Author name code: kohl
ADS astronomy entries on 2022-09-14
author:"Kohl, John L."
------------------------------------------------------------------------
Title: Global helium abundance measurements in the solar corona
Authors: Moses, John D.; Antonucci, Ester; Newmark, Jeffrey; Auchère,
Frédéric; Fineschi, Silvano; Romoli, Marco; Telloni, Daniele;
Massone, Giuseppe; Zangrilli, Luca; Focardi, Mauro; Landini, Federico;
Pancrazzi, Maurizio; Rossi, Guglielmo; Malvezzi, Andrea M.; Wang,
Dennis; Leclec'h, Jean-Christophe; Moalic, Jean-Pierre; Rouesnel,
Frédéric; Abbo, Lucia; Canou, Aurélien; Barbey, Nicolas; Guennou,
Chloé; Laming, John M.; Lemen, James; Wuelser, Jean-Pierre; Kohl,
John L.; Gardner, Lawrence D.
Bibcode: 2020NatAs...4.1134M
Altcode: 2020NatAs.tmp..152M
Solar abundances have been historically assumed to be representative
of cosmic abundances. However, our knowledge of the solar abundance
of helium, the second most abundant element, relies mainly on
models1 and indirect measurements through helioseismic
observations2, because actual measurements of helium in the
solar atmosphere are very scarce. Helium cannot be directly measured
in the photosphere because of its high first ionization potential,
and measurements of its abundance in the inner corona have been
sporadic3,4. In this Letter, we present simultaneous global
images of the helium (out to a heliocentric distance of 3R⊙
(solar radii)) and hydrogen emission in the solar corona during
the minimum of solar activity of cycle 23 and directly derive the
helium abundance in the streamer region and surrounding corona
(out to 2.2R⊙). The morphology of the He+
corona is markedly different from that of the H corona, owing to
significant spatial variations in helium abundance. The observations
show that the helium abundance is shaped according to and modulated
by the structure of the large-scale coronal magnetic field and that
helium is almost completely depleted in the equatorial regions during
the quiet Sun. This measurement provides a trace back to the coronal
source of the anomalously slow solar wind observed in the heliosphere
at the Sun-Earth Lagrangian point L1 in 2009, during the exceptionally
long-lasting minimum of solar activity cycle 23.
Title: The Evolution of Plasma Parameters on a Coronal Source Surface
at 2.3 R ⊙ during Solar Minimum
Authors: Strachan, L.; Panasyuk, A. V.; Kohl, J. L.; Lamy, P.
Bibcode: 2012ApJ...745...51S
Altcode: 2011arXiv1111.1206S
We analyze data from the Solar and Heliospheric Observatory to
produce global maps of coronal outflow velocities and densities
in the regions where the solar wind is undergoing acceleration. The
maps use UV and white light coronal data obtained from the Ultraviolet
Coronagraph Spectrometer and the Large Angle Spectroscopic Coronagraph,
respectively, and a Doppler dimming analysis to determine the mean
outflow velocities. The outflow velocities are defined on a sphere at
2.3 R ⊙ from Sun-center and are organized by Carrington
Rotations during the solar minimum period at the start of solar cycle
23. We use the outflow velocity and density maps to show that while the
solar minimum corona is relatively stable during its early stages, the
shrinkage of the north polar hole in the later stages leads to changes
in both the global areal expansion of the coronal hole and the derived
internal flux tube expansion factors of the solar wind. The polar hole
areal expansion factor and the flux tube expansion factors (between
the coronal base and 2.3 R ⊙) start out as super-radial
but then they become more nearly radial as the corona progresses away
from solar minimum. The results also support the idea that the largest
flux tube expansion factors are located near the coronal hole/streamer
interface, at least during the deepest part of the solar minimum period.
Title: UVCS/SOHO Search for Coronal Suprathermal Seed Particles:
2011 Campaign
Authors: Kohl, J. L.; Panasyuk, A. V.; Cranmer, S. R.; Raymond, J. C.;
Rosati, R. E.
Bibcode: 2011AGUFMSH33D..05K
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory is being used to measure precise coronal
H I Ly-alpha spectral line profiles out to several Doppler half
widths. Such observations can be used to reveal the proton velocity
distribution along the line-of-sight. Departures from a Maxwellian
distribution are believed to be needed for the acceleration of solar
energetic particles (SEPs) by coronal mass ejection (CME) shocks. It is
generally believed that the seed particle population needed to produce
the numbers of SEPs observed in large events would have 0.001 to 0.01
of the particles with speeds that exceed 1000 km/s. Assuming a kappa
distribution that is symmetric in the tangential plane and Maxwellian
in the radial direction, this would correspond to a distribution
with kappa = 3.5 or smaller. We have shown that UVCS observations can
distinguish a Gaussian from a kappa exponent of 4 or less. Previously
reported observations near solar minimum have not yielded any such
distributions, but the sampling of the corona was not very systematic. A
new observational campaign was begun on 28 April 2011. Observations
are all at a heliographic height of 2.7 solar radii from Sun-center
and at a solar position angle of 290 degrees. Observations are made
on a continuous basis except during SOHO Keyhole periods when UVCS
observations are not possible, and at a few other times. Results of this
campaign and some earlier observations will be reported. This work is
supported by the National Aeronautics and Space Administration (NASA)
under Grant NNX11AM46G to the Smithsonian Astrophysical Observatory.
Title: Comparison of Velocity, Density, Temperature, and Mass Flux
Results with Solar Coronal Models
Authors: Strachan, L.; Cranmer, S. R.; Panasyuk, A.; Kohl, J. L.;
Lamy, P. L.
Bibcode: 2011AGUFMSH53C..07S
Altcode:
We have recently computed a series of global maps of plasma parameters
in the extended corona using data from the Solar and Heliospheric
Observatory (SOHO). The synoptic maps of velocity, density, temperature,
and mass flux were derived from UV and white light coronal data
obtained from the Ultraviolet Coronagraph Spectrometer (UVCS) and
the Large Angle Spectroscopic Coronagraph (LASCO). The parameters
are defined on a sphere at 2.3~ R⊙ from Sun-center and
are organized by Carrington Rotations during the 1996 -- 1998 solar
minimum for Solar Cycle 23. The data imply that there are large flux
tube expansion factors near the coronal hole/streamer boundaries,
but these factors change significantly as the corona evolves from
minimum to the rising phase. We compare these data to an independently
developed theoretical model that includes damping and acceleration
by Alfven waves in the corona (see Cranmer et al. 2007, ApJS, 171,
520). The data set will be extended in the future and it will be used
for constraining other theoretical models of the corona and solar wind.
Title: The Coronal Physics Investigator (cpi) Experiment For Iss:
A New Vision For Understanding Solar Wind Acceleration
Authors: Raymond, John C.; Janzen, P. H.; Kohl, J. L.; Reisenfeld,
D. B.; Chandran, B. D. G.; Cranmer, S. R.; Forbes, T. G.; Isenberg,
P. A.; Panasyuk, A. V.; van Ballegooijen, A. A.
Bibcode: 2011SPD....42.2406R
Altcode: 2011BAAS..43S.2406R
We propose an Explorer Mission of Opportunity program to develop and
operate a large-aperture ultraviolet coronagraph spectrometer called
the Coronal Physics Investigator (CPI) as an attached International
Space Station (ISS) payload. The primary goal of this program is
to identify and characterize the physical processes that heat and
accelerate the primary and secondary components of the fast and slow
solar wind. Also, CPI can make key measurements needed to understand
CMEs. CPI is dedicated to high spectral resolution measurements of
the off-limb extended corona with far better stray light suppression
than can be achieved by a conventional instrument. UVCS/SOHO allowed
us to identify what additional measurements need to be made to answer
the fundamental questions about how solar wind streams are produced,
and CPI's next-generation capabilities were designed specifically to
make those measurements. Compared to previous instruments, CPI provides
unprecedented sensitivity, a wavelength range extending from 25.7 to
126 nm, higher temporal resolution, and the capability to measure line
profiles of He II, N V, Ne VII, Ne VIII, Si VIII, S IX, Ar VIII, Ca IX,
and Fe X, never before seen in coronal holes above 1.3 solar radii. CPI
will constrain the properties and effects of coronal MHD waves by (1)
observing many ions over a large range of charge and mass,(2) providing
simultaneous measurements of proton and electron temperatures to probe
turbulent dissipation mechanisms, and (3) measuring amplitudes of
low-frequency compressive fluctuations. CPI is an internally occulted
ultraviolet coronagraph that provides the required high sensitivity
without the need for a deployable boom, and with all technically mature
hardware including an ICCD detector. A highly experienced Explorer and
ISS contractor, L-3 Com Integrated Optical Systems and Com Systems East
will provide the tracking and pointing system as well as the instrument,
and the integration to the ISS.
Title: The Coronal Physics Investigator (CPI) Experiment for ISS:
A New Vision for Understanding Solar Wind Acceleration
Authors: Kohl, J. L.; Cranmer, S. R.; Raymond, J. C.; Norton, T. J.;
Cucchiaro, P. J.; Reisenfeld, D. B.; Janzen, P. H.; Chandran, B. D. G.;
Forbes, T. G.; Isenberg, P. A.; Panasyuk, A. V.; van Ballegooijen,
A. A.
Bibcode: 2011arXiv1104.3817K
Altcode:
In February 2011 we proposed a NASA Explorer Mission of Opportunity
program to develop and operate a large-aperture ultraviolet
coronagraph spectrometer called the Coronal Physics Investigator
(CPI) as an attached International Space Station (ISS) payload. The
primary goal of this program is to identify and characterize the
physical processes that heat and accelerate the primary and secondary
components of the fast and slow solar wind. In addition, CPI can make
key measurements needed to understand CMEs. UVCS/SOHO allowed us to
identify what additional measurements need to be made to answer the
fundamental questions about how solar wind streams are produced, and
CPI's next-generation capabilities were designed specifically to make
those measurements. Compared to previous instruments, CPI provides
unprecedented sensitivity, a wavelength range extending from 25.7 to
126 nm, higher temporal resolution, and the capability to measure line
profiles of He II, N V, Ne VII, Ne VIII, Si VIII, S IX, Ar VIII, Ca IX,
and Fe X, never before seen in coronal holes above 1.3 solar radii. CPI
will constrain the properties and effects of coronal MHD waves by
(1) observing many ions over a large range of charge and mass, (2)
providing simultaneous measurements of proton and electron temperatures
to probe turbulent dissipation mechanisms, and (3) measuring amplitudes
of low-frequency compressive fluctuations. CPI is an internally occulted
ultraviolet coronagraph that provides the required high sensitivity
without the need for a deployable boom, and with all technically mature
hardware including an ICCD detector. A highly experienced Explorer and
ISS contractor, L-3 Com Integrated Optical Systems and Com Systems East,
will provide the tracking and pointing system as well as the instrument,
and the integration to the ISS.
Title: Testing Coronal and Solar Wind MHD Models with UV Spectroscopic
and Visible Light Coronagraph Data
Authors: Strachan, L.; Panasyuk, A.; Kohl, J. L.; Woolsey, L.; Lamy,
P. L.
Bibcode: 2010AGUFMSH42A..08S
Altcode:
We present synoptic maps of coronal outflow velocities obtained at 2.3
Rs in the solar wind acceleration region of the corona during Solar
Cycle 23. The outflow velocities are obtained by using data from the
SOHO coronagraphs: H I Lyman alpha and O VI line profiles (from UVCS)
and white light polarized brightness data (from LASCO). The information
contained in the maps provide constraints on the electron densities,
bulk outflow speeds, and anisotropic kinetic temperatures (velocity
distributions for protons and minor ions. We show some examples of how
these data can be used to test MHD models of the solar corona and solar
wind. The data set can be used to compare empirically derived plasma
parameters directly with the MHD model parameters or alternatively it
can be used to compare the observed profiles with synthetic profiles
obtained by forward modeling of the MHD data.
Title: Ultraviolet Coronagraph Spectroscopy: A Key Capability for
Understanding the Physics of Solar Wind Acceleration
Authors: Cranmer, S. R.; Kohl, J. L.; Alexander, D.; Bhattacharjee,
A.; Breech, B. A.; Brickhouse, N. S.; Chandran, B. D. G.; Dupree,
A. K.; Esser, R.; Gary, S. P.; Hollweg, J. V.; Isenberg, P. A.; Kahler,
S. W.; Ko, Y. -K.; Laming, J. M.; Landi, E.; Matthaeus, W. H.; Murphy,
N. A.; Oughton, S.; Raymond, J. C.; Reisenfeld, D. B.; Suess, S. T.;
van Ballegooijen, A. A.; Wood, B. E.
Bibcode: 2010arXiv1011.2469C
Altcode:
Understanding the physical processes responsible for accelerating the
solar wind requires detailed measurements of the collisionless plasma
in the extended solar corona. Some key clues about these processes
have come from instruments that combine the power of an ultraviolet
(UV) spectrometer with an occulted telescope. This combination enables
measurements of ion emission lines far from the bright solar disk,
where most of the solar wind acceleration occurs. Although the UVCS
instrument on SOHO made several key discoveries, many questions remain
unanswered because its capabilities were limited. This white paper
summarizes these past achievements and also describes what can be
accomplished with next-generation instrumentation of this kind.
Title: Time Evolution of a Coronal Velocity Source Surface during
Solar Cycle 23
Authors: Strachan, L.; Panasyuk, A. V.; Kohl, J. L.
Bibcode: 2010ASPC..428..187S
Altcode:
We present preliminary results of a study to create coronal outflow
velocity maps for the period from 1996 to 2005. The velocities are
derived from the UVCS/SOHO synoptic observations of the O VI 103.2 nm
and 103.7 nm intensities. The maps are made at a constant heliocentric
height of 2.3 Rsun, near the traditional coronal source
surface height of 2.5 Rsun. Our results for the Cycle
22/23 minimum show that the classic solar minimum conditions, where
high-speed wind dominates the polar regions, lasted only until May
1997. However, during the same time period there was very little change
in the fraction of fast or slow speed wind at low heliographic latitudes
(< 30°). When completed, the coronal velocity maps will be used to
show the connections between structures in the corona and solar wind
streams at greater distances from the Sun. It will also help clarify
how variations in the spatial distribution of outflow velocities are
controlled by the coronal magnetic field and plasma conditions at the
source regions.
Title: SOHO-23: Understanding a Peculiar Solar Minimum
Authors: Cranmer, S. R.; Hoeksema, J. T.; Kohl, J. L.
Bibcode: 2010ASPC..428.....C
Altcode:
No abstract at ADS
Title: Extended Coronal Heating and Solar Wind Acceleration over
the Solar Cycle
Authors: Cranmer, S. R.; Kohl, J. L.; Miralles, M. P.; van
Ballegooijen, A. A.
Bibcode: 2010ASPC..428..209C
Altcode: 2010arXiv1002.0297C
This paper reviews our growing understanding of the physics behind
coronal heating (in open-field regions) and the acceleration of the
solar wind. Many new insights have come from the last solar cycle's
worth of observations and theoretical work. Measurements of the
plasma properties in the extended corona, where the primary solar wind
acceleration occurs, have been key to discriminating between competing
theories. We describe how UVCS/SOHO measurements of coronal holes and
streamers over the last 14 years have provided clues about the detailed
kinetic processes that energize both fast and slow wind regions. We also
present a brief survey of current ideas involving the coronal source
regions of fast and slow wind streams, and how these change over the
solar cycle. These source regions are discussed in the context of recent
theoretical models (based on Alfvén waves and MHD turbulence) that have
begun to successfully predict both the heating and acceleration in fast
and slow wind regions with essentially no free parameters. Some new
results regarding these models—including a quantitative prediction
of the lower density and temperature at 1 AU seen during the present
solar minimum in comparison to the prior minimum—are also shown.
Title: Variations in the Absolute Ultraviolet Intensities of Polar
Coronal Holes
Authors: Gardner, L. D.; Kohl, J. L.; Cranmer, S. R.; Lin, M.;
Panasyuk, A. V.; Uzzo, M.
Bibcode: 2010ASPC..428..191G
Altcode:
The well-maintained UVCS/SOHO radiometric calibration is used
to determine the variations in the ultraviolet intensities in
polar coronal holes between the Solar Cycle 22/23 and Cycle 23/24
minima. The radiometric calibration has been carefully monitored
and updated during the mission by observing an ensemble of B stars,
which, as a group, are believed to have a stable mean irradiance. These
observations, along with data from the freshly calibrated Ultraviolet
Coronal Spectrometer on the Spartan 201 satellite in 1998, have been
used to determine the changes in the calibration. The Spartan 201
inter-calibration, together with the original laboratory calibration,
was used to establish the in-flight absolute radiometric calibration
scale. This paper summarizes the in-flight radiometric calibration of
UVCS/SOHO and observed variations in polar coronal hole intensities
as a function of heliographic height above the poles of the Sun.
Title: A Model for the Stray-Light Contamination of the UVCS
Instrument on SOHO
Authors: Cranmer, S. R.; Gardner, L. D.; Kohl, J. L.
Bibcode: 2010SoPh..263..275C
Altcode: 2010arXiv1001.3843C; 2010SoPh..tmp...31C
We present a detailed model of stray-light suppression in the
spectrometer channels of the Ultraviolet Coronagraph Spectrometer (UVCS)
on the SOHO spacecraft. The control of diffracted and scattered stray
light from the bright solar disk is one of the most important tasks of
a coronagraph. We compute the fractions of light that diffract past the
UVCS external occulter and non-specularly pass into the spectrometer
slit. The diffracted component of the stray light depends on the
finite aperture of the primary mirror and on its figure. The amount
of non-specular scattering depends mainly on the micro-roughness of
the mirror. For reasonable choices of these quantities, the modeled
stray-light fraction agrees well with measurements of stray light
made both in the laboratory and during the UVCS mission. The models
were constructed for the bright H I Lyα emission line, but they are
applicable to other spectral lines as well.
Title: Improved Constraints on the Preferential Heating and
Acceleration of Oxygen Ions in the Extended Solar Corona
Authors: Cranmer, Steven R.; Panasyuk, Alexander V.; Kohl, John L.
Bibcode: 2008ApJ...678.1480C
Altcode: 2008arXiv0802.0144C
We present a detailed analysis of oxygen ion velocity distributions
in the extended solar corona, based on observations made with
the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO
spacecraft. Polar coronal holes exhibit broad line widths and unusual
intensity ratios of the O VI λλ1032, 1037 emission-line doublet. A
traditional interpretation of these features is that oxygen ions have
a strong temperature anisotropy, with the temperature perpendicular
to the magnetic field being much larger than the temperature parallel
to the field. However, recent work by Raouafi and Solanki suggested it
may be possible to model the observations using an isotropic velocity
distribution. In this paper we analyze an expanded data set to show
that the original interpretation of an anisotropic distribution is the
only one fully consistent with the observations. It is necessary to
search the full range of ion plasma parameters to determine the values
with the highest probability of agreement with the UVCS data. The
derived ion outflow speeds and perpendicular kinetic temperatures
are consistent with earlier results, and there continues to be strong
evidence for preferential ion heating and acceleration with respect to
hydrogen. At heliocentric heights above 2.1 solar radii, every UVCS
data point is more consistent with an anisotropic distribution than
with an isotropic distribution. At heights above 3 solar radii, the
exact probability of isotropy depends on the electron density chosen
to simulate the line-of-sight distribution of O VI emissivity. The
most realistic electron densities (which decrease steeply from 3 to
6 solar radii) produce the lowest probabilities of isotropy and most
probable temperature anisotropy ratios that exceed 10.
Title: Inclined Beams Measurements of Electron Impact Excitation at
the Harvard-Smithsonian CfA
Authors: Gardner, Larry D.; Rosati, R. E.; Kohl, J. L.
Bibcode: 2008AAS...212.0316G
Altcode: 2008BAAS...40S.186G
The analysis of absolute spectral line intensities and intensity
ratios with spectroscopic diagnostic techniques provides empirical
determinations of plasma parameters in astrophysical objects. Since
spectral line intensities and their ratios are controlled by the
excitation rate coefficients for the electron temperature of the
observed astrophysical structure, it is imperative that one have
accurate values for the relevant rate coefficients. The technique
employed at CfA utilizes a modulated beam of a single ion species,
which is crossed at 45 degrees with a similarly modulated electron
beam. Photons from the decay of ions excited by collisions with
the electrons are collected synchronously with the beams' modulation
pattern by an absolutely calibrated optical system. We will illustrate
our experimental approach by discussing our current measurements
of EIE in C2+ (2s2 1S0
- 2s2p 1Po1), which dominates the
emission of CIII 97.7 nm in the Sun. Since the wavelength of the decay
photons is below the transmission cutoff of window materials, our new
detection system utilizes an open microchannel plate detector and a
spherical mirror coated with Al/MgF2/B4C. These
new components have been thoroughly calibrated at the wavelengths
relevant to this experiment and at wavelengths relevant to forthcoming
measurements in O4+. The latest research results will
be reported. This work is supported by NASA Supporting Research and
Technology grant NNG06GE49G in Solar and Heliospheric Physics and by
the Smithsonian Astrophysical Observatory.
Title: Physical Properties of a Coronal Streamer at 2.5 Solar Radii
Authors: Uzzo, M.; Strachan, L.; Kohl, J.; Vourlidas, A.
Bibcode: 2008AGUSMSH51B..03U
Altcode:
In this presentation the plasma properties of a streamer observed in
April of 2007 at 2.5 solar radii are examined. The data comes from
observations conducted by the Ultraviolet Coronagraph Spectrometer
(UVCS) and the Large Angle Spectroscopic Coronagraph (LASCO) C2
instrument aboard the Solar and Heliospheric Observatory (SOHO). From
the UV spectral profiles the proton and oxygen kinetic temperatures can
be derived as a function of latitude across the streamer. The observed
line intensities are used to calculate the photospheric normalized
absolute elemental abundances for O, S, N and Fe. The abundances
are analyzed with respect to the FIP effect and compared to in situ
measurements at SOHO. An estimate for the electron density is determined
from both the UV data and the polarized white light data from LASCO C2.
Title: UVCS/SOHO Search for Coronal Suprathermal Seed Particles:
Results for Solar Minimum
Authors: Kohl, J. L.; Panasyuk, A. V.; Cranmer, S. R.; Gardner, L. D.;
Raymond, J. C.
Bibcode: 2008AGUSMSH41B..05K
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory is being used to measure precise coronal H I
Ly-alpha spectral line profiles out to several Doppler half widths. Such
observations can be used to reveal the proton velocity distribution
along the line-of-sight. Departures from a Maxwellian distribution are
believed to be needed for the acceleration of solar energetic particles
(SEPs) by coronal mass ejection (CME) shocks. We have now completed
all required instrument characterizations and refined the observations
to the point where it is possible to distinguish a Gaussian coronal
velocity distribution from a power law tail of sufficient strength
to accelerate SEPs. It is generally believed that the required seed
particle population needed to produce SEPs of interest with a CME shock
would have a velocity distribution with 0.001 to 0.01 of the particles
with speeds that exceed 1000 km/s. Assuming a kappa distribution that
is symmetric in the tangential plane and Maxwellian in the radial
direction, this would correspond to a distribution with kappa = 3.5
or smaller. We show that UVCS observations can distinguish a Gaussian
from a kappa of 4 or less. This paper will report the results of
examining observations during 2006-2008 and report on any departures
from a Maxwellian distribution. It will also report the CME/flare
predecessor history of each observation. This work is supported by
the National Aeronautics and Space Administration (NASA) under Grant
NNX07AL72G to the Smithsonian Astrophysical Observatory.
Title: Next generation UV coronagraph instrumentation for solar
cycle-24
Authors: Kohl, John L.; Jain, Rajmal; Cranmer, Steven R.; Gardner,
Larry D.; Pradhan, Anil K.; Raymond, John C.; Strachan, Leonard
Bibcode: 2008JApA...29..321K
Altcode:
No abstract at ADS
Title: Investigation of the solar wind outflows and joint observations
during the total solar eclipse of March 29, 2006
Authors: Abbo, Lucia; Zangrilli, Luca; Antonucci, Ester; Fineschi,
Silvano; Kohl, John; Giordano, Silvio; Massone, Giuseppe; Capobianco,
Gerardo; Calcidese, Paolo; Porcu, Francesco
Bibcode: 2008cosp...37....7A
Altcode: 2008cosp.meet....7A
During the total solar eclipse of 29 March 2006, SOHO observations of
JOP158 were coordinated with ground based instruments. In particular,
the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO has
observed the south coronal hole in the OVI doublet emission in order
to probe the role of plume and interplume regions in the dynamics of
the fast solar wind. From the analysis of the polarized K-solar corona
measurements obtained with the EKPol polarimeter from the site of c
(desert of Sahara, Lybia), we estimate the coronal electron density
radial profiles and perform a Doppler dimming analysis of the OVI
doublet line intensities to measure the outflow velocity.
Title: Assessment and Validation of MHD Models for the Solar Corona
and Inner Heliosphere
Authors: Strachan, L.; Zurbuchen, T. H.; Kohl, J. L.; Panasyuk, A. V.;
Raymond, J. R.; van Ballegooijen, A.
Bibcode: 2007AGUFMSH31A0238S
Altcode:
We describe the status of a model assessment and validation project
for testing MHD codes that simulate the solar corona and inner
heliosphere. The goal of the project is to test MHD codes by applying
firm empirical constraints to their boundary conditions in the corona
and at 1 AU. The project has produced a database of coronal and solar
wind observations from SOHO, ACE, Wind, and Ulysses. In addition to the
database, software tools for comparing these data sets to the outputs
for the MHD model codes under test will be demonstrated. The first
step is to take the plasma parameters that are produced from the model
codes and apply forward modeling to simulate the coronal observations
of emission lines (H I Lyman alpha and O VI 103.2 nm). In situ solar
wind data are used not only to provide benchmarks near 1 AU but also
to provide coronal constraints for the coronal source regions of the
solar wind. Future stages will involve making more direct comparisons
of the plasma properties predicted from the model codes through the
use of empirical coronal and solar wind models. We also describe a
set of metrics that are used for making comparisons between the model
code outputs and the empirical data. This work is supported by NASA
under Grants NNX07AB98G to the Smithsonian Astrophysical Observatory
and NNX07AB99G to the University of Michigan.
Title: Hydrogen Lyman Alpha Spectral Line Profiles in Coronal Holes
from 1.5 - 6.5 Solar Radii
Authors: Suleiman, R. M.; Kohl, J. L.; Cranmer, S. R.
Bibcode: 2007AGUFMSH21A0285S
Altcode:
UVCS has made detailed measurements of H I Lyα spectral line profiles
in a polar coronal hole at projected heliocentric heights from 3.5
to 6.5 R\odot during 1998 January 5 -- 11. Similar polar coronal
hole measurements were made during 1998 June 16 -- 21. Earlier UVCS
observations obtained at 1.5 to 2.5 R\odot are used for comparison. In
addition, new measurements are being made for the current phase of
the solar cycle. From these measurements we derive 1/e half widths of
coronal velocity distributions at the observed heights. The velocity
distribution includes all motions contributing to the Doppler shifts
along the line of sight (LOS). We also measure absolute intensities that
can be used to derive outflow speeds via a Doppler dimming analysis. At
large heights in coronal holes, the outflowing coronal plasma becomes
nearly collisionless and the ionization balance is believed to become
frozen. H I Lyα profile measurements characterize the neutral hydrogen
velocity distribution, which at lower heights can also be used to
describe the proton distribution. However, in the regions above
3~R\odot, the H0 velocity distribution may not be the same as that
for the protons because the characteristic time for charge transfer
between H0 and protons becomes longer than the time it takes for the
plasma to flow through a density scale height. Hence, the H0 velocity
distribution may not be directly affected by transverse wave motion
or wave damping. An indication of an adiabatic radial decrease in the
neutral hydrogen temperature would indicate a decoupling of the protons
and neutral hydrogen, and also indicate the absence of mechanisms that
would heat the neutrals. We will compare the observations with the
predictions of a theoretical model of the combined electron, proton and
neutral hydrogen plasma. Such a comparison could lead to an improved
knowledge of the proton heating at these large heights. This work is
supported by the National Aeronautics and Space Administration (NASA)
under Grant NNX07AL72G to the Smithsonian Astrophysical Observatory.
Title: UVCS Empirical Constraints on Theoretical Models of Solar
Wind Source Regions
Authors: Kohl, J. L.; Cranmer, S. R.; Miralles, M. P.; Panasyuk, A.;
Strachan, L.
Bibcode: 2007AGUFMSH22B..02K
Altcode:
Spectroscopic observations from the Ultraviolet Coronagraph
Spectrometer (UVCS) on the Solar and Heliospheric Observatory
(SOHO) have resulted in empirical models of polar coronal holes,
polar plumes, coronal jets and streamers. These findings have
been used to make significant progress toward identifying and
characterizing the physical processes that produce extended heating
in the corona and accelerate fast and slow solar wind streams. The
UVCS scientific observations, which began in April 1996 and continue
at this writing, have provided determinations of proton and minor ion
temperatures (including evidence for anisotropic microscopic velocity
distributions in coronal holes and quiescent equatorial streamers),
outflow velocities, and elemental abundances. The variations in these
quantities over the solar cycle also have been determined. For example,
observations of large polar coronal holes at different phases of the
solar cycle indicate that line width is positively correlated with
outflow speed and anti-correlated with electron density. This paper
will review these results, and present new results from measurements
taken as the current solar activity cycle approaches solar minimum. The
results regarding preferential ion heating and acceleration of heavy
ions (i.e., O5+) in polar coronal holes have contributed in a major
way to the advances in understanding solar wind acceleration that
have occurred during the past decade. It is important to verify and
confirm the key features of these findings. Hence, the results from a
new analysis of an expanded set of UVCS data from polar coronal holes
at solar minimum by S. R. Cranmer, A. Panasyuk and J. L. Kohl will be
presented. This work has been supported by the National Aeronautics
and Space Administration (NASA) under Grants NNG06G188G and NNX07AL72G
and NNX06AG95G to the Smithsonian Astrophysical Observatory.
Title: Polar Coronal Jets During the 2007 Joint SOHO/Hinode Campaigns
Authors: Miralles, M. P.; Cranmer, S. R.; Raymond, J. C.; Kohl, J. L.
Bibcode: 2007AGUFMSH21B..02M
Altcode:
We will present ultraviolet spectroscopy of polar coronal jets obtained
by the Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) during the
two SOHO/Hinode observing campaigns (9-21 January and 12-20 March,
2007) for the north and south polar coronal holes. The emphasis is on
identifying and tracing polar jets from the solar surface out into the
accelerating solar wind and determining their physical properties as a
function of height and time. UVCS/SOHO observed ultraviolet counterparts
in the extended corona of the hot jets resolved by Hinode/XRT. These
polar jets observed by UVCS have different characteristics in the
acceleration region of the solar wind than the cooler jets identified
at the last solar minimum by LASCO, UVCS, and EIT. Observations
such as these are needed to clarify the relationship between the
episodic jets, the longer-lived polar plumes, and the fast solar
wind. This work is supported by NASA grants NNX06AG95G and NNX07AL72G
to the Smithsonian Astrophysical Observatory. SOHO is a project of
international cooperation between ESA and NASA.
Title: Measurements of Coronal Proton Velocity Distributions
Authors: Kohl, J. L.; Panasyuk, A.; Cranmer, S. R.; Gardner, L. D.;
Raymond, J. C.
Bibcode: 2007AGUFMSH21A0298K
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory is being used to measure precise coronal H I
Ly-alpha spectral line profiles out to several Doppler half widths. Such
observations can be used to reveal the proton velocity distribution
along the line-of-sight. Departures from a Maxwellian distribution are
believed to be needed for the acceleration of solar energetic particles
(SEPs) by coronal mass ejection (CME) shocks. Our initial attempt to
measure suprathermal proton velocity distributions has been described
by Kohl et al. (2006). We have made considerable additional progress
on such measurements since then. Improvements include the following:
a much more accurate instrument spectral line profile, an increase
in the wavelength range used for the observations, an increase in the
statistical accuracy of the observations by increasing the observation
time, and inclusion of a background measurement as part of every set of
observations. We have also investigated the sensitivity to the detector
high voltage, investigated the effects of diffraction in the instrument,
determined the stray light effects and the Thompson scattering
effects, which both turn out to be small except for scattering of Si
III 120.6 nm. That scattered light is out of the primary wavelength
range of interest. We believe that we have now demonstrated that
UVCS has the sensitivity to distinguish between a Gaussian coronal
velocity distribution and a kappa = 4 or smaller distribution. It is
generally believed that the required seed particle population needed
to produce SEPs of interest with a CME shock would have a velocity
distribution with 0.001 to 0.01 of the particles with speeds that
exceed 1000 km/s. Assuming a kappa distribution that is symmetric
in the tangential plane and Maxwellian in the radial direction, this
would correspond to a distribution with kappa = 3.5 or smaller. This
paper will report the results of examining a fairly large body of new
observations obtained with the new procedure and report the departures
from a Maxwellian distribution. It will also report the CME predecessor
history of each observation. This work is supported by the National
Aeronautics and Space Administration (NASA) under Grant NNX07AL72G to
the Smithsonian Astrophysical Observatory. Kohl J. L., Cranmer, S. R.,
Fineschi, S., Gardner, L. D., Phillips, D. H., Raymond, J. C., and Uzzo,
M., Proc. SOHO 17 - 10 Years of SOHO and Beyond (ESA SP-617, July 2006).
Title: Multi-Instrument Searches for Polar Jets: Characterizing Jet
Heating and Cooling
Authors: Miralles, M. P.; Cranmer, S. R.; Raymond, J. C.; Kohl, J. L.
Bibcode: 2007IUGG...24..691M
Altcode:
We will present the preliminary results obtained with SOHO, in
particular UVCS, during the SOHO-TRACE-Hinode coordinated observation
campaign (8-21 January 2007) for the north and south polar coronal
holes. The emphasis is on identifying and tracing polar jets from the
solar surface out into the accelerating solar wind and determining
their physical properties as a function of height and time. It is still
unclear whether the hot jets resolved by Hinode are the same phenomenon
as the cooler jets identified at the last solar minimum by EIT, LASCO,
and UVCS. We also aim to clarify the relationship between the episodic
jets and the longer-lived polar plumes.
Title: Tracking UVCS/SOHO Responsivity with Observations of ζ Tau
Authors: Valcu, Bogdan; Smith, Peter L.; Gardner, Larry D.; Raymond,
John C.; Miralles, Mari-Paz; Kohl, John L.
Bibcode: 2007SoPh..243...93V
Altcode:
We have tracked the spectral responsivity of the ultraviolet channels of
the UVCS (Ultraviolet Coronagraph Spectrometer) instrument on SOHO by
repeated observations of a stable hot star. We demonstrate first that
the ultraviolet spectral irradiance of the Be star ζ Tau (HD 37202)
for the 100- to 125-nm wavelength range has been sufficiently constant
for our purposes when measured periodically over the course of the
SOHO mission. We then use ζ Tau as a radiometric transfer standard to
determine an average decrease beginning in November of 1998 of 13.0%
per year in the responsivity of the UVCS O VI channel for wavelengths
near H I Ly α and for a particular UVCS unvignetted aperture used
for science observations. The calibration tracking method involves
separating two ζ Tau spectral regions that are overlapped on part
of the detector. The change in the responsivity of UVCS/SOHO began in
late 1998 as determined by comparison of simultaneous observations of
the corona carried out with UVCS/SOHO and the freshly-calibrated UVCS
instrument on the Spartan 201 satellite in early November of 1998.
Title: Towards the UVCS Coronal Hole Atlas for Solar Cycle 23:
The Data
Authors: Miralles, Mari Paz; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2007AAS...210.3005M
Altcode: 2007BAAS...39..143M
We have measured with the SOHO Ultraviolet Coronagraph Spectrometer
(UVCS) the physical properties of over 165 large coronal holes that
produced a variety of high-speed solar wind conditions at 1 AU. This
data set includes observations of coronal holes of different sizes and
latitudes having a range of magnetic field properties. We will
present measured parameters (intensities, line widths) for protons and
oxygen ions, as well as electron density as constrained by polarization
brightness (pB), for the coronal holes observed from the last solar
minimum in 1996 to the present. We will also present selected portions
of in-situ solar wind data that are matched, where possible, to source
regions in the corona, which have been characterized by UVCS. The
UVCS atlas of coronal holes will provide information about the H I
Lyman alpha and O VI line profiles in the extended corona. The atlas
will be made available in electronic format, with machine readable
tables, as a supplement to a leading archival journal. This work
is supported by NASA under Grants NNX06AG95G and NNG06GI88G to the
Smithsonian Astrophysical Observatory, by the Italian Space Agency,
and by PRODEX (Swiss contribution).
Title: Transition Region Emission and Energy Input to Thermal Plasma
during the Impulsive Phase of Solar Flares
Authors: Raymond, John C.; Holman, Gordon; Ciaravella, A.; Panasyuk,
A.; Ko, Y. -K.; Kohl, J.
Bibcode: 2007ApJ...659..750R
Altcode: 2007astro.ph..1359R
The energy released in a solar flare is partitioned between thermal
and nonthermal particle energy and lost to thermal conduction and
radiation over a broad range of wavelengths. It is difficult to
determine the conductive losses and the energy radiated at transition
region temperatures during the impulsive phases of flares. We
use UVCS measurements of O VI photons produced by five flares and
subsequently scattered by O VI ions in the corona to determine the
5.0<=logT<=6.0 transition region luminosities. We compare
them with the rates of increase of thermal energy and the conductive
losses deduced from RHESSI and GOES X-ray data using areas from RHESSI
images to estimate the loop volumes, cross-sectional areas, and scale
lengths. The transition region luminosities during the impulsive phase
exceed the X-ray luminosities for the first few minutes, but they are
smaller than the rates of increase of thermal energy unless the filling
factor of the X-ray-emitting gas is ~0.01. The estimated conductive
losses from the hot gas are too large to be balanced by radiative
losses or heating of evaporated plasma, and we conclude that the area
of the flare magnetic flux tubes is much smaller than the effective
area measured by RHESSI during this phase of the flares. For the 2002
July 23 flare, the energy deposited by nonthermal particles exceeds
the energy radiated in X-rays, the energy radiated at transition region
temperatures, and the rate of increase of the thermal energy.
Title: 2006 LWS TR & T Solar Wind Focused Science Topic Team:
The Beginnings
Authors: Miralles, M. P.; Bhattacharjee, A.; Landi, E.; Markovskii,
S.; Cranmer, S. R.; Doschek, G. A.; Forbes, T. G.; Isenberg, P. A.;
Kohl, J. L.; Ng, C.; Raymond, J. C.; Vasquez, B. J.
Bibcode: 2006AGUFMSH11A0371M
Altcode:
The Solar Wind Focused Science Topic (FST) team was created to
apply a combination of theoretical studies, numerical simulations,
and observations to the understanding of how the fast and slow solar
wind are heated and accelerated. Four proposals were selected for this
FST team. They will investigate the role of energy sources and kinetic
mechanisms responsible for the heating and acceleration of the solar
wind. In particular, the FST team will examine magnetic reconnection
and turbulence as possible heating mechanisms. Plasma properties and
their evolution over the solar cycle, determined from the analysis of
remote and in situ measurements, will be used to put firm constraints
on the models. The work of the Solar Wind FST team is in its initial
stages. The organization, planning, and findings resulting from the
first FST team meeting will be reported.
