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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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Overview of CASALog Message
Main Window (on terminal)
Image Viewer(type vieweron the main window)
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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 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)
QuickTime˛ Ç∆ êLí£ÉvÉçÉOÉâÉÄ
ǙDZÇÃÉsÉNÉ`ÉÉÇ å©ÇÈÇΩÇflÇ…ÇÕïKóvÇ≈Ç∑ÅB
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)
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CASA DocumentationCASA Cookbook: http://casa.nrao.
edu/Doc/Cookbook/casa_cookbook.pdf
CASA User Reference Manual: http://casa.nrao.edu/docs/casaref/CasaRef.html
Python: http://python.org/doc
IPython: http://ipython.scipy.
org/moin/Documentation
matplotlib: http://matplotlib.sourceforge.net/