A&A 520, A3 (2010)DOI: 10.1051/0004-6361/200912837c○ ESO 2010<strong>Pre</strong>-launch status of the <strong>Planck</strong> missionAstronomy&AstrophysicsSpecial feature<strong>Planck</strong> pre-launch status: The <strong>Planck</strong> -LFI programmeN. Mandolesi 1 ,M.Bersanelli 2 ,R.C.Butler 1 ,E.Artal 7 ,C.Baccigalupi 8,36,6 ,A.Balbi 5 ,A.J.Banday 9,40 ,R. B. Barreiro 17 ,M.Bartelmann 9 ,K.Bennett 27 ,P.Bhandari 10 ,A.Bonaldi 3 ,J.Borrill 38,39 ,M.Bremer 27 ,C.Burigana 1 ,R. C. Bowman 10 ,P.Cabella 5,46 ,C.Cantalupo 39 ,B.Cappellini 2 ,T.Courvoisier 11 ,G.Crone 12 ,F.Cuttaia 1 ,L.Danese 8 ,O. D’Arcangelo 13 ,R.D.Davies 14 ,R.J.Davis 14 ,L.DeAngelis 15 ,G.deGasperis 5 ,A.DeRosa 1 ,G.DeTroia 5 ,G. de Zotti 3 ,J.Dick 8 ,C.Dickinson 14 ,J.M.Diego 17 ,S.Donzelli 22,23 ,U.Dörl 9 ,X.Dupac 41 ,T.A.Enßlin 9 ,H. K. Eriksen 22,23 ,M.C.Falvella 15 ,F.Finelli 1,35 ,M.Frailis 6 ,E.Franceschi 1 ,T.Gaier 10 ,S.Galeotta 6 ,F.Gasparo 6 ,G. Giardino 27 ,F.Gomez 18 ,J.Gonzalez-Nuevo 8 ,K.M.Górski 10,42 ,A.Gregorio 16 ,A.Gruppuso 1 ,F.Hansen 22,23 ,R. Hell 9 ,D.Herranz 17 ,J.M.Herreros 18 ,S.Hildebrandt 18 ,W.Hovest 9 ,R.Hoyland 18 ,K.Huffenberger 44 ,M.Janssen 10 ,T. Jaffe 14 ,E.Keihänen 19 ,R.Keskitalo 19,34 ,T.Kisner 39 ,H.Kurki-Suonio 19,34 ,A.Lähteenmäki 20 ,C.R.Lawrence 10 ,S. M. Leach 8,36 ,J.P.Leahy 14 ,R.Leonardi 21 ,S.Levin 10 ,P.B.Lilje 22,23 ,M.López-Caniego 17,43 ,S.R.Lowe 14 ,P. M. Lubin 21 ,D.Maino 2 ,M.Malaspina 1 ,M.Maris 6 ,J.Marti-Canales 12 ,E.Martinez-Gonzalez 17 ,M.Massardi 3 ,S. Matarrese 4 ,F.Matthai 9 ,P.Meinhold 21 ,A.Melchiorri 46 ,L.Mendes 24 ,A.Mennella 2 ,G.Morgante 1 ,G.Morigi 1 ,N. Morisset 11 ,A.Moss 30 ,A.Nash 10 ,P.Natoli 5,37,45,1 ,R.Nesti 25 ,C.Paine 10 ,B.Partridge 26 ,F.Pasian 6 ,T.Passvogel 12 ,D. Pearson 10 ,L.Pérez-Cuevas 12 ,F.Perrotta 8 ,G.Polenta 45,46,47 ,L.A.Popa 28 ,T.Poutanen 34,19,20 ,G.<strong>Pre</strong>zeau 10 ,M. Prina 10 ,J.P.Rachen 9 ,R.Rebolo 18 ,M.Reinecke 9 ,S.Ricciardi 1,38,39 ,T.Riller 9 ,G.Rocha 10 ,N.Roddis 14 ,R. Rohlfs 11 ,J.A.Rubiño-Martin 18 ,E.Salerno 48 ,M.Sandri 1 ,D.Scott 30 ,M.Seiffert 10 ,J.Silk 31 ,A.Simonetto 13 ,G. F. Smoot 29,32 ,C.Sozzi 13 ,J.Sternberg 27 ,F.Stivoli 38,39 ,L.Stringhetti 1 ,J.Tauber 27 ,L.Terenzi 1 ,M.Tomasi 2 ,J. Tuovinen 33 ,M.Türler 11 ,L.Valenziano 1 ,J.Varis 33 ,P.Vielva 17 ,F.Villa 1 ,N.Vittorio 5,37 ,L.Wade 10 ,M.White 49 ,S. White 9 ,A.Wilkinson 14 ,A.Zacchei 6 ,andA.Zonca 2(Affiliations can be found after the references)Received 6 July 2009 / Accepted 27 October 2009ABSTRACTThis paper provides an overview of the Low Frequency Instrument (LFI) programme within the ESA <strong>Planck</strong> mission. The LFI instrument has beendeveloped to produce high precision maps of the microwave sky at frequencies in the range 27−77 GHz, below the peak of the cosmic microwavebackground (CMB) radiation spectrum. The scientific goals are described, ranging from fundamental cosmology to Galactic and extragalacticastrophysics. The instrument design and development are outlined, together with the model philosophy and testing strategy. The instrument ispresented in the context of the <strong>Planck</strong> mission. The LFI approach to ground and inflight calibration is described. We also describe the LFI groundsegment. We