EIS Bright Point trigger#
This page contains some notes and comments about the EIS BP trigger.
The intention for the bright point trigger is for it to be used for quiet Sun data-sets, and to use 2" slit rasters to do the hunting, with either a 1" or 2" raster to be the response study.
The quiet Sun was monitored for 3 days continuously during 22-26 January 2008 (HOP 59) using a 180" x 360" raster made with the 2" slit with 30s exposures. This data has thus been studied to investigate how to make the hunter study.
Two options for triggers are:
- a density sensitive line such as Fe XIII 203.82 or Fe XII 186.88
- a high temperature line such as Fe XV 284.16 or Fe XVI 262.98
Since bright points are more dense than surrounding quiet Sun, then density sensitive lines show BPs in a greater contrast relative to the background.
The quiet Sun shows only very weak Fe XV emission and no Fe XVI, however many bright points will show these lines.
Trigger region size and level#
The bright point flag requires that a region of size nx * ny pixels within an exposure (so x here refers to wavelength) must be such that each pixel has a pixel DN value above some value L.
Studying the data from the HOP 59 run it seems bright points can be detected quite well if nx=1 and ny=7. Values of ny less than 7 may lead to SAA events triggering the EIS response. Setting nx larger than 1 does not seem to be necessary.
For Fe XIII 203.83 a bright point could be identified by setting L=800 DN.
One issue for the observer to consider is whether the data obtained using the hunter study will be scientifically useful. If it is not, then the hunter study could just contain the hunter line, and could skip one position in X (i.e., use the 2" slit and jump 4").