explanation blue bibcodes open ADS page with paths to full text
Author name code: rabin
ADS astronomy entries on 2022-09-14
author:"Rabin, Douglas M."
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Title: First Imaging Spectroscopy of 92-115 Angstrom Solar Soft
X-rays by EUNIS: Implications for Solar Coronal Heating
Authors: Brosius, Jeffrey; Daw, Adrian; Rabin, Douglas; Landi, Enrico;
Schmit, Donald
2021AGUFMSH12B..04B Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket waslaunched from White Sands Missile Range, NM, on
May 18, 2021. The instrumentcomprised a pair of coaligned imaging
spectrographs, one of which observed solarline emission in first
order at wavelengths between 525 and 639 A, and the secondof which
observed line emission in third order at wavelengths between 92 and
115 Aand in first order between 277 and 345 A. Images of AR 12824,
quiet-sun area, andoff-limb area were obtained by rastering the slits
over the selected targets. Thisis the first time that solar imaging
spectroscopy has been performed in the 92-115A soft X-ray range. This
waveband was selected to (1) observe Fe XVIII 93.932 and103.948 A
and Fe XIX 108.355 A line emission in a quiescent active region, and
(2)explore a relatively unobserved portion of the solar electromagnetic
spectrum. Theinstrument performed well during its 6-minute observing
run. We report preliminaryresults on observations of Fe XVIII and Fe
XIX in the quiescent active region, anddiscuss implications for the
nanoflare model of solar coronal heating. EUNIS wassupported by NASA
Heliophysics Low Cost Access to Space award 13-HTIDS13_2-0074.
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Title: Distributed Space Telescopes Enabled by Constellation of
Small Satellites
Authors: Kamalabadi, Farzad; Lightsey, E.; Rabin, Douglas; Daw,
Adrian; D'Amico, Simone; Koenig, Adam; Chamberlin, Philip; Woods,
Thomas; Gupta, Subhanshu; Ekici, Eylem; Sample, John; Park, Hyeongjun;
Alexeenko, Alina; Hwang, John; Denis, Kevin; Klimchuk, James
2021AGUFM.A33C..03K Altcode:
New pathways to high-resolution sensing and imaging for a multitude
of high-priority scientific investigations are being realized by small
multi-spacecraft systems. Such pathfinder mission concepts circumvent
the limitations of conventional remote sensing/imaging systems by
utilizing multiple baselines, synthesized apertures, diffractive
optics, combined with computational imaging via interferometry,
tomography, or super-resolution. Regardless of the specific scientific
questions targeted, such small satellite constellation pathfinders
require technological breakthroughs in precision formation flying
and associated advances in guidance, navigation, and control;
proximity operations and associated autonomy and robust orbit
design with passive safety; innovations in sensor miniaturization;
inter-satellite communication; and sophisticated computational sensing
and reconstruction algorithms. We describe recent advances in such
enabling technologies in the context of a scalable ultra-high-resolution
spectral imaging mission for investigating the solar corona currently
under development by a multi-university consortium in collaboration
with NASA and under sponsorship by NSF.
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Title: Solar Coronagraphs
Authors: Rabin, Douglas
2021hai3.book..339R Altcode:
No abstract at ADS
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Title: Photon sieves and the future of EUV imaging spectroscopy
Authors: Daw, Adrian N.; Rabin, Douglas M.; Schmit, Donald James;
Denis, Kevin
2019AAS...23412605D Altcode:
Large-aperture photon sieves fabricated at NASA-GSFC can provide
diffraction-limited imaging at EUV and X-ray wavelengths, that is,
spatial scales down to milli-arcseconds, and are also being used to
provide monochromatic, collimated beams for the calibration of solar
EUV instruments such as the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS). EUNIS is a two-channel imaging spectrograph
with unprecedented dynamic range and broad spectral coverage (9-11 nm
and 52-64 nm), scheduled for a sounding rocket flight in September
2019. This will be the first time the 9-11 nm wavelength range of
the Sun has ever been observed by an imaging spectrograph, despite
the importance of these short EUV/soft X-ray wavelengths to observing
the hottest (>5MK) plasma in the non-flaring atmosphere, which is
critical to understanding the energization of the solar corona. Recent
results will be presented, and capabilities for future solar EUV
missions will be discussed.
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Title: Ultrahigh-Resolution Imaging of the Solar Corona using a
Distributed Diffractive Telescope
Authors: Rabin, Douglas M.; Daw, Adrian N.; Denis, Kevin; Kamalabadi,
Farzad; Klimchuk, James A.
2019AAS...23410704R Altcode:
Several observational and theoretical considerations suggest that
energy is often released in the solar corona on small spatial scales
of order 100 km. It has been a longstanding goal of solar physics to
subject this hypothesis to direct observational test. However, extreme
ultraviolet (EUV) and soft x-ray (SXR) telescopes rarely approach
diffraction-limited performance because conventional reflective optics
of adequate size typically cannot be manufactured to the requisite
figure accuracy. Diffractive optics can overcome the angular-resolution
limitations of EUV/SXR mirrors. We describe a mission approach that
employs diffractive optics and small satellites flying in formation
to form a distributed solar telescope operating at EUV wavelengths.
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Title: Ultrahigh-Resolution Solar Imaging with Diffractive Optics
Authors: Rabin, Douglas; Davila, Joseph M.; Daw, Adrian Nigel; Denis,
Kevin; Shah, Neerav; Mason, Emily; Novo-Gradac, Anne-Marie; Widmyer,
Thomas
2018tess.conf40443R Altcode:
Extreme ultraviolet (EUV) and soft X-ray (SXR) telescopes rarely achieve
diffraction-limited performance because conventional reflective optics
of the required size typically cannot be manufactured to the requisite
figure accuracy. Diffractive optics can overcome the angular-resolution
limitations of EUV/SXR mirrors but present other design and performance
challenges. A diffractive telescope is well-suited for probing for the
first time the expected energy dissipation scales of the solar corona
(<100 km). We have previously described the fabrication of photon
sieves and Fresnel zone plates as large as 80-mm clear aperture,
as well as laboratory measurements and vibration testing. Here we
report on the design of more efficient phase zone plates, the path
to larger apertures, and our approach to a virtual telescope based on
formation-flying smallsats.
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Title: Building a Futuristic Telescope on the Moon - A Fun Project
for Research, Science Teaching, and Outreach
Authors: Chen, Peter C.; Rabin, Douglas M.; Haas, J. Patrick;
Mirel, Paul
2018AAS...23136107C Altcode:
We present the design and demonstrate the operation of a model
lunar observatory. While this is a research project, it is also
intended to stimulate student interest in space science, astronomy,
physics, chemistry, and engineering. First, we discuss the science
objectives of a lunar observatory. The Moon is a great location for
astronomy. Why? What science can best be done from there? What are
exoplanets? We would like to see what planets around other stars
look like. Why is it so difficult? What are optical interferometers
and why do we need them? Next, we discuss the physics, chemistry,
and engineering principles involved. The lunar environment is totally
different from Earth. It features high vacuum, low gravity, very slow
rotation rate, cryogenic temperatures, and dust. How can an observatory
be designed that not only survives, but can take advantage of the
environment? We present a “cool” solution (the model uses liquid
nitrogen) that combines the following elements: high temperature
superconductors, telescope mirrors made of “moondust”, novel
telescope support system, an observatory structure made of simulated
lunar soil, 3D printing, and methods for dust mitigation. Information
will be provided on how similar systems can be built and what further
refinements (e.g. voice control, precision stepper drives, autonomous
operation, and telerobotics) can be added.
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Title: Mission Concepts for High-Resolution Solar Imaging with a
Photon Sieve
Authors: Rabin, Douglas M.; Davila, Joseph; Daw, Adrian N.; Denis,
Kevin L.; Novo-Gradac, Anne-Marie; Shah, Neerav; Widmyer, Thomas R.
2017SPD....4811006R Altcode:
The best EUV coronal imagers are unable to probe the expected
energy dissipation scales of the solar corona (<100 km) because
conventional optics cannot be figured to near diffraction-limited
accuracy at these wavelengths. Davila (2011) has proposed that a
photon sieve, a diffractive imaging element similar to a Fresnel zone
plate, provides a technically feasible path to the required angular
resolution. We have produced photon sieves as large as 80 mm clear
aperture. We discuss laboratory measurements of these devices and the
path to larger apertures. The focal length of a sieve with high EUV
resolution is at least 10 m. Options for solar imaging with such a
sieve include a sounding rocket, a single spacecraft with a deployed
boom, and two spacecraft flying in precise formation.
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Title: Electron temperature maps of the low solar corona: ISCORE
results from the total solar eclipse of 1 August 2008 in China
Authors: Reginald, Nelson L.; Davila, Joseph M.; St. Cyr, Orville C.;
Rabin, Douglas M.
2017JGRA..122.5856R Altcode:
We conducted an experiment in conjunction with the total solar eclipse
of 1 August 2008 in China to determine the thermal electron temperature
in the low solar corona close to the solar limb. The instrument, Imaging
Spectrograph of Coronal Electrons (ISCORE), consisted of an 8 inch f/10
Schmidt Cassegrain telescope with a thermoelectrically cooled CCD camera
at the focal plane. Results are electron temperatures of 1 MK at 1.08
R<SUB>⊙</SUB> and 1.13 R<SUB>⊙</SUB> from the Sun center in the
polar and equatorial regions, respectively. This experiment confirms
the results of an earlier experiment conducted in conjunction with
the total eclipse of 29 March 2006 in Libya, and results are that at
a given coronal height the electron temperature in the polar region
is larger than at the equatorial region. In this paper we show the
importance of using the correct photospheric spectrum pertinent to
the solar activity phase at the time of the experiment, which is a
required parameter for modeling the underlying theoretical concept
for temperature interpretation of the measured intensity ratios using
color filters.
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Title: Detecting the Beacons of Life with Exo-Life Beacon Space
Telescope (ELBST)
Authors: Airapetian, V. S.; Danchi, W. C.; Chen, P. C.; Rabin, D. M.;
Carpenter, K. G.; Mlynczak, M. G.
2017LPICo1989.8214A Altcode:
We propose a new observational strategy, the “Exo-Life Beacon Space
Telescope,” for detecting the signatures of “beacons” of life
defined as high signal and low spectral resolution thermal emission
from molecules associated with life signatures.
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Title: Diffraction Analysis of Solar Coronagraphs
Authors: Rabin, Douglas M.; gong, qian
2016SPD....4730601R Altcode:
The design of a solar coronagraph is predicated on controlling
diffracted and scattered light using principles dating back to Bernard
Lyot in the 1930’s. The existence of many successful ground-
and space-based coronagraphs testifies to our ability to apply
these principles in specific cases, but it is difficult to explore
a significant range of design parameters because the calculations are
tricky and time-consuming. Indeed, scattered light is so design-specific
that ad hoc analysis is unavoidable once guidelines from experience
are used to create a first-guess system of baffles and low-scatter
surfaces. Here we describe a combination of analytic and computational
approaches that has the potential to explore coronagraph design space
somewhat more systematically with respect to diffracted light.
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Title: Milli-Arcsecond (MAS) Imaging of the Solar Corona
Authors: Davila, Joseph M.; Oktem, Figen S.; Kamalabadi, Farzad;
O'Neill, John; Novo-Gradac, Anne-Marie; Daw, Adrian N.; Rabin,
Douglas M.
2016SPD....47.0310D Altcode:
Dissipation in the solar corona is believed to occur in extremely
thin current sheets of order 1-100 km. Emission from these hot
but thin current sheets should be visible in coronal EUV emission
lines. However, this spatial scale is far below the resolution
of existing imaging instruments, so these dissipation sites have
never been observed individually. Conventional optics cannot be
manufactured with sufficient surface figure accuracy to obtain the
required spatial resolution in the extreme-ultraviolet where these
hot plasmas radiate. A photon sieve, a diffractive imaging element
similar to a Fresnel zone plate, can be manufactured to provide a
few milli-arcsec (MAS) resolution, with much more readily achievable
tolerances than with conventional imaging technology. Prototype photon
sieve elements have been fabricated and tested in the laboratory. A
full-scale ultra-high resolution instrument will require formation
flying and computational image deconvolution. Significant progress has
been made in overcoming these challenges, and some recent results in
these areas are discussed. A simple design for a sounding rocket concept
demonstration payload is presented that obtains 80 MAS (0.080 arcsec)
imaging with a 100 mm diameter photon sieve to image Fe XIV 334 and
Fe XVI 335. These images will show the structure of the corona at a
resolution never before obtained, and they will also allow a study of
the temperature structure in the dissipation region.
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Title: Evidence for Nanoflare Heating of the Solar Corona from the
EUNIS Sounding Rocket
Authors: Brosius, J. W.; Daw, A. N.; Rabin, D. M.
2015AGUFMSH31D..01B Altcode:
We present spatially resolved EUV spectroscopic measurements
ofpervasive, faint Fe XIX 592.2 A line emission in AR 11726,observed
during the 2013 April 23 flight of the Extreme UltravioletNormal
Incidence Spectrograph (EUNIS-13) sounding rocket instrument. With
cooled detectors, high sensitivity, and high spectralresolution,
EUNIS-13 resolves the lines of Fe XIX at 592.2 A (formedat temperature
T around 8.9 MK) and Fe XII at 592.6 A (T around 1.6MK). The Fe XIX
line emission, observed over an area in excess of4920 square arcsec
(2.58x10^9 square km, more than 60% of the activeregion), provides
strong evidence for the nanoflare heating model ofthe solar corona. No
GOES events occurred in the region less than 2hours before the rocket
flight, but a microflare was observed northand east of the region with
RHESSI and EUNIS during the flight. Theabsence of significant upward
velocities anywhere in the region,particularly the microflare, indicates
that the pervasive Fe XIXemission is not propelled outward from the
microflare site, but ismost likely attributed to localized heating (due
to reconnection,wave dissipation, or some other mechanism) consistent
with thenanoflare heating model of the solar corona. We measure average
FeXIX/Fe XII intensity ratios of 0.070 outside the AR core, 0.22 inarea
of bright coronal emission (the area in which the Fe XIIintensity
exceeds half its maximum observed value), and 0.55 in theregion's hot
core. Using the CHIANTI atomic physics database andassuming ionization
equilibrium, we estimate corresponding Fe XIX/FeXII emission measure
ratios of about 0.076, 0.23 and 0.59. Theemission measure ratios must
be viewed with caution in light oflingering uncertainties in the Fe XII
contribution functions.EUNIS-13 was supported by the NASA Heliophysics
Division through itsLow Cost Access to Space program.
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Title: A Geomagnetic Precursor Technique for Predicting the Solar
Activity Cycle
Authors: Sobel, E. I.; Rabin, D. M.
2015AGUFMSH23A2427S Altcode:
The Western hemisphere has been recording sunspot numbers since Galileo
discovered sunspots in the early 17th century, and the roughly 11-year
solar cycle has been recognized since the 19th century. However,
predicting the strength of any particular cycle remains a relatively
imprecise task. This project's aim was to update and improve a
forecasting technique based on geomagnetic precursors of future solar
activity The model is a refinement of R. J. Thompson's 1993 paper that
relates the number of geomagnetically disturbed days, as defined by
the aa and Ap indices, to the sum of the sunspot number in the current
and the previous cycle, Rn + Rn-1.[1] The method exploits the fact
that two cycles coexist for some period on the Sun near solar minimum
and therefore that the number of sunspots and disturbed days during
the declining phase of one cycle gives an indication of the following
cycle's strength. We wrote and updated IDL software procedures to define
disturbed days with varying threshold values and graphed Rn + Rn-1
against them. The aa threshold was derived from the Ap threshold. After
comparing the graphs for Ap values from 20 to 50, an Ap threshold of
30 and the corresponding aa threshold of 44 were chosen as yielding
the best correlation. Confidence regions were computed to provide a
quantitative uncertainty on future predictions. The 80% confidence
region gives a range of ±40 in sunspot number. <P />[1] Thompson,
R. J. (1993). A technique for predicting the amplitude of the solar
cycle. Solar Physics, 148, 2, 383-388.
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Title: EUNIS 2013: Unambiguous Evidence for Impulsive Coronal Heating,
Data Available
Authors: Daw, Adrian; Brosius, Jeffrey; Haas, J. Patrick; Plummer,
Thomas; Rabin, Douglas
2015TESS....120401D Altcode:
The broad spectral coverage (303-370 Å, 527-635 Å) and unprecedented
dynamic range of the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS) 2013 sounding rocket observations includes emission lines of
ionization stages from He I to Fe XX, and thus a wide temperature range
of 0.03 to 10 MK. Pervasive, faint Fe XIX 592 Å line emission was
observed in active regions. Comparison of observed line intensities
with calculations demonstrates that the Fe XIX emission, formed at
temperatures around 8 MK, is evidence of the faint hot emission
predicted by impulsive heating models of the solar corona (e.g.,
‘nano-flares’). The calibration and availability of the EUNIS-2013
dataset is discussed as well.
