MARVEL is a new facility at the Mercator Observatory which comprises an array of four 0.8m 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 MARVEL spectrograph records five R = 90, 000 spectra simultaneously in a single exposure across a wavelength range of 380–950nm. The optical design makes use of simple spherical optics wherever possible, and specifies high-transmission lithography glasses. To confirm that the design performance is within reach, a five-stage optical tolerancing study was undertaken. The resulting tolerances not only directly reveal optical manufacturing requirements, but also inform the optomechanical mounting schemes that will be implemented. The required operational stability of the instrument was calculated in terms of maximum allowable displacement or tilt for each individual component or co-mounted group, translating into requirements on the environmental stability of the instrument, inside and outside the vacuum vessel.
KEYWORDS: Telescopes, Spectrographs, Calibration, Fabry Perot interferometers, Observatories, Control systems, Sensors, Control software, Equipment, Domes
MARVEL is a new facility at the Roque de los Muchachos Observatory (La Palma) which comprises an array of four 0.8m 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.
The MARVEL instrument is an array of four 80cm telescopes feeding a high-resolution echelle spectrograph designed to provide high precision radial-velocity measurements and is being led by KU Leuven (Belgium). The UK ATC is responsible for the delivery of the detector work package; a fully characterised STA1600LN optical CCD housed in a custom cryostat. As a large image area detector, the STA1600LN has been used in a variety of astronomy applications for imaging. This paper will detail the characterisation testing done by the UK ATC Electronics and Detectors group, to verify that this detector meets the requirements for a high-resolution spectrograph of this type. Testing includes measures of read noise, dark current, and the effects of the dither clocking on detector performance and stability, among others.
CubeSpec is an in-orbit demonstration CubeSat mission in the ESA GSTP programme, developed and funded by the Belgian federal space policy BELSPO. The goal of the mission is to demonstrate high-spectral-resolution astronomical spectroscopy from a 12-unit CubeSat. The technological challenges are numerous. The optical payload, consisting of an off-axis Cassegrain telescope and a compact Echelle spectrometer have been designed to fit in the bigger half of a 12U CubeSat (12x20x30cm). The telescope is built entirely from a ceramic material to limit defocusing when the spacecraft thermal environment changes. The payload radiator is shielded from the Sun via a deploying Sun shade, allowing pointing to a large part of the sky without illuminating the radiator panel. The high resolution spectrograph requires arcsecond-level pointing stability. This is achieved using a performant 3-axis wheel stabilised attitude control system with two star trackers augmented with a piezo-actuated 3-axis fine beam steering mechanism in the payload. CubeSpec is now starting the implementation phase, with a planned launch in 2026. A qualification and a flight model are being constructed and tested. We give an overview of the mission, its technologies and qualification status.
CubeSpec is an ESA in-orbit-demonstration mission, based on a 12U CubeSat, targeting high-resolution optical astronomical spectroscopy of bright targets. It is developed and funded in Belgium and scheduled for launch early 2026. The CubeSpec payload consists of an off-axis Cassegrain telescope with a rectangular aperture filling the surface area of two CubeSat units, followed by a prism cross-dispersed echelle spectrograph folded behind the primary mirror of the telescope. The complete optical payload fits in approximately 6 units (∼12 x 20 x 30 cm) of the spacecraft. CubeSpec delivers a spectral resolution of R = 55 000 and covers the wavelength range from 420 to 620 nm. The optical design is sufficiently flexible to allow tuning it with minimum hardware changes to a wide range of spectral resolution and coverage. A fine-guidance system consisting of a piezo-actuated fine steering mirror and a fine-guidance sensor provide arcsec-precise centering of the source image on the slit of the spectrograph, cancelling out pointing errors and spacecraft jitter. In this contribution, we describe the optical and optomechanical design of the CubeSpec payload, and discuss the challenged imposed by the extremely compact size and the large temperature excursions endured during each orbit.
