====== Beams and C(l) ======

 --- //[[hivon@iap.fr|Eric Hivon]] 2018/07/16 09:09//

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=== 2018/07/16 ===
The beam computed at 150GHz, at a location offset by 10cm in the X (=co-scan) direction is now also available, on top of the central beam and Y=10cm beams generated earlier this month.\\
{{:systematicswg:maps_x10cm_feed_150ghz.png?direct&500}}

Two different effects are now visible on the power spectra:
  * an overall rotation of the polarization by 1.74 deg, showing up as a strong EE to BB leakage when the full IQU beam is used instead of assuming a copolar beam (something we did **not** see in the (X,Y)=(0,0) and (0,10cm) cases)
  * the ell-dependent leakage from EE to BB seen previously is now larger than before.

{{:systematicswg:w_qp_pico150_cxy_v1_picobeams.png?direct&500}}
{{:systematicswg:w_qp_pico150_cxy_pol_v1_picobeams.png?direct&500}}

=== 2018/07/13 ===
Same exercise as on July 02, this time considering a beam at 150GHz located 10cm in the Y (=cross-scan) direction from the focal plane center (in a focal plane of 45cm in diameter).\\
We see this time a much larger contamination of BB, which looks like an ell-increasing leakage from EE to BB, probably due to the m=4 components (=square-like shape) of the beam map.
As for the central beam, the pure copolar and full IQU beam models return the same power spectra.

{{:systematicswg:maps_y10cm_feed_150ghz.png?direct&500}}

{{:systematicswg:w_qp_pico150_cxy_v1_picobeams_old.png?direct&500}}

=== 2018/07/02 ===
First GRASP simulations by Karl Young of PICO main beam responses at 150GHz at the center of focal plane, for 2 orthogonal detectors.

The FWHMs were found to be ~4.9arcmin, the elongations (ratio of the major and minor axes) 1.01,
and the ratios of U/I about 1.e-4 for both beams, meaning that the beams are very much co-polar, with very little spurious rotation (~<0.5 arcmin).\\
{{:systematicswg:maps_center_feed_150ghz_crop.png?direct&500}}



The same exercise would have to be repeated at a more representative position (ie, off-axis) where systematics (=elongation of beam and rotation of polarization) could be larger.

The plot below shows how the various spectra are affected for either the purely copolar beam (ignoring the U beam component, green dashes) or the "full" beam (red dashes), as computed by [[mcsim_angles|QuickPol]] assuming a scanning strategy adapted from 
[[baseline | July 1st 2018 baseline]] (α=30º, T<sub>prec</sub>=10h, β=65º, T<sub>spin</sub>=1mn, sampling = 151Hz, 2 years of observation, N<sub>side</sub>=1024).

{{:systematicswg:w_qp_pico150_v1_picobeams.png?direct&500}}


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