Progress:
Draft Scheme August 7, 1995 Distribution August 12, 1995Objective: Clarify the nature of the diffuse corona at and above the limb. Determine whether or not the plasma is contained in magnetically closed structures.Determine the plasma properties as a function of height using CDS, SUMER, UVCS and LASCO.
Conditions Necessary to Run: Minimum requirement is the operation of CDS or SUMER on a diffuse or quiet region of the corona at and above the limb. The region should as far as possible be separated from active regions, bright points and other manifestations of coronal activity. An appropriate region can be selected from Yohkoh or EIT full-sun images.
Scheme: CDS and SUMER should execute a series of radial spatial scans
starting inside the limb and moving out into the diffuse structure with the aim
of obtaining EM and T as f(h) for a series of line temperatures in the range 1 -
5.106K. Density diagnostic lines should also be chosen within this range so that
the diffuse region can ideally be mapped and ne compared with values deduced
from image based knowledge (Yohkoh, EIT) of the overall structure volume. Line
widths should be measured and the inferred temperature compared with measured
electron temperatures whenever the line profile statistics permit. LASCO and
UVCS observations will be used to extend the height coverage of the regions and
to provide a better delineation of the region volume.
Diffuse emission is pervasive in the corona. It is of interest to establish -
Pointing: Based on Yohkoh and EIT inputs, ahomogeneous diffuse region should be selected with symmetrical structure in front of and beyond the limb. It should as far as possible be unrelated to activity and active regions. Radial scans should be made with height with CDS and SUMER.
Frequency: As often as well developed and stable diffuse regions are available at and beyond the limb.
Operations: Assuming observations of a comparatively large structure ~ 10 arc min in radial extent above the limb and ~ 20 arc min around the limb, the following should be used -
Spectrometer: NI
Slit: 5x240 arc sec
Area scanned: Up to five adjacent radial scans equi-spaced around the
limb. Each
radial scan should be progressively outwards in 60 steps of 10 arc sec. Each
radial scan would occupy 250 minutes and so total coverage of the region could
be spread if necessary over a period of days.
Lines: Similar to JOP 28 for Streamers. Lines provide a wide range of
temperature sensitivity together with some density sensitivity. A He I line is
observed to ensure co-registration. Lines are -
Ion Wavelength () log Te Comment He I 522.20 4.3 Cool line for registration Fe X 345.74 6.1 Fe XI 369.16 6.1 Fe XII (a) 338.26 6.2 Density pair with (b) Fe XII (b) 364.47 6.2 " " " (a) Fe XIII (c) 348.18 6.2 " " " (d) Fe XIII (d) 359.64 6.2 " " " (c) Fe XIV 334.17 6.3 Fe XVI 335.40 6.4
TBD
Similar pointing coverage to CDS. Line selections to emphasize similar
temperature range to CDS but with the aim of identifying non-thermal broadening
in the emission lines.
TBD
Extend observations to higher altitudes
TBD
Extend observations to higher altitudes