KU Leuven’s CubeSpec mission is pioneering the use of a CubeSat platform for advanced space-based spectroscopy.1 This innovation is partly due to its payload electronics, which must be space-efficient and powerconscious. To achieve exceptional pointing accuracy, CubeSpec employs a High-Pointing Precision Platform (HPPP) that works in tandem with the onboard Attitude Determination and Control System (ADCS). The HPPP utilizes a Fine Steering Mirror (FSM), controlled by piezo actuators, to direct light precisely onto the spectrograph slit. The design incorporates a DC-DC boost converter and a linear amplifier to meet the highvoltage demands of the piezo actuators. The HPPP setup is controlled in a closed-loop system with a Fine Guidance Sensor (FGS), a CMOS detector, and strain gauges that provide real-time feedback. The spectrograph output is captured by the Science Detector, which is the same detector model as the FGS. Due to stringent time requirements, a Xilinx Zynq 7000 FPGA manages the detector readout. The payload processor can communicate with the OBC over a CAN bus employing the CubeSat Space Protocol. This paper outlines the current progression in the development of CubeSpec’s payload electronics.
iLocater is a new, near-infrared, extreme precision radial velocity (EPRV) spectrograph under construction for the dual 8.4m diameter Large Binocular Telescope (LBT). The instrument uses single-mode fibers (SMFs) injected with adaptive optics for illumination. We present the integration process for the spectrograph and cryostat systems, and the laboratory performance testing that has been completed. Testing has included optical performance characterization at ambient and cryogenic temperatures, assessment of cryogenic thermal control of the system (80-100K) at sub-mK level, and instrument detector performance (an H4RG-10). The optimized spectrograph and cryostat system will be delivered to the LBT in 2024.
The Keck Planet Finder (KPF) is a fiber-fed, high-resolution, echelle spectrometer that specializes in the discovery and characterization of exoplanets using Doppler spectroscopy. In designing KPF, the guiding principles were high throughput to promote survey speed and access to faint targets, and high stability to keep uncalibrated systematic Doppler measurement errors below 30 cm s−1. KPF achieves optical illumination stability with a tip-tilt injection system, octagonal cross-section optical fibers, a double scrambler, and active fiber agitation. The optical bench and optics with integral mounts are made of Zerodur to provide thermo-mechanical stability. The spectrometer includes a slicer to reformat the optical input, green and red channels (445–600 nm and 600–870 nm), and achieves a resolving power of ∼97,000. Additional subsystems include a separate, medium-resolution UV spectrometer (383–402 nm) to record the Ca II H & K lines, an exposure meter for real-time flux monitoring, a solar feed for sunlight injection, and a calibration system with a laser frequency comb and etalon for wavelength calibration. KPF was installed and commissioned at the W. M. Keck Observatory in late 2022 and early 2023 and is now in regular use for scientific observations. This paper presents an overview of the as-built KPF instrument and its subsystems, design considerations, and initial on-sky performance.
MARVEL is a new state-of-the-art facility at the Mercator Observatory (La Palma, Spain) targeting high precision radial velocity measurements. The facility consists of an array of four 80-cm telescopes feeding a single stabilized high-resolution echelle spectrograph. It will provide essential ground-based RV follow-up on transit measurements by previous and upcoming space missions with an RV precision of 1 m/s. This precision requires simultaneous wavelength calibration monitoring on a reliable wavelength reference calibration source. The MARVEL calibration system will be powered by a continuum white light source spanning the target wavelength range of 380-950 nm, and both a ThAr hollow-cathode lamp and a Fabry-P´erot etalon, whose light will be used as a wavelength reference. The light from the continuum source will be divided for use in spectral flat fielding, and for the illumination of the Fabry-P´erot etalon. The wavelength comb of transmission peaks produced by the etalon will be tracked against the hyperfine lines of rubidium, for continuous evaluation of residual etalon drift. Furthermore, the ThAr lamp will serve as an absolute reference for the etalon spectrum. Optical fiber switches will select one of the three calibration sources, as well as transport the light to its destination: the spectrograph, the science fibers at the focus of each telescope, or to a flux monitoring system. In this contribution, we describe the MARVEL wavelength calibration system and the strategy that will be deployed to maximize calibration precision and long-term stability.
