</SUP>. The locations of these downflows
close to the spines agree with predictions from the convective gap
model (the "gappy penumbra") proposed six years ago, and more recent
three-dimensional magnetohydrodynamic simulations. We also confirm the
existence of strong convective flows throughout the entire penumbra,
showing the expected correlation between temperature and vertical
velocity, and having vertical root mean square velocities of about
1.2 km s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Search for Alfvén waves in a bright network element observed
in Hα
Authors: Koza, J.; Sütterlin, P.; Gömöry, P.; Rybák, J.;
Kučera, A.
2013CoSka..43....5K Altcode: 2013arXiv1304.4027K
Alfvén waves are considered as potential transporters of energy
heating the solar corona. We seek spectroscopic signatures of the
Alfvén waves in the chromosphere occupied by a bright network element,
investigating temporal variations of the spectral width, intensity,
Dopplershift, and the asymmetry of the core of the Hα spectral
line observed by the tunable Lyot filter installed on the Dutch Open
Telescope. The spectral characteristics are derived through the fitting
of five intensity samples, separated from each other by 0.35 Å, by a
4<SUP>th</SUP>-order polynomial. The bright network element displays
the most pronounced variations of the Dopplershift varying from 0 to 4
km s<SUP>-1</SUP> about the average of 1.5 km s<SUP>-1</SUP>. This fact
implies a persistent redshift of the Hα core with a redward asymmetry
of about 0.5 km s<SUP>-1</SUP>, suggesting an inverse-C bisector. The
variations of the core intensity up to ±10 % and the core width up to
±5 % about the respective averages are much less pronounced, but still
detectable. The core intensity variations lag behind the Dopplershift
variations about 2.1 min. The Hα core width tends to correlate with
the Dopplershift and anticorrelate with the asymmetry, suggesting that
more redshifted Hα profiles are wider and the broadening of the Hα
core is accompanied with a change of the core asymmetry from redward
to blueward. We also found a striking anticorrelation between the
core asymmetry and the Dopplershift, suggesting a change of the core
asymmetry from redward to blueward with an increasing redshift of the
Hα core. The data and the applied analysis do not show meaningful
tracks of Alfvén waves in the selected network element.
---------------------------------------------------------
Title: Large-field high-resolution mosaic movies
Authors: Hammerschlag, Robert H.; Sliepen, Guus; Bettonvil, Felix
C. M.; Jägers, Aswin P. L.; Sütterlin, Peter; Martin, Sara F.
2012SPIE.8444E..06H Altcode:
Movies with fields-of-view larger than normal for high-resolution
telescopes will give a better understanding of processes on the
Sun, such as filament and active region developments and their
possible interactions. New active regions can influence, by their
emergence, their environment to the extent of possibly serving
as an igniter of the eruption of a nearby filament. A method to
create a large field-of-view is to join several fields-of-view into
a mosaic. Fields are imaged quickly one after another using fast
telescope-pointing. Such a pointing cycle has been automated at the
Dutch Open Telescope (DOT), a high-resolution solar telescope located
on the Canary Island La Palma. The observer can draw with the computer
mouse the desired total field in the guider-telescope image of the
whole Sun. The guider telescope is equipped with an H-alpha filter and
electronic enhancement of contrast in the image for good visibility of
filaments and prominences. The number and positions of the subfields
are calculated automatically and represented by an array of bright
points indicating the subfield centers inside the drawn rectangle of
the total field on the computer screen with the whole-sun image. When
the exposures start the telescope repeats automatically the sequence of
subfields. Automatic production of flats is also programmed including
defocusing and fast motion over the solar disk of the image field. For
the first time mosaic movies were programmed from stored information
on automated telescope motions from one field to the next. The mosaic
movies fill the gap between whole-sun images with limited resolution
of synoptic telescopes including space instruments and small-field
high-cadence movies of high-resolution solar telescopes.
---------------------------------------------------------
Title: Sunlight refraction in the mesosphere of Venus during the
transit on June 8th, 2004
Authors: Tanga, P.; Widemann, T.; Sicardy, B.; Pasachoff, J. M.;
Arnaud, J.; Comolli, L.; Rondi, A.; Rondi, S.; Sütterlin, P.
2012Icar..218..207T Altcode: 2011arXiv1112.3136T
Many observers in the past gave detailed descriptions of the telescopic
aspect of Venus during its extremely rare transits across the Solar
disk. In particular, at the ingress and egress, the portion of the
planet’s disk outside the Solar photosphere has been repeatedly
perceived as outlined by a thin, bright arc (“aureole”). Those
historical visual observations allowed inferring the existence of
Venus’ atmosphere, the bright arc being correctly ascribed to the
refraction of light by the outer layers of a dense atmosphere. On June
8th, 2004, fast photometry based on electronic imaging devices allowed
the first quantitative analysis of the phenomenon. Several observers
used a variety of acquisition systems to image the event - ranging from
amateur-sized to professional telescopes and cameras - thus collecting
for the first time a large amount of quantitative information on this
atmospheric phenomenon. In this paper, after reviewing some elements
brought by the historical records, we give a detailed report of the
ground based observations of the 2004 transit. Besides confirming the
historical descriptions, we perform the first photometric analysis of
the aureole using various acquisition systems. The spatially resolved
data provide measurements of the aureole flux as a function of the
planetocentric latitude along the limb. A new differential refraction
model of solar disk through the upper atmosphere allows us to relate
the variable photometry to the latitudinal dependency of scale-height
with temperature in the South polar region, as well as the latitudinal
variation of the cloud-top layer altitude. We compare our measurements
to recent analysis of the Venus Express VIRTIS-M, VMC and SPICAV/SOIR
thermal field and aerosol distribution. Our results can be used a
starting point for new, more optimized experiments during the 2012
transit event.
---------------------------------------------------------
Title: Multi-wavelength fine structure and mass flows in solar
microflares
Authors: Berkebile-Stoiser, S.; Gömöry, P.; Veronig, A. M.; Rybák,
J.; Sütterlin, P.
2009A&A...505..811B Altcode:
Aims: We study the multi-wavelength characteristics at high spatial
resolution, as well as chromospheric evaporation signatures of solar
microflares. To this end, we analyze the fine structure and mass
flow dynamics in the chromosphere, transition region and corona of
three homologous microflares (GOES class <A9/0.7 with/without
background), which occurred on July 4, 2006 in AR 10898. <BR
/>Methods: A multi-wavelength analysis using temporally and spatially
highly resolved imaging data from the Dutch open telescope (Hα,
Ca ii H), the transition region and coronal explorer (17.1 nm),
the extreme-ultraviolet imaging telescope (19.5 nm), and the Reuven
Ramaty high energy solar spectroscopic imager (≳3 keV) was carried
out. EUV line spectra provided by the coronal diagnostic spectrometer
are searched for Doppler shifts in order to study associated
plasma flows at chromospheric (He i, T∼3.9× 10<SUP>4</SUP> K),
transition region (e.g. O v, T∼ 2.6× 10<SUP>5</SUP> K), and
coronal temperatures (Si xii, T∼ 2× 10<SUP>6</SUP> K). RHESSI
X-ray spectra provide information about non-thermal electrons. <BR
/>Results: The multi-wavelength appearance of the microflares is in
basic agreement with the characteristics of large flares. For the
first event, a complex flare sequence is observed in TRACE 17.1 nm
images (T≈ 1 MK), which show several brightenings, narrow loops
of enhanced emission, and an EUV jet. EIT 19.5 nm data (T≈ 1.5 MK)
exhibit similar features for the third event. DOT measurements show
finely structured chromospheric flare brightenings for all three events,
loop-shaped fibrils of increased emission between Hα brightenings, as
well as a similar feature in Ca ii. For all three events, a RHESSI X-ray
source (3-8 keV, T ≳ 10 MK) is located in between two chromospheric
brightenings situated in magnetic flux of opposite polarity. We find
the flow dynamics associated with the events to be very complex. In
the chromosphere and transition region, CDS observed downflows for
the first (v ≲ 40 km s<SUP>-1</SUP>), and upflows for the second
event (v ≲ 40 km s<SUP>-1</SUP>). During the third microflare, we
find upflows of ≲ 20 km s<SUP>-1</SUP> and also weak downflows of
≲20 km s<SUP>-1</SUP> in two separate brightenings. For all three
microflares, multi-component fitting is needed for several profiles
of He i, O v, and Ne vi lines observed at the flare peaks, which
indicate spatially unresolved, oppositely directed flows of ≲180
km s<SUP>-1</SUP>. We interpret these flows as twisting motions of
the flare loops. Loop-shaped fibrils in between Hα brightenings
showing opposite flow directions (v≈5 km s<SUP>-1</SUP>) are also
observed in DOT Hα Dopplergrams. RHESSI X-ray spectra show evidence
of non-thermal bremsstrahlung for two of the three microflares. The
electron beam flux density deposited in the chromosphere for these
events is estimated to straddle the threshold heating flux between
gentle and explosive evaporation. <P />Appendix A and the movie are
only available in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Multi-wavelength Observations of Microflares Near an Active
Region
Authors: Bein, B.; Veronig, A.; Rybak, J.; Gömöry, P.;
Berkebile-Stoiser, S.; Sütterlin, P.