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Title: Carbon nanotube optical mirrors
Authors: Chen, Peter C.; Rabin, Douglas
2015JATIS...1a4005C Altcode:
We report the fabrication of imaging quality optical mirrors
with smooth surfaces using carbon nanotubes (CNT) embedded in an
epoxy matrix. CNT/epoxy is a multifunctional composite material
that has sensing capabilities and can be made to incorporate
self-actuation. Moreover, as the precursor is a low density liquid,
large and lightweight mirrors can be fabricated by processes such as
replication, spincasting, and three-dimensional printing. Therefore,
the technology holds promise for the development of a new generation of
lightweight, compact "smart" telescope mirrors with figure sensing and
active or adaptive figure control. We report on measurements made of
optical and mechanical characteristics, active optics experiments, and
numerical modeling. We discuss possible paths for future development.
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Title: New Approaches to Externally Occulted Coronagraphs
Authors: Rabin, D. M.; Chamberlin, P. C.; Davila, J. M.; Shah, N.
2014AGUFMSH53B4226R Altcode:
The rapidly advancing capabilities of low-cost space platforms
prompts us to reconsider concepts for externally occulted solar
coronagraphs. Placing the occulter on a separate platform offers
superior diffraction control but requires an analysis of alignment
and separation tolerances that is different from that applied to
conventional architectures. New forms of occulter (e.g., an inflatable
sphere or ellipsoid) have potential advantages such as low mass and
fabrication cost, simple deployment, and less stringent demands on
the relative alignment of the platforms. However, the diffraction
behavior of occulters that incorporate curved surfaces (Buffington
2000) is less explored than for edge-type occulters. We illustrate
the new possibilities by calculating the performance of some candidate
systems using an analytic framework adapted from radio wave propagation
(Vogler 1985) and alignment tolerances based on a recent concept for
a two-platform guidance, navigation, and control system.
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Title: Eunis Observation of Pervasive Faint Fe XIX Line Emission
from a Solar Active Region: Evidence for Coronal Heating By Nanoflares
Authors: Brosius, J. W.; Daw, A. N.; Rabin, D. M.
2014AGUFMSH13C4130B Altcode:
We present spatially resolved EUV spectroscopic measurements
ofpervasive, faint Fe XIX 592.2 A line emission in an active
regionobserved during the 2013 April 23 flight of the Extreme
UltravioletNormal Incidence Spectrograph (EUNIS-13) sounding
rocket instrument. With cooled detectors, high sensitivity, and
high spectralresolution, EUNIS-13 resolves the lines of Fe XIX at
592.2 A (formedat temperature T around 8.9 MK) and Fe XII at 592.6 A
(T around 1.6MK). The Fe XIX line emission, observed over an area
in excess of4920 square arcsec (2.58x10^9 square km, more than 60%
of the activeregion), provides strong evidence for the nanoflare
heating model ofthe solar corona. No GOES events occurred in the
region less than 2hours before the rocket flight, but a microflare
was observed northand east of the region with RHESSI and EUNIS during
the flight. Theabsence of significant upward velocities anywhere in
the region,particularly the microflare, indicates that the pervasive
Fe XIXemission is not propelled outward from the microflare site, but
ismost likely attributed to localized heating (due to reconnection,wave
dissipation, or some other mechanism) consistent with thenanoflare
heating model of the solar corona. We measure average FeXIX/Fe XII
intensity ratios of 0.070 outside the AR core, 0.22 inarea of bright
coronal emission (the area in which the Fe XIIintensity exceeds half
its maximum observed value), and 0.55 in theregion's hot core. Using
the CHIANTI atomic physics database andassuming ionization equilibrium,
we estimate corresponding Fe XIX/FeXII emission measure ratios of about
0.076, 0.23 and 0.59. Theemission measure ratios must be viewed with
caution in light oflingering uncertainties in the Fe XII contribution
functions.EUNIS-13 was supported by the NASA Heliophysics Division
through itsLow Cost Access to Space program.
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Title: Smart materials optical mirrors
Authors: Chen, Peter C.; Rabin, Douglas M.
2014SPIE.9143E..50C Altcode:
We report the fabrication of imaging quality optical mirrors with smooth
surfaces using carbon nanotubes embedded in an epoxy matrix. CNT/epoxy
is a multifunctional or `smart' composite material that has sensing
capabilities and can be made to incorporate self-actuation as
well. Moreover, since the precursor is a low density liquid, large and
lightweight mirrors can be fabricated by processes such as replication,
spincasting, and 3D printing. The technology therefore holds promise
for development of a new generation of lightweight, compact `smart'
telescope mirrors with figure sensing and active or adaptive figure
control. We report on measurements made of optical and mechanical
characteristics. We discuss possible paths for future development.
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Title: Pervasive Faint Fe XIX Emission from a Solar Active Region
Observed with EUNIS-13: Evidence for Nanoflare Heating
Authors: Brosius, Jeffrey W.; Daw, Adrian N.; Rabin, D. M.
2014ApJ...790..112B Altcode:
We present spatially resolved EUV spectroscopic measurements
of pervasive, faint Fe XIX 592.2 Å line emission in an active
region observed during the 2013 April 23 flight of the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS-13) sounding
rocket instrument. With cooled detectors, high sensitivity, and high
spectral resolution, EUNIS-13 resolves the lines of Fe XIX at 592.2 Å
(formed at temperature T ≈ 8.9 MK) and Fe XII at 592.6 Å (T ≈
1.6 MK). The Fe XIX line emission, observed over an area in excess
of 4920 arcsec<SUP>2</SUP> (2.58 × 10<SUP>9</SUP> km<SUP>2</SUP>,
more than 60% of the active region), provides strong evidence for the
nanoflare heating model of the solar corona. No GOES events occurred
in the region less than 2 hr before the rocket flight, but a microflare
was observed north and east of the region with RHESSI and EUNIS during
the flight. The absence of significant upward velocities anywhere in
the region, particularly the microflare, indicates that the pervasive
Fe XIX emission is not propelled outward from the microflare site, but
is most likely attributed to localized heating (not necessarily due
to reconnection) consistent with the nanoflare heating model of the
solar corona. Assuming ionization equilibrium we estimate Fe XIX/Fe
XII emission measure ratios of ~0.076 just outside the AR core and
~0.59 in the core.
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Title: Composite telescope technology
Authors: Chen, Peter C.; Rabin, Douglas
2014SPIE.9151E..30C Altcode:
We report the development of optical mirrors based on polymer matrix
composite materials. Advantages of this technology are low cost and
versatility. By using appropriate combinations of polymers and various
metallic and nonmetallic particles and fibers, the properties of the
materials can be tailored to suit a wide variety of applications. We
report the fabrication and testing of flat and curved mirrors made
with metal powders, multiple mirrors replicated with high degree of
uniformity from the same mandrels, cryogenic testing, mirrors made of
ferromagnetic materials that can be actively or adaptively controlled
by non-contact actuation, optics with very smooth surfaces made by
replication, and by spincasting. We discuss development of a new
generation of ultra-compact, low power active optics and 3D printing
of athermal telescopes.
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Title: Further Analysis of Active Region Thermal Structure from
EUNIS-13
Authors: Rabin, Douglas M.; Landi, Enrico; Daw, Adrian N.; Brosius,
Jeffrey W.
2014AAS...22432339R Altcode:
The 2013 April 23 flight of the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument returned high-quality
spectra in two wavelength bands, 30.0-37.0 nm and 52.7-63.5 nm, sampling
three active regions (11723, 11724, and 11726). The spectral lines
in these bands probe a wide temperature range, 0.03 MK to 8 MK. We
have demonstrated that the differential emission measure (DEM) varies
significantly between different sub-regions of AR 11726. We extend
this analysis to ARs 11723 and 11724 and include a wider selection of
spectral lines to delineate better the variations in thermal structure.
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Title: Evidence for Impulsive Coronal Heating from EUNIS 2013
Authors: Daw, Adrian N.; Brosius, Jeffrey W.; Rabin, Douglas M.;
Landi, Enrico; Klimchuk, James A.
2014AAS...22431204D Altcode:
Pervasive, faint Fe XIX 592 Å line emission was observed in active
regions by the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket instrument on 23 April 2013. The broad spectral coverage
(303-370 Å, 527-635 Å) and unprecedented dynamic range of the EUNIS
observations includes emission lines of ionization stages from He I to
Fe XX, and thus a wide temperature range of 0.03 to 10 MK. Comparison
of observed line intensities with calculations demonstrates that the
Fe XIX emission, formed at temperatures around 8 MK, is evidence of
the faint hot emission predicted by impulsive heating models of the
solar corona (such as nanoflares).
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Title: EUNIS 2013 and Beyond: Resolving the AIA 94 and 131 Å
Bandpasses
Authors: Daw, Adrian N.; Brosius, J. W.; Haas, J. P.; Landi, E.;
Plummer, T.; Rabin, D. M.; Wang, T.
2013SPD....44...10D Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument is a two-channel imaging spectrograph that observes
the solar corona and transition region with high spectral resolution
and a rapid cadence made possible by unprecedented sensitivity. The
2013 flight on 23 April at 17:30 UT incorporated a new wavelength
channel covering the range 525-630 Å, the previously-flown 300-370
Å channel, and the first flight demonstration of cooled active
pixel sensor (APS) arrays, resulting in high-signal-to-noise spectral
coverage spanning a wide temperature range of 0.025 to 10 MK. Absolute
radiometric calibration of the two channels is performed using a hollow
cathode discharge lamp and NIST-calibrated AXUV-100G photodiode. For
the 2013 flight, EUNIS co-observed dynamic coronal phenomena with
DST/IBIS, SoHO/CDS, SDO/AIA and Hinode/EIS and contributes to the
absolute radiometric calibrations of these instruments. Plans for
future wavelength channels to cover the AIA 94 and 131 Å bandpasses
and address the currently unresolved spectral lines (and therefore
temperature responses) within them are presented.
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Title: First Results from the EUNIS 2013 Sounding Rocket Campaign
Authors: Daw, Adrian N.; Rabin, D. M.; Brosius, J. W.; Haas, J. P.;
Plummer, T.; Cauzzi, G.; Reardon, K. P.; Beck, C.
2013SPD....4410501D Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
sounding rocket launched 23 April 2013 at 17:30 UT, as part of a
campaign including co-ordinated observations with the Dunn Solar
Telescope/IBIS, Hinode/EIS, SoHO/CDS, RHESSI and SDO. EUNIS obtained
the highest-resolution observations of the solar spectrum from 52-63 nm
observed to date, as well as observations with the previously-flown
waveband from 30-37 nm. The broad spectral coverage of the EUV
observations includes emission lines of ionization stages from He I to
Fe XIX, and thus a wide temperature range of 0.025 to 10 MK. Absolute
radiometric calibration of EUNIS provides underflight calibration of
CDS, EIS and AIA. Spectra were obtained with a 1.3 s cadence as the
660-arcsec long slit was rastered across two different regions. The
observations captured a B-class flare in active region NOAA 11726 as
well as active regions 11723, 11724, off-limb, quiet sun and a coronal
hole. We discuss first results from anaysis of this rich and extensive
data set.
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Title: PICTURE: a sounding rocket experiment for direct imaging of
an extrasolar planetary environment
Authors: Mendillo, Christopher B.; Hicks, Brian A.; Cook, Timothy
A.; Bifano, Thomas G.; Content, David A.; Lane, Benjamin F.; Levine,
B. Martin; Rabin, Douglas; Rao, Shanti R.; Samuele, Rocco; Schmidtlin,
Edouard; Shao, Michael; Wallace, J. Kent; Chakrabarti, Supriya
2012SPIE.8442E..0EM Altcode:
The Planetary Imaging Concept Testbed Using a Rocket Experiment
(PICTURE 36.225 UG) was designed to directly image the exozodiacal
dust disk of ǫ Eridani (K2V, 3.22 pc) down to an inner radius of
1.5 AU. PICTURE carried four key enabling technologies on board
a NASA sounding rocket at 4:25 MDT on October 8th, 2011: a 0.5 m
light-weight primary mirror (4.5 kg), a visible nulling coronagraph
(VNC) (600-750 nm), a 32x32 element MEMS deformable mirror and a
milliarcsecond-class fine pointing system. Unfortunately, due to a
telemetry failure, the PICTURE mission did not achieve scientific
success. Nonetheless, this flight validated the flight-worthiness
of the lightweight primary and the VNC. The fine pointing system,
a key requirement for future planet-imaging missions, demonstrated
5.1 mas RMS in-flight pointing stability. We describe the experiment,
its subsystems and flight results. We outline the challenges we faced
in developing this complex payload and our technical approaches.
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Title: Underflight Calibration of SOHO/CDS and Hinode/EIS with
EUNIS-07
Authors: Wang, Tongjiang; Thomas, Roger J.; Brosius, Jeffrey W.; Young,
Peter R.; Rabin, Douglas M.; Davila, Joseph M.; Del Zanna, Giulio
2011ApJS..197...32W Altcode: 2011arXiv1109.6598W
Flights of Goddard Space Flight Center's Extreme Ultraviolet
Normal Incidence Spectrograph (EUNIS) sounding rocket in 2006
and 2007 provided updated radiometric calibrations for Solar and
Heliospheric Observatory/Coronal Diagnostic Spectrometer (SOHO/CDS)
and Hinode/Extreme Ultraviolet Imaging Spectrometer (Hinode/EIS). EUNIS
carried two independent imaging spectrographs covering wavebands of
300-370 Å in first order and 170-205 Å in second order. After each
flight, end-to-end radiometric calibrations of the rocket payload were
carried out in the same facility used for pre-launch calibrations of
CDS and EIS. During the 2007 flight, EUNIS, SOHO/CDS, and Hinode/EIS
observed the same solar locations, allowing the EUNIS calibrations to
be directly applied to both CDS and EIS. The measured CDS NIS 1 line
intensities calibrated with the standard (version 4) responsivities with
the standard long-term corrections are found to be too low by a factor
of 1.5 due to the decrease in responsivity. The EIS calibration update
is performed in two ways. One uses the direct calibration transfer of
the calibrated EUNIS-07 short wavelength (SW) channel. The other uses
the insensitive line pairs, in which one member was observed by the
EUNIS-07 long wavelength (LW) channel and the other by EIS in either the
LW or SW waveband. Measurements from both methods are in good agreement,
and confirm (within the measurement uncertainties) the EIS responsivity
measured directly before the instrument's launch. The measurements also
suggest that the EIS responsivity decreased by a factor of about 1.2
after the first year of operation (although the size of the measurement
uncertainties is comparable to this decrease). The shape of the EIS SW
response curve obtained by EUNIS-07 is consistent with the one measured
in laboratory prior to launch. The absolute value of the quiet-Sun
He II 304 Å intensity measured by EUNIS-07 is consistent with the
radiance measured by CDS NIS in quiet regions near the disk center
and the solar minimum irradiance recently obtained by CDS NIS and the
Solar Dynamics Observatory/Extreme Ultraviolet Variability Experiment.
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Title: Quantitative Evaluation of Continuous Diffractive Baffles
for Heliospheric Imagers
Authors: Rabin, D. M.
2011AGUFMSH13B1971R Altcode:
Wide-angle heliospheric imagers such as those carried on the SMEI and
STEREO spacecraft require highly effective baffle systems to exclude
diffracted light from the solar disk as well as other sources of
stray light. Buffington (2000, Appl. Opt. 39, 2683-2686) has proposed
replacing multi-vane baffle systems with a curved surface that can be
thought of as the limiting case of closely spaced vanes. Buffington's
experimental data showed that the diffractive performance of a
continuous baffle is consistent with the limiting form expected from
multi-vane diffraction on heuristic grounds, but a detailed prediction
was not possible because multi-vane diffraction calculations assume
that the diffractive edges act independently, an assumption that
breaks down for a continuous surface. I present analytic calculations
of diffraction from a curved surface and use them to evaluate the
effectiveness of continuous-surface baffles for heliospheric imagers.
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Title: First Solar Images Using a Photon Sieve
Authors: Daw, A. N.; Rabin, D. M.; Dunlap, L.; Vievering, J.
2011AGUFMSH13B1962D Altcode:
The first solar images using a photon sieve were obtained in H-alpha at
NASA Goddard Space Flight Center. The first sieve used consists of 1500
fresnel zones comprising 15 million holes in a chrome layer on a glass
substrate to yield a focal length of 400 mm at a wavelength of 656.3
nm. Results of the observations are discussed, as well as the positive
implications for the use of diffractive optics on deployable membranes
for extremely high resolution (0.01 arcsec) imaging from space.
