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Author name code: poland
ADS astronomy entries on 2022-09-14
author:"Poland, Arthur I."
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Title: The Importance of Non-Isotropic Conduction in Multi-Dimensional
MHD Calculations of Coronal Magnetic Loops
Authors: Poland, Arthur I.; Forjan, G.
2009SPD....40.1207P Altcode:
Much progress has recently been made in modeling and observations
of coronal loops. Most recent modeling has focused on 1-D models
to investigate the location of the heating responsible for the high
temperatures of these loops and the corona in general. More specifically
the focus has been on various forms of pulsed heating with much argument
as to whether these pulses arise in the corona or the transition
region. There has been very little work done using multi-dimensional
models for two reasons: 1) to do this correctly one must treat thermal
conduction in a non-isotropic manner, only along the magnetic field
lines, and 2) to have the calculations be meaningful one must adequately
resolve the transition region, to approximately 12 km resolution. We
have addressed both of these problems in using the University of Chicago
Flash code to model the solar atmosphere from a temperature of 8,000K
to over 1,000,000K. Adequate resolution was achieved by setting the
adaptive mesh parameter to a sufficiently large value that dynamic
regridding gave the needed 12 km resolution. Thermal conduction was
originally handled in the program as an isotropic quantity. However,
we have developed new modules for the code such that conduction
was calculated as occurring only along the magnetic field lines. <P
/>Preliminary results show that the 2-D results with non-isotropic
conduction more closely match the 1-D results than the 2-D results with
isotropic conduction. This indicates that 1-D calculations are still
valuable. We also find that with sufficiently detailed observations
one should be able to discriminate between heating originating in the
transition region and heating originating in the corona.
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Title: Automated Detection of CMEs with SOHO and STEREO Coronagraph
Observations
Authors: Olmedo, O.; Zhang, J.; Wechsler, H.; Poland, A.; Borne, K.
2008AGUSMSP43A..02O Altcode:
A Solar Eruptive Event Detection System (SEEDS) has been developed
to automatically detect, track, and catalog coronal mass ejections
(CMEs) with SOHO and STEREO corona observations. The method developed
is based on decomposing 2-D Coronagraph images to 1-D and looking
for outstanding bright regions. Thresholds determine these regions,
and in time sequences, CMEs can be located and tracked. A complete
catalog of CMEs using LASCO C2 coronagraphs has been compiled
using the SEEDS software and the results are made available online
(http://spaceweather.gmu.edu/seeds). A preliminary catalog has been
made using SECCHI COR2 coronagraphs and is also available online. We
have been experimenting with real-time detection and make these results
available online on a daily basis. We present statistics comparing
the detections made with LASCO C2 with the CDAW CME catalog for the
whole solar cycle 23. It is found that SEEDS is able to identify
approximately 75% of the CMEs found within the CDAW CME catalog
(omitting CMEs with quality index of 0 indicating an ill-defined
CME). We look into approximately 100% more events detected by SEEDS
which were not in CDAW and study the nature of these events.
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Title: Automatic Detection and Tracking of Coronal Mass Ejections
in Coronagraph Time Series
Authors: Olmedo, O.; Zhang, J.; Wechsler, H.; Poland, A.; Borne, K.
2008SoPh..248..485O Altcode: 2008SoPh..tmp....6O
We present the current capabilities of a software tool to automatically
detect coronal mass ejections (CMEs) based on time series of coronagraph
images: the solar eruptive event detection system (SEEDS). The software
developed consists of several modules: preprocessing, detection,
tracking, and event cataloging. The detection algorithm is based on
a 2D to 1D projection method, where CMEs are assumed to be bright
regions moving radially outward as observed in a running-difference
time series. The height, velocity, and acceleration of the CME are
automatically determined. A threshold-segmentation technique is applied
to the individual detections to automatically extract an approximate
shape of the CME leading edge. We have applied this method to a
12-month period of continuous coronagraph images sequence taken at
a 20-minute cadence by the Large Angle and Spectrometric Coronagraph
(LASCO) instrument (using the C2 instrument only) onboard the Solar
and Heliospheric Observatory (SOHO) spacecraft. Our automated method,
with a high computational efficiency, successfully detected about
75% of the CMEs listed in the CDAW CME catalog, which was created by
using human visual inspection. Furthermore, the tool picked up about
100% more small-size or anomalous transient coronagraph events that
were ignored by human visual inspection. The output of the software
is made available online at http://spaceweather.gmu.edu/seeds/. The
parameters of scientific importance extracted by the software package
are the position angle, angular width, velocity, peak, and average
brightness. Other parameters could easily be added if needed. The
identification of CMEs is known to be somewhat subjective. As our
system is further developed, we expect to make the process significantly
more objective.
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Title: The Advancement Of An Automatic Solar Eruptive Event Detection
System (seeds) To A Near Real-time System
Authors: Olmedo, Oscar; Zhang, J.; Wechsler, H.; Poland, A.; Borne, K.
2007AAS...210.2929O Altcode: 2007BAAS...39..325O
We have been working on a tool to automatically detect, track and
catalogue Coronal Mass Ejections as observed by the LASCO C2 instrument
on board the SOHO spacecraft. The software developed follows a simple
algorithm, which is based on decomposing 2-D Coronagraph images to 1-D
and looking for outstanding bright regions. Thresholds determine these
regions, and in time sequences, CMEs can be located and tracked. Many
improvements to the algorithm have been made in recent months dealing
with the preprocessing of the input images as well as the tracking of
CME detections. Most importantly the system has advanced to the point
that it can make detections of CMEs in near real-time. What is meant
by near real-time detection is; first, the downloading images, as they
are made available by the instrument team, and second, the processing
and reporting of CME events as they occur on a daily basis. The true
positive rate of detections is over 75% as compared with the CDAW CME
catalog, and will continue to improve with further experimentation
of threshold values. Output from the SEEDS algorithm can be found
at http://solar.gmu.edu/research/autocme/ (Still showing preliminary
results). Currently, the software is being adapted to accept STEREO
images as input, preliminary test with STEREO COR2 data show promising
results.
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Title: Sentinels of the Sun: Forecasting Space Weather
Authors: Poland, Arthur I.
2006SpWea...4.8007P Altcode:
The story of humanity's interest in space weather may go back to
prehistoric times when people at high latitudes noticed the northern
lights. Interest became more acute after the development of electrical
technologies such as the telegraph, and certainly during World War
II when shortwave radio communication came into practical use. Solar
observing actually began to be supported by the military, with the
observatory at Climax, Colorado being established to monitor the Sun
during the war. With the advent of satellites and manned space travel
to the Moon, space weather became a seriously funded endeavor both for
basic research and forecasting. In the book, Sentinels of the Sun:
Forecasting Space Weather, Barbara Poppe does an excellent job of
telling this story for the nonprofessional. Moreover, as a professional
who has studied space weather since before humans landed on the Moon,
I found the book to be a very enjoyable read.
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Title: The Development of an Automatic Solar Eruptive Event Detection
System (SEEDS)
Authors: Olmedo, Oscar A., Jr.; Zhang, J.; Wechsler, H.; Borne, K.;
Poland, A.
2006SPD....37.0817O Altcode: 2006BAAS...38..233O
We present a software tool that automatically detects Coronal Mass
Ejections (CMEs) as observed by the LASCO C2 instrument on board the
SOHO spacecraft. The software developed follows a simple algorithm,
which is based on decomposing 2-D Coronagraph images to 1-D and
looking for outstanding bright regions. Thresholds determine these
regions, and in time sequences, CMEs can be located and tracked. We
have applied this method on a 12-month period of LASCO C2 data and
have found about 75% more events than the NRL-GSFC-CUA CME catalog
generated by human visual inspection. The automatic method gives a
true positive rate of approximately 75% using the manual catalog as
a benchmark. The software being presented is to be part a suite of
software tools in the Solar Eruptive Event Detection System (SEEDS),
being developed at George Mason University. The main purpose of SEEDS
is to make associations of solar transient events observed by different
instruments based on high-dimensional temporal and spatial data. An
example problem SEEDS may be able to answer is whether or not a CME
event seen In a Coronagraph is associated with a flareing/dimming
event seen in coronal images. With many future spac missions underway,
such as STEREO and SDO, SEEDS hopes to be utilized in aiding to the
gain of scientific knowledge in an efficient and effective way, to the
ultimate goal of making real time forecasting of space weather events.
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Title: Automatic detection of Coronal Mass Ejections using Computer
Vision.
Authors: Olmedo, O. A.; Zhang, J.; Wechsler, H.; Poland, A.; Borne,
K. D.
2006AGUSMSH43A..02O Altcode:
We present a software tool that automatically detects Coronal Mass
Ejections (CMEs) as observed by the LASCO C2 instrument on board the
SOHO spacecraft. The software developed follows a simple algorithm,
which is based on decomposing 2-D Coronagraph images to 1-D and
looking for outstanding bright regions. Thresholds determine these
regions, and in time sequences, CMEs can be located and tracked. We
have applied this method on a 12-month period of LASCO C2 data and
have found about 75% more events than the NRL-GSFC-CUA CME catalog
generated by human visual inspection. The automatic method gives a
true positive rate of approximately 75% using the manual catalog as
a benchmark. The software being presented is to be part a suite of
software tools in the Solar Eruptive Event Detection System (SEEDS),
being developed at George Mason University. The main purpose of SEEDS
is to make associations of solar transient events observed by different
instruments based on high-dimensional temporal and spatial data. An
example problem SEEDS may be able to answer is whether or not a CME
event seen In a Coronagraph is associated with a flareing/dimming
event seen in coronal images. With many future spac missions underway,
such as STEREO and SDO, SEEDS hopes to be utilized in aiding to the
gain of scientific knowledge in an efficient and effective way, to the
ultimate goal of making real time forecasting of space weather events.
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Title: Heating the Solar Corona: Observations for Model Boundary
Conditions
Authors: Nestlerode, C. M.; Poland, A. I.
2005AAS...20711107N Altcode: 2005BAAS...37.1342N
A prominent question in solar physics concerns the sources of coronal
heating. This problem can be addressed through observations of closed
magnetic loops which have high enough density to provide adequate
temporal, spatial, and spectral resolution. Measurements of temperature,
density, and velocity throughout the loop can be used for boundary
conditions and compared with quantities for model calculations. In
this paper, we present Solar Ultraviolet Measurements from Emitted
Radiation (SUMER) data from the Solar and Heliospheric Observatory's
(SOHO's) JOP 161 program. The SUMER instrument has high spatial and
spectral resolution over several different spectral lines and therefore
the data cover a large temperature range. The analyzed lines include
Mg VIII, Mg IX, N III, N IV, Ne VIII, O IV, O V, S IV, S V, and S X
with temperatures ranging from 60,000 K (S IV) to 0.9 MK (Mg IX). The
velocity profiles are created using Gaussian fitting with wavelength
calibration determined using average quiet Sun velocities from known
Doppler velocity shifts. The velocity profiles show important changes
in solar foot point plasma speed both spatially and temporally. This
analysis builds on previous analysis of solar spectral lines observed
with the SOHO Coronal Diagnostic Spectrometer (CDS); the advantage
of the SUMER instrument is better resolution, both spectrally and
spatially. This work was funded by NASA, Living with a Star Program.
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Title: Solar Eruptive Event Detection System (SEEDS)
Authors: Olmedo, O.; Zhang, J.; Wechsler, H.; Borne, K.; Poland, A.
2005AAS...20711106O Altcode: 2005BAAS...37.1342O
We report the progresses in developing a suite of software tools
to automatically detect and classify transient astrophysical
events. Astrophysical data is being created at the rate beyond human
operators capable of analyzing. Our team, composed of scientist in the
astronomy and computer science departments at George Mason University
(GMU), is particularly interested in tackling this problem. This project
is in its early stage and to date we are concentrating on solar eruptive
events, calling our analyzing scheme Solar Eruptive Event Detection
System (SEEDS). We have successfully developed tools to detect and
classify coronal mass ejections (CMEs) observed by LASCO instrument on
board the SOHO spacecraft. SEEDS proceeds as follows; firstly advanced
image processing techniques are used to detect transient features and a
time-dependent causal filter is applied for tracking the features, from
here, the detected events are put through a machine learning algorithm
where they are classified and event catalogs are created. The next
step is to make association of transient events observed by different
instruments based on high-dimensinal temporal and spatial data. A
scientific question, for example, that may be answered with SEES is
whether or not a CME event seen in a Coronagraph is associated with a
flareing/dimming event seen in coronal images. With many future space
observing missions underway, such as STEREO and SDO, SEEDS hopes to be
utilized in aiding to the gain of scientific knowledge in an efficient
and effective way, to the ultimate goal of making real time forecasting
of space weather events.
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Title: Space Weather At George Mason University
Authors: Poland, A. I.; Zhang, J.
2005AGUSMED11A..04P Altcode:
George Mason University (GMU), located in Fairfax, Virginia has an
exciting and rapidly growing set of graduate programs in Astrophysics,
Space Weather, Planetary Sciences, and Earth Sciences. The faculty
members in these programs are affiliated with the Department of Physics
and Astronomy and the School of Computational Sciences (SCS). The
synergy between these two departments creates opportunities for
learning not found in traditional programs. Our curriculum emphasizes
multi-disciplinary science that crosses traditional department
boundaries. Space Weather/solar terrestrial physics is one of these
multi-disciplinary areas. We expect our students to develop a deep
understanding of the Sun, the heliosphere, geospace, and their
interactions; we emphasize a systems view. The graduate program in
Space Weather at GMU offers degrees at the Masters (M.S.) and Doctoral
(Ph. D) levels through the School of Computational Sciences (SCS)
and the Department of Physics and Astronomy of the College of Arts and
Sciences (CAS). A wide variety of relevant courses are offered through
(SCS) in partnership with (CAS). Students also have the opportunity to
do research associated with the Goddard Space Flight Center and the
Navel Research Laboratory. For more information on the program see:
http://www.scs.gmu.edu/spaceweather/ Undergraduates and people from
local industry are also taking some of our courses to further their
education in this area. Many of them are finding the lectures directly
relevant to their daily work, such as satellite orbit maintenance.
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Title: Doppler Shift Velocity Calculations of Multi-Wavelength Coronal
Diagnostic Spectrometer Data Using Various Background Corrections
Authors: Duffin, R. T.; Poland, A. I.; McIntosh, S. W.
2004ESASP.575..545D Altcode: 2004soho...15..545D
No abstract at ADS
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Title: Detailed SUMER Observations of Coronal Loop Footpoint Dynamics
Authors: McIntosh, Scott W.; Poland, Arthur I.
2004ApJ...604..449M Altcode:
For the most part, the characteristics of heating in the open corona
and in closed coronal loops are determined by observing the emitted
plasma intensity as a function of position and comparing this with
model calculations. There are also some efforts that include observed
velocity and still others that use theoretical physical processes
such as electrodynamic or turbulent heating, for example. With a
view toward future modeling endeavors, we investigate the temporal
behavior of the intensity and velocity of a magnetic loop footpoint
as observed by SUMER on the Solar and Heliospheric Observatory (SOHO)
spacecraft as part of SOHO/TRACE Joint Observing Program 72. We study
these quantities in emission lines that were specifically chosen to
span the temperature domain of the upper chromospheric and transition
region plasmas (10<SUP>5</SUP>-10<SUP>6</SUP> K). We discuss the
implications of these observations, suggest improvements, and present
some new avenues of exploration. The most significant result is the
demonstration of the importance of including the measurement of velocity
as a function of time in the loop footpoint region.
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Title: International heliophysical year: a program of global research
continuing the tradition of previous international years
Authors: Davila, Joseph M.; Poland, Arthur I.; Harrison, Richard A.
2004AdSpR..34.2453D Altcode:
In 1957 a program of international research, inspired by the
International Polar Years of 1882-1883 and 1932-1933, was organized
as the International Geophysical Year (IGY) to study global phenomena
of the Earth and geospace. The IGY involved about 60,000 scientists
from 66 nations, working at thousands of stations from pole to pole,
in an effort to obtain simultaneous, global observations on Earth
and in space. There had never been anything like it before. The 50th
anniversary of the International Geophysical Year will occur in 2007. We
propose to organize an international program of scientific collaboration
for this time period called the International Heliophysical Year
(IHY). Like its predecessors, the IHY will focus on fundamental global
questions of Earth science.
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Title: Nonlinear interactions in coronal heating
Authors: Einaudi, G.; Dahlburg, R. B.; Rappazzo, A. F.; Poland, A.;
Li, Y.
2004cosp...35.3938E Altcode: 2004cosp.meet.3938E
The dynamics of the solar corona as well as its very existence are
due to the dynamics of plasmas and magnetic fields which, at the
global scales of coronal loops, prominences and helmet streamers
may be described by magnetohydrodynamics. Here we will discuss the
importance and role of nonlinear interactions in the heating of the
solar corona, which relies on the transfer, storage and dissipation of
the mechanical energy present in photospheric motion (Einaudi and Velli
1999). Nonlinear interactions including the coupling of coronal fields
to the motions and emerging flux through the photosphere determine both
the rate of heating and the topology of coronal magnetic fields. The
dependence of the heating rate on the time and space scales of the
photospheric motions will be considered. In particular we compare the
results of the numerical simulations performed using as input the MDI
data on the features of the photospheric motions at the base of some
coronal loops with the behavior of the loops themselves as deduced
from TRACE. G. Einaudi and M. Velli, Phys. Plasmas 6, 4146 (1999).
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Title: Road Map of Solar-Terrestrial Programs in the USA
Authors: Poland, A. I.
2003JKAS...36S.151P Altcode:
No abstract at ADS
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Title: Coronal Loops Heated by Magnetohydrodynamic Turbulence. I. A
Model of Isobaric Quiet-Sun Loops with Constant Cross Sections
Authors: Chae, Jongchul; Poland, Arthur I.; Aschwanden, Markus J.
