Monday, June 30, 2008

Need Larger Fonts on Plots

I'm trying to get the labels for my plots in AIPS to be much larger than the default. LWPLA has an option to specify the font size, dparm(8), but after playing with it, it seems like 24pt is the maximum font size. I would really like to use something bigger than this. I can modify the labels manually in Illustrator, but that requires repositioning all the labels, which is way too time intensive. Any other ideas?

UPDATE: Solution using ASPMM parameter in LWPLA detailed in comments.

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Saturday, June 28, 2008

Bins in UVPLT

You know what is a great easy way to visualize your data that I often forget about? Bin your data in UVPLT! For example, if you are making a UV distance vs. Amplitude plot, then you can actually see the amplitude structure instead of just seeing tons of points ranging all the way down to an amplitude of zero.

All you have to do is set BPARM(8) = 50 or the number of bins you want.

I think it also plots up faster this way then plotting lots of individual points!
Of course, if what you care about is a handful of really pathelogical points, than this is not the right strategy. But if you are, say, trying to identify a bad baseline or something, this works great!

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Tuesday, June 17, 2008

Calibrating Data without a Flux Calibrator

Sometimes when I get data from the archive, it appears that the observers have not observed a flux calibrator. There is a phase calibrator. Is it possible to use this data? Is the data really only good for imaging and getting the morphology of an object, but you can not trust it for absolute fluxes? I feel like I should be able to do something clever to get fluxes...

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Sunday, June 8, 2008

Flagging After A&P Self Calibration?

I've been wondering lately-- when you run an Amplitude & Phase Self-Cal run, often times this can make certain parts of your data look anomalously high or low. Usually it's pretty mild, but a couple of times, it has been rather dramatic. A bit distressing, as I don't really understand why CALIB chose to make my amplitudes worse...

But anyway, does anyone out there have opinions on whether you should flag your data again after an A&P self cal? If you do flag, do you then copy the flag table over to the un-A&P-self-calibrated data set, and the re-self-calibrate using this new flag table? And iterate so on till no more "bad" data pops up on the A&P self cal?

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Friday, June 6, 2008

DBCONing Data Sets From Different Epochs

If you are an archive monger like me, you might find yourself reducing one J2000. data set and one B1950. data set, and then wanting to concatenate them together. If you try to do this, DBCON will yell at you. So...

You will have to run EPOSWTCH on the 1950 data set to bring it into epoch 2000. However, if you try to run DBCON now, DBCON will still yell at you and say:

tsingt> DBCON1: Purports to die of UNNATURAL causes

As explained by Eric Greisen here , this is because the image you EPOSWTCHed now has a Declination axis with a rotation imposed upon it. For example:

AIPS 1: Image=NGC1569 (UV) Filename=N1569_3B .SC_P1 . 1
AIPS 1: Telescope=VLA Receiver=VLA
AIPS 1: Observer=AA116 User #= 53
AIPS 1: Observ. date=21-AUG-1990 Map date=06-JUN-2008
AIPS 1: # visibilities 135940 Sort order TB
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type Pixels Coord value at Pixel Coord incr Rotat
AIPS 1: COMPLEX 1 1.0000000E+00 1.00 1.0000000E+00 0.00
AIPS 1: STOKES 4 -1.0000000E+00 1.00 -1.0000000E+00 0.00
AIPS 1: FREQ 1 8.4149000E+09 1.00 5.0000000E+07 0.00
AIPS 1: IF 2 1.0000000E+00 1.00 1.0000000E+00 0.00
AIPS 1: RA 1 04 30 49.498 1.00 3600.000 0.00
AIPS 1: DEC 1 64 50 59.587 1.00 3600.000 -0.60
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Rest freq 0.000 Vel type: OPTICAL wrt YOU
AIPS 1: Alt ref. value 0.00000E+00 wrt pixel 1.00
AIPS 1: Maximum version number of extension files of type FQ is 1
AIPS 1: Maximum version number of extension files of type HI is 1
AIPS 1: Maximum version number of extension files of type AN is 1
AIPS 1: Maximum version number of extension files of type WX is 1
AIPS 1: Maximum version number of extension files of type FG is 1

You can get rid of this rotation using UVSRT:

AIPS 1: UVSRT: Task which sorts UV data
AIPS 1: Adverbs Values Comments
AIPS 1: ----------------------------------------------------------------
AIPS 1: INNAME 'N1569_3B' Input UV file name (name)
AIPS 1: INCLASS 'SC_P1' Input UV file name (class)
AIPS 1: INSEQ 1 Input UV file name (seq. #)
AIPS 1: INDISK 1 Disk unit # of input UV data
AIPS 1: OUTNAME ' ' Sorted UV file name (name)
AIPS 1: OUTCLASS 'ROTAT' Sorted UV file name (class)
AIPS 1: OUTSEQ 0 Sorted UV file name (seq. #)
AIPS 1: OUTDISK 0 Disk unit # of sorted UV data
AIPS 1: 0 => highest with space
AIPS 1: If outfile spec. equals the
AIPS 1: infile spec., output will
AIPS 1: overwrite the input
AIPS 1: BADDISK *all 0 Disk drive #'s to avoid
AIPS 1: SORT ' ' Two char. sort order, eg.'XY'
AIPS 1: blank => 'XY'
AIPS 1: ROTATE 0.6 Angle thru which to rotate.
AIPS 1: positive rotates CCW
AIPS 1: DEFER 0 Defer output file creation?

Note that the ROTATE parameter is the negative of the rotation noted in the header. Now you should be able to DBCON the EPOSWTCHed data with the other J2000 data set!

(You may have to UVSRT the DBCONed data so that it is in TB order again.)

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Monday, June 2, 2008

Calibrating One Calibrator with Two UVranges

The VLA calibrator manual recommends that if you are using 3c286 as your flux calibrator at 20 cm in A configuration, you should use the uvrange 0-18 AND 90-180 (for the latter, decrease flux by 6%). This makes me wonder how on earth one would do this. First of all, I do not know how to calibrate on two separate uvranges and then merge that information. Second of all, I do not know how to reduce a flux by 6%. Anyone? Anyone?

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