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Author name code: tritschler
ADS astronomy entries on 2022-09-14
author:"Tritschler, Aexandra"
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Title: The National Science Foundation's Daniel K. Inouye Solar
Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
Mathioudakis, M.; Dkist Team
2021AAS...23810601R Altcode:
The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
(DKIST) on Haleakala, Maui is now the largest solar telescope in the
world. DKIST's superb resolution and polarimetric sensitivity will
enable astronomers to unravel many of the mysteries the Sun presents,
including the origin of solar magnetism, the mechanisms of coronal
heating and drivers of flares and coronal mass ejections. Five
instruments, four of which provide highly sensitive measurements
of solar magnetic fields, including the illusive magnetic field of
the faint solar corona. The DKIST instruments will produce large and
complex data sets, which will be distributed through the NSO/DKIST Data
Center. DKIST has achieved first engineering solar light in December
of 2019. Due to COVID the start of the operations commissioning phase
is delayed and is now expected for fall of 2021. We present a status
update for the construction effort and progress with the operations
commissioning phase.
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Title: Solar physics in the 2020s: DKIST, parker solar probe, and
solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
2020arXiv200408632M Altcode:
The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
(DKIST) is about to start operations at the summit of Haleakala
(Hawaii). DKIST will join the early science phases of the NASA
and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
combining in-situ measurements of the near-sun plasma environment and
detail remote observations of multiple layers of the Sun, the three
observatories form an unprecedented multi-messenger constellation to
study the magnetic connectivity inside the solar system. This white
paper outlines the synergistic science that this multi-messenger
suite enables.
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Title: An Overview of DKIST Operations Commissioning and Tools
Authors: Alexov, A.; Tritschler, A.; Rimmele, T.; Marshall, H.;
Parraguez, A.
2020ASPC..527..435A Altcode: 2020adass..29..435A
The Daniel K. Inouye Solar Telescope (DKIST) is a 4-meter clear aperture
solar telescope nearing the end of its construction on the summit
of Haleakalā on the island of Maui, Hawai'i. It will be the largest
solar telescope in the world when completed in summer 2020. We present
a condensed overview of the DKIST Operations Commissioning Phase (OCP)
which will start after the completion of construction. This Operations
Commissioning phase will allow for a manageable transition from the
end of construction into steady-state operations over the course of
approximately one year. During this phase, science operations will
specifically integrate, test and streamline its procedures by exercising
through all steps of the DKIST's Science Operations Lifecycle. We
will also briefly introduce software tools that are or will be used
by Science Operations, Technical Operations and the DKIST Data Center.
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Title: High-resolution imaging and near-infrared spectroscopy of
penumbral decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei,
R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.;
Diercke, A.; González Manrique, S. J.
2018A&A...614A...2V Altcode: 2018arXiv180103686V
<BR /> Aims: Combining high-resolution spectropolarimetric and imaging
data is key to understanding the decay process of sunspots as it
allows us to scrutinize the velocity and magnetic fields of sunspots
and their surroundings. <BR /> Methods: Active region NOAA 12597
was observed on 2016 September 24 with the 1.5-meter GREGOR solar
telescope using high-spatial-resolution imaging as well as imaging
spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal
proper motions were estimated with local correlation tracking, whereas
line-of-sight (LOS) velocities were computed with spectral line fitting
methods. The magnetic field properties were inferred with the "Stokes
Inversions based on Response functions" (SIR) code for the Si I and Ca
I NIR lines. <BR /> Results: At the time of the GREGOR observations,
the leading sunspot had two light bridges indicating the onset of
its decay. One of the light bridges disappeared, and an elongated,
dark umbral core at its edge appeared in a decaying penumbral sector
facing the newly emerging flux. The flow and magnetic field properties
of this penumbral sector exhibited weak Evershed flow, moat flow, and
horizontal magnetic field. The penumbral gap adjacent to the elongated
umbral core and the penumbra in that penumbral sector displayed LOS
velocities similar to granulation. The separating polarities of a new
flux system interacted with the leading and central part of the already
established active region. As a consequence, the leading spot rotated
55° clockwise over 12 h. <BR /> Conclusions: In the high-resolution
observations of a decaying sunspot, the penumbral filaments facing the
flux emergence site contained a darkened area resembling an umbral core
filled with umbral dots. This umbral core had velocity and magnetic
field properties similar to the sunspot umbra. This implies that the
horizontal magnetic fields in the decaying penumbra became vertical
as observed in flare-induced rapid penumbral decay, but on a very
different time-scale.
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Title: High-resolution Observations of Hα Spectra with a Subtractive
Double Pass
Authors: Beck, C.; Rezaei, R.; Choudhary, D. P.; Gosain, S.;
Tritschler, A.; Louis, R. E.
2018SoPh..293...36B Altcode: 2017arXiv171207077B
High-resolution imaging spectroscopy in solar physics has relied on
Fabry-Pérot interferometers (FPIs) in recent years. FPI systems,
however, become technically challenging and expensive for telescopes
larger than the 1 m class. A conventional slit spectrograph with a
diffraction-limited performance over a large field of view (FOV) can
be built at much lower cost and effort. It can be converted into an
imaging spectro(polari)meter using the concept of a subtractive double
pass (SDP). We demonstrate that an SDP system can reach a similar
performance as FPI-based systems with a high spatial and moderate
spectral resolution across a FOV of 100<SUP>″</SUP>×100<SUP>″</SUP>
with a spectral coverage of 1 nm. We use Hα spectra taken with an SDP
system at the Dunn Solar Telescope and complementary full-disc data to
infer the properties of small-scale superpenumbral filaments. We find
that the majority of all filaments end in patches of opposite-polarity
fields. The internal fine-structure in the line-core intensity of Hα
at spatial scales of about 0.″5 exceeds that in other parameters
such as the line width, indicating small-scale opacity effects in a
larger-scale structure with common properties. We conclude that SDP
systems in combination with (multi-conjugate) adaptive optics are a
valid alternative to FPI systems when high spatial resolution and a
large FOV are required. They can also reach a cadence that is comparable
to that of FPI systems, while providing a much larger spectral range
and a simultaneous multi-line capability.
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Title: Plasma flows and magnetic field interplay during the formation
of a pore
Authors: Ermolli, I.; Cristaldi, A.; Giorgi, F.; Giannattasio, F.;
Stangalini, M.; Romano, P.; Tritschler, A.; Zuccarello, F.
2017A&A...600A.102E Altcode: 2017arXiv170106440E
<BR /> Aims: Recent simulations of solar magneto-convection have offered
new levels of understanding of the interplay between plasma motions
and magnetic fields in evolving active regions. We aim at verifying
some aspects of the formation of magnetic regions derived from recent
numerical studies in observational data. <BR /> Methods: We studied the
formation of a pore in the active region (AR) NOAA 11462. We analysed
data obtained with the Interferometric Bidimensional Spectrometer
(IBIS) at the Dunn Solar Telescope on April 17, 2012, consisting of
full Stokes measurements of the Fe I 617.3 nm lines. Furthermore, we
analysed SDO/HMI observations in the continuum and vector magnetograms
derived from the Fe I 617.3 nm line data taken from April 15 to 19,
2012. We estimated the magnetic field strength and vector components
and the line-of-sight (LOS) and horizontal motions in the photospheric
region hosting the pore formation. We discuss our results in light
of other observational studies and recent advances of numerical
simulations. <BR /> Results: The pore formation occurs in less than
1 h in the leading region of the AR. We observe that the evolution
of the flux patch in the leading part of the AR is faster (<12 h)
than the evolution (20-30 h) of the more diffuse and smaller scale
flux patches in the trailing region. During the pore formation,
the ratio between magnetic and dark area decreases from 5 to 2. We
observe strong downflows at the forming pore boundary and diverging
proper motions of plasma in the vicinity of the evolving feature that
are directed towards the forming pore. The average values and trends of
the various quantities estimated in the AR are in agreement with results
of former observational studies of steady pores and with their modelled
counterparts, as seen in recent numerical simulations of a rising-tube
process. The agreement with the outcomes of the numerical studies holds
for both the signatures of the flux emergence process (e.g. appearance
of small-scale mixed polarity patterns and elongated granules) and the
evolution of the region. The processes driving the formation of the pore
are identified with the emergence of a magnetic flux concentration and
the subsequent reorganization of the emerged flux, by the combined
effect of velocity and magnetic field, in and around the evolving
structure. <P />Movies associated to Figs. 1 and 4 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201526144/olm">http://www.aanda.org</A>
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Title: Daniel K. Inouye Solar Telescope: High-resolution observing
of the dynamic Sun
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
Kuhn, J. R.; Lin, H.; Rast, M. P.; McMullin, J. P.; Schmidt, W.;
Wöger, F.; DKIST Team
2016AN....337.1064T Altcode:
The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
known as the Advanced Technology Solar Telescope (ATST) is currently
under construction on Haleakalā (Maui, Hawai'i) projected to
start operations in 2019. At the time of completion, DKIST will be
the largest ground-based solar telescope providing unprecedented
resolution and photon collecting power. The DKIST will be equipped
with a set of first-light facility-class instruments offering unique
imaging, spectroscopic and spectropolarimetric observing opportunities
covering the visible to infrared wavelength range. This first-light
instrumentation suite will include: a Visible Broadband Imager (VBI) for
high-spatial and -temporal resolution imaging of the solar atmosphere; a
Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line
spectropolarimetry; a Fabry-Pérot based Visible Tunable Filter
(VTF) for high-spatial resolution spectropolarimetry; a fiber-fed
Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP)
for two-dimensional high-spatial resolution spectropolarimetry
(simultaneous spatial and spectral information); and a Cryogenic Near
Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field
measurements and on-disk observations of, e.g., the CO lines at 4.7
μm. We will provide an overview of the DKIST's unique capabilities
with strong focus on the first-light instrumentation suite, highlight
some of the additional properties supporting observations of transient
and dynamic solar phenomena, and touch on some operational strategies
and the DKIST critical science plan.
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Title: He I Vector Magnetic Field Maps of a Sunspot and Its
Superpenumbral Fine-Structure
Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A.
2015SoPh..290.1607S Altcode: 2015arXiv150505567S; 2015SoPh..tmp...60S
Advanced inversions of high-resolution spectropolarimetric observations
of the He I triplet at 1083 nm are used to generate unique maps of
the chromospheric magnetic field vector across a sunspot and its
superpenumbral canopy. The observations were acquired by the Facility
Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST)
on 29 January 2012. Multiple atmospheric models are employed in the
inversions because superpenumbral Stokes profiles are dominated by
atomic-level polarization, while sunspot profiles are Zeeman-dominated,
but also exhibit signatures that might be induced by symmetry-breaking
effects of the radiation field incident on the chromospheric
material. We derive the equilibrium magnetic structure of a sunspot in
the chromosphere and furthermore show that the superpenumbral magnetic
field does not appear to be finely structured, unlike the observed
intensity structure. This suggests that fibrils are not concentrations
of magnetic flux, but are instead distinguished by individualized
thermalization. We also directly compare our inverted values with a
current-free extrapolation of the chromospheric field. With improved
measurements in the future, the average shear angle between the inferred
magnetic field and the potential field may offer a means to quantify
the non-potentiality of the chromospheric magnetic field to study the
onset of explosive solar phenomena.
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Title: Understanding the Fe I Line Measurements Returned by the
Helioseismic and Magnetic Imager (HMI)
Authors: Cohen, D. P.; Criscuoli, S.; Farris, L.; Tritschler, A.
2015SoPh..290..689C Altcode: 2015SoPh..tmp...17C; 2015arXiv150202559C
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) observes the Sun at the Fe I 6173 Å line and
returns full-disk maps of line-of-sight (LOS) observables including
the magnetic flux density, velocities, Fe I line width, line depth, and
continuum intensity. These data are estimated through an algorithm (the
MDI-like algorithm, hereafter) that combines observables obtained at six
wavelength positions within the Fe I 6173 Å line. To properly interpret
such data, it is important to understand any effects of the instrument
and of the pipeline that generates these data products. We tested
the accuracy of the line width, line depth, and continuum intensity
returned by the MDI-like algorithm using various one-dimensional (1D)
atmosphere models. It was found that HMI estimates of these quantities
are highly dependent on the shape of the line, therefore on the LOS
angle and the magnetic flux density associated with the model, and less
to line shifts with respect to the central positions of the instrument
transmission profiles. In general, the relative difference between
synthesized values and HMI estimates increases toward the limb and
with the increase of the field; the MDI-like algorithm seems to fail
in regions with fields larger than approximately 2000 G. Instrumental
effects were investigated by analyzing HMI data obtained at daily
intervals for a span of three years at disk center in the quiet Sun
and hourly intervals for a span of 200 hours. The analysis revealed
periodicities induced by the variation of the orbital velocity of the
observatory with respect to the Sun, and long-term trends attributed to
instrument adjustments, re-calibrations, and instrumental degradation.
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Title: DKIST: Observing the Sun at High Resolution
Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.;
Craig, S. C.; Elmore, D. F.; Hubbard, R. P.; Kuhn, J. R.; Lin, H.;
McMullin, J. P.; Reardon, K. P.; Schmidt, W.; Warner, M.; Woger, F.
2015csss...18..933T Altcode:
The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly
known as the Advanced Technology Solar Telescope (ATST) and currently
under construction on Haleakalā (Maui, Hawai'i) will be the largest
solar ground-based telescope and leading resource for studying the
dynamic Sun and its phenomena at high spatial, spectral and temporal
resolution. Accurate and sensitive polarimetric observations at
high-spatial resolution throughout the solar atmosphere including the
corona is a high priority and a major science driver. As such the DKIST
will offer a combination of state-of-the-art instruments with imaging
and/or spectropolarimetric capabilities covering a broad wavelength
range. This first-light instrumentation suite will include: a Visible
Broadband Imager (VBI) for high-spatial and -temporal resolution
imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP)
for sensitive and accurate multi-line spectropolarimetry; a double
Fabry-Pérot based Visible Tunable Filter (VTF) for high-spatial
resolution spectropolarimetry; a fiber-fed 2D Diffraction-Limited Near
Infra-Red Spectro-Polarimeter (DL-NIRSP); and a Cryogenic Near Infra-Red
Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements
and on-disk observations of e.g. the CO lines at 4.7 microns. We
will provide a brief overview of the DKIST's unique capabilities to
perform spectroscopic and spectropolarimetric measurements of the solar
atmosphere using its first-light instrumentation suite, the status of
the construction project, and how facility and data access is provided
to the US and international community.
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Title: The DKIST Operations Lifecycle: From Proposal Preparation
to Completion
Authors: Tritschler, A.; Berukoff, S. J.; Rimmele, T. R.
