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SIMDATA SimulationSIMDATA Simulation
Shigehisa Takakuwa (ASIAA)Shigehisa Takakuwa (ASIAA)
ALMA Users Meeting 2011
Preparing for the ALMA Proposal
What can you really get with ALMA observations ?
Can ALMA provide you with what you want to see ?
--> ALMA Observing Simulations
Theoretical model Images@ ALMA observing band
``Observed’’ Images
Theoretical Physical Parameters ofyour favorite astronomical objects
``Observed’’ Physical Parameters
2 SED fitting
ALMA Imaging Simulation
Radiative Transfer Code
Compare !!SciencePower of ALMA
ALMA observing Simulation
ALMA Observation
• Data we obtain are ``Visibilities V (u,v)’’,
V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdyx, y: Sky Spatial Coordinateu, v: Antenna Tracks projected on the sky
V (u,v) consists of amplitude and phase
Fourier-Transform of Source Images I (x,y)
ALMA Imaging --> To obtain I (x,y)
Ideally:V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdy
In reality: Vobs (u,v) = S (u,v) ∬ I (x,y)exp {-2πi (ux+vy)} dxdy
S(u,v): Sampling Function
Fourier-Transform of Vobs (u,v) is NOTReal I(x, y), but we call it Dirty-Image ID(x,y)Methods to guess real I(x,y) from ID (x,y)
---> Clean, MEM, etc…
How to evaluate the imaging quantitatively ?
---> Introducing ``Fidelity’’
Fidelity (i, j) = --------------------------------------------abs[ Model (i, j) ]At each image pixel (i, j);
abs[Model (i, j) - Simulated (i, j)]
So Fidelity is an image.Pety et al. 2001
Model (J CMT SCUBA) 12-m Array only 12-m Array +TP 12-m Array +ACA
DecOff(arcsec)
RA Off (arcsec)
Fidelities
ε ERIDANI Debris Disk 8 5 0 μm @ distance of 1 3 pc
Greaves et al. 2 0 0 5
Model| Model - Simulation |
Fidelity =
Example of the ALMA Imaging Simulation:Debris Disk
ACA is crucial to recover the flux from debris disks.(Takakuwa et al. 2008)
ALMA Observing SimulatorTask ``simdata’’: One of the tasks in CASA,
the ALMA data reduction software
Create model visibilities from model images,with observing parameters such as the antenna location,specified by the user.
Fourier-Transform the Visibility, and ``CLEAN’’ the imagewith the user-specified imaging parameters,such as weighting on the visibility sampling points.
Products from simdataSynthetic visibilities
A synthesized CLEANed image
Image of the Difference between the model and simulated image, and Fidelity
ALL you need is a model of the skyALMA. (E)VLA, SMA simulations possible
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Simdata Example: Forming Planets in ProtoSimdata Example: Forming Planets in Protoplanetary Diskplanetary Disk
Proto-Planetary Disk Simulation
Effects of the Different antenna Effects of the Different antenna configurationsconfigurations
Hands-on Exercise:Hands-on Exercise:Read input fits image into CASARead input fits image into CASA
PC with CASA installed
+Input Image File(in FITS)
casapydefault(‘importfits’)fitsimage=‘input50pc_672GHz.fits’imagename=‘input50pc_672GHz’goviewer();
casapydefault(‘importfits’)fitsimage=‘input50pc_672GHz.fits’imagename=‘input50pc_672GHz’goviewer();
default(‘simdata’)skymodel = ‘input50pc_672GHz’project = ‘psim2’ (rm -rf psim2* for the 2nd time)direction=‘center’mapsize=‘0.76arcsec’antennalist=‘/Applications/CASA.app/Contents/data/alma/simmos/alma.out20.cfg’(Try different antenna configurations !)imsize=[192,192]threshold=‘1e-7Jy’niter=10000totaltime=‘1200s’graphics=‘both’image=Trueanalyze=Truego