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Title: Electron Temperatures and Flow Speeds of the Low Solar Corona:
MACS Results from the Total Solar Eclipse of 29 March 2006 in Libya
Authors: Reginald, Nelson L.; Davila, Joseph M.; St. Cyr, O. C.; Rabin,
Douglas M.; Guhathakurta, Madhulika; Hassler, Donald M.; Gashut, Hadi
2011SoPh..270..235R Altcode: 2011SoPh..tmp...68R; 2011SoPh..tmp...48R
An experiment was conducted in conjunction with the total solar eclipse
on 29 March 2006 in Libya to measure both the electron temperature
and its flow speed simultaneously at multiple locations in the low
solar corona by measuring the visible K-coronal spectrum. Coronal model
spectra incorporating the effects of electron temperature and its flow
speed were matched with the measured K-coronal spectra to interpret
the observations. Results show electron temperatures of (1.10±0.05)
MK, (0.70±0.08) MK, and (0.98±0.12) MK, at 1.1 R<SUB>⊙</SUB>
from Sun center in the solar north, east and west, respectively, and
(0.93±0.12) MK, at 1.2 R<SUB>⊙</SUB> from Sun center in the solar
west. The corresponding outflow speeds obtained from the spectral
fit are (103±92) km s<SUP>−1</SUP>, (0+10) km s<SUP>−1</SUP>,
(0+10) km s<SUP>−1</SUP>, and (0+10) km s<SUP>−1</SUP>. Since
the observations were taken only at 1.1 R<SUB>⊙</SUB> and 1.2
R<SUB>⊙</SUB> from Sun center, these speeds, consistent with zero
outflow, are in agreement with expectations and provide additional
confirmation that the spectral fitting method is working. The electron
temperature at 1.1 R<SUB>⊙</SUB> from Sun center is larger at the
north (polar region) than the east and west (equatorial region).
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Title: Coronal Bright Points and Quiet Sun Areas Observed with
EUNIS-07 and EIS
Authors: Brosius, Jeffrey W.; Wang, T. J.; Rabin, D. M.; Thomas,
R. J.; Landi, E.
2011SPD....42.1828B Altcode: 2011BAAS..43S.1828B
The Extreme-Ultraviolet Normal-Incidence Spectrograph is a
sounding rocket instrument with two independent but co-pointing
imaging spectrographs. One spectrograph observes emission lines in a
long-wavelength (LW) channel (300-370 A), while a second observes lines
in a short-wavelength (SW) channel (170-205 A). The instrument was last
flown on 6 November 2007 (EUNIS-07), when there were no active regions
on the solar disk. After the flight, the absolute radiometric responses
of both channels were derived from laboratory measurements obtained
in the same facility used for pre-flight calibrations of SOHO/CDS and
Hinode/EIS. Coordinated EUNIS-07 and EIS observations of quiet sun area
near disk center reveal that the sensitivity of both EIS wavebands had
diminished to 82% of their pre-launch values (Wang et al. 2011). Here
we use the combined EUNIS-07 and EIS spectra to investigate quiet sun
areas and small bright points observed by both instruments, as well
as a larger, brighter bright point that was observed only by EUNIS-07.
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Title: Evaluation of Diffraction by a Rounded Surface
Authors: Rabin, Douglas M.
2011SPD....42.1510R Altcode: 2011BAAS..43S.1510R
Wide-angle heliospheric imagers such as those carried on the SMEI and
STEREO spacecraft require highly effective baffle systems to exclude
diffracted light from the solar disk as well as other sources of
stray light. Buffington (2000, Appl. Opt. 39, 2683-2686) has proposed
replacing multi-vane baffle systems with a curved surface that can be
thought of as the limiting case of closely spaced vanes. Buffington's
experimental data showed that the diffractive performance of a
continuous baffle is consistent with the limiting form expected
from multi-vane diffraction on dimensional grounds, but a detailed
prediction was not possible because multi-vane diffraction calculations
assume that the diffractive edges act independently, an assumption that
breaks down for a continuous surface. I describe analytic calculations
of diffraction from a smooth rounded surface based on the approach of
Vogler (1985, Radio Sci. 20, 582-590).
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Title: New Capabilities of the EUNIS Sounding Rocket Instrument
Authors: Daw, Adrian N.; Brosius, J.; Criscuolo, E.; Davila, J.;
Haas, J. P.; Hilton, G.; Linard, D.; Plummer, T.; Rabin, D.; Thomas,
R.; Varney, D.; Wang, T.
2011SPD....42.1502D Altcode: 2011BAAS..43S.1502D
The upcoming flight of the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument, a two-channel imaging
spectrograph that observes the solar corona and transition region
with high spectral resolution and a rapid cadence made possible by
unprecedented sensitivity, will incorporate a new wavelength channel
and cooling of the active pixel sensor (APS) arrays. The new 52.4-63.0
nm channel incorporates a Toroidal Varied Line Space (TVLS) grating
coated with B<SUB>4</SUB>C/Ir, providing broad spectral coverage and
a wide temperature range of 0.025 to 10 MK. The APS arrays for both
the 52-63 nm and 30-37 nm channels will be cooled to -20 C to reduce
dark current noise. With the resulting read-noise limited performance,
over a dozen new diagnostic line pairs become available in the two
wavelength channels. To our knowledge, this will be the first flight
demonstration of cooled APS arrays. EUNIS will co-observe dynamic
coronal phenomena with SDO/AIA and Hinode/EIS and will contribute to
the absolute radiometric calibrations of these instruments. <P />EUNIS
is supported by NASA through the Low Cost Access to Space Program in
Solar and Heliospheric Physics.
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Title: An Investigation of Solar Coronal Bright Points Based on EUV
Spectra Obtained with EUNIS-07
Authors: Schaefer, R.; Brosius, J. W.; Bruhweiler, F.; Rabin, D. M.;
Thomas, R.; Wang, T.
2010AGUFMSH31C1805S Altcode:
The EUNIS sounding rocket instrument is a two-channel imaging
spectrograph that observes the solar corona with a rapid cadence made
possible by unprecedented sensitivity. The instrument was successfully
flown on 2006 April 12 (EUNIS-06) and 2007 November 6 (EUNIS-07),
providing hundreds of spectra in the wavelength ranges 170-205 A and
300-370 A with sustained cadences as fast as 1.3 s. The EUNIS-07
data have provided the first on-orbit radiometric calibration of
Hinode's EIS and STEREO's SECCHI/EUVI. Although there were no active
regions on the solar disk during this flight, EUNIS-07 repeatedly
scanned across several small coronal bright points within a large
area of quiet Sun near disk center. We fitted Gaussian profiles to
emission lines formed at temperatures ranging from 0.05 MK to 2 MK
(with particular attention to He II 304 A, Mg IX 368 A, and Fe XIV
334 A) in the spatially resolved EUV spectra. The resulting line
profile fits are used to derive a series of bright point images that
we investigate for brightness variations on time scales of one minute,
as well as relative Doppler velocities. Evolution of the bright points
on time scales of hours are investigated with magnetograms from SOHO's
MDI. EUNIS is supported by the NASA Heliophysics Division through its
Low Cost Access to Space Program in Solar and Heliospheric Physics,
and is scheduled to fly again in 2011. EUNIS data are freely available
to the solar physics community. RS acknowledges support under NSF/REU
grant ATM-00552671 to CUA. JWB is supported by NASA grant NNX10AK45G.
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Title: Science Objectives for an X-Ray Microcalorimeter Observing
the Sun
Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M;
Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse,
N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.;
DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra,
A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg,
C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.;
Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska,
J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres,
G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.;
Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz,
J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.;
Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B.
2010arXiv1011.4052L Altcode:
We present the science case for a broadband X-ray imager with
high-resolution spectroscopy, including simulations of X-ray spectral
diagnostics of both active regions and solar flares. This is part of
a trilogy of white papers discussing science, instrument (Bandler et
al. 2010), and missions (Bookbinder et al. 2010) to exploit major
advances recently made in transition-edge sensor (TES) detector
technology that enable resolution better than 2 eV in an array that
can handle high count rates. Combined with a modest X-ray mirror, this
instrument would combine arcsecondscale imaging with high-resolution
spectra over a field of view sufficiently large for the study of
active regions and flares, enabling a wide range of studies such as
the detection of microheating in active regions, ion-resolved velocity
flows, and the presence of non-thermal electrons in hot plasmas. It
would also enable more direct comparisons between solar and stellar
soft X-ray spectra, a waveband in which (unusually) we currently have
much better stellar data than we do of the Sun.
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Title: Absolute Radiometric Calibration Of EUNIS, And Calibration
Updates For Hinode/EIS And SOHO/CDS
Authors: Wang, Tongjiang; Thomas, R. J.; Brosius, J. W.; Young, P. R.;
Rabin, D. M.; Davila, J. M.
2010AAS...21640704W Altcode: 2010BAAS...41..860W
The Extreme-Ultraviolet Normal-Incidence Spectrograph sounding rocket
payload was flown in 2006 (EUNIS-06) and 2007 (EUNIS-07), each time
carrying two independent imaging spectrographs covering wave bands
of 300-370 Angstrom in first order and 170-205 Angstrom in second
order. For each flight, the absolute radiometric response of the EUNIS
long-wavelength (LW) channel was directly measured in the same facility
used for pre-flight calibrations of SOHO/CDS and Hinode/EIS. The
wavelength range of the EUNIS LW channel overlaps that of CDS/NIS-1,
and so can provide a direct calibration update for it. The EUNIS-06
observation shows that the efficiency of CDS/NIS-1 has decreased by
a factor about 1.7 compared to that of the previously implemented
calibration. Here we present an update to the absolute calibration for
Hinode/EIS derived with a technique that combines a direct comparison
of line intensities observed in cospatial EUNIS-07 and EIS spectra,
along with density- and temperature-insensitive line intensity ratios.
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Title: Absolute Radiometric Calibration of the EUNIS-06 170-205
Å Channel and Calibration Update for Coronal Diagnostic
Spectrometer/Normal-Incidence Spectrometer
Authors: Wang, Tongjiang; Brosius, Jeffrey W.; Thomas, Roger J.;
Rabin, Douglas M.; Davila, Joseph M.
2010ApJS..186..222W Altcode: 2009arXiv0912.2328W
The Extreme-Ultraviolet Normal-Incidence Spectrograph sounding-rocket
payload was flown on 2006 April 12 (EUNIS-06), carrying two independent
imaging spectrographs covering wavebands of 300-370 Å in first order
and 170-205 Å in second order, respectively. The absolute radiometric
response of the EUNIS-06 long-wavelength (LW) channel was directly
measured in the same facility used to calibrate Coronal Diagnostic
Spectrometer (CDS) prior to the Solar and Heliospheric Observatory
(SOHO) launch. Because the absolute calibration of the short-wavelength
(SW) channel could not be obtained from the same lab configuration,
we here present a technique to derive it using a combination of solar
LW spectra and density- and temperature-insensitive line intensity
ratios. The first step in this procedure is to use the coordinated,
cospatial EUNIS and SOHO/CDS spectra to carry out an intensity
calibration update for the CDS NIS-1 waveband, which shows that its
efficiency has decreased by a factor about 1.7 compared to that of the
previously implemented calibration. Then, theoretical insensitive line
ratios obtained from CHIANTI allow us to determine absolute intensities
of emission lines within the EUNIS SW bandpass from those of cospatial
CDS/NIS-1 spectra after the EUNIS LW calibration correction. A total
of 12 ratios derived from intensities of 5 CDS and 12 SW emission
lines from Fe X to Fe XIII yield an instrumental response curve for
the EUNIS-06 SW channel that matches well to a relative calibration
which relied on combining measurements of individual optical
components. Taking into account all potential sources of error, we
estimate that the EUNIS-06 SW absolute calibration is accurate to ±20%.
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Title: A Scalable Superconductor Bearing System For Lunar Telescopes
And Instruments
Authors: Chen, Peter C.; Rabin, D.; Van Steenberg, M. E.
2010AAS...21548102C Altcode: 2010BAAS...42R.570C
We report on a new concept for a telescope mount on the Moon based
on high temperature superconductors (HTS). Lunar nights are long
(15 days), and temperatures range from 100 K to 30 K inside shadowed
craters. Telescopes on the Moon therefore require bearing systems that
can position and track precisely under cryogenic conditions, over long
time periods, preferably with no maintenance, and preferably do not
fail with loss of power. HTS bearings, consisting of permanent magnets
levitated over bulk superconductors, are well suited to the task. The
components do not make physical contact, hence there is no wear. The
levitation is passive and stable; no power is required to maintain
position. We report on the design and laboratory demonstration of
a prototype two-axis pointing system. Unlike previous designs, this
new configuration is simple and easy to implement. Most importantly,
it can be scaled to accommodate instruments ranging in size from
decimeters (laser communication systems) to meters (solar panels,
communication dishes, optical telescopes, optical interferometers)
to decameters and beyond (VLA-type radio interferometer elements).
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Title: Electron-Temperature Maps of the Low Solar Corona: ISCORE
Results from the Total Solar Eclipse of 29 March 2006 in Libya
Authors: Reginald, Nelson L.; St. Cyr, O. C.; Davila, Joseph M.;
Rabin, Douglas M.; Guhathakurta, Madhulika; Hassler, Donald M.
2009SoPh..260..347R Altcode:
We conducted an experiment in conjunction with the total solar
eclipse of 29 March 2006 in Libya that measured the coronal
intensity through two filters centered at 3850 Å and 4100 Å with
bandwidths of ≈ 40 Å. The purpose of these measurements was to
obtain the intensity ratio through these two filters to determine
the electron temperature. The instrument, Imaging Spectrograph of
Coronal Electrons (ISCORE), consisted of an eight inch, f/10 Schmidt
Cassegrain telescope with a thermoelectrically-cooled CCD camera at
the focal plane. Results show electron temperatures of 10<SUP>5</SUP>
K close to the limb to 3×10<SUP>6</SUP> K at 1.3R<SUB>⊙</SUB>. We
describe this novel technique, and we compare our results to other
relevant measurements. This technique could be easily implemented on
a space-based platform using a coronagraph to produce global maps of
the electron temperature of the solar corona.
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Title: Transition Region Velocity Oscillations Observed by EUNIS-06
Authors: Jess, D. B.; Rabin, D. M.; Thomas, R. J.; Brosius, J. W.;
Mathioudakis, M.; Keenan, F. P.
2008ApJ...682.1363J Altcode: 2008arXiv0804.1629J
Spectroscopic measurements of NOAA AR 10871, obtained with the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket
instrument on 2006 April 12, reveal velocity oscillations in the He
II 303.8 Å emission line formed at T ≈ 5 × 10<SUP>4</SUP> K. The
oscillations appear to arise in a bright active region loop arcade
about 25<SUP>”</SUP> wide which crosses the EUNIS slit. The period
of these transition region oscillations is 26 +/- 4 s, coupled with
a velocity amplitude of ±10 km s<SUP>-1</SUP>, detected over four
complete cycles. Similar oscillations are observed in lines formed at
temperatures up to T ≈ 4 × 10<SUP>5</SUP> K, but we find no evidence
for the coupling of these velocity oscillations with corresponding
phenomena in the corona. We interpret the detected oscillations as
originating from an almost purely adiabatic plasma, and infer that
they are generated by the resonant transmission of MHD waves through
the lower active region atmospheres. Through the use of seismological
techniques, we establish that the observed velocity oscillations display
wave properties most characteristic of fast body global sausage modes.
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Title: Rapid Cadence EUNIS-06 Observations of a He II Transient
Brightening in the Quiet Sun
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.
2008ApJ...682..630B Altcode:
We observed a transient brightening in the quiet Sun at rapid cadence
(2.10 s) with the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS-06) sounding rocket instrument on 2006 April 12. The transient
was visible only in He II at 303.78 Å (T ≈ 5 × 10<SUP>4</SUP> K),
and its maximum temperature T was <4 × 10<SUP>5</SUP> K. Taking
its linear extent along the EUNIS slit to be the diameter of a circular
feature, the transient's solar surface area was 7.8 × 10<SUP>7</SUP>
km<SUP>2</SUP>. EUNIS observed the brightening to begin at 18:12:52
and peak at 18:13:29 UT; coordinated observations with SOHO's EIT
confirm that EUNIS observed the onset of the brightening. EUNIS
spectra yield maximum and average He II intensity enhancements
of 2.09 and 1.46, respectively, relative to the pre-event quiet
Sun. He II line profiles from EUNIS reveal that relative upflows
were persistent during the transient (with a maximum speed around
20 km s<SUP>-1</SUP>) and that the upflow speed and intensity were
positively correlated. Variations in the observed He II intensity
and relative Doppler velocity were neither abrupt not impulsive, but
occurred slowly compared to the EUNIS cadence. The local photospheric
longitudinal magnetic field strength measured with SOHO's MDI revealed
no significant variability. The transient's measured properties are
consistent with its identification as a blinker or an elementary
blinker, and its observed behavior suggests a formation mechanism
involving gentle chromospheric evaporation.
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Title: EUNIS-07: First Look
Authors: Rabin, D. M.; Thomas, R. J.; Brosius, J. W.
