dewijn

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Author name code: dewijn
ADS astronomy entries on 2022-09-14
author:"De Wijn, Alfred G."

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Title: Multi-height Measurements Of The Solar Vector Magnetic Field:
A White Paper Submitted To The Decadal Survey For Solar And Space
Physics (Heliophysics) 2024-2033
Authors: Bertello, L.; Arge, N.; De Wijn, A. G.; Gosain, S.; Henney,
C.; Leka, K. D.; Linker, J.; Liu, Y.; Luhmann, J.; Macniece, P. J.;
Petrie, G.; Pevtsov, A.; Pevtsov, A. A.
2022arXiv220904453B Altcode:
This white paper advocates the importance of multi-height measurements
of the vector magnetic field in the solar atmosphere. As briefly
described in this document, these measurements are critical for
addressing some of the most fundamental questions in solar and
heliospheric physics today, including: (1) What is the origin
of the magnetic field observed in the solar atmosphere? (2) What
is the coupling between magnetic fields and flows throughout the
solar atmosphere? Accurate measurements of the photospheric and
chromospheric three-dimensional magnetic fields are required for
a precise determination of the emergence and evolution of active
regions. Newly emerging magnetic flux in pre-existing magnetic regions
causes an increase in the topological complexity of the magnetic field,
which leads to flares and coronal mass ejections. Measurements of the
vector magnetic field constitute also the primary product for space
weather operations, research, and modeling of the solar atmosphere
and heliosphere. The proposed next generation Ground-based solar
Observing Network Group (ngGONG), a coordinated system of multi-platform
instruments, will address these questions and provide large datasets
for statistical investigations of solar feature behavior and evolution
and continuity in monitoring for space-weather focused endeavors
both research and operational. It will also enable sun-as-a-star
investigations, crucial as we look toward understanding other
planet-hosting stars.

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Title: Ground-based instrumentation and observational techniques
Authors: Rimmele, Thomas; Kuhn, Jeff; Woeger, Friedrich; Tritschler,
. Alexandra; Lin, Haosheng; Casini, Roberto; Schad, Thomas; Jaeggli,
Sarah; de Wijn, Alfred; Fehlmann, Andre; Anan, Tetsu; Schmidt, Dirk
2022cosp...44.2507R Altcode:
We'll review the current state-of-the-art for ground-based
instrumentation and techniques to achieve high-resolution
observations. We'll use the 4m Daniel K. Inouye Solar Telescope
(DKIST), the European Solar Telescope (EST) and other ground-based
instrumentation as examples to demonstrate instrument designs
and observing techniques. Using adaptive optics and post-facto
image processing techniques, the recently completed DKIST provides
unprecedented resolution and high polarimetric sensitivity that
enables 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. Versatile
ground-based instruments provide highly sensitive measurements of solar
magnetic fields, that in the case of DKIST, also include measurements
of the illusive magnetic field of the faint solar corona. Ground-based
instruments produce large and diverse data sets that require complex
calibration and data processing to provide science-ready to a broad
community. We'll briefly touch on ongoing and future instrumentation
developments, including multi-conjugate adaptive optics.

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Title: The Visible Spectro-Polarimeter of the Daniel K. Inouye
Solar Telescope
Authors: de Wijn, A. G.; Casini, R.; Carlile, A.; Lecinski, A. R.;
Sewell, S.; Zmarzly, P.; Eigenbrot, A. D.; Beck, C.; Wöger, F.;
Knölker, M.
2022SoPh..297...22D Altcode: 2022arXiv220300117D
The Daniel K. Inouye Solar Telescope (DKIST) Visible Spectro-Polarimeter
(ViSP) is a traditional slit-scanning spectrograph with the ability
to observe solar regions up to a 120 ×78 arcsec2 area. The
design implements dual-beam polarimetry, a polychromatic polarization
modulator, a high-dispersion echelle grating, and three spectral
channels that can be automatically positioned. A defining feature of
the instrument is its capability to tune anywhere within the 380 - 900
nm range of the solar spectrum, allowing for a virtually infinite number
of combinations of three wavelengths to be observed simultaneously. This
enables the ViSP user to pursue well-established spectro-polarimetric
studies of the magnetic structure and plasma dynamics of the solar
atmosphere, as well as completely novel investigations of the solar
spectrum. Within the suite of first-generation instruments at the DKIST,
ViSP is the only wavelength-versatile spectro-polarimeter available to
the scientific community. It was specifically designed as a discovery
instrument to explore new spectroscopic and polarimetric diagnostics
and test improved models of polarized line formation through high
spatial-, spectral-, and temporal-resolution observations of the Sun's
polarized spectrum. In this instrument article, we describe the science
requirements and design drivers of ViSP and present preliminary science
data collected during the commissioning of the instrument.

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Title: The Next Generation GONG (ngGONG) Project: Ground-based
Synoptic Studies of the Sun
Authors: Pillet, Valentin; Gilbert, Holly; Pevtsov, Alexei; de Wijn,
Alfred
2021AGUFMSH45E2406P Altcode:
Ground-based synoptic solar observations provide crucial contextual
data used to model the large-scale state of the heliosphere. Existing
ground-based synoptic programs are aging rapidly and are used in
ways that differ from their original objectives. Most prominently,
GONG was designed for helioseismology but is most demanded today
as a provider of the magnetic boundary conditions for solar wind
models. A wealth of theoretical knowledge about the connectivity
between the Sun and the planets has emerged in recent years. NSO and
HAO (and other international partners) are collaborating in defining
a next-generation GONG (ngGONG) network that incorporates this
knowledge. This contribution describes current and future contextual
synoptic observations needed to fully exploit our new understanding of
the underlying microphysics that leads to magnetic linkages between
the Earth and the Sun. This combination of a better understanding of
small-scale processes and the appropriate global context will enable
a physics-based approach to Space Weather comparable to Terrestrial
Weather forecasting.

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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: Enhancements to Hinode/SOT-SP Vector Magnetic Field Data
Products
Authors: DeRosa, M. L.; Leka, K. D.; Barnes, G.; Wagner, E.; Centeno,
R.; De Wijn, A.; Bethge, C.
2021AAS...23821305D Altcode:
The Solar Optical Telescope Spectro-Polarimeter (SOT-SP), on board the
Hinode spacecraft (launched in 2006), is a scanning-slit spectrograph
that continues to provide polarization spectra useful for inferring the
vector (three-component) magnetic field at the solar photosphere. SOT-SP
achieves this goal by obtaining line profiles of two magnetically
sensitive lines, namely the Fe I 6302 Angstrom doublet, using a
0.16"×164" slit as it scans a region of interest. Once the data are
merged, a Milne-Eddington based spectropolarimetric inversion scheme is
used to infer multiple physical parameters in the solar photosphere,
including the vector magnetic field, from the calibrated polarization
spectra. All of these data are publicly available once the processing
has occurred. As of this year, the Hinode/SOT team is also making
available the disambiguated vector magnetic field and the re-projected
heliographic components of the field. In making the disambiguated vector
field data product, the 180° ambiguity in the plane-of-sky component
of the vector magnetic field inherent in the spectropolarimetric
inversion process has been resolved. This ambiguity is resolved
using the Minimum-Energy algorithm, which is the same algorithm used
within the pipeline producing the vector-magnetogram data product
for the Helioseismic and Magnetic Imager aboard the Solar Dynamics
Observatory. The heliographic field components (Bphi,
Btheta, Br) on the same grid as the inverted data
are also now provided. This poster provides more details about these
data product enhancements, and some examples on how the scientific
community may readily obtain these data.

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Title: Design and Performance Analysis of a Highly Efficient
Polychromatic Full Stokes Polarization Modulator for the CRISP
Imaging Spectrometer
Authors: de Wijn, A. G.; de la Cruz Rodríguez, J.; Scharmer, G. B.;
Sliepen, G.; Sütterlin, P.
2021AJ....161...89D Altcode: 2021arXiv210201231D
We present the design and performance of a polychromatic polarization
modulator for the CRisp Imaging SpectroPolarimeter (CRISP) Fabry-Perot
tunable narrow-band imaging spectropolarimer at the Swedish 1 m Solar
Telescope (SST). We discuss the design process in depth, compare
two possible modulator designs through a tolerance analysis, and
investigate thermal sensitivity of the selected design. The trade-offs
and procedures described in this paper are generally applicable in the
development of broadband polarization modulators. The modulator was
built and has been operational since 2015. Its measured performance
is close to optimal between 500 and 900 nm, and differences between
the design and as-built modulator are largely understood. We show some
example data, and briefly review scientific work that used data from
SST/CRISP and this modulator.

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Title: Coronagraphy from the Ground: Current and Future Observations
Authors: Burkepile, J.; Tomczyk, S.; Zmarzly, P.; de Wijn, A.; Gibson,
S. E.; de Toma, G.; Galloy, M. D.
2020AGUFMSH031..03B Altcode:
Ground-based coronagraphs provided the first observations of the
ethereal corona outside of a total solar eclipse in 1931. Invented by
Bernard Lyot, coronagraphs enabled long time-series images and movies
of the emission line corona. Advances in technology have led to more
sophisticated coronagraphs capable of observing polarized light from
spectral lines and the coronal continuum. These observations, coupled
with advances in our understanding of resonance scattering-induced
polarization, have greatly facilitated our knowledge of coronal physics
and explosive events such as Coronal Mass Ejections (CMEs). While
space-based coronagraphs provide spectacular observations of the
extended corona, ground-based coronagraphs continue to contribute
important, unique and complementary inner coronal observations at
a fraction of the cost of a space-based mission. We discuss current
ground-based solar coronagraphs, observations and data products and
highlight future instruments and network capabilities and benefits.

