August 11, 1999 Eclipse
SOHO & TRACE
Ground-Based Expedition
Support Requests
SOHO & TRACE
Ground-Based Expedition
Support Requests
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SOHO & TRACE Ground-Based Expedition Support Requests |
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Salvatore Orlando
(orlando@so.estec.esa.nl )
Bernard H. Foing
(bfoing@estec.esa.nl)
Solar System Division, ESA Space Science Dept., ESTEC
Szombathely (Hungary)
Totality at Szombathely (Hungary), 10:46:23 - 10:48:45 UT;
Multi-site observing campaign from UK (10:10 UT) to Romania (11:10 UT)
The Space Science Department (SSD) of ESA is organizing a multi-site
observing campaign (UK, France, Germany, Austria, Hungary, Romania) to
be coordinated with SOHO. A multi-site eclipse campaign will provide a
longer sequence of coronal observations (from 10:10 UT to 11:10 UT).
Some of the eclipse images will be transmitted for live internet
distribution.
The core SSD science experiments will be set in Szombathely (Hungary),
where the totality is expected from 10:46:23 to 10:48:45 UT on August
11, 1999. The main objectives of the expedition are to study
temperature and density structure and dynamics in the corona, and to
search for cool material in the very hot corona. These eclipse results
will be analyzed with SOHO data. More specifically, the scientific
objectives of the SOHO-coordinated Eclipse campaign are:
For the experiment A, LASCO C2 and C3 will support the expedition with
synoptic observations in white-light over the range 2-30 solar radii,
completing the ground-based eclipse observations in white-light over
the range 1-2 solar radii. During the totality in Szombathely (10:47 UT
+/- 15 mn), LASCO C1 will provide observations in the green corona line
of Fe XIV (at 5303 A) over a 1.1-3 solar radii field of view, giving
information on the inner corona plasma at 2e6 K. The synoptic
observations from MDI will provide a map of the surface magnetic field
to be compared with 3-D coronal structures.
For the experiment C, the main purpose is to analyze the presence of
cool material distribution in the corona. An important aspect of this
program is the search for cool material in the very hot corona of
active regions. The program we propose aims to identify an active
region and/or loops evident against the dark background at the solar
limb during the totality in Szombathely (10:47 UT +/- 15 mn). Then we
propose to coordinate the ground-based eclipse observations of the
active region (loop) selected with the observations from SOHO in the
light of many emission lines simultaneously so as to study the coronal
plasma conditions over a wide range of temperatures, from chromospheric
to coronal ones. For this program, the request for SOHO observations is
the following:
He I 584.00 A, (log T(K) = 4.6)
O III 599.60 A, (log T(K) = 5.0)
O IV 554.37 A, (log T(K) = 5.2)
O V 629.73 A, (log T(K) = 5.4)
Ne VI 561.38 A, (log T(K) = 5.6)
Mg X 625.28 A, (log T(K) = 6.0)
Si XII 521.10 A, (log T(K) = 6.2)
Jay Pasachoff
(jmp@williams.edu )
Williams College
To provide CCD green-line observations of the
middle corona to extend the EIT observations to higher coronal levels
and to bridge the gap between the EIT and the LASCO C2 images. The
images will be reduced in radial-filter mode to show the
magnetic-field structure over 3 solar radii, and how it links with the
disk structures observed with EIT. The similar 1998 eclipse
observations could also be used to assess the scattered light in LASCO
C1, a comparison we are scheduled to make in the fall.
Williams College Expedition is planning to observe at or near the 5303
line with a field of view matching the C1 LASCO
coronagraph, in formal liaison with EIT. We hope for an EIT sequence
as close as possible to eclipse time at the peak of the eclipse in
Ramnicu Valcea, Romania, UT 11:02-11:04.
Our image taken at the 1998 eclipse matching the C1 observations and
merged with an EIT image, and a color image (with a simulated
radial filter) merged with an EIT temperature ratio map are posted at
http://www.williams.edu/Astronomy/eclipse98.
Ramnicu-Valcea, Romania 24 deg 22'E 45 deg 06'N
A set of EIT observations at each wavelength as close to UT 11:02-11:04 as possible, as well as LASCO C2 and C3 observations also as close as possible. These times are the peak of the eclipse.
Ken Phillips, Principal Investigator
( K.J.H.Phillips@rlac.uk )
Peter Gallagher
( P.Gallagher@qub.ac.uk )
Rutherford Appleton Laboratory (RAL)
To search for fast changes and possible periodicities in the green-line coronal emission. This may be used to identify the source of the heating of the solar corona in the form of either travelling waves or short-lived phenomena that might be related to nano-flares. Refer to SECIS WWW site for more details.