2014AGUFMSH41C4161T Altcode:
The 4-m aperture Daniel Ken Inouye Solar Telescope (DKIST), formerly
known as the Advanced Technology Solar Telescope (ATST), will be the
largest ground-based solar telescope when construction is completed
in 2019. Community access to the facility and its high-resolution
optical and infrared instrumentation suite will be provided through a
proposal merit and approval process, optimizing DKIST for high-impact
scientific use and emphasizing a high operational efficiency of the
facility. In this presentation we provide a high-level overview of,
and guide through, the planned phases of the operations lifecycle
relevant to anyone wishing to make use of this facility. The lifecycle
is initiated by the preparation and submission of scientific proposals
by Principal Investigators, and concluded by the successful execution of
all observations relevant to an approved proposal, as well as storage
and management of acquired data and metadata.
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Title: The Daniel K. Inouye Solar Telescope: A Project Update.
Authors: Rimmele, T.; Berger, T.; McMullin, J.; Warner, M.; Casinsi,
R.; Kuhn, J.; Lin, H.; Woeger, F.; Schmidt, W.; Tritschler, A.;
Inouye, Daniel K.; Solar Telescope Team
2014amos.confE..43R Altcode:
The Advanced Technology Solar Telescope will be the largest solar
facility ever built. Designed and developed to meet the needs of
critical high resolution and high sensitivity spectral and polarimetric
observations of the sun, this facility will support key experiments
for the study of solar magnetism and its influence on the solar wind,
flares, coronal mass ejections and solar irradiance variability. The
4-meter diameter facility will operate over a broad wavelength range
(0.35 to 28 microns), using state-of-the-art adaptive optics systems to
provide diffraction limited imaging and the ability to resolve features
approximately 20 km on the Sun. Five first light instruments will be
available at the start of operations. Key subsystems have been designed
and fabrication is well underway, including the site construction,
which began in December 2012. We provide an update on the development
of the facilities both on site at the Haleakala Observatories in Maui
and the development of components around the world. We present the
overall construction and integration schedule leading to the start of
operations in mid-2019 and touch on operations aspects.
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Title: Spectral Signatures of Penumbral Transients
Authors: Reardon, K.; Tritschler, A.; Katsukawa, Y.
2013ApJ...779..143R Altcode:
In this work we investigate the properties of penumbral transients
observed in the upper photospheric and chromospheric region above a
sunspot penumbra using two-dimensional spectroscopic observations
of the Ca II 854.21 nm line with a 5 s cadence. In our 30 minutes
of observations, we identify several penumbral-micro jets (PMJs)
with cotemporal observations from Dunn Solar Telescope/IBIS and
Hinode/SOT. We find that the line profiles of these PMJ events
show emission in the two wings of the line (±0.05 nm), but
little modification of the line core. These are reminiscent of
the line profiles of Ellerman bombs observed in plage and network
regions. Furthermore, we find evidence that some PMJ events have a
precursor phase starting 1 minute prior to the main brightening that
might indicate initial heating of the plasma prior to an acoustic or
bow shock event. With the IBIS data, we also find several other types
of transient brightenings with timescales of less than 1 minute that
are not clearly seen in the Hinode/SOT data. The spectral profiles and
other characteristics of these events are significantly different from
those of PMJs. The different appearances of all these transients are
an indicator of the general complexity of the chromospheric magnetic
field and underscore the highly dynamic behavior above sunspots. It
also highlights the care that is needed in interpreting broadband
filter images of chromospheric lines, which may conceal very different
spectral profiles, and the underlying physical mechanisms at work.
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Title: Statistical study of magnetic cancellations and on-disk
type-II spicules
Authors: Chen, Xin; Deng, N.; Lamb, D.; Jing, J.; Tritschler, A.;
Reardon, K. P.; Wang, H.
2013SPD....44...04C Altcode:
We present a study using coordinated observations of the Interferometric
BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope and
Hinode / Solar Optical Telescope of a quiet sun (QS) region near
disk center. Our goal is to analyze the relationship between the
cancellation of opposite magnetic polarities in the photosphere and
"Rapid Blueshifted Excursions" (RBEs) by comparing quasi-simultaneous
magnetograms and chromospheric Hα line profiles. On the one hand,
the RBEs are considered the on-disk counterpart of the type-II
spicules observed at the limb that are most likely caused by
magnetic reconnection on small scales. On the other hand, the
magnetic cancellation is a signature after small-scale reconnection
in the QS. We developed an automatic tracking algorithm for detecting
magnetic cancellation events in the photosphere, based on the existing
SWAMIS code which is good at tracking magnetic flux emergence. Our
code can find characteristics of each cancellation event and the
detected cancellation sites appear to outline the supergranular
network. Furthermore, another automatic tracking code for RBEs has been
developed for the spectroscopic observations obtained with IBIS. We
are able to show a statistical distribution of the properties of RBEs,
such as lifetime, shape, and line-of-sight velocity. Finally, using the
spatial and temporal tracking of both magnetic cancellation events and
RBEs, we find that there is no simple one-to-one correspondence. The
majority of RBEs are related to magnetic cancellation events, however
a subset of them are not.
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Title: Velocity and Magnetic Field Distribution in a Forming Penumbra
Authors: Romano, P.; Frasca, D.; Guglielmino, S. L.; Ermolli, I.;
Tritschler, A.; Reardon, K. P.; Zuccarello, F.
2013ApJ...771L...3R Altcode:
We present results from the analysis of high-resolution
spectropolarimetric and spectroscopic observations of the solar
photosphere and chromosphere, obtained shortly before the formation of a
penumbra in one of the leading polarity sunspots of NOAA active region
11490. The observations were performed at the Dunn Solar Telescope of
the National Solar Observatory on 2012 May 28, using the Interferometric
Bidimensional Spectrometer. The data set is comprised of a 1 hr time
sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines
(full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I
only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to
derive magnetic field parameters and the line-of-sight (LOS) velocity
at the photospheric level. We characterize chromospheric LOS velocities
by the Doppler shift of the centroid of the Ca II 854.2 nm line. We
find that, before the formation of the penumbra, an annular zone of
3”-5” width is visible around the sunspot. In the photosphere, we
find that this zone is characterized by an uncombed structure of the
magnetic field although no visible penumbra has formed yet. We also
find that the chromospheric LOS velocity field shows several elongated
structures characterized by downflow and upflow motions in the inner
and outer parts of the annular zone, respectively.
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Title: High-Cadence and High-Resolution Halpha Imaging Spectroscopy
of a Circular Flare's Remote Ribbon with IBIS
Authors: Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Liu, C.;
Reardon, K. P.; Denker, C.; Xu, Y.; Wang, H.
2013SPD....4440404D Altcode:
We present an unprecedented high-resolution halpha imaging
spectroscopic observation of a C4.1 flare taken with IBIS on 2011
October 22. The flare consists of a main circular ribbon that occurred
in a parasitic magnetic configuration and a remote ribbon that was
observed by the IBIS. Such a circular-ribbon flare with a remote
brightening is predicted in 3D fan-spine reconnection but so far has
been rarely reported. During the flare impulsive phase, we define
"core" and "halo" structures in the observed ribbon. Examining the
halpha emission spectra averaged in the flare core and halo areas,
we find that only those from the flare cores show typical nonthermal
electron beam heating characteristics. These characteristics include:
broad and centrally reversed emission spectra, excess emission in
the red wing with regard to the blue wing (i.e., red asymmetry),
and redshifted bisectors of the emission spectra. We also observe
rather quick timescales for the heating (30 s) and cooling (14--33
s) in the flare core locations. Therefore, we suggest that the flare
cores revealed by IBIS track the sites of electron beam precipitation
with exceptional spatial and temporal resolution. The flare cores
show two-stage motion (a parallel motion along the ribbon followed
by an expansion motion perpendicular to the ribbon) during the two
impulsive phases of the flare. Some cores jump quickly (30 km/s)
between discrete magnetic elements implying reconnection involving
different flux tubes. We observe a very high temporal correlation
(>0.9) between the integrated halpha and HXR emission during the
flare impulsive phase. A short time delay (4.6 s) is also found in the
halpha emission spikes relative to HXR bursts. The ionization timescale
of the cool chromosphere and the extra time taken for the electrons
to travel to the remote ribbon site may contribute to this delay.
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Title: He I Spectropolarimetry with FIRS: Towards Vector Magnetometry
of Chromospheric Fibrils Plus New Diagnostics of Coronal Rain
Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A.
2012ASPC..463...25S Altcode:
At the Dunn Solar Telescope, the Interferometric Bidimensional
Spectrometer (IBIS) can measure the full Stokes vector of the Ca II
854.2 nm spectral line while the Facility Infrared Spectropolarimeter
(FIRS) measures the Stokes vector of the He I triplet at 1083
nm. We analyze the He I triplet observed in two widely different
features above NOAA AR 11295 on 19 September 2011 - thin (< 1″)
chromospheric fibrils and a large-scale loop hosting a high-velocity
coronal rain event. These two features are shown to first demonstrate
the diagnostic potential of the He I triplet for magnetic fields in the
chromosphere/transition region and second to stress the need to pair
large-aperture facilities with flexible instrumentation. Inversions of
the He I triplet near the penumbral boundary return azimuthal directions
of the magnetic field aligned with fine-scale fibrils observed in the
line core of Ca II. The coronal rain event shows Doppler velocities
up to 195 km s<SUP>-1</SUP>, among the largest reported. We observe
measurable polarization within the raining material, which may be a
good magnetic diagnostic of chromospheric-like material higher in the
corona within condensating loops.
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Title: The Sunspot Penumbra in the Photosphere: Results from Forward
Synthesized Spectroscopy
Authors: Tritschler, A.; Uitenbroek, H.; Rempel, M.
2012ASPC..463...89T Altcode:
We present first results from a spectral synthesis of the
Zeeman-insensitive Fe 1 557.6 nm line for two different viewing angles
(0° and 30°) using numerical simulations of a sunspot as an input
model. We performed a bisector analysis to calculate two-dimensional
maps of line-of-sight Doppler velocities and the line width. We analyze
azimuthal cuts of the LOS velocity at different penumbral radii and
calculate the radial behavior of azimuthal averages of line width and
intensity. Both are compared with observational results. The properties
of dark cores in penumbral filaments are discussed briefly. Within the
limitations of this study, we find that the results from the forward
synthesized spectroscopy are in good agreement with the observations,
corroborating that the photospheric structure and dynamics of the
penumbra is a signature of overturning anisotropic magneto-convection.
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Title: Solar Limb Adaptive Optics: A Test of Wavefront Sensors
and Algorithms
Authors: Taylor, G. E.; Rimmele, T. R.; Marino, J.; Tritschler, A.;
McAteer, R. T. J.
2012ASPC..463..321T Altcode:
In order to advance our understanding of solar prominences, we need
to be able to observe them at high spatial, spectral and temporal
resolution. In order to determine physical properties of these cool
and faint coronal structures, however, one is forced to use long
exposure times, particularly in spectroscopic and spectropolarimetric
applications. It is thus crucial that image stabilization is provided,
preferrably in form of an adaptive optics (AO) system that is capable
to lock onto the off-limb prominence structure, potentially providing
diffraction limited imaging. We investigate the preliminary design
of such a solar-limb AO system based on a correlating Shack-Hartmann
sensor. As an alternative we also studied a solar-limb AO wavefront
sensor using a phase-diverse approach.
---------------------------------------------------------
Title: The Influence of Molecular Lines on the Measurement of
Photospheric Velocities
Authors: Uitenbroek, H.; Dumont, N.; Tritschler, A.
2012ASPC..463...99U Altcode:
We use different solar atmospheric models to investigate the influence
of molecular lines on the accuracy with which line-of-sight velocities
of mass flows can be measured from Doppler shifts. Particularly in
relatively cool atmospheres molecules become more abundant and give
rise to a thick forest of perturbing lines. Using bisectors we estimate
the apparent shift introduced in the positions of the C I 538.0 nm
and Fe I 557.6 nm lines by molecular lines in one-dimensional models
with different effective temperatures, ranging from 3750 K to 6250 K,
and in a three-dimensional section from a solar magneto-convection
simulation. We find that the core of the iron line is mostly unaffected,
and that by contrast the carbon line is severely compromised by
molecular lines, even in environments with effective temperatures
similar to those in the quiet Sun.
---------------------------------------------------------
Title: Halpha Imaging Spectroscopy of a C-class flare with IBIS
Authors: Deng, N.; Tritschler, A.; Jing, J.; Chen, X.; Reardon, K.;
Liu, C.; Xu, Y.; Wang, H.
2012IAUSS...6E.307D Altcode:
We present a rare high cadence and high spatial resolution spectroscopic
observation of a C4.1 Flare taken with the Interferometric Bidimensional
Spectrometer (IBIS) in conjunction with the adaptive optics system at
the 76 cm Dunn Solar Telescope on 2011 October 22 in NOAA AR 11324. The
IBIS with a round FOV of 90" x 90" and 0.1"/pixel detector image scale
scanned the Halpha line from 6561.1 to 6563.8 Angstrom with 0.1 Angstrom
stepsize for 28 steps. Each scan takes about 4.8 s. The flare occurred
in a mixed polarity region with two parasite configurations. The
flare shows multiple bright ribbons in the chromosphere spreading
over a region of 120" x 60". IBIS observed a remote ribbon of the
flare and fully covered its temporal evolution. The Halpha emission
integrated over this ribbon area exhibits several bursts over four
minutes during the flare impulsive phase that are temporally correlated
with the subpeaks of RHESSI hard X-ray (HXR) light curves. During the
strong bursts of the Halpha emission, we observe a central reversal
patten in the Halpha line core, which is believed to be a signature of
nonthermal process caused by direct electron precipitation. The line
core shows blueward shift that increases with the Halpha emission,
which might be related to chromospheric evaporation. The Halpha
emission is stronger in the red wing than in the blue wing during the
strong bursts. Substructures within the ribbon are also identified. A
bright core feature that is 30% brighter than the entire ribbon moves
at an apparent velocity of about 30 km/s within the ribbon during the
strongest burst of Halpha emission co-temporal with a strong subpeak of
HXR. The bright core disappeared in the decay phase of the flare. We
suggest that this running bright core feature tracks the site of
electron precipitation.
---------------------------------------------------------
Title: Science with Large Solar Telescopes
Authors: Cauzzi, G.; Tritschler, A.; Deng, Y.
2012IAUSS...6E....C Altcode:
With several large aperture optical/IR telescopes coming on-line,
and scheduled for the near future, solar physics is on the verge
of a quantum leap in observational capabilities. An efficient use
of such facilities will require new and innovative approaches to
both observatory operations and data handling. <P />This two-days
long Special Session will discuss the science expected with large
solar telescopes, and start addressing the strategies necessary to
optimize their scientific return. Cutting edge solar science as derived
from state of the art observations and numerical simulations will be
presented, and discussions will be held on the role of large facilities
in satisfying the demanding requirements of spatial and temporal
resolution, stray-light, and spectro-polarimetric accuracy. Building on
the experience of recently commissioned telescopes, we will then discuss
critical issues for the development of future facilities including
operational issues peculiar to large telecopes, and strategies for
their best use.
---------------------------------------------------------
Title: The Visible Broadband Imager: The Sun at High Spatial and
Temporal Resolution
Authors: Wöger, F.; McBride, W.; Ferayorni, A.; Gregory, S.; Hegwer,
S.; Tritschler, A.; Uitenbroek, H.
