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"EIT, eclipses and Jean-Pierre"

The small part of a life during a great solar cycle (1994- 2005) in the

“Eclipse-Corona Land”

Boudine DaysIAS- 20 oct. 2005

Boudine DaysIAS- 20 oct. 2005

Serge Koutchmy, Institut d’Astrophysique de Paris, CNRS and UPMC

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SoHO was launched in Dec. 2, 1995 with its now famous EIT exp-t.

Jean-Pierre tried for the 1st time to observe (unsuccessfully) the W-L Solar Corona, at the total solar eclipse of Nov. 4, 1994 from the Chilian Altiplano…where, ironically, G. Bruckner did

his 1st and, unfortunately, his last visual observations of the Corona (as a member of the team of IAP).

The W-L. eclipse corona observed by the joint team of IAP/IAS, with the main positions

of the slit of the spectrograph shown in red. These spectra showed the extension of the

FeXIV emissions in equatorial regions up to 2.3 solar radii, with excellent S/N ratio.

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Almost 4 Years later, after getting from space thousands of images with EIT, a couple of major discoveries and highly successful movies,

Jean-Pierre was allowed to visually observe the corona, for the 1st time, during the Guadeloupe total eclipse of Feb. 26, 1998.

W-L observation by Christian Viladrich, in Guadeloupe; inserted : the X-rays corona from Yohkoh

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Jean-Pierre survived the 1998 eclipse and after this unforgetable experience, he decided to seriously observe the corona using a new

digital CCD camera he paid from his own pocket. He had to wait the time of the « heroic » total eclipse of June 21, 2001 observed from Angola, a country in state of war at that time (not mentionning the

malaria) !

As the 25 Years civil war ended a few months after the eclipse, it is reasonable to assume that Jean-Pierre successfuly visited Angola with some rather peaceful

projects…

We will come back to that after briefly and qualitatively reviewing

a few interesting examples of new physical phenomena discovered during the EIT era,

trying to keep the « critical wisdom attitude » that Jean-Pierre always promoted when coronal observations are evaluated.

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One of the topic I want to approach here is the interpretation of EIT filaments and prominences

discovered on 304 (He+ with i.p. >54 eV) images

14 Sept 1999, 7:19 UT

This is of fundamental importance to understand:

-The origin and evolution of CMEs:their initiation; the lifting of large coronal masses;the abnormal abondances in the IM

-What are the dark EUV channels ? including the transient darkening at time of CMEs (also called EUV dimming);

- Coronal cavities and emptinesses

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Comparing disk EIT « filaments » taken in He+ 304 and those seen in H Meudon SHG:

In He II 304, infamous dark « channels » are seen, in addition to filaments

seen in H : what are they ??

Observed in Sept. 14, 1999 (after Brigitte Schmieder, 2004)

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304 (He+) EUV Filaments and channels are difficult to understand : sometimes they fill up some space corresponding to the classical H filaments, sometimes they do NOT, sometimes it is the opposite...

A possible explanation was proposed by B. Schmieder, P. Heinzel, and others (based on opacity effects considerations and so-called « extension »):

(after Brigitte Schmieder, 2004)

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A good way to test this assumption was to look at DEEP images of prominences (filaments above the limb) taken at the time of a total eclipse, when the background W-L corona is well exposed and do show all coronal densities presumably surrounding the prominences, simultaneously with

H emissions.

W- limb of the Aug. 11, 1999 eclipse corona simultaneously observed from SoHO/EIT and from Iran

EIT-304

9m focal lengthEclipse camera

MTO-1000 eclipse survey camera

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An other view of the same region to also show the Fe XII 195 emissions

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A special experiment was prepared at the 2001 total eclipse to simultaneously look at the He I (D3) line and the HeII(304) line emissions, together with the background corona,

including H emissions:

EIT He II 304 D3 HeI + continuum H HI + continuum

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Short (2 min) eclipse movie taken by Daniel Crussaire in Angola (June 21, 2001 total eclipse) HeI D 3 line emissions and continuum (electron densities) simultaneously

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Preliminary conclusions :

- EIT HeII 304 prominences do not show any extensions nor H prominences do;

- The coronal background shows highly dynamical phenomena at very small scales, including condensation-like processes;

- A new EIT- 304 experiment with much better cadence and increased resolution is needed to understand these

newly discovered EIT prominences and filaments.

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An other very interesting and major topic opened by EIT is the

famous EIT waves

What can an eclipse snapshot bring to that subject ?

Let’s think about the radially propagating wave....

(we are NOT talking about the dimming effect, or the opening processes occuring during the CME, etc)

It should correspond to the propagation of a « perturbation »/Not a mass motion/

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Best resolution deep W-L calibrated coronal image taken above an activated filament of the maximum type corona observed on July 11, 1991 using the CFH telescope of 3.6 m aperture

(corresponding to just an 18 cm aperture 304 telescope!)

At high resolution,, many interlaced loop like structures are observed in W-L : They are density/pressure perturbations due to the slowexpansion of the magnetic field.An interesting aspect of this image is the observed quasi-stratification which remind the instantaneous wave front seen during the propagation of an EIT wave.

From Koutchmy et al. 1994

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In case the EIT wave (emission measure variations) propagates « across » the local field, the speed could be typically the sound speed,

and the « excitation front » could propagate even faster. This seems to be the case with radially propagating EIT waves induced by small flares occuring in compact active regions with

inserted filament and subsequent eruption. The observed wave is then more like a hydro-dynamic wave

slightly modified by the magnetic field, occuring inside an already stratified in large loops medium giving

the amplitude of the wave....

Let’s go a little bit further...

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Here is our oriented image of the 2001 eclipse corona taken from Angola, with the radial gradient removed thanks to the use of the radial gradient filter.

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The same corona using a more sophisticated processing and composing 8 images to improve the S/N ratio (by Milo Druckmuller- Brno 2003)

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Using more processing to show very faint modulations...

Again, we see on this excellent

large scale image, several systems

of wave-like big faint loops,

especially at S-W, suggesting that the middle

Corona is indeed made of loops.

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Are the wave-like structures really a general property of the solar corona resulting from instabilities induced,

for ex., by the heating processes ?

It could at least be important to look at the EIT- radially propagating waves

taking into account, when doing numerical modeling, the magnetically stratified background corona

where the waves propagate.

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Finally, some memories related to this 2001 eclipse:

Jean- Pierre preparing his eclipse experiment from a site in Angola

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Eclipse image taken by Jean-Pierre from Angola (2001)

After some processing, composing and orienting by Frederic Auchère

Small misalignment and not oriented sample image

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The day after.... during the briefing at Luanda

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2 Years after, during a site testing mission in Lubango (Angola) as a « goodwill ambassador »

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Thank you Jean-Pierre!

Among your friends:

Jame Vilinga Katia DaRosaJean Mouette

Daniel CrussaireThierry Legault

Christian ViladrichPhilippe Marty Conceicao Silva

Pedro Teta and many others...!