**JOP177 ENERGY INPUT IN PROMINENCES.**

**WHO ?**

J. Aboudarham and Z. Mouradian (Observatoire de Paris),

A. Nikoghossian (Byurakan Observatory, Armenia).

**WHEN ?**

SOHO **C**ampaign of June 3 -- 17, 2004

Received: 24 May 2004

**WHY ?**

The target of this proposal is the study of fluctuation of energy-input
in prominences, by the measure of temperature variation. A prominence is
a continually renewed structure, never the same. During its lifetime a
prominence can undergo an important increase in energy input, which
induces a \"sudden disappearance\" and consequently the obliteration of
the prominence from Hα image, the usual wavelength for prominence
observations. SKY LAB had shown such variation of visibility produced by
changes in ionisation degree of plasma and thereby the complete
ionisation of hydrogen. The effect of heating is an apparent
disappearance of prominence in H I lines and its appearance in lines of
Transition Zone or soft X-ray images, depending how much the
energy-input is. This process was called \"thermal disappearance\", with
respect to \"dynamic disappearance\" which is the ejection of plasma
into the corona (Mouradian et al., Proc. of the Japan-France Seminar on
Solar Physics 1981, p. 195; Tandberg-Hanssen, The Nature of Solar
Prominences, 1995, p.240). So, we are led to distinguish two sorts of
prominence disappearance: thermal and dynamic, with different
consequences on CME formation (Mouradian et al, Solar Phys. 1995,
**158**, 269). Note that after a certain time the heating being stopped,
cooling restores Hα prominence.

In an earlier paper, we studied the possibility for a thermal
disappearance of prominence produced by resonant absorption of Alfvén
waves and concluded to the efficiency of this process (Ofman &
Mouradian, A&A 1996, **308**, 631).

The SOHO/SUMER spectrometer allowed us to start a campaign in order to
study the thermal variability. An arch-shaped prominence was observed on
March 31, 1996 and we determined the distribution of temperature
variation over the prominence surface (Ofman et al, Solar Phys. 1998,
**183**, 97). The method used for the measure of temperature was the
intensity ratio at two wavelengths in Lyman continuum (I~908~ / I~877~),
quantity which is only temperature dependent. In order to calculate this
dependence, we used GHV model for H I, which works in the range 4300 to
15000K (Heinzel, Vial & Gouttebroze, A&A Suppl., 1993, **99**, 513). We
effectively observed the heating process, as mentioned above, but the
time-constant of observation was too long to detect the *heating
characteristics* and *topology of energy flow*. These observations
showed some topological effects of heating never pointed out before,
which have to be studied and confirmed for other prominences. For these
reasons we intend to start a new and more complete campaign of
observation.

The SOHO/EIT imaging telescope will be associated to the above-mentioned
heating program, because it improves and completes the temperature range
covered by SUMER and can show the heating propagation in the whole body
of the prominence. Working simultaneously with both instruments (SUMER
and EIT) we can watch the unfolding of heating through the He II
ionisation and Fe IX + X excitation. The observation of He II emission
during a disappearance and appearance of prominence may contribute to
the understanding of He excitation.

During the 2004 campaign we would like to use again the Ly cont.
sequence and we also intend to observe the temperature variation using
Ly β + O VI, as well as by Ly decrement, which were considered but not
performed in the preceding period. We propose to study the profiles of
emission lines of Ly β and O VI. In case of disappearance of prominence
in H I lines, O VI becomes emissive with the same shape. The C II lines
will be used for wavelength reference. The third way for temperature
measure is given by Lyman decrement using the lines Ly 6 to Ly 20 of H
I. We also intend to study the role of multiple scattering for the H I
line formation, in the different physical conditions present in
prominences.

### ALTERNATIVE PROGRAM

In case of a lack of prominences, Ly β + O VI sequence can be applied
for spicule observations as well. Here again the target will be the
heating of spicules related to their upward motion.

**HOW ?**

In order to obtain a good approach of the prominence-heating problem it
seems necessary to observe about 4-5 different prominences, each of them
being watched for about 6 hours.

The selection of targets will be done the day before. The west limb
prominences will be preferred.