2002ApJ...581..726C Altcode:
Several recent papers have presented new observational results
indicating that many coronal loops in active regions are nearly
isothermal. It is expected that quiet-Sun loops may have similar thermal
structures, since quiet-Sun differential emission measures look similar
to those in active regions. In the quiet Sun, it is well known from
observations that the nonthermal velocity inferred from the excess
broadening of a line over thermal broadening reaches a peak of about
30 km s<SUP>-1</SUP> around 3×10<SUP>5</SUP> K and then decreases
with temperature, having a value of about 20 km s<SUP>-1</SUP> at
1×10<SUP>6</SUP> K. In the present work, we make the assumption
that the observed nonthermal velocities are a manifestation of
magnetohydrodynamic (MHD) turbulence and present a model of static,
isobaric coronal loops heated by turbulence. Instead of solving the
MHD equations, we adopt simple energy spectra in MHD turbulence and
infer the heating rate as a function of temperature from the observed
nonthermal velocities. By solving the steady state energy equation
of a loop in which temperature monotonically increases with height,
we obtain the following results: (1) The heating rate is predominantly
near the footpoints and decreases with the loop arc length. (2) There
is a critical temperature above which the loop cannot be maintained
in a steady state. (3) The loop is denser and is more isothermal than
uniformly heated loops, being compatible with recent observations. (4)
The theoretical differential emission measures are in good agreement
with the empirical values at temperatures above 10<SUP>5</SUP> K. Below
this temperature, we still have a large discrepancy. (5) It is possible
to explain the observed strong correlation between intensity and
nonthermal velocity of a spectral line in the quiet Sun. Our results
support the idea that quasi-statically driven MHD turbulence of the
direct current (DC) type in the stratified medium (transition region
and corona) is a viable mechanism for coronal heating.
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Title: The International Heliophysical Year (IHY)
Authors: Davila, J. M.; Harrison, R.; Poland, A.; Thompson, B.;
Gopalswamy, N.
2002AGUFMSH21A0518D Altcode:
In 1957 a program of international research, inspired by the
International Polar Years of 1882-83 and 1932-33, was organized as
the International Geophysical Year (IGY) to study global phenomena of
the Earth and geospace. The IGY involved about 60,000 scientists from
66 nations, working at thousands of stations, from pole to pole to
obtain simultaneous, global observations on Earth and in space. There
had never been anything like it before. The fiftieth anniversary of
the International Geophysical Year will occur in 2007. We propose to
organize an international program of scientific collaboration for this
time period called the International Heliophysical Year (IHY). Like
it predecessors, the IHY will focus on fundamental global questions
of Earth science.
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Title: The International Heliophysical Year Concept
Authors: Davila, J.; Harrison, R.; Poland, A.; St-Cyr, O.; Thompson, B.
2002cosp...34E.529D Altcode: 2002cosp.meetE.529D
In 1957 a program of international research, inspired by the
International Polar Years of 1882-83 and 1932-33, was organized as
the International Geophysical Year (IGY) to study global phenomena of
the Earth and geospace. The IGY involved about 60,000 scientists from
66 nations, working at thousands of stations, from pole to pole to
obtain simultaneous, global observations on Earth and in space. There
had never been anything like it before. The fiftieth anniversary of
the International Geophysical Year will occur in 2007. We propose to
organize an international program of scientific collaboration for this
time period called the International Heliophysical Year (IHY). Like
its predecessors, the IHY will focus on fundamental global questions
of Earth science.
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Title: The New Solar Corona
Authors: Aschwanden, Markus J.; Poland, Arthur I.; Rabin, Douglas M.
2001ARA&A..39..175A Altcode:
We focus on new observational capabilities (Yohkoh, SoHO,
TRACE), observations, modeling approaches, and insights into
physical processes of the solar corona. The most impressive new
results and problems discussed in this article can be appreciated
from the movies available on the Annual Reviews website and at
http://www.lmsal.com/pub/araa/araa.html. "The Sun is new each
day." Heraclites (ca 530-475 BC) "Everything flows." Heraclites (ca
530-475 BC)
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Title: Technology for the SEC Theme at NASA
Authors: Poland, A. I.
2000SPD....31.1604P Altcode: 2000BAAS...32..849P
Technology advances are essential to achieve a high quality of science
in NASA missions. In the past, instrument technology has been funded
either through the SR&T program or during development of accepted
flight programs. Some changes are occuring in NASA to improve our
ability to advance technology for our future programs. I will discuss
some of the new program ideas and relate them to the SEC Roadmap and
other SEC technology documents being developed at GSFC.
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Title: Four years of SOHO discoveries - some highlights.
Authors: Fleck, B.; Brekke, P.; Haugan, S.; Duarte, L. S.; Domingo,
V.; Gurman, J. B.; Poland, A. I.
2000ESABu.102...68F Altcode:
Analysis of the helioseismic data from SOHO has shed new light on
solar and heliosheric physics: the structure and dynamics of the
solar interior, the heating and dynamics of the solar corona, and the
acceleration and composition of the solar wind.
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Title: Modeling of Solar Transition Region Outflows
Authors: Poland, A. I.; Chae, J.
1999AAS...194.9312P Altcode: 1999BAAS...31..990P
The problem of observing outflow of material from the Sun has been an
interesting issue in solar physics for several decades. The problem is
that we know material flows from the Sun since there is a solar wind
measured at Earth and in interplanetary space. However, observations in
the chromosphere, transition region, and lower corona show mostly inflow
with almost no outflow. In a recent paper by Hassler and coworkers it
was shown that there is a significant outflow at network boundaries
as seen in NeVIII (Te 800,000K), but no significant outflows have been
observed at other temperatures. In our earlier work we demonstrated why
one would expect to see only inflows below 100,000K. The energy balance
between conduction, radiation, and enthalpy resulted in gradients
being too steep to observe outflowing material. We have extended that
work to 1,000,000K and included the observed effects of the spreading
magnetic field with temperature. These new calculation results seem
to be in agreement with the observations and indicate that outflows
should only be observable in the 800,000K range.
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Title: Observations of Hydrogen and Helium Continua in Solar
Prominences
Authors: Andretta, V.; Kucera, T. A.; Poland, A. I.
1999ASPC..158..162A Altcode: 1999ssa..conf..162A
No abstract at ADS
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Title: Active Regions
Authors: Holman, G. D.; Cheng, C. -C.; Gurman, J. B.; Haisch, B. M.;
Poland, A. I.; Porter, J. G.; Saba, J. L. R.; Schmieder, B.; Strong,
K. T.
1999mfs..conf...41H Altcode:
Magnetic Field Strength and Strucutre Results Prior to SMM First Results
with SMM Subsequent Results: 1983-1987 The Coronal Magnetic Structures
Observing Campaign Coronal Magnetic Field Studies after SMM Dynamics
and Heating of the Solar Corona FCS Line-Broadening Measurements
Large Nonthermal Velocities Spatial Variations Correlation Studies FCS
Line-Broadening Data Interpreting the FCS Line Broadening Constraints
on Mass Motions Link to Heating Discussion Coronal Heating, Magnetic
Fields, and Flares UVSP Obervations of Active Regions Transition Region
Brightenings: UV Microflares Sunspots Magnetic Field and Height of the
Transition Region Sunspot Plumes Sunspot Flows Horizontal Flows Vertical
Flows Nonthermal Line Broadening Umbral Oscillations A Look Backward,
a Look Forward Prominences and Filaments Prominence Environment and
Structure Steady Flows in Prominence Material Activity in Prominences
Postflare Loops and Surges Conclusion
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Title: Neutral Hydrogen Column Depths in Prominences Using EUV
Absorption Features
Authors: Kucera, T. A.; Andretta, V.; Poland, A. I.
1998SoPh..183..107K Altcode:
Observations of prominence regions in hot coronal lines (≳106 K)
at wavelengths below the hydrogen Lyman absorption limit show what
appear to be absorption features. Other authors have suggested that
these observed features may be due to H and He continuum absorption. But
there has, as yet, been no conclusive evidence that this is indeed the
case. In this paper we present new Solar and Heliospheric Observatory
(SOHO) observations that allow us to address this problem in a
quantitative manner. We find that continuum absorption is the best
explanation for the absorption observed in imaging data from the Coronal
Diagnostic Spectrometer (CDS) on board SOHO. Furthermore, we discuss
a new technique to measure the column depth of neutral hydrogen in a
prominence, and use it to obtain estimates of the prominence filling
factors as well. We calculate the column depth of neutral hydrogen,
ξH∼1018 cm−2, and the filling factor, f≳0.3.
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Title: SUMER Observations of the Evolution and the Disappearance of
a Solar Prominence
Authors: Ofman, L.; Kucera, T. A.; Mouradian, Z.; Poland, A. I.
1998SoPh..183...97O Altcode:
The mechanisms that lead to the formation and the disappearance of
prominences are poorly understood, at present. An arch-shaped prominence
was observed with the Solar Ultraviolet Measurements of Emitted
Radiation (SUMER) spectrometer on board the Solar and Heliospheric
Observatory (SOHO) on 31 March-1 April 1996. The observations were
performed at three wave-bands in the Lyman continuum. Ten successive
images were obtained at 41-minute time intervals. Based on computed
models of Gouttebroze, Heinzel, and Vial (1993), we have determined the
temperature distribution of the prominence using the intensity ratio of
876 Å and 907 Å. The observed time sequence shows that parts of the
prominence disappear possibly by heating, while other parts exhibit
heating and cooling with apparent outward motion. We model the heat
input with the linearized MHD equations using a prescribed initial
density and a broad-band spectrum of Alfvén waves. We find a good
qualitative agreement with observations. In the model the prominence
is heated by the resonant absorption of Alfvén waves with frequencies
that match the resonant condition for a particular flux tube structure
that is determined by the magnetic field topology and plasma density.
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Title: Temperature Dependence of Ultraviolet Line Average Doppler
Shifts in the Quiet Sun
Authors: Chae, J.; Yun, H. S.; Poland, A. I.
1998ApJS..114..151C Altcode:
The existence of prevailing redshifts in the UV lines formed in the
solar transition region raises an important question concerning its
physical origin and its role in the mass and energy balance of the
outer solar atmosphere. A series of UV spectral lines observed by
SUMER has been analyzed to obtain the spatial average of Doppler
shifts in the quiet Sun as a function of temperature. The UV lines
used for the analysis cover temperatures ranging from 10<SUP>4</SUP>
to 10<SUP>6</SUP> K. The wavelength calibration has been done in
reference to the coolest chromospheric lines such as neutral lines
of silicon and sulfur. The positioning of the line center in blended
lines has been made by employing a constrained multi-Gaussian fitting
technique. The error in the measured average of the Doppler shifts is
estimated to be smaller than 1 km s<SUP>-1</SUP>. <P />Our results show
that the average Doppler shift at the base of the transition region is
about 1-2 km s<SUP>-1</SUP>, increasing with temperature with a peak
value of 11 km s<SUP>-1</SUP> near T = 2.3 × 10<SUP>5</SUP> K. Then
it decreases but remains still above zero (5 km s<SUP>-1</SUP> in
Ne VIII lines and 4 km s<SUP>-1</SUP> in Mg X lines). We find that
this behavior can be explained by the dominance of emission from
plasma flowing downward from the upper hot region to the lower cool
region along flux tubes with varying cross section. Assuming that
pressure and mass flux are constant along a flux tube, the cross
section of a typical flux tube has been estimated as a function of
temperature. It turns out that the cross section is nearly constant
below T = 10<SUP>5</SUP> K and then expands by a factor of about 30 at
T = 10<SUP>6</SUP> K. This behavior is fairly well represented by an
analytical functional form, A(T)/A(T<SUB>h</SUB>) = [1 + (Γ<SUP>2</SUP>
- 1)(T/T<SUB>h</SUB>)<SUP>ν</SUP>]<SUP>1/2</SUP>/Γ with parameters
of T<SUB>h</SUB> = 10<SUP>6</SUP> K, Γ = 30, and ν = 3.6.
---------------------------------------------------------
Title: Helio-Atmospheric Links Explorer (HALE): A MIDEX Experiment
for Exploring the Emergence of Magnetic Flux from Below the Solar
Photosphere through the Corona
Authors: Scherrer, P. H.; Title, A. M.; Bush, R. I.; Duvall, T. L.,
Jr.; Gurman, J. B.; Kosovichev, J. T.; Hoeksema, A. G.; Poland, A. I.;
Tarbell, T. D.
1998ESASP.417..285S Altcode: 1998cesh.conf..285S
No abstract at ADS
---------------------------------------------------------
Title: Helical Structure in an Eruptive Prominence Related to a CME
(SUMER, CDS, LASCO)
Authors: Kucera, T. A.; Poland, A. I.; Wiik, J. E.; Schmieder, B.;
Simnett, G.
1998ASPC..150..318K Altcode: 1998IAUCo.167..318K; 1998npsp.conf..318K
SOHO (SUMER/CDS) observed an eruptive prominence on May 1,1996,
associated with a CME observed by LASCO. We investigate the
physical conditions of this prominence in order to quantify velocity,
temperature, and density. SUMER spectra in Si IV and O IV lines are used
to obtain Doppler-shift images of the prominence. The prominence shows
large-scale red and blueshifted regions, revealing a large helical
structure with a global twist. In addition, fine structure analysis
shows multiple components in the line profile, suggesting integration
of many threads along the line-of-sight with a large dispersion of
velocities (∼150 km s<SUP>-1</SUP>).
---------------------------------------------------------
Title: Dynamics and Fine Structures in Quiescent Prominences (MSDP/Pic
du Midi, SOHO/SUMER and CDS)
Authors: Li, K.; Malherbe, J. -M.; Wiik, J. E.; Schmieder, B.; Roudier,
Th.; Kucera, T.; Poland, A.
1998ASPC..150...32L Altcode: 1998IAUCo.167...32L; 1998npsp.conf...32L
No abstract at ADS
---------------------------------------------------------
Title: Observation of Prominence Heating and the Heating Mechanism
Authors: Ofman, L.; Mouradian, Z.; Kucera, T. A.; Poland, A. I.
1998ASPC..150..159O Altcode: 1998IAUCo.167..159O; 1998npsp.conf..159O
No abstract at ADS
---------------------------------------------------------
Title: Velocity Fields of a Filament Region Observed with Ground-Based
Telescopes and from SOHO
Authors: Mein, P.; Schmieder, B.; Malherbe, J. -M.; Wiik, J. E.;
Engvold, O.; Brekke, P.; Zirker, J. B.; Poland, A. I.; Delaboudiniere,
J. -P.; Staiger, J.
1998ASPC..150..135M Altcode: 1998npsp.conf..135M; 1998IAUCo.167..135M
No abstract at ADS
---------------------------------------------------------
Title: Eruptive prominence and associated CME observed with SUMER,
CDS and LASCO (SOHO)
Authors: Wiik, J. E.; Schmieder, B.; Kucera, T.; Poland, A.; Brekke,
P.; Simnett, G.
1997SoPh..175..411W Altcode:
Observations of an eruptive prominence were obtained on 1 May 1996,
with the SUMER and CDS instruments aboard SOHO during the preparatory
phase of the Joint Observing Programme JOP12. A coronal mass ejection
observed with LASCO is associated temporally and spatially with this
prominence. The main objective of JOP12 is to study the dynamics of
prominences and the prominence-corona interface. By analysing the
spectra of Oiv and Siiv lines observed with SUMER and the spectra of
15 lines with CDS, Doppler shifts, temperatures and electron densities
(ratio of Oiv 1401 to 1399Å) were derived in different structures of
the prominence. The eruptive part of the prominence consists of a bubble
(plasmoid) of material already at transition region temperatures with
red shifts up to 100 km s<SUP>-1</SUP> and an electron density of the
order of 10<SUP>10</SUP>cm<SUP>-3</SUP>. The whole prominence was very
active. It developed both a large helical loop and several smaller loops
consisting of twisted threads or multiple ropes. These may be studied
in the SUMER movie (movie 2). The profiles of the SUMER lines show a
large dispersion of velocities (±50 km s<SUP>-1</SUP>) and the ratio
of the Oiv lines indicates a large dispersion in electron density (3 x
10<SUP>9</SUP>cm<SUP>-3</SUP> to 3x 10<SUP>11</SUP>cm<SUP>-3</SUP>). The
CME observed by LASCO left the corona some tens of minutes before the
prominence erupted. This is evidence that the prominence eruptions are
probably the result of the removal of the restraining coronal magnetic
fields which are in part responsible for the original stability of
the prominence.
---------------------------------------------------------
Title: Effects of Non-LTE Radiative Loss and Partial Ionization on
the Structure of the Transition Region
Authors: Chae, J.; Yun, H. S.; Poland, A. I.
1997ApJ...480..817C Altcode:
In this paper we address the question of how non-LTE radiative losses
with partial ionization of hydrogen and helium affects the energetics
and structure of the solar transition region. To accomplish this we
have constructed theoretical models of a thin rigid magnetic flux
tube with a steady material flow, which is embedded vertically in
the solar atmosphere. These models include the effects of material
flow, conduction, non-LTE radiative transfer in H and He, and partial
ionization. We find from this study that the effect of non-LTE radiative
transfer with partial ionization is significant near the base of the
transition region at temperatures less than 2.5 × 10<SUP>4</SUP>
K. This leads to a 1 order of magnitude increase in the differential
emission measure in comparison with the optically thin approximation
with complete ionization in the low (less than 2.5 × 10<SUP>4</SUP> K)
temperature regime. Above this region the non-LTE and opacity effects
are small. In the upflow case the conductive and convective energy
processes dominate to such a large extent that non-LTE radiative
process and partial ionization are not important. <P />In this work
we also confirm the previous work of other authors who provided the
explanation for why downflowing transition region material is much
more visible than upflowing material. We present the results in a
manner that gives a good physical understanding as to why this occurs.
