ANALYSIS AND CHARACTERIZATION OF SYSTEMATIC EFFECTS RELATED TO THE STUDY OF COSMIC MICROWAVE BACKGROUND ANISOTROPIES WITH THE PLANCK LFI INSTRUMENT

2013/2014Il satellite Planck è il diretto successore europeo del satellite americano WMAP. Planck è lo strumento di terza generazione per lo studio del CMB dallo spazio ed è composto da una matrice di 74 ricevitori suddivisi in due strumenti, Low Frequency Instrument (LFI) e High Frequency Instrument (HFI), che osserva il cielo in nove frequenze nell'intervallo tra i 30 GHz ed 857 GHz. Tutti i ricevitori osservano il cielo contemporaneamente e continuamente con una risoluzione angolare che va dai ~30 arcominuti, alla frequenza più bassa, ai ~5 arcominuti, alla frequenza più alta, ed una sensibilità dell'odine di ~10^(-6). Planck è stato lanciato nel Maggio del 2009 e, prima del suo completo spegnimento nell'Ottobre del 2013, lo strumento LFI ha continuamente e stabilmente osservato il cielo per 1513 giorni operativi (OD), che corrispondono a otto complete mappe del cielo. I dati di Planck rilasciati nel 2013 includono le mappe di temperatura del CMB basate sul periodo nominale della missione, che copre gli OD dal 91 al 563. Questa tesi presenta la caratterizzazione degli effetti sistematici di LFI effettuata per i dati di Planck rilasciati nel 2013, con una particolare attenzione all'effetto spikes a 1 Hz. Dall'analisi effettuata, tutti gli effetti sistematici conoscuti di LFI risultano sotto controllo e il loro contributo nello spettro di potenza delle mappe di temperatura del cielo prodotte è sensibilmente inferiore al segnale delle anisotropie del CMB. Dai null test effettuati risulta inoltre che tutti gli effetti sono propriamente corretti. nell'analisi dei dati e che non è presente alcun indizio di ulteriori sistematici sconosciuti. L'effetto delle spikes a 1 Hz è causato da una inattesa interferenza tra le linee di acquisizione dei dati scientifici e quelle dell'housekeeping, che avviene nell'elettronica di lettura di LFI. Questo effetto, individuato per la prima volta durante i test a terra dello strumento, si manifesta come un'onda quadra alla frequenza di 1 Hz che si sovrappone alle tensioni in uscita da tutti i ricevitori di LFI. I ricevitori che più risentono di questo effetto sono quelli a 44 GHz. La tecnica di rimozione di questo disturbo nell'analisi dei dati effettuata per i dati di Planck rilasciati nel 2013 consiste nel sottrarre un template di onda quadra dalle tensioni prodotte dai ricevitori. Tra le diverse tecniche utilizzate per la costruzione del template descritte nella tesi, quella del template filtrato utilizzata nei dati del 2013 risulta essere la più efficiente. Nei canali a 44 GHz dove la rimozione è implementata, il contributo delle spikes nello spettro di potenza delle mappe di LFI è ridotto di due ordini di grandezza, sia in temperatura che in polarizzazione. L'utilizzo di un unico template da sottrarre per l'intera missione per ogni segnale misurato, cielo e riferimento per ogni ricevitore, è giustificato dall'estrema stabilità del template sia in fase che in ampiezza nell'arco di tutta la missione. Dopo la correzione dei dati, la stima del residuo del segnale di spikes nelle mappe dovuto a piccole fluttuazioni dell'ampiezza del template nel corso della missione permette di concludere che l'effetto delle spikes a 1 Hz di LFI è totalmente sotto controllo. Siccome il contributo del segnale di spikes nei canali a 30 GHz e 70 GHz è molto piccolo e siccome il template a queste frequenze sembra non essere molto stabile in ampiezza, la possibilità di rimuovere le spikes anche da questi canali è ancora in fase di studio. In particolare, è importante controllare la possibile introduzione di artefatti nei dati come risultato del processo di rimozione. Avendo a disposizione i dati di tutta la missione, nella tesi si è inoltre studiata la possibilità di aumentare la risoluzione dei template, con lo scopo di investigare la possibilità di ottenere dei template più stabili da utilizzare per i canali a 30 GHz e 70 GHz. I template ad alta risoluzione danno dei risultati identici ai template filtrati nei canali a 44 GHz, mentre nei canali a 30 Ghz e 70 GHz, nonostante la stabilità sia migliore, i template sono ancora dominati dal rumore. Nonostante questo, la produzione dei template ad alta risoluzione ha permesso di verificare la stabilità dello strumento fino a risoluzioni di 1/2^(16) s. Inoltre è stato possibile tracciare in dettaglio il comportamento dello strumento LFI sull'intera missione, osservando variazioni del template delle spikes ben al disotto della risoluzione utilizzata per la rimozione delle spikes dai dati di Planck rilasciati nel 2013. Questi nuovi template hanno idividuato 5 OD in tutta la missione dove lo strumento presenta un comportamento peculiare. In tutti questi casi si è scoperto che le variazioni osservate sono legate ad operazioni note effettuate sullo strumento. Da un confronto diretto dei template per i canali a 44 GHz, non si osservano cambiamenti incrementandone la risoluzione. L'effetto finale sulle mappe e sulla stima dei parametri cosmologici è ancora in fase di studio. Al momento non si rende necessario modificare i template utilizzati nella release di Planck del 2013 per la quella del 2014. L'analisi sull'effetto della rimozione dei template ad alta risoluzione dai canali dei 30 GHz e 70 GHz ed il loro possibile utilizzo in release future è ancora in corso.The Planck satellite is the European direct successor of the American WMAP satellite. Planck is the 3rd generation instrument for the CMB study from space. It consists in an array of 74 detectors divided into two instruments, Low Frequency Instrument (LFI) and High Frequency Instrument (HFI) scanning the sky with nine frequencies in the range 30 GHz to 857 GHz. All the detectors observe simultaneously and continuously the sky with an angular resolution varying between ~30 arcmin at the lowest frequencies, and ~5 arcmin, at the highest, and a resolution of the order of ~10^(-6). Planck was lauched in may 2009 and, before the compete switch off in October 2013, the LFI instrument has stably and continuously observed the sky for 1513 operational days (OD), corresponding to eight complete sky surveys. The 2013 Planck data release includes the CMB temperature maps based on the nominal period of the mission, covering the OD from 91 to 563. This thesis describes the characterization of the systematic effects of LFI realized for the 2013 Planck data release, with a particular focus on the 1 Hz spikes effect. From the analysis performed, all the known LFI systematic effects result to be under control and their contribution in the temperature power spectrum is well below the CMB anisotropies signal. From the null tests it is possible to conclude that all the systematic effects are properly corrected in the data analysis and there are no evidence of new unknown systematic effects The 1 Hz spikes effect is due to an unexpected cross-talk between the scientific acquisition and the housekeeping data lines in the LFI read out electronics. It appears as a square wave with 1 Hz frequency signal, added to the output voltages of all the LFI detectors. The channels where this effect is more prominent are the 44 GHz. The spikes removal technique used in the 2013 Planck data release consist in subtracting from data an estimated spikes template. Among the different methods used in the estimation of the spikes template, the filtered template used in the 2013 Planck data release is the more effective. In the 44 GHz channels, where the spikes are corrected in the data, the final contribution on LFI maps power spectra is reduced by two orders of magnitude both in temperature and polarization. Using a unique template for every signal (sky and reference) for each detector to be subtracted from data among the whole mission is justified by the extreme stability of the template, both in amplitude and phase through all the mission. After correcting for the spikes systematic effect, the estimate of the residual spikes signal in maps due to small amplitude fluctuation of the template during the mission allows to conclude that the spikes effect in the LFI maps is completely understood. Since the spikes signal in the 30 GHz and 70 GHz channels is very small, and since the template seems not to be very stable in these frequencies, the possibility of removing spikes even in these channels is still under evaluation. In particular, it is very important to assess the possible introduction of artifacts for these unstable templates as a result of the spikes removal process. By using ll the mission data, in the thesis, it has been studied the possibility to increase the resolution of the templates used in the spikes removal process by producing high resolution templates aimed to better investigate the instabilities in the 30 GHz and 70 GHz templates. In the 44 GHz, the high resolution template give results identical to the filtered template while in the other frequencies, even if the resulting template is more stable, the templates are still dominated by noise. In addition, the high resolution template production allowed to verify the instrument stability up to the resolution of 1/2^(16) s. Moreover it was possible to track the LFI behaviour over all the mission, checking for variations in the spikes template well below the resolution of the 2013 Planck data release templates. This new templates identified 5 OD over the whole mission where the instrument has a variation from its stable behaviour. It has been discovered that all these variations are directly related to major operations performed on the instrument. From a direct comparison between the templates, for the 44 GHz channels, there is no change in the increase of the resolution. The final contribution on LFI maps and the final contribution in the estimate of the cosmological parameters is still under investigation. At the moment it seems not necessary to modify the templates used in the 2013 Planck data release for the 2014 data release. The possibility to introduce the the high resolution spikes template removal in the future Planck data releases is still under investigation.XXVI Ciclo198

