[daip] [!16519]: AIPS - Issues with UF002BC & UF002BD
Luis Fernandez
nraohelp at nrao.edu
Fri Jul 10 10:51:05 EDT 2020
Luis Fernandez updated #16519
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Issues with UF002BC & UF002BD
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Ticket ID: 16519
URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/16519
Name: Luis Fernandez
Email address: lfernan at gmu.edu
Creator: User
Department: AIPS Data Reduction
Staff (Owner): -- Unassigned --
Type: Issue
Status: Open
Priority: Default
SLA: NRAO E2E
Template group: Default
Created: 10 July 2020 02:50 PM
Updated: 10 July 2020 02:50 PM
Reply due: 14 July 2020 02:50 PM (4d 0h 0m)
Resolution due: 06 April 2023 12:00 AM (999d 9h 10m)
Hello,
My name is Luis Fernandez. I am currently working with the two data sets listed in the subject line. This is part of a 6 month survey examining 3 point sources which are included in the following data sets: UF002BA, UF002BB, UF002BC, UF002BD, UF002BE, UF002BF. It seems there was an issue regarding IF 4 for both observations in data sets UF002BC & UF002BD. The issue we are finding is that the flux density and the peak flux drops by more than half for the observed targets and phase calibrator compared to the other data sets. Which is surprising since this shouldn't effect the peak flux by this much let alone for all target sources. This is an issue because our project means to determine accurate measurements of fluxes for these objects. Each data set was calibrated in AIPS the same way and will be listed as follows:
Loading the data file (Separated different UV files for each target source. I.E. NGC2992 with corresponding phase calibrator, NGC3079 with corresponding phase calibrator, etc.)
Using FITLD
Parameter CLINT 0.1
Parameter ANTNAME 'VLBA'
Calibrating for Ionosphere
Using VLBATECR
Calibrating for Earth Orientation
Using VLBAEOPS
Calibrating for correlator sampler threshold errors
Using VLBACCOR
Checking for best reference antenna and time range for initial phase/delay calibration using the phase calibrator as the source
Using VLBACRPL
Parameter SOLINT -1
This is where I found that all IF 4 in both data sets had issues with Phase/Amp and decided to flag out all IF 4 to obtain better fringe fitting. (Note: I tried both with and without flagging out IF 4 and obtained similar results when cleaning images)
Using UVFLG
Calibrate for initial phase/delay using phase calibrator
Using VLBAPCOR
Parameter CALSOUR 'phase calibrator'
Parameter TIMERANGE 'corresponding best time'
Parameter REFANT 'best reference antenna'
Calibrate Bandpass using same parameters as VLBAPCOR
Using VLBABPSS
Calibrate amplitude
Using VLBAAMP
Calibrate for parallactic angle
Using VLBAPANG
Flagged any bad data points one source at a time
Using EDITR
Parameter DOCAL 1
Parameter GAINU 0
Parameter CROWDED 1
Parameter DO3COL 1
Parameter DOBAND 1
Parameter BPVER 1
Parameter ANTUSE 1 2 3 4 5 6 7 8 9 10
Fringe-fit the data using the phase calibrator and best reference antenna
Using FRING
Parameter SEARCH 2 9 5 4 1 3 7 8
Parameter GAINU 0
Parameter SOLINT 0.25
Parameter DOBAND 1
Parameter BPVER 1
Parameter APARM(9) 1
Parameter DOCAL 1
Apply calibration to source and phase calibrator using best reference antenna
Using CLCAL
Parameter INTERPOL '2pt'
Parameter GAINVER 0
Parameter GAINUS 0
Parameter SNVER 5
Parameter CALSOUR 'phase calibrator'
Split out the calibrated sources to make images
Using SPLIT
Parameter DOCAL 1
Parameter GAINU 0
Parameter DOBAND 1
Parameter BPVER 1
Parameter APARM 2 0
Flag out any high amplitudes as well as any remaining RFI issues for each source
Using WIPER
Parameter IMSIZE 512
Make initial images for each source making a box over the point source
Using IMAGR
Parameter CELLSIZE 0.0008
Parameter IMSIZE 512
Parameter NITER 5000
Parameter ROBUST 0 (I also checked different robust parameters from 0 to 5 to see if there where any variations)
Parameter GAIN 0.03
Parameter MINPATCH 255
Using a self calibration method I tried to make the best cleaned images utilizing the initial cleaned image
Using CALIB
Parameter GETN 'Source Split File'
Parameter GET2N 'Initial cleaned image of source'
Parameter SOLINT 1
Parameter SOLMOD 'P'
Parameter SOLTY 'L1R'
Parameter REFANT 'best reference antenna'
Clean the CALIB file using same parameters as initial image
Check Histogram RMS for both initial image and first self calibrated image for improvements
Using IMEAN
With improvement continue self calibration process using same parameters except for the following
Parameter GET2N 'Image cleaned from first Calib file'
Parameter SOLINT 0.5
Clean image from second Calib file using same parameters and check RMS from histogram.
If RMS improves make a new Calib file and reduce solution interval to 0.1 and repeat same process outlined above. If RMS does not improve, delete last Calib file and its respective cleaned image files.
Last self calibration is to also include amplitude as part of the solution since previously we calibrated phases as best as possible. All parameters remain the same using CALIB except for,
Parameter GETN 'Best model Calib file'
Parameter GET2N 'Cleaned image from best Calib file'
Parameter SOLINT 1
Parameter SOLMOD 'A&P'
Clean Calib file with same parameters and check RMS histogram. (Note: At any point, images became warped or nonsensical, resorted to using last best image as best cleaned image to be used and analyzed)
After the above process was completed for all data sets, I analyzed the flux density and peak fluxes for all 3 targets in each data set and found consistently that for data sets UF002BC & UF002BD (Month of February and March), all targets where more than half lower compared to the others.
The following graphs are for the 6 month observation and show the maximum peaks for each data set after self calibrating images. UF002BC & UF002BD are the lowest two points in all graphs. (Note: For NGC2992 there were non-detections for these two data sets and used 2.5 times the noise RMS to obtain points)
The following are the flux densities of each target without self calibration as a comparison using parameter ROBUST 0 and 5 to check for variations.
You can see that for all 3 targets, data sets UF002BC & UF002BD, are all much lower than the other data sets.
I wanted to know if there is anything that could be done to correct for these issues?
Thank you for your time,
Luis Fernandez
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Staff CP: https://help.nrao.edu/staff
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