Note: for this tutorial you will require basic UNIX so if needed
try one of these tutorials.
You also need some familiarity with data reduction software,
such as MIDAS ,
GIPSY
and IDL,
many of which have python versions. In this tutorial I only deal with IRAF, deveolped by NOAO,
which is the most popular and most complete optical data reduction package.
A self-exploding beginners Guide to IRAF can be found
HERE
As well as the Sample IRAF sessions shown here, you should
take the time to look at the NOAO tutorials. I am adapting these
for the current version of IRAF and as they are completed I will
place links to them on this page.
NOAO IRAF Tutorial 1 : basics (recommended!)
IN XTERM
mkdir iraf # make "iraf" directory or any name you like
cd iraf
mkiraf # select terminal type "xgterm": xgterm supports a graphics window
xgterm & # this will start the xgterm window
ds9 & # this should start up the image display program "SAOIMAGE ds9"
IN XGTERM
cl # starts iraf, you will now see cl> prompt
# all iraf commands from now on assume that you have the cl> prompt
# or something similar; if you subsequently load a pagage
# of utilities (try typing for example "noao") the prompt
# will change (in this case to "no>")
# note: if you need to erase something on the cl> line
# you need to use the "delete" key
# There is a keystroke history you can use, type "e" and then
# you can scroll the command line up and down: in THIS mode
# L/R arrows also work, "backspace" also moves the cursor,
# and you can add characters to the string.
cl> displ dev$pix
# this sends the image called "dev$pix" to ds9 - however, iraf needs to
# know which of the four possible buffers you wish to use
# and has prompted "(1)" so hit return to accept this
# ds9 should then show M51.
# move the mouse over the image and see the X,Y coordinates changing
# go across to the star at approx 404,274 and click on it with the MIDDLE
# button. This should change the centre of the display such that the star
# is at the centre.
cl> imexam # this causes the cursor to blink - move it over to the
# star at 404,274 and type "r" at the prompt, this should
# produce a plot of the radial dependence of the light.
# Note that in this case the star has a flat-top - it is "saturated".
# The "a" key, while imexam is still active, will generate
# measurement data on the star under the cursor, e.g. its exact
# position expressed in pixels, in this case 404.53 274.25
# Also the flux enclosed by the edge of the star will be calculated
cd # To quit imexam type "q" while the cursor is still on the image.
# Now let us do something arbitrary just to show what can be done.
# create an image "temp1" which is M51 rotated by 180 degrees:
cl> rotate dev$pix temp1 180.0
# now subtract this image from the orginal, the difference image will be "test2"
cl> imarith dev$pix - temp1 temp2
# note that some star images now appear "black" as they have been inverted.
Datareduction and interpretation exercise
We make use of the "Astronomical Images" CDROM by Walter Jaffe:
CCD properties and data reduction
Gallery of available images # Select one of the science exercises on the Jaffee CD. IN XTERM mkdir OT # can be anywhere where there is a lot of disk space, # in this example it is a subdirectory of "iraf" # cd OT # this is your working directory # copy your desired images to OT, e.g. cp (PATH)/cdrom/data/images/m1/v.1 m1v1.fits cl> imhead cl> displ m1v1 cl> reset stdimage=imt2048 # image display was too small # experiment with image display if it is new to you # some useful quick operations cl> imexam key = "a" fit a star PSF - try also "r" "v" = vector plot "x" = x,y,value "q" = quit cl> imhead m1v1 lo+ | page # get information on the observation # eg date, exp time, ra and dec # here, 24/10/95 and about 05:31 +21:58 (PATH)/cdrom/doc/stdstar.cat # find the best standard star # and copy it to (eg) l95149v1.fits # obtain the flux and exposure time (eg 1.4E6 in 6 sec) # look up the appropriate magnitude V=11.6 # what's the filter bandwidth (here 890AA) # calculate the system efficiency - does the value make sense? # find a feature in the main object, for example a particularly bright or interesting blob, and work out its coordinates so you can bring it to the attention of your colleagues
For errors or other discussion related to these pages: ndouglas@astro.rug.nl.
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