SXT Status Report 18 November 1996 - 09 December 1996 (Weeks 50-52) H. Hudson, S. Savy, M. Weber SUMMARY Yohkoh has entered its sixth New Year's holiday, and both spacecraft and SXT are operating smoothly. This is the final SXT status report of 1996. Solar activity remained at a low level but with interesting features. A coordinated observation of polar jets (S. Koutchmy, H. Hara) was extremely successful. Another wonderful CME happened on December 22. The Internet across the Pacific remains virtually useless for data transfer. SOLAR ACTIVITY The complex of activity whose highlight was AR7978, and which produced the X-class flare of July 9, finally seems to have lost most of its strength. However active regions appeared at other longitudes, both old-cycle and new-cycle. SXT INSTRUMENT STATUS SXT continues to perform well and to return excellent observations. Another CCD streak artifact appeared on Dec. 12, coinciding approximately with the long exposures of the polar jet campaign. The artifact disappeared on an e-folding time scale of about one day, similar to the behavior observed in earlier cases. The SXT team has carried out some analysis and discussed the situation. These artifacts do not appear to be serious enough at present either to warrant an effort on cosmetic software or to require changed operations. The CO's will be judicious about the use of long shutter-open periods when bright active regions are at the limb. We note that even physically large active regions, such as those following in AR7978's footsteps, have compact structures with extremely high surface brightness. This is a reason for the concentration of streak artifacts in a few pixels commonly at the limb. The "long OP" that carries Yohkoh over the New Year's holiday will see SXT getting mainly medium-rate data (10" pixel size), with about 30-40% coverage between December 28 and January 4. The ejection-oriented flare table is still running, and the starting DPEs for the PFIs have been adjusted downwards to avoid saturation. SXT CALIBRATION ACTIVITIES The program to collect images for stray-light correction is up to date, and the following table summarizes the acquisition of these terminator images since the third filter rupture (ie, since August 29, through December 17): Al.1 AlMg Be Al12 Mg Open 19 11 2 1 4 ND 2 2 0 0 0 These images include the thin filters at all the EW offpoint positions needed for this time period. The redefinition of Yohkoh normal pointing, reported last time, resulted in better NS locations for current filters. The Yohkoh attitude control system is undergoing its annual motion according to the pattern of previous years, which puts the maximum deviation to the south during December, and as it recovers from whatever forces cause this motion we will probably re-adjust the normal pointing to compensate. The Al.1 stray-light corrections continue to be somewhat imperfect, though, as judged from the standard movie composite images. These frequently show traces of the filter pinhole leak at the SE limb, either from overcorrection or undercorrection of the stray light. We feel that we have adequate data to make perfect corrections, but something minor is still missing from the software and should be the focus of somebody's New Year's resolutions. PASS CONFLICTS There is presently little overlap between Yohkoh and ASCA KSC-Pass times. Akebono continues to take infrequent KSC passes from Yohkoh. Preparations for the launch of VSOP in February - a very important milestone for ISAS, since this will be the first flight of the M5 launcher - will take some KSC passes in January. CAMPAIGNS A joint observing campaign with SOHO (JOP057) and ground-based observatories resulted in successful observations of polar jets. SXT obtained three sets of long-exposure observations of the north polar hole to support this campaign, guided by S. Koutchmy and H. Hara. As mentioned above, these observations coincided with the appearance of a compact, bright active region on the east limb, and this may have contributed to the artifact noted on December 12. Another notable observation, but not really part of a joint campaign, came with the special SOHO observations starting December 21. In these observations LASCO and EIT got better telemetry coverage. EIT made one full-Sun image every 12 minutes in FeXII 195 A. This was rewarded with spectacular observations of CMEs, especially on December 23. SXT also obtained limited observations of this event, or rather of the flare associated with it, but only in the full-frame images and unfortunately during the weekly dark calibration. However this brings the list of Yohkoh/SOHO CME events to at least four, so this winter has seen the beginning of a sufficient database for the "calibration" of soft X-ray signatures of CMEs against the real thing. 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 There were no science visitors to ISAS during the reporting period, not counting Cheng Fang for one day (see below). SEMINARS December 24 FANG Cheng (Nanjing): "Characteristics and mechanisms of two types of white-light flares" Because of the holidays, the abnormal date, and the occurrence of an important committee meeting (related to Solar-B) at ISAS on that day, the attendance was limited. However the discussion was extremely vigorous and reminded us again that the Yohkoh white-light flare data still need analysis and publication as a unique set of data. Fang pointed out that except for the impulsive component of the white-light flare emission, we do not have good theoretical ideas to explain the continuum emission. SCIENCE Khan, Uchida and others have almost gotten the "Ebi Tempura" arcade/CME event ready for publication. The CME association is of course hypothetical, but the event is well observed and promises to help clarify the eruption process. Hudson and Joe Gurman (SOHO) continued to exchange files showing CMEs, this time the event of December 22. The EIT movie in FeXII shows a wonderful void-plus-front structure that strongly resembles a classical white-light CME. But the power of the X-ray observations is again revealed by the ability of EIT (and SXT) to track the disturbance down almost to the photosphere. PERSONNEL Mark Weber returned to Montana, but not until after establishing a lot more discipline on the Chief Observer routine. This included updating the CO manual with a new section on the streak artifacts, plus general filing and orderliness. For a general CO New Year's resolution, we vow to keep the system up, including real-time filing and the use of the CO checklists. TELEVISION In the last SXT status message we neglected to include a comment about the NHK television special on solar eclipses. This will include Yohkoh, of course, and rumor has it that the broadcast footage will include views of key SXT persons - for example, closeups of skilled fingers typing important commands into the mainframe keyboards during real-time Yohkoh operations. This program will be aired in Japan in March. Week 50 Tohbans SSOC: S. Savy, J. Shin KSC: S. Kubo, S. Sano SXT CO: M. Weber Software: --- Week 51 Tohbans SSOC: K. Kato and M. Shimojo KSC: T. Noguchi, S. Sano SXT CO: M. Weber Software: --- Week 52 Tohbans SSOC: T. Sakao, T. Sakurai KSC: T. Noguchi, S. Sano SXT CO: H. Hudson Software: --- HAPPY NEW YEAR!