NIKA2 Run 6 Offline processing results
This private page is dedicated to results we get from a closer look to the raw data :
Calibrated Kidpar from the beammap 20161010s19 from the previous run
Using the beam map 20161010s19 (Uranus) from the the previous run (same configuration as the one we have now) we get the following KID positions after 2 iterations:
We use the skydip scan 20161026s115 of this run as it displays really good fits and the ratio tau_2mm/tau_1mm is around 0.65 as expected given the NIKA2 bandwidths. Therefore, the second iteration of the beammap processing takes into account opacity corrections which allows us to compute the KIDs calibration coefficients. The second step of the calibration coefficient computation consist in using the Kidpar and process several Uranus beammaps to get different measurements of its flux. We can then rescale the KID calibration coefficients so than the mean of the flux measurement distribution matches the expected Uranus fluxes at 1 and 2 mm. We use the beammaps 20161010s19, 20161010s37, 20161026s113, 20161026s114 as those are the only one we have on Uranus for this configuration. We get the following results:
Ones the calibration coefficients are rescaled we can test this new Kidpar (kidpar_20161010s19_v2_FR_rescale_calib.fits) other sources to see if the measured fluxes matches the ones we expect. Using the beammaps we have on Neptune (20161026s80, 20161026s82) we get the following results:
We see that the measured fluxes (~17 Jy at 1 mm and ~7 Jy at 2 mm) are consistent with the expected fluxes of 16.54 and 6.93 Jy at 1 and 2 mm respectively. Therefore, the calibration coefficients seems correct to estimate the fluxes of the planets. We now test the calibration coefficients on a quasar. Using 2 beammaps on 3C84 (20161027s31, 20161027s32) and this new Kidpar, we get the following results:
Eventually, we consider weaker sources to test the calibration. Flux measurements on CRL618 using the scans 20161028s54 and 20161028s55:
Flux measurements on Vesta using the scans 20161028s62 and 20161028s63:
FoV distortion from run5
Skydip analysis
FXD: Following the multi-scan analysis [http://www.iram.fr/wiki/nika2/index.php/April_12th,_2016,_FXD,_a_multi-scan_method_to_analyse_skydip_measurements], here are the figures for the 2 skydips of the 10th October 2016
The plot shows that we recover the expected ratio of 0.65 between the opacity at 2mm and 1.2mm.
The other plot displays (on the right) the extended source sensitivity (established with the 2 skydips) vs. the PS sensitivity (established on Uranus). Note that the correlation is linear and goes through zero for the 2mm array whereas the 1mm arrays (blue and yellow) show a (too) wide range of PS sensitivities. This issue has been raised several times now.
Here is the update with 8 skydips taken during this run 6 only. The ratio of tau2mm/tau1mm is 0.61. The two opacities (at 1 and 2mm) follow each other accurately. The 225GHz taumeter shows more fluctuations but is still a good quick indicator of the atmosphere. New kidpar with updated c0 and C1 can be found on svn: Kidpars/kidpar_20161010s37_v3_skd8_match_calib_NP_recal.fits
Map-making test on Orion KL: impact of an inaccurate intercalibration of the detectors
Orion KL was observed on 20161028 (scans 58 and 59) through high opacity (~0.6 to 0.7).
The data were reduced up to "level 1" (i.e. flux calibration and opacity correction) with the pipeline, using the most up-to-date kidpar (kidpar_20161010s37_v3_skd_match_calib_NP_recal.fits), and then up to "level 2" (i.e. atmosphere and noise subtraction, and projection) with scanam_nika (adapted from Scanamorphos for Herschel).
Two versions were produced: the first with the default point-source calibration (left panel in the plots below), and the second with a first-order extended-source calibration (right panel in the plots), that does not change the global response of the combined arrays 1 and 3 at 1mm nor the global response of array 2 at 2mm, but that changes the relative responses of the individual detectors. Ideally, the relative gains of the detectors should be derived from an analysis of all long scans of run 19, but for the time being they are derived only from the two Orion KL scans themselves.
The plots below show that: at 2mm, the two versions of the map are very similar ; but at 1mm, the second version is much better (less residual correlated noise, diffuse emission more faithfully restored) than the first. This is because errors on the multiplicative effects (responses of the detectors) have a large impact on the additive effects corrected afterwards (low-frequency noise subtraction).
HR, Oct. 29
result at 1mm (square root scale, high cut applied):
result at 2mm (square root scale, high cut applied):
Beam shape study using beammaps of this run