Title: Comparison of UVCS/SOHO Streamer Properties with 1 AU Solar
Wind Measurements
Authors: Strachan, L.; Panasyuk, A. V.; Miralles, M. P.; Kohl, J. L.
Bibcode: 2006ESASP.617E.108S
Altcode: 2006soho...17E.108S
No abstract at ADS
Title: Spectroscopic Observations of the Extended Solar Corona Above
Quiet Sun Regions
Authors: Suleiman, R. M.; Kohl, J. L.; Strachan, L.; Phillips, D.;
Uzzo, M.
Bibcode: 2006ESASP.617E.109S
Altcode: 2006soho...17E.109S
No abstract at ADS
Title: Coronal Hole Properties During the First Decade of UVCS/SOHO
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2006ESASP.617E..15M
Altcode: 2006soho...17E..15M
No abstract at ADS
Title: Progress Toward Measurements of Suprathermal Tails in Coronal
Proton Velocity Distributions
Authors: Kohl, J. L.; Panazyuk, A. V.; Cranmer, S. R.; Fineschi, S.;
Gardner, L. D.; Phillips, D. H.; Raymond, J. C.; Uzzo, M.
Bibcode: 2006ESASP.617E..25K
Altcode: 2006soho...17E..25K
No abstract at ADS
Title: Comparisons of H I Ly-Alpha Line Widths in Streamers and
Coronal Holes Measured with UVCS/SOHO and UVCS/Spartan-201 in
November 1998
Authors: Gardner, L. D.; Miralles, M. -P.; Panasyuk, A.; Strachan,
L.; Kohl, J. L.
Bibcode: 2006ESASP.617E..90G
Altcode: 2006soho...17E..90G
No abstract at ADS
Title: The First Decade of UVCS/SOHO: Coronal Hole Properties
Authors: Miralles, Mari Paz; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2006SPD....37.1003M
Altcode: 2006SPD....37.1003P; 2006BAAS...38R.237M
We have measured with the SOHO Ultraviolet Coronagraph Spectrometer
(UVCS) the physical properties of over 155 large coronal holes that
produced a variety of high-speed solar wind conditions at 1 AU. This
data set includes observations of coronal holes of different sizes
and latitudinal locations present throughout solar cycle 23.In the
spring of 2006, the polar coronal holes have not yet evolved to the
fully quiescent minimum state seen in 1996-1997, although the next
solar minimum is expected to occur during 2006-2007. We will present
the solar cycle dependence of the derived plasma parameters for O5+
and protons from the last solar minimum in 1996 to present and compare
them, where possible, with the in situ solar wind properties.This
work is supported by NASA under Grant NNG05GG38G tothe Smithsonian
Astrophysical Observatory, by the Italian Space Agency, and by PRODEX
(Swiss contribution).
Title: Comparison Between Coronal and In Situ Plasma Properties Over
The Solar Cycle
Authors: Strachan, Leonard, Jr.; Panasyuk, A. V.; Miralles, M. P.;
Kohl, J. L.
Bibcode: 2006SPD....37.1004S
Altcode: 2006BAAS...38..238S
The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO has made
detailed observations of coronal streamers in the extended corona
(1.5 Ro < r < 10 Ro) for almost a complete
solar cycle. Measurements of ultraviolet line profiles and intensities
and polarized white light intensities are used to determine plasma
parameters (proton and ion temperatures, electron densities, and ion
outflow speeds) for these large scale coronal structures. In this
paper we compare the variations in streamer properties obtained in
the extended corona with the properties found in the solar wind at
1 AU. Solar wind velocities and densities derived from in situ data
are used for comparisons. Such comparisons may be used to distinguish
between solar wind variations due to changes in physical parameters
of streamers at the Sun as opposed to changes in flow geometry. This
work was supported by NASA grants NAG5-12781 and NNG05GG38G to the
Smithsonian Astrophysical Observatory.
Title: Ultraviolet spectroscopy of the extended solar corona
Authors: Kohl, John L.; Noci, Giancarlo; Cranmer, Steven R.; Raymond,
John C.
Bibcode: 2006A&ARv..13...31K
Altcode: 2006A&ARv.tmp....1K
The first observations of ultraviolet spectral line profiles
and intensities from the extended solar corona (i.e., more than
1.5 solar radii from Sun-center) were obtained on 13 April 1979
when a rocket-borne ultraviolet coronagraph spectrometer of the
Harvard-Smithsonian Center for Astrophysics made direct measurements
of proton kinetic temperatures, and obtained upper limits on outflow
velocities in a quiet coronal region and a polar coronal hole. Following
those observations, ultraviolet coronagraphic spectroscopy has
expanded to include observations of over 60 spectral lines in
coronal holes, streamers, coronal jets, and solar flare/coronal
mass ejection (CME) events. Spectroscopic diagnostic techniques
have been developed to determine proton, electron and ion kinetic
temperatures and velocity distributions, proton and ion bulk flow
speeds and chemical abundances. The observations have been made during
three sounding rocket flights, four Shuttle deployed and retrieved
Spartan 201 flights, and the Solar and Heliospheric Observatory (SOHO)
mission. Ultraviolet spectroscopy of the extended solar corona has led
to fundamentally new views of the acceleration regions of the solar wind
and CMEs. Observations with the Ultraviolet Coronagraph Spectrometer
(UVCS) on SOHO revealed surprisingly large temperatures, outflow speeds,
and velocity distribution anisotropies in coronal holes, especially for
minor ions. Those measurements have guided theorists to discard some
candidate physical processes of solar wind acceleration and to increase
and expand investigations of ion cyclotron resonance and related
processes. Analyses of UVCS observations of CME plasma properties
and the evolution of CMEs have provided the following: temperatures,
inflow velocities and derived values of resistivity and reconnection
rates in CME current sheets, compression ratios and extremely high ion
temperatures behind CME shocks, and three dimensional flow velocities
and magnetic field chirality in CMEs. Ultraviolet spectroscopy has
been used to determine the thermal energy content of CMEs allowing the
total energy budget to be known for the first time. Such spectroscopic
observations are capable of providing detailed empirical descriptions
of solar energetic particle (SEP) source regions that allow theoretical
models of SEP acceleration to be tailored to specific events, thereby
enabling in situ measurements of freshly emitted SEPs to be used for
testing and guiding the evolution of SEP acceleration theory. Here we
review the history of ultraviolet coronagraph spectroscopy, summarize
the physics of spectral line formation in the extended corona, describe
the spectroscopic diagnostic techniques, review the advances in our
understanding of solar wind source regions and flare/CME events provided
by ultraviolet spectroscopy and discuss the scientific potential of
next generation ultraviolet coronagraph spectrometers.
Title: Measurements of Electron Impact Excitation Cross Sections at
the Harvard-Smithsonian Center for Astrophysics
Authors: Gardner, L. D.; Kohl, J. L.
Bibcode: 2006nla..conf..186G
Altcode:
The analysis of absolute spectral line intensities and intensity
ratios with spectroscopic diagnostic techniques provides empirical
determinations of chemical abundances, electron densities and
temperatures in astrophysical objects. Since spectral line intensities
and their ratios are controlled by the excitation rate coefficients
for the electron temperature of the observed astrophysical structure,
it is imperative that one have accurate values for the relevant rate
coefficients. Here at the Harvard-Smithsonian Center for Astrophysics,
we have been carrying out measurements of electron impact excitation
(EIE) for more than 25 years. We will illustrate our experimental
approach and apparatus by discussing a measurement of EIE in C^{2+}
(2s2p ^3P^o → 2p^2 ^3P).
Title: Ultraviolet spectroscopy of the extended solar corona
Authors: Kohl, J.
Bibcode: 2006cosp...36.3317K
Altcode: 2006cosp.meet.3317K
Since the first observations of HI Ly-alpha spectral line profiles and
intensities of the extended solar corona were obtained on 13 April 1979
with a rocket-borne ultraviolet coronagraph spectrometer ultraviolet
coronagraphic spectroscopy has expanded to include observations of
over 60 spectral lines in coronal holes streamers coronal jets and
solar flare coronal mass ejection CME events Spectroscopic diagnostic
techniques have been developed to determine proton electron and ion
kinetic temperatures and velocity distributions proton and ion bulk flow
speeds and chemical abundances Ultraviolet coronagraph spectroscopy has
led to fundamentally new views of the acceleration regions of the solar
wind and CMEs Significant progress has been made toward identifying
and characterizing the physical processes that heat the extended corona
accelerate the various plasma components of the solar wind and produce
a wide range of non-equilibrium phenomena in CMEs Perhaps most notably
the surprisingly extreme plasma conditions observed by UVCS SOHO in
coronal holes have guided theorists to discard some candidate physical
processes and to further investigate others The UVCS observations
of coronal holes---and subsequent theoretical investigations of ion
cyclotron resonance---have been cited increasingly in literature devoted
to other plasma environments such as the Earth s aurora Gavrishchaka
et al backslash 2000 and they have guided new investigations in pure
plasma physics e g Mizuta backslash Hoshino 2001 Chen et al backslash
Title: A Solar Energetic Particle Mission (SEPM) for the S3C Great
Observatory
Authors: Strachan, L.; Kohl, J. L.; Cranmer, S. R.; Esser, R.; Gardner,
L. D.; Lin, J.; Raymond, J. C.; van Ballegooijen, A.; Socker, D. G.
Bibcode: 2005AGUFMSH51C1221S
Altcode:
The S3C Great Observatory concept is guided by a systems approach
to understanding the heliosphere. A Solar Energetic Particle Mission
(SEPM) can make valuable contributions to this Great Observatory in
conjunction with upcoming Living with a Star (LWS) missions e.g. Solar
Dynamics Observatory and Sentinels. SEPM can provide the remote sensing
component to a program for better understanding how, when, and where
solar energetic particles (SEPs) are produced. Such a coordinated
approach will include coronagraphic UV spectroscopy and visible light
polarimetery with SEPM, along with in situ particles and fields,
X-ray and gamma-ray measurements from spacecraft close to the Sun
(Inner Heliospheric Sentinels). While SEPM will use plasma diagnostics
that are derived from the UVCS and LASCO coronagaraphs on SOHO, it
will have an order of magnitude improvement in its capabilities.
Title: An Initial Attempt to Measure Suprathermal Tails in Coronal
Proton Velocity Distributions
Authors: Kohl, J. L.; Cranmer, S. R.; Fineschi, S.; Gardner, L. D.;
Panasyuk, A. V.; Raymond, J. C.; Uzzo, M.
Bibcode: 2005AGUFMSH44A..05K
Altcode:
Test observations made with the Ultraviolet Coronagraph Spectrometer
(UVCS) on SOHO in August 2005 are being used to make an initial
assessment of the possibility of measuring suprathermal tails in the
proton velocity distribution functions. Any successful theory of solar
energetic particle (SEP) production by CME shocks must account for the
large observed variations in SEP spectral characteristics and elemental
abundances. Some have proposed that this variability arises from an
inherently variable population of suprathermal seed particles (e.g.,
Mason et al. 2005): some that exist all the time in the solar wind
(with varying properties depending on wind speed) and some that are
associated with prior flares and CME shocks (e.g., Kahler 2004; Tylka
et al. 2005). As yet, though, the suprathermal particle population in
the solar corona has never been measured. The seed particle number
density predicted for typical gradual SEP events is about 0.002 -
0.01 times the thermal population (e.g., Lee 2005), and should, in at
least some cases, correspond to a measurable enhancement in the wing
of the H I Ly-alpha profile. In August 2005, the Ly-alpha channel of
UVCS was recommissioned and used to observe HI Ly-alpha line profiles
at 2.0 solar radii in coronal holes, helmet streamers, above active
regions and after a CME. The holographically ruled diffraction grating
provides the low stray light level needed to observe the tail of the
line profile out to about 0.5 nm from line center. New observations
as well as measurements from the original UVCS laboratory calibration
and in flight measurements from earlier in the mission are being
used to characterize the instrument response to monochromatic light
so such instrument effects can be removed. Initial results will be
reported. This work is supported by NASA Grant NNG05GG38G to the
Smithsonian Astrophysical Observatory Kahler, S. W. 2004, ApJ, 603,
330. Lee, M. A. 2005, ApJ Supp., 158, 38. Mason, G., Desai, M.,
Mazur, J., & Dwyer, J. 2005, COSPAR 35th Scientific Assemly,
p. 1596. Tylka, A. J., et al. 2005, ApJ, 625, 474.
Title: Capabilities of UV Coronagraphic Spectroscopy for Studying
the Source Regions of Solar Energetic Particles and the Solar Wind
Authors: Kohl, J. L.; Cranmer, S. R.; Gardner, L. D.; Lin, Jun;
Raymond, John C.; Strachan, Leonard
Bibcode: 2005ESASP.592..677K
Altcode: 2005astro.ph..6509K; 2005ESASP.592E.135K; 2005soho...16E.135K
We summarize the unique capabilities of UV coronagraphic spectroscopy
for determining the detailed plasma properties (e.g., density,
temperature, outflow speed, composition) of the source regions of both
transient phenomena such as CMEs, flares, and solar energetic particles
(SEPs) and more time-steady solar wind streams. UVCS/SOHO observations
have provided the first detailed diagnostics of the physical conditions
of CME plasma in the extended corona. It provided new insights into
the roles of shock waves, reconnection, and magnetic helicity in CME
eruptions. We summarize past observations and discuss the diagnostic
potential of UV coronagraphic spectroscopy for characterizing two
possible sites of SEP production: CME shocks and reconnection current
sheets. UVCS/SOHO has also led to fundamentally new views of the
acceleration region of the solar wind. Understanding the physical
processes in this region, which ranges from the low corona (1.1 to
1.5 Rsun) past the sonic points (greater than 5 Rsun), is key to
linking the results of solar imaging to in situ particle and field
detection. Despite the advances that have resulted from UVCS/SOHO,
more advanced instrumentation could determine properties of additional
ions with a wider sampling of charge/mass combinations. This would
provide much better constraints on the specific kinds of waves that are
present as well as the specific collisionless damping modes. Electron
temperatures and departures from Maxwellian velocity distributions
could also be measured. The instrumentation capable of making the
above observations will be described.
Title: Ultraviolet spectroscopy of solar energetic particle source
regions
Authors: Kohl, J. L.; Cranmer, S.; Esser, R.; Gardner, L. D.; Fineschi,
S.; Lin, J.; Panasyuk, A.; Raymond, J. C.; Strachan, L.
Bibcode: 2005SPIE.5901..262K
Altcode:
A problem of fundamental importance for future space travel to the
Moon and Mars is the determination and prediction of the radiation
environment generated by the Sun. The sources of solar energetic
particles (SEP) and the physical processes associated with their
acceleration and propagation are not well understood. Ultraviolet
coronagraphic spectroscopy uniquely has the capabilities for determining
the detailed plasma properties of the likely source regions of such
particles. This information can be used to develop empirical models
of the source regions for specific events, and it can provide the key
information needed to identify and understand the physical processes
that produce SEP hazards. UVCS/SOHO observations have provided the first
detailed diagnostics of the plasma parameters of coronal mass ejections
(CMEs) in the extended corona. These observations have provided new
insights into the roles of shock waves, reconnection and magnetic
helicity in CME eruptions. Next generation ultraviolet coronagraph
spectrometers could provide additional diagnostic capabilities. This
paper summarizes past observations, and discusses the diagnostic
potential of advanced ultraviolet coronagraphic spectroscopy for
characterizing two possible sites of SEP production: CME shocks and
reconnection current sheets.
Title: Absolute empirical rate coefficient for the excitation of
the 117.6 nm line in C III
Authors: Gardner, L. D.; Daw, A. N.; Janzen, P. H.; Atkins, N.; Kohl,
J. L.
Bibcode: 2005AGUSMSP21B..04G
Altcode:
We have measured the absolute cross sections for electron impact
excitation (EIE) of C2+ (2s2p 3P° - 2p2 3P) for energies from below
threshold to 17 eV above and derived EIE rate coefficients required for
astrophysical applications. The uncertainty in the rate coefficient at a
typical solar temperature of formation of C2+ is less than ± 6 %. Ions
are produced in a 5 GHz Electron Cyclotron Resonance (ECR) ion source,
extracted, formed into a beam, and transported to a collision chamber
where they collide with electrons from an electron beam inclined at
45 degrees. The beams are modulated and the radiation from the decay
of the excited ions at λ 117.6 nm is detected synchronously using an
absolutely calibrated optical system that subtends slightly over π
steradians. The fractional population of the C2+ metastable state in
the incident ion beam has been determined experimentally to be 0.42 ±
0.03 (1.65 σ). At the reported ± 15 % total experimental uncertainty
level (1.65 σ), the measured structure and absolute scale of the cross
section are in fairly good agreement with 6-term close-coupling R-matrix
calculations and 90-term R-matrix with pseudo-states calculations,
although some minor differences are seen just above threshold. As
density-sensitive line intensity ratios vary by only about a factor
of 5 as the density changes by nearly a factor of 100, even a 30 %
uncertainty in the excitation rate can lead to a factor of 3 error in
density. This work is supported by NASA Supporting Research and
Technology grants NAG5- 9516 and NAG5-12863 in Solar and Heliospheric
Physics and by the Smithsonian Astrophysical Observatory.
Title: Solar Cycle Variations of Coronal Hole Properties
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2005AGUSMSP51B..07M
Altcode:
As of early 2005, we have measured with the SOHO Ultraviolet
Coronagraph Spectrometer (UVCS) the physical properties of at least
136 large coronal holes that produced a variety of high-speed solar
wind conditions at 1 AU. UVCS has been used to observe O VI (103.2 and
103.7 nm) and H I Lyman alpha (121.6 nm) emission lines as a function
of heliocentric distance in coronal holes since 1996. The analysis of
their spectroscopic parameters allows us to identify similarities
and differences among coronal holes at different phases of the
solar cycle. From such measurements we can derive plasma parameters
(densities, temperatures, velocity distribution anisotropies, and
outflow speeds) for O5+ and protons as a function of heliocentric
distance in the coronal holes. These properties, combined with other
observed quantities such as white-light polarization brightness and the
more-or-less unipolar magnetic fluxes measured on-disk, let us map out
the "allowed parameter space" of coronal hole plasma properties more
fully than ever before. We will present the solar cycle dependence
of the above plasma parameters from the last solar minimum in 1996
to present and compare them, where possible, with the in situ solar
wind properties. We will also present an update on the pattern that
is beginning to emerge, i.e., coronal holes with lower densities at
a given heliocentric distance tend to exhibit faster ion outflow and
higher ion temperatures. This information will thus be used to set firm
empirical constraints on coronal heating and solar wind acceleration in
coronal holes. In 2005, the polar coronal holes have not yet evolved
to the fully quiescent minimum state seen in 1996-1997, though the
next solar minimum is expected to occur in about 1.5 to 2 years. This
work is supported by NASA under Grant NNG04GE84G to the Smithsonian
Astrophysical Observatory, by the Italian Space Agency, and by PRODEX
(Swiss contribution).
Title: New Synoptic Maps of the Solar Corona from UVCS Observations
Authors: Strachan, L.; Panasyuk, A. V.; Miralles, M.; Kohl, J. L.;
Baham, M.
Bibcode: 2005AGUSMSH43A..01S
Altcode:
We present for the first time synoptic maps of the extended solar corona
(r/Ro > 1.5) based on eight years of data from the SOHO Ultraviolet
Coronagraph Spectrometer (UVCS). The data reveal the changes in the
physical properties of the large scale features in the corona. Maps of O
VI line intensities, line widths, and line ratios for the O VI 1032/1037
doublet and intensities and line widths for the H I Ly-alpha line reveal
information about the evolution of coronal densities, temperatures,
and outflow velocities over the solar cycle. In particular these data
are used in support of program to understand the solar cycle variation
of coronal holes and coronal streamers. This work is supported by
NASA Grant NAG5-12781 to the Smithsonian Astrophysical Observatory and
NASA subcontract OGSP21010200061SAO awarded to SAO through a grant to
Southern Universty at Baton Rouge.
Title: On the Incompatibility Between UVCS/SOHO Observations of
Polar Coronal Holes and Isotropic Oxygen Velocity Distributions
Authors: Cranmer, S. R.; Panasyuk, A. V.; Kohl, J. L.
Bibcode: 2005AGUSMSP33A..02C
Altcode:
We present a reanalysis of UVCS/SOHO observations of the O VI 1032,
1037 emission line doublet at large heliocentric distances in polar
coronal holes during the last solar minimum (1996-1997). The traditional
interpretation of the broad line widths and unusual intensity ratios
has been that the oxygen ions exhibit a strong temperature anisotropy,
with the temperature perpendicular to the magnetic field being much
larger than the temperature parallel to the field. However, a recent
paper by Raouafi and Solanki suggested that it may be possible to
model the observations using an isotropic velocity distribution of
(still very hot) oxygen ions. In this presentation we show that the
standard interpretation of an anisotropic distribution is the only
one that is fully consistent with the observational data. Using the
same electron density and magnetic field models assumed by Raouafi
and Solanki, we varied the 3 main ion properties (outflow speed and
the 2 bi-Maxwellian temperature components) in a 3D data-cube that
exhaustively treated all possibilities. This data-cube spans the
parameter space of both earlier UVCS/SOHO empirical models and the new
proposal of Raouafi and Solanki. Even so, we find that above about 2.5
solar radii the only points in the data-cube that reproduce the actual
observed line widths and intensity ratios are those with substantial
temperature anisotropies.
Title: Absolute Cross Section for Electron Impact Excitation of
Metastable C2+
Authors: Daw, Adrian; Gardner, Larry; Janzen, Paul; Kohl, John
Bibcode: 2004APS..DMP.P1103D
Altcode:
Progress toward measurements of the absolute cross section for electron
impact excitation (EIE) of C^2+ (2s2p ^3P^o - 2p^2 ^3P) for energies
below threshold to 15 eV above is reported. These measurements will be
used to determine the EIE rate coefficients required for astrophysical
applications. Ions are produced in a 5 GHz Electron Cyclotron Resonance
(ECR) ion source. A modulated beams technique with inclined electron
and ion beams is being used. The radiation from the excited ions
at λ 117.5 nm is detected using an absolutely calibrated optical
system that subtends slightly over π steradians. The population
of the C^2+ metastable state in the incident ion beam is determined
experimentally. This work is supported by NASA Supporting Research and
Technology grants NAG5-9516 and NAG5-12863 in Solar and Heliospheric
Physics and by the Smithsonian Astrophysical Observatory.
Title: Advantages of the Photon Detection Method for Beams
Measurements of Electron Impact Excitation Rates
Authors: Kohl, J. L.; Gardner, L. D.; Daw, A.
Bibcode: 2004AAS...204.5106K
Altcode: 2004BAAS...36R.753K
Beams experiments are well suited to measurements of electron impact
excitation (EIE) cross sections for specific transitions of positive
ions. Excitation events can be determined directly by detecting
either the emitted photon following excitation and radiative decay
or by detecting the inelastically scattered electron. The photon
method has been used at Harvard-Smithsonian to measure absolute cross
sections involved in the production of C II 133.5 nm, C III 117.6 nm,
C IV 155.0 nm, and Si III 120.6 nm. The experiments allow the cross
sections to be determined completely from measured quantities such as
the distribution of electrons and ions in the beams, the beam energy,
the photon emission rate and the ground state and metastable state
population fractions (when required). Typical standard uncertainties
are +/- 9 percent. Population fractions are determined by two methods:
1) the beams attenuation method, which relies on differences between
the ground state and metastable state charge transfer cross sections
with a selected gas target, and 2) measurement of the radiative decay
intensity from metastable ions in the incident beam. Collision energies
from threshold to well above threshold are accessable allowing the
determination of empirical electron collision rates for both maxwellian
and non-maxwellian electron velocity distributions. Recent results,
comparison to theoretical values, astrophysical applications, the
experimental method and the apparatus, including a new 5 GHz Electron
Cyclotron Resonance (ECR) ion source, will be described. This work was
supported by NASA Grant NAG5-12863 to the Smithsonian Astrophysical
Observatory.
Title: Towards a Physical Characterization of Large Coronal Holes
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2004AAS...204.7106M
Altcode: 2004BAAS...36S.797M
The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO was used
to observe O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm)
emission lines as a function of heliocentric distance in more than 85
coronal holes, in order to characterize the physical properties of
coronal holes at different phases of the solar cycle. Our previous
analyses of UVCS observations have shown that polar and equatorial
coronal holes produce different acceleration profiles and have
different oxygen kinetic temperatures. We examine the variation
in the characteristics of representative large coronal holes
producing a variety of high-speed conditions at 1 AU. This
work is supported by NASA under Grant NAG5-12865 to the Smithsonian
Astrophysical Observatory, by the Italian Space Agency and by PRODEX
(Swiss contribution).
Title: Differences in Plasma Conditions Among 85 Large Coronal Holes
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2004AGUSMSH41A..03M
Altcode:
We have measured ultraviolet spectroscopic parameters as a function
of heliocentric distance for more than 85 coronal holes, in order to
characterize the physical properties of coronal holes at different
phases of the solar cycle. The Ultraviolet Coronagraph Spectrometer
(UVCS) aboard SOHO was used to observed O VI (103.2 and 103.7 nm)
and H I Lyman alpha (121.6 nm) emission lines to determine kinetic
temperatures, average densities, and outflow speeds in coronal
holes. UVCS observations provide unique information on the heating and
acceleration processes in the corona. Our previous analyses of UVCS
observations have shown that solar minimum (polar) and solar maximum
(equatorial) coronal holes produce different acceleration profiles
and have different oxygen kinetic temperatures. We also examine the
differences in the characteristics of representative coronal holes
producing a variety of high-speed conditions (550-800 km/s) at 1
AU. These analyses provide limits on the coronal plasma properties
and put constraints on the physical processes that are responsible
for the heating of the extended corona and the acceleration of the
solar wind. This work is supported by NASA under Grant NAG5-12865 to
the Smithsonian Astrophysical Observatory, by the Italian Space Agency
and by PRODEX (Swiss contribution).
Title: Contributions from Ultraviolet Spectroscopy to the Prediction
of High-energy Proton Hazards from CME Shocks
Authors: Lin, J.; Raymond, J. C.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2004AAS...204.7205L
Altcode: 2004BAAS...36Q.799L
A significant potential hazard to astronauts and their equipment
in interplanetary space is the relativistic proton flux produced by
coronal mass ejections (CMEs) and solar flares. The longest-duration
phase of solar energetic particle (SEP) activity is believed to come
from the CME shock as it propagates through the extended corona and
heliosphere. Ultraviolet spectroscopy by SOHO has revealed a means
for: (1) detecting and characterizing CME shocks in the corona, and
(2) determining the plasma conditions in the pre-CME corona which are
needed to understand the formation and evolution of shocks. Such remote
sensing - combined with models of SEP acceleration and transport -
can be used to predict the strength, duration, and production sites of
the radiation. This poster describes the specific means by which
ultraviolet spectroscopy and other remote-sensing data can be used to
determine the inputs and boundary conditions for individual events (such
as the October-November 2003 storms) in existing SEP model codes. We
also discuss an additional potential source of SEP radiation associated
with electric fields in the current sheets that form in flare regions
in the wake of CME. Both observations and model calculations show that
the reconnection-induced electric field can reach a maximum strength
of a few V/cm within tens of minutes after the onset of the eruption,
then decreases gradually over several hours. SEPs produced in these
regions may account for X-rays and γ -rays observed prior to the
formation of CME shocks. Ultraviolet spectroscopy has been shown to
provide constraints on the plasma properties in all of the above CME
features. This work is supported by NASA under grant NAG5-12865 to
the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana,
and by the Swiss contribution to ESA's PRODEX program.
Title: Measurement of the Absolute Electron Impact Excitation Cross
Section for the C III 117.6 nm Transition
Authors: Daw, A.; Janzen, P. H.; Gardner, L. D.; Kohl, J. L.
Bibcode: 2004AAS...204.7309D
Altcode: 2004BAAS...36..801D
An inclined beams arrangement is being used to measure the absolute
cross section for electron impact excitation of the C2+
(2s2p 3Po - 2p2 3P)
transition for energies below threshold to 15 eV above. These cross
sections determine the EIE rate coefficients required for astrophysical
applications. Ions are produced in a 5 GHz Electron Cyclotron Resonance
(ECR) ion source. A modulated beams technique with inclined electron
and ion beams is being used. The radiation from the excited ions at
a wavelength of 117.5 nm is detected using an absolutely calibrated
optical system that subtends slightly over pi steradians. The
population of the C2+ metastable state in the incident ion
beam is determined experimentally. The measured cross sections will
be presented and compared to those predicted by theory. This work is
supported by NASA Supporting Research and Technology grants NAG5-9516
and NAG5-12863 in Solar and Heliospheric Physics and by the Smithsonian
Astrophysical Observatory.
Title: Low-latitude coronal holes during solar maximum
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2004AdSpR..33..696M
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO has been used
to observe large low-latitude coronal holes during solar maximum that
produced fast solar wind streams. UVCS observations show that large
low-latitude coronal holes at solar maximum, coronal holes of at
least 10° in longitude, have plasma properties that seem to bridge
the gap between solar minimum polar coronal holes and streamers. The
ion kinetic perpendicular temperatures in equatorial coronal holes are
about 2 times larger than those in a solar minimum equatorial streamer,
and about a factor of 2 smaller than those in polar coronal holes
above 2 Rsolar. The outflow speeds for the large equatorial
coronal holes observed by UVCS are 3-4 times lower than those in polar
coronal holes between 2 and 3 Rsolar. The values for high-
and mid-latitude coronal holes are in between those. In all these cases,
the in situ data corresponding to these coronal holes showed high-speed
wind streams with asymptotic speeds of 600-750 km s-1. These
wind speeds approach those observed over polar coronal holes at solar
minimum, but the outflow speeds in these coronal holes between 2 and
3 Rsolar are different. In contrast to the polar coronal
holes, the bulk of the solar wind acceleration must occur above
3 Rsolar for large low-latitude coronal holes at solar
maximum. These observations provide detailed empirical constraints
for theoretical models and may be key to understanding how the various
types of solar wind plasma are heated and accelerated.
Title: Coordinated UVCS/SOHO and VLA Observations of the Solar Corona
Authors: Miralles, M. P.; Cranmer, S. R.; Raymond, J. C.; Spangler,
S. R.; Kohl, J. L.
Bibcode: 2003AGUFMSH22A0188M
Altcode:
Coordinated UVCS/SOHO and VLA coronal observations took place during
August 16--19, 2003. The radio source 3C 228 passed behind a streamer
in the northeast at a heliocentric distance of about 7 solar radii,
and behind the north coronal hole at about 4 solar radii in the latter
part of the radio observation. The goal of this campaign is to combine
the analysis of radio polarimetric sounding measurements of the corona
with ultraviolet spectroscopy of the same regions, in order to obtain
qualitatively new information about the properties of the solar coronal
plasma. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO
observed O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm)
emission lines to determine kinetic temperatures, average densities
and outflow speeds in the corona. UVCS observations provide unique
information on the heating and acceleration processes in the corona. The
Very Large Array (VLA) observations reveal the Faraday rotation of
polarized radio waves due to passage through the magnetized plasma of
the corona. These measurements provide limits on the coronal magnetic
field strength and constrain the properties of magnetohydrodynamic (MHD)
waves. Radio propagation techniques are a useful complementary tool
to ultraviolet coronagraphic spectroscopy in determining the physical
processes that are responsible for the heating of the extended corona
and the acceleration of the solar wind. This work is supported by NASA
under Grant NAG5-12865 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: Empirically Determined Anisotropic Velocity Distributions and
Outflows of O5+ Ions in a Coronal Streamer at Solar Minimum
Authors: Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2003ApJ...597.1145F
Altcode:
Empirical constraints on the O5+ velocity distributions
and outflow speeds in a solar minimum equatorial streamer between 2.6
and 5.1 Rsolar are determined using a spectral synthesis
code that includes O VI Doppler dimming. These constraints follow
directly from UV spectra taken on 1996 October 12 with the Ultraviolet
Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric
Observatory (SOHO) satellite and three-dimensional electron densities
derived from tomography applied to a time series of polarized
white-light images taken with the Large Angle and Spectrometric
Coronagraph (LASCO) also on SOHO. Four conclusions result from this
work: (1) our analysis shows O5+ velocity distribution
anisotropy in the streamer legs and stalk and gives strong evidence that
the microscopic velocity distribution (which excludes wave motions that
equally affect all charged particles) is anisotropic, where the most
probable speed perpendicular to the magnetic field direction exceeds
that in the parallel direction; (2) there is preferential heating of the
O5+ ions over the protons in the streamer stalk and legs;
(3) there is no evidence for preferential O5+ heating in
the core; and (4) the outflow velocity of the O5+ ions is
determined at heights above 4.6 Rsolar. All results have
a confidence level of at least 70%.
Title: Plasma properties above coronal active regions inferred from
SOHO/UVCS and radio spectrograph observations
Authors: Mancuso, S.; Raymond, J. C.; Kohl, J.; Ko, Y. -K.; Uzzo,
M.; Wu, R.
Bibcode: 2003A&A...400..347M
Altcode:
Information on coronal plasma was inferred from the joint analysis of
type {II} radio bursts and SOHO UltraViolet Coronagraph Spectrometer
(UVCS) observations. The data sample comprises 37 metric type {II}
radio bursts observed by ground-based radio spectrographs in 1999,
during the rising phase of the solar cycle. The coronal electron
densities n_e were estimated with the diagnostic provided by UVCS
observations of the O Vi doublet line intensities. Upper limits to
the coronal Alfvén speed above active regions were inferred from
the derived shock speeds by requiring that the disturbances propagate
at least faster than the local characteristic speed. Information on
the magnetic field strength B and plasma beta in the middle corona
were finally extracted from the coronal Alfvén speed upper limits. A
major improvement with respect to previous studies that used type {II}
radio bursts to derive plasma properties, is that density profiles of
the pre-shock plasma obtained a few hours before the passage of the
shock were used instead of general electron density models taken from
literature. Our main result is expressed by the inequality B(r) <=
(0.6 +/- 0.3) (r-1)-1.2 G, that is valid in the range
1.5 <= r <= 2.3 solar radii, and is consistent with previous
estimates of the magnetic field above coronal active regions.
Title: Advanced spectroscopic and coronographic explorer: science
payload design concept
Authors: Gardner, Larry D.; Kohl, John L.; Daigneau, Peter S.; Smith,
Peter L.; Strachan, Leonard, Jr.; Howard, Russell A.; Socker, Dennis
G.; Davila, Joseph M.; Noci, Giancarlo C.; Romoli, Marco; Fineschi,
Silvano
Bibcode: 2003SPIE.4843....1G
Altcode:
The Advanced Spectroscopic and Coronagraphic Explorer (ASCE) was
proposed in 2001 to NASA's Medium-Class Explorer (MIDEX) program
by the Smithsonian Astrophysical Observatory in collaboration with
the Naval Research Laboratory, Goddard Space Flight Center and the
Italian Space Agency. It is one of four missions selected for Phase A
study in 2002. ASCE is composed of three instrument units: an Advanced
Ultraviolet Coronagraph Spectrometer (AUVCS), an Advanced Large Aperture
visible light Spectroscopic Coronagraph (ALASCO), and an Advanced Solar
Disk Spectrometer (ASDS). ASCE makes use of a 13 m long boom that is
extended on orbit and positions the external occulters of AUVCS and
ALASCO nearly 15 m in front of their respective telescope mirrors. The
optical design concepts for the instruments will be discussed.
Title: The ASCE EUV Polarimeter
Authors: Romoli, M.; Fineschi, S.; Uslenghi, M.; Corti, G.; Pace,
E.; Ciaravella, A.; Tondello, G.; Noci, G.; Gardner, L. D.; Kohl, J. L.
Bibcode: 2003MmSAI..74..835R
Altcode:
The SOHO mission has achieved important results in the physics of
solar wind and coronal mass ejection acceleration, but most of the
processes that drive this acceleration have not yet been explained. The
Advanced Spectroscopic and Coronagraphic Explorer (ASCE) mission will
carry on-board spectroscopic and polarimetric instrumentation of new
generation that is designed to address the fundamental questions on this
processes. Following a brief description of ASCE scientific objectives
and instrumentation, the EUV polarimetric channel is described. The
EUV Polarimeter (EUVP) is designed to measure for the first time the
magnetic field vector in the extended corona through the Hanle effect,
and the anisotropy of the ion velocity. The EUVP represents the
contribution of the Italian solar physics community to the ASCE mission.
Title: The Advanced Spectroscopic and Coronagraphic Explorer (ASCE)
Mission Concept Study
Authors: Kohl, J.; Howard, R.; Davila, J.; Noci, G.; Gardner, L.;
Socker, D.; Romoli, M.; Strachan, L.; Floyd, L.; Cranmer, S.; Raymond,
J.; van Ballegooijen, A.
Bibcode: 2002AGUFMSH52A0463K
Altcode:
The ASCE Mission is currently in a Phase A feasibility study as a
candidate for the upcoming MIDEX selection. The ASCE science payload
provides next generation spectroscopic and polarimetric instrumentation
aimed at identifying the physical processes governing solar wind
generation and coronal mass ejections (CMEs). During the current phase,
engineering design and analyses have demonstrated the feasibility of
accomplishing the original mission objectives within the MIDEX mission
constraints. The launch is planned for early 2007 and the operations
and analyses are expected to continue for 5 years. ASCE data along with
data analysis software and calibration data will be unrestricted and
available to the scientific community via an automated web site. A
Guest Investigator program is planned with an average of 15 grants
running concurrently during 2008 to 2012. Grants would be awarded in
response to proposals submitted during the first and subsequent years
of the mission.
Title: UVCS/SOHO Observations of Large Coronal Holes During Solar
Cycle 23
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2002AGUFMSH52A0451M
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) aboard SOHO has been
collecting spectroscopic data from numerous coronal holes as part of
an ongoing campaign to determine the plasma properties of the solar
wind acceleration region throughout the current solar cycle. The
UVCS observations show marked variations of ion properties (in the
acceleration region of the high-speed solar wind) in different types of
coronal holes. We present empirical models for the physical properties
of large coronal holes and the acceleration of the associated high-speed
solar wind derived from ultraviolet coronagraphic spectroscopy. We
discuss the role of solar cycle trends and the variation of ambient
coronal-hole properties (e.g., magnetic field, geometry, density). We
use these observations to test phenomenological models of coronal
heating and solar wind acceleration. This work is supported by NASA
under Grant NAG5-11420 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: Cyclical variations in the plasma properties of coronal holes
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2002ESASP.508..351M
Altcode: 2002soho...11..351M
UVCS/SOHO has been used to measure the plasma properties of several
types of coronal holes from 1996 to early 2002 at heights from
1.5 to 3.5 Rsolar. UVCS observations show a variation
in ion properties between coronal holes from solar minimum to solar
maximum. Different coronal holes seem to exhibit different heating and
acceleration rates. Polar coronal holes at solar minimum exhibited
the most extreme ion properties with O5+ perpendicular
temperatures in excess of 2×108K, O5+ outflow
speeds of at least 400 km/s by 3 Rsolar, and the lowest
densities. Equatorial coronal holes at solar maximum exhibited the
least extreme ion plasma properties with O5+ perpendicular
temperatures less than 8×107K, O5+ outflow
speeds of only 100 km/s by 3 Rsolar, and the largest
densities. However, large polar and equatorial coronal holes produce
interplanetary wind streams with similar speeds (v ~ 700 km/s). Thus,
most of the solar wind acceleration in large equatorial coronal
holes must occur above 3 Rsolar. The first high-latitude
coronal hole of the new negative magnetic polarity observed at the
north in 2001 exhibited extreme properties similar to those of the
1996 - 1997 polar coronal holes, even though it was 6 years prior to
the next minimum. During 2001 - 2002, we have observed mid-latitude
coronal holes, with properties in between large polar and equatorial
coronal holes.
