Microshutter Arrays Research Articles

The NIRSpec Wide GTO Survey

The Near-infrared Spectrograph (NIRSpec) on the James Webb Space Telescope is uniquely suited to studying galaxies in the distant Universe with its combination of multi-object capabilities and sensitivity over a large range in wavelength (0.6 − 5.3 μm). Here we present the NIRSpec Wide survey, part of the NIRSpec Instrument Science Team’s Guaranteed Time Observations, using NIRSpec’s microshutter array to obtain spectra of more than 3200 galaxies at z > 1 at both low and high resolution (R ≈ 100 and 2700) for a total of 105 hours. With 31 pointings covering ≈320 arcmin2 across the five CANDELS fields with exquisite ancillary photometry from the Hubble Space Telescope, the NIRSpec Wide survey represents a fast and efficient way of probing galaxies in the early Universe. Pointing centers are determined to maximize the observability of the rarest, high-value sources. Subsequently, the microshutter configurations are optimized to observe the maximum number of “census” galaxies with a selection function based primarily on HST/F160W magnitude, photometric or slitless grism redshift, and predicted Hα flux tracing the bulk of the galaxy population at cosmic noon (zmed = 2.0). We present details on the survey strategy, the target selection, an outline of the motivating science cases, and discuss upcoming public data releases to the community.

JADES

Finding the first generation of stars formed out of pristine gas in the early Universe, known as Population III (PopIII) stars, is one of the most important goals of modern astrophysics. Recent models have suggested that PopIII stars may form in pockets of pristine gas in the halo of more evolved galaxies. We present NIRSpec integral field spectroscopy and micro-shutter array spectroscopic observations of the region around GN-z11, an exceptionally luminous galaxy at z = 10.6, that reveal a greater than 5σ detection of a feature consistent with being HeIIλ1640 emission at the redshift of GN-z11. The very high equivalent width of the putative HeII emission in this clump (log(EWrest(HeII)/Å) = 1.79−0.25+0.15) and a lack of metal lines can be explained in terms of photoionisation by PopIII stars, while photoionisation by PopII stars is inconsistent with the data. The high equivalent width would also indicate that the putative PopIII stars likely have an initial mass function with an upper cutoff reaching at least 500 M⊙. The PopIII bolometric luminosity inferred from the HeII line would be ∼7 × 109 L⊙, which would imply a total stellar mass formed in the burst of ∼2 × 105 M⊙. We find that photoionisation by the active galactic nucleus (AGN) in GN-z11 cannot account for the HeII luminosity observed in the clump but can potentially be responsible for an additional HeII emission observed closer to GN-z11. We also consider the possibility of in situ photoionisation by an accreting direct collapse black hole hosted by the HeII clump. We find that this scenario is less favoured, but it remains a possible alternative interpretation. We also report the detection of a Lyα halo stemming out of GN-z11 and extending out to ∼2 kpc as well as resolved funnel-shaped CIII emission likely tracing the ionisation cone of the AGN.

An Electrothermally Actuated Microshutter Array With Enhanced Power Efficiency for Intelligent Lighting Control

An Electrothermally Actuated Microshutter Array With Enhanced Power Efficiency for Intelligent Lighting Control

JWST/NIRSpec Measurements of Extremely Low Metallicities in High Equivalent Width Lyα Emitters

Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (M UV ≈ −15; 0.01 L ⋆) at z = 2.9−6.7 due to their strong Lyα emission with no detectable continuum. The implied Lyα equivalent widths can be in excess of 100–200 Å, challenging existing models of normal star formation and indicating extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec’s microshutter array to follow up 45 of these galaxies (11 hr in G235M/F170LP and 7 hr in G395M/F290LP), as well as 45 lower-equivalent width Lyα emitters. Our spectroscopy covers the range 1.7−5.1 micron in order to target strong optical emission lines: Hα, [O iii], Hβ, and [N II]. Individual measurements as well as stacks reveal line ratios consistent with a metal-poor nature (2%−40% Z ⊙, depending on the calibration). The galaxies with the highest equivalent widths of Lyα, in excess of 90 Å, have lower [N II]/Hα (1.9σ) and [O iii]/Hβ (2.2σ) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4σ. This implies a selection based on Lyα equivalent width is an efficient technique for identifying younger, less chemically enriched systems.

