HFI-bottom up

Like all experiments, Planck/HFI had a number of "issues" which it needed to track and verify were not compromising the data. While these are discussed in appropriate sections, here we gather them together to give brief summaries of the issues and refer the reader to the appropriate section for more details.

• Cosmic Rays - Unprotected by the atmosphere and more sensitive than previous bolometric experiment, HFI was subjected to many more cosmic ray hits than previous experiments. These were detected, the worst parts of the data flagged as unusable, and "tails" were modeled and removed. This is described in XXXXX
• Elephants - Cosmic rays also hit the 100 mK stage and cause the temperature to vary, inducing small temperature and thus noise variations in the detectors. This is described in XXXXX
• 1.6 K Stage Fluctuations
• 4 K Stage Fluctuations
• Popcorn Noise - Some channels were occasionally affected by what seems to be a "split-level" noise, which has been variously called popcorn noise or random telegraphic signal. These data are usually flagged. This is described in XXXXX
• Jumps - Similar to but distinct from popcorn noise, small jumps were occasionally found in the data streams. These data are usually corrected. This is described in XXXXX.
• 4 K Cooler-Induced EM Noise - The 4 K cooler induced noise in the detectors with very specific frequency signatures, which is filtered. This is described in XXXXX.
• 4 K Cooler-Induced Microphonics - The mechanical cooler was shown in XXXXX to cause very little microphonic parasites in the detector data.
• Pointing-Change Microphonics - The changes in pointing after each pointing period were shown in XXXXX to cause very little microphonic parasitic signal in the detector data.
• Compression - Onboard compression is used to overcome our telemetry bandwidth limitations. This is explained in XXXXX.
• Noise Correlations - Correlations in noise between detectors seems to be negligble but for two polarization sensitive detectors in the same horn. This is discussed in XXXXX.
• Electrical Cross-Talk - Cross-talk is discussed in XXXXX.

• Pointing - The final pointing reconstruction for Planck is near the arcsecond level. This is discussed in XXXXX.
• Focal Plane Geometry - The relative positions of different horns in the focal plane is reconstructed using planets. This is discussed in XXXXX.
• Main Beam - The main beams for HFI are discussed in XXXXX.
• Ruze Envelope - Random imperfections or dust on the mirrors can increase the size of the beam a bit. This is discussed in XXXXX.
• Dimpling - The mirror support structure causes a pattern of small imperfections in the beams, which cause small sidelobe responses outside the main beam. This is discussed in XXXXX.
• Far Sidelobes - Small amounts of light can sometimes hit the detectors from just above the primary or secondary mirrors, or even from reflecting off the baffles. While small, when the Galactic center is in the right position, this can be detected in the highest frequency channels, so this is removed from the data. This is discussed in XXXXX.
• Planet Fluxes - Comparing the known fluxes of planets with the calibration on the CMB dipole is a useful check of calibration. This is done in XXXXX.
• Point Source Fluxes - As with planet fluxes, we also compare fluxes of known, bright point sources with the CMB dipole calibration. This is done in XXXXX.

• Time Constants - The HFI bolometers do not react instantaneously to light; there are small time constants, discussed XXXXX.
• ADC Correction - The HFI Analog-to-Digital Converters are not perfect, and are not used perfectly. Their effects on the calibration are discussed in XXXXX.
• Gain changes with Temperature Changes
• Optical Cross-Talk - This is discussed in XXXXX.
• Bandpass - The transmission curves, or "bandpass" has shown up in a number of places. This is discussed in XXXXX and YYYYY.
• Saturation - While this is mostly an issue only for Jupiter observations, it should be remembered that the HFI detectors cannot observe arbitrarily bright objects. This is discussed in XXXXX.