---------------------------------------------------------
Title: Measuring the He I/H ratio in a prominence using Lyman
absorption
Authors: Kucera, T. A.; Andretta, V.; Poland, A. I.
1997SPD....28.0112K Altcode: 1997BAAS...29Q.881K
We investigate a method for measuring the ratio of neutral helium to
hydrogen in solar prominences. The upper limit to the Lyman continuum
occurs at 911 Angstroms for H, 504 Angstroms for He I, and 228 Angstroms
for He II. Lyman absorption by prominences and other structures is
clearly visible in emission of hot coronal lines observed by the Coronal
Diagnostic Spectrometer (CDS) and Extreme Ultraviolet Imaging Telescope
(EIT) aboard the Solar and Heliospheric Observatory (SOHO). By comparing
the absorption in lines absorbed by H only and by H and He I, the ratio
of He I to H in prominences can be determined. We attempt to do this
by comparing the absorption by a prominence in the Mg X line at 624.9
Angstroms and the Mg IX line at 368.1 Angstroms, both observed by CDS.
---------------------------------------------------------
Title: A New Look at the Quiet Sun Network in the Upper Atmosphere
During a Minimum of Activity Cycle
Authors: Lemaire, P.; Schuehle, U.; Curdt, W.; Wilhelm, K.; Poland,
A.; Falciani, R.
1997ESASP.404..517L Altcode: 1997cswn.conf..517L
No abstract at ADS
---------------------------------------------------------
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
I. Spectra and Spectroradiometry
Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.;
Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber,
M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P.
1997SoPh..170...75W Altcode:
SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation
instrument on the Solar and Heliospheric Observatory (SOHO) - observed
its first light on January 24, 1996, and subsequently obtained a
detailed spectrum with detector B in the wavelength range from 660
to 1490 Å (in first order) inside and above the limb in the north
polar coronal hole. Using detector A of the instrument, this range
was later extended to 1610 Å. The second-order spectra of detectors
A and B cover 330 to 805 Å and are superimposed on the first-order
spectra. Many more features and areas of the Sun and their spectra
have been observed since, including coronal holes, polar plumes and
active regions. The atoms and ions emitting this radiation exist at
temperatures below 2 × 10<SUP>6</SUP> K and are thus ideally suited
to investigate the solar transition region where the temperature
increases from chromospheric to coronal values. SUMER can also be
operated in a manner such that it makes images or spectroheliograms
of different sizes in selected spectral lines. A detailed line profile
with spectral resolution elements between 22 and 45 mÅ is produced for
each line at each spatial location along the slit. From the line width,
intensity and wavelength position we are able to deduce temperature,
density, and velocity of the emitting atoms and ions for each emission
line and spatial element in the spectroheliogram. Because of the high
spectral resolution and low noise of SUMER, we have been able to detect
faint lines not previously observed and, in addition, to determine
their spectral profiles. SUMER has already recorded over 2000 extreme
ultraviolet emission lines and many identifications have been made on
the disk and in the corona.
---------------------------------------------------------
Title: High resolution solar ultraviolet measurements
Authors: Lemaire, P.; Wilhelm, K.; Schühle, U.; Curdt, W.; Poland,
A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial, J. -C.
1997AdSpR..20.2249L Altcode:
The increase of our understanding of the processes acting in the solar
corona and maintaining it is strongly dependent on the quality of the
data that are obtained to check theories. The fine structure of the
solar atmosphere seen from the photosphere and extending to the hottest
parts of the corona requires data with high resolution in all parameter
space (angular, spectral and temporal). To constrain the hypotheses that
are proposed to describe the solar corona, it is necessary to establish
an accurate energy budget taking into account the processes which are
acting from the chromosphere to the corona. Some requirements can be
established and compared with the data collected so far (or about to
be collected) with the present SUMER (Solar Utraviolet Measurements
of Emitted Radiations) instrumentation.
---------------------------------------------------------
Title: First Results of the SUMER Telescope and Spectrometer on SOHO -
II. Imagery and Data Management
Authors: Lemaire, P.; Wilhelm, K.; Curdt, W.; SchÜle, U.; Marsch,
E.; Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Vial,
J. C.; KÜhne, M.; Huber, M. C. E.; Siegmund, O. H. W.; Gabriel, A.;
Timothy, J. G.; Grewing, M.
1997SoPh..170..105L Altcode:
SUMER - Solar Ultraviolet Measurements of Emitted Radiation - is not
only an extreme ultraviolet (EUV) spectrometer capable of obtaining
detailed spectra in the range from 500 to 1610 Å, but, using the
telescope mechanisms, it also provides monochromatic images over
the full solar disk and beyond, into the corona, with high spatial
resolution. We report on some aspects of the observation programmes
that have already led us to a new view of many aspects of the Sun,
including quiet Sun, chromospheric and transition region network,
coronal hole, polar plume, prominence and active region studies. After
an introduction, where we compare the SUMER imaging capabilities to
previous experiments in our wavelength range, we describe the results
of tests performed in order to characterize and optimize the telescope
under operational conditions. We find the spatial resolution to be
1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along
the slit. Resolution and sensitivity are adequate to provide details
on the structure, physical properties, and evolution of several solar
features which we then present. Finally some information is given on
the data availability and the data management system.
---------------------------------------------------------
Title: High-Resolution Observations of the Extreme Ultraviolet Sun
Authors: Harrison, R. A.; Fludra, A.; Pike, C. D.; Payne, J.;
Thompson, W. T.; Poland, A. I.; Breeveld, E. R.; Breeveld, A. A.;
Culhane, J. L.; Kjeldseth-Moe, O.; Huber, M. C. E.; Aschenbach, B.
1997SoPh..170..123H Altcode:
This paper presents first results of the Coronal Diagnostic Spectrometer
(CDS) recently launched aboard the Solar and Heliospheric Observatory
(SOHO). CDS is a twin spectrometer, operating in the extreme ultraviolet
range 151-785 Å. Thus, it can detect emission lines from trace
elements in the corona and transition region which will be used to
provide diagnostic information on the solar atmosphere. In this paper,
we present early spectra and images, to illustrate the performance of
the instrument and to pave the way for future studies.
---------------------------------------------------------
Title: Coordinated Observations of Prominences with SUMER/CDS and
Ground Observatories
Authors: Wiik, J. E.; Schmieder, B.; Kucera, T.; Poland, A.
1997ASPC..118..278W Altcode: 1997fasp.conf..278W
An international campaign for the observation of prominences
and filaments was successfully accomplished between June 3 and
9 1996. Several ground observatories took part in the campaign
which included the space observatories SOHO and Yohkoh. The main
objective of this campaign was to study the dynamics of prominences
and the prominence-corona interface, the formation of filaments and
the fine structures at different temperatures. We will reported on
two Joint Observing Programmes of SUMER and CDS aboard SOHO (JOP 12
and JOP 17), which have been achieved. Finally we will present as an
exemple a prominence observed on May 1, 1996 during the tests of the
programme JOP 12. This prominence was associated with a CME (observed
with LASCO). Very active parts with Dopplershifs up to +/- 36kms(-1)
were measured in the SUMER spectra of the prominence, indicating the
presence of twisted ropes during the eruption. Mean electron densities
have spatial and temporal dispersion of one order of magnitude (10(9)
- 10(10) cm(-3) ).
---------------------------------------------------------
Title: The structure of the solar corona as observed by the Solar
Extreme Ultraviolet Rocket Telescope and Spectrograph
Authors: Davila, Joseph M.; Thomas, Roger J.; Brosius, Jeffrey;
Poland, Arthur
1997AdSpR..20.2293D Altcode:
Data from the Solar Extreme-ultraviolet Rocket Telescope and
Spectrograph (SERTS) have been used to address a number of important
scientific problems. The primary strength of the SERTS data is the
fact that this spectral range is rich with emission lines. Over 270
lines are seen in the SERTS active Sun spectrum, from 57 different
ions. For example, multiple (>= 4) lines are observed for all
ionization states of iron from Fe IX to Fe XVII. Temperatures and
densities have been derived for a number of active and quiet Sun
regions, the coronal magnetic field strength has been estimated for
both a plage region and an active region.
---------------------------------------------------------
Title: "Prominences, filaments and chromospheric activity" June 1996
campaign with SOHO, YOHKOH and Wrocław.
Authors: Wiik, J. E.; Rudawy, P.; Schmieder, B.; Kucera, T.; Rompolt,
B.; Poland, A.
1997joso.proc...93W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The sun as never viewed before
Authors: Poland, A. I.
1997EOSTr..78..133P Altcode:
With the launch of the Solar and Heliospheric Observatory (SOHO), on
December 2, 1995, solar physics entered a new era of “viewing”
the Sun and heliosphere without interferences from the Earth's
atmosphere. SOHO is a mission of international cooperation between the
European Space Agency (ESA) and NASA. The most exciting new discoveries
from SOHO include the unexpectedly high magnetic activity observed
during the very minimum of the solar cycle and the “observation”
of the interior structure of the Sun (helioseismology). The coronal
instruments are showing that coronal mass ejections (CMEs) leave the
Sun more frequently than expected, at the rate of approximately one
per day. The helioseismology experiments, with their extremely low
noise due to the absence of the Earth's atmospheric interference,
are showing that convective cells under the solar surface are shaped
like pancakes, not spheres as was previously assumed.
---------------------------------------------------------
Title: Extreme ultraviolet observations of the solar corona: first
results from the coronal diagnostic spectrometer on SOHO
Authors: Harrison, R. A.; Fludra, A.; Sawyer, E. C.; Culhane, J. L.;
Norman, K.; Poland, A. I.; Thompson, W. T.; Kjeldseth-Moe, O.;
Aschenbach, B.; Huber, M. C. E.; Gabriel, A. H.; Mason, H. E.
1997AdSpR..20.2239H Altcode:
We present first results from the Coronal Diagnostic Spectrometer (CDS)
aboard the ESA/NASA Solar and Heliospheric Observatory (SOHO). CDS is
a double spectrometer operating in the 151-785 A˚ range. This region
of the solar spectrum is rich in emission lines from trace elements
in the solar atmosphere, which can be used to derive diagnostic
information on coronal and transition region plasma. Early spectra are
presented and well identified lines are listed. In addition, examples
of images in selected wavelength ranges are shown, for a prominence,
a loop system and a bright point, demonstrating well the power of such
extreme ultraviolet observations.
---------------------------------------------------------
Title: The first results from SOHO.
Authors: Domingo, V.; Fleck, B.; Poland, A.
1996ESABu..87....7D Altcode:
SOHO, launched by an Atlas II-AS from Cape Canaveral on 2 December 1995,
was inserted into its halo orbit around the L1 Lagrangian point. Typical
examples of the unique results being obtained with SOHO's instruments
are presented.
---------------------------------------------------------
Title: SOHO-Solar and Heliospheric Observatory
Authors: Poland, A. I.
1996AAS...188.4901P Altcode: 1996BAAS...28..896P
With the successful launch of SOHO on Dec. 2, 1995 we are beginning a
new era of solar and heliospheric observations. SOHO is a space mission
of international co-operation between the European Space Agency (ESA)
and NASA designed to study the sun and heliosphere from the vicinity
of the sun-earth L1 point. In this talk I will give an overview of
the first results and planned observations in the three areas of the
sun/heliosphere system: the solar interior as studied through the
techniques of helioseismology; the solar atmosphere and studies of the
heating and acceleration of the solar wind; and in-situ measurements
of the solar wind as observed at L1. I will also discuss the framework
in which SOHO is operated and how other scientist, not already involved
in the SOHO mission, can get involved with the program.
---------------------------------------------------------
Title: A Solar EUV Spectral Atlas Observed with SUMER
Authors: Brekke, P.; Wilhelm, K.; Lemaire, P.; Curdt, W.; Schuhle,
U.; Poland, A.; Kucera, T.; Hassler, D. M.; Siegmund, O. H. W.
1996AAS...188.3713B Altcode: 1996BAAS...28..879B
We present the first solar EUV spectral atlas in the wavelength range
500 -- 1600 { Angstroms}. The spectra were recorded with the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) which is part
of the ESA/NASA Solar and Heliospheric Observatory (SOHO). The solar
spectrum below 1200 { Angstroms} is not very well known. Thus, the
present spectral atlas, and SUMER observations in general, represents
a new important diagnostic tool to study essential physical parameters
of the solar atmosphere. It includes emission from atoms and ions in
the temperature range 10(4) to 2 x 10(6) K. Thus, emission lines and
continua emitted from the lower chromosphere to the lower corona
can be studied. The atlas is also useful as a planning tool for
SUMER studies to determine useful dwell times, possible blends, and
to select proper data extraction windows. The angular resolution of
SUMER is close to 1 arcsec, but the atlas presented here represents an
average along part of the 1-arcsec wide slit, typically 30 arcsec. The
spectral resolving power of the instrument is lambda /Delta lambda =
17770-38300. For more details about the SUMER instrument we refer to
Wilhelm et al. (Solar Physics, 162, 189, 1995). The spectral data in
this atlas were obtained with the spectrometer slit positioned at the
center of the solar disk with a dwell time of 300 s to bring up weak
lines and continua. The full spectral range was put together from
a number of exposures each covering approximately 20 { Angstroms}
in 1st order on the coated, and therefore most sensitive, part (KrB)
of the detector. 1st and 2nd order spectra are superimposed. The
spectral atlas is available in a computer readable format together
with a IDL program to read and display the data using a widget
interface. The atlas and the programs can be obtained via the World
Wide Web (http://hydra.mpae.gwdg.de/mpae_projects/SUMER/sumer.html)
or by contacting one of the authors.
---------------------------------------------------------
Title: Preface
Authors: Fleck, B.; Domingo, V.; Poland, A.
1995SoPh..162D...9F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Coronal Diagnostic Spectrometer for the Solar and
Heliospheric Observatory
Authors: Harrison, R. A.; Sawyer, E. C.; Carter, M. K.; Cruise,
A. M.; Cutler, R. M.; Fludra, A.; Hayes, R. W.; Kent, B. J.; Lang,
J.; Parker, D. J.; Payne, J.; Pike, C. D.; Peskett, S. C.; Richards,
A. G.; Gulhane, J. L.; Norman, K.; Breeveld, A. A.; Breeveld, E. R.; Al
Janabi, K. F.; Mccalden, A. J.; Parkinson, J. H.; Self, D. G.; Thomas,
P. D.; Poland, A. I.; Thomas, R. J.; Thompson, W. T.; Kjeldseth-Moe,
O.; Brekke, P.; Karud, J.; Maltby, P.; Aschenbach, B.; Bräuninger,
H.; Kühne, M.; Hollandt, J.; Siegmund, O. H. W.; Huber, M. C. E.;
Gabriel, A. H.; Mason, H. E.; Bromage, B. J. I.
1995SoPh..162..233H Altcode:
The Coronal Diagnostic Spectrometer is designed to probe the solar
atmosphere through the detection of spectral emission lines in the
extreme ultraviolet wavelength range 150 - 800 å. By observing
the intensities of selected lines and line profiles, we may derive
temperature, density, flow and abundance information for the plasmas
in the solar atmosphere. Spatial and temporal resolutions of down to
a few arcseconds and seconds, respectively, allow such studies to be
made within the fine-scale structure of the solar corona. Futhermore,
coverage of large wavelength bands provides the capability for
simultaneously observing the properties of plasmas across the wide
temperature ranges of the solar atmosphere.
---------------------------------------------------------
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schühle, U.; Lemaire,
P.; Gabriel, A.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.; Jordan,
S. D.; Poland, A. I.; Thomas, R. J.; Kühne, M.; Timothy, J. G.;
Hassler, D. M.; Siegmund, O. H. W.
1995SoPh..162..189W Altcode:
The instrument SUMER - Solar Ultraviolet Measurements of Emitted
Radiation is designed to investigate structures and associated dynamical
processes occurring in the solar atmosphere, from the chromosphere
through the transition region to the inner corona, over a temperature
range from 10<SUP>4</SUP> to 2 × 10<SUP>6</SUP>K and above. These
observations will permit detailed spectroscopic diagnostics of plasma
densities and temperatures in many solar features, and will support
penetrating studies of underlying physical processes, including plasma
flows, turbulence and wave motions, diffusion transport processes,
events associated with solar magnetic activity, atmospheric heating,
and solar wind acceleration in the inner corona. Specifically, SUMER
will measure profiles and intensities of EUV lines; determine Doppler
shifts and line broadenings with high accuracy; provide stigmatic
images of the Sun in the EUV with high spatial, spectral, and temporal
resolution; and obtain monochromatic maps of the full Sun and the inner
corona or selected areas thereof. SUMER will be flown on the Solar
and Heliospheric Observatory (SOHO), scheduled for launch in November,
1995. This paper has been written to familiarize solar physicists with
SUMER and to demonstrate some command procedures for achieving certain
scientific observations.
---------------------------------------------------------
Title: The SOHO mission.
Authors: Fleck, B.; Domingo, V.; Poland, A. I.
1995SoPh..162.....F Altcode:
SOHO, the Solar and Heliospheric Observatory, is a project of
international cooperation between ESA and NASA to study the Sun, from
its deep core to the outer corona. This special issue is dedicated to
the SOHO payload and to its operation.
---------------------------------------------------------
Title: The SOHO Mission: an Overview
Authors: Domingo, V.; Fleck, B.; Poland, A. I.
