SXT Status Report 3 June 1996 - 24 June 1996 (Weeks 23 - 25) ----------- Mark Weber Hugh Hudson INTRODUCTION The month of June has been relatively placid for Yohkoh operations. Many scientists attended the AAS/SPD Meeting in Madison, Wisconsin, so there was little call for special observations, or coordinated campaigns. (An exception was the Schmieder campaign, discussed later.) The SXT experienced no problems or errors of significance. SOLAR ACTIVITY Solar activity has continued to wax and wane around A-level, with B-class flares not being uncommon. The three largest flares of this period have exceeded B.3, but no C-class flares have been evident in the GOES record. It appears that the greater proportion of active regions recently has been in the northern hemisphere, for both old- and new-cycle complexes. The new-cycle region (#7972) at N30 created coronal loops and was still visible at the end of the reporting period. The active longitudes seem to be mostly 180 degrees apart, with some exceptions. SXT INSTRUMENT STATUS The SXT instrument has continued to work well. There were no significant SXT errors. SXT CALIBRATION ACTIVITIES Hudson and Weber have continued to consider the process by which terminator images are obtained. These images are important for ana- lyzing and calibrating SXT data against the "straylight problem". In particular, the terminator-gathering process is complicated by minor imprecisions in predicting and controlling the pointing of the instrument. They have looked at orbital variations in SXT pointing for recent data to determine if another level of accuracy can be achieved by considering the time-dependence of the orbital drift. This work is based on similar examinations made by Acton and others. In the meantime, we continue to refine the data base of terminator images. SXT has been obtaining long-exposure images through the Be filter as a possible aid in calibrating the orbital phase dependence of the BCS rest wavelength in the SXV channel. Any variations of the rest wavelength position would reflect spacecraft flexure, which we know quite well for SXT (and HXT) but not so well at present for BCS. This is most directly done when a single active region is present, in order not to have confused spectra. CAMPAIGNS As mentioned previously, the number of special observation operations have been minimal in Weeks 23 - 25. On June 6 there was a "micro-campaign" (coordinated by George Fisher) with SoHO/SUMER,CDS to observe NOAA AR 7968. We also participated in a longer campaign (June 2 to June 10), directed by Brigitte Schmieder with Meudon and SoHO/SUMER,CDS, to observe coronal loops. In general there are now many opportunities for Yohkoh and SoHO to work together, and we would like to stay as closely in touch as possible. For Yohkoh operations, there is a text file accessible with "finger campaign@isass0.solar.isas.ac.jp | more" or the Web at "http://www.space.lockheed.com/SXT/homepage.html". See "http://sohowww.nascom.nasa.gov/operations/targets/today" for SoHO target planning. VISITORS Scientific visitors to ISAS during this period included Wang Jingxiu from Beijing, B. Somov from Moscow, and Y. Suematsu of NAO. The Minister of Education, Sports, and Culture visited ISAS on 24 June and was given a full briefing on Yohkoh. SCIENCE Wang Jingxiu and various colleagues (Savy, Shibata, Slater among others) have been working diligently on the apparent expansions and contractions of magnetic loops in a well-observed active region. They appear to be learning a great deal about the magnetic origins of such motions. In the meanwhile, the SoHO LASCO experiment reportedly has detected abundant outward motions of magnetic loops, suggesting that the original Uchida et al. identification of the expanding active-region loops with the slow component of the solar wind may have some validity. The Suematsu seminar on June 20 reported observations of flares on 13 Oct. 1995, interpreting them as magnetic reconnection in an emerging- flux model (Heyvaerts-Priest-Rust). These and related flares produced type II and IV bursts, transient coronal holes or "dimming" events, and excellent examples of bi-lobed expansions. SEMINARS June 6: B. Somov, "Solar Physics at Moscow State University" June 20: Y. Suematsu, "Horseshoe-Shaped H-alpha Flares On 13 October 1995" PERSONNEL Hudson, Savy, and Weber in residence. Nitta and Slater returned to California. Week 23 Tohbans SSOC: T Bushimata, S Sano KSC: S Nagai, M Yamamoto SXT Chief Observer: H Hudson, M Weber Week 24 Tohbans SSOC: J Koyama, T. Sakao KSC: M Yamamoto, T Magara SXT Chief Observer: M Weber Week 25 SSOC: H Tonooka, Y Hanaoka KSC: T Magara, S Tanuma SXT Chief Observer: M Weber