The Near-Infrared Spectrograph (NIRSpec) on theJames WebbSpace Telescope

We present an overview of the capabilities and key algorithms employed in the so-called eMPT software suite developed for planning scientifically optimized, multi-object spectroscopic (MOS) observations with the Micro-Shutter Array (MSA) of the Near-Infrared Spectrograph (NIRSpec) instrument on board theJames WebbSpace Telescope, the first multi-object spectrograph to operate in space. NIRSpec MOS mode is enabled by a programmable MSA, a regular grid of ~250 000 individual apertures that projects to a static, semi-regular pattern of available slits on the sky and makes the planning and optimization of an MSA observation a rather complex task. As such, the eMPT package is offered to the NIRSpec user community as a supplement to the MSA Planning Tool (MPT) included in the STScI Astronomer’s Proposal Tool (APT) to assist in the planning of NIRSpec MOS proposals requiring advanced functionality to meet ambitious science goals. The eMPT produces output that can readily be imported and incorporated into the user’s observing program within the APT to generate a customized MPT MOS observation. Furthermore, its novel algorithms and modular approach make it highly flexible and customizable, providing users the option to finely control the workflow and even insert their own software modules to tune their MSA slit masks to the particular scientific objectives at hand.

In-orbit Performance of the Near-infrared Spectrograph NIRSpec on the James Webb Space Telescope

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope. In this paper, we summarize the in-orbit performance of NIRSpec, as derived from data collected during its commissioning campaign and the first few months of nominal science operations. More specifically, we discuss the performance of some critical hardware components such as the two NIRSpec Hawaii-2RG detectors, wheel mechanisms, and the microshutter array. We also summarize the accuracy of the two target acquisition procedures used to accurately place science targets into the slit apertures, discuss the current status of the spectrophotometric and wavelength calibration of NIRSpec spectra, and provide the “as measured” sensitivity in all NIRSpec science modes. Finally, we point out a few important considerations for the preparation of NIRSpec science programs.

An Electromagnetic-Driven Microshutter Array in a Field-of-View Gated Image System for All-Time Star Sensors

Aiming at the application requirements of a field of view (FOV) gated imaging system for all-time star sensors, a key device of a microshutter array with large unit size, high duty cycle, and fast response speed based on the electromagnetic actuation is designed. The proposed microshutter array adopts the principle that the current-carrying coil is subjected to the magnetic force in the magnetic field. The coil element is deflected by the loading current and acts as a light barrier in realizing the optical switch function. The effects of the coil element parameters on the magnetic force torque, torsion beam resistance torque, and switch response time are analyzed, and the structural parameters of the coil element are determined. A sample of the proposed microshutter array based on the electromagnetic actuation with a 4-mm period and a 2.8-mm aperture is fabricated and tested. The test results demonstrate the good switching function of the proposed microshutter array and show that the switch response time of the microshutter element is approximately 2.5 ms. This proposed microshutter array is used to gate an instantaneous small FOV to suppress the sky's background radiation and make a FOV-gated imaging system realize the multi-stars detection by switching the gated FOV rapidly. This will solve the problem that only one star can be detected within the FOV by a traditional all-time star tracker and promote the all-time star sensor to realize star pattern recognition and autonomous astronomical navigation in the daytime.

Microshutter Array Design of Field-of-view Gated Imaging Systems for All-time Star Sensor

Microshutter Array Design of Field-of-view Gated Imaging Systems for All-time Star Sensor

Optical imaging system for an all-time star sensor based on field of view gated technology.

