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Calibration of wrong Tsys

Posted: Tue May 16, 2017 3:19 pm
by liuby
Hi~

In c3086 we were using 6a array to observe the 21cm absorption lines towards LMC/SMC. Some sources were observed in more than one day.
0540-6718, for example, was observed in 161123, 170419, 170426, 170427 and 170430. While in 3 of these 5 days, the amplitude of sources looks to be separated to two values. Take 170427 as example, it looks like this:
0540-6718_170427.png
0540-6718_170427.png (104.81 KiB) Viewed 111033 times
Plotting all the stokes:
0540-6718_170427_allstokes.png
0540-6718_170427_allstokes.png (122.26 KiB) Viewed 111033 times
1934-638 from the same day has a similar problem:
1934-638_170427_allstokes.png
1934-638_170427_allstokes.png (133.42 KiB) Viewed 111033 times
Is this caused by wrong Tsys measurements? If so how to correct it?
I've tried attsys but it seems not helping much. If attsys is the right tool, how to use it correctly?

Thank you!!

Boyang Liu

Re: Calibration of wrong Tsys

Posted: Tue May 16, 2017 5:00 pm
by ste616
Hi Boyang,

This looks to me like you have not set your delays correctly, which also affects the Tsys measurements. What do your phases look like over your channel range while observing 1934-638?

Re: Calibration of wrong Tsys

Posted: Tue May 16, 2017 8:43 pm
by liuby
ste616 wrote:Hi Boyang,

This looks to me like you have not set your delays correctly, which also affects the Tsys measurements. What do your phases look like over your channel range while observing 1934-638?
Thank you Jamie! Do you mean these plots?
1934-638_170427_time,phase.png
1934-638_170427_time,phase.png (148.64 KiB) Viewed 111029 times
1934-638_170427_phase,amp.png
1934-638_170427_phase,amp.png (81.07 KiB) Viewed 111029 times

Re: Calibration of wrong Tsys

Posted: Wed May 17, 2017 1:22 pm
by ste616
Hi Boyang,

No, I mean the ouput of uvspec, with vis=1934-638, stokes=xx,yy options=nopass,nopol,nocal, axis=chan,phase and yrange=-180,180.

Re: Calibration of wrong Tsys

Posted: Wed May 17, 2017 5:00 pm
by liuby
ste616 wrote:Hi Boyang,

No, I mean the ouput of uvspec, with vis=1934-638, stokes=xx,yy options=nopass,nopol,nocal, axis=chan,phase and yrange=-180,180.
Hi Jamie, you're right. The channels > 4500 are bad, after flagging all the channels > 4500, it looks as normal as it should be~!