We present the current design of WFOS, a wide-field UV/optical (0.31-1.0 µm) imaging spectrograph planned for first-light on the TMT International Observatory 30 m telescope. WFOS is optimized for high sensitivity across the entire optical waveband for low-to-moderate resolution (R ∼ 1500-5000) long-slit and multi-slit spectroscopy of very faint targets over a contiguous field of view of 8′ .3×3 ′ .0 at the f/15 Nasmyth focus of TMT. A key design goal for WFOS is stability and repeatability in all observing modes, made possible by its gravity-invariant opto-mechanical structure, with a vertical rotation axis and all reconfigurable components moving only in planes defined by tiered optical benches parallel to the Nasmyth platform. WFOS’s optics include a linear ADC correcting a 9′ diameter field, including both the science FoV and 4 patrolling acquisition, guiding, and wavefront sensing camera systems; a novel 2-mirror reflective collimator allowing the science FoV to be centered on the telescope optical axis; a dichroic beamsplitter dividing the collimated beam into 2 wavelength-optimized spectrometer channels (blue: 0.31-0.56 µm; red: 0.54-1.04 µm); selectable transmissive dispersers (VPH and/or VBG) with remotely configurable grating tilt (angle of incidence) and camera articulation that enable optimization of diffraction efficiency and wavelength coverage in each channel; all-refractive, wavelength-optimized f/2 spectrograph cameras, and UV/blue and red-optimized detector systems. The predicted instrumental through put of WFOS for spectroscopy averages > 56% over the full 0.31-1 µm range, from the ADC to the detector. When combined with the 30 m TMT aperture, WFOS will realize a factor of ∼20 gain in sensitivity compared to the current state of the art on 8-10 m-class telescopes.
Since the start of science operations in 1993, the twin 10-meter W. M. Keck Observatory (WMKO) telescopes have continued to maximize their scientific impact and to produce transformative discoveries that keep the observing community on the frontiers of astronomical research. Upgraded capabilities and new instrumentation are provided though collaborative partnerships with Caltech, the University of California, and the University of Hawaii instrument development teams, as well as industry and other organizations. This paper summarizes the performance of recently commissioned infrastructure projects, technology upgrades, and new additions to the suite of observatory instrumentation. We also provide a status of projects currently in design or development phases and, since we keep our eye on the future, summarize projects in exploratory phases that originate from our 2022 strategic plan developed in collaboration with our science community to adapt and respond to evolving science needs.
Many areas of astronomical research rely on deep blue wide-field imaging. Mauna Kea enjoys the very best UV transparency from the ground and the Keck telescopes with 10 meter f/1.75 primaries are well suited to a prime focus camera with a large angular field. Swinburne University leads a proposal to provide a camera (KWFI, for Keck Wide Field Imager) that is optimized in the UV but works well to 1μm wavelength. Keck has interchangeable top end modules, of which one is now unused and easily capable of housing the required corrector lens and detector enclosure. This paper concentrates on details of the KWFI optical design.
Ground-layer adaptive optics (GLAO) systems offer the possibility of improving the ”seeing” of large ground-based telescopes and increasing the efficiency and sensitivity of observations over a wide field-of-view. We explore the utility and feasibility of deploying a GLAO system at the W. M. Keck Observatory in order to feed existing and future multi-object spectrographs and wide-field imagers. We also briefly summarize science cases spanning exoplanets to high-redshift galaxy evolution that would benefit from a Keck GLAO system. Initial simulations indicate that a Keck GLAO system would deliver a 1.5x and 2x improvement in FWHM at optical (500 nm) and infrared (1.5
μm), respectively. The infrared instrument, MOSFIRE, is ideally suited for a Keck GLAO feed in that it has excellent image quality and is on the telescope’s optical axis. However, it lacks an atmospheric dispersion compensator, which would limit the minimum usable slit size for long-exposure science cases. Similarly, while LRIS and DEIMOS may be able to accept a GLAO feed based on their internal image quality, they lack either an atmospheric dispersion compensator (DEIMOS) or flexure compensation (LRIS) to utilize narrower slits matched to the GLAO image quality. However, some science cases needing shorter exposures may still benefit from Keck GLAO and we will investigate the possibility of installing an ADC.
The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) achieved first light on the W. M. Keck Observatory’s Keck I telescope on 4 April 2012 and quickly became the most popular Keck I instrument. One of the primary reasons for the instrument’s popularity is that it uses a configurable slitmask unit developed by the Centre Suisse d’Electronique et Microtechnique (CSEM SA) to isolate the light from up to 46 objects simultaneously. In collaboration with the instrument development team and CSEM engineers, the Keck observatory staff present how MOSFIRE is successfully used, and we identify what contributed to routine and trouble free nighttime operations.
