SIMDATA Simulation Shigehisa Takakuwa (ASIAA) ALMA Users Meeting 2011.
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Transcript of SIMDATA Simulation Shigehisa Takakuwa (ASIAA) ALMA Users Meeting 2011.
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