1995SoPh..162....1D Altcode:
The Solar and Heliospheric Observatory (SOHO) is a space mission
that forms part of the Solar-Terrestrial Science Program (STSP),
developed in a collaborative effort by the European Space Agency (ESA)
and the National Aeronautics and Space Administration (NASA). The
STSP constitutes the first "cornerstone" of ESA's long-term
programme known as "Space Science — Horizon 2000". The principal
scientific objectives of the SOHO mission are a) to reach a better
understanding of the structure and dynamics of the solar interior
using techniques of helioseismology, and b) to gain better insight
into the physical processes that form and heat the Sun's corona,
maintain it and give rise to its acceleration into the solar wind. To
achieve these goals, SOHO carries a payload consisting of 12 sets of
complementary instruments. SOHO is a three-axis stabilized spacecraft
with a total mass of 1850 kg; 1150 W of power will be provided by
the solar panels. The payload weighs about 640 kg and will consume
450 W in orbit. SOHO will be launched by an ATLAS II-AS and will
be placed in a halo orbit around the Sun-Earth L1 Lagrangian point
where it will be continuously pointing to Sun centre with an accuracy
of 10 arcsec. Pointing stability will be better than 1 arcsec over
15 min intervals. The SOHO payload produces a continuous science
data stream of 40 kbits/s which will be increased by 160 kbits/s
whenever the solar oscillations imaging instrument is operated in its
highrate mode. Telemetry will be received by NASA's Deep Space Network
(DSN). Planning, coordination and operation of the spacecraft and the
scientific payload will be conducted from the Experiment Operations
Facility (EOF) at NASA's Goddard Space Flight Center (GSFC).
---------------------------------------------------------
Title: Some design and performance features of SUMER: solar
ultraviolet measurements of emitted radiation
Authors: Wilhelm, Klaus; Curdt, W.; Marsh, E.; Schuehle, Udo H.;
Lemaire, Philippe; Gabriel, Alan H.; Vial, J. -C.; Grewing, Michael;
Huber, Martin C.; Jordan, S. D.; Poland, Arthur I.; Thomas, Roger J.;
Kuehne, Mikhael; Timothy, J. Gethyn; Hassler, Donald M.; Siegmund,
Oswald H.
1995SPIE.2517....2W Altcode:
The instrument SUMER (solar ultraviolet measurements of emitted
radiation) is designed to investigate structures and associated
dynamical processes occurring in the solar atmosphere from the
chromosphere through the transition region to the inner corona, over a
temperature range from 10<SUP>4</SUP> to 2 multiplied by 10<SUP>6</SUP>
K and above. The observations will be performed, on board SOHO (solar
and heliospheric observatory) scheduled for launch in November 1995,
by a scanning, normal-incidence telescope/spectrometer system in
the wavelength range from 500 to 1610 angstrom. Spatial resolution
requirements compatible with the pointing stability of SOHO are less
than 1000 km corresponding to about 1-arcsec angular resolution. Doppler
observations of EUV line shifts and broadenings should permit solar
plasma velocity measurements down to 1 km s<SUP>-1</SUP>. We report
here on some specific features of this instrument related to its
pointing as well as its spatial and spectral resolution capabilities.
---------------------------------------------------------
Title: Coronal Diagnostic Spectrometer: an extreme-ultraviolet
spectrometer for the Solar and Heliospheric Observatory
Authors: Kent, Barry J.; Harrison, Richard A.; Sawyer, Eric C.;
Hayes, R. W.; Richards, Anthony G.; Culhane, John L.; Norman, K.;
Breeveld, A. A.; Thomas, P. D.; Poland, Arthur I.; Thomas, Roger J.;
Thompson, William T.; Aschenbach, Bernd R.; Braeuninger, Heinrich
W.; Kjeldseth-Moe, O.; Kuehne, Mikhael; Hollandt, J.; Paustian, W.;
Bromage, B. J.
1995SPIE.2517...12K Altcode:
The coronal diagnostic spectrometer is designed to probe the solar
atmosphere through the detection of spectral emission lines in the
extreme ultraviolet wavelength range 15.0 - 80.0 nm. By observing
the intensities of selected lines and line profiles, it is possible
to derive temperature, density, flow, and abundance information for
the plasmas in the solar atmosphere. Spatial resolution down to
a few arcseconds and temporal resolution of seconds, allows such
studies to be made within the fine-scale structure of the solar
corona. Furthermore, coverage of a large wavelength band provides
the capability for simultaneously observing the properties of plasma
across the wide temperature ranges of the solar atmosphere. The
CDS design makes use of a Wolter-Schwarzschild II telescope which
simultaneously illuminates two spectrometer systems, one operating
in normal incidence the other in grazing incidence. In this paper we
describe the salient features of the design of the CDS instrument and
discuss the performance characteristics of CDS as established through
pre-delivery test and calibration activities.
---------------------------------------------------------
Title: SOHO: The Solar and Heliospheric Observatory
Authors: Domingo, V.; Fleck, B.; Poland, A. I.
1995SSRv...72...81D Altcode:
The Solar and Heliospheric Observatory (SOHO), together with the Cluster
mission, constitutes ESA's Solar Terrestrial Science Programme (STSP),
the first “Cornerstone” of the Agency's long-term programme “Space
Science — Horizon 2000”. STSP, which is being developed in a strong
collaborative effort with NASA, will allow comprehensive studies
to be made of the both the Sun's interior and its outer atmosphere,
the acceleration and propagation of the solar wind and its interaction
with the Earth. This paper gives a brief overview of one part of STSP,
the SOHO mission.
---------------------------------------------------------
Title: The SOHO mission
Authors: Fleck, B.; Domingo, V.; Poland, A.
1995somi.book.....F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SOHO: The Solar and Heliospheric Observatory
Authors: Domingo, V.; Fleck, B.; Poland, A. I.
1995hlh..conf...81D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The SOHO mission Poland.
Authors: Fleck, B.; Domingo, V.; Poland, Arthur I.
1995sohp.book.....F Altcode: 1995QB521.S5828....
No abstract at ADS
---------------------------------------------------------
Title: Coronal fine structure as seen in the Skylab white light
coronagraph
Authors: Poland, A. I.
1994ESASP.373..227P Altcode: 1994soho....3..227P
No abstract at ADS
---------------------------------------------------------
Title: The scientific payload of the space-based Solar and
Heliospheric Observatory (SOHO)
Authors: Domingo, V.; Fleck, B.; Poland, A. I.
1994SSRv...70....7D Altcode:
The space-based Solar and Heliospheric Observatory (SOHO) is a joint
venture of ESA and NASA within the frame of the Solar Terrestrial
Science Programme (STSP), the first “Cornerstone” of ESA's long-term
programme “Space Science — Horizon 2000”. The principal scientific
objectives of the SOHO mission are: a) a better understanding of
the structure and dynamics of the solar interior using techniques of
helioseismology, and b) a better insight into the physical processes
that form and heat the Sun's corona, maintain it and give rise to
its acceleration into the solar wind. To achieve these goals, SOHO
carries a payload consisting of 12 sets of complementary instruments
which are briefly described here.
---------------------------------------------------------
Title: SOHO operations and ground system
Authors: Poland, A. I.; Domingo, V.; Fleck, B.
1994SSRv...70...13P Altcode:
SOHO is a joint ESA/NASA mission to study the sun from its interior to,
and including, the solar wind in interplanetary space. It is currently
scheduled for launch in 1995. After launch SOHO with be operated from
the Experiment Operations Facility (EOF) at Goddard Space Flight Center
(GSFC). The EOF will consist of facilities for instrument commanding,
data reception, data reduction and data analysis. In this paper the
operations concepts including instrument ground commanding from the EOF
and communications capabilities between the EOF and ground observatories
and the public networks in general will be described.
---------------------------------------------------------
Title: Delay-line detectors for the UVCS and SUMER instruments on
the SOHO Satellite
Authors: Siegmund, Oswald H.; Stock, Joseph M.; Marsh, Daniel R.;
Gummin, Mark A.; Raffanti, Richard; Hull, Jeffrey; Gaines, Geoffrey
A.; Welsh, Barry Y.; Donakowski, B.; Jelinsky, Patrick N.; Sasseen,
Timothy; Tom, James L.; Higgins, B.; Magoncelli, T.; Hamilton, Jon W.;
Battel, Steven J.; Poland, Arthur I.; Jhabvala, Murzy D.; Sizemore,
K.; Shannon, J.
1994SPIE.2280...89S Altcode:
Microchannel plate based detectors with cross delay line image readout
have been rapidly implemented for the SUMER and UVCS instruments
aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to
be launched in July 1995. In October 1993 a fast track program to
build and characterize detectors and detector control electronics
was initiated. We present the detector system design for the SOHO
UVCS and SUMER detector programs, and results from the detector test
program. Two deliverable detectors have been built at this point, a
demonstration model for UVCS, and the flight Ly (alpha) detector for
UVCS, both of which are to be delivered in the next few weeks. Test
results have also been obtained with one other demonstration detector
system. The detector format is 26mm x 9mm, with 1024 x 360 digitized
pixels,using a low resistance Z stack of microchannel plates (MCP's) and
a multilayer cross delay line anode (XDL). This configuration provides
gains of approximately equals 2 X 10(superscript 7) with good pulse
height distributions (<50% FWHM) under uniform flood illumination,
and background levels typical for this configuration (approximately
equals 0.6 event cm(superscript -2) sec(superscript -1)). Local counting
rates up to approximately equals 400 event/pixel/sec have been achieved
with no degradation of the MCP gain. The detector and event encoding
electronics achieves approximately equals 25 micrometers FWHM with
good linearity (+/- approximately equals 1 pixel) and is stable to high
global counting rates (>4 X 10(superscript 5) events sec(superscript
-1)). Flat field images are dominated by MCP fixed pattern noise and
are stable, but the MCP multifiber modulation usually expected is
uncharacteristically absent. The detector and electronics have also
successfully passed both thermal vacuum and vibration tests.
---------------------------------------------------------
Title: 'SUMER' - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Gabriel, A. H.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Kuhne, M.; Lemaire, P.; Marsch, E.; Poland,
A. I.; Schuhle, U.; Thomas, R. J.; Timothy, J. G.; Vial, J. -C.
1994scs..conf..619W Altcode: 1994IAUCo.144..619W
SUMER is designed for the investigations of plasma flow characteristics,
turbulence and wave motions, plasma densities and temperatures,
structures and events associated with solar magnetic activity in the
chromosphere, the transition zone and the corona. The spatial and
spectral resolution capabilities of the instrument are considered in
some detail, and a new detector concept is introduced.
---------------------------------------------------------
Title: SOHO Science Opportunities
Authors: Fleck, B.; Domingo, V.; Poland, A. I.
1994scs..conf..609F Altcode: 1994IAUCo.144..609F
The principal scientific objectives of the SOHO mission are: a)
a better understanding of the structure and dynamics of the solar
interior using techniques of helioseismology, and b) a better insight
into the physical processes that form and heat the Sun's corona,
maintain it and give rise to its acceleration into the solar wind. To
achieve these goals, SOHO carries a payload consisting of 12 sets of
complementary instruments which are briefly described here.
---------------------------------------------------------
Title: SOHO Operations
Authors: Fleck, B.; Domingo, V.; Poland, A. I.
1994scs..conf..614F Altcode: 1994IAUCo.144..614F
SOHO, the Solar and Heliospheric Observatory, is currently scheduled
for launch in 1995. After launch SOHO will be operated from the
Experiment Operations Faciliy (EOF) at Goddard Space Flight Center
(GSFC). The EOF will consist of facilities for instrument commanding,
data reception, data reduction and data analysis. This paper briefly
describes the operations concepts.
---------------------------------------------------------
Title: SOHO: science objectives and capabilities
Authors: Fleck, B.; Domingo, V.; Poland, A. I.
1994ASIC..433..517F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SUMER - Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Curdt, W.; Marsch, E.; Schuehle, U.; Gabriel,
A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber, M. C. E.;
Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Kuehne, M.; Timothy, J. G.
1993BAAS...25.1192W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Invited Talk: (SOHO Coronal Observations)
Authors: Poland, A. I.
1993BAAS...25.1195P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: SUMER: temperatures, densities, and velocities in the outer
solar atmosphere.
Authors: Lemaire, P.; Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel,
A. H.; Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kuehne, M.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
1992ESASP.348...13L Altcode: 1992cscl.work...13L
The SUMER instrumentation, that will be mounted on the SOHO spacecraft,
is in development under MPAE leadership. It has some capability
to improve the solar angular resolution and the spectral resolution
already obtained in the far UV to the extreme UV, corresponding to the
temperature range between 10<SUP>4</SUP> and a few 10<SUP>6</SUP>K. The
authors give some insights into the SUMER spectrometer that is developed
to study the dynamics and to infer temperatures and densities of the
low corona and the chromosphere-corona transition zone in using the
50 - 160 nm wavelength range. First, they recall the SUMER scientific
goals and the technics used. Then, after a brief description of the
instrumentation the expected performances are described. The way the
observations can be conducted is emphasized and it is shown how SUMER
is operated in coordination with other SOHO instrumentations and in
cooperation with ground-based observations.
---------------------------------------------------------
Title: Measurements of an intensified CCD detector for the solar
and heliospheric observatory
Authors: Thompson, William T.; Poland, Arthur I.; Siegmund, Oswald H.;
Swartz, Marvin; Leviton, Douglas B.; Payne, Leslie J.
1992SPIE.1743..464T Altcode:
An engineering model intensified CCD detector for the SOHO Coronal
Diagnostics Spectrometer has been built and tested at the NASA Goddard
Space Flight Center. A windowless MCP intensifier tube converts EUV
radiation (30 - 65 nm) into visible light, which is focused via a lens
system onto a Tektronix 1024 X 1024 CCD. Tests have been made of this
engineering model to determine the following characteristics: quantum
efficiency, resolution, throughput, linearity, statistical variation,
readout noise, scattering, and flat-field response. In almost all
respects, the detector performed as expected. This detector has been
delivered, and work is underway on the flight detector.
---------------------------------------------------------
Title: "SUMER" - Solar Ultraviolet Measurements of Emitted Radiation.
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, S. D.; Kühne, M.; Lemaire, P.;
Marsch, E.; Poland, A. I.; Richter, A. K.; Thomas, R. J.; Timothy,
J. G.; Vial, J. C.
1992eocm.rept..225W Altcode:
The experiment Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) is designed for the investigations of plasma flow
characteristics, turbulence and wave motions, plasma densities
and temperatures, structures and events associated with solar
magnetic activity in the chromosphere, the transition zone and the
corona. Specifically, SUMER will measure profiles and intensities
of extreme ultraviolet (EUV) lines emitted in the solar atmosphere
ranging from the upper chromosphere to the lower corona; determine line
broadenings, spectral positions and Doppler shifts with high accuracy;
provide stigmatic images of selected areas of the Sun in the EUV with
high spatial, temporal and spectral resolution and obtain full images of
the Sun and the inner corona in selectable EUV lines, corresponding to a
temperature range from 10<SUP>4</SUP> to more than 1.8×10<SUP>6</SUP>K.
---------------------------------------------------------
Title: SOHO - An Observatory to Study the Solar Interior and the
Solar Atmosphere
Authors: Poland, A. I.
1992AAS...180.3306P Altcode: 1992BAAS...24..781P
No abstract at ADS
---------------------------------------------------------
Title: Opacity Effects on the Radiative Losses of Coronal Loops
Authors: Kuin, N. P. M.; Poland, A. I.
1991ApJ...370..763K Altcode:
This paper presents calculations of radiative losses, which include the
effects of geometry and optical depth, that can be used to improve the
energy losses in many flux-tube calculations for loops with constant
and variable cross sections. The results include the non-LTE ionization
state of hydrogen and helium, thus allowing the determination of the
ionization energy in the gas and the relative importance of collisional
and radiative processes. These calculations show that optical depth
effects are important under solar conditions in the temperature range
of 8000-40,000 K.
---------------------------------------------------------
Title: The SOHO Space Satellite: UV instrumentation.
Authors: Poland, Arthur I.; Domingo, Vicente
1991SPIE.1343..310P Altcode:
The solar and heliospheric observatory, SOHO will be placed into a halo
orbit around the L1 sun-earth Lagrangian point in 1995. The authors
describe the ultra-violet and EUV instruments designed to study
the solar atmosphere from the chromosphere through the corona. The
instruments and their basic characteristics are: 1) SUMER - a normal
incidence telescope with a normal incidence spherical concave grating
for stigmatic imaging to measure line profiles and images in the
wavelength range from 500 Å to 1600 Å with a 1.5″resolution; 2) CDS
- a grazing incidence telescope with one grazing incidence astigmatic
spectrograph and one normal incidence toroidal grating spectrograph
to measure line ratios and images in the range from 170 Å to 800
Å with a 2″resolution; 3) EIT - a normal incidence multilayered
telescope to produce narrow band pass images in the spectral lines at
171 Å, 195 Å, 284 Å, and 304 Å with a 3″resolution; 4) UVCS - a
normal incidence coronagraph with a normal incidence toroidal grating
spectrograph to measure line profiles and images of several EUV lines
from ≡500 Å to ≡1200 Å with a several arcsecond resolution;
and 5) SWAN - a lens with hydrogen absorption cell and interference
filter to measure Ly-α profiles in the far corona and heliosphere.
---------------------------------------------------------
Title: An intensified CCD detector using the phosphor TPB.
Authors: Thompson, William T.; Swartz, Marvin; Poland, Arthur I.
1990SPIE.1344..415T Altcode: 1990exrg.conf..415T
The Research Amplifying Imaging Detector (RAID) consists of a
microchannel plate image intensifier with a thin coating (3500 - 10,000
Å) of the phosphor tetraphenyl-butadiene (TPB) on the entrance window
to convert EUV radiation to visible, and coupled via a lens to a CCD
detector. This design allows great flexibility in selecting the pixel
size and field of view, with a simple mechanical design. Tests have
been made at visible and EUV (304 Å) wavelengths of the following
performance aspects: EUV spectral sensitivity, spatial resolution
both of components and of the system as a whole, noise, linearity,
and dynamic range.
