SXT Status Report 5 March 1996 - 18 March 1996 (Weeks 10 - 11) ---------- Hugh Hudson 18-Mar-96 SXT operations have been straightforward, except for the SoHO polar plumes campaign described below. SOLAR ACTIVITY The Sun has been mostly quiet, but an active region (NOAA 7952) did make an appearance. It was quite active with microflares, but alas only one exceeded the C level and there were no Yohkoh flare-mode triggers. The SXT flare mode has reverted to the standard pattern, ie with multiple filters. We already have data in single-filter mode (Be) and may try this again (perhaps with Al.1) when activity resumes. SXT INSTRUMENT STATUS The SXT instrument has continued to work well. There were no significant SXT errors. During week 11, however, Yohkoh lost track on Canopus due to an erroneous command sequence. At the time of writing, the status was not known to have returned to normal, but there is a high probability that it was fixed before the weekend operations at the end of Week 11. When this sort of thing happens there is almost no perceptible effect on the SXT images because of the excellent roll stability of Yohkoh. Because of a 3-day shutdown of the ISAS operations mainframe computer in Week 12, operations will be reduced to the basic minimum of standard observations. We are planning to obtain the weekly dark calibration as well if schedule is maintained. SXT CALIBRATION ACTIVITIES The main effort for SXT calibration continues to be the "terminator" program, whereby correction images are obtained by acquiring pictures when the X-ray sun has set but the visible sun is unaffected by atmospheric absorption. These images still show the scattered optical light, and we have found that excellent corrections for this effect can be made by proper use of the terminator data. We continue to work on ways of getting such correction images efficiently and in the right filters. In particular, to cover the use of the Mg filter in the SoHO campaign, we have been acquiring additional Mg terminator images. PASS CONFLICTS The pass conflicts with the ISAS/NASDA/MITI Space Flyer Unit spacecraft have ended with its successful recovery by the Space Shuttle. Conflicts with ASCA, both at KSC and also for DSN stations, continue. However there is only about a 60% overlap range with the KSC passes now, and the number of conflicted passes is steadily decreasing (Week 10: 4 passes lost at KSC, out of a possible 30). CAMPAIGNS SoHO conducted its first observing campaign, JOP_039 on polar plumes, 7-8 Mar. To support this SXT PFI's were placed at the S pole to study the high-temperature components of any bright points. Indeed, bright points occurred, but at the time of writing the SXT data reduction has not been completed. Please see the SoHO Web material for further details. SCIENCE Visitors at ISAS/Yohkoh included N. Gopalswamy and G. Haerendel, both of whom presented seminars, and M. Kundu. Gopalswamy is quite interested in the comparison of radio observations with Yohkoh data, which is an extremely fruitful area. He is visiting Hiraiso and Nobeyama. Kundu will be at Mitaka mainly, for about three months, and we expect to see more of him at ISAS. SEMINARS Wednesday 6 March: H. Koshiishi, NRO: "A Deep-CLEAN Imaging Method Applied to the Nobeyama Radioheliograph: Observations of Polar-Cap Brightenings and Their Association with Coronal Holes". This presentation was quite interesting, because the new CLEAN technique greatly suppresses the background fluctuations on the quiet Sun, perhaps by an order of magnitude. Wednesday 6 March: N. Gopalswamy (U. Md.): "A Coronal Mass Ejection observed by SXT and the Nobeyama Radioheliograph". The event studied appears to have the traditional three-part structure of a CME observed by a coronagraph. In this case a detailed record of the filament motion was available in the Nobeyama 17 GHz data. Thursday 7 March: G. Haerendel, "The Relevance of Narrow Current Filaments in Solar Active Regions and Solar Flares". The work presented here seeks an alternative to macroscopic reconnection theories for active-region and flare heating. This seminar was treated as an ISAS colloquium and had a large audience. I found it exhilarating! PERSONNEL Nariaki Nitta departed, followed by Savy and Hudson. The Bath meeting on reconnection has drawn away most of the active Yohkoh research workers! Week 12 will see D-toh virtually deserted, with M. Shimojo and T. Yoshida acting as caretakers. Week 10 Tohbans: SSOC: M. Shimojo, N. Nitta KSC: S. Kubo, H. Sekiguchi SXT Chief Observer: N. Nitta SXT Systems and Data Engineer: Week 11 Tohbans: SSOC: M. Nishio, K. Yaji KSC: H. Sekiguchi, Y. Nakagawa SXT Chief Observer: H. Hudson SXT Systems and Data Engineer: