Absolute Amplitude (Flux) Calibration Source Measurements

TIP Last Update: JeffMangum - 23 May 2014


Action Items

  • Add Mercury flux model to CASA (Greve etal 2009).
  • Calibrate asteroids relative to Uranus and give to Mueller for analysis.
  • Include Bolonia group in this work; incorporate polarization studies?
  • Ganymede, Callisto, and Titan off by ~10% when compared to CASA2012 models. Arielle check? Why are CASA2010 models in better agreement?
  • Re-analysis of the December 2013 run using just Uranus as the primary flux calibrator.
  • Exact observing sequence used for calibration runs.
  • Check of parent/satellite separation limit (2*theta_b+25 arcsec).
  • Additional asteroids to consider.
  • Total flux calculation method (pick amongst gaussian fit, extrapolation to zero spacing, etc.).


ALMA dedicates upwards of 24-hour "campaigns" to calibrator (both amplitude and phase) measurements. This wiki page summarizes the details of these calibration runs (how they are executed, observing parameters associated with their measurement, reduction procedures, etc.). See Ruediger's calibration wiki page for additional information.

Observing Detail

Pointing and Focus

How often is the pointing and focus checked during a typical run? Is the pointing and focus stability checked for each run to understand the limitations imposed by these measurements?

Observing Procedures

  • What is the minimum distance allowed between parent and satellite? 2*theta_b + 25 arcsec? How is this limit determined?
  • Observe in TDM model only?
  • What are "standard" observing bands? Do they include (potential) spectral lines from planets?
  • Include Band 9 in future runs.

Standard Frequency Bands

From a discussion thread culminated by the following from Harvey Liszt on 2013-01-15: Here is a slight tweak on Todd Hunter's list of recommended tunings that will henceforth be used for single continuum and polarization TDM experiments. It was decided that the OT would validate on these for polarization, presumably it would do the same for single continuum as well (?). Template SG's and/or some other simple way of using these setups should/will be provided. For band 3 there is a slight preference in Trcvr for lower frequency but mostly I moved the LO down to get away from the cloud radar at 94-94.1 GHz. For band 9 the OT is hard-wired to put four windows in the same sideband. Bands 4 and 8 aren't in the OT yet, they might deserve later tweaks.

Band Baseband Centers LO1
3 90.5*, 92.5, 102.5, 104.5** 97.5
> 4 138, 140, 150, 152 145
6 224*, 226, 240, 242** 233
7 336.5, 338.5*, 348.5, 350.5** 343.5
> 8 398, 400, 410, 412 405
9 676**, 678*, 680, 682 679
*=best Tsky **=worst Tsky (to use as rep. freq, differences are not large)

Minimum Observing Distance Between Solar System Objects

From Todd:

The moon center must be at least this far from the planet center: 2*(beam_FWHM) + 25 arcsec , where 25 arcsec is simply a quick/dirty way to specify the maximum radius of the largest planet (i.e Jupiter).

Procedure for Selecting Appropriate Solar System Objects for Science Observations

From Crystal, Todd, and Ed discussion of 2013-02-05:

  • Step 1: Determine which SS Objects are "up" (using current criteria on elevation, distance from sun etc) given Science target location, this
subset retaining their grades will be tested in order as described below until one meets the criteria. If none skip to Step 6.
  • Step 2: Convert the baseline length distribution to lambda using the mean frequency.
  • Step 3: Use CASA measures to determine the Solar System Object's size in arcseconds = S(arc).
  • Step 4: Convert S(arc) to lambda(length) using lambda(length) = 1 / [S(arc)*4.848e-6].
  • Step 5: If >= 25%/75% of baselines are less than lambda(length) for the Main Array / ACA, use that object. If not, check next source. This limit ensures that at least 5 antennas "survive" data reduction heuristics to be included in calibration of resolved flux cal, in many cases it is 6 or 7 (allowing for some down antennas). The percentage number needs to be one that is easy to adjust. We will need to change the percentages for Cycle 2. It is very dependent on distribution of short spacings/# of antennas. Indeed, we've discovered that Cycle 1 configs 4 and 5 have more short spacings than you would expect...
  • Step 6: If no SS Object that is up passes, use the best "Grid Monitored" quasar using current heuristic for Flux cals.

Analysis Procedure

  • What is the standard analysis procedure?
  • Is a limb-darkened disk used as the fit model?
  • Use only one primary flux standard (Uranus?) and reference everything to it.