present the results of a number of tests demonstrating the capability of the LFI data processing centre (DPC) to properly reduceand analyse LFI flight data, from telemetry information to calibrated and cleaned time ordered data, sky maps at each frequency (in temperatureand polarization), component emission maps (CMB and diffuse foregrounds), catalogs for various classes of sources (the Early Release CompactSource Catalogue and the Final Compact Source Catalogue). The organization of the LFI consortium is briefly presented as well as the role of thecore team in data analysis and scientific exploitation. All tests carried out on the LFI flight model demonstrate the excellent performance of theinstrument and its various subunits. The data analysis pipeline has been tested and its main steps verified. In the first three months after launch,the commissioning, calibration, performance, and verification phases will be completed, after which <strong>Planck</strong> will begin its operational life, in whichLFI will have an integral part.Key words. cosmic microwave background – space vehicles: instruments – instrumentation: detectors – instrumentation: polarimeters –submillimeter: general – telescopes1. IntroductionIn 1992, the COsmic Background Explorer (COBE) team announcedthe discovery of intrinsic temperature fluctuationsin the cosmic microwave background radiation (CMB; seeAppendix A for a list of the acronyms appearing in this paper)on angular scales greater than 7 ◦ and at a level of afew tens of µK (Smoot et al. 1992). One year later twospaceborne CMB experiments were proposed to the EuropeanSpace Agency (ESA) in the framework of the Horizon2000 scientific programme: the COsmic Background RadiationAnisotropy Satellite (COBRAS; Mandolesi et al. 1994), an arrayof receivers based on high electron mobility transistor(HEMT) amplifiers; and the SAtellite for Measurement ofBackground Anisotropies (SAMBA), an array of detectors basedon bolometers (Tauber et al. 1994). The two proposals wereaccepted for an assessment study with the recommendationto merge. In 1996, ESA selected a combined mission calledCOBRAS/SAMBA, subsequently renamed <strong>Planck</strong>, asthethirdArticle published by EDP Sciences Page 1 of 24
A&A 520, A3 (2010)Horizon 2000 medium-sized mission. Today <strong>Planck</strong> forms partof the “Horizon 2000” ESA programme.The <strong>Planck</strong> CMB anisotropy probe 1 , the first Europeanand third generation mission after COBE and WMAP(Wilkinson Microwave Anisotropy Probe), represents the stateof-the-artin precision cosmology today (Tauber et al. 2010;Bersanelli et al. 2010; Lamarre et al. 2010). The <strong>Planck</strong> payload(telescope instrument and cooling chain) is a single, highly integratedspaceborne CMB experiment. <strong>Planck</strong> is equipped witha1.5-m effective aperture telescope with two actively-cooled instrumentsthat will scan the sky in nine frequency channels from30 GHz to 857 GHz: the Low Frequency Instrument (LFI) operatingat 20 K with pseudo-correlation radiometers, and the HighFrequency Instrument (HFI; Lamarre et al. 2010) withbolometersoperating at 100 mK. Each instrument has a specific role inthe programme. The present paper describes the