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.
BepiColombo, an European Space Agency (ESA) mission being conducted in cooperation with the Japan space agency, will explore Mercury with a set of eleven instruments onboard the spacecraft Mercury ...Planetary Orbiter (MPO). Among them, SIMBIO-SYS (Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem) is a complex instrument that will provide images and spectra in the 400–2000nm wavelength range of the entire surface of Mercury. Pre-flight calibration of the SYMBIO-SYS instrument is mandatory for reliable scientific interpretation of images and spectra returned from the planet Mercury. This paper presents the calibration device designed and implemented for the specific requirements of this instrument. It mainly consists of a thermal vacuum chamber simulating the space environment, an optical bench collecting calibration sources and optical elements that simulate the conditions of Mercury observations, mechanical interfaces used for positioning the three channels inside the vacuum chamber, thermal interfaces to explore the operating temperatures, computer interfaces that allow to communicate with both the instrument and the calibration elements and synchronize the calibrations sequences with the status of the calibration device. As the major goal is the characterization of the radiometric performances of the three channels of SIMBIO-SYS, radiometric performances of the test setup evaluated by simulations and measurements are emphasized.
●The on-ground device dedicated to the calibration of SIMBIO-SYS is described.●Radiometric performances of the setup is evaluated by simulations and measurements.●Their compliance with the objectives of the calibration are modeled and validated.
The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (
PILOT
) is a balloon-borne astronomy experiment designed to study the linear polarization of thermal dust ...emission in two photometric bands centred at wavelengths 240
μ
m (1.2 THz) and 550
μ
m (545 GHz), with an angular resolution of a few arcminutes. Several end-to-end tests of the instrument were performed on the ground between 2012 and 2014, in order to prepare for the first scientific flight of the experiment that took place in September 2015 from Timmins, Ontario, Canada. This paper presents the results of those tests, focussing on an evaluation of the instrument’s optical performance. We quantify image quality across the extent of the focal plane, and describe the tests that we conducted to determine the focal plane geometry, the optimal focus position, and sources of internal straylight. We present estimates of the detector response, obtained using an internal calibration source, and estimates of the background intensity and background polarization.
PILOT is a balloon-borne experiment designed to perform large-scale surveys of the polarized interstellar emission in the submillimeter. It is based on the use of an off-axis Gregorian type ...telescope, with a 1 m diameter primary mirror, and a large focal plane equipped with detectors arrays providing a
field of view. All optical elements except the primary mirror are located inside a large liquid He cryostat, cooled down to 3 K. Strong constraints are then imposed on the alignment between the primary mirror and the cold optics. The characterization and optimization of the optical system performances are critical to the success of the mission. In this paper, we present the modelling and measurements performed on the primary mirror for this purpose. The optical and mechanical parameters of the as-built primary mirror have been determined using a method based on 3D measurements of the mirror surface. The deformations expected under flight conditions due to temperature variations and flexion under gravity have been estimated. We have also performed measurements using a submillimeter test bench in order to control the image quality and derive the main optical parameters. The parameters derived from the modeling using 3D measurements are in agreement with the requirements except for the conic constant. The best positioning of the mirror has been optimized consequently. The modeling has also allowed us to determine the pre-flight alignment parameters of the mirror as a function of the expected structure temperature at ceiling altitude. We have shown that this adjustment will enable to keep the tight requirements on the focus position (
600 μm) within a range of
C around the ceiling temperature value. The submillimeter measurements have validated the results derived from the 3D measurement based modeling. The image quality was investigated by performing a spatial exploration in azimuth and elevation around the nominal focus position, and along the optical axis. The deviation between the predicted and measured positions of the best focus are 80 μm and 11″ in translation along the optical axis and in rotation respectively. The best image pattern is also close to the nominal one, with a sphericity deviation lower than 2 μm RMS. These results will be used for the end-to-end tests of the integrated instrument, and for the optimization of the alignment before flight.
The Polarized Instrument for Long-wavelength Observation of the Tenuous interstellar medium (
PILOT
) is a balloon-borne experiment that aims to measure the polarized emission of thermal dust at a ...wavelength of 240 µm (1.2 THz). A first
PILOT
flight of the experiment took place from Timmins, Ontario, Canada, in September 2015 and a second flight took place from Alice Springs, Australia in April 2017. In this paper, we present the inflight performance of the instrument. Here we concentrate on the instrument performance as measured during the second flight, but refer to the performance observed during the first flight, if it was significantly different. We present a short description of the instrument and the flights. We measure the time constants of the detectors using the decay of the observed signal during flight following high energy particle impacts (glitches) and switching off the instrument’s internal calibration source. We use these time constants to deconvolve the timelines and analyze the optical quality of the instrument as measured on planets. We then analyze the structure and polarization of the instrumental background. We measure the detector response flat field and its time variations using the signal from the residual atmosphere and from the internal calibration source. Finally, we analyze the spectral and temporal properties of the detector noise. The inflight performance is found to be satisfactory and globally in line with expectations from ground calibrations. We conclude by assessing the expected inflight sensitivity of the instrument in light of the measured inflight performance.
In this article, we describe the Mid-Infrared Imager Module (MIRIM), which provides broadband imaging in the 5-27 μm wavelength range for the James Webb Space Telescope. The imager has a pixel scale ...and a total unobstructed view of 74″ × 113″. The remainder of its nominal 113″ × 113″ 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.
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