SOHO Joint Observing Programme 174 PLASMA CONDENSATION AND TEMPORAL VARIATIONS IN ACTIVE REGION LOOPS Short title: Condensation and Variation in AR Loops Authors: T. Fredvik (CDS), O. Kjeldseth-Moe (CDS), W. Curdt (SUMER), K. Schrijver (TRACE), T. Tarbell (TRACE) Progress: Version 1.0: February 11 2004 Version 1.1: March 26 2004 Version 1.2: March 29 2004 Version 2.0: April 14 2005 (new SUMER study included for MEDOC 15) Participating instruments: CDS, SUMER and TRACE. MDI and EIT for target selection purposes. DOES NOT APPLY FOR MEDOC 15: SST (The Swedish Solar Telescope on La Palma) may participate, but is neither a necessary nor important part of the JOP.) Scientific Objective: To study plasma condensation, downflow and other time variable phenomena in active region loops, especially at transition region temperatures. Operational Considerations: The target should be an active region at the limb. EIT 171 A images and MDI magnetograms should be used to pick a small to medium sized active region with a fairly simple magnetic configuration. Part of the CDS O_LOOP1/O_LOOP5 FOV must be inside the limb, since the mean wavelength on the disc will be used as a reference wavelength for the spectral lines observed. The CDS O_LOOP11 FOV should be placed approximately 20 arc seconds off limb. See Operating Details below for further information on the CDS pointing. No part of the SUMER slit should be closer to the solar limb than 10". The major part of the SUMER slit should be within the CDS FOV. The FOV of TRACE must cover as much as possible of the active region observed by CDS and SUMER. DOES NOT APPLY FOR MEDOC 15: The SST will observe active regions as they approach (or leave) the west (or east) limb. Scientific Justification: CDS observations show rapid temporal variations in the emission from loops at transition region temperatures. Loops change their appearance appreciably or even appear or disappear over periods of 10-20 minutes. On shorter time scales we see intensity enhancements moving along the transition region loop structures down to the surface of the sun. These elements of strong emission may be the result of condensation of hot coronal plasma. The spatial resolution of the fast CDS raster is relatively poor, and observations from an imaging instrument like TRACE are therefore needed. Cooling and downflow in coronal loops have previously been observed with TRACE on multiple temperatures. CDS observes temporal variations not only in the transition region, but also in the coronal lines. However, these variations are less extensive than those observed in the transition region lines. The Grazing Incidence Spectrometer of CDS can observe spectral lines emitted from the upper transition region, and will be used to search for an upper temperature limit for strong temporal variations. GIS does not build up 2D images, and simultaneous observations with TRACE are therefore needed. The SUMER instrument has better spectral resolution than CDS, and will therefore provide more accurate Dopplershift measurements. SUMER also reveal multiple line components that CDS cannot distinguish. Owing to the high spatial resolution along the SUMER slit, observations can show if the intensity within a single CDS pixel originates from more than one loop structure. The high temporal resolution will provide observations of intensity and Dopplershift variations that are too fast to be recorded by CDS. Observations of density sensitive line pairs will enable us to study the temporal variation of the density of the active region loops. DOES NOT APPLY FOR MEDOC 15: The goal of the SST is diffraction-limited imaging, meaning a spatial resolution close to 0.1" in the visible part of the spectrum. Images obtained with this telescope is showing fine structure of sunspots and active regions that few, if any, other instruments is capable of resolving. For this JOP the SST observations will be used for context purposes only. Operating Details: CDS: