<font face="Verdana, Arial, Helvetica" size="2">Regarding OBIT and AIPS: BDFLIST and BDF2AIPS<br />
---------------------------------------------<br />
<br />
<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: 20 November 2020 05:22 PM</div>
<div style="margin-left: 40px;">Reply due: 24 November 2020 05:22 PM (4d 0h 0m)</div>
<div style="margin-left: 40px;">Resolution due: 13 August 2023 12:00 AM (995d 6h 37m)</div>
<br />
<br />
<br />
1. After performing the calibration (I used both flux and phase cal. for the target source this time), I used the task 'LISTR' with optype 'LIST' and DOCALIB 2; GAINUSE 2 (the latest cal file extension is 2) to check the amplitude values (both scalar and vector averaged) for the calibration sources. These are similar to the values obtained with the tasks SETJY and GETJY. Using OPTYPE 'LIST' in LISTR and using VPLOT, I also examined the amplitude and rms values. The rms=10 that I mentioned corresponds to 0.1 Jy. The scale reads 1000 = 10 Jy. My bad. I am attaching two separate files containing part of the output obtained from running LISTR with optype 'LIST' and 'MATX' on the science target.<br />
1233+169_LISTR_LIST file: The scale reads 1000 = 1.00 Jy; It looks like that the amplitude values range from as low as 3 mJy to as high as 600 mJy and above. For e.g., the baselines 0207 0307 0407 show very low amplitude values. Are these problematic? How can one tell? The same thing is represented in the VPLOT output (I tried this out like you suggested; please see the attached snapshot AIPS1.png). I see the varying amplitudes. In this particular example, the variation across time within a baseline is not so much, but amp. variation across baselines is there. How low is low if one has to decide that a particular baseline has bad data? Or in other words, what is the typical permissible range of amplitude?1233+169_LISTR_MATX : This shows the high rms values for 1233+169. Values range from 0.01 Jy to 0.2 Jy. My question here is the same as above. Are all these values acceptable? Or how high is high for a particular rms value to indicate problems?<br />
2. I checked if the scalar avgd. amp. >> vector averaged amplitudes. The scalar and vector averaged amplitude values are similar. Is this enough to conclude that there is no problem with the phases? Or is an additional check required?<br />
3. There are several options for INTERPOL within task 'CLCAL'. If one decides to use more cal sources, which INTERPOL option should one use instead of '2pt'? Also, a guideline on the use of phase cal sources says that the cal source should be within 10 degrees of the target source. So even if the observation has several cal sources, all of them may not be useable? <br />
4. Can the flux density calibrator also be used as a phase calibrator?<br />
5. What do the vector-averaged, scalar-averaged and rms values signify? <br />
6. Like you suggested, I calibrated the cal sources and tried making clean images of them. I let the cleaning algorithm run till the time the 'total cleaned flux density' value did not become stable/started to decrease. Then I used TVSTAT to get an estimate of the flux within a small region enclosing the sources. The values that I get from TVSTAT are reasonably close to the values obtained with SETJY and GETJY (please see the attached file tvstat and snapshot AIPS4.png). Does this mean that the calibration and imaging is being done correctly? Or are there other ways to test the same? <br />
Thank you for your time.<br />
Juhi<br />
<br />
On Thursday, 19 November, 2020, 10:42:47 pm IST, Eric Greisen wrote: <br />
<br />
<br />
1. I did not say that you could not make an image from these data - just that snapshot images from the VLA have bad sidelobes and with only 1 scan poor S/N.<br />
<br />
2. I do not use LISTR much any more and so am not familiar with what it says for rms. An rms of 10 Jy is way way too large. Why don't you check your calibration with VPLOT (DOTV=1) or OPTYPE='LIST' in LISTR? Are the numbers all over the map (as 10 Jy rms would suggest). Are the numbers for your cal sources reasonably close to the source fluxes?<br />
<br />
3. One standard way to see about phase is to compare the scalar and vector averaged amplitudes. If the source has reasonable S/N, then scalar >> vector means unstable phase. At L band this is unlikely.<br />
<br />
4. The more the merrier - but CLCAL with 2PT simply interpolates the cal scan on either side of the target scan. But I would recommend also calibrating the calibrators and making images of them to be sure that the calibration and imaging are being done right.<br />
<br />
5. Yes the known source is a better cal than the secondary one - use all.<br />
<br />
Eric Greisen<br />
<br />
<br />
<br />
<br />
<br />
Ticket Details<br />
Ticket ID: 17215<br />
Department: AIPS Data Reduction<br />
Type: Issue<br />
Status: Open<br />
Priority: Default<br />
<br />
Helpdesk: <a href="https://help.nrao.edu/index.php?" target="_blank">https://help.nrao.edu/index.php?</a><br />
<br />
<br />
<HR style="margin-bottom: 6px; height: 1px; BORDER: none; color: #cfcfcf; background-color: #cfcfcf;" />
Staff CP: <a href="https://help.nrao.edu/staff" target="_blank">https://help.nrao.edu/staff</a><br />
</font>