The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT) that will be used to sample the corrected adaptive optics field by NFIRAOS with a near-infrared (0.8 - 2.4 µm) imaging camera and Integral Field Spectrograph (IFS). In order to understand the science case specifications of the IRIS instrument, we use the IRIS data simulator to characterize photometric precision and accuracy of the IRIS imager. We present the results of investigation into the effects of potential ghosting in the IRIS optical design. Each source in the IRIS imager field of view results in ghost images on the detector from IRIS’s wedge filters, entrance window, and Atmospheric Dispersion Corrector (ADC) prism. We incorporated each of these ghosts into the IRIS simulator by simulating an appropriate magnitude point source at a specified pixel distance, and for the case of the extended ghosts redistributing flux evenly over the area specified by IRIS’s optical design. We simulate the ghosting impact on the photometric capabilities, and found that ghosts generally contribute negligible effects on the flux counts for point sources except for extreme cases where ghosts coalign with a star of ▵m>2 fainter than the ghost source. Lastly, we explore the photometric precision and accuracy for single sources and crowded field photometry on the IRIS imager.
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.
Knowledge of the point spread function (PSF) is critical to many astronomical science cases. However, the PSF can be very difficult to estimate for cases where there are many crowded point sources or for observations of extended objects. Additionally, for adaptive optics observations, the PSF can be very complex with both spatial and temporal variability in the PSF. Integral-field spectroscopy behind adaptive optics is especially challenging because the fields of view are typically too small to sample the halo for even a single PSF. Here, we present a method for semi-empirical PSF reconstruction for integral field spectrographs using a combination of point source observations on a parallel imager, instrumental aberration measurements, and atmospheric turbulence profiles. This work builds upon the PSF reconstruction project AIROPA designed for imaging and extending it to IFU work (AIROPA-IFU). By using empirical calibrators from the parallel imager, which has a much larger field of view, and accounting for anisoplantic effects and instrumental aberrations, we can predict the PSF on the spectrograph. An important aspect is being able to predict the PSF at many different wavelengths based on observations from broad-band imaging. Here, we discuss how science cases such as observations of stars at the Galactic center can benefit from this method. We also establish metrics to quantitatively assess the performance of PSF reconstruction. We show that for bright stars, AIROPA-IFU can produce spectra with signal to noise ratio 50% higher than with simple aperture extraction of a data cube.
Infrared Imaging Spectrograph (IRIS) is the first light instrument for the Thirty Meter Telescope (TMT) that consists of a near-infrared (0.84 to 2.4 micron) imager and integral field spectrograph (IFS) which operates at the diffraction-limit utilizing the Narrow-Field Infrared Adaptive Optics System (NFIRAOS). The imager will have a 34 arcsec x 34 arcsec field of view with 4 milliarcsecond (mas) pixels. The IFS consists of a lenslet array and slicer, enabling four plate scales from 4 mas to 50 mas, multiple gratings and filters, which in turn will operate hundreds of individual modes. IRIS, operating in concert with NFIRAOS will pose many challenges for the data reduction system (DRS). Here we present the updated design of the real-time and post-processing DRS. The DRS will support two modes of operation of IRIS: (1) writing the raw readouts sent from the detectors and performing the sampling on all of the readouts for a given exposure to create a raw science frame; and (2) reduction of data from the imager, lenslet array and slicer IFS. IRIS is planning to save the raw readouts for a given exposure to enable sophisticated processing capabilities to the end users, such as the ability to remove individual poor seeing readouts to improve signal-to-noise, or from advanced knowledge of the point spread function (PSF). The readout processor (ROP) is a key part of the IRIS DRS design for writing and sampling of the raw readouts into a raw science frame, which will be passed to the TMT data archive. We discuss the use of sub-arrays on the imager detectors for saturation/persistence mitigation, on-detector guide windows, and fast readout science cases (< 1 second).
The integral field spectrograph OSIRIS at Keck I has been used to measure the motion of the stars around the supermassive black hole at the Center of the Galaxy. The small field of view provided and the crowding of the region prevent any good PSF estimate. A parallel imager can be used simultaneously to the IFU. However, its distance of 19 arcseconds prevents the observed PSF to be directly applied to the IFU because of anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has developed an algorithms to predict PSF variability for Keck AO images (Off-axis PSF reconstruction, AIROPA software package). AIROPA allows us to use the parallel imager to correctly predict the IFU’s PSF. We modified this package to adapt it to the case of OSIRIS imager and IFU (AIROPA-IFU) and characterized the instrumental aberrations of both detectors. Here, we present preliminary results of the application of this post-processing tool to OSIRIS datasets of the Galactic Center.