  • Mercury flux model? Use Greve etal 2009?
  • Include Pluto and Iapetus?
    • Pluto: 250 year orbit, and need ~10 minute integration to get ~5% accurate flux at 345 GHz.
      • From Arielle: About Iapetus, well Raphael Hagen could tell you that it is not a good idea to use it as a calibrator with the level of knowledge we have now, since he has found a rotation curve of about 20-30% if I remember well. This is a case where I think it would be possible to make a very good reliable model if we could obtain more, well calibrated data, data. Given the long rotation period (~80 days), you'd need to make observations every 4 weeks. I did that with the SMA which is flexible enough - I hardly see how we could pull that off with ALMA. So it's really a matter of choosing to put effort in it or not.
    • Iapetus: ~0.5 Jy at 345 GHz. Has large but predictable flux variations (Arielle SMA measurements).
      • From Arielle: As for Pluto, it is tiny (~15 mJy at 1.3 mm) but the modeling of its surface is very good, and based on that it should not have a terribly variable average brightness temperature. Lellouch worked a lot on this, found a 1.3 mm lightcurve with <10% amplitude, and a 4% variation in the mid-IR (Spitzer). In fact, I am a co-I in the team of M. Gurwell who just got awarded time on ALMA to better the determination of Pluto's thermal lightcurve.


  • Arielle: Additional asteroid suggestions (email 2014-04-24):
    • Here are a few suggestions based on objects which are close to opposition in May (and their estimated flux at B7).
      • Objects with small lightcurve (probably roundish):
        • Cybele 0.37 Jy
        • Amphitrite 0.26 Jy
        • Egeria 0.32 Jy
      • Objective with significant lightcurves (and rotation period)
        • Eunomia 0.32 Jy , 6h
        • Metis 0.3 Jy, 5 h
        • Eugenia 0.5 Jy, 6h
    • The ones with significant lightcurves will be harder for us to model, and would require a good temporal sampling (at least every hour).
  • Comments from Thomas Muller (2014-05-16):
    • I am a bit puzzled by your new list of asteroids. They are not included in my list of 12 asteroids which I recommended for Herschel, SOFIA, APEX, ALMA, .... and they are only partially included in my larger list of 55 asteroids which could be pushed towards meaningful flux calibrators. I just checked your list for a few important criteria:
      • 65 Cybele 0.37 roundish
        • might be used, see paper by Mueller & Blommert 2004, A&A 418, 347
        • additional WISE, Akari fluxes available
        • but does not have a good shape model available
        • spherical or ellipsoidal shape model could be used, but observed lightcurve amplitude was up to 8% (peak-to-peak)
        • was an ISOPHOT calibrator (based on elliptical shape model)
      • 29 Amphitrite 0.26 roundish
        • has a good quality shape model available
        • model has not yet been optimised for size and albedo
        • lots of thermal data available
        • might be turned into a reasonable calibrator
      • 13 Egeria 0.32 roundish
        • has an ambiguity in the spin vector (two models available)
        • model has not yet been optimised for size and albedo
        • lightcurve amplitude of up to 12% was observed
        • lots of thermal data available
        • might be turned into a reasonable calibrator
      • 15 Eunomia 0.32 6h rotation
        • has a good quality shape model available
        • model has not yet been optimised for size and albedo
        • lots of thermal data available
        • lightcurve amplitudes between 0.30 and 0.54 mag were observed
        • strongly variable source
      • 9 Metis 0.30 5h rotation
        • there are two shape models available, but poor match to the observed occultation, looks like a complicated target
        • lots of thermal data available
        • also size information available
        • overall: a difficult target
      • 45 Eugenia 0.50 6h rotation
        • shape model available
        • can have a lightcurve amplitude up to 0.41 mag
        • strongly variable
        • lots of thermal data available
        • model has not yet been optimised for size and albedo
        • binary asteroid
    • The first 3 (Cybele, Amphitrite, Egeria) might be turned into reasonable calibrators, but that would clearly require some work. The first 2 (Cybele, Amphitrite) also have Herschel-PACS and SPIRE data! If you really want to include new objects, then go for Cybele and Amphitrite.

Observing Runs

December 2013

February 2014

Put summary and results here.
  • Ed has posted these data to polaris:/home/ftp/NRAO-staff/efomalon/ACA-data.
  • Files are B3_all.ms, B6_all.ms, B7_all.ms
  • He says: These are the concatenated data sets from the Feb ACA calibrator run. They include the usual apriori calibrations and flagging and bandpass. I have assumed that 3c279 has a flux density of 1.0 Jy, so any flux density measurements need appropriate scaling using the best planetary objects available. The observations are a bit spotty because of many problems during the runs. My quick look at suggests that not that much can be learnt from reasonably systematic analysis of the data, but I really haven't given it much of a chance.

May 2014

Limited LST. Measured Pallas (among others):

2014-05-18T02:33:36.813 Pallas 2014-05-18T02:37:29.297 Pallas

-- JeffMangum - 2014-04-30
Topic revision: r5 - 2014-05-23, JeffMangum
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback