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Calibration and Data reduction Strategies

This document outlines comprehensive calibration and data reduction strategies for Mopra observations, focusing on measuring source intensity and background emission. It covers essential techniques for quantifying Telescope System Temperature (Tsys) and Antenna Temperature (TA*), highlighting the significance of calibration against known standards. The data acquisition processes, including frequent Tsys measurements, polynomial fitting, and averaging of individual spectra, are also discussed. Understanding beam patterns and source sizes is critical for optimizing measurement accuracy.

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Calibration and Data reduction Strategies

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  1. Calibration and Data reduction Strategies Cormac Purcell & Ned Ladd Mopra Training Weekend May 2005

  2. I Calibration

  3. Measuring Source Intensity

  4. Background Emission (CMB) Source Atmosphere … t (Opacity) Electronic Noise

  5. Measuring Source Intensity Pon-src = C [ Isrc e-t + J(Tatm)(1-e-t) + Ibg e-t+ IRx ] Source Atmosphere Microwave Background Electronic Noise Poff-src = C [ J(Tatm)(1-e-t) + Ibg e-t+ IRx ] Isrc = (Pon-source – Poff-source) (et/C)

  6. Measuring Source Intensity Tsys Isrc Tsys = Poff-source et/C Tsys is a measure of noise in the whole system. 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)

  7. Measuring Tsys with a Hot Load Compare blank sky to a known temperature standard: Psky Pload

  8. Compare power from blank sky and known load: Poff-src J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Poff-src Iload + IRx - J(Tatm)(1-e-t) - Ibge-t - IRx = Measuring Tsys with a Hot Load Power measered from blackbody paddle: Pload = C[Iload + Irx]

  9. Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky J(Tatm) e-t - Ibge-t = 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)

  10. Tsys J(Tatm)et – J(Tatm) + Ibg + IRxet J(Tatm) - Ibg = Psky Pload – Psky Tsys J(Tatm) - Ibg = Measured Assumed : 300 K & < 1K Measuring Tsys with a Hot Load Psky J(Tatm)(1-e-t) + Ibge-t + IRx Pload – Psky J(Tatm) e-t - Ibge-t =

  11. 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.

  12. 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

  13. Calibration to TA* scale (Pon-source – Poff-source) Poff-source TA* = Tsys Psky Pload- Psky Tsys= (J(Tload) – Ibg) Assumed 300 K (Ambient temperature) <1 K From CMB

  14. TA* is Not Enough:Calibrating 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

  15. 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…

  16. 2003 Beam Greyscale: 10% - 100% Contours: 1% - 10%

  17. 2004 Beam Greyscale: 10% - 100% Contours: 1% - 10%

  18. Pb(f)

  19. Extended beam +/- 80’’ Main Beam +/- 40’’

  20. Tsource(f)Pmb(f) dW TA* = hmb 2p Pmb(f) dW 2p Main Beam brightness temperature Tmb = TA*/hmb Main Beam Efficiency, hmb Pmb(f) dW Tsource(f)Pmb(f) dW TA* = 2p 2p Pb(f) dW Pmb(f) dW 2p 2p

  21. Main Beam Brightness Temperature Scale • Tmb = Tsource for a source which fills only the main beam • @Mopra, this means sources with size ~80” • For smaller sources, need to consider beam dilution • i.e., Tmb = <TR> over the main beam • hmb = 0.4 @86 GHz in 2004

  22. Tsource(f)Pxb(f) dW TA* = hxb 2p Pxb(f) dW 2p Extended Beam brightness temperature Txb = TA*/hxb Extended Beam Efficiency, hxb Pxb(f) dW Tsource(f)Pxb(f) dW TA* = 2p 2p Pb(f) dW Pxb(f) dW 2p 2p

  23. Extended Beam Brightness Temperature Scale • Txb = Tsource for a source which fills both the main and extended beams • @Mopra, this means sources with size >150” • hmb ~ 0.6 @86 GHz in 2003

  24. 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

  25. II Data Reduction

  26. 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

  27. ATNF Single-dish Analysis Package

  28. ATNF Single-dish Analysis Package

  29. ATNF Single-dish Analysis Package

  30. 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

  31. Exporting your data Direct export from ASAP to FITS coming soon!

  32. Questions?

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