Since the start of operations in 1993, the twin 10 meter W. M. Keck Observatory 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 and UC instrument development teams. The observatory adapts and responds to the observers’ evolving needs as defined in the observatory’s strategic plan, periodically refreshed in collaboration with the science community. This paper summarizes the performance of recently commissioned infrastructure projects, technology upgrades, and new additions to the suite of instrumentation at the observatory. We will also provide a status of projects currently in the design or development phase, and since we need to keep our eye on the future, we mention projects in exploratory phases that originate from our strategic plan. Recently commissioned projects include telescope control system upgrades, OSIRIS spectrometer and imager upgrades, and deployments of the Keck Cosmic Web Imager (KCWI), the Near-Infrared Echellette Spectrometer (NIRES), and the Keck I Deployable Tertiary Mirror (KIDM3). Under development are upgrades to the NIRSPEC instrument and adaptive optics (AO) system. Major instrumentation in design phases include the Keck Cosmic Reionization Mapper and the Keck Planet Finder. Future instrumentation studies and proposals underway include a Ground Layer Adaptive Optics system, NIRC2 upgrades, the energy sensitive instrument KRAKENS, an integral field spectrograph LIGER, and a laser tomography AO upgrade. Last, we briefly discuss recovering MOSFIRE and its return to science operations.
General relativity can be tested in the strong gravity regime by monitoring stars orbiting the supermassive black hole at the Galactic Center with adaptive optics. However, the limiting source of uncertainty is the spatial PSF variability due to atmospheric anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has completed a project developing algorithms to predict PSF variability for Keck AO images. We have created a new software package (AIROPA), based on modified versions of StarFinder and Arroyo, that takes atmospheric turbulence profiles, instrumental aberration maps, and images as inputs and delivers improved photometry and astrometry on crowded fields. This software package will be made publicly available soon.
IRIS (InfraRed Imaging Spectrograph) is the diffraction-limited first light instrument for the Thirty Meter Telescope (TMT) that consists of a near-infrared (0.84 to 2.4 μm) imager and integral field spectrograph (IFS). The IFS makes use of a lenslet array and slicer for spatial sampling, which will be able to operate in 100’s of different modes, including a combination of four plate scales from 4 milliarcseconds (mas) to 50 mas with a large range of filters and gratings. The imager will have a field of view of 34×34 arcsec2 with a plate scale of 4 mas with many selectable filters. We present the preliminary design of the data reduction system (DRS) for IRIS that need to address all of these observing modes. Reduction of IRIS data will have unique challenges since it will provide real-time reduction and analysis of the imaging and spectroscopic data during observational sequences, as well as advanced post-processing algorithms. The DRS will support three basic modes of operation of IRIS; reducing data from the imager, the lenslet IFS, and slicer IFS. The DRS will be written in Python, making use of open-source astronomical packages available. In addition to real-time data reduction, the DRS will utilize real-time visualization tools, providing astronomers with up-to-date evaluation of the target acquisition and data quality. The quick look suite will include visualization tools for 1D, 2D, and 3D raw and reduced images. We discuss the overall requirements of the DRS and visualization tools, as well as necessary calibration data to achieve optimal data quality in order to exploit science cases across all cosmic distance scales.
The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared Imaging Spectrograph) will complete its preliminary design phase in 2016. The IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral field spectrograph (IFS) and imager that are able to conduct simultaneous diffraction-limited observations behind the advanced adaptive optics system NFIRAOS. The IRIS science cases have continued to be developed and new science studies have been investigated to aid in technical performance and design requirements. In this development phase, the IRIS science team has paid particular attention to the selection of filters, gratings, sensitivities of the entire system, and science cases that will benefit from the parallel mode of the IFS and imaging camera. We present new science cases for IRIS using the latest end-to-end data simulator on the following topics: Solar System bodies, the Galactic center, active galactic nuclei (AGN), and distant gravitationally-lensed galaxies. We then briefly discuss the necessity of an advanced data management system and data reduction pipeline.
One of the primary scientific limitations of adaptive optics (AO) has been the incomplete knowledge of the point spread function (PSF), which has made it difficult to use AO for accurate photometry and astrometry in both crowded and sparse fields, for extracting intrinsic morphologies and spatially resolved kinematics, and for detecting faint sources in the presence of brighter sources. To address this limitation, we initiated a program to determine and demonstrate PSF reconstruction for science observations obtained with Keck AO. This paper aims to give a broad view of the progress achieved in implementing a PSF reconstruction capability for Keck AO science observations.
This paper describes the implementation of the algorithms, and the design and development of the prototype operational tools for automated PSF reconstruction. On-sky performance is discussed by comparing the reconstructed PSFs to the measured PSF’s on the NIRC2 science camera. The importance of knowing the control loop performance, accurate mapping of the telescope pupil to the deformable mirror and the science instrument pupil, and the telescope segment piston error are highlighted. We close by discussing lessons learned and near-term future plans.