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Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
Wampler, Stephen B.; Williams, Timothy R.; White, Charles
2020SoPh..295..172R Altcode:
We present an overview of the National Science Foundation's Daniel
K. Inouye Solar Telescope (DKIST), its instruments, and support
facilities. The 4 m aperture DKIST provides the highest-resolution
observations of the Sun ever achieved. The large aperture of
DKIST combined with state-of-the-art instrumentation provide the
sensitivity to measure the vector magnetic field in the chromosphere
and in the faint corona, i.e. for the first time with DKIST we will
be able to measure and study the most important free-energy source
in the outer solar atmosphere - the coronal magnetic field. Over its
operational lifetime DKIST will advance our knowledge of fundamental
astronomical processes, including highly dynamic solar eruptions
that are at the source of space-weather events that impact our
technological society. Design and construction of DKIST took over two
decades. DKIST implements a fast (f/2), off-axis Gregorian optical
design. The maximum available field-of-view is 5 arcmin. A complex
thermal-control system was implemented in order to remove at prime
focus the majority of the 13 kW collected by the primary mirror and
to keep optical surfaces and structures at ambient temperature, thus
avoiding self-induced local seeing. A high-order adaptive-optics
system with 1600 actuators corrects atmospheric seeing enabling
diffraction limited imaging and spectroscopy. Five instruments, four
of which are polarimeters, provide powerful diagnostic capability
over a broad wavelength range covering the visible, near-infrared,
and mid-infrared spectrum. New polarization-calibration strategies
were developed to achieve the stringent polarization accuracy
requirement of 5×10−4. Instruments can be combined and
operated simultaneously in order to obtain a maximum of observational
information. Observing time on DKIST is allocated through an open,
merit-based proposal process. DKIST will be operated primarily in
"service mode" and is expected to on average produce 3 PB of raw
data per year. A newly developed data center located at the NSO
Headquarters in Boulder will initially serve fully calibrated data to
the international users community. Higher-level data products, such as
physical parameters obtained from inversions of spectro-polarimetric
data will be added as resources allow.

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Title: Venus Transitis the Solar Corona
Authors: De Wijn, Alfred; Können, Gunther
2020S&T...140d..11D Altcode:
No abstract at ADS

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Title: Coronal Solar Magnetism Observatory Science Objectives
Authors: Gibson, S. E.; Tomczyk, S.; Burkepile, J.; Casini, R.;
DeLuca, E.; de Toma, G.; de Wijn, A.; Fan, Y.; Golub, L.; Judge,
P. G.; Landi, E.; McIntosh, S. W.; Reeves, K.; Seaton, D. B.; Zhang, J.
2019AGUFMSH11C3395G Altcode:
Space-weather forecast capability is held back by our current
lack of basic scientific understanding of CME magnetic evolution,
and the coronal magnetism that structures and drives the solar
wind. Comprehensive observations of the global magnetothermal
environment of the solar atmosphere are needed for progress. When fully
implemented, the COSMO suite of synoptic ground-based telescopes will
provide the community with comprehensive and simultaneous measurements
of magnetism, temperature, density and plasma flows and waves from the
photosphere through the chromosphere and out into the corona. We will
discuss how these observations will uniquely address a set of science
objectives that are central to the field of solar and space physics:
in particular, to understand the storage and release of magnetic energy,
to understand CME dynamics and consequences for shocks, to determine the
role of waves in solar atmospheric heating and solar wind acceleration,
to understand how the coronal magnetic field relates to the solar
dynamo, and to constrain and improve space-weather forecast models.

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Title: ngGONG: The Next Generation GONG - A New Solar Synoptic
Observational Network
Authors: Hill, Frank; Hammel, Heidi; Martinez-Pillet, Valentin; de
Wijn, A.; Gosain, S.; Burkepile, J.; Henney, C. J.; McAteer, J.; Bain,
H. M.; Manchester, W.; Lin, H.; Roth, M.; Ichimoto, K.; Suematsu, Y.
2019BAAS...51g..74H Altcode: 2019astro2020U..74H
The white paper describes a next-generation GONG, a ground-based
geographically distributed network of instrumentation to continually
observe the Sun. This would provide data for solar magnetic field
research and space weather forecasting, and would extend the time
coverage of helioseismology.

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Title: Investigating Coronal Magnetism with COSMO: Science on
the Critical Path To Understanding The “Weather” of Stars and
Stellarspheres
Authors: McIntosh, Scott; Tomczyk, Steven; Gibson, Sarah E.; Burkepile,
Joan; de Wijn, Alfred; Fan, Yuhong; deToma, Giuliana; Casini, Roberto;
Landi, Enrico; Zhang, Jie; DeLuca, Edward E.; Reeves, Katharine K.;
Golub, Leon; Raymond, John; Seaton, Daniel B.; Lin, Haosheng
2019BAAS...51g.165M Altcode: 2019astro2020U.165M
The Coronal Solar Magnetism Observatory (COSMO) is a unique ground-based
facility designed to address the shortfall in our capability to measure
magnetic fields in the solar corona.

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Title: Status Update of the COSMO ChroMag
Authors: de Wijn, Alfred G.
2019shin.confE.193D Altcode:
I present an overview of the COSMO ChroMag instrument, its status,
and discuss the inclusion of an instrument with similar capabilities
in a potential future global network of ground-based observatories
from a forecasters and researchers perspective.

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Title: Synoptic Studies of the Sun as a Key to Understanding Stellar
Astrospheres
Authors: Martinez Pillet, Valentin; Hill, Frank; Hammel, Heidi B.;
de Wijn, Alfred G.; Gosain, Sanjay; Burkepile, Joan; Henney, Carl;
McAteer, R. T. James; Bain, Hazel; Manchester, Ward; Lin, Haosheng;
Roth, Markus; Ichimoto, Kiyoshi; Suematsu, Yoshinori
2019BAAS...51c.110M Altcode: 2019astro2020T.110M; 2019arXiv190306944M
Ground-based solar observations provide key contextual data (i.e., the
"big picture") to produce a complete description of the only astrosphere
we can study in situ: our Sun's heliosphere. This white paper outlines
the current paradigm for ground-based solar synoptic observations,
and indicates those areas that will benefit from focused attention.

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Title: First Results from the Chromosphere and Prominence Magnetometer
Authors: de Wijn, A. G.
2019ASPC..526..353D Altcode:
The Chromosphere and Prominence Magnetometer (ChroMag) is an instrument
with the goal of quantifying the intertwined dynamics and magnetism
of the solar chromosphere and prominences through synoptic imaging
spectro-polarimetry of the full solar disk. The picture of chromospheric
magnetism and dynamics is rapidly developing, and a pressing need exists
for breakthrough measurements of the chromospheric vector magnetic
field, which can be considered to represent the lower boundary of
the heliospheric system. ChroMag will provide measurements that will
enable scientists to study and better understand the energetics of the
solar atmosphere, how prominences are formed, how energy is stored in
the magnetic field structure of the atmosphere, and how it is released
during space weather events like flares and coronal mass ejections. A
prototype ChroMag instrument is currently deployed in Boulder, CO,
USA. We present an overview of the instrument capabilities, a progress
update on the ChroMag development, and show initial results.

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Title: Characterization of Cameras for the COSMO K-coronagraph
Authors: de Wijn, A. G.
2019AJ....157....8D Altcode: 2018arXiv181205182D
Digital image sensors are ubiquitous in astronomical instrumentation and
it is well known that they suffer from issues that must be corrected
for data to be scientifically useful. I present discussion on errors
resulting from digitization and characterization of nonlinearity
and ADC errors of the PhotonFocus MV-D1024E cameras selected for the
K-coronagraph of the Coronal Solar Magnetism Observatory. I derive an
analytic expression for quantization errors. The MV-D1024E camera has
adequate bit depth for which quantization error is not an issue. I
show that this is not the case for all cameras, particularly those
with deep wells and low read noise. The impact of nonlinearity and ADC
errors on science observations of the K-coronagraph is analyzed using
a simplified telescope model. Errors caused by the camera ADCs result
in systematic errors in the measurement of the polarimetric signal
of several times 10-9 B ⊙, which is about
an order of magnitude above the desired sensitivity. I demonstrate
a method for post-facto data correction using a lookup table and
derive parameters from camera characterization measurements that were
made with a lab setup. Nonlinearity is traditionally addressed with
a global correction. I show through analysis of calibration data
that for the MV-D1024E this correction leaves residual systematic
errors after dark and gain correction of up to 1% of the signal. I
demonstrate that a pixel-wise correction of nonlinearity reduces
the errors to below 0.1%. These corrections are necessary for the
K-coronagraph data products to meet the science requirements. They
have been implemented in the instrument data acquisition system
and data reduction pipeline. While no other instruments besides the
K-coronagraph or cameras besides the MV-D1024E are discussed here,
the results are illustrative for all instruments and cameras.

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Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
2018AAS...23231601R Altcode:
The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
construction on Haleakala, Maui will be the world’s largest solar
telescope. Designed to meet the needs of critical high resolution and
high sensitivity spectral and polarimetric observations of the sun,
this facility will perform key observations of our nearest star that
matters most to humankind. DKIST’s superb resolution and sensitivity
will enable astronomers to address many of the fundamental problems
in solar and stellar astrophysics, including the origin of stellar
magnetism, the mechanisms of coronal heating and drivers of the
solar wind, flares, coronal mass ejections and variability in solar
and stellar output. DKIST will also address basic research aspects of
Space Weather and help improve predictive capabilities. In combination
with synoptic observations and theoretical modeling DKIST will unravel
the many remaining mysteries of the Sun.The construction of DKIST is
progressing on schedule with 80% of the facility complete. Operations
are scheduled to begin early 2020. DKIST will replace the NSO
facilities on Kitt Peak and Sac Peak with a national facility with
worldwide unique capabilities. The design allows DKIST to operate as
a coronagraph. Taking advantage of its large aperture and infrared
polarimeters DKIST will be capable to routinely measure the currently
illusive coronal magnetic fields. The state-of-the-art adaptive optics
system provides diffraction limited imaging and the ability to resolve
features approximately 20 km on the Sun. Achieving this resolution
is critical for the ability to observe magnetic structures at their
intrinsic, fundamental scales. Five instruments will be available at
the start of operations, four of which will provide highly sensitive
measurements of solar magnetic fields throughout the solar atmosphere
- from the photosphere to the corona. The data from these instruments
will be distributed to the world wide community via the NSO/DKIST data
center located in Boulder. We present examples of science objectives
and provide an overview of the facility and project status, including
the ongoing efforts of the community to develop the critical science
plan for the first 2-3 years of operations.

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Title: First Detection of Sign-reversed Linear Polarization from
the Forbidden [O I] 630.03 nm Line
Authors: de Wijn, A. G.; Socas-Navarro, H.; Vitas, N.
2017ApJ...836...29D Altcode: 2017arXiv170108793D
We report on the detection of linear polarization of the forbidden
[O I] 630.03 nm spectral line. The observations were carried out
in the broader context of the determination of the solar oxygen
abundance, an important problem in astrophysics that still remains
unresolved. We obtained spectro-polarimetric data of the forbidden
[O I] line at 630.03 nm as well as other neighboring permitted lines
with the Solar Optical Telescope of the Hinode satellite. A novel
averaging technique was used, yielding very high signal-to-noise ratios
in excess of 105. We confirm that the linear polarization
is sign-reversed compared to permitted lines as a result of the line
being dominated by a magnetic dipole transition. Our observations
open a new window for solar oxygen abundance studies, offering an
alternative method to disentangle the Ni I blend from the [O I] line
at 630.03 nm that has the advantage of simple LTE formation physics.