Title: Empirical Densities, Kinetic Temperatures, and Outflow
Velocities in the Equatorial Streamer Belt at Solar Minimum
Authors: Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker,
D. A.; Kohl, J. L.
Bibcode: 2002ApJ...571.1008S
Altcode:
We use combined Ultraviolet Coronagraph Spectrometer and Large Angle
Spectroscopic Coronagraph data to determine the O5+
outflow velocities as a function of height along the axis of an
equatorial streamer at solar minimum and as a function of latitude
(at 2.3 Rsolar from Sun center). The results show that
outflow increases rather abruptly in the region between 3.6 and 4.1
Rsolar near the streamer cusp and gradually increases to ~90
km s-1 at ~5 Rsolar in the streamer stalk beyond
the cusp. The latitudinal variation at 2.3 Rsolar shows that
there is no outflow (within the measurement uncertainties) in the center
of the streamer, called the core, and that a steep increase in outflow
occurs just beyond the streamer legs, where the O VI λ1032 intensity
relative to H I λ1216 (Lyα) is higher than in the core. Velocity
variations in both height and latitude show that the transitions from
no measurable outflow to positive outflow are relatively sharp and thus
can be used to infer the location of the transition from closed to open
field lines in streamer magnetic field topologies. Such information,
including the densities and kinetic temperatures derived from the
observations, provides hard constraints for realistic theoretical
models of streamers and the source regions of the slow solar wind.
Title: Empirically Determined Anisotropic Velocity Distributions
and Outflows of O5+\ Ions in a Coronal Streamer at
Solar Minimum
Authors: Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2002AAS...200.1601F
Altcode: 2002BAAS...34..667F
Empirical constraints on the O5+\ velocity distributions
and outflow speeds in a solar minimum equatorial streamer between 2.6
and 5.1 Rsun\ are determined using a spectral synthesis
code that includes O VI Doppler dimming. These constraints follow
directly from UV spectra taken on 12 October 1996 with the Ultraviolet
Coronagraph Spectrometer (UVCS) on the SOHO satellite and 3D electron
densities derived from tomography applied to a time series of polarized
white-light images taken with the Large Angle Spectrometric Coronagraph
Experiment (LASCO) on SOHO. Four conclusions result from this work: 1)
Our analysis shows O5+\ velocity distribution anisotropy
in the streamer legs and stalk and that the microscopic velocity
distribution (which excludes wave motions that equally affect all
charged particles) is also anisotropic, where the most probable
speed perpendicular to the magnetic field direction exceeds that in
the parallel direction. 2) There is no evidence of anisotropy in the
streamer core. 3) There is preferential heating of the O5+\
ions over the protons in the streamer stalk and legs, but not in the
core. 4) The outflow velocity of the O5+\ ions is determined
at heights above 4.6 Rsun. All results have a confidence
level of at least 70%. The evidence for microscopic anisotropy in the
O5+\ velocity distributions and preferential heating of the
O5+\ ions over the protons presented here is reminiscent
of that provided for coronal holes by Cranmer et al. (1999). One
particularly favorable candidate mechanism to explain these phenomena
is ion cyclotron resonance, in which high frequency Alfvén waves
are absorbed by the heavy ions. Cranmer et al. discuss the relevance
of this process to an empirical model of a polar coronal hole. Our
data suggest that the dominant processes that heat the heavy ions in
coronal holes may also be important in streamers. Reference: Cranmer,
S.R., et al. 1999, ApJ, 511, 481
Title: Empirical densities, kinetic temperatures, and outflow
velocities in the equatorial streamer belt at solar minimum
Authors: Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker,
D. A.; Kohl, J. L.
Bibcode: 2002AAS...200.5715S
Altcode: 2002BAAS...34..739S
We use combined Ultraviolet Coronagraph Spectrometer (UVCS) and Large
Angle Spectroscopic Coronagraph (LASCO) data to determine the O(5+)
outflow velocities as a function of height along the axis of an
equatorial streamer at solar minimum and as a function of latitude
(at 2.3 solar radii from sun center). The results show that outflow
increases rather abruptly in the region between 3.6 and 4.1 solar radii
near the streamer cusp, and gradually increases to 90 km/s at about
5 solar radii in the streamer stalk beyond the cusp. The latitudinal
variation at 2.3 solar radii shows that there is no outflow (within
the measurement uncertainties) in the center of the streamer called
the core, and that a steep increase in outflow occurs just beyond the
streamer legs, where the O VI 1032 intensity relative to H I 1216 (Ly
alpha) is higer than in the core. Velocity variations in both height
and latitude show that the transitions from no measurable outflow to
positive outflow are relatively sharp and thus can be used to infer the
location of the transition from closed to open field lines in streamer
magnetic field topologies. Such information, including the densities
and kinetic temperatures derived from the observations, provides
hard constraints for realistic theoretical models of streamers and
the source regions of the slow solar wind. This work is supported by
NASA Grant NAG5-11420 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency, and by the ESA PRODEX program (Swiss
contribution). do not accept author defined LaTeX macros.
Title: Empirically Determined Anisotropic Velocity Distributions
and Outflows of O5+\ ions in a Coronal Streamer at
Solar Minimum
Authors: Frazin, R. A.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2002AGUSMSH21B..06F
Altcode:
Empirical constraints on the O5+\ velocity distributions
and outflow speeds in a solar minimum equatorial streamer between 2.6
and 5.1 Rsun\ are determined using a spectral synthesis
code that includes O VI Doppler dimming. These constraints follow
directly from UV spectra taken on 12 October 1996 with the Ultraviolet
Coronagraph Spectrometer (UVCS) on the SOHO satellite and 3D electron
densities derived from tomography applied to a time series of polarized
white-light images taken with the Large Angle Spectrometric Coronagraph
Experiment (LASCO) on SOHO. Four conclusions result from this work:
1) Our analysis shows O5+\ anisotropy in the streamer legs
and stalk. The microscopic velocity distribution (which excludes wave
motions that equally affect all charged particles) is also found to
be anisotropic, where the most probable speed perpendicular to the
magnetic field direction exceeds that in the parallel direction. 2)
There is no evidence of such anisotropy in the streamer core. 3)
There is preferential heating of the O5+ions over the
protons in the streamer stalk and legs, but not in the core. 4) The
outflow velocity of the O5+\ ions is determined at heights
above 4.6 Rsun. This work is supported by NASA under grant
NAG5-10093 to the Smithsonian Astrophysical Observatory.
Title: The Helium Focusing Cone of the Local Interstellar Medium
Close to the Sun
Authors: Michels, J. G.; Raymond, J. C.; Bertaux, J. L.; Quémerais,
E.; Lallement, R.; Ko, Y. -K.; Spadaro, D.; Gardner, L. D.; Giordano,
S.; O'Neal, R.; Fineschi, S.; Kohl, J. L.; Benna, C.; Ciaravella,
A.; Romoli, M.; Judge, D.
Bibcode: 2002ApJ...568..385M
Altcode:
The Solar and Heliospheric Observatory (SOHO) Ultraviolet Coronagraph
Spectrometer is used to observe the interplanetary He focusing cone
within 1 AU. Taken over 2 yr and from differing orbit positions, the
series of observations includes measurements of He I 584 Å and Lyβ
intensities. The cone itself is spatially well defined, and the He I
intensity within the cone was ~45 R in 1996 December, compared with
~1 R for lines of sight outward from 1 AU. Between 1996 December and
1998 June, the focusing cone dimmed by a factor of 3.3 as the level of
solar activity rose. This is the first time that interstellar helium
is observed so near the Sun. Measured intensities are compared to a
detailed temperature and density model of interstellar helium in the
solar system. The model includes EUV ionization but does not include
ionization by electron impact from solar wind electrons. There are
several features in the data model comparison that we attribute to
the absence of electron impact ionization in the model. The absolute
maximum intensity of 45 R first measured in 1996 December calls for
an ionization 45% more intense than the EUV photoionization alone as
measured by the Solar EUV Monitor/Charge, Element, and Isotope Analysis
System (SEM/CELIAS) on SOHO. Important day-to-day variations of the
intensity are observed, as well as a general decrease as the solar
activity rises (both absolute and divided by a model with a constant
ionization). This general decrease is even larger than predicted by a
model run with the SEM/CELIAS photoionization rate alone, in spite of a
factor of 1.5 increase of this rate from 1996 December to 1998 June. At
this time, an additional ionization rate of 0.56×10-7
s-1 (compared with 1.00×10-7 s-1 from
solar EUV) is required to fit the measured low intensity. We attribute
this additional rate to solar wind electron impact ionization of the
atoms. This shows that the helium intensity pattern is a very sensitive
indicator of the electron density and temperature near the Sun.
Title: Far-Ultraviolet Observations of Comet 2P/Encke at Perihelion
Authors: Raymond, J. C.; Uzzo, M.; Ko, Y. -K.; Mancuso, S.; Wu, R.;
Gardner, L.; Kohl, J. L.; Marsden, B.; Smith, P. L.
Bibcode: 2002ApJ...564.1054R
Altcode:
Comet 2P/Encke was observed with UVCS/SOHO near perihelion (2000
September 9 and 11) in the Lyman lines of hydrogen. We present a Lyα
image reconstructed from a series of long-slit spectra, along with
the intensity ratios of Lyα, Lyβ, and Lyγ. The narrow Lyα profile
indicates that the observed photons are scattered from hydrogen atoms
produced by dissociation of H2O and OH, though a broader
profile far from the coma suggests a contribution from hydrogen atoms
produced by charge transfer with solar wind protons. The outgassing rate
derived from the Lyα intensity distribution is in excellent agreement
with Sekanina's model of two active vents. We also present upper limits
for the outgassing rates of the noble gases helium, neon, and argon.
Title: White Light Intercalibrations of UVCS, LASCO-C2 and Spartan
201/WLC
Authors: Frazin, R. A.; Romoli, M.; Kohl, J. L.; Gardner, L. D.;
Wang, D.; Howard, R. A.; Kucera, T. A.
Bibcode: 2002ISSIR...2..249F
Altcode: 2002ESASR...2..249F; 2002rcs..conf..249F
This paper describes comparisons among white light polarized radiances
(pB) as measured by the Ultraviolet Coronagraph Spectrometer White
Light Channel (UVCS/WLC), the Large Angle and Spectrometric Coronagraph
Experiment C2 instrument (LASCOC2) and the Spartan 201 White Light
Coronagraph (Spartan 201/WLC). UVCS/WLC and LASCO-C2 are generally in
agreement, although there are some systematic trends and discrepancies
that still require explanation. UVCS/WLC and Spartan 201/WLC agree
to within the measurement uncertainties. Spartan 201/WLC and LASCO-C2
are not directly compared to each other in this paper.
Title: Empirical outflow velocities in an equatorial coronal streamer
Authors: Strachan, L.; Suleiman, R.; Panasyuk, A.; Biesecker, D.;
Kohl, J.
Bibcode: 2002cosp...34E1120S
Altcode: 2002cosp.meetE1120S
We use combined Ultraviolet Coronagraph Spectrometer (UVCS) and Large
Angle Spectroscopic Coronagraph (LASCO) data to determine the O5+
outflow velocities as a function of height along the axis of an
equatorial streamer at solar minimum and as a function of latitude
(at 2.3 solar radii from sun center). The results show that outflow
increases rather abruptly in the region between 3.6 and 4.1 solar radii
near the streamer cusp, and gradually increases to 90 km/s at about
5 solar radii in the streamer stalk beyond the cusp. The latitudinal
variation at 2.3 solar radii shows that there is no outflow (within
the measurement uncertainties) in the center of the streamer called
the core, and that a steep increase in outflow occurs just beyond
the streamer legs, where the O VI 1032 intensity relative to H I 1216
(Ly) is higher than in the core. Velocity variations in both height
and latitude show that the transitions from no measurable outflow to
positive outflow are relatively sharp and thus can be used to infer the
location of the transition from closed to open field lines in streamer
magnetic field topologies. Such information, including the densities
and kinetic temperatures derived from the observations, provides hard
constraints for realistic theoretical models of streamers and the source
regions of the slow solar wind. This work is supported by NASA Grant
NAG5-11420 to the Smithsonian Astrophysical Observatory, by the Italian
Space Agency, and by the ESA PRODEX program (Swiss contribution).
Title: UVCS/SOHO observations of a CME-driven shock: Consequences
on ion heating mechanisms behind a coronal shock
Authors: Mancuso, S.; Raymond, J. C.; Kohl, J.; Ko, Y. -K.; Uzzo,
M.; Wu, R.
Bibcode: 2002A&A...383..267M
Altcode:
We report the observation of a 1100 km s-1 CME-driven
shock with the UltraViolet Coronagraph Spectrometer (UVCS) telescope
operating on board SOHO on March 3, 2000. The shock speed was derived
from the type II radio burst drift rate and from UVCS observations
that can yield the density profile just before the passage of the
shock. A CME projected speed of 920 km s-1 was deduced
from the Large Angle Spectrometric Coronagraph (LASCO) white light
images, indicating that the CME leading edge was lagging behind at
about 20% of the shock speed. The spectral profiles of both the O VI
and Lyalpha lines were Doppler dimmed and broadened at the passage
of the shock by the emission from shocked material along the line of
sight. The observed line broadening for both protons and oxygen ions
was modeled by adopting a mechanism in which the heating is due to the
nondeflection of the ions at the shock ramp in a quasi-perpendicular
shock wave. This specific ion heating model was able to reproduce the
observed spectroscopic properties of the shocked plasma.
Title: Low-latitude Coronal Holes during Solar Maximum
Authors: Miralles, M.; Cranmer, S.; Kohl, J.
Bibcode: 2002cosp...34E1125M
Altcode: 2002cosp.meetE1125M
Analyses of in situ observations have shown that some small coronal
holes are sources of slow solar wind near solar maximum when
polar coronal holes become smaller and disappear. However, not all
coronal holes at solar maximum produce slow wind. The Ultraviolet
Coronagraph Spectrometer (UVCS) aboard SOHO has been used to observe
large low-latitude coronal holes during solar maximum that produced
fast solar wind. UVCS observations show that large equatorial holes
at solar maximum have plasma properties that seem to bridge the gap
between solar minimum polar coronal holes and streamers. The ion kinetic
temperatures in equatorial holes are about 2 times larger than those in
a solar minimum equatorial streamer, and about a factor of 2 smaller
than those in polar coronal holes above 2 R . The outflow speeds for
the large equatorial holes observed by UVCS are only about 100 km s-1
, a factor of 4 smaller than those in polar holes, at 3 R . However,
in situ data corresponding to these equatorial coronal holes showed
asymptotic wind speeds of 600-700 km s-1 . These wind speeds are similar
to those observed over polar coronal holes at solar minimum. In contrast
to the polar coronal holes, the bulk of the solar wind acceleration
in large equatorial coronal holes at solar maximum must occur above
3 R . Thus, the combination of spectroscopic measurements in the
extended corona, where the primary solar wind acceleration occurs, and
in situ measurements made in the solar wind can be used to obtain the
solar wind acceleration as a function of heliocentric distance. These
observations provide detailed empirical constraints for theoretical
models and may be key to understanding how the various types of solar
wind plasma are heated and accelerated. This work is supported by NASA
under Grant NAG5-11420 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: In-flight Calibration of the UVCS White Light Channel
Authors: Romoli, M.; Frazin, R. A.; Kohl, J. L.; Gardner, L. D.;
Cranmer, S. R.; Reardon, K.; Fineschi, S.
Bibcode: 2002ISSIR...2..181R
Altcode: 2002ESASR...2..181R; 2002rcs..conf..181R
The UVCS White Light Channel (WLC) is designed to measure the linearly
polarized radiance (pB) of the corona, in the wavelength band from 450
nm to 600 nm, in order to derive one of the fundamental parameters of
the solar corona: the electron density. This paper gives a thorough
description of the in-flight radiometric calibration of the WLC, which
uses the star α Leo and the planet Jupiter as transfer standards
and is based on calibrations of ground-based instruments. The
method for computing the polarized radiance from the measurements
is also described, together with the stray light and polarization
characterizations obtained from dedicated, in-flight measurements.
Title: UV Radiometric Calibration of UVCS
Authors: Gardner, L. D.; Smith, P. L.; Kohl, J. L.; Atkins, N.;
Ciaravella, A.; Miralles, M. P.; Panasyuk, A.; Raymond, J. C.;
Strachan, L., Jr.; Suleiman, R. M.; Romoli, M.; Fineschi, S.
Bibcode: 2002ISSIR...2..161G
Altcode: 2002ESASR...2..161G; 2002rcs..conf..161G
The Ultraviolet Coronagraph Spectrometer (UVCS) was characterized
and radiometrically calibrated in the laboratory as a system at the
Harvard-Smithsonian Center for Astrophysics in June of 1995. Component
level calibrations of optical components and detectors were also
performed. After launch, an in-flight calibration activity was carried
out that extended the laboratory calibration, compared UVCS measurements
of stars to those of other instruments and monitored the radiometric
stability of UVCS through repeated measurements of stars that are
believed to have nearly constant ultraviolet irradiance. In-flight
measurements have, in general, confirmed the laboratory radiometric
calibration. Comparisons to Spartan 201 observations of the same coronal
structures agree within 10 %. The system responsivity, although it has
changed somewhat during the six years of operation, is well behaved
and characterizable. This paper describes the UVCS calibration and
its results.
Title: UVCS/SOHO Observations of Coronal Holes from Solar Minimum
to Solar Maximum
Authors: Miralles, M. P.; Cranmer, S. R.; Esser, R.; Kohl, J. L.
Bibcode: 2001AGUFMSH32A0721M
Altcode:
Coronal holes are open field, low-density source regions of the solar
wind. At solar minimum, large coronal holes are present at the poles
and are the dominant source of the solar wind flow for this part of
the solar cycle. At solar maximum, coronal holes of varying sizes and
shapes appear at all latitudes and last for several rotations. During
this stage of the cycle, the dominant component is mainly slow wind,
but fast wind streams are generated by large coronal holes. UVCS/SOHO
has been used to measure the plasma properties in several types
of coronal holes from 1996 to 2001. Spectroscopic diagnostics of
O5+ velocity distributions and outflow velocities are
derived from measurements of intensities and line widths for O~VI
103.2 and 103.7 nm as a function of height. We compare the plasma
properties of coronal holes from solar minimum to solar maximum and
discuss the evolution of coronal holes during the solar cycle. We
also study the compatibility between the growing database of coronal
hole plasma properties and theoretical models of extended coronal
heating via ion cyclotron resonance. This work is supported by NASA
under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: Modelling of a CME-driven Shock Detected by UVCS/SoHO on
March 3, 2000
Authors: Mancuso, S.; Raymond, J. C.; Kohl, J. L.; Ko, Y.; Uzzo, M.;
Wu, R.
Bibcode: 2001AGUFMSH21B..05M
Altcode:
We report the observation of a 1100 km/s CME-driven shock with the
UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on
board SoHO on March 3, 2000. The CME was observed by the Large Angle
Spectroscopic Coronagraph (LASCO), and the radio signature of the
shock was detected by the Hiraiso and Culgoora radio spectrographs as
an intense type II radio burst. We derived the density profile just
before the passage of the shock from UVCS observations and obtained
a reliable estimate of the shock speed from the type II radio burst
drift rate. The spectral profiles of both the O VI and Lyman alpha
lines were Doppler dimmed at the passage of the shock and showed broad
wings caused by the emission from shocked material along the line
of sight. By estimating a compression ratio of 1.8 from the observed
splitting of the radio emission bands in the spectrographs and assuming
perpendicular propagation of the shock we derive a magnetic field
strength of 1 Gauss at 1.8 solar radii and an Alfvenic Mach number of
1.7. The observed line broadening for both the protons and the Oxygen
ions was modeled by adopting a mechanism in which the heating is due
to the nondeflection of the ions at the shock ramp.
Title: The Advanced Spectroscopic and Coronagraphic Explorer Mission
Authors: Kohl, J. L.; Howard, R.; Davila, J.; Noci, G.; Esser, R.;
Ciaravella, A.; Cranmer, S.; Fineschi, S.; Gardner, L.; Raymond, J.;
Romoli, M.; Smith, P.; Socker, D.; Strachan, L.; Van Ballegooijen, A.
Bibcode: 2001AGUFMSH31B0711K
Altcode:
SOHO has provided profound insights into the physics of solar wind
acceleration and coronal mass ejections. Although significant
progress has been made, most of the dominant physical processes
controlling these phenomena are still not identified. The Advanced
Spectroscopic and Coronagraphic Explorer Mission provides next
generation spectroscopic and polarimetric instrumentation aimed at
identifying these processes. The launch is planned for March 2007 with
mission operations and data analysis continuing for 5 years. The data
will be unrestricted and available to the community. The envisioned
program includes a Guest Investigator Program with an average of 15
grants to be awarded in response to proposals submitted during the
first year of the mission. Information about the proposed scientific
goals and instrumentation will be presented.
Title: Polarized Intensity Measurements of the Corona during the 21
June 2001 Total Solar Eclipse
Authors: Habbal, S. R.; Arnaud, J.; Johnson, J.; Hegwer, S.; Ene, A.;
Hale, J.; Esser, R.; Arndt, M.; Kohl, J. L.; Daw, A.; Faurobert, M.;
Woo, R.; Habbal, F.; Havasy, R.; Alford, J. N.
Bibcode: 2001AGUFMSH11C0716H
Altcode:
We report on the first successful simultaneous polarimetric measurements
of the brightness of the Thompson-scattered white light and intensity
of the near-infrared Fe XIII 10747 Å line, the strongest of the
coronal iron forbidden lines. These observations which extended out
to 3 Rs in the corona were obtained during the total solar
eclipse of 21 June 2001. The novel technique used to acquire these
measurements will be presented. Polarized intensity measurements of the
resonantly scattered component of coronal emission lines are the only
tools to date that can yield the direction of the coronal magnetic
field. Through these simultaneous measurements, we show how the
direction of the coronal magnetic field can be placed in the context
of coronal density structures. We also discuss the implications of
these simultaneous measurements for the source of the solar wind.
Title: SOHO Ultraviolet Coronagraph Spectrometer (UVCS) Mission
Operations and Data Analysis
Authors: Kohl, John L.
Bibcode: 2001STIN...0212280K
Altcode:
The scientific goal of Ultraviolet Coronagraph Spectrometer (UVCS)
is to obtain detailed empirical descriptions of the extended
solar corona as it evolves through the solar activity cycle and
to use those descriptions to identify and understand the physical
processes responsible for coronal heating, solar wind acceleration,
coronal mass ejections (CMEs), and the phenomena that establish the
plasma properties of the solar wind as measured by 'in situ' solar
wind instruments. The UVCS on the Solar and Heliospheric Observatory
(SOHO) has made major advances in identifying the physical processes
responsible for solar wind acceleration, and it has made the first
high resolution ultraviolet spectroscopic measurements of CMEs. The
UVCS has resulted in over 220 scientific publications.
Title: Ultraviolet Coronagraph Spectrometer Observations of a
High-Latitude Coronal Hole with High Oxygen Temperatures and the
Next Solar Cycle Polarity
Authors: Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2001ApJ...560L.193M
Altcode:
We announce the resurgence of extreme ion properties in a large,
high-latitude coronal hole observed above the north heliographic pole
in 2001 February at solar maximum. The observations were taken with
the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric
Observatory. These observations are part of an ongoing campaign to
determine the plasma properties of coronal holes during the current
solar cycle. In this Letter, we compare the observations and analysis
of O VI λλ1032, 1037 spectral lines of a high-latitude coronal hole
in 2001 with observations of an equatorial solar maximum hole in 1999
and polar coronal holes observed near solar minimum (1996-1997). These
lines provide spectroscopic diagnostics of O+5 velocity
distributions and outflow velocities. The O VI line profiles show
a narrow core and broad wings. The narrow core is attributed to
foreground and background streamers and, possibly, dense polar plumes
at the lowest observed heights. The broad wings are attributed to the
coronal hole. The comparison of the coronal hole line widths shows
that the O+5 perpendicular kinetic temperatures in the 2001
high-latitude hole are similar to those observed in polar coronal holes
at solar minimum. These observations of extremely high ion kinetic
temperatures (exceeding 108 K) at the north pole in 2001
occurred nearly simultaneously with the polarity change of the Sun's
magnetic field, as seen in recent magnetogram data. This coronal hole
in 2001 may represent the first manifestation of the negative polarity
polar coronal holes that will dominate the Sun's open magnetic flux
tubes at the next solar minimum. The reappearance of broad O VI
profiles at a time when not all of the ``new polarity'' magnetic
flux has migrated to the poles was an interesting development. The
variations in coronal hole parameters with the solar cycle provide
constraints on models of extended coronal heating.
Title: Solar Cycle 23: Variation of the Solar Corona in the
Ultraviolet from Solar Minimum to Solar Maximum
Authors: Miralles, M. P.; Panasyuk, A. V.; Strachan, L.; Gardner,
L. D.; Suleiman, R.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2001iscs.symp...59M
Altcode:
UVCS/SOHO measurements of H I Ly-alpha and O VI (103.2 nm and 103.7 nm)
intensities in the solar corona have been made from solar Cycle 23's
minimum in 1996 to its current maximum. At solar minimum, the corona
consisted of large coronal holes at the poles and quiescent streamers at
the equator. During the approach to solar maximum, equatorial coronal
holes and high latitude streamers became more conspicuous. Recently,
coronal holes at higher latitudes have reappeared, allowing a comparison
to be made of O VI intensities and line widths of coronal holes at
different latitudes. We also characterize the variation of coronal
hole properties with height, and location over the solar cycle. This
work is supported by NASA under Grant NAG5-10093 to the Smithsonian
Astrophysical Observatory, by the Italian Space Agency and by PRODEX
(Swiss contribution)
Title: Observations of a High-latitude Coronal Hole at Solar Maximum
Authors: Miralles, M.; Cranmer, S. R.; Kohl, J. L.
Bibcode: 2001AGUSM..SH21B07M
Altcode:
A large coronal hole at a latitude of about 60 degrees was observed
above the north pole with the Ultraviolet Coronagraph Spectrometer
(UVCS) aboard SOHO during 10--19 February 2001. These observations
are part of an ongoing campaign to characterize equatorial and
mid-latitude coronal holes during the active phase of the current
solar cycle. Observations in H~I Lyα and O~VI 103.2 and 103.7 nm
provided spectroscopic diagnostics of proton and O5+
velocity distributions. The O~VI line profiles show a narrow core
and broad wings. The narrow core is attributed to the foreground and
background streamers. The broad wings are attributed to the coronal
hole. We compare the observed line intensities and widths of this
high-latitude hole with those of other solar maximum (lower latitude)
holes and solar minimum polar coronal holes. The comparison of the
line widths shows that the O~VI line widths of this solar maximum
hole are similar to those observed in polar coronal holes at solar
minimum. The observation of extremely high ion kinetic temperatures at
the north pole occurs simultaneously with the polarity change of the
Sun's magnetic field, as seen in recent magnetogram data. This coronal
hole may represent the first manifestation of the stable polar coronal
holes that will dominate the Sun's open magnetic flux tubes at the next
solar minimum. The re-appearance of broad O~VI profiles at a time when
not all of the ``new polarity'' magnetic flux has migrated to the poles
is an interesting development that may provide a crucial constraint
on models of extended coronal heating. This work is supported by NASA
under Grant NAG5-10093 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: Observed Variations of O5+ Velocity Distributions
with Electron Density
Authors: Kohl, J. L.; Cranmer, S. R.; Frazin, R. A.; Miralles, M.;
Strachan, L.
Bibcode: 2001AGUSM..SH21B08K
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite
has been used to measure the line profiles of O~VI 103.2 and 103.7
nm versus heliographic height in a variety of coronal holes and
streamers during the period from 1996 to 2001. Those observations
have been used to derive velocity distributions in the line-of-sight
direction, which is typically perpendicular to the apparent magnetic
field direction. In the case of polar coronal holes at solar minimum,
the electron density is the smallest observed and the most-probable
speed is the largest observed reaching values as high as 500 km/s at the
largest heights. The O5+ most-probable speed is much larger
than the hydrogen speed in those structures. The ratio of O5+
to hydrogen most-probable speeds increases with height. In contrast,
the O5+ values are much smaller than those of hydrogen at
the base of high-latitude streamers and never reach the hydrogen values
at any observed height. The electron density in those structures is
much greater than in the solar minimum coronal holes. Other structures
have intermediate values of the electron density and O5+
most-probable speeds. In general, the O5+ most-probable speed
and its ratio to the hydrogen value seem to decrease with increasing
density. This apparent observational correlation may be related to
thermalization from higher collision rates or it might be related to the
physical process that causes the extreme O5+ perpendicular
heating. This work is supported by NASA under Grant NAG5-10093 to the
Smithsonian Astrophysical Observatory, by the Italian Space Agency,
and by PRODEX (Swiss Contribution).
Title: Where in the Streamer Belt does the Slow Speed Wind Originate?
Authors: Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker,
D. A.; Kohl, J. L.
Bibcode: 2001AGUSM..SH41B07S
Altcode:
The Ulysses high latitude mission showed that the slow speed wind at
solar minimum appears to come from equatorial regions in the heliosphere
that are dominated by helmet streamers. However, there are few coronal
measurements of the detailed latitudinal variation of the outflow
velocity across a streamer. Such measurements are needed to identify the
region of the streamer that gives rise to the slow speed wind. For this
study we use UVCS and LASCO observations of a solar minimum streamer to
make a detailed model of the outflow velocities for O+5 as
a function of position angle from the streamer axis. This new work goes
beyond using the OVI line ratios to define the boundaries between fast
and slow wind. We constrain the coronal plasma parameters (velocities,
temperature anisotropies, densities, etc.) using OVI and Ly-alpha line
profiles, and white light polarized brightness data. We will discuss
various possibilities for the latitudinal profile for the coronal
outflow in the streamer belt. This work is supported by NASA Grant
NAG5-7822 to the Smithsonian Astrophysical Observatory, by the Italian
Space Agency, and by the ESA PRODEX program (Swiss contribution).
Title: Coordinated UVCS/LASCO/EIT Observations of a High Latitude CME
Authors: Karovska, M.; Esser, R.; Dobrzycka, D.; Kohl, J.
Bibcode: 2001AGUSM..SH22A10K
Altcode:
We present here the results of our coordinated UVCS/LASCO/EIT
observations of a CME on 2000 March 5. The northern polar region of
the Sun at a position angle 270 degrees was monitored with UVCS at 2
solar radii for about 8 hours. During that time interval a spectacular
CME developed in the northern hemisphere. This event was also detected
and monitored with LASCO C2 and C3 and the EIT for several hours. We
compare the edge-enhanced LASCO and EIT images of this event with the
increased intensities of the H I Lyman-alpha spectral line and the line
pair O VI 1031.91 A and 1037.61 A seen in the UVCS observations. LASCO
and EIT images are essential in providing the larger scale context for
this event and for correlating the small-scale sub-structure observed
in white light with the the plasma morphology as observed with the UVCS.
Title: Plasma Conditions in Polar Plumes and Interplume Regions in
Polar Coronal Holes
Authors: Cranmer, S. R.; Kohl, J. L.; Miralles, M.; Panasyuk, A. V.
Bibcode: 2001AGUSM..SH41B08C
Altcode:
During times of low solar activity, large polar coronal holes are
observed to contain bright raylike polar plumes that appear to follow
open magnetic field lines. Plumes are believed to be flux tubes that
are heated impulsively at their base, which leads to a higher density,
a lower outflow speed, and a lower overall temperature in the extended
corona, compared to the surrounding interplume regions. Despite years
of white light and spectroscopic observations, though, the differences
in mass, momentum, and energy flux in plumes and between plumes are not
known precisely. This poster presents an updated survey of data from the
Ultraviolet Coronagraph Spectrometer (UVCS), aboard SOHO, that attempts
to sort out the local plume and interplume conditions. These results
will be compared with previous analyses that characterized the ``mean''
plume/interplume coronal hole, averaged over many lines of sight through
varying concentrations of plumes. Limits on the relative contributions
of plumes and interplume regions to the high-speed solar wind will be
determined, with emphasis on the proton outflow speed in the corona
and at 1 AU. Implications for theoretical models of coronal heating and
solar wind acceleration will be discussed. This work is supported by the
National Aeronautics and Space Administration under grant NAG5-10093 to
the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana,
and by the Swiss contribution to the ESA PRODEX program.
Title: Comparison of Empirical Models for Polar and Equatorial
Coronal Holes
Authors: Miralles, M. P.; Cranmer, S. R.; Panasyuk, A. V.; Romoli,
M.; Kohl, J. L.
Bibcode: 2001ApJ...549L.257M
Altcode:
We present a self-consistent empirical model for several plasma
parameters of a large equatorial coronal hole observed on 1999 November
12 near solar maximum. The model was derived from observations with
the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric
Observatory. In this Letter, we compare the observations of O VI
λλ1032, 1037 emission lines with previous observations of a polar
coronal hole observed near solar minimum. At the time of the 1999
observations, there was no evidence of large polar coronal holes. The
resulting empirical model for the equatorial coronal hole describes
the outflow velocities and most probable speeds for O5+, and
we compared the derived ion properties with the empirical model for a
solar minimum polar coronal hole. The comparison of the empirical models
shows that the 1999 equatorial hole has lower O5+ outflow
speeds and perpendicular temperatures than its polar counterpart from
1996 to 1997 at heights between 2 and 3 Rsolar. However,
in situ asymptotic speeds of the wind streams coming from the
1996-1997 polar hole and from the 1999 equatorial hole are only ~15%
different. Thus, the bulk of the solar wind acceleration must occur
above 3 Rsolar for the equatorial coronal hole. The
equatorial hole also has a higher density than the polar hole at
similar heights. It is not yet known whether the higher densities
are responsible for the seeming inhibition of the fast ion outflow
speeds and extremely large perpendicular temperatures that occur in
polar coronal holes at solar minimum. We discuss the constraints
and implications on various theoretical models of coronal heating
and acceleration.
Title: Efficiency variations of UVCS/SOHO based on laboratory
measurements of replica gratings
Authors: Gardner, Larry D.; Atkins, Nigel; Fineschi, Silvano; Smith,
Peter L.; Kohl, John L.; Maccari, L.; Romoli, Marco
Bibcode: 2000SPIE.4139..362G
Altcode:
We have carried out measurements of efficiency as functions of position
across the surfaces of replica grating made from the same masters
as the UVCS/SOHO flight units. Variations in first order efficiency
which significantly affect the interpretation of UVCS data are found
along the direction perpendicular to the grooves. Variations are also
found along the direction parallel to the grooves, but these do not
seriously affect UVCS data interpretation. The measurements and their
application to the radiometric calibration of UVCS/SOHO are discussed.
Title: Corongraphic Observations and Analyses of The Ultraviolet
Solar Corona
Authors: Kohl, John L.
Bibcode: 2000STIN...0014831K
Altcode:
The activities supported under NASA Grant NAG5-613 included
the following: 1) reduction and scientific analysis of data from
three sounding rocket flights of the Rocket Ultraviolet Coronagraph
Spectrometer, 2) development of ultraviolet spectroscopic diagnostic
techniques to provide a detailed empirical description of the extended
solar corona, 3) extensive upgrade of the rocket instrument to
become the Ultraviolet Coronal Spectrometer (UVCS) for Spartan 201,4)
instrument scientific calibration and characterization, 5) observation
planning and mission support for a series of five Spartan 201 missions
(fully successful except for STS 87 where the Spartan spacecraft was
not successfully deployed and the instruments were not activated),
and 6) reduction and scientific analysis of the UVCS/Spartan 201
observational data. The Ultraviolet Coronal Spectrometer for Spartan
201 was one unit of a joint payload and the other unit was a White
Light Coronagraph (WLC) provided by the High Altitude Observatory
and the Goddard Space Flight Center. The two instruments were used
in concert to determine plasma parameters describing structures in
the extended solar corona. They provided data that could be used
individually or jointly in scientific analyses. The WLC provided
electron column densities in high spatial resolution and high time
resolution. UVCS/Spartan provided hydrogen velocity distributions, and
line of sight hydrogen velocities. The hydrogen intensities from UVCS
together with the electron densities from WLC were used to determine
hydrogen outflow velocities. The UVCS also provided O VI intensities
which were used to develop diagnostics for velocity distributions and
outflow velocities of minor ions.
Title: UVCS/SOHO Observations of Equatorial and Polar Coronal Holes
Authors: Kohl, J. L.; Miralles, M. P.; Cranmer, S. R.; Suleiman, R. M.
Bibcode: 2000SPD....31.0232K
Altcode: 2000BAAS...32..816K
A large equatorial coronal hole was observed above the west limb with
the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO from November
1999 to March 2000. Observations in H I Lyα and O VI 103.2, 103.7
nm provided spectroscopic diagnostics of proton and O5+
velocity distributions and outflow velocities. These properties will be
compared to those of the large polar coronal holes observed near solar
minimum. The equatorial coronal hole corresponded to a high-speed
solar wind stream at 1 AU, but there were significant differences
between the interplanetary properties of this stream and the steady
high-speed wind seen over the poles at solar minimum. The several
obvious differences between the two structures in the extended corona
may be associated with the different densities and magnetic field
configurations and flux tube expansion factors. Preliminary results
from a detailed empirical model of the equatorial coronal hole will
be presented. This work is supported by NASA under Grant NAG5-7822 to
the Smithsonian Astrophysical Observatory, by the Italian Space Agency
and by PRODEX (Swiss contribution).
Title: Solar Cycle Variations of O VI and H I Lyman Alpha Intensities
in the Solar Corona
Authors: Miralles, M. P.; Panasyuk, A. V.; Strachan, L.; Gardner,
L. D.; Suleiman, R. M.; Smith, P. L.; Kohl, J. L.
Bibcode: 2000SPD....31.0229M
Altcode: 2000BAAS...32..815M
UVCS/SOHO measurements of O VI (103.2 and 103.7 nm) and H I Lyman alpha
intensities in the solar corona have been made from 1996 to the present
spanning the rising phase of cycle 23. During solar minimum the corona
consisted of large coronal holes at the poles and quiescent streamers
at the equator. During the ascending phase of the cycle, the corona
presented high latitude streamers and finally polar streamers as the
Sun approached solar maximum. Recent observations of the solar corona
show the presence of coronal holes at the equator and streamers at
the poles. Our observations provide descriptions of these structures
over the rising phase of the solar cycle. We compare the properties
of quiescent equatorial streamers which occurred at solar minimum to
high latitude and polar streamers observed toward solar maximum. We
also compare solar minimum polar coronal holes to equatorial coronal
holes present at solar maximum. We discuss how these results are
related to the plasma properties. This work is supported by NASA
under Grant NAG5-7822 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by PRODEX (Swiss contribution).
Title: Comparison of UVCS and EISCAT observations of a mid- and
high-latitude streamer during the Third Whole Sun Month Campaign
Authors: Strachan, L.; Panasyuk, A. V.; Kohl, J. L.; Breen, A.