The wide field of view (FOV) of traditional star sensor optical systems restricts the ability to suppress atmospheric background. An optical imaging system for an all-time star sensor based on FOV gated technology is proposed. In this system, a wide FOV telescope is used to observe a large sky area containing multiple stars. A microlens and microshutter array is employed to subdivide the wide FOV and gate a narrow FOV to suppress atmospheric background radiation. Assisted by a common imaging lens, each set of microlens and microshutter elements corresponds to a FOV gated imaging channel. With the rapid switching of gated FOV, multiple stellar images are obtained on a common detection during daytime. As an example, a FOV gated optical imaging system with 0.4° gated FOV and 61 imaging channels is designed. In addition, a simplified prototype is developed, and a preliminary experiment of FOV gated imaging is performed near the ground. The results verify the capability of multiple stellar detections during daytime. The proposed optical imaging system has a strong capability of suppressing atmospheric background radiation and provides sufficient FOV gated imaging channels to enhance the probability of detecting multiple stars. It provides an effective technical way to develop all-time star sensors based on star pattern recognition and enables a completely autonomous attitude determination possible for platforms inside the atmosphere during daytime.

Modelling analysis for design of microshutters with new electrode configuration

The Next Generation Microshutter Array (NGMSA) is an all-electrostatic actuated, programmable light transmission device used for multi-object spectroscopy. The latest NGMSA is designed to operate by applying a voltage difference between the shutter blade electrode and a single back wall electrode. We investigate the effects of different wall electrode configurations and present a bi-electrode design that allows reliable shutter actuation at a voltage difference of 70V.

The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

We provide an overview of the capabilities and performance of the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope when used in its multi-object spectroscopy (MOS) mode employing a novel Micro Shutter Array (MSA) slit device. The MSA consists of four separate 98″ × 91″ quadrants each containing 365 × 171 individually addressable shutters whose open areas on the sky measure 0.20″ × 0.46″ on a 0.27″ × 0.53″ pitch. This is the first time that a configurable multi-object spectrograph has been available on a space mission. The levels of multiplexing achievable with NIRSpec MOS mode are quantified and we show that NIRSpec will be able to observe typically fifty to two hundred objects simultaneously with the pattern of close to a quarter of a million shutters provided by the MSA. This pattern is fixed and regular, and we identify the specific constraints that it yields for NIRSpec observation planning. In particular, the roll angle at which a given NIRSpec MSA observation will be executed will, in most cases, not be known before the observation is actually scheduled. As a consequence, NIRSpec users planning MOS mode observations cannot at the proposal stage know precisely which subset of their intended targets will be observable, and will therefore need to intentionally oversize their submitted target catalogues accordingly. We also present the data processing and calibration steps planned for the NIRSpec MOS data. The significant variation in size of the mostly diffraction-limited instrument point spread function over the large wavelength range of 0.6–5.3 µm covered by the instrument, combined with the fact that most targets observed with the MSA cannot be expected to be perfectly centred within their respective slits, makes the spectrophotometric and wavelength calibration of the obtained spectra particularly complex. This is reflected by the inclusion of specific steps such as the wavelength zero-point correction nd the relative path loss correction in the NIRSpec data processing and calibration flow. The processing of spectra of morphologically extended targets will require additional attention and development. These challenges notwithstanding, the sensitivity and multiplexing capabilities anticipated of NIRSpec in MOS mode are unprecedented, and should enable significant progress to be made in addressing a wide range of outstanding astrophysical problems.