---------------------------------------------------------
Title: SOHO - an Observatory to Study the Solar Interior and the
Solar Atmosphere
Authors: Poland, A. I.; Domingo, V.
1990ASSL..166..277P Altcode: 1990oeob.coll..277P; 1990IAUCo.123..277P
The Solar and Heliospheric Observatory (SOHO) is described. The two
main objectives of SOHO are to improve understanding of solar coronal
phenomena and to study solar structure and interior dynamics from
its core to the photosphere. The primary goals of the coronal and
solar wind studies are to understand the coronal heating mechanism
and its expansion into the solar wind. These goals will be achieved
both by remote sensing of the solar atmosphere with high resolution
spectrometers and telescopes and by in situ measurement of the
composition and energy of the resulting solar wind and the energetic
particles that propagate through it. The structure and interior dynamics
are to be studied by helioseismological methods and the measurement
of solar irradiance variations. The SOHO spacecraft will be three-axis
stabilized and located in a halo orbit around the L1 Lagrangian point
(approximately 1 percent of the distance from the Earth to the Sun). It
is currently scheduled for launch in July 1995.
---------------------------------------------------------
Title: Mass and Energy Flow in Prominences
Authors: Poland, Arthur I.
1990LNP...363..120P Altcode: 1990doqp.coll..120P; 1990IAUCo.117..120P
Mass and energy flow in quiescent prominences is considered based on the
hypothesis that active region prominences have a different structure
and thus different mass and energy flow characteristics. Several
important physical parameters have been plotted using the computational
model, representing the evolutionary process after the prominence
formation. The temperature, velocity, conductive flux, and enthalpy
flux are plotted against distance from the highest point in the loop
to the coolest part of the prominence. It is shown that the maximum
velocity is only about 5 km/s. The model calculations indicate that the
transition region of prominences is dominated by complex processes. It
is necessary to take into account mass flow at temperatures below
200,000 K, and both mass flow and optical depth effects in hydrogen
at temperatures below 30,000 K. Both of these effects lead to a less
steep temperature gradient through the prominence corona interface
than can be obtained from the conduction alone.
---------------------------------------------------------
Title: The Eruption of a Quiescent Prominence as Observed in
Ultraviolet Lines
Authors: Fontenla, J. M.; Poland, A. I.
1989SoPh..123..143F Altcode:
We compare observations of an eruptive and a quiescent prominence
in order to better understand the energetic processes in an eruptive
prominence. Observations of an eruptive prominence were obtained in
Hα, several UV emission lines (1215-1640 Å), and coronal white light
at approximately 19:00 UT on September 20, 1980. The data we present
shows the development of the eruption in the Hα and UV emission lines
and is compared with the intensities from similar observations of a
quiescent prominence. While the event is coincident with some coronal
changes, above 1.2 and up to 1.5 solar radii, it does not result in
a true coronal mass ejection event.
---------------------------------------------------------
Title: SUMER - Solar ultraviolet measurements of emitted radiation.
Authors: Curdt, W.; Wilhelm, K.; Axford, W. I.; Marsch, E.; Richter,
A. K.; Gabriel, A. H.; Lemaire, P.; Vial, J. -C.; Grewing, M.; Huber,
M. C. E.; Jordan, S. D.; Poland, A. I.; Thomas, R. J.; Timothy, J. G.
1989AGAb....2...14C Altcode: 1989amt..conf...14C
No abstract at ADS
---------------------------------------------------------
Title: Opacity Effects on the Radiative Losses of Coronal Loops
Authors: Kuin, N. P. M.; Poland, A. I.
1989BAAS...21Q.711K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1989epos.conf..225C Altcode:
The work of this group was concerned with how the energy released
in a solar flare is transported through the solar atmosphere before
escaping in the form of radiant and mechanical energy.
---------------------------------------------------------
Title: SOHO: an observatory to study the solar interior and the
solar atmosphere
Authors: Domingo, V.; Poland, A. I.
1988sohi.rept....7D Altcode:
The Solar and Heliospheric Observatory (SOHO) is described. The two
main objectives of SOHO are to improve understanding of solar coronal
phenomena and to study solar structure and interior dynamics from
its core to the photosphere. The primary goals of the coronal and
solar wind studies are to understand the coronal heating mechanism
and its expansion into the solar wind. These goals will be achieved
both by remote sensing of the solar atmosphere with high resolution
spectrometers and telescopes and by in situ measurement of the
composition and energy of the resulting solar wind and the energetic
particles that propagate through it. The structure and interior dynamics
are to be studied by helioseismological methods and the measurement
of solar irradiance variations. The SOHO spacecraft will be three-axis
stabilized and located in a halo orbit around the L1 Lagrangian point
(approximately 1 percent of the distance from the Earth to the Sun). It
is currently scheduled for launch in July 1995.
---------------------------------------------------------
Title: SUMER: Solar Ultraviolet Measurements of Emitted Radiation
Authors: Wilhelm, K.; Axford, W. I.; Curdt, W.; Gabriel, A. H.;
Grewing, M.; Huber, M. C. E.; Jordan, M. C. E.; Lemaire, P.; Marsch,
E.; Poland, A. I.
1988sohi.rept...31W Altcode:
The SUMER (solar ultraviolet measurements of emitted radiation)
experiment is described. It will study flows, turbulent motions, waves,
temperatures and densities of the plasma in the upper atmosphere of
the Sun. Structures and events associated with solar magnetic activity
will be observed on various spatial and temporal scales. This will
contribute to the understanding of coronal heating processes and the
solar wind expansion. The instrument will take images of the Sun in EUV
(extreme ultra violet) light with high resolution in space, wavelength
and time. The spatial resolution and spectral resolving power of the
instrument are described. Spectral shifts can be determined with
subpixel accuracy. The wavelength range extends from 500 to 1600
angstroms. The integration time can be as short as one second. Line
profiles, shifts and broadenings are studied. Ratios of temperature
and density sensitive EUV emission lines are established.
---------------------------------------------------------
Title: An Intensified CCD EUV Camera for the SOHO/CDS Experiment
Authors: Golub, L.; Kalata, K.; Poland, A. I.; Thomas, R. J.
1988BAAS...20..980G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hydrogen and Helium Excitation by Extreme Ultraviolet Radiation
for the Production of White-Light Flares
Authors: Poland, A. I.; Milkey, R. W.; Thompson, W. T.
1988SoPh..115..277P Altcode:
White-light flares are defined as those flares that produce significant
enhancement of emission in the visible light continuum. The source
of energy for this emission has not yet been identified with several
possibilities being suggested: heating of the lower chromosphere by some
mechanical or magnetic means, or by soft X-ray or extreme ultraviolet
radiation from coronal loops being absorbed in the lower chromosphere
and re-emitted in the visible.
---------------------------------------------------------
Title: Some dynamical aspects of a quiescent filament
Authors: Schmieder, B.; Demoulin, P.; Poland, A.; Thompson, B.
1988A&A...197..281S Altcode:
A typical quiescent filament was observed on the disk in the Hα
and C IV lines during a period of approximately one hour. Vertical
velocities (<2.5 km s<SUP>-1</SUP>) with a time scale of 5 min and
a spatial scale of a few tens of seconds of arc were detected in Hα,
and associated with microturbulence in both lines. The C IV observations
correlated well with those in Hα, and showed no indication of material
heating from Hα to C IV temperatures. Two mechanisms to explain these
observations are proposed: mass motion along twisted magnetic field
or instabilities triggering waves along the filament.
---------------------------------------------------------
Title: The SOHO project: helioseismology investigations
Authors: Domingo, V.; Poland, A.
1988AdSpR...8k.109D Altcode: 1988AdSpR...8..109D
The solar and heliospheric observatory, Soho, will be placed into a
halo orbit around the L1 Sun-Earth Lagrangian point in 1995. It will
carry a set of instruments to study the physical phenomena in the
solar atmosphere that heat the solar corona, the mechanisms by which
the solar corona expands into the solar wind, and investigate the
structure of the solar interior by the study of solar oscillations,
both in velocity and in intensity (Helioseismology). <P />In this paper
we describe the mission and the investigations to be carried out with
the helioseismology instruments in the payload. A solar oscillations
imager will measure velocity oscillations of degree up to 4000, while
two other instruments will measure very long series of low degree modes
of oscillation, one of them in velocity and the other in irradiance. The
data obtained will be used to study the radial stratification and the
longitudinal variation of the physical characteristics of the Sun,
as well as many dynamical phenomena of the upper layers of the solar
atmosphere.
---------------------------------------------------------
Title: A model for the structure and formation of prominences.
Authors: Poland, A. I.; Mariska, J. T.
1988dssp.conf..133P Altcode:
The authors present a geometric model for the magnetic structure of
a prominence inspired by recent high resolution images and magnetic
field measurements of filaments and prominences. In this model the
observed prominence structures are a mapping of locations in the
magnetic field structure where material can condense without falling
to the chromosphere. Vertical structures near the footpoints are a
series of near potential fields.
---------------------------------------------------------
Title: Current Understanding and Issues on Electron Beam Injection
in Space
Authors: Poland, A. I.; Domingo, V.
1988AdSpR...8k.101P Altcode: 1988AdSpR...8Q.101P
The Solar and Heliospheric Observatory (SOHO) satellite mission is
planned to study the solar interior, to investigate the physical
phenomena related to the formation of the solar corona and the solar
wind, and to make in situ measurements of the solar wind. The SOHO
instruments designed to study the solar atmosphere and the solar wind
are described. The experiments include the study of solar UV radiation,
a coronal diagnostic spectrometer, an extreme UV imaging telescope, a UV
coronagraph spectrometer, a white light and spectrometric coronagraph,
and a study of solar wind anisotropies.
---------------------------------------------------------
Title: Soho and Cluster - the scientific instruments.
Authors: Domingo, V.; Schmidt, R.; Poland, A. I.; Goldstein, M. L.
1988ESABu..56...24D Altcode:
The need to understand the complex processes that control the structure
and dynamics of our daylight star and define the Earth's environment
in space, has long been widely realised. Its continuing importance is
reflected by the fact that twenty-three Principal Investigators and
several hundred Co-Investigators from more than eighteen countries
are now actively involved in the preparations for and execution of
the Soho and Cluster missions.
---------------------------------------------------------
Title: A Model for the Structure and Formation of Prominences
Authors: Poland, A. I.; Mariska, J. T.
1987dssp.work..133P Altcode: 1987ASSL..150..133P
No abstract at ADS
---------------------------------------------------------
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf..3.4C Altcode: 1986epos.confC...4C
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf.3.34C Altcode: 1986epos.confBC.34C
No abstract at ADS
---------------------------------------------------------
Title: Coronal and Prominence Plasmas: proceedings of workshops held
at Goddard Space Flight Center, April 9-11, 1985, April 8-10, 1986
Authors: Poland, Arthur I.
1986NASCP2442.....P Altcode: 1986copp.nasa.....P
No abstract at ADS
---------------------------------------------------------
Title: Numerical simulations of a siphon mechanism for quiescent
prominence formation.
Authors: Poland, A. I.; Mariska, J. T.; Klimchuk, J. A.
1986NASCP2442...57P Altcode: 1986copp.nasa...57P
Quiescent prominences represent a significant challenge to our
understanding of the flow of mass and energy in the outer layers of
the solar atmosphere. A small number of quiescent prominences contain
as much mass as the entire corona (Athay, 1976). The problem then is
how to get that much material into the relatively small volume of
a prominence and maintain it at a temperature of 10,000 K in close
proximity to material at one million K. The thermal insulation to
conduction provided by the magnetic field explains the disparate
temperatures. The mass source problem is less well understood. One
method for supplying mass to the prominence is to siphon it from the
chromosphere. The siphon mechanism begins with a magnetic loop that
evolves into a configuration with a gravitational well, such as that
described by Kippenhahn and Schluter (1957). This could be formed, for
example, by a twist in the magnetic field. A gravitational well could
also be formed by a condensation induced sag in the field. This could
further enhance the condensation process. Once this well has formed,
or as it is forming, the material in the well area of the loop must
cool and condense to the point where radiative losses exceed any
heat input. Additional material must also flow into the well from
the underlying chromosphere to supply the mass required to form the
prominence. One example from a series of numerical simulations that were
performed to study the formation of quiescent prominences is presented.
---------------------------------------------------------
Title: Constraints on filament models deduced from dynamical analysis.
Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Malherbe, J. M.;
Poland, A. I.
1986NASCP2442..177S Altcode: 1986copp.nasa..177S
The conclusions deduced from simultaneous observations with the
Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum
Mission satellite, and the Multichannel Subtractive Double Pass (MSPD)
spectrographs at Meudon and Pic du Midi observatories are presented. The
observations were obtained in 1980 and 1984. All instruments have
almost the same field of view and provide intensity and velocity maps
at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha
line and 3" for C IV. The high resolution and simultaneity of the two
types of observations allows a more accurate description of the flows
in prominences as functions of temperature and position. The results
put some contraints on the models and show that dynamical aspects must
be taken into account.
---------------------------------------------------------
Title: Dynamics of solar filaments. VI - Center-to-limb study of
H-alpha and C IV velocities in a quiescent filament
Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Poland, A. I.
1986A&A...166..319S Altcode:
The rotation of a stable quiescent filament from near disk center to
the limb has been observed. Observations of intensity and velocity
were made in H-alpha and C IV, and compared with magnetic field
measurements. From the H-alpha observations, it is concluded that the
filament is made up of many small scale magnetic features that are
not coherently aligned along the neutral line. They are especially
convoluted at the apparent 'footpoints'. The measured velocities are
of the order of a few kilometers per second in both lines. However,
the comparison of the standard deviations of the C IV velocities in
and out of the filament as it rotates toward the limb shows that the
vertical velocities in the filament are greater than the horizontal
velocities. Measurements of velocity do not make it possible to
distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter
(1957) models for prominences because neither theory is adequately
developed for this comparison. However, the observation of the many
fine loops brings into question the correctness of either model.
---------------------------------------------------------
Title: Hydrogen and Helium Excitation by EUV Radiation for the
Production of White-Light Falres
Authors: Thompson, W. T.; Poland, A. I.; Milkey, R. W.
1986BAAS...18..899T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ephemeral active regions and coronal bright points: A solar
maximum Mission 2 guest investigator study
Authors: Harvey, K. L.; Tang, F. Y. C.; Gaizauskas, V.; Poland, A. I.
1986gsfc.rept.....H Altcode:
A dominate association of coronal bright points (as seen in He
wavelength 10830) was confirmed with the approach and subsequent
disappearance of opposite polarity magnetic network. While coronal
bright points do occur with ephemeral regions, this association is a
factor of 2 to 4 less than with sites of disappearing magnetic flux. The
intensity variations seen in He I wavelength 10830 are intermittent
and often rapid, varying over the 3 minute time resolution of the
data; their bright point counterparts in the C IV wavelength 1548
and 20 cm wavelength show similar, though not always coincident time
variations. Ejecta are associated with about 1/3 of the dark points and
are evident in the C IV and H alpha data. These results support the
idea that the anti-correlation of X-ray bright points with the solar
cycle can be explained by the correlation of these coronal emission
structures with sites of cancelling flux, indicating that, in some
cases, the process of magnetic flux removal results in the release of
energy. That the intensity variations are rapid and variable suggests
that this process works intermittently.
---------------------------------------------------------
Title: A Siphon Mechanism for Supplying Prominence Mass
Authors: Poland, A. I.; Mariska, J. T.
1986SoPh..104..303P Altcode:
We examine a siphon-like mechanism for moving mass from the chromosphere
to a gravitational well at the top of a magnetic loop to form a
prominence. The calculations assume no apriori flow velocity at the loop
base. Instead heating in the loop legs drives the flow. The prominence
formation process requires two steps. First, the background heating
rate must be reduced to on the order of 1 % of the initial heating
rate required to maintain the coronal loop. This forms an initial
condensation at the top of the loop. Second, the heating must take
place only in the loop legs in order to produce a pressure differential
which drives mass up into the well at the top of the loop. The heating
rate in the loop must be increased once the prominence has begun to
form or full prominence densities can not be achieved in a reasonable
time. We conclude that this heating driven siphon-like mechanism is
feasible for producing and maintaining prominences.
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986NASCP2439....3C Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.
---------------------------------------------------------
Title: On V and hard X-rays, observations and model calculations.
Authors: Poland, A. I.; Mariska, J. T.
1986NASCP2449..279P Altcode: 1986rfsf.nasa..279P
This paper is an amalgamation of two published works that discuss
the observation and theoretical calculations of O V (T ≡ 250,000K)
and hard X-rays (30 - 100 keV) emitted during flares. The papers are
by Poland et al. (1984, see Abstr. 37.073.132) and Mariska and Poland
(1985, see Abstr. 39.076.024). The observations of hard X-rays and
O V show that the excitation processes for each type of emission are
closely coupled. Except for small differences the two types of emission
rise and fall together during a flare. Model calculations are able
to reproduce this behavior to a large extent, only when conductive
processes do not dominate the energy transport processes.
---------------------------------------------------------
Title: Dynamics of solar filaments. IV - Structure and mass flow of
an active region filament
Authors: Schmieder, B.; Malherbe, J. M.; Simon, G.; Poland, A. I.
1985A&A...153...64S Altcode:
An active region filament near the center of the solar disk was observed
on September 29-30, 1980, with the Multichannel Subtractive Double Pass
Spectrograph of the Meudon solar tower and the UV Spectrograph and
Polarimeter aboard the SMM satellite. H-alpha and C IV measurements
are presently used to study brightness and material velocity in the
10,000 and 100,000 K temperature ranges, and photospheric magnetograms
are used to investigate the underlying magnetic field. Attention is
given to the constraints imposed on possible filament structures by
observations, as well as the expected MHD relationships.