2009CEAB...33..179B Altcode:
We study the multi-wavelength characteristics of a microflaring active
region (AR 10898) near disc centre. The analysed data were from the
4^{th} of July 2006, and were recorded by DOT (Hα, Ca II H), RHESSI
(X-rays), TRACE (EUV) and SOHO/MDI (magnetograms). The identified
microflare events were studied with respect to their magnetic field
configuration and their multi-wavelength time evolution.
---------------------------------------------------------
Title: CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
Authors: Scharmer, G. B.; Narayan, G.; Hillberg, T.; de la Cruz
Rodriguez, J.; Löfdahl, M. G.; Kiselman, D.; Sütterlin, P.; van
Noort, M.; Lagg, A.
2008ApJ...689L..69S Altcode: 2008arXiv0806.1638S
We discuss penumbral fine structure in a small part of a pore,
observed with the CRISP imaging spectropolarimeter at the Swedish
1-m Solar Telescope (SST), close to its diffraction limit of
0.16”. Milne-Eddington inversions applied to these Stokes data
reveal large variations of field strength and inclination angle over
dark-cored penumbral intrusions and a dark-cored light bridge. The
mid-outer part of this penumbra structure shows ~0.3” wide spines,
separated by ~1.6” (1200 km) and associated with 30° inclination
variations. Between these spines, there are no small-scale magnetic
structures that easily can be identified with individual flux tubes. A
structure with nearly 10° more vertical and weaker magnetic field is
seen midway between two spines. This structure is cospatial with the
brightest penumbral filament, possibly indicating the location of a
convective upflow from below.
---------------------------------------------------------
Title: Photospheric flows around a quiescent filament at Large and
small scale and their ffects on filament destabilization
Authors: Roudier, Th.; Malherbe, J. M.; Švanda, M.; Molodij, G.;
Keil, S.; Sütterlin, P.; Schmieder, B.; Bommier, V.; Aulanier, G.;
Meunier, N.; Rieutord, M.; Rondi, S.
2008sf2a.conf..569R Altcode:
We study the influence of large and small scales photospheric
motions on the destabilization of an eruptive filament, observed
on October 6, 7, and 8, 2004 as part of an international observing
campaign (JOP 178). Large-scale horizontal flows are invetigated
from a series of MDI/SOHO full-disc Dopplergrams and magnetograms
from THEMIS. Small-scale horizontal flows were derived using local
correlation tracking on TRACE satellite, Dutch Open Telescope (DOT)
and The Dunn Solar telescope (DST) data. The topology of the flow field
changed significantly during the filament eruptive phase, suggesting
a possible coupling between the surface flow field and the coronal
magnetic field. We measured an increase of the shear below the point
where the eruption starts and a decrease in shear after the eruption. We
conclude that there is probably a link between changes in surface flow
and the disappearance of the eruptive filament.
---------------------------------------------------------
Title: Spectropolarimetry of Sunspots at 0.16 ARCSEC resolution
Authors: Scharmer, G.; Henriques, V.; Hillberg, T.; Kiselman, D.;
Löfdahl, M.; Narayan, G.; Sütterlin, P.; van Noort, M.; de la Cruz
Rodríguez, J.
2008ESPM...12..2.5S Altcode:
We present first observations of sunspots with the imaging
spectropolarimeter CRISP, recently installed at the Swedish 1-m
Solar Telescope (SST) on La Palma. This spectropolarimeter is based
on a high-fidelity dual Fabry-Perot filter system. <P />Two liquid
crystals and a polarizing beam splitter are used to reduce seeing
induced I,Q,U,V crosstalk by simultaneously recording images with
two 1kx1k back-illuminated Sarnoff CCD's. A third CCD simultaneously
records broadband images through the pre-filter of the FPI filter
system, allowing image reconstruction and co-alignment of images of
different polarization states and at different wavelengths in Zeeman
sensitive spectral lines. <P />The first data, recorded in April 2008,
demonstrate the capability of this system to record high cadence,
high S/N polarimetric data with a spatial resolution at or close to
the diffraction limit of the SST at 630 nm, 0.16 arcsec. We discuss
the analysis of first spectropolarimetric data for sunspots, based on
Milne-Eddington inversion techniques.
---------------------------------------------------------
Title: DOT Tomography of the Solar Atmosphere VII. Chromospheric
Response to Acoustic Events
Authors: Rutten, R. J.; van Veelen, B.; Sütterlin, P.
2008SoPh..251..533R Altcode: 2008arXiv0801.0374R; 2008SoPh..tmp...28R
We use synchronous movies from the Dutch Open Telescope sampling the G
band, Ca II H, and Hα with five-wavelength profile sampling to study
the response of the chromosphere to acoustic events in the underlying
photosphere. We first compare the visibility of the chromosphere in
Ca II H and Hα, demonstrate that studying the chromosphere requires
Hα data, and summarize recent developments in understanding why this
is so. We construct divergence and vorticity maps of the photospheric
flow field from the G-band images and locate specific events through
the appearance of bright Ca II H grains. The reaction of the Hα
chromosphere is diagnosed in terms of brightness and Doppler shift. We
show and discuss three particular cases in detail: a regular acoustic
grain marking shock excitation by granular dynamics, a persistent
flasher, which probably marks magnetic-field concentration, and an
exploding granule. All three appear to buffet overlying fibrils, most
clearly in Dopplergrams. Although our diagnostic displays to dissect
these phenomena are unprecedentedly comprehensive, adding even more
information (photospheric Doppler tomography and magnetograms along
with chromospheric imaging and Doppler mapping in the ultraviolet)
is warranted.
---------------------------------------------------------
Title: Dynamic Fibrils in Ly-alpha
Authors: Koza, J.; Rutten, R. J.; Vourlidas, A.; Suetterlin, P.
2008ESPM...12.2.16K Altcode:
We have detected dynamic fibrils (DFs) in Ly-alpha filtergrams taken
with the rocket-borne Very high Angular resolution ULtraviolet Telescope
(VAULT). Although the data consist of only a 1-min sequence of 4
images taken near the solar limb during the second VAULT flight, they
enable us to identify and study the time evolution of over 50 DFs. Most
show parabolic trajectories in their angular extent, with supersonic
maximum velocities. The measured decelerations vary from sub-ballistic
to super-ballistic. The similarities with DFs seen in Halpha suggest a
common cause, possibly the presence of hot transition-region interfaces
around cool oscillation-fed jets.