2012ASPC..463..431W Altcode:
The Visible Broadband Imager (VBI) will be the primary first-light
instrument for the Advanced Technology Solar Telescope (ATST). It is
designed to observe the solar atmosphere at heights ranging from the
photosphere to chromosphere. High frame-rate detectors that sample
the FOV of up to 2.8 arcmin in diameter critically at the diffraction
limit of ATST's 4 meter aperture will provide near real-time speckle
reconstruction imaging. With its focus on high-spatial resolution, the
VBI will be addressing scientific questions related to the smallest
structures visible in the solar atmosphere with high photometric
precision. The capability to observe the solar atmosphere with a
cadence of about 3 seconds per reconstructed image will enable the VBI
to temporally resolve fast evolving structures. In this contribution we
present the major aspects of the current design of the VBI and highlight
some scientific questions related to fast evolving, small-scale features
within the solar atmosphere that the VBI will address.
---------------------------------------------------------
Title: Construction of the Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S.; McMullin, J.; Knölker, M.; Kuhn,
J. R.; Goode, P. R.; Rosner, R.; Casini, R.; Lin, H.; Tritschler,
A.; Wöger, F.; ATST Team
2012ASPC..463..377R Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope and the world's leading ground-based resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. The
project has entered its construction phase. Major subsystems have
been contracted. As its highest priority science driver ATST shall
provide high resolution and high sensitivity observations of the
dynamic solar magnetic fields throughout the solar atmosphere,
including the corona at infrared wavelengths. With its 4m aperture,
ATST will resolve features at 0.″03 at visible wavelengths and
obtain 0.″1 resolution at the magnetically highly sensitive near
infrared wavelengths. A high order adaptive optics system delivers a
corrected beam to the initial set of state-of-the-art, facility class
instrumentation located in the Coudé laboratory facility. The initial
set of first generation instruments consists of five facility class
instruments, including imagers and spectro-polarimeters. The high
polarimetric sensitivity and accuracy required for measurements of
the illusive solar magnetic fields place strong constraints on the
polarization analysis and calibration. Development and construction
of a four-meter solar telescope presents many technical challenges,
including thermal control of the enclosure, telescope structure and
optics and wavefront control. A brief overview of the science goals
and observational requirements of the ATST will be given, followed by a
summary of the design status of the telescope and its instrumentation,
including design status of major subsystems, such as the telescope
mount assembly, enclosure, mirror assemblies, and wavefront correction
---------------------------------------------------------
Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from
the Photosphere to the Corona
Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera,
M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.;
Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M.
2012ASPC..463.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observing strategies for future solar facilities: the ATST
test case
Authors: Uitenbroek, H.; Tritschler, A.
2012IAUSS...6E.401U Altcode:
Traditionally solar observations have been scheduled and performed
very differently from night time efforts, in particular because we have
been observing the Sun for a long time, requiring new combinations of
observables to make progress, and because solar physics observations
are often event driven on time scales of hours to days. With the
proposal pressure that is expected for new large-aperture facilities,
we can no longer afford the time spent on custom setups, and will have
to rethink our scheduling and operations. We will discuss our efforts
at Sac Peak in preparing for this new era, and outline the planned
scheduling and operations planning for the ATST in particular.
---------------------------------------------------------
Title: Multi-wavelength Spectropolarimetry Of A Sunspot Superpenumbra
With Firs And Ibis
Authors: Schad, Thomas A.; Tritschler, A.; Penn, M. J.
2012AAS...22020302S Altcode:
Extending nearly radially from magnetic field concentrations like
sunspot umbrae or pores, threadlike fibrils observed in the chromosphere
and transition region host a variety of dynamic behavior and have long
been considered local tracers for the magnetic field. Morphologically,
fibrils are similar to spicules seen on the limb. The connectivity
of fibrils outside of the magnetic field concentrations with the
photosphere and/or corona is not well understood, and probing the
magnetic field in these features remains challenging. In this
contribution we describe multi-wavelength spectropolarimetric
observations from the Dunn Solar Telescope in New Mexico using the
Facility Infrared Spectropolarimeter (FIRS) and the Interferometric
BiDimensional Spectropolarimeter (IBIS). FIRS performs high resolution
slit spectropolarimetry in the He I triplet at 1083 nm, which is a
promising diagnostic of chromospheric vector fields. Significant
progress has been made to boost the accuracy and sensitivity of
these measurements. Here we present measurements of an active region
sunspot at a spatial resolution of 0.3 arcsec and an RMS noise in
Stokes Q,U,V spectra down to 0.0003 in units of the local continuum
(SNR > 3300). We perform full inversions of these spectra taking
into account both Zeeman and Hanle effects. Initial results lend
support for field-aligned fibrils near the penumbral boundary of a
sunspot. Jointly with the FIRS observations, we use IBIS to observe the
Stokes vectors of Ca II 854.2 nm and Fe I 617.3 nm and the intensity
spectrum of H-alpha 656.3 nm. As a spectral imaging instrument, IBIS
rapidly scans through the three spectral lines over a 45” by 95” FOV
at an overall cadence of 50 seconds, allowing a much better description
the dynamics of fibrils observed by both FIRS and IBIS.
---------------------------------------------------------
Title: Multi-height Spectropolarimetry Of Sunspots With Firs And Ibis
Authors: Jaeggli, Sarah A.; Lin, H.; Tritschler, A.
2012AAS...22020606J Altcode:
The effects of radiative transfer prevent the characterization of
the magnetic field at a single geometric height in the photosphere
of a sunspot. Therefore, a full 3D characterization of the magnetic
field is necessary to understand many properties of sunspots, such as
the true state of hydrostatic equilibrium. Many current and proposed
solar spectropolarimeters are capable of taking near-simultaneous
observations at multiple wavelengths. Combining these rich datasets
provides a welcome problem to the community. We present the first joint
observations of the magnetically sensitive photospheric Fe I lines at
630 and 1565 nm taken with the Facility Infrared Spectropolarimeter
(FIRS); and the chromospheric Ca II line at 854 nm taken with the
Interferometric Bi-Dimensional Spectrometer (IBIS); both instruments
operated at the Dunn Solar Telescope. These wavelengths allow us to
probe the magnetic field over a broad range of heights, from the
bottom of the photosphere to the chromosphere. We investigate the
magnetic field topologies of several sunspots of different size and
magnetic complexity.
---------------------------------------------------------
Title: High Cadence and High Resolution Halpha Imaging Spectroscopy
of a C4.1 Flare with IBIS
Authors: Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Reardon, K.;
Liu, C.; Xu, Y.; Wang, H.
2012AAS...22020449D Altcode:
We present a rare high cadence and high spatial resolution spectroscopic
observation of a C4.1 Flare taken with the Interferometric Bidimensional
Spectrometer (IBIS) in conjunction with the adaptive optics system at
the 76cm Dunn Solar Telescope on 2011 October 22 in NOAA AR11324. The
IBIS with a round FOV of 90"X90" and 0.1"/pix detector image scale
scanned the Halpha line from 6561.1 to 6563.8 A with 0.1 A stepsize for
28 steps. Each scan takes about 4.8s. The flare occurred in a mixed
polarity region with two parasite configurations. The flare shows
multiple bright ribbons in the chromosphere spreading over a region
of 120"X60". IBIS observed a remote ribbon of the flare and fully
covered its temporal evolution. The Halpha emission integrated over
this ribbon area exhibits several bursts over four minutes during the
flare impulsive phase that are temporally correlated with the subpeaks
of RHESSI hard X-ray (HXR) light curves. During the strongest burst of
the Halpha emission, we observe a central reversal patten in the Halpha
line core, which is believed to be a signature of nonthermal process
caused by direct electron precipitation. The line core shows blueward
shift that increases with the Halpha emission, which might be related
to chromospheric evaporation. The line width also increases with the
emission. The Halpha emission is stronger in the red wing than in the
blue wing during the strong bursts. Substructures within the ribbon are
also identified. A bright core feature that is 30% brighter than the
entire ribbon moves at an apparent velocity of about 30 km/s within
the ribbon during the strongest burst of Halpha emission co-temporal
with a strong subpeak of HXR. The bright core disappeared in the decay
phase of the flare. We suggest that this running bright core feature
tracks the site of electron precipitation.
---------------------------------------------------------
Title: Coordinated Observations Of On-disk Type II Spicules With
IBIS And Hinode
Authors: Chen, Xin; Na, D.; Jing, J.; Tritschler, A.; Reardon, K.;
Wang, H.
2012AAS...22020310C Altcode:
Ubiquitous small-scale spicules/jets in the chromosphere are believed
to be an important ingredient contributing to coronal heating and
solar wind by supplying energy and mass upwards. In particular, type II
spicules discovered at the solar limb (De Pontieu et al. 2007) and their
highly probable chromospheric on disk counterpart "Rapid Blueshifted
Excursions" (RBEs; Langangen et al. 2008) have drawn much attention in
recent years. Their rapid heating, high speed upflow and association
with magnetic field indicate that the most possible underlying
driving mechanism is magnetic reconnection on small scales. In order
to understand the physical properties of these features, we carried
out a coordinated high resolution and high cadence observation of
chromospheric RBEs using the Interferometric BIdimensional Spectrometer
(IBIS) at the Dunn Solar Telescope and photospheric magnetic fields
using Hinode SOT/SP and SOT/NFI in October 2011. Different targets near
disk center were observed, such as quite sun and active regions. For
each target region, both Halpha and Ca II 854.2 nm lines were scanned
by IBIS with high-spatial ( 0.1 arcsec/pixel, with adaptive optics),
high-temporal ( 6s) and moderate-spectral ( 0.1 angstrom) resolution. At
the same time Hinode/SP and NFI pointing at the same area providing the
geometry and time evolution of photospheric magnetic fields, such as
flux emergence, convergence and cancellation on small spatial scales. We
identify RBEs based on the IBIS observations, study their properties
(velocity, density, temperature and statistical distribution) and search
for signatures of small-scale magnetic reconnection in the Hinode
magnetograms. The poster will show the details of the temporal and
spatial relation between chromospheric RBEs and photospheric magnetic
field activities. <P />References: <P />De Pontieu, B. et al. 2007,
PASJ, 59, 655-662 <P />Langangen, O. et al. 2008, ApJ, 679, L167
---------------------------------------------------------
Title: The Observed Red Asymmetry in the Bisectors of the
Chromospheric CaII 854.2 nm Line
Authors: Burleigh, Kaylan; Tritschler, A.; Uitenbroek, H.
2011SPD....42.0304B Altcode: 2011BAAS..43S.0304B
The bisector analysis of chromospheric spatially and temporally
unresolved Ca II atlas profiles reveals a red asymmetry of the
Doppler core in form of an "inverse C” (Uitenbroek, 2005). The
origin of this red asymmetry is yet unknown. We use spatially and
temporally resolved 2D spectroscopic chromospheric (CaII 854.2 nm)
observations of the quiet and more active sun obtained with the Dunn
Solar Telescope's Interferometric BIdimensional Spectrometer (IBIS) to
determine where the inverse C-shape appears with respect to granules,
inter-granular lanes, and magnetic features. To this end we generate
masks of the spatial location of the red asymmetry. We also examine
the temporal behavior of profiles showing this red asymmetry. In the
chromosphere, we find the red asymmetry most concentrated in dark region
outside of magnetic networks; it avoids nearly all bright regions. It
disappears almost entirely within magnetic networks which suggests
magnetic activity "damps out” the red asymmetry. Relative to the
underlying photosphere, the red asymmetry preferentially occurs over
or just slightly offset from inter-granular lanes; very rarely does
it occur over granules. The temporal behavior of at least one red
asymmetry profile shows a periodicity near 3 min. We speculate that
the red asymmetry forms from upward traveling acoustic shock waves. <P
/>This work was supported by the National Solar Observatory's Research
Experiences for Undergraduate (REU) program which is co-funded by
the Department of Defense in partnership with the National Science
foundation REU Program.
---------------------------------------------------------
Title: The Visible Broadband Imager: The Sun at High Spatial and
Temporal Resolution
Authors: Friedrich, Woeger; Tritschler, A.; Uitenbroek, H.; Rimmele, T.
2011SPD....42.2001F Altcode: 2011BAAS..43S.2001F
The Visible Broadband Imager (VBI) will be the first of the five
first-light instruments for the Advanced Technology Solar Telescope
(ATST). It is designed to observe the solar atmosphere at heights
ranging from photosphere to chromosphere. High frame-rate detectors
that sample the FOV of up to 2.8 arcmin in diameter critically near or
at the diffraction limit of ATST's 4 meter aperture will facilitate near
real-time speckle reconstruction imaging. With its focus on high-spatial
resolution, the VBI will be addressing scientific questions related to
the smallest structures visible in the solar atmosphere today with high
photometric precision. The capability to observe the solar atmosphere
with a cadence of about 3 seconds per reconstructed image will enable
the VBI to temporally resolve fast evolving structures. <P />In this
contribution we present the current design of the VBI and highlight
some scientific questions related to fast evolving, small-scale features
within the solar atmosphere that the VBI will address.
---------------------------------------------------------
Title: IBIS 2D Spectropolarimetry: Analysis of G-band Bright Points
Authors: Viticchiè, B.; Del Moro, D.; Berrilli, F.; Rubio, L. B.;
Tritschler, A.
2011ASPC..437...75V Altcode:
We present the results derived from the analysis of the first
spectropolarimetric (SP) data obtained through the Interferometric
BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope (NSO). The
analysis is focused on 10<SUP>3</SUP> G small scale (∼100 km) magnetic
field concentrations observed, in a quiet Sun region, as bright points
in G-band filtergrams. The combination of high spatial and temporal
resolution of both SP and G-band datasets allowed us to analyze in
detail the magnetic properties of bright points over different spatial
scales (from ∼eq. 0.4" up to 2"- 3") and temporal scales (from 10
min up to > 60 min) and, beside this, to focus on the dependence
of significant physical quantities (i.e., magnetic field strength and
filling factor derived from Stokes profile inversion) in relation with
such evolutions. <P />We present two main results of our analysis: i)
evolution of bright points over small spatial scales and short time
intervals (by considering the coalescence of small and faint bright
points into a single high brightness one); ii) magnetic properties of
bright points over large spatial scales (by examining a small network
patch). Our study indicates an interesting correlation between G-band
brightness and magnetic filling factor fluctuations. On the contrary,
we have not observed any correlation between G-band brightness and
magnetic field strength. Such a result can help us to conclude on the
possible fine structuring of kG concentrations in the solar photosphere
which produce brightness enhancement in G-band filtergrams.
---------------------------------------------------------
Title: Line Shape Effects on Intensity Measurements of Solar Features:
Brightness Correction to SOHO MDI Continuum Images
Authors: Criscuoli, S.; Ermolli, I.; Del Moro, D.; Giorgi, F.;
Tritschler, A.; Uitenbroek, H.; Vitas, N.