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Title: What’s New at the Mauna Loa Solar Observatory
Authors: Burkepile, Joan; de Toma, Giuliana; Galloy, Michael; Kolinski,
Don; Berkey, Ben; Stueben, Allen; Tomczyk, Steven; De Wijn, Alfred;
Casini, Roberto; Card, Greg; Larson, Brandon; Stanger, Andrew; Oakley,
Phil; Gallagher, Dennis; Waters, Lisa; Rose, Greg; Sewell, Scott
2016SPD....47.0801B Altcode:
The Mauna Loa Solar Observatory (MLSO) is located at 3440 meters
on the island of Hawaii. The site provides the dark, clear skies
required for observing the solar corona. The National Center for
Atmosphere Research (NCAR) High Altitude Observatory (HAO) operates two
coronagraphs at the site: the Coronal Multi-Channel Polarimeter (CoMP)
and the COSMO K-Coronagraph (K-Cor). CoMP is designed to study coronal
magnetic fields by observing full Stokes polarimetry of two forbidden
emission lines of FeXIII at 1074.7 and 1079.8 nm. CoMP also observes
active and erupting prominences over the solar limb in neutral Helium
emission at 1083.nm. The K-Cor is designed to study the onset and early
evolution of coronal mass ejections (CMEs). It is the only white light
coronagraph to routinely view the low corona down to 1.05 solar radii
in order to capture the formation of CMEs. Information is provided on
new Helium data products of active and erupting prominences observed
by the CoMP instrument as well as results from the K-Cor observations
of CMEs. Information on current and upcoming upgrades to the MLSO
facility, instrument hardware, and calibrations are reported along
with an accounting of new data products, tools and services from the
MLSO website.

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Title: A Progress Update for the COronal Solar Magnetism Observatory
for Coronal and Chromospheric Polarimetry
Authors: de Wijn, A. G.; Tomczyk, S.; Burkepile, J.
2014ASPC..489..323D Altcode:
We present a progress update for the COronal Solar Magnetism
Observatory (COSMO), consisting of a suite of three instruments:
a large-aperture coronagraph for coronal magnetometry, a full-disk
imaging spectro-polarimeter for magnetometry and plasma diagnostics
of the chromosphere and prominences, and a white-light coronagraph
to observe the K-corona. COSMO will provide unique observations of
the global coronal magnetic fields and its environment to enhance the
value of data collected by other observatories on the ground and in
space. We provide an overview of COSMO, and discuss each instrument
in some detail.

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Title: On the instrument profile of slit spectrographs
Authors: Casini, R.; de Wijn, A. G.
2014JOSAA..31.2002C Altcode: 2014arXiv1409.0137C
We derive an analytic expression for the instrument profile of a
slit spectrograph, also known as the line spread function. While
this problem is not new, our treatment relies on the operatorial
approach to the description of diffractive optical systems, which
provides a general framework for the analysis of the performance of
slit spectrographs under different illumination conditions. Based on
our results, we propose an approximation to the spectral resolution of
slit spectrographs, taking into account diffraction effects and sampling
by the detector, which improves upon the often adopted approximation
based on the root-sumsquare of the individual contributions from the
slit, the grating, and the detector pixel.

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Title: The Chromosphere and Prominence Magnetometer
Authors: de Wijn, Alfred G.; McIntosh, Scott W.; Tomczyk, Steven
2014shin.confE..76D Altcode:
The Chromosphere and Prominence Magnetometer (ChroMag) is a synoptic
instrument with the goal of quantifying the intertwined dynamics
and magnetism of the solar chromosphere and in prominences through
imaging spectro-polarimetry of the full solar disk in a synoptic
fashion. The picture of chromospheric magnetism and dynamics is
rapidly developing, and a pressing need exists for breakthrough
observations of chromospheric vector magnetic field measurements
at the true lower boundary of the heliospheric system. ChroMag will
provide measurements that will enable scientists to study and better
understand the energetics of the solar atmosphere, how prominences are
formed, how energy is stored in the magnetic field structure of the
atmosphere and how it is released during space weather events like
flares and coronal mass ejections. An essential part of the ChroMag
program is a commitment to develop and provide community access to the
`inversion' tools necessary to interpret the measurements and derive
the magneto-hydrodynamic parameters of the plasma. Measurements of an
instrument like ChroMag provide critical physical context for the Solar
Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph
(IRIS) as well as ground-based observatories such as the future Daniel
K. Inouye Solar Telescope (DKIST). A prototype is currently
deployed in Boulder, CO, USA. We will present an overview of instrument
capabilities and a progress update on the ChroMag development.

---------------------------------------------------------
Title: Design and measurement of the Stokes polarimeter for the
COSMO K-coronagraph
Authors: Hou, Junfeng; de Wijn, Alfred G.; Tomczyk, Steven
2013ApJ...774...85H Altcode:
We present the Stokes polarimeter for the new Coronal Solar Magnetism
Observatory K-coronagraph. The polarimeter can be used in two modes. In
observation mode, it is sensitive to linear polarization only and
operates as a "Stokes definition" polarimeter. In the ideal case, such
a modulator isolates a particular Stokes parameter in each modulation
state. For calibrations, the polarimeter can diagnose the full Stokes
vector. We present here the design process of the polarimeter, analyze
its tolerances with a Monte Carlo method, develop a way to align
the individual elements, and measure and evaluate its performance in
both modes.

---------------------------------------------------------
Title: The Chromosphere and Prominence Magnetometer
Authors: de Wijn, Alfred; Bethge, Christian; McIntosh, Scott; Tomczyk,
Steven; Burkepile, Joan
2013EGUGA..1512765D Altcode:
The Chromosphere and Prominence Magnetometer (ChroMag) is a synoptic
instrument with the goal of quantifying the intertwined dynamics
and magnetism of the solar chromosphere and in prominences through
imaging spectro-polarimetry of the full solar disk in a synoptic
fashion. The picture of chromospheric magnetism and dynamics is
rapidly developing, and a pressing need exists for breakthrough
observations of chromospheric vector magnetic field measurements
at the true lower boundary of the heliospheric system. ChroMag will
provide measurements that will enable scientists to study and better
understand the energetics of the solar atmosphere, how prominences are
formed, how energy is stored in the magnetic field structure of the
atmosphere and how it is released during space weather events like
flares and coronal mass ejections. An essential part of the ChroMag
program is a commitment to develop and provide community access to the
`inversion' tools necessary to interpret the measurements and derive
the magneto-hydrodynamic parameters of the plasma. Measurements of an
instrument like ChroMag provide critical physical context for the Solar
Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph
(IRIS) as well as ground-based observatories such as the future Advanced
Technology Solar Telescope (ATST). A prototype is currently under
construction at the High Altitude Observatory of the National Center
for Atmospheric Research in Boulder, CO, USA. The heart of the ChroMag
instrument is an electro-optically tunable wide-fielded narrow-band
birefringent six-stage Lyot filter with a built-in polarimeter. We
will present a progress update on the ChroMag design, and present
results from the prototype instrument.

---------------------------------------------------------
Title: Measuring Magnetic Fields in the Solar Atmosphere
Authors: de Wijn, A. G.
2013ASPC..470...65D Altcode: 2012arXiv1207.0943D
Since the discovery by Hale in the early 1900s that sunspots harbor
strong magnetic field, magnetism has become increasingly important in
our understanding of processes on the Sun and in the Heliosphere. Many
current and planned instruments are capable of diagnosing magnetic
field in the solar atmosphere. Photospheric magnetometry is now
well-established. However, many challenges remain. For instance, the
diagnosis of magnetic field in the chromosphere and corona is difficult,
and interpretation of measurements is harder still. As a result only
very few measurements have been made so far, yet it is clear that if we
are to understand the outer solar atmosphere we must study the magnetic
field. I will review the history of solar magnetic field measurements,
describe and discuss the three types of magnetometry, and close with
an outlook on the future.

---------------------------------------------------------
Title: Measuring Solar Magnetism
Authors: de Wijn, Alfred G.
2012Sci...338..476D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Probable Identification of the On-disk Counterpart of Spicules
in Hinode Ca II H Observations
Authors: de Wijn, A. G.
2012ApJ...757L..17D Altcode: 2012arXiv1208.6329D
I present a study of high-resolution time series of Ca II H images and
Fe I 630.15 nm spectra taken with the Solar Optical Telescope on the
Hinode spacecraft. There is excellent correspondence between the Ca
II H and the Fe I line core intensity, except tenuous emission around
the network field concentrations in the former that is absent in the
latter. Analysis of on-disk observations and a comparison with limb
observations suggests that this "network haze" corresponds to spicules,
and likely to type-II spicules in particular. They are known to appear
in emission in on-disk broadband Ca II H diagnostics and the network
haze is strongest in those areas where features similar to type-II
spicules are produced in simulations.

---------------------------------------------------------
Title: Stray light and polarimetry considerations for the COSMO
K-Coronagraph
Authors: de Wijn, Alfred G.; Burkepile, Joan T.; Tomczyk, Steven;
Nelson, Peter G.; Huang, Pei; Gallagher, Dennis
2012SPIE.8444E..3ND Altcode: 2012arXiv1207.0978D
The COSMO K-Coronagraph is scheduled to replace the aging Mk4
K-Coronameter at the Mauna Loa Solar Observatory of the National Center
for Atmospheric Research in 2013. We present briefly the science
objectives and derived requirements, and the optical design. We
single out two topics for more in-depth discussion: stray light,
and performance of the camera and polarimeter.

---------------------------------------------------------
Title: Design of a full-Stokes polarimeter for VLT/X-shooter
Authors: Snik, Frans; van Harten, Gerard; Navarro, Ramon; Groot,
Paul; Kaper, Lex; de Wijn, Alfred
2012SPIE.8446E..25S Altcode: 2012arXiv1207.2965S
X-shooter is one of the most popular instruments at the VLT, offering
instantaneous spectroscopy from 300 to 2500 nm. We present the design
of a single polarimetric unit at the polarization-free Cassegrain focus
that serves all three spectrograph arms of X-shooter. It consists of
a calcite Savart plate as a polarizing beam-splitter and a rotatable
crystal retarder stack as a "polychromatic modulator". Since even
"superachromatic" wave plates have a wavelength range that is too
limited for X-shooter, this novel modulator is designed to offer
close-to-optimal polarimetric efficiencies for all Stokes parameters
at all wavelengths. We analyze the modulator design in terms of its
polarimetric performance, its temperature sensitivity, and its polarized
fringes. Furthermore, we present the optical design of the polarimetric
unit. The X-shooter polarimeter will furnish a myriad of science cases:
from measuring stellar magnetic fields (e.g., Ap stars, white dwarfs,
massive stars) to determining asymmetric structures around young stars
and in supernova explosions.