2008AGUSMSP51A..07R Altcode:
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument is a two-channel imaging spectrograph that observes
the solar corona with high spectral resolution and a rapid cadence
made possible by unprecedented sensitivity. EUNIS flew for the
first time on 2006 April 12 (EUNIS-06), returning over 140 science
exposures at a cadence of 2.1 s; each exposure comprises six 1K x 1K
active pixel sensor (APS) images, three for each wavelength channel
(170-205 Å and 300-370 Å. Analysis of EUNIS-06 data has so far shed
new light on the nature of coronal bright points, cool transients, and
coronal loop arcades and has enabled calibration updates for TRACE and
SOHO's CDS and EIT. EUNIS flew successfully again on 2007 November 6
(EUNIS-07). Because the APS arrays were operated in video rather than
snapshot mode, a faster cadence of 1.3 s was possible (97% duty cycle),
resulting in 276 science exposures. We present an overview of the
EUNIS-07 spectra and describe the coordinated observing program executed
by the Hinode Extreme ultraviolet Imaging Spectrograph (EIS) that will,
in conjunction with the absolute radiometric calibration of EUNIS-07,
result in the first on-orbit radiometric calibration of EIS. EUNIS data
are freely available to the solar physics community. EUNIS is supported
by the NASA Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics.
---------------------------------------------------------
Title: EUNIS-06 Rapid Cadence Observations of a He II Transient
Brightening in the Quiet Sun
Authors: Brosius, J. W.; Rabin, D. M.; Thomas, R. J.
2008AGUSMSP51A..06B Altcode:
We observed a transient brightening in the quiet Sun at rapid cadence
(2.10 s) with the Extreme Ultraviolet Normal Incidence Spectrograph
(EUNIS-06) sounding rocket instrument on 2006 April 12. The transient
was visible only in He II at 303.78 Å (T ≍ 5 × 104 K), and its
maximum temperature T was < 4 × 105 K. Taking its linear extent
along the EUNIS slit to be the diameter of a circular feature, the
transient's solar surface area was 7.8 × 107 km2. EUNIS observed the
brightening to begin at 18:12:52 and peak at 18:13:29 UT; coordinated
observations with SOHO's EIT confirm that EUNIS observed the onset
of the brightening. EUNIS spectra yield maximum and average He II
intensity enhancements of 2.09 and 1.46, respectively, relative to
the pre-event quiet Sun. He II line profiles from EUNIS reveal that
relative upflows were persistent during the transient (with a maximum
speed around 20 km s-1) and that the upflow speed and intensity were
positively correlated. Variations in the observed He II intensity
and relative Doppler velocity were neither abrupt not impulsive, but
occurred slowly compared to the EUNIS cadence. The local photospheric
magnetic flux measured with SOHO's MDI revealed no significant
variability. The transient's measured properties are consistent with
its identification as a blinker or an elementary blinker, and its
observed behavior suggests a formation mechanism involving gentle
chromospheric evaporation. The EUNIS program is supported by NASA's
Heliophysics Division through its Low Cost Access to Space Program in
Solar and Heliospheric Physics.
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Title: EUNIS Underflight Calibrations of CDS, EIT, TRACE, EIS,
and EUVI
Authors: Thomas, R.; Wang, T.; Rabin, D. M.; Jess, D. B.; Brosius,
J. W.
2008AGUSMSP51B..04T Altcode:
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a
sounding rocket instrument that obtains imaged high-resolution solar
spectra. It has now had two successful flights, on 2006 April 12 and
2007 November 16, providing data to support underflight calibrations
for a number of orbiting solar experiments on both occasions. A regular
part of each campaign is the end-to-end radiometric calibration of
the rocket payload carried out at RAL in the UK, using the same
facility that provided pre-flight CDS and EIS calibrations. The
measurements, traceable to primary radiometric standards, can establish
the absolute EUNIS response within a total uncertainty of 10% over
its full longwave bandpass of 300--370Å. During each EUNIS flight,
coordinated observations are made of overlapping solar locations by
all participating space experiments, and identified by subsequent
image co-registrations, allowing the EUNIS calibrations to be applied
to these other instruments as well. The calibration transfer is
straightforward for wavelengths within the EUNIS LW bandpass, and is
extended to other wavelengths by means of a series of temperature-
and density-insensitive line-ratios, with one line of each pair in
the calibrated band and the other in the transfer band. In this way,
the EUNIS-06 flight is able to update the radiometric calibrations of
CDS NIS1 (and 2nd-order NIS2 near 2x304Å), all four channels of EIT,
and the three EUV channels of TRACE. The EUNIS-07 flight will further
update those missions, as well as both channels of Hinode/EIS and all
four channels of STEREO/SECCHI/EUVI. Future EUNIS flights have been
proposed that will continue this underflight calibration service. EUNIS
is supported by the NASA Heliophysics Division through its Low Cost
Access to Space Program in Solar and Heliospheric Physics.
---------------------------------------------------------
Title: Analysis of a Solar Coronal Bright Point Extreme Ultraviolet
Spectrum from the EUNIS Sounding Rocket Instrument
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.;
Landi, Enrico
2008ApJ...677..781B Altcode:
We present a well-calibrated EUV spectrum of a solar coronal bright
point observed with the Extreme Ultraviolet Normal Incidence
Spectrograph (EUNIS) sounding rocket instrument on 2006 April
12. The coronal bright point brightened around 06:30 UT during a
period of emerging magnetic flux and remained bright at least until
the rocket flight around 18:12 UT, while the magnetic flux merged
and canceled. Density-sensitive line intensity ratios yield mutually
consistent coronal electron densities (N<SUB>e</SUB> in cm<SUP>-3</SUP>)
of log N<SUB>e</SUB> ≈ 9.4. The differential emission measure
(DEM, in cm<SUP>-5</SUP> K<SUP>-1</SUP>) curve derived from the
spectrum yields a peak of log DEM ≈ 20.70 at log T ≈ 6.15 and a
local minimum of log DEM ≈ 20.15 at log T ≈ 5.35. Photospheric
(not coronal) element abundances are required to achieve equality
and consistency in the DEM derived from lines of Mg V, Mg VI, Mg VII,
and Ca VII (with a low first ionization potential, or FIP) and lines
from Ne IV and Ne V (with a high FIP) formed at transition region
temperatures. The bright point's photospheric abundance is likely
produced by reconnection-driven chromospheric evaporation, a process
that is not only central to existing bright point models, but also
consistent with measurements of relative Doppler velocities.
---------------------------------------------------------
Title: Analysis of a Bright Point Spectrum From the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS) Sounding Rocket
Instrument
Authors: Brosius, J. W.; Rabin, D. M.; Thomas, R. J.
2007AGUFMSH21B..04B Altcode:
We present a well-calibrated spectrum of a bright point observed with
EUNIS on 2006 April 12. Coordinated observations with SOHO's EIT and
MDI were also obtained. The bright point brightened around 06:30 UT
during a period of emerging magnetic flux, and remained bright at least
until the rocket flight around 18:12 UT while the magnetic flux merged
and canceled. Density-sensitive line intensity ratios yield mutually
consistent coronal electron densities log Ne ~ 9.5. Based on the method
of Landi & Landini (1997), the differential emission measure (DEM)
curve derived from the spectrum yields a peak of log DEM ~ 20.70 at log
T ~ 6.15, and a local minimum of log DEM ~ 20.15 at log T ~ 5.35. We
find that photospheric (not coronal) element abundances are required to
achieve equality and consistency in the DEM derived from lines of Mg V,
Mg VI, Mg VII, Ca VII (with a low first ionization potential, or FIP)
and lines from Ne IV and Ne V (with a high FIP) formed at transition
region temperatures. The bright point's photospheric abundance is
likely produced by reconnection-driven chromospheric evaporation,
a process that is not only central to existing bright point models
(e.g., Priest, Parnell, & Martin 1994; Longcope 1998), but also
consistent with measurements of relative Doppler velocities (e.g.,
± 26 km/s for Fe XIV, ± 35 km/s for Fe XVI) previously presented by
Brosius, Rabin, & Thomas (2007). The EUNIS program is supported
by NASA's Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics. We thank the entire EUNIS
team for the concerted effort that led to a successful first flight.
---------------------------------------------------------
Title: Radiometric Calibration of EUNIS-06 With Theoretical Predicted
`Insensitive' Line Ratios
Authors: Wang, T.; Brosius, J. W.; Thomas, R. J.; Rabin, D. M.
2007AGUFMSH53A1049W Altcode:
The Extreme-Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a
sounding-rocket payload that obtains imaged high-resolution spectra
of solar active and quiet-Sun regions, providing information about
the corona and upper transition region. EUNIS incorporates two
independent, co-pointing imaging spectrographs, one covering EUV
lines between 300 and 370 Å\ seen in first order (the longwave
[LW] channel), and a second covering lines between 170 and 205 Å\
seen in second order (the shortwave [SW] channel). Shortly after
the payload's initial successful flight on 2006 April 12, a complete
end-to-end radiometric calibration of its LW bandpass was carried out
at the Rutherford Appleton Laboratory in England. Here we develop and
apply a technique for deriving the absolute radiometric calibration
of its SW bandpass from these direct LW results by means of density-
and temperature-insensitive line intensity ratios. The first step
is to use the EUNIS LW calibration to get absolute intensities for
EUV lines recorded from solar positions along its LW slit during the
2006 flight. Then co-registered SOHO/CDS images taken within minutes
of the flight are used to transfer these absolute values to solar
locations observed by the EUNIS SW slit, spatially offset by about 1
arcmin. Finally, theoretical `insensitive' line ratios obtained from
CHIANTI allow us to determine absolute intensities of emission lines
within the EUNIS SW bandpass from those observed in its LW channel. A
total of 29 ratios composed of 11 LW and 15 SW emission lines from Fe~X
- Fe~XIII yield an instrumental response curve that matches very well
to a relative calibration which relied on combining measurements of
individual optical components. The second EUNIS flight, now scheduled
for 2007 October 30, will make coordinated observations and provide
similar calibration updates for Hinode/EIS. We will also present some
preliminary results from the new observations. EUNIS is supported by
the NASA Heliophysics Division through its Low Cost Access to Space
Program in Solar and Heliospheric Physics.
---------------------------------------------------------
Title: Advances in Solar Coronagraphy
Authors: Rabin, D.; St. Cyr, O. C.; Davila, J. M.
2007lyot.confE..18R Altcode:
Could Bernard Lyot have imagined the protean forms in which his most
notable invention, the coronagraph, would appear 75 years later? Could
he have foreseen that the most widely used solar coronagraphs would be
based in space, or that coronagraphs would seek to image planets and
disks around other stars? Perhaps so - he was far more than a builder
of creative instruments. I will discuss advances in solar coronagraphy
since Lyot's time, in both the science that drives the observations
and the technology that sustains them.
---------------------------------------------------------
Title: Absolute Radiometric Calibration of EUNIS-06
Authors: Thomas, Roger J.; Rabin, D. M.; Haas, J. P.; Kent, B. J.;
Paustian, W.; Jess, D. B.
2007AAS...210.2508T Altcode: 2007BAAS...39..132T
The Extreme-Ultraviolet Normal-Incidence Spectrometer (EUNIS) is a
sounding-rocket payload that obtains imaged high-resolution spectra of
individual solar features, providing information about the Sun's corona
and upper transition region. Shortly after its successful initial
flight last year, a complete end-to-end calibration was carried out
to determine the instrument's absolute radiometric response over
its longwave bandpass of 300 - 370 Å. The measurements were done
at the Rutherford-Appleton Laboratory (RAL) in England, using the
same vacuum facility and EUV radiation source used in the pre-flight
calibrations of both SOHO/CDS and Hinode/EIS, as well as in three
post-flight calibrations of our SERTS sounding rocket payload,
the precursor to EUNIS. The unique radiation source provided by
the Physikalisch-Technische Bundesanstalt (PTB) had been absolutely
calibrated to a relative uncertainty of 7% (1σ) at 12 wavelengths
covering our bandpass directly against the Berlin electron storage ring
BESSY, which is itself a primary radiometric source standard. Scans
of the EUNIS aperture were made to determine the instrument's absolute
spectral sensitivity to ± 25%, considering all sources of error, and
demonstrate that EUNIS-06 was the most sensitive solar EUV spectrometer
flown to date. The results will be matched against prior calibrations
which relied on combining measurements of individual optical components,
and on comparisons with theoretically predicted 'insensitive' line
ratios. Coordinated observations were made during the EUNIS-06 flight by
SOHO/CDS and EIT that will allow re-calibrations of those instruments as
well. In addition, future EUNIS flights will provide similar calibration
updates for TRACE, Hinode/EIS, and STEREO/SECCHI/EUVI. <P />EUNIS
is supported by the NASA Heliophysics Division through its Low Cost
Access to Space Program in Solar and Heliospheric Physics.
---------------------------------------------------------
Title: Forecast of the Amplitude of Solar Cycle 24 Based on the
Disturbed Days Precursor
Authors: Rabin, Douglas M.
2007AAS...210.9205R Altcode: 2007BAAS...39..209R
R. J. Thompson (1993, Solar Physics 148, 383) exhibited a significant
linear relationship between the number of geomagnetically disturbed
days (those that exceed some threshold value of the Ap or aa index) in
a solar cycle and the sum of the peak sunspot number in that cycle and
the next cycle. Thus, the number of disturbed days during a full cycle,
together with the peak sunspot number in that cycle, is a predictor
of the amplitude of the next cycle. The work reported here applies
Thompson’s method to the current cycle. Linear relationships as
described above are derived both for the pure aa record (1868-2006)
and for a composite of aa (1868-1931) and Ap (1932-2006). For the
composite record, the relationship between aa and Ap is determined
cycle-by-cycle during the period of overlap. The method is tested
for sensitivity to the adopted Ap (or equivalent aa) threshold. The
highest smoothed monthly sunspot number for Cycle 24 is forecasted to
be R<SUB>z</SUB> = 115 ± 30, where the uncertainty is conservatively
based on the full spread of the data around the fitted line in the
sunspot number direction. In terms of smoothed monthly 10.7-cm radio
flux, the forecast is F10.7 = 164 ± 28.
---------------------------------------------------------
Title: EUNIS And SOHO Observations Of A Cool Transient Brightening
In The Quiet Sun
Authors: Brosius, Jeffrey W.; Rabin, D. M.; Thomas, R. J.
2007AAS...210.2507B Altcode: 2007BAAS...39..132B
The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument observed a cool transient brightening in the quiet
Sun during its first flight on 2006 April 12. The brightening appeared
in emission from He II, formed at temperatures around 50,000 K (log
T = 4.7), but was not evident in emission from ions formed at greater
temperatures, including Mg VI (log T = 5.6), Mg IX (log T = 6.0), and
Fe XIV (log T = 6.3). Of these and other lines in the EUNIS spectra,
only lines from He II and Mg IX were strong enough in the quiet Sun
to measure relative Doppler velocities during this transient; He II
revealed continuous upflows around 15 km/s while Mg IX revealed no
significant velocities. The average He II intensity enhancement factor
observed with EUNIS was 1.34, and its maximum was 1.84. Coordinated
observations with SOHO's EIT reveal a source area of 3.3x10^7 km^2,
in which the average He II intensity enhancement factor was 1.39 and
its maximum was 1.81; the transient did not appear in EIT's hotter
wavebands. Variations in the local magnetic field strength measured with
SOHO's MDI were marginal. The EUNIS program is supported by NASA through
its Low Cost Access to Space Program in Solar and Heliospheric Physics.
---------------------------------------------------------
Title: Doppler Velocities Measured in Coronal Emission Lines from
a Bright Point Observed with the EUNIS Sounding Rocket
Authors: Brosius, Jeffrey W.; Rabin, Douglas M.; Thomas, Roger J.
2007ApJ...656L..41B Altcode:
Spectroscopic measurements of a coronal bright point obtained with
the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding
rocket instrument on 2006 April 12 show both upflows and downflows in
all five of the best observed emission lines. Relative velocities on
opposite sides of the feature were found to be +/-15 km s<SUP>-1</SUP>
in the line of He II 303.8 Å (formed at T~5×10<SUP>4</SUP> K),
+/-14 km s<SUP>-1</SUP> in Mg IX 368.1 Å (T~9.5×10<SUP>5</SUP> K),
+/-26 km s<SUP>-1</SUP> in Fe XIV 334.2 Å (T~2.0×10<SUP>6</SUP>
K), and +/-35 km s<SUP>-1</SUP> in both Fe XVI 335.4 and 360.8 Å
(T~2.5×10<SUP>6</SUP> K). The latter are the hottest lines for which
Doppler velocities have been reported in a bright point. Photospheric
longitudinal magnetograms reveal that the photospheric magnetic
fields underlying the bright point were canceling during the EUNIS
observation. Based on existing bright point models, this suggests that
the observed hot flows were associated with magnetic reconnection.
---------------------------------------------------------
Title: Preliminary EUNIS-06 EUV Spectral Catalog
Authors: Thomas, Roger J.; Rabin, D. M.
2006SPD....37.0105T Altcode: 2006BAAS...38..216T
The recent 2006 April 12 flight of NASA/GSFC's sounding rocket payload,
the EUV Normal-Incidence Spectrograph (EUNIS-06), produced 145 spectral
images in each of two optical channels with passbands of 170--205 Å
and 300--370 Å, respectively. These spectra are spatially resolved
along slit lengths of about 660 arcsec covering portions of NOAA Active
Region 10871 at S07E28, as well as quiet areas near disk center. We
present here examples of spatial variations recorded in some of the
stronger lines, along with a preliminary catalog of all spectral lines
found by averaging the complete data set.EUNIS is supported by the NASA
Heliophysics Division's Solar & Heliospheric Physics Supporting
Research and Technology and Low Cost Access to Space Program.
