CHAMP+ Efficiency Measurements

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Date Source Θd["] ηf (λ) Subarray ν[GHz] Θmb["] ηs(λ)  Notes
Observing Campaign: July-September 2014
10.09.2014 Mars 6.58 0.95 LFA 660.4 9.1 0.43

Observations with new closed-cycle calibration unit.

Results are consistent with previous LN2 calibrations.
HFA 807.1 7.7 0.32
10.07.2014 Mars 8.94 0.95 LFA 691.9 8.7 0.41

Cal Unit out of operation.

Calibration performed manually with LN2 paddle.
HFA 807.1 7.7 0.34
Observing Campaign: November 2012
07.11.2012 Jupiter 47.4 0.95 LFA 691.9 8.9 0.49 Mars to weak. Because Jupiter is consistent
with previous observations, use 2009 efficiencies
for compact targets.
HFA 807.1 7.7 0.48
 Observing Campaign: July 2010
23.07.2010 Jupiter 43.1 0.95 LFA 691 8.9 0.48  LFA efficiencies are 10% on the low side,
 for all sources
0.95 HFA 809 7.7 0.48  to be investigated in September 2010
19.-25.07. Mars 4.85 0.95 LFA 691 0.36
0.95 HFA 809 0.36
23.07.2010 Uranus 3.56 0.95 LFA 691 0.34
0.95 HFA 809 0.32
 Observing Campaign: August 2009  optics corrected, surface adjusted
04.08.2009 Moon 1765 0.95 LFA 691 8.9 0.82  close to full moon
0.95 HFA 806 7.6 0.84
04.08.2009 Jupiter 47.3 0.95 LFA 691 8.9 0.52
0.95 HFA 806 7.6 0.49
04.08.2009 Mars 5.4 0.95 LFA 661 8.7 0.43  LFA beam is smaller than "nominal"
0.95 HFA 809 7.6 0.35
 Observing Campaign: June 2009  CHAMP+ optics anomaly (5)
16.06.2009 Jupiter 42.36 0.95 LFA 661 9.3 0.46  dewar position: 97 deg
0.95 HFA 809 7.7 0.40
22.06.2009 Mars 4.86 0.95 LFA 689 8.8 0.40  dewar position: 90 deg
HFA  no data, recommend to use 0.35
 Observing Campaign: September 2008  after telescope surface adjustment
14.09.2008 Moon 1855 0.95 LFA 691 8.9 0.82  full moon
      0.95 HFA 806 7.7 0.78  
09.09.2008 Jupiter 41.1 0.95 LFA 658 9.4 0.48  
      0.95 HFA 815 7.7 0.45  
      0.95 HFA 881 7.0 0.44  
14.09.2008 Uranus 3.64 0.95 LFA 691 8.9 0.38  
      0.95 HFA        too weak for cal, use Oct 07 numbers
 Observing Campaign: July 2008  prior to tel. adjustment; after subreflector change
18.07.2008 Jupiter 45.8 0.95 LFA 661 9.3 0.45  
      0.95 HFA 809 7.7 0.43  
05.07.2008 Mars 4.36 0.95 LFA 691 8.9 0.28  
      0.95 HFA 806 7.7 0.30  
 Observing Campaign: October 2007  calibration with internal cold/losses
22.10.2007 Jupiter 32.5 0.95 LFA 661 9.3 0.45  
      0.95 HFA 809 7.7 0.42  
23.10.2007 Mars 11.4 0.95 LFA 691 8.9 0.38  
      0.95 HFA 806 7.7 0.35  

Addendum:

  1. The CHAMP+ beams are diffraction limited, use ΘFWHP  ≈ 1.2 λ/D.
  2. The forward efficiency ηf (λ) is best estimated (0.95 ± 0.02); so far we have been unable to establish stable skydip analysis for submm wavelength (incl. self-consistent solution for the sky temperature in atm).
  3. Efficiencies are generally uniform across the arrays (within a few per cent); except for HFA pixels #1 and #2, for which in 09-2008 we derive slightly lower source couplings (ηs(#1) = 0.85 and ηs(#2) = 0.89 times the table figures). This can be supplied by the apexOfflineCalibrator.
  4. Image gains: for the 2007 measurements, a gain ratio of 0.05 is a good figure. Due to the transport damage to the refurbished cryo-optics, in 2008 sideband suppressions vary with frequency and with pixel position. But generally are better than 10 dB in the IF band center. Currently the calibrator cannot handle IF-variable image gains.
  5. The June 2009 observations were affected by an anomaly in the warm optics (relaxed mirror fixation). This made the LFA beam toggle on the subreflector depending on the cryostat position. In consequence we have a coupling efficiency that depends on the orientation of the dewar (Fig). Fortunately, because we make use of the 60 deg symmetry of the array, most of the observations are carried out in an angular range that compares with the angle used for typical efficiency measurements. For proper calibration (1) inspect the range of the dewar angles used for your observation and (2) correct with the tools made available, if necessary (contact F. Wyrowski about the procedures). The HFA efficiency was somewhat reduced, but independent of the dewar orientation.
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