The need for a multi-purpose, optical\u2013NIR space facility after HST and JWST

In the early 2030s, after the end of operations for the epochal Hubble Space Telescope and the long-anticipated James Webb Space Telescope, astrophysics will lose access to a general purpose high-spatial resolution space observatory to cover the UV–optical–NIR wavelength range with a variety of imaging bandpasses and high-multiplexing mid-resolution spectroscopy. This will greatly impact astrophysical “discovery space” at visible wavelengths, in stark contrast to progress at most other wavelengths enabled by groundbreaking new facilities between 2010 and 2030. This capability gap will foreseeably limit progress in a number of fundamental research directions anticipated to be pressing in the 2030’s and beyond such as: What are the histories of star formation and cosmic element production in nearby galaxies?What can we learn about the nature of dark matter from dwarf galaxies?What is the local value of the Hubble Constant?A multi-purpose optical–NIR imaging and multiplexed spectroscopy Workhorse Camera (HWC) onboard NASA’s 4m-class Habitable Exoplanet Observatory (HabEx) space mission would provide access to these required data. HabEx is currently under study by NASA for the US Decadal Survey on Astronomy and Astrophysics 2020, and if selected would launch around 2035. Aside from its direct imaging of Earth-like exoplanets, it will have a general-observatory complement of instrumentation. The versatile Workhorse Camera will provide imaging and Rsim 1000 spectroscopy from 370nm to 1800nm, diffraction-limited over the whole wavelength range, with simultaneous observations of the visible and NIR. Spectroscopic multiplexing will be achieved through microshutter arrays. All necessary HWC technology is already at Technology Readiness Level 5, hence technological risks are low. HWC has a rough-order-of-magnitude (ROM) cost of 300 M€, and could be European-funded within the cost envelope of an ESA S-class mission in the Voyage 2050 program, with matching funds by national funding agencies to construct HWC by a European instrument consortium. This White Paper is intended to put a European HabEx Workhorse Camera into ESA’s considerations. If ESA shares the wide interest and if HabEx were to be selected by NASA, there would be ample time to identify interested institutes for a European instrument consortium, including MPIA, to design, finance, and build the HabEx Workhorse Camera.

Actuation force analysis and design optimization of microshutter array by numerical simulation method

Next Generation Microshutter Array (NGMSA) is an electrostatically operated micro electro-mechanical system (MEMS) device for programmable spatial light filtering application. Original microshutter array (MSA), which is magnetically operated, was developed for the James Webb Space Telescope (JWST) NIRSpec multi-object spectrometer, and NGMSA inherited its design from the original MSA. Even though there has been incremental design changes in order to achieve stable electrostatic actuation, NGMSA operation still requires further study. Previous simulation efforts to model NGMSA’s actuation mechanics allowed to gain only general understanding of the behavior due to inadequate simulation and experimental methods. In this study, a novel electrostatic numerical simulation model is presented using COMSOL Multiphysics to accurately predict microshutter’s motion during actuation. The new model addresses all the issues that hinder realistic modeling. Current Microshutter Array yield and operation performance issues related to fabrication process are analyzed with this numerical model and a potential optimized design is proposed. The result shows that a few μm shorter shutter blade allows stable electrostatic actuation as well as better tolerance to the fabrication accuracy. Also, modified blade side shape reduces undesirable asymmetrical motions which cause failed stuck shutters.

Successful Demonstration of an Electrostatically Actuated Microshutter System for Space Telescope Flight Missions

After developing a magnetically actuated microshutter array sub-system, which acts as a field object selector for the James Webb Space Telescope (JWST), our team at the NASA Goddard Space Flight Center (GSFC) focused on the development of electrostatically actuated microshutter arrays – the Next Generation Microshutter Arrays (NGMSA). This letter describes the first NGMSA array that performed shutter operations for telescope imaging and spectroscopy in space. The carrier telescope, the Next-Generation Far-UV Off Rowland-circle Telescope for Imaging and Spectroscopy (NG-FORTIS) was produced by Prof. Stephan McCandliss and his team at Johns Hopkins University and launched into space successfully. [2020-0226]

The role of the JWST near-infrared spectrograph NIRSpec in understanding the assembly and evolution of galaxies

AbstractThe near-infrared spectrograph NIRSpec is one of four instruments aboard the James Webb Space Telescope (JWST). It offers seven dispersers covering the wavelength range from 0.6 to 5.3 micron with resolutions from R ∼ 100 to R ∼ 2700. Using an array of micro-shutters for target selection, the multi-object spectroscopy mode of NIRSpec will be capable of obtaining spectra from a few tens to more than 200 objects simultaneously. It also features an integral field unit with a 3 by 3 arcseconds field of view, and various slits for high contrast spectroscopy of individual objects. We will provide an overview of the capabilities and performances of these three observing modes highlighting how NIRSpec will contribute to the quest to further understand the assembly and evolution of galaxies from the end of re-ionisation epoch to the present day.

