JPW02:

H-alpha Flare Observations with the Polarimeter                

GOAL:

Observe H-alpha linear polarization during flares.

KEY FEATURES OF THE SETUP:

- Small rasters of a part of an active region with high flare probability.
  Preferably an active region which is *not* too close to disk center.

- Repeated scans at a rate of 1 scan every 30 seconds.



                     SMALL SCANS                      CO-REGISTRATION SCANS

- Pinhole            200 microns                        same
- Slit width         20 microns                          "
- Approximate Fiber Optic Positions
  #1                 0.2875                              "
  #2                 0.2772                              "
  #3                 0.2595                              "
  #4                 0.2431                              "
- LDG                4                                   "
- P+S                1                                   "
- PGA                1                                   "
- Revs/Point         1                                   "
- Wavelength         6563.8 A                            "
- Prefilter          -100                                "
- ms per rev         2000                              500
- Scan step size     -8.49 arcsec                      -5.66 arcsec
- Scan size          4x4, 3x5, 2x8 etc                 25x25, 30x30 etc
- Program            STOKES                            SPECTRUM
- Spectrum Adjustments (Readings of two micrometers on top of spectrograph)
  O5P                 991 
  O5S                 115 

OBSERVING PROCEDURES:

- Do a calibration once per day with the same balance as used for the data.
- Since the scan repetition rate should be around 30 s, only very small scans
  can be made.  The total number of pixels should be around 15.  Possible
  scan formats include 4x4, 2x8, 3x5, depending on the shape of the active
  region.  If the active region is much too big, then a long and skinny scan
  should be made across the magnetic neutral line.  
- Use the H-alpha monitor image to select a frame with high flare probability.  
- Run scans continuously.  (Ask Elaine.  She made a modified version of the 
  polarimeter program for this purpose called "jpw".)  
- The capacity of the polarimeter disk is limited, so you might have to delete 
  observations every few hours if no flare occurred.  
- Run the MCCD on the same region simultaneously whenever possible.

CO-REGISTRATION SCANS:

The small scans are difficult to register with other data.  Therefore, a larger
scan of the active region (including several sunspots!) should be made 
once for each new scan center position and after a flare has occurred.
Use a smaller step size and a larger format.  A 25x25 scan with 
a step size of 5.66 arc sec should work, however, a larger scan may be required 
to observe several sunspots in some cases.  *Important*: The co-registration
scan must use the same scan center as the small data scans!


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