Bibcode: 2000SPD....31.0237S
Altcode: 2000BAAS...32..817S
We compare the plasma properties of two different streamer regions in
the extended corona (1.5 to 6 solar radii) with solar wind velocity
measurements made at larger distances during the Third Whole Sun Month
Campaign. Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) measurements
were made of H Ly-alpha intensities and profiles and O VI 1032/1037
intensities in order to put constraints on the plasma conditions in
these regions. The UVCS/SOHO measurements were centered at position
angles 70 deg (CCW from NHP) during 12-21 Sept. 1999 and 190 deg during
22-25 Sept. 1999. Streamer kinetic temperatures and outflow velocities
are compared with measurements of outflow velocities determined by
EISCAT interplanetary scintillation observations at the same position
angles. The EISCAT measurements showed slow flow above the streamers
at 25 to 80 solar radii, with steep gradients on the boundaries as
flow speeds increased above the inter-streamer regions. Comparisons
of EISCAT measurements from 25-35 solar radii and UVCS/SOHO coronal
measurements should cast light on the acceleration of the slow solar
wind. This work is supported by NASA under Grant NAG5-7822 to the
Smithsonian Astrophysical Observatory, by the Italian Space Agency
and by PRODEX (Swiss contribution).
Title: UVCS Observations of a High Latitude Streamer From 2-11
November 1999
Authors: Strachan, L.; Miralles, M. P.; Frazin, R.; Kohl, J. L.
Bibcode: 2000AGUSM..SH42A04S
Altcode:
A high latitude coronal streamer was observed with the Ultraviolet
Coronagraph Spectrometer UVCS on SOHO for ten days during the period 2 -
11 November 1999. The streamer was formed above a filament channel on
the disk and, at the start of the observations, was located on the east
limb at a position angle of about 150 deg. During the following ten
days the streamer moved across the face of the Sun andand presented
different aspect angles to the observed line of sight. We compare
UVCS measurements of intensities and line widths of H Ly-alpha and
O VI profiles obtained from 1.5 to 3.0 solar radii with equatorial
streamer observations made near solar minimum. This work demonstrates
that geometry effects are important when interpreting spectroscopic
observations of coronal structures. In the future these observations
will be used to model ion velocity distributions and outflow velocities
in these high latitude streamer structures. This work is supported in
part by NASA under grant NAG5-7822 to the Smithsonian Astrophysical
Observatory, by the Italian Space Agency, and by Swiss funding agencies.
Title: New Diagnostics of Coronal Heating and Solar Wind Acceleration
Processes Achievable With The Advanced Solar Coronal Explorer (ASCE)
Authors: Cranmer, S. R.; Kohl, J. L.; Gardner, L. D.; Raymond, J. C.;
Strachan, L.; Smith, P. L.; Howard, R. A.; Davila, J. M.; Fisher,
R. R.; Noci, G.; Tondello, G.; Socker, D. G.; Moses, D.
Bibcode: 2000SPD....31.0297C
Altcode: 2000BAAS...32..828C
The Advanced Solar Coronal Explorer (ASCE) is a proposed NASA
Medium-class Explorer (MIDEX) mission that underwent a detailed
Concept Study in 1999. The science payload includes large aperture EUV
and visible light coronagraphs. ASCE's unprecedented spectral range,
spatial resolution, and sensitivity (30 to 100 times the EUV sensitivity
of UVCS/SOHO) provide measurements needed to investigate the role of
high-frequency and low-frequency waves in heating and accelerating
the fast and slow speed solar wind. This presentation will outline
the advanced capabilities of ASCE for obtaining detailed empirical
descriptions of solar wind acceleration regions, specifying coronal
temperatures, flow speeds, densities, and elemental abundances. Velocity
distributions for electrons and more than 10 to 20 ion species with
mass-to-charge ratios from 4 to 1 (including singly ionized helium) can
be measured by ASCE in coronal holes and streamers. This information
is sufficient to derive the wavenumber power spectrum of magnetic
fluctuations that affect the primary electron/proton plasma. The main
goal is to identify the physical processes responsible for heating
and acceleration of the primary particles and minor ions in the fast
and slow speed solar wind.
Title: Surf's Still Up: UVCS/SOHO Observations as Strong Constraints
on Coronal Heating Theories
Authors: Cranmer, S. R.; Kohl, J. L.
Bibcode: 2000SPD....31.1502C
Altcode: 2000BAAS...32..848C
In 1996, the Ultraviolet Coronagraph Spectrometer (UVCS) instrument
aboard SOHO observed surprisingly broad line profiles of the O VI 1032,
1037 doublet in polar coronal holes. These measurements indicated
perpendicular ion temperatures of at least 100--200 million K above
two solar radii in the nascent high-speed solar wind. Since then,
these observations have been supplemented by profiles of other ions,
Doppler dimming measurements made possible by Spartan 201, and a
great deal of theoretical work. This talk outlines the current state of
understanding about coronal heating and solar wind acceleration that has
been facilitated by UVCS. The most promising mechanism for heating and
accelerating minor ions remains the dissipation of high-frequency (10 to
10,000 Hz) ion cyclotron waves, but heating the protons is a more open
question. The physics of the ion cyclotron interaction in the corona has
only begun to be explored, and we will discuss recent insights into the
generation and damping of these waves. A self-consistent theory of wave
damping and turbulent cascade ``replenishment'' would allow the question
of proton heating to be answered more definitively. Also, a kinetic
approach to ion cyclotron heating yields non-bi-Maxwellian ``resonant
shell'' velocity distributions that could produce emission line profiles
narrower than expected from their most probable speeds. Thus, the UVCS
measurements of 100--200 million K ion temperatures may only be lower
limits. This work is supported by the National Aeronautics and Space
Administration under grant NAG5-7822 to the Smithsonian Astrophysical
Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program
(Swiss contribution).
Title: Identification of the Coronal Sources of the Fast Solar Wind
Authors: Giordano, S.; Antonucci, E.; Noci, G.; Romoli, M.; Kohl, J. L.
Bibcode: 2000ApJ...531L..79G
Altcode: 2000astro.ph..1257G
The present spectroscopic study of the ultraviolet coronal emission in a
polar hole, detected on 1996 April 6-9 with the Ultraviolet Coronagraph
Spectrometer aboard the Solar and Heliospheric Observatory spacecraft,
identifies the interplume lanes and background coronal hole regions
as the channels in which the fast solar wind is preferentially
accelerated. In interplume lanes, at heliocentric distance 1.7
Rsolar, the corona expands at a rate between 105 and 150 km
s-1, that is, much faster than in plumes in which the outflow
velocity is between 0 and 65 km s-1. The wind velocity is
inferred from the Doppler dimming of the O VI λλ1032, 1037 lines,
within a range of values, whose lower and upper limit corresponds to
anisotropic and isotropic velocity distribution of the oxygen coronal
ions, respectively.
Title: Latitudinal dependence of outflow velocities from O VI Doppler
dimming observations during the Whole Sun Month
Authors: Strachan, Leonard; Panasyuk, Alexander V.; Dobrzycka, Danuta;
Kohl, John L.; Noci, Giancarlo; Gibson, Sarah E.; Biesecker, Douglas A.
Bibcode: 2000JGR...105.2345S
Altcode:
Empirical determinations of outflow velocities in the solar corona
provide a much needed constraint, along with density and temperature
determinations, of the acceleration and heating mechanisms in the
extended corona. Much progress has been made on density determinations
from white light polarized brightness observations but outflow
velocities have been more difficult to determine. We present the
first determinations of outflow velocities versus height and latitude
based on a three-dimensional (3-D) reconstruction of the O VI 1032
and 1037 Å emissivities. The Doppler dimming (and pumping) of the
local emissivities give true localized outflow velocities at the
selected locations in the extended corona from ~ 1.75 to 2.75 solar
radii. The velocities are based on an empirical model of the corona
which is constrained by the reconstructed O VI emissivities derived
from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) synoptic
observations and by electron density determinations based on white
light measurements from the SOHO Large Angle Spectroscopic Coronagraph
(LASCO) and Mauna Loa Solar Observatory (MLSO) Mk III coronameter.
Title: UVCS WLC Observations of Compressional Waves in the South
Polar Coronal Hole
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
Bibcode: 2000ApJ...529..592O
Altcode:
Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) white light
channel (WLC) observations of the south polar coronal hole plumes and
interplume regions produce signatures of quasi-periodic variations in
the polarized brightness (pB) at a heliocentric distance of 1.9 solar
radii (Rsolar). The Fourier power spectrum of the pB time
series shows significant peaks at about 1.6-2.5 mHz and additional
smaller peaks at longer and shorter timescales. Wavelet analysis of
the pB time series shows that the coherence time of the fluctuations
is about 30 minutes. The new observations strongly suggest that the
fluctuations are compressional wave packets propagating in the coronal
hole high above the limb. The presence of compressional waves may have
important implications that help to explain the heating of coronal
holes and the fast solar wind acceleration.
Title: Solar and Heliospheric Observatory Observations of a Helical
Coronal Mass Ejection
Authors: Ciaravella, A.; Raymond, J. C.; Thompson, B. J.; van
Ballegooijen, A.; Strachan, L.; Li, J.; Gardner, L.; O'Neal, R.;
Antonucci, E.; Kohl, J.; Noci, G.
Bibcode: 2000ApJ...529..575C
Altcode:
The EUV Imaging Telescope (EIT), Large Angle Spectrometric Coronagraph
(LASCO), and Ultraviolet Coronagraph Spectrometer (UVCS) instruments
aboard the SOHO satellite observed a prominence eruption (coronal mass
ejection) on 1997 December 12. Ejected plasma moved at about 130 km
s-1 in the plane of the sky and showed Doppler shifts between
-350 and +30 km s-1. The eruption appeared as a strongly
curved arch in EIT images low in the corona. Emission in ions ranging
from Si III to O VI in the UVCS spectra indicates a temperature range
between 104.5 and 105.5 K. The morphology of the
bright emission regions seen by all three instruments suggests several
strands of a helical structure of moderate pitch angle. A reasonable
fit to the spatial structure and the velocity evolution measured by
UVCS is provided by a left-handed helix untwisting at a rate of about
9×10-4 radians s-1.
Title: Streamer HI Ly-α Line Profiles During the Spartan 201-05/SOHO
Coordinated Observations
Authors: Miralles, M. P.; Strachan, L.; Gardner, L. D.; Dobryzcka,
D.; Ko, Y. -K.; Michels, J.; Panasyuk, A.; Suleiman, R.; Kohl, J. L.
Bibcode: 1999ESASP.448.1193M
Altcode: 1999mfsp.conf.1193M
We present H I Lyalpha observations of coronal streamers obtained
by UVCS/SOHO during the coordinated observations with UVCS/Spartan
on 1 3 November 1998. Two different streamer regions were observed,
one relatively stable above the Northeast limb, and a postCME streamer
complex above the Southwest limb. H~I Lyalpha profiles and intensities
were measured at ~1.5 and 2 Ro in the NE streamer and its boundary
regions, and also at heights ranging from 1.5 to 2.5 Ro in the SW
streamer complex. We analyze integrated intensities and line widths
in each streamer structure.
Title: Polarimetry of the UV solar corona with ASCE
Authors: Fineschi, Silvano; Gardner, Larry D.; Kohl, John L.; Romoli,
Marco; Pace, Emanuele; Corti, Gianni; Noci, Giancarlo C.
Bibcode: 1999SPIE.3764..147F
Altcode:
The Advanced Solar Coronal Explorer (ASCE) is a mid-explorer (MidEx)
mission selected, together with other five, for the a Phase A Concept
Study in the 1999 round of MidEX proposal. ASCE's spacecraft bus is
a SPARTAN 400 reusable carrier deployed in low Earth orbit by the
Space Shuttle. ASCE's payload comprises two instrument modules,
the Spectroscopic and Polarimetric Coronagraph (SPC) and the
Extreme Ultraviolet Imager (EUVI). The scientific objective of the
mission is the investigation, through spectroscopic and polarimetric
techniques, of the physics of the coronal heating and of the solar
wind acceleration. A critical physical parameter of the corona is the
magnetic field. Polarimetric measurements of UV coronal radiation
and their interpretation through the Hanle effect can be used for
coronal magnetic field diagnostics. One of the SPC spectrometers,
the Spectroscopy/Polarimetry channel (SPCH), includes a reflecting
Brewster-angle polarimeter for measurements of the linear polarization
of the HI Lyman series lines (i.e., Ly-(alpha) , -(beta) , and (gamma)
) and of the O VI 1032 Angstrom line. In this paper, the optical design
of the SPCH polarimeter is described. A relevant element of this design
is the external occulter (EXO) that is supported on a boom, which is
extended 10 m beyond the instrument aperture, once the instrument is in
station. The analysis of the stray- light reduction provided by this
occulting system is described in this paper. The principal source of
stray light is solar disk light that is diffracted from the edge of the
EXO and scattered from the telescope mirror. The analysis shows that the
stray-light is less than 10-2 the coronal signal. This level
of stray-light rejection minimizes the polarized stray light that may
be introduced by the EXO's straight edge. The most appropriate material
for the polarizer has been found to be CaF2. The material
selection criteria are described. Finally, the paper illustrates with
an example that if the linear polarization can be measured better than
1%, then the instrumental sensitivity to magnetic fields may reach a
few gauss (greater than 2 gauss), in coronal active regions.
Title: Flat field of UVCS detectors for early part of SOHO mission
Authors: Cosmo, Mario L.; Smith, Peter L.; Atkins, Nigel; Suleiman,
R. M.; Gardner, Larry D.; Kohl, John L.
Bibcode: 1999SPIE.3764..161C
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory (SOHO) comprises two telescopes and two
spectrometer channels for spatially resolved ultraviolet spectral
diagnostics of the solar corona. The principal lines for which the
two channels are optimized are the H I 'Lyman-(alpha) ' line at 121.5
nm and the O VI (O5+) doublet at 103.2 and 103.7 nm. An
'in-flight' method, using observations of stars and scattered solar
disk light, has been devised to determine the flat field function,
i.e., the relative detection efficiency of the detector pixels. We
present the details and results of this process. Local pixel-to-pixel
efficiency variation is found to be, typically, about plus or minus 9%
to plus or minus 17% (1 (sigma) ) for the H I Lyman-(alpha) channel
and plus or minus 9% for the O VI channel.
Title: Coronal Magnetic Field Diagnostics with UV Spectropolarimetry
Authors: Fineschi, S.; van Ballegoijen, A.; Kohl, J. L.
Bibcode: 1999ESASP.446..317F
Altcode: 1999soho....8..317F
No abstract at ADS
Title: The impact of ion-cyclotron wave dissipation on heating and
accelerating the fast solar wind
Authors: Cranmer, Steven R.; Field, George B.; Kohl, John L.
Bibcode: 1999AIPC..471...35C
Altcode: 1999sowi.conf...35C
Using empirical ion velocity distributions derived from UVCS and
SUMER ultraviolet spectroscopy, we construct theoretical models of
the nonequilibrium plasma state of the polar solar corona. The primary
energy deposition mechanism we investigate is the dissipation of high
frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which
can heat and accelerate ions differently depending on their charge
and mass. We find that it is possible to explain many of the kinetic
properties of the plasma with relatively small amplitudes for the
resonant waves. There is evidence for steepening of the Alfvén wave
spectrum between the coronal base and the largest heights observed
spectroscopically, and it is important to take Coulomb collisions into
account to understand observations at the lowest heights. Because the
ion-cyclotron wave dissipation is rapid, the extended heating seems to
demand a constantly replenished population of waves over several solar
radii. This indicates that the waves are probably generated throughout
the wind rather than propagated up from the base of the corona.
Title: UVCS/SOHO observations of coronal streamers
Authors: Frazin, R. A.; Modigliani, A.; Ciaravella, A.; Dennis, E.;
Fineschi, S.; Gardner, L. D.; Michels, J.; O'Neal, R.; Raymond, J. C.;
Wu, C. -R.; Noci, G.; Kohl, J. L.
Bibcode: 1999AIPC..471..235F
Altcode: 1999sowi.conf..235F
We used the Ultraviolet Coronagraph Spectrometer (UVCS) on the
Solar and Heliospheric Observatory (SOHO) to obtain line profiles
in mid-latitude coronal streamers between 1.3 Rsolar and
5.5 Rsolar during a period of moderate solar activity. We
present a summary of the preliminary results. These results clearly
indicate that the mid-latitude streamers observed during this time
period have very different spectral properties than the equatorial
streamers observed near solar minimum.
Title: Physical properties of coronal streamers as observed by
Spartan 201
Authors: Miralles, M. P.; Strachan, L.; Gardner, L. D.; Smith, P. L.;
Kohl, J. L.; Guhathakurta, M.; Fisher, R. R.
Bibcode: 1999AIPC..471..239M
Altcode: 1999sowi.conf..239M
The three Spartan 201 flights from 1993 to 1995 provided us with
observations in HI Lyman-α of several streamers in the declining
phase of the current solar cycle. Analysis of the heliocentric height
dependence of the HI Ly-α LOS velocity distribution width clearly show
that there is a maximum in the proton 1/e velocities at heights ranging
from 2.1 to 2.5 Rsolar for all of the observed streamers. We
compare UVCS/Spartan results with proton velocity distributions from
UVCS/SOHO during solar minimum. We also discuss differences in the
proton velocity distributions for different types of streamers over
the three year period of Spartan 201 observations.
Title: Spectroscopic Constraints on Models of Ion Cyclotron Resonance
Heating in the Polar Solar Corona and High-Speed Solar Wind
Authors: Cranmer, Steven R.; Field, George B.; Kohl, John L.
Bibcode: 1999ApJ...518..937C
Altcode:
Using empirical ion velocity distributions derived from Ultraviolet
Coronagraph Spectrometer (UVCS) and Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) ultraviolet spectroscopy, we construct
theoretical models of the nonequilibrium plasma state of the polar solar
corona. The primary energy deposition mechanism we investigate is the
dissipation of high-frequency (10-10,000 Hz) ion cyclotron resonant
Alfvén waves which can heat and accelerate ions differently depending
on their charge and mass. We solve the internal energy conservation
equations for the ion temperature components parallel and perpendicular
to the superradially expanding magnetic field lines and use empirical
constraints for the remaining parameters. We find that it is possible
to explain many of the kinetic properties of the plasma (such as high
perpendicular ion temperatures and strong temperature anisotropies)
with relatively small amplitudes for the resonant waves. There is
suggestive evidence for steepening of the Alfvén wave spectrum between
the coronal base and the largest heights observed spectroscopically, and
it is important to take Coulomb collisions into account to understand
observations at the lowest heights. Because the ion cyclotron wave
dissipation is rapid, the extended heating seems to demand a constantly
replenished population of waves over several solar radii. This indicates
that the waves are generated gradually throughout the wind rather than
propagated up from the base of the corona.
Title: Comparison of outflow velocity determinations with UVCS and
LASCO for the coronal mass ejection of 13-14 August 1997
Authors: Strachan, L.; Ciaravella, A.; Raymond, J. C.; Fineschi, S.;
O'Neal, R.; Kohl, J. L.; Modigliani, A.; Noci, G.; Andrews, M. D.
Bibcode: 1999AIPC..471..637S
Altcode: 1999sowi.conf..637S
The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO observed
a Coronal Mass Ejection (CME) on 13-14 August 1997. The event was
observed simultaneously with the LASCO white light coronagraphs. This
paper describes the results from a comparison of outflow velocities
determined from UVCS Doppler dimming studies with the velocities
determined by examining the proper motions of the CME as measured by
LASCO. In addition, estimates for line of sight velocities, densities
and kinetic temperatures are discussed.
Title: Geometry, physical properties and outflow velocities from
the polar and equatorial coronal holes-UVCS/SOHO observations
Authors: Dobrzycka, Danuta; Panasyuk, Alexander V.; Strachan, Leonard;
Kohl, John L.
Bibcode: 1999AIPC..471..305D
Altcode: 1999sowi.conf..305D
We analyzed the UVCS/SOHO data obtained during the Whole Sun
Month campaign in 1996 and compared the H I Lyα (1216Å) and O VI
(1032Å,1037Å) emission in the polar and equatorial coronal holes. We
found that the emission lines have similar characteristics in these
two types of coronal holes. Both types show evidence for superradially
diverging boundaries. We used the O VI (1032Å) and O VI (1037Å) local
emissivities, determined from the 3D tomographic reconstruction of
the solar corona, to investigate the outflow velocities from the polar
and equatorial coronal holes. The latitudinal distribution of the O VI
ratio at 2.21 Rsolar, free from the line-of-sight effect,
shows evidence that the equatorial coronal hole may have O+5
outflow velocities lower than in the polar coronal holes.
Title: Whole Sun Month at solar minimum: An introduction
Authors: Galvin, Antoinette B.; Kohl, John L.
Bibcode: 1999JGR...104.9673G
Altcode:
The Whole Sun Month was a collaborative project of the IACG Campaign
4 and the SOHO Joint Observing Programs to characterize and model the
structure of the global corona during solar minimum conditions. This
introduction provides a brief description of the campaign objectives,
the missions, and observatories involved and highlights some of the
scientific results reported elsewhere in this special section.
Title: Study of the latitudinal dependence of H I Lyman α and O VI
emission in the solar corona: Evidence for the superradial geometry
of the outflow in the polar coronal holes
Authors: Dobrzycka, Danuta; Cranmer, Steven R.; Panasyuk, Alexander
V.; Strachan, Leonard; Kohl, John L.
Bibcode: 1999JGR...104.9791D
Altcode:
We study the latitudinal distribution of the H I Lyman α and O VI
(103.2 nm and 103.7 nm) line emission during the period of the Whole
Sun Month campaign (August 10 to September 8, 1996) when the Sun was
close to the minimum of its activity. The H I Lyman α and O VI line
intensities appeared to be almost constant with latitude within the
polar coronal holes and have abrupt increases toward the streamer
region. We found that both north and south polar coronal holes had
similar line intensities and line-of-sight velocities, as well as
kinetic temperatures of H0 and O5+. The dependence
of these parameters on latitude and radius is provided. We derived
boundaries of the polar coronal holes based on the H I Lyman α and O VI
line intensity distributions for several days during the Whole Sun Month
campaign. We found that the polar coronal hole boundaries clearly have
a superradial geometry with diverging factor fmax ranging
from 6.0 to 7.5, and they are consistent with boundaries previously
derived from the electron density distributions. We also found that,
in general, they are not symmetric with respect to the heliographic
poles, and their size and geometry change over periods of days. The H
I Lyman α, O VI (103.2 nm), and the O VI (103.7 nm) line intensities
showed similar boundaries within the uncertainties of our data. We
modeled the latitudinal distribution of the H I Lyman α and O VI
(103.2 nm and 103.7 nm) line intensities in the south polar coronal
hole on August 17, 1996, assuming the coronal plasma outflow along
either purely radial or nonradial flux tubes. A comparison of model
predictions with the observed distributions shows evidence that the
outflow velocity vectors follow nonradial intensity pattern.
Title: The Advanced Solar Coronal Explorer Mission (ASCE)
Authors: Kohl, J.; Cranmer, S.; Gardner, L.; Golub, L.; Raymond, J.;
Smith, P. L.; Strachan, L.; Howard, R.; Moses, D.; Socker, D.; Wang,
D.; Fisher, R. R.; Davila, J.; St. Cyr, C.; Noci, G.; Tondello, G.
Bibcode: 1999AAS...194.6506K
Altcode: 1999BAAS...31Q.928K
The Advanced Solar Coronal Explorer (ASCE) mission was selected
for a Phase A Concept Study in the current round of proposed MIDEX
missions. It addresses three fundamental problems: 1) What physical
processes heat coronal holes and drive the fast solar wind? 2) What
physical processes heat streamers and drive the slow solar wind? and 3)
How are coronal mass ejections (CMEs) heated and accelerated, and what
role to they play in the evolution of the solar magnetic field. ASCE
has two instruments, the Spectroscopic and Polarimetric Coronagraph
(SPC) and the Extreme Ultraviolet Imager (EUVI). A deployable boom
supports a distant external occulter that allows large aperture optics
for the SPC coronagraphic channels. SPC's EUV channels will provide
spectroscopy of the extended solar corona with 30 - 200 times the
sensitivity of UVCS/SOHO and the first He II 30.4 nm spectroscopy of
the extended corona. SPC's Large Aperture Spectroscopic Coronagraph
channel will provide two orders of magnitude improvement in stray
light suppression for wide field visible spectroscopy and 2 arcsec
resolution elements for imaging and polarimetry. EUVI provides full
disk imaging with 0.9 arcsec resolution elements and extremely high
cadence. ASCE is designed to determine the thermal, kinetic, and
wave energy densities in coronal structures, determine the rates of
transformation among these forms of energy, their flow in space, and
their loss to radiation, and determine the composition and ionization
state of the corona in static and transient conditions.
Title: Joint H I Lyalpha Observations with UVCS/Spartan and UVCS/SOHO
During the STS-95 Mission
Authors: Dobrzycka, D.; Kohl, J. L.; Gardner, L. D.; Strachan, L.;
Miralles, M. P.; Smith, P. L.; Suleiman, R.; Panasyuk, A.; Michels,
J.; Ko, Y. -K.
Bibcode: 1999AAS...194.1609D
Altcode: 1999BAAS...31..851D
The Spartan 201 Ultraviolet Coronal Spectrometer (UVCS/Spartan)
is an instrument developed to conduct spectroscopic studies of the
extended solar corona and its expansion into the solar wind. It was
designed to be Shuttle deployed and retrieved and has already flown in
1993, 1994, 1995, 1997, and 1998 providing a consistent set of data
that span several years of the declining and rising phases of the
solar cycle. The advantage of this instrument is that its inflight
performance characteristics can be determined from the preflight and
postflight laboratory calibration. The last, Spartan 201-5 mission was
launched aboard the Space Shuttle Discovery (STS-95) on 29 October 1998
at 2:19:20 PM (EST). Spartan 201 made autonomous observations of the
Sun and its corona for approximately 43 hours during 26 orbits around
the Earth. These observations were coordinated with the Ultraviolet
Coronagraph Spectrometer on board the Solar and Heliospheric Observatory
(UVCS/SOHO). One of the main goals of the Spartan 201-5 mission was
to update calibration of the UVCS/SOHO and to provide continuity of
measurements from the period before and after solar minimum. We review
the successfully accomplished goals of the UVCS/Spartan on the Spartan
201-5 flight and describe the radiometric and spectrometric comparison
of the streamer data to that of UVCS/SOHO. This work is supported by
NASA under Grant NAG 5-613 to the Smithsonian Astrophysical Observatory
and by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical
Observatory, by the Italian Space Agency, and by Swiss Funding Agencies.
Title: SOHO/Spartan 201 Coordinated Observations
Authors: Kohl, J. L.; Gardner, L. D.; Strachan, L.; Miralles, M. P.;
Smith, P. L.; Suleiman, R.; Dobrzycka, D.
Bibcode: 1999EOSTr..80..263K
Altcode:
We present preliminary results from the simultaneous H I Lyman alpha
observations carried out during 1-3 November 1998 with the UVCS/SOHO
and UVCS/Spartan instruments. The main objective of this mission was
to provide information on the physical conditions of the solar corona
during the rising phase of the solar activity cycle. The analysis of
the H I Lyman alpha profile measurements made with both instruments
provides us with hydrogen kinetic temperatures. These observations are
also used to update the calibration of the UVCS/SOHO instrument. This
cross-calibration provides continuity between the earlier results of
Spartan 201 and more recent results from SOHO, and consequently it
provides information on how the corona varies from the period before
the activity minimum to the period approaching the time of maximum
solar activity. This work is supported by NASA under Grants NAG 5-613
and NAG5-3192 to the Smithsonian Astrophysical Observatory.
Title: UVCS/Spartan Observations of Coronal Streamers
Authors: Miralles, M. P.; Strachan, L.; Gardner, L. D.; Smith, P. L.;
Kohl, J. L.; Guhathakurta, M.; Fisher, R. R.
Bibcode: 1999EOSTr..80..263M
Altcode:
We present H I Lyman alpha observations of coronal streamers obtained
by the UVCS instrument aboard Spartan 201 satellite during four
flights between 1993 and 1998. The analysis of the data allows us to
study the velocity structure of various streamer regions at different
phases of the solar activity cycle. We compare physical properties of
streamers derived from the UVCS/Spartan H I Lyman alpha measurements
before solar minimum with results from UVCS/SOHO and UVCS/Spartan
after solar minimum. This work is supported by NASA under Grants NAG
5-613 and 5-3192 to the Smithsonian Astrophysical Observatory.
Title: Latitudinal properties of the Lyman alpha and O VI profiles
in the extended solar corona
Authors: Zangrilli, L.; Nicolosi, P.; Poletto, G.; Noci, G.; Romoli,
M.; Kohl, J. L.
Bibcode: 1999A&A...342..592Z
Altcode:
We have analysed the latitudinal properties of the profiles of the H I
Lyman alpha line at 1215.6 protect Angstroms and of the O VI doublet at
1031.9 protect Angstroms and 1037.6 protect Angstroms in the extended
solar corona, between 1.5 R_sun and 2.0 R_sun. Observations have
been performed with the UltraViolet Coronagraph Spectrometer (UVCS)
on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheric
Observatory). The results show that these lines have quite a different
behaviour with latitude: the Ly alpha line has larger full width at
half maximum (FWHM) values in the streamer region and narrower ones
towards polar latitudes, while the O VI lines have a minimum FWHM at
the center of the streamer, which almost steadily increases towards
polar regions. The observations have been analysed looking also
for an interpretation in terms of selective heating mechanisms. The
implications of our results for coronal heating theories are also
examined. In particular we discuss the possibility for the presence
of the ion-cyclotron coronal heating mechanism. Moreover, we point out
an interesting correlation between the intensity of the coronal lines
and their widths, which may be relevant to the open question of the
different morphological features visible in the Ly alpha and O VI lines.
Title: An Empirical Model of a Polar Coronal Hole at Solar Minimum
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Strachan, L.; Panasyuk, A. V.;
Gardner, L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond,
J. C.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.;
Ciaravella, A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.;
Martin, R.; Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal,
R. H.; Pernechele, C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
Bibcode: 1999ApJ...511..481C
Altcode:
We present a comprehensive and self-consistent empirical model
for several plasma parameters in the extended solar corona above
a polar coronal hole. The model is derived from observations
with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO)
during the period between 1996 November and 1997 April. We compare
observations of H I Lyα and O VI λλ1032, 1037 emission lines
with detailed three-dimensional models of the plasma parameters and
iterate for optimal consistency between measured and synthesized
observable quantities. Empirical constraints are obtained for
the radial and latitudinal distribution of density for electrons,
H0, and O5+, as well as the outflow velocity
and unresolved anisotropic most probable speeds for H0 and
O5+. The electron density measured by UVCS/SOHO is consistent
with previous solar minimum determinations of the white-light coronal
structure; we also perform a statistical analysis of the distribution
of polar plumes using a long time series. From the emission lines we
find that the unexpectedly large line widths of H0 atoms
and O5+ ions at most heights are the result of anisotropic
velocity distributions. These distributions are not consistent with
purely thermal motions or the expected motions from a combination of
thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. Also, the
latitudinal dependence of intensity constrains the geometry of the
wind velocity vectors, and superradial expansion is more consistent
with observations than radial flow. We discuss the constraints and
implications on various theoretical models of coronal heating and
acceleration.
Title: EUV Spectral Line Profiles in Polar Coronal Holes from 1.3
to 3.0 Rsolar
Authors: Kohl, J. L.; Esser, R.; Cranmer, S. R.; Fineschi, S.; Gardner,
L. D.; Panasyuk, A. V.; Strachan, L.; Suleiman, R. M.; Frazin, R. A.;
Noci, G.
Bibcode: 1999ApJ...510L..59K
Altcode:
Spectral line profiles have been measured for H I λ1216, O VI λλ1032,
1037, and Mg X λ625 in a polar coronal hole observed during 1997
September 15-29, at projected heliographic heights ρ between 1.34
and 2.0 Rsolar. Observations of H I λ1216 and the O
VI doublet from 1997 January for ρ=1.5-3.0 Rsolar are
provided for comparison. The O VI lines are well fit to a narrow and
broad component which appear to be associated with regions of higher
and lower spectral radiance, respectively. The narrow components
dominate at low heights and become a small fraction of the lines at
higher heights. Mg X λ625 is observed to have a narrow component at
ρ=1.34 Rsolar which accounts for only a small fraction of
the observed spectral radiance. In the case of the broad components,
the values of v1/e for O VI are only slightly larger than
those for H I at ρ=1.34 Rsolar but are significantly
larger at ρ=1.5 Rsolar and much larger for ρ>1.75
Rsolar. In contrast, the Mg X values are less than those
of H I up to 1.75 and then increase rapidly up to at least ρ=2.0
Rsolar but never reach the values of O VI.
Title: Properties of Coronal Hole/Streamer Boundaries and Adjacent
Regions as Observed by SPARTAN 201
Authors: Miralles, M. P.; Strachan, L.; Gardner, L. D.; Smith, P. L.;
Kohl, J. L.; Guhathakurta, M.; Fisher, R. R.
Bibcode: 1999SSRv...87..277M
Altcode:
The Spartan 201 flights from 1993 to 1995 provided us with
observations in H I Lyman-α of several coronal hole/streamer
boundaries and adjacent streamers during the declining phase of the
current solar cycle: Analysis of the latitudinal dependence of the
line intensities clearly shows that there is a boundary region at
the coronal hole/streamer interface where the H I Lyman-α intensity
reaches a minimum value. Similar results are also found in UVCS/SOHO
observations. We also discuss differences in the coronal hole/streamer
boundaries for different types of streamers and their changes over
the three year period of Spartan 201 observations.
Title: Variation of Polar Coronal Hole Profiles with Solar Cycle
Authors: Dobrzycka, D.; Strachan, L.; Miralles, M. P.; Kohl, J. L.;
Gardner, L. D.; Smith, P.; Guhathakurta, M.; Fisher, R.
Bibcode: 1999SSRv...87..177D
Altcode:
We compared the H I Lyα polar coronal hole profiles obtained during
the three Spartan 201 flights (in 1993, 1994, and 1995) and during the
more recent UVCS/SOHO mission. We found that at 2.1 R⊙
there are no significant variations of the line shape over the several
years of the descending phase of the solar cycle. However, there may be
some evidence for the 1.8 R⊙ profiles being broader towards
solar minimum. The profiles at 2.1 R⊙ are different from
profiles obtained at 1.8 R⊙; they have clearly narrower
cores and wide wings. We fitted the profiles with single and/or multiple
Gaussian functions and calculated their typical 1/e half widths.
Title: Plasma Properties in Coronal Holes Derived from Measurements
of Minor Ion Spectral Lines and Polarized White Light Intensity
Authors: Esser, Ruth; Fineschi, Silvano; Dobrzycka, Danuta; Habbal,
Shadia R.; Edgar, Richard J.; Raymond, John C.; Kohl, John L.;
Guhathakurta, Madhulika
Bibcode: 1999ApJ...510L..63E
Altcode:
Recent observations of the Lyα λ1216, Mg X λ625, and O VI λ1038
spectral lines carried out with the Ultraviolet Coronagraph Spectrometer
(UVCS) on board SOHO at distances in the range 1.35-2.1 RS in
the northern coronal hole are used to place limits on the turbulent wave
motions of the background plasma and the thermal motions of the protons
and Mg+9 and O+5 ions. Limits on the turbulent
wave motion are estimated from the measured line widths and electron
densities derived from white light coronagraph observations, assuming
WKB approximation at radial distances covered by the observations. It
is shown that the contribution of the turbulent wave motion to the
widths of the measured spectral lines is small compared to thermal
broadening. The observations show that the proton temperature slowly
increases between 1.35 and 2.7 RS and does not exceed
3×106 K in that region. The temperature of the minor ions
exceeds the proton temperature at all distances, but the temperatures
are neither mass proportional nor mass-to -charge proportional. It is
shown, for the first time, that collision times between protons and
minor ions are small compared to the solar wind expansion times in
the inner corona. At 1.35 RS the expansion time exceeds
the proton Mg+9 collision time by more than an order of
magnitude. Nevertheless, the temperature of the Mg ions is significantly
larger than the proton temperature, which indicates that the heating
mechanism has to act on timescales faster than minutes. When the
expansion time starts to exceed the collision times a rapid increase
of the O+5 ion spectral line width is seen. This indicates
that the heavier and hotter ions lose energy to the protons as long as
collision frequencies are high, and that the ion spectral line width
increases rapidly as soon as this energy loss stops.
Title: Ultraviolet and Optical Observations of a Coronal Transient
with SOHO
Authors: Ciaravella, A.; Raymond, J. C.; Strachan, L.; Thompson,
B. J.; Cyr, O. C. St.; Gardner, L.; Modigliani, A.; Antonucci, E.;
Kohl, J.; Noci, G.
Bibcode: 1999ApJ...510.1053C
Altcode:
A coronal transient was observed on 1997 March 6 at 1.6
Rsolar over an active region on the east limb. We observed
both the edge of horizontally compressed gas and the diffuse curtain of
coronal material. The region was monitored for 4 hr, and the H I Lyα,
O VI λλ1031.91, 1037.61, N V λλ1242.80, 1238.80, and O V] λ1218.35
lines were detected during the ejection evolution. The density,
velocity, temperature, and oxygen abundance of the ejected plasma have
been obtained from the observed spectra. Intermediate temperature lines
of N V, O VI, and O V show a large enhancement, suggesting a quite
narrow range of plasma temperature around 4×105 K. Doppler
shifts of the ejected material evolve from an initial blueshift of 100
km s-1 to a redshift of 145 km s-1. The outflow
velocity, as determined by Doppler dimming analysis of the O VI doublet,
is only about 20 km s-1.
Title: Ulysses-UVCS Coordinated Observations
Authors: Suess, S. T.; Poletto, G.; Corti, G.; Simnett, G.; Noci,
G.; Romoli, M.; Kohl, J.; Goldstein, B.
Bibcode: 1999SSRv...87..319S
Altcode:
We present results from SOHO/UVCS measurements of the density and
flow speed of plasma at the Sun and again of the same plasma by
Ulysses/SWOOPS in the solar wind. UVCS made measurements at 3.5 and
4.5 solar radii and Ulysses was at 5.1 AU. Data were taken for nearly
2 weeks in May June 1997 at 9 10 degrees north of the equator in the
streamer belt on the east limb. Density and flow speed were compared
to see if near Sun characteristics are preserved in the interplanetary
medium. By chance, Ulysses was at the very northern edge of the streamer
belt. Nevertheless, no evidence was found of fast wind or mixing of slow
wind with fast wind coming from the northern polar coronal hole. The
morphology of the streamer belt was similar at the beginning and end
of the observing period, but was markedly different during the middle
of the period. A corresponding change in density (but not flow speed)
was noted at Ulysses.
Title: UVCS/SOHO Observations of H I Lyman Alpha Line Profiles in
Coronal Holes at Heliocentric Heights Above 3.0 R⊙
Authors: Suleiman, R. M.; Kohl, J. L.; Panasyuk, A. V.; Ciaravella,
A.; Cranmer, S. R.; Gardner, L. D.; Frazin, R.; Hauck, R.; Smith,
P. L.; Noci, G.
Bibcode: 1999SSRv...87..327S
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory (SOHO) has been used to measure spectral line
profiles for H I Lyα in the south polar coronal hole at projected
heliocentric heights from 3.5 to 6.0 R⊙ during 1998
January 5 11. Observations from 1.5 to 2.5 R⊙ were made
for comparison. The H I Lyα profile is the only one observable with
UVCS above 3.5 R⊙ in coronal holes. Within this region
the outflowing coronal plasma becomes nearly collisionless and the
ionization balance is believed to become frozen.
