Center for High Angular Resolution Astronomy
Georgia State University, Atlanta
Director: Douglas Gies

Array
Mount Wilson Observatory, CA
Director: Gail Schaefer
16 staff members onsite
Operations funded through the NSF, GSU, collaboration partners

CHARA timeline

• 1984 - "CHARA" established
• 1992 - Engineering studies
• 1994 - GSU: $5.6 mil 5-telescope array, NSF: $6.3 mil, university matching
• 1996 - Mt. Wilson ground broken
• 1998 - Keck $1.5 mil for 6th telescope
• 1999 - First fringes between S1/S2
• 2001 - First starlight fringes on longest baseline
• 2003 - Construction completed
• 2005 - First journal paper - dia. of Regulus (McAlister)
• 2007 - Image of surface of Altair (Monnier)
• 2010 - Open access program initiated

• 2026 - 294 refereed papers & 61 PhD dissertations so far 

   

" technical improvements in both hardware and software will continue indefinitely.

one rationale for the facility is to serve as a testbed for new developments in optical interferometry."

https://chara.gsu.edu/astronomers/journal-articles

Georgia State University

The CHARA Array is operated by the Center for High Angular Resolution Astronomy at Georgia State University in Atlanta.

The two-telescope CLASSIC beam combiner

University of Michigan

The MIRC-X H-band combiner. A six-telescope cryogenic K-band beam combiner, MYSTIC

University of Exeter

The upgrades to the six-telescope MIRC-X combiner

l’Observatoire de la Côte d’Azur

SPICA combines all six-telescopes and provides a range of spectral dispersions at visible wavelengths.

Sydney University

Precision Astronomical Visible Observations (PAVO) instrument

Australian National University

The (PAVO) visible beam combiner

Université de Limoges

the ALOHA fiber experiment.

Kyoto Sangyo University

Pushing the sensitivity limits of the Array in order to resolve the cores of Active Galactic Nuclei.

National Optical-Infrared Astronomy Research Laboratory

Open access time at the CHARA Array is available to the astronomical community through the National Optical-Infrared Astronomy Research Laboratory (NOIR Lab). 

The CHARA Consortium

CHARA Science Meeting 2025 - Nice, France

CHARA/MROI Science Meeting and New Visions in Optical Interferometry Workshop 2026 - Socorro, NM

workshop supported by 

Eaton Fire Jan 2025

• Jan 7 - fire broke out in high winds
• Jan 9 - fire reached MWO 
• Jan 24 - staff back on-site 

Station Fire (2009)

Bobcat Fire (2020)

Eaton Fire (2025)

Fizeau - 1850s

Michelson - 1890s

Brown & Twiss - 1950s

1920 - measured Betelgeuse (with Pease)

1956 - HBT effect, correlation b/t coherent photons

Intensity interferometry

details can be gained through interferometric measures

details can be gained through interferometric measures

details can be gained through interferometric measures

Image credit: ESO

Direct detection

Examples:

• PTI 
• KI 
• NPOI
• CHARA
• MROI
• IOTA
• VLTI
• SUSI
• LBTI

Labeyrie - 1975

diameter

Lawson 2003, S&T

Placement matters

the CHARA Array

Spatial resolution

• 0.20 mas at R (650 nm)

• 0.52 mas at H (1.67 μm)

• 0.66 mas at K (2.13 μm)

34 to 331m

• 15 baselines
• 10 closure triangles

Sigma Geminorum

Roettenbacher+2017

TelAO

Anugu+2026

Optical Path Length Equalizers (OPLE) system

• original system: VME (>20yo) 
• modern Linux-based system was installed and tested - 2021 to 2024
• tracking uncertainties ~ 12 μm

LabAO

MIRC-X/Mystic

MIRC-X

• dispersed spectral channels
• J and H-bands (simultaneous 4-beam → 6-beam soon)
• MIRC-X/MYSTIC can be used simultaneously  
• images of stellar surfaces and circumstellar disks
• precision closure phases
• faint binary companions.

Anugu 2020

Setterholm et al. 2023

MYSTIC

• K-band, cryogenic, 6-beam combiner
• All-in-One 6T or high sensitivity 4T gravity chip

Pannetier et al. 2021

SPICA

(Stellar Parameters and Imaging with a Cophased Array)

The goal of the SPICA project is to provide a large and homogeneous set of stellar parameters across the HR-diagram.  