MARVEL is a novel facility, consisting of an array of four robotic 80-cm telescopes and one highresolution Èchelle spectrograph. It targets extreme precision radial velocity observations for measuring the mass of exoplanets. The MARVEL spectrograph will be linked to the telescopes through a set of optical fibres. This fibre link consists of a combination of circular and octagonal fibres in an effort to maximize the photometric scrambling gain and hence, the illumination stability of the spectrograph. In this contribution, we present the design of the fibre link, as well as the results of a test campaign that evaluated the relevant characteristics of several circular and octagonal fibres. Based on this, we also report on the expected performances of the MARVEL fibre link.
MAVIS is the world’s first facility-grade visible MCAO instrument, currently under development for the VLT. The AO system will feed an imager and an integral field spectrograph, with 50% sky coverage at the Galactic pole. MAVIS has unique angular resolution and sensitivity at visible wavelengths, and is highly complementary to both JWST and ELTs. We describe both instruments in detail and the broad range of science cases enabled by them. The imager will be diffraction-limited in V, with 7.36 mas per pixel covering a 30” FOV. A set of at least 7 broad-band and 15 narrow-band filters will provide imaging from u to z. The spectrograph uses an advanced image slicer with a selectable spatial sampling of 25 or 50 mas to provide integral field spectroscopy over a FOV of 2.5”x3.6”, or 5”x7.2”. The spectrograph has two identical arms each covering half the FOV. Four interchangeable grisms allow spectroscopy with R=5,000 to R=15,000, from 380-950 nm.
MAVIS is the next instrument to go on the VLT. It is an imager and IFU spectrograph fed by Multi-Conjugate Adaptive Optics. It is presently in Phase-B (Preliminary Design Phase). The spectrograph will be preceded by an Integral Field Unit (IFU) with a choice of fields of 3.6"x2.5" with square spaxels 25 mas wide or 7.2"x5.0" with 50 mas spaxels. Two sets of interchangeable fore-optics permit the change of field size. The IFU will be based on the concept of Advanced Image Slicer present in many instruments as MUSE and KMOS on the VLT. In the present design, the field is first split in 2 and each subfield is imaged on a slicer mirror array made of long thin mirrors that slice the field into 50 images and send them in different directions to be reimaged side by side on the slit by another mirror array. A final and third mirror array on the slit places the pupil of each slice image at the right place in the spectrograph. Toroidal surfaces in each fore optics arm give the 2X magnification needed in the spectral direction. Each of the 2 subfields has its own lens spectrograph with a 9k x 9k detector and 4 interchangeable grisms giving a resolution from 5000 to 15000. High transmission glasses are used to ensure excellent throughput across the full wavelength range into the blue, covering 370- 950 nm. The slice width being near the diffraction limit, special consideration was given to the diffraction focal ratio degradation.
The proposed MAVIS instrument for the VLT UT4 delivers a 30" x 30" MCAO-corrected field for 370-950nm. It includes an integral-field spectroscopic mode, whereby a subsection of the field is delivered to an image slicer and spectrograph, with either 25mas or 50mas spatial sampling, and R<4000 and R<10000 modes in either the red or the blue. Three designs are being considered for the image slicer, two with all-reflective optics, and the other, presented here, derived from the existing WiFeS spectrograph and including arrays of small lenses. A spectrograph design is also presented, challenging because of the need to be close to diffraction-limited across the entire wavelength range, while maintaining high throughput, in all 4 modes and over the entire 9cm x 9cm detector.