Title: Comparison of Polar and Equatorial Coronal Holes Observed by
UVCS/SOHO: Geometry and Physical Properties
Authors: Dobrzycka, D.; Panasyuk, A.; Strachan, L.; Kohl, J.
Bibcode: 1999SSRv...87..173D
Altcode:
We analyzed UVCS/SOHO data and compared the H I Lyα (121.6 nm) and O
VI (103.2 nm, 103.7 nm) emission in the polar and equatorial coronal
holes. We found that the emission lines have similar characteristics
in these two types of coronal holes. Both types show evidence for
superradially diverging boundaries. The latitudinal distribution of
the O VI line ratio may indicate that the equatorial coronal hole has
O+5 outflow velocities lower than in the polar coronal holes.
Title: Constraints on Coronal Outflow Velocities Derived from UVCS
Doppler Dimming Measurements and in-Situ Charge State Data
Authors: Strachan, L.; Ko, Y. -K.; Panasyuk, A. V.; Dobrzycka, D.;
Kohl, J. L.; Romoli, M.; Noci, G.; Gibson, S. E.; Biesecker, D. A.
Bibcode: 1999SSRv...87..311S
Altcode:
We constrain coronal outflow velocity solutions, resolved along the
line-of-sight, by using Doppler dimming models of H I Lyman alpha and
O VI 1032/1037 Å emissivities obtained with data from the Ultraviolet
Coronagraph Spectrometer (UVCS) on SOHO. The local emissivities, from
heliocentric heights of 1.5 to 3.0 solar radii, were determined from 3-D
reconstructions of line-of-sight intensities obtained during the first
Whole Sun Month Campaign (10 August to 8 September 1996). The models use
electron densities derived from polarized brightness measurements made
with the visible light coronagraphs on UVCS and LASCO, supplemented
with data from Mark III at NCAR/MLSO. Electron temperature profiles
are derived from 'freezing-in' temperatures obtained from an analysis
of charge state data from SWICS/Ulysses. The work concentrates on
neutral hydrogen outflow velocities which depend on modeling the
absolute coronal H I Lyα emissivities. We use an iterative method to
determine the neutral hydrogen outflow velocity with consistent values
for the electron temperatures derived from a freezing-in model.
Title: Coronal Holes and Solar Wind Acceleration, Proceedings of
the SOHO-7 Workshop.
Authors: Kohl, John L.; Cranmer, Steven R.
Bibcode: 1999soho....7.....K
Altcode:
No abstract at ADS
Title: UVCS/SOHO Ion Kinetics in Coronal Streamers
Authors: Frazin, R. A.; Ciaravella, A.; Dennis, E.; Fineschi, S.;
Gardner, L. D.; Michels, J.; O'Neal, R.; Raymond, J. C.; Wu, C. -R.;
Kohl, J. L.; Modigliani, A.; Noci, G.
Bibcode: 1999SSRv...87..189F
Altcode:
We made streamer observations with the Ultraviolet Coronagraph
Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO)
during the early part of 1998, which was a time of moderate solar
activity. We present an empirical study of coronal ion kinetics using
the line profiles from these observations. Our first and most striking
result is that the mid-latitude (ML) streamers have much narrower
O VI 1032 Å line profiles than the solar minimum equatorial (SME)
streamers. Our second result is that the line profiles from a small
collection of ions in ML streamers do not seem to be consistent with
the ions having a single temperature and turbulent velocity. We discuss
several interpretations, including line of sight (LOS) effects. This
work is supported by the National Aeronautics and Space Administration
under grant NAG-3192 to the Smithsonian Astrophysical Observatory.
Title: Ly-α Observation of a Coronal Streamer with UVCS/SOHO
Authors: Maccari, L.; Noci, G.; Modigliani, A.; Romoli, M.; Fineschi,
S.; Kohl, J. L.
Bibcode: 1999SSRv...87..265M
Altcode:
In this paper we discuss some characteristics of an equatorial streamer
observed by UVCS in July 1997. We determine the height distribution
of the Ly-α total intensity and of its width. We focus our attention,
in particular, on the time variability of these parameters.
Title: Foreword
Authors: Kohl, John L.; Cranmer, Steven R.
Bibcode: 1999SSRv...87....9K
Altcode:
No abstract at ADS
Title: UVCS/SOHO Observations of Spectral Line Profiles in Polar
Coronal Holes
Authors: Kohl, J. L.; Fineschi, S.; Esser, R.; Ciaravella, A.; Cranmer,
S. R.; Gardner, L. D.; Suleiman, R.; Noci, G.; Modigliani, A.
Bibcode: 1999SSRv...87..233K
Altcode:
Ultraviolet emission line profiles have been measured on 15-29 September
1997 for H I 1216 Å, O VI 1032, 1037 Å and Mg X 625 Å in a polar
coronal hole, at heliographic heights ϱ (in solar radii) between 1.34
and 2.0. Observations of H I 1216 Å and the O VI doublet from January
1997 for ϱ = 1.5 to 3.0 are provided for comparison. Mg X 625 Å is
observed to have a narrow component at ϱ = 1.34 which accounts for
only a small fraction of the observed spectral radiance, and a broad
component that exists at all observed heights. The widths of O VI broad
components are only slightly larger than those for H I at ϱ = 1.34,
but are significantly larger at ϱ = 1.5 and much larger for ϱ >
1.75. In contrast, the Mg X values are less than those of H I up to
1.75 and then increase rapidly up to at least ϱ = 2.0, but never
reach the values of O VI.
Title: What Can UVCS Observations Tell Us about Coronal Mass Ejections
Authors: Strachan, L.; Ciaravella, A.; Raymond, J. C.; Kohl, J. L.
Bibcode: 1999EOSTr..80..254S
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO has observed a
number of Coronal Mass Ejections at various heights and heliographic
latitudes. We will focus on the changes in the physical conditions
of the coronal plasma that can be observed with uv spectroscopic
techniques. These changes may provide a clue to the origin of the
material ejected by the CME. This work is supported in part by NASA
under grant NAG-3192 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Swiss funding agencies.
Title: Coronal holes and solar wind acceleration. Proceedings. SOHO-7
Workshop, Northeast Harbor, ME (USA), 28 Sep - 1 Oct 1998.
Authors: Kohl, J. L.; Cranmer, S. R.
Bibcode: 1999SSRv...87.....K
Altcode:
The following topics were dealt with: solar coronal holes, solar wind
acceleration, solar wind models, high speed solar wind, compositional
variations, coronal loops, solar magnetic fields, plasma waves, solar
polar region, coronal heating, streamers.
Title: Variation of H I Lyman Alpha Profiles in the Solar Corona
from 1993 to 1998
Authors: Miralles, M. P.; Strachan, L.; Gardner, L. D.; Dobryzcka,
D.; Smith, P. L.; Kohl, J. L.
Bibcode: 1999EOSTr..80..818M
Altcode:
UVCS/Spartan and UVCS/SOHO Lyman alpha intensity and profile
measurements of the solar corona have been made from 1993 to the
present, spanning the declining phase of cycle 22 through the rising
phase of cycle 23. These measurements can be used to characterize
the plasma in the regions where solar wind acceleration and heating
mechanisms are important. The H I Lyman alpha intensity observations
provide information about electron temperature and outflow velocity as
well as density. The analysis of the line profile provides information
about the line of sight velocity distribution of the protons. The recent
coordinated SOHO/Spartan 201-5 mission confirmed the UVCS/SOHO spectral
characterization and radiometric calibration an allows a continuity of
measurements from the period before minimum to the present rising phase
toward solar maximum. We show how streamer and coronal hole profiles
change over this period. This work is supported by NASA under Grants
NAG 5-613 and 5-3192 to the Smithsonian Astrophysical Observatory.
Title: SOHO Observations of Density Fluctuations in Coronal Holes
Authors: Ofman, L.; Romoli, M.; Noci, G.; Poletto, G.; Kohl, J. L.;
Howard, R. A.; Cyr, C. St.; Deforest, C. E.
Bibcode: 1999SSRv...87..287O
Altcode:
In recent UVCS/SOHO White Light Channel (WLC) observations we found
quasi-periodic variations in the polarized brightness (pB) in the
polar coronal holes at heliocentric distances of 1.9 to 2.45 solar
radii. The motivation for the observation is the 2.5D MHD model of
solar wind acceleration by nonlinear waves, that predicts compressive
fluctuations in coronal holes. In February 1998 we performed new
observations using the UVCS/WLC in the coronal hole and obtained
additional data. The new data corroborate our earlier findings with
higher statistical significance. The new longer observations show that
the power spectrum peaks in the 10 12 minute range. These timescales
agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort
to further establish the coronal origin of the fluctuations.
Title: Spectroscopic Constraints on Models of Ion-cyclotron Resonance
Heating in the Polar Solar Corona
Authors: Cranmer, S. R.; Field, G. B.; Kohl, J. L.
Bibcode: 1999SSRv...87..149C
Altcode:
Using empirical velocity distributions derived from UVCS and
SUMER ultraviolet spectroscopy, we construct theoretical models of
anisotropic ion temperatures in the polar solar corona. The primary
energy deposition mechanism we investigate is the dissipation of high
frequency (10-10000 Hz) ion-cyclotron resonant Alfvén waves which
can heat and accelerate ions differently depending on their charge
and mass. We find that it is possible to explain the observed high
perpendicular temperatures and strong anisotropies with relatively small
amplitudes for the resonant waves. There is suggestive evidence for
steepening of the Alfvén wave spectrum between the coronal base and the
largest heights observed spectroscopically. Because the ion-cyclotron
wave dissipation is rapid, even for minor ions like O5+,
the observed extended heating seems to demand a constantly replenished
population of waves over several solar radii. This indicates that
the waves are generated gradually throughout the wind rather than
propagated up from the base of the corona.
Title: Spectroscopic Constraints on Models of Ion-Cyclotron Resonance
Heating in the Polar Solar Corona and Fast Solar Wind
Authors: Cranmer, S. R.; Field, G. B.; Kohl, J. L.
Bibcode: 1998EOSTr..79..722C
Altcode:
We present preliminary results from a theoretical model of the heating
of minor ions in the fast solar wind. We examine the compatibility
between these models and spectroscopic determinations of velocity
distribution functions from the UVCS and SUMER instruments aboard
SOHO. By examining the dependence of line shapes (which probe
the perpendicular velocity distribution) on ion charge and mass,
detailed information can be extracted about the preferential heating
and the Coulomb collisional coupling. The primary momentum and energy
deposition mechanism we investigate is the dissipation of high-frequency
(ion-cyclotron resonant) Alfven waves, which can accelerate and heat
ions differently depending on their charge and mass. Minor ions which
do not appreciably damp the resonant wave amplitudes can be used to
constrain the slope of the fluctuation spectrum. SUMER measurements of
several ions at heliocentric heights between 1.02 and 1.07 solar radii
allow the ``base'' spectrum to be analyzed, and UVCS O VI line widths
measured between 1.5 and 3.5 solar radii provide information about
the radial evolution of the spectrum. This work is supported by the
National Aeronautics and Space Administration under grant NAG5-3192 to
the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana,
and by the ESA PRODEX program (Swiss contribution).
Title: White-light stray light test of the SOHO UVCS
Authors: Leviton, Douglas B.; Gardner, Larry D.; Fineschi, Silvano;
Jhabvala, Murzy D.; Kohl, John L.; Romoli, Marco; Noci, Giancarlo C.
Bibcode: 1998SPIE.3443...50L
Altcode:
During the late stages of integration at MATRA-Marconi in Toulouse,
France of the Ultraviolet Coronagraph Spectrometer (UVCS) for the joint
NASA/ESA (European Space Agency) Solar and Heliospheric Observatory
(SOHO), project management for the International Solar and Terrestrial
Physics Project (ISTP) at Goddard Space Flight Center (GSFC) became
concerned that the instrument's elaborate stray light rejection system
had not been tested and might possibly be misaligned such that the
instrument could not deliver promised scientific returns. A white light
stray light test, which would place an upper bound on UVCS's stray
light rejection capability, was commissioned, conceived, and carried
out. This upper bound value would be indicative of the weakest coronal
features the spectrometer would be capable of discerning. The test was
rapidly developed at GSFC, in parallel with spacecraft integration,
in coordination with science team members from Harvard- Smithsonian
Center for Astrophysics (CFA) and was carried out at MATRA in late
February 1995. The outcome of this test helped justify later impact
to integration schedule to conduct similar much needed testing with
visible and far ultraviolet light at CFA in a facility specifically
designed to perform such tests.
Title: Grating stray light analysis and control in the UVCS/SOHO
Authors: Fineschi, Silvano; Gardner, Larry D.; Kohl, John L.; Romoli,
Marco; Noci, Giancarlo C.
Bibcode: 1998SPIE.3443...67F
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) of the Solar and
Heliospheric (SOHO) mission has been developed for spectroscopic
and polarimetric determinations of temperatures, densities and
flow velocities in the extended solar corona. The instrument
consists of a visible light (VL) polarimeter, and two ultraviolet
(UV) spectrometers, optimized for the H I Lyman (alpha) (Ly-(alpha)
) line ((lambda) 1216 angstrom) and for the O VI doublet ((lambda)
(lambda) 1032/1037 angstrom). The stray-light profile of the Ly-(alpha)
holographic grating has been measured, in a laboratory set-up, in
both the spatial and spectral directions. The observed profile has
been found to be a combination of two components: the scattering
from the grating surface, and the Fraunhofer diffraction due to the
vignetting of the grating. An analytical expression for the scattering
component of the grating point spread function (PSF) has been derived
from a simple model of the grating surface roughness. The stray-light
profile generated by the analytical expression of the grating PSF gives
a good fit of stray-light profile measured in the laboratory. This
instrument function has been used in the analysis of in-flight UVCS
observations of the profile of electron scattered Ly- (alpha) from the
solar corona. These observations have resulted, for the first time,
in the most direct measurement of the coronal electron temperature.
Title: Solar Wind at 6.8 Solar Radii from UVCS Observation of Comet
C/1996Y1
Authors: Raymond, John C.; Fineschi, S.; Smith, P. L.; Gardner, L.;
O'Neal, R.; Ciaravella, A.; Kohl, J. L.; Marsden, B.; Williams, G. V.;
Benna, C.; Giordano, S.; Noci, G.; Jewitt, D.
Bibcode: 1998ApJ...508..410R
Altcode:
The comet C/1996Y1, a member of the Kreutz family of Sun-grazing comets,
was observed with the Ultraviolet Coronagraph Spectrometer (UVCS)
aboard the Solar and Heliospheric Observatory (SOHO) satellite. The
Lyα line profile and spatial distribution are interpreted in terms
of the theory of bow shocks driven by mass-loading. At the time of
the observation, the comet was 6.8 R⊙ from the Sun in
a region of high-speed wind, a region difficult to observe directly
with the SOHO instruments but an important region for testing models
of solar wind acceleration and heating. We find a solar wind speed
below 640 km s-1 and a constraint on the combination of
solar wind speed and proton temperature. The total energy per proton at
6.8 R⊙ is 50%-75% of the energy at 1 AU, indicating that
significant heating occurs at larger radii. The centroid and width
of the Lyα line generally confirm the predictions of models of the
cometary bow shock driven by mass-loading as cometary molecules are
ionized and swept up in the solar wind. We estimate an outgassing rate
of 20 kg s-1, which implies an active area of the nucleus
only about 6.7 m in diameter at 6.8 R⊙. This is likely
to be the size of the nucleus, because any inert mantle would have
probably been blown off during the approach to the Sun.
Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
Bibcode: 1998ApJ...507L.189O
Altcode:
In the Letter ``Ultraviolet Coronagraph Spectrometer
Observations of Density Fluctuations in the Solar Wind'' by
L. Ofman, M. Romoli, G. Poletto, G. Noci, and J. L. Kohl (ApJ, 491, L111 [1997]), there was
an error in the data reduction of the polarized brightness (pB). It
was assumed that the cadence of the data and the exposure time are
equal. However, the correct cadence is30 s longer than the exposure
time because of the time it takes the polarizer to change orientation
between exposures. This error does not affect the main result of the
Letter, i.e., the detection of quasi-periodic density fluctuations in
the solar wind. However, the correct cadences of the data in Table 1
are 30 s longer. This correction can be taken into account in Figure
1 by multiplying the times by 1.5 and dividing the frequencies by
the same factor. Thus, the highest peak in the power spectrum is at
1.8+/-0.07 mHz (the corresponding period is 9.3+/-0.4 minutes). The
correction factor is 1.1 in Figure 2 because of the longer exposure
time in this observation.
Title: Physical Structure of a Coronal Streamer in the Closed-Field
Region as Observed from UVCS/SOHO and SXT/Yohkoh
Authors: Li, J.; Raymond, J. C.; Acton, L. W.; Kohl, J. L.; Romoli,
M.; Noci, G.; Naletto, G.
Bibcode: 1998ApJ...506..431L
Altcode:
We analyze a coronal helmet streamer observed on 1996 July 25 using
instruments aboard two solar spacecraft, the Ultraviolet Coronagraph
Spectrometer (UVCS) on board Solar and Heliospheric Observatory
(SOHO) and the Soft X-Ray Telescope (SXT) on board Yohkoh. We derive
temperatures and electron densities at 1.15 R⊙ from
SXT/Yohkoh observations. At this height, the streamer temperature is
about log T (K) = 6.28 +/- 0.05, and the electron density is about
log ne(cm-3) = 8.09 +/- 0.26, while at 1.5
R⊙ a temperature of log T (K) = 6.2 and a density of log
ne(cm-3) = 7.1 are obtained by UVCS/SOHO. Within
the measurement uncertainty this suggests a constant temperature from
the base of the streamer to 1.5 R⊙. Electron density
measurements suggest that the gas in the streamer core is close to
hydrostatic equilibrium. Comparison with potential field models for the
magnetic field suggests a plasma β larger than 1 in the closed-field
region in the streamer. In deriving electron densities and temperatures
from the SXT/Yohkoh data, we include the effects of abundance anomalies
on the SXT filter response. We use the elemental abundances derived from
the UVCS/SOHO observations to estimate the first ionization potential
and gravitational settling effects. We then give the set of abundances
for the solar corona, which agrees with our observations. In addition,
we analyzed the SXT data from 6 consecutive days. We found that from
1996 July 22 to July 27, the physical properties of the streamer are
nearly constant. We conclude that we may be observing the same loop
system over 6 days.
Title: The Effect of Temperature Anisotropy on Observations of
Doppler Dimming and Pumping in the Inner Corona
Authors: Li, Xing; Habbal, Shadia Rifai; Kohl, John L.; Noci, Giancarlo
Bibcode: 1998ApJ...501L.133L
Altcode: 1998astro.ph..5021L
Recent observations of the spectral line profiles and intensity ratio
of the O VI λλ1032 and 1037.6 doublet by the Ultraviolet Coronagraph
Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO),
made in coronal holes below 3.5 RS, provide evidence
for Doppler dimming of the O VI λ1037.6 line and pumping by the
chromospheric C II λ1037.0182 line. Evidence for a significant kinetic
temperature anisotropy of O5+ ions was also derived from
these observations. We show in this Letter how the component of the
kinetic temperature in the direction perpendicular to the magnetic
field, for both isotropic and anisotropic temperature distributions,
affects both the amount of Doppler dimming and pumping. Taking this
component into account, we further show that the observation of the O
VI doublet intensity ratio less than unity can be accounted for only
if pumping by C II λ1036.3367 in addition to C II λ1037.0182 is in
effect. The inclusion of the C II λ1036.3367 pumping implies that the
speed of the O5+ ions can reach 400 km s-1 around
3 RS, which is significantly higher than the reported UVCS
values for atomic hydrogen in polar coronal holes. These results imply
that oxygen ions flow much faster than protons at that heliocentric
distance.
Title: UVCS/SOHO Empirical Determinations of Anisotropic Velocity
Distributions in the Solar Corona
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Cranmer, S. R.; Strachan, L.; Panasyuk, A. V.; Gardner,
L. D.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond, J. C.;
Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Benna, C.; Ciaravella,
A.; Giordano, S.; Habbal, S. R.; Karovska, M.; Li, X.; Martin, R.;
Michels, J. G.; Modigliani, A.; Naletto, G.; O'Neal, R. H.; Pernechele,
C.; Poletto, G.; Smith, P. L.; Suleiman, R. M.
Bibcode: 1998ApJ...501L.127K
Altcode:
We present a self-consistent empirical model for several plasma
parameters of a polar coronal hole near solar minimum, derived from
observations with the Solar and Heliospheric Observatory Ultraviolet
Coronagraph Spectrometer. The model describes the radial distribution of
density for electrons, H0, and O5+ and the outflow
velocity and unresolved most probable velocities for H0
and O5+ during the period between 1996 November and 1997
April. In this Letter, we compare observations of H I Lyα and O
VI λλ1032, 1037 emission lines with spatial models of the plasma
parameters, and we iterate for optimal consistency between measured and
synthesized observable quantities. The unexpectedly large line widths
of H0 atoms and O5+ ions at most radii are the
result of anisotropic velocity distributions, which are not consistent
with purely thermal motions or the expected motions from a combination
of thermal and transverse wave velocities. Above 2 Rsolar,
the observed transverse, most probable speeds for O5+ are
significantly larger than the corresponding motions for H0,
and the outflow velocities of O5+ are also significantly
larger than the corresponding velocities of H0. We discuss
the constraints and implications on various theoretical models of
coronal heating and acceleration.
Title: Elemental Abundances in Coronal Structures
Authors: Raymond, John C.; Suleiman, Raid; Kohl, John L.; Noci,
Giancarlo
Bibcode: 1998SSRv...85..283R
Altcode:
A great deal of evidence for elemental abundance variations among
different structures in the solar corona has accumulated over the
years. Many of the observations show changes in the relative abundances
of high- and low-First Ionization Potential elements, but relatively
few show the absolute elemental abundances. Recent observations from the
SOHO satellite give absolute abundances in coronal streamers. Along the
streamer edges, and at low heights in the streamer, they show roughly
photospheric abundances for the low-FIP elements, and a factor of 3
depletion of high-FIP elements. In the streamer core at 1.5 R·, both
high- and low-FIP elements are depleted by an additional factor of 3,
which appears to result from gravitational settling.
Title: UVCS/SOHO: The First Two Years
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.
Bibcode: 1998SSRv...85..341C
Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has observed
the extended solar corona between 1 and 10 R· for more than two
years. We review spectroscopic and polarimetric measurements made
in coronal holes, equatorial streamers, and coronal mass ejections,
as well as selected non-solar targets. UVCS/SOHO has provided a great
amount of empirical information about the physical processes that heat
and accelerate the solar wind, and about detailed coronal structure
and evolution.
Title: Absolute Cross Section for Electron Impact Excitation of
Metastable Si^2+
Authors: Janzen, P. H.; Reisenfeld, D. B.; Gardner, L. D.; Kohl, J. L.
Bibcode: 1998APS..DMP..LP31J
Altcode:
We have measured the absolute cross section for electron impact
excitation (EIE) of Si^2+(3s3p ^3P^o - 3s3p ^1P) for energies near
threshold. A beams modulation technique with inclined electron and ion
beams was used. The radiation from the excited ions at λ120.6 nm was
detected using an absolutely calibrated optical system that subtends
slightly over π steradians. The population of the Si^2+(3s3p ^3P^o)
metastable state in the incident ion beam was determined using a
beam attenuation method and by making an absolute measurement of the
intensity of the λ189.2 nm light from the beam due to radiative decay
of the metastable state. A metastable fraction of 22.4 ± 2.5% was
measured. Because of the small metastable fraction, the EIE signal
is rather small. Nevertheless, the complex resonance structure of
the cross section is clearly resolved. Research progress and the
experimental apparatus will be described. This work was supported by
NASA Supporting Research and Technology Program in Solar Physics grant
NAG5-5059 and the Smithsonian Astrophysical Observatory.
Title: Absolute Cross Section for Electron Impact Excitation of
Ground State Si^2+
Authors: Reisenfeld, D. B.; Janzen, P. H.; Gardner, L. D.; Savin,
D. W.; Kohl, J. L.
Bibcode: 1998APS..DMP..K608R
Altcode:
We have measured the absolute cross section for electron impact
excitation (EIE) of Si^2+(3s^2 ^1S - 3s3p ^1P) for energies below
threshold to 11 eV above. A beams modulation technique with inclined
electron and ion beams was used, where the radiation from the excited
ions at λ120.6 nm was detected using an absolutely calibrated optical
system. The population of the Si^2+(3s3p ^3P^o) metastable state in
the incident ion beam was determined to be 22.4 ± 2.5%. The data
have been corrected for contributions to the signal from excitation
of the metastable state, and for higher energies, from excitation of
the ground state to levels above the 3s3p ^1P level. The experimental
0.5 ± 0.05 eV energy spread allowed us to resolve complex resonance
structure throughout the studied energy range. At the reported 15%
uncertainty level (90% confidence limit), the measured structure
and absolute scale of the cross section are in good agreement with
12-state close-coupling R-matrix calculations(D. C. Griffin et al).,
Phys. Rev. A 47, 2871 (1993).^,(P. L. Dufton & A. E. Kingston,
MNRAS 241), 209 (1989).. This work was supported by NASA Supporting
Research and Technology Program in Solar Physics grants NAGW-1687
and NAG5-5059, NASA Training Grant NGT-51081 and the Smithsonian
Astrophysical Observatory.
Title: Ultraviolet Spectroscopy of the Extended Solar Corona with
UVCS/SOHO
Authors: Kohl, John
Bibcode: 1998APS..DMP..K104K
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and
Heliospheric Observatory (SOHO) is designed to obtain an empirical
description of the extended solar corona and its expansion into the
solar wind. During its first two years of operation, UVCS has been
used to determine velocity distributions and bulk motions of protons,
electrons and minor ions; particle densities, and elemental abundances
from near the base of the solar corona to heliocentric heights up to 10
solar radii. Measurements of spectral line profiles and comparisons of
observed intensities with self consistent coronal models are used to
derive values for the coronal plasma parameters. The measurements are
challenging the current theories on the composition and acceleration of
the solar wind. The velocity distributions for coronal ions are found
to be anisotropic by as much as a factor of 15 and the most probable
speeds in the direction perpendicular to the coronal magnetic field are
extremely large reaching values corresponding to temperatures of over
2 × 10^8 K in a thermalized plasma. Elemental abundances in specific
coronal structures can be an order of magnitude smaller than in the
solar photosphere. Similarities between abundances in the corona and
abundances in fast and slow wind streams provide clues about the coronal
source regions of the wind. The physical processes and atomic parameters
required to derive the coronal parameters from the observations will
be discussed. Current ideas about the theoretical explanation for the
derived empirical description of the corona will also be described
briefly. This work is supported by the National Aeronautics and Space
Administration under grant NAG5-3192 to the Smithsonian Astrophysical
Observatory, by Agenzia Spaziale Italiana and by Swiss funding agencies.
Title: Study of the Latitudinal Dependence of HI Lyman alpha and OVI
Emission - Evidence for the Super-Radial Geometry of the Outflow in
the Polar Coronal Holes
Authors: Dobrzycka, D.; Strachan, L.; Panasyuk, A.; Cranmer, S. R.;
Kohl, J. L.; Romoli, M.
Bibcode: 1998EOSTr..79..283D
Altcode:
The observations obtained during the Whole Sun Month (WSM) campaign
(Aug.10 - Sept.08, 1996) provide us with detailed information about
the Sun and solar corona near the minimum of solar activity. This data
set is especially important for analysis of the latitudinal dependence
of the emission from the solar corona, since at solar minimum the
polar coronal holes are large, stable structures and streamers are
long lasting features occupying a narrow region in the equatorial
plane. We present our analysis of the UVCS/SOHO data acquired during
the period of the WSM campaign. We describe the distribution of the
HI Lyman alpha and O VI (1032,1037 A) emission as a function of both
latitude and radius and derive characteristic plasma parameters like
velocities along the line of sight and kinetic temperatures. We put
constraints on the boundaries of the polar coronal holes by modeling
them with flow tubes that expand radially or super-radially and
compare our results with constraints from other instruments. We also
model the latitudinal distribution of the Lyman alpha and O VI line
intensities assuming outflow either along purely radial or non-radial
flux tubes. This work was supported by NASA under Grant NAG5-3192 to
the Smithsonian Astrophysical Observatory, by the Italian Space Agency,
and by Swiss Funding Agencies.
Title: Acceleration and Heating of the Fast Solar Wind: Diagnostics
and Theory
Authors: Cranmer, S. R.; Field, G. B.; Noci, G.; Kohl, J. L.
Bibcode: 1998EOSTr..79..278C
Altcode:
We present empirical models based on UVCS/SOHO observational data
for several plasma parameters in the fast solar wind emerging
from near-solar-minimum polar coronal holes. We also discuss the
constraints on various theoretical processes of coronal heating and
acceleration, and present preliminary kinetic models of the velocity
distributions. UVCS/SOHO has measured hydrogen kinetic temperatures
in polar coronal holes in excess of 3 million K, and O5+
ion kinetic temperatures of at least 200 million K. The velocity
distributions parallel to the open magnetic field are smaller than
those perpendicular to the field, possibly implying temperature
anisotropy ratios of order 100 for minor ions. In addition, Doppler
dimming and pumping of the emission line intensities indicates that the
O5+ ions may have higher outflow velocities than the protons;
the ions may reach 500 km/s by a radius of 4 solar radii. We examine
various features of plasma heating by the dissipation of high-frequency
ion-cyclotron resonance Alfven waves, which may be the most natural
physical mechanism to produce the observed plasma conditions. This
resonant wave damping produces anisotropic velocity-space diffusion and
a significant outward acceleration in addition to that provided to ions
by the magnetic mirror force. Because different ions have different
resonant frequencies, they receive different amounts of heating and
acceleration as a function of radius. Thus, the more ionic species
that are observed, the greater the extent in frequency space the wave
spectrum can be inferred and spatially mapped.
Title: Tomographic Reconstructions of the Corona from UVCS/SOHO
Synoptic Observations
Authors: Panasyuk, A. V.; Strachan, L.; Finesehi, S.; Gardner, L. D.;
Raymond, J.; Kohl, J. L.; Antonucci, E.; Giordano, S.; Romoli, M.
Bibcode: 1998ASPC..140..407P
Altcode: 1998ssp..conf..407P
No abstract at ADS
Title: UVCS/SOHO: The First Two Years
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.
Bibcode: 1998sce..conf..341C
Altcode:
No abstract at ADS
Title: UVCS observations of polar regions
Authors: Poletto, G.; Corti, G.; Romoli, M.; Kohl, J. L.; Noci, G.
Bibcode: 1998ESASP.421...69P
Altcode: 1998sjcp.conf...69P
In order to facilitate the interpretation of UVCS data, the first
section of this paper gives a short summary of the mechanisms of line
formation in the extended corona and of the diagnostic techniques
adopted to analyze UVCS observations. This allows us to interpret, in
a semiqualitative way, the morphology of polar regions, as revealed
by UVCS, which are next illustrated. Results of data analysis,
i.e. densities, kinetic temperatures and flow speeds at heliocentric
distances between 1.5 and 3.5 Rsun are then discussed. The
ensuing scenario has a strong impact on the theories of heating
and acceleration of the solar wind plasma: we briefly outline the
theoretical implications emerging from UVCS results and the theories
which may comply with the observational requirements.
Title: The Impact of UVCS/SOHO Observations on Models of Ion-Cyclotron
Resonance Heating of the Solar Corona
Authors: Cranmer, Steven R.; Field, George B.; Kohl, John L.
Bibcode: 1998ASPC..154..592C
Altcode: 1998csss...10..592C
We examine the compatibility between theoretical models and observations
of the temperatures and anisotropic velocity distributions of hydrogen
and minor ions in the solar corona. The UVCS instrument on board SOHO
has measured hydrogen kinetic temperatures along lines of sight in
coronal holes in excess of 3 x 106 K, and O^{+5} ion kinetic
temperatures of at least 2 x 108 K. In addition, the velocity
distributions in the radial direction (mainly perpendicular to the
line of sight) are smaller, possibly implying temperature anisotropies
of order Tperp / Tparallel ~ 100 for the oxygen
ions. These properties can be understood only in terms of a mechanism
which heats and/or accelerates heavier ions more than lighter ones
(possibly proportionally to mionalpha, where
alpha >~ 1), and preferentially in directions perpendicular to the
magnetic field. We examine various features of plasma heating by the
dissipation of high-frequency ion-cyclotron resonance Alfven waves,
which may be the most natural physical mechanism to produce such
plasma conditions. We show that a quantitative model should predict
the spectrum of waves required to reproduce the observations.
Title: Absolute Cross Section for Electron Impact Excitation of
Ground State Si2+
Authors: Reisenfeld, D. B.; Janzen, P. H.; Gardner, L. D.; Savin,
D. W.; Kohl, J. L.
Bibcode: 1998lss..work..219R
Altcode:
No abstract at ADS
Title: The white light polarimeter of SOHO/UVCS
Authors: Romoli, M.; Benna, C.; Fineschi, S.; Gardner, L. D.; Kohl,
J. L.; Noci, G.
Bibcode: 1998MmSAI..69..703R
Altcode:
No abstract at ADS
Title: Comparison of SPARTAN and UVCS/SOHO observations.
Authors: Dobrzycka, D.; Strachan, L.; Miralles, M. P.; Kohl, J. L.;
Gardner, L. D.; Smith, P. L.; Cranmer, S. R.; Guhathakurta, M.;
Fisher, R.
Bibcode: 1998ASPC..154..601D
Altcode:
The authors present a comparison of the H I Lyα Spartan Ultraviolet
Coronal Spectrometer observations of the north and south polar coronal
holes in 1993 - 1995 with SOHO Ultraviolet Coronograph Spectrometer
data obtained near solar minimum. These data span several years of
the declining phase of the current solar cycle. Detailed analysis of
the data revealed that the average H I Lyα intensities at similar
heights decreased towards solar minimum in both polar coronal hole
regions. In 1993 the authors observed a 15% - 40% scatter in the
intensities measured at the same height but different position angles
within the same coronal hole. Towards solar minimum the scatter was
clearly reduced. Also the shape of the Lyα profile changed over
the last four years. The narrow component present in 1993 data being
attributed to the contribution from streamers along the line-of-sight
disappeared in 1996/97. They interpret these effects as mainly due to
a decrease in the number of high latitude streamers. At solar minimum
streamers occupy mostly the equatorial region and do not contribute
to the line-of-sight intensity as much as in 1993.
Title: Ultraviolet Spectroscopy of a Coronal Mass Ejection
Authors: Ciaravella, A.; Raymond, J. C.; Fineschi, S.; Romoli,
M.; Benna, C.; Gardner, L.; Giordano, S.; Michels, J.; O'Neal, R.;
Antonucci, E.; Kohl, J.; Noci, G.
Bibcode: 1998ASPC..150..370C
Altcode: 1998npsp.conf..370C; 1998IAUCo.167..370C
No abstract at ADS
Title: Absolute Cross Section for Electron Impact Excitation of
Metastable Si2+
Authors: Janzen, P. H.; Reisenfeld, D. B.; Gardner, L. D.; Kohl, J. L.
Bibcode: 1998lss..work..169J
Altcode:
No abstract at ADS
Title: Comparison of SPARTAN and UVCS/SOHO Observations
Authors: Dobrzycka, D.; Strachan, L.; Miralles, M. P.; Kohl, J. L.;
Gardner, L. D.; Smith, P. L.; Cranmer, S. R.; Guhathakurta, M.;
Fisher, R.
Bibcode: 1998ASPC..154..607D
Altcode: 1998csss...10..607D
We present a comparison of the H 1 Lyalpha Spartan Ultraviolet Coronal
Spectrometer observations of the north and south polar coronal holes in
1993-1995 with SOHO Ultraviolet Coronograph Spectrometer data obtained
near solar minimum. These data span several years of the declining phase
of the current solar cycle. Detailed analysis of the data revealed that
the average H 1 Lyalpha intensities at similar heights decreased towards
solar minimum in both polar coronal hole regions. In 1993 we observed
a 15% - 40% scatter in the intensities measured at the same height but
different position angles within the same coronal hole. Towards solar
minimum the scatter was clearly reduced. Also the shape of the Lyalpha
profile changed over the last four years. The narrow component present
in 1993 data being attributed to the contribution from streamers along
the line-of-sight disappeared in 1996/97. We interpret these effects as
mainly due to a decrease in the number of high latitude streamers. At
solar minimum streamers occupy mostly the equatorial region and do
not contribute to the line-of-sight intensity as much as in 1993.
Title: Elemental Abundances in Coronal Structures
Authors: Raymond, J.; Suleiman, R.; Kohl, J. L.; Noci, G.
Bibcode: 1998sce..conf..283R
Altcode:
No abstract at ADS
Title: Velocity Fields in the Solar Corona during Mass Ejections as
Observed with UVCS-SOHO
Authors: Antonucci, E.; Kohl, J. L.; Noci, G.; Tondello, G.; Huber,
M. C. E.; Gardner, L. D.; Nicolosi, P.; Giordano, S.; Spadaro, D.;
Ciaravella, A.; Raymond, C. J.; Naletto, G.; Fineschi, S.; Romoli, M.;
Siegmund, O. H. W.; Benna, C.; Michels, J.; Modigliani, A.; Panasyuk,
A.; Pernechele, C.; Smith, P. L.; Strachan, L.; Ventura, R.
Bibcode: 1997ApJ...490L.183A
Altcode:
This Letter presents the observations of the first two coronal mass
ejections (CMEs) obtained with the Ultraviolet Coronagraph Spectrometer
of SOHO. Both CMEs were observed at high spectral resolution in the
ultraviolet domain. The first event on 1996 June 6-7 was observed in H I
Lyα λ1216 and Lyβ λ1026, O VI λλ1032 and 1037, Si XII λλ499 and
521 and imaged within 1.5 and 5 Rsolar. The second event on
1996 December 23 was observed in several H I lines and cool lines such
as C III λ977, N III λλ990-992, and O V λ630. The analysis of line
profiles has allowed us to determine the line-of-sight velocities of the
extended corona during a mass ejection. In particular there is evidence
for mass motions consistent with untwisting magnetic fields around an
erupted flux tube in one of the events and line of sight velocities of
200 km s-1 in the early phase of the second event presumably
related to the expansion of the leading arch of the transient.
Title: Solar Wind Acceleration in the Solar Corona
Authors: Giordano, S.; Antonucci, E.; Benna, C.; Kohl, J. L.; Noci,
G.; Michels, J.; Fineschi, S.
Bibcode: 1997ESASP.415..327G
Altcode: 1997cpsh.conf..327G
No abstract at ADS
Title: Determination of 3D Coronal Structures from UVCS/SOHO Synoptic
Observations
Authors: Strachan, L.; Panasyuk, A. V.; Fineschi, S.; Gardner, L. D.;
Raymond, J. C.; ANtonucci, E.; Giordano, S.; Romoli, M.; Noci, G.;
Kohl, J. L.
Bibcode: 1997ESASP.415..539S
Altcode: 1997cpsh.conf..539S
No abstract at ADS
Title: Ultraviolet Coronagraph Spectrometer Observations of Density
Fluctuations in the Solar Wind
Authors: Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.