---------------------------------------------------------
Title: The chromosphere and prominence magnetometer
Authors: de Wijn, Alfred G.; Bethge, Christian; Tomczyk, Steven;
McIntosh, Scott
2012SPIE.8446E..78D Altcode: 2012arXiv1207.0969D
The Chromosphere and Prominence Magnetometer (ChroMag) is conceived
with the goal of quantifying the intertwined dynamics and magnetism
of the solar chromosphere and in prominences through imaging spectro-
polarimetry of the full solar disk. The picture of chromospheric
magnetism and dynamics is rapidly developing, and a pressing need
exists for breakthrough observations of chromospheric vector magnetic
field measurements at the true lower boundary of the heliospheric
system. ChroMag will provide measurements that will enable scientists
to study and better understand the energetics of the solar atmosphere,
how prominences are formed, how energy is stored in the magnetic field
structure of the atmosphere and how it is released during space weather
events like flares and coronal mass ejections. An integral part of the
ChroMag program is a commitment to develop and provide community access
to the "inversion" tools necessary for the difficult interpretation
of the measurements and derive the magneto-hydrodynamic parameters of
the plasma. Measurements of an instrument like ChroMag provide critical
physical context for the Solar Dynamics Observatory (SDO) and Interface
Region Imaging Spectrograph (IRIS) as well as ground-based observatories
such as the future Advanced Technology Solar Telescope (ATST).

---------------------------------------------------------
Title: Analysis of Seeing-induced Polarization Cross-talk and
Modulation Scheme Performance
Authors: Casini, R.; de Wijn, A. G.; Judge, P. G.
2012ApJ...757...45C Altcode: 2011arXiv1107.0367C
We analyze the generation of polarization cross-talk in Stokes
polarimeters by atmospheric seeing, and its effects on the noise
statistics of spectropolarimetric measurements for both single-beam
and dual-beam instruments. We investigate the time evolution of
seeing-induced correlations between different states of one modulation
cycle and compare the response to these correlations of two popular
polarization modulation schemes in a dual-beam system. Extension of
the formalism to encompass an arbitrary number of modulation cycles
enables us to compare our results with earlier work. Even though we
discuss examples pertinent to solar physics, the general treatment
of the subject and its fundamental results might be useful to a wider
community.

---------------------------------------------------------
Title: Preliminary design of the visible spectro-polarimeter for
the Advanced Technology Solar Telescope
Authors: de Wijn, Alfred G.; Casini, Roberto; Nelson, Peter G.;
Huang, Pei
2012SPIE.8446E..6XD Altcode: 2012arXiv1207.0976D
The Visible Spectro-Polarimeter (ViSP) is one of the first light
instruments for the Advanced Technology Solar Telescope (ATST). It is
an echelle spectrograph designed to measure three different regions
of the solar spectrum in three separate focal planes simultaneously
between 380 and 900 nm. It will use the polarimetric capabilities
of the ATST to measure the full Stokes parameters across the line
profiles. By measuring the polarization in magnetically sensitive
spectral lines the magnetic field vector as a function of height in the
solar atmosphere can be obtained, along with the associated variation of
the thermodynamic properties. The ViSP will have a spatial resolution
of 0.04 arcsec over a 2 arcmin field of view (at 600 nm). The minimum
spectral resolving power for all the focal planes is 180,000. The
spectrograph supports up to 4 diffraction gratings and is fully
automated to allow for rapid reconfiguration.

---------------------------------------------------------
Title: The Chromospheric Magnetometer ChroMag
Authors: Bethge, Christian; de Wijn, A. G.; McIntosh, S. W.; Tomczyk,
S.; Casini, R.
2012AAS...22013506B Altcode:
We present the Chromosphere Magnetometer (ChroMag), which is part of
the Coronal Solar Magnetism Observatory (COSMO) proposed by the High
Altitude Observatory (HAO) in collaboration with the University of
Hawaii and the University of Michigan. ChroMag will perform routine
measurements of chromospheric magnetic fields in a synoptic manner. A prototype is currently being assembled at HAO. The main component of
the instrument is a Lyot-type filtergraph polarimeter for both on-disk
and off-limb polarization measurements in the spectral lines of
H alpha at 656.3 nm, Fe I 617.3 nm, Ca II 854.2 nm, He I 587.6 nm,
and He I 1083.0 nm. The Lyot filter is tunable at a fast rate. This
allows to determine line-of-sight velocities in addition to the
magnetic field measurements. The instrument has a field-of-view of
up to 2.5 solar radii and will acquire data at a cadence of less than
1 minute and at a spatial resolution of 2 arcsec. The community will
have open access to the data as well as to a set of inversion tools
for an easier interpretation of the measurements. We show an overview
of the proposed instrument and first results from the protoype.

---------------------------------------------------------
Title: A High-Resolution Study of Ca II H Time Series
Authors: de Wijn, A. G.
2012ASPC..456...49D Altcode:
I present a study of high-resolution, high-cadence time series of Ca
II H images and Fe I 630.15 nm spectra taken with the Solar Optical
Telescope on the Hinode spacecraft. There is excellent correspondence
between the Ca II H and Fe I line core intensity, except tenuous
emission around the network field concentrations in the former that
is absent in the latter. Comparison with limb observations shows that
this “network haze” most likely corresponds to type-II spicules.

---------------------------------------------------------
Title: The Chromosphere and Prominence Magnetometer
Authors: de Wijn, Alfred; Bethge, Christian; McIntosh, Scott; Tomczyk,
Steven; Casini, Roberto
2012decs.confE..63D Altcode:
ChroMag is an imaging polarimeter designed to measure on-disk
chromosphere and off-disk prominence magnetic fields using the
spectral lines of He I (587.6 and 1083 nm). It is part of the planned
CoSMO suite, which includes two more instruments: a large 1.5-m
refracting coronagraph for coronal magnetic field measurements, and
the K-Coronagraph for measurement of the coronal density. ChroMag
will provide insights in the energetics of the solar atmosphere,
how prominences are formed, and how energy is stored and released
in the magnetic field structure of the atmosphere. An essential
part of the ChroMag program is a commitment to develop and provide
community access to the "inversion" tools necessary to interpret the
measurements and derive the magneto-hydrodynamic parameters of the
plasma. A prototype instrument is currently under construction at the
High Altitude Observatory. We will present an overview of the ChroMag
instrument concept, target science, and prototype status.

---------------------------------------------------------
Title: Synoptic measurements of chromospheric and prominence magnetic
fields with the Chromosphere Magnetometer ChroMag
Authors: Bethge, C.; de Wijn, A. G.; McIntosh, S. W.; Tomczyk, S.;
Casini, R.
2012decs.confE..62B Altcode:
The Chromosphere Magnetometer is part of the Coronal Solar Magnetism
Observatory (COSMO) proposed by the High Altitude Observatory (HAO)
in collaboration with the University of Hawaii and the University of
Michigan. Routine measurements of chromospheric and coronal magnetic
fields are vital if we want to understand fundamental problems like
the energy and mass balance of the corona, the onset and acceleration
of the solar wind, the emergence of CMEs, and how these phenomena
influence space weather. ChroMag is designed as a Lyot-type filtergraph
polarimeter with an FOV of 2.5 solar radii, i.e., it will be capable of
both on-disk and off-limb polarimetric measurements. The Lyot filter
- currently being built at HAO - is tunable at a fast rate, which
allows to determine line-of-sight velocities. This will be done in
the spectral lines of H alpha at 656.3 nm, Fe I 617.3 nm, Ca II 854.2
nm, He I 587.6 nm, and He I 1083.0 nm at a high cadence of less than
1 minute, and at a moderate spatial resolution of 2 arcsec. ChroMag
data will be freely accessible to the community, along with inversion
tools for an easier interpretation of the data. A protoype instrument
for ChroMag is currently being assembled at HAO and is expected to
perform first measurements at the Boulder Mesa Lab in Summer 2012. We
present an overview of the ChroMag instrument and the current status
of the protoype.

---------------------------------------------------------
Title: Quiet-Sun imaging asymmetries in Na I D1 compared
with other strong Fraunhofer lines
Authors: Rutten, R. J.; Leenaarts, J.; Rouppe van der Voort, L. H. M.;
de Wijn, A. G.; Carlsson, M.; Hansteen, V.
2011A&A...531A..17R Altcode: 2011arXiv1104.4307R
Imaging spectroscopy of the solar atmosphere using the Na I
D1 line yields marked asymmetry between the blue and
red line wings: sampling a quiet-Sun area in the blue wing displays
reversed granulation, whereas sampling in the red wing displays normal
granulation. The Mg I b2 line of comparable strength does
not show this asymmetry, nor does the stronger Ca II 8542 Å line. We
demonstrate the phenomenon with near-simultaneous spectral images in
Na I D1, Mg I b2, and Ca II 8542 Å from the
Swedish 1-m Solar Telescope. We then explain it with line-formation
insights from classical 1D modeling and with a 3D magnetohydrodynamical
simulation combined with NLTE spectral line synthesis that permits
detailed comparison with the observations in a common format. The
cause of the imaging asymmetry is the combination of correlations
between intensity and Dopplershift modulation in granular overshoot
and the sensitivity to these of the steep profile flanks of the Na
I D1 line. The Mg I b2 line has similar core
formation but much wider wings due to larger opacity buildup and
damping in the photosphere. Both lines obtain marked core asymmetry
from photospheric shocks in or near strong magnetic concentrations,
less from higher-up internetwork shocks that produce similar asymmetry
in the spatially averaged Ca II 8542 Å profile.

---------------------------------------------------------
Title: Wavelength-diverse Polarization Modulators for Stokes
Polarimetry
Authors: de Wijn, A. G.; Tomczyk, S.; Casini, R.; Nelson, P. G.
2011ASPC..437..413D Altcode:
An increasing number of astronomical applications depend on the
measurement of polarized light. For example, our knowledge of solar
magnetism relies heavily on our ability to measure and interpret
polarization signatures introduced by magnetic field. Many new
instruments have consequently focused considerable attention
on polarimetry. For solar applications, spectro-polarimeters in
particular are often designed to observe the solar atmosphere in
multiple spectral lines simultaneously, thus requiring that the
polarization modulator employed is efficient at all wavelengths of
interest. We present designs of polarization modulators that exhibit
near-optimal modulation characteristics over broad spectral ranges. Our
design process employs a computer code to optimize the efficiency of
the modulator at specified wavelengths. We will present several examples
of modulator designs based on rotating stacks of Quartz waveplates and
ferroelectric liquid crystals (FLCs). An FLC-based modulator of this
design was recently deployed for the ProMag instrument at the Evans
Solar Facility of NSO/SP.