2011ApJ...728...92C Altcode: 2010arXiv1012.2561C
Continuum intensity observations obtained with the Michelson
Doppler Imager (MDI) on board the SOHO mission provide long time
series of filtergrams that are ideal for studying the evolution of
large-scale phenomena in the solar atmosphere and their dependence on
solar activity. These filtergrams, however, are not taken in a pure
continuum spectral band, but are constructed from a proxy, namely a
combination of filtergrams sampling the Ni I 6768 Å line. We studied
the sensitivity of this continuum proxy to the shape of the nickel line
and to the degradation in the instrumental transmission profiles. We
compared continuum intensity measurements near the nickel line with
MDI proxy values in three sets of high-resolution spectro-polarimetric
data obtained with the Interferometric Bidimensional Spectrometer,
and in synthetic data, obtained from multi-dimensional simulations of
magneto-convection and one-dimensional atmosphere models. We found that
MDI continuum measurements require brightness corrections which depend
on magnetic field strength, temperature and, to a smaller extent, plasma
velocity. The correction ranges from 2% to 25% in sunspots, and is,
on average, less than 2% for other features. The brightness correction
also varies with position on the disk, with larger variations obtained
for sunspots, and smaller variations obtained for quiet Sun, faculae,
and micropores. Correction factors derived from observations agree
with those deduced from the numerical simulations when observational
effects are taken into account. Finally, we found that the investigated
potential uncertainties in the transmission characteristics of MDI
filters only slightly affect the brightness correction to proxy
measurements.
---------------------------------------------------------
Title: Magnetic Field Measurements at the Photosphere and Coronal Base
Authors: Judge, P. G.; Centeno, R.; Tritschler, A.; Uitenbroek, H.;
Jaeggli, S.; Lin, H.
2010AGUFMSH31A1783J Altcode:
We have obtained vector polarimetric measurements in lines of Fe I
(630nm), Ca II (854nm) and He I (1083nm) of several active regions
during 3-14 June 2010. The measurements were made at the Dunn Solar
Telescope at Sacramento Peak Observatory, using the FIRS and IBIS
instruments simultaneously. We discuss these and SDO data for NOAA
11076. The seeing was very good or excellent and the adaptive
optics system functioned well. In this preliminary analysis we
compare extrapolations of photospheric fields with the constraints
available from Stokes polarimetry, including the morphology and
kinematic properties of fibrils. Connections to the corona will also be
discussed. The implications for field extrapolations from photospheric
measurements will be discussed. We will make the reduced data freely
available on the web for interested researchers.
---------------------------------------------------------
Title: Two-dimensional solar spectropolarimetry with the KIS/IAA
Visible Imaging Polarimeter
Authors: Beck, C.; Bellot Rubio, L. R.; Kentischer, T. J.; Tritschler,
A.; Del Toro Iniesta, J. C.
2010A&A...520A.115B Altcode: 2010arXiv1007.1153B
Context. Spectropolarimetry at high spatial and spectral resolution
is a basic tool to characterize the magnetic properties of the solar
atmosphere. <BR /> Aims: We introduce the KIS/IAA Visible Imaging
Polarimeter (VIP), a new post-focus instrument that upgrades the TESOS
spectrometer at the German Vacuum Tower Telescope (VTT) into a full
vector polarimeter. VIP is a collaboration between the Kiepenheuer
Institut für Sonnenphysik (KIS) and the Instituto de Astrofísica
de Andalucía (IAA-CSIC). <BR /> Methods: We describe the optical
setup of VIP, the data acquisition procedure, and the calibration of
the spectropolarimetric measurements. We show examples of data taken
between 2005 and 2008 to illustrate the potential of the instrument. <BR
/> Results: VIP is capable of measuring the four Stokes profiles of
spectral lines in the range from 420 to 700 nm with a spatial resolution
better than 0farcs5. Lines can be sampled at 40 wavelength positions
in 60 s, achieving a noise level of about 2 × 10<SUP>-3</SUP> with
exposure times of 300 ms and pixel sizes of 0farcs17 × 0farcs17 (2
× 2 binning). The polarization modulation is stable over periods of a
few days, ensuring high polarimetric accuracy. The excellent spectral
resolution of TESOS allows the use of sophisticated data analysis
techniques such as Stokes inversions. One of the first scientific
results of VIP presented here is that the ribbon-like magnetic
structures of the network are associated with a distinct pattern of
net circular polarization away from disk center. <BR /> Conclusions:
VIP performs spectropolarimetric measurements of solar magnetic fields
at a spatial resolution that is only slightly worse than that of the
Hinode spectropolarimeter, while providing a 2D field field of view and
the possibility to observe up to four spectral regions sequentially
with high cadence. VIP can be used as a stand-alone instrument or in
combination with other spectropolarimeters and imaging systems of the
VTT for extended wavelength coverage.
---------------------------------------------------------
Title: Magnetic field measurements at the photosphere and coronal base
Authors: Judge, Philip; Centeno, R.; Tritschler, A.; Uitenbroek, H.;
Jaeggli, S.; Lin, H.
2010shin.confE..56J Altcode:
We have obtained vector polarimetric measurements in lines of Fe I
(630nm), Ca II (854nm) and He I (1083) of several active regions during
3-14 June 2010. The measurements were made at the Dunn Solar Telescope
at Sacramento Peak Observatory, using the FIRS and IBIS instruments
simultaneously. We discuss data for NOAA 11076 observed on 4 June
2010. The seeing was very good or excellent and the adaptive optics
system functioned well. In this preliminary analysis we compare linear
extrapolations of photospheric fields with the constraints available
from Stokes polarimetry, including the morphology and kinematic
properties of fibrils. The implications for field extrapolations from
photospheric measurements will be discussed. We will make the reduced
data freely available on the web for interested researchers.
---------------------------------------------------------
Title: The Big Bear Solar Observatory Ca II K-line index for solar
cycle 23
Authors: Naqvi, M. F.; Marquette, W. H.; Tritschler, A.; Denker, C.
2010AN....331..696N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A chromospheric dark-cored fibril in Ca II IR spectra
Authors: Beck, C.; Tritschler, A.; Wöger, F.
2010AN....331..574B Altcode:
We investigate the thermodynamical and magnetic properties of a
“dark-cored" fibril seen in the chromospheric Ca II IR line at 854.2
nm to determine the physical process behind its appearance. We analyse
a time series of spectropolarimetric observations obtained in the Ca
II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We
simultaneously invert the spectra in both wavelength ranges with the
SIR code to obtain the temperature and velocity stratification with
height in the solar atmosphere and the magnetic field properties in the
photosphere. The structure can be clearly traced in the line-of-sight
(LOS) velocity and the temperature maps. It connects from a small
pore with kG fields to a region with lower field strength. The flow
velocity and the temperature indicate that the height of the structure
increases with increasing distance from the inner footpoint. The Stokes
V signal of 854.2 nm shows a Doppler-shifted polarization signal with
the same displacement as in the intensity profile, indicating that the
supersonic flow seen in the LOS velocity is located within magnetized
plasma. We conclude that the chromospheric dark-cored fibril traces
a siphon flow along magnetic field lines, driven by the gas pressure
difference caused by the higher magnetic field strength at the inner
footpoint. We suggest that fast flows guided by the magnetic field lead
to the appearance of “dark-cored" fibrils in intensity images. Although
the observations included the determination of the polarization signal
in the chromospheric Ca II IR line, the signal could not be analysed
quantitatively due to the low S/N. Chromospheric polarimetry will thus
require telescopes of larger aperture able to collect a sufficient
number of photons for a reliable determination of polarization in deep
and only weakly polarized spectral lines.
---------------------------------------------------------
Title: Delving into the Chromosphere: New Observational Tools
Authors: Reardon, Kevin P.; Cauzzi, G.; Tritschler, A.; Uitenbroek, H.
2010AAS...21630503R Altcode:
The chromosphere lies at the boundary between the near-equilibrium
photosphere and the hot, expanding corona. This region combines both
large interconnecting magnetic structures, and fine-scaled dynamics into
an intriguingly complex whole. Studying this behavior is a significant
observational challenge, requiring sizable fields of view (60-90")
sampled at high spatial (< 0.3") and temporal resolution (< 30
seconds), with full spectral information in multiple lines. We will
describe how instruments based on Fabry-Perot interferometers have
recently begun to routinely deliver such observations. We will review
some of the most exciting results obtained and the deeper insights
they have provided into the characteristics of the solar chromosphere.
---------------------------------------------------------
Title: Chromospheric Structure and Dynamics. From Old Wisdom to
New Insights
Authors: Tritschler, A.; Reardon, K.; Uitenbroek, H.
2010MmSAI..81..533T Altcode: 2010MmSAI..81..533R
No abstract at ADS
---------------------------------------------------------
Title: The Growth of a Primitive Penumbra
Authors: Sreejith, P.; Tritschler, A.; Sankarasubramanian, K.
2010ASSP...19..413S Altcode: 2010mcia.conf..413S
We report on the penumbral formation in active region NOAA 10837. The
penumbra observed on continuum intensity images grew from a quiet-Sun
area to a primitive penumbra and then to a fully developed penumbra
over about 5 h. The growth indicates nonlinear development with time.
---------------------------------------------------------
Title: Dual-Line Spectral Imaging of the Chromosphere
Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.;
Uitenbroek, H.
2010ASSP...19..513C Altcode: 2010mcia.conf..513C
Hα filtergrams are notoriously difficult to interpret, "beautiful
to view but not fit for analysis." We try to remedy this by using
the IBIS bi-dimensional spectrometer at the Dunn Solar Telescope at
NSO/Sacramento Peak to compare the quiet-sun chromosphere observed in
Hα to what is observed simultaneously in Ca II 854.2 nm, sampling both
lines with high angular and spectral resolution and extended coverage
of space, time, and wavelength. Per (x, y, t) pixel we measured the
intensity and Dopplershift of the minimum of each line's profile at
that pixel, as well as the width of their inner chromospheric cores. A
paper submitted to A&A (December 2008) compares these measurements
in detail.
---------------------------------------------------------
Title: Service-Mode Observations for Ground-Based Solar Physics
Authors: Reardon, K. P.; Rimmele, T.; Tritschler, A.; Cauzzi, G.;
Wöger, F.; Uitenbroek, H.; Tsuneta, S.; Berger, T.
2009ASPC..415..332R Altcode: 2009arXiv0909.1522R
There are significant advantages in combining Hinode observations
with ground-based instruments that can observe additional spectral
diagnostics at higher data rates and with greater flexibility. However,
ground-based observations, because of the random effects of weather
and seeing as well as the complexities data analysis due to changing
instrumental configurations, have traditionally been less efficient
than satellite observations in producing useful datasets. Future large
ground-based telescopes will need to find new ways to optimize both
their operational efficiency and scientific output. <P />We have begun
experimenting with service-mode or queue-mode observations at the Dunn
Solar Telescope using the Interferometric Bidimensional Spectrometer
(IBIS) as part of joint Hinode campaigns. We describe our experiences
and the advantag es of such an observing mode for solar physics.
---------------------------------------------------------
Title: Structure and Dynamics of Sunspots (Keynote)
Authors: Tritschler, A.
2009ASPC..415..339T Altcode: 2009arXiv0903.1300T
The physics of Sunspots is a fascinating and demanding field
of research in solar astronomy. Interaction of magnetic fields
and plasma flows takes place in a tangled magnetic geometry and
occurs on spatial scales that pose a continuous challenge for
existing instrumentation and for the unambiguous interpretation
of spectropolarimetric observations. Thus, the main properties of
sunspots are well established but its fine structure is not yet fully
understood. <P />In this contribution we summarize the current knowledge
of the magnetic and dynamic properties of sunspots at the photospheric
level based on selected observations featuring the highest possible
spatial and spectral resolution. We concentrate on light bridges, umbral
dots, penumbral filaments and the notorious dark cores in penumbral
filaments. We report on the morphology of the fine structure elements
but mostly focus on observations of their line-of-sight velocities and
magnetic field parameters. We briefly comment on results from recent
radiative MHD simulations and more schematic model ideas that attempt
to rationalize observations of the penumbra.
---------------------------------------------------------
Title: The solar chromosphere at high resolution with
IBIS. IV. Dual-line evidence of heating in chromospheric network
Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.;
Uitenbroek, H.
2009A&A...503..577C Altcode: 2009arXiv0906.2083C
The structure and energy balance of the solar chromosphere remain
poorly known. We used the imaging spectrometer IBIS at the Dunn Solar
Telescope to obtain fast-cadence, multi-wavelength profile sampling
of Hα and Ca ii 854.2 nm over a sizable two-dimensional field of view
encompassing quiet-Sun network. We provide a first inventory of how the
quiet chromosphere appears in these two lines by comparing basic profile
measurements in the form of image displays, temporal-average displays,
time slices, and pixel-by-pixel correlations. We find that the two lines
can be markedly dissimilar in their rendering of the chromosphere,
but that, nevertheless, both show evidence of chromospheric heating,
particularly in and around network: Hα in its core width and Ca ii
854.2 nm in its brightness. We discuss venues for improved modeling.
---------------------------------------------------------
Title: Imaging Spectropolarimetry with IBIS: Evolution of Bright
Points in the Quiet Sun
Authors: Viticchié, B.; Del Moro, D.; Berrilli, F.; Bellot Rubio,
L.; Tritschler, A.
2009ApJ...700L.145V Altcode: 2009arXiv0906.2663V
We present the results from first spectropolarimetric observations
of the solar photosphere acquired at the Dunn Solar Telescope with
the Interferometric Bidimensional Spectrometer. Full Stokes profiles
were measured in the Fe I 630.15 nm and Fe I 630.25 nm lines with high
spatial and spectral resolutions for 53 minutes, with a Stokes V noise
of 3 × 10<SUP>-3</SUP> the continuum intensity level. The data set
allows us to study the evolution of several magnetic features associated
with G-band bright points (BPs) in the quiet Sun. Here we focus on
the analysis of three distinct processes, namely the coalescence,
fragmentation, and cancellation of G-band BPs. Our analysis is
based on an SIR inversion of the Stokes I and V profiles of both Fe
I lines. The high spatial resolution of the G-band images combined
with the inversion results helps to interpret the undergoing physical
processes. The appearance (dissolution) of high-contrast G-band BPs is
found to be related to the local increase (decrease) of the magnetic
filling factor, without appreciable changes in the field strength. The
cancellation of opposite-polarity BPs can be the signature of either
magnetic reconnection or the emergence/submergence of magnetic loops.
---------------------------------------------------------
Title: Spectropolarimetry of Ca II 8542: Probing the Chromospheric
Magnetic Field
Authors: Kleint, L.; Reardon, K.; Stenflo, J. O.; Uitenbroek, H.;
Tritschler, A.
2009ASPC..405..247K Altcode:
We present spectropolarimetric observations of the chromospheric Ca II
8542 and photospheric Fe I 6302 lines obtained with the Interferometric
Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope. The
high spatial resolution over a large field of view (FOV) allows us to
connect the observed profiles to the overall topology of the target
region. After suitable calibrations we can extract Stokes profiles
for each point in the FOV. The Stokes V profiles observed in the Ca II
line show a large variety of shapes, indicating widely varying vertical
behavior of the field strength, velocity, and temperature. We examine
the center-of-gravity method for determining a representative field
strength from the observed profiles and use it to directly compare
photospheric and chromospheric magnetic fields.