---------------------------------------------------------
Title: First Results from EUNIS-06
Authors: Rabin, Douglas M.; Thomas, R. J.; Davila, J. M.
2006SPD....37.0106R Altcode: 2006BAAS...38..216R
The Extreme Ultraviolet Normal-Incidence Spectrograph (EUNIS) sounding
rocket experiment successfully completed its first flight on 12
April 2006 from White Sands Missile Range, obtaining 145 science
images in each of two wavelength channels. EUNIS is designed to
investigate the energetics of the solar corona and hotter transition
region through high-resolution imaging spectroscopy with a rapid
(2-3 second) cadence. The two independent optical systems of EUNIS
simultaneously record spectra over two passbands (170-205 Å and
300-370 Å), each spatially resolved along slit lengths of about
660 arcsec. The longwave channel includes He II 304 Å and strong
lines from Fe XI-XVI. The shortwave passband has a sequence of very
strong Fe IX-XIII lines. Together, the EUNIS telescopes furnish a wide
range of temperature and density diagnostics and enables underflight
calibration of instrumental passbands on the SOHO, TRACE, Solar-B,
and STEREO missions. <P />We present an overview of the science images
from the first flight with emphasis on transient phenomena. The target
was active region NOAA 10871 and adjacent quiet areas. Spectra were
recorded with exposure times as short as 0.1 s, demonstrating that EUNIS
is the most sensitive solar EUV spectrograph in operation, with over 100
times the throughput of its predecessor, the Solar Extreme ultraviolet
Research Telescope and Spectrograph (SERTS). <P />EUNIS is supported
by the NASA Heliophysics Division's Solar & Heliospheric Physics
Supporting Research and Technology and Low Cost Access to Space Program.
---------------------------------------------------------
Title: Component Radiometric Calibrations of the EUV Normal-Incidence
Spectrograph (EUNIS)
Authors: Thomas, R. J.; Rabin, D. M.
2005AAS...20711111T Altcode: 2005BAAS...37.1343T
The EUV Normal-Incidence Spectrograph (EUNIS) is a sounding rocket
experiment that will investigate the energetics of the solar corona and
hotter transition region through high-resolution imaging spectroscopy
with a rapid (2 s) cadence. EUNIS features independent optical
systems to record spatially co-aligned spectra simultaneously over
its two bandpasses of 170--205 and 300--370 Å. All the components
in the detection chain have been characterized, including multilayer
telescope mirrors, lithographic slits, multilayer diffraction gratings,
microchannel-plate intensifiers, and active-pixel sensors. The results
demonstrate that EUNIS is the most sensitive solar EUV spectrograph
in existence. Its first flight is scheduled for 2005 November. EUNIS
is supported by NASA RTOP 432-03-31.
---------------------------------------------------------
Title: First Results From EUNIS 2005
Authors: Rabin, D. M.; Thomas, R. J.; Davila, J. M.; Brosius, J. W.;
Swartz, M.; Jordan, S. D.
2005AGUFMSH41B1122R Altcode:
The Extreme Ultraviolet Normal-Incidence Spectrograph (EUNIS) is
a sounding rocket experiment to investigate the energetics of the
solar corona and hotter transition region through high-resolution
imaging spectroscopy with a rapid (2 second) cadence. Pre-flight
characterization of throughput has demonstrated that EUNIS is the
most sensitive solar EUV spectrograph in existence, having over
100 times the throughput of its predecessor, the Solar Extreme
ultraviolet Research Telescope and Spectrograph (SERTS). We report
initial results from the first flight in November 2005 from White
Sands Missile Range. The main scientific goal of the first EUNIS
flight is to extend the investigation of transient phenomena, such as
nanoflares and blinkers, to shorter timescales than has been possible
with previous EUV spectrographs. The two independent optical systems
of EUNIS record spatially co-aligned spectra over two passbands
(170--205 Å and 300--370 Å) simultaneously with spectral resolution
of 60 mÅ or 120 mÅ, respectively. The longwave passband includes
He II 304 Å and strong lines from Fe XI--XVI. The shortwave passband
has a sequence of very strong Fe IX--XIII lines. Together, the EUNIS
telescopes furnish a wide range of temperature and density diagnostics
and enable underflight calibration of instrumental passbands on the
SOHO, TRACE, Solar-B, and STEREO missions.
---------------------------------------------------------
Title: Measured Pre-Flight Performance of the Extreme Ultraviolet
Normal Incidence Spectrograph (EUNIS)
Authors: Thomas, R. J.; Rabin, D. M.; Nowak, M. D.; Gum, J. S.; Seely,
J. F.; Seshadri, S.; Siegmund, O. H.
2005AGUSMSP43A..06T Altcode:
The Extreme Ultraviolet Normal-Incidence Spectrograph (EUNIS) is a
sounding rocket experiment that will investigate the energetics of
the solar corona and hotter transition region through high-resolution
imaging spectroscopy with a rapid (2 s) cadence. EUNIS features
independent optical systems to record spatially co-aligned spectra over
the two bandpasses 170--205 Å and 300--370 Å simultaneously. All
the components in the detection chain have been characterized,
including multilayer telescope mirrors, lithographic slits, multilayer
diffraction gratings, microchannel plate intensifiers, and active pixel
sensors. The results demonstrate that EUNIS is the most sensitive
solar EUV spectrograph in existence. Its first flight is scheduled
for 2005 August.
---------------------------------------------------------
Title: Coronal Heating, Spicules, and SolarB
Authors: Moore, R. L.; Falconer, D. A.; Porter, J. G.; Hathaway,
D. H.; Yamauchi, Y.; Rabin, D. M.
2004ASPC..325..283M Altcode:
We summarize certain observations of coronal luminosity, network
magnetic flux, spicules, and macrospicules. These observations together
imply that in quiet regions that are not influenced by active regions
the coronal heating comes from magnetic activity in the edges of the
network flux, possibly from explosions of sheared core fields around
granule-sized inclusions of opposite-polarity flux. This scenario can
be tested by SolarB.
---------------------------------------------------------
Title: The Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS)
Authors: Rabin, D.; Davila, J.; Thomas, R. J.; Engler, C.; Irish,
S.; Keski-Kuha, R.; Novello, J.; Nowak, M.; Payne, L.; Rodriguez, I.;
Saha, T.; Scott, R.; Swartz, M.; Trimble, M.; White, L.; Seshadri, S.
2003SPD....34.2007R Altcode: 2003BAAS...35..845R
EUNIS is a high-efficiency extreme ultraviolet spectrometer that
is expected to fly for the first time in 2004 as a sounding rocket
payload. Using two independent optical systems, EUNIS will probe
the structure and dynamics of the inner solar corona high spectral
resolution in two wavelength regions: 17-21 nm with 3.5 pm resolution
and 30-37 nm with 7 pm resolution. The long wavelength channel includes
He II 30.4 nm and strong lines from Fe XI-XVI; the short wavelength
channel includes strong lines of Fe IX-XIII. Angular resolution of
2 arcsec is maintained along a slit covering a full solar radius. <P
/>EUNIS will have 100 times the throughput of the highly successful
SERTS payloads that have preceded it. There are only two reflections in
each optical channel, from the superpolished, off-axis paraboloidal
primary and the toroidal grating. Each optical element is coated
with a high-efficiency multilayer coating optimized for its spectral
bandpass. The detector in each channel is a microchannel plate image
intensifier fiber-coupled to three 1K x 1K active pixel sensors. <P
/>EUNIS will obtain spectra with a cadence as short as 1 sec, allowing
unprecedented studies of the physical properties of evolving and
transient structures. Diagnostics of wave heating and reconnection wil
be studied at heights above 2 solar radii, in the wind acceleration
region. The broad spectral coverage and high spectral resolution will
provide superior temperature and density diagnostics and will enable
underflight calibration of several orbital instruments, including
SOHO/CDS and EIT, TRACE, Solar-B/EIS, and STEREO/EUVI. <P />EUNIS
is supported by NASA through the Low Cost Access to Space Program in
Solar and Heliospheric Physics.
---------------------------------------------------------
Title: SUMI - The Solar Ultraviolet Magnetograph Investigation
Authors: Porter, J. G.; West, E. A.; Davis, J. M.; Gary, G. A.; Noble,
M. W.; Thomas, R. J.; Rabin, D. M.; Uitenbroek, H.
2003SPD....34.2015P Altcode: 2003BAAS...35..847P
Solar physics has been successful in characterizing the full vector
magnetic field in the photosphere, where the ratio of gas pressure to
magnetic pressure (β ) is greater than 1. However, at higher levels
in the atmosphere, where β is much less than 1 and flares and CMEs
are believed to be triggered, observations are difficult, severely
limiting the understanding of these processes. In response to this
situation, we are developing SUMI (the Solar Ultraviolet Magnetograph
Investigation) a unique instrument designed to measure the circular
and linear polarization of upper chromospheric Mg II lines (280 nm) and
circular polarization of transition region C IV lines (155 nm). To date
the telescope mirrors have been built, tested and coated with dielectric
stacks designed to reflect only the wavelengths of interest. We have
also developed a unique UV polarimeter and completed the design of a
high-resolution spectrograph that uses dual toroidal varied-line-space
(TVLS) gratings. Incorporating measurements of those components
developed so far, the revised estimate of the system throughput exceeds
our original estimate by more than an order of magnitude. A sounding
rocket flight is anticipated in 2006. Our objectives and progress
are detailed in this presentation. <P />This work is supported by
NASA SR&T.
---------------------------------------------------------
Title: SHARPI: Solar High Angular Resolution Photometric Imager
Authors: Rabin, D.; Davila, J.; Content, D.; Keski-Kuha, R.;
Michael, S.
2002AAS...200.5606R Altcode: 2002BAAS...34..735R
Observing the lower solar atmosphere with enough linear resolution (<
100 km) to study individual magnetic flux tubes and other features on
scales comparable to the photon mean free path remains a challenging and
elusive goal. Space-borne instruments based on conventional heavy optics
proved to be too expensive, and adaptive optics on the ground made slow
progress for many years. Yet, the scientific case for high-resolution
imaging and magnetography has only become more compelling over the last
ten years. Today, ground-based adaptive optics is a promising approach
for small fields of view at visible wavelengths. Space experiments
will need to employ lightweight optics and low-cost platforms. The
Sunrise balloon experiment is one example. We describe a concept for
a sounding rocket experiment that will achieve 0.1-arcsecond imaging
using a lightweight, ultraprecise 55-cm mirror in the far ultraviolet
(160 nm continuum, Lyman alpha, and possibly C IV 155 nm). The f/1.2
parabolic primary mirror is entering the final stages of production. The
mirror is a ULE honeycomb design with front and back face sheets. The
front sheet will be figured to 6.3 nm rms with microroughness 1 nm
or better. For the initial proof of concept, we describe a no-frills,
high-cadence imager aboard a Black Brant sounding rocket. Development
of lightweight UV/EUV optics at Goddard Space Flight Center has been
supported by the GSFC Internal Research and Development program.
---------------------------------------------------------
Title: Observed properties of the solar cycle dynamo
Authors: Rabin, Douglas
2002ocnd.confE..32R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The New Solar Corona
Authors: Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.
2001ARA&A..39..175A Altcode:
We focus on new observational capabilities (Yohkoh, SoHO,
TRACE), observations, modeling approaches, and insights into
physical processes of the solar corona. The most impressive new
results and problems discussed in this article can be appreciated
from the movies available on the Annual Reviews website and at
http://www.lmsal.com/pub/araa/araa.html. "The Sun is new each
day." Heraclites (ca 530-475 BC) "Everything flows." Heraclites (ca
530-475 BC)
---------------------------------------------------------
Title: Overview of the Solar Ultraviolet Magnetograph Investigation
Authors: West, Edward A.; Porter, Jason G.; Davis, John M.; Gary,
G. Allen; Rabin, Douglas M.; Thomas, Roger J.; Davila, Joseph M.
2000SPIE.4139..350W Altcode:
Traditional magnetographs measure the solar magnetic field at the
visible 'surface' of the Sun, the photosphere. The Solar Ultraviolet
Magnetograph Investigation (SUMI) is a hardware development study
for an instrument to measure the solar magnetic field higher in the
atmosphere, in the upper chromosphere and in the transition region at
the base of the corona. The magnetic pressure at these levels is much
stronger than the gas pressure (in contrast to the situation at the
photosphere), so the field controls the structure and dynamics of the
atmosphere. Rapid changes in the magnetic structure of the atmosphere
become possible at this height, with the release of energy. Measurements
of the vector magnetic field in this region will significantly improve
our understanding of the physical processes heating the Sun's upper
atmosphere and driving transient phenomena such as flares and coronal
mass ejections. The instrument will incorporate new technologies to
achieve the polarization efficiencies required to measure the magnetic
splitting of lines in the VUV an UV (C<SUB>IV</SUB> at 1550 angstrom and
Mg<SUB>II</SUB> at 2800 angstrom). We describe the scientific goals,
the optical components that are being developed for a sounding rocket
program, and the SUMI baseline design.
---------------------------------------------------------
Title: Chromosphere: Fibrils
Authors: Rabin, D.
2000eaa..bookE2004R Altcode:
Fibrils are dark, elongated, curvilinear patterns in the CHROMOSPHERE
as seen through a filter that isolates the Hα spectral absorption
line of hydrogen. Well-developed fibrils occur in and around SOLAR
ACTIVE REGIONS (figure 1) and SOLAR FILAMENT CHANNELS....
---------------------------------------------------------
Title: The Spatial Distribution of Molecules in Sunspots
Authors: Rabin, D. M.; Clark, T. A.; Bergman, M. W.
2000SPD....31.0118R Altcode: 2000BAAS...32..804R
We report preliminary results from a program to map the concentration
of H<SUB>2</SUB>O, OH, and SiO in the atmospheres of sunspots using
imaging infrared spectroscopy. The water molecule is confined to
the inner core of the umbra, whereas OH can sometimes be detected
in the penumbra. Plots of line depth against continuum intensity
show an abrupt onset of absorption at a different intensity for
each molecule. A larger sample is needed to decide to what extent
such features are characteristic. Evershed flow is seen in OH in the
penumbra of spots near the limb, with typical outward velocities of
1-2 km s<SUP>-1</SUP>. Spatial imaging of molecular concentrations in
sunspots should eventually provide new diagnostics for the temperature
structure of the umbral atmosphere, as yet poorly determined. This work
has been supported by the University of Calgary and by the National
Science Foundation through its support of NSO/NOAO.
---------------------------------------------------------
Title: SUMI: The Solar Ultraviolet Magnetograph
Authors: Davis, J. M.; Porter, J. G.; Gary, G. A.; West, E. A.; Rabin,
D. M.; Thomas, R. J.; Davila, J. M.
2000SPD....31.0299D Altcode: 2000BAAS...32..828D
A major focus of solar physics is the measurement of the temporal
and spatial variability of solar magnetic fields from the photosphere
into the lower corona, together with the study of how their behavior
produces the dynamic phenomena in this region such as flares and
CMEs. Considerable success has been achieved in the characterization of
the full vector field in the photosphere, where β , the ratio of the
gas pressure to the magnetic pressure, is gtrsim1. At higher levels
in the atmosphere where β <<1, the magnetic field (through
the Lorentz force) controls the structure and dynamics of the solar
atmosphere, and rapid changes in structure with release of energy
become possible. However, observations of the field at these higher
levels have proven to be difficult, placing a serious limitation on our
understanding of the physical processes occurring there. This poster
will discuss the Solar Ultraviolet Magnetograph Investigation (SUMI),
a hardware development study for an instrument capable of measuring
the polarization in ultraviolet lines of C IV and Mg II formed in the
transition region and upper chromosphere. We are currently developing
optical technologies necessary to build an instrument that will
achieve a major advance in performance over that of earlier attempts
(e.g., SMM/UVSP). Initially configured as a sounding rocket payload,
such a UV magnetograph would allow us to make exploratory measurements
extending the observation of solar magnetic fields into new and dynamic
regimes. This work is supported by NASA through the SEC Program in
Solar Physics and the program for Technology Development for Explorer
Missions and Sofia.
---------------------------------------------------------
Title: Synoptic Solar Physics -- 18th NSO/Sacramento Peak Summer
Workshop
Authors: Balasubramaniam, K. S.; Harvey, Jack; Rabin, D.
1998ASPC..140.....B Altcode: 1998ssp..conf.....H
No abstract at ADS
---------------------------------------------------------
Title: The Solar Magnetic Field in Three Dimensions
Authors: Rabin, Douglas
1997SoPh..174..281R Altcode:
Historically, our understanding of the solar magnetic field has been
shaped by an interplay between theoretical ideas about the subsurface
dynamo and precise measurements of magnetic flux at the level of the
photosphere. Today we have an unprecedented ability to measure, or to
infer from measurements, properties of the magnetic field at every level
from the solar interior to interplanetary space, although photospheric
observations still lead the way in completeness and precision. I review
the state of our capabilities to measure or calculate the magnetic
field and suggest that the next major goal should be to follow specific
magnetic structures in space and time from before they emerge until
they can no longer be detected at any level.
