SOHO Intercalibration Joint Observing Programme oo9 Above Limb Intercalibration Author: J. Kohl (UVCS) Progress: ______________________________________________________________________ Draft Scheme May 3, 1995 Discussion at SICWG May 3, 1995 Revised Draft Scheme February 9, 1996 Discussion at SICWG February 9, 1996 Discussion at SICWG March 16, 1996 Issue #1 March 26, 1996 ______________________________________________________________________ Objective: To intercalibrate UVCS, and SUMER, and to co-register UVCS and LASCO. A secondary objective is to compare spectral line positions for H I Ly alpha by UVCS to Fe XIV by LASCO. Conditions Necessary to Run: Requires UVCS, SUMER, and the presence of a bright and well defined streamer near the East or West limb. Scheme: Phase 1: UVCS, SUMER and LASCO are directed at the same location on a streamer near the East or West limb, and wavelength bands are selected which are appropriate for intercalibration. Phase 2: UVCS is rolled to a polar region and wavelength bands are selected which are appropriate for stray light comparisons. The following considerations are taken into account: - A large co-incident field of view is required to ensure good co-registration and significant spatial overlap - yet it must be small enough to be observed in a reasonable amount of time. - Observed wavelengths are the following: (1) SUMER and UVCS = 519.66 - 521.66 A, 608.79 - 610.79 A, 1024.72 - 1026.72 A, 1030.91 - 1032.91, 1036.61 - 1038.61, 1214.67 - 1216.67 A, and 1241.01 - 1243.01 A. - Exposure times should be chosen to produce 3 percent (1 sigma) counting statistics or better. - The preferred target area for Phase 1 is a bright streamer and the preferred target for Phase 2 is a polar coronal hole. - Prior to this intercalibration, SUMER should be intercalibrated with CDS, EIT and CELIAS/SEM using Intercal 2 (002). Specific Wavelength Selection: SUMER will observe the following spectral lines with a band pass of +/- 1 A: OVI 1037.61, OVI 1031.91, HI 1025.72, HI 1215.67, Mg X 609.79, Fe XII 1242.01, Si XII 520.666. UVCS will observe Four bands: Si XII 520.7, O VI 1032, 1037, H I 1025.7 (1022 - 1047 A), H I 1215.7, Mg X 610 (1210.3 - 1224.8 A), S X 1196, H I 1215.7 (1187.5 - 1222.2 A), and N V 1238, 1242, Fe XII 1242 (1236.3 - 1246.1 A). Pointing: Phase 1: SUMER should be directed to a streamer with raster corner coordinates of (-1040, 150), (- 1040, -150), (- 1580, 150), (- 1580, -150). UVCS should be directed at the same target with raster corner coordinates of (- 1361, 150),(-1361, -150), (-1580, 150), (-1580, -150). LASCO will observe the same region with its C1 Coronagraph. Phase 2 (optional) UVCS will be rolled to a polar coronal hole and additional measurements will be made at a region centered on 1.5 solar radii. Sumer would be repointed with slit perpendicular to the limb tangent. The Sumer field of view would have raster corner coordinates of (-150, 1152.14), (+150, 1152.14), (-150, 1452.14), (+150, 1452.14). Frequency: Phase 1 will be run once every two weeks, possibly falling to once per month if it is established that any changes are occurring slowly. This JOP would normally be run after Intercal JOP's 1 and 2. Phase 2 will be run as appropriate. Operating Details: Phase 1: Both instruments scan their designated area. This requires 182.347 minutes. In the case of UVCS, the area is scanned once with narrow (wide) slits for the Ly alpha (OVI) channel in 91.17 minutes, and then the area is scanned again with wide (narrow) slits for the Ly alpha (O VI) channel in 91.17 minutes. This observation is then repeated in the opposite order for a total duration of 364.69 minutes. In the case of Sumer, the designated area is scanned at all designated wavelengths in a total of 182.347 minutes. This is followed by a series of 24.5 minute exposures at the following values of xii: +/- 1580, +/- 1460, +/- 1340, +/- 1220, +/- 1100 at wavelengths of 1030.91 - 1032.91 A. The total duration of the Sumer observations is 305.053 minutes. Phase 2: UVCS rolls to the pole. Sumer repoints. Both instruments scan their designated areas. The UVCS program is identical to that of Phase 1. The Sumer program is TBD. UVCS instrument configuration: The UVCS instrument configuration is as follows: For Phase 1 and 2, the UVCS instrument is pointed at nominal sun center. The instrument is rolled to the east limb with the nominal central pixel at yii = 0.0. The instrument is configured for a nominal observation at xii = -1361; OVI slits are set initially at 265 micrometers; Ly-alpha slits are set at 50 micrometers; the telescope mirror step size is 73 arcsec which corresponds to 265 micrometers. The internal occulter is fixed at its nominal r = 1.4 value. Three positions of the mirror are needed to cover the designated area. The measurement is repeated with 265 micrometer O VI slits and 50 micrometer Ly alpha slits. It is then repeated again in the opposite order. UVCS also does a measurement of diffracted H I 1216 light to support the comparison of H I 1216 (UVCS) and Fe XIV (LASCO) line positions. For that measurement, the UVCS internal occulter is pulled back so that the telescope spectrally reflects diffracted light from the external occulter into the spectrometer. SUMER instrument configuration: The Sumer slit is 4 * 300 arcsec. The H I Ly alpha line is on the active portion of the detector. The telemetry rate for the first observing segment of 182.247 min duration is 9.6 kbits/s and the individual integration times are 60 sec. The telescope mirror step size is 6.08 arcsec. A total of 89 steps are required for each detector or a total of 178 to cover the designated area at all selected wavelengths. For the second observing segment, a series of 360 sec integration times are used at selected regions of the designated area. A total of 24.54 minutes are spent at each selected region, and only O VI 1031.91 +/- 1A is observed. In all, 5 selected regions (i.e., slit positions) are observed. Time of the observation for Phase 1: The initial observing segment takes 182.347 minutes for UVCS and Sumer. The second observing segment takes 122.706 minutes for Sumer and 182.347 minutes for UVCS. The third observing segment requires 60 minutes for the exposures and 20 minutes to roll UVCS. The total time required for Intercal 09 is 7 hours and 25 minutes.