63 research outputs found
Optical performance of the JWST MIRI flight model: characterization of the point spread function at high-resolution
The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard
the James Webb Space Telescope (JWST), providing imaging, coronagraphy and
spectroscopy over the 5-28 microns band. To verify the optical performance of
the instrument, extensive tests were performed at CEA on the flight model (FM)
of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the
infrared. This paper reports on the point spread function (PSF) measurements at
5.6 microns, the shortest operating wavelength for imaging. At 5.6 microns the
PSF is not Nyquist-sampled, so we use am original technique that combines a
microscanning measurement strategy with a deconvolution algorithm to obtain an
over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a
point source on the focal plane. A data inversion method is used to reconstruct
PSF images that are over-resolved by a factor of 7 compared to the native
resolution of MIRI. We show that the FWHM of the high-resolution PSFs were
5-10% wider than that obtained with Zemax simulations. The main cause was
identified as an out-of-specification tilt of the M4 mirror. After correction,
two additional test campaigns were carried out, and we show that the shape of
the PSF is conform to expectations. The FWHM of the PSFs are 0.18-0.20 arcsec,
in agreement with simulations. 56.1-59.2% of the total encircled energy
(normalized to a 5 arcsec radius) is contained within the first dark Airy ring,
over the whole field of view. At longer wavelengths (7.7-25.5 microns), this
percentage is 57-68%. MIRIM is thus compliant with the optical quality
requirements. This characterization of the MIRIM PSF, as well as the
deconvolution method presented here, are of particular importance, not only for
the verification of the optical quality and the MIRI calibration, but also for
scientific applications.Comment: 13 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium
Future cosmology space missions will concentrate on measuring the
polarization of the Cosmic Microwave Background, which potentially carries
invaluable information about the earliest phases of the evolution of our
universe. Such ambitious projects will ultimately be limited by the sensitivity
of the instrument and by the accuracy at which polarized foreground emission
from our own Galaxy can be subtracted out. We present the PILOT balloon project
which will aim at characterizing one of these foreground sources, the
polarization of the dust continuum emission in the diffuse interstellar medium.
The PILOT experiment will also constitute a test-bed for using multiplexed
bolometer arrays for polarization measurements. We present the results of
ground tests obtained just before the first flight of the instrument.Comment: 17 pages, 13 figures. Presented at SPIE, Millimeter, Submillimeter,
and Far-Infrared Detectors and Instrumentation for Astronomy VII. To be
published in Proc. SPIE volume 915
PLANCK-HFI : Performances of an optical concept for the cosmic microwave background anisotropies measurement
PLANCK is a project of the European Space Agency to be launched in February 2007 by an Ariane V rocket with the Herschel Space Observatory. It is designed for imaging the temperature and polarization anisotropies of the millimetre and sub-millimetre radiation over the whole sky with unprecedented sensitivity, accuracy and angular resolution using 9 frequency channels ranging between 25 and 1000 GHz. The main source at these frequencies is the Cosmic Microwave Background (CMB), i.e. the radiation emitted by the early universe when, about 300000 years old, ionised hydrogen recombined and became transparent from the visible to radio frequencies of the electromagnetic spectrum. The main goal of the PLANCK mission is to retrieve the main cosmological parameters of the Universe with accuracies of a few percent from the observation and analysis of random small contrast (10-4) features in the CMB. The angular power spectrum of the CMB anisotropies is a function of the fundamental cosmological parameters. A proper measurement of all the angular frequencies of the CMB is essential for an accurate interpretation of the data. In consequence the optical performances of Planck will directly impact the ability of retrieving theses parameters. Recent results of the Willkinson Microwave Anisotropy Probe (WMAP) mission show that polarization information of CMB radiation is very challenging, and that the precise measurement of the CMB could completely change the knowledge we have on our universe. The focal plane assembly (FPA) of the PLANCK telescope is composed of two instruments. The High Frequency Instrument (HFI) of PLANCK is the most sensitive CMB experiment ever planned. Together with the Low Frequency Instrument (LFI), this will make a unique tool to measure the full sky and to separate various components of its spectrum. This paper describes the main performances of the HFI beams and compares results obtained with 2 different softwares: GRASP8 and an home-made software developed at the Ireland National University of Maynooth. Specials attention will be paid to polarized beams (100, 143, 217, 353 GHz) and multimoded channels (545 and 857 GHz)
Planck pre-launch status: HFI beam expectations from the optical optimisation of the focal plane