---------------------------------------------------------
Title: Observations of solar scattering polarization at high spatial
resolution
Authors: Snik, F.; de Wijn, A. G.; Ichimoto, K.; Fischer, C. E.;
Keller, C. U.; Lites, B. W.
2010A&A...519A..18S Altcode: 2010arXiv1005.5042S
Context. The weak, turbulent magnetic fields that supposedly
permeate most of the solar photosphere are difficult to observe,
because the Zeeman effect is virtually blind to them. The Hanle
effect, acting on the scattering polarization in suitable lines,
can in principle be used as a diagnostic for these fields. However,
the prediction that the majority of the weak, turbulent field resides
in intergranular lanes also poses significant challenges to scattering
polarization observations because high spatial resolution is usually
difficult to attain. Aims: We aim to measure the difference
in scattering polarization between granules and intergranules. We
present the respective center-to-limb variations, which may serve as
input for future models. Methods: We perform full Stokes filter
polarimetry at different solar limb positions with the CN band filter
of the Hinode-SOT Broadband Filter Imager, which represents the first
scattering polarization observations with sufficient spatial resolution
to discern the granulation. Hinode-SOT offers unprecedented spatial
resolution in combination with high polarimetric sensitivity. The CN
band is known to have a significant scattering polarization signal,
and is sensitive to the Hanle effect. We extend the instrumental
polarization calibration routine to the observing wavelength,
and correct for various systematic effects. Results: The
scattering polarization for granules (i.e., regions brighter than
the median intensity of non-magnetic pixels) is significantly larger
than for intergranules. We derive that the intergranules (i.e., the
remaining non-magnetic pixels) exhibit (9.8±3.0)% less scattering
polarization for 0.2 &lt; μ ≤ 0.3, although systematic effects cannot
be completely excluded. Conclusions: These observations constrain
MHD models in combination with (polarized) radiative transfer in terms
of CN band line formation, radiation anisotropy, and magnetic fields.

---------------------------------------------------------
Title: The polychromatic polarization modulator
Authors: de Wijn, Alfred G.; Tomczyk, Steven; Casini, Roberto; Nelson,
Peter G.
2010SPIE.7735E..4AD Altcode: 2010SPIE.7735E.143D
An increasing number of astronomical applications depend on the
measurement of polarized light. For example, our knowledge of solar
magnetism relies heavily on our ability to measure and interpret
polarization signatures introduced by magnetic field. Many new
instruments have consequently focused considerable attention on
polarimetry. For solar applications, spectro-polarimeters in particular
are often designed to observe the solar atmosphere in multiple spectral
lines simultaneously, thus requiring that the polarization modulator
employed is efficient at all wavelengths of interest. We present
designs of polarization modulators that exhibit near-optimal modulation
characteristics over broad spectral ranges. Our design process employs a
computer code to optimize the efficiency of the modulator at specified
wavelengths. We will present several examples of modulator designs
based on rotating stacks of Quartz waveplates and Ferroelectric Liquid
Crystals (FLCs). An FLC-based modulator of this design was recently
deployed for the ProMag instrument at the Evans Solar Facility of
NSO/SP. We show that this modulator behaves according to its design.

---------------------------------------------------------
Title: The Visible Spectro-Polarimeter (ViSP) for the Advanced
Technology Solar Telescope
Authors: Nelson, Peter G.; Casini, Roberto; de Wijn, Alfred G.;
Knoelker, Michael
2010SPIE.7735E..8CN Altcode: 2010SPIE.7735E.271N
The Visible Spectro-Polarimeter (ViSP) is one of the first light
instruments for the Advanced Technology Solar Telescope (ATST). It is
an echelle spectrograph designed to measure three different regions
of the solar spectrum in three separate focal planes simultaneously
between 380 and 1600nm. It will use the polarimetric capabilities
of the ATST to measure the full Stokes parameters across the line
profiles. By measuring the polarization in magnetically sensitive
spectral lines the magnetic field vector as a function of height
in the solar atmosphere, along with the associated variation of
the thermodynamic properties can be obtained. The ViSP will have a
spatial resolution of 0.04 arc seconds over a 2 minute field of view
(at 600nm). The minimum resolving power for all the focal planes is
180,000. The spectrograph supports up to 5 diffraction gratings and
is fully automated to allow for rapid reconfiguration.

---------------------------------------------------------
Title: NCAR COSMO K-Coronagraph and Chromospheric Magnetometer
Authors: Burkepile, Joan T.; Tomczyk, Steve; Nelson, Pete; de Wijn,
Alfred; Sewell, Scott; Casini, Roberto; Elmore, David; McIntosh,
Scott; Kolinski, Don; Summers, Rich
2010shin.confE...3B Altcode:
We discuss the status of the COronal Solar Magnetism Observatory
(COSMO), a proposed facility dedicated to studying coronal and
chromospheric magnetic fields and their role in driving solar
activity such as coronal mass ejections (CMEs). COSMO is comprised of
3 instruments: 1) a 1.5 m coronagraph dedicated to the study of coronal
magnetic fields; 2) a chromospheric and prominence magnetometer; and 3)
a K-coronagraph designed to study the formation of CMEs and the density
structure of the low corona. The National Center for Atmospheric
Research (NCAR) is fully funding the COSMO K-coronagraph which will
be deployed at the end of 2012. It will observe the white light solar
corona from 1.05 to 3 solar radii at 15 second time cadence in order to
the formation of coronal mass ejections (CMEs) and their interactions
with surrounding coronal structures and related activity (e.g. flares,
prominence eruptions and shock waves). The COSMO K-coronagraph will
replace the aging Mauna Loa Solar Observatory (MLSO) K-coronameter which
has been in operation since 1980. The High Altitude Observatory
(HAO) is funding the design and fabrication of the prototype for the
chromospheric magnetometer. This prototype will include the narrow-band
fully tunable Lyot filter capable of observing from the optical
into the near infrared that is required by the COSMO Chromospheric
Magnetometer. The prototype for the COSMO 1.5 m coronagraph is
the Coronal Multi-Channel Polarimeter (CoMP), designed and funded by
HAO and NCAR. Scientific results from this fully operational prototype
have been reported (e.g. Tomczyk et al. 2007). CoMP has recently been
deployed to MLSO for full time operations (see poster by Sitongia et
al.) The COSMO facility will be designed, built and operated by
the High Altitude Observatory of the National Center for Atmospheric
Research in collaboration with the University of Hawaii and the
University of Michigan. It will replace the current Mauna Loa Solar
Observatory which has been collecting observations of the corona,
chromosphere and photosphere since 1945. NCAR science is supported by
the National Science Foundation (NSF).

---------------------------------------------------------
Title: Wavelength-diverse polarization modulators for Stokes
polarimetry
Authors: Tomczyk, Steven; Casini, Roberto; de Wijn, Alfred G.; Nelson,
Peter G.
2010ApOpt..49.3580T Altcode: 2010arXiv1006.3581T
Information about the three-dimensional structure of solar magnetic
fields is encoded in the polarized spectra of solar radiation by a host
of physical processes. To extract this information, solar spectra must
be obtained in a variety of magnetically sensitive spectral lines at
high spatial, spectral, and temporal resolution with high precision. The
need to observe many different spectral lines drives the development
of Stokes polarimeters with a high degree of wavelength diversity. We
present a new paradigm for the design of polarization modulators that
operate over a wide wavelength range with near optimal polarimetric
efficiency and are directly applicable to the next generation of
multi-line Stokes polarimeters. These modulators are not achromatic
in the usual sense because their polarimetric properties vary with
wavelength, but they do so in an optimal way. Thus we refer to
these modulators as polychromatic. We present here the theory behind
polychromatic modulators, illustrate the concept with design examples,
and present the performance properties of a prototype polychromatic
modulator.

---------------------------------------------------------
Title: Fabry-Pérot Versus Slit Spectropolarimetry of Pores and
Active Network: Analysis of IBIS and Hinode Data
Authors: Judge, Philip G.; Tritschler, Alexandra; Uitenbroek, Han;
Reardon, Kevin; Cauzzi, Gianna; de Wijn, Alfred
2010ApJ...710.1486J Altcode: 2010arXiv1001.0561J
We discuss spectropolarimetric measurements of photospheric (Fe I
630.25 nm) and chromospheric (Ca II 854.21 nm) spectral lines in and
around small magnetic flux concentrations, including a pore. Our
long-term goal is to diagnose properties of the magnetic field
near the base of the corona. We compare ground-based two-dimensional
spectropolarimetric measurements with (almost) simultaneous space-based
slit spectropolarimetry. We address the question of noise and crosstalk
in the measurements and attempt to determine the suitability of Ca II
measurements with imaging spectropolarimeters for the determination
of chromospheric magnetic fields. The ground-based observations
were obtained 2008 May 20, with the Interferometric Bidimensional
Spectrometer (IBIS) in spectropolarimetric mode operated at the Dunn
Solar Telescope at Sunspot, NM. The space observations were obtained
with the Spectro-Polarimeter of the Solar Optical Telescope aboard the
Japanese Hinode satellite. The agreement between the near-simultaneous
co-spatial IBIS and Hinode Stokes-V profiles at 630.25 nm is
excellent, with V/I amplitudes compatible to within 1%. The IBIS QU
measurements are affected by residual crosstalk from V, arising from
calibration inaccuracies, not from any inherent limitation of imaging
spectroscopy. We use a Principal Component Analysis to quantify the
detected crosstalk. QU profiles with V crosstalk subtracted are in
good agreement with the Hinode measurements, but are noisier owing to
fewer collected photons. Chromospheric magnetic fields are notoriously
difficult to constrain by polarization of Ca II lines alone. However,
we demonstrate that high cadence, high angular resolution monochromatic
images of fibrils in Ca II and Hα, seen clearly in IBIS observations,
can be used to improve the magnetic field constraints, under conditions
of high electrical conductivity. Such work is possible only with time
series data sets from two-dimensional spectroscopic instruments such
as IBIS, under conditions of good seeing.

