PPdisk simdata (CASA 3.1)

From CASA Guides
Jump to navigationJump to search

↵ Simulating Observations in CASA

Protoplanetary disk


  • Explanation of the script:


Set simdata2 as current task and reset all parameters 

 default("simdata2")

Specify sky model image 

 modelimage         =  "input50pc_672GHz.fits"

Image coordinate system can be verified 

 imhead("input50pc_672GHz.fits")

Image center can be identified 

 # ia.open("input50pc_672GHz.fits")
 # ia.shape()
 # [257L, 257L, 1L, 1L]
 # ia.toworld([128.5,128.5])
 # {'numeric': array([  4.71239120e+00,  -4.01423802e-01,   1.00000000e+00,  6.72000001e+11])}
 # qa.formxxx("4.71239120rad",format='hms',prec=5)
 # '18:00:00.03052'
 # qa.formxxx("-0.401423802rad",format='dms',prec=5)
 # '-022.59.59.602743'
 # ia.done()

Brightness scale can be viewed with 'imstat' task 

 # imstat("input50pc_672GHz.fits")
 # ...
 #  'max': array([  6.52469971e-05]),
 # ...
 # that's 0.0652 mJy/pixel.

Let's leave the brightness of the image as it is. 

 inbright           =  "unchanged"

Let's call our project psim2 

 project            =  "psim2"

We'll leave the sky model the way it is -- simdata2 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
 modifymodel        =  False  
 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 simdata2 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 out20 configuration: 

 predict            =  True
 totaltime          =  "1200s"

Use appropriate antenna configurations based on desired angular resolution 

 repodir=os.getenv("CASAPATH").split(' ')[0]
 antennalist        =  repodir+"/data/alma/simmos/alma.out20.cfg"

Deconvolve the visibilities back into an image 

 image              =  True
 vis                =  "$project.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: 

 showarray          =  True
 showuv             =  False

Plot both to the screen and the png files, and giving us lots of messages: 

 graphics           =  "both"
 verbose            =  True
 overwrite = True
  • To run the script, type
 CASA<> execfile("Ppdisk.simdata2.txt")

 CASA<> go simdata2


  • Output results:


Input:
 Predict:
Image:
 Analyze:
Retrieved from "https://casaguides.nrao.edu/index.php?title=PPdisk_simdata_(CASA_3.1)&oldid=3962"