For a good positioning of prominence structures on the slit, before
starting observation, the slit must be first adjusted crossing the solar
limb. A spectral range with low sensibility of the receiver should be
used to take a few spectra. Then the slit will be shifted along itself
toward the prominence to overlap it and a few spectra in He II 942 Å
(935-945 Å) will be taken, necessary for comparison with simultaneous
EIT images. The observation program can only start after having set the
slit.

SUMER and EIT observations have to be simultaneous and at daytime in
Europe, in order to be supply the SOHO observations with ground base
instruments.

#### Lyman continuum 

SUMER:

> The 4 observing windows: 877 ± 3; 890 ± 3; 900 ± 3; 908 ± 3 Å, (with
> binning)
>
> Slit: 1 × 300 arcsec.
>
> Exposure time: 30 sec
>
> Frequency: 2 / min
>
> Run time: 6 hours of continue observation

EIT:

Small field images (300\" × 300\") in He II (304 Å) and Fe IX +XI (171
Å),

> Frequency: every 15 min
>
> Run time: 6 hours of continue observation

#### Ly β + O VI

SUMER:

Spectral range: 1024 -- 1040 Å; (annexe 1)

> Slit: 1 × 300 arcsec.
>
> Exposure time: 45 sec
>
> Frequency: every 45 sec.
>
> Run time: 6 hours of continue observation

EIT:

Small field images (300\" × 300\") in He II (304 Å) and Fe IX +XI (171
Å);

> Frequency: every 15 min
>
> Run time: 6 hours of continue observation

#### 

#### 

#### Ly decrement.

SUMER:

> Spectral range: 910 -- 939 Å; (annexe 2)
>
> Slit: 1 × 300 arcsec.
>
> Exposure time: 30 sec
>
> Frequency: 2 / min
>
> Run time: 6 hours of continue observation

EIT:

Small field images (300\" × 300\") in He II (304 Å) and Fe IX +XI (171
Å),

> Frequency: every 15 min
>
> Run time: 6 hours of continue observation

#### Ly β + O VI -- Spicule (this program will be repeated for 2 - 3 days)

SUMER:

Slit position parallel to limb, at altitude 6\" (4400 km) and 11\" (8000
km) above limb. A similar procedure for slit positioning will be used.

> Slit: 0.3 × 120 arcsec.
>
> Exposure time: 20 sec
>
> Frequency: 3 / min
>
> Run time: 6 hours of continue observation

EIT:

Small field images (300\" × 300\") in He II (304 Å) and Fe IX +XI (171
Å),

> Frequency: every 15 min
>
> Run time: 6 hours of continue observation

**Ground Based Support:**

Meudon Observatory in K3 prom. specroheliogram.

Pic du Midi Observatory Hα coronograph filtrogram.

Kanzelhöhe Observatory, Hα prominence filtrogram.

Frequency of support image: every 15 min.(hour + 0; + 15; + 30; + 45
min.)

###### ANNEXE 1

###### Spectral range for Ly β + O VI ---- Prominences and Spicules

  -------------------------------- --------------------------------------
  λ Å                              Spectral element

  1025.30                          H II

  1025.72                          Ly β

  1031.92                          O VI

  1036.34                          C II

  1037.02                          C II

  1037.61                          O VI
  -------------------------------- --------------------------------------

###### ANNEXE 2

**Spectral range for Lyman decrement ---- Prominences**

  ------------------------------------- ---------------------------------
  λ Å                                   Spectral element

  910 -- 912.5                          H I Ly cont

  913.6                                 H I Ly 20

  913.9                                 H I Ly 19

  914.2                                 H I Ly 18

  914.5                                 H I Ly 17

  914.8                                 H I Ly 16

  915.4                                 H I Ly 15

  915.8                                 H I Ly 14

  916.4                                 H I Ly 13

  916.7                                 S VIII

  917.2                                 H I Ly 12

  918.2                                 H I Ly 11

  919.4                                 H I Ly 10

  920.9                                 H I Ly 9

  923.2                                 H I Ly 8

  926.2                                 H I Ly 7

  930.74                                H I Ly 6

  933.10                                S VI + He II

  937.80                                H I Ly 5
  ------------------------------------- ---------------------------------