A tracking mirror or heliostat directs sunlight into the horizontally mounted telescope. A beam splitter along the optical path directs light into two CCD cameras, one with a 530.3 nm (green line) filter, the other with a broad-band (10 nm) filter at about 550 nm. The instrument will image the solar corona during eclipse totality with a spatial resolution of about 1.75 arcsecs over a sky area of approximately 0.5x0.5 solar radii. A specific region will be chosen from inspection of Yohkoh and SOHO images immediately before the eclipse. Refer to SECIS WWW site for more details.
- CDS: Full Sun Scans
- CDS: Scans on selected 4x4 arcmin region across the eclipse timeframe
- CDS: Full Sun Scans
Frederic Clette (fred@oma.be )
Royal Observatory of Belgium (ROB)
Joint Organisation for Solar Observations (JOSO)
TECONet (Trans-European Coronal Observing Network): France to India
Reference stations :
- Niederbronn-les-Bains, France > Long: -07d39m, Lat: +48d58m, Alt: 250m
- Rimnicu-Vilcea, Romania > Long: -24d22m, Lat: +45d06m, Alt: 100m
START : 10h20m UT
END : 11h40m UT for European segment, 12h35m UT for India
Reference stations :
- Niederbronn-les-Bains, France > Mid-totality : 10h31m UT
- Rimnicu-Vilcea, Romania > Mid-totality : 11h03m UT
SOHO JOINT OBSERVATIONS:
For more details, see the
JOSO TECONet page
Institut d'Astrophysique de Paris- CNRS/ leading Organization:
Dr. S. Koutchmy; J. Mouette; P-A. Grorod
Institut d'Astrophysique Spatiale- CNRS, Univ. Paris XI & Obs. de Paris:
Dr. F. Baudin; Dr. K. Bocchialini
Laboratoire d'Astronomie Spatiale- Marseille (CNRS): Dr. Ph. Lamy
Societe Astronomique de France (SAF):
Mr R. Leguet; Mr. C. LeRoux; Mr. G. Mahoux; Dr. R. Robley
in collaboration with a team from the Tabriz University (Iran):
Dr. A. Adjabshirizadeh et al.
Observations to be performed from a mountain site in Iran, near Ispahan- 100 km toward NWW. Probability of having a clear sky is 95%; altitude 2200 m; totality will occur at U.T. 12:03. The corona is expected to have the shape of a pre-maximum corona close to the polatity reversal at the N-pole but not at all in the S-pole region. Prominences and active regions at the limb should be observed, as well as streamers in projection over the N-pole.
We concentrate on the INTERMEDIATE W-L corona (between the very inner
corona, where loops and jets dominate, and the outer corona, where the
outward flow dominates) which cannot be measured from space due to the
vignetting by occulting systems.
We do an absolute photometry using simultaneously imaged stars in the
same field of view. A precise polarimetry is planned as well as the
use of a radial gradient filter of 150 mm diameter. These data are required
to complement spaceborne observations regarding the precise measurements of
plasma densities in the main part of the corona. They will be compared to
the values recently obtained during the solar minimum. High spatial
resolution imaging is an other advantage of the method.
We also plan to do some deep imaging to look at the so-called cool corona
around the occulting Moon, in Halpha, KCaII lines and narrow-band continuum.
For that, we use both radial filters of 50 mm diameter and narrow band
interference filters with small telescopes. Both photographic film and
CCD camera are used.
The hot topic considered with this last set up is the analysis of the
recently discovered solar PROLATENESS (ovalization) at the high chromospheric
level (e.g. AA:1998, 336, L57); we want to go further out in the low corona.
Until now, the prolateness was measured only up to 6 to 7000 km heights,
using EIT(SoHO)-HeII emissions and, of course, at lower levels in Halpha,
KCaII, etc. In Halpha the prolateness is well seen up to the 'top' of
spicules and could be a fundamental indicator of the mechanism converting
the magnetic turbulence energy into convecting plasma flow near separatrix
layers.
We prepared spectrogaphs for both i) HIGH dispersion to look at the profile of
the FeXIV coronal emission line for different radial distances and
different position angles, and ii) LOW dispersion analysis
to simultaneously look at several lines and deduce the temperature
inhomogeneities of the whole corona.
High sensitive film and CCD DV-cameras are selected as detectors.
