Selecting solar system objects as amplitude calibrators

Sent to JAO on February 5, 2013

SS Objects ordered by how accurate their models are expected to be.

• 1=few percent
• 2=5%
• 3=10%
• Mars 1
• Venus 2
• Jupiter 2
• Uranus 2
• Neptune 2
• Titan 2
• Ceres 2
• Ganymede 3
• Callisto 3
• Pallas 3

Recommended procedure for selecting SS Object

• 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 >= XX% of baselines are less than lambda(length) use that object. If not, check next source. We have verified that for *Cycle 1*:
  • Main Array: XX=25%
  • ACA: XX=75%

We believe this ensures 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.

-- ToddHunter - 2014-04-08