---------------------------------------------------------
Title: Toward Zeeman Magnetometry in the Corona: Line-of-Sight Effects
Authors: Rabin, D.
1997SPD....28.0144R Altcode: 1997BAAS...29..887R
One of the motivations for a large-aperture ground-based coronagraph
is the possibility of measuring magnetic flux in the solar corona
using the Zeeman sensitivity (Lande g = 1.5) of emission lines such
as Fe XIV 530.3 nm, Fe X 637.4 nm, and Fe XIII 1074.7 nm. However,
because the corona is optically thin, it is necessary to consider the
effects of superposition along the line-of-sight on the interpretation
of a detected Zeeman signal. Simple models are used to explore and
illustrate the likely importance of line-of-sight confusion.
---------------------------------------------------------
Title: F. Espenak and J. Anderson, Total Solar Eclipse of 1999 August
11, NASA Reference Publication 1398
Authors: Rabin, Douglas
1997EM&P...76..123R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microflaring in Sheared Core Magnetic Fields and Episodic
Heating in Large Coronal Loops
Authors: Porter, J. G.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.; Shimizu, T.
1996AAS...188.7018P Altcode: 1996BAAS...28..941P
We have previously reported that large, outstandingly-bright coronal
loops within an active region or stemming from an active region have
one end rooted around a magnetic island of included polarity that is
itself a site of locally enhanced coronal heating (X-ray bright point)
[Porter et al 1996, in Proceedings of the Yohkoh Solar/Stellar IAU
Symposium, ed. Y. Uchida, T. Kosugi, H.S. Hudson (Kluwer: Dordrecht), in
press]. This suggests that exceptional magnetic structure in and around
the magnetic island fosters magnetic activity, such as microflaring,
that results in the enhanced coronal heating in both the compact core
field around the island and in the body of large loops that extend
from this site. We have also reported that enhanced coronal heating
in active regions goes hand-in-hand with strong magnetic shear in
the core magnetic fields along polarity neutral lines (Falconer et al
1995, BAAS, 27(2), 976). Here, by combining MSFC vector magnetograms
with an NSO full-disk magnetogram and Yohkoh SXT coronal images, we
examine the incidence of sheared core fields, enhanced coronal heating,
and microflaring in two active regions having several good examples
of enhanced extended coronal loops. It appears that the localized
microflaring activity in sheared core fields is basically similar
whether the core field is on the neutral line around an island of
included polarity or on the main neutral line of an entire bipolar
active region. This suggests that the enhanced coronal heating in an
extended loop stemming from near a polarity inversion line requires a
special field configuration at its foot to plug it into the activity at
the neutral line, rather than a different kind of activity in the core
field on the neutral line. We also examine whether the waxing and waning
of the coronal brightness of extended loops shows any correlation with
the vigor or frequency of microflaring at the feet. This research was
supported by the Solar Physics Branch of NASA's Office of Space Science.
---------------------------------------------------------
Title: NIM-2 -- A Near Infrared Imaging Vector Magnetograph
Authors: Rabin, D.; Keller, C.; Jaksha, D.
1996AAS...188.6706R Altcode: 1996BAAS...28R.934R
NIM-1 is a spectrograph-based Stokes polarimeter for measuring the
strength and orientation of magnetic fields in the solar photosphere
using two Zeeman-sensitive Fe I lines (g = 3 and g_geff = 1.53) near
1565 nm. NIM-2, now under construction, also uses these spectral
lines but is based on a high-resolution Fabry-Perot etalon. NIM-2
will eliminate the image scanning and consequent spatial distortions
of NIM-1 and will be compact and light enough to serve as a prototype
for balloon or space instruments. The Queensgate etalon will provide a
spectral resolving power of 10(5) over a 1-nm free spectral range. The
initial detector will be the 256(2) InSb array shared with NIM-1, but
NIM-2 is designed to accommodate a 512(2) or 1024(2) “Aladdin” InSb
array. The data system, also shared with NIM-1, is being upgraded to
handle the faster switching speed ( ~ 8 ms) of improved liquid-crystal
variable retarders. NOAO is operated for the NSF by the Association of
Universities for Research in Astronomy. Near-infrared magnetometry at
NSO is supported by the the NASA Space Physics Division through the
SR&T program in solar physics.
---------------------------------------------------------
Title: Observations of Solar Carbon Monoxide with an Imaging Infrared
Spectrograph. I. Thermal Bifurcation Revisited
Authors: Ayres, Thomas R.; Rabin, Douglas
1996ApJ...460.1042A Altcode:
We describe long-slit spectroscopy of the solar 4.7 μm carbon monoxide
(CO) Δυ = 1 bands at the Main spectrograph of the NSO McMath-Pierce
telescope. We utilized stigmatic imaging of the temperature-
and velocity-sensitive CO absorptions to map quiet regions near
disk center and at the extreme limb. At Sun center the dominant
long-lived spatial structures are small-scale hot spots associated
with fragments of the supergranulation network seen in cotemporal Ca
II filtergrams. Oscillatory thermal and velocity fluctuations of the
global p-mode interference pattern are a pervasive feature of the
maps, but the rms amplitudes (≍70 K and ≍240 m s<SUP>-1</SUP>)
are perturbations on a relatively unstructured outer photosphere. We
occasionally see small-scale transient cooling episodes longer lived
than the p-mode wavepackets that might be overshooting granules
or rising magnetic flux ropes. The events are too rare, however,
to influence the global properties of the CO fundamental bands. <P
/>Seeing-selected frames of the off-limb CO emissions show a typical
extension of 0".6 for the strongest lines, with little variation along
the limb. The off-limb extensions indicate the presence of cool gas
up to 350 km above the "T<SUB>min</SUB>" of popular reference models
of the solar chromosphere. <P />We carried out two-dimensional model
atmosphere simulations to study the effects of thermal inhomogeneities
on the disk-center, extreme-limb, and off-limb behavior of the CO
lines. The models are spherically symmetric, static, and in LTE. Our
data favor a scenario in which the bulk of the low chromosphere
below the base of the magnetic "canopy" is in reality a "COmosphere"
dominated by gas colder than the minimum temperature in conventional
models. <P />The moderate-scale (≍5"), mild thermal perturbations
of the p-mode pattern have little influence on the CO Δυ = 1
spectra. Small-scale (≍1") hot regions embedded in a cool average
atmosphere are strongly "shadowed" at the extreme limb. The shadowing
is of little consequence, however, because the atmosphere already is
dominated by the cool component. The opposite scenario-small-scale
cold regions in a warm average produce effective shadowing at the
limb for granule-size (≍1"-2") dark points only if the covering
fraction is relatively large (f &#8819 0.2). That scenario is
ruled out: it predicts high-contrast dark spots at disk center,
contrary to our observations. We also argue against the possibility
of shadowing by even smaller, subresolution (≍0"3) cold spots with
f &#8819 0.1. <P />We show that multistep reactions, rather than
direct radiative associations, dominate the gas-phase chemistry of
CO molecules under conditions typical of the outer photosphere. The
CO formation and radiative cooling timescales are fast enough that
low-temperature plasma conditions can be restored following disruption
by a localized heating event such as a Ca II K<SUB>2v</SUB> "flash." In
cool giant stars, the chemical formation timescales are much longer than
in dwarfs like the Sun. Nevertheless, the density dependence is such
that the molecular cooling proceeds proportionately more rapidly than
the gas dynamics, ensuring an even more important role for autocatalyzed
"thermal bifurcation."
---------------------------------------------------------
Title: Magnetic Roots of Enhanced High Coronal Loops
Authors: Porter, J. C.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.; Shimizu, T.
1996mpsa.conf..429P Altcode: 1996IAUCo.153..429P
No abstract at ADS
---------------------------------------------------------
Title: Line-of-sight magnetic flux imbalances caused by electric
currents
Authors: Gary, G. Allen; Rabin, Douglas
1995SoPh..157..185G Altcode: 1995SoPh..157..185A
Several physical and observational effects may contribute to the
significant imbalances of magnetic flux that are often observed in
active regions. We consider an effect not previously treated: the
influence of electric currents in the photosphere. Electric currents can
cause a line-of-sight flux imbalance because of the directionality of
the magnetic field they produce. Currents associated with magnetic flux
tubes produce larger imbalances than do smoothly-varying distributions
of flux and current. We estimate the magnitude of this effect for
current densities, total currents, and magnetic geometry consistent
with observations. The expected imbalances lie approximately in
the range 0-15%, depending on the character of the current-carrying
fields and the angle from which they are viewed. Observationally,
current-induced flux imbalances could be indicated by a statistical
dependence of the imbalance on angular distance from disk center. A
general study of magnetic flux balance in active regions is needed to
determine the relative importance of other - probably larger -effects
such as dilute flux (too weak to measure or rendered invisible by
radiative transfer effects), merging with weak background fields,
and long-range connections between active regions.
---------------------------------------------------------
Title: Photospheric Origins of Enhanced High Coronal Loops
Authors: Porter, J. G.; Falconer, D. A.; Moore, R. L.; Harvey, K. L.;
Rabin, D. M.
1995SPD....26..704P Altcode: 1995BAAS...27..966P
No abstract at ADS
---------------------------------------------------------
Title: Eclipse Measurements of the Distribution of CO Emission Above
the Solar Limb
Authors: Clark, T. A.; Lindsey, C.; Rabin, D. M.; Livingston, W. C.
1995itsa.conf..133C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Next Generation of Near-Infrared Solar Magnetographs
(Abstract only)
Authors: Rabin, D.
1995itsa.conf...87R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Scaling of Solar Magnetic Fields
Authors: Ruzmaikin, A.; Cadavid, C.; Lawrence, J.; Rabin, D.; Lin,
H. -S.
1995itsa.conf..375R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stokes Polarimetry with the Near Infrared Magnetograph ---
Telescope Polarization Effects
Authors: Rabin, D.
1994AAS...18512302R Altcode: 1994BAAS...26.1522R
NIM produces spatial images of magnetic field properties in the
low photosphere from polarized spectra of the g = 3 line Fe I
6388.64 cm^{-1} (1.5648 \micron). Designed initially for circular
polarimetry, NIM can now acquire full Stokes information. I discuss
the approximate polarization transfer (Mueller) matrix for NIM as
used at the McMath-Pierce Telescope and compare it with the transfer
matrix at visible wavelengths. Although telescope polarization
effects are generally smaller in the infrared, in one respect the
infrared requires careful treatment. In the visible, the net linear
polarization due to the Zeeman effect is often small enough compared to
circular polarization that linear-to-circular instrumental crosstalk
is unimportant. In the infrared, the Zeeman components are usually so
strongly split that the linearly polarized Stokes components (Q and U)
are comparable in magnitude to the circular component (V). This work
has been supported by the NASA SR&T program in solar physics.
---------------------------------------------------------
Title: Eclipse Observations of the Extreme Solar Limb Profile of HI
Pfund beta Emission.
Authors: Clark, T. A.; Lindsey, C. A.; Rabin, D. M.; Livingston, W. C.
1994AAS...185.4412C Altcode: 1994BAAS...26.1378C
A region of the infrared solar spectrum (2147.7 - 2150.1 cm(-1)
) around the HI Pfund beta line (2148.79 cm(-1) ) was monitored
through 3 eclipse "contacts" with the Amber InSb array on the Main
spectrograph on the McMath-Pierce telescope during the 10 May 1994
partial solar eclipse over Kitt Peak National Observatory to produce
limb profiles of intensity and line width to an angular resolution
of 0.15 arc second. This line is broad (FWHM = 0.9 cm(-1) and shallow
(5.7%) in absorption at disk center but shows a narrow emission core
above the continuum envelope at 2 arc seconds inside the limb which
remains visible out to 4.5 arc seconds beyond the continuum limb. The
Pfund beta peak intensity appears to follow the continuum profile at
the limb but then intensifies again to reach a peak at about 1000 km
above the limb in a manner similar to that of the HeI D3 line. The line
width becomes narrower with height above the limb, reaching a FWHM of
0.22 cm(-1) at several arc seconds above the limb. These profiles will
be discussed in relation to those of other HI lines above the solar
limb. This work was supported by NSERC of Canada and by NSO, Tucson.
---------------------------------------------------------
Title: Imaging spectroscopy of the solar CO lines at 4.67 microns
Authors: Uitenbroek, Han; Noyes, R. W.; Rabin, Douglas
1994ApJ...432L..67U Altcode:
We analyze spatially and temporally resolved spectra of the fundamental
vibration-rotation transitions of carbon monoxide (CO) in the solar
spectrum at 4.67 micrometers. Our observations imply that, in the quiet
Sun, spatial variations in CO intensity are largely dynamical in nature,
reinforcing the suggestion that dynamical effects play a key role in
the formation of the dark CO cores. Time sequences of resolved spectra
exhibit mainly 3 minute power in line-core intensity but mainly a 5
minute period in Doppler shift. The weak 7-6 R68 line shows normal
Evershed flow in the penumbra of a sunspot; we find evidence for the
onset of inverse Evershed flow in the strong 3-2 R14 line. Spectra at
the limb indicate that 3-2 R14 emission extends approximately 360 km
beyond the continuum limb.
---------------------------------------------------------
Title: A Magnetic Field Strength vs. Temperature Relation in Sunspots
Authors: Kopp, G.; Rabin, D.
1994IAUS..154..477K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Near Infrared Imaging Magnetometry
Authors: Rabin, D.
1994IAUS..154..449R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Infrared solar physics: proceedings of the 154th Symposium
of the International Astronomical Union, held in Tucson, Arizona,
U.S.A., March 2-6, 1992.
Authors: Rabin, D. M.; Jefferies, John T.; Lindsey, C.
1994IAUS..154.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Recent array-detector Observations of the solar CO Fundamental
vibration--rotation Transitions at 4.67 microns
Authors: Uitenbroek, H.; Noyes, R. W.; Rabin, D.
1993AAS...183.5902U Altcode: 1993BAAS...25.1386U
We present recent observations of lines of the fundamental
vibration--rotation transitions of carbon monoxide (CO) in the solar
atmosphere obtained with the 256(2) infrared array detector at the
McMath telescope on Kitt Peak. Standard, plane parallel, solar models
have these lines form in LTE around the temperature minimum region;
they should be indicative of electron temperatures there. However,
matching observed line profiles in a standard solar model requires
temperatures as low as 3700 K which are not confirmed by any other
spectral diagnostic. We investigate whether this discrepancy can be
solved by invoking spatial inhomogeneities or temporal variations
or a combination of both. To this end we obtained series of
spectra-spectroheliograms at different positions on the disk as well
as time series of slit-spectra at a single position. The former type
of observations allow us to study spatial inhomogeneities in stronger
and weaker lines and the IR continuum at 4.6 microns and to distinguish
between variations due to the 5-minute oscillations and the more steady
patterns due to magnetic fields by comparing heliograms taken several
minutes apart. We also obtained spectra with the slit crossing the limb
giving us a more rigid registration of the intensity variations above
the limb as compared to previous single-detector measurements. Early
analysis shows that high and low excitation lines behave differently
at the limb which may bear information on the temperature structure
of the atmosphere just above the minimum.
---------------------------------------------------------
Title: A Magnetograph Comparison Workshop
Authors: Jones, H.; Bogart, R.; Canfield, R.; Chapman, G.; Henney,
C.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet, V.;
Rabin, D.; Ulrich, R.; Walton, S.
1993BAAS...25.1216J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intercomparison of Seven Magnetographs
Authors: Walton, S. R.; Bogart, R. S.; Chapman, G. A.; Henney, C.;
Jones, H.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet,
V.; Rabin, D.
1993BAAS...25.1205W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of p-Mode Energy Propagation in the Quiet Solar
Photosphere
Authors: Fontenla, J. M.; Rabin, D.; Hathaway, D. H.; Moore, R. L.
1993ApJ...405..787F Altcode:
We have measured and analyzed the p-mode oscillations in the profile
of the Mg I 4571 A line in a quiet region near disk center. The
oscillations are found to be mostly standing waves, in agreement with
previous work. However, a small propagating component is measured, and
we determine the direction, magnitude, and vertical variation of the
energy propagation. The work integral indicates an upward energy flow of
about 2 x 10 exp 7 ergs/sq cm/s at a height of 50 km above the base of
the photosphere for waves with frequencies of 2-16 mHz. This energy flow
decreases exponentially with height and drops below 10 exp 5 ergs/sq
cm/s in the uppermost photosphere. The energy flow leaving the upper
photosphere is at least an order of magnitude too small to constitute a
significant source of heating for the chromosphere. However, the p-mode
damping in the lower photosphere approaches levels large enough to
account for the measured p-mode line widths. The relative amplitudes
and phases of the thermodynamic quantities indicate that the p-mode
are neither adiabatic nor isothermal in the photosphere.
