SXT Status Report 25 September 1996 - 21 October 1996 (Weeks 39 - 42) L. Acton, H. Hudson, S. Savy SUMMARY Solar activity continued at a low level. SXT and Yohkoh continued normal operations and there was considerable joint observation with various SOHO programs. SOLAR ACTIVITY In our last status report, we stated "...the fourth (and final?) rotation of AR 7978 brought few surprises...". This was wrong on two counts - it DID bring a major surprise, and it was NOT the final rotation. The surprise was a splendid CME event, the second only for which we know we have good joint observations with SOHO (the other was on 25 September in the southern polar crown region, near disk center). SXT INSTRUMENT STATUS SXT conducted a one-day bakeout, somewhat difficult to schedule because of the many joint observing programs Yohkoh is involved with. This was the first bakeout since February, 1996. The warm status of the CCD gives a better look at the dark signal and therefore any degradation. The gradual increase of dark signal noted previously has continued, but there also appear to have been areas of annealing behavior. The CCD basically looks healthy, but we will try to do these bakeouts more systematically in the future and have established a three-month interval. SXT CALIBRATION ACTIVITIES The gradual degradation of the signal levels of both HXA sensors (X slightly faster than Y) caused software problems for SXT image registration over the last few months, as described in the last . report. The HXT team has now increased the gain on the HXA-X sensor output, and Jean-Pierre Wuelser has updated his alignment software to handle the degradation. At the time of writing the fix is in place and database reconstruction for the missed interval is under way. The HXA problem is a gradual one, and may in a year or two require additional steps, so we will try to monitor the HXA outputs more regularly in the future. This is not the only way to calibrate the Yohkoh gyros for fine pointing, but it is the easiest and probably the best. PASS CONFLICTS The ASCA pass conflicts are gradually disappearing as the ASCA and Yohkoh orbits precess relative to one another. During this reporting interval, however, ISAS established a new staffing policy for the Kagoshima ground station. This means that there will be occasional passes lost to Akebono (magnetospheric space mission, not sumo wrestler). There will be few passes lost this way on average; for example only two (out of a weekly total of 30) were lost in Week 40. CAMPAIGNS Several SOHO-related campaigns of scientific interest to Yohkoh took place, including JOP-3 (CME onset), JOP-033 (jets), and observations aimed at loop structure. The ideal scenario for JOP-033 would be to have Yohkoh identify an emerging-flux region or the appropriately jet-active part of an existing AR, and then let SOHO know the location in nearly real time. This is not an easy job, and the first attempts produced no results. We hope eventually to catch a jet and apply the SOHO spectroscopic instruments to understanding the physical conditions. As for CMEs, this reporting interval produced two beautiful sets of observations (25 September and 5 October), alas neither of them during the JOP programs. Nevertheless there were excellent synoptic observations, and because the 5 October event occurred in the faint remnants of the isolated active region that we have been watching, the SXT partial-frame images were making long exposures at full resolution during the eruption. The resulting movie is spectacular, and a comparison of the low-corona structures SXT sees with the full CME development seen by LASCO should be extremely informative. These two events are the first for which we know that we have simultaneous Yohkoh and SOHO observations of CMEs, and the low level of solar activity seems to be a help since the X-ray signatures may be quite faint. For Yohkoh operations, the SXT weekly observing plan is available on the Web at http://www.space.lockheed.com/SXT/html2/First_Light.html or with "finger campaign@isass0.solar.isas.ac.jp | more" See http://sohowww.nascom.nasa.gov/operations/targets/today" for SoHO target planning. VISITORS Heng Zhang (Yunnan Observatory) and Hongqi Zhang (Beijing Observatory) visited. SEMINARS Oct. 17 Hongqi ZHANG (Beijing Astron. Obs.) "Observation and research on solar magnetic fields at Huairou" Heng ZHANG (Yunnan Obs.) "Observations of p-mode/s-mode conversion in magnetic fields and the absorption of p-modes by sunspots" There was a bit of a seminar hiatus during this interval because of holidays and the occurrence of ASJ meeting in Mizusawa. SCIENCE SXT science activities at ISAS were dominated by getting ready for the "Yoyogi meeting." Yohkoh 5th Anniversary Symposium on OBSERVATIONAL PLASMA ASTROPHYSICS: FIVE YEARS OF YOHKOH AND BEYOND November 6 - 8, 1996 National Olympics Memorial Youth Center Yoyogi, Tokyo, Japan Several studies related to AR 7978-7982-7984... have been going on. One of the real pecularities of the structure of this region is is large extent connected with its strong low-altitude concentration. The GOES low-channel flux, for example, disappeared with an e-folding time of only 40 minutes during the principal occultation event at the end of the first rotation. The soft X-ray variation of the Sun viewed as a star during the occurrence of this event was more than two decades even outside flare times. How can the Sun be this variable, when X-rays from other ordinary stars are not so variable? PERSONNEL Jean-Pierre Wuelser returned to Palo Alto; Greg Slater arrived. Loren Acton arrived in time to supervise and analyze the bakeout, and will stay through the Yoyogi meeting. Week 39 Tohbans SSOC: M. Shimojo and M. Yamamoto KSC : Y. Hanaoka and S. Watari SXT CO: J.-P. Wuelser Week 40 Tohbans SSOC: M. Irie and K. Marubashi KSC: S. Watari and K. Nakakubo SXT CO: J.-P. Wuelser and H. Hudson Week 41 Tohbans SSOC: S. Yasuno and K. Yoshimura KSC: K. Nakakubo and K. Ichimoto SXT CO: S. Savy and H. Hudson Week 42 Tohbans SSOC: T. Shimizu and H. Imai KSC: K. Ichimoto and T. Yoshida SXT CO: S. Savy and H. Hudson