---------------------------------------------------------
Title: SST/CRISP Magnetometry with Fe I 630.2 nm
Authors: Narayan, G.; Scharmer, G. B.; Hillberg, T.; Lofdahl, M.;
van Noort, M.; Sutterlin, P.; Lagg, A.
2008ESPM...122.120N Altcode:
We present recent full Stokes observations in the Fe I 630.2 nm
line with CRISP, an imaging spectropolarimeter at the Swedish 1-m
Solar Telescope (SST). The observations reach a spatial resolution
of 0".16, close to the diffraction limit of the SST, representing
a major improvement over any past ground based or space based
spectropolarimetric data. We describe the data acquisition and reduction
methods and present results of Milne-Eddington(ME) inversions applied
on observations of plage.
---------------------------------------------------------
Title: Search for photospheric footpoints of quiet Sun transition
region loops
Authors: Sánchez Almeida, J.; Teriaca, L.; Sütterlin, P.; Spadaro,
D.; Schühle, U.; Rutten, R. J.
2007A&A...475.1101S Altcode: 2007arXiv0709.3451S
Context: The footpoints of quiet Sun Transition Region (TR) loops
do not seem to coincide with the photospheric magnetic structures
appearing in traditional low-sensitivity magnetograms. <BR />Aims: We
look for the so-far unidentified photospheric footpoints of TR loops
using G-band bright points (BPs) as proxies for photospheric magnetic
field concentrations. <BR />Methods: We compare TR measurements with
SoHO/SUMER and photospheric magnetic field observations obtained with
the Dutch Open Telescope. <BR />Results: Photospheric BPs are associated
with bright TR structures, but they seem to avoid the brightest parts
of the structure. BPs appear in regions that are globally redshifted,
but they avoid extreme velocities. TR explosive events are not clearly
associated with BPs. <BR />Conclusions: The observations are not
inconsistent with the BPs being footpoints of TR loops, although we
have not succeeded to uniquely identify particular BPs with specific
TR loops.
---------------------------------------------------------
Title: Magnetic properties of G-band bright points in a sunspot moat
Authors: Beck, C.; Bellot Rubio, L. R.; Schlichenmaier, R.;
Sütterlin, P.
2007A&A...472..607B Altcode: 2007arXiv0707.1232B
We present simultaneous spectropolarimetric observations of four
visible (630 nm) and three infrared (1565 nm) spectral lines from the
German Vacuum Tower Telescope, together with speckle-reconstructed
filtergrams in the G-band and the Ca II H line core from the Dutch
Open Telescope. After alignment of the data sets, we used the G-band
intensity to locate bright points (BPs) in the moat of a regular
sunspot. With the cospatial and cotemporal information provided by the
polarimetric data, we characterize the magnetic, kinematic, and thermal
properties of the BPs. We find that (a) 94% of the BPs are associated
with magnetic fields; (b) their field strengths range between 500 and
1400 G, with a rather flat distribution; (c) the contrast of BPs in the
G-band depends on the angle between the vector magnetic field and the
line of sight; (d) the BPs harbor downflows of magnetized plasma and
exhibit Stokes V profiles with large area and amplitude asymmetries;
(e) the magnetic interior of BPs is hotter than the immediate field-free
surroundings by about 1000 K at equal optical depth; and (f) the mean
effective diameter of BPs in our data set is 150 km, with very few
BPs larger than 300 km. Most of these properties can be explained
by the classical magnetic flux tube model. However, the wide range
of BP parameters found in this study indicates that not all G-band
BPs are identical to stable long-lived flux tubes or sheets of kG
strength. <P />Appendices A-C are only available in electronic form
at http://www.aanda.org
---------------------------------------------------------
Title: Photospheric flows around a quiescent filament
Authors: Rondi, S.; Roudier, Th.; Molodij, G.; Bommier, V.; Keil,
S.; Sütterlin, P.; Malherbe, J. M.; Meunier, N.; Schmieder, B.;
Maloney, P.
2007A&A...467.1289R Altcode:
Context: The horizontal photospheric flows below and around a
filament are one of the components in the formation and evolution of
filaments. Few studies exist because they require multiwalength time
sequences at high spatial resolution. <BR />Aims: Our objective
is to measure the horizontal photospheric flows associated
with the evolution and eruption of a filament. <BR />Methods:
We present observations obtained in 2004 during the international
JOP 178 campaign which involved eleven instruments both in space
and at ground based observatories. We use TRACE WL, DOT and DST
observation to derive flow maps which are then coaligned with
intensity images and with the vector magnetic field map obtained with
THEMIS/MTR. <BR />Results: Several supergranulation cells cross the
Polarity Inversion Line (PIL) and can transport magnetic flux through
the PIL, in particular parasitic polarities. We present a detailed
example of the formation of a secondary magnetic dip at the location
of a filament footpoint. Large-scale converging flows, which could
exist along the filament channel and contribute to its formation, are
not observed. Before the filament's eruptive phase, we observe both
parasitic and normal polarities being swept by a continuously diverging
horizontal flow located in the filament gap. The disappearance of the
filament initiates in this gap. Such purely horizontal motions could
lead to destabilization of the filament and could trigger the sudden
filament disappearance.
---------------------------------------------------------
Title: Temporal Variations in Fibril Orientation
Authors: Koza, J.; Sütterlin, P.; Kučera, A.; Rybák, J.
2007ASPC..368..115K Altcode: 2007astro.ph..3733K
We measure variations in orientation of fourteen dynamic fibrils as
a function of time in a small isolated plage and nearby network using
a 10-min time sequence of Hα filtergrams obtained by the Dutch Open
Telescope. We found motions with average angular velocities of the
order of 1 deg min<SUP>-1</SUP> suggesting systematic turning from
one limit position to another, particularly apparent in the case of
fibrils with lifetimes of a few minutes. Shorter fibrils tend to turn
faster than longer ones, which we interpret as due to vortex flows in
the underlying granulation that twist magnetic fields.
---------------------------------------------------------
Title: Magnetic properties of G-band bright points
Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Schlichenmaier,
R.; Sütterlin, P.
2007msfa.conf..165B Altcode:
Bright points (BPs) visible in the G band at 430 nm are commonly used
as tracers of magnetic fields, indicating the location of kG flux
concentrations. To study the actual magnetic properties of G-band BPs,
we took observations in 2003 and 2005, employing simultaneously a
speckle setup in the G band and vector spectropolarimetry to derive
the magnetic field vector. From the analysis of the co-aligned
polarimetric data we find that the BPs show a broad range of field
strengths, magnetic fluxes, and field inclinations. Many G-band
BPs are not co-spatial with the central part of the nearby flux
concentrations. Even at the small heliocentric angle of only 12°,
the BPs appear projected on adjacent granules, whereas the magnetic
field is concentrated in the intergranular lanes. Our findings support
the view that the G-band BPs are a result of the "hot wall effect". The
downward shift of the optical depth scale in the presence of magnetic
fields allows to see deeper and hotter layers in the hot granules next
to the field concentrations, where CH dissociates. Thus, information
drawn from imaging observations of BPs has limited use to investigate
the actual magnetic field structure, when the BPs are not co-spatial
with the central part of the flux concentrations.
---------------------------------------------------------
Title: Polarimetric Observations of the Formation of a G-Band
Bright Point
Authors: Beck, C.; Schmidt, W.; Bellot Rubio, L. R.; Schlichenmaier,
R.; Sütterlin, P.; Lites, B. W.
