Introduction to CASA Shigehisa Takakuwa (ASIAA). Table of Contents 1.ALMA Observation & Calibration...

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Introduction to CASA Shigehisa Takakuwa (ASIAA)

Transcript of Introduction to CASA Shigehisa Takakuwa (ASIAA). Table of Contents 1.ALMA Observation & Calibration...

Introduction to CASA

Shigehisa Takakuwa(ASIAA)

Table of Contents

1.ALMA Observation & Calibration

2.CASA

3.How to use CASA

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1. ALMA Observation & Calibration

• 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)

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Calibration of Visibilities

• Ideally: Vobs = Vsource

• Vobs: Observed Visibility

• Vsource: True Source Visibility

• In reality: Vobs ≠ Vsource ---> Vobs = G Vsource

(Due to sky, instruments, etc..)

Estimation of the G term is calibration !!

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Two kinds of Vis. Calibration

Frequency-Dependent: Bandpass Calibration

observe ``flat’’ ν-response source (planets)

Time-Dependent: Gain Calibration

->observe known visibility source (quasars)

Vobs (ν 、 t) = G (ν) G (t) Vsource (ν 、 t)ν: Frequency t: Time

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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…

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2. CASA

Platform:Fedora Core 6, Fedora 7

RH Linux 4, 5

Mac OSX Intel

RH Linux 4, ACS 6.0.4

Version 3.0.0 Release Dec. 15, 2009

ALMA Data Reduction SoftwareCommon Astronomy Software Applications

Being developed by U.S.A. (NRAO) for the interferometric part

Japan (NAOJ) for the single-dish part

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Structure of CASA

Task A

Toolkits

in C++

Calibration Scripts

Imaging Scripts

Task B

Task T

Python scriptsusing Toolkits

Python Scriptsusing Tasks

Users can make their own Scripts,even Tasks.

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ALMA Data Reduction with CASA

Data Inspection& Flagging

Passband & Gain Calibration

Imaging,Clean

Tasks

plotxy

flagdataViewer

ImmomentsImfit…

listobs

setjy

bandpassgaincalplotcal

fluxscale

applycal

clean

featherwidefield

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Reduction Philosophy

Visibility data is imported into MS

(Measurement Set)

keep original DATA inviolate

calibration is carried in cal-tables

imaging creates images from MS

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3. How to use CASAAfter installing CASA, on the terminal you type

> casapy

And then you can get…

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Overview of CASALog Message

Main Window (on terminal)

Image Viewer(type vieweron the main window)

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You type commands on the Main Window

Bad parameter value

Parameter list

Task name & Tips

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To start a task, you first type> default(‘taskname’)Or> tget taskname (get the latest task parameters)

See the task parameters> inp

Change the parameters> Integration = `10s’ (for example)

Run the task> go

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To see the list of tasks> tasklist

To see the manual of the task> help taskname

You can write python scripts to do all the job,Then you do not type commands, but just type> execfile(‘scriptname.py’)(Please check the scripts we provide)

To save the parameter list of the task> saveinputs(‘parm.text’)

Exec it> execfile(‘parm.text’)

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Example plotxy Inputs

plot amplitude vs. uv-distance

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Example plotxy plot

Quasar 1331+305 from previous inputs

can hit Next to get next antenna (iteration)

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Plotting Cal-tables

(task plotcal)

Example of Calibration: Passband Calibration (See Demo by Dr. Hiramatsu)

Data of Passband Calibrator(task plotxy)

MakeTable

(task bandpass)

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Imaging (See Demo by Dr. Kawasaki)

Interactive CLEANuses the viewer

can change cycles during cleaning

draw boxes and polygon regions for masking

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Task immoments make Moment ImagesThen use viewer

Overlay contours of moment 1

(velocity) on moment 0

(intensity)

NGC5921 moment images

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ALMA imaging simulation:task simdata (My Demo)

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MODEL Simulated Obs.MODEL - Obs.

Fidelity uv-track Beam

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Single-Dish (= ACA) Data Analyses

(See Demo By Dr. Kawasaki)ATNF Spectral Analysis Package (ASAP) is usedmade for single pointing single dish data analysis

All the ASAP functionality is available via CASA

Adapted to handle GBT data

Under development ---> NAOJ Group !

- ASAP main page: http://www.atnf.csiro.au/computing/software/asap/- CASA Cookbook(Chapter8)

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CASA Webhttp://casa.nrao.edu -- CASA Home Page

Main resource for end users

http://my.nrao.edu -- NRAO Services (incl. registration/download of CASA)