This paper describes the as-built performance of MOSFIRE, the multi-object spectrometer and imager for the Cassegrain
focus of the 10-m Keck 1 telescope. MOSFIRE provides near-infrared (0.97 to 2.41 μm) multi-object spectroscopy over
a 6.1' x 6.1' field of view with a resolving power of R~3,500 for a 0.7" (0.508 mm) slit (2.9 pixels in the dispersion
direction), or imaging over a field of view of ~6.9' diameter with ~0.18" per pixel sampling. A single diffraction grating
can be set at two fixed angles, and order-sorting filters provide spectra that cover the K, H, J or Y bands by selecting 3rd,
4th, 5th or 6th order respectively. A folding flat following the field lens is equipped with piezo transducers to provide
tip/tilt control for flexure compensation at the <0.1 pixel level. Instead of fabricated focal plane masks requiring frequent
cryo-cycling of the instrument, MOSFIRE is equipped with a cryogenic Configurable Slit Unit (CSU) developed in
collaboration with the Swiss Center for Electronics and Microtechnology (CSEM). Under remote control the CSU can
form masks containing up to 46 slits with ~0.007-0.014" precision. Reconfiguration time is < 6 minutes. Slits are formed
by moving opposable bars from both sides of the focal plane. An individual slit has a length of 7.0" but bar positions can
be aligned to make longer slits in increments of 7.5". When masking bars are retracted from the field of view and the
grating is changed to a mirror, MOSFIRE becomes a wide-field imager. The detector is a 2K x 2K H2-RG HgCdTe
array from Teledyne Imaging Sensors with low dark current and low noise. Results from integration and commissioning
are presented.
MOSFIRE is a new multi-object near-infrared spectrometer for the Keck 1 telescope with a spectral resolving
power of R~3500 for a 0.7″ slit (2.9 pixels). The detector is a substrate-removed 2K × 2K HAWAII 2-RG HgCdTe
array from Teledyne Imaging Sensors with a cut-off wavelength of 2.5 μm and an operational temperature of
77K. Spectroscopy of faint objects sets the requirement for low dark current and low noise. MOSFIRE is also
an infrared camera with a 6.9′ field of view projected onto the detector with 0.18″ pixel sampling. Broad-band
imaging drives the requirement for 32-channel readout and MOSFIREs fast camera optics implies the need for
a very at detector. In this paper we report the final performance of the detector selected for MOSFIRE. The
array is operated using the SIDECAR ASIC chip inside the MOSFIRE dewar and v2.3 of the HxRG software.
Dark current plus instrument background is measured at <0.008 ē s−1 pixel−1 on average. Multiple Correlated
Double Sampling (MCDS) and Up-The-Ramp (UTR) sampling are both available. A read noise of <5ē rms is
achieved with MCDS 16 and the lowest noise of 3ē rms occurs for 64 samples. Charge persistence depends on
exposure level and shows a large gradient across this detector. However, the decay time constant is always ~660
seconds. Linearity and stability are also discussed.
Multi-object spectroscopy via custom slitmasks is a key capability on three instruments at the W. M. Keck Observatory.
Before observers can acquire spectra they must complete a complex procedure to align each slit with its corresponding
science target. We developed the Slitmask Alignment Tool (SAT), to replace a complex, inefficient, and error-prone
slitmask alignment process that often resulted in lost sky time for novice and experienced observers alike.
The SAT accomplishes rapid initial mask alignment, prevents field misidentification, accurately predicts alignment box
image locations, corrects for flexure-induced image displacement, verifies the instrument and exposure configuration,
and accommodates both rectangular and trapezoidal alignment box shapes. The SAT is designed to lead observers
through the alignment process and coordinate image acquisition with instrument and telescope moves to improve
efficiencies. By simplifying the process to just a few mouse clicks, the SAT enables even novice observers to achieve
robust, efficient, and accurate alignment of slitmasks on all three Keck instruments supporting multislit spectroscopy,
saving substantial observing time.