---------------------------------------------------------
Title: Siphon Flow Across the Magnetic Neutral-Line of an Active
Region
Authors: Solanki, S. K.; Ruedi, I.; Rabin, D.
1993ASPC...46..534S Altcode: 1993IAUCo.141..534S; 1993mvfs.conf..534S
No abstract at ADS
---------------------------------------------------------
Title: NIM --- A Near Infrared Magnetograph
Authors: Rabin, D.; Jaksha, D.; Kopp, G.; Mahaffey, C.
1992AAS...181.8101R Altcode: 1992BAAS...24.1251R
\newcommand{\micron}{microns} \newcommand{\kayser}{cm(-1)
} \newcommand{\NIM}{NIM} We describe a new instrument for mapping
magnetic field strength in the active solar photosphere. \NIM\ is a
Stokes spectropolarimeter that exploits the high Zeeman sensitivity of
the line Fe I 6388.64 \kayser\ (15648.5 Angstroms, e\:(7D_1) -- 3d(6) 4s
5p\:(7D^) o_1, Lande g = 3.00, chi_e = 5.36 eV) to measure vec {B}. For
|B| ga 850 G, the magnitude of the field is derived, without adjustable
parameters, from the complete splitting of the Zeeman components. The
relative strengths of the Stokes components indicate the direction of
the field. The absolute strength of the polarized signal depends on
the areal filling factor, inclination, continuum contrast, and line
strength of the magnetic flux tubes within the angular resolution
element. \NIM\ comprises the following subsystems: precision image
scanner liquid crystal polarization modulators and control electronics
slit spectrograph transfer and minification optics 128 times 128 InSb
infrared array camera computer for data acquisition and user interface
\NIM\ builds up a two-dimensional array of polarized spectra by scanning
the solar image across the spectrograph slit. The spatial and spectral
sampling frequencies are 1.0 arcsec or 0.5 arcsec per pixel (depending
on which telescope is used) and 0.025 \kayser\ per pixel. At each slit
position, 8 polarization pairs for each Stokes parameter (e.g., +/- V)
are acquired at 7 Hz, averaged, and recorded in FITS format. A 128 times
128 arcsec(2) map is acquired in about 20 minutes. \NIM\ is available
to NSO visiting observers at the McMath-Pierce Telescope on Kitt Peak.
---------------------------------------------------------
Title: Solar infrared presensitization photography
Authors: Geary, Joseph M.; Rabin, Douglas
1992OptEn..31.2694G Altcode:
Infrared presensitization photography (IRPP) is used to acquire images
of the solar disk in the 1 to 2 micrometers regime. This is the first
time IRPP has been employed at such short IR wavelengths, used against
a thermal (instead of a laser) source, and applied to astronomy. The
experiments demonstrate the feasibility of IRPP for solar imaging,
but the image quality needs improvement for solar research.
---------------------------------------------------------
Title: A Photometric Study of Faculae and Sunspots Between 1.2-MICRONS
and 1.6-MICRONS
Authors: Moran, T.; Foukal, P.; Rabin, D.
1992SoPh..142...35M Altcode:
We investigate further the interpretation of dark magnetic faculae
observed in previous imaging of the solar photosphere at 1.63 μm. We
show that their contrast at 1.63 μm increases with magnetic flux
beyond a threshold value of Φ ∼ 2 × 10<SUP>18</SUP> Mx and blends
smoothly with the contrast vs flux relation measured at this wavelength
for larger structures of sunspot size. Not all facular structures that
are bright in Ca K are dark at 1.63 μm, apparently because their
magnetic flux is not large enough. After correction for blurring,
the contrast of the dark faculae observed near the disc center at
1.63 μm is approximately 4%. But our observations at 1.23 μm,
which probe slightly higher photospheric levels, do not show these
dark faculae. These results indicate that magnetic flux tubes of
diameter as small as 500 km significantly inhibit convective heat
flow to the photosphere, much as do sunspot flux tubes of much larger
diameter. They also suggest that, in even smaller flux tubes, the
inhibition becomes rapidly less significant. Finally, we show that the
sunspot-size dependence of umbral infrared contrast versus wavelength
that we observe can probably be explained in terms of instrumental
blurring. Observations with lower scattered light will be required
to determine whether a real decrease of contrast with diameter also
plays a role.
---------------------------------------------------------
Title: A Relation Between Magnetic Field Strength and Temperature
in Sunspots
Authors: Kopp, Greg; Rabin, Douglas
1992SoPh..141..253K Altcode:
We present Stokes I Zeeman splitting measurements of sunspots using the
highly sensitive (g = 3) Fe I line at λ = 1.5649 μm. The splittings
are compared with simultaneous intensity measurements in the adjacent
continuum. The relation between magnetic field strength and temperature
has a characteristic, nonlinear shape in all the spots studied. In the
umbra, there is an approximately linear relation between B<SUP>2</SUP>
and T<SUB>b</SUB>, consistent with magnetohydrostatic equilibrium in
a nearly vertical field. A distinct flattening of the B<SUP>2</SUP> vs
T<SUB>b</SUB>relationship in the inner penumbra may be due to changes
in the lateral pressure balance as the magnetic field becomes more
horizontal; spatially unresolved intensity inhomogeneities may also
influence the observed relation.
---------------------------------------------------------
Title: Pervasive Variability in the Quiet Solar Transition Region
Authors: Rabin, Douglas; Dowdy, James F., Jr.
1992ApJ...398..665R Altcode:
Extreme UV spectroheliograms from an experimental time series are
employed to investigate the nature of the quiet solar transition
region with respect to temporal variability. A statistical treatment
is developed to analyze the fraction of spatial elements that yield
intensity variations significantly higher than the signal noise. The
EUV intensity in every spatial resolution varies on a time scale
of minutes by about 10-30 percent, and the fractional amplitude of
the temporal variations is found to be nearly independent of mean
intensity. The paper concludes that the quiet solar transition region
is probably generated and modulated by small-scale magnetic activity,
since the temporal variability in the transition region is spatially
uniform and rather pervasive.
---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. IV -
Discovery of a siphon flow
Authors: Rueedi, I.; Solanki, S. K.; Rabin, D.
1992A&A...261L..21R Altcode:
Spectra of two neighboring IR lines, Fe I 15648.5 A and Fe I 15652.9 A,
are analyzed. The spectra were obtained with an IR array detector in
active region plages with the entrance slit of the spectrograph placed
across the polarity-inversion (neutral) line. Near the neutral line the
positive polarity field is weaker (about 1200 G) and shows an upflow
of up to 2 km/s, while the negative polarity field is stronger (about
1500 G) and exhibits a downflow of up to 1 km/s. This configuration
corresponds to the expected signature of a siphon flow along a loop
connecting flux tubes across the neutral line.
---------------------------------------------------------
Title: Spatially Extended Measurements of Magnetic Field Strength
in Solar Plages
Authors: Rabin, Douglas
1992ApJ...391..832R Altcode:
The study determines magnetic field strengths along one spatial
dimension of a plage region from circularly polarized (Stokes V) spectra
of a highly Zeeman-sensitive iron line at 6388.6/cm (1.565 micron). The
measured fields are found to lie primarily in the range 1200-1700
G. The mean formal precision for a single determination is +/-65 G. More
than 90 percent of the magnetic flux is kilogauss-strength fields. The
field strength is coherently organized on spatial scales from 1 arcmin
to the limit of angular resolution (2 arcsec). It is inferred from
the amplitude of the V signal that the spatial filling factor of the
strong-field elements can approach 0.5 within a 2-arcsec resolution
element. Magnetic field strength and amplitude are correlated in the
sense that locations with stronger mean fields have larger V amplitudes,
but the relationship shows more scatter than can be explained by errors
in measurement. The individual sigma-components of the V profile are
broader than an average quiet-sun line profile would produce by an
amount corresponding to 625 G or 4.1 km/s; Zeeman broadening due to
a range of magnetic field strength within the resolution element is
proposed as the likely explanation.
---------------------------------------------------------
Title: A True-Field Magnetogram in a Solar Plage Region
Authors: Rabin, Douglas
1992ApJ...390L.103R Altcode:
The Near-Infrared Magnetograph is used to make the first 2D image of
true magnetic field strength in the solar photosphere. The magnitude
of the magnetic field vector is derived with a typical formal
precision of + or - 75 G (2 sigma) from circularly polarized spectra
of a highly Zeeman-sensitive iron line at 6388.6/cm. The true-field
map demonstrates that the properties of 'kilogauss' flux tubes vary
coherently on a variety of spatial scales within the 1-arcmin field of
view. The measured fields span the range 1000-1700 G. The amplitude
of the polarized signal implies that the spatial filling factor of
the flux tubes can approach 0.3 at the seeing-limited resolution of 2
arcsec. Magnetic field strength and magnetic flux are statistically
related in the sense that weak-field areas are weak-flux areas, but
strong fields are present in both strong-flux and weak-flux areas. This
implies a degree of independence in the relationship between the
filling factor of flux tubes and their individual properties, such as
field strength, pressure, and temperature.
---------------------------------------------------------
Title: Infrared Determinations of Magnetic Profiles in Sunspots
Authors: Kopp, G.; Kuhn, J.; Lin, H.; Rabin, D.
1992AAS...180.1202K Altcode: 1992BAAS...24R.747K
We present measurements of a sunspot using unpolarized observations of
the magnetically-sensitive (Lande g=3) Fe I line at lambda =1.5649
microns (6388.6 cm(-1) ). We compare the magnetic field profile
from this fairly symmetric spot with model profiles. Splittings
in this infrared line are nearly a factor of 3 greater than in a
comparable visible line, since Zeeman splitting as a fraction of
linewidth increases linearly with wavelength. The infrared is also
less affected by stray light than the visible, because the intensity
contrast is reduced, decreasing the effects of stray light, and because
instrumental scatter is lower in the infrared. The combination of the
magnetic and stray light advantages of the infrared and the recent
availability of “large” infrared arrays has made possible more
sensitive determinations of the magnetic field profile throughout
sunspots. From observations of several sunspots, we find that the
magnetic field strength, determined in the strong field regime, is not
a smooth function of radius from spot center, and that single radial
parameter models do not accurately describe the observed spots.
---------------------------------------------------------
Title: Solar infrared presensitization photography
Authors: Geary, Joseph M.; Rabin, Douglas
1992SPIE.1638...63G Altcode:
Infrared presensitization photography (IRPP) is used to acquire images
of the solar disk in the 1 to 2 micrometers regime. This is the first
time IRPP has been employed at such short IR wavelengths, used against
a thermal (instead of a laser) source, and applied to astronomy. The
experiments demonstrate the feasibility of IRPP for solar imaging,
but the image quality needs improvement for solar research.
---------------------------------------------------------
Title: Magnetic Field Strength; Continuum Intensity Measurements of
Sunspots at 1.56 microns
Authors: Kopp, M. G.; Rabin, D.
1992ASPC...26..246K Altcode: 1992csss....7..246K
No abstract at ADS
---------------------------------------------------------
Title: Fine-Scale Magnetic Fields in the Solar Photosphere (Invited
Review)
Authors: Rabin, D.
1992ASPC...26..201R Altcode: 1992csss....7..201R
No abstract at ADS
---------------------------------------------------------
Title: Energy Balance in Coronal Funnels
Authors: Rabin, Douglas
1991ApJ...383..407R Altcode:
The energy balance in magnetic flux tubes is examined semianalytically
for the case in which thermal conduction balances radiation or in which
enthalpy transport occurs. Different values are considered for areal
constriction, shape, length, and maximum temperature. The overall
energy budget of the solar corona is not significantly affected by
magnetic constriction. A bowl-shaped funnel with a constriction factor
of 4 describes the empirical differential-emission measure for log-T
values between approximately 5.3 and 6.0. Loop-scaling relationships
are derived for the full range of models to illustrate the dependence
of the constant of proportionality on the properties of the magnetic
constriction. Constriction can reduce the total energy requirement of
the funnel by a factor of 5 and not affect the differential emission
in flow-dominated models.
---------------------------------------------------------
Title: A True-Field Magnetogram
Authors: Rabin, D.; Cole, L.; Jaksha, D.; Iwata, K.
1991BAAS...23.1030R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zeeman Splitting and Continuum Measurements of Sunspots at
1.56 μm
Authors: Kopp, G.; Rabin, D.; Lindsey, C.
1991BAAS...23.1055K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plage magnetic field strengths from near-infrared spectra.
Authors: Rabin, D.; Jaksha, D.; Plymate, C.; Wagner, J.; Iwata, K.
1991sopo.work..361R Altcode:
The authors have measured magnetic field strenghts in a small sample
of plages from Stokes V spectra of two Zeeman-sensitive iron lines
near 6388 cm<SUP>-1</SUP>(1.565 μm). The detected fields are strong
(≡10<SUP>3</SUP>gauss), but their strength varies significantly from
feature to feature. The individual σ-components are broader than
an average quiet-Sun line profile; if this broadening is primarily
magnetic, there is typically about a 20% range in field strength within
a 2-arcsecond resolution element. These observations represent the
first stage of a project to build a near-infrared magnetograph that
will produce two-dimensional maps of local magnetic field strength in
the low photosphere.
---------------------------------------------------------
Title: The solar activity cycle.
Authors: Rabin, Douglas M.; DeVore, C. R.; Sheeley, Neil R., Jr.;
Harvey, Karen L.; Hoeksema, J. T.
1991sia..book..781R Altcode:
Study of the solar cycle is entering a new era dominated by objective,
precise measurements of magnetic, velocity and radiation fields over the
surface of the Sun. This review emphasizes observations of photospheric
magnetic flux during cycle 21 (1976 - 1986) and how these measurements
have been used to model the cyclic variability of the heliospheric
magnetic field. Indices of solar activity are discussed in terms of
their potential to figure in theoretical or empirical models. Other
recent data, such as measurements of large-scale surface flows and
information on the Sun's internal rotation from helioseismology, as
well as the magnetic flux observations, are considered in the context
of Babcock's phenomenological model of the solar cycle: can this model
still serve? Is there anything better to replace it?
---------------------------------------------------------
Title: Solar IR presensitization photography
Authors: Geary, Joseph M.; Rabin, Douglas; Lindmayer, Joseph
1990SPIE.1235..181G Altcode:
The principles involved in the IR presensitization photography (IRPP)
are discussed, and the feasibility of using IRPP in solar IR astronomy
is investigated. Images of the solar disk were acquired in the 1-
to 2-micron regime, demonstrating that IRPP is a feasible technique
for solar imaging. However, in order to use IRPP images for solar
research, the image quality needs improvement in terms of resolution
and photometric accuracy.
---------------------------------------------------------
Title: Infrared Imaging of Faculae at the Deepest Photospheric Layers
Authors: Foukal, P.; Little, R.; Graves, J.; Rabin, D.; Lynch, D.
1990ApJ...353..712F Altcode:
The NOAO 58 x 62 InSb array and the National Solar Observatory McMath
telescope are used to image the deepest photospheric layers of three
active regions at the 1.63-micron opacity minimum. The faculae are
darker than the photosphere, with a measured contrast of at least 2
percent at positions on the disk with mu = 0.75-1.0. Near the limb,
they are brighter than the photosphere, as in the visible. At mu =
0.5-0.75, they are difficult to detect at 1.63 micron. The observation
that faculae and their immediate surroundings exhibit a clear deficit
of brightness temperature near disk center at 1.63 micron seems to
rule out the hillock model put forward to explain their center-to-limb
contrast variation.
---------------------------------------------------------
Title: Magnetic Loops in the Chromospheric Network
Authors: Moore, R. L.; Rabin, D. M.; Dowdy, J. F., Jr.
1990BAAS...22..815M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurement of Dissipation or Pumping of P-Modes in the
Solar Photosphere
Authors: Fontenla, J. M.; Hathaway, D. H.; Rabin, D.; Moore, R.
1990BAAS...22..856F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spatially Resolved Measurements of Magnetic Field Strength
Outside Sunspots
Authors: Rabin, D. M.
1990BAAS...22..840R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Infrared Imaging of Faculae at the Deepest Photospheric Layers
Authors: Foukal, P.; Little, R.; Graves, B.; Rabin, D.; Lynch, D.
1989BAAS...21..828F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ubiquity of magnetic Loops in the Chromospheric Network
Authors: Moore, R. L.; Rabin, D. M.; Dowdy, J. F., Jr.
1989BAAS...21..864M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measuring Sunspot Magnetic Fields with the Infrared Line
Fe Iλ15649
Authors: Rabin, D. M.; Graves, J. E.
1989BAAS...21R.854R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric explosions.
