One of the leading direct Imaging techniques, particularly in ground-based imaging, uses a coronagraphic system and integral field spectrograph (IFS). The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an IFS that has been built for the Subaru telescope. CHARIS has been delivered to the observatory and now sits behind the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. CHARIS has ‘high’ and ‘low’ resolution operating modes. The high-resolution mode is used to characterize targets in J, H, and K bands at R70. The low-resolution prism is meant for discovery and spans J+H+K bands (1.15-2.37 microns) with a spectral resolution of R18. This discovery mode has already proven better than 15-sigma detections of HR8799c,d,e when combining ADI+SDI. Using SDI alone, planets c and d have been detected in a single 24 second image. The CHARIS team is optimizing instrument performance and refining ADI+SDI recombination to maximize our contrast detection limit. In addition to the new observing modes, CHARIS has demonstrated a design with high robustness to spectral crosstalk. CHARIS has completed commissioning and is open for science observations.
A primary goal of direct imaging techniques is to spectrally characterize the atmospheres of planets around other stars at extremely high contrast levels. To achieve this goal, coronagraphic instruments have favored integral field spectrographs (IFS) as the science cameras to disperse the entire search area at once and obtain spectra at each location, since the planet position is not known a priori. These spectrographs are useful against confusion from speckles and background objects, and can also help in the speckle subtraction and wavefront control stages of the coronagraphic observation. We present a software package, the Coronagraph and Rapid Imaging Spectrograph in Python (crispy) to simulate the IFS of the WFIRST Coronagraph Instrument (CGI). The software propagates input science cubes using spatially and spectrally resolved coronagraphic focal plane cubes, transforms them into IFS detector maps and ultimately reconstructs the spatio-spectral input scene as a 3D datacube. Simulated IFS cubes can be used to test data extraction techniques, refine sensitivity analyses and carry out design trade studies of the flight CGI-IFS instrument. crispy is a publicly available Python package and can be adapted to other IFS designs.
The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an integral field spectrograph (IFS) that has been built for the Subaru telescope. CHARIS has two imaging modes; the high-resolution mode is R82, R69, and R82 in J, H, and K bands respectively while the low-resolution discovery mode uses a second low-resolution prism with R19 spanning 1.15-2.37 microns (J+H+K bands). The discovery mode is meant to augment the low inner working angle of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) adaptive optics system, which feeds CHARIS a coronagraphic image. The goal is to detect and characterize brown dwarfs and hot Jovian planets down to contrasts five orders of magnitude dimmer than their parent star at an inner working angle as low as 80 milliarcseconds. CHARIS constrains spectral crosstalk through several key aspects of the optical design. Additionally, the repeatability of alignment of certain optical components is critical to the calibrations required for the data pipeline. Specifically, the relative alignment of the lenslet array, prism, and detector must be highly stable and repeatable between imaging modes. We report on the measured repeatability and stability of these mechanisms, measurements of spectral crosstalk in the instrument, and the propagation of these errors through the data pipeline. Another key design feature of CHARIS is the prism, which pairs Barium Fluoride with Ohara L-BBH2 high index glass. The dispersion of the prism is significantly more uniform than other glass choices, and the CHARIS prisms represent the first NIR astronomical instrument that uses L-BBH2 as the high index material. This material choice was key to the utility of the discovery mode, so significant efforts were put into cryogenic characterization of the material. The final performance of the prism assemblies in their operating environment is described in detail. The spectrograph is going through final alignment, cryogenic cycling, and is being delivered to the Subaru telescope in April 2016. This paper is a report on the laboratory performance of the spectrograph, and its current status in the commissioning process so that observers will better understand the instrument capabilities. We will also discuss the lessons learned during the testing process and their impact on future high-contrast imaging spectrographs for wavefront control.