Optical design for CETUS: a wide-field 1.5-m aperture UV payload being studied for a NASA probe class mission study

As part of a study funded by NASA headquarters, we are developing a probe-class mission concept called the Cosmic Evolution through UV Spectroscopy (CETUS). CETUS includes a 1.5-m aperture diameter telescope with a large field of view (FOV). CETUS includes three scientific instruments: a far ultraviolet (FUV) and near ultraviolet (NUV) imaging camera (CAM); a NUV multiobject spectrograph (MOS); and a dual-channel point/slit spectrograph (PSS) in the Lyman ultraviolet (LUV), FUV, and NUV spectral regions. The large FOV three-mirror anastigmatic (TMA) optical telescope assembly (OTA) simultaneously feeds the three separate scientific instruments. That is, the instruments view separate portions of the TMA image plane, enabling parallel operation by the three instruments. The field viewed by the MOS, whose design is based on an Offner-type spectrographic configuration to provide wide FOV correction, is actively configured to select and isolate numerous field sources using a next-generation micro-shutter array. The two-channel CAM design is also based on an Offner-like configuration. The PSS performs high spectral resolution spectroscopy on unresolved objects over the NUV region with spectral resolving power, R ∼ 40,000, in an echelle mode. The PSS also performs long-slit imaging spectroscopy at R ∼ 20,000 in the LUV and FUV spectral regions with two aberration-corrected, blazed, holographic gratings used in a Rowland-like configuration. The optical system also includes two fine guidance sensors, and wavefront sensors that sample numerous locations over the full OTA FOV. In-flight wavelength calibration is performed by a wavelength calibration system, and flat-fielding is also performed, both using in-flight calibration sources. We describe the current optical design of CETUS and the major trade studies leading to the design.

Abundant serendipitous emission line sources with JWST/NIRSpec

Abstract The James Webb Space Telescope will provide observational capabilities that far exceed those of current ground- or space-based instrumentation. In particular, the Near-Infrared Spectrograph (NIRSpec) instrument will take highly sensitive spectroscopic data for hundreds of objects simultaneously from 0.6 to 5.3 $\mu$m. Current photometric observations suggest a large and increasing number of faint (MUV > −16) galaxies at high redshift, with increasing evidence that galaxies at these redshifts have optical emission lines with extremely high equivalent widths. A simple model of their emission line fluxes and number density evolution with redshift is used to predict the number of galaxies that NIRSpec will serendipitously observe during normal observations with the microshutter array. At exposure times of ≈20 h in the low-resolution prism mode, the model predicts that, on average, every open 1 × 3 ‘microslit’ will contain an un-targeted galaxy with a detectable [O iii] and/or H α emission line; while most of these detections are predicted to be of [O iii], H α detections alone would still number 0.56 per open ‘microslit’ for this exposure time. Many of these objects are spectroscopically detectable even when they are fainter than current photometric limits and/or their flux centroids lie outside of the open microshutter area. The predicted number counts for such galaxies match z ∼ 2 observations of [O iii] emitters from slitless grism spectroscopic surveys, as well as theoretical predictions based on sophisticated modelling of galaxy spectral energy distributions. These serendipitous detections could provide the largest numbers of z > 6 spectroscopic confirmations in the deepest NIRSpec surveys.

Evaluation of digital micromirror devices for use in space-based multiobject spectrometer application

