SXT Status Report 19 December 1994 - 8 January 1995 --- 9 January 1995 Nariaki Nitta SUMMARY Despite usual slow-down due to the holiday season, satellite operations are going well without major problems. The Sun is quiet but is far from boring. SOLAR ACTIVITY During this three-week period, solar activity has been persistently low, with only 4 flares above the GOES C1 level. For the last couple of days, the GOES background level has been down at A1. Toward the end of last year, AR 7817 repeatedly produced jets and showed interactions with surrounding regions. This year we have been able to look at the SXT images after 3 January. They reveal two active regions AR 7823 and AR 7825, which are not very active. However, there is a filament in the NW direction from them. It showed a beautiful eruption on 5 January, which was observed both by SXT and Mees Observatory. In accordance with reports from KSC, i.e. GBO mails, we have been seeing many X-ray bright points; another XBP campaign in coordination with groundbased observatories, Kitt Peak in particular, will be kicked off in a couple of hours from now. OPERATIONS On 22 December 1994, the normal pointing of Yohkoh was changed to NE by about 3 arcmin, because it had drifted south so much that the north limb of the Sun was almost touching the top of the CCD. The new pointing was chosen so that the solar limb avoids the more damaged part of the CCD and the two pin holes of thin aluminum filter comes outside the disk. The number of limbs unmasked by the HXA fiducial marks has been 3 or 4 since the repointing. The KSC tohban Masuda-san reported on Boxing Day that temperature monitored at MRT (SXT front support plate) exceeded the threshold of 25 C; a temperature higher than 25 C appears on the KSC quick look screen in red as a warning. Other parts of the SXT also showed slightly higher temperatures than usual. This did not surprise Loren Acton, who analyzed it as an indication of degradation of front side thermal properties of Yohkoh, predicting that the temperature would soon drop a few degrees. Indeed, after the turn of the year, we confirmed that the MRT temperature of 20.8 C. Computers at KSC became ill, causing some operational inconvenience. There was something funny in the creation of temporary Sirius database, which our near real-time monitoring of the instrument health depends on. However, these problems seem to be part of the New Year syndrome and are being sorted out. By the initiative of Hawai'ians (Mees Observatory), we were trying to observe a filament which seemed to come from an old active region. Although uploading of the special table was not in time because of the problems at KSC, we caught a nice eruption of the filament in the full-disk images (5 January, 18-19 UT). CALIBRATION Loren Acton spent long time and huge energy in calibration, coming up with some nice results, which are seen in "show_pix". One of them is orbital variation of dark current, which decreases rapidly as the satellite gets into day followed by a much slower decrease during day. Loren reached this conclusion based on the recent data, but at the same showed that old data, such as those of November 1991, behave in a very similar way, suggesting that accurate dark subtraction will be possible on all the images whether they were taken before or after the entrance filter failure. Another important achievement is in the correction of straylight. He showed the amount of straylight for different filters, and set up a better criterion to take successful terminator images to be used for straylight correction. Thank you very much, Acton san; we know you are the ideal Chief Observer. SCIENCE Yohkoh science seminar was held at ISAS on 5 January 1995. Speakers and titles were N. Nitta : Study of Homologous Flares in AR 7260 H. Hudson: Eruptive Event of 13 Nov. 1994: a CME being launched? In spite of this holiday season, some interesting works have come to final stages. The following are just a few of them. M. Shimojo and his mentor K. Shibata are completing a compilation and classification of X-ray jets. They show varieties of jets and try to explain them in terms of recent simulations by T. Yokoyama and K. Shibata. M. Kundu, J.-P. Raulin, N. Nitta and H. Hudson are showing a good example of the association of a type III burst (as observed at Nancay) and an X-ray jet at the edge of an active region. J. Khan, H. Hudson, J. Lemen, L. Harra-Murnion and A. Sterling are presenting an interesting result of a sequence of limb flares in a same active region, extracting the BCS signals from the purely loop-top source. H. Hara studies the latitudinal distribution of quiet Sun X-ray brightness based on the SFM database, and shows a possible relation with active regions. N. Gopalswamy, J.-P. Raulin, M. Kundu, N. Nitta and J. Lemen is finishing a comprehensive analysis of an M class flare which was observed by VLA and Yohkoh. PERSONNEL L. Acton departed on 22 December after his unmeasurable contributions to calibrating the SXT instrument. N. Nitta arrived on 20 December followed by J. Lemen and G. Slater on 5 and 6 January, respectively. Tohbans for Week 51 SSOC: T. Sakurai and K. Shinoda KSC: M. Takahashi and S. Masuda Tohbans for Week 52 SSOC: T. Kosugi KSC: S. Masuda Tohbans for Week 1 SSOC: H. Hara and L. Harra-Murnion KSC: K. Yaji SXT Chief Observer: L. Acton (- 21 Dec) and N. Nitta (22 Dec -) SXT Systems and Data Engineer: G. Slater (7 Jan -) REQUEST We sincerely hope that IDL will soon be installed on the _new_ Sun workstations at ISAS, which have been sitting here just as X terminals for 7 months, and that at the same time upgrade of IDL will take place on other Sun workstations as well. RSI does not support MIPS machine beyond version 3.0. More and more Yohkoh software is being written and tested on a workstation that carries a more recent version of IDL (3.5 or 3.6). Although the difference between versions 3.0 and 3.5 might appear minor to those who do relatively unsophisticated analysis, it is getting bigger as one is sucked more deeply into Yohkoh software. In near future, even operations-related software will be affected as lower level routines cease to work.