---------------------------------------------------------
Title: Numerical Simulation of a Siphon Mechanism for Quiescent
Prominences
Authors: Mariska, J. T.; Poland, A. I.
1985BAAS...17..842M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energetics of a double flare on November 8, 1980
Authors: Doyle, J. G.; Byrne, P. B.; Dennis, B. R.; Emslie, A. G.;
Poland, A. I.; Simnett, G. M.
1985SoPh...98..141D Altcode:
Here we complete an energy balance analysis of a double impulsive
hard X-ray flare. From spatial observations, we deduce both
flares probably occur in the same loop within the resolution of the
data. For the first flare, the energy in the fast electrons (assuming
a thick-target model) is comparable to the convective up-flow energy,
suggesting that these are related successive modes of energy storage and
transfer. The total energy lost through radiation and conduction, 2.0 ×
10<SUP>28</SUP> erg, is comparable to the energy in fast electrons 2.5
× 10<SUP>28</SUP> erg. For the second flare, the energy in the fast
electrons is more than one order of magnitude greater than the energy
of the convective up-flow. Total energy losses are within a factor
of two lower than the calculated fast electron energy. We interpret
the observations as showing that the first flare occurred in a small
loop with fast electrons heating the chromosphere and resulting in
chromospheric evaporation increasing the density in the loop. For the
second flare most of the heating occurred at the electron acceleration
site. The two symmetrical components of the Ca XIX resonance line and a
high velocity down-flow of 115 km s <SUP>−1</SUP> observed at the end
of the second hard X-ray burst are consistent with the flare eruption
(reconnection) region being high in the flare loop. The estimated
altitude of the acceleration site is 5500 km above the photosphere.
---------------------------------------------------------
Title: The Relation Between Hard X-Ray and Transition Region Line
Emission in Solar Flares
Authors: Mariska, J. T.; Poland, A. I.
1985SoPh...96..317M Altcode:
Observational evidence suggests that both the hard X-ray and ultraviolet
emission from the impulsive phase of flares result from an electron
beam. We present the results of model calculations that are consistent
with this theory. The impulsive phase is envisioned as occurring
in many small magnetically confined loops, each of which maintains
an electron beam for only a few seconds. This model successfully
matches several observed aspects of the impulsive phase. The corona is
heated to less than 2 × 10<SUP>6</SUP> K, maximum enhanced emission
occurs in lines formed near 10<SUP>5</SUP> K, and there is only
slight enhancement between 10<SUP>5</SUP> and 2 × 10<SUP>6</SUP>
K. The slope of the observed relationship between hard X-ray and
OV 1371 Å emission is also matched, but the relative emission is
not. The calculations indicate that UV emission lines formed below a
temperature of about 10<SUP>5</SUP> K will arise predominantly from
the chromospheric region heated by the electron beam to transition
region temperatures. Emission lines formed at higher temperatures will
be produced in the transition region. This should be detectable in
density-sensitive line ratios. To account successfully for the impulsive
UV emission, the peak temperature in the impulsively heated loops must
remain below about 2 × 10<SUP>6</SUP> K. Thus our model implies that
the impulsive heating takes place in different loops from the hotter
gradual phase emission.
---------------------------------------------------------
Title: Performance testing of the high altitude observatory PDS
microdensitometer
Authors: Poland, A.; Munro, R.; Friend, D.
1984asmd.conf...19P Altcode:
High Altitude Observatory HAO microdensitometer undergoes monthly
testing to assure its consistent performance. These tests check
positional and photometric stability at the 10 micron aperture
level. The HAO test procedure is designed to run without operator
intervention following initial configuration of the microdensitometer
for each subprocedure. Specialized test software is resident in
the PDP 8. The operator selects the proper subprocedure by entering
commands. Once computer control is established, it is not relinquished
until the test is complete.
---------------------------------------------------------
Title: The energy relation between hard X-ray and O V emission in
solar flares
Authors: Poland, A. I.; Orwig, L. E.; Mariska, J. T.; Auer, L. H.;
Nakatsuka, R.
1984ApJ...280..457P Altcode:
The relationship between energy emitted in hard X-rays and the
ultraviolet during the impulsive phase of solar flares provides
an important diagnostic for understanding the energy flow from
nonthermal to thermal. Many flares were observed from the Solar
Maximum Mission satellite simultaneously in hard X-rays and the O V
line at 1371 A formed at 250,000 K, providing information relevant to
this problem. Previous work has shown that short time scale peaks in
emission of these two types of radiation coincide in time to within 1
s. In this work the energy relation between the two types of emission
is investigated and it is found that for any given flare there is a
definite relation between hard X-ray and O V emissions throughout
the flare, but from one flare to the next this relation varies
markedly. These differences are attributed to the initial conditions in
the flaring loops and some exploratory model calculations are presented
to support this hypothesis.
---------------------------------------------------------
Title: A Multiwavelength Study of a Double Impulsive Flare
Authors: Strong, K. T.; Benz, A. O.; Dennis, B. R.; Leibacher, J. W.;
Mewe, R.; Poland, A. I.; Schrijver, J.; Simnett, G.; Smith, J. B.,
Jr.; Sylwester, J.
1984SoPh...91..325S Altcode:
Extensive data from the Solar Maximum Mission (SMM) and ground-based
observatories are presented for two flares; the first occurred at
12:48 UT on 31 August, 1980 and the second just 3 min later. They were
both compact events located in the same part of the active region. The
first flare appeared as a typical X-ray flare: the CaXIX X-ray lines
were broadened (≡ 190±40 km s<SUP>-1</SUP>) and blue shifted (≡
60±20 km s<SUP>-1</SUP>) during the impulsive phase, and there was
a delay of about 30 s between the hard and soft X-ray maxima. The
relative brightness of the two flares was different depending on
the spectral region being used to observe them, the first being the
brighter at microwave and hard X-ray wavelengths but fainter in soft
X-rays. The second flare showed no significant mass motions, and the
impulsive and gradual phases were almost simultaneous. The physical
characteristics of the two flares are derived and compared. The main
difference between them was in the pre-flare state of the coronal plasma
at the flare site: before the first flare it was relatively cool (3 ×
10<SUP>6</SUP> K) and tenuous (4 × 10<SUP>9</SUP> cm<SUP>-3</SUP>),
but owing to the residual effects of the first flare the coronal plasma
was hotter (5 × 10<SUP>6</SUP> K) and more dense (3 × 10<SUP>11</SUP>
cm<SUP>-3</SUP>) at the onset of the second flare. We are led to believe
from these data that the plasma filling the flaring loops absorbed most
of the energy released during the impulsive phase of the second flare,
so that only a fraction of the energy could reach the chromosphere to
produce mass motions and turbulence.
---------------------------------------------------------
Title: The Relation Between Hard X-Ray and Transition-Region Line
Emission in Solar Flares
Authors: Mariska, J. T.; Poland, A. I.
1984BAAS...16R.543M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Development and Plans for a Solar Extreme Ultraviolet Telescope
and Spectrograph (SEUTS)
Authors: Epstein, G. L.; Neupert, W. M.; Poland, A. I.; Thomas, R. J.
1984BAAS...16..546E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Ionization During the Impulsive Phase of A Solar Flare
Authors: Waldron, W. L.; Poland, A. I.
1984BAAS...16..545W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Performance testing of the High Altitude Observatory PDS
microdensitometer.
Authors: Poland, A.; Munro, R.; Friend, D.
1984NASCP2317...19P Altcode:
The High Altitude Observatory PDS microdensitometer, purchased in 1972,
is one of the earlier machines produced. Particular features of this
machine include: PDP-8 control, 12 bit A/D converter, high density
log amplifier, updated locking microscope head, auto-loc, teflon
drive screws and nuts, and high speed operation (up to 60 mm/sec). The
microdensitometer is generally used with 10 or 50 micron apertures on 35
mm and 70 mm film. The HAO microdensitometer undergoes monthly testing
to assure its consistent performance. These tests are designed to check
positional and photometric stability at the 10 micron aperture level.
---------------------------------------------------------
Title: Performance Testing of the High Altitude Observatory PDS
Microdensitometer
Authors: Poland, A. I.; Munro, R.; Friend, D.
1984amd..conf...19P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetohydrodynamic simulation of the coronal transient
associated with the solar limb flare of 1980, June 29, 18∶21 UT
Authors: Wu, S. T.; Wang, S.; Dryer, M.; Poland, A. I.; Sime, D. G.;
Wolfson, C. J.; Orwig, L. E.; Maxwell, A.
1983SoPh...85..351W Altcode:
Soft X-ray data from the XRP experiment on SMM are used to generate
the temperature and density in the flaring region of the 1980, June
29 (18∶21 UT) solar flare. The temporal data (T<SUB>max</SUB> ∼-
20 × 10<SUP>6</SUP> K and n<SUB>max</SUB> ∼- 4 × 10<SUP>11</SUP>
cm<SUP>−3</SUP>), together with an assumed velocity, are used to
simulate mass injection as the input pulse for the MHD model of Wu
et al. (1982a, 1983a). The spatial and temporal coronal response is
compared with the ground-based, Mark III K-coronameter observations
of the subsequent coronal transient. The simulation produces a
spatially-wide, large amplitude, temporarily-steepened MHD wave
for either of the two `canonical' magnetic topologies (closed and
open), but no shock wave. This result appears to be confirmed by the
fact that a type II radio event was observed late in the event for
only a few minutes, thereby indicating that a steepening wave with
temporary, marginal shock formation, was indeed present. The density
enhancements produced by the simulation move away from the Sun at the
same velocity observed by the K-coronameter. However, the observation
of the coronal transient included a rarefaction that does not appear
in the simulation. A probable explanation for this discrepancy is the
likelihood that the magnitude and temporal profile of the density of
the soft X-ray emitting plasma should not have been used as part of the
mass injection pulse. We believe that the temperature profile alone,
as suggested by earlier simulations, might have been a necessary and
sufficient condition to produce both the compression and rarefaction of
the ambient corona as indicated by the K-coronameter data. Hence, the
dense plasma observed by XRP was probably confined, for the most part,
close to the Sun during the ∼ 17 min duration of the observations.
---------------------------------------------------------
Title: Physical Conditions in a Quiescent Prominence Derived
from Ultraviolet Spectra Obtained with the UVSP Instrument on the
Solar-Maximum
Authors: Poland, A. I.; Tandberg-Hanssen, E.
1983SoPh...84...63P Altcode:
A quiescent prominence observed above the north-west limb on November
20, 1980, is analyzed using data obtained with the Ultraviolet
Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission
(SMM). The spectral data include the lines 1215 Å of HI, 1401 Å of
OIV, 1402 Å of SiIV, 1548 Å of CIV, 1640 Å of HeI, and 1655 Å of
CI. From an analysis of these lines and their emission patterns we
deduce physical characteristics of the prominence plasma, and suggest
in particular that the prominence consisted of flux tubes at various
temperatures. In the hotter parts of the plasma the number density
reached values of about 3 × 10<SUP>11</SUP> cm<SUP>#X2212;3</SUP>.
---------------------------------------------------------
Title: Relation Between Hard X-ray and OV Energy Emitted During
Solar Flares
Authors: Poland, A. I.; Orwing, L. E.; Mariska, J. T.; Auer, L. H.
1983BAAS...15..713P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous ultraviolet line and hard X-ray bursts in the
impulsive phase of solar flares
Authors: Woodgate, B. E.; Shine, R. A.; Poland, A. I.; Orwig, L. E.
1983ApJ...265..530W Altcode:
Several fast impulsive phase solar flare bursts were observed by
the Solar Maximum Mission instruments on 1980 November 8. The bursts
were seen to be coincident in the O V 1371 Å line formed at 2.5 ×
10<SUP>5</SUP> K and in 25-300 keV X-rays, to within the resolution
time of 1 s. This lack of time difference is inconsistent with models
for these flares in which the hard X-rays are produced at the top of
a loop, followed by the formation of a thermal conduction front which
travels to the footpoint where a UV burst is produced by heating. Models
in which both X-rays and UV radiation are produced at the footpoint,
or an electron beam transmits energy between loop top and footpoint
is less than 1 s, are allowed.
---------------------------------------------------------
Title: Ultraviolet Observations of Solar Flares
Authors: Poland, A. I.
1982Obs...102..123P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Impulsive and Gradual Phases of a Solar Limb Flare as
Observed from the Solar Maximum Mission Satellite
Authors: Poland, A. I.; Machado, M. E.; Wolfson, C. J.; Frost,
K. J.; Woodgate, B. E.; Shine, R. A.; Kenny, P. J.; Cheng, C. C.;
Tandberg-Hanssen, E. A.; Bruner, E. C.; Henze, W.
1982SoPh...78..201P Altcode:
Simultaneous observations of a solar limb flare in the X-ray and
ultraviolet regions of the spectrum are presented. Temporal and
spectral X-ray observations were obtained for the 25-300 keV range
while temporal, spectral, and spatial X-ray observations were obtained
for the 30-0.3 keV range. The ultraviolet observations were images
with a 10″ spatial resolution in the lines of O v (T<SUB>e</SUB>
∼ 2.5 × 10<SUP>5</SUP> K) and Fe XXI (T<SUB>e</SUB> ∼ 1.1 ×
10<SUP>7</SUP> K). The hard X-ray and O v data indicate that the
impulsive phase began in the photosphere or chromosphere and continued
for several minutes as material was ejected into the corona. Impulsive
excitation was observed up to 30 000 km above the solar surface at
specific points in the flare loop. The Fe XXI observations indicate a
preheating before the impulsive phase and showed the formation of hot
post-flare loops. This later formation was confirmed by soft X-ray
observations. These observations provide limitations for current
flare models and will provide the data needed for initial conditions
in modeling the concurrent coronal transient.
---------------------------------------------------------
Title: Coronal activity below 2 solar radii - 1980 February 15-17
Authors: Fisher, R. R.; Poland, A. I.
1981ApJ...246.1004F Altcode:
Coronal observations concerning the area between the solar surface
and 2.0 solar radii can now be conducted by making use of a new
ground-based K-coronameter and a prominence monitor on Mauna Loa in
Hawaii. Observations made by the K-coronameter on three consecutive
days surrounding the eclipse of 1980 February 16 show that the solar
corona was very active during this time. Definite changes occurred
between each day's observations. During one period of K-coronameter
observations (1980 February 15) a coronal transient was observed to move
through the coronameter's field of view. A description is presented of
the general changes which occurred in the corona during this period,
taking into account the coronal transient observed by the prominence
monitor and K-coronameter. The most important aspects of these new
observations pertain to the relationship between the H alpha prominence
and the surrounding coronal material.
---------------------------------------------------------
Title: The Evolution of a Coronal Streamer and the Photospheric
Magnetic Field
Authors: Poland, A. I.; MacQueen, R. M.
1981SoPh...71..361P Altcode:
A large equatorial coronal streamer observed in the outer corona
(3R<SUB>⊙</SUB>) grew in brightness and size during successive limb
passages between October 6, 1973 and January 10, 1974 (solar rotations
1606-1611). Unlike previous studies of streamers and their photospheric
associations, no definite surface feature could be identified in the
present case. This suggests that the streamer is associated with the
large scale photospheric magnetic field. Comparison of the streamer
growth with observed underlying photospheric magnetic flux changes
indicated that as the streamer increased in brightness, areal extent,
and density, the photospheric magnetic flux decreased. Three possible
explanations for the streamer's growth are presented; the conceptually
simplest being that the decrease in photospheric field results in an
opening of the flux tubes under the streamer which permits an increased
mass flux through the streamer.
---------------------------------------------------------
Title: New Mauna Loa coronagraph systems
Authors: Fisher, R. R.; Lee, R. H.; MacQueen, R. M.; Poland, A. I.
1981ApOpt..20.1094F Altcode:
A new set of instruments, consisting of two coronagraph systems,
has been installed and is operating at the Mauna Loa Observing
Station, Hawaii. The instruments are the 23-cm objective Mark III
K-coronameter (K-III) system, a photoelectric instrument used to
observe the inner solar corona from 1.2 R0 to 2.2 R0 and the 12.5-cm
objective Prominence Monitor system used for the detection of H-alpha
limb activity. New features of the K-coronameter system include the
use of achromatic wave plates for wide bandpass operation and linear
diode array detectors. Raster scans of the coronal image are obtained
in 1.5 min for a critical sampling scheme of 20-sec of arc resolution
(10 x 10-sec of arc pixels) in the coronal pB image. This represents
a 350 information gain factor for each detection channel when compared
with the previous Mauna Loa K-coronameters.
---------------------------------------------------------
Title: Coronal Transients Near Sunspot Maximum
Authors: Poland, A. I.; Howard, R. A.; Koomen, M. J.; Michels, D. J.;
Sheeley, N. R., Jr.
1981SoPh...69..169P Altcode:
The Naval Research Laboratory's most recent Earth-orbiting coronagraph,
called Solwind, has been observing the Sun's outer corona (2.6-10.0
R<SUB>⊙</SUB>) at 10-min intervals since March 28, 1979. These
observations provide the first comprehensive view of coronal transients
near the peak of a sunspot cycle. Six, well-defined transients in
our quick-look data have masses ranging from 7 × 10<SUP>14</SUP>
g to 2 × 10<SUP>16</SUP> g and outward speeds ranging from 150 km
s<SUP>−1</SUP> to 900 km s<SUP>−1</SUP>. These values are comparable
to the ones that were obtained with the OSO-7 and Skylab observations
during the declining phase of the last sunspot cycle. Although the
amount of quick-look data is not sufficient to provide meaningful
statistics, the coronal transients near sunspot maximum seem to occur
with a greater frequency and a wider latitude range than the transients
during the declining phase of the cycle. In both eras, there is a good,
but imperfect, association between the occurrence of coronal transients
and surface phenomena such as eruptive prominences and flares.