Bibcode: 1997ApJ...491L.111O
Altcode:
Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light
channel (WLC) observations on board the Solar and Heliospheric
Observatory (SOHO) indicate quasi-periodic variations in the
polarized brightness (pB) in the polar coronal holes. This is
the first observation of possible signatures of compressional
waves high above the limb (at heliocentric distances in the range
1.9-2.45 Rsolar). The Fourier power spectrum of the
pB time series at 1.9 Rsolar shows significant peak
at about 6 minutes and possible fluctuations on longer timescales
(20-50 minutes). The observation at 1.9 Rsolar is the only
currently available WLC data set with sufficient cadence to resolve
the 6 minute period. These preliminary observations may result from
density fluctuations caused by compressional waves propagating in
polar coronal holes. We stress that our results are preliminary, and
we plan future high-cadence observations in both plume and interplume
regions of coronal holes. Recently, Ofman & Davila used a 2.5 D
MHD model and found that Alfvén waves with an amplitude of 20-70 km
s-1 at the base of the coronal hole can generate nonlinear,
high-amplitude compressional waves that can contribute significantly to
the acceleration of the fast solar wind. The nonlinear solitary-like
waves appear as fluctuations in the density and the radial outflow
velocity and contribute significantly to solar wind acceleration
in open magnetic field structures. The motivation for the reported
observations is the MHD model prediction.
Title: A User's Guide to UVCS/SOHO
Authors: Kohl, J. L.; Noci, G.; Cranmer, S. R.; Fineschi, S.; Gardner,
L. D.; Halas, C. D.; Smith, P. L.; Strachan, L.; Suleiman, R. M.
Bibcode: 1997AAS...191.7309K
Altcode: 1997BAAS...29Q1322K
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is currently
being used to observe the extended solar corona between 1 and 10
heliocentric radii. In its first two years of operation, UVCS/SOHO
has made spectroscopic measurements leading to the determination of
densities, velocities, temperatures, and elemental abundances in coronal
holes, equatorial streamers, and coronal mass ejections. Observations
of selected non-solar targets, such as near-ecliptic stars, planets,
comets, and interplanetary hydrogen and helium, have also produced
interesting astronomical results. This poster presents a brief
review of the UVCS/SOHO spectroscopic and polarimetric diagnostic
capabilities, highlighted by pertinent observational data. Most
importantly, we summarize the procedures that have been designed
to allow UVCS/SOHO data to be used by a wide array of researchers,
and invite participation in this unique investigation. Scientists
interested in UVCS/SOHO observations are encouraged to fill
out the ``Get Involved'' questionnaire located on the WWW at:
http://cfa-www.harvard.edu/uvcs/ This work is supported by the National
Aeronautics and Space Administration under grant NAG5-3192 to the
Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana,
and by Swiss funding agencies.
Title: Ultraviolet Observations of Coronal Mass Ejections
Authors: Ciaravella, A.; Raymond, J. C.; Benna, C.; Fineschi, S.;
Gardner, L. D.; Giordano, S.; O'Neal, R. H.; Reale, F.; Romoli, M.;
Michels, J.; Antonucci, E.; Kohl, J. L.; Noci, G.
Bibcode: 1997ESASP.415..543C
Altcode: 1997cpsh.conf..543C
No abstract at ADS
Title: Ultraviolet Coronagraph Spectrometer Observation of the 1996
December 23 Coronal Mass Ejection
Authors: Ciaravella, A.; Raymond, J. C.; Fineschi, S.; Romoli,
M.; Benna, C.; Gardner, L.; Giordano, S.; Michels, J.; O'Neal, R.;
Antonucci, E.; Kohl, J.; Noci, G.
Bibcode: 1997ApJ...491L..59C
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar
and Heliospheric Observatory (SOHO) observed a spectacular coronal
mass ejection (CME) caused by a prominence eruption on 1996 December
23. The evolution of the ejected prominence material was followed for
1 hr and 50 minutes. The observation consists of a series of 5 minute
exposures, at a fixed heliocentric distance of 1.5 Rsolar
in several spectral ranges. The Lyman lines of hydrogen brighten
more than 2 orders of magnitude during the CME. The C III 977.02 Å
line is very bright, and many other low-temperature lines have been
detected. Line intensities and profiles provide important diagnostics
for the physical and dynamical parameters of the ejected plasma. Lines
widths show nonthermal line broadening due to a plasma expansion with
velocity larger than 50 km s-1. The Lyα inside the CME
region shows red and blue shifts, up to 0.2 Å (50 km s-1)
and 0.8 Å (200 km s-1), respectively. A preliminary estimate
shows a flat emission measure distribution 3 or 4 orders of magnitude
smaller than typical prominence emission measures. Essentially the same
structure in space and velocity is seen in the Lyman lines, in C III
(105 K) and in O VI (3×105 K).
Title: Absolute Abundances in Streamers from UVCS
Authors: Raymond, J. C.; Suleiman, R. M.; van Ballegooijen, A. A.;
Kohl, J. L.
Bibcode: 1997ESASP.415..383R
Altcode: 1997cpsh.conf..383R
The Ultraviolet Coronagraph Spectrometer on SOHO covers the 940-1350
Angstrom range as well as the 470-630 Angstrom range in second
order. It has detected coronal emission lines of H, N, O, Mg, Al, Si,
S, Ar, Ca, Fe and Ni in coronal streamers. We are able to determine
the ionization state and the absolute elemental abundances in the
gas. There is a strong First Ionization Potential (FIP) dependence in
the abundances. Oxygen is depleted relative to hydrogen, by a full order
of magnitude for oxygen in the center of a quiescent streamer. Here, we
extend the earlier work by considering greater heights in the streamer
and by estimating the projection effects (the line of sight passing
through the streamer edges). We suggest that the FIP fractionation
occurs in the chromosphere, but that in addition gravitational settling
produces an overall depletion at large heights in the closed-field
region. We present numerical results of diffusion models.
Title: The Impact of UVCS/SOHO Observations on Models of Ion-Cyclotron
Resonance Heating of the Solar Corona
Authors: Cranmer, S. R.; Field, G. B.; Noci, G.; Kohl, J. L.
Bibcode: 1997ESASP.415...89C
Altcode: 1997cpsh.conf...89C
No abstract at ADS
Title: The Impact of Ion-Cyclotron Wave Dissipation on Minor Ion
Velocity Distributions in the Solar Corona
Authors: Cranmer, S. R.; Field, G. B.; Noci, G.; Kohl, J. L.
Bibcode: 1997AAS...191.7411C
Altcode: 1997BAAS...29.1325C
We present theoretical models of the acceleration and heating
of minor ions in the solar wind, as well as detailed anisotropic
velocity distribution functions computed numerically by solving the
Boltzmann transport equation. We examine the compatibility between
these models and spectroscopic measurements of the velocities
and kinetic temperatures of various particle species in the solar
corona. The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO)
has measured hydrogen kinetic temperatures in polar coronal holes in
excess of 3 million K, and O VI ion kinetic temperatures of at least
200 million K. In addition, the velocity distributions parallel to
the open magnetic field are smaller than those perpendicular to the
field, possibly implying temperature anisotropy ratios of order 100
for minor ions. We examine various features of plasma heating by the
dissipation of high-frequency ion-cyclotron resonance Alfven waves,
which may be the most natural physical mechanism to produce the
observed plasma conditions. The modeled ion velocity distributions
depend sensitively on the assumed amplitudes and frequencies of the
waves, and these computations can be used to accurately predict many
quantitative features of the wave power spectrum. Indeed, the more
ionic species that are observed spectroscopically, the greater the
extent in frequency space the wave spectrum can be inferred. This work
is supported by the National Aeronautics and Space Administration
under grant NAG5-3192 to the Smithsonian Astrophysical Observatory,
by Agenzia Spaziale Italiana, and by Swiss funding agencies.
Title: Origins of the Slow and the Ubiquitous Fast Solar Wind
Authors: Habbal, S. R.; Woo, R.; Fineschi, S.; O'Neal, R.; Kohl, J.;
Noci, G.; Korendyke, C.
Bibcode: 1997ApJ...489L.103H
Altcode: 1997astro.ph..9021H
We present in this Letter the first coordinated radio occultation
measurements and ultraviolet observations of the inner corona below
5.5Rs, obtained during the Galileo solar conjunction in
1997 January, to establish the origin of the slow solar wind. Limits
on the flow speed are derived from the Doppler dimming of the
resonantly scattered component of the oxygen 1032 and 1037.6 Å
lines as measured with the ultraviolet coronagraph spectrometer
(UVCS) on the Solar and Heliospheric Observatory (SOHO). White light
images of the corona from the large-angle spectroscopic coronagraph
(LASCO) on SOHO taken simultaneously are used to place the Doppler
radio scintillation and ultraviolet measurements in the context of
coronal structures. These combined observations provide the first
direct confirmation of the view recently proposed by Woo & Martin
that the slow solar wind is associated with the axes, also known as
stalks, of streamers. Furthermore, the ultraviolet observations also
show how the fast solar wind is ubiquitous in the inner corona and
that a velocity shear between the fast and slow solar wind develops
along the streamer stalks.
Title: Composition of Coronal Streamers from the SOHO Ultraviolet
Coronagraph Spectrometer
Authors: Raymond, J. C.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Gardner, L. D.; Nicolosi, P.; Fineschi,
S.; Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.; Ciaravella,
A.; Cranmer, S.; Giordano, S.; Karovska, M.; Martin, R.; Michels, J.;
Modigliani, A.; Naletto, G.; Panasyuk, A.; Pernechele, C.; Poletto,
G.; Smith, Peter L.; Suleiman, R. M.; Strachan, L.
Bibcode: 1997SoPh..175..645R
Altcode:
The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers
the 940-1350 Å range as well as the 470-630 Å range in second
order. It has detected coronal emission lines of H, N, O, Mg, Al, Si,
S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance
scattering of emission lines from the solar disk dominates the
intensities of a few lines, but electron collisional excitation produces
most of the lines observed. Resonance, intercombination and forbidden
lines are seen, and their relative line intensities are diagnostics
for the ionization state and elemental abundances of the coronal gas.
Title: First Results from the SOHO Ultraviolet Coronagraph
Spectrometer
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Gardner, L. D.; Nicolosi, P.; Strachan, L.; Fineschi, S.;
Raymond, J. C.; Romoli, M.; Spadaro, D.; Panasyuk, A.; Siegmund,
O. H. W.; Benna, C.; Ciaravella, A.; Cranmer, S. R.; Giordano, S.;
Karovska, M.; Martin, R.; Michels, J.; Modigliani, A.; Naletto, G.;
Pernechele, C.; Poletto, G.; Smith, P. L.
Bibcode: 1997SoPh..175..613K
Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being
used to observe the extended solar corona from 1.25 to 10 R⊙ from
Sun center. Initial observations of polar coronal holes and equatorial
streamers are described. The observations include measurements of
spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å,
Mgx 625 Å, Fexii 1242 Å and several others. Intensities for Mgx
610 Å, Sixii 499 Å, and 520 Å, Sx 1196 Å, and 22 others have been
observed. Preliminary results for derived H0, O5+,
Mg9+, and Fe11+ velocity distributions and initial
indications of outflow velocities for O5+ are described. In
streamers, the H0 velocity distribution along the line of
sight (specified by the value at e-1, along the line of
sight) decreases from a maximum value of about 180 km s-1
at 2 R⊙ to about 140 km s-1 at 8 R⊙. The value for
O5+ increases with height reaching a value of 150 km
s-1 at 4.7 R⊙. In polar coronal holes, the O5+
velocity at e-1 is about equal to that of H0
at 1.7 R⊙ and significantly larger at 2.1 R⊙. The O5+
in both streamers and coronal holes were found to have anisotropic
velocity distributions with the smaller values in the radial direction.
Title: Empirical Models of the Extended Solar Corona
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Ciaravella, A.;
Cranmer, S.; Dobrzycka, D.; Fineschi, S.; Gardner, L. D.; Huber,
M. C. E.; Panasyuk, A.; Raymond, J. C.; Strachan, L.
Bibcode: 1997SPD....28.0303K
Altcode: 1997BAAS...29..907K
Ultraviolet spectroscopy is being used to produce self consistent
empirical models of polar coronal holes and equatorial streamers in the
extended solar corona. The models are intended to provide experimental
values for many of the primary plasma parameters of the extended corona,
which can then be used to constrain theoretical coronal and solar
wind models. The empirical models are based on synoptic observations
and other measurements of spectral line profiles and intensities of
H I Lyalpha , O VI 1032 Angstroms and 1037 Angstroms, Fe XII 1242
Angstroms, Mg X 625 Angstroms and several others. Information about
velocity distributions, outflow velocities, densities and elemental
abundances as derived from the observations are specified in the
models. The models used to specify the empirically derived parameters
include a description of well established theoretical processes such
as those controlling ionization balance, collisional excitation,
and resonant scattering. They do not include any descriptions of
less well established processes such as heating functions, transverse
wave motions or direct momentum deposition by waves. The intent is to
provide, to the maximum extent possible, empirical descriptions that
can be used, together with theoretical models, to help identify the
dominant physical processes responsible for coronal heating, solar wind
acceleration and the chemical composition of the solar wind. This work
is supported by NASA Grant NAG5-3192 to the Smithsonian Astrophysical
Observatory, the Italian Space Agency and Swiss funding sources.
Title: UVCS/SOHO Synoptic Observations of the Extended Corona during
the Whole Sun Month Campaign
Authors: Strachan, L.; Fineschi, S.; Gardner, L. D.; Panasyuk, A. V.;
Kohl, J. L.; Antonucci, E.; Giordano, S.; Romoli, M.
Bibcode: 1997SPD....28.0122S
Altcode: 1997BAAS...29..883S
Daily synoptic observations were made with UVCS/SOHO during the Whole
Sun Month (10 August to 8 September 1996) in order to characterize
the large-scale spatial distributions of plasma parameters in the
solar corona from 1.5 to 3 solar radii. We use observed line profiles
and intensities of H I Lyman alpha and O VI 1032/1037 Angstroms,
and white light polarized brightness measurements to derive physical
properties of the plasma in the solar wind acceleration region. Line of
sight velocity distributions and bulk outflow velocities for neutral
hydrogen and for O({5) +}, and electron densities can be derived from
these measurements. We show some results from the on-going effort and
present some of these data as synoptic maps. The ultimate goal of this
work is to produce a data set that can be used in developing empirical
models that describe the solar minimum conditions of the extended
corona. This work is supported by NASA under Grant NAG5-3192 to the
Smithsonian Astrophysical Observatory, by the Italian Space Agency,
and by Swiss funding sources.
Title: Absolute Elemental Abundances in Streamers
Authors: Raymond, J. C.; Kohl, J.; Suleiman, R.; Ciaravella, A.;
Fineschi, S.; Gardner, L.; Panasyuk, A.; Strachan, L.; Noci, G.;
Antonucci, E.; Nicolosi, P.; Naletto, G.; Giordano, S.; Benna, C.
Bibcode: 1997SPD....28.0114R
Altcode: 1997BAAS...29..881R
The UVCS instrument aboard the SOHO satellite has measured the
intensities of emission lines of H, N, O, Mg, Al, S, Ar, Ca ,Fe and Ni
at 1.5 solar radii in a quiescent equatorial helmet streamer and in an
active region streamer. The First Ionization Potential (FIP) effect is
clearly seen. Low FIP elements show nearly photospheric abundances above
the active region and along the edges of the equatorial streamer, while
high FIP elements are depleted by a factor of 2-3. Near the center of
the streamer, presumably the closed field region, the low-FIP elements
are at about 1/3 photospheric abundances, and the high FIP elements
are near 1/10 their photospheric values.
Title: Expansion Factors in Coronal Holes and Plume/Interplume
UVCS Observations
Authors: Poletto, G.; Corti, G.; Noci, G.; Kohl, J.; Suess, S.
Bibcode: 1997SPD....28.0108P
Altcode: 1997BAAS...29..880P
We show that expansion factors in plumes and coronal hole areas devoid
of plumes are nearly equal because the plasma beta is <<1. Hence,
the overall coronal hole expansion factor is equal to the expansion
factors of its densest structures. UVCS plume and interplume
observations of coronal holes are illustrated, with the purpose of
showing the data capabilities. Integration along the line of sight,
through a medium containing high and low pressure regions, and the
rapid decrease with heliocentric distance of plume intensity, presently
hinder an observational determination of the expansion factors between
1.5 and 2 solar radii.
Title: Comparison of SPARTAN and UVCS/SOHO Observations
Authors: Dobrzycka, D.; Strachan, L.; Kohl, J. L.; Gardner, L. D.;
Smith, P. L.; Cranmer, S. R.; Guhathakurta, M.; Fisher, R.
Bibcode: 1997EOSTr..78..242D
Altcode:
Three SPARTAN flights in 1993, 1994, and 1995 provided us with
observations of HI Lyman alpha in the south and north polar coronal
hole regions. These data span several years of the declining phase of
the current solar cycle. We analyzed the data using various diagnostic
techniques and obtained strong constraints on the geometry of coronal
holes, electron density distributions, hydrogen velocity distributions
and outflow velocities. We compare SPARTAN HI Lyman alpha observations
with UVCS/SOHO data obtained in solar minimum to characterize changes
of the plasma parameters in the polar coronal holes over a four year
period. This work is supported by NASA under Grant NAG 5-613 to the
Smithsonian Astrophysical Observatory and by NASA under Grant NAG5-3192
to the Smithsonian Astrophysical Observatory, by the Italian Space
Agency, and by Swiss Funding Agencies.
Title: Evidence for Nonradial Solar Wind Acceleration in Magnetostatic
Coronal Holes
Authors: Cranmer, S. R.; Strachan, L.; Romoli, M.; Dobrzycka, D.;
Panasyuk, A. V.; Kohl, J. L.
Bibcode: 1997EOSTr..78..258C
Altcode:
We compare UVCS/SOHO observations of densities and outflow velocities
in polar coronal holes with theoretical mass-conservation models of an
idealized force-free magnetostatic geometry. Open flux tubes bordering
the closed-field streamer belt initially expand much more rapidly than
flux tubes over the poles, then turn nearly radial and expandless
rapidly. In the past, this variation in the super radial expansion
factor has been inversely correlated with solar wind velocity at 1 AU,
but we find an even stronger inverse correlation in the acceleration
region of the solar wind (1 to 10 solar radii). A considerable
reduction in the wind speed of low-latitude flux tubes, compared with
those over the poles, results in a geometry-dependent variation in the
Doppler dimming of UV resonance lines such as H I Lyman alpha. Thus,
we are able to use these emission diagnostics not only to infer the
magnitude of the solar wind velocity, but also to map out the geometry
of the solar wind emerging from large polar coronal holes. This work is
supported by NASA under Grant NAG5-3192 to the Smithsonian Astrophysical
Observatory, by the Italian Space Agency, and by Switzerland.
Title: Optical performances of the Ultraviolet Coronagraph
Spectrometer of the Solar Heliospheric Observatory
Authors: Pernechele, Claudio; Naletto, Giampiero; Nicolosi,
Piergiorgio; Tondello, Giuseppe; Fineschi, Silvano; Romoli, Marco;
Noci, Giancarlo; Spadaro, Daniele; Kohl, John L.
Bibcode: 1997ApOpt..36..813P
Altcode:
No abstract at ADS
Title: Plume and interplume regions and solar wind acceleration in
polar coronal holes between 1.5 and 3.5 R
Authors: Giordano, S.; Antonucci, E.; Benna, C.; Romoli, M.; Noci,
G.; Kohl, J. L.; Fineschi, S.; Michels, J.; Naletto, G.
Bibcode: 1997ESASP.404..413G
Altcode: 1997cswn.conf..413G
No abstract at ADS
Title: Ultraviolet spectroscopy of a coronal mass ejection with UVCS
Authors: Ciaravella, A.; Raymond, J.; Fineschi, S.; Romoli, M.; Benna,
C.; Gardner, L.; Giordano, S.; O'Neal, R.; Michels, J.; Antonucci,
E.; Noci, G.; Kohl, J.
Bibcode: 1997ESASP.404..279C
Altcode: 1997cswn.conf..279C
No abstract at ADS
Title: Intercomparison between UVCS/WLC and LASCO/C2 measured
polarized brightness
Authors: Romoli, M.; Biesecker, D.; Benna, C.; Fineschi, S.; Lamy,
P. L.; Llebaria, A.; Kohl, J. L.; Noci, G.
Bibcode: 1997ESASP.404..637R
Altcode: 1997cswn.conf..637R
No abstract at ADS
Title: Signature of open magnetic field lines in the extended solar
corona and of solar wind acceleration
Authors: Antonucci, E.; Giordano, S.; Benna, C.; Kohl, J. L.; Noci,
G.; Michels, J.; Fineschi, S.
Bibcode: 1997ESASP.404..175A
Altcode: 1997cswn.conf..175A
No abstract at ADS
Title: KCorona polarized brightness and electron density measurement
with the visible light polarimeter of UVCS
Authors: Romoli, M.; Benna, C.; Cranmer, S.; Fineschi, S.; Gardner,
L. D.; Strachan, L.; Kohl, J. L.; Noci, G.
Bibcode: 1997ESASP.404..633R
Altcode: 1997cswn.conf..633R
No abstract at ADS
Title: UVCS/SOHO empirical models of solar coronal holes
Authors: Cranmer, S. R.; Kohl, J. L.; Noci, G.; Strachan, L.;
Panasyuk, A. V.; Romoli, M.; Fineschi, S.; Dobrzycka, D.; Raymond,
J. C.; Suleiman, R. M.; O'Neal, R. H.
Bibcode: 1997ESASP.404..295C
Altcode: 1997cswn.conf..295C
No abstract at ADS
Title: Possible Signatures of Nonlinear MHD Waves in the Solar Wind:
UVCS Observatio ns and Models
Authors: Ofman, L.; Romoli, M.; Davila, J. M.; Poletto, G.; Kohl,
J.; Noci, G.
Bibcode: 1997ESASP.404..571O
Altcode: 1997cswn.conf..571O
No abstract at ADS
Title: Spectroscopic observations of the extended corona during the
SOHO whole sun month
Authors: Strachan, L.; Raymond, J. C.; Panasyuk, A. V.; Fineschi,
S.; Gardner, L. D.; Antonucci, E.; Giordano, S.; Romoli, M.; Noci,
G.; Kohl, J. L.
Bibcode: 1997ESASP.404..691S
Altcode: 1997cswn.conf..691S
No abstract at ADS
Title: First Results from UVCS: Dynamics of the Extended Corona
Authors: Antonucci, E.; Noci, G.; Kohl, J. L.; Tondello, G.; Huber,
M. C. E.; Giordano, S.; Benna, C.; Ciaravella, A.; Fineschi, S.;
Gardner, L. D.; Martin, R.; Michels, J.; Naletto, G.; Nicolosi, P.;
Panasyuk, A.; Raymond, C. J.; Romoli, M.; Spadaro, D.; Strachan, L.;
van Ballegooijen, A.
Bibcode: 1997ASPC..118..273A
Altcode: 1997fasp.conf..273A
The Ultraviolet Coronagraph Spectrometer (UVCS) started to observe
the Sun at the end of January 1996. Here we present a selection of
results obtained with the UVCS in the first months of operation. UV
spectral line profiles in coronal holes, and in general in regions
with open magnetic field lines, are much broader than in closed
field line regions; that is, line-of-sight velocities are much
larger in open field lines . Polar plumes have narrower profiles
than interplume regions. The O VI ratio diagnostics indicates that in
polar coronal holes the outflow velocity is progressively increasing
with heliodistance and exceeds 100 km/sec near 2--2.5 solar radii. A
coronal mass ejection observation has revealed line--of--sight plasma
motions of 100 km/sec and a complex dynamics.
Title: SOHO observations of the north polar solar wind
Authors: Peres, G.; Ciaravella, A.; Betta, R.; Orlando, S.; Reale,
F.; Kohl, J.; Noci, G.; Fineschi, S.; Romoli, M.; Brekke, P.; Fludra,
A.; Gurman, J. B.; Lemaire, P.; Schuhle, U.
Bibcode: 1997ESASP.404..587P
Altcode: 1997cswn.conf..587P
No abstract at ADS
Title: First results from UVCS/SOHO
Authors: Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Fineschi, S.; Gardner, L. D.; Naletto, G.; Nicolosi, P.;
Raymond, J. C.; Romoli, M.; Spadaro, D.; Siegmund, O. H. W.; Benna, C.;
Ciaravella, A.; Giordano, S.; Michels, J.; Modigliani, A.; Panasyuk,
A.; Pernechele, C.; Poletto, G.; Smith, P. L.; Strachan, L.
Bibcode: 1997AdSpR..20.2219N
Altcode:
We present here the first results obtained by the Ultraviolet
Coronagraph Spectrometer (UVCS) operating on board the SOHO
satellite. The UVCS started to observe the extended corona at the end
of January 1996; it routinely obtains coronal spectra in the 1145 A˚ -
1287 A˚, 984 A˚ - 1080 A˚ ranges, and intensity data in the visible
continuum. Through the composition of slit images it also produces
monocromatic images of the extended corona. The performance of the
instrument is excellent and the data obtained up to now are of great
interest. We briefly describe preliminary results concerning polar
coronal holes, streamers and a coronal mass ejection, in particular: the
very large r.m.s. velocities of ions in polar holes (hundreds km/sec
for OVI and MgX); the puzzling difference between the HI Ly-alpha
image and that in the OVI resonance doublet, for most streamers; the
different signatures of the core and external layers of the streamers
in the width of the ion lines and in the OVI doublet ratio, indicating
larger line-of-sight (l.o.s.) and outflow velocities in the latter.
Title: Physical Parameters in Plume and Interplume Regions from
UVCS Observations
Authors: Corti, G.; Poletto, G.; Romoli, M.; Michels, J.; Kohl, J.;
Noci, G.
Bibcode: 1997ESASP.404..289C
Altcode: 1997cswn.conf..289C
No abstract at ADS
Title: The quiescent corona and slow solar wind
Authors: Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Fineschi, S.; Gardner, L. D.; Korendyke, C. M.; Nicolosi,
P.; Romoli, M.; Spadaro, D.; Maccari, L.; Raymond, J. C.; Siegmund,
O. H. W.; Benna, C.; Ciaravella, A.; Giordano, S.; Michels, J.;
Modigliani, A.; Naletto, G.; Panasyuk, A.; Pernechele, C.; Poletto,
G.; Smith, P. L.; Strachan, L.
Bibcode: 1997ESASP.404...75N
Altcode: 1997cswn.conf...75N; 1997soho....5...75N
No abstract at ADS
Title: UV spectroscopy of the extended solar corona: Results from
UVCS/Spartan
Authors: Strachan, Leonard; Gardner, Larry D.; Smith, Peter L.; Kohl,
John L.
Bibcode: 1997AIPC..385..113S
Altcode: 1997recs.conf..113S
Remote sensing of the solar corona using ultraviolet spectroscopy can
be used to characterize the physical state of the plasma along a wide
region around the trajectory of a near-Sun flyby spacecraft (solar
probe). Data from such an instrument can be used to separate spatial
from temporal variations in the data received from in situ instruments
aboard the probe. We present results from the UVCS/Spartan space
shuttle missions in order to show examples of diagnostic techniques
that can be used to determine velocity distributions and bulk outflow
velocities of protons and minor ions in the solar wind.
Title: Stray light, radiometric, and spectral characterization of
UVCS/SOHO: laboratory calibration and flight performance
Authors: Gardner, Larry D.; Kohl, J. L.; Daigneau, P. S.; Dennis,
E. F.; Fineschi, Silvano; Michels, J.; Nystrom, George U.;
Panasyuk, Alexander; Raymond, John C.; Reisenfeld, D. J.; Smith,
Peter L.; Strachan, Leonard; Suleiman, R.; Noci, G. C.; Romoli, Marco;
Ciaravella, A.; Modigliani, A.; Huber, Martin C.; Antonucci, E.; Benna,
C.; Giordano, S.; Tondello, Giuseppe; Nicolosi, Piergiorgio; Naletto,
Giampiero; Pernechele, Claudio; Spadaro, D.; Siegmund, Oswald H.;
Allegra, A.; Carosso, Paolo A.; Jhabvala, Murzy D.
Bibcode: 1996SPIE.2831....2G
Altcode:
The Ultraviolet Coronagraph Spectrometer is one of the instruments
on board the Solar and Heliospheric Observatory spacecraft, which
was launched in December, 1995. The instrument is designed to make
ultraviolet spectrometric measurements and visible polarimetric
measurements of the extended solar corona. Prior to launch laboratory
measurements were carried out to determine system level values for
many of the key performance parameters. Further measurements on
instrument performance have been carried out since launch. Presented
are descriptions of measurement techniques and representative results.
Title: Measurement of Hydrogen Velocity Distributions in the Extended
Solar Corona
Authors: Kohl, J. L.; Strachan, L.; Gardner, L. D.
Bibcode: 1996ApJ...465L.141K
Altcode:
H I Ly alpha spectral line profiles have been measured in polar
regions of the solar corona at projected heliocentric heights of
1.8--3.5 Rsolar. Observations were made with the Ultraviolet Coronal
Spectrometer on the Spartan 201 satellite from 16:52 to 04:04 UT on
1993 April 11--12 (south pole) and from 12:28 to 22:09 UT on 1993
April 12 (north pole). In general, the coronal profiles cannot be
accurately curve-fitted with a single-Gaussian function. The fits
with two Gaussians yield most probable velocities of 158 and 322 km
s-1 (south) and 98 and 266 km s-1 (north). These parameters vary by
less than 10% (1 sigma ) over the observed heights. The observations
are consistent with a line-of-sight model that attributes the narrow
component to background streamers and to sites within polar coronal
holes or a surrounding diffuse corona, and the broad component to
the polar coronal holes and/or plumes. This interpretation suggests
that there are regions within the observed coronal holes that have
hydrogen and proton kinetic temperatures of (4--6) x 106 K, which is
4--10 times higher than the expected electron temperatures at the same
heights. However, other models with, for example, local non-Maxwellian
velocity distributions are also consistent with the observations.
Title: Coordinated SOHO Observations of Polar Plumes
Authors: Deforest, C. E.; Scherrer, P. H.; Tarbell, T.; Harrison,
R. A.; Fludra, A.; Delaboudiniere, J. P.; Gurman, J. B.; Wilhelm,
K.; Lemaire, P.; Hassler, D. M.; Kohl, J. L.; Noci, G.; Fineschi,
S.; Brueckner, G. E.; Howard, R. A.; Cyr, O. C. St.
Bibcode: 1996AAS...188.4909D
Altcode: 1996BAAS...28R.898D
On 7 and 8 March 1996, SOHO instruments engaged in their first
joint science operation, a 12-hr observation of polar plumes
over the South polar coronal hole. The observing mini-campaign
included observations from SOHO, other spacecraft, and ground-based
observatories. Contributing SOHO instruments -- in order of altitude,
MDI, CDS, SUMER, EIT, UVCS, and LASCO -- made overlapping, simultaneous
observations of plume structures from the photosphere out to the
LASCO C3 limit of 32 solar radii. MDI provided line-of-sight surface
magnetograms with a one-min cadence and 0.6 arcsec resolution;
CDS, SUMER, and EIT supplied temperature-sensitive images of the
lower corona with varying cadences and resolutions; UVCS measured
fluctuations in Ly B intensity across the coronal hole with a one-min
cadence at 1.4 R0; and LASCO imaged the entire corona out to 30 R0 in
various visible passbands. Plume footpoints in the lower corona are
observed by EIT and CDS to vary by a factor of two in EUV brightness
with a timescale of tens of minutes, while the structures above are
(as as been previously observed) quiescent on at least a ten-hr time
scale. We present preliminary results of cross-instrument analysis
of the observed plumes, and suggest how this and similar future data
sets can be used to constrain quiet-sun wind acceleration and coronal
heating models for the coronal hole. This research is supported by
the SOI-MDI NASA contract NAG5-3077 at Stanford University. SOHO is
project of international cooperation between NASA and ESA.
Title: In-Flight Performance of the SOHO Ultraviolet Coronagraph
Spectrometer
Authors: Gardner, L. D.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Ciaravella, A.; Fineschi, S.; Giordano,
S.; Moran, T.; Naletto, G.; Nicolosi, P.; Romoli, M.; Strachan,
L.; Benna, C.; Pernechele, C.; Raymond, J. C.; Siegmund, O. H. W.;
Spadaro, D.; Smith, P. L.
Bibcode: 1996AAS...188.3705G
Altcode: 1996BAAS...28..878G
The in-flight performance of the SOHO Ultraviolet Coronagraph
Spectrometer (UVCS/SOHO) is consistent with the pre-launch
characterization and meets all planned observational
requirements. Measurements of the key UVCS/SOHO performance
characteristics have been performed. This paper describes the
measurement techniques and the results. In-flight values for the
spectral and spatial resolutions, wavelength scales, the flat
fields, the geometric distortions, radiometric calibrations,
and stray light levels for the two ultraviolet channels have been
determined. Comparisons will be made to pre-flight measurements at both
the component level and system level. This work is supported by NASA
under contract NAS5-31250 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Switzerland.
Title: Spectroscopic Diagnostic Techniques with the SOHO Ultraviolet
Coronagraph Spectrometer
Authors: Romoli, M.; Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello,
G.; Huber, M. C. E.; Fineschi, S.; Karovska, M.; Moran, T.; Strachan,
L.; Ciaravella, A.; Benna, C.; Gardner, L. D.; Giordano, S.; Naletto,
G.; Nicolosi, P.; Raymond, J. C.; Siegmund, O. H. W.; Spadaro, D.;
Smith, P. L.
Bibcode: 1996AAS...188.3703R
Altcode: 1996BAAS...28R.877R
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) uses
spectroscopic diagnostic techniques and polarimetry to determine
velocity distributions, temperatures, outflow velocities and densities
of protons, electrons, and several minor ions in the extended solar
corona. This paper describes the initial use of these techniques with
UVCS/SOHO. Velocity distributions are derived from the observed spectral
line profiles. In some cases, grating scans are used to improve the
spectral resolution. The Doppler dimming method is used to determine
radial outflow velocities and spectral line shifts are used for line of
sight velocity measurements. The electron densities are derived from
visible polarized radiance measurements. The status of attempts to
derive electron temperatures from observations of electron scattered
HI Lyman-alpha will be presented. This research is supported by NASA
Contract NAS5-31250 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Switzerland.
Title: Ultraviolet Imaging of the Extended Solar Corona with the
SOHO Ultraviolet Coronagraph Spectrometer
Authors: Noci, G.; Kohl, J. L.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Strachan, L.; Giordano, S.; Panasyuk, A.; Benna, C.;
Ciaravella, A.; Fineschi, S.; Gardner, L. D.; Naletto, G.; Nicolosi,
P.; Raymond, J. C.; Romoli, M.; Siegmund, O. H. W.; Spadaro, D.;
Smith, P. L.
Bibcode: 1996AAS...188.3701N
Altcode: 1996BAAS...28..877N
Spectroscopic observations of the extended solar corona with the SOHO
Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) can be used to produce
images of the extended solar corona in several ultraviolet spectral
lines. The images are produced by scanning coronal images across the
spectrometer entrance slits. The slits intercept a 40 arcminute slice of
the corona parallel to the limb tangent. Telescope mirror motions can
be used to scan from about 1.25 to 10 R_⊙. The instrument is rolled
about its Sun-center axis to obtain images of the full corona. The
spatial resolution depends on the selected slit width and the combined
resolution of the spectrometer and XDL detectors. It is limited by
diffraction for observations near the Sun where only a narrow strip of
the telescope mirror is unvignetted by the external occulter. Images
of equatorial streamers in HI Lyman-alpha and beta, and in O VI 103.2
nm will be presented. Ultraviolet images of polar plumes will also be
provided. In some cases, interpolation techniques are used to fill-in
gaps in the raster pattern. This research is supported by NASA Contract
NAS5-31250 to the Smithsonian Astrophysical Observatory, by the Italian
Space Agency and by Switzerland.
Title: Coordinated SOHO Observations of Polar Plumes: Ultraviolet
Spectroscopy with UVCS
Authors: Fineschi, S.; Kohl, J. L.; Noci, G.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Gardner, L. D.; Giordano, S.; Romoli,
M.; Benna, C.; Ciaravella, A.; Naletto, G.; Nicolosi, P.; Raymond,
J. C.; Siegmund, O. H. W.; Spadaro, D.; Smith, P. L.; Strachan, L.
Bibcode: 1996AAS...188.3704F
Altcode: 1996BAAS...28..877F
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) observed polar
plumes at the south polar coronal hole on 7 March 1996. Observations
were made in H I Ly-alpha, Ly-beta and O VI 103.2 and 103.7
nm. Heliocentric heights from 1.5 to 3.2 R_⊙ were observed. In
addition, HI Ly-alpha observations with 60 sec time resolution were
obtained at a heliocentric height of 1.6 solar radii. The polar plumes
are clearly distinguishable in both H I Ly-alpha and O VI. These
measurements were made in coordination with time resolved magnetograms
by the Michelson Doppler Imager (MDI) and time resolved XUV images
by the Extreme-Ultraviolet Imaging Telescope (EIT). This work is
supported by NASA Contract NAS5-31250 to the Smithsonian Astrophysical
Observatory, by the Italian Space Agency and by Switzerland.
Title: First Results from the SOHO Ultraviolet Coronagraph
Spectrometer
Authors: Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello, G.; Huber,
M. C. E.; Benna, C.; Ciaravella, A.; Fineschi, S.; Gardner, L. D.;
Giordano, S.; Karovska, M.; Michels, J.; Naletto, G.; Nicolosi, P.;
Poletto, G.; Pernechele, C.; Raymond, J. C.; Romoli, M.; Siegmund,
O. H. W.; Spadaro, D.; Smith, P. L.; Strachan, L.
Bibcode: 1996AAS...188.4906K
Altcode: 1996BAAS...28R.897K
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used
to observe the extended solar corona from 1.25 to 10 R_⊙ from Sun
center. Initial observations of polar coronal holes, polar plumes,
equatorial streamers and the diffuse mid-latitude corona will be
presented. The observations include measurements of spectral line
profiles for HI Lyman alpha and beta, and O VI 103.2 and 103.7
nm. Line intensities for Mg X 61.0 nm, Si XII 49.9 and 52.0 nm,
S X 119.6 nm, Fe XII 124.2 nm and several other minor ions have been
observed. Observations with moderate time resolution (about 1 minute) at
one strip of the corona will also be presented. Preliminary results for
derived proton and O VI velocity distributions and initial indications
of outflow velocities for protons, and O VI will be discussed as
well as preliminary results for other spectroscopic diagnostics
techniques. This research is supported by NASA Contract NAS5-31250 to
the Smithsonian Astrophysical Observatory, by the Italian Space Agency
and by Switzerland.
Title: Coronal Emission Lines with UVCS
Authors: Raymond, J. C.; Noci, G.; Kohl, J. L.; Antonucci, E.;
Tondello, G.; Huber, M. C. E.; Benna, C.; Ciaravella, A.; Fineschi, S.;
Gardner, L. D.; Giordano, S.; Naletto, G.; Nicolosi, P.; Romoli, M.;
Siegmund, O. H. W.; Spadaro, D.; Smith, P. L.; Strachan, L.; Martin, R.
