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Minutes of the regular SπRALS telecon meetings

Fortnightly on Wednesdays at 01:00 UTC Meetings: [[#20200422|2020-04-22]], [[#20200408|2020-04-08]]

[[#20200422]] Minutes: 2020-04-22

Hardware

  • "Cd and Wa receiver upgrade": Ray has ten amplifiers which need lab testing after quarantine ends. Good nominal specs, 30K antenna temperatures, good in the 3.5-8 GHz range.
  • "Measuring Tsys at Wa": Wa has noise diodes from Haystack, but not implemented. SEFD of roughly 650 Jy, but no reliable Tsys estimates. New receiver should increase sensitivity by a factor of 2. How to measure Tsys better?
  • "Wa broadband linear polarizations": something wrong, polarizer problem?
  • "Cd multi-frequency wideband observations": using the 4.1 GHz and 6.7 GHz receivers at the same time requires on-site work and Brett. Not trivial now.
  • "Cd linear broadband": can the quarter-wave plate removed to have linear polarizations? is it easy? should we? Peter McCulloch knows more about this.
  • Yg receiver upgrade is definitely postponed, lockdown is still going.

Software

  • PCONV testing on a single scan looks very good, could recover all parallel hands. However there is a time variability still as R-L phase is not constant. Next check: Maybe a time drift in parallactic angles and PANG correction not properly applied?
  • After PCONV works as a standalone program, it should be integrated in reduction pipeline at the very end, after all possible phase corrections.

Observations

  • We will try to do observations weekly on Fridays from now on, day is booked.
  • G232 observations continued last week and two more epochs are scheduled with more calibrators, pol calibrators included.
  • Next step is to observe a few epochs for station position and start the first science targets: G287 and G323. G287 has parallax peak on Jun 1.
  • Organizing things on homepage, including observation and correlation guidelines.

Station position

  • Wa shared several epochs of AUA geodetic S/X experiments from last year which include AuScope and the Warkworth antennas (no Cd). Previous antenna position have been determined from a similar set of experiments around 5 years ago, led by Lucia. Ask her for more info and help.
  • We will conduct our own 24-h geodetic block-style observations over several epochs, too. Discuss offline the details.

[[#20200408]] Minutes: 2020-04-08

Hardware

  • Warkworth and Ceduna receivers

Cooled (50K), 3-7 GHz, linear receivers. They are being developed by Ray, work can go ahead even in lockdown. Sergei: can the range be increased to 2-9 GHz? Are there feedhorn limits? Send current performance specs of amplifiers and rx of Wa and Cd to Ray. Another hardware issue: how to observe two frequencies at once at these telescopes?

  • Yarragadee upgrade

Probably not May, Gabor will follow up on this.

Software

  • PCONV: converting polarizations to a common basis

PCONV will be an AIPS task Mark is writing, that will deal with the linear and circular polarization conversion issues for our astrometry in a simplified way. Mark is now testing it on s001c data. Seems to work so far, some AIPS issues remain. add pdf file from Mark and more description

Procedures and Tests

  • How many maser can be shared in a track?

Lucas tested by flagging every other scan in MultiView test data (his PhD data). The astrometric repeatability went from 30-40 uas (unflagged), to 70-100 uas. Will test some more, but initial observations won't be shared track.

  • How many ring QSOs are optimal: 4, 5 or 6?

Start with 6-7 in first epoch of the initial experiment and see if they can be reduced (depends a lot on calibrator quality). Each ring cycle should be as short as possible to better sample ionospheric structure. Upper limit is in the 10-20 min range. add more to this from Richard's email

  • What are the top maser and QSOs for first parallaxes? Are we missing QSOs?

Nine sources selected for initial measurements based on compactness (how good is the maser for measuring a parallax) and calibrator availability. An additional source is also targeted that has a parallax from BeSSeL, to test and compare results. Haven't yet checked the missing QSO problem in the calibrator survey. add the initial target list from the text file

  • Do we have station locations to less than 1cm accuracy?

Do this in C-band instead due to rx limitations at the moment. Wa had a local tie survey (tying to position to Ww 12m) and a few geo-VLBI sessions in the recent years. How accurate is the position? (Cd is only about 2-3 cm, the rest of UTAScope is probably better. Gabor will look this up.)

We will do this experiment after the initial parallax experiments finished (12-hr solid geoblock observations in C-band, probably more than one epoch). Also, what was the issue with the KVN station position being not that good for a long time? add comments from Sergei, Richard, others

  • Start a parallax sequence for 1 or 2 masers, continue G232 maser sequence

These will be scheduled over the next few weeks. Will focus on: 

 # G323.740-0.263: bright, compact, good looking calibrator distribution
 # G287.371+0.644: good LST range that can be observed with others in a single long experiment without sharing a track.
 # G232.620+0.996: Already did an epoch back in september and π peaks is now. Used to test and compare to BeSSeL.

Although G323 and G287 are far from parallax optimums (which will be in June-August), they are good for the first observation to test logistics.

  • Test using wide C-band geoblock setup

For example 256 MHz each at 3.3 and 6.7 GHz. Will do this in the near future on Hb-Ke single baseline. Cd possibility of doing multiple frequencies at once? (see HW section)