---------------------------------------------------------
Title: Changes in the Characteristics of the Coronal Plasma During
Two Impulsive Flares
Authors: Strong, K. T.; Sylwester, J.; Parmar, A.; Dennis, B.;
Poland, A.
1980BAAS...12R.911S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Development of Flares Observed in the Spectral Lines OV
1371 Å, FeXXI 1354 Å, and in Hard X-Rays
Authors: Woodgate, B. E.; Bruner, E. C.; Cheng, C. C.; Dennis, B. R.;
Gurman, J. B.; Frost, K. J.; Hyder, C. L.; Kiplinger, A.; Mason,
H. E.; Orwig, L. E.; Poland, A. I.; Schoolman, S. A.; Shine, R. A.;
Tandberg-Hanssen, E. A.
1980BAAS...12..911W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: UV Observations of the June 29, 1980 Flare at 18:24UT
Authors: Poland, A. I.; Woodgate, B. E.; Shine, R. A.; Frost, K. J.;
Kenny, P.; Bruner, E. C.; Wolfson, J.; Cheng, C. C.; Tandberg-Hanssen,
E. A.; Gurman, J.; Henze, W.; Machado, M.
1980BAAS...12..903P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The observation of a high-latitude coronal transient
Authors: Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels,
D. J.; Poland, A. I.
1980ApJ...238L.161S Altcode:
On 1979 September 27 NRL's earth-orbiting coronagraph (Solwind)
observed a coronal mass ejection whose outward direction in the plane
of the sky was within 12 deg of the sun's north polar axis. Such
high-latitude transients were not observed by the OSO 7 and Skylab
coronagraphs during the declining phase of the last sunspot cycle,
but may be relatively common near sunspot maximum.
---------------------------------------------------------
Title: K-coronameter observations of the solar corona, 15 - 16
February 1980.
Authors: Fisher, R.; Poland, A. I.
1980BAAS...12..750F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio and white-light observations of the 1973 August 21
coronal transient.
Authors: Gergely, T. E.; Kundu, M. R.; Munro, R. H.; Poland, A. I.
1979ApJ...230..575G Altcode:
A coronal transient, which occurred on August 21, 1973, has
been observed simultaneously in white light and at decameter
radio wavelengths. The radio observations were obtained with a
two-dimensional swept-frequency array (called the Teepee Tee). The
white-light observations consist of a series of photographs taken by
the High Altitude Observatory's coronagraph aboard Skylab. The radio
emission associated with the transient was continuum in nature and
lasted for almost 5 hours. The source of emission was observed to be
cospatial with the lower part of one of the secondary white-light
loops. A lower limit of 0.6 solar radius for the depth (extension
along the line of sight) of this part of the transient was derived
from considerations of radio-wave propagation in the corona. The radio
source showed no dispersion of height with frequency, and, therefore,
the emission is attributed to gyrosynchrotron radiation. Based on this
assumption, the magnetic-field strength in the lower part of the loop
is estimated to be in the 2.0-4.5-gauss range at a height of 2.1 solar
radii from the center of the sun.
---------------------------------------------------------
Title: The association of coronal mass ejection transients with
other forms of solar activity.
Authors: Munro, R. H.; Gosling, J. T.; Hildner, E.; MacQueen, R. M.;
Poland, A. I.; Ross, C. L.
1979SoPh...61..201M Altcode:
Coronal mass ejection transients observed with the white light
coronagraph on Skylab are found to be associated with several other
forms of solar activity. There is a strong correlation between
such mass ejection transients and chromospheric Hα activity, with
three-quarters of the transients apparently originating in or near
active regions. We infer that 40% of transients are associated with
flares, 50% are associated with eruptive prominences solely (without
flares), and more than 70% are associated with eruptive prominences or
filament disappearances (with or without flares). Nine of ten flares
which displayed apparent mass ejections of Hα-emitting material from
the flare site could be associated with coronal transients. Within
each class of activity, the more energetic events are more likely to
be associated with an observable mass ejection.
---------------------------------------------------------
Title: Mass flow in loop type coronal transients.
Authors: Anzer, U.; Poland, A. I.
1979SoPh...61...95A Altcode:
The white light coronagraph on Skylab observed many loop type coronal
transients. These loops travel through the coronagraph's field of view
(2-6R<SUB>⊙</SUB>) over a period of a few hours, after which the legs
of the loops usually remain visible for a few days. In this paper we
investigate the temporal changes in density and mass per unit length
measured along the legs of such loops during the several days after
the initial eruption. Examination of 8 transients shows that the mass
and density in the legs decrease during the few hours after the top of
the loop has travelled beyond the coronagraph's field of view. The mass
and density then increase slowly, during the next one half to one day,
then decrease again over approximately the same period. These changes
are generally shown to be too rapid to be explained by solar rotation,
indicating that the transient legs have a lifetime of only a few days.
---------------------------------------------------------
Title: Physical Conditions in a Limb Flare
Authors: Fisher, R. R.; Poland, A. I.
1978BAAS...10..657F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Motions and mass changes of a persistent coronal streamer.
Authors: Poland, A. I.
1978SoPh...57..141P Altcode:
A coronal streamer was observed by the white light coronagraph on
Skylab during 5 successive limb passages between 1 June, 1973 and 6
August, 1973. The Skylab data give independent measures of coronal
brightness and polarization, as functions of time. These permit the
distinction between changes in the coronal streamer's appearance
due to solar rotation and actual structural changes. The streamer's
visual appearance changed slightly between successive limb passages
indicating that it was not a steady state feature. Measurements of the
streamer's latitude, brightness, and polarization during 3 east limb
passages show that: (1) the streamer's axis migrated southward from
25° N at first east limb passage to 11° N at second east limb passage
to 8° N latitude at third east limb passage; (2) the streamer's mass
(and mass gradient with height), varied by between 20 and 50% from one
east limb passage to the next; (3) the streamer's longitudinal extent
was also observed to be less on successive east limb passages; and (4)
mass changes (distinct from coronal transients) occurring over hours
were detected during at least two limb passages. Comparison of the
outer coronal observations with observations from lower in the solar
atmosphere indicate that the streamer was associated with a complex of
solar activity consisting of active regions and filaments. This complex
of activity shifted southward by the same amount as the streamer. The
variations detected in the streamer preclude the detailed determination
of its three-dimensional structure.
---------------------------------------------------------
Title: Expansion and broadening of coronal loop transients: a
theoretical explanation.
Authors: Mouschovias, T. Ch.; Poland, A. I.
1978ApJ...220..675M Altcode:
Consequences are examined of the assumption that an observed coronal
loop transient is a twisted rope of magnetic-field lines expanding and
broadening in the background coronal plasma and magnetic field. It
is shown that the expansion can be accounted for by the azimuthal
component of the field; the observed broadening of the loop as it
moves outward can be accounted for by the longitudinal component of
the field. In order to have a net outward force and at the same time
avoid a classical pinch (sausage) instability, the two components of
the field must satisfy a certain inequality. It is predicted that,
as the loop rises, the width (h) of its top portion should vary
proportionally with distance (R) from the sun's center. This is in
good agreement with measurements that show h is proportional to the
0.8 power of R. The prediction that the radius of curvature of the
top portion of the loop should be proportional to R differs from the
measured variation. The difference could be accounted for by a drag
due to the background coronal field that flattens the loop's top.
---------------------------------------------------------
Title: Temporal evolution of the equatorial K-corona.
Authors: MacQueen, R. M.; Poland, A. I.
1977SoPh...55..143M Altcode:
Observations of the equatorialK-coronal radiance at 2.5R<SUB>⊙</SUB>
from Sun center and its variation with time, on a daily basis,
during the Skylab mission (May 1973-February 1974) are presented. The
observations are subdivided into three periods, each characterized
by a different variation of the radiance pattern with time. During
the initial period, encompassing two solar rotations, there are
several data gaps, but the radiance pattern shows a more or less
smooth variation with time; however, during the second period (also
about two solar rotations duration) the radiance signal is neither
persistent on the short term nor recurrent from one limb passage to
the next. Finally, during the last period, of five solar rotations
duration, the radiance signal exhibits an orderly periodic behavior
of increasing intensity. These results are interpreted as indicating
a general simplification of the coronal magnetic field through the
mission and, in comparison with harmonic analysis of the surface
magnetic field (Levine, 1977), as indicating a rapid response of
equatorial outer coronal structures to abrupt changes in the global
surface field structure.
---------------------------------------------------------
Title: A study of the background corona near solar minimum.
Authors: Saito, K.; Poland, A. I.; Munro, R. H.
1977SoPh...55..121S Altcode:
The white light coronagraph data from Skylab is used to investigate
the equatorial and polarK andF coronal components during the
declining phase of the solar cycle near solar minimum. Measurements
of coronal brightness and polarization brightness product between 2.5
and 5.5R<SUB>⊙</SUB> during the period of observation (May 1973 to
February 1974) lead to the conclusions that: (1) the equatorial corona
is dominated by either streamers or coronal holes seen in projections
on the limb approximately 50% and 30% of the time, respectively; (2)
despite the domination by streamers and holes, two periods of time
were found which were free from the influences of streamers or holes
(neither streamers nor holes were within 30° in longitude of the limb);
(3) the derived equatorial background density model is less than 15%
below the minimum equatorial models of Newkirk (1967) and Saito (1970);
(4) a spherically symmetric density model for equatorial coronal holes
yields densities one half those of the background density model; and
(5) the inferred brightness of theF-corona is constant to within ±10%
and ±5% for the equatorial and polar values, respectively, over the
observation period. While theF-corona is symmetric at 2R<SUB>⊙</SUB>
it begins to show increasing asymmetry beyond this radius such that
at 5R<SUB>⊙</SUB> the equatorialF-coronal brightness is 25% greater
than the polar brightness.
---------------------------------------------------------
Title: Radiance calibration of the High Altitude Observatory
white-light coronagraph on Skylab.
Authors: Poland, A. I.; Gosling, J. T.; MacQueen, R. M.; Munro, R. H.
1977ApOpt..16..926P Altcode:
The processing of over 35,000 photographs of the solar corona obtained
by the white-light coronograph on Skylab is described. Calibration of
the vast amount of data was complicated by temporal effects of radiation
fog and latent image loss. These effects were compensated by imaging
a calibration step wedge on each data frame. Absolute calibration of
the wedge was accomplished through comparison with a set of previously
calibrated glass opal filters. Analysis employed average characteristic
curves derived from measurements of step wedges from many frames within
a given camera half-load. The net absolute accuracy of a given radiance
measurement is estimated to be 20%.
---------------------------------------------------------
Title: Measurement of stray radiance in the High Altitude
Observatory's Skylab coronagraph.
Authors: Csoeke-Poeckh, A.; MacQueen, R. M.; Poland, A. I.
1977ApOpt..16..931C Altcode:
The paper outlines two techniques used for determining the instrumental
stray radiance from orbital results obtained with the Skylab white light
coronagraph. The first technique employs images of the lunar disk made
near the time of solar eclipse to compare the apparent contrasts of
maria and highlands recorded by the coronograph with those of previous
studies and then determine the magnitude of the stray radiance and its
variation along a radius. The second method determines the azimuthal
variation of the stray radiance by measuring the change in the net
radiance of a point in the coronal images as the image is rotated.
---------------------------------------------------------
Title: The Background Corona Near Solar Minimum.
Authors: Saito, K.; Poland, A.; Munro, R.; MacQueen, R.
1977BAAS....9Q.371S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interpretation of broad-band polarimetry of solar coronal
transients: importance of the Halpha emission.
Authors: Poland, A. I.; Munro, R. H.
1976ApJ...209..927P Altcode:
An eruptive prominence and coronal transient was observed in H-alpha,
He II 304-A, and coronal white light (3700-7000 A). This event was
generically similar to many other coronal transients associated with
eruptive prominences in that loops of material propagated outward
through the corona. It differed in that some of the prominence material
was observed above 1.75 solar radii in both coronal white light and
He II. Polarization analysis of the white-light data shows that the
observed radiance from the loop-like transient was entirely due to
free electron or Thomson scattering, whereas the white-light radiance
from the prominence material was dominated by H-alpha emission. By
comparing the white-light observations with model calculations, the
densities along the loop and limits on the temperature and density of
the prominence are obtained. Material observed in both white light
and He II is shown to be cool prominence material, whereas analysis
indicates that the transient-loop material is hot and coronal in
origin. The time sequence of observations leads to the hypothesis that
the prominence material is heated as it is ejected from the sun.
---------------------------------------------------------
Title: Expansion and Broadening of Coronal Loop Transients.
Authors: Mouschovias, T. Ch.; Poland, A. I.
1976BAAS....8..534M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Structure and Fluctuations of a Coronal Streamer.
Authors: Poland, A. I.
1976BAAS....8Q.532P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The speeds of coronal mass ejection events.
Authors: Gosling, J. T.; Hildner, E.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1976SoPh...48..389G Altcode:
The outward speeds of mass ejection events observed with the
white light coronagraph experiment on Skylab varied over a range
extending from less than 100 km s<SUP>−1</SUP> to greater than
1200 km s<SUP>−1</SUP>. For all events the average speed within
the field of view of the experiment (1.75 to 6 solar radii) was 470
km s<SUP>−1</SUP>. Typically, flare associated events (Importance
1 or greater) traveled faster (775 km s<SUP>−1</SUP>) than events
associated with eruptive prominences (330 km s<SUP>−1</SUP>); no
flare associated event had a speed less than 360 km s<SUP>−1</SUP>,
and only one eruptive prominence associated event had a speed greater
than 600 km s<SUP>−1</SUP>. Speeds versus height profiles for a
limited number of events indicate that the leading edges of the ejecta
move outward with constant or increasing speeds.
---------------------------------------------------------
Title: Initial Results from the High Altitude Observatory White
Light Coronagraph on Skylab - A Progress Report
Authors: MacQueen, R. M.; Gosling, J. T.; Hildner, E.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1976RSPTA.281..405M Altcode: 1976RSLPT.281..405M
The frequent, periodic observations by the white light coronagraph
allow an examination of coronal variations over a broad range of
temporal scales. Examples of the slowest and most rapid variations
are presented. An example of extremely slow coronal variations is the
gradual evolution - to a large equatorial streamer - in association
with a marked decrease in solar activity, as the total magnetic flux
in one hemisphere decreased. Another example is given of a long-lived
quasi-stable coronal streamer, apparently associated with a stable
filament channel; comparison of this streamer with coronal potential
magnetic field computations show little correlation. The remainder
of the paper summarizes some results on coronal transients - the most
rapid variations observed. Characteristic mass and energies involved
in mass ejection transients, their temporal and spatial distributions,
their associations with surface phenomena and possible interplanetary
signatures, and finally their role in coronal evolution are briefly
noted.
---------------------------------------------------------
Title: Frequency of coronal transients and solar activity.
Authors: Hildner, E.; Gosling, J. T.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1976SoPh...48..127H Altcode:
The High Altitude Observatory's white light coronagraph aboard Skylab
observed some 110 coronal transients - rapid changes in appearance
of the corona - during its 227 days of operation. The longitudes
of the origins of these transients were not distributed uniformly
around the solar surface (51 of the 100 events observed in seven
solar rotations arose from a single quadrant of longitude). Further,
the frequency of transient production from each segment of the solar
surface was well correlated with the sunspot number and Ca II plage
(area × brightness) index in the segment, rotation by rotation. This
correlation implies that transients occur more often above strong
photospheric and chromospheric magnetic fields, that is, in regions
where the coronal magnetic field is stronger and, perhaps, more
variable. This pattern of occurrence is consistent with our belief
that the forces propelling transient material outward are, primarily,
magnetic. A quantitative relation between transient production from
an area and the Zürich sunspot number appropriate to that area is
derived, and we speculate that the relation is independent of phase
in the solar activity cycle. If true, the Sun may give rise to as many
as 100 white light coronal transients per month at solar cycle maximum.
---------------------------------------------------------
Title: The Speeds of Coronal Mass Ejection Events
Authors: Hildner, E.; MacQueen, R. M.; Munro, R. H.; Poland, A. I.;
Ross, C. L.; Gosling, J. T.
1976BAAS....8R.368H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Movie of Comet Kohoutek (1973f) as Observed Near Minimum
Elongation by the Hao Coronagraph Aboard SKYLAB
Authors: Hildner, E.; Gosling, J. T.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1976NASSP.393..124H Altcode: 1976IAUCo..25..124H
No abstract at ADS
---------------------------------------------------------
Title: A search for forward scattering of sunlight from lunar
libration clouds
Authors: Munro, R. H.; Gosling, J. T.; Hildner, E.; MacQueen, R. M.;
Poland, A. I.; Ross, C. L.; Hopfield, A.
1975P&SS...23.1313M Altcode:
An attempt to determine the radiance of forward scattered sunlight
from particles in lunar libration regions was made with the white light
coronagraph on Skylab. The libration regions could not be distinguished
against the solar K + F coronal background; an upper limit to the
libration cloud radiance is determined to be 2·5 × 10 <SUP>-11</SUP>B
<SUB>⊚</SUB>, where B <SUB>⊚</SUB> is the mean radiance of the
solar disk. Employing a model of the particle composition and size
distribution which has been proposed for the interplanetary medium,
we determine upper limits for the density enhancements in the libration
region from the upper limit of the forward scattered radiance presented
herein. Similarly, the actual spatial density enhancement is calculated
using the earlier observations of the libration region backscattered
radiance (Roach, 1975). Enhancements of a factor of 10 <SUP>2</SUP>-10
<SUP>3</SUP> are thus determined, depending upon material composition
and size distribution used. By combining the forward and backscatter
observations, it is possible to eliminate from consideration clouds
whose power law particle size distribution exponent k is 2·5
and complex index of refraction m is 1·33-0.05 i and 1·50-0.05 i
(i.e. absorbing ice and quartz particles, respectively). Finally, the
radiance contrast of a possible model libration cloud is calculated with
respect to the K- and F-corona/zodiaal light background and is shown
to be a maximum in the vicinity of solar elongation angle ∼30 deg.