Bibcode: 1996AAS...188.3702R
Altcode: 1996BAAS...28Q.877R
The Ultraviolet Coronagraph Spectrometer aboard the SOHO satellite has
observed the extended solar corona in H I Lyalpha and O VI lines for
coronal diagnostics, but other, fainter, lines are also present. We
discuss a spectral atlas obtained from emission in equatorial streamers
and above solar active regions, pointing out lines which are especially
useful for determining the elemental abundances, ionization state,
and density of the emitting plasma. This work is supported by NASA
under contract NAS5-31250 to the Smithsonian Astrophysical Observatory.
Title: Intercalibration and Co-Registration of the LASCO, UVCS and
SUMER instruments on SOHO
Authors: Michels, J.; Kohl, J. L.; Noci, G.; Antonucci, E.; Tondello,
G.; Huber, M. C. E.; Curdt, W.; Hollandt, J.; Lemaire, P.; Schuhle,
U.; Wilhelm, K.; Korendyke, C.; Moran, T.; Raymond, J. C.; Romoli,
M.; Benna, C.; Ciaravella, A.; Fineschi, S.; Gardner, L. D.; Giordano,
S.; Naletto, G.; Nicolosi, P.; Siegmund, O. H. W.; Spadaro, D.; Smith,
P. L.; Strachan, L.
Bibcode: 1996AAS...188.3706M
Altcode: 1996BAAS...28..878M
Joint observations of equatorial streamers by three SOHO instruments
have been used for radiometric intercalibration, co-registration and
other spectroscopic comparisons. The results are used to track the
stability of the radiometric calibrations of the Ultraviolet Coronagraph
Spectrometer (UVCS) and the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) experiment at overlapping wavelenghs. Observations
of equatorial streamers at heliocentric heights from 1.25 to 1.5
R_⊙ are used for the intercalibrations. The results are compared to
pre-launch laboratory calibrations and to observations of stars. The
first stellar observation was for 38 AQI. These UV observations are
compared to coronal green line (Fe XIV) observations obtained with the
Large Angle Spectrometric Coronagraph (LASCO) C1 coronagraph obtained
in the same time frame. Intercomparisons of spectral line profiles
among LASCO, SUMER, and UVCS are also planned. The LASCO research is
supported by NASA Grant NDPR S92835D; the UVCS research is supported by
NASA Contract NAS5-31250 to the Smithsonian Astrophysical Observatory,
by the Italian Space Agency and by Switzerland, and SUMER is financially
supported by BMFT/DARA, CNES, NASA and PRODEX (Swiss Contribution).
Title: New atomic data for the FeXII coronal ion
Authors: Binello, A. M.; Mason, H. E.; Storey, P. J.; Kohl, J.
Bibcode: 1996ASPC..109..251B
Altcode: 1996csss....9..251B
No abstract at ADS
Title: Proton Temperatures, Electron Temperatures and Outflows in
the Extended Solar Corona.
Authors: Kohl, J. L.; Gardner, L. D.; Strachan, L.; Cohen, C. M. S.;
Galvin, A. B.; Gloeckler, G.; Guhathakurta, M.; Fisher, R. R.; Ko,
Y. -K.; Geiss, J.; von Steiger, R.
Bibcode: 1996ASPC..109...99K
Altcode: 1996csss....9...99K
No abstract at ADS
Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory
Authors: Kohl, J. L.; Esser, R.; Gardner, L. D.; Habbal, S.; Daigneau,
P. S.; Dennis, E. F.; Nystrom, G. U.; Panasyuk, A.; Raymond, J. C.;
Smith, P. L.; Strachan, L.; Van Ballegooijen, A. A.; Noci, G.;
Fineschi, S.; Romoli, M.; Ciaravella, A.; Modigliani, A.; Huber,
M. C. E.; Antonucci, E.; Benna, C.; Giordano, S.; Tondello, G.;
Nicolosi, P.; Naletto, G.; Pernechele, C.; Spadaro, D.; Poletto, G.;
Livi, S.; Von Der Lühe, O.; Geiss, J.; Timothy, J. G.; Gloeckler,
G.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.;
Fowler, W.; Fisher, R.; Jhabvala, M.
Bibcode: 1995SoPh..162..313K
Altcode:
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of
three reflecting telescopes with external and internal occultation and
a spectrometer assembly consisting of two toric grating spectrometers
and a visible light polarimeter. The purpose of the UVCS instrument is
to provide a body of data that can be used to address a broad range
of scientific questions regarding the nature of the solar corona and
the generation of the solar wind. The primary scientific goals are
the following: to locate and characterize the coronal source regions
of the solar wind, to identify and understand the dominant physical
processes that accelerate the solar wind, to understand how the coronal
plasma is heated in solar wind acceleration regions, and to increase the
knowledge of coronal phenomena that control the physical properties of
the solar wind as determined byin situ measurements. To progress toward
these goals, the UVCS will perform ultraviolet spectroscopy and visible
polarimetry to be combined with plasma diagnostic analysis techniques
to provide detailed empirical descriptions of the extended solar corona
from the coronal base to a heliocentric height of 12 solar radii.
Title: Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory: instrument description and calibration
overview
Authors: Kohl, J. L.; Esser, R.; Gardner, Larry D.; Habbal, S.;
Daigneau, P. S.; Nystrom, George U.; Raymond, John C.; Strachan,
Leonard; van Ballegooijen, A. A.; Noci, G.; Fineschi, Silvano; Romoli,
Marco; Ciaravella, A.; Modigliani, A.; Huber, Martin C.; Antonucci, E.;
Benna, C.; Giordano, S.; von der Luehe, Oskar; Tondello, Giuseppe;
Nicolosi, Piergiorgio; Naletto, Giampiero; Pernechele, Claudio;
Geiss, J.; Gloeckler, G.; Poletto, G.; Spadaro, D.; Allegra, A.;
Basile, G.; Brusa, R.; Wood, B.; Siegmund, Oswald H.
Bibcode: 1995SPIE.2517...40K
Altcode:
The SOHO ultraviolet coronagraph spectrometer (UVCS/SOHO) is
composed of three reflecting telescopes with external and internal
occultation and a spectrometer assembly consisting of two toric grating
spectrometers and a visible light polarimeter. The UVCS will perform
ultraviolet spectroscopy and visible polarimetry to be combined with
plasma diagnostic analysis techniques to provide detailed empirical
descriptions of the extended solar corona from the coronal base to a
heliographic height of 12 R. In this paper, the salient features of
the design of the UVCS instrument are described. An overview of the
UVCS test and calibration activities is presented. The results from
the calibration activity have demonstrated that the UVCS can achieve
all its primary scientific observational goals.
Title: Determining coronal electron temperatures from observations
with UVCS/SOHO
Authors: Fineschi, S.; Esser, R.; Habbal, S. R.; Karovska, M.; Romoli,
M.; Strachan, L.; Kohl, J. L.; Huber, M. C. E.
Bibcode: 1995sowi.confQ..68F
Altcode:
The electron temperature is a fundamental physical parameter of the
coronal plasma. Currently, there are no direct measurements of this
quantity in the extended corona. Observations with the Ultraviolet
Coronagraph Spectrometer (UVCS) aboard the upcoming Solar and
Heliospheric Observatory (SOHO) mission can provide the most direct
determination of the electron kinetic temperature (or, more precisely,
the electron velocity distribution along the line of sight). This
measurement is based on the observation of the Thomson-scattered Lyman
alpha (Ly-alpha) profile. This observation is made particularly
challenging by the fact that the integrated intensity of the
electron-scattered Ly-alpha line is about 103 times fainter
than that of the resonantly-scattered Ly-alpha component. In addition,
the former is distributed across 50 A (FWHM), unlike the latter that
is concentrated in 1 A. These facts impose stringent requirements on
the stray-light rejection properties of the coronagraph/spectrometer,
and in particular on the requirements for the grating. We make use of
laboratory measurements of the UVCS Ly-alpha grating stray-light, and of
simulated electron-scattered Ly-alpha profiles to estimate the expected
confidence levels of electron temperature determination. Models of
different structures typical of the corona (e.g., streamers, coronal
holes) are used for this parameter study.
Title: Spectroscopic diagnostics of extended corona and solar wind
with UVCS/Spartan
Authors: Strachan, L.; Gardner, L. D.; Kohl, J. L.
Bibcode: 1995sowi.conf...29S
Altcode:
The primary goal of the Ultraviolet Coronal Spectrometer on Spartan 201
(UVCS/Spartan) is to make spectroscopic diagnostic measurements that can
be used to derive plasma parameters in the extended solar corona where
it is believed that significant heating of the corona and acceleration
of the solar wind take place. Direct and indirect measurements of
particle velocity distribution, thermal and non-thermal temperatures,
and bulk outflow velocities are crucial to aid in the identification
of physical processes that may be responsible for coronal heating
and solar wind acceleration. UVCS/Spartan has made two flights in
April 1993 and September 1994, the latter coinciding with the South
Polar Passage of the Ulysses spacecraft. Observations were made of
the large-scale structures and sub-structures of coronal holes and
streamers at heliocentric heights between 1.5 solar radii and 3.5
solar radii. Measurements were made of H I Lyman-alpha intensities
and profiles, and line intensities of minor ions like O(5+) and
Fe(11+). We will present results from the flights and discuss how
these measurements are used to constrain values for the proton thermal
and non-thermal kinetic temperatures, proton bulk outflow velocities,
and minor ion temperatures and bulk outflow velocities. Plans for the
upcoming flight in July 1995 will also be discussed.
Title: SPARTAN 201 Coronal Spectroscopy During the Polar Passes
of ULYSSES
Authors: Kohl, J. L.; Gardner, L. D.; Strachan, L.; Fisher, R.;
Guhathakurta, M.
Bibcode: 1995SSRv...72...29K
Altcode:
Spartan 201 is a shuttle deployed spacecraft that is scheduled to
perform ultraviolet spectroscopy and white light polarimetry of the
extended solar corona during two 40 hour missions to occur in September
1994 and August 1995. The spectroscopy is done with an ultraviolet
coronal spectrometer which measures the intensity and spectral line
profile of HI Lyα up to heliocentric heights of 3.5 solar radii. It
also measures the intensities of the OVI doublet at 1032 and 1037
Å and of Fe XII at 1242 Å. The HI Lyα line profile measurements
are used to determine the random velocity distribution of coronal
protons along the line-of-sight. The absolute HI Lyα intensities
can be used together with electron densities from the white light
coronagraph to estimate electron temperatures from hydrogen ionization
balance calculations, and bulk outflow velocities from models of
Doppler dimmed resonant scattering. Intensities of minor ion lines
are used to determine coronal abundances and outflow velocities of
O5+. Ultraviolet spectroscopy of extended coronal regions
from the 11 April 1993 mission of Spartan 201 are discussed.
Title: New Results for Outflow and LOS Velocities in the Solar Wind
Acceleration Region of the Corona
Authors: Strachan, L.; Gardner, L. D.; Kohl, J. L.; Guhathakurta,
M.; Fisher, R. R.; Cohen, C. M. S.; Galvin, A. B.; Gloeckler, G.;
Ko, Y. -K.; Geiss, J.; von Steiger, R.
Bibcode: 1995SPD....26..719S
Altcode: 1995BAAS...27..970S
No abstract at ADS
Title: The Ultraviolet Coronagraph Spectrometer for the Solar and
Hellospheric Observatory
Authors: Raymond, J. C.; Kohl, J. L.; Esser, R.; Gardner, L. D.;
Habbal, S.; Strachan, L.; van Ballegooijen, A. A.; Noci, G.; Fineschi,
S.; Romoli, M.; Huber, M. C. E.; Antonucci, E.; Benna, C.; von der
Luhe, O.; Naletto, G.; Nicolosi, P.; Pernechele, C.; Tondello, G.;
Geiss, J.; Gloeckler, G.; Spadaro, D.; Daigneau, P. S.; Nystrom,
G. U.; Allegra, A.; Basile, G.; Brusa, R.; Wood, B.; Siegmund, O. H. W.
Bibcode: 1995SPD....26..720R
Altcode: 1995BAAS...27..970R
No abstract at ADS
Title: Absolute-rate coefficient for C3 + (2s --> 2p)
electron-impact excitation
Authors: Savin, D. W.; Gardner, L. D.; Reisenfeld, D. B.; Young,
A. R.; Kohl, J. L.
Bibcode: 1995PhRvA..51.2162S
Altcode:
We have measured the absolute-rate coefficient for
electron-impact excitation (EIE) of C3+(2s
2S1/2-->2p 2P1/2,3/2)
for energies near threshold. A delayed coincidence technique with
inclined beams was used. Radiation from the excited ions was detected
using an optical system that subtends slightly over π steradians. At
an ion-rest-frame energy of 10.10 eV the measured rate coefficient
was (7.79+/-2.10)×10-8 cm3 s-1
and the measured cross section was (4.15+/-1.12)×10-16
cm2. The uncertainties quoted here represent the total
experimental uncertainty, statistical and systematic, at a confidence
level considered to be equivalent to a statistical 90% confidence
level. Good agreement is found with other measurements. Agreement
is not good with Coulomb-Born with exchange and two-state
close-coupling calculations, both of which fall outside our 90%
confidence limits. Nine-state close-coupling calculations are in
better agreement. However, the calculations lie at the extreme edge
of our uncertainty limits. Taking into account previous measurements
of EIE in C3+ and also a measurement of EIE in Li-like
Be+ that falls significantly below theory at threshold, there
is a suggestion that the C3+(2s-->2p) EIE rate coefficient
near threshold may fall slightly below presently accepted values.
Title: The Ultraviolet Coronagraph Spectrometer
Authors: Noci, G.; Kohl, J. L.; Huber, M. C. E.; Antonucci, E.;
Fineschi, S.; Gardner, L. D.; Naletto, G.; Nicolosi, P.; Raymond,
J. C.; Romoli, M.; Spadaro, D.; Strachan, L.; Tondello, G.; van
Ballegooijen, A.
Bibcode: 1995LNP...444..261N
Altcode: 1995cmer.conf..261N
The Ultraviolet Coronagraph Spectrometer (UVCS) is an instrument onboard
the Solar and Heliospheric (SOHO) spacecraft, a joint ESA/NASA mission
to be launched in 1995. The UVCS will provide ultraviolet spectroscopic
measurements to determine the primary plasma parameters of the solar
corona (temperatures, densities, velocities), from its base to as high
as 10 R⊙. We review briefly, here, its science objectives
and give an instrument description.
Title: SPARTAN 201 Coronal Spectroscopy During the Polar Passes
of ULYSSES
Authors: Kohl, J. L.; Gardner, L. D.; Strachan, L.; Fisher, R.;
Guhathakurta, M.
Bibcode: 1995hlh..conf...29K
Altcode:
No abstract at ADS
Title: UVCS Science from SOHO
Authors: Antonucci, E.; Kohl, J. L.; Noci, G.; Huber, M. C. E.;
Fineschi, S.; Gardner, L. D.; Naletto, G.; Nicolosi, P.; Pernechele,
C.; Raymond, J. C.; Romoli, M.; Spadaro, Daniele; Strachan, L.;
Tondello, G.; van Ballegooijen, A.
Bibcode: 1995jena.conf...80A
Altcode:
The ultraviolet Coronagraph Spectrometer (UVCS), to be launched on
board SOHO in 1995, has been designed to determine the primary plasma
parameters in order to obtain a far more complete description of the
coronal plasma than presently exists. This will be accomplished by
obtaining ultraviolet spectroscopic observations in some EUV lines (HI
Ly Alpha, O VI, Mg X, Si XII, Fe XII) and in the visible continuum,
form the base of the solar corona to as high as 12 solar radii. The
profiles and intensities of the measured UV lines are sensitive
to effective temperature of protons, minor ions and electrons; ion
densities; chemical abundances; and outflow velocities of protons and
ions into the solar wind. The electron density is determined by means
of white light observations. The UVCS data will be used to address a
broad range of scientific questions concerning the nature of the solar
corona and the generation of the solar wind. The primary scientific
objectives are in fact those of identifying the source regions of the
slow and fast solar wind, understanding the dominant processes that
accelerate the solar wind, and the mechanisms for heating the coronal
plasma in the extended corona.
Title: UVCS/SOHO capability for determining coronal conditions before,
during and after CMEs
Authors: Strachan, L.; Raymond, J. C.; Kohl, J. L.; Noci, G.;
Antonucci, E.; Tondello, G.; Huber, M. C. E.; Fineschi, S.; Gardner,
L. D.; Nicolosi, P.; Romoli, M.
Bibcode: 1994ESASP.373..421S
Altcode: 1994soho....3..421S
No abstract at ADS
Title: Ly-alpha and white light observations of a CME during the
Spartan 201-1 mission
Authors: Hassler, D. M.; Strachan, L.; Gardner, L. D.; Kohl, J. L.;
Guhathakurta, M.; Fisher, R. R.; Strong, K.
Bibcode: 1994ESASP.373..363H
Altcode: 1994soho....3..363H
No abstract at ADS
Title: Polarization characterization of LY alpha holographic gratings
with a triple-reflection polarizer
Authors: Romoli, Marco; Fineschi, Silvano; Gardner, Larry D.; Kohl,
J. L.
Bibcode: 1994SPIE.2283..288R
Altcode:
The diffraction efficiency of holographic gratings depends on the
degree and orientation of the linear polarization of the incident
light. A test has been run to measure the reflectance efficiency at Kr
1236 angstrom of two holographic gratings in the orders +1, 0, $min1,
as a function of the angle of the incident beam polarization plane. To
this purpose, a triple-reflection polarizer, optimized for Ly(alpha)
(1216 angstrom) has been fabricated and characterized. The test has
been run to demonstrate that the coronal resonantly scattered Ly(alpha)
can be measured using a holographic grating in the Ly(alpha) channel
of the ultraviolet coronagraph spectrograph (UVCS) of the Solar
and Heliospheric Observatory (SOHO) without introducing relevant
polarization biases inside the instrument.
Title: Ultraviolet Coronagraph Spectrometer for the Solar and
Heliospheric Observatory: optical testings
Authors: Fineschi, Silvano; Romoli, Marco; Gardner, Larry D.; Kohl,
J. L.; Noci, G.; Tondello, Giuseppe
Bibcode: 1994SPIE.2283...30F
Altcode:
The Ultraviolet Coronagraph Spectrometer (UVCS) of the Solar and
Heliospheric (SOHO) mission has been developed for spectroscopic
and polarimetric determinations of temperatures, densities and flow
velocities in the extended solar corona. The instrument consists of two
ultraviolet (UV) spectrometers and a visible light (VL) polarimeter. The
grating of the UV channel optimized for the HI Lyman (alpha) (Ly-(alpha)
) line ((lambda) 1236 angstrom) and that for the OVI doublet ((lambda)
(lambda) 1032/1037 angstrom) have been characterized.
Title: Ultraviolet spectroscopy of the extended solar corona during
the SPARTAN 201 mission
Authors: Kohl, J. L.; Gardner, L. D.; Strachan, L.; Hassler, D. M.
Bibcode: 1994SSRv...70..253K
Altcode:
The instruments on the Spartan 201 spacecraft are an Ultraviolet Coronal
Spectrometer and a White Light Coronagraph. Spartan 201 was deployed
by the Space Shuttle on 11 April 1993 and observed the extended solar
corona for about 40 hours. The Ultraviolet Coronal Spectrometer measured
the intensity and spectral line profile of HI Lyα and the intensities
of OVI 103.2 and 103.7 nm. Observations were made at heliocentric
heights between 1.39 and 3.5 R⊙. Four coronal targets were
observed, a helmet streamer at heliographic position angle 135°, the
north and south polar coronal holes, and an active region above the west
limb. Measurements of the HI Lyα geocorona and the solar irradiance
were also made. The instrument performed as expected. Straylight
suppression, spectral focus, radiometric sensitivity and background
levels all appear to be satisfactory. The uv observations are aimed at
determining proton temperatures and outflow velocities of hydrogen,
protons and oxygen ions. Preliminary results from the north polar
coronal hole observations are discussed.
Title: Preliminary results from SPARTAN 201: coronal streamer
observations
Authors: Strachan, L.; Gardner, L. D.; Hassler, D. M.; Kohl, J. L.
Bibcode: 1994SSRv...70..263S
Altcode:
The Ultraviolet Coronal Spectrometer on Spartan 201 obtained
measurements of HI Ly α line profiles and O VI λ103.2/103.7 nm
integrated intensities in a helmet streamer. Similar measurements
were made on the solar disk to characterize the incident radiation
which is the source for the resonantly scattered component of the
lines. A description of the H I Ly α observations in the streamer
will be presented. A more complete physical description of the observed
coronal regions will become available after the analysis of additional
data from coordinated observations made by visible coronagraphs and
x-ray telescopes.
Title: Coronagraphic observations and analyses of the ultraviolet
solar corona
Authors: Kohl, John L.
Bibcode: 1994sao..reptR....K
Altcode:
This status report for the period 1 October 1992 to 30 September 1994
covers the final preparation and first observations with the Spartan
Ultraviolet Coronal Spectrometer on Spartan 201-1, and the preparation
and second flight for Spartan 201-2. Both flights were fully successful
and resulted in high quality spectroscopic observations of the extended
solar corona out to 3.5 solar radii from Sun-center. The primary focus
of this report is the results from Spartan 201-1. There is also a
brief description of the evaluation of the quick look data from the
second flight. Highlights from the first flight include a discovery
that the proton velocity distribution in coronal holes is complex and
consists of a central core with elevated high velocity wings compared
to a Gaussian shape.
Title: GAUSSFIT: A Simple Way for Robust Estimate
Authors: Kohl, J. L.
Bibcode: 1994bas..conf..185K
Altcode:
No abstract at ADS
Title: SPARTAN 201 Observations of the Ultraviolet Extended Solar
Corona
Authors: Gardner, L. D.; Hassler, D. M.; Strachan, L.; Kohl, J. L.
Bibcode: 1994scs..conf..631G
Altcode: 1994IAUCo.144..631G
The instruments on the Spartan 201 spacecraft are an Ultraviolet Coronal
Spectrometer and a White Light Coronagraph. Spatan 201 observed the
extended solar corona for about 40 hours. Four coronal targets were
observed, a helmet streamer at heliographic position angle 135°,
the north and south polar coronal holes, and an active region above
the west limb. Measurements of the H I Lyα geocorona and the solar
irradiance were also made.
Title: The SPARTAN 201 Ultraviolet Coronal Spectrometer
Authors: Gardner, L. D.; Kohl, J. L.; Strachan, L.; Hassler, D. M.
Bibcode: 1993AAS...183.0801G
Altcode: 1993BAAS...25Q1300G
The Spartan 201 spacecraft, a free-flying autonomous satellite carried
into orbit, released, and then recovered by the Space Shuttle, completed
its first mission in April 1993. Spartan 201 carries two instruments:
a UV Coronagraph (Spartan/UVCS) from the Harvard-Smithsonian Center
for Astrophysics and a White Light Coronagraph from Goddard Space
Flight Center and the High Altitude Observatory. The optical system
of the Spartan/UVCS consists of an externally and internally occulted
coronagraph with two telescope mirrors coupled to a dual spectrograph
system, one of which makes line profile and intensity measurements
near lambda 1216 Angstroms. The other makes intensity measurements
of each of the OVI doublet lines at lambda lambda 1032 and 1037
Angstroms. A summary of the observations from the first mission will be
presented. We will also describe the Spartan/UVCS instrument and discuss
the instrument's characterization and flight performance. Plans for the
next mission in September 1994 will be discussed. Supported in part by
NASA Grant no. NAG 5-613 to the Smithsonian Astrophysical Observatory.
Title: SPARTAN 201 H I Lyman-Alpha Observations of a Polar Coronal
Region
Authors: Kohl, J. L.; Gardner, L. D.; Hassler, D. M.; Strachan, L.
Bibcode: 1993AAS...183.5906K
Altcode: 1993BAAS...25.1386K
Measurements of H I Lyman-alpha spectral line profiles were made during
the Spartan 201-1 Mission on 11 April 1993. The spectral resolution
elements were 0.025 nm and the spatial elements were 0.5 arc min. by
2.5 arc min. Observations were made between 1.35 and 3.5 solar radii
from sun-center. The line shapes are found to be complex. Velocity
distributions derived from the line profiles will be presented. Broad
wings on the profiles indicate proton velocity distributions that
deviate significantly from that expected in a purely Maxwellian thermal
distribution. Possible explanations for the observed high velocities
will be discussed. Supported in part by NASA Grant no. NAG 5-613 to
the Smithsonian Astrophysical Observatory.
Title: A Doppler Dimming Determination of Coronal Outflow Velocity
Authors: Strachan, Leonard; Kohl, John L.; Weiser, Heinz; Withbroe,
George L.; Munro, Richard H.
Bibcode: 1993ApJ...412..410S
Altcode:
Outflow velocities in a polar coronal hole are derived from observations
made during a 1982 sounding rocket flight. The velocity results are
derived from a Doppler dimming analysis of resonantly scattered H I
Ly-alpha. This analysis indicates radial outflow velocities of 217
km/s at 2 solar radii from sun-center with an uncertainty range of
153 to 251 km/s at a confidence level of 67 percent. These results are
best characterized as strong evidence for supersonic outflow within 2
solar radii of sun-center in a polar coronal hole. Several means for
obtaining improved accuracy in future observations are discussed.
Title: Stray-light suppression in a reflecting white-light coronagraph
Authors: Romoli, Marco; Weiser, Heinz; Gardner, Larry D.; Kohl, John L.
Bibcode: 1993ApOpt..32.3559R
Altcode: 1993ApOpt..32.3559W
An analysis of stray-light suppression in the white-light channel
of the Ultraviolet Coronagraph Spectrometer experiment for the
Solar and Heliospheric Observatory is reported. The white-light
channel consists of a reflecting telescope with external and internal
occultation and a polarimeter section. Laboratory tests and analytical
methods are used to perform the analysis. The various stray-light
contributions are classified in two main categories: the contribution
from sunlight that passes directly through the entrance aperture
and the contribution of sunlight that is diffracted by the edges of
the entrance aperture. Values of the stray-light contributions from
various sources and the total stray-light level for observations at
heliocentric heights from 1.4 to 5 solar radii are derived. Anticipated
signal-to-stray-light ratios are presented together with the effective
stray-light rejection by the polarimeter, demonstrating the efficacy
of the stray-light suppression design.
Title: Ultraviolet Coronal Spectrometer Observations During Spartan
Mission 201-1
Authors: Gardner, L. D.; Fineschi, S.; Hassler, D.; Romoli, M.;
Strachan, L.; Kohl, J. L.
Bibcode: 1993BAAS...25.1200G
Altcode:
No abstract at ADS
Title: Ultraviolet Spectroscopic Observations of Polar Coronal Holes
During Spartan Mission 201-1
Authors: Kohl, J. L.; Gardner, L. D.; Hassler, D.; Strachan, L.
Bibcode: 1993BAAS...25.1209K
Altcode:
No abstract at ADS
Title: Ultraviolet Spectroscopic Observations of a Helmet Streamer
During Spartan Mission 201-1
Authors: Strachan, L.; Gardner, L. D.; Hassler, D.; Kohl, J. L.
Bibcode: 1993BAAS...25.1209S
Altcode:
No abstract at ADS
Title: Measuring electron temperature in the extended corona.
Authors: Hassler, Donald M.; Gardner, L. D.; Kohl, John L.
Bibcode: 1992ESASP.348..375H
Altcode: 1992cscl.work..375H
The authors discuss a technique for measuring electron temperature in
the extended corona from the line profile of the electron scattered
component of coronal H I Ly-α produced by Thomson scattering of
chromospheric Ly-α emission. They present an evaluation of this
technique based on simulated measurements and discuss the subsequent
instrumental requirements necessary to make a meaningful determination
of the electron temperature. Estimates of uncertainties in the measured
electron temperature are related to critical instrument parameters
such as grating stray light suppression.
Title: "UVCS" - the Ultraviolet Coronagraph Spectrometer for SOHO.
Authors: Kohl, John L.; Noci, Giancarlo
Bibcode: 1992ESASP.348...23K
Altcode: 1992cscl.work...23K
The Ultraviolet Coronagraph Spectrometer (UVCS) will provide
spectroscopic observations of the solar corona out to 10 solar radii
from Sun-center. This capability is expected to expand greatly the
number of plasma parameters that can be specified by remote sensing
techniques. UVCS plasma diagnostic techniques are expected to provide
a sufficient number of empirically derived parameters to constrain
significantly theories of solar wind acceleration, coronal heating,
and solar wind composition. The measured line profiles and intensities
are sensitive to random velocity distributions, densities, and outflow
velocities of coronal protons, electrons, and ions.
Title: Simulated O VI Doppler dimming measurements of coronal
outflow velocities.
Authors: Strachan, Leonard; Gardner, L. D.; Kohl, John L.
Bibcode: 1992ESASP.348..121S
Altcode: 1992cscl.work..121S
The authors investigate the possibility of determining O5+
outflow velocities by using a Doppler dimming analysis of the
resonantly scattered intensities of O VI λ1031.9 and λ1037.6. The
technique is sensitive to outflow velocities, W, in the range 30 <
W < 250 km s-1 and can be used for probing regions of
the inner solar corona, where significant coronal heating and solar
wind acceleration may be occurring. These velocity measurements,
when combined with measurements of other plasma parameters (i.e.,
temperatures and densities of ions and electrons), can be used to
estimate the energy and mass flux of O5+. In particular,
it may be possible to locate where the flow changes from subsonic
to supersonic and to identify source regions for the high- and
low-speed solar wind. The velocity diagnostic technique is discussed
with emphasis placed on the requirements needed for accurate outflow
velocity determinations. Model determinations of outflow velocities
based on simulated Doppler dimming observations are presented.
Title: Measuring the Electron Scattered Component of H I Ly-α to
Determine Te
Authors: Hassler, D. M.; Gardner, L. D.; Kohl, J. L.
Bibcode: 1992AAS...180.5205H
Altcode: 1992BAAS...24R.816H
No abstract at ADS
Title: The SPARTAN Ultraviolet Coronagraph
Authors: Gardner, L. D.; Esser, R.; Habbal, S. R.; Hassler, D. M.;
Raymond, J. C.; Strachan, L.; van Ballegooijen, A. A.; Kohl, J. L.;
Fineschi, S.
Bibcode: 1992AAS...180.5202G
Altcode: 1992BAAS...24..815G
An ultraviolet coronagraph (UVC) is being prepared for a series of
orbital flights on NASA's Spartan 201 which is deployed and retrieved
by Shuttle. The Spartan 201 payload consists of the UVC and a white
light coronagraph developed by the High Altitude Observatory. Spartan
is expected to provide 26 orbits of solar observations per flight. The
first flight is scheduled for May 1993 and subsequent flights
are planned to occur at each polar passage of Ulysses (1994 and
1995). The UVC measures the intensity and spectral line profile of
resonantly scattered H I Ly-alpha and the intensities of O VI lambda
1032 and lambda 1037 at heliocentric heights between 1.3 and 3.5 solar
radii. A description of the UVC instrument, its characteristics, and the
observing program for the first flight will be presented. The initial
scientific objective is to determine the random velocity distribution
and bulk outflow velocity of coronal protons and the density and outflow
velocity of O(5+) in polar coronal holes and adjoining high latitude
streamers. This work is supported by NASA under Grant No. NAG5-613 to
the Smithsonian Astrophysical Observatory.
Title: Experimental Dielectronic Recombination Results and their
Implications for the Solar Transition Region
Authors: Savin, D. W.; Reisenfeld, D. B.; Gardner, L. D.; Young,
A. R.; Raymond, J. C.; Kohl, J. L.
Bibcode: 1992AAS...180.0516S
Altcode: 1992BAAS...24..736S
Electric and magnetic fields of the magnitudes found in the solar
atmosphere can significantly enhance dielectronic recombination (DR)
rate coefficients. An experiment to measure DR rates as a function of
the external electric field strength will be described. An initial
result for the C(3+) DR rate coefficient through the 2s-2p core
transition indicates that the DR rate for a 12 V/cm field is a factor
of 7.2+/-1.8 (1sigma ) larger than calculated zero field values. This
is a field strength comparable to the plasma microfield strength
found in the upper transition region where C(3+) is abundant. We will
present calculations showing the implications of field enhanced DR
rates on the carbon ionization balance and on observations of solar UV
emission lines. In particular, we show that the field enhanced C(3+)
DR rate could lead to as much as a factor of 4 reduction in previously
reported C(3+) fractional abundances. This requires a corresponding
increase in emission measures to match the C IV lambda 1550 Angstroms
emission line intensities observed in the Sun and late-type stars. This
work is supported by NASA under Grant NAGW-1687 to the Harvard College
Observatory.
Title: Plans for Measuring Coronal O(5+) Outflow Velocities with
SPARTAN 201
Authors: Strachan, L.; Gardner, L. D.; Kohl, J. L.
Bibcode: 1992AAS...180.5203S
Altcode: 1992BAAS...24..815S
A goal of the Spartan 201 mission is to derive outflow velocities, W,
of coronal O(5+) by using a Doppler dimming analysis of the expected
resonantly scattered intensities of OVI lambda 1031.9 and lambda
1037.6. The technique is sensitive to velocities in the range 30 <
W < 250 km s(-1) and will be used for probing regions of the inner
solar corona, between 1.3 and 3.5 Rsun, where significant
coronal heating and solar wind acceleration may be occurring. These
velocity measurements, when combined with measurements of other plasma
parameters (i.e., temperatures and densities of ions and electrons),
can be used to estimate the energy and mass fluxes of coronal ions. In
particular, it may be possible to locate where the flow changes from
subsonic to supersonic and to identify source regions for the high- and
low-speed solar wind. The velocity diagnostic technique is discussed
with emphasis placed on the requirements needed for accurate outflow
velocity determinations. Model calculations of outflow velocities
based on expected detector count rates are also presented. This work
is supported by NASA under Grant No. NAG5-613 to the Smithsonian
Astrophysical Observatory.
Title: The Ultraviolet Coronagraph Spectrometer for SOHO (UVCS)
Authors: Kohl, J. L.; Noci, G.
Bibcode: 1992AAS...180.3308K
Altcode: 1992BAAS...24..781K
The purpose of the Ultraviolet Coronagraph Spectrometer (UVCS) is to
provide information about the behavior, in the extended corona, of
the primary particles (protons and electrons) and several minor ions
(O(5+) , Mg(9+) , Si(11+) , and Fe(11+) ). Spectroscopic diagnostic
techniques will be used to determine random velocity distributions,
densities, and bulk outflow velocities for these particles. The
resulting empirical description of the extended corona can be used to
address a broad range of scientific questions regarding the nature of
the solar corona and the generation of the solar wind. The instrument
consists of an externally and internally occulted telescope assembly
and a spectrometer assembly. It has three channels whose purposes are
the following: 1) VUV spectroscopy and absolute radiometry in the 1130
to 1361 Angstroms wavelength range with spectral resolution up to 9800
and spatial resolution elements of 7" or larger, 2) EUV spectroscopy
and absolute radiometry in the 937 to 1127 Angstroms (first order) and
469 to 655 Angstroms (second order) wavelength ranges with spectral
resolution up to 12000 and the same spatial resolution as the VUV
channel, and 3) White light polarimetry with a wavelength band pass
of 4500 -- 6000 Angstroms and a single 14" by 14" spatial resolution
element. MAMA detectors provide simultaneous ultraviolet observations
of a 40' long strip (parallel to a limb tangent) of the corona. Mirror
and instrument motions allow this instantaneous field-of-view to scan
out to heliocentric heights of 10 Rsun and onto the solar
disk. This work is supported by NASA under contract NAS5-31250 to the
Smithsonian Astrophysical Observatory.
Title: On the Density and Field Sensitivities of Dielectronic
Recombination
Authors: Reisenfeld, Daniel B.; Raymond, John C.; Young, Albert R.;
Kohl, John L.
Bibcode: 1992ApJ...389L..37R
Altcode:
Dielectronic recombination dominates the recombination rates
of most ions in coronal plasmas at their temperatures of peak
concentration. Because dielectronic recombination goes by way of high nl
doubly excited levels, it is susceptible to collisional excitation and
ionization, leading to a decreased rate. On the other hand, theoretical
studies show that Stark mixing of the nl levels by a modest electric
field enhances the dielectronic recombination rate severalfold. The
ionization balance is computed here as as function of density, and it
is found that the new results require increased emission measures to
match the C IV emission line intensities observed in the sun and in
late-type stars. They also make it more difficult to interpret the
overall EUV emission line spectrum of the sun.
Title: Laboratory studies in ultraviolet solar physics
Authors: Parkinson, W. H.; Kohl, J. L.; Gardner, L. D.; Raymond,
J. C.; Smith, P. L.
Bibcode: 1991STIN...9226029P
Altcode:
The research activity comprised the measurement of basic atomic
processes and parameters which relate directly to the interpretation of
solar ultraviolet observations and to the development of comprehensive
models of the component structures of the solar atmosphere. The research
was specifically directed towards providing the relevant atomic
data needed to perform and to improve solar diagnostic techniques
which probe active and quiet portions of the solar chromosphere, the
transition zone, the inner corona, and the solar wind acceleration
regions of the extended corona. The accuracy with which the physical
conditions in these structures can be determined depends directly on
the accuracy and completeness of the atomic and molecular data. These
laboratory data are used to support the analysis programs of past and
current solar observations (e.g., the Orbiting solar Observatories,
the Solar Maximum Mission, the Skylab Apollo Telescope Mount, and the
Naval Research Laboratory's rocket-borne High Resolution Telescope
and Spectrograph). In addition, we attempted to anticipate the needs
of future space-borne solar studies such as from the joint ESA/NASA
Solar and Heliospheric Observatory (SOHO) spacecraft. Our laboratory
activities stressed two categories of study: (1) the measurement of
absolute rate coefficients for dielectronic recombination and electron
impact excitation; and (2) the measurement of atomic transition
probabilities for solar density diagnostics. A brief summary of the
research activity is provided.
Title: UV observational techniques for the extended solar corona
Authors: Kohl, J. L.; Gardner, L. D.; Huber, M. C. E.; Nicolosi,
P.; Noci, G.; Naletto, G.; Romoli, M.; Spadaro, D.; Tondello, G.;
Weiser, H.
Bibcode: 1991AdSpR..11a.359K
Altcode: 1991AdSpR..11..359K
The SOHO Ultraviolet Coronagraph Spectrometer is being developed for
spectroscopic determinations of temperatures, densities and flow
velocities in the extended solar corona. Determinations of plasma
parameters for the primary particles (electrons and protons) and for
several minor ions are planned. The techniques and instrumentation
to be used must overcome the relatively low intensity levels and
potentially high stray light levels intrinsic to observations of the
extended corona while also providing high radiometric and spectrometric
accuracy and relatively high spectral and spatial resolution. This
paper concentrates on the instrument characteristics that are required
to observe the resonantly scatter HI Lyman-alpha line at heliocentric
heights from 1 to 10 solar radii.
Title: The Spartan 201 Mission Observations of the Extended Solar
Corona
Authors: Gardner, L. D.; Kohl, J. L.; Strachan, L.; Weiser, H.;
Fisher, R.; Sime, D.
Bibcode: 1990BAAS...22..852G
Altcode:
No abstract at ADS
Title: Measurement of Dielectronic Recombination in CIV in an External
Electric Field
Authors: Young, A. R.; Gardner, L. D.; Kohl, J. L.; Raymond, J. C.;
Savin, D. W.; Reisenfeld, D. B.
Bibcode: 1990BAAS...22..799Y
Altcode:
No abstract at ADS
Title: The Ultraviolet Coronagraph Spectrometer for SOHO
Authors: Kohl, J. L.; Noci, G.