2006ASPC..358...72B Altcode:
We investigate the kinematic and magnetic properties of G-band bright
points in the moat of a regular sunspot. The analysis is based on vector
polarimetric measurements made at the German Vacuum Tower Telescope in
visible (630 nm) and infrared (1565 nm) spectral lines, complemented
by high-resolution filtergrams in the G-band at 430.6 nm and the core
of the Ca II H line at 396.7 nm from the Dutch Open Telescope. The
spectro-polarimetric data has been inverted to derive the magnetic
field properties of the observed region. We witness the formation of a
G-band bright point from a patch of diffuse flux with an initial field
strength of 0.4 kG. The magnetic field strength increases to 0.9 kG in
the course of several minutes, accompanied by a downflow of magnetized
plasma. A few minutes after the field intensification, a G-band bright
point is seen at the location of the flux concentration. The formation
of the bright point shows the signatures of convective collapse.
---------------------------------------------------------
Title: Magnetic Patches in Internetwork Areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
Sütterlin, P.
2006ASPC..354...20D Altcode:
We present a study of internetwork magnetic elements that appear as
bright points in G-band (photosphere) and Ca II H (low chromosphere)
image sequences from the Dutch Open Telescope. Many bright points
appear intermittently in groups of long-lived structures that we call
“magnetic patches”. We develop an algorithm for the identification
of bright points and magnetic patches. The average internetwork bright
point lifetimes is measured to be 3.5 minutes in the G band, and 4.3
minutes in the Ca II H. We find an internetwork bright point number
density of 0.02 Mm^{-2} in the G-band sequence and 0.05 Mm^{-2} in
the Ca II H sequence. The bright points show a bimodal distribution
of the frame-to-frame horizontal velocities, with a peak at 0 km
s^{-1} and a wide hump centered around 1.2 km s^{-1}. The patches
last much longer than granular time scales (about nine hours) and
outline cell-like structures on mesogranular scale. We conclude that
transient internetwork bright points trace the locations of strong
magnetic fields that exist before the bright point appears and remain
after it disappears.
---------------------------------------------------------
Title: Tunable H-alpha Lyot filter with advanced servo system and
image processing: instrument design and new scientific results with
the Dutch Open Telescope
Authors: Bettonvil, Felix C. M.; Hammerschlag, Robert H.; Sütterlin,
Peter; Rutten, Robert J.; Jägers, Aswin P. L.; Sliepen, Guus
2006SPIE.6269E..0EB Altcode: 2006SPIE.6269E..12B
The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma
is a revolutionary open solar telescope, on an excellent site, on
top of a transparent tower of steel framework, and uses natural
air flow to minimize local seeing. The DOT is a high-resolution
multi-wavelength imager capable of long-duration time series aiming
at magnetic fine structure, topology and dynamics in the photosphere
and low- and high chromosphere. In this paper we describe the latest
addition to the multi-wavelength imaging system: a Lyot H-alpha
camera channel operating at a wavelength of 656.3 nm, being of major
interest for high-chromospheric phenomena. The channel is operated
strictly synchronous with the other channels and all data are speckle
reconstructed. The channel permits profile sampling and delivers
Dopplergrams in a 15 second time cadence, up to several hours long
and adding up to a total data amount of 1.6 Terabyte/day. A dedicated
computer (DSP, DOT Speckle Processor) has been built for processing
the data overnight.
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. VI. Magnetic elements
as bright points in the blue wing of Hα
Authors: Leenaarts, J.; Rutten, R. J.; Sütterlin, P.; Carlsson, M.;
Uitenbroek, H.
2006A&A...449.1209L Altcode:
High-resolution solar images taken in the blue wing of the Balmer H
α line with the Dutch Open Telescope show intergranular magnetic
elements as strikingly bright features, similar to, but with
appreciably larger contrast over the surrounding granulation than
their more familiar manifestation as G-band bright points. Part of
this prominent appearance is due to low granular contrast, without
granule/lane brightness reversal as, e.g., in the wings of Ca II H
& K. We use 1D and 2D radiative transfer modeling and 3D solar
convection and magnetoconvection simulations to reproduce and explain
the H α wing images. We find that the blue H α wing obeys near-LTE
line formation. It appears particularly bright in magnetic elements
through low temperature gradients. The granulation observed in the blue
wing of H α has low contrast because of the lack of H α opacity in the
upper photosphere, Doppler cancellation, and large opacity sensitivity
to temperature working against source function sensitivity. We conclude
that the blue H α wing represents a promising proxy magnetometer to
locate and track isolated intermittent magnetic elements, a better one
than the G band and the wings of Ca II H & K although less sharp
at given aperture.
---------------------------------------------------------
Title: Unveiling the atmosphere of Venus during the June 2004
solar transit
Authors: Tanga, P.; Arnaud, J.; Colas, F.; Comolli, L.; Rondi, S.,
A.; Sicardy, B.; Suetterlin, P.; Unione Astrofili Italiani-“Planets"
Section Team
2005DPS....37.5718T Altcode: 2005BAAS...37.1571T
Visual and CCD observations of Venus transiting in front of the Sun
on June 8, 2004, revealed traces of the light passing through the
atmosphere of the planet. As several witness of past events have
accounted for [1][2], the event happens close to the ingress and
egress phases, when the disk of the planet is crossing the Solar
limb. The portion of atmosphere that is projected against the darker
sky background appears bright, at least in part, due to refracted
light (mainly). <P />The 2004 opportunity was the first observed by
electronic equipment. Sets of several images were acquired by widely
different instruments, at different wavelengths. <P />The images were
processed in order to subtract the sky background, and normalized. The
brightness of the atmospheric arc was measured; its spatial structure
and its variation in time are discussed. A latitude dependence of
the arc brightness is clearly detected, with an intensity maximum
close to the planet polar regions. Even comparing CCD images to
visual observations, an investigation of the variability of the arc
brightness from one event to the other encounters several difficulties,
mainly due to the evolution of instruments in time. <P />[1] F. Link,
Eclipse phenomena in Astronomy, Springer Verlag (Berlin 1969) <P />[2]
H.N. Russell, ApJ 9, 284 (1899)
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. V. Analysis of a
surge from AR10486
Authors: Tziotziou, K.; Tsiropoula, G.; Sütterlin, P.
2005A&A...444..265T Altcode:
We present an analysis of high temporal and spatial resolution CaII H
chromospheric limb observations obtained with the Dutch Open Telescope
(DOT). We focus on a solar surge observed both by the DOT in CaII H and
the Transition Region and Coronal Explorer (TRACE) satellite in the
195 Å and 1600 Å passbands. The surge is observed in active region
AR10486 located near the solar limb, a region which two hours later
produced the largest X-flare ever recorded. It consists of relatively
cold gas of about 10<SUP>4</SUP>-10<SUP>5</SUP> K. In TRACE images
the surge is followed for almost 2.5 h, shrinking and expanding at
the same location several times. From DOT images we find outward
propagating intensity disturbances, with velocities higher than 50
km s<SUP>-1</SUP>, indicative of upward material motion. The latter
is also suggested by the good correlation between the DOT and TRACE
surge apparent height curves, their apparent time delay and a phase
difference analysis. A spectral wavelet analysis of the brightness
variations within and along the surge shows a predominant period of
~6 min, the first ever reported for this kind of structures. Magnetic
reconnection at the bottom of the surge as its driving mechanism is
suggested by the observed inverted "Y" shape configuration and is
further supported by a phase difference analysis.
---------------------------------------------------------
Title: Small Scale Magnetic Elements as Bright Points in the Blue
Hα Wing
Authors: Leenaarts, J.; Sütterlin, P.; Rutten, R. J.; Carlsson, M.;
Uitenbroek, H.
