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

demodemodemodemo

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

Hands-on Exercise: simdata simulation, chHands-on Exercise: simdata simulation, changing input model parametersanging input model parameters

modifymodel=Trueincenter=‘230GHz’inwidth=‘2GHz’incell=‘0.0155arcsec’go