---------------------------------------------------------
Title: On the propagation of p-modes into the solar chromosphere
Authors: de Wijn, A. G.; McIntosh, S. W.; De Pontieu, B.
2010MmSAI..81..588D Altcode:
We employ tomographic observations of a small region of plage to study
the propagation of waves from the solar photosphere to the chromosphere
using a Fourier phase-difference analysis. Our results show the expected
vertical propagation for waves with periods of 3 minutes. Waves with
5-minute periods, i.e., above the acoustic cut-off period, are found to
propagate only at the periphery of the plage, and only in the direction
in which the field can be reasonably expected to expand. We conclude
that field inclination is critically important in the leakage of p-mode
oscillations from the photosphere into the chromosphere.

---------------------------------------------------------
Title: Hinode's SP and G-band Co-Alignment
Authors: Centeno, R.; Lites, B.; de Wijn, A. G.; Elmore, D.
2009ASPC..415..323C Altcode: 2009arXiv0902.0027C
We analyze the co-alignment between Hinode's BFI-Gband images and
simultaneous SP maps with the aim of characterizing the general off-sets
between them and the second order non-linear effects in SP's slit
scanning mechanism. We provide calibration functions and parameters
to correct for the nominal pixel scales and positioning

---------------------------------------------------------
Title: On the Relationship Between Magnetic Field and Mesogranulation
Authors: de Wijn, A. G.; Müller, D.
2009ASPC..415..211D Altcode: 2009arXiv0902.1967D
We investigate the relation between Trees of Fragmenting Granules
(TFGs) and the locations of concentrated magnetic flux in
internetwork areas. The former have previously been identified with
mesogranulation. While a relationship has been suggested to exist
between these features, no direct evidence has yet been provided. We
present some preliminary results that show that concentrated magnetic
flux indeed collects on the borders of TFGs.

---------------------------------------------------------
Title: Statistics of Convective Collapse Events in the Photosphere
and Chromosphere Observed with the HINODE SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
Keller, C. U.
2009ASPC..415..127F Altcode:
Convective collapse, a theoretically predicted process that
intensifies existing weak magnetic fields in the solar atmosphere,
was first directly observed in a single event by Nagata et al. (2008)
using the high resolution Solar Optical Telescope (SOT) of the Hinode
satellite. Using the same space telescope, we observed 49 such events
and present a statistical analysis of convective collapse events. Our
data sets consist of high resolution time series of polarimetric
spectral scans of two iron lines formed in the lower photosphere and
filter images in Mg I b2 and Ca II H. We were thus able
to study the implication of convective collapse events on the high
photospheric and the chromospheric layers. The physical parameters from
the full Stokes profiles were obtained with the MERLIN Milne-Eddington
inversion code. For each of the 49 events we determined the duration,
maximum photospheric downflow, and field strength increase. We found
event durations of about 10 minutes and field strengths of up to
1.65 kG.

---------------------------------------------------------
Title: Observations of Large-Scale Dynamic Bubbles in Prominences
Authors: de Toma, G.; Casini, R.; Berger, T. E.; Low, B. C.; de Wijn,
A. G.; Burkepile, J. T.; Balasubramaniam, K. S.
2009ASPC..415..163D Altcode:
Solar prominences are very dynamic objects, showing continuous motions
down to their smallest resolvable spatial and temporal scales. However,
as macroscopic magnetic structures, they are remarkably stable during
their quiescent phase. We present recent ground-based and Hinode
observations of large-scale bubble-like, dynamic sub-structures that
form within and rise through quiescent prominences without disrupting
them. We investigate the similarities and differences of the Hinode
and ground-based observations and discuss their implications for models
of prominences.

---------------------------------------------------------
Title: Interactions Between Reversed Granulation, p-Modes, and
Magnetism?
Authors: de Wijn, A. G.; McIntosh, S. W.; de Pontieu, B.
2009ASPC..415...36D Altcode: 2009arXiv0902.1966D
We investigate features that are observed in Ca II H sequences from
Hinode in places where reversed granulation seems to interact with
p-modes. These features appear ubiquitously in the quiet sun. They
are co-spatial with reversed granulation, and display similar
general properties, but have sharper edges and show fast brightness
changes. They also appear predominantly above wide intergranular
lanes, indicating a potential connection with magnetism. We report on
the appearance and dynamics of these features using high-resolution,
high-cadence observations from Hinode, and we discuss their possible
origin.

---------------------------------------------------------
Title: On the Propagation of p-Modes Into the Solar Chromosphere
Authors: de Wijn, A. G.; McIntosh, S. W.; De Pontieu, B.
2009ApJ...702L.168D Altcode: 2009arXiv0908.1383D
We employ tomographic observations of a small region of plage to study
the propagation of waves from the solar photosphere to the chromosphere
using a Fourier phase-difference analysis. Our results show the expected
vertical propagation for waves with periods of 3 minutes. Waves with
5 minute periods, i.e., above the acoustic cutoff period, are found to
propagate only at the periphery of the plage, and only in the direction
in which the field can be reasonably expected to expand. We conclude
that field inclination is critically important in the leakage of p-mode
oscillations from the photosphere into the chromosphere.

---------------------------------------------------------
Title: Statistics of convective collapse events in the photosphere
and chromosphere observed with the Hinode SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
Keller, C. U.
2009A&A...504..583F Altcode: 2009arXiv0906.2308F
Convective collapse, a theoretically predicted process that intensifies
existing weak magnetic fields in the solar atmosphere, was first
directly observed in a single event by Nagata et al. (2008, ApJ,
677, L145) using the high resolution Solar Optical Telescope (SOT)
of the Hinode satellite. Using the same space telescope, we observed
49 such events and present a statistical analysis of convective
collapse events. Our data sets consist of high resolution time series
of polarimetric spectral scans of two iron lines formed in the lower
photosphere and filter images in Mg I b{2} and Ca II H, spectral lines
that are formed in the high photosphere and the lower chromosphere,
respectively. We were thus able to study the implication of convective
collapse events on the high photospheric and the chromospheric
layers. We found that in all cases, the event was accompanied by a
continuum bright point and nearly always by a brightening in the Ca
II H images. The magnesium dopplergram exhibits a strong downflow in
about three quarters of the events that took place within the field
of view of the magnesium dopplergram. The physical parameters from
the full Stokes profiles were obtained with the MERLIN Milne-Eddington
inversion code. For each of the 49 events we determined the duration,
maximum photospheric downflow, field strength increase and size. We
found event durations of about 10 min, magnetic element radii of about
0.43 arcsec and 0.35 arcsec, before and after the event, respectively,
and field strengths of up to 1.65 kG.

---------------------------------------------------------
Title: Direct Imaging of Fine Structure in the Chromosphere of a
Sunspot Umbra
Authors: Socas-Navarro, H.; McIntosh, S. W.; Centeno, R.; de Wijn,
A. G.; Lites, B. W.
2009ApJ...696.1683S Altcode: 2008arXiv0810.0597S
High-resolution imaging observations from the Hinode spacecraft in the
Ca II H line are employed to study the dynamics of the chromosphere
above a sunspot. We find that umbral flashes and other brightenings
produced by the oscillation are extremely rich in fine structure,
even beyond the resolving limit of our observations (0farcs22). The
umbra is tremendously dynamic to the point that our time cadence of
20 s does not suffice to resolve the fast lateral (probably apparent)
motion of the emission source. Some bright elements in our data set
move with horizontal propagation speeds of 30 km s-1. We have
detected filamentary structures inside the umbra (some of which have a
horizontal extension of ~1500 km) which, to our best knowledge, had not
been reported before. The power spectra of the intensity fluctuations
reveal a few distinct areas with different properties within the umbra
that seem to correspond with the umbral cores that form it. Inside
each one of these areas the dominant frequencies of the oscillation
are coherent, but they vary considerably from one core to another.

---------------------------------------------------------
Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
2009SSRv..144..275D Altcode: 2008SSRv..tmp..190D; 2008SSRv..tmp..191D; 2008arXiv0812.4465D
As we resolve ever smaller structures in the solar atmosphere,
it has become clear that magnetism is an important component of
those small structures. Small-scale magnetism holds the key to many
poorly understood facets of solar magnetism on all scales, such as the
existence of a local dynamo, chromospheric heating, and flux emergence,
to name a few. Here, we review our knowledge of small-scale photospheric
fields, with particular emphasis on quiet-sun field, and discuss the
implications of several results obtained recently using new instruments,
as well as future prospects in this field of research.

---------------------------------------------------------
Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
2009odsm.book..275D Altcode:
As we resolve ever smaller structures in the solar atmosphere,
it has become clear that magnetism is an important component of
those small structures. Small-scale magnetism holds the key to many
poorly understood facets of solar magnetism on all scales, such as the
existence of a local dynamo, chromospheric heating, and flux emergence,
to name a few. Here, we review our knowledge of small-scale photospheric
fields, with particular emphasis on quiet-sun field, and discuss the
implications of several results obtained recently using new instruments,
as well as future prospects in this field of research.

---------------------------------------------------------
Title: Hinode Observations of Magnetic Elements in Internetwork Areas
Authors: de Wijn, A. G.; Lites, B. W.; Berger, T. E.; Frank, Z. A.;
Tarbell, T. D.; Ishikawa, R.
2008ApJ...684.1469D Altcode: 2008arXiv0806.0345D
We use sequences of images and magnetograms from Hinode to
study magnetic elements in internetwork parts of the quiet solar
photosphere. Visual inspection shows the existence of many long-lived
(several hours) structures that interact frequently and may migrate
over distances of ~7 Mm over a period of a few hours. About a fifth
of the elements have an associated bright point in G-band or Ca
II H intensity. We apply a hysteresis-based algorithm to identify
elements. The algorithm is able to track elements for about 10 minutes
on average. Elements intermittently drop below the detection limit,
although the associated flux apparently persists and often reappears
some time later. We infer proper motions of elements from their
successive positions and find that they obey a Gaussian distribution
with an rms of 1.57 +/- 0.08 km s-1. The apparent flows
indicate a bias of about 0.2 km s-1 toward the network
boundary. Elements of negative polarity show a higher bias than elements
of positive polarity, perhaps as a result of the dominant positive
polarity of the network in the field of view or because of increased
mobility due to their smaller size. A preference for motions in X is
likely explained by higher supergranular flow in that direction. We
search for emerging bipoles by grouping elements of opposite polarity
that appear close together in space and time. We find no evidence
supporting Joy's law at arcsecond scales.