Planck is a European Space Agency (ESA) satellite, launched in May 2009, which will map the cosmic microwave background anisotropies in intensity and polarisation with unprecedented detail and sensitivity. It will also provide full-sky maps of astrophysical foregrounds. An accurate knowledge of the telescope beam patterns is an essential element for a correct analysis of the acquired astrophysical data. We present a detailed description of the optical design of the High Frequency Instrument (HFI) together with some of the optical performances measured during the calibration campaigns. We report on the evolution of the knowledge of the pre-launch HFI beam patterns when coupled to ideal telescope elements, and on their significance for the HFI data analysis procedure
Planck-HFI focal plane concept
The future ESA space mission Planck Surveyor mission will measure the Cosmic Microwave Background temperature and polarisation anisotropies in a frequency domain comprised between 30GHz and 1THz. On board two instruments, LFI based on HEMT technology and HFI using bolometric detectors. We present the optical solutions adopted for this mission, in particular the focal plane design of HFI, concept which has been applied already to other instruments such as the balloon borne experiment Archeops
The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager
In this article, we describe the MIRI Imager module (MIRIM), which provides
broad-band imaging in the 5 - 27 microns wavelength range for the James Webb
Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed
view of 74"x113". The remainder of its nominal 113"x113" field is occupied by
the coronagraphs and the low resolution spectrometer. We present the instrument
optical and mechanical design. We show that the test data, as measured during
the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton
Laboratory, and at the NASA Goddard Space Flight Center, indicate that the
instrument complies with its design requirements and goals. We also discuss the
operational requirements (multiple dithers and exposures) needed for optimal
scientific utilization of the MIRIM.Comment: 29 pages, 9 figure
Planck pre-launch status: The optical architecture of the HFI
The Planck High Frequency Instrument, HFI, has been designed to allow a clear unobscured view of the CMB sky through an offaxis
Gregorian telescope. The prime science target is to measure the polarized anisotropy of the CMB with a sensitivity of 1 part
in 106 with a maximum spatial resolution of 5 arcmin (Cl ∼ 3000) in four spectral bands with two further high-frequency channels
measuring total power for foreground removal. These requirements place critical constraints on both the telescope configuration and
the receiver coupling and require precise determination of the spectral and spatial characteristics at the pixel level, whilst maintaining
control of the polarisation. To meet with the sensitivity requirements, the focal plane needs to be cooled with the optics at a few
Kelvin and detectors at 100 mK. To limit inherent instrumental thermal emission and diffraction effects, there is no vacuum window,
so the detector feedhorns view the telescope secondary directly. This requires that the instrument is launched warm with the cooler
chain only being activated during its cruise to L2. Here we present the novel optical configuration designed to meet with all the above
criteria
The geometry of the magnetic field in the central molecular zone measured by PILOT
We present the first far infrared (FIR) dust emission polarization map covering the full extent of Milky Way’s central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic center region − 2° < ℓ < 2°, − 4° < b < 3° at a wavelength of 240 μm and an angular resolution of 2.2′. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky (POS) that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of ≃22° clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonally to the field traced by GHz radio synchrotron emission in the Galactic center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 and 50 km s−1 molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. The low polarization fraction in the Galactic center region measured with Planck at 353 GHz combined with a highly ordered projected field orientation is unusual. This feature actually extends to the whole inner Galactic plane. We propose that it could be caused by the increased number of turbulent cells for the long lines of sight towards the inner Galactic plane or to dust properties specific to the inner regions of the Galaxy. Assuming equipartition between magnetic pressure and ram pressure, we obtain magnetic field strength estimates of the order of 1 mG for several CMZ molecular clouds
Pilot optical alignment
PILOT (Polarized Instrument for Long wavelength Observations of the Tenuous interstellar medium) is a balloonborne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our Galaxy. The PILOT instrument allows observations at wavelengths 240 μm and 550 μm with an angular resolution of about two arcminutes. The observations performed during the two first flights performed from Timmins, Ontario Canada, and from Alice-springs, Australia, respectively in September 2015 and in April 2017 have demonstrated the good performances of the instrument. Pilot optics is composed of an off axis Gregorian type telescope combined with a refractive re-imager system. All optical elements, except the primary mirror, which is at ambient temperature, are inside a cryostat and cooled down to 3K. The whole optical system is aligned on ground at room temperature using dedicated means and procedures in order to keep the tight requirements on the focus position and ensure the instrument optical performances during the various phases of a flight. We’ll present the optical performances and the firsts results obtained during the two first flight campaigns. The talk describes the system analysis, the alignment methods, and finally the inflight performances
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