==================================================================== SOHO Joint Observing Programme 067 INVESTIGATION OF THE STRUCTURE OF THE LOWER CORONA AND THE CONTRIBUTION OF SMALL EJECTA TO THE SOLAR WIND. Authors: Mark Lyons (LASCO, Birmingham), Richard Harrison (CDS, RAL), Ester Antonucci (UVCS, Torino), Don Michels (LASCO, NRL), Philippe Lemaire (SUMER, Orsay), Ludwig Klein (Paris-Meudon Observatory, France), Henry Aurass & Gottfried Mann (Astrophysical Institute Potsdam, Germany) E-mail Addresses: mal@star.sr.bham.ac.uk harrison@solg2.bnsc.rl.ac.uk antonucci@to.astro.it michels@maple.nrl.navy.mil (local coordinator at GSFC) lemaire@sumop1.nascom.nasa.gov ludwig.klein@obspm.fr haurass@aip.de gmann@aip.de Progress: Fourth Draft July 22, 1997 Objective: To observe the stucture and evolution of the lower corona (1-2.8R) and the onset phase of the small CME 'blobs' in the streamer belt with EUV, UV and white-light data. Conditions Necessary to Run: We require, at a minimum, the synoptic operation of LASCO, with sufficient numbers of C1 images and C2/3 images to identify 'blob' events. Ideally, we would like CDS, UVCS and SUMER observing the limb region. At a minimum, any one of these should be in operation. Scientific Case: LASCO has identified in C2 and C3 small ejecta in the streamer belts, often referred to as blobs, which are first detected around 3 R. These events have been interpreted as tracers of the slow solar wind (Sheeley et al. ApJ, 1997 (in press)). C1 has viewed the ejection of small balloon-like CMEs between closed loop structures. These loops do not seem to be significantly disrupted by these CMEs and the foot-point positions of the overlying streamer belts also do not vary much with time. In addition, X-ray observations with Yohkoh have shown the frequent expansion of hot loops into the high corona. It is essential to identify these activities in various wavelengths in order to investigate the physical connection between them and to understand the structure of the lower corona. We wish to determine the onset processes of the small blob-like events and to determine their relationship with the Yohkoh-type loops and the other events seen by LASCO. As well as investigating their onsets, any observations which can provide information on the mass ejected and the event rates can provide an estimate for the contribution these events make to the slow solar wind. The non-ideal evolution of coronal structures should be revealed by energy release processes such as heating and particle acceleration. Coherent radio emission at decimetric and metric wavelengths is a sensitive tracer of non-Maxwellian electron populations (beams or loss-cone distributions) in the corona, both during flares and in events where much smaller amounts of energy are released in association e.g. with bright points or quiescent active regions. The radio observations will look for such signatures of coronal reconfiguration, with the attempt to identify the spectrum and the site of the nonthermal emissions. Basic Method: LASCO should operate the synoptic programme - but ensure good C1 and C2 coverage of the west limb. UVCS should be directed to the region above the west limb (at 1.7R). CDS and SUMER should target the limb itself or be just off the limb. The radio instruments will operate as detailed below. Pointing and Target Selection: Pointing must be to the west limb to ensure collaboration with SUMER and to allow observation of the structures being viewed prior to their arrival at the limb. Operating Details: CDS - 12x4 arcminute field of view formed from three 4x4 arcminute rasters, in approximately 6 lines, as follows; Ion Wavelength Temperature He I 584 A 20,000 K O V 629 A 250,000 K Mg IX 368 A 1,000,000 K Fe XVI 360 A 2,000,000 K Si X 347 A 1,000,000 K ) Density sensitive Si X 356 A 1,000,000 K ) line pair. Long axis of the field should be directed N-S. The field should be centred either on the limb or just off-limb, probably just north or south of the equator. The latest C1 images should be used and CDS should sit such that the 12x4 field extends just north or south enough to see the edge of the streamer. Cadence time 15 minutes or longer, possibly with two exposures set for observations on disc or limb. SUMER - Observations will be taken about 30" above the western limb. The 4 x 300 arcsec^2 slit will be used every minute during 8 hours to provide profiles of O IV, 790 A N IV, 765 A O V, 760 A Ne VIII, 765 A. These can be repeated as necessary. UVCS - Sit & Stare at 1.7 Ro. Nominal UV (LYA and OVI channels)+ VL observation of 8h (+30m for trasmission and mechanisms delays). Pointing Total Dwell Exp time x repetitions ---------------------------------------------- 1.7 Ro 28800 200 sec x 144 Mask details: -------------------------------------------------------------- LYA OVI -------------------------------------------------------------- Slit width 50 um 35 um Grating Pos 110000 225000 Mask LYA_CME110 OVI_CME225 Spatial Bin 5pix(35") 6pix(42") Number of panels 5 5 Selected spatial range 36-355 (64 bins) 15-338 (54 bins) Spatial bins trasmitted 64 64 ============================================================= Spectral Range column interval column interval Panel # 0 295-334 (20x2) 101-236 (136x1) Si II 1264.74 Si XII 520.66 OVI 1037.61 OVI 1031.91 Panel # 1 446-511 (66x1) 248-313 (33x2) Fe XII 1242 H Ly-b 1025.72 N V 1238.82 Panel # 2 598-701 (104x1) 536-557 (22x1) Ly-a 1215.67 Si XII 499.37 Panel # 3 702-749 (48x1) 608-647 (40x1) Si III 1206.51 N III 991.58 N III 989.79 Panel # 4 750-823 (74x1) 748-828 (81x1) S X 1196.24 C III 977.02 H Ly-g 972.54 ------------------------------------------------------------ Tot. spectral bins 312 312 Bins per channel 64x312=19968 64x312=19968 Mask Trasmission time 101 s 101 s LASCO - The present synoptic programme will be run placing emphasis on higher cadence C2 one-limb observations, whenever possible. The western limb will be favoured for the reasons outlined above in the pointing selection. Longer exposure C1 images in Fe XIV and Fe X will be taken to help investigate the region of overlap between the C1 and C2 fields of view. RADIO - Two complementary instruments will be used for this study. The whole-Sun flux density spectrum will be obtained by the Tremsdorf spectrograph of the Potsdam Astrophysical Institute in the range 40 to 800 MHz, i.e. roughly between the base of the corona and two solar radii above the photosphere (observing time: 7-15 UT). Images of the Sun will be provided by the Nancay Radioheliograph at five frequencies in the range 150 to 450 MHz (observing time: 8-16 UT)