JOP # 4 DIAGNOSTIC OF ERUPTING PROMINENCES AS ONSETS OF CMEs Jean-Claude Vial, 9 May 1995, revised 9 September 1995 Objective: To study the eruption of a (limb) prominence as the onset of a coronal mass ejection Scientific case: The point of studying the onset of CME has been made in the JOP 3 document authored by Harrison et al. and is still a motivation for the proposed program. But our objective is more focused here on the investigation of the conditions of the eruption of a prominence often associated with the CME (statistically more than 75%). Of special interet here, is the determination of the physical conditions in the EP (densities, ionization degree and especially temperature, badly known up to now). From ground-based observations, one will try to derive the magnetic conditions which may be necessary and/or sufficient for the eruption. On SOHO, one will get as much information as possible on the thermodynamic state of the plasma, before, during and after the eruption. All coronal instruments are observing together. Method: The method is described in JOP3. In this program, we stress the importance of a reliable diagnostic of the plasma in a very large temperature range since prominences are certainly made of cool material (about 7000 K) which is (partially?) heated to coronal temperatures (106K). CDS and SUMER cover such a temperature range but the large field of view (fov) combined with a not negligible temporal resolution makes the observation of faint to moderate lines somewhat difficult. This is the reason why, with SUMER, we propose to observe the FULL profile of the Lalpha line which offers a powerful diagnostic tool, provided one uses the results of Non-LTE transfer modeling. Moreover, this diagnostic will complement the diagnostic performed at larger heights with UVCS. Basically, our SUMER program differs from JOP3 because we want to retrieve the full Lalpha profile. Pointing and Target Selection: See JOP3. Operating Details: CDS, EIT, LASCO, UVCS programs are unchanged. SUMER: The method is different from the one proposed in JOP 3 in different aspects: 1/ choice of lines: we propose to drop the N V (1238) and Fe XII (1242) lines because the Fe XII line is very faint and could noticeably increase only for a compact flare-like event. We choose instead the S X (1196) line which provides the higher temperature limit (5 105 K). In this way, we access other lines such as N I (1200) and Si II (1194.5). The lines selection is as follows: O V (1218.4), La (1215.6), Si III (1206.5), N I (1200), S X (1196), Si II (1194.5). 2/data extraction: Contrary to JOP 3, we want 'full' line profile information. For optically thin lines, we propose to compute the 2 moments of the line profiles: integrated and Doppler shift. These parameters are necessary for a comprehensive diagnostic of the plasma, including its motions. For the optically thick Lalpha it is necessary to keep the wealth of information contained in a profile which may be complex because of a combination of temperature, density, and velocity variations. 3/ although the fov is rather large (120*300 arcsec2), it may be necessary to follow the expanding structure, so a 'flag' initiated by the detection of an apparent motion should be available and result in a move of the pointing. This flag could be initiated by SUMER but also by CDS and EIT which have a larger fov. Operational Sequence Initial pointing: selected limb position Slit 1x120 arcsec^2 Scan Area 120*300 arcsec^2 Step Size 0.76 arcsec; 5 steps over 2s Resulting Number of Scan Locations : 400 elementary steps 80 exposures Dwell Time 2 s Duration of Scan 160 s Number of Scans preplanned: 100; after an event occurs: 100 Number of Scan Mirror Settings 1 Repointing: none except if FLAG Total Duration: 4 hours and a half (if no event) Line Selection Ly alpha (1216.7A) (on the bare MCP); O V (1218), Si III (1206.5), N I (1200), S X (1196), Si II (1194.5) Bins Accross Line: 25 pixels (Ly alpha), 2 'pixels' for other lines Estimated Reduction Factor * Selection 1x25x24 (Ly alpha); 5*2*24 (other 5 lines) * Compression: for all lines, average over 5 spatial pixels; 2 moments computation for all lines except Ly alpha * Reduction Co-operation Requirements: all SOHO coronal instruments (see the CME program JOP 3) Notes (for Sumer): The raster is made in the 'smear step' mode. For data extraction, a mixture of different formats is required; a special UDP is being written The flag criteria (apparent motion in the field-of-view) and the reaction to the flag (repointing) must be worked out.