We present an overview of the design of IRIS, an infrared (0.84 - 2.4 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
IRIS (InfraRed Imaging Spectrograph) is a first light near-infrared diffraction limited imager and integral field
spectrograph being designed for the future Thirty Meter Telescope (TMT). IRIS is optimized to perform astronomical
studies across a significant fraction of cosmic time, from our Solar System to distant newly formed galaxies (Barton et
al. ). We present a selection of the innovative science cases that are unique to IRIS in the era of upcoming space and
ground-based telescopes. We focus on integral field spectroscopy of directly imaged exoplanet atmospheres, probing
fundamental physics in the Galactic Center, measuring 104 to 1010 M supermassive black hole masses, resolved
spectroscopy of young star-forming galaxies (1 < z < 5) and first light galaxies (6 < z < 12), and resolved spectroscopy
of strong gravitational lensed sources to measure dark matter substructure. For each of these science cases we use the
IRIS simulator (Wright et al. , Do et al. ) to explore IRIS capabilities. To highlight the unique IRIS capabilities, we
also update the point and resolved source sensitivities for the integral field spectrograph (IFS) in all five broadband
filters (Z, Y, J, H, K) for the finest spatial scale of 0.004" per spaxel. We briefly discuss future development plans for the
data reduction pipeline and quicklook software for the IRIS instrument suite.
The Thirty Meter Telescope (TMT) with its first-light multi-conjugate adaptive optics system, NFIRAOS, and high-resolution imager, IRIS, is expected to take differential astrometric measurements with an accuracy on the order of tens of micro arcsec. This requires the control, correction, characterization and calibration of a large number of error sources and uncertainties, many of which have magnitudes much in excess of this level of accuracy. In addition to designing the observatory such that very high precision and accuracy astrometric observations are enabled, satisfying the TMT requirements can only be achieved by a careful calibration, observation and data reduction strategy. In this paper, we present descriptions of the individual errors sources, how and when they apply to different astrometry science cases and the mitigation methods required for each of them, as well as example results for individual error terms and the overall error budgets for a variety of different science cases.
Adaptive Optics observations have dramatically improved the quality and versatility of high angular resolution measurements of the center of our Galaxy. In this paper, we quantify the quality of our Adaptive Optics observations and report on the astrometric precision for the young stellar population that appears to reside in a stellar disk structure in the central parsec. We show that with our improved astrometry and a 16 year baseline, including 10 years of speckle and 6 years of laser guide star AO imaging, we reliably detect accelerations in the plane of the sky as small as 70 μas yr-2 (~2.5 km s-1 yr-1) and out to a projected radius from the supermassive black hole of 1."5 (~0.06 pc). With an increase in sensitivity to accelerations by a factor of ~6 over our previous efforts, we are able to directly probe the kinematic structure of the young stellar disk, which appears to have an inner radius of 0."8. We find that candidate disk members are on eccentric orbits, with a mean eccentricity of < e > = 0.30 ± 0.07. Such eccentricities cannot be explained by the relaxation of a circular disk with a normal initial mass function, which suggests the existence of a top-heavy IMF or formation in an initially eccentric disk.
Anisoplanatism is a primary source of photometric and astrometric error in single-conjugate adaptive optics. We present initial results of a project to model the off-axis optical transfer function in the adaptive optics system at the Keck II telescope. The model currently accounts for the effects of atmospheric anisoplanatism in natural guide star observations. The model for the atmospheric contribution to the anisoplanatic transfer function uses contemporaneous MASS/ DIMM measurements. Here we present the results of a validation campaign using observations of naturally guided visual binary stars under varying conditions, parameterized by the r0 and θ0 parameters of the C2n atmospheric turbulence profile. We are working to construct a model of the instrumental field-dependent aberrations in the NIRC2 camera using an artificial source in the Nasmyth focal plane. We also discuss our plans to extend the work to laser guide star operation.
Large ground-based telescopes equipped with adaptive optics (AO) systems have ushered in a new era of highresolution
infrared photometry and astrometry. Relative astrometric accuracies of <0.2 mas have already been
demonstrated from infrared images with spatial resolutions of 55-95 mas resolution over 10-20" fields of view.
Relative photometric accuracies of 3% and absolute photometric accuracies of 5%-20% are also possible. I will
review improvements and current limitations in astrometry and photometry with adaptive optics of crowded
stellar fields. These capabilities enable experiments such as measuring orbits for brown dwarfs and exoplanets,
studying our Galaxy's supermassive black hole and its environment, and identifying individual stars in young
star clusters, which can be used test the universality of the initial mass function.