Protoplanetary Disk Simulation (CASA 3.4)

From CASA Guides
Jump to navigationJump to search
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.

Simulating Observations in CASA

Data

For this CASA Guide we will use a protoplanetary disk model from S. Wolf. If you use this FITS data for anything more than learning CASA, please cite Wolf & D'Angelo 2005.

  • simobserve and simanalyze version for CASA 3.4


Explanation of the script

Set sim_observe as current task and reset all parameters
# Setting everything in simobserve to original defaults
default("simobserve")
Image coordinate system can be verified
# This reports image header parameters in the Log Messages window
imhead("input50pc_672GHz.fits")
Image center can be identified
# These are tools found in the CASA toolkit
# They are very useful, but the interface is not as straightforward as the tasks
# You can find the tool reference manual here: http://casa.nrao.edu/docs/CasaRef/CasaRef.html
# The following command is used to open an image (this is part of the image analysis toolkit)
# Whenever data are being viewed/manipulated by tools, what is being operated on needs to be explicitly opened
# and closed (i.e. an image, a table, etc.)
ia.open("input50pc_672GHz.fits")
#  Out[9]: True
#
# Reports the length of each axis in the opened image
ia.shape()
#  Out[11]: [257L, 257L, 1L, 1L]
#
# This command converts from pixel (our source file) to world coordinates (something usable by simdata)
ia.toworld([128.5,128.5])
#  Out[12]:
#{'numeric': array([  4.71239120e+00,  -4.01423802e-01,   1.00000000e+00,
#         6.72000001e+11])}
#
# Formats the coordinate just converted into hms
qa.formxxx("4.71239120rad",format='hms',prec=5)
#  Out[13]: '18:00:00.03052'
#
# Formats one of the other coordinates into dms
qa.formxxx("-0.401423802rad",format='dms',prec=5)
#  Out[14]: '-022.59.59.602743'
#
# Final housekeeping by closing the image tool
# The image tool will now be detached from the image
ia.close()
Brightness scale can be viewed with 'imstat' task
# Default parameters are adequate for this
imstat("input50pc_672GHz.fits")
# ...
#  'max': array([  6.52469971e-05]),
# ...
# that's 0.0652 mJy/pixel.
Let's call our project psim2
default("simobserve")
# This defines the root prefix for any output files from simobserve
project            =  "psim2"
We'll leave the sky model the way it is: simobserve will create psim2.skymodel CASA image since this model is a fits file, and most but not all of CASA routines can operate directly on fits
skymodel           =  "input50pc_672GHz.fits"
We need to decide where to point the telescope. The image is 2/3 arcsec in size, so we only need one pointing. We could put that in a text file ourself, or let simobserve create the ascii pointing file for us.
setpointings       =  True
direction          =  "J2000 18h00m00.031s -22d59m59.6s"
mapsize            =  "0.76arcsec"
The default pointingspacing is fine: we'll only fit one pointing in the small mapsize the default calculation maptype hexagonal is ok too since only one will fit anyway.
We do want to calculate visibilities in a measurement set: let's do a 20 min snapshot observation using the "out20" ALMA antenna configuration:
obsmode            =  "int"
totaltime          =  "1200s"
Use appropriate antenna configurations based on desired angular resolution (configuration 20 - alma.out20.cfg in this case - is the largest "compact" configuration)
antennalist        =  "alma.out20.cfg"
simobserve()
Deconvolve the visibilities back into an image
default ("simanalyze")
project            =  "psim2"
image              =  True
# Prior image to use in clean
modelimage         =  "input50pc_672GHz.fits"
vis                =  project+".alma.out20.ms"
imsize             =  [192, 192]
Specify number of iteration of cleaning task with proper threshold and weighting
niter              =  10000
threshold          =  "1e-7Jy"
weighting          =  "natural"
We'd like to calculate a difference and fidelity image, and see some diagnostics:
analyze            =  True
And see the array but not the UV coverage:
showuv             =  False
showresidual       =  True  
showconvolved      =  True
Plot both to the screen and the png files with lots of messages:
graphics           =  "both"
verbose            =  True
overwrite = True

Run simdata

# This commands CASA to execute simanalyze
simanalyze()


  • Output results:


Input:
Psim2.skymodel.png
Predict:
Psim2.alma.out20.observe.png
Image:
Psim2.alma.out20.image.png
Analyze:
Psim2.analysis.png

Simulating Observations in CASA

Last checked on CASA Version 3.4.0.