Bibcode: 1989BAAS...21..831K
Altcode:
No abstract at ADS
Title: Doppler Dimming Measurement of Solar Wind Outflow
Authors: Strachan, L.; Kohl, J. L.; Munro, R. H.; Withbroe, G. L.
Bibcode: 1989BAAS...21..840S
Altcode:
No abstract at ADS
Title: Observations of the Extended Solar Corona from a Spartan
Carrier
Authors: Gardner, L. D.; Kohl, J. L.; Weiser, H.; Fisher, R.; Sime, D.
Bibcode: 1989BAAS...21..840G
Altcode:
No abstract at ADS
Title: Coronagraph observations and analyses of the ultraviolet
solar corona
Authors: Kohl, John L.
Bibcode: 1989sao..rept.....K
Altcode:
The major activities on the Spartan Ultraviolet Coronal Spectrometer
project include both scientific and experimental/technical efforts. In
the scientific area, a detailed analysis of the previously reported
Doppler dimming of HI Ly-alpha from the July 1982 rocket flight has
determined an outflow velocity at 2 solar radii from sun center to
be between 153 and 251 km/s at 67 percent confidence. The technical
activities include, several improvements made to the instrument that
will result in enhanced scientific performance or in regaining a
capability that had deteriorated during the delay time in the launch
date. These include testing and characterizing the detector for
OVI radiation, characterizing a serrated occulter at UV and visible
wavelengths, fabricating and testing telescope mirrors with improved
edges, testing and evaluating a new array detector system, modifying the
slit mask mechanism and installing a mask in the instrument to block
the Ly-alpha resonance line when the electron scattered component is
being observed.
Title: Spectroscopic measurements of solar wind parameters near
the sun.
Authors: Kohl, J. L.; Weizer, H.; Livi, S.
Bibcode: 1989GMS....54...81K
Altcode: 1989sspp.conf...81K
Instrumentation and plasma diagnostic techniques are being developed
to obtain a detailed empirical description of solar wind acceleration
regions at heights between the coronal base and about 10 solar radii
from sun center. The instruments which are being developed for remote
sensing of the extended corona consist of an occulted telescope system
and a high resolution spectrometer. The basic design was proven on
three sounding rocket flights. Initial data on proton temperatures
and solar wind outflow velocities for heliospheric heights between
1.5 and 3.5 solar radii from sun center have been obtained.
Title: UVCS: An Ultraviolet Coronagraph Spectrometer for SOHO
Authors: Kohl, J. L.; Hartmann, L. W.; van Ballegooijen, A. A.;
Withbroe, G. L.; Rayomnd, J. C.; Weiser, H.; Noci, G.; Antonucci,
E.; Geiss, J.; Gloeckler, G.
Bibcode: 1989ESASP1104...49K
Altcode:
The UltraViolet Coronagraph Spectrometer (UVCS) of SOHO (solar
and heliospheric observatory) provides ultraviolet spectroscopic
observations of the solar corona out to ten solar radii from
suncenter. This capability is expected to greatly expand the
number of plasma parameters that can be specified by remote sensing
techniques. Plasma diagnostic techniques are expected to provide a
sufficient number of empirically derived parameters to significantly
constrain theories of solar wind acceleration, coronal heating, and
solar wind composition. The spectral line profiles and intensities
are sensitive to random velocity distributions and to the effective
temperatures of protons, minor ions, and electrons. Ion densities,
chemical abundances, and outflow velocities of coronal protons and
ions into the solar wind are also taken into consideration.
Title: UVCS: an Ultraviolet Coronagraph Spectrometer for SOHO
Authors: Kohl, J. L.; Hartmann, L. W.; van Ballegooijen, A. A.;
Withbroe, G. L.; Raymond, J. C.; Weiser, H.; Noci, G.; Antonucci,
E.; Geiss, J.; Gloeckler, G.
Bibcode: 1988sohi.rept...49K
Altcode:
The UltraViolet Coronagraph Spectrometer (UVCS) of SOHO (solar
and heliospheric observatory) provides ultraviolet spectroscopic
observations of the solar corona out to ten solar radii from
sun-center. This capability is expected to greatly expand the
number of plasma parameters that can be specified by remote sensing
techniques. Plasma diagnostic techniques are expected to provide a
sufficient number of empirically derived parameters to significantly
constrain theories of solar wind acceleration, coronal heating, and
solar wind composition. The spectral line profiles and intensities
are sensitive to random velocity distributions and to the effective
temperatures of protons, minor ions, and electrons. Ion densities,
chemical abundances, and outflow velocities of coronal protons and
ions into the solar wind are also taken into consideration.
Title: Instrument for Ultraviolet Spectroscopy of the Extended
Solar Corona
Authors: Kohl, John L.
Bibcode: 1988soae.conf...30K
Altcode:
No abstract at ADS
Title: Measurement of electron-impact excitation in boronlike carbon
Authors: Lafyatis, G. P.; Kohl, J. L.
Bibcode: 1987PhRvA..36...59L
Altcode:
The cross section for the electron-impact excitation of C(+) (2s2
2p 2P0)-(2s2p2 2D) is measured in a colliding-beams apparatus for
several collision energies near the threshold for the process. A cross
section of (1.1 + or - 0.3) x 10 to the -16th sq cm at threshold is
found. Reasonable agreement is found with close-coupling calculations.
Title: Solar Wind Diagnostics from Doppler-enhanced Scattering
Authors: Noci, Giancarlo; Kohl, John L.; Withbroe, George L.
Bibcode: 1987ApJ...315..706N
Altcode:
Solar wind ions can attain sufficient outflow speed, w, to cause line
excitation by chromospheric or transition region radiation in a nearby
line. It is shown that this extends the diagnostic possibilities of a
coronal EUV line to much larger values of w than would be possible if
pumping were limited to radiation from the same spectral line. For the
1037.6 A coronal line of O VI, the pumping effect of the chromospheric
C II 1037.0 A line is efficient for w between 100 and 250 km/s. An
approximate expression for the line ratio for a doublet of the Li or
Na isoelectronic sequences is derived, and the diagnostic capabilities
of doublet line ratios, either by themselves or combined with the
observation of other quantities, are discussed. In particular, that
the determination of doublet line ratios at several heights can be
sufficient to yield the solar wind velocity at those heights together
with a constraint on other coronal parameters.
Title: Photometry and activity of the nucleus of P/Halley at
heliocentric distances larger than 4.6 AU, pre-perihelion
Authors: Festou, M. C.; Lecacheux, J.; Kohl, J. L.; Encrenaz, T.;
Baudrand, J.
Bibcode: 1986A&A...169..336F
Altcode:
Photometric data collected during the preperihelion phase of the passage
of Comet Halley are discussed in terms of the observed brightness
variations and the rotation period of the comet. The primary data were
collected at four different terrestrial observatories. Reflected light
from the nucleus within 8 AU distance is determined to be only partially
responsible for the photometric variations, leading to the conclusion
that it is at the present time not possible to quantify the rotational
period of a comet by its photometric variations. The behavior of the
brightness variations at various distances from the sun indicated that
outbursts are not temperature dependent and that the energy released
is proportional to the energy stored at a given distance from the sun.
Title: Analysis of Coronal H i Lyman-Alpha Measurements in a Polar
Region of the Sun Observed in 1979
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.
Bibcode: 1986ApJ...307..381W
Altcode:
Measurements of the intensities and spectral line profiles of resonantly
scattered hydrogen Ly-alpha radiation have been used to determine
hydrogen kinetic temperatures and electron densities between r = 1.5
and 2.2 solar radii in a polar region of the corona observed in 1979
near solar maximum. The mean temperature, 1.8 x 10 to the 6th K, in
this region is significantly higher, by about 60 percent, than that
obtained in a similar region observed in a 1980 rocket flight. The
densities in these two polar regions are similar and are a factor
of about 4 larger than in polar coronal holes observed at solar
minimum. The flow velocities in both regions are most likely subsonic
for r less than about 4 solar radii. The results reported here support
the hypothesis that polar coronal holes observed at different times
during the solar cycle can have different temperatures, densities,
and possibly flow velocities.
Title: Concept study of a UV coronagraph spectrometer for the
pinhole-occulter facility
Authors: Kohl, J. L.
Bibcode: 1986sao..reptQ....K
Altcode:
The results of a very short study to define an Ultraviolet
Coronagraph-Spectrometer (UVCS) for the Pinhole/Occulter Facility (P/OF)
are summarized. The P/OF instrument was based on docummentation from
the Definition Phase of the Spacelab Coronographs Program which was
effectively completed in August 1980. The primary differences between
the P/OF instrument and the Spacelab experiment are the remote occulter
mask, the telescope size , and the deployable structure to accommodate
P/OF's length restrictions. Requirement for P/OF that are associated
with these features are briefly considered, but further study is need
to more fully consider the unusual implications, particularly in the
interplay between the instrument pointing and the P/OF boom control.
Title: Spacelab Lyman Alpha-White Light Coronagraph Program
Authors: Kohl, J. L.
Bibcode: 1986sao..reptR....K
Altcode:
The Spacelab Lyman Alpha Coronagraph (SLAC) of the Smithsonian
Astrophysical Observatory (SAO) and the White Light Coronagraph (WLC)
to be provided by the High Altitude Observatory (HAO) are two separate
coronagraphs which would be operated in a joint fashion during Spacelab
missions to be flown by the Space Shuttle. The two instruments would be
used to perform joint observations of solar coronal structures from 1.2
to 8.0 solar radii from sun-center in vacuum ultraviolet and visible
radiations. Temperatures, densities, and flow velocities throughout
the solar wing acceleration region of the inner solar corona were
measured. The Phase I Definition activity resulted in the successful
definition and preliminary design of the experiment/instrumentation
subsystem and associated software, ground support equipment and
interfaces to the extended required to accurately estimate the scope
of the investigation and prepare an Investigational Development Plan;
the performance of the necessary functional, operations, and safety
analyses necessary to complete the Experiment Requirements document.
Title: Bi-dimensional Observations of Several Molecules in Comet
Halley's Coma
Authors: Kohl, J. L.; Lecacheux, J.; Festou, M. C.; Picat, J. P.;
Vapillon, L.
Bibcode: 1986BAAS...18..826K
Altcode:
No abstract at ADS
Title: The Spectrophotometer of the National Observatory
Authors: Codina Landaberry, S. J.; Freitas Pacheco, J. A.; Kohl,
J. L.; Bazzanella, B.; Ribeiro, R. T.
Bibcode: 1986RMxAA..12..405C
Altcode:
No abstract at ADS
Title: The spectrophotometer of the National Observatory.
Authors: Landaberry, S. J. C.; de Freitas Pacheco, J. A.; Kohl, J. L.;
Bazzanella, B.; Ribeiro, R. T.
Bibcode: 1986RMxAA..12..405L
Altcode:
No abstract at ADS
Title: OVI Diagnostics of Solar Wind Generation
Authors: Noci, G.; Kohl, J. L.; Withbroe, G. L.
Bibcode: 1986ASSL..123...53N
Altcode: 1986shtd.symp...53N
The O VI resonance doublet is partly collisionally and partly
radiatively excited in the solar corona. In the solar wind the O VI
ions can attain sufficient outflow speed to cause excitation of the
2P1/2 level by the chromospheric C II λ1037.0 line. The
authors show that this extends the diagnostic possibilities of the O VI
resonance doublet. In particular, the determination of the intensity
ratio of the doublet lines at several heights can be sufficient to
yield the solar wind velocity at those heights and hence information
on the mechanisms of solar wind acceleration.
Title: Coronal Spectroscopy and Imaging from Spartan during the
Polar Passage of Ulysses
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Noci, G.; Munro,
R. H.
Bibcode: 1986ASSL..123...39K
Altcode: 1986shtd.symp...39K
A joint payload consisting of a UV Coronal Spectrometer and a White
Light Coronagraph is being developed for a series of flights on NASA's
Spartan carrier. Spartan, which is deployed and retrieved by Shuttle,
is intended to provide at least 27 orbits of solar observations per
mission. The first flight of this payload is planned for October 1986,
and it is anticipated that a subsequent flight will occur at each polar
passage of Ulysses. Coordinated measurements of solar wind acceleration
parameters in polar regions of the solar corona with Spartan and
'in situ' measurements of the polar wind from Ulysses will provide a
unique opportunity to establish empirical constraints on polar wind
models. Spectroscopic diagnostics to be provided by Spartan include
determinations of the electron and neutral hydrogen random velocities,
outflow velocities in the 30 to 300 km/s range and electron densities.
Title: Coronal temperatures, heating, and energy flow in a polar
region of the sun at solar maximum
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.
Bibcode: 1985ApJ...297..324W
Altcode:
The profiles of resonantly scattered Lyman-alpha coronal radiation have
been used to determine the hydrogen kinetic temperature from 1.5 to 4
solar radius from the center of the polar region of the corona observed
in 1980 at solar maximum. Hydrogen temperatures derived from the line
profiles were found to decrease with height from 1.2 million K at r =
1.5 solar radii to 600,000 K at r = 4 solar radius. Comparison of the
measured kinetic temperatures with predictions from a semiempirical
two-fluid model showed evidence of a small amount of heating or a
nonthermal contribution to the motions of coronal protons between
1.5 and 4 solar radius. The widths of the profiles confirmed an upper
limit of 110 + or - 15 km/s on the rms magnitude of the line-of-sight
component of velocities between 1.5 and 4 solar radius. Density
measurements obtained in situ in the solar wind in the ecliptic were
used to locate the sources of low speed and high-speed winds in the
polar region. An eclipse photograph of the corona at solar maximum
is provided.
Title: Evidence for Supersonic Solar Wind Velocities at 2.1
R⊙
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Zapata, C. A.;
Munro, R. H.
Bibcode: 1984BAAS...16..531K
Altcode:
No abstract at ADS
Title: Cross Section Measurement for Electron Impact Excitation of
C II
Authors: Lafyatis, G. P.; Deutsch, L. K.; Kohl, J. L.
Bibcode: 1984BAAS...16..529L
Altcode:
No abstract at ADS
Title: Measurements of Absolute Collisional Cross Sections at
Harvard-Smithsonian CFA
Authors: Kohl, J. L.; Deutsch, L. K.; Gardner, L. D.; Lafyatis, G. P.;
Young, A. R.
Bibcode: 1984uxsa.coll..179K
Altcode: 1984uxsa.conf..179K; 1984IAUCo..86..179K
No abstract at ADS
Title: Photodissociation of Neutral Free Radicals of Astrophysical
Interest
Authors: Gardner, L. D.; Graff, M. M.; Kohl, J. L.
Bibcode: 1984uxsa.coll..167G
Altcode: 1984IAUCo..86..167G; 1984uxsa.conf..167G
No abstract at ADS
Title: The Solar Wind Generation Experiment for SPARTAN Mission 201
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.
Bibcode: 1984uxsa.coll...29K
Altcode: 1984uxsa.conf...29K; 1984IAUCo..86...29K
No abstract at ADS
Title: Spectroscopic measurements of solar wind generation.
Authors: Kohl, J. L.; Withbroe, G. L.; Zapata, C. A.; Noci, G.
Bibcode: 1983NASCP.2280..47K
Altcode: 1983sowi.conf...47K
Spectroscopically observable quantities are described which are
sensitive to the primary plasma parameters of the solar wind's source
region. The method is discussed in which those observable quantities are
used as constraints in the construction of empirical models of various
coronal structures. Simulated observations are used to examine the
fractional contributions to observed spectral intensities from coronal
structures of interest which co-exist with other coronal structures
along simulated lines-of-sight. The sensitivity of spectroscopic
observables to the physical parameters within each of those structures
is discussed.
Title: New Observations of the Extended Ultraviolet Corona
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.;
Noci, G.
Bibcode: 1982BAAS...14..976K
Altcode:
No abstract at ADS
Title: Measurements of Electron Impact Excitation of C II and Si IV
Authors: Lafyatis, G. P.; Kohl, J. L.
Bibcode: 1982BAAS...14..923L
Altcode:
No abstract at ADS
Title: EUV spectroscopic plasma diagnostics for the solar wind
acceleration region
Authors: Kohl, J. L.; Withbroe, G. L.
Bibcode: 1982ApJ...256..263K
Altcode:
Possibilities are considered for probing physical conditions in the
solar corona with strong EUV resonance lines from ions such as N V, O
VI, Ne VIII, Mg X, and Si XII. Through measurements of the intensities
and profiles of EUV spectral lines with coronagraphic instrumentation
employing normal incidence reflecting optics, it is possible to
acquire information on electron, proton, and ion temperatures and
velocity distributions; electron, H I, and ion densities; mass flow
and nonthermal velocities; and chemical abundances. This information
will provide critical empirical constraints on physical processes
responsible for plasma heating, solar wind acceleration, and transport
of mass, momentum, and energy in the solar corona, as well as providing
constraints on theoretical models for solar and stellar coronae and
mass loss.
Title: Analysis of coronal H I Lyman alpha measurements from a rocket
flight on 1979 April 13
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Noci, G.; Munro,
R. H.
Bibcode: 1982ApJ...254..361W
Altcode:
It is noted that measurements of the profiles of resonantly scattered
hydrogen Lyman-alpha coronal radiation have been used in determining
hydrogen kinetic temperatures from 1.5 to 4 solar radii from sun
center in a quiet region of the corona. Proton temperatures derived
using the line widths decrease with height from 2.6 x 10 to the 6th
K at 1.5 solar radii to 1.2 x 10 to the 6th K at 4 solar radii. These
measurements, together with temperatures for lower heights determined
from earlier Skylab and eclipse data, suggest that there is a
maximum in the quiet coronal proton temperature at about 1.5 solar
radii. Comparison of measured Lyman-alpha intensities with those
calculated using a representative model for the radial variation of
the coronal electron density yields information on the magnitude of
the electron temperature gradient and suggests that the solar wind
flow was subsonic for distances less than 4 solar radii.
Title: Probing the solar wind acceleration region using spectroscopic
techniques.
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.
Bibcode: 1982SSRv...33...17W
Altcode:
Measurements of the intensities and profiles of UV and EUV spectral
lines can provide a powerful tool for probing the physical
conditions in the solar corona out to 8 R ⊙ and
beyond. We discuss here how measurements of spectral line radiation
in conjunction with measurements of the white light K-corona can
provide information on electron, proton and ion temperatures and
velocity distribution functions; densities; chemical abundances and
mass flow velocities. Because of the fundamental importance of such
information, we provide a comprehensive review of the formation of
coronal resonance line radiation, with particular emphasis on the H i
Lα line, and discuss observational considerations such as requirements
for rejection of stray light and effects of emission from the geocorona
and interplanetary dust. Finally, we summarize some results of coronal H
i Lα and white light observations acquired on sounding rocket flights.
Title: 1980 rocket coronagraph measurements of the solar wind
acceleration region.
Authors: Withbroe, G. L.; Kohl, J. L.; Munro, R. H.; Weiser, H.
Bibcode: 1982SAOSR.392A..99W
Altcode: 1982csss....2...99W
Spectroscopic measurements of temperatures, densities and flow
velocities in the solar wind acceleration region provide critical
empirical constraints on solar stellar wind theory. Preliminary results
of an analysis of H I Lyman-alpha and white light measurements made on
16 February 1980 in a polar coronal region are reported. The hydrogen
kinetic temperatures in the observed region were found to be nearly
constant with THI approximately equals 10 degrees K at
heliocentric distances between 1.5 and 4 solar radii. The outflow
velocities were found to be subsonic indicating that the critical
point in the observed region was located at r approximately greater
than 4 solar radii.
Title: Shuttle contamination effects on ultraviolet coronagraphic
observations
Authors: Kohl, J. L.; Weiser, H.
Bibcode: 1982SPIE..287...35K
Altcode:
The ultraviolet light coronagraph being developed for Shuttle by the
Harvard-Smithsonian Center for Astrophysics is described. Effects of
Shuttle contaminants on ultraviolet coronagraphic observations are
discussed and column densities for acceptable attenuation are provided
which are generally applicable to high spectral resolution measurements
in the 600 A - 1700 A spectral range.
Title: The Spacelab Lyman-Alpha and White Light Coronagraphs Program
Authors: Kohl, J. L.; Withbroe, G. L.; Weiser, H.; MacQueen, R. M.;
Munro, R. H.
Bibcode: 1981SSRv...29..419K
Altcode:
The Harvard-Smithsonian Center for Astrophysics and the High Altitude
Observatory have defined a joint coronagraphs experiment for a
future Spacelab mission. The instrumentation package would include an
ultraviolet light coronagraph to measure the intensity and profiles of
spectral lines formed between 1.2 and 8 solar radii from Sun center and
a white light coronagraph to measure the intensity and polarization
of visible light. The overall goals of the joint program are to use
new coronal plasma diagnostic techniques to understand the physical
processes and mechanisms operating in the solar corona, to understand
the acceleration of high-speed and low-speed solar wind streams and to
extrapolate this knowledge to other stars in order to help understand
the physics of stellar coronae and stellar mass loss.
Title: Ion Beam Measurements of Electron Excitation Coefficients
Authors: Kohl, J. L.; Lafyatis, G. P.; Parkinson, W. H.
Bibcode: 1981BAAS...13Q.911K
Altcode:
No abstract at ADS
Title: The Pinhole/Occulter Facility
Authors: Hudson, H. S.; Kohl, J. L.; Lin, R. P.; MacQueen, R. M.;
Tandberg-Hanssen, E.; Pabbs, J. R.
Bibcode: 1981pof..rept.....H
Altcode:
A large occulting system in space can be used for high resolution
X-ray observations and for large aperture coronagraphic observations in
visible and UV light. The X-ray observations can combine high angular
resolution in hand (10 keV) X-radiation with the high sensitivity
of a multiple pinhole camera, and can permit sensitive observations
of bremsstrahlung from nonthermal particles in the corona. The
large aperture coronagraphs have two major advantages: high angular
resolution and good photon collection. This will permit observations
of small scale structures in the corona for the first time and will
give sufficient counting rates above the coronal background rates
for sensitive diagnostic analysis of intensities and line profiles
for coronal structures in the solar wind acceleration region. The
technical basis for performing observations with a large occulting
system in these three wavelength ranges is described as well as a
pinhole/occulter facility presently being considered for Spacelab. Some
indications about future developments are included.
Title: Results of Ly-α Coronagraphic Observations Following the
1980 Eclipse
Authors: Weiser, H.; Kohl, J. L.; Munro, R. H.; Withbroe, G. L.
Bibcode: 1981BAAS...13R.913W
Altcode:
No abstract at ADS
Title: Coronal Outflow Velocities: 1980 Rocket Measurements
Authors: Munro, R. H.; Kohl, J. L.; Weiser, H.; Withbroe, G. L.
Bibcode: 1981BAAS...13..912M
Altcode:
No abstract at ADS
Title: Shuttle contamination effects on ultraviolet coronographic
observations.
Authors: Kohl, J. L.; Weiser, H.
Bibcode: 1981SPIE..287...35K
Altcode:
No abstract at ADS
Title: Solar spectral radiance and irradiance at 225.2-319.6
nanometers
Authors: Kohl, J. L.; Parkinson, W. H.; Zapata, C. A.
Bibcode: 1980ApJS...44..295K
Altcode:
Mean absolute intensities (spectral radiance) over 0.1 nm intervals
between 225.2 nm and 319.6 nm at disk center and near the limb of
the sun (mu = 0.23 + or - 0.04) are derived from the high spectral
resolution measurements published by Kohl, Parkinson, and Kurucz. The
corresponding limb-to-center ratios and spectral irradiance values are
provided. A comparison with existing measurements of solar spectral
radiance and spectral irradiance for the most part shows agreement
within the estimated error limits, although some narrow band variations
may be outside experimental errors. The contribution to the solar
constant of the 230-305 nm band is derived to be 19.7 W/square m +
or - 12%.
Title: Measurements of coronal kinetic temperatures from 1.5 to 3
solar radii
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Noyes, R. W.;
Parkinson, W. H.; Reeves, E. M.; Munro, R. H.; MacQueen, R. M.
Bibcode: 1980ApJ...241L.117K
Altcode:
A rocket-borne Lyman-alpha coronagraph has been used to make the first
measurements of the spectral line profile of resonantly scattered
hydrogen Lyman-alpha coronal radiation between 1.5 and 3 solar
radii. These data provide, for the first time, direct measurements of
coronal temperatures above 1.5 solar radii. Data were obtained in a
coronal hole, quiet region, and streamer. The widths of the profiles
from the quiet region decrease with height and correspond to a steady
decrease in hydrogen kinetic temperature, with increasing radius, from
about 2.5 million K at r = 2 solar radii to about 1 million K at r =
9 solar radii. In the coronal hole the measured line widths indicate
a kinetic temperature of 1.8 million K at r = 2.5 solar radii.
Title: Coronagraphic H I Lyman-Alpha Observations following the 1980
Solar Eclipse
Authors: Weiser, H.; Kohl, J. L.; Parkinson, W. H.; Withbroe, G. L.
Bibcode: 1980BAAS...12R.917W
Altcode:
No abstract at ADS
Title: The Spacelab Lyman-Alpha and White-Light Coronagraphs Program
Authors: Kohl, J. L.; MacQueen, R. W.; Withbroe, G. L.; Munro, R.;
Weiser, H.
Bibcode: 1980BAAS...12..793K
Altcode:
No abstract at ADS
Title: Implications of Lyman α Measurements on Coronal Electron
and Proton Temperatures between 2.0 and 4.0 R⊙
Authors: Withbroe, G. L.; Kohl, J. L.; Weiser, H.
Bibcode: 1980BAAS...12Q.917W
Altcode:
No abstract at ADS
Title: (Invited Paper) Spectroscopy of the Corona between 1 and 8
Solar Radii
Authors: Withbroe, G.; Kohl, J.
Bibcode: 1980BAAS...12..544W
Altcode:
No abstract at ADS
Title: Computer assisted performance tests of the Lyman Alpha
Coronagraph
Authors: Parkinson, W. H.; Kohl, J. L.
Bibcode: 1979hco..rept.....P
Altcode:
Preflight calibration and performance tests of the Lyman Alpha
Coronagraph rocket instrument in the laboratory, with the experiment
in its flight configuration and illumination levels near those
expected during flight were successfully carried out using a pulse
code modulation telemetry system simulator interfaced in real time to
a PDP 11/10 computer system. Post acquisition data reduction programs
developed and implemented on the same computer system aided in the
interpretation of test and calibration data.
Title: High resolution atmospheric transmission calculations down
to 28.7 km in the 200-243-nm spectral range (TE)
Authors: Cann, M. W. P.; Evans, W. F. J.; Kohl, J. L.; Kurucz, R.;
Parkinson, W. H.; Reeves, E. M.; Nicholls, Ralph W.
Bibcode: 1979ApOpt..18..964C
Altcode:
Decrease in stratospheric ozone absorption and increase in oxygen
absorption with decreasing wavelength combine to produce a window
of maximum atmospheric transmission near 210 nm. Since solar
radiation in this spectral region dissociates molecular oxygen,
the deep atmospheric penetration at this wavelength is of particular
aeronomical interest. High resolution calculations of the transmittance
down to 28.65 km were made for the 200-243-nm spectral range in this
window region, in support of a stratospheric balloon flight from Fort
Churchill in July 1974. The calculations were made by dividing the
atmosphere into layers which were chosen so that each could be assumed
homogeneous; optical depths were calculated separately for each of
these layers and then summed to obtain the over-all transmittance of the
atmosphere. Absorption by molecular oxygen (line and continuum) and by
ozone was included, as well as extinction through Rayleigh scattering
by air molecules. The calculated transmittances were combined with high
altitude (above 100-km) rocket measurements of the sun-center spectrum
and center-to-limb variations to give residual high resolution solar
spectral flux for several altitudes and solar zenith angles.
Title: Lyman Alpha Line Profiles from 1.5 to 3.0 Solar Radii.
Authors: Kohl, J. L.; Weiser, H.; Withbroe, G. L.; Munro, R. H.;
Parkinson, W. H.; Reeves, E. M.
Bibcode: 1979BAAS...11..398K
Altcode:
No abstract at ADS
Title: Comparison of Satellite and Rocket Coronal Observations around
April 13, 1979
Authors: Howard, R. A.; Michels, D. J.; Koomen, M. J.; Sheeley, N. R.,
Jr.; Kohl, J. L.; Munro, R. H.; Weiser, H.
Bibcode: 1979BAAS...11..408H
Altcode:
No abstract at ADS
Title: Lyman-α and White Light Observations of the Outer Solar
Corona.
Authors: Munro, R. H.; Kohl, J. L.; MacQueen, R. M.; Noyes, R. W.;
Parkinson, W. H.; Weiser, H.; Withbroe, G. L.
Bibcode: 1979BAAS...11..398M
Altcode:
No abstract at ADS
Title: The Rocket Lyman Alpha Coronagraph
Authors: Weiser, H.; Kohl, J. L.; Kirkham, B.
Bibcode: 1979BAAS...11..397W
Altcode:
No abstract at ADS
Title: Spectroscopic mapping of solar wind velocities
Authors: Kohl, J. L.
Bibcode: 1978clus.nasa..354K
Altcode:
During the total solar eclipse of 1970, measurements of resonantly
scattered Lyman-alpha radiation from the solar corona revealed a means
to determine temperatures and densities in the solar corona beyond 1.5
R solar radii. A natural extension of this work is to use the Solar
Probe to measure the spectral line profile of Lyman-alpha radiation
backscattered toward the Sun from coronal regions between 4 R solar
radii and 10 R solar radii. The backscattered profile would provide
unique and quantitative determinations of the outlaw velocities of
coronal material into the solar wind. Such information is of critical
importance for understanding solar-wind formation and solar-terrestrial
effects on the earth's climate. There is no known way to obtain this
information without a Solar Probe-type mission.
Title: Absolute cross section for photoionization of atomic oxygen
Authors: Kohl, J. L.; Lafyatis, G. P.; Palenius, H. P.; Parkinson,
W. H.
Bibcode: 1978PhRvA..18..571K
Altcode:
The absolute cross section for photoionization of atomic oxygen from
the 2p4 3P ground state of O(0) to the 2p3 4S ground state of O(+)
has been measured at five narrow wavelength intervals between 89.8 and
76.2 nm. The cross section near the 2p3 4S threshold is 4.5 Mb + or -
7%. Recent calculations by Taylor and Burke (1976) and by Pradhan
and Saraph (1977) are in reasonable agreement with this work. The
dipole-length results of Taylor and Burke (4.1 Mb) are in better
agreement with the experiment than their dipole-velocity results
(3.2 Mb).
Title: The Lyman alpha coronagraph.
Authors: Kohl, J. L.; Reeves, E. M.; Kirkham, B.
Bibcode: 1978nisa.symp...91K
Altcode: 1978nisa.conf...91K
No abstract at ADS
Title: Center and limb solar spectrum in high spectral resolution
225.2 NM to 319.6 NM
Authors: Kohl, John L.; Parkinson, William H.; Kurucz, Robert L.
Bibcode: 1978clss.book.....K
Altcode: 1978QB551.K63......
The atlas has been designed to fulfill the need in solar and stellar
astronomy, in aeronomy, and in space science for a convenient reference
source that provides a detailed and accurate record of the measured
solar ultraviolet spectrum in high spectral resolution for the
wavelength range from 225.2 nm to 319.6 nm. The atlas also contains
a preliminary synthetic solar spectrum with a legend for identifying
and describing the features of the synthetic spectrum. Attention is
given to aspects of instrumentation, the radiometric calibration,
the wavelength scale, background noise random fluctuations and
data filtering, intermittent noise, the observational conditions,
the experimental uncertainty, the atlas format, references, tables,
and plots.
Title: The Lyman alpha coronagraph
Authors: Kohl, J. L.; Reeves, E. M.; Kirkham, B.
Bibcode: 1977cosp.meetU....K
Altcode:
The rocket-borne Lyman alpha coronagraph (RLAC) is to be used in the
absence of a natural solar eclipse to determine coronal temperatures
from measurements of the line width of Lyman-alpha and to determine
neutral hydrogen densities of coronal material from the absolute
intensity. The coronagraph consists of a 75-cm Fastie-Ebert scanning
spectrometer with an AMR 641 photoelectric detection system, an off-axis
parabolic primary mirror, and an occulting system. A special optical
arrangement achieves rejection of radiation from the solar disk.
Title: The solar boron abundance.
Authors: Kohl, J. L.; Parkinson, W. H.; Withbroe, G. L.
Bibcode: 1977ApJ...212L.101K
Altcode:
Positive evidence for the presence of boron in the sun is reported,
and the chemical abundance of boron in the photosphere is derived from
photoelectric measurements of the solar spectrum near 2500 A obtained
with a rocketborne high-resolution spectrometer. Short sections
of the spectrum in the vicinities of the B I lines at 2496.772
and 2497.723 A are plotted. The photospheric boron abundance is
determined primarily by analyzing the solar-center spectrum near the
first of the two lines in the framework of several single-component
photospheric models. The logarithmic boron abundance obtained is 2.6,
with an estimated uncertainty of plus or minus 0.3 dex, on the scale
where that of hydrogen is 12.0. This value is shown to be in excellent
agreement with that predicted for a nucleosynthesis model in which Li,
Be, and B are produced by cosmic-ray spallation.
Title: The components of the Balmer-alpha line of He II in the Sun.
Authors: Kohl, J. L.
Bibcode: 1977ApJ...211..958K
Altcode:
New photoelectric measurements of the absolute intensities of the
components of the Balmera line of He ii in the Sun with a spectral
resolution of 0.029 A are reported. Highly constrained curve fits are
used to test the consistency of the measurements with the line widths
that are predicted by a recombination model, a collisional excitation
model, and a combination of the two. Neither model alone is fully
consistent with the measurements. For the "quiet Sun," about 287o of
the total intensity of the Balmer-a line of He ii is attributed to the
recombination mechanism. Collisional excitation appears to dominate
for the n = 3 level. The recombination mechanism is apparently more
important in the active Sun because measurements of a very quiet Sun do
not show the narrow He ii peaks that were observed in measurements of
a more active Sun. Subject headings: Sun: chromosphere - Sun: corona -
Sun: spectra
Title: Absolute Photoionization Cross-Section for 0 I 3p -->
0 II 4S0.
Authors: Kohl, J. L.; Lafayetis, G.; Polenius, H. P.; Parkinson, W. H.
Bibcode: 1977uxsa.coll....5K
Altcode: 1977IAUCo..43....5K
No abstract at ADS
Title: Absolute measurement of the photoionization cross section of
atomic hydrogen with a shock tube for the extreme ultraviolet
Authors: Palenius, H. P.; Kohl, J. L.; Parkinson, W. H.
Bibcode: 1976PhRvA..13.1805P
Altcode:
The paper reports an experiment which is part of a program to measure
the absolute values of the atomic photoionization cross sections of
astrophysically abundant elements, particularly in stars and planetary
atmospheres. An aerodynamic pressure-driven shock tube constructed from
stainless steel with a quadratic cross section was used to measure the
photoionization cross section of H I at 19 wavelength points from 910
to 609 A with experimental uncertainties between 7 and 20%. The shock
tube was used to produce fully dissociated hydrogen and neon mixtures
for the photoabsorption measurements.
Title: The Mg II h and k lines. I. Absolute center and limb
measurements of the solar profiles.
Authors: Kohl, J. L.; Parkinson, W. H.
Bibcode: 1976ApJ...205..599K
Altcode:
We report new measurements of the solar Mg II h and k lines with
uncertainties in the absolute intensities at k1 and h1 of - 20 to +
12 percent with smaller uncertainties for higher intensities. The
spectral resolution, defined by the full width at half-maximum of the
instrumental profile, was 0.028 A, and the angular resolution element
was 184" by 1,5. Measurements were made for a quiet region near the disk
center and for a quiet region at cos 0 = 0.23. The measured profiles
are suitable for detailed comparisons with theoretical solar and stellar
profiles, as will be discussed in the paper by Ayres and Linsky (Paper
II) that will follow in a later issue. Our measured minimum intensities
(k1 and h1) relative to the core intensities (k3 and h3) and to the
average peak intensities (k2 and h2) are fainter than the corresponding
intensities that were reported by Lemaire and Skumanich. Subject
headings: line profiles - Sun: spectra - ultraviolet: spectra
Title: The Solar Profiles of the Hyperfine Components of HeII 1640
A From Rocket Observations.
Authors: Kohl, J. L.; Parkinson, W. H.
Bibcode: 1975BAAS....7..450K
Altcode:
No abstract at ADS
Title: Measurements of Solar Line Profiles between 1175 and 3200 Å
Authors: Kohl, J. L.; Parkinson, W. H.; Reeves, E. M.
Bibcode: 1975BAAS....7R.360K
Altcode:
No abstract at ADS
Title: Rocket spectrometer for investigation of the far ultraviolet
solar spectrum
Authors: Parkinson, W. H.; Reeves, E. M.; Kohl, J. L.
Bibcode: 1974hco..rept.....P
Altcode:
A rocket-borne Ebert spectrometer and telescope were used for
analysis of the solar spectrum. The instrument was arranged in the high
resolution line scanning mode. Selected emission lines between 1170 and
1640 A were scanned, and a complete wavelength scan was made from 1170
A to 1850 A. Accurate measurements were made of the line profiles of
the He II lines at 1640 A, C IV lines at 1550 A, Si IV lines at 1400
A, C II lines at 1335 A, the N V lines at 1240 A, and the C III lines
at 1175 A. Accurate intensity measurements of the quiet sun spectrum
for wavelengths between 1174 A and 3220 A were obtained. Spectral
resolution was better than 0.03 A over most of the range and spatial
resolution was relatively low so that the observations are averaged
over the chromospheric network. Plots of absolute intensity versus wave
length were prepared for the full wavelength range of the observations.
Title: Absolute Intensity Calibration of a High-Resolution Rocket
Spectrometer
Authors: Kohl, J. L.; Parkinson, W. H.
Bibcode: 1974spop.conf..511K
Altcode:
No abstract at ADS
Title: Measurement of the Neutral-Aluminum Photoionization
Cross-Section and Parameters of the 3p 2PO-3s3p2 2S112 Autoionization
Doublet
Authors: Kohl, J. L.; Parkinson, W. H.
Bibcode: 1973ApJ...184..641K
Altcode:
The photoionization cross-section of neutral aluminum for absorption
from the 3p 2P0 ground state was measured between 207.0 and 173
nanometers (hm) by use of the aerodynamic shock tube. The population
number density of the ground state was determined directly and precisely
by using hook-method measurements of the 3p 2P'112,312-4s 2S112
transitions. Our measured value at the first ionization limit of 65 i 7
Mbarns is considerably greater than earlier theoretical and experimental
values. This cross-section, when used in the solar model of Vernazza,
Avrett, and Loeser, improves the agreement between the predicted solar
intensity below the aluminum limit and the observations. The absolute
values of the Shore autoionization parameters for the aluminum doublet
at 193.20 and 193.64 nm were found to be equal within the experimental
accuracy and are b = 133Mb + l2percent,F = 6.84 x 10-15ergs j 3percent,a
= -55Mb + 32percentforthemoreaccurately determined line at 193.64
nm. Subject headings:autoionization - opacities - spectra, solar -
spectra, ultraviolet - transition probabilities
Title: High Resolution Rocket Observations of Solar Line Profiles
between 166.0 and 154.7 nm
Authors: Kohl, J. L.; Parkinson, W. H.; Reeves, E. M.
Bibcode: 1973BAAS....5R.274K
Altcode:
No abstract at ADS