NHSC HIFI DP workshop Caltech, 7-9 February 2011

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Steve Lord Steve Lord (lord@ipac.caltech.edu)(lord@ipac.caltech.edu)

Conversions of Conversions of Intensity Scales Intensity Scales and Frequency and Frequency UnitsUnits

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X-Axis Conversions

• HIFI can change the Spectrum Explorer labeling of a Spectral Data Set. – Can add an auxiliary axis (e.g. add LSB or IF or USB)

– Can then alter that axis to show Velocity w.r.t. a reference frequency

– See Developer's reference manual Chapter 8.1.1

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X-Axis Conversions

• We can use the command line to change the X-units of a data set: – ConvertFrequencyTask – HIFI Timeline Products or Spectral Data Sets

– Converts between 4 views: USB, LSB, IF and Velocity

– For velocity, user must specify Reference Frequency and whether that is in the USB or LSB (!)

–see HIFI-um Chapter 8.2

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X-Axis Conversions

• We can use the command line to change the X-units of a data set: –  ConvertWaveScale – Converts a Spectral Data Set

– Converts between Frequency, Velocity (w/ref. f), Wavelength and Wavenumber [GHz, km/s, MHz, mm, m/s,1/m, MHz)]

– See Developer's reference manual Chapter 2.77

– routine has some issues to be resolved for HCSS 6.0

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Changing Flux Units

• ConvertK2Jy has been implemented in 12/2010• Operates on Herschel Timeline Products and Spectral Data Sets

• Is entirely a HIFI routine• Uses the fact that K "brightness temperature" converts to Jy/sr in the radio astronomy of using the Rayleigh Jeans approximation strictly, and the user can provide steradians.

• Uses the fact that the effective aperture is "known" for all HIFI frequencies, as well as beam efficiencies from using the HIFI cal tree. (This is accessed either locally or remotely – time consuming).

• Requires use input of a source size (diameter~HPBW

• ConvertK2Jy – has been implemented 2010

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ConvertK2Jy (con't)

• Basic Algorithm – 3 cases:• The size in arc second of the source observed.

• 1) If the size = 0 the pointing like source formula is used: S/Ta (Jy/K) = 2k / (Ageom * eta_A), where:

S is the Energy flux expressed in Jansky Ta is the Antenna Temperature measured in Kelvin k is the Boltzman constant, Ageom is the effective area of the telescope, which we have assumed to be

3.28m, so diameter. So, Ageom = 8.45m2 eta_A is the aperture efficiency, to be extracted from the calibration tree for the frequency of interest

• 2) If the size <= HPBW: S = Ta * 2k / (eta_B* size^2 /HPBW^2) , where:

eta_B is the Main beam efficiency HPBW is the Half Power Beam Width (HPBW) of the telescope expressed in

square arc second

• 3) In case of size >= HPBW S ~= Ta * 2k / (eta_B* f_BEAM * lambda^2)

f_Beam is the beam filling factor

NHSC HIFI DP workshop Caltech, 7-9 February 2011

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Unit Conversion Tool for HerschelRuns alternatively: • within HIPE – can take array• as external JAVA tool• as a website (server) Converts:• Flux• Flux Density• Intensity• Integrated IntensityIncludes Help Files