---------------------------------------------------------
Title: High-resolution observations of extremely bright penumbral
grains
Authors: Denker, C.; Tritschler, A.; Deng, N.; Verdoni, A. P.
2008AN....329..773D Altcode:
We observed a cluster of extremely bright penumbral grains located at
the inner limb-side penumbra of the leading sunspot in active region
NOAA 10892. The penumbral grains in the cluster showed a typical peak
intensity of 1.58 times the intensity I_0 of the granulation surrounding
the sunspot. The brightest specimen even reached values of 1.8--2.0
I_0, thus, exceeding the temperatures of the brightest granules in the
immediate surroundings of the sunspot. We find that the observed sample
of extremely bright penumbral grains is an intermittent phenomenon,
that disappears on time scales of hours. Horizontal flow maps indicating
proper motions reveal that the cluster leaves a distinct imprint on
the penumbral flow field. We find that the divergence line co-located
with the cluster is displaced from the middle penumbra closer towards
the umbra and that the radial outflow velocities are significantly
increased to speeds in excess of 2 km s^{-1}. The extremely bright
penumbral grains, which are located at the inner limb-side penumbra,
are also discernible in off-band Hα images down to Hα ± 0.045 nm. We
interpret the observations in the context of the moving flux tube model
arguing that hotter than normal material is rapidly ascending along
the inner footpoint of the embedded flux tube, i.e., the ascending hot
material is the cause of the extremely bright penumbral grains. This
study is based on speckle-reconstructed broad-band images taken at 600
nm and chromospheric Hα observations obtained with two-dimensional
spectroscopy. All data were taken with adaptive optics under very
good seeing conditions at the Dunn Solar Telescope, National Solar
Observatory/Sacramento Peak, New Mexico on 2006 June 10.
---------------------------------------------------------
Title: Evidence for a Current Sheet above a Sunspot Umbra
Authors: Tritschler, A.; Uitenbroek, H.; Reardon, K.
2008ApJ...686L..45T Altcode:
We present observational evidence for the existence of a current
sheet in the chromosphere above a sunspot umbra based on high angular
resolution two-dimensional spectroscopic observations in the Ca II
854.21 nm line. In the core of this line we observe a very stable bright
ribbon-like structure separating magnetic field configurations that
connect to different parts of the active region. We make plausible
that the structure is a string of sheets carrying vertical currents
that result from dissipation when the different parts of the active
region are moved around in the photosphere. To our knowledge this is
the first direct observation of the heating caused by the dissipation
in such a current sheet in the chromosphere.
---------------------------------------------------------
Title: Imaging Spectropolarimetry of the Photosphere and Chromosphere
with IBIS
Authors: Reardon, K.; Tritschler, A.; Uitenbroek, H.; et al.
2008ESPM...12.2.31R Altcode:
We present recent results based on high-resolution spectropolarimetry
using IBIS, a dual Fabry-Perot imaging spectrometer. We describe
the characteristics of the instrument and its capability to measure
the full Stokes vector in a range of photospheric and chromospheric
spectral lines. <P />Since late 2006 IBIS has been regularly used in
spectropolarimetric mode and observations have included solar pores,
quiet sun network and internetwork areas, and the disk passage of active
regions NOAA 10941 and 10940. Measurements are primarily performed in
the Fe I 630.2 and the Ca II 854.2 nm lines to provide information on
both photospheric to chromospheric heights. We present results on the
highly dynamical nature of both the vertical and horizontal components
of quiet Sun magnetic fields. We also show the fine structure and
height variation of the magnetic field in a large sunspot.
---------------------------------------------------------
Title: Solar Chromospheric Dynamics: Onwards and Upwards
Authors: Cauzzi, G.; Reardon, K.; Rimmele, T.; Rutten, R.; Tritschler,
A.; Uitenbroek, H.; Woeger, F.
2008AGUSMSP41B..03C Altcode:
We present a study of chromospheric dynamics and its relation with the
driving photospheric magneto-convection in a variety of solar targets,
from quiet Sun to more active regions. To this end high resolution
observations were obtained in CaII 854.2 nm, Hα, and photospheric
FeI lines with the Interferometric BIdimensional Spectrometer (IBIS)
installed at the Dunn Solar Telescope of the NSO. The availability of
full spectroscopic information on extended fields of view allows us
to derive a comprehensive view of the intrinsically 3-D chromospheric
scene. A coherent picture is emerging that involves the propagation
and dissipation of photospheric acoustic waves into the chromospheric
layers, but selected and guided by the local and highly variable
magnetic topology. In particular, ubiquitous fibrilar structures,
apparently originating from even the smallest magnetic elements,
appear an integral part of the dynamic chromosphere.
---------------------------------------------------------
Title: WHI Targeted Campaigns on Coronal Holes and Quiet Sun: High
Resolution Observations of the Lower Atmosphere With IBIS
Authors: Cauzzi, G.; Reardon, K. P.; Rimmele, T.; Tritschler, A.;
Uitebroek, H.; Woeger, F.; Deforest, C.; McIntosh, S.
2008AGUSMSH51A..02C Altcode:
The Interferometric BIdimensional Spectrometer (IBIS) is a dual
Fabry-Perot instrument installed at the Dunn Solar Telescope that allows
two-dimensional spectroscopic observations in a variety of spectral
lines. The IBIS/DST will participate in the WHI targeted campaigns
on coronal holes (April 3-9) and quiet Sun dynamics (April 10-16)
performing simultaneous high-resolution observations of the dynamics of
the photosphere and chromosphere in the coordinated targets. The aim is
to obtain insights on the role of the lower atmosphere's dynamics and
energetics into the structuring of the coronal plasma and, possibly,
into the origin of the solar wind. In this paper we will present the
observations obtained as well as first results, and attempt to relate
them with recent work performed on quiet Sun chromospheric dynamics.
---------------------------------------------------------
Title: Simulations of Atmospheric Turbulence and Instrumentation on
Solar Observations
Authors: Weber, M.; Tritschler, A.; Woeger, F.
2008AGUSMSP51B..08W Altcode:
We investigate the influence of atmospheric turbulence and
instrumentation on solar observations. The focus of this study
is the determination of the amount of bias introduced in velocity
measurements by these effects. The magnetically insensitive Fe I
557.6 nm line is synthesized using three-dimensional simulations of
solar magneto-convection as an input model for a radiation transfer
code. The synthesized spectra are then subjected to different
atmospheric conditions characterized by the Fried parameters r0 = 7,
10, and 15 cm. To simulate realistic observations at NSO's Dunn solar
telescope (DST), we mimic the influence of a 0.76 m aperture telescope,
a high-order adaptive optics (AO) system and a tunable filtergraph on
the atmospherically distorted spectra.
---------------------------------------------------------
Title: Spectropolarimetry of a Decaying Sunspot Penumbra
Authors: Bellot Rubio, L. R.; Tritschler, A.; Martínez Pillet, V.
2008ApJ...676..698B Altcode: 2007arXiv0712.2937B
We report on high angular resolution, high-precision spectropolarimetric
measurements of a decaying sunspot. The spot gradually lost
its penumbra during the course of 3 days. In the late stages of
evolution, where the only remnant of the spot is a naked umbra, we
find small-scale inhomogeneities in the magnetic canopy surrounding
it. The inhomogeneities are observed as finger-like structures
of weak and nearly horizontal magnetic fields extending 1”-2”
from the border of the umbra. These fields are not associated with
filamentary structures in continuum intensity or with conspicuous
Evershed flows. The Stokes profiles emerging from the fingers exhibit
blueshifts, which we interpret as upward motions. This previously
unknown fine structure may be related to penumbral field lines that
no longer carry strong Evershed flows and rise to the chromosphere,
producing the disappearance of the penumbra at photospheric levels.
---------------------------------------------------------
Title: Fine Structure of the Net Circular Polarization in a Sunspot
Penumbra
Authors: Tritschler, A.; Müller, D. A. N.; Schlichenmaier, R.;
Hagenaar, H. J.
2007ApJ...671L..85T Altcode: 2007arXiv0710.4545T
We present novel evidence for fine structure observed in the
net circular polarization (NCP) of a sunspot penumbra based on
spectropolarimetric measurements utilizing the Zeeman-sensitive Fe
I 630.2 nm line. For the first time we detect filamentary organized
fine structure of the NCP on spatial scales that are similar to the
inhomogeneities found in the penumbral flow field. We also observe an
additional property of the visible NCP, a zero-crossing of the NCP
in the outer parts of the center-side penumbra, which has not been
recognized before. In order to interpret the observations we solve the
radiative transfer equations for polarized light in a model penumbra
with embedded magnetic flux tubes. We demonstrate that the observed
zero-crossing of the NCP can be explained by an increased magnetic
field strength inside magnetic flux tubes in the outer penumbra combined
with a decreased magnetic field strength in the background field. Our
results strongly support the concept of the uncombed penumbra.
---------------------------------------------------------
Title: Two-Dimensional Spectroscopy of Photospheric Shear Flows in
a Small δ Spot
Authors: Denker, C.; Deng, N.; Tritschler, A.; Yurchyshyn, V.
2007SoPh..245..219D Altcode: 2007arXiv0708.3490D
In recent high-resolution observations of complex active regions,
long-lasting and well-defined regions of strong flows were identified
in major flares and associated with bright kernels of visible,
near-infrared, and X-ray radiation. These flows, which occurred in the
proximity of the magnetic neutral line, significantly contributed to
the generation of magnetic shear. Signatures of these shear flows are
strongly curved penumbral filaments, which are almost tangential to
sunspot umbrae rather than exhibiting the typical radial filamentary
structure. Solar active region NOAA 10756 was a moderately complex
βδ sunspot group, which provided an opportunity to extend previous
studies of such shear flows to quieter settings. We conclude that
shear flows are a common phenomenon in complex active regions and δ
spots. However, they are not necessarily a prerequisite condition for
flaring. Indeed, in the present observations, the photospheric shear
flows along the magnetic neutral line are not related to any change of
the local magnetic shear. We present high-resolution observations of
NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar
Observatory (BBSO). Time series of speckle-reconstructed white-light
images and two-dimensional spectroscopic data were combined to study
the temporal evolution of the three-dimensional vector flow field
in the βδ sunspot group. An hour-long data set of consistent high
quality was obtained, which had a cadence of better than 30 seconds
and subarcsecond spatial resolution.
---------------------------------------------------------
Title: The Discrepancy in G-Band Contrast: Where is the Quiet Sun?
Authors: Uitenbroek, H.; Tritschler, A.; Rimmele, T.
2007ApJ...668..586U Altcode: 2007arXiv0704.3637U
We compare the rms contrast in observed speckle reconstructed G-band
images with synthetic filtergrams computed from two magnetohydrodynamic
simulation snapshots. The observations consist of 103 bursts of 80
frames each, taken at the Dunn Solar Telescope (DST), sampled at twice
the diffraction limit of the telescope. The speckle reconstructions
account for the actions of the adaptive optics (AO) system at the DST in
order to supply reliable photometry. We find a considerable discrepancy
between the observed rms contrast of 14.1% for the best reconstructed
images and the synthetic rms contrast of 21.5% in a simulation snapshot
thought to be representative of the quiet Sun. The areas of features
in the synthetic filtergrams that have positive or negative contrast
beyond the minimum and maximum values in the reconstructed images have
spatial scales that should be resolved. This leads us to conclude that
there are fundamental differences in the rms G-band contrast between
observed and computed filtergrams. On the basis of the substantially
reduced granular contrast of 16.3% in the synthetic plage filtergram,
we speculate that the quiet Sun may contain more weak magnetic field
than previously thought.
---------------------------------------------------------
Title: Synoptic Observing at Big Bear Solar Observatory
Authors: Denker, C.; Naqvi, M.; Deng, N.; Tritschler, A.; Marquette,
W. H.
2007ASPC..368..515D Altcode:
Synoptic solar observations in the chromospheric absorption lines
Ca II K and Hα have a long tradition at Big Bear Solar Observatory
(BBSO). The advent of the New Solar Telescope (NST) will shift the
focus of BBSO's synoptic observing program toward high-resolution
observations. We present an overview of the telescopes and
instrumentation and show some of the most recent results. This includes
Ca II K data to track solar irradiance variations, Hα full-disk data to
monitor eruptive events, Dopplergrams from two-dimensional spectroscopy,
as well as image restorations of diffraction-limited quality.
---------------------------------------------------------
Title: Two-dimensional Spectroscopy Of Chromospheric And Photospheric
Sunspot Fine-structure
Authors: Denker, Carsten; Verdoni, A. P.; Naqvi, M.; Deng, N.;
Tritschler, A.
2007AAS...21010002D Altcode: 2007BAAS...39..227D
In preparation for the future 1.6-meter New Solar Telescope (NST) at
Big Bear Solar Observatory, a suite of instruments has been developed
for observations with high-spatial and high-temporal resolution. Two of
these instruments, a fast CCD camera system for image restoration and
the Visible-light Imaging Magnetograph (VIM), were moved to the National
Solar Observatory/Sacramento Peak, while NST is under construction. In
this study, we report results of observations obtained with the
high-order adaptive optics system at the Dunn Solar Telescope on 2006
June 10. We observed active region NOAA 10892 in broad-band continuum
(600 nm) and in the chromsopheric lines (Hα and Na D<SUB>2</SUB>). We
obtained photospheric and chromospheric flow fields based on local
correlation tracking and Doppler measurements and discuss them in
the context of sunspot fine-structure. <P />This work was supported
by NSF under grants ATM 00-86999, ATM 02-36945, IIS ITR 03-24816,
and AST MRI 00-79482 and by NASA under grant NAG 5-12782.
---------------------------------------------------------
Title: Three-Dimensional Structure of Evershed Flows
Authors: Deng, Na; Choudhary, D. P.; Denker, C.; Verdoni, A.;
Tritschler, A.
2007AAS...210.9506D Altcode: 2007BAAS...39..224D
The Evershed flow is known as the unceasing radially outward mass flow
in sunspot penumbrae observed in the photosphere, which is most clearly
seen near the solar limb. The Evershed flow reverses its direction in
the chromosphere, where an inward mass flow is observed. In order to
quantitatively explore the three-dimensional structure of the Evershed
flow from photosphere to chromosphere, we observed a sunspot group
(NOAA 10892) at the limb using the Horizontal Spectrograph (HSG)
at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2006
June 04. Spectral data sets were obtained simultaneously at four solar
absorbtion lines: Fe 630.15 nm and 630.25 nm (photosphere), NaD 588.99
nm (lower chromosphere), and Hα 656.28 nm (chromosphere). Spectral
analysis and different methods of determining Doppler velocities will
be presented and compared. <P />This work is supported by NSF under
grant ATM 02-36945, ATM 03-42560, ATM 05-48260 and MRI AST 00-79482
and by NASA under grant NAG 5-13661.
---------------------------------------------------------
Title: Observations of Quiet Sun Chromosphere Dynamics
Authors: Verdoni, Angelo; Denker, C.; Deng, N.; Tritschler, A.