We present the design, integration, and test of the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES) integral field spectrograph (IFS). The PISCES design meets the science requirements for the Wide-Field InfraRed Survey Telescope (WFIRST) Coronagraph Instrument (CGI). PISCES was integrated and tested in the integral field spectroscopy laboratory at NASA Goddard. In June 2016, PISCES was delivered to the Jet Propulsion Laboratory (JPL) where it was integrated with the Shaped Pupil Coronagraph (SPC) High Contrast Imaging Testbed (HCIT). The SPC/PISCES configuration will demonstrate high contrast integral field spectroscopy as part of the WFIRST CGI technology development program.
The Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) is an integral field spectrograph (IFS) being built for the Subaru telescope. CHARIS will take spectra of brown dwarfs and hot Jovian planets in the coronagraphic image provided by the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) and AO188 adaptive optics systems.1, 2 The system is designed to detect objects five orders of magnitude dimmer than their parent star down to an 80 milliarcsecond inner working angle. For characterization, CHARIS has a high-resolution prism providing an average spectral resolution of R82, R69, and R82 in J, H, and K bands respectively. The so-called discovery mode uses a second low-resolution prism with an average spectral resolution of R19 spanning 1.15-2.37 microns (J+H+K bands). This is unique compared to other high contrast IFS designs. It augments low inner working angle performance by reducing the separation at which we can rely on spectral differential imaging. The principal challenge for a high-contrast IFS is quasi-static speckles, which cause undue levels of spectral crosstalk. CHARIS has addressed this through several key design aspects that should constrain crosstalk between adjacent spectral features to be below 1%. Sitting on the Nasmyth platform, the alignment between the lenslet array, prism, and detector will be highly stable, key for the performance of the data pipeline. Nearly every component has arrived and the project is entering its final build phase. Here we review the science case, the resulting design, status of final construction, and lessons learned that are directly applicable to future exoplanet instruments.
The PISCES (Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies) is a lenslet array based integral field spectrograph (IFS) designed to advance the technology readiness of the WFIRST-AFTA high contrast Coronagraph Instrument. We present the end to end optical simulator and plans for the data reduction pipeline (DRP). The optical simulator was created with a combination of the IDL-based PROPER library and Zemax, while the data reduction pipeline is a modified version of the Gemini Planet Imager's (GPI) IDL pipeline. The simulations of the propagation of light through the instrument are based on Fourier transform algorithms. The DRP enables transformation of the PISCES IFS data to calibrated spectral data cubes.
We describe the expected scientific capabilities of CHARIS, a high-contrast integral-field spectrograph (IFS) currently under construction for the Subaru telescope. CHARIS is part of a new generation of instruments, enabled by extreme adaptive optics (AO) systems (including SCExAO at Subaru), that promise greatly improved contrasts at small angular separation thanks to their ability to use spectral information to distinguish planets from quasistatic speckles in the stellar point-spread function (PSF). CHARIS is similar in concept to GPI and SPHERE, on Gemini South and the Very Large Telescope, respectively, but will be unique in its ability to simultaneously cover the entire near-infrared J, H, and K bands with a low-resolution mode. This extraordinarily broad wavelength coverage will enable spectral differential imaging down to angular separations of a few λ/D, corresponding to ~0".1. SCExAO will also offer contrast approaching 10-5 at similar separations, ~0".1–0".2. The discovery yield of a CHARIS survey will depend on the exoplanet distribution function at around 10 AU. If the distribution of planets discovered by radial velocity surveys extends unchanged to ~20 AU, observations of ~200 mostly young, nearby stars targeted by existing high-contrast instruments might find ~1–3 planets. Carefully optimizing the target sample could improve this yield by a factor of a few, while an upturn in frequency at a few AU could also increase the number of detections. CHARIS, with a higher spectral resolution mode of R ~ 75, will also be among the best instruments to characterize planets and brown dwarfs like HR 8799 cde and κ and b.
