Paris jan, 1998

from:  Paris Inst-t d'Astrophysique- CNRS (SK) 

to: P. Martens; SoHO teams; eclipse teams 

Object: Eclipse exp-ts in Guadeloupe by CNRS teams and 
        collaborative studies; 
        Request of SoHO support


 Several typical exp-ts put near Guery (Gde-Terre; Long= 61gr30'W; 
Lat= 16gr29'N) are planned: 

A- Morphological Imaging Analysis using different cameras put at several 
   locations to increase the probability to get a good resolution over a large 
   fov. Photographic film is used: film-sheets 18x13 cm (focus: 1.5 m)
   with a radial neutral filter of 100 mm diam.; 120 and 135 type roll films  
   with different focal lengths cameras and telescopes (800 to 3000 mm). 
   A priority is put on the analysis of the inner and the intermediate 
   corona with color films to get both the cool and especially the hot 
   fully ionized components. A 1 arcsec effective resolution is looked for. 

B- Spectroscopic analysis of the  corona using low spectral resolution 
   slit- spectra at different positions and radial distances (+/- 3 Ro) 
   covering a large spectral range on each spectrum, from UV to IR. 
   Different spectrographs, detectors and mounts will be used.       

C- Collaborative studies: 
   C1- In collaboration with the team of NSO/SP (leader: R. Smartt), a 
   green line (Fe XIV) polarisation  exp-t using a CCD detector will be 
   attempted; 
   C2- In collaboration with the IZMIRAN team (leader: M. Molodensky) a 
   W-L polarisation exp-t will be performed. 
  
The aim of A- is to provide additional material to SoHO observations 
focussed on the physics of the inner corona (heating; cooling; dynamics 
and ejections) in order to measure the density structures at small scales 
thanks to i/ precise calibration available at total eclipses; 
ii/ precise polarimetric data given by multiple positioning of the linear 
polarizer and iii/ colorimetric index measurements. 
W-L loops and plumes are the favorite W-L structures to be 
studied but the search of intermediate temperature plasmoids and the 
relation to the highly dynamical TR and cooler structures is an other topic 
we consider. 

The aim of B is to concentrate on the simultaneous measurement of both the 
electron and ion temperatures using the measurements of forbidden lines and 
using the Grotrian's method for electrons (smearing of the F spectrum by 
Thomson's scattering). The long slit crossing the whole corona (and eventually 
the Moon) will provide a limited spatial resolution good enough to measure 
the radial gradients of temperatures and subtract the F-component. The IR part 
of the spectra will also be recorded, up to 1.1 micron. Large scale 
temperature inhomogeneities in the inner 1st solar radius distance will be 
analyzed all around the Sun in an attempt to understand the origin of the 
wind. 

The aim of C1 is to provide a good coverage of the green line measurements 
in the intermediate corona, including a magnetic field sensitive analysis 
of the linear polarisation. The C2 exp-t is aimed at providing some 3D 
understanding of the W-L coronal structures. 

 Time of observations: 
 --------------------
The totality is expected from 18:31:05 to 18:34:00 UT on Feb. 26, 1998; 
eclipse magnitude is 1.040; height of the Sun: 49 deg. 


 Request for SoHO observations: 
 ----------------------------

a- EIT full disk image in 304 (HeII/SiXI) at 18:32:30 UT (+/- 1 mn); 
b- EIT full disk images in coronal lines taken at +/- 15 mn that time; 
c- Lasco-C1  images in Green line (530.3 nm) taken near 18:30 +/- 15 mn 
   possibly with polarisation analysis; 
d- Lasco-C2 and C3 images using the synoptic program at the same time as c- 
e- SUMER: (by Alan Gabriel)

During the eclipse, the team of Koutchmy will make some spectroscopic
measurements in the polar cronal hole.  They will measure electron temperature
by the Fraunhofer dilution method, and of course they and many others will 
measure electron densities. We would like to try to measure the abindance of
one or more of the heavier elements at the same time.  I believe that there is
reason to suspect that these abundances are notably higher with respect to
hydrogen or electrons in the coronal holes. I speak of large factors like X 10.

For this I would propose that the SUMER slit is placed above the limb on the 
central meridian in the hole so as to cover the range 1.1 to 1.3 Ro, for a long exposure,
with the range O VI, Lyman beta and the C II lines in the wavelength band.  If it is
feasible, it would be best to take a second exposure, displaced
laterally so that the same height range is covered in the closed corona.

Contact person for the eclipse exp-ts: Serge Koutchmy 
                                      e/mail:   koutchmy@iap.fr