2007AAS...21010003V Altcode: 2007BAAS...39..228V
The quiet Sun shows a multitude of fine structure in both the
photosphere and chromosphere. Observations with high spatial and
temporal resolution are required to study their dynamics. In June 2006,
simultaneous broad-band continuum (600 nm) and narrow-band spectroscopic
(Hα and Na 589.0 nm) data were obtained of a quiet Sun region near disk
center using the Dunn Solar Telescope and high-order adaptive optics
at the National Solar Observatory/Sacramento Peak. The time-series
of continuum data was restored using the speckle masking technique
to achieve almost diffraction-limited resolution across the entire
field-of-view (80" by 80"). The spectroscopic data were taken with a
two-dimensional spectrometer, which is currently being upgraded for
spectro-polarimetry. The Visible-light Imaging Magnetograph (VIM) is
a telecentric two-dimensional Fabry-Perot based spectro-polarimeter,
which will become one of the first-light instruments of the future
1.6-meter New Solar Telescope (NST) at Big Bear Solar Observatory
(BBSO). <P />This work was supported by NSF under grants ATM 00-86999,
ATM 02-36945, IIS ITR 03-24816, and AST MRI 00-79482 and by NASA under
grant NAG 5-12782.
---------------------------------------------------------
Title: Field-Dependent Adaptive Optics Correction Derived with the
Spectral Ratio Technique
Authors: Denker, C.; Deng, N.; Rimmele, T. R.; Tritschler, A.;
Verdoni, A.
2007SoPh..241..411D Altcode:
In this empirical study, we compare high-resolution observations
obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory
(BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National
Solar Observatory/Sacramento Peak (NSO/SP) in 2006. We measure the
correction of the high-order adaptive optics (AO) systems across
the field of view (FOV) using the spectral ratio technique, which
is commonly employed in speckle masking imaging, and differential
image motion measurements. The AO correction is typically much larger
(10<SUP>”</SUP> to 25<SUP>”</SUP>) than the isoplanatic angle and
can be described by a radially symmetric function with a central core
and extended wings. The full-width at half-maximum (FWHM) of the core
represents a measure of the AO correction. The average FWHM values
for BBSO and NSO/SP are 23.5<SUP>”</SUP> and 18.2<SUP>”</SUP>,
respectively. The extended wings of the function show that the
AO systems still contribute to an improved speckle reconstruction
at the periphery of the 80<SUP>”</SUP>×80<SUP>”</SUP> FOV. The
major differences in the level of AO correction between BBSO and
NSO/SP can be explained by different contributions of ground-layer-
and free-atmosphere-dominated seeing, as well as different FOVs of
the wavefront sensors. In addition, we find an anisotropic spectral
ratio in sunspot penumbrae caused by the quasi-one-dimensional nature
of penumbral filaments, which introduces a significant error in the
estimation of the Fourier amplitudes during the image restoration
process.
---------------------------------------------------------
Title: Narrow-band imaging in the CN band at 388.33 nm
Authors: Uitenbroek, H.; Tritschler, A.
2007A&A...462.1157U Altcode: 2006astro.ph.11407U
Aims:We promote the use of narrow-band (0.05-0.20 nm FWHM) imaging in
the molecular CN band head at 388.33 nm as an effective method for
monitoring small-scale magnetic field elements because it renders
them with exceptionally high contrast. <BR />Methods: We create
synthetic narrow-band CN filtergrams from spectra computed from a
three-dimensional snapshot of a magnetohydrodynamic simulation of the
solar convection to illustrate the expected high contrast and explain
its nature. In addition, we performed observations with the horizontal
slit spectrograph at the Dunn Solar Tower at 388.3 nm to experimentally
confirm the high bright-point contrast, and to characterize and optimize
the transmission profile of a narrow-band (0.04 FWHM) Lyot filter, which
was built by Lyot and tailored to the CN band at Sacramento Peak in
the early 70's. <BR />Results: The presented theoretical computations
predict that bright-point contrast in narrow-band (0.04 FWHM) CN
filtergrams is more than 3 times higher than in CN filtergrams taken
with 1 nm FWHM wide filters, and in typical G-band filtergrams. Images
taken through the Lyot filter after optimizing its passband confirm that
the filter is capable of rendering small-scale magnetic elements with
contrasts that are much higher than in traditional G-band imaging. The
filter will be available as an user instrument at the Dunn Solar Tower.
---------------------------------------------------------
Title: On the fine structure of the quiet solar Ca II K atmosphere
Authors: Tritschler, A.; Schmidt, W.; Uitenbroek, H.; Wedemeyer-Böhm,
S.
2007A&A...462..303T Altcode: 2006astro.ph.11402T
Aims:We investigate the morphological, dynamical, and evolutionary
properties of the internetwork and network fine structure of the quiet
sun at disk centre. <BR />Methods: The analysis is based on a ~6 h
time sequence of narrow-band filtergrams centred on the inner-wing
Ca II K2v reversal at 393.3 nm. To examine the temporal evolution of
network and internetwork areas separately we employ a double-Gaussian
decomposition of the mean intensity distribution. An autocorrelation
analysis is performed to determine the respective characteristic
time scales. In order to analyse statistical properties of the fine
structure we apply image segmentation techniques. <BR />Results: The
results for the internetwork are related to predictions derived from
numerical simulations of the quiet sun. The average evolutionary time
scale of the internetwork in our observations is 52 s. Internetwork
grains show a tendency to appear on a mesh-like pattern with a
mean cell size of ~4-5 arcsec. Based on this size and the spatial
organisation of the mesh we speculate that this pattern is related to
the existence of photospheric downdrafts as predicted by convection
simulations. The image segmentation shows that typical sizes of both
network and internetwork grains are in the order of 1.6 arcsec.
---------------------------------------------------------
Title: The Contrast of Magnetic Flux Concentrations at Near-Infrared
and Visible Wavelengths
Authors: Tritschler, A.; Uitenbroek, H.
2006ApJ...648..741T Altcode:
To reconcile discrepancies in the observed contrast of magnetic
flux concentrations, we compute synthetic filtergrams from solar
magnetoconvection models in four different passbands: two continuum
bands, at 1626 and 575 nm, the G band, and the line wing of the Ca
II K line. Magnetic flux concentrations are selected by their G-band
brightness. In the near-infrared the selected flux concentrations
appear inconspicuous with intensities that are on average below that of
the synthetic average quiet Sun, while their contrast in the visible
passband is mostly positive. When we account for limited telescope
resolution and imperfect seeing, the contrasts of bright points in the
visible become increasingly negative as a result of mixing with the
dark intergranular lanes in which they are embedded. The correlation in
bright-point intensity between different passbands becomes increasingly
poor from the G band to the visible and the near-infrared. This is
caused in part by the varying amount of spectral lines in each of the
bands. Further, we find that the largest magnetic field concentrations,
representative of micropores or magnetic knots, are dark in all
four passbands. The brightenings in the Ca II K line wing do not
coincide with magnetic flux concentrations on the spatial scale of
the simulation. Finally, we find that the rms intensity contrast in
all four passbands depends on the amount of magnetic field present
in the simulation, with higher contrast for lower average magnetic
field strength.
---------------------------------------------------------
Title: VIP - 2D Vector Spectropolarimetry of the Solar Atmosphere
near the Diffraction Limit
Authors: Bellot Rubio, L. R.; Tritschler, A.; Kentischer, T.; Beck,
C.; Del Toro Iniesta, J. C.
2006IAUJD...3E..58B Altcode:
The KIS/IAA Vector Imaging Polarimeter (VIP) is a new instrument for
two-dimensional spectropolarimetry of the solar atmosphere. It is used
with TESOS, the triple etalon Fabry-Perot interferometer installed at
the German Vacuum Tower Telescope of Observatorio del Teide (Tenerife,
Spain). The polarimeter is based on a pair of nematic liquid crystal
retarders and a Wollaston prism. VIP and TESOS are able to observe
any spectral line in the range from 450 nm to 750 nm with a spectral
resolving power of about 250000 and spatial resolutions better than
0.5" (thanks to the Kiepenheuer Adaptive Optics System). Typically,
the four Stokes parameters of a line can be measured at 40 wavelength
points in less than 60 s, with a noise level of 1-2 x 10^-3 and a
pixel size of 0.18" x 0.18" (2x2 binning). The modulation matrix of
VIP is derived using the polarimetric calibration unit installed at
the telescope. Here we present first-light observations of VIP carried
out in November 2005. We recorded the full Stokes profiles of the 630.1
and 630.2 nm Fe I lines emerging from a solar pore and its surroundings
at a spatial resolution of ~0.4". Based on these data, we discuss the
performance and capabilities of VIP as a powerful instrument for high
spatial and temporal resolution measurements of vector magnetic fields
in the solar atmosphere.
---------------------------------------------------------
Title: Evidence for a Siphon Flow Ending near the Edge of a Pore
Authors: Uitenbroek, H.; Balasubramaniam, K. S.; Tritschler, A.
2006ApJ...645..776U Altcode:
Observations of NOAA AR 9431, taken with the Vacuum Tower at Kitt
Peak on 2001 April 18 in the Ca II 854.21 nm line in both circular
polarizations, show evidence for a strong supersonic downflow ending
near the edge of a magnetic pore. The observed supersonic motion is
interpreted as a siphon flow along a magnetic loop connecting a patch
of weaker field to the pore of opposite polarity in the same active
region. The 854.21 nm line data reveal the upflow at one footpoint of
the loop, as well as the acceleration of the flow toward the footpoint
at the pore, where the flow reaches line-of-sight velocities of well
over 20 km s<SUP>-1</SUP>, substantially larger than the critical
speed. Numerical radiative transfer modeling of the 854.21 nm line
indicates the presence of a strong discontinuity in the flow velocity,
which we interpret as evidence for a tube shock in the downwind leg
of the siphon.
---------------------------------------------------------
Title: The influence of image reconstruction on two-dimensional
spectrograms of the solar photosphere
Authors: Mikurda, K.; Tritschler, A.; Schmidt, W.
2006A&A...454..359M Altcode:
Aims.We present a spectral analysis of small-scale structures in
the solar photosphere and investigate the influence of the speckle
deconvolution technique on the line profiles.<BR /> Methods: . A
short sequence of two-dimensional spectra is used, taken with the
Telecentric Etalon Solar Spectrometer (TESOS) at the German Vacuum
Tower Telescope on Tenerife. We observed two small pores surrounded by
disturbed and by regular granulation in the non-magnetic neutral Iron
line at 557.6 nm. In a first step, a speckle reconstruction is computed
by applying an extended Knox-Thompson algorithm to the broad-band
data. In a second step, the individual narrow-band filtergrams are
deconvolved utilizing the information gained in the first step. We
then perform a spectral analysis of the 2D spectra and compare the
results obtained with the raw and the restored data.<BR /> Results:
.Important spectral quantities, e.g. line position, line depression
and line asymmetry are largely unchanged by the image reconstruction
process. We derive the line asymmetry and the line-of-sight flow for
granules and intergranular lanes and also for an isolated G-band bright
point and find important differences between quiet and magnetically
disturbed granulation: the granule centers in the quiet region show a
strong asymmetry with significant blue shift (300 m/s) toward deeper
layers, while the velocity in the disturbed area show virtually
no height dependence. For the intergranular lanes the situation is
reversed: no height dependence in the quiet area, significant red-shift
toward deeper layers in the disturbed part. An isolated G-band bright
point does not show any line-of-sight motion relative to its immediate
surroundings. The map of LOS velocities derived from line-wing shifts
shows a significant downflow around one of the pores measured in deep
layers of the photosphere.<BR /> Conclusions: .In most cases we do
not find any artefacts in the reconstructed line profiles that would
compromise their usage for quantitative spectroscopy.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of a sunspot. III. Thermal and
kinematic structure of the penumbra at 0.5 arcsec resolution
Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A.
2006A&A...453.1117B Altcode: 2006astro.ph..1423B
We investigate the thermal and kinematic configuration of a sunspot
penumbra using high spectral and spatial resolution intensity profiles
of the non-magnetic Fe I 557.6 nm line. The data set was acquired
with the 2D solar spectrometer TESOS. The profiles are inverted using
a one-component model atmosphere with gradients of the physical
quantities. From this inversion we obtain the stratification with
depth of temperature, line-of-sight velocity, and microturbulence
across the penumbra. Our results suggest that the physical mechanism(s)
responsible for the penumbral filaments operate preferentially in the
lower photosphere. The spot, located at an heliocentric angle of 23°,
exhibits larger continuum intensities in the center-side penumbra
as compared with the limb side, which translates into an average
temperature difference of 100-150 K at log τ<SUB>500</SUB> = 0. We
investigate the nature of the bright ring that appears in the inner
penumbra when sunspots are observed in the wing of spectral lines. It
is suggested that the bright ring does not reflect a temperature
enhancement in the mid photospheric layers. The line-of-sight velocities
retrieved from the inversion are used to determine the flow geometry
at different heights in the photosphere. Both the flow speed and
flow angle increase with optical depth and radial distance. Downflows
are detected in the mid and outer penumbra, but only in deep layers
(log τ<SUB>500</SUB> ≥ -1.4). We demonstrate that the velocity
stratifications retrieved from the inversion are consistent with the
idea of penumbral flux tubes channeling the Evershed flow. Finally, we
show that larger Evershed flows are associated with brighter continuum
intensities in the inner center-side penumbra. Dark structures,
however, are also associated with significant Evershed flows. This
leads us to suggest that the bright and dark filaments seen at 0.5
arcsec resolution are not individual flow channels, but a collection
of them. Our analysis highlights the importance of very high spatial
resolution spectroscopic and spectropolarimetric measurements for a
better understanding of sunspot penumbrae.
---------------------------------------------------------
Title: Progress on the 1.6-meter New Solar Telescope at Big Bear
Solar Observatory
Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.;
Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter,
R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.;
Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A.
2006SPIE.6267E..0AD Altcode: 2006SPIE.6267E..10D
The New Solar Telescope (NST) project at Big Bear Solar Observatory
(BBSO) now has all major contracts for design and fabrication in place
and construction of components is well underway. NST is a collaboration
between BBSO, the Korean Astronomical Observatory (KAO) and Institute
for Astronomy (IfA) at the University of Hawaii. The project will
install a 1.6-meter, off-axis telescope at BBSO, replacing a number
of older solar telescopes. The NST will be located in a recently
refurbished dome on the BBSO causeway, which projects 300 meters into
the Big Bear Lake. Recent site surveys have confirmed that BBSO is
one of the premier solar observing sites in the world. NST will be
uniquely equipped to take advantage of the long periods of excellent
seeing common at the lake site. An up-to-date progress report will
be presented including an overview of the project and details on the
current state of the design. The report provides a detailed description
of the optical design, the thermal control of the new dome, the optical
support structure, the telescope control systems, active and adaptive
optics systems, and the post-focus instrumentation for high-resolution
spectro-polarimetry.