MOSFIRE is a unique multi-object spectrometer and imager for the Cassegrain focus of the 10 m Keck 1 telescope. A
refractive optical design provides near-IR (0.97 to 2.45 μm) multi-object spectroscopy over a 6.14' x 6.14' field of view
with a resolving power of R~3,270 for a 0.7" slit width (2.9 pixels in the dispersion direction), or imaging over a field of
view of 6.8' diameter with 0.18" per pixel sampling. A single diffraction grating can be set at two fixed angles, and
order-sorting filters provide spectra that cover the K, H, J or Y bands by selecting 3rd, 4th, 5th or 6th order respectively. A
folding flat following the field lens is equipped with piezo transducers to provide tip/tilt control for flexure compensation
at the 0.1 pixel level. A special feature of MOSFIRE is that its multiplex advantage of up to 46 slits is achieved using a
cryogenic Configurable Slit Unit or CSU developed in collaboration with the Swiss Centre for Electronics and Micro
Technology (CSEM). The CSU is reconfigurable under remote control in less than 5 minutes without any thermal
cycling of the instrument. Slits are formed by moving opposable bars from both sides of the focal plane. An individual
slit has a length of 7.1" but bar positions can be aligned to make longer slits. When masking bars are removed to their
full extent and the grating is changed to a mirror, MOSFIRE becomes a wide-field imager. Using a single, ASIC-driven,
2K x 2K H2-RG HgCdTe array from Teledyne Imaging Sensors with exceptionally low dark current and low noise,
MOSFIRE will be extremely sensitive and ideal for a wide range of science applications. This paper describes the design
and testing of the instrument prior to delivery later in 2010.
MOSFIRE, the multi-object spectrometer for infra-red exploration, is a near-IR (0.97-2.45 micron) spectrograph and
imager for the Cassegrain focus of the Keck I telescope. The optical design provides imaging and multi-object
spectroscopy over a field of view (FOV) of 6.14' x 6.14' with a resolving power of R~3,270 for a slit width of 0.7 arc
seconds (2.9 pixels along dispersion). The detector is a 2.5 micron cut-off 2K x 2K H2-RG HgCdTe array with a
SIDECAR ASIC for detector control. A special feature of MOSFIRE is that its multiplex advantage of up to 46 slits is
achieved using a cryogenic Configurable Slit Unit (developed in collaboration with the Swiss Centre for Electronics and
Micro Technology) reconfigurable under remote control in <5 minutes without thermal cycling. Slits are formed by
moving opposable bars from both sides of the focal plane. An individual slit has a length of ~7.1 arc seconds but bar
positions can be aligned to make longer slits. A single diffraction grating in two positions along with order-sorting filters
gives essentially full coverage of the K, H, J and Y bands using 3rd, 4th, 5th or 6th order respectively. The grating and a
mirror are mounted back-to-back, and when the bars are retracted from the FOV MOSFIRE becomes a wide-field
imager. A piezo tip-tilt mirror following the field lens is used to provide flexure compensation at the 0.1 pixel level. Two
large CCR heads allow the instrument to reach operating temperature in ~7 days. MOSFIRE is currently in construction.
Marc Davis, Sandra Faber, Jeffrey Newman, Andrew Phillips, Richard Ellis, Charles Steidel, C. Conselice, Alison Coil, D. Finkbeiner, David Koo, Puragra Guhathakurta, B. Weiner, Ricardo Schiavon, C. Willmer, Nicholas Kaiser, Gerard Luppino, Gregory Wirth, Andrew Connolly, Peter Eisenhardt, M. Cooper, B. Gerke
The DEIMOS spectrograph has now been installed on the Keck-II telescope and commissioning is nearly complete. The DEEP2 Redshift Survey, which will take approximately 120 nights at the Keck Observatory over a three year period and has been designed to utilize the power of DEIMOS, began in the summer of 2002. The multiplexing power and high efficiency of DEIMOS enables us to target 1000 faint galaxies per clear night. Our goal is to gather high-quality spectra of ≈ 60,000 galaxies with z>0.75 in order to study the properties and large scale clustering of galaxies at z ≈ 1. The survey will be executed at high spectral resolution, R=λ/Δλ ≈ 5000, allowing us to work between the bright OH sky emission lines and to infer linewidths for many of the target galaxies (for several thousand objects, we will obtain rotation curves as well). The linewidth data will facilitate the execution of the classical redshift-volume cosmological test, which can provide a precision measurement of the equation of state of the Universe. This talk reviews the project, summarizes our science goals and presents some early DEIMOS data.
There has been considerable progress made in the discovery, observation, and understanding of high redshift galaxies in the last few years; most of this progress is attributable to greatly improved spectroscopy throughput made possible by state-of-the-art instruments on the new generation of 8-10m telescopes. Here we review a few of the areas in which substantial progress has been made, and discuss the future of high redshift galaxy work in the context of the observational facilities that are either in operation or soon to come.
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