SXT Status Report 26 January 1997 to 9 February 1997 (Weeks 5-6) N. Nitta, H. Hudson, S. Savy SUMMARY Yohkoh and SXT continue to operate smoothly. Solar activity has been low but another remarkable CME event occurred on Feb. 7, from the same region that apparently produced the Jan. 6 "halo CME". MUSES-B Muses-B was successfully launched, into the correct orbit, on Feb. 12 after a one-day weather hold. SOLAR ACTIVITY One C-class solar flare occurred during the reporting period. The CME event of Feb. 7 consisted of a large faint arcade, plus possibly related brightenings in two other activity centers, one of them a new-cycle region in the north. SXT INSTRUMENT STATUS SXT continues to perform well and to return excellent observations. The results from last month's long bakeout were favorable. SXT CALIBRATION ACTIVITIES The terminator program continued to keep up to date. The current program emphasizes getting a more detailed grid of points in the thin Al filter, as well as rounding out the offpoint positions and the ND filter settings. We have noticed that some conspiracy of orbit mechanics makes it easier to get valid terminator images in the summer. Luckily, the most recent reset of the terminator program happened in late summer 1996 and has been dealt with quite well by the system. Yohkoh is considering a possible program of special observations to develop better models for HXT gain variations across an orbit, and for HXT and BCS background variations as a function of position and time. The BCS background is especially interesting in the SXV channel because it sees the faintest corona best among the four BCS channels. Even so, and even with the large area of the BCS, the S XV channel is strictly background limited at the quietest times. In the new program we are considering locking Yohkoh onto flare mode, medium rate for several orbits per week until all possible orbit configurations are properly sampled. Part of the motivation for this calibration program was the discovery (by Sawa) that last month's SXT bakeout induced unexpected gain changes in the HXT instrument, the result of subtle temperature effects. PASS CONFLICTS At the time of writing, there is massive confusion about Yohkoh uplink and downlink at KSC. This is the result of the MUSES_B launch. This activity has resulted in at least two extra off days in Week 7, to be reported in the next status message. Week 5: 1 KSC pass cancelled for ASCA, 1 pass for MUSES-B Week 6: 3 KSC passes lost to ASCA, 2 to AKEBONO, 3 to MUSES-Bi CAMPAIGNS There were no formal campaigns during this reporting period. For Yohkoh target planning, 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 R. Schwartz is visiting from GSFC, and N. Gopalswamy has been spending some time at ISAS during his Nobeyama visit. Sam Freeland and Greg Slater are both in residence, with Sam's main task being the installation of the SolarSoft IDL system. SEMINARS N. Gopalswamy (U. Md.) gave a talk on shock waves in flares and in the interplanetary medium. Are there two kinds of shock waves, ie those created by flares (coronal Type II bursts; Moreton waves) and those created by CMEs (interplanetary Type II's; direct observations; SSC's)? Gopal thinks "yes" and pretty much convinced the audience. The seminar will continue this month with other talks on shock waves. A recent reference would be the Burgess article in SCIENCE Science activities revolved around hard X-rays (Schwartz) and filament eruptions (Gopalswamy) during this period. PERSONNEL Freeland, Schwartz, and Slater arrived. Savy departed for a short visit to Palo Alto. Week 5 Tohbans SSOC: Shin and T. Yoshida KSC: T. Yokoyama and Saita SXT CO: N. Nitta Software: G. Slater Week 6 Tohbans SSOC: A. Sterling and Nishino KSC: Saita and Tonooka SXT CO: N. Nitta Software: G. Slater, S. Freeland