---------------------------------------------------------
Title: High-Resolution Studies of Complex Solar Active Regions
Authors: Deng, Na; Wang, H.; Liu, C.; Yang, G.; Xu, Y.; Tritschler,
A.; Cao, W.; Rimmele, T. R.; Denker, C.
2006SPD....37.3401D Altcode: 2006BAAS...38..258D
Most Flares and CMEs occur or originate in solar active regions,
typically in sunspots with complex magnetic fields such as
delta-spots. Rapid and substantial changes of the sunspot structure have
been discovered to be associated with flares/CMEs. Rapid penumbral decay
and umbral enhancements are intensity changes, which are interpreted as
signatures of magnetic reconnection during the flare. The magnetic field
lines switch from an inclined to a more vertical orientation. Strong and
long-lived shear flows near the flaring magnetic inversion line have
been detected using Local Correlation Tracking (LCT) techniques based
on multi-wavelength high resolution observations. A newly observed and
important phenomenon is the increased local shear flow and magnetic
shear right after the flare in spite of theoretical models requiring
an overall decrease in the magnetic free energy. The emergence of a
twisted or pre-sheared flux rope near the neutral line is a possible
interpretation. Using high-order adaptive optics combined post-facto
speckle masking image reconstruction, we can obtain time-series with
highly improved image quality and spatial resolution in the order of
0.14" or about 100 km on the solar surface. We combine the observed
longitudinal Dopplergrams obtained with two-dimensional imaging
spectrometer and transverse LCT flow maps derived from time-series
of speckle reconstructed images to create real local 3D flow maps
(view from above). Using these precise 3D flow maps observed in a
typical sunspot in the course of its center to limb disc passage,
we observe distinct division line between radially inward and outward
flow in the penumbra and its evolution during the decaying phase of
the sunspot. The inclination angles of penumbral flow channels are
also calculated.Acknowledgments: This work is supported by NSF under
grant ATM 03-42560, ATM 03-13591, ATM 02-36945, ATM 05-48952, and MRI
AST 00-79482 and by NASA under grant NAG 5-13661.
---------------------------------------------------------
Title: Two-Dimensional Spectroscopy at Big Bear Solar Observatory
Authors: Denker, Carsten; Deng, N.; Tritschler, A.
2006SPD....37.3702D Altcode:
Two-dimensional spectroscopy is an important tool to measure the
physical parameters related to solar activity in both the photosphere
and chromosphere. We present a description of the visible-light
post-focus instrumentation at the Big Bear Solar Observatory (BBSO)
including adaptive optics and image restoration. We report the first
science observations obtained with two-dimensional spectroscopy during
the 2005 observing season. In particular we discuss the properties
of flows associated with a small delta-spot in solar active region
NOAA 10756.
---------------------------------------------------------
Title: Narrow-band Imaging In Ihe Cn Band Head
Authors: Uitenbroek, Han; Tritschler, A.
2006SPD....37.0717U Altcode: 2006BAAS...38..662U
We report on results of an observing campaign intended to revive an old
CN Lyot filter originally built by Bernhard Lyot himself, but modified
at Sacramento Peak. The filter has two band-width settings of 0.025
nm and 0.05 nm which can be fine tuned thermally. We characterise
the passband of the Lyot filter and the employed prefilter based
on osbervations performed with a spectrograph. We also performed an
imaging experiment in an attempt to obtain data visualizing the imaging
capability of the filter. Our results show that the CN filter is in
a surprisingly good condition and is most suited for observations
to verify theoretical predictions about the brightness of magnetic
elements in the CN bandhead at 388.3\,nm.
---------------------------------------------------------
Title: The Contrast of Magnetic Elements in Synthetic CH- and CN-Band
Images of Solar Magnetoconvection
Authors: Uitenbroek, H.; Tritschler, A.
2006ApJ...639..525U Altcode: 2005astro.ph.10333U
We present a comparative study of the intensity contrast in synthetic
CH-band and violet CN-band filtergrams computed from a high-resolution
simulation of solar magnetoconvection. The underlying simulation
has an average vertical magnetic field of 250 G with kilogauss fields
concentrated in its intergranular lanes and is representative of a plage
region. To simulate filtergrams typically obtained in CH- and CN-band
observations we computed spatially resolved spectra in both bands and
integrated these spectra over 1 nm FWHM filter functions centered at
430.5 and 388.3 nm, respectively. We find that the average contrast
of magnetic bright points in the simulated filtergrams is lower in
the CN band by a factor of 0.96. In comparison, earlier semiempirical
modeling and recent observations both estimated that the bright point
contrast in the CN band is higher by a factor of 1.4. We argue that
the near equality of the bright point contrast in the two bands in
the present simulation is a natural consequence of the mechanism that
causes magnetic flux elements to be particularly bright in the CN and
CH filtergrams, namely, the partial evacuation of these elements and
the concomitant weakening of molecular spectral lines in the filter
passbands. We find that the rms intensity contrast in the whole field
of view of the filtergrams is 20.5% in the G band and 22.0% in the CN
band and conclude that this slight difference in contrast is caused
by the shorter wavelength of the latter. Both the bright point and rms
intensity contrast in the CN band are sensitive to the precise choice
of the central wavelength of the filter.
---------------------------------------------------------
Title: The Visible--Light Magnetograph at the Big Bear Solar
Observatory: Hardware and Software
Authors: Shumko, S.; Abramenko, V.; Denker, C.; Goode, P.; Tritschler,
A.; Varsik, J.
2005ASPC..347..509S Altcode: 2005adass..14..509S
In this paper we report about the current status of the control and
acquisition software package developed to control the visible-light
imaging magnetograph (VIM) system at the Big Bear Solar Observatory
(BBSO). The instrument is designed to perform high-spatial and
high-temporal observations of the solar photosphere and chromosphere
utilizing the remodeled Coudé-feed of the 65 cm vacuum telescope.
---------------------------------------------------------
Title: The New Solar Telescope at Big Bear Solar Observatory -
A Progress Report
Authors: Denker, C.; Cao, W.; Chae, J.; Coulter, R.; Kuhn, J. R.;
Marquette, W. H.; Moon, Y.; Park, Y.; Ren, D.; Tritschler, A.; Varsik,
J. R.; Wang, H.; Yang, G.; Shoumko, S.; Goode, P. R.
2005AGUSMSP43A..07D Altcode:
The New Solar Telescope (NST) is a new 1.6-meter, off-axis telescope
for the Big Bear Solar Observatory (BBSO) in California. The NST is
collaboration between BBSO, the Korean Astronomical Observatory (KAO)
and Institute for Astronomy (IfA) at the University of Hawaii. BBSO
is an ideal site for high-spatial resolution observations, since this
mountain-lake site provides consistent seeing conditions with extended
periods of excellent seeing from sunrise to sunset. These unique seeing
characteristics make BBSO ideally suited for combined high-resolution
campaigns and synoptic observations, which are essential for studies
of solar activity and space weather. In this progress report, we
present the latest information on the optical design, the optical
support structure, the telescope control system and the requisite
instrumentation for the telescope. Acknowledgements: This work has been
supported by NSF under grants ATM-0236945, ATM-0342560, MRI-0320540,
and Air Force DURIP F-49620-03-1-0271.
---------------------------------------------------------
Title: Flow filaments linking bright and dark filaments in a sunspot
penumbra
Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R.
2005AGUSMSP11A..08T Altcode:
We present two-dimensional spectroscopic sunspot observations of
high spatial (≍ 0.5 arcsec) and high spectral resolution (λ/Δλ
= 250000). The observations were taken with the Telecentric Solar
Spectrometer (TESOS) operated at the German Vacuum Tower Telescope on
Tenerife. We examine a single scan taken in the popular non-magnetic
neutral iron line at 557.6 nm and concentrate our analysis on the
unsettled issue of the relation between the Evershed flow and the
intensity structure in a sunspot penumbra. At the end of the 20th
century, observers concluded that the highest flow velocities are
connected to the dark filaments which harbour more horizontal magnetic
fields than the bright filaments. Based on a correlation analysis we
find that the correlation between flows and intensity varies from the
inner to the outer penumbra, from the center-side to the limb-side
penumbra, and depends on the length of the trace used to perform
the correlation. The line-of-sight velocity maps reveal that the
Evershed flow on the center-side penumbra appears highly organised in
narrow flow filaments, while the flows in the red-shifted limb-side
penumbra do not show a filamentary fine-structure. A high correlation
between flow speed and intensity is only observed over small spatial
scales, i.e. considering short traces cutting individual features. The
correlation is positive in the inner centre and limb-side penumbra, and
tends to be negative in the outer penumbra. Our results imply that the
Evershed flow is present in bright and dark filaments. In individual
cases we find that flow filaments connect bright and dark filaments
supporting the moving tube model for the penumbral fine structure.
---------------------------------------------------------
Title: High Resolution Chromospheric Flow Fields in Solar Active
Region NOAA 9393 Before and After an X20 Flare
Authors: Smith, G. A.; Tritschler, A.; Denker, C.
2005AGUSMSP23B..02S Altcode:
Hα full-disk images of the Sun obtained at the Big Bear Solar
Observatory (BBSO) are used to measure the chromospheric flow field
before and after the X20 flare in solar active region NOAA 9393 on
April 2, 2001. Local correlation tracking is used to determine global
(differential rotation) and local flow fields (flows in active regions
and filaments). We present high-resolution (2k × 2k pixel) flow maps to
analyze the dynamics of the chromosphere before and after the flare. If
there is a typical pattern in the motions of a flaring active region,
it can be used to predict flare activity and/or the onset of Coronal
Mass Ejections (CMEs). The high quality of the limb-darkening corrected
and contrast-enhanced Hα full-disk images make them an ideal data
set for these types of studies due to their high-temporal resolution
(1-minute cadence) and extended coverage (more than 500 filtergrams).
---------------------------------------------------------
Title: Spectro-polarimetry of the G band
Authors: Uitenbroek, H.; Balasubramaniam, K.; Tritschler, A.
2005AGUSMSP41B..03U Altcode:
Narrow-band filter imaging in the G band at 430 nm has been used to
track the evolution of small-scale magnetic field elements for more
than two decades. Because of the presence of many lines of the CH
molecule, and the relatively high contrast at this short wavelength
the G-band region is exceptionally suitable for this task. However,
despite the frequent use of G-band brightness as magnetic field proxy
it has not yet been well established what the precise mechanism is that
makes the small scale magnetic elements appear bright. In particular,
it is unclear why there is no one-to-one correlation between G-band
brightness and magnetic field, as established from co-spatial
magnetograms in atomic lines. To obtain a better understanding of
the elusive G-band brightening mechanism we obtained high spatial-
and spectral resolution spectra of the G-band region in Stokes I and V
at the Dunn Solar Telescope on Sacramento Peak. We use the molecular
Zeeman effect to determine line-of-sight magnetic field strength
directly in the CH lines that provide most of the opacity in the G
band, avoiding difficulties with co-aligning images and magnetograms
taken seperately. We compare our observations with radiative transfer
modeling of the Stokes profiles in snapshots of a magneto-hydrodynamic
simulation of solar convection.
---------------------------------------------------------
Title: On the relation between penumbral intensity and flow filaments
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A.
2005AN....326..301S Altcode:
Taking advantage of high spatial (≈ 0.5 arcsec) and high spectral
(λ/δλ = 250 000) resolution observations obtained with the 2D
spectrometer TESOS, we analyze a sunspot located at a heliocentric angle
of 23<SUP>o</SUP>. We elaborate on the issue of a correlation between
dark filaments and the Evershed flow in sunspot penumbrae. Controversies
on the existence of such a correlation are resolved: It varies from
the inner to the outer penumbra, from the center-side to the limb-side
penumbra, and depends on the length of the trace which is used to
perform the correlation. The flow map exhibits flow filaments in the
center-side penumbra while the red-shifted limb-side penumbra does not
show filamentary fine-structure. High correlation coefficients, |C|
≈ 0.9 are only found if small scales, i.e. short traces cutting
individual features are considered. C is positive in the inner
center and limb-side penumbra, and tends to be negative in the outer
penumbra. Our results imply that the Evershed flow is present in bright
and dark filaments. In individual cases we find that bright and dark
intensities are connected by a flow filament supporting the moving
tube model for the penumbral fine structure.
---------------------------------------------------------
Title: Phase diversity restoration of sunspot images. I. Relations
between penumbral and photospheric features
Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.;
Tritschler, A.
2004A&A...423..737B Altcode: 2004astro.ph..5542B
We investigate the dynamics of and the relations between small-scale
penumbral and photospheric features near the outer penumbral
boundary: penumbral grains (PGs), dark penumbral fibrils, granules,
and photospheric G-band bright points. The analysis is based on a 2 h
time sequence of a sunspot close to disc center, taken simultaneously
in the G-band and in the blue continuum at 450.7 nm. Observations
were performed at the Swedish Vacuum Solar Telescope (La Palma)
in July 1999. A total of 2564 images (46 arcsec × 75 arcsec) were
corrected for telescope aberrations and turbulence perturbations by
applying the inversion method of phase diversity. Our findings can by
summarized as follows: (a) one third of the outward-moving PGs pass
through the outer penumbral boundary and then either continue moving
as small bright features or expand and develop into granules. (b)
Former PGs and G-band bright points next to the spot reveal a different
nature. The latter have not been identified as a continuation of PGs
escaping from the penumbra. The G-band bright points are mostly born
close to dark penumbral fibrils where the magnetic field is strong,
whereas PGs stem from the less-magnetized penumbral component and
evolve presumably to non-magnetic granules or small bright features.
---------------------------------------------------------
Title: Towards 2D-Spectropolarimetry with TESOS and Adaptive Optics
Authors: Tritschler, A.; Bellot Rubio, L. R.; Kentischer, T. J.
2004AAS...204.6902T Altcode: 2004BAAS...36Q.794T
The TElecentric SOlar Spectrometer (TESOS) is a 2D tunable filtergraph
installed at the Vacuum Tower Telescope of Teide Observatory (Tenerife,
Spain). The instrument features a high spectral resolution (λ /Δ
λ ∼ 250000 at 633 nm) and is capable of scanning solar lines
over a broad wavelength range (430 - 700 nm). Together with the
Kiepenheuer-Institute Adaptive Optics System (KAOS), it is able to
achieve spatial resolutions of the order of 0.5 arcsec on a regular
basis. Here we present the first spectropolarimetric observations of
a sunspot and its immediate surroundings using TESOS. We describe the
optical setup, characterize the performance of TESOS operated in the
polarimetric mode, and investigate the appearance of the sunspot as
seen in circular polarized light with an angular resolution better
than 0.5 arcsec. Our results demonstrate the feasibility of using
TESOS as a polarimeter, and may be of interest for the design of
a TESOS-like multiple-etalon magnetograph for the 4-m NSO/Advanced
Technology Solar Telescope.
---------------------------------------------------------
Title: The VIsible and InfraRed Imaging Magnetograph (VIM-IRIM)
at Big Bear Solar Observatory
Authors: Cao, W.; Tritschler, A.; Denker, C.; Wang, H.; Shumko, S.;
Ma, J.; Wang, J.; Marquette, B.
