SXT Status Report
                     May 25 through June 6, 1999
                            (Weeks 22-23)
 
                       H. Hudson, D. McKenzie


SUMMARY

Solar activity remained at a high background level, but with ony four
M-class flares.  SXT conducted many joint observations with SOHO, TRACE,
and ground-based observatories (notably Tenerife). There were no technical
problems with SXT.

SOLAR ACTIVITY

There were many active regions, including several rather fine sigmoid
structures. The science nugget for Week 23 deals with the sigmoid
consequences, which nicely erupted (according to expectations) but waited
for a long time before doing so (no handle on that yet). Most of the
M-class flares occurred during orbit day, but there was good coverage for
the one on May 29. It was interesting and was observed well (as a clear
loop) at Nobeyama. Rumor has it that the June 2 event provided
confirmation (via data from another satellite) of the accretion flow
found by McKenzie in the Jan. 20 event - one of SXT's big discoveries
(according to HSH).

AR 8558 - not at all sigmoidal - developed a sunspot area of 600
millionths but few flares.

OBSERVING CAMPAIGNS

This has been another busy season for observing campaigns, owing partly
to the activity at the Swedish Vacuum Solar Telescope (La Palma). This
has included a long series of observations (SOHO JOP 103) aiming at
"moss", for which it appears that the SXT data (high temperature, high
pressure) may play a key role in the interpretation of the newly
discovered transition-region structure. The correspondents here have been
Tom Berger and Bart Depontieu from LMSAL. In Week 23 we will carry out a
collaboration with UVCS and others (correspondents Jing Li from Hawaii,
John Raymond from CfA), for which we are doing an offpoint. This is the
first systematic offpoint observation we have attempted in a long time,
and in the meanwhile we have learned a great deal about the key factor of
stray-light corrections. So we have hopes to be able to make effective
comparisons between SXT temperatures and parameters measured by UVCS and
the others.

SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES

One cycle of offpoint terminators is complete (3 filters), and the
normal-pointing terminators (10 filters) is  almost complete for the
epoch commencing April 18, 1999 (spacecraft points to E9.89 S2.77 in arc
min roughly, relative to the normal pointing position). Unfortunately we
still lack Be for the normal pointing but are striving mightily.

The "streak artifact" noted in the last status report has disappeared,
and we have not carried out the threatened redefinition of the "normal
point" coordinates. We should return to this after the offpoint campaign
and after the April 18 epoch is completely covered.

SXT OBSERVING SEQUENCE TABLES

     --------------------------------------------------------
    JST Day/UT Day  Pass     Table ID
     ========================================================
    Mon  24-May-99     2      990524 P2 ARS1 STD
    Tue  25-May-99     2      990525 P2 ARS1 DARKCAL
    Wed  26-May-99     2      990526 P2 ARS2 ST+J103
    Thu  27-May-99     2      990527 P2 ARS2 DF+J103
    Fri  28-May-99     2      990528 P2 ARS2 ST+J103
    Sat  29-May-99     2      990529 P2 ARS1 STD
    Mon  31-MAY-99     2      990530 P2 ARS2 STJ103*
    Mon  31-MAY-99     5      990530 P5 ARS2 STJ103*
    Tue   1-JUN-99     3      990531 P3 ARS2 DIJ103*
    Wed   2-JUN-99     3      990601 P3 ARS2 DAJ103*
    Thu   3-JUN-99     4      990602 P4 ARS2 STJ103*
    Fri   4-JUN-99     4      990604 P4 ARS2 STJ103*
    Sat   5-JUN-99     3      990604 P3 ARS1 STD*
     =======================================================


SCIENCE

Weekly science nuggets were:
  
             4-Jun-99: "Two 'loaded guns.' Two clean misses"
            28-May-99: "An anemone. A flasher"
            21-May-99: "Plasma ejection and flow"

The full list of nuggets is kept on
  http://www.solar.isas.ac.jp/sxt_co/index.html , 
and the current week's nugget also normally resides on
  http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html .

For those of you who are curious, the "loaded gun" is a reference to a
comment by A. C. Sterling in the NASA press conference on sigmoids - an
active region described this way (typically American, eh?) may well
unload its stress into an eruption and a CME.

SEMINARS

May 23:  "Soft X-ray Counterparts of Magnetic Flux Ropes"
          S. Watari (CRL)

Clearly an important subject, since SXT sees so many nice signatures of
large-scale coronal organization, and yet there are such strong links to
the physics of compact structures. It's also a very practical subject (cf
the June 4 science nugget, whose too-cute title refers of course to
coronal mass ejections.

YOHKOH OPERATIONS ISSUES

No particular issues during this period.

VISITORS AND PERSONNEL

Greg Slater arrived to a tumultuous welcome, just missing a very nice
birthday party. Dave McKenzie left, on his way directly to Chicago to see
how many SPD meeting participants would stay until the very end of the
conference just to appreciate magnetic reconection.

TOHBANS (spacecraft operators)

Tohbans for week 22 

  SSOC: K.Yaji, S.Watari
  KSC:  R.Haga, R.Kano
  SXT_CO: D. McKenzie 
  SXT_SW: -

Tohbans for week 23

  SSOC:  M.Sawa, S.Nagata
  KSC:  R.Kano, Y.Nakagawa
  SXT_CO: H. Hudson
  SXT_SW: G. Slater