Operational challenges for astronomical instrumentation in Antarctica: results from five years of environmental monitoring of AMICA at Dome C

The Antarctic Plateau is one of the best observing sites on Earth, especially for infrared astronomy. The extremely low temperatures (down to -80°C), the low pressure (around 650 mbar) and the very dry atmosphere (PWV less than 1 mm) allow for a very clear and dark sky, as well as for a very low instrumental background. These unique properties, however, make it also very difficult to install and operate astronomical instrumentation. AMICA (Antarctic Multiband Infrared CAmera) is an instrument especially designed for Antarctic operation, whose installation at Dome C has been completed in 2013. Since then it has been continuously working over the last five years, monitoring and controlling in particular the environmental and operating conditions through a dedicated application, its Environmental Control System (ECS). The recorded behavior of AMICA highlighted a set of peculiar aspects of the site that are hard to consider a priori. Although mechanical and electronic COTS components can reliably work in thermally insulated and controlled boxes, simple insulation causes their overheating because of the air dryness and rarefaction which make the heat transfer extremely inefficient. Heat removal is also a real problem when managing heavy-duty devices like cryocoolers, whose excess power removal needs to be fast and efficient. Finally, the lack of an electrical ground generates a wide variety of transient electrical and electromagnetic phenomena which often make electronic instrumentation very unstable. A list of new recommendations is therefore presented, as a guideline for future astronomical instruments operating in Antarctica