High dispersion is used to look at the properties of propagating waves
in the intermediate corona, thanks to the measurement of the Doppler effects,
including the Doppler widths, and the determination of the so-called
non-thermal velocities as a function of radial distances and latitudes.
We plan to get data up to 2 solar radii from the sun's center, based on
previous experiences (Chili 94 and Guadeloupe 98).
Low dispersion is used to simultaneously measure several forbidden lines
and look at the temperature inhomogeneities at large scale (+/- 3 solar
radii) from the analysis of the distribution of the emission measures.
Electron temperatures will also tentatively be studied, using the Grotrian's
method over the bMgI and DNaI lines.
The use of new-technology fast CCD cameras should be relatively efficient at
eclipses. We hope to significantly improve what has been done in the past
with plates and films, although new fine-grain films are also available.
Further, the coordinated effort (with ESA, NASA and ISAS) to perform
well defined and selected observations using the spaceborne facilities,
especially the CDS, SUMER, EIT and the LASCO exp-ts of the SoHO mission,
the SXT of YOHKOH and possibly, the TRACE mission, makes our observations
more effective than it was in the past. We have now an excellent coverage
of coronal phenomena occuring before and after the eclipse which makes
eclipse results more reliable and more effective to process and to interpret.
During the total eclipse, a large amount of photons is available
(the corona is as bright as a full Moon) such that it is more easy and
evidently cheaper to conduct sophisticated investigations, especially at high
resolution and dispersion. Of course, this is possible during just the
short time (a few min) of the totality! Only spaceborne observations and
long duration missions permit a survey of coronal and solar phenomena.
The results of our 1991 observations are published in a series of papers
in Astron.Astrophys., Astr.Rep. and ApJ. We discovered very fine W-L structures
at the base of the intermediate corona (down to the 300 km scales); some of
them have short lifetime (like 40 sec). During more than 200 sec at high
cadence we got what we believe is a coronal plasmoid (small cloud of 2000 km
diameter with changing shape, moving at 100 km/s speed) which
travelled across more radial coronal structures (a spectacular movie was
assembled), showing interactions leading to a splitting of its core, etc.
The dynamics of the corona at small scales was found surprisingly large; the
so-called turbulence seen on coronal line profiles (20 to 30 km/s) is
resolved in the inner corona at scales under 1". To give a good idea of what
was seen in 1991, let us mention that the dynamics is already evidenced
watching the original W-L video movie of a narrow fov (80" size), without
introducing any acceleration. These CFHT data confirm our earlier
observations of plasmoids and jets (spike) obtained since 1973.
From our large scale images taken in 1991 (active corona) with a
radial filter from 2 different locations (Hawaii and Brazil) with a 1H 40 mn
separation in time, we compared the position of SHARP EDGES of streamers and
we succeeded in using the effect of the so-called rigid rotation of the corona
to look at the 3-D structure (stereo-effect) /results published in Nature
1992, 360, 717 in collaboration with russian scientists/.
Results tell us that the coronal plasma at large scale is well confined
in sheets and the topology of those sheets is a new very interesting topic
we are trying to consider using numerical simulations (paper in press in
collaboration with IZMIRAN).
We intend to repeat this exp-t in collaboration with the team from Kiev;
however, the Lasco/SoHO coronagraphs accumulated a large number of W-L
images of the more external corona and we can now look at these images and
improve our eclipse results.
From our 1994 spectroscopic exp-t, using a long slit, we got the line
profiles of the green line of FeXIV in several locations, with the following
main conclusions:
Over one polar region, the profiles are broader but intensities are really
low, although well measurable up to 0.2 solar radii (coronal hole boundaries;
plumes, etc.) from the limb. They tell us that small regions with 2 millions
kelvin ionic temperature definitely exist over the poles. These regions could
be related to the locations where X-ray polar jetlets (Yohkoh observations,
see AA, 1997, 320, L33) are observed and where magnetic reconnections are
occuring.
Over the equatorial regions, we measured line profiles of large intensity,
in streamers, and even some small but significant (#10 km/s) line
shifts at radial distances of 0.5 and more from the limb.
We think that a large part of the broadening could be due to ubiquitous
propagating waves which could explain the acceleration of the slow wind.
Those propagating magneto-acoustic waves were quite recently seen using
chromospheric lines formed in the network (AA:1995, 299, 893; AA:1996,
314, L9). However, it is not yet clear what is the best diagnostic to reveal
reconnections (temperature effects; plasmoids..) and/or propagating waves
(Doppler effects) and their dissipation, taking into account the brievity
e.g. limitations of eclipse observations. More works is needed at the
forthcoming eclipses of the next Millennium !!!
