REPORT FROM ISAS Monday, 11-May-92, L. Acton Sorry for the long time between status reports from Japan. It has been such a busy and interesting time! Presently Linford, Nitta, Acton, Metcalf, Kane and McTiernen are presently at ISAS from the SXT U-team. Morrison returns tomorrow, Hudson next Sunday. The Osaka meeting of the Astronomical Society of Japan takes place this week. There are about 50 papers in the solar sessions (more than ever before) and 35 or so of these are some way involved with Yohkoh. The drafts of the collection of initial Yohkoh papers to be published in PASJ are appearing daily. I have finally completed the first draft of the paper to be submitted to SCIENCE. I intend to complete and submit this before I depart ISAS on 10 June. NEW STUFF We did an off-pointing experiment for 3 orbits on 8 May to record the x-ray corona out as far as we could with 15 second exposures. The composite picture is really quite lovely, stretching over 72 arcminutes from east to west. The corona is visible out to 1 solar radius. The pictures were acquired from about 0300 to 0600 UT on 8 May. I wonder if anyone has coronameter data around that time? Now about filament eruptions and surges. On 20 April at around 2300 UT SXT observed a fantastic hair-pin shaped expanding loop on the SW limb that was superbly recorded in H-alpha, Fe XIV and white light at Norikura observatory. The x-ray loop extended at about 400 km/sec and we expect (although the careful overlays have not yet been done) the H-alpha to be nestled inside. SXT PI and experienced observer T. Hirayama first called this a surge but upon closer examination clear loop threads are seen in the H-alpha so now it is called a filament eruption. This is probably therefore a CME and is particularly interesting because we see it end-on, accounting for the narrowness of the H-alpha and x-ray features. This one will get a lot of attention I predict! At our weekly Saturday afternoon science meeting Shibata san showed us a "real" H-alpha surge from the Mitaka flare telescope that had an x-ray brightening observed by SXT at its base. P. Sturrock, come on over and have a look. Perhaps what you've been looking for has been observed! Sorry I don't have a date on this one. Great discoveries proliferate daily. Hudson and I found that the umbra of the small sunspot which was the site of the action of the 15 November 1991 X-flare actually moved about 3 arcsec north during the 8 minutes of the impulsive flare activity. This corresponds to a motion of 4+ km/sec. You may recall that this was a white light flare. Hugh Hudson measured the peak intensity of the brightest kernel at 30% brighter than the 4310 A photosphere! This represents a whopping amount of energy. The wonders of this flare never seem to cease. Yesterday Hiro Hara showed me some work that he had done that showed x-ray loops having the footpoints in the magnetic network. Yesterday, independently, I noticed that a particular set of faint large loops were rooted in the bright parts (avoided the dark parts) of our 4308 aspect sensor picture. Thanks, Tom Pope, for suggesting use of this wavelength for the SXT narrow band filter. JOINT OBSERVING The Lockheed team is now set up on LaPalma with the Soup/OSL tunable filter system. They do their best to observe the same regions as SXT has chosen and plan to continue their campaign until July. Of course, Mees Solar Observatory continues to devote their work to Yohkoh joint observing and the Imaging Vector Magnetograph is now coming on-line. Hiraiso Observatory is taking digital high resolution H-alpha of superb quality on the Yohkoh Observing region and Norikura and Hida observatories jointly observe whenever the weather permits. At this time GBO-MAIL goes out to 36 addressees at every Yohkoh station contact, giving the present SXT pointing. The system is working and we can expect a rich harvest of results. Marilym Bruner is flying her UV/XUV rocket experiment tomorrow. A link has been set up that permits transmitting SXT images to WSMR over internet to support this mission. Good luck MEB! HARDWARE STUFF Working with the off-point data reminded me that we had not yet done anything about correcting SXT images for off-axis response. I've now derived a correction array from lab calibration data that appears to do quite a reasonable job of correcting the images to permit a nearly seamless overlay of the offset images to construct the large image. This work will be passed on to Sam Freeland and Co. to put into the analysis library in a usable form for everyone to use to correct SXT data for off-axis response. At the limb of the sun the correction is roughly 20% but in the far corners of the CCD it reaches a factor of 5. The CCD gain was determined by Mons Morrison from calibrations ran last October and 2 weeks ago. The Data Number conversion factor was discovered to be close to 90 electons/Data Number for both cases. This is about 10% lower that the pre-launch value of 100 e/DN and should be used for absolute flux derivations until further notice. Tom Metcalf, who is visiting from Hawaii has derived the co_alignment of the SXT aspect and x-ray telescopes. The numbers come out as follows [dX represents the difference in the centers of the NaBan and X-ray images in the east-west coordinate, while dY represents the difference in the north-south coordinate. dR gives the difference in the radii.]: dX = -0.36 +/- 0.177 pixels. X-ray image is WEST of NaBan dY = 1.47 +/- 0.283 pixels. X-ray image is SOUTH of NaBan dR = -1.34 +/- 0.128 pixels. NaBan image smaller than X-ray Recall that a single SXT pixel subtends 2.453 seconds of arc. The extremely good match in image scale between the 2 systems is a tribute to some very difficult and careful raytracing and lab work by Bill Brown, Tom Cruz and Bill Rosenberg at Lockheed. Marilyn Bruner, Bruce Jurcevich and Mons Morrison sweated through the co-alignment adjustment. Yea, team!! Whatever is outgassing to contaminate the SXT optical system hasn't finished yet. The aspect signal continues to decrease although the curve is flattening out. As of 9 May we'd lost 11% of the signal we recorded on 1-April. You recall that some kind of volatile contamination on the CCD disappeared during the warm up on 8 April. Now, a month later it is beginning to appear again. We are planning another 1-day warmup next week.