1,335 research outputs found
Full Sky Study of Diffuse Galactic Emission at Decimeter Wavelengths
A detailed knowledge of the Galactic radio continuum is of high interest for
studies of the dynamics and structure of the Galaxy as well as for the problem
of foreground removal in Cosmic Microwave Background measurements. In this work
we present a full-sky study of the diffuse Galactic emission at frequencies of
few GHz, where synchrotron radiation is by far the dominant component. We
perform a detailed combined analysis of the extended surveys at 408, 1420 and
2326 MHz (by Haslam et al. 1982, Reich 1982, Reich & Reich, 1986 and Jonas et
al. 1998, respectively). Using the technique applied by Schlegel et al. (1998)
to the IRAS data, we produce destriped versions of the three maps. This allows
us to construct a nearly-full-sky map of the spectral index and of the
normalization factor with sub-degree angular resolution. The resulting
distribution of the spectral indices has an average of beta = 2.695 and
dispersion sigma_{beta} = 0.120. This is representative for the Galactic
diffuse synchrotron emission, with only minor effects from free-free emission
and point sources.Comment: 10 pages, 16 jpeg figures, accepted to Astronomy & Astrophysics,
Comments and figure adde
The Planck Low Frequency Instrument
The Low Frequency Instrument (LFI) of the "Planck Surveyor" ESA mission will
perform high-resolution imaging of the Cosmic Microwave Background anisotropies
at four frequencies in the 30-100 GHz range. We review the LFI main scientific
objectives, the current status of the instrument design and the on-going effort
to develop software simulations of the LFI observations. In particular we
discuss the design status of the PLANCK telescope, which is critical for
reaching adequate effective angular resolution.Comment: 10 pages, Latex (use epsfig.sty); 4 Postscript figures; Astrophys.
Lett & Comm, in press. Proc. of the Conference: "The Cosmic Microwave
Background and the Planck Mission", Santander, Spain, 22-25 June 199
Planck early results. III. First assessment of the Low Frequency Instrument in-flight performance
Planck Low Frequency Instrument: Beam Patterns
The Low Frequency Instrument on board the ESA Planck satellite is coupled to
the Planck 1.5 meter off-axis dual reflector telescope by an array of 27
corrugated feed horns operating at 30, 44, 70, and 100 GHz. We briefly present
here a detailed study of the optical interface devoted to optimize the angular
resolution (10 arcmin at 100 GHz as a goal) and at the same time to minimize
all the systematics coming from the sidelobes of the radiation pattern. Through
optical simulations, we provide shapes, locations on the sky, angular
resolutions, and polarization properties of each beam.Comment: On behalf of the Planck collaboration. 3 pages, 1 figure. Article
published in the Proceedings of the 2K1BC Experimental Cosmology at
millimetre wavelength
Advanced modelling of the Planck-LFI radiometers
The Low Frequency Instrument (LFI) is a radiometer array covering the 30-70
GHz spectral range on-board the ESA Planck satellite, launched on May 14th,
2009 to observe the cosmic microwave background (CMB) with unprecedented
precision. In this paper we describe the development and validation of a
software model of the LFI pseudo-correlation receivers which enables to
reproduce and predict all the main system parameters of interest as measured at
each of the 44 LFI detectors. These include system total gain, noise
temperature, band-pass response, non-linear response. The LFI Advanced RF Model
(LARFM) has been constructed by using commercial software tools and data of
each radiometer component as measured at single unit level. The LARFM has been
successfully used to reproduce the LFI behavior observed during the LFI
ground-test campaign. The model is an essential element in the database of LFI
data processing center and will be available for any detailed study of
radiometer behaviour during the survey.Comment: 21 pages, 15 figures, this paper is part of the Prelaunch status LFI
papers published on JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/jins
Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument
We give a description of the design, construction and testing of the 30 and
44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the
Planck mission to be launched in 2009. The scientific requirements of the
mission determine the performance parameters to be met by the FEMs, including
their linear polarization characteristics.
The FEM design is that of a differential pseudo-correlation radiometer in
which the signal from the sky is compared with a 4-K blackbody load. The Low
Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High
Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel
phase-switch design which gives excellent amplitude and phase match across the
band.
The noise temperature requirements are met within the measurement errors at
the two frequencies. For the most sensitive LNAs, the noise temperature at the
band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively.
For some of the FEMs, the noise temperature is still falling as the ambient
temperature is reduced to 20 K. Stability tests of the FEMs, including a
measurement of the 1/f knee frequency, also meet mission requirements.
The 30 and 44 GHz FEMs have met or bettered the mission requirements in all
critical aspects. The most sensitive LNAs have reached new limits of noise
temperature for HEMTs at their band centres. The FEMs have well-defined linear
polarization characteristcs.Comment: 39 pages, 33 figures (33 EPS files), 12 tables. Planck LFI technical
papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths
We report on the design, fabrication and testing of a set of high performance
corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced
prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission.
The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70
GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and
by electro-formation at higher frequencies. The measured performances on side
lobes and return loss meet the stringent Planck requirements over the large
(20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape
and side lobes levels of the dual profiled designs has been demonstrated.Comment: 16 pages, 7 figures, accepted for publication in Experimental
Astronom
Dynamic validation of the Planck/LFI thermal model
The Low Frequency Instrument (LFI) is an array of cryogenically cooled
radiometers on board the Planck satellite, designed to measure the temperature
and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44
and 70 GHz. The thermal requirements of the LFI, and in particular the
stringent limits to acceptable thermal fluctuations in the 20 K focal plane,
are a critical element to achieve the instrument scientific performance.
Thermal tests were carried out as part of the on-ground calibration campaign at
various stages of instrument integration. In this paper we describe the results
and analysis of the tests on the LFI flight model (FM) performed at Thales
Laboratories in Milan (Italy) during 2006, with the purpose of experimentally
sampling the thermal transfer functions and consequently validating the
numerical thermal model describing the dynamic response of the LFI focal plane.
This model has been used extensively to assess the ability of LFI to achieve
its scientific goals: its validation is therefore extremely important in the
context of the Planck mission. Our analysis shows that the measured thermal
properties of the instrument show a thermal damping level better than
predicted, therefore further reducing the expected systematic effect induced in
the LFI maps. We then propose an explanation of the increased damping in terms
of non-ideal thermal contacts.Comment: Planck LFI technical papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
Imaging the first light: experimental challenges and future perspectives in the observation of the Cosmic Microwave Background Anisotropy
Measurements of the cosmic microwave background (CMB) allow high precision
observation of the Last Scattering Surface at redshift 1100. After the
success of the NASA satellite COBE, that in 1992 provided the first detection
of the CMB anisotropy, results from many ground-based and balloon-borne
experiments have showed a remarkable consistency between different results and
provided quantitative estimates of fundamental cosmological properties. During
2003 the team of the NASA WMAP satellite has released the first improved
full-sky maps of the CMB since COBE, leading to a deeper insight into the
origin and evolution of the Universe. The ESA satellite Planck, scheduled for
launch in 2007, is designed to provide the ultimate measurement of the CMB
temperature anisotropy over the full sky, with an accuracy that will be limited
only by astrophysical foregrounds, and robust detection of polarisation
anisotropy. In this paper we review the experimental challenges in high
precision CMB experiments and discuss the future perspectives opened by second
and third generation space missions like WMAP and Planck.Comment: To be published in "Recent Research Developments in Astronomy &
Astrophysics Astrophysiscs" - Vol I
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