CHARA Array

CHARA Array
Name	CHARA Array
Organization	Georgia State University; formerly Center for High Angular Resolution Astronomy
Location	Mount Wilson Observatory, Los Angeles County, California
Altitude	1742 m
Established	1996
Telescope type	Optical/infrared interferometer
Telescopes	Six 1-metre

CHARA Array

The CHARA Array is a ground-based optical/infrared interferometric facility operated by Georgia State University on Mount Wilson Observatory in Los Angeles County, California. It synthesizes apertures using six 1-metre telescopes to achieve high angular resolution for studies of stellar surfaces, binary systems, and circumstellar environments. The Array serves a wide community including researchers from NASA, major universities such as University of California, Berkeley, Massachusetts Institute of Technology, and international institutions like Max Planck Society and Observatoire de Paris.

Overview

The facility combines light from six telescopes arranged along Y-shaped arms to produce baselines up to 330 metres, enabling milli-arcsecond and sub-milli-arcsecond imaging of astronomical targets. Its instrument suite supports near-infrared and visible wavelengths, permitting detailed characterization of sources observed by space missions such as Kepler and TESS as well as complementary follow-up of objects found by Hubble Space Telescope and Spitzer Space Telescope. The Array enables interferometric techniques analogous to those used at facilities like Very Large Telescope Interferometer and Navy Precision Optical Interferometer.

History and development

Planning for the Array began in the late 1980s within the Georgia State University astronomy group, with site selection culminating in a lease at Mount Wilson Observatory, a site historically associated with projects by George Ellery Hale and instruments like the 100-inch Hooker telescope. Construction of the Array proceeded through the 1990s, with first fringes achieved in the late 1990s and formal science operations initiated in the early 2000s. Key development milestones involved collaborations with organizations such as National Science Foundation and partnerships with institutions including California Institute of Technology, Stanford University, and University of Michigan. Over time the Array incorporated upgrades influenced by technical advances from projects like CHARA Instrumentation Project teams and methodologies adopted at Keck Interferometer.

Instrumentation and design

The Array comprises six 1-metre siderostats feeding a central beam-combination facility via vacuum delay lines and active optical trains, a design heritage shared with arrays including Palomar Testbed Interferometer and Infrared Spatial Interferometer. Beam combiners at the facility include instruments for near-infrared fringe tracking and visible-light beam combination, developed through collaborations with groups from University of Arizona, University of Cambridge, and University of Sydney. Adaptive optics elements and tip-tilt correction draw on technologies from teams at Jet Propulsion Laboratory and Laboratory for Astronomical Instrumentation, while metrology systems use laser references similar to those engineered by European Southern Observatory teams. Detectors encompass near-infrared arrays and visible CCDs, leveraging designs adopted by projects at National Optical Astronomy Observatory.

Observing techniques and capabilities

The Array performs long-baseline optical interferometry using closure phase, visibility amplitude, and fringe-tracking techniques to reconstruct brightness distributions on stellar scales. Observing modes include spectro-interferometry, aperture synthesis imaging, and high-precision astrometry, enabling synergy with programs at Gaia and follow-up of radial-velocity surveys from HARPS and Keck Observatory. Calibration strategies rely on reference stars from catalogs maintained by Hipparcos teams and comparison with catalogs produced by Two Micron All-Sky Survey researchers. Scheduling and queue operations are coordinated with user groups spanning European Southern Observatory, National Aeronautics and Space Administration, and community consortia, facilitating multi-wavelength campaigns that integrate data from facilities such as Subaru Telescope and ALMA.

Scientific discoveries and contributions

The Array has produced direct images and diameter measurements of nearby stars including rapid rotators and evolved giants, contributing to stellar physics topics investigated by researchers at Princeton University, University of Chicago, and Harvard–Smithsonian Center for Astrophysics. It resolved close binary orbits and measured fundamental parameters used to calibrate models employed by teams at Lowell Observatory and University of Hawaii. Results have informed studies of stellar surface convection and spots analogous to work on the Sun by National Solar Observatory and others, and have constrained properties of protoplanetary disks relevant to research by Carnegie Institution for Science and Caltech groups. The Array's astrometric and imaging outputs have been cited in multi-facility programs with Hubble Space Telescope and Spitzer Space Telescope investigators, and in stellar evolution modeling efforts tied to researchers at University of Geneva and Max Planck Institute for Astronomy.

Operations and management

Operational management resides at Georgia State University with scientific oversight provided by advisory committees formed from partner institutions including University of Texas at Austin, Yale University, and University of Cambridge. Funding and programmatic support have involved awards and grants from the National Science Foundation and cooperative agreements with NASA programs. The facility supports visiting observers, postdoctoral researchers, and instrument teams drawn from institutions such as University of Florida, Boston University, and University of Southern California. Outreach and education efforts connect with programs at California State University campuses and public initiatives coordinated with Mount Wilson Observatory staff.

Category:Optical telescopes