Three studies are run: O_LOOP1 (NIS), O_LOOP5 (NIS) and O_LOOP11 (GIS): O_LOOP1 builds up a 160 x 240 arc second raster in 6 wavelength bands (He I 584.33 A, O III 599.66 A, O V 629.73 A, Ne VI 562 A, Mg IX 368.06 A, and Fe XVI 360.76 A) by stepping the 4 arc second slit in steps of 4 arc seconds. The exposure time at each position is 10 seconds giving a cadence of approximately 10.5 minutes. O_LOOP5 builds up a 60 x 240 arc second raster in the same 6 wavelength bands as O_LOOP1, by stepping the 4 arc second slit in steps of 8 arc seconds. The exposure time at each position is 10 seconds, giving a cadence of approximately 2 minutes. O_LOOP11 uses the 4 x 4 arc second slit to record spectrograms with all 4 GIS detectors. The study consists of 10 exposures each having an exposure time of 60 seconds, giving a total duration of approximately 10.5 minutes. These programs will be run in the following two sequences: Alternative 1: 3 x O_LOOP1 ( ~31 minutes) at least 120 x O_LOOP5 ( > 4 hours) 3 x O_LOOP1 ( ~31 minutes) Pointing: A part of the FOVs must be on the disc Alternative 2: 3 x O_LOOP1 ( ~31 minutes) at least 24 x O_LOOP11 ( > 4 hours) 3 x O_LOOP1 ( ~31 minutes) Pointing: In the EIT Fe IX/X 171 image pick a location (x,y) exactly at the limb where activity may be expected. Read out the (x,y) values from image_tool, then adjust the pointing for both GIS O_LOOP11 and NIS O_LOOP1 to (x+20", y-23"). SUMER: A new (April 2005) is to be run during MEDOC 15: a modified version of FW_1E5_KBR (the name of the new study TBD). This study covers the complete region from approximately 1398 A to 1408.5 A, and includes several density sensitive O IV line pairs. The 4" X 300" slit is placed at a fixed position close to the solar limb (~15"-30") for several hours. No binning along the slit, all lines on the KBr part of detector A, 60 s exposure time. The 5 data windows are carefully centered at: 1399.00 (O IV) 1401.10 (Ar VIII, OIV) 1403.20 (Si IV) 1405.30 (O IV/O III(2)/S IV, O III(2), S IV) 1407.40 (O IV, O III(2)) Due to the state of the SUMER detector A, the data windows will be 50 X 120 pixels (not 360 pixels high). * Older studies that have been run: FW_1E5_KBR and CME_WATCH_UF2 (May 2004), plus LOOP_NV_DEC2000 and LOOP_CIV_OCT2001_0 (latter also ran in May 2004): FW_1E5_KBR covers the complete region from ~1399 A to 1405.5 A, including some O IV lines that can be used for density diagnostics, but the new program (April 2005) covers more density sensitive line pairs. 4 X 300 arc second slit, 45 s exposure time. CME_WATCH_UF2 observes 5 data windows covering cool O III and O IV lines and hot Mg IX, Na IX and Si IX lines. 4 X 300 arc second slit, binning size = 3 pixels along the slit, 60 s exposure time. Due to the binning this study yields a good signal to noise ratio, but rather poor spatial resolution. LOOP_NV_DEC2000 covers a wavelength band that includes N V 1238 A, Mg X 624 A and O V 629 A. The exposure time is 45 s. LOOP_CIV_OCT2001_0 covers a wavelength band that includes Ne VIII 770 A, C IV 1548 A and C IV 1550 A. The exposure time is 90 s. For the LOOP_* studies, the 1 x 300 arc second slit is used. The slit is placed at a fixed position close to the solar limb, and series of spectrograms are recorded for several hours with one of the observing programs before changing to the other program. The exact duration of each run should be decided in cooperation with the CDS planner. TRACE: TRACE cycles through the sequence 1600 A, Lyman alpha 1216 A and Fe IX/X 171 A. The fixed exposure times of the three passbands are 27.6, 19.5 and 16.4, respectively. The cadence of the full cycle is approximately 80 s, the field of view is 320 x 320 arc seconds and full spatial resolution (0.5"/pix) is used. EIT: EIT images in the Fe IX/X 171 A band is needed for planning and target selection. MDI: MDI magnetograms could be used for planning and target selection. SST: SST will provide diffraction-limited images of the active regions.