Princeton University is building the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS),
an integral field spectrograph (IFS) for the Subaru telescope. CHARIS is funded by the National Astronomical
Observatory of Japan and is designed to take high contrast spectra of brown dwarfs and hot Jovian planets in
the coronagraphic image provided by the Coronagraphic Extreme Adaptive Optics (SCExAO) and the AO188
adaptive optics systems. The project is now in the build and test phase at Princeton University. Once laboratory
testing has been completed CHARIS will be integrated with SCExAO and AO188 in the winter of 2016. CHARIS
has a high-resolution characterization mode in J, H, and K bands. The average spectral resolution in J, H, and
K bands are R82, R68, and R82 respectively, the uniformity of which is a direct result of a new high index
material, L-BBH2. CHARIS also has a second low-resolution imaging mode that spans J,H, and K bands with
an average spectral resolution of R19, a feature unique to this instrument. The field of view in both imaging
modes is 2.07x2.07 arcseconds. SCExAO+CHARIS will detect objects five orders of magnitude dimmer than
their parent star down to an 80 milliarcsecond inner working angle. The primary challenge with exoplanet
imaging is the presence of quasi-static speckles in the coronagraphic image. SCExAO has a wavefront control
system to suppress these speckles and CHARIS will address their impact on spectral crosstalk through hardware
design, which drives its optical and mechanical design. CHARIS constrains crosstalk to be below 1% for an
adjacent source that is a full order of magnitude brighter than the neighboring spectra. Since CHARIS is on the
Nasmyth platform, the optical alignment between the lenslet array and prism is highly stable. This improves the
stability of the spectra and their orientation on the detector and results in greater stability in the wavelength
solution for the data pipeline. This means less uncertainty in the post-processing and less overhead for on-sky
calibration procedures required by the data pipeline. Here we present the science case, design, and construction
status of CHARIS. The design and lessons learned from testing CHARIS highlights the choices that must be
considered to design an IFS for high signal-to-noise spectra in a coronagraphic image. The design considerations
and lessons learned are directly applicable to future exoplanet instrumentation for extremely large telescopes
and space observatories capable of detecting rocky planets in the habitable zone.
ERIS is an image simulator for CHARIS, the high-contrast exoplanet integral field spectrograph (IFS) being built at Princeton University for the Subaru telescope. We present here the software design and implementation of the ERIS code. ERIS simulates CHARIS FITS images and data cubes that are used for developing the data reduction pipeline and verifying the expected CHARIS performance. Components of the software include detailed models of the light source (such as a star or exoplanet), atmosphere, telescope, adaptive optics systems (AO188 and SCExAO), CHARIS IFS and the Hawaii2-RG infrared detector. Code includes novel details such as the phase errors at the lenslet array, optical wavefront error maps and pinholes for reducing crosstalk, just to list a few. The details of the code as well as several simulated images are presented in this paper. This IFS simulator is critical for the CHARIS data analysis pipeline development, minimizing troubleshooting in the lab and on-sky and the characterization of crosstalk.
High-contrast imaging techniques now make possible both imaging and spectroscopy of planets around nearby stars. We present the optical design for the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph (IFS) for imaging exoplanets on the Subaru telescope. The IFS will provide spectral information for 138 × 138 spatial elements over a 2.07 arcsec × 2.07 arcsec field of view (FOV). CHARIS will operate in the near infrared (λ = 1.15 - 2.5μm) and will feature two spectral resolution modes of R ~ 18 (low-res mode) and R ~ 73 (high-res mode). Taking advantage of the Subaru telescope adaptive optics systems and coronagraphs (AO188 and SCExAO), CHARIS will provide sufficient contrast to obtain spectra of young self-luminous Jupiter-mass exoplanets. CHARIS will undergo CDR in October 2013 and is projected to have first light by the end of 2015. We report here on the current optical design of CHARIS and its unique innovations.
