Preparing EIS observations
Usually when we observe a feature on the Sun with EIS,
we need to decide 1-3 days in advance what we want to look at.
It takes this long because the three Hinode instrument teams
need to agree on what to observe, and then time is spent creating
the observing plans and uploading them to the satellite. However,
we know that the Sun is very dynamic and what seems an interesting
thing to observe may end up fizzling out by the time we actually
get to observe it.
EIS has a special ability whereby it is capable of deciding for
itself if there's an interesting feature in its field-of-view
and then automatically change the observing plan to focus only on this feature.
We refer to this as the 'Bright Point Trigger'.
How it works
Imagine you're idly gazing out of your window at home and you suddenly
see a bright flash across the street from one of the houses there.
Your eye will immediately focus on where the flash occurred, and perhaps
you'll spend a few seconds looking at this spot to try and work out what happened.
This is a bit like how our Bright Point Trigger works.
We have an observation sequence called a 'hunter study' that scans
across a large area on the Sun. As the scan progresses, EIS checks
to see how bright the Sun is at each position. If the brightness is
above a certain level, then EIS notes the brightness and position.
After finishing the scan, EIS decides which of the positions had the
highest brightness, and switches to a 'response study' whereby it
zooms in on the bright point to do a smaller, more detailed scan.
We tested the EIS bright point trigger for the first time in June, and it worked perfectly!
Figure 1:
Results of the test bright point trigger study run in June 2010.
The results from the test of the bright point trigger are shown in
Figure 1. The image on the left shows what the
hunter study saw - a large patch of Sun with a number of little bright points
scattered about. We've drawn a cirlce around the brightest of these features.
EIS successfully found this bright point and 'zoomed in' to create the picture
on the right. We were very happy to find that EIS did its job properly, with
the bright point nicely centred in the picture.
A great benefit of using the bright point trigger is that it allows us to make
best use of our data. EIS data is sent from the satellite at a fixed rate and so
there's a limit to how much data we can obtain each day. If we didn't have the
bright point trigger, then we'd end up wasting a lot of data by trying to guess
where the bright points are. Now we can take a quick scan across a large portion
of Sun, and find exactly where the bright point is.
