SXT Status Report 11 September - 24 September 1995 (Weeks 37 and 38) --------- Nariaki Nitta 24-Sep-95 The central activities of the SXT team at ISAS were to attend the Hirayama workshop (see the last report) in week 37 and to carry out another X-ray bright point (XBP) campaign with Karen Harvey during week 38. Autumn in general sees many typhoons in Japan. A big one hit the Tokyo area last week, and another one has just passed Kyushu, jeopardizing satellite operations at KSC. Indeed, we had to cancel the last day of the XBP campaign because we could not send commands to change the observing sequence. There were two Japanese holidays in this period - the 15th (to respect old people) and the 23rd (autumnal equinox). In the capacity of the former, I wish all the Yohkoh seniorities the best health and high productivity. SOLAR ACTIVITY The Sun was typically that of solar minimum. Only one region AR 7907 was moderately active producing a C-class and several B-class flares. This was a good time to observe XBPs. SXT INSTRUMENT STATUS The SXT instrument continued to be operational without problem. Even a Bitmap error did not occur during the past two weeks. An important thing to report is that we changed the setup of the patrol images (from Mg, DPE=14 to Al/Mg, DPE=17) to prepare for the Sun having no bright features. The automatic region selection (ARS), one of SXT's key features, searches over a patrol image (in quarter resolution) for the brightest area, on which partial frame images will be positioned. Sometimes a hot spot on the CCD outside the Sun has been selected when the brightness of any brightest region averaged over a 2.6' x 2.6' box was less than that of the false region. After the adjustment, even a not-so-bright active region has been selected. CALIBRATION STATUS Several terminator images were taken. To study the status of the CCD and straylight in detail, we took some long exposure full-resolution images. In the Al.1 images we noticed a significant bleed, which is probably due to the strong saturation through the SE pinhole. A complete set of these full-resolution images took more than 20 min and special operations were needed to ensure that they should not be overwritten. Because of timing of a DP control command with respect to a long exposure, DP set an error flag, but SXT remained unaffected. PASS CONFLICTS Due to conflicts with ASCA, we lost a total of 6 passes in Week 37, and 9 passes in Week 38. CAMPAIGNS During 15-23 September, we used most visible orbits to run special sequences for the XBP campaign. Three areas were selected from the northern hemisphere, and each of them was tracked for a couple of days. The last area was selected so that we could observe both XBPs and a small filament to study their relationship. They are often identified with magnetic flux cancellation. In order to comply with Karen Harvey's request to take deeper (30 s) exposure images, we decided to make the field of view a mosaic of 4 (EW) x 1 (NS), i.e. 10.4' x 2.6'. This was to better utilize an exposure than if the field of view had been 3 x 1 as in the previous XBP campaigns. We met a request by Karen Harvey and Keith Strong, and took full-disk images with successively longer exposures to see if the number of perceptible XBPs changes. Based on a quick look at these images, there was not much difference between the images of 30 s and 85 s exposures (Al/Mg) as to the number of XBPs. SCIENCE Quite a few local students were working here. This was probably to prepare talks and posters at a meeting of the Japan Astronomical Society (early October). Following the first successful detection of faint jets in the north pole region, we made a second attempt using the same observing sequence. However, we did not have much luck, because emission from the other side of the Sun was rather bright. Ron Moore is trying to find good examples of eruptive events that appear to be consistent with his models. Hudson resumed work on the 13-Nov-94 eruptive event to show that it contradicts the usual reconnection scenario. Nitta analyzed more limb flares to show eruptions, if ever, do not generally precede the impulsive phase. SEMINARS On 11 and 12 September, an extend Yohkoh operations meeting (but in reality a science meeting) was held, which featured Prof. Hirayama giving four lectures. About 50 people gathered. Hirayama, SXT-J PI, is leaving for Munich on 1 October. On 13 September, V. Martinez Pillet (HAO) was invited to a Yohkoh seminar to speak on "Photospheric Magnetic Flux Losses as Observed with the Advanced Stokes Polarimeter." On 20 September, two Yohkoh insiders, Hugh Hudson and Tetsuya Watanabe, were the speakers. The titles were "Is the `Superhot' property of a flare really something new and different?" (Hudson) and "The maximum temperatures of solar flare plasmas" (Watanabe). PERSONNEL Slater completed his work at ISAS and is now enjoying a personal trip with a Japan railroad pass. Reardon went home, carrying substantial souvenirs to Hawai`i. All the SXT Chief Observers (Hudson, Weber and Nitta) either have left or are leaving shortly before the next crew (Lemen, Savy and Shing) arrive. Week 37 Tohban: SSOC: A. Takeda and Dhani Herdiwijaya KSC: S. Nagata and R. Kano SXT Chief Observer: N. Nitta SXT Systems and Data Engineer: G. Slater Week 38 Tohban: SSOC: T. Yokoyama and J. Khan (with K. Hori) KSC: R. Kano and S. Hashizume SXT Chief Observer: N. Nitta SXT Systems and Data Engineer: G. Slater