Excluding single-channel flux peaks

Reader Linda asks

I'm trying to use the AIPS task BLANK to blank an HI data cube. I am using the method where you blank a convolved version of your cube to exclude flux < 2-3*noise and then use that convolved cube as a filter to blank your original image. With the help of other kind folks, I've got this part worked out. But I would also like to exclude single-channel flux peaks. Does anyone know of a way to ask AIPS to only keep pixels with signal that is above a set level in a specified number of consecutive channels? It seems like using OPCODE = 'FLTW' might be helpful, but my attempts at using this haven't produced anything useful.

I'd really appreciate any help!

Any suggestions?

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BPLOT is a really cool task

I recently learned about a task in AIPS which is very good for assessing bandpass stability---BPLOT. If you have multiple bandpass solutions, it will plot each one, stacking them one on top of each other as a time sequence. To the left is an example plot from BPLOT. Try it, you'll like it!

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Getting rid of distracting black lines in TVFLG/SPFLG

Have you ever loaded your data into TVFLG or SPFLG and seen what looks like lots of blank times (manifested as horizontal black lines cutting through your data)?

This is because TVFLG/SPFLG is trying to load your data with a time bin that is not a multiple of your integration time. So---the solution is to set DPARM(6)! Set DPARM(6) to your integration time in seconds; e.g., for GMRT data:

DPARM(6) = 16.7

(or, if you have time averaged your data, set it equal to your averaging time).

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Watch out for the STOKES parameter when plotting (even if you don't care about polarization)

When using the many plotting/flagging programs in AIPS, make sure to check the value of the STOKES parameter before plotting (try help stokes to see the options and select the one appropriate for that data set). Different tasks have different STOKES defaults, so sometimes displaying data in one program results in a totally different plot than in another program because one is including some polarizations the other is not. This particularly can be a problem if you have cross-polarization values you don't care about (yet).

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CVEL bug

I received an email yesterday informing people of a bug in CVEL - that is, if you run CVEL on a data set after SPLIT with an NX table, you are affected! I wanted to post it here in case you're not on the Midnight Job (MNJ) list (which I wasn't). Essentially, CVEL will only shift the first scan to the new velocity axis, while the other scans are not shifted. This bug is explained here. I think the possible fixes are to either run CVEL before SPLIT or to run the midnight job to update your AIPS version and then rerun the new CVEL version on your data.

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CASA guides

Hey! If you're learning CASA, check out this new collection of tips and tutorials that I've been contributing to:
http://casaguides.nrao.edu/

And let me know if you see obvious holes in the documentation there (which is, clearly, still under development).

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Error in PCAL

Here's a question from Akshaya Rane:

I am doing polarization calibration and while trying to run 'pcal', I have encountered the following error. Does this has to do something with qualifiers?

PCAL 3: TOTAL INTENSITIES MUST BE PROVIDED
PCAL 3: Purports to die of UNNATURAL causes

Any thoughts?

I should add that Eric Greisen says that if you spend an hour trying to figure out something in AIPS, and you can't, you should feel free to email him and ask his help.

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