2005ESASP.596E..15L Altcode: 2005ccmf.confE..15L
No abstract at ADS
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. IV. Magnetic patches
in internetwork areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
Sütterlin, P.
2005A&A...441.1183D Altcode: 2007arXiv0706.2008D
We use G-band and Ca ii H image sequences from the Dutch Open
Telescope (DOT) to study magnetic elements that appear as bright
points in internetwork parts of the quiet solar photosphere and
chromosphere. We find that many of these bright points appear
recurrently with varying intensity and horizontal motion within
longer-lived magnetic patches. We develop an algorithm for detection
of the patches and find that all patches identified last much longer
than the granulation. The patches outline cell patterns on mesogranular
scales, indicating that magnetic flux tubes are advected by granular
flows to mesogranular boundaries. Statistical analysis of the emergence
and disappearance of the patches points to an average patch lifetime
as long as 530±50~min (about nine hours), which suggests that the
magnetic elements constituting strong internetwork fields are not
generated by a local turbulent dynamo.
---------------------------------------------------------
Title: DOT++: the Dutch Open Telescope with 1.4-m aperture
Authors: Bettonvil, Felix C.; Hammerschlag, Robert H.; Sütterlin,
Peter; Rutten, Robert J.; Jägers, Aswin P.; Snik, Frans
2004SPIE.5489..362B Altcode:
The Dutch Open Telescope (DOT; http://dot.astro.uu.nl) on La Palma is
a revolutionary open solar telescope, on an excellent site, on top
of a transparent steel tower, and uses natural air flow to minimize
local seeing. The aim is long-duration high-resolution imaging with
a multi-wavelength camera system. In order to achieve this, the DOT
is equipped with a diffraction limited imaging system and uses the
speckle reconstruction technique for removing the remaining atmospheric
turbulence. The DOT optical system is simple and consists currently of
a 0.45m/F4.44 parabolic mirror and a 10x enlargement lens system. We
present our plans to increase the aperture of the DOT from 0.45m to
1.4m. The mirror support and telescope top shall be redesigned, but
telescope, tower, multi-wavelength camera system and speckle system
remain intact. The new optical design permits user selectable choice
between angular resolution and field size, as well as transversal pupil
shift introducing the possibility to use obstruction free apertures up
to 65cm. The design will include a low order AO system, which improves
the speckle S/N substantially during moderate seeing conditions.
---------------------------------------------------------
Title: Asymmetrical appearance of dark-cored filaments in sunspot
penumbrae
Authors: Sütterlin, P.; Bellot Rubio, L. R.; Schlichenmaier, R.
2004A&A...424.1049S Altcode:
Recent sunspot observations at unprecedented resolution have led to the
discovery of dark cores in the bright filaments that form the penumbra
(\citealt{scharmer02_Nat420}). The discovery paper considered spots
at disk center only, so the properties of the dark-cored filaments
remain largely unknown. Here we analyze a speckle-reconstructed time
series of G-band and blue continuum images of a sunspot acquired with
the Dutch Open Telescope. The target was located at an heliocentric
angle of 27 deg. We confirm the existence of dark-cored penumbral
filaments also in spots outside the disk center, and report on distinct
differences between the center and limb-side penumbra. In the inner
center-side penumbra, filaments are detected as two narrow bright
streaks separated by a central obscuration. These structures move
together as a single entity. On the limb side, dark cores are hardly
seen. The time series is used to determine the sizes (∼200-250 km),
proper motions (∼280 m s<SUP>-1</SUP>), and lifetimes (⪉45 min)
of typical dark-cored filaments.
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. II. Reversed
granulation in Ca II H
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.
2004A&A...416..333R Altcode:
High-quality simultaneous image sequences from the Dutch Open Telescope
(DOT) in the G band and the Ca II H line are used to quantify the
occurrence of reversed granulation as a constituent of the subsonic
brightness pattern observed as a background to acoustic oscillations
in the quiet-Sun internetwork atmosphere. In the middle photosphere
reversed granulation constitutes a much larger part of this background
than at the larger heights sampled by ultraviolet radiation. The
anticorrelation with the underlying granulation reaches about 50% at a
temporal delay of 2-3 min, and increases with spatial image smoothing to
mesogranular resolution. We discuss the nature of reversed granulation
in terms of convection reversal, gravity waves, acoustic waves, and
intergranular magnetism, suggest that the internetwork background
pattern is primarily a mixture of the first two ingredients, and
speculate that it is also an inverse canopy mapper.
---------------------------------------------------------
Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
K.; de Wijn, A. G.
2004IAUS..223..597R Altcode: 2005IAUS..223..597R
The Dutch Open Telescope (DOT) on La Palma is an innovative solar
telescope combining open telescope structure and an open support tower
with a multi-wavelength imaging assembly and with synchronous speckle
cameras to generate high-resolution movies which sample different
layers of the solar atmosphere simultaneously and co-spatially at high
resolution over long durations. The DOT test and development phase is
nearly concluded. The installation of an advanced speckle processor
enables full science utilization including "Open-DOT" time allocation
to the international community. Co-pointing with spectropolarimeters
at other Canary Island telescopes and with TRACE furnishes valuable
Solar-B precursor capabilities.
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. I. Telescope summary
and program definition
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
Sütterlin, P.; de Wijn, A. G.
2004A&A...413.1183R Altcode:
The Dutch Open Telescope (DOT) on La Palma is an innovative optical
solar telescope capable of reaching 0.2 arcsec angular resolution
over extended durations. The DOT presently progresses from technology
testbed to a stable science configuration providing multi-wavelength
imaging and multi-camera speckle data acquisition for tomographic
mapping of the solar atmosphere. Large-volume speckle processing will
soon enable frequent usage and community-wide time allocation, in
particular for tandem operation with other solar telescopes pursuing
spectropolarimetry and EUV imaging. We summarize the DOT hardware and
software in the context of this increasing availability and outline
the corresponding “open-DOT” program.
---------------------------------------------------------
Title: La Palma observations of umbral flashes
Authors: Rouppe van der Voort, L. H. M.; Rutten, R. J.; Sütterlin,
P.; Sloover, P. J.; Krijger, J. M.
2003A&A...403..277R Altcode:
We present high-quality Ca II H & K data showing chromospheric
flashes in sunspot umbrae collected with the Swedish Vacuum Solar
Telescope, the Dutch Open Telescope, and the Swedish 1-m Solar Telescope
at the Roque de los Muchachos Observatory on La Palma. Differential
movies, time slices, spectrograms, and Fourier power maps demonstrate
that umbral flashes and running penumbral waves are closely related
oscillatory phenomena, combining upward shock propagation with coherent
wave spreading over the entire spot. We attribute the flash brightening
to large redshift by post-shock material higher up. We find no obvious
relation between umbral dots and umbral flashes.
---------------------------------------------------------
Title: Motions of Isolated G-Band Bright Points in the Solar
Photosphere
Authors: Nisenson, P.; van Ballegooijen, A. A.; de Wijn, A. G.;
Sütterlin, P.
2003ApJ...587..458N Altcode: 2002astro.ph.12306N
Magnetic elements on the quiet Sun are buffeted by convective flows
that cause lateral motions on timescales of minutes. The magnetic
elements can be observed as bright points (BPs) in the G band at 4305
Å. We present observations of BPs based on a long sequence of G-band
images recorded with the Dutch Open Telescope and postprocessed using
speckle-masking techniques. From these images we measured the proper
motions of isolated BPs and derived the autocorrelation function of
their velocity relative to the solar granulation pattern. The accuracy
of BP position measurements is estimated to be less than 23 km on
the Sun. The rms velocity of BPs (corrected for measurement errors)
is about 0.89 km s<SUP>-1</SUP>, and the correlation time of BP motions
is about 60 s. This rms velocity is about 3 times the velocity measured
using cork tracking, almost certainly due to the fact that isolated BPs
move more rapidly than clusters of BPs. We also searched for evidence
of vorticity in the motions of G-band BPs.
