SOHO Intercalibration Joint Observing Programme 10 HiRES/SUMER/CDS/CELIAS SEM/EIT CROSS CALIBRATION Author(s): J. Gethyn Timothy (HiRES/SUMER/CDS), Progress: ______________________________________________________________________________ Draft Scheme 21 May 1996 Distributed to Relevant Parties 23 May 1996 Telecon to EOF 30 May 1996 1st Update on Web: 6 Jun 1996 ______________________________________________________________________________ Objectives: SUMER and CDS radiometric cross-calibration using the HiRES spectroheliometer. SUMER and CDS wavelength cross-calibration using the HiRES spectroheliometer. CELIAS SEM and EIT radiometric cross-calibration using the HiRES XUV photodiodes. Conditions Necessary to Run: Same day full disk measurements with EIT, CELIAS SEM, and with SUMER and CDS in selected strong lines. Simultaneous raster scans of a quiet region near sun centre with SUMER and CDS during the HiRES flight. Description of the HiRES Payload: The High-Resolution EUV Spectroheliometer (HiRES) is our first step towards the 0.1 arc sec angular resolution goal at EUV wavelengths. The HiRES instrument consists of a Gregory telescope with a 45-cm-diameter primary mirror, and an imaging EUV spectrometer, employing a single-reflection toric diffraction grating in a Rowland circle mounting and an imaging pulse-counting Multi-Anode Microchannel Array (MAMA) detector system. The diffraction limit of the HiRES telescope is ~0.03 arc sec at 500 A. The telescope, which is superpolished and has an active focus system, has a 16 arc min field-of-view, set by a stop at the primary mirror focus. The spectrometer slit is centred within this field and has dimensions 8 arc min in length by 0.5 arc sec in width. The toric grating gives an inverse dispersion of 2.78 A mm-1 and a stigmatic spectrum from 510 to 630 A. The spectrometer slit is highly-polished and reflects the visible-light solar image to a narrow band H-a filter and CCD camera. The camera has a 6:1 motorized zoom lens with a maximum angular resolution of ~0.3 arc sec. Real-time images are transmitted during flight to provide information for controlling the telescope focus and for commanding the SPARCS attitude control system. The (2048 x 2048)-pixel MAMA detector covers a 71-A range in first order with a spectral resolution of 70 mA (two detector pixels). Doppler shifts can be determined to a resolution 2 mA at wavelengths near 600 A (~1.0 km s-1). The wavelength range selected for the first flight is from 560 to 631 A. An on-board Pt/Ne lamp impresses a wavelength calibration spectrum on the upper part of the detector while the solar spectrum is recorded simultaneously on the lower part. The MAMA operates in the photon time-tag mode with the time-of-arrival and address of each detected photon transmitted over a 16 Mb s-1 data link to the ground. The time history of the photons allows correction of the SPARCS pointing jitter. The HiRES spectrometer slit is pointed to a feature in the solar atmosphere using real-time control of the SPARCS. In addition, SPARCS can be commanded to execute a linear (push broom) scan of the spectrometer slit across the sun. Finally, two EUV photodiodes mounted forward of the telescope secondary mirror, are used to measure the absolute solar irradiances and the atmospheric extinction profiles in two wavelength bands centered at 304 A and 584 A respectively. A small total irradiance spectrometer covering the wavelength range from ~270 to 1350 A with a spectral resolution ~ 1 A will be added for later flights. For the first flight the spectroheliometer will be calibrated pre-flight at the component level. The XUV diodes will be calibrated pre-flight at NIST. Post-flight calibration of the spectroheliometer is expected to be carried out at the system level. Post-flight calibration of the XUV diodes will again be at NIST. Operation: A. Launch Rules i. HiRES requires an active region with a sunspot on the disk. ii. HiRES will be master of JOP timing. iii. HiRES launch window will be 1200 noon to 1230 pm. iv. Preliminary target selection at T-7 days. v. Targets defined at T-24 hours. vi. Targets confirmed at T-4 hours. Vii. Coordinate system for HiRES/SOHO coalignment will be Carrington latitudes and longitudes. B. Schedule i. Test run of JOP by SOHO 18 July 1996. ii. Target date for HiRES flight on, or shortly after, 30 July 1996. C. Instruments 1. HiRES XUV photodiodes operate throughout flight from T+75 s (98 km altitude) to T+437 s (93 km altitude). Spectroheliometer operates from T+105 s (143 km altitude) to T+420 s (120 km altitude). He I 584 observable above 130 km. Three targets: - active region with sunspot - 4 arc min push broom scan by 8 arc min slit. Total time 90 s. - polar hole - 4 arc min push broom scan by 8 arc min slit. Total time 90 s. - quiet region near sun centre - 2 arc min push broom scan, 10 s fixed pointing, 2 arc min push broom scan, 10 s fixed pointing. Total time 65 s. Quiet region is selected as target 3 for maximum photometric stability. Slit roll orientation solar North-South to permit co-alignment with SUMER. Launch as close to noon at White Sands Missile Range, New Mexico (32.5 deg N, 106.5deg W). 2. SUMER Pre- and post-flight full disk raster scans at He I 584.3 A, and at Mg X 624.9 A plus O V 629.7 A. One of the two bands will be selected for simultaneous measurements because of the need to cross H Ly-alpha. Requires HV off and a time of > 20 s. During HiRES flight alternate raster scans of quiet region centered along HiRES slit in two bands 1225-1265 A and 1164-1204 A. Slit 1 x 360 (arc sec)2, scan length 240 arc sec. HiRES and SUMER slit axes co-aligned. SUMER contact is Udo Schuehle at 301-386-3221. 3. CDS Pre- and post-flight full disk raster scan at 304 A (He II plus Si XI) and at Fe IX 171 A. Scan at 304 A will be run with the NIS (second order), 171 A scan TBD. During HiRES flight NIS push broom scans of quiet region centered along HiRES slit in band 513-633 A. Lines to be read out are He I 584 A, Mg X 610 A, (Mg X 625 A if possible), and O V 630 A. Slit 2 x 240 (arc sec)2, scan length 240 arc sec. HiRES and CDS slit axes co-aligned. CDS contact TBD. 4. EIT Full sun images at He I 304 A and Fe IX 171 A before, during, and after the HiRES flight. Operate with enhanced telemetry. EIT contact TBD. 5. CELIAS SEM Measure 304 A and 170-700 A intensities before, during, and after the HiRES flight. SEM contact TBD. 6. UVCS UVCS will run Intercalibration JOP 09 as close as feasible to the HiRES JOP 10. UVCS contact is John Kohl at 301-286-3136. I am not sure if this should be part of a generic HiRES JOP or a separate JOP, but it is extremely desirable to obtain MDI high-resolution magnetograms for each of the HiRES scan fields at, or very near, the time of the HiRES flight. MDI team has yet to be contacted. ***************************************** J. Gethyn Timothy Centre for Space Research University of New Brunswick Post Office Box 4400 Fredericton, New Brunswick CANADA E3B 5A3 Tel: +1-506-453-5031 Fax: +1-506-453-4813 Internet: gethyn@unb.ca SolarMail: jgtimothy@solar.stanford.edu *****************************************