MARVEL is an upcoming facility which comprises an array of four 0.8 m telescopes, each feeding via fibre link into a single high-resolution echelle spectrograph. The facility is designed to provide dedicated reconnaissance and follow-up observational capability for exoplanet searches through radial velocity measurements at a precision of 1 m s−1 . The optical design of the MARVEL spectrograph is built around a white pupil relay with a single parabolic mirror, a prism as cross-disperser, and a purely spherical refractive camera. The spectrograph records a wavelength range of 380–950 nm at spectral resolution R∼90,000 in a single arm with a large CCD detector. The final design has intentionally been kept simple, avoiding aspheric optics and using readily available high transmission glasses. We present an overview of the requirements and optical design process; a brief discussion of the design avenues that were considered and decided against; and details about the expected performance of the instrument’s final design.
MARVEL is a novel facility targeting extreme-precision radial velocity observations. Dedicated to confirming and characterizing planet candidates from the TESS and future PLATO missions, MARVEL will provide mass measurements of a multitude of exoplanets. The MARVEL instrument consists of an array of four 80-cm robotic telescopes, linked to one state-of-the-art high-resolution echelle spectrograph, through a set of optical fibers. MARVEL can observe the radial velocities of four different stars simultaneously or, alternatively, combine the flux from four telescopes pointing to a single faint target in one spectrum. It will be installed next to the Mercator Telescope at the Roque De Los Muchachos Observatory on La Palma (SPAIN). MARVEL is designed and built by a KU Leuven (Belgium) led consortium, with contributions from Australia, Austria, Denmark, Germany, Spain, Sweden and the UK.
CubeSpec is an in-orbit CubeSat mission aiming to demonstrate high-spectral-resolution astronomical spectroscopy with a 10 × 20cm2 aperture telescope. A robust calibration system is crucial for CubeSpec’s spectrograph to operate reliably and autonomously. Typically, flat-field illumination defines order locations, while a line source ties wavelength values to detector pixels. The main challenge is to fit everything into a 10 × 10 × 20cm3 volume without forfeiting quality and control. This work proposes Calibration Unit for CUbespec (CUCU). CUCU offers a compact, energy-efficient calibration solution for space-borne spectrograph platforms, miniaturizing both calibration stages. A blue and white LED coupled into one fiber produce the continuum light source, spanning the spectrograph’s operational range of 420nm to 620nm. The line standards emerge from injecting collimated LED light into a solid Fabry-P´erot etalon. To satisfy the mission requirements, CUCU should deliver calibration exposures with an SNR of 200. Throughput measurements estimate calibration exposures to take no longer than 0.5s.
CubeSpec is an ESA in-orbit-demonstration mission, based on a 6U CubeSat, targeting high-resolution astronomical spectroscopy. It is developed and funded in Belgium and scheduled for launch at the end of 2024. The CubeSpec payload consists of an off-axis Cassegrain telescope with a rectangular aperture (186x82mm2 ) and a prism cross-dispersed echelle spectrograph. The telescope aperture almost completely covers the surface area of 2 CubeSat units and the entire optical system fits in 4 units (10x20x20cm) of the spacecraft. CubeSpec delivers a spectral resolution of R=55000 and covers the wavelength range from 420 to 620 nm. Furthermore, it is equipped with a fine-guidance system based on a fast beam-steering mirror and a fine-guidance sensor that provide accurate centering of the source image on the spectrograph slit to compensate for spacecraft pointing jitter. In this contribution, we present the optical design of the CubeSpec payload.
The future ESA space mission PLATO aims to detect thousands of exoplanets, including Earth-like planets, and constrain their radius and mean density. To achieve this goal, the space based photometric observations are not enough but need to be complemented by ground-based observations to measure the Radial Velocity (RV) of the exoplanet host stars. MARVEL is such a facility consisting of four 80 cm telescope linked through optical fibers to a single high-resolution ´echelle spectrograph, designed for high-precision RV measurements with a uncertainty of ∼ 1 ms−1 . MARVEL is build by a consortium led by the KU Leuven with contributions from the UK, Austria, Australia, Sweden, Denmark, and Spain, and will be commissioned in 2023. To reach such high RV precision, not only ultra-stable hardware is currently being developed, but also a state-of-the-art data processing pipeline for which we present the first results in this poster.
