CHARIS

CHARIS
Name	CHARIS
Caption	CHARIS instrument mounted on Subaru Telescope
Type	Integral field spectrograph
Telescope	Subaru Telescope
Wavelength	Near-infrared (1.1–2.4 μm)
First light	2013
Location	Mauna Kea, Hawaii
Operator	National Astronomical Observatory of Japan

CHARIS

CHARIS is a high-contrast near-infrared integral field spectrograph designed for direct imaging and spectroscopy of exoplanets, circumstellar disks, and faint companions. Installed on the Subaru Telescope at Mauna Kea, it operates behind adaptive optics systems to deliver spatially resolved spectra across the J, H, and K bands. CHARIS complements instruments such as SPHERE, GPI, and NIRC2 by providing broad-band spectral characterization at moderate spectral resolution.

Overview

CHARIS, developed through collaboration among institutions including the National Astronomical Observatory of Japan, University of Tokyo, Princeton University, and NASA Jet Propulsion Laboratory, was conceived to address questions about young giant planets and protoplanetary environments first identified by facilities like Keck Observatory and Very Large Telescope. The instrument leverages techniques pioneered with instruments such as OSIRIS and Project 1640 to achieve speckle suppression and spectro-photometric fidelity. CHARIS provides integral field spectroscopy over a contiguous field of view, enabling simultaneous spatial and spectral measurements analogous to capabilities demonstrated by SINFONI and MUSE on the European Southern Observatory platforms.

Instrument Design and Specifications

CHARIS is an integral field spectrograph that uses a lenslet array to produce a grid of microspectra on a cryogenically cooled detector, following design principles used in IFU systems like NIFS and KCWI. The instrument covers approximately 1.1–2.4 μm with selectable spectral modes: a low-resolution broad-band mode (R~20) and a higher-resolution mode (R~70–90) optimized for characterization, similar in concept to spectral modes in GPI and SPHERE-IFS. The opto-mechanical train incorporates a cryostat, cold pupil stop, filter wheels, and dispersing elements derived from collaborations with groups experienced on Gemini Observatory instrumentation. CHARIS is mounted behind Subaru’s adaptive optics module, AO188, and the coronagraphic masks share heritage with vortex and Lyot coronagraph concepts tested on Palomar Observatory instruments. The detector is a near-infrared array akin to those supplied to projects like JWST NIRCam and HST WFC3/IR, cooled to reduce dark current and thermal background for high-contrast performance.

Science Objectives and Capabilities

CHARIS’s principal science objectives include direct detection and spectroscopic characterization of young exoplanets, study of protoplanetary and debris disks, and multiplicity surveys of low-mass companions similar to programs on Keck II and VLT. By delivering spectrophotometry across JHK bands, CHARIS enables atmospheric retrievals for molecular species such as H2O, CH4, and CO by comparison to models developed by groups associated with NASA Ames Research Center and University of Arizona. The instrument supports studies of formation pathways by measuring spectral signatures tied to effective temperature, surface gravity, and metallicity, providing constraints complementary to radial velocity surveys like those from HARPS and transit observations from Kepler and TESS. CHARIS’s high-contrast imaging capabilities also facilitate investigations of disk substructures revealed previously by ALMA and scattered-light imaging from Hubble Space Telescope instruments.

Operational History and Observations

CHARIS achieved first light on the Subaru Telescope in the 2010s and entered regular science operations integrated with Subaru programs and large surveys analogous to collaborations that used SEEDS and SHINE. Observing campaigns using CHARIS targeted benchmark systems such as young moving group members identified by surveys from Gaia and follow-up programs from WISE and 2MASS. Notable observational results include spectra of widely separated planetary-mass companions and resolved imaging of transition disk features comparable to discoveries reported with SPHERE and GPI. CHARIS observations have been scheduled through time allocation committees at institutions like NAOJ and international partnerships, contributing to multi-wavelength campaigns that combine data from facilities including ALMA, Keck, and HST.

Data Processing and Analysis Methods

Data reduction for CHARIS uses pipelines that perform detector-level corrections, wavelength calibration, and assembly of three-dimensional data cubes, methodologies rooted in software developed for OSIRIS and GPI with adaptations from the IRAF-era tools and modern Python-based libraries. Post-processing emphasizes point-spread function subtraction and speckle suppression using algorithms such as Angular Differential Imaging, Spectral Differential Imaging, LOCI, and principal component analysis approaches pioneered in studies by teams at STScI and MPIA. Spectral extraction routines tie to atmospheric models from groups like ExoMol and opacities curated by researchers at Columbia University for forward-model fitting and Bayesian retrievals. Data products are used in combined analyses with archival catalogs from Sloan Digital Sky Survey and kinematic databases informed by Gaia astrometry.

Collaborations and Funding

CHARIS was developed through an international consortium including NAOJ, University of Tokyo, Princeton University, Caltech, and collaborators at U.S. national laboratories such as NASA JPL, with funding and technical support from national science agencies including Japan Society for the Promotion of Science and National Science Foundation. Collaborative science teams mirror those formed for instruments like GPI and SPHERE, involving researchers from universities and observatories worldwide who contribute through observing programs, pipeline development, and theoretical interpretation. Ongoing support and upgrades are coordinated with Subaru facility staff and partner institutions to maintain CHARIS’s role alongside evolving projects at major observatories.

Category:Infrared spectrographs Category:Subaru Telescope instruments