principal goalsof LFI, its instrument characteristics and programme. The coordinateduse of the two different instrument technologies andanalyses of their output data will allow optimal control and suppressionof systematic effects, including discrimination of astrophysicalsources. All the LFI channels and four of the HFI channelswill be sensitive to the linear polarisation of the CMB.While HFI is more sensitive and should achieve higher angularresolution, the combination of the two instruments is required toaccurately subtract Galactic emission, thereby allowing a reconstructionof the primordial CMB anisotropies to high precision.LFI (see Bersanelli et al. 2010, formoredetails)consistsofan array of 11 corrugated horns feeding 22 polarisation-sensitive(see Leahy et al. 2010, formoredetails)pseudo-correlationradiometersbased on HEMT transistors and MMIC technology,which are actively cooled to 20 K by a new concept sorptioncooler specifically designed to deliver high efficiency, long durationcooling power (Wade et al. 2000; Bhandari et al. 2004;Morgante et al. 2009). A differential scheme for the radiometersis adopted in which the signal from the sky is compared withastablereferenceloadat∼4 K(Valenziano et al. 2009). Theradiometers cover three frequency bands centred on 30 GHz,44 GHz, and 70 GHz. The design of the radiometers was drivenby the need to minimize the introduction of systematic errorsand suppress noise fluctuations generated in the amplifiers.Originally, LFI was to include seventeen 100 GHz horns with34 high sensitivity radiometers. This system, which could havegranted redundancy and cross-calibration with HFI as well asacross-checkofsystematics,wasnotimplemented.The design of the horns is optimized to produce beams of thehighest resolution in the sky and the lowest side lobes. TypicalLFI main beams have full width half maximum (FWHM) resolutionsof about 33 ′ ,27 ′ ,and13 ′ ,respectivelyat30GHz,44 GHz, and 70 GHz, slightly superior to the requirements listedin Table 1 for the cosmologically oriented 70 GHz channel.The beams are approximately elliptical with and ellipticity ratio(i.e., major/minor axis) of ≃1.15−1.40. The beam profiles will bemeasured in-flight by observing planets and strong radio sources(Burigana et al. 2001).AsummaryoftheLFIperformancerequirementsadoptedtohelp develop the instrument design is reported in Table 1.1 <strong>Planck</strong> (http://www.esa.int/<strong>Planck</strong>) is a project of theEuropean Space Agency – ESA – with instruments provided by two scientificConsortia funded by ESA member states (in particular the leadcountries: France and Italy) with contributions from NASA (USA), andtelescope reflectors provided in a collaboration between ESA and a scientificConsortium led and funded by Denmark.Table 1. LFI performance requirements.Frequency channel 30 GHz 44 GHz 70 GHzInP detector technology MIC MIC MMICAngular resolution [arcmin] 33 24 14δT per 30 ′ pixel [µK] 8 8 8δT/T per pixel [µK/K] 2.67 3.67 6.29Number of radiometers (or feeds) 4 (2) 6 (3) 12 (6)Effective bandwidth [GHz] 6 8.8 14System noise temperature [K] 10.7 16.6 29.2White noise per channel [µK · √s] 116 113 105Systematic effects [µK]
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