2004AAS...204.6907C Altcode: 2004BAAS...36..795C
The Visible-light and the InfraRed Imaging Magnetograph (VIM-IRIM) are
Fabry-Perot based filtergraphs working in a telecentric configuration,
planned to upgrade the capability for measuring solar magnetic fields
at BBSO. Both filtergraph instruments are designed to work with
the combination of a narrow-band prefilter and a single Fabry-Perot
etalon. VIM and IRIM will provide high temporal resolution, high spatial
resolution (< 0.2 "/pixel image scale), high spectral resolution
(< 0.1 Å) simultaneous observation at 600-700 nm and 1.0-1.6 μ
m with a substantial field of view 170", respectively. Modifications
in the setup allow also for scanning different spectral lines that
cover the height range from the solar photosphere up to the solar
chromopshere. Here we describe the optical setup and present first
observations to demonstrate the feasibility of the instrument. After
the instrument has proven to work as a 2D-spectrometer, the upgrade
to a 2D spectropolarimeter is planned.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of a sunspot. II. Penumbral
line asymmetries
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A.
2004A&A...415..731S Altcode:
We present, analyse, and interpret line asymmetries from Fe I 557.6
nm of a sunspot penumbra at a heliocentric angle of 23<SUP>o</SUP>
with high spatial (0.5 arcsec) and spectral (λ/\triangleλ=250 000)
resolution. The data set is described and presented in the first paper
of this series \citep{tritschler+etal2003}. Line bisectors are used
to quantify the line asymmetries. Our findings are: (1) For averaged
limb and center side bisectors the shift increases linearly with the
bisector intensity level, but the limb side bisector is more inclined
than the center side bisector. (2) Individual bisectors exhibit kinks,
such that the bisector at high intensity levels is shifted towards the
red for both, limb and center side bisectors. Some of the kinks produce
bisector reversals in the outer center side penumbra. The bisector
properties and their intriguing differences between center and limb side
can be explained if one assumes downflows in deep atmospheric layers
(\log τ > -1). This is demonstrated by synthetic bisectors. The
differences between the two penumbral sides are due to projection
effects of non-horizontal flow channels. Our findings also imply that
bisectors reversals are not due to elevated channels, but due to the
presence of downflows. Along a specific center side flow filament the
bisector shift is found to be largest in the line wing, except for the
outer end of the filament, where a kink at high bisector intensities
toward the red is found. This is consistent with an upflow at the
inner footpoint, a deep lying horizontal flow, and, after a spatial
distance of 4 arcsec, with a downflow at the end of the flow filament.
---------------------------------------------------------
Title: Two-dimensional spectroscopy of a sunspot. I. Properties of
the penumbral fine structure
Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R.;
KAOS Team; Berkefeld, T.; Schelenz, T.
2004A&A...415..717T Altcode:
We investigate the properties of the fine structure of a sunspot
penumbra based on spectroscopic measurements with high spectral
(λ/δλ=250 000) and high spatial (≈0.5 arcsec) resolution. The
magnetically insensitive Fe I 557.6 nm line is used to probe the
penumbral atmosphere. The data was taken at the German Vacuum Tower
Telescope with the 2D-spectrometer TESOS, taking advantage of the
recently installed Kiepenheuer Adaptive Optics System (KAOS). The field
of view covers a sunspot located at 23<SUP>o</SUP> off the disk center
and its immediate surroundings. The penumbral structure is studied
by means of maps computed for the line-of-sight velocity, the line
width, the equivalent width and the line depression. Line-of-sight
velocities are derived from the Doppler shifts at different bisector
levels. From these maps we infer the flow field geometry and study the
azimuthal and radial dependences of the line parameters. Our findings
can be summarized as follows: (a) the flow pattern has a conspicuous
filamentary structure in the deep photospheric layers and is rather
diffuse in the high layers. (b) The flow field slightly spreads and
fans out with height. (c) The flow geometry confirms the presence of
an upflow component in the inner penumbra and a downflow component in
the middle and outer penumbra. (d) We find an enhanced brightness of
the mid-penumbra (“bright ring”) in the line wings, but not in the
continuum or line core. (e) The azimuthal average of the equivalent
width, the line width and the absolute flow velocity increase with
radial distance within the penumbra. (f) Small-scale variations of
the equivalent width and the line width on the center-side penumbra
are co-spatial and correlated with (blue-shifted) fluctuations in
the line-of-sight velocity. (g) Inner limb-side penumbral grains are
associated with blue-shifts of v≤-400 m s<SUP>-1</SUP>, indicating
upflows. (h) One umbral dot in our sample is associated with a
blue-shift of v=-200 m s<SUP>-1</SUP>.
---------------------------------------------------------
Title: Thermal Kinematic Structure of a Sunspot at 0.5 arcsec
Resolution
Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A.
2003ANS...324..104B Altcode: 2003ANS...324..P10B
No abstract at ADS
---------------------------------------------------------
Title: Penumbral Line Asymmetries of Fe I 557.6 nm: Implications on
the Flow Geometry of a Sunspot Penumbra
Authors: Schlichenmaier, P.; Bellot Rubio, L.; Tritschler, A.
2003ANS...324..105S Altcode: 2003ANS...324..P11S
No abstract at ADS
---------------------------------------------------------
Title: Two-dimensional Spectroscopy of G-band Bright Structures in
the Solar Photosphere
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
2003ANS...324...54L Altcode: 2003ANS...324..P06L; 2003ANS...324b..54L
No abstract at ADS
---------------------------------------------------------
Title: 2D Spectroscopy with a Triple Gabry-Perot Spectrometer and
Adaptive Optics
Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rutbio, L.
2003ANS...324...21T Altcode: 2003ANS...324..C02T
No abstract at ADS
---------------------------------------------------------
Title: Observations of G-band bright structures with TESOS
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
2003AN....324..354L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-resolution solar spectroscopy with TESOS - Upgrade from
a double to a triple system
Authors: Tritschler, A.; Schmidt, W.; Langhans, K.; Kentischer, T.
2002SoPh..211...17T Altcode:
We present the characteristics and demonstrate the performance of the
Triple Etalon SOlar Spectrometer (TESOS) operated at the German Vacuum
Tower Telescope (VTT) on Tenerife. The Fabry-Pérot interferometer
TESOS is ideally suited for precise measurements of photospheric and
chromospheric motion. Installed in 1997 and equipped with two etalons,
TESOS has recently been completed with a third etalon and upgraded
with two high-speed, backside-illuminated CCD cameras. The image scale
of 0.089 arc sec pixel<SUP>−1</SUP> is adapted to the resolution of
the telescope. The improved system enables frame rates up to 5 frames
per second. The spectral resolution of 300 000 allows for spectral
diagnostics of weak photospheric lines, including individual CH-lines
within the G-band at 430.6 nm.
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Title: Network and internetwork bright points in the solar
chromosphere
Authors: Tritschler, A.; Schmidt, W.
2002ESASP.506..785T Altcode: 2002ESPM...10..785T; 2002svco.conf..785T
We investigate the properties of chromospheric bright points from
time sequences of narrow-band filtergrams centered on the Ca II
K<SUB>2v</SUB> emission peak at 393.3 nm. We compute power maps and
extract the contributions with periods at 3 min and 5 min and find that
the internetwork is dominated by the power at 3 min, whereas the network
shows strong signal at 5 min, cospatial with concentrated magnetic
field seen in the photosphere. We use image segmentation techniques to
derive the size by means of the cell size and an effective diameter
as well as the peak brightness and the local background intensity of
the bright points.
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Title: Downflows around a solar pore
Authors: Tritschler, A.; Schmidt, W.; Rimmele, T.
2002ESASP.506..477T Altcode: 2002svco.conf..477T; 2002ESPM...10..477T
We used the Fabry-Perot interferometer TESOS to observe a solar
pore near disk center in two photospheric spectral lines (Fe I 557.6
nm and Fe I 569.1 nm) which correspond to different heights in the
atmosphere. The measurements were made during the joint campaign with
the NSO/Sacramento-Peak adaptive optics system installed at the German
Vacuum Tower Telescope (VTT). The Doppler-velocity measurements show an
annular downflow around the outer edge of the pore. This downflow is
persistent during the whole observation period, which is demonstrated
in the time-averaged Dopplergrams and the corresponding azimuthally
integrated and time-averaged radial velocity profiles.
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Title: 2D-spectroscopic observations of G-band bright structures
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
2002ESASP.506..455L Altcode: 2002ESPM...10..455L; 2002svco.conf..455L
We took two-dimensional spectra with the filter spectrometer TESOS at
the German Vacuum Tower Telescope, Tenerife, of an absorption line
of the CH-molecule and a Fe II-line in the G-band at 430.3 nm. We
observed a region of granulation near a pore, close to disk center that
showed many structures with enhanced G-band intensity. We introduce a
Bright Point Index (BPI) defined by the ratio of the normalized line
depressions of the Fe II and the CH-line. The BPI allows to characterize
the bright structures by a quantity based on their spectroscopic
signature. Bright structures, caused by significant weakening (up to
40% less absorption) of the absorption lines of the CH-molecule, have
high BPI values and are accompanied by downflows. The remaining G-band
bright structures, only caused by an enhanced continuum intensity,
have low BPI and are related to granules.
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Title: 2D-spectroscopic observations of vec G-band bright structures
in the solar photosphere
Authors: Langhans, K.; Schmidt, W.; Tritschler, A.
2002A&A...394.1069L Altcode:
We took two-dimensional spectra with the filter spectrometer TESOS
at the German Vacuum Tower Telescope, Tenerife, of an absorption
line of the CH molecule and a Fe II-line in the G-band at 430.3
nm. We observed a region, close to disk center of the Sun, that
showed a lot of structures with enhanced G-band intensity (up to 1.3
times the mean intensity of normal granulation). Our spectroscopic
investigation of these structures suggests two classes which differ
in their spectroscopic signature: (a) Bright structures caused by
significant (up to 40\%) weakening of absorption lines of the CH
molecule; (b) bright structures only caused by an enhanced continuum
intensity. In order to distinguish between those two classes we
introduce a Bright Point Index (BPI) defined by the ratio of the
normalized line depressions of the Fe~II and the CH-line. The bright
structures caused by weakening of the CH-lines have high BPI values and
are accompanied by downflows. The remaining G-band bright structures
have low BPI and are related to granules.
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Title: Sunspot photometry with phase diversity. II. Fine-structure
characteristics
Authors: Tritschler, A.; Schmidt, W.
2002A&A...388.1048T Altcode:
We investigate the thermal and morphological fine structure of a small
sunspot, which includes the determination of brightness temperatures
and characteristic spatial scales as well as their distribution
inside the sunspot. The identification and isolation of sunspot fine
structure is accomplished by means of a feature-finding algorithm
applied to a high-resolution time sequence taken simultaneously in
three continuum bands of the solar spectrum. In order to compensate for
seeing and instrumental effects, we apply the phase-diversity technique
combined with a deconvolution method. The findings can be summarized
as follows: (1) umbral dots are found to be on average 760 K cooler
than the immediate surrounding photosphere outside the spot. (2) Some
exceptional hot penumbral grains exceed the average temperature of the
brightest granules of the spots surroundings by typically 150 K. (3)
The size distribution of umbral dots and penumbral grains support the
idea that the smallest structures are still spatially unresolved. (4)
The distribution function of umbral dot peak intensities points to
the existence of two umbral dot “populations” indicating different
efficiency of energy transport. (5) The classification of penumbral
filaments into “dark” and “bright” depends on the immediate
surroundings.
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Title: Sunspot photometry with phase diversity. I. Methods and global
sunspot parameters
Authors: Tritschler, A.; Schmidt, W.
2002A&A...382.1093T Altcode:
The global brightness structure of a small sunspot is
investigated. Seeing and instrumental effects are compensated by
application of the phase-diversity technique and a conventional
deconvolution method. We calculate brightness temperatures for the
reconstructed data in three simultaneously observed continuum bands of
the solar spectrum (402.1 nm, 569.5 nm, 709.1 nm). The darkest umbral
regions are on average 0.17I<SUP>sun</SUP>, 0.27I<SUP>sun</SUP> and
0.32I<SUP>sun</SUP> bright. The corresponding temperatures lie in the
range around 4790 K, 4600 K and 4460 K. The spatially averaged penumbral
brightness amounts to 0.72I<SUP>sun</SUP>, 0.81I<SUP>sun</SUP> and
0.85I<SUP>sun</SUP>, which corresponds to 5910 K, 5750 K and 5640 K,
respectively. Although the spectral distribution of the umbral and
penumbral intensities is consistent with former measurements, the
derived values support the idea that there exist a real difference in
the thermal properties between the umbrae of small and large sunspots.
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Title: Thermal Structure of a Sunspot: An Application of Phase
Diversity
Authors: Tritschler, A.; Schmidt, W.; Knölker, M.
1999ASPC..183..108T Altcode: 1999hrsp.conf..108T
No abstract at ADS
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Title: Some properties of sunspot umbral dots.
Authors: Tritschler, A.; Schmidt, W.
1997A&A...321..643T Altcode:
High resolution Stokes-I spectra of the Zeeman-sensitive lines
at λ846.85nm and λ 630.25nm were used to determine the magnetic
field strength and the brightness temperature of a simple, relatively
symmetric sunspot umbra and its umbral dots (UDs). We find a decrease
in brightness temperature for central (~30%) and peripheral UDs (20-25%)
compared to the surrounding quiet sun. This corresponds to a difference
in temperature of about 1600K and 1200-1400K respectively. The magnetic
field strength within the umbra is derived from the Zeeman splitting of
the Stokes-I profile. Field strengths within the umbra vary between 1500
and 3000G. Further analysis of the λ846.85nm spectra indicates that the
magnetic field strength within the umbral features is not significantly
reduced neither for centrally (<=3%) nor for peripherically located
UDs (1-2%). The λ630.25nm line yields an enhanced weakening of field
strength of 7% for an isolated located UD. The measured properties of
UDs do not vary significantly during a 40min observation sequence.
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Title: Phase Diversity Applied to Sunspot Observations
Authors: Tritschler, A.; Schmidt, W.; Knolker, M.
1997ASPC..118..170T Altcode: 1997fasp.conf..170T
We present preliminary results of a multi-colour phase diversity
experiment carried out with the Multichannel Filter System of the
Vacuum Tower Telescope at the Observatorio del Teide on Tenerife. We
apply phase-diversity imaging to a time sequence of sunspot filtergrams
taken in three continuum bands and correct the seeing influence for
each image. A newly developed phase diversity device allowing for
the projection of both the focused and the defocused image onto a
single CCD chip was used in one of the wavelength channels. With the
information about the wavefront obtained by the image reconstruction
algorithm the restoration of the other two bands can be performed as
well. The processed and restored data set will then be used to derive
the temperature and proper motion of the umbral dots. Data analysis
is still under way, and final results will be given in a forthcoming
article.
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Title: Phase diversity image reconstruction of sunspot umbral dots.
Authors: Tritschler, A.; Schmidt, W.
1996AGAb...12...93T Altcode:
No abstract at ADS
