SXT Status Report 18 March - 13 April, 1998 (Weeks 12-15) N. Nitta, H. Hudson SUMMARY This report covers four weeks because of a clerical error at the end of week 11. Yohkoh and SXT continue to operate well, except for an SEU on April 11 (see below). SOLAR ACTIVITY Solar activity remained at a high level. with 8 M-class events during the interval. Most of the activity was in the south (in the latitude zone between S30 and S15), and there were numerous active regions (NOAA #8176 through #8202, with #8179 having a spot area of 800 millionths in a delta configuration on March 18). SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES Just at the time of writing of this report, an SEU (particle-induced error in the SXT camera logic) occurred prior to the last contact pass for the week. When this happens (but it is rare), SXT must remain off the air for the whole weekend, because it usually takes two real-time passes to understand the error and recover from it. SXT observations will resume about 03:00 UT, April 13. The Yohkoh Canopus sensor had problems associated with software for command generation (ground support software). There was a long interval during Week 12 (Mar. 17 - Mar. 20) during which lock on Canopus (the spacecraft Z-axis roll reference) may have been lost. On the 20th normal tracking resumed. The Yohkoh pointing (X, Y) was adjusted by about 20 arcsec to compensate for normal seasonal flexure. We are trying to keep Sun center within a small range in order to improve the stray-light corrections. This plus the improved software (resulting from changes installed in January) are making the Al.1 movie images look better than they have looked in the past. The patrol image window (half the CCD height) was moved downwards in order to observe high loops of the active region complex that was about to appear on the SE limb. Then it was moved upwards again to cover a high latitude cusp in the northern hemiphere. So far we have not had a problem, but the SXT Chief Observer needs to be constantly prepared for a high latitude region. Data archiving is complete through Week 12 (ending at Spring Equinox). SCIENCE The third SOHO-Yohkoh CDAW (Coordinated Data Analysis Workshop) took place the week of April 4. Everything worked fine, with perhaps 25 workstations simultaneously cranking away on things related to the theme, magnetic connectivity between the corona and photosphere. Data were accessible, the workstations were set up properly, Internet-based projection facilities made presentations easy, and best of all the software (SolarSoft, including now the new mapping package written by Dominic Zarro), worked brilliantly. For many of the participants this was the first time to have a chance to do proper overlays of SOHO data, including MDI magnetograms crucial to the connectivity, with Yohkoh and other images. SolarSoft should be the standard environment for future data analysis work. Most of the work of the workshop was captured in Web documents, which are currently being edited (Workshop group 1 is already complete, thanks to efficient work by Barry LaBonte, and the material from groups 2 and 3 will be done this week). The scheme of weekly reporting by the SXT Chief Observer on Web pages has continued. The current "science nugget" is normally at ftp://isass0.solar.isas.ac.jp/pub/sxt_co/SXTweekly.html which links to this report and other pages, the previous science nuggets reported by SXT chief observers. See index.html for access to the full list. The new ones are: 980320.html Cavity with bright core 980327.html AR dependence of flare characteristics 980403.html Message from the back side of the Sun 980410.html Further analysis of the 7-Apr-97 flare CME The last entry is also called SXTweekly.html and contains links to current-week operations information. We SXT chief observers seem to like this system - it helps us make current affairs available - and we would always appreciate feedback. We plan to reorganize the Web site over the next few weeks. OPERATIONS ISSUES In week 12, 1 passe was lost due to HALCA operation, 5 passes due to AKEBONO, and 5 passes due to 20m antenna maintenance. In week 13, 1 passe was lost due to AKEBONO operation, and 6 passes due to 20m antenna maintenance. In week 14, 6 passes was be lost due to 20m antenna maintenance. In week 15, one pass was be lost to 20m antenna maintenance but none to spacecraft conflicts. The maintenance work on the KSC 20-m telemetry dish is now complete. There were no special joint-observation campaigns during the past four weeks. VISITORS AND PERSONNEL Nitta arrived. Hudson departed and returned. There were many visitors for the CDAW, among whom Davey, Freeland, and Zarro contributed a lot to the software environment; B. Thompson (NASA) and H. Aurass (Potsdam) will remain at ISAS for one and two weeks, respectively, for further data analysis. SEMINARS March 19: K. Nakakubo (Gakugei U.) "Variation of X-ray Bright Point Numbers in the Solar Activity Cycle" T. Yoshida (NAO) "XUV Doppler Telescope" The first of these talks dealt with the long-term variability of the X-ray bright points. Nakakubo and Hara have developed software for counting them, and there will be many applications of the resulting data. We hope to put the first results (the solar-cycle variation, or lack thereof) on one of our weekly science nuggets. The second talk was a general review of data analysis on the X-ray Doppler observations by the XDT sounding rocket. Much has been done, including the difficult task of coaligning XDT and EIT images. As reported at the CDAW by Kano, this coalignment still is not better than a few arc sec. In the overlapping field observed by CDS and XDT, the CDS spectroscopy reportedly confirms a large velocity signal detected by XDT in active-region loops. TOHBANS Tohbans for Week 12 SSOC : K. Akita KSC : S. Kubo & K. Shinoda SXT_CO: H. Hudson, D. McKenzie SXT_SW: - Tohbans for Week 13 SSOC : S. Morita KSC : K. Shinoda & Y. Iizuka SXT_CO: N. Nitta, H. Hudson SXT_SW: - Tohbans for Week 14 SSOC : S. Sano, Y. Iizuka KSC : S. Nagata, K. Kobayashi SXT_CO: N. Nitta SXT_SW: - Tohbans for Week 15 SSOC : K. Hori, Watanabe_Te et al. KSC : S. Sano, Nakagawa SXT_CO: N. Nitta SXT_SW: S. Freeland