We present a novel optical integral field spectrograph (IFS) called the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES), which will be a facility class instrument within the NASA Exoplanet Exploration Program's High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory. Integral field spectroscopy is ideal for imaging faint exoplanets: it enables spectral characterization of exoplanet atmospheres and can improve contrast by providing chromatic measurements of the target star's point-spread function (PSF). PISCES at the HCIT will be the first IFS to demonstrate imaging spectroscopy in the 10-9 contrast regime required for characterizing exoplanets imaged in scattered light. It is directly relevant as a prototype for IFS science instruments that could fly with the AFTA Coronagraph, the Exoplanet Probe missions currently under study, and/or the ATLAST mission concept. We present the instrument requirements, a baseline design for PISCES, a simulation of its performance, a solution to mitigate spectral crosstalk, experimental verification of our simulator, and the final vacuum compatible opto-mechanical design. PISCES will be assembled and tested at the Goddard Space Flight Center (GSFC), and subsequently delivered and integrated into the HCIT facility. Testing at HCIT will verify the performance of PISCES and its ability to meet the requirements of a space mission, will enable investigations into broadband wavefront control using the IFS as an image plane sensor, and will allow tests of contrast enhancement via multiwavelength differential imaging post-processing. Together with wavefront control and starlight suppression, PISCES is thus a key element for maturing the overall integrated system for a future coronagraphic space mission. PISCES is scheduled to receive first light in the HCIT in 2015.
Princeton University is building an integral field spectrograph (IFS), the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), for integration with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system and the AO188 adaptive optics system on the Subaru telescope. CHARIS and SCExAO will measure spectra of hot, young Jovian planets in a coronagraphic image across J, H, and K bands down to an 80 milliarcsecond inner working angle. SCExAO’s coronagraphs and wavefront control system will make it possible to detect companions five orders of magnitude dimmer than their parent star. However, quasi-static speckles in the image contaminate the signal from the planet. In an IFS this also causes uncertainty in the spectra due to diffractive cross-contamination, commonly referred to as crosstalk. Post-processing techniques can subtract these speckles, but they can potentially skew spectral measurements, become less effective at small angular separation, and at best can only reduce the crosstalk down to the photon noise limit of the contaminating signal. CHARIS will address crosstalk effects of a high contrast image through hardware design, which drives the optical and mechanical design of the assembly. The work presented here sheds light on the optical and mechanical considerations taken in designing the IFS to provide high signal-to-noise spectra in a coronagraphic image from and extreme adaptive optics image. The design considerations and lessons learned are directly applicable to future exoplanet instrumentation for extremely large telescopes and space observatories capable of detecting rocky planets in the habitable zone.
Recent developments in high-contrast imaging techniques now make possible both imaging and spectroscopy of planets around nearby stars. We present the conceptual design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph (IFS) for imaging exo-planets on the Subaru telescope. The IFS will provide spectral information for 140x140 spatial elements over a 1.75 arcsecs x 1.75 arcsecs field of view (FOV). CHARIS will operate in the near infrared (λ = 0.9-2.5μm) and provide a spectral resolution of R = 14, 33, and 65 in three separate observing modes. Taking advantage of the adaptive optics systems and advanced coronagraphs (AO188 and SCExAO) on the Subaru telescope, CHARIS will provide sufficient contrast to obtain spectra of young self-luminous Jupiter-mass exoplanets. CHARIS is in the early design phases and is projected to have first light by the end of 2015. We report here on the current conceptual design of CHARIS and the design challenges.
Ground-based telescopes equipped with adaptive-optics (AO) systems and specialized science cameras are now capable of directly detecting extrasolar planets. We present the expected scientific capabilities of CHARIS, the Coronagraphic High Angular Resolution Imaging Spectrograph, which is being built for the Subaru 8.2 m telescope of the National Astronomical Observatory of Japan. CHARIS will be implemented behind the new extreme adaptive optics system at Subaru, SCExAO, and the existing 188-actuator system AO188. CHARIS will offer three observing modes over near-infrared wavelengths from 0.9 to 2.4 μm (the y-, J-, H-, and K-bands), including a low-spectral-resolution mode covering this entire wavelength range and a high-resolution mode within a single band. With these capabilities, CHARIS will offer exceptional sensitivity for discovering giant exoplanets, and will enable detailed characterization of their atmospheres. CHARIS, the only planned high-contrast integral field spectrograph on an 8m-class telescope in the Northern Hemisphere, will complement the similar instruments such as Project 1640 at Palomar, and GPI and SPHERE in Chile.