• measure the angular diameters of 1000 stars
• spectral resolutions of R = 140, 4300, and 13300
• two instruments:
  • the visible-light combiner (SPICA-VIS)
  • H-band integrated optic 6-beam ABCD combiner (SPICA-FT) installed into the MIRC-X instrument.
• SPICA-FT provides group-delay and phase-delay tracking for SPICA-VIS.

spectrograph

Aug 2023 - First fringes with SPICA/MIRC-X/MYSTIC

Lanthermann+2022,  2026, SPIE 14148-81

Silmaril

• 3T simultaneous H/K combiner
• Bulk optics / designed for high sensitivity
• CRED-1
• R=35
• pair of narcissus mirrors to reduce background
• J-band dichroic → Niro detector (from Classic) as angle tracker (Strider) 
• expect limiting magnitude of H=10-11
• PI: ten Brummelaar (GSU), Tuthill (Sydney)

CHARIOT

(CHARA Array Integrated Optics Testbed)

collaboration with Leibniz-Institut fur Astrophysik Potsdam, University of Cologne, Heriot-Watt University

ULI optics for JHK bands

Apr 2024 - First fringes

Mobile Telescope Transport (TR116)

CMAP

(CHARA Michelson Array Pathfinder)

Ligon+2022

S4

S3

ALOHA – Univ. Limoges
Single-mode PM fibers
λ=810nm,  240m long
Laying on the ground
Connect S1+S2
On-sky fringes Magri+2024
CMAP
Single-mode PM fibers
λ=1.6μm, 650m long
Trench: 18 inches deep

20 ← 34 - 331 → 579 m

S3

S4

Single-mode PM fibers
λ=1.6 μm, 650 m long
Trench: 18 inches deep

1100 m

W5

S3

S4

Earliest Science

Rapid Rotators

Regulus -- Che et al. 2011, ApJ, 732, 68

Rasalhague -- Zhao et al. 2009, ApJ, 701, 209

Altair -- Monnier et al. 2007, Science, 317, 324

Alderamin -- Zhao et al. 2009, ApJ, 701, 209

Beta Cas -- Che et al. 2011, ApJ, 732, 68

Star spots

Evans et al. 2024, ApJ, 971, 190

Polaris

Roettenbacher et al., 2017, ApJ, 849, 120.

sigma Geminorum

Roettenbacher et al. 2016, Nature, 533, 217

zeta Andromedae

Schaefer et al. 2014, Nature, 515, 234

Expansion curve of Nova Del 2013.

• Changes in apparent expansion – optically thick core surrounded by diffuse envelope that cools over time
• Geometric disk: 4.5 kpc
• Asymmetric shape detected as early as 2d

Nova fireballs and dust envelope

Kloppenborg et al. 2010, Nature, 464, 870

AAVSO, Hopkins et al. (2012)

Gies, D. R., et al. 2007, ApJ, 654, 527

Mourard, D., et al. 2015, A&A, 577, 51

Schaefer, G. H., et al. 2010, AJ, 140, 1838

Touhami, Y., et al. 2013, ApJ, 768, 128

Be stars

P = 12.9 d
a = 0.87 mas

Zhao et al. 2008, ApJ, 684, 95

RECENT SCIENTIFIC RESULTS

Exoplanet Systems

• angular size, parallax, and bolometric flux → stellar radius, Teff, and luminosity

Stellar Pulsations

• Cepheid variable stars → period - luminosity relation → distances of local galaxies  
  • ​distances, angular diameters, binarity, orbits, masses, limb darkening, imaging
• ​independent verification for asteroseismology - particularly important for evolved, core helium-burning stars.

Circumstellar Environments

• planet-forming disks of Young Stellar Objects
• Be star decretion disks - gas from the rapidly spinning star is launched outwards into an ionized gas disk
• massive stars become very luminous and variable as they grow to become cool supergiants.
• asymmetrical mass loss can result from energetic processes in binary systems

Binary and Multiple Star Systems

• fundamental means to measure stellar masses.

