MARVEL is a new facility at the Mercator Observatory (La Palma) which comprises an array of four 0.8 metre telescopes, each feeding via fibre link into a single high-resolution spectrograph. The facility will provide dedicated target vetting and follow-up capability to support large exoplanet surveys through radial velocity measurements with precision at the metre-per-second level. The observatory site, with four new domes and a standalone stabilised spectrograph building, will soon be complete and ready for hardware installation and commissioning. Here we present an overview of the facility and a status update on several component subsystems: the telescope hardware, control software, and scheduling software; the fibre injection units at each telescope; the optical and mechanical design and tolerances of the spectrograph and vacuum vessel; the calibration system hardware and calibration strategies; and the progress in development of the instrument's data reduction pipeline.
In mid-2025, the initial sub-systems for METIS, the Mid-Infrared E-ELT Imager and Spectrometer, are anticipated to reach the system-level Assembly, Integration, and Testing (AIT) facility at Leiden University. The AIT process is projected to extend over three years. Throughout this period, the comprehensive testing and calibration of the entire METIS system will be conducted. The preparation for integration encompasses diverse aspects, including the planning of various assembly, integration, and verification steps. This involves the development of the integration facility, provision of support equipment, and ensuring the readiness of all requisite software to facilitate the instrument's efficient qualification. As subsystems are nearing completion, also the AIT facility is being finalized, with an expected delivery date of end-July 2024.
The JWST Mid-Infrared Instrument (MIRI) detector arrays are Si:As blocked impurity band devices, direct descendants of the Spitzer/IRAC long wavelength arrays. Similarly to the IRAC row-column effect, analysis of flightlike MIRI detector data has shown that columns and rows in which source signals are located can suffer from pull up (brightness increase) or pull down (brightness decrease) in the flux image. Here we present results from the JPL MIRI detector characterisation campaigns dedicated to understanding this row-column effect as well as the first results showing the effect in the flight detectors for MIRI. We show the effect is flux dependent and confirm that the effect manifests differently for rows versus columns. We discuss the origin of the flux offset, which is related to a change in the signal output in time that distorts the input ramp as a function of the saturation level of illuminated pixels. We conclude by discussing the row-column effect in the context of different MIRI instrument modes and present preliminary proposals to mitigate and/or correct the effect in MIRI data.
This paper describes the Optical Ground Support Equipment (OGSE) that is being developed for the payload level testing of the Ariel Space Telescope. Ariel has been adopted as ESA’s “M4” mission in its Cosmic Visions Programme and will launch in 2029 to the second Earth-Sun Lagrange point. During four years of operation the Ariel payload (PL – the cryogenic payload module plus warm units) will perform precise transit spectroscopy of approximately 1000 known exoplanetary atmospheres using a 1.1 m × 0.7 m telescope coupled to two instruments: the Fine Guidance Sensor (FGS) and the Ariel Infrared Spectrometer (AIRS). These instruments provide three spectrometric channels that cover 1.0 to 7.8 μm wavelength range and three photometric channels between 0.5 and 1.1 μm. The Ariel OGSE will verify the optical and radiometric performance of the integrated Ariel PL under vacuum and cryogenic (<40 K) test conditions within the limitations of operation under Earth’s gravity and vibration environments. To achieve these verification requirements the OGSE is integrated with the main Ariel ground test 5 m thermal vacuum chamber. The test chamber contains a cryogenic enclosure (the Cryogenic Test Rig) that surrounds the PL and the OGSE itself comprises of four subsystems. (1) A cryogenic vacuum chamber and integrating sphere illumination module that is fed by visible, near infrared and thermal infrared sources. The illumination module is mounted external to the Ariel test chamber and coupled via a vacuum feedthrough that relays a 22 mm diameter test beam into the Cryogenic Test Rig. The test beam is then relayed using (2) an injection module that steers the beam to maintain alignment during cool-down and scan the Ariel telescope field of view. The beam is then expanded to partially illuminate the Ariel telescope primary mirror using an (3) ~0.3 m diameter target projector collimating mirror. The final optical component of the OGSE is a (4) beam expander placed on the Ariel common optical bench to compensate for the sub-aperture illumination of the primary and to ensure that the spectrometer modules provide illumination with correct cone angles during ground testing. It is planned to use the OGSE in 2026 for a full range of calibration and verification tests of the end-to-end telescope and instrument performance, including detectors, field of view and alignment. These tests will then ensure that Ariel meets it challenging photometric and spectral performance requirements.