---------------------------------------------------------
Title: Multi-wavelength imaging system for the Dutch Open Telescope
Authors: Bettonvil, Felix C.; Suetterlin, Peter; Hammerschlag, Robert
H.; Jagers, Aswin P.; Rutten, Robert J.
2003SPIE.4853..306B Altcode:
The Dutch Open Telescope (DOT) is an innovative solar telescope,
completely open, on an open steel tower, without a vacuum system. The
aim is long-duration high resolution imaging and in order to achieve
this the DOT is equipped with a diffraction limited imaging system
in combination with a data acquisition system designed for use with
the speckle masking reconstruction technique for removing atmospheric
aberrations. Currently the DOT is being equipped with a multi-wavelength
system forming a high-resolution tomographic imager of magnetic
fine structure, topology and dynamics in the photosphere and low-
and high chromosphere. Finally the system will contain 6 channels:
G-band (430.5 nm), Ca II H (K) (396.8 nm), H-α (656.3 nm), Ba II
(455.4 nm), and two continuum channels (432 and 651 nm). Two channels
are in full operation now and observations show that the DOT produces
real diffraction limited movies (with 0.2" resolution) over hours in
G-band (430.5 nm) and continuum (432 nm).
---------------------------------------------------------
Title: Dutch Open Telescope: status, results, prospects
Authors: Rutten, Robert J.; Sütterlin, Peter; de Wijn, Alfred G.;
Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Hoogendoorn, Piet W.;
Jägers, Aswin P. L.
2002ESASP.506..903R Altcode: 2002svco.conf..903R; 2002ESPM...10..903R
The Dutch Open Telescope (DOT) on La Palma is a revolutionary telescope
achieving high-resolution imaging of the solar surface. The DOT combines
a pioneering open design at an excellent wind-swept site with image
restoration through speckle interferometry. Its open principle is now
followed in major solar-telescope projects elsewhere. In the past three
years the DOT became the first solar telescope to regularly obtain 0.2"
resolution in extended image sequences, i.e., reaching the diffraction
limit of its 45-cm primary mirror. Our aim for 2003-2005 is to turn
the DOT into a 0.2" tomographic mapper of the solar atmosphere with
frequent partnership in international multi-telescope campaigns through
student-serviced time allocation. After 2005 we aim to triple the DOT
resolution to 0.07" by increasing the aperture to 140 cm and to renew
the speckle cameras and the speckle pipeline in order to increase
the field size and sequence duration appreciably. These upgrades will
maintain the DOT's niche as a tomographic high-resolution mapper in
the era when GREGOR, Solar-B and SDO set the stage.
---------------------------------------------------------
Title: Opening the Dutch Open Telescope
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.; Bettonvil,
F. C. M.; Hammerschlag, R. H.
2002ESASP.505..565R Altcode: 2002IAUCo.188..565R; 2002solm.conf..565R
We hope to "open the DOT" to the international solar physics
community as a facility for high-resolution tomography of the solar
atmosphere. Our aim is to do so combining peer-review time allocation
with service-mode operation in a "hands-on-telescope" education
program bringing students to La Palma to assist in the observing and
processing. The largest step needed is considerable speedup of the
DOT speckle processing.
---------------------------------------------------------
Title: THEMIS and DOT joint observations on NOAA 9716
Authors: Briand, C.; Collados, M.; Sütterlin, P.
2002ESASP.505..361B Altcode: 2002IAUCo.188..361B; 2002solm.conf..361B
Ephemeral magnetic emergence has been detected in a decaying β region
observed in December 2001 simultaneously with the DOT and THEMIS. We
present here the main characteristics of this phenomenon. Also the
time evolution of a small group of pores is shown together with the
time evolution of an horizontal magnetic field overlying them.
---------------------------------------------------------
Title: Fine structure in sunspots. IV. Penumbral grains in speckle
reconstructed images
Authors: Sobotka, M.; Sütterlin, P.
2001A&A...380..714S Altcode:
The properties of penumbral grains (PGs) in a large regular sunspot
are studied from a 70 min sequence of G-band images acquired on 20
September 1999 at the Dutch Open Telescope, La Palma. The frames were
processed using the speckle masking algorithm, resulting in an almost
diffraction-limited time series (30 s cadence), basically free of
atmospheric distortions. Applying feature tracking to a movie of 140
frames yields proper motions, intensities, and lifetimes for a set of
1058 PGs with lifetimes longer than 10 min. About 54% of the PGs move
toward the umbra and 46% toward the photosphere. The inward-moving
PGs are located mostly in the inner penumbra (up to 0.6 of the
distance from the umbra to the photosphere). Their average lifetime
and median speed are 50 min and 0.52 km s<SUP>-1</SUP>. Most of the
outward-moving PGs are observed in the outer penumbra and their average
lifetime and median speed are 31 min and 0.75 km s<SUP>-1</SUP>. These
measurements confirm the previous results published by Sobotka et
al. (\cite{sobotka99_AA348}).
---------------------------------------------------------
Title: Penumbral finestructure: need for larger telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AN....322..367B Altcode:
We obtained at the same time G-band images at the Dutch Open Telescope
(DOT) on La Palma and spectropolarimetric data in the near infrared
at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright
filaments have a smaller magnetic field s trength, and higher
Evershed velocities occur in dark structures. This result is in
agreement with some previous observations, but also in contradiction
to others. However, we suffer from the fact that the resolution limit
of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial
power spectra derived from the DOT data indicate a typical width of
250 km for penumbral filaments. Obviously a solar telescope with an
aperture of at least 1.5~m is needed to obtain sophisticated results
for penumbral structures.
---------------------------------------------------------
Title: Ba II 4554 Å speckle imaging as solar Doppler diagnostic
Authors: Sütterlin, P.; Rutten, R. J.; Skomorovsky, V. I.
2001A&A...378..251S Altcode:
We present observations testing the Dopplergram capability of a
narrow-band (80 mÅ) Lyot filter imaging the solar surface in the
wings of the Ba II 4554 Å resonance line in combination with speckle
reconstruction to obtain high angular resolution. The Ba II 4554 Å line
is found to be an excellent tool for high-resolution Doppler mapping
thanks to opacity insensitivity to temperature variations and line-width
insensitivity to thermal broadening. The resulting Dopplergrams show
concentrated downflows of 1.2-2.2 km;s<SUP>-1</SUP> in intergranular
lanes that probably mark magnetic fluxtubes. Two-wavelength
profile sampling is found to suffice for high-resolution Dopplergram
construction. The filter will be installed as part of a multi-wavelength
speckle imaging system on the new Dutch Open Telescope.
---------------------------------------------------------
Title: The size of penumbral fine structure
Authors: Sütterlin, P.
2001A&A...374L..21S Altcode:
I present power spectra of penumbral and granular intensity variations
from a speckle-restored G-band image sequence of sunspot NOAA 9407 taken
on April 1, 2001 with the Dutch Open Telescope on La Palma. I compare
spatial power spectra of the sunspot penumbra with spatial power spectra
from granulation with and without filigree. Relative to the granular
power distribution, the penumbral power spectrum is enhanced over a wide
range in spatial frequency peaking at 0\farcs35. For smaller scales,
the penumbral power distribution closely resembles that of the granular
intensity variations. In contrast, the power spectrum of granulation
with filigree exhibits increased power down to the resolution limit
of 0\farcs22, indicating the presence of unresolved magnetic elements.