---------------------------------------------------------
Title: The Emission Sources and Geometry of the Coronal Transient
of 21 August 1973.
Authors: Poland, A. I.; Munro, R. H.
1975BAAS....7..473P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Large Coronal Transient of 10 June 1973. I: Observational
Description
Authors: Hildner, E.; Gosling, J. T.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1975SoPh...42..163H Altcode:
During the 8.5 month flight of the High Altitude Observatory's white
light coronagraph on board Skylab, over 100 coronal transients were
observed. In this paper we present a description of one well observed
loop transient, that of 10 June 1973. The transient apparently resulted
from the eruption of a quiescent prominence on the limb; the emergence
of a new, bipolar active region near the prominence may have caused
the eruptior. The transient's leading edge rose from 3.6 to 5.0
solar radii (R<SUB>⊙</SUB>) from Sun center at approximately 500 km
s<SUP>−1</SUP> during the 32 min of coronagraph observations. Material
in a pre-existing streamer was swept away by the transient, causing
the streamer to disappear. The mass ejected into the corona above a
projected height of 2 R<SUB>⊙</SUB> was ≈ 5.4 × 10<SUP>15</SUP> g,
the potential energy associated with the ejected transient material was
⩾7.0 × 10<SUP>30</SUP> erg, and the kinetic energy of the ejected
material is estimated as 1.7 × 10<SUP>30</SUP> erg. The 10 June 1973
transient was, in most respects, typical of other loop transients
observed by Skylab.
---------------------------------------------------------
Title: Observations of a Long Lived Coronal Streamer
Authors: Poland, A. I.
1975BAAS....7..356P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Direct Observations of a Flare Related Coronal and Solar
Wind Disturbance
Authors: Gosling, J. T.; Hildner, E.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1975SoPh...40..439G Altcode:
Numerous mass ejections from the Sun have been detected with orbiting
coronagraphs. Here for the first time we document and discuss the direct
association of a coronagraph observed mass ejection, which followed a
2B flare, with a large interplanetary shock wave disturbance observed
at 1 AU. Estimates of the mass (2.4 × 10<SUP>16</SUP> g) and energy
content (1.1 × 10<SUP>32</SUP> erg) of the coronal disturbance are
in reasonably good agreement with estimates of the mass and energy
content of the solar wind disturbance at 1 AU. The energy estimates as
well as the transit time of the disturbance are also in good agreement
with numerical models of shock wave propagation in the solar wind.
---------------------------------------------------------
Title: Reticulation: effects and cure.
Authors: Poland, A. I.; Gosling, J. T.
1975AASPB...9...14P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photography of comet Kohoutek by Skylab white light
coronagraph.
Authors: MacQueen, R. M.; Gosling, J. T.; Hildner, E.; Munro, R. H.;
Poland, A. I.; Ross, C. L.; Keller, H. U.; Schmidt, H. U.
1975NASSP.355...19M Altcode: 1975coko.conf...19M
No abstract at ADS
---------------------------------------------------------
Title: Mass ejections from the Sun: A view from Skylab
Authors: Gosling, J. T.; Hildner, E.; MacQueen, R. M.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1974JGR....79.4581G Altcode:
More than 30 instances of sudden mass ejections from the sun were
observed with the white light coronagraph experiment aboard Skylab
during the first 118 days of the mission. Typically, these ejections
appear as large magnetic loops rooted at the sun, yet expanding
outward through the solar corona at speeds of the order of 400 km
s<SUP>-1</SUP>. The loops always appear to retain their magnetic
connection to the sun. Eighteen of these ejections were associated
with active and eruptive prominences and surges; only three ejections
appear to have been flare initiated. Associations with ground-detected
metric wavelength type 2 and 4 radio bursts occur for about 30% of these
events; however, ground-detected type 2 and 4 radio bursts originating
near the limb are almost invariably accompanied by coronagraph-observed
ejections. Pressure or MHD waves run out ahead of the transient material
ejecta; at times these waves can be detected by their effects on nearby
coronal structures. For one event, that of August 10, 1973, we make
the following estimates: (1) mass content, 4 × 10<SUP>15</SUP> grams;
(2) mass flow rate, 1.1 × 10<SUP>12</SUP> grams s<SUP>-1</SUP> (3)
energy content, 8.4 × 10<SUP>30</SUP> ergs; and (4) energy flow rate,
7.7 × 10<SUP>26</SUP> ergs s<SUP>-1</SUP>. Locally, this represents
a significant mass and energy input to the solar wind; we suggest that
the ejections are the coronal counterparts of nonrecurrent (including
shocks) solar wind disturbances detected near the orbit of the earth.
---------------------------------------------------------
Title: Theoretical Helium i Emission-Line Intensities for Quiescent
Prominences
Authors: Heasley, J. N.; Mihalas, Dimitri; Poland, A. I.
1974ApJ...192..181H Altcode:
Self-consistent solutions of the combined statistical equilibrium
and transfer equations have been carried out for a rather
complete multilevel, multi-ion model helium atom in model quiescent
prominences. The excitation and ionization of both He I and He ii were
considered simultaneously, and detailed calculations of the radiative
transfer in the resonance lines and ground-state continua of both
these ions were made, allowing for the effects of overlapping hydrogen
transitions. A large number of excited states have been included in the
computation, so that a fairly comprehensive set of predicted subordinate
line intensities are now available for comparison with observation. A
preliminary comparison of the predicted values with published singleti
triplet ratio observations shows good agreement for all the pairs of
lines considered. Subject headings: atomic processes - line formation -
prominences, solar
---------------------------------------------------------
Title: The High Altitude Observatory White Light Coronagraph
Experiment
Authors: MacQueen, R. M.; Gosling, J. T.; Hildner, E.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1974IAUS...57..505M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical helium I emission line intensities for quiescent
prominences.
Authors: Heasley, J. N.; Mihalas, D.; Poland, A. I.
1974BAAS....6..219H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The High Altitude Observatory white light coronagraph
Authors: MacQueen, R. M.; Gosling, J. T.; Hildner, E.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1974SPIE...44..207M Altcode:
Most of the instruments of the Apollo Telescope Mount are
satellite-borne because they observe in regions of the electromagnetic
spectrum where the telluric atmosphere is opaque. For the coronagraph of
the High Altitude Observatory, observing in visible light, this is not
so. The structure of the solar corona is obscured from ground-based
observations by scattered light in the earth's atmosphere, and
observations from space are required to reduce this scattered light
to a level which is negligible with respect to the brightness of the
outer solar corona.
---------------------------------------------------------
Title: The eruptive prominence of August 21, 1973 observed from
Skylab in the white light corona and in the He II 304 Å chromosphere.
Authors: Poland, A. I.; Bohlin, J. D.; Brueckner, G. E.; Purcell,
J. D.; Scherrer, V. E.; Sheeley, N. R.; Tousey, R.
1974BAAS....6..219P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Helium I Emission Line Intensities for Quiescent
Prominences.
Authors: Heasley, J. N.; Mihalas, D.; Poland, A. I.
1974BAAS....6..220H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Outer Solar Corona as Observed from Skylab: Preliminary
Results
Authors: MacQueen, R. M.; Eddy, J. A.; Gosling, J. T.; Hildner, E.;
Munro, R. H.; Newkirk, G. A., Jr.; Poland, A. I.; Ross, C. L.
1974ApJ...187L..85M Altcode:
The white-light coronagraph experiment has made frequent, periodic
observations of the solar corona from 1.5 R0 to 6.0 R0 during the Skylab
mission, and these observations will permit the determination of the
three-dimensional extent of coronal forms. There are several time
scales on which visual changes in coronal structures occur, ranging
from approximately one-half rotation to less than hours. A number of
events corresponding to the shortest time scale - coronal transients
- cause major restructuring of the corona. Subject headings: corona,
solar - solar wind
---------------------------------------------------------
Title: The Eruptive Prominence of August 21, 1973 Observed from
Skylab in the White Light Corona and in the He II 304Å Chromosphere.
Authors: Poland, A. I.; Bohlin, J. D.; Brueckner, G. E.; Purcell,
J. D.; Scherrer, V. E.; Sheeley, N. R.; Tousey, R.
1974BAAS....6..220P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The High Altitude Observatory white light coronagraph.
Authors: MacQueen, R. M.; Gosling, J. T.; Hildner, E.; Munro, R. H.;
Poland, A. I.; Ross, C. L.
1974inas.conf..207M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Outer Solar Corona as Observed from Skylab: Preliminary
Results.
Authors: Poland, A. I.; Gosling, J. T.; Hildner, E. G.; MacQueen,
R. M.; Munro, R. H.; Ross, C. L.
1973BAAS....5..419P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Coronal Forms: 7 March - 7 June 1970
Authors: Hansen, R. T.; Hansen, S. F.; Newkirk, G. A.; MacQueen,
R. M.; Gosling, J. T.; Poland, A. I.
1972BAAS....4T.383H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Helium in hot stars
Authors: Poland, A. I.
1972Obs....92...17P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energy Balance in Cool Quiescent Prominences
Authors: Poland, A.; Anzer, U.
1971SoPh...19..401P Altcode:
The energy balance for cool quiescent prominences is examined using
a 6000 km, 6000 K isothermal slab model prominence with a density
gradient dictated by a modified Kippenhahn-Schlüter model. The
model is irradiated from both sides by the coronal, chromospheric,
and photospheric radiation fields. The radiative transfer problem is
solved in detail for the Lyman continuum and Hα to determine the net
radiative energy loss for hydrogen. An estimate of the energy loss for
Ca II H and K indicates that this source of energy loss is unimportant
when compared with the hydrogen radiation. The radiative energy loss
is easily balanced by the conductive energy gain from the corona.
---------------------------------------------------------
Title: Hydrogen Ionization and n=2 Population for Model Spicules
and Prominences
Authors: Poland, A.; Skumanich, A.; Athay, R. G.; Tandberg-Hanssen, E.
1971SoPh...18..391P Altcode:
Using slab model atmospheres that are irradiated from both sides by
photospheric, chromospheric, and coronal radiation fields we have
determined the ionization and excitation equilibrium for hydrogen.
---------------------------------------------------------
Title: Energy balance in quiescent prominences.
Authors: Poland, A.; Anzer, U.
1971BAAS....3..353P Altcode:
No abstract at ADS
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Title: On the Application of the Newton-Raphson Method to the
Excitation and Transfer of Continuum Radiation
Authors: Domenico, B. A.; Poland, A. I.; Skumanich, A.
1971BAAS....3....9D Altcode:
No abstract at ADS
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Title: -Non-LTE effects for He i in early B type stars
Authors: Poland, A.; Skumanich, A.
1971MNRAS.152P..18P Altcode:
The contention by Hearn and Leckrone that non-LTE affects helium
abundances derived for early main sequence stars is shown to be in
error. Although the cores of some lines exhibit non-LTE effects, their
equivalent widths, which are dominated by line wings that remain in
LTE, are unaffected and yield the same helium abundances as in LTE. The
lines A6678 and A587S have weak wings and remain affected by non-LTE.
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Title: The Ionization Equilibrium and the N = 2 Population of Hydrogen
in Quiescent Prominences
Authors: Poland, A.; Athay, R. G.; Skumanich, A.; Tandberg-Hanssen, E.
1970BAAS....2R.338P Altcode:
No abstract at ADS
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Title: Neutral Helium Lines and the Helium Anomaly in Hot Stars
Authors: Poland, Arthur I.
1970ApJ...160..609P Altcode:
Using our previously calculated departures from LTE for He r in hot
stars we have calculated nonLTE and LTE line profiles and equivalent
widths for the 2SAP, 2P-4S, 2P-5S, and 2P-4D transitions in the singlet
and triplet systems of neutral helium in model atmospheres of 20000 and
30000 K with log g = 4. In comparing the LTE and non-LTE calculations
we found that: (1) the cores of the stronger lines are deepened by
including non-LTE; (2) for some of the weaker lines non-LTE raises
the core of the line; (3) the wings of the lines are formed in LTE,
as are the forbidden components of the 2P-4D transitions; and (4) the
equivalent widths of the lines are almost unaffected by non-LTE. Because
the forbidden components of the 2P-4D transitions are formed in LTE
and the allowed cores of these lines are strongly affected by non-LTE,
we have formed a ratio of line depth in the allowed component to
line depth in the forbidden component to compare the non-LTE effect
wfth observations. A comparison of LTE, non-LTE, and observed ratios
shows that only the non-LTE results agree with the observations. Since
the equivalent widths of the lines are not affected by non-LTE, we
have calculated LTE widths for a series of model atmospheres and have
found that the helium anomaly can be explained by LTE alone. In fact,
the helium anomaly is basically a strong line/weak line effect. A
comparison of our equivalent widths with observations indicates that
the helium abundance in early-type dwarfs is about He/H = 0.12.
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Title: The rotational temperature of a TiO band in the spectrum of
R Hydrae.
Authors: Keller, C. F.; Jackson, B. V.; Poland, A. I.; Peery,
B. F., Jr.
1970A&A.....4..415K Altcode:
A procedure is presented for the determination of a rotational
temperature from observations of the (1.0) ?`8 TiO band. The method is
based upon comparison between accurately measured wavelengths of blended
absorption features in the band and corresponding wavelengths in the
computed band proffle. The rotational temperature found from McDonald
coude' spectrograms of R Hydrae is Trot = 1430 290 0K. Key words:
R Hydrae, long period variable - molecular spectroscopy, TiO-temperature
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Title: Neutral helium lines and departures from LTE in hot stars
Authors: Johnson, Hollis Ralph; Poland, Arthur I.
1970PGLO...94.1151J Altcode:
No abstract at ADS
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Title: Neutral helium lines and the helium anomaly in hot stars
Authors: Poland, Arthur I.
1970PGLO...98..609P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Departures from LTE for neutral helium lines in hot stars
Authors: Poland, Arthur Ira Art
1969PhDT........91P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Departures from LTE for Neutral Helium Lines in Hot Stars.
Authors: Poland, Arthur Ira
1969PhDT.........4P Altcode:
No abstract at ADS
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Title: Neutral helium lines and departures from LTE in hot stars.
Authors: Johnson, H. R.; Poland, A. I.
1969JQSRT...9.1151J Altcode:
No abstract at ADS
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Title: Calculations of Solar Hydrogen Lines: Comparative Solutions
for a Standard Line Transfer Problem
Authors: Athay, R. G.; Avrett, E. H.; Beebe, H. A.; Johnson, H. R.;
Poland, A. I.; Cuny, Y.
1968rla..conf..169A Altcode:
No abstract at ADS
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Title: On the Equilibrium of Hydrogen in Early-Type Stars
Authors: Beebe, H. A.; Hollis, H. R.; Poland, A. I.
1968rla..conf..393B Altcode:
No abstract at ADS
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Title: Neutral Helium Lines and Departures from LTE in Hot Stars
Authors: Johnson, H. R.; Poland, A. I.
1968rla..conf..413J Altcode:
No abstract at ADS
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Title: Departures from Equilibrium in Neutral Helium for Hot Stars.
Authors: Johnson, Hollis K.; Poland, Arthur I.
1968AJS....73Q.186J Altcode:
Departures from equilibrium for He I are calculated for theoretical
models of early-type stars by solving self-consistently the equations
for radiative transfer and steady state for a model atom. These
calculations are aimed at an understanding of the observations of
anomalous singlet/triplet intensity ratios in hot stars. Atmospheric
models chosen are: T= 20 0000K, log g =4 (Strom, S., and Avrett, F.,
A strophys. J. Suppl. 12, 1, 1965) and T=300000K, log g=4 (Mihalas, D.,
Apstrophys. J. Suppl. 9, 321,1964). Various atomic models have been
chosen in order to test their effects on the final result. Extensive
calculations show that the singlets and triplets can be effectively
decoupled and solved separately. Final solutions for the singlets
involved the levels: 1S, 2S, 2P, 3, 4, 5, 6, 7-9,10-14,15-20, with
a similar atom for the triplets. All collisional and radiative rates
were included for all levels up to n =6. Above n =6, each level was
connected radiatively to 2S, 2P, and 3 and collisionally to 1'S, 25, 2P,
3, and the adjacent levels. Actual calculations show that the ignored
transitions are unimportant for the observed lines. At the surface
of the star (r =0), the non-LTF parameter b1= 180 for the 20 0000K
model and bi=3.4 for the 30 0000K. Results for the 20 0000K model at a
height where r(43-23P) = 2.4 are listed below. j bj j bj 1'S 1.17 21S
1.41 2~S 1.30 2'P 1.41 2~P 1.22 31 1.02 33 1.05 41 1.00 43 1.00 Thus
in the region of formation of the subordinate lines of neutral helium,
departures from thermodynamic equilibrium are quite small for a 20 0000K
star, in agreement with observations. Calculations are underway for a 30
0000K star, where significant departures from equilibrium are expected.
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Title: Effects in the Two-Color Diagram of the Rotation of A and
F Stars.
Authors: Peters, James G.; Poland, Arthur I.; Wrubel, Marshal H.
1966AJ.....71S.174P Altcode:
The method described by Collins (Astrophys. J. 138, 1134, 1963) for
computing the observed radiation of rotating stars as a function
of angular velocity and inclination, has been extended to include
departures from grayness. Computed displacements of rotating A and F
stars in the two-color diagram are compared with earlier observations
(Kraft and Wrubel, Astrophys. J. 142, 703,1965).