NIKA2 run #4 March 2016

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Goals of the run

Continue tests on the instrument with same arrays since run 1 and same NIKEL boards as run 3.

1. Check data & flags consistency & synchronization: Raw, FIT for Pipeline, IMBFIT.

2. Test possible improvement on synchronization of NIKA2 tunings and decalage with telescope scans information (e.g. subscan start and stop, etc.): more direct link with ELVIN or use to UDP to a nika2-a port) [see with Granada staff], check tuning and decalage durations vs time between subscans.
3. Investigate best threshold for decalage between subscan, because systematic ftone jumps between subscans will kill the sky noise low frequency decorrelation. So decalage between subscan should be only in case sky background variations would be so big that we would loose the resonnaces otherwise, hence the scan. An optimum has to be found.

4. Test synchronization of NIKA2 samples with telescope coordinates: some hints in previous data of possible systematic error (e.i. using PPS time maybe not sufficient) → to test this possibility do scans (beam maps) at various speed and and scan pattern (not only zig-zag, but also only increasing azimuth, only decreasing azimuth etc.→ need to edit PaKo scripts to do that!), and also various acquisition frequency.

5. Optimisation of tone comb position: arrays 1 and 3 have systematically about one line of pixels missing per multiplexed feed line; this is due to the limited bandwidth of the NIKEL boards w.r.t. the resonance frequencies span, we may recover a number of pixels by optimizing the tone comb position.

6. Understand possible stability difference between array 1 and array 3: array 1 seems more stable though both arrays are identical, electronic boards are possible suspects → exchange boards and do beam maps.

7. Beams characterization is still a priority, we needs additional maps to investigate beyond current status(*): more beam maps for better statistics, XYZ focus optimization (first probing various locations on the focal plane like run 2 focus campaign (see the commisionning how to page), then with several beam maps near optimal XYZ focus position). Pay attention also at the possible dependence with elevation.

8. Elements that come "for free" with the additional beam maps done for previous items: increase statistics on kid stability, photometry, sensitivity and time line features.
9. Regular skydips: at least once per day.
10. A session of KIDs working point optimization (e.g. gain, dftone modulation frequency and amplitude, etc. see with specialists of the instrument like Alessandro, Martino, Alain...) ?
11. Continue observations of many calibrators to monitor our sensitivity and photometry.
12. Continue tests on polarization mode: beam maps, various scan speed and sampling frequencies.
13. Depending on the completion of previous items, in particular characterization of pointing and optimal focus stability, and KIDs optimization and stability, do a deep integration on a sub mJy source for several hours (~10), to check stability of sensitivity (rms vs sqrt(time)).
14. Depending on the completion of previous items, go for more advanced characterizations, and mapping extended features (test various map making strategies in analysis software [Pipeline, scanamorphos, etc.]).

15. Consider NGC891 to make a show case for NIKA2, in particular for the polarization mode (edge on galaxy → ~5% dust polar expected...)

(*) Status of beams characterization from previous runs:

• At 2mm the dichroic deformation is dominant, besides the array (CPW + bondings design) is visibly more unstable than 1mm arrays (micro strip design).
• On all bands there is an asymmetry on beams pedestal, which is also visible on lab measures, indicating a possible optics problem in the cryostat, though simulations can't re-create it without more destructive effects so far. Need deeper analysis of lab measures vs beams at telescope. If we don; t solve this in the coming weeks, we have to consider shipping the sky simulator and adaptator lens to Pico Veleta for the next run to make maps of the fake planet in order to distinguish optics problem from the cryostat internal elements versus external elements.
• On all bands the 1st side lobe is at 10% level of the peak against 2% predicted per pure diffraction plus elliptic side lobes. Optics simulations show various possibilities to create such effects. Two of them seem realistic and at least partially recognised: non-optimal XYZ focus, and telescope astigmatism due to high order deformations terms not compensated by the homology structure of the parabola. From holography measurements and beam efficiency obtained with heterodyne instruments (which have 14dB edge taper and thus reduce significantly this effect), simulations show that telescope astigmatism is a significant component. Is it all of it ? We are tempted to think NIKA2 suffer from another additional component distorting its beams, but to investigate this we need beam maps at optimal XYZ focus, at various elevation and various period of the day; the stable weather low opacity mid night optimal conditions being the most important one.

The detailed characterization plan established for run 1 is still valid, but needs to be updated; you can still look at it to check possible missing action items: http://www.iram.fr/wiki/nika2/index.php/NIKA2_Run1_30m_CharacterizationPlan
A more concise version, including a status summary will be written ... when I find time for this... (SL).

Preparation of the run

Telescope Schedule week 1 Telescope Schedule weeks 2

Staff of the run: table of the nights spent at the observatory for the NIKA2 collaboration members participating to the run (T means Tuesday, S means Saturday, first night with NIKA2 staff is Tuesday 29 September, last night is Monday 9 November, 1 stands for night scheduled at the telescope, p stands for possible extension in case of problem with the cryostat).

AOD: A.Sievers/P.Garcia on week 1; F.Damour/J.L.Santaren (operators) on week 2. Astronomer on Duty