---------------------------------------------------------
Title: Chromospheric and Transition-Region Dynamics in Plage
Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J.
2007ASPC..368..137D Altcode:
We study the dynamical interaction of the solar chromosphere with
the transition region in mossy and non-mossy active-region plage. We
carefully align image sequences taken with the Transition Region And
Coronal Explorer (TRACE) in the ultraviolet passbands around 1550, 1600,
and 1700 Å and the extreme ultraviolet passbands at 171 and 195 Å. We
compute Fourier phase-difference spectra that are spatially averaged
separately over mossy and non-mossy plage to study temporal modulations
as a function of temporal frequency. The 1550 versus 171 Å comparison
shows zero phase difference in non-mossy plage. In mossy plage, the
phase differences between all UV and EUV passbands show pronounced
upward trends with increasing frequency, which abruptly changes
into zero phase difference beyond 4 -- 6 mHz. The phase difference
between the 171 and 195 Å sequences exhibits a shallow dip below 3
mHz and then also turns to zero phase difference beyond this value. We
attribute the various similarities between the UV and EUV diagnostics
that are evident in the phase-difference diagrams to the contribution
of the C IV resonance lines in the 1550 and 1600 Å passbands. The
strong upward trend at the lower frequencies indicates the presence of
upward-traveling disturbances. It points to correspondence between the
lower chromosphere and the upper transition region, perhaps by slow-mode
magnetosonic disturbances, or by a connection between chromospheric and
coronal heating mechanisms. The transition from this upward trend to
zero phase difference at higher frequencies is due to the intermittent
obscuration by fibrils that occult the foot points of hot loops,
which are bright in the EUV and C IV lines, in oscillatory manner.

---------------------------------------------------------
Title: Magnetic Patches in Internetwork Quiet Sun
Authors: De Wijn, Alfred; Lites, B.; Berger, T.; Shine, R.; Title,
A.; Katsukawa, Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Hinode Team
2007AAS...210.9412D Altcode: 2007BAAS...39Q.219D
We study strong flux elements in the quiet sun in the context of
the nature of quiet-sun magnetism, its coupling to chromospheric,
transition-region and coronal fields, and the nature of a local
turbulent dynamo. Strong, kilogauss flux elements show up intermittently
as small bright points in G-band and Ca II H images. Although
bright points have been extensively studied in the magnetic network,
internetwork magnetism has only come under scrutiny in recent years. A
full spectrum of field strengths seems to be ubiquitously present in
the internetwork at small spatial scales, with the stronger elements
residing in intergranular lanes. De Wijn et al. (2005) found that bright
points in quiet sun internetwork areas appear recurrently with varying
intensity and horizontal motion within long-lived patches that outline
cell patterns on mesogranular scales. They estimate that the "magnetic
patches" have a mean lifetime of nine hours, much longer than granular
timescales. We use multi-hour sequences of G-band and Ca II H images
as well as magnetograms recorded by the Hinode satellite to follow up
on their results. The larger field of view, the longer sequences, the
addition of magnetograms, and the absence of atmospheric seeing allows
us to better constrain the patch lifetime, to provide much improved
statistics on IBP lifetime, to compare IBPs to network bright points,
and to study field polarity of IBPs in patches and between nearby
patches. Hinode is an international project supported by JAXA,
NASA, PPARC and ESA. We are grateful to the Hinode team for all their
efforts in the design, build and operation of the mission.

---------------------------------------------------------
Title: Fourier Analysis of Active-Region Plage
Authors: de Wijn, A. G.; De Pontieu, B.; Rutten, R. J.
2007ApJ...654.1128D Altcode: 2007arXiv0706.2014D
We study the dynamical interaction of the solar chromosphere with
the transition region in mossy and nonmossy active-region plage. We
carefully align image sequences taken with the Transition Region And
Coronal Explorer (TRACE) in the ultraviolet passbands around 1550,
1600, and 1700 Å and the extreme ultraviolet passbands at 171 and 195
Å. We compute Fourier phase-difference spectra that are spatially
averaged separately over mossy and nonmossy plage to study temporal
modulations as a function of temporal frequency. The 1550 versus 171
Å comparison shows zero phase difference in nonmossy plage. In mossy
plage, the phase differences between all UV and EUV passbands show
pronounced upward trends with increasing frequency, which abruptly
changes into zero phase difference beyond 4-6 mHz. The phase difference
between the 171 and 195 Å sequences exhibits a shallow dip below 3
mHz and then also turns to zero phase difference beyond this value. We
attribute the various similarities between the UV and EUV diagnostics
that are evident in the phase-difference diagrams to the contribution
of the C IV resonance lines in the 1550 and 1600 Å passbands. The
strong upward trend at the lower frequencies indicates the presence of
upward-traveling disturbances. It points to correspondence between the
lower chromosphere and the upper transition region, perhaps by slow-mode
magnetosonic disturbances, or by a connection between chromospheric and
coronal heating mechanisms. The transition from this upward trend to
zero phase difference at higher frequencies is due to the intermittent
obscuration by fibrils that occult the footpoints of hot loops, which
are bright in the EUV and C IV lines, in an oscillatory manner.

---------------------------------------------------------
Title: Magnetic Patches in Internetwork Areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
Sütterlin, P.
2006ASPC..354...20D Altcode:
We present a study of internetwork magnetic elements that appear as
bright points in G-band (photosphere) and Ca II H (low chromosphere)
image sequences from the Dutch Open Telescope. Many bright points
appear intermittently in groups of long-lived structures that we call
“magnetic patches”. We develop an algorithm for the identification
of bright points and magnetic patches. The average internetwork bright
point lifetimes is measured to be 3.5 minutes in the G band, and 4.3
minutes in the Ca II H. We find an internetwork bright point number
density of 0.02 Mm^{-2} in the G-band sequence and 0.05 Mm^{-2} in
the Ca II H sequence. The bright points show a bimodal distribution
of the frame-to-frame horizontal velocities, with a peak at 0 km
s^{-1} and a wide hump centered around 1.2 km s^{-1}. The patches
last much longer than granular time scales (about nine hours) and
outline cell-like structures on mesogranular scale. We conclude that
transient internetwork bright points trace the locations of strong
magnetic fields that exist before the bright point appears and remain
after it disappears.

---------------------------------------------------------
Title: Fourier analysis of chromospheric and transition region
emission above active region plage
Authors: de Wijn, A. G.; de Pontieu, B.; Rutten, R. J.
2006AGUFMSH23B0364D Altcode:
We study the dynamical interaction of the solar chromosphere with the
transition region (TR) in mossy and non-mossy active region plage, and
find evidence for correlated brightness changes or upward travelling
disturbances between the low chromosphere and the upper transition
region. We carefully align image sequences taken with the Transition
Region and Coronal Explorer (TRACE) in the ultraviolet passbands around
1550, 1600 and 1700 Å\ (indicative of low chromosphere and low TR)
and the extreme ultraviolet passbands at 171 and 195 Å\ (indicative of
upper transition region). We compute Fourier phase-difference spectra
that are spatially averaged separately over mossy and non-mossy plage to
study temporal modulations as a function of temporal frequency. We find
that in non-mossy plage there is zero phase difference between 1550 Å\
and 171 Å. In mossy plage, the phase differences between all UV and EUV
passbands show pronounced upward trends with increasing frequency, which
abruptly changes into zero phase differences for frequencies beyond 4-6
mHz. The phase difference between the 171 and 195 Å\ sequences exhibits
a shallow dip below 3 mHz and then also turns to zero phase difference
beyond this value. We attribute some of the various similarities between
the UV and EUV diagnostics that are evident in the phase-difference
diagrams to the contribution of the C IV resonance lines in the 1550 and
1600 Å\ passbands. The strong upward trend at lower frequencies in the
phase difference between all UV passbands (including 1700 Å) and 171
Å\ indicates the presence of upward travelling disturbances. Since
1700 Å\ does not contain C IV emission (low TR), this points to a
correlation between brightness changes in the lower chromosphere and
the upper TR, perhaps by slow-mode disturbances, or by a connection
between chromospheric and coronal heating mechanisms. We find that
such correlated brightness changes first occur in the low chromosphere,
and are followed about 400 s later in the upper TR. The transition from
the upward trend in phase difference at low frequencies to zero phase
difference at higher frequencies is due to the intermittent obscuration
by fibrils. These chromospheric jets occult the footpoints of hot loops,
which are bright in the EUV and C IV lines, in oscillatory manner.

---------------------------------------------------------
Title: Dynamic fibrils in Hα and C IV
Authors: de Wijn, A. G.; De Pontieu, B.
2006A&A...460..309D Altcode: 2007arXiv0706.2011D
Aims.To study the interaction of the solar chromosphere with the
transition region, in particular active-region jets in the transition
region and their relation to chromospheric fibrils. Methods:
.We carefully align image sequences taken simultaneously in C iv with
the Transition Region and Coronal Explorer and in Hα with the Swedish
1-m Solar Telescope. We examine the temporal evolution of "dynamic
fibrils", i.e., individual short-lived active-region chromospheric
jet-like features in Hα. Results: .All dynamic fibrils appear
as absorption features in Hα that progress from the blue to the red
wing through the line, and often show recurrent behavior. Some of them,
but not all, appear also as bright features in C iv which develop at or
just beyond the apex of the Hα darkening. They tend to best resemble
the Hα fibril at +700 mÅ half a minute earlier. Conclusions:
.Dynamic chromospheric fibrils observed in Hα regularly correspond to
transition-region jets observed in the ultraviolet. This correspondence
suggests that some plasma associated with dynamic fibrils is heated
to transition-region temperatures.

---------------------------------------------------------
Title: Dynamics of fine structure in the solar chromosphere
Authors: de Wijn, A. G.
2006PhDT.......161D Altcode:
This thesis is concerned with the dynamics of fine structure of
the solar chromosphere and transition region, in both quiet sun and
active regions. It contains six chapters of observational studies. It
presents a study on the spatial structure and temporal dynamics of
reversed granulation; a study on the patterning of magnetic fields
in internetwork areas in the photosphere and chromosphere; a study
on oscillations in the chromosphere and transition region; a study on
the appearance of dynamic fibrils in the chromosphere and transition
region; and a study on the relation of the high photosphere to the
transition region.