• angular orbit + distance estimate → total mass of components

• angular orbit + radial velocity orbits → individual masses + independent distance measurement

  →  stellar evolution processes and interactions between binary stars

Ashley Elliott 2024

Diameters of Stars

Ashley Elliott (LSU) has compiled interferometric measurements from CHARA and more to create an empirical HR diagram.

Angular Dia. + Parallax  → Linear Radius

Diameter + Bolometric Flux → Teff

SCIENTIFIC RESULTS

Yu et al. 2023

interferometric angular diameters provide key benchmark data to evaluate calibrations of effective temperature from large-scale spectroscopic and photometric surveys - SED/CHARA

693 stars, σθ < 5%

Torres et al. 2022

Torres et al. 2024

Binary & Multiple Stars

Castor A and B

• resolved the inner binary components
• masses and 3D orbits
• mutual orientations of the different components.

HD 284163

hierarchical quadruple system

• orbits of the inner (2.39 d) and first outer (43.1 yr) are nearly orthogonal
• Accurate masses including that of the secondary
• (0.5245 ± 0.0047 M⊙) is now the lowest mass star with a dynamical mass measurement in the Hyades cluster.

Caballero et al. 2022

Gleise 486

• M3.5 V star at ~8 pc
• transit every 1.467 days.
• MIRC-X → angular size of the the host star
• physical radius and effective temperature.  
• transit light curve → ratio of planetary to stellar radius
• exoplanet diameter
• HPRV captured the reflex motion of the star and led to an exoplanet mass
• model of the interior structure and possible atmosphere of this other world in the solar neighborhood.

Exoplanet Systems

Interferometric observations of exoplanet host stars provide the means to determine the detailed stellar characteristics that are required to find the exoplanet properties.

• Radius and Teff of host
• Mass + age from evolutionary tracks
• Size of habitable zone
• Radius of transiting planets

Anugu et al. 2023

Exoplanet Systems

Planet formation is generally considered in the context of young stars, but mass loss in older stars may also play a role in making planets at the end of a star's life.  

Circumbinary disk with close to a polar alignment with respect to the binary orbit.

• Any planet formed in the disk would be relatively stable.
• central cavity in the disk could be result of such a planet.

If so, represents the first example of a polar circumbinary planet.

Martin et al. 2023

Image credit: Dr Mark A. Garlick / markgarlick.com

post-AGB star AC Her 

• binary system
• surrounded large disk of gas and dust.
• Anugu determined the first 3D orbit for AC Her
• first for any post-AGB system

→ the large cavity in the center of the circumbinary disk is not created by the tidal action of the central binary.

Ibrahim et al. 2023

Disks Around Young Stars

The process of planet formation involves the development of instabilities in the disk that can be followed through time series interferometric observations at very high angular resolutions.

luminous Herbig Be star HD 190073

•  YSO disk is viewed almost face-on (i<20°)
• clear view of the full extent of the inner gas disk.
• discovered a bright spot in the disk that migrated by 27° over of 32 days  

V1925 Aql

NGC 4151

Active Galactic Nuclei

bright central region of the active galactic nucleus of the Seyfert galaxy NGC 4151.  

• Central structure resolved at the 0.5 mas scale.
• ring-like structure viewed at an inclination of 40°
• perpendicular to the radio jet
• K-band flux probably originates in a dust sublimation region on the face of the torus surrounding the black hole.

Exoplanet Systems

• 51 Eridani system - resolved planet in 32 yr orbit, PARSEC evolutionary models ​→ stellar mass and age, & a planetary mass of 4MJup Elliott+2024

Stellar Pulsations

• Polaris faint companion detected, 29 yr orbit, Polaris mass 5.13 ± 0.28M⊙, spotted surface image Evans+2024
• various Cepheid model - observation mismatches

Circumstellar Environments

• inner disk of Herbig Ae star HD 163296 → possible tidal wake from wide proto-planet Setterholm+2025
• binary disk system Ibrahim+2026
• T Tauri HD 143006 - inner/outer disk misalignment mystery Codron+2025
• post-mass transfer Be star, smallest orbit yet resolved by the Array = 0.663 mas Rivinius+2026
• imaging of fast nova V1674 Her and slow nova V1405 Cas Aydi+2025

Interferometric Methods

Anugu+2026 first experiments in dual field interferometry at the CHARA Array

• 5" fov into MIRC-X/MYSTIC combiners individually

→ yields measurements of the differential positions

• fringe track on one target and integrate on the other (fainter) target
• observations of the α Psc multiple system.
• B component is itself a close binary

α Psc → hierarchical triple. 