The astronomical community continues to be interested in suitable programmable slit masks for use in multi-object spectrometers (MOSs) on space missions. There have been ground-based MOS utilizing digital micromirror devices (DMDs) and they have proven to be highly accurate and reliable instruments. This paper summarizes the results of a continuing study to investigate the performance of DMDs under conditions associated with space deployment. This includes the response of DMDs to radiation, to the vibration and mechanical shock loads associated with launch, and the operability of DMD under cryogenic temperatures. The optical contrast ratio and a study of the long-term reflectance of a bare device have also been investigated. The results of the radiation testing demonstrate that DMDs in orbit would experience negligible heavy-ion induced single event upset (SEU) rate burden, we predict SEU rate of 5.6 micromirrors per 24 hours. Vibration and mechanical shock testing was performed according to the NASA General Environmental Verification Standard (GEVS), no mirrors failed in the devices tested. The results of low temperature testing suggest that DMDs are not affected by the thermal load and operate smoothly at temperatures at least as low as 78 K. The reflectivity of a bare DMD did not measurably change even after being exposed to ambient conditions over a period of 13 months. The measured contrast ratio (on state vs off state of the DMD micromirrors) was greater than 6000/:1 when illuminated with an f/4 optical beam. Overall, DMDs are extremely robust and promise to provide a reliable alternative to micro shutter arrays (MSA) to be used in space as remotely programmable slit masks for MOS design.

James Webb Space Telescope microshutter arrays and beyond

Microshutter array (MSA) subsystems were developed at NASA Goddard Space Flight Center as multiobject selectors for the Near-Infrared Spectrograph (NIRSpec) instrument on the James Webb Space Telescope (JWST). The subsystem will enable NIRSpec to simultaneously obtain spectra from >100 targets, which, in turn, increases instrument efficiency 100-fold. This system represents one of the three major innovations on the JWST that is scheduled to be launched in 2018 as the successor to the Hubble Space Telescope. Featuring torsion hinges, light shields, magnetic actuation, and electrostatic latching and addressing, microshutters are designed for the selective transmission of light with high efficiency and contrast. Complete MSA assemblies consisting of 365×171 microshutters were successfully fabricated and tested, and passed a series of critical reviews for programmable 2-D addressing, life tests, and optical contrast tests. At the final stage of the JWST MSA fabrication, we began to develop the next generation microshutter arrays (NGMSA) for future telescopes. These telescopes will require a much larger field of view than JWSTs. We discussed strategies for fabrication of a proof-of-concept NGMSA that will be modular in design and electrostatically actuated. The details of NGMSA development will be discussed in a follow-up paper.

All NIRspec Needs is HST/WFC3 Pre-Imaging? The Use of Milky Way Stars in WFC3 Imaging to Register NIRspec MSA Observations

The James Webb Space Telescope (JWST) will be an exquisite new near-infrared observatory with imaging and multi-object spectroscopy through ESA’s NIRspec instrument with its unique Micro-Shutter Array (MSA), allowing for slits to be positioned on astronomical targets by opening specific [Formula: see text]-wide micro shutter doors. To ensure proper Target Acquisition (TA), the on-sky position of the MSA needs to be verified before spectroscopic observations start. An onboard centroiding program registers the position of pre-identified guide stars in a TA image, a short pre-spectroscopy exposure without dispersion (image mode) through the MSA with all shutters open. The outstanding issue is the availability of Galactic stars in the right luminosity range for TA relative to typical high redshift targets. We explore this here using the stars and [Formula: see text] candidate galaxies identified in the source extractor catalogs of Brightest of Reionizing Galaxies survey (BoRG[z8]), a pure-parallel program with Hubble Space Telescope Wide-Field Camera 3. We find that (a) a single WFC3 field contains enough Galactic stars to satisfy the NIRspec astrometry requirement (20 milli-arcseconds), provided its and the NIRspec TA’s are [Formula: see text] AB in WFC3 [Formula: see text], (b) a single WFC3 image can therefore serve as the pre-image if need be, (c) a WFC3 mosaic and accompanying TA image satisfy the astrometry requirement at [Formula: see text] AB mag in WFC3 [Formula: see text], (d) no specific Galactic latitude requires deeper TA imaging due to a lack of Galactic stars, and (e) a depth of [Formula: see text] AB mag in WFC3 [Formula: see text] is needed if a guide star in the same MSA quadrant as a target is required. We take the example of a BoRG identified [Formula: see text] candidate galaxy and require a Galactic star within 20[Formula: see text] of it. In this case, a depth of 25.5 AB in [Formula: see text] is required (with [Formula: see text]97% confidence).