Calibration and Data reduction Strategies

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Calibration and Data reduction Strategies
Cormac Purcell Ned Ladd Mopra Training
Weekend May 2005
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I Calibration
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Measuring Source Intensity
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(No Transcript)
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Measuring Source Intensity
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Measuring Source Intensity
TA (Pon-source Poff-source)
Poff-source
Poff-source et C
C J(Tatm)(1-e-t) Ibge-t Irx
et/C
Tsys J(Tatm)et J(Tatm) Ibg Irxet
. . . (1)
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Measuring Tsys with a Hot Load
Compare blank sky to a known temperature standard
Psky
Pload
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Measuring Tsys with a Hot Load
Power measered from blackbody paddle
Pload CIload Irx
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Measuring Tsys with a Hot Load
Psky J(Tatm)(1-e-t)
Ibge-t IRx Pload Psky Iload -
J(Tatm)(1-e-t) - Ibge-t

Assume Tload Tatm i.e. Iload
J(Tatm)
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Measuring Tsys with a Hot Load
Psky J(Tatm)(1-e-t)
Ibge-t IRx Pload Psky
J(Tatm) e-t - Ibge-t

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What if Tload Tatm?
Psky J(Tatm)(1-e-t)
Ibge-t IRx Pload Psky Iload -
J(Tatm)(1-e-t) - Ibge-t

Cannot merge terms.
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What if Tload Tatm?
Psky J(Tatm)(1-e-t)
Ibge-t IRx Pload Psky (Iload
J(Tatm)) J(Tatm)e-t - Ibge-t

J(Tatm)et J(Tatm) Ibg IRxet (Iload
J(Tatm))et J(Tatm) - Ibg

Tsys (Iload J(Tatm))et
J(Tatm) - Ibg

Tsys no longer depends on Measurable Quantities
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Calibration to TA scale
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TA is Not EnoughCalibrating to a
Telescope-Independent Scale

• TA scale assumes source emission fills the
  forward hemisphere
• TA Tsource only if this is true
• In practice, one needs to consider the coupling
  between the source intensity distribution and the
  telescope response as a function of angle

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Antenna Temperature from an Extended Source
Tsource(f) Pb(f) dW
TA
2p
Tsource(f)
Pb(f) dW
2p
Pb(f)
f
need to know something about the beam
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2003 Beam
Greyscale 10 - 100 Contours 1 - 10
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2004 Beam
Greyscale 10 - 100 Contours 1 - 10
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Pb(f)
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Extended beam /- 80
Main Beam /- 40
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Main Beam Efficiency, hmb
Tsource(f)Pmb(f) dW
Pmb(f) dW
TA
2p
2p
Pmb(f) dW
Pb(f) dW
2p
2p
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Main Beam Brightness Temperature Scale

• Tmb Tsource for a source which fills only the
  main beam
• _at_Mopra, this means sources with size 80
• For smaller sources, need to consider beam
  dilution
• i.e., Tmb ltTRgt over the main beam
• hmb 0.4 _at_86 GHz in 2004

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Extended Beam Efficiency, hxb
Tsource(f)Pxb(f) dW
Pxb(f) dW
TA
2p
2p
Pxb(f) dW
Pb(f) dW
2p
2p
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Extended Beam Brightness Temperature Scale

• Txb Tsource for a source which fills both the
  main and extended beams
• _at_Mopra, this means sources with size gt150
• hmb 0.6 _at_86 GHz in 2003

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Calibration of Mopra Data

• Frequent Tsys measurements
• Every 20 minutes in good weather
• Always after changing target source
• ? TA scale
• Knowledge of source size
• Choose efficiency based on coupling between
  source intensity distribution and beam pattern
• ? Tmb, Txb, or Tsource

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II Data Reduction
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Reduction Steps

• Remove band-pass (off position)
• Fit a polynomial to the baseline
• Average individual spectra
• Scale to required temperature scale
• Measure line profiles - e.g. fit with Gaussian

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ATNF Single-dish Analysis Package
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ATNF Single-dish Analysis Package
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ATNF Single-dish Analysis Package
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Exporting your data

• Export from ASAP
• Export as an ASCII text file (e.g. TA vs V)
• Export from SPC
• Export as FITS use perl script to fix headers
• Import to CLASS
• Read ASCII file manualy fill headers
• Use CFITS to convert from SPC-FITS

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Exporting your data

• Direct export from ASAP to FITS coming soon!

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Questions?