---------------------------------------------------------
Title: Active Region Oscillations: Results from SOHO JOP 097
Authors: O'Shea, E.; Fleck, B.; Muglach, K.; Sütterlin, P.
2001AGUSM..SH41A02O Altcode:
We present here an analysis of data obtained in a sunspot region,
using the Coronal Diagnostic Spectrometer (CDS) on SOHO. These data
were obtained in the context of the Joint Observing Program (JOP)
97 which, together with CDS, included the Michelson Doppler Imaging
(MDI) instrument on SOHO, the TRACE satellite and various ground
based observatories, e.g. the DOT on La Palma. Using the lines of
Fe XVI 335, Mg IX 368, He I 584, O III 599, Mg X 624 and O V 624 of
CDS time series data were obtained in the pore and plage regions of
sunspots associated with active regions AR 9166, 9166 and 9169 between
September 19-29 2000. In addition to the time series datasets we also
obtained 240 arcsec x 240 arcsec raster images of the sunspot regions
examined. Using different time series analysis techniques we analyse
the different periods of oscillation found in time series datasets and
present the results here. This research is part of the European Solar
Magnetometry Network supported by the EC through the TMR programme.
---------------------------------------------------------
Title: Penumbral Finestructure: Need for Larger Telescopes
Authors: Balthasar, H.; Sütterlin, P.; Collados, M.
2001AGM....18S1003B Altcode:
We obtained at the same time G-band images at the Dutch Open
Telescope (DOT) on La Palma and spectropolarimetric data in the near
infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The
spectropolarimetric data show interesting correlations. Bright filaments
have a smaller magnetic field strength, and higher Evershed velocities
occur in dark structures. This result is in agreement with some previous
observations, but also in contradiction to others. However, we suffer
from the fact that the resolution limit of the VTT at a wavelength
of 1.565 μm corresponding to 400 km. Spatial power spectra derived
from the DOT data indicate a typical width of 250 km for the penumbral
filaments. Obviously a solar telescope with an aperture of at least 1.5
m is needed to obtain sophisticated results for penumbral structures.
---------------------------------------------------------
Title: Proxy Magnetometry with the Dutch Open Telescope
Authors: Rutten, R. J.; Hammerschlag, R. H.; Sütterlin, P.; Bettonvil,
F. C. M.
2001ASPC..236...25R Altcode: 2001aspt.conf...25R
No abstract at ADS
---------------------------------------------------------
Title: A Multi-Channel Speckle Imaging System for the DOT
Authors: Sütterlin, P.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
Rutten, R. J.; Skomorovsky, V. I.; Domyshev, G. N.
2001ASPC..236..431S Altcode: 2001aspt.conf..431S
No abstract at ADS
---------------------------------------------------------
Title: Dutch Open Telescope: Status and Prospects
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. M.;
Suetterlin, P.
2000SPD....3102107R Altcode: 2000BAAS...32.1290R
The Dutch Open Telescope (DOT) on La Palma in the Canary Islands is
a small but revolutionary solar telescope of which the image quality
matches the superb imaging of the Swedish Vacuum Solar Telescope (from
whose building the DOT is operated). The DOT is an open parabolic 45cm
reflector on an open 15m high tower, relying on mirror flushing by the
trade winds that bring the best seeing at La Palma to avoid internal
turbulence. A water-cooled field stop in the primary image reflects
most sunlight and heat out of the telescope. The first data from the
DOT combined with speckle reconstruction have yielded sunspot movies
of outstanding quality. At present, a multi-channel imaging system is
in construction for simultaneous registration of speckle sequences in
the G band, in Ca II K and in Hα. The data pipeline permits continuous
speckle data acquisition up to 0.5 Tb per day. The advantage of speckle
reconstruction over adaptive optics is the much larger field of the
restored scene, with the DOT camera's 100x130 arcsec at 0.2 arcsec
resolution. The DOT science program is to study magnetic topology and
dynamics throughout the photosphere and chromosphere.
---------------------------------------------------------
Title: Applying speckle masking to spectra
Authors: Sütterlin, P.; Wiehr, E.
2000SoPh..194...35S Altcode:
We have applied the technique of speckle masking to spectra. The
observation of elongated solar structures avoids the problem of missing
information in one-dimensional spectra. Image motion perpendicular
to the slit was diminished by a one-dimensional image stabilization
system. The remaining influence of the Earth's atmosphere was removed
by a modified speckle-masking algorithm, adapted to the single spatial
dimension occurring in the spectra. The reconstructed spectra achieve
the diffraction limit of the telescope and the spectrograph.
---------------------------------------------------------
Title: Solar Magnetometry with the Dutch Open Telescope
Authors: Rutten, R.; Hammerschlag, R. H.; Sutterlin, P.; Bettonvil,
F. C. M.; van der Zalm, E. B. J.
2000ESASP.463..611R Altcode: 2000sctc.proc..611R
No abstract at ADS
---------------------------------------------------------
Title: Continuum photometry of solar white-light faculae
Authors: Sütterlin, P.; Wiehr, E.; Stellmacher, G.
1999SoPh..189...57S Altcode:
We have determined absolute continuum intensities and brightness
temperatures of individual facular grains at a spatial resolution
limited by the φ=50 cm aperture of the SVST on La Palma. A facular
region at θ≈57° was observed simultaneously in three narrow
continuum windows at 450.5, 658.7, and 863.5 nm. We corrected for
image degradation by the Earth's atmosphere using the speckle masking
method. The brightness temperatures do not exactly follow the Planck
law. The differences of T<SUB>blue</SUB>−T<SUB>red</SUB>=220
K and T<SUB>ir</SUB>−T<SUB>red</SUB>=−42 K reflect the
wavelength dependence of the continuum formation depth. The (red)
temperatures of 250 facular grains show excesses between 250
and 450 K above their undisturbed neighborhood. The wavelength
dependence of the relative intensity ratios C<SUB>λ</SUB>=
[I<SUP>fac</SUP>/I<SUP>phot</SUP>] <SUB>λ</SUB>show a large scatter
around mean values of C<SUB>blue</SUB>/C<SUB>red</SUB>=1.075 and
C<SUB>ir</SUB>/C<SUB>red</SUB>=0.98. We determined the center-to-limb
variation of the 863.5 nm continuum contrast for 0.17>cosθ>0.39
by measuring 270 grains in reconstructed facular images. The
upper envelope of the data points increases linearly to 1.5 at
cos θ=0.17. Application of the mean color dependence yields green
contrasts up to C<SUB>550</SUB>=1.7, which is far higher than previously
observed values. The behaviour for cos θ>0.17 is estimated from
(unreconstructed) frame-selected best images taken over a time interval
of 7 hours. Six distinct facular regions clearly discernible during
the whole time interval indicate a slight contrast decrease towards
the extreme limb. The observed quantities are useful for an adjustment
of model calculations and for a discrimination of competing models.
---------------------------------------------------------
Title: Automatic guiding of the primary image of solar Gregory
telescopes
Authors: Küveler, G.; Wiehr, E.; Thomas, D.; Harzer, M.; Bianda,
M.; Epple, A.; Sütterlin, P.; Weisshaar, E.
1998SoPh..182..247K Altcode:
The primary image reflected from the field stop of solar Gregory
telescopes is used for automatic guiding. This new system avoids
temporal varying influences from the bending of the telescope tube by
the main mirror's gravity and from offsets between the telescope and
a separate guiding refractor. The required stiffness of the guider
mechanics and the small areas of the sensors demand small f numbers
for the guider optics, which cause problems with the image quality and
with heat. Problems also arise from the pinhole in the telescope's
field stop which is imaged as a dark dot on the sensor. Pointing
errors introduced by the telescope affect shifts of the solar image
on the sensor. These are numerically determined by Fourier methods
which are found to be less sensitive to noise than profile centering
methods. Several types of guiders are tested, the final equipment,
now installed at the Gregory telescopes at Tenerife and at Locarno,
is described.