KEYWORDS: Spectrographs, New and emerging technologies, Velocity measurements, Single mode fibers, Adaptive optics, Near infrared, Cameras, Sensors, Optical design, Relays
Small diameter single-mode fiber (SMF) allows for the design of compact spectrographs that operate at the diffraction limit. The small instrument scale, in turn, allows cost-effective configuration flexibility to use the instrument as a testbed for infrared SMF spectrograph technologies. The same base instrument could be coupled to different adaptive optics (AO) and non-AO SMF feeds. We present the build for such a spectrograph, Iranti, which works in the near-infrared (NIR) range and incorporates novel techniques. Our implementation of this instrument has sufficient cross dispersion to allow testing of a range of input fiber links, including multiple fibers or multi-core fibers (MCFs); the camera optics and detector can also be swapped out easily for different wavelength ranges. The base system uses a white pupil design that relays a slow beam between the collimator, an R6 echelle grating with 13.33 lines/mm and a volume phase holographic grating (VPH) as a cross disperser. In Iranti, we also address mechanical and thermal considerations to improve stability in the instrument. We configure the instrument for ranges in 800 to 1300 nm and characterize system efficiency and stability.
Fiber modal noise is a performance limiting factor in high-resolution spectroscopy, both with respect to achieving high signal-to-noise ratios or when targeting high-precision radial velocity measurements, with multi-mode fiber-fed high resolution spectrographs. Traditionally, modal noise is reduced by agitating or “shaking” the fiber. This way, the light propagating in the fiber is redistributed over many different modes. However, in case of fibers with only a limited number of modes, e.g. at near-infrared wavelengths or in adaptive-optics assisted systems, this method becomes very inefficient. The strong agitation that would be needed stresses the fiber and could lead to focal ratio degradation, or worse, to damaging the fiber. As an alternative approach, we propose to make use of a classic optical double scrambler, a device that is already implemented in many high-precision radial-velocity spectrographs, to mitigate the effect of modal noise by rotating the scrambler’s first fiber end during each exposure. Because of the rotating illumination pattern of the scrambler’s second fiber, the modes that are excited vary continuously. This leads to very efficient averaging of the modal pattern at the fiber exit and to a strong reduction of modal noise. In this contribution, we present a prototype design and preliminary laboratory results of the rotating double scrambler.
Since the first discovery of a planet outside of our Solar System in 1995, exoplanet research has shifted from detecting to characterizing worlds around other stars. The TESS (NASA, launched 2019) and PLATO mission (ESA, planned launch 2026) will find and constrain the size of thousands of exoplanets around bright stars all over the sky. Radial velocity measurements are needed to characterize the orbit and mass, and complete the picture of densities and composition of the exoplanet systems found. The Ariel mission (ESA, planned launch 2028) will characterize exoplanet atmospheres with infrared spectroscopy. Characterization of stellar activity using optical spectroscopy from the ground is key to retrieve the spectral footprint of the planetary atmosphere in Ariel’s spectra. To enable the scientific harvest of the TESS, PLATO and Ariel space missions, we plan to install MARVEL as an extension of the existing Mercator Telescope at the Roque De Los Muchachos Observatory on La Palma (SPAIN). MARVEL consists of an array of four 80 cm telescopes linked through optical fibers to a single high-resolution echelle spectrograph, optimized for extreme-precision radial velocity measurements. It can observe the radial velocities of four different stars simultaneously or, alternatively, combine the flux from four telescopes pointing to a single faint target in one spectrum. MARVEL is constructed by a KU Leuven (Belgium) led collaboration, with contributions from the UK, Austria, Australia, Sweden, Denmark and Spain. In this paper, we present the MARVEL instrument with special focus on the optical design and expected performance of the spectrograph, and report on the status of the project.
