Download presentation
Presentation is loading. Please wait.
Published byElizabeth Stephens Modified over 9 years ago
1
SIMDATA Simulation Shigehisa Takakuwa (ASIAA) ALMA Users Meeting 2011
2
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
3
Theoretical model Images @ ALMA observing band ``Observed’’ Images Theoretical Physical Parameters of your favorite astronomical objects ``Observed’’ Physical Parameters 2 SED fitting ALMA Imaging Simulation Radiative Transfer Code Compare !! Science Power of ALMA ALMA observing Simulation
4
ALMA Observation Data we obtain are ``Visibilities V (u,v)’’, V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdy x, y: Sky Spatial Coordinate u, v: Antenna Tracks projected on the sky V (u,v) consists of amplitude and phase Fourier-Transform of Source Images I (x,y)
5
ALMA Imaging --> To obtain I (x,y) Ideally: V (u,v) = ∬ I (x,y) exp {-2πi (ux+vy)} dxdy In reality: V obs (u,v) = S (u,v) ∬ I (x,y) exp {-2πi (ux+vy)} dxdy S(u,v): Sampling Function Fourier-Transform of V obs (u,v) is NOT Real I(x, y), but we call it Dirty-Image I D (x,y) Methods to guess real I(x,y) from I D (x,y) ---> Clean, MEM, etc…
6
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
7
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)
8
ALMA Observing Simulator Task ``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 image with the user-specified imaging parameters, such as weighting on the visibility sampling points.
9
Products from simdata Synthetic 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 sky ALMA. (E)VLA, SMA simulations possible
10
Simdata Example: Forming Planets in Protoplanetary Disk
11
Proto-Planetary Disk Simulation Effects of the Different antenna configurations
12
demodemo
13
Hands-on Exercise: Read input fits image into CASA PC with CASA installed + Input Image File (in FITS ) casapy default(‘importfits’) fitsimage=‘input50pc_672GHz.fits’ imagename=‘input50pc_672GHz’ go viewer();
14
casapy default(‘importfits’) fitsimage=‘input50pc_672GHz.fits’ imagename=‘input50pc_672GHz’ go viewer(); 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.cf g’ (Try different antenna configurations !) imsize=[192,192] threshold=‘1e-7Jy’ niter=10000 totaltime=‘1200s’ graphics=‘both’ image=True analyze=True go
15
Hands-on Exercise: simdata simulation, changing input model parameters modifymodel=True incenter=‘230GHz’ inwidth=‘2GHz’ incell=‘0.0155arcsec’ go
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.