SXT REPORT FOR WEEK 5: 24-30 January 1993 ========================================= General Status -------------- SXT continued to function well and got useful data, although the Sun remained relatively quiet. SXT has now amassed over 875,000 full-frame and partial frame images. Personnel --------- There have been no changes in SXT personnel at ISAS this week. Keith Strong leaves ISAS to spend a week in California on Sunday. Nariaki Nitta has volunteered to take over as Chief Observer. Dick Canfield leaves next week. Karen Harvey comes to visit in early February. We changed the operations manning policy to a system of two SSOC tobans this week; Joe Kahn and Sakao-san. The two KSC tobans were Shimizu-san and Suematseu-san. We had a seminar by Professor Enome about the Nobeyama Radioheliograph. He showed some of the synthesized images that they have been obtaining from Nobeyama since it came into operation in June 1992. These images look extremely high qulaity. He pointed out several collaborations were underway with Yohkoh already and encouraged more such joint work in the future. There was a great deal of interesting debate about the filament eruption of 31 July 1992 which was observed by both SXT and the radioheliograph. It shows a rising arcade corresponding to the filament (presumably) visible in the 2-cm data and beneath it an exquisite arcade of X-ray emitting loops. He also reminded us of the meeting that he is organising in September called "A New Look At The Sun With An Ephasis On Advanced Observations of Coronal Dynamics and Flares- What Do We See With Yohkoh and Nobeyama Radioheliograph". He encourgaged more of our US and UK Colleagues to attend - it is not too late! Solar Activitiy and Interesting Events -------------------------------------- If you are interested in flares this was not a stellar week for you. We only had one C flare and the GOES background never got above the B5 level. However, for those who are working on coronal holes, filament eruptions, X-ray bright points and large-scale coronal structures there was lots of good data. We observed two large coronal holes; one stretching from the northern polar hole across the equator and the other, about a 120 degrees behind the first in longitude, originating in the southern polar hole and stretching into the northern hemisphere. They have an interesting contrast in boundary characteristics; the northern hemisphere hole seems to have very low laying boundaries (angle of less than 45 degrees) whereas the southern coronal hole had high, curtain-like boundaries. "Active" Region 7407 produced a beautiful filament eruption on 26 Jan 93 before 17:46 UT. The bright, complex arcade it produced stretched over 100,000 km across the disk. It slowly grew and dimmed over the next day. This region produced several loop arcade activations on 27/28 Jan 93. The new active region that appeared in the southeast looked promising but has slowly faded as it came onto the disk. X-Ray bright points seem numerous and produed several XBP flares. Science Progress ---------------- We have been consumed here by several lively debates about the relative roles of particles and conduction in flares. These discussions have been stimulated by some results that Dick Canfield has got from the 15 November 1991 flare and a separate study of impulsive heating found by Hugh Hudson and Keith Strong. Hugh Hudson has been modelling the contribution of nonthermal emission to these impulsive bursts. Nariaki Nitta has continued his study of active region developmentin relation to flare productivity and has extended it to another region. Greg Slater has continued work on developing synoptic maps from the X-ray data as part of a study of global structures. Gary Linford has been working on getting a simpler and more accurate temperature and emission measure code operational. He has been applying to flare data. Preparations for the science meeting in February near ISAS are progressing apace with the release of a detailed meeting schedule and travel arrangements. SXT Operations -------------- Several changes were made to the SXT tables. They were all loaded up sucessfully with the exception of the final table of the week which could not be transfered to KSC because of an apparent communications problem. This has meant that we continued to take calibration images periodically, there is no loss of science data. The most complex plan involved doing one of our periodic offpoints to make a deep exposure of the high corona. While the offpoints worked flawlessly thanks to the hard work and talent of the SSOC and KCS tobans , the scientific results were a disappointment. The scattered light appears to make the long exposure unusable in each of the filters (Mg, Dag, thick Al) that we used. More quantitative statements need to be made, but new patterns of leaking light appeared with this orientation of the telescope. The operation itself was perfect, no glitches. The offpoint was from the patched OG, and the return was via BC's since the return OG had not been updated yet to allow for the re-point done to clear the HXA fiducial marks recently. We may go ahead with an E offpoint, on the off chance that the scattered light will be appreciably different in that direction. Still further off-axis (i.e., beyond the safe-hold limit) wouldn't seem to offer much hope, although that could eventually be tried too, if both E and W 18 arc min offsets are bad. There is presumably almost no field-of-view restriction by the thermal close-out or other instrument or spacecraft parts, so that sunlight could find its way in through the hole even many degrees off axis. Keith Strong, 30 January 1993