The correction of differential atmospheric dispersion is important for a broad range of astronomical observations, from high precision coronagraphy and astrometry to extremely stable fiber coupling in Doppler spectroscopy. The wide availability of adaptive optics systems, and the push to bluer wavelengths in particular, requires very highperformance designs. The choice of glasses for typical atmospheric dispersion corrector (ADC) configurations is a surprisingly challenging task, and depends on a range of parameters, in particular the wavelength range, with considerations on the level of dispersion correction as well as transmission and mechanical parameters. Finding the optimal glass combination with optical raytracing programs is time consuming, and it is hard to verify the solution is optimal. We describe a numerical method that uses Python to evaluate all possible unique combinations of two glasses from an input catalogue. This enables easy identification of potentially good candidate pairs for further, detailed investigation.
The applicability of optical fibers to astronomical spectroscopy in the infrared depends heavily on the fiber's wavelength-dependent transmission properties. Standard silica fibers typically allow transmission at wavelengths as red as 1550nm but absorb strongly at redder wavelengths, limiting their use for the infrared instruments. Fibers using fluoride glasses transmit redward of this range, opening up the infrared K band, corresponding to a window of transmission in the Earth's atmosphere. In order to further assess their feasibility for astronomical instrumentation, the characteristics of these fibers must be well-known. Here initial measurements and analysis of the focal ratio degradation (FRD) of two types of fluoride fibers are reported.
The MCAO Assisted Visible Imager and Spectrograph (MAVIS) is a facility-grade visible MCAO instrument, currently under development for the Adaptive Optics Facility at the VLT. The adaptive optics system will feed both an imager and an integral field spectrograph, with unprecedented sky coverage of 50% at the Galactic Pole. The imager will deliver diffraction-limited image quality in the V band, cover a 30" x 30" field of view, with imaging from U to z bands. The conceptual design for the spectrograph has a selectable field-of-view of 2.5" x 3.6", or 5" x 7.2", with a spatial sampling of 25 or 50 mas respectively. It will deliver a spectral resolving power of R=5,000 to R=15,000, covering a wavelength range from 380 - 950 nm. The combined angular resolution and sensitivity of MAVIS fill a unique parameter space at optical wavelengths, that is highly complementary to that of future next-generation facilities like JWST and ELTs, optimised for infrared wavelengths. MAVIS will facilitate a broad range of science, including monitoring solar system bodies in support of space missions; resolving protoplanetary- and accretion-disk mechanisms around stars; combining radial velocities and proper motions to detect intermediate-mass black holes; characterising resolved stellar populations in galaxies beyond the local group; resolving galaxies spectrally and spatially on parsec scales out to 50 Mpc; tracing the role of star clusters across cosmic time; and characterising the first globular clusters in formation via gravitational lensing. We describe the science cases and the concept designs for the imager and spectrograph.
The Keck Planet Finder (KPF) is a fiber-fed, high-resolution, high-stability spectrometer in development at the UC Berkeley Space Sciences Laboratory for the W.M. Keck Observatory. KPF is designed to characterize exoplanets via Doppler spectroscopy with a goal of a single measurement precision of 0.3 m s-1 or better, however its resolution and stability will enable a wide variety of astrophysical pursuits. Here we provide post-preliminary design review design updates for several subsystems, including: the main spectrometer, the fabrication of the Zerodur optical bench; the data reduction pipeline; fiber agitator; fiber cable design; fiber scrambler; VPH testing results and the exposure meter.
The Macquarie University campus observatory has recently undergone a significant upgrade, with a new fully- automated 0.6 m telescope and on-site facilities including an instrumentation laboratory. Here we report on the design, assembly, and first on-sky tests of a new high-resolution echelle spectrograph for the observatory. This spectrograph will be a key resource at our campus observatory, providing high fidelity measurements that will enable future research, in particular Master and PhD theses that require stellar spectroscopy or radial velocity measurements. The instrument will also form a cornerstone of the laboratory components of the undergraduate astronomy degree, and together with the new 0.6 m telescope, a key tool for project-based learning at the campus observatory. The instrument has been developed with radial velocity precision as the driving metric, and with future work on the environmental stabilisation it is expected to reach a radial velocity precision of 3 m s−1, enabling the observation of a wide range of exoplanets.
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