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We have written an mc script that will take the requested number of
exposures at 4 different positions. If you have centered the
object on the chip the pattern will put the object in each of the 4
quadrants of the chip.

The script is called "square" and there are three arguments separated
by spaces. They are the offset in arcseconds for the x and y inst plane
offset, the exposure time in seconds, and the number of exposures at each
position.

You will have to run it from the mc* ( or from remark using the tester
buttons ). First you need to make the mc aware of the script. You do this
by loading the source file. The "square" script is in a file on tycho
called /export/home/long/dither.tcl, and to load it into the mc you need to
type

source /export/home/long/dither.tcl

* To get an mc window, start a telnet session to tycho, login as visitor1,
and type "mcnode". This will give you a connection to the mc. Once you
have an mcnode connection you will also need to issue the mc command "pri
1" in order to have the priority to issue comands.


EXAMPLE:
You are using grim in f/5 mode and say the K filter. The field of
view in f/5 is 120 arcseconds, so if the object is centered on the chip, an
offset of 30 arcseconds in x and y will place the object in the center of a
quadrant. A 10 sec exposure is a reasonable time for f/5 K. The command
to to the dither for 1 exposure at each position would then be

square 30 10 1

When you are done you should have four images with the object at (30,30),
(30,-30), (-30,30), and (-30,-30) arcsec offsets from the starting
position. The telescope will be returned to where it was before the script
started ( assuming you had no inst plane offsets when you started ).

A point about offsets should be made here. The dither program uses
absolute instrument plane offsets, so you should use object plane offsets
to center up on the chip so that the script starts from where you centered
up. INST and OBJ offsets are independent so an object offset will not be
zeroed out by and inst plane offset, just added to it.


There is another script similar to square, for doing a sky dither
pattern. It is simply called "sky" and is in the file
/export/home/long/dither_sky.tcl
As above you will need to load it into the mc with the source command.
It will offset to a sky position supplied by the user and take
exposures at4 different positions offset from each other by 5 arcseconds.

The command has 4 arguments. They are the x offset in arcseconds, the y
offset in arcseconds, integration time, and number of integrations at each
dither postion. ( Note: For a rotation of 0 deg obj, x=RA and y=Dec ).

EXAMPLE:
Say you wanted a sky offset 300 arcsec in y ( North for 0 deg obj
rotation ), and take 1 10 sec exposure at each of the 4 positions. The
command would then be

sky 0 300 10 1

When you are done you should have four images centered at (0,300), (5,305),
(5,295), (-5,295). The telescope will be returned to where it was before
the script started ( assuming you had no inst plane offsets when you
started ).


We hope this will be useful to you. If you have any questions about the
scripts or suggestions for future modifications, please let the Observing Specialists
know.

-Dan Long

Last updated July 14, 2003 - JMD