JOP169 Observations of Evolving Active Region Loops


Received 23 June 2003


SHORT TITLE:

 Evolving Active Region Loops


CONTACTS:

 Harry Warren   [hwarren@nrl.navy.mil]
 Amy Winebarger [winebarger@nrl.navy.mil]


INSTRUMENTS:

 TRACE, CDS, SUMER


SCIENCE OBJECTIVES:

 We propose a JOP to study the structure and dynamics of active region
 loops in the solar corona. Recent work with TRACE has shown that many
 loops near 1 MK are overdense relative to the predictions of static
 loops models with uniform heating. These loops are also observed to
 have flat 195 to 171 filter ratios, suggestive of isothermal plasma
 along the loop. The interpretation of the TRACE filter ratios is not
 unique, however, and spectrally resolved observations are required to
 study the temperature structure of these loops. Also, recent analysis
 has indicated that while these loops do persist for longer than a
 characteristic cooling time, there is a progression in the emission
 from the hotter filters to the cooler filters. There is a clear need
 to understand the temperature and density structure of active region
 loops and how the physical properties of the loop evolves with time.


OBSERVATIONS:

 TRACE : Observations should cycle through 195, 171, and 284. Images
         in 1600 should be taken in context. The 195, 171, and 1600
         data should be full-resolution, 1024x1024 images. The 284
         should be full CCD reads summed 2x2 to improve
         cadence. Exposure times should emphasize obtaining good
         counting statistics in individual images over high cadence.

 CDS   : Each run should include the following

         [1] a run of the NIS spectral atlas (NISAT) in the middle of
             the active region

         [2] a large (244x240) context raster in He I 584, O V 629, Mg
             IX 368, Mg X 625, Si XII 521, and Fe XVI 361. 
         [3] a series of rasters in the following lines: O V 629, Mg
             IX 368, Mg X 625, Si XII 521, and Fe XVI 361 for DEM
             analysis, and Si X 356/347, and Fe XIV 359/334 for
             density analysis. The exposures should be deep enough to
             get good counting statistics in the weaker lines, but not
             so deep that the detector is saturated (~60s). Also, the
             rasters should be sparse, with only 10 exposures covering
             180 arcsec. This should provide a cadence of about 10
             minutes, sufficient to follow the evolution of the loops.

 SUMER : Observations should include the density sensitive line pairs
         Si VIII 1445/1440 and S X 1213/1196 as well as the 1098-1138
         wavelength range which includes Ca X 557, Ca XIII 1133, and
         Fe XIX 1118. Each of these three spectral bands should be
         integrated for 200s so that the cadence for this set is about
         600s. The 300x1 or 300x4 slit should be used.


SCHEDULING:

 We would like the first run for this JOP to take place from August
 25-31. Approximately 8 hours of observing per day is desirable. A
 brief test run several weeks before the JOP would be be very useful.


POINTING:

 The target will be an active region above the limb.