Atacama Pathfinder EXperiment APEX SABOCA
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SABOCA Calibration

Intensity calibration

• Zenith opacities

  The opacity of the sky is usually determined by skydip measurements. However, the values are not very accurate and for a more reliable opacity estimate, one has to combine the skydips, taumeter measurements and calibrator fluxes.
  
  
  • SABOCA sky opacities search interface.

• Absolute calibration scale

  The raw data coming from SABOCA just have the detector voltage output as intensity. In order to obtain the intensity in astronomical units, the data have to be multiplied with a conversion factor.
  f = 4.8±0.5 Jy/mV
  This factor has been determined on the primary calibrators Mars, Uranus, and Neptune during the commissioning period.

• SABOCA calibrators

  
  
  • SABOCA primary and secondary calibration factors search interface.

  Values in the table below based on the file $BOA_HOME_SABOCA/saboca-secondary-fluxes.py, dated 2010-05-05.

  Source	RA(2000)	Dec(2000)	Flux[Jy]
  HLTAU	04:31:38.45	+18:13:59.0	8.0
  CRL618	04:42:53.6	+36:06:53.7	19.2
  V883-ORI	05:38:19.0	-07:02:20.0	12.33
  N2071IR	05:47:04.85	+00:21:47.1	36.4
  VYCma	07:22:58.33	-25:46:03.2	10.14
  CW-LEO	09:47:57.38	+13:16:43.6	26.0
  B13134	13:16:43.15	-62:58:31.6	180.0
  IRAS16293	16:32:22.9	-24:28:35.6	135.0
  G5.89	18:00:30.38	-24:04:00.5	230.0
  G10.62	18:10:28.66	-19:55:49.7	340.0
  G34.3	18:53:18.50	+01:14:58.6	430.0
  G45.1	19:13:22.07	+10:50:53.4	105.0
  K3-50A	20:01:45.69	+33:32:43.5	112.0
  CRL2688	21:02:18.80	+36:41:37.7	49.0
  NGC253	hh:mm:ss.ss	ddd:mm:dd.s	45.0
  IRAS16342	16:37:40.10	-38:20:17.0	9.5

  
  Note: As of May 2010 no reliable determination of calibrators yet available - values for testing to be replaced soon

  Pointing & Focus

  • SABOCA Pointing Model

    We have established a pointing model for SABOCA, based on measurements of planets, secondary calibrators, and bright QSOs. The rms of this model is 2″ in azimuth and 4″ in elevations.
    During an observing run, sources as weak as 600mJy can be used under good weather conditions to verify the telescope pointing.

  • Focus

    The focus settings in the three subreflector displacement axes (x, y, and z) have been verified by various measurements on Venus, Mars, Jupiter, and Saturn.

  Beam shape & angular resolution

  From beam maps on Mars the angular size of the telescope beam was measured for individual bolometers. After deconvolution by the planet and pixel size we found:

  FWHM = 7.8″ ± 0.5″

  The shape of the main beam is an almost circular Gaussian. At intensities below 6% of the peak, the beam starts to deviate from a Gaussian.

  Array parameters

  For a multi-channel receiver, the array parameters include the relative offsets of the individual channels as well as their relative gains. Both can be estimated from fully sampled maps (for all channels) on strong compact objects.
  We have summarized the array parameters for all observing periods from SABOCA commissioning until now. The channel offsets normally are expected to change only if physical work is done at the rerceiver itself (repair, upgrade, or maintenance). However, the relative gains can also change with every warm-up of the instrument.
  

  • SABOCA Array Parameters

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  Last update: August 30th, 2010