Authors: Doschek, G. A.; Antiochos, S. K.; Antonucci, E.; Cheng,
C. -C.; Culhane, J. L.; Fisher, G. H.; Jordan, C.; Leibacher, J. W.;
MacNiece, P.; McWhirter, R. W. P.; Moore, R. L.; Rabin, D. M.; Rust,
D. M.; Shine, R. A.
1989epos.conf..303D Altcode:
The work of this team addressed the question of the response and
relationship of the flare chromosphere and transition region to the
hot coronal loops that reach temperatures of about 10<SUP>7</SUP>K
and higher. Flare related phenomena such as surges and sprays were
also discussed. The team members debate three main topics: 1) whether
the blue-shifted components of X-ray spectral lines are signatures of
"chromospheric evaporation"; 2) whether the excess line broadening of UV
and X-ray lines is accounted for by "convective velocity distribution"
in evaporation; and 3) whether most chromospheric heating is driven by
electron beams. These debates illustrated the strengths and weaknesses
of our current observations and theories.
---------------------------------------------------------
Title: A Three-Dimensional View of the DQ Herculis Nova Shell
Authors: Barden, S. C.; Rabin, D. M.; Wade, R. A.
1988BAAS...20R1052B Altcode: 1988BAAS...20Z1052B
No abstract at ADS
---------------------------------------------------------
Title: Observed Magnetic Structure and Activity in the Quiet Solar
Atmosphere
Authors: Moore, R. L.; Dowdy, J. F., Jr.; Rabin, D. M.
1988BAAS...20.1009M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: How Quiet is Quiet?-Movies of the Quiet Sun in EUV Emission
Lines
Authors: Rabin, D. M.; Dowdy, J. F., Jr.; Withbroe, G. L.
1988BAAS...20.1009R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: 10.7 cm solar radio flux and the magnetic complexity of
active regions.
Authors: Wilson, Robert M.; Rabin, Douglas; Moore, Ronald L.
1987SoPh..111..279W Altcode:
During sunspot cycles 20 and 21, the maximum in smoothed 10.7-cm solar
radio flux occurred about 1.5 yr after the maximum smoothed sunspot
number, whereas during cycles 18 and 19 no lag was observed. Thus,
although 10.7-cm radio flux and Zürich suspot number are highly
correlated, they are not interchangeable, especially near solar
maximum. The 10.7-cm flux more closely follows the number of sunspots
visible on the solar disk, while the Zürich sunspot number more
closely follows the number of sunspot groups. The number of sunspots
in an active region is one measure of the complexity of the magnetic
structure of the region, and the coincidence in the maxima of radio
flux and number of sunspots apparently reflects higher radio emission
from active regions of greater magnetic complexity. The presence
of a lag between sunspot-number maximum and radio-flux maximum in
some cycles but not in others argues that some aspect of the average
magnetic complexity near solar maximum must vary from cycle to cycle. A
speculative possibility is that the radio-flux lag discriminates between
long-period and short-period cycles, being another indicator that the
solar cycle switches between long-period and short-period modes.
---------------------------------------------------------
Title: Thermal Conduction in Magnetic Funnels
Authors: Rabin, D. M.
1987BAAS...19..940R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The prominence-corona interface and its relationship to the
chromosphere-corona transition.
Authors: Rabin, Douglas
1986NASCP2442..135R Altcode: 1986copp.nasa..135R
The classical model of the chromosphere-corona transition does not
account for the observed behavior of the differential emission measure
for T approx. less than 100,000 K. Several models have been proposed
to resolve this discrepancy in physically different ways. Because
the observed differential emission measure at the prominence-corona
interface is on average nearly the same as in the chromosphere-corona
transition, prominences offer a fresh testing ground for models tailored
to the chromosphere-corona transition. The researcher considered three
such models and concluded that none extends in a natural way to the
environment of prominences. The researcher advanced a simple idea
involving thermal conduction both along and across the magnetic field
from the corona into cool threads.
---------------------------------------------------------
Title: The Prominence-Corona Interface
Authors: Rabin, D. M.
1986BAAS...18..991R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Magnetic Structure of the Quiet Transition Region
Authors: Dowdy, J. F., Jr.; Rabin, D.; Moore, R. L.
1986SoPh..105...35D Altcode:
Existing models of the quiet chromosphere-corona transition region
predict a distribution of emission measure over temperature that agrees
with observation for T ≳ 10<SUP>5</SUP> K. These `network' models
assume that all magnetic field lines that emerge from the photosphere
extend into and are in thermal contact with the corona. We show
that the observed fine-scale structure of the photospheric magnetic
network instead suggests a two-component picture in which magnetic
funnels that open into the corona emerge from only a fraction of the
network. The gas that makes up the hotter transition region is mostly
contained within these funnels, as in standard models, but, because
the funnels are more constricted in our picture, the heat flowing
into the cooler transition region from the corona is reduced by up
to an order of magnitude. The remainder of the network is occupied
by a population of low-lying loops with lengths ≲ 10<SUP>4</SUP>
km. We propose that the cooler transition region is mainly located
within such loops, which are magnetically insulated from the corona
and must, therefore, be heated internally. The fine-scale structure
of ultraviolet spectroheliograms is consistent with this proposal,
and theoretical models of internally heated loops can explain the
behavior of the emission measure below T ≈ 10<SUP>5</SUP> K.
---------------------------------------------------------
Title: Bimodality of the solar cycle
Authors: Rabin, D.; Wilson, R. M.; Moore, R. L.
1986GeoRL..13..352R Altcode:
For sunspot cycles 1-20 (1755-1976), all cycles occurred in strings
(two to six cycles in length) during which the period remained longer
or shorter than the sample mean period. These strings have coincided
with long-term trends of growth or decay in the amplitude of the
cycle. In six out of six cases, the period of the cycle has switched
from long to short (or the reverse) in coincidence with turning points
in the long-term trend. This suggests that the solar dynamo has two
modes with different mean periods. In the short-period mode, the
amplitude of the cycle grows; in the long-period mode, the amplitude
decays. The transition between modes has occurred at irregular
intervals. A persistence of the long-period mode would eventually
produce a grand minimum such as the Maunder minimum; a persistence
of the short-period mode would produce a grand maximum. Unless the
present interval between transitions turns out to be shorter than any
previously observed interval, the present cycle (cycle 21) is part of a
long-period, decaying trend and will be of longer-than-average duration
(>133 months).
---------------------------------------------------------
Title: Chromospheric explosions.
Authors: Doschek, G. A.; Antiochos, S. K.; Antonucci, E.; Cheng,
C. -C.; Culhane, J. L.; Fisher, G. H.; Jordan, C.; Leibacher, J. W.;
MacNiece, P.; McWhirter, R. W. P.; Moore, R. L.; Rabin, D. M.; Rust,
D. M.; Shine, R. A.
1986NASCP2439....4D Altcode:
The work of this team addressed the question of the response and
relationship of the flare chromosphere and transition region to the
hot coronal loops that reach temperatures of about 10<SUP>7</SUP>K
and higher. Flare related phenomena such as surges and sprays are
also discussed. The team members debated three main topics: 1. whether
the blue-shifted components of X-ray spectral lines are signatures of
"chromospheric evaporation"; 2. whether the excess line broadening of UV
and X-ray lines is accounted for by "convective velocity distribution"
in evaporation; and 3. whether most chromospheric heating is driven
by electron beams.
---------------------------------------------------------
Title: Measurement and interpretation of magnetic shear in solar
active regions
Authors: Hagyard, M. J.; Rabin, D. M.
1986AdSpR...6f...7H Altcode: 1986AdSpR...6....7H
In this paper we summarize and synthesize the results on the role of
magnetic shear in the flare process that have been derived from the
series of Flare Buildup Study Workshops in the Solar Maximum Analysis
program. With emphasis on observations, we discuss the mechanisms that
seem to produce the sheared magnetic configurations observed in flaring
active regions. The spatial and temporal correlations of this shear with
the onset of solar flares are determined from quantitative analyses of
measurements of the vector magnetic field. The question of why some
areas of sheared magnetic fields are the sites of flares and others
are not is investigated observationally. We conclude by synthesizing
these findings with current theoretical models of stressed magnetic
fields that lead to the eruption of a flare.
---------------------------------------------------------
Title: Evidence for submergencew of magnetic flux in a growing
active region
Authors: Rabin, D. M.; Moore, R. L.; Hagyard, M. J.
1985svmf.nasa..437R Altcode:
In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th power
maxwell of magnetic flux concentrated within a 30" circular area
disappeared overnight. Vector magnetograms show that all components of
the magnetic field weakened together. If the field had weakened through
diffusion or fluid flow, 80% of the original flux would still have been
detected by the magnetograph within a suitably enlarged area. In fact
there was at least a threefold decrease in detected flux. Evidently,
magnetic field was removed from the photosphere. Since the disappearing
flux was located in a region of low magnetic shear and low activity,
it is unlikely that the field dissipated through reconnection. The most
likely possibility is that flux submerged. Observations suggest that
even in the growth phase of active regions, submergence is a strong
process comparable in magnitude to emergence.
---------------------------------------------------------
Title: Sunspots.
Authors: Moore, R.; Rabin, D.
1985ARA&A..23..239M Altcode:
It is pointed out that the sun provides a close-up view of many
astrophysically important phenomena, nearly all connected with the
causes and effects of solar magnetic fields. The present article
provides a review of the role of sunspots in a number of new areas
of research. Connections with other solar phenomena are examined,
taking into account flares, the solar magnetic cycle, global flows,
luminosity variation, and global oscillations. A selective review of
the structure and dynamic phenomena observed within sunspots is also
presented. It is found that sunspots are usually contorted during the
growth phase of an active region as magnetic field rapidly emerges
and sunspots form, coalesce, and move past or even through each
other. Attention is given to structure and flows, oscillations and
waves, and plans for future studies.
---------------------------------------------------------
Title: Evidence for submergence of magnetic flux in a growing
active region.
Authors: Rabin, D. M.; Moore, R. L.; Hagyard, M. J.
1985NASCP2374..437R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Graphic displays of vector magnetograph data.
Authors: Rabin, D. M.; West, E. A.
1985NASCP2374..454R Altcode:
The authors summarize their experience with graphic displays that
have proved useful in dealing with vector magnetograph data in three
settings: real-time control, analysis, and final presentation. Among
the topics discussed are: flexible, implicit data-scaling; geometrical
transformations; methods of comparing fields (e.g., transverse
vs. longitudinal; observed vs. computed; one time vs. another);
displaying the magnitude and direction of the transverse field;
minimizing the display time of serial graphics devices; graphic file
structure; and graphic interaction with operators and observers.
---------------------------------------------------------
Title: A case for submergence of magnetic flux in a solar active
region
Authors: Rabin, D.; Moore, R.; Hagyard, M. J.
1984ApJ...287..404R Altcode:
In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th maxwells
of magnetic flux concentrated in an area 30 arcsec across disappeared
overnight. Vector magnetograms show that all components of the magnetic
field weakened together. If the field had weakened through diffusion
or fluid flow, 90 percent of the original flux would still have been
detected by the magnetograph within a suitably enlarged area. In fact
there was a threefold decrease in detected flux. Evidently, magnetic
field was removed from the photosphere. Since the disappearing flux
was located in a region of low magnetic shear and low activity in
H-alpha and Ly-alpha, it is unlikely that the field dissipated through
reconnection. It is argued that the most likely possibility is that
flux submerged. The observations suggest that even during the growth
phase of active regions, submergence is a strong process comparable
in magnitude to emergence.
---------------------------------------------------------
Title: Heating the sun's lower transition region with fine-scale
electric currents
Authors: Rabin, D.; Moore, R.
1984ApJ...285..359R Altcode:
This paper discusses the hypothesis that the lower transition region is
locally heated by the dissipation of electric currents. It proposes a
model based on ohmic heating by filamentary electric currents that flow
along the magnetic field. The current filaments must be of fine scale,
with a narrow dimension in the range 1 cm to 1 km, and the ambient
magnetic field must be greater than about 10 gauss. An ensemble
of filamentary currents that agree in sign across the horizontal
scale of a photospheric granule can generate enough heat to match
observations without the need for anomalous resistivity. Thermal
conduction perpendicular to the axis of a current filament produces
a distribution of emission measure over temperature that is in good
agreement with observations.
---------------------------------------------------------
Title: Bimodality of the Solar Cycle
Authors: Rabin, D. M.; Moore, R. L.; Wilson, R. M.
1984BAAS...16Q.993R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Oscillations and the Short-Period Cutoff for Global
p-Mode Oscillations
Authors: Moore, R.; Rabin, D.
1984BAAS...16..978M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photospheric Electric Current and Transition Region Brightness
Within an Active Region
Authors: Deloach, A. C.; Hagyard, M. J.; Rabin, D.; Moore, R. L.;
Smith, B. J., Jr.; West, E. A.; Tandberg-Hanssen, E.
1984SoPh...91..235D Altcode:
Distributions of vertical electric current density (J<SUB>z</SUB>)
calculated from vector measurements of the photospheric magnetic
field are compared with ultraviolet spectroheliograms to investigate
whether resistive heating is an important source of enhanced emission
in the transition region. The photospheric magnetic fields in Active
Region 2372 were measured on 6 and 7 April, 1980 with the MSFC vector
magnetograph; ultraviolet wavelength spectroheliograms (Lα and Nv
1239 Å) were obtained with the UVSP experiment aboard the Solar
Maximum Mission satellite. Spatial registration of the J<SUB>z</SUB>
(5 arc sec resolution) and UV (3 arc sec resolution) maps indicates that
the maximum current density is cospatial with a minor but persistent UV
enhancement, but there is little detected current associated with other
nearby bright areas. We conclude that although resistive heating may be
important in the transition region, the currents responsible for the
heating are largely unresolved in our measurements and have no simple
correlation with the residual current measured on 5 arc sec scales.
---------------------------------------------------------
Title: On the Formation of Magnetic Shear: Clues from a Well-Observed
Active Region
Authors: Moore, R. L.; Rabin, D. M.
1984BAAS...16..528M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Case for Submergence of Magnetic Flux in a Solar Active
Region
Authors: Rabin, D. M.; Moore, R. L.
1984BAAS...16..528R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Heating the Lower Transition Region with Fine-Scale Currents
Authors: Rabin, D. M.; Moore, R. L.
1983BAAS...15..700R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of integrated spectra of red star clusters in the
Magellanic Clouds.
Authors: Rabin, D.
1982ApJ...261...85R Altcode:
The present investigation has the objective to demonstrate that
integrated spectra can play an important role in the quantitative
analysis of the ages and abundances of star clusters. In particular,
it is shown that by comparing the strength of the Balmer lines with
the strength of a metallic feature, and guided by a sequence of model
star clusters and the empirical sequence of Galactic globular clusters,
one may infer age differences between fairly old clusters, for each
of which a color-magnitude study to extremely faint magnitudes would
be necessary to approach the main sequence. Most Magellanic Cloud
clusters are younger than Galactic globulars and lack a developed
horizontal branch.
---------------------------------------------------------
Title: Structure of the Lower Transition Zone in an Active Region
Authors: Rabin, D. M.; Moore, R. L.
1982BAAS...14..925R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Carbon Stars
Authors: Alksne, Z. K.; Klaunieks, Y. Y.; Baumert, J. H.; Rabin, D.
1982JBAA...92Q.153A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Studies of Stellar Populations: Star Clusters in M31, the
Galaxy and the Magellanic Clouds.
Authors: Rabin, D. M.
1981PhDT.........2R Altcode: 1981PhDT.......114R
Medium resolution spectra of the integrated light of star clusters in
our own Galaxy and in three nearby systems M31 and the two Magellanic
Clouds are described. Since only integrated properties will normally be
observable for clusters in more distant galaxies, or for the galaxies
themselves, it is important to develop quantitative techniques which
relate features of the integrated light to physical characteristics
such as age and chemical composition. Here, digital spectra, are
analyzed both internally, as multivariate data sets, and externally by
comparison with evolutionary models of star clusters and with detailed
observations of nearby clusters.
---------------------------------------------------------
Title: Studies of stellar population: star clusters in M31, the
galaxy and the Magellanic clouds
Authors: Rabin, Douglas Mark
1981PhDT.......129R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Studies of stellar populations: Star clusters in M31. The
galaxy and the Magellanic Clouds
Authors: Rabin, Douglas Mark
1981ssps.book.....R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal holes, the height of the chromosphere,and the origin
of spicules.
Authors: Rabin, D.; Moore, R. L.
1980ApJ...241..394R Altcode:
Analysis of 650 microphotometric scans across the solar limb reveals
that the H(alpha) chromosphere is slightly taller inside coronal holes
than in quiet regions outside holes. The change in height occurs as
a step at the hole boundaries; this suggests that the increase with
latitude in the average height of spicules found by Lippincott and
by Athay was the average result of upward steps at the polar hole
boundaries rather than a gradual latitude trend. It is estimated that
the power consumed by spicules is of the same order as that returning
by conduction from the corona, but the bulk of the spicules (which
sets the height of the chromosphere) shows almost no response. It is
concluded that spicules are not caused by heat conduction from the
corona but are driven from below, suggesting that spicules are more
closely connected with the heating of the corona than with its cooling.
---------------------------------------------------------
Title: Polar Coronal Holes and the Variation with Latitude of the
Height of the Hα Chromosphere.
Authors: Rabin, D. M.; Moore, R. L.
1978BAAS...10..430R Altcode:
No abstract at ADS