---------------------------------------------------------
Title: Dynamics of fine structure in the solar chromosphere
Authors: de Wijn, Alfred Gustaf
2006PhDT.......180D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A. G.; de Pontieu, B.; Erdélyi, R.
2005ESASP.600E..14D Altcode: 2005ESPM...11...14D; 2005dysu.confE..14D
No abstract at ADS

---------------------------------------------------------
Title: a Comparison Between Spicules in Hα and CIV
Authors: de Wijn, A.; de Pontieu, B.; Erdélyi, R.
2005ESASP.596E..33D Altcode: 2005ccmf.confE..33D
No abstract at ADS

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. IV. Magnetic patches
in internetwork areas
Authors: de Wijn, A. G.; Rutten, R. J.; Haverkamp, E. M. W. P.;
Sütterlin, P.
2005A&A...441.1183D Altcode: 2007arXiv0706.2008D
We use G-band and Ca ii H image sequences from the Dutch Open
Telescope (DOT) to study magnetic elements that appear as bright
points in internetwork parts of the quiet solar photosphere and
chromosphere. We find that many of these bright points appear
recurrently with varying intensity and horizontal motion within
longer-lived magnetic patches. We develop an algorithm for detection
of the patches and find that all patches identified last much longer
than the granulation. The patches outline cell patterns on mesogranular
scales, indicating that magnetic flux tubes are advected by granular
flows to mesogranular boundaries. Statistical analysis of the emergence
and disappearance of the patches points to an average patch lifetime
as long as 530±50~min (about nine hours), which suggests that the
magnetic elements constituting strong internetwork fields are not
generated by a local turbulent dynamo.

---------------------------------------------------------
Title: Dynamics of the solar chromosphere. V. High-frequency
modulation in ultraviolet image sequences from TRACE
Authors: de Wijn, A. G.; Rutten, R. J.; Tarbell, T. D.
2005A&A...430.1119D Altcode: 2007arXiv0706.1987D
We search for signatures of high-frequency oscillations in the upper
solar photosphere and low chromosphere in the context of acoustic
heating of outer stellar atmospheres. We use ultraviolet image
sequences of a quiet center-disk area from the Transition Region
and Coronal Explorer (TRACE) mission which were taken with strict
cadence regularity. The latter permits more reliable high-frequency
diagnosis than in earlier work. Spatial Fourier power maps, spatially
averaged coherence and phase-difference spectra, and spatio-temporal
(kh,f) decompositions all contain high-frequency features
that at first sight seem of considerable intrinsic interest but actually
are more likely to represent artifacts of different nature. Spatially
averaged phase difference measurement provides the most sensitive
diagnostic and indicates the presence of acoustic modulation up to
f≈20 mHz (periods down to 50 s) in internetwork areas.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. II. Reversed
granulation in Ca II H
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.
2004A&A...416..333R Altcode:
High-quality simultaneous image sequences from the Dutch Open Telescope
(DOT) in the G band and the Ca II H line are used to quantify the
occurrence of reversed granulation as a constituent of the subsonic
brightness pattern observed as a background to acoustic oscillations
in the quiet-Sun internetwork atmosphere. In the middle photosphere
reversed granulation constitutes a much larger part of this background
than at the larger heights sampled by ultraviolet radiation. The
anticorrelation with the underlying granulation reaches about 50% at a
temporal delay of 2-3 min, and increases with spatial image smoothing to
mesogranular resolution. We discuss the nature of reversed granulation
in terms of convection reversal, gravity waves, acoustic waves, and
intergranular magnetism, suggest that the internetwork background
pattern is primarily a mixture of the first two ingredients, and
speculate that it is also an inverse canopy mapper.

---------------------------------------------------------
Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
K.; de Wijn, A. G.
2004IAUS..223..597R Altcode: 2005IAUS..223..597R
The Dutch Open Telescope (DOT) on La Palma is an innovative solar
telescope combining open telescope structure and an open support tower
with a multi-wavelength imaging assembly and with synchronous speckle
cameras to generate high-resolution movies which sample different
layers of the solar atmosphere simultaneously and co-spatially at high
resolution over long durations. The DOT test and development phase is
nearly concluded. The installation of an advanced speckle processor
enables full science utilization including "Open-DOT" time allocation
to the international community. Co-pointing with spectropolarimeters
at other Canary Island telescopes and with TRACE furnishes valuable
Solar-B precursor capabilities.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. I. Telescope summary
and program definition
Authors: Rutten, R. J.; Hammerschlag, R. H.; Bettonvil, F. C. M.;
Sütterlin, P.; de Wijn, A. G.
2004A&A...413.1183R Altcode:
The Dutch Open Telescope (DOT) on La Palma is an innovative optical
solar telescope capable of reaching 0.2 arcsec angular resolution
over extended durations. The DOT presently progresses from technology
testbed to a stable science configuration providing multi-wavelength
imaging and multi-camera speckle data acquisition for tomographic
mapping of the solar atmosphere. Large-volume speckle processing will
soon enable frequent usage and community-wide time allocation, in
particular for tandem operation with other solar telescopes pursuing
spectropolarimetry and EUV imaging. We summarize the DOT hardware and
software in the context of this increasing availability and outline
the corresponding “open-DOT” program.

---------------------------------------------------------
Title: Intensity Oscillations in the upper transition region above
active region plage
Authors: de Pontieu, B.; Erdelyi, R.; de Wijn, A.; Loefdahl, M.
2003AGUFMSH42B0540D Altcode:
Although there are now many observations showing the presence
of oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (so-called
moss) above active region plage. Here we report on a wavelet analysis
of observations (made with TRACE, the Transition Region and Coronal
Explorer) of strong ( ∼ 5-15%) intensity oscillations in the upper
TR footpoints of hot coronal loops. They show a range of periods from
200 to 600 seconds, typically persisting for 4 to 7 cycles. These
oscillations are not associated with sunspots, as they usually occur at
the periphery of plage regions. A majority of the upper TR oscillations
are directly associated with upper chromospheric oscillations observed
in Hα , i.e., periodic flows in spicular structures. The presence of
such strong oscillations at low heights (of order 3,000 km) provides
an ideal opportunity to study the propagation of oscillations from
photosphere and chromosphere into the TR and corona, and improve
our understanding of the magnetic connectivity in the chromosphere
and TR. In addition, we use new high resolution observations of the
photosphere and chromosphere, taken with the Swedish Solar Telescope, to
shed light on the source of chromospheric mass flows such as spicules.

---------------------------------------------------------
Title: Intensity Oscillations in the Upper Transition Region above
Active Region Plage
Authors: De Pontieu, B.; Erdélyi, R.; de Wijn, A. G.
2003ApJ...595L..63D Altcode:
Although there are now many observations showing the presence of
oscillations in the corona, almost no observational studies have
focused on the bright upper transition region (TR) emission (the
so-called moss) above active region plage. Here we report on a wavelet
analysis of observations (made with the Transition Region and Coronal
Explorer) of strong (~5%-15%) intensity oscillations in the upper TR
footpoints of hot coronal loops. They show a range of periods from 200
to 600 s, typically persisting for 4-7 cycles. These oscillations are
not associated with sunspots, as they usually occur at the periphery
of plage regions. A preliminary comparison to photospheric vertical
velocities (using the Michelson Doppler Imager on board the Solar and
Heliospheric Observatory) reveals that some upper TR oscillations
show a correlation with p-modes in the photosphere. In addition,
a majority of the upper TR oscillations are directly associated with
upper chromospheric oscillations observed in Hα, i.e., periodic flows
in spicular structures. The presence of such strong oscillations at
low heights (of the order of 3000 km) provides an ideal opportunity to
study the propagation of oscillations from photosphere and chromosphere
into the TR and corona. It can also help us understand the magnetic
connectivity in the chromosphere and TR and shed light on the source
of chromospheric mass flows such as spicules.

---------------------------------------------------------
Title: Motions of Isolated G-Band Bright Points in the Solar
Photosphere
Authors: Nisenson, P.; van Ballegooijen, A. A.; de Wijn, A. G.;
Sütterlin, P.
2003ApJ...587..458N Altcode: 2002astro.ph.12306N
Magnetic elements on the quiet Sun are buffeted by convective flows
that cause lateral motions on timescales of minutes. The magnetic
elements can be observed as bright points (BPs) in the G band at 4305
Å. We present observations of BPs based on a long sequence of G-band
images recorded with the Dutch Open Telescope and postprocessed using
speckle-masking techniques. From these images we measured the proper
motions of isolated BPs and derived the autocorrelation function of
their velocity relative to the solar granulation pattern. The accuracy
of BP position measurements is estimated to be less than 23 km on
the Sun. The rms velocity of BPs (corrected for measurement errors)
is about 0.89 km s-1, and the correlation time of BP motions
is about 60 s. This rms velocity is about 3 times the velocity measured
using cork tracking, almost certainly due to the fact that isolated BPs
move more rapidly than clusters of BPs. We also searched for evidence
of vorticity in the motions of G-band BPs.

---------------------------------------------------------
Title: Dutch Open Telescope: status, results, prospects
Authors: Rutten, Robert J.; Sütterlin, Peter; de Wijn, Alfred G.;
Hammerschlag, Robert H.; Bettonvil, Felix C. M.; Hoogendoorn, Piet W.;
Jägers, Aswin P. L.
2002ESASP.506..903R Altcode: 2002svco.conf..903R; 2002ESPM...10..903R
The Dutch Open Telescope (DOT) on La Palma is a revolutionary telescope
achieving high-resolution imaging of the solar surface. The DOT combines
a pioneering open design at an excellent wind-swept site with image
restoration through speckle interferometry. Its open principle is now
followed in major solar-telescope projects elsewhere. In the past three
years the DOT became the first solar telescope to regularly obtain 0.2"
resolution in extended image sequences, i.e., reaching the diffraction
limit of its 45-cm primary mirror. Our aim for 2003-2005 is to turn
the DOT into a 0.2" tomographic mapper of the solar atmosphere with
frequent partnership in international multi-telescope campaigns through
student-serviced time allocation. After 2005 we aim to triple the DOT
resolution to 0.07" by increasing the aperture to 140 cm and to renew
the speckle cameras and the speckle pipeline in order to increase
the field size and sequence duration appreciably. These upgrades will
maintain the DOT's niche as a tomographic high-resolution mapper in
the era when GREGOR, Solar-B and SDO set the stage.

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Title: Opening the Dutch Open Telescope
Authors: Rutten, R. J.; de Wijn, A. G.; Sütterlin, P.; Bettonvil,
F. C. M.; Hammerschlag, R. H.
2002ESASP.505..565R Altcode: 2002IAUCo.188..565R; 2002solm.conf..565R
We hope to "open the DOT" to the international solar physics
community as a facility for high-resolution tomography of the solar
atmosphere. Our aim is to do so combining peer-review time allocation
with service-mode operation in a "hands-on-telescope" education
program bringing students to La Palma to assist in the observing and
processing. The largest step needed is considerable speedup of the
DOT speckle processing.