Planck Pre-Launch Status Papers - APC - Université Paris Diderot ...

A&A 520, A12 (2010)Fig. 15. Composite projection of the focal plane on the sky, including allpredicted main beams. The third row from the top shows the previousmulti-mode channels beam simulations (545 and 857 GHz) which arebeing re-computed for better predictions (Murphy et al. 2010).Table 7. Telescope beam performances: from simulations assuming perfectoptical components.Detection Beam width Ellipticity Polarisation angleassembly (arcmin) on sky (deg) a&b100-1 a&b 9.6 0.14 22.5/−67.5100-2 a&b 9.6 0.14 45.0/−45.0100-3 a&b 9.6 0.14 0.0/−90.0100-4 a&b 9.6 0.14 −22.5/67.5143-1 a&b 7.0 0.12 45.1/−44.9143-2 a&b 7.0 0.07 45.0/−45.0143-3 a&b 7.0 0.07 0.0/−90.1143-4 a&b 7.0 0.12 −0.1/−90.2143-5&-8 7.2 0.07 Not polarised143-6&-7 7.1 0.05 Not polarised217-1&-4 5.0 0.14 Not polarised217-2&-3 4.8 0.12 Not polarised217-5 a&b 4.7 0.12 45.1/−44.9217-6 a&b 4.5 0.09 45.1/−45.0217-7 a&b 4.5 0.09 −0.1/−90.0217-8 a&b 4.7 0.12 −0.1/−90.1353-1&-8 4.6 0.2 Not polarised353-2&-7 4.5 0.1 Not polarised353-3 a&b 4.8 0.09 45.1/−44.9353-4 a&b 4.8 0.05 45.0/−45.0353-5 a&b 4.8 0.07 0.0/−90.0353-6 a&b 4.8 0.12 −0.1/−90.1Notes. Computations were performed at the central frequency of eachspectral band following Eqs. (4) and(5).All main beams are shown on the composite projection of thefocal plane on the sky given in Fig. 15 and a sub-set of co andcross-polarisation beam maps are given for each of the polarisedchannel in Figs. 16, 20, 21, and22. Thecolorscaleofthemaprepresents the gain, while the contours are given in dB respectivelyto the maximum (−1, −3, −5, −10, −15, −20, −25, −30,−40, −50 and −60 dB)Fig. 16. Top:co-polarisation;bottom: cross-polarisationmainbeamintensitymaps for the polarised detector 100-2a. Simulations performedusing ideal telescope and horns at the central frequency of 100 GHz.Color scale: gain. Contours in dB respectively to maximum.It is important to note that the cross-polarisation beams computedhere do not take into account the cross-polarisation of thefull detection assemblies which is dominated by the horn to PSBcoupling as mentioned in the previous section (few % typically).In the beam simulation only the polarisation effects of perfecthorns and mirrors (about −40 dB level) are taken into account.Similarly we have assumed perfectly aligned PSBs inthe focal plane. Measurements of the real polarisation angles(Rosset et al. 2010) showthattherearevariationsof0.4degupto 2 deg between theoretical and real angles in the focal planereference system.The pre-launch HFI main beam pattern predictions includingthe real mirrors (measured surfaces) and measured telescopealignment can be found in Tauber et al. (2010a). A limited numberof beam patterns on the sky were also computed using measuredhorn patterns. Since only the horn power patterns (but notthe phases) were measured, an algorithm combining the measuredpower with the theoretical (model) phases was developed.The term worst-case denotes the maximum discrepancy betweenthe ideal horn patterns and the measurements. These limited discrepanciesdo not affect the main beam region of the beam on thesky, but can have some influence on the spillover performance ofthe telescope.7.2. Beam width variation with frequencyTheoretical horn beam patterns computed for five frequencieswithin each spectral band (see for example Fig. 8 for thePage 12 of 15