KEYWORDS: Point spread functions, Data modeling, James Webb Space Telescope, Infrared telescopes, Fringe analysis, Detection and tracking algorithms, Astronomy
Similarly to other spectroscopic instruments operating in the infrared wavelength range, the observations of the Mid-Infrared Instrument (MIRI) on-board the James Webb Space Telescope (JWST) are subject to fringing. The different layers in the detectors act as Fabry-P´erot etalons, causing fringes up to 30% in depth. The depth and phase of these detector fringes is not constant for all source geometries on the sky, and depends on the illumination of the MIRI pupil. This means that point sources will show a different fringe pattern from semi-extended sources and extended sources. In fact, it has been found that a smooth change in depth and phase occurs depending on what part of the point spread function (PSF) is sampled. Here, we aim to use the predictable change in fringe pattern to find evidence for the presence of an additional body in what is seemingly a single point source. To do this, we create a forward model of the PSF including fringes and insert this into a Bayesian retrieval loop. The Bayesian loop finds the coordinates on the detector for one or more point sources that best fits the data of two point sources added together. We find that the code is able to identify the along-slice coordinates of the two point sources, but there is less of a dependency on the fringes with the across-slice coordinate. Using commissioning and Cycle 1 data, we will be able to better characterise the fringes, and improve the forward models.
The Mid-Infrared Instrument MIRI on-board the James Webb Space Telescope uses three Si:As impurity band conduction detector arrays. MIRI medium resolution spectroscopic measurements (R~3500-1500) in the 5 μm to 28 μm wavelength range show a 10-30% modulation of the spectral baseline; coherent reflections of infrared light within the Si:As detector arrays result in fringing. We quantify the shape and impact of fringes on spectra of optical sources observed with MIRI during ground testing and develop an optical model to simulate the observed modulation. We use our optical model in conjunction with the MIRI spectroscopic data to show that the properties of the buried contact inside the MIRI Si:As detector have a significant effect on the fringing behavior.
KEYWORDS: Point spread functions, Image sensors, Detection and tracking algorithms, Calibration, James Webb Space Telescope, Signal detection, Spectroscopy, 3D image processing
The Mid-Infrared Instrument (MIRI) on-board the James Webb Space Telescope (JWST) performs mediumresolution spectroscopy in the 5 to 28.5micron wavelength range. In this paper two algorithms are presented that will be used to extract 1D spectra from the 2D absolutely calibrated detector science frames acquired with the Medium-Resolution Spectrometer (MRS) of MIRI. The first spectral extraction algorithm performs standard aperture photometry on point and extended sources. The second algorithm, applicable only to point sources, uses the instrument point spread function (PSF) and the pixel signal variance as a weighting function, to extract the signal from the detector pixels in an optimized way. This "optimal" extraction is also optimal in the case of faint source observations. The two algorithms are tested on MIRI ground test data and compared. For point sources, the optimal extraction algorithm is found to be more reliable than the aperture extraction algorithm.
The Mid-Infrared Instrument (MIRI) on-board the James Webb Space Telescope (JWST) performs medium resolution spectroscopy in the 5 to 28.5micron wavelength range. The Medium-Resolution Spectrometer (MRS) of MIRI uses two Si:As impurity band conduction detector arrays. Coherent reflection of infrared light within the MIRI MRS detectors results in fringing; the detector layers act as efficient Fabry-Pérot etalons. In this paper we present three methods to calibrate out the fringes, as part of the MIRI data reduction pipeline. The methods are presented in the context of the investigations on the fringing seen in the MIRI flight model ground test data. The investigations show that the detector fringe transmission depends on the illumination pattern of the observed source on the detector. Optical stimuli of different spatial extents and position in the field-of-view yield different fringe patterns in their extracted spectra. An optical model of the MIRI detectors is hence proposed. By solving the Fresnel equations across the model optical layers, a source-specific fringe correction is derived.
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