Bruce Lites , David Elmore, Philip Judge
We request observations from SOHO-EIT and TRACE in support of an experiment
based in Austria. Following the successful experiment ran from Curacao on Feb
26 1998 (Lites et al., Solar Physics to be submitted), we will field an
experiment designed to 0.5 second cadence, 1 arc-second pixel size, broadband
red light images of the corona just above the solar limb with a field of about
10 by 8 arc minutes.
One of the goals of the 1999 eclipse expedition is to verify the presence of
very small amplitude perturbations of the broad-band visible light corona in
the region of polar plumes, as revealed by the 1998 Curacao observations.
Rapid cadence, high precision and rather high angular resolution observations
are required by the ground based instrument. The fortuitous occurrence of an
EUV jet during totality of the 1998 eclipse emphasized the value of EUV
simultaneous EUV observations. Therefore we request a similar time series of
EUV observations from both TRACE and SOHO/EIT for the time around totality in
Austria (details will be provided if the EUV observations are approved). The
EUV observations, together with the visible light observations that are
sensitive to coronal electron density only, one may tightly constrain the
density and temperature fluctuations of the observed dynamical events.
Based upon the present state of the corona, the target most likely is the
north polar region.
The requested support ideally consists of two parts:
Lites et al (1999) recorded changes in the white-light coronal
emission during the 3.3 minutes of totality of the 1998 total solar
eclipse at Curacao, Netherlands Antillies.
The most prominent of these changes is associated with an EUV jet
(region "a" in the figures) that is embedded in a polar plume near the
south solar pole. This disturbance appears to propagate radially away
from the Sun at speeds of about 200 km/s as observed in both white
light and Fe XII 195. The appearance of this jet in the EUV image
sequence shows it to be a very narrow structure (its width is only
about 5 arcsec near the solar limb) that simultaneously moves both
outward and from right to left (west-east). Furthermore, the EUV
image sequence reveals that the emission source of the jet and plume
at the base of the corona undergoes a slight but definite
corresponding motion from west-east. The observational facts
constrain the possible nature of the jet phenomenon, related to the
magnetic enviroment at the base of the corona. Lites et al. discuss
models involving bi-polar magentic structure in the coronal hole
region.
Other perturbations seen in the PEPPI image sequences in the loop and
streamer structure (e.g. features `f', `g', `h', and `i' sustain hope
that some day one might identify propagating Alfven waves in the
corona. The duration of totality appears to be be too short to
measure propagation speeds for these disturbances, and the level of
the disturbance is too low to allow us to say much about their other
observed properties, even the direction of propagation along the
loops. It is not clear that eclipse measurements similar to those of
PEPPI will add substantial new information: the duration of totality
is simply too short. However, coupled with longer timeseries data
from EIT and TRACE spanning the 1999 Aug 11 eclipse, such data may
hold the key to better understanding of these disturbances and their
consequences for heating the corona.
Figure 1 (postscript)
Fig 1:
The upper left panel shows a radially enhanced PEPPI image at
the start of totality. The darkened region at the tops of
each image is a mask applied for all positions < 20 arcsec
above the lunar limb at second contact. Sobel edge
enhancement of the PEPPI image in the upper right panel
reveals fine structure in the image that largely persists
throughout the eclipse. The lower left panel is a difference
of summed images near the end of totality from that near the
start of totality. Features indicated by letters in the
images are discussed in the text. Lines of constant
normalized solar radial coordinate from 1.05 to 1.30 shown in
the lower left panel trace the locations of the inferred
fluctuations in fractional intensity variation shown in the
lower right panel, where the tick spacing on the ordinate is
0.01.
Figure 2 (postscript)
Fig 2:
The ratio of emission in the bands 195/171 is shown on
a logarithmic intensity scale to accommodate the substantial
range of this ratio within the image. The images were obtained at
16:00/15:46 UT on the day of the eclipse. The low relative
emission in Fe XII (171) in this south polar region, including
polar plumes, indicates temperatures below 1 MK.
OVERVIEW OF RESULTS FROM 1998 ECLIPSE- WHITE LIGHT+EIT
SAO expedition in Syria (broad-band pB of the K corona at heliocentric heights: 1.1 - 2.5 solar radii)
Support from UVCS and LASCO requested.
French-Czechoslovakian observation from Bucharest ground-based observatory in Romania (visible light narrow-band spectroscopy of the Rayleigh emission from coronal neutral hydrogen)
Support from UVCS and LASCO requested.