---------------------------------------------------------
Title: Temperature mapping of sunspots and pores from speckle
reconstructed three colour photometry
Authors: Suetterlin, P.; Wiehr, E.
1998A&A...336..367S Altcode:
The two-dimensional temperature distribution in a highly structured
sunspot and in two small umbrae is determined from a three-colour
photometry in narrow spectral continua. Disturbing influences from
the earth's atmosphere are removed by speckle masking techniques,
yielding a spatial resolution limited by the telescope's aperture. The
corresponding colour temperatures are consistent over a range of
more than 2000 K, although the numerical correction introduced by
the reconstruction differs largely for the three colours. Part of the
scatter in the temperature relation disappears when convoluting the
final images with artificial PSFs that compensate for the different,
colour dependent spatial resolution. The remaining spread in the
scatter plots does not reflect noise, but is related to local
variations of the temperature difference between the continuum
emitting layers. This is most obvious for a small umbra which yields
`branches' in the scatter plots the `bluer' of which corresponding to
the limb-side umbral border. Here, the `hot rim' of a Wilson depressed
umbra becomes visible. The temperature map of the large spot shows that
the bright umbral dots do not reach the temperature of the non-spot
surroundings. Instead, they exceed the 2000 K cooler umbral temperature
minimum by 900-1300 K. The filamentary structure of the surrounding
penumbra has spatial temperature fluctuations of typically 700 K,
a value which fits earlier observed contrasts. However, the mean
temperatures of 5650 K in the dark and 6250 K in the bright penumbral
fine structures exceed former findings. Exceptionally bright penumbral
grains are 250 K hotter than the mean solar surface and thus exceed
even brightest granules.
---------------------------------------------------------
Title: Properties of solar pores
Authors: Suetterlin, Peter
1998A&A...333..305S Altcode:
We present the results of an extensive investigation of the properties
of solar pores. Spectra of all 4 Stokes parameters of several magnetic
sensitive absorption lines as well as Stokes ( I ) only spectra of lines
with low or vanishing Lande-factor have been observed. An inversion code
based on the Levenberg-Marquardt algorithm was written, incorporating
the full radiative transfer equations. This code adapts a set of
parameters that are used to represent the magnetic and thermodynamic
state of the atmosphere to best-fit a set of observed line profiles. The
results show that the value of all relevant parameters are intimately
related to the size of the pores, therewith confirming the role of solar
pores as a link between (bright) magnetic flux tubes and sunspots. In
particular the inclination of the magnetic field lines at the outer
rim of a pore, which is affected by the vertical field gradient, seems
to put an upper limit on the diameter of pores where the inclination
reaches a value that might trigger the formation of a penumbra.
---------------------------------------------------------
Title: Simultaneous Observations with the GCT and SoHO: High Velocity
Events in the Upper Chromosphere
Authors: Muglach, K.; Sütterlin, P.
1998ASPC..155..341M Altcode: 1998sasp.conf..341M
No abstract at ADS
---------------------------------------------------------
Title: 3-Color Photometry of a Sunspot Using Speckle Masking
Techniques
Authors: Sütterlin, P.; Wiehr, E.
1998ASPC..155...44S Altcode: 1998sasp.conf...44S
No abstract at ADS
---------------------------------------------------------
Title: Prominence Emissions with SUMER and Optical Telescopes
Authors: Wiehr, E.; Stellmacher, G.; de Boer, C. R.; Sütterlin, P.
1998ASPC..155..331W Altcode: 1998sasp.conf..331W
No abstract at ADS
---------------------------------------------------------
Title: Problems in measuring prominence oscillations.
Authors: Suetterlin, P.; Wiehr, E.; Bianda, M.; Kueveler, G.
1997A&A...321..921S Altcode:
Time variations of Doppler shifts of the Ca^+^ 8542Å emission in
quiescent solar prominences have been measured. A new type of 'limb
guider' assures a highly constant distance of the spectrograph slit from
the solar limb and furthermore removes low frequency image motion in the
direction perpendicular to the slit. Remaining image motion along the
slit is usually removed by a correlation of subsequent spectra. This
procedure, however, cannot be applied globally to the whole spatial
height in the spectra if individual structures exhibit lateral motions
along the slit or even decay or arise during the observation. We
therefore correlate defined individual emission maxima from successive
spectra. The finally obtained power spectra show oscillations with a
variety of periods at restricted locations. The data favour the known
general presence of periods near 20 and 60-min, however they give only
slight indication for `typical' periods near 3 and 5 min.
---------------------------------------------------------
Title: Three colour photometry of a sunspot using speckle masking
techniques.
Authors: Sütterlin, P.; Wiehr, E.
1997AGAb...13...10S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emission Lines in a Quiescent Prominence Observed with the
SUMER, VTT, a nd Gregory Telescopes
Authors: Wiehr, E.; de Boer, C. R.; Stellmacher, G.; Sutterlin, P.
1997ASPC..118..294W Altcode: 1997fasp.conf..294W
A number of emission lines have been observed in a quiescent prominence
with the two German telescopes on Tenerife and with SUMER. The Gregory
telescope monitored simultaneously the lines H_8 3889, He 3888, Ca(+\:)
8498, the VTT simultaneously the lines H_β, He-D_3, Ca(+\:) 8542, and
H_α slit jaw pictures on 1024 x 1024 CCDs. At the same time, SUMER
monitored successively three combinations of EUV lines containing He
584, He 537 in the second, and Ar, N(+) , C, C(++) , O, O(+) , O(++)
, S(++) , S(+++) lines in the first order. Two dimensional images in
the various EUV lines establish the anti-relation between temperature
and Balmer brightness.
---------------------------------------------------------
Title: Polarimetry of Solar Pores
Authors: Sütterlin, P.; Schröter, E. H.; Muglach, K.
1996SoPh..164..311S Altcode:
We address the magnetic field structure of solar pores. The data
were obtained at the Gregory Coudè telescope at Izaña using
the AT1 CCD camera system to observe pores with three spectral
lines: one magnetically sensitive line, recording all 4 Stokes
profiles, and two g = 0 lines where only the intensity profiles
were measured. The data reduction included the standard procedure
(removing dark current and flatfielding) as well as destretching of
the polarimetric spectra and removing the non-magnetic straylight by
means of a 2-d deconvolution of the observed intensity variation using
a Lucy-Richardson restoration algorithm. In the following analysis we
first determined the temperature- and pressure stratification of the
pore using the g = 0 lines and then applied an inversion of the Stokes
profiles to get the parameters of the magnetic field. Across the pore
we find a strong variation of the resulting field strength as well as
of the inclination and the azimuth, consistent with the assumption of
a canopy forming in the higher atmosphere.
---------------------------------------------------------
Title: Über die Struktur von solaren Poren
---------------------------------------------------------
Title: Über die Struktur
von solaren Poren
---------------------------------------------------------
Title: On the structure of solar pores;
Authors: Sütterlin, Peter Pit
1996PhDT.......153S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Neue Verarbeitungstechniken für CCD-Bilder. Einige Anregungen.
Authors: Sütterlin, P.
1994S&W....33..311S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the magneto-thermodynamical structure of a solar pore
Authors: Sütterlin, P.; Thim, F.; Schröter, E. H.
1994smf..conf..213S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erfahrungen mit CCD-Kameras in der Amateurastronomie.
Authors: Sütterlin, P.
1994aks..1995Q....S Altcode:
No abstract at ADS