<font face="Verdana, Arial, Helvetica" size="2">Regarding OBIT and AIPS: BDFLIST and BDF2AIPS<br />
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<div style="margin-left: 40px;">Ticket ID: 17215</div>
<div style="margin-left: 40px;">URL: <a href="https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/17215">https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/17215</a></div>
<div style="margin-left: 40px;">Name: Juhi Tiwari</div>
<div style="margin-left: 40px;">Email address: <a href="mailto:j_aquarian_t@yahoo.co.in">j_aquarian_t@yahoo.co.in</a></div>
<div style="margin-left: 40px;">Creator: User</div>
<div style="margin-left: 40px;">Department: AIPS Data Reduction</div>
<div style="margin-left: 40px;">Staff (Owner): Eric Greisen</div>
<div style="margin-left: 40px;">Type: Issue</div>
<div style="margin-left: 40px;">Status: Open</div>
<div style="margin-left: 40px;">Priority: Default</div>
<div style="margin-left: 40px;">SLA: NRAO E2E</div>
<div style="margin-left: 40px;">Template group: Default</div>
<div style="margin-left: 40px;">Created: 26 October 2020 03:42 PM</div>
<div style="margin-left: 40px;">Updated: 19 November 2020 02:28 PM</div>
<div style="margin-left: 40px;">Reply due: 23 November 2020 02:28 PM (4d 0h 0m)</div>
<div style="margin-left: 40px;">Resolution due: 13 August 2023 12:00 AM (996d 9h 32m)</div>
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Thanks for all the help, Eric.<br />
I only have a few more questions and then I will be good to go to the imaging step.<br />
1. Thank you for pointing out that the observation I am analysing currently does not have enough data for the source I wish to study. Regardless, as a beginner, I have learnt quite a few things in AIPS data reduction with this observation. What is the typical necessary observing time for a radio scan (cumulative time for multiple scans) to make a decent image? <br />
2. I tried out the calibration steps on the target source along with the self-calibration of the flux density and phase calibrators. After doing the calibration I went back and checked the amplitude and rms values for the source as well as calibration sources using the task LISTR. For the source (1233+169) the amp. rms values for certain baselines are rather large. For eg., the rms values for the source range from 1 to 10. Some are as high as 11 and 13. Should these be flagged? I would also like to know if bad data (very low amplitudes and high rms values after calibration) is identified only on the basis of the cal. sources or should it involve the target source too? What about the 'editing' part you mentioned in your previous email?<br />
3. While making a check for bad data, I used both DPARM 3,1,0 and 3,0,0 in LISTR OPTYPE='MATX', since the former does the scalar averaging and phases are not considered. How does one identify bad data in a phase-sensitive way? Does one also use DPARM(1)=1? I mean if one should check for the individual phase values like one checks for the amplitudes?<br />
4. How many phase calibrators should be used in the calibration process (if there is more than one in the observation)? Is it like.. the more the better? (since the phase solutions obtained for the time ranges of the calibrators are interpolated for the sources and the more info you have at more times, the better the interpolated values?)<br />
5. Should the science target be calibrated based on both the amplitude and phase calibrators? eg., TASK 'CLCAL' SOURCE '1233+169' CALSOURCE 'fluxcal_name' 'phasecal_name' or CALSOURCE 'phasecal_name' ?<br />
Juhi<br />
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On Wednesday, 18 November, 2020, 11:13:03 pm IST, Eric Greisen wrote: <br />
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I remember writing a reply to this - I wonder where it went.<br />
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1. I have no idea why so many sources were observed. I assume this was a source monitoring program that tried to find the fluxes of a large number of sources. I note that two of the sources in the observation are in the same field of view.<br />
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2. You are making way too much of the data flagging. There should not be any bad data (to first order anyway). It is possible that individual times can be bad and it is possible for a baseline to be bad. BUT it is also possible for the gains of the antennas to differ and so make a baseline - before calibration - look too low when it is perfectly able to be calibrated. You have almost no data on this source in this run. There are about 75 different observations of this source in the archive at L band. There are many tasks that let you look at UV data - TVFLG is a popular one. But I suggest flagging only grossly bad things and then doing the calibration. After calibration more things wrong may become visible.<br />
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3. If in flagging you find, for example, that antenna 1 is bad on all calibration scans, then that flag should be extended to the target as well. Minor bad points in the cal scan should not extend to the target unless they occur on both sides of the target scan. Then, AFTER you apply the calibration to the target, you may need to do some editing. But you have so little data it would be a shame to flag it all away.<br />
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4. Yes the Stokes are RR, LL, RL, and LR. This is not a polarization experiment so you can ignore RL and LR. Imaging will average RR and LL to makes Stokes I (unless you tell IMAGR to do only RR or LL). Flagging is usually done separately on RR and LL.<br />
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Eric Greisen<br />
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Ticket Details<br />
Ticket ID: 17215<br />
Department: AIPS Data Reduction<br />
Type: Issue<br />
Status: Open<br />
Priority: Default<br />
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