The importance of band pass and frequency dependent beam modelling in CMB experiment, lessons learned from Planck/LFI

The high level of accuracy required by recent CMB experiments can be obtained accounting for very tiny effects while calibrating them. Among those effect it must be considered the fact that the cosmological dipole, usually used as primary calibrator, must be convolved with the full-sky beam pattern of the instrument and averaged over its bandpass. This is in particular true for a multi horn instrument as Planck/LFI. In this communication we discuss this problem, common to all the CMB missions, in the light of the experience gained on the Planck/LFI instrument. <P /

In-flight calibration and verification of the Planck-LFI instrument

In this paper we discuss the Planck-LFI in-flight calibration campaign. After a brief overview of the ground test campaigns, we describe in detail the calibration and performance verification (CPV) phase, carried out in space during and just after the cool-down of LFI. We discuss in detail the functionality verification, the tuning of the front-end and warm electronics, the preliminary performance assessment and the thermal susceptibility tests. The logic, sequence, goals and results of the in-flight tests are discussed. All the calibration activities were successfully carried out and the instrument response was comparable to the one observed on ground. For some channels the in-flight tuning activity allowed us to improve significantly the noise performance.Comment: Long technical paper on Planck LFI in flight calibration campaign: 109 pages in this (not final) version, 100 page in the final JINST versio

Planck-LFI commissioning: LFI from OFF to DAE setup

Planck-LFI commissioningSwitch On the LFI and verify the functionalities of the LFI REBA and DAE. The LFI is switched on in two steps: first LFI Comm-1 (LFI goes to Stand-by mode); then LFI Comm-2 (LFI goes to DAE Set-up mode)

Planck-LFI CPV: 1 Hz frequency spikes

Planck LFI Commissioning and Performance Verification (CPV)Spurious frequency spikes at the fundamental frequency of 1 Hz are known to be present in the LFI scientific data caused by an anomalous interaction between the DAE housekeeping sequencer and the scientific channels. The effect is a spurious signal that adds to the radiometric output after detection and is characterized by frequency spikes at the fundamental frequency of 1 Hz. These spikes are characterized by a series of tests run during all the test campaign in order to check this effect in different situations. Tests performed on ground at satellite level have shown that the effect of these spikes on the LFI science is expected to be very small; therefore the main objectives of the same tests performed during CPV is to compare results with those obtained during the CSL test campaign

Planck-LFI In-Orbit Calibration and Verification Phase Report: Executive Summary

Planck LFI Commissioning and Performance Verification (CPV)This document summarises the results obtained during the commissioning tests performed on the LFI integrated on the Planck satellite. Tests have been conducted from June the 4th 2009 to June 26th 2009. Details of the performed activities are discussed in specific reports that will be available after the CPV

Planck-LFI CPV: stability check before bias tuning

Planck LFI Commissioning and Performance Verification (CPV)This test consists of a 12-hours data acquisition performed with the instrument set with “CRYO” biases, i.e. the biases that have been obtained in CSL after the tuning activities. The objective of this test is to verify the readiness of the instrument for the CPV bias tuning activity from the signal stability point of view. As during this test the 4K temperature was still around 20 K and the stability was not optimized yet the check on knee frequency is meaningful just from the functionality point of view. No comparison is done between the calculated knee frequencies and the LFI scientific requirements

Planck-LFI CPV: Phase Switch tuning and verification

Planck LFI Commissioning and Performance Verification (CPV)This document describes the activities performed during the first phase switch (PSW) tuning and verification test performed during CPV. The objective of this test, composed of two steps, is to find the optimal bias currents to the front-end phase switches that balance the wave amplitude in the two-phase switch states. An optimal balance has an impact on the receiver isolation, therefore the first part of the test (P_PVP_LFI_0004_01, namely tuning) was performed before the tuning of the front-end modules amplifiers. The second part (P_PVP_LFI_0004_02, namely verification) was performed after the tuning of the front-end modules to verify the impact on phase switch balancing of different amplifiers biases. The test was performed only on 30 and 44GHz RCAs as planned

Planck-LFI CPV: noise properties verification

Planck LFI Commissioning and Performance Verification (CPV)The assessment of the noise properties of the LFI instrument is the main objective of this test. The test is split into two parts. In the first part, the LFI is run unswitched acquiring data in all four phase switch configurations. Power spectra from unswitched data is compared in order to assess whether there is any configuration that is preferable from the point of 1/f noise slope. In the second part, the LFI is run switched for several hours and the full noise properties are characterised in both switching configurations (A/C or B/D) while the non-switching phase switch is kept in its nominal position