Weekly Notes from the Yohkoh Soft X-Ray Telescope

(Week 7, 1998)

14-Feb-98 17:00 UT

Instrument Status

The SXT instrument continued to operate without problems. See the weekly operations report for details. The GOES time series for the week:

In the display above (click to enlarge), the colored lines show the times of SXT images that currently are on-line at ISAS. The purple lines are flare mode. Alas, the scale is too compressed here to be able to see individual data! Most of the gaps will be filled in when the NASA telemetry arrives. For a summary index listing of the weekly science reports, click here.

Science nugget: Observation of expanding active-region loops

The internet provides an interconnectivity between the world's solar observatories that allows us to tell each other what we're doing from day to day. In many cases this allows us to collaborate, as is the case with this week's Science Nugget. The SOHO Operations plan on the web showed that CDS was planning to make observations of the active region AR 8151; we were able to adjust the SXT commands to follow the CDS plan, so that SXT also observed AR 8151 on 12-Feb and 13-Feb.

CDS investigator P. Maltby expressed that they were interested in detecting "the CDS counterpart to expansion flow detected by Uchida et al. (1992, Publ. Astron. Soc. Japan, vol. 44, L155)." In that paper, Uchida et al. described the expansion of coronal loops in the outer portions of active regions.

As SXT and CDS were watching AR 8151, SXT observed expansion in the northwest portion of the target region, a movie of which can be seen at URL:

http://www.solar.isas.ac.jp/~freeland/movies/dmck_ar8151_expand.html
Very preliminary calculations suggest the leading edge of the X-ray brightening travels to the northwest at a speed of only 10-30 km/sec. With luck, Doppler measurements from CDS will tell us whether we're actually seeing plasma motion, or the appearance of plasma motion (i.e., a succession of loops brightening in turn).

Special notes: Preparation for the Eclipse of Feb. 26

A well-situated solar eclipse is coming up on Feb. 26, and we are engaged in planning observations from Yohkoh. The rapid motion of Yohkoh makes it whiz in and out of eclipse several times, as shown in the plots below. Please refer to the planning page for further details, and we will present a view of the real thing in our notes for Week 9.

David McKenzie and Hugh Hudson, 14-Feb-97 UT (email mckenzie@isass0.solar.isas.ac.jp, hudson@isass0.solar.isas.ac.jp)