# Introduction to CASA Shigehisa Takakuwa (ASIAA). Table of Contents 1.ALMA Observation & Calibration 2.CASA 3.How to use CASA.

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Introduction to CASA Shigehisa Takakuwa (ASIAA)

3 1. ALMA Observation & Calibration 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)

4 Calibration of Visibilities Ideally: V obs = V source V obs : Observed Visibility V source : True Source Visibility In reality: V obs ≠ V source ---> V obs = G V source (Due to sky, instruments, etc..) Estimation of the G term is calibration !!

5 Two kinds of Vis. Calibration Frequency-Dependent: Bandpass Calibration  observe ``flat’’ ν-response source (planets) Time-Dependent: Gain Calibration ->observe known visibility source (quasars) V obs (ν 、 t) = G (ν) G (t) V source (ν 、 t) ν: Frequencyt: Time

6 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…

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8 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 Software Common Astronomy Software Applications Being developed by U.S.A. (NRAO) for the interferometric part Japan (NAOJ) for the single-dish part

9 Structure of CASA Task A Toolkits in C++ Calibration Scripts Imaging Scripts Task B Task T Python scripts using Toolkits Python Scripts using Tasks Users can make their own Scripts, even Tasks.

10 ALMA Data Reduction with CASA Data Inspection & Flagging Passband & Gain Calibration Imaging, Clean Tasks plotxy flagdata Viewer Immoments Imfit… listobs setjy bandpass gaincal plotcal fluxscale applycal clean feather widefield

11 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

12 3. How to use CASA After installing CASA, on the terminal you type > casapy And then you can get…

13 Overview of CASA Log Message Main Window (on terminal) Image Viewer (type viewer on the main window)

14 You type commands on the Main Window Bad parameter value Parameter list Task name & Tips

15 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

16 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’)

17 Example plotxy Inputs plot amplitude vs. uv-distance

18 Example plotxy plot Quasar 1331+305 from previous inputs can hit Next to get next antenna (iteration)

19 Plotting Cal-tables (task plotcal) Example of Calibration: Passband Calibration (See Demo by Dr. Hiramatsu) Data of Passband Calibrator (task plotxy) Make Table (task bandpass)

20 Imaging (See Demo by Dr. Kawasaki) Interactive CLEAN uses the viewer can change cycles during cleaning draw boxes and polygon regions for masking

21 Task immoments make Moment Images Then use viewer Overlay contours of moment 1 (velocity) on moment 0 (intensity) NGC5921 moment images

22 ALMA imaging simulation: task simdata (My Demo) MODELSimulated Obs.MODEL - Obs. Fidelity uv-trackBeam

23 Single-Dish (= ACA) Data Analyses (See Demo By Dr. Kawasaki) ATNF Spectral Analysis Package (ASAP) is used made 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) http://www.atnf.csiro.au/computing/software/asap/