UPDATE (4/18/07): I think I've tracked the errors down to very bad amplitude solutions for antenna 1 for about an hour of one day. Still working on a solution. I'm tempted to flag antenna 1 for that time frame since it seems so self-contained, but that makes me a bit nervous.
UPDATE (4/23/07): I ended up flagging antenna 1 for the time where the solutions weren't converging and one scan on antenna 28. Now the data look fabulous. These antennas had phase errors in the phase calibrators during the relevant periods of time, so I'm feeling better about flagging them.
This isn't completely relevant to this blog because I'm doing it in Miriad, but I'm getting some funny artifacts when I amplitude+phase self-cal in Miriad. The phase self-cal goes fine, but I get these cheap carpet patterns when I amplitude+phase self-cal. The first image below is no cleaning, phase self-cal only. I can get rid of the swirls with cleaning. The second image is no cleaning, amplitude+phase self-cal. Weird! Any idea of the origin of this pattern? Has anyone else seen something like this?
I'm wondering if I can ignore the amplitude self-calibration and just do the phase self-calibration.....
Tuesday, April 17, 2007
Self-Cal Wackiness
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8 comments:
i think we're all still really unsure about the a&p self-cal steps. i've never seen it change the structure of the noise in my map though. did you set cparm(2) or not?
What is your solint for A&P self cal? Did you do what Claudia's post said, and apply the P self cal (with split) first, then do the A&P on this with much longer solint?
I don't know if I really like this A&P self cal. I really do think it majorly changes your fluxes. (Even if you set cparm) and often times for the worse. I have not seen your scary herringbones before, though, I don't think. Much it looks to me like it's introducing errors, not fixing them.
What do your SN tables look like?
This can be a miriad blog too! Just an interferometry data reduction blog!
Oh, and yes, I think it's fine to not do an A&P self cal. Everything I've read seems to imply that it's optional.
Optionally sucky :)
Miriad scales the gains so that the rms gain amplitude is 1 by default, which is equivalent to cparm(2)=1. See my comment on on Laura's Flux Conservation Entry for the goodness of setting cparm(2) during A+P calibration.
I was using a longer solution interval, but let me look into whether I'm actually applying the self-calibration tables from the phase calibration before doing a A+P calibration.
Why does that make you nervous? Because you're afraid it's spilling over to other times and you dont' see it?
I'd rather flag based on my original calibration solution than flag based on a self-cal solution, just because the self-cal solution isn't necessarily unique or correct since its based on a model.
Looking back on the reduction logs, however, the secondary calibrator was wonky during this time as well, so I don't feel too back about flagging it.
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