Anugu et al. (2026)

ρ = 1.85"

Outer A-B

• 468 proposals submitted since 2010

• 132 unique OA PIs

• 90 distinct institutions

• up to 300 nights over 3 years of open access time via NOIRLab

• dedicated to community growth in US and beyond

• staff assist new investigators with planning observations, collecting data, and reducing data

• calibrated oifits files provided

NOIRLab Open Access

• started in 2025
• 1n per month available

  open to all observers

• confirmation of high impact findings
• feasibility exploratory
• following-up on events
• completion to allow publication

New Fast Turnaround Snapshot Imaging Mode

​Priority for observers who do not have existing time and for targets not already included in programs with awarded time.

https://chara.gsu.edu/observers/applying-for-chara-time

Exoplanets

Clusters & Ages

AGN

Engineering

Program Stats (2010-2026)

<5% loss to technical issues

Future Plans

• telescope dichroic & STST upgrade ($1.4m NSF MRI1 funded)

  • optimize simultaneous observations in visible + NIR

• AOB upgrades ($16k GSU funded)
• automated alignment/tracking
• painting/AC at domes
• continue quantum initiatives
• exploring the feasibility of a B-band combiner (440 nm) → 0.13 mas
• next-gen AO systems
• fibers to all telescopes
• W5/Channel 13 site (1100m)
  • expanded / double-pass delay
• nulling instrument(s)
• central 2m telescope
• upgrade existing 1m telescopes to 2m telescopes
• The Michelson Array

2028

2028+

AO upgrades

Current sensitivity limits:​

• Tiptilt, AO: V = 10-12 mag​

• Visible/NIR fringe recording: 8.0 mag​

• Sensitivity improvements → K = 10-11 mag​

• WFS / control max 1kHz / 13-18Hz

• Injection into fibers at telescope

• STST Strehl~55–70% (H), 5-15% (R)

Next-gen AO system (planning):

• new DM, WFS(s), ADC
  • 90-100 actuators (50-60 sub-apertures)
• current beam dia or compress/re-expand?
• DM at M4 or move elsewhere (M2?)
• UV LGS
• reduce maintenance & alignment
• Strehl from 12-15% → >50% in R-band

Central 2m Telescope

• Vacuum beam transport with fiber option
• Bundled with Delay Line Upgrades

20 to 1100m

• 0.06 mas at R

• 0.16 mas at H

• 0.20 mas at K

The full Michelson Array would offer 12 total positions, creating 66 possible baselines.

Image an exoplanet during transit

There are some 250 known exoplanets with host stars accessible to CHARA.

The new baselines will enable resolution of solar-like stars out to about 70pc in H-band.

Numerical simulations of the transiting hot-Jupiter in HD189773 indicate that the silhouette of the planet can be measured in long baseline observations made during transits.

backup slides

Binary and Multiple Star Systems

• Pleides member star, Atlas: orbit, mass, and rotational distortion of evolved primary Torres+2025

• interferometry + spectroscopy of 6 solar-mass binaries in the Hyades cluster Torres+2025

Interferometric Methods

• first experiments in dual field interferometry at the CHARA Array Anugu+2026

  • α Psc → hierarchical triple system

• observations of Vega via 2x 240m fibers at 810nm from S1 & S2 Magri+2025

• starspot locations on rotating stars using spherical harmonics

  • open-access code harmonix → reconstruct the intensity map based upon a simulation of observations Dholakia&Pope2026

Binary and Multiple Stars

Torres+2025 binary star Atlas, in the Pleiades cluster, age = 104 Myr

• 291d angular orbit + radial velocity measurements → mass 5.04 ± 0.17M⊙ and 3.64 ± 0.12M⊙.
• brighter star is rapid rotator
• rotationally distorted shape + spectroscopic projected rotation velocity → equatorial rotational velocity of 233 ± 45 km s−1 (77% of the critical)​

→ Rotational distortion of evolved primary

Relative orbit of companion to Atlas

Image Reconstruction of AZ Cyg
Norris et al. (2021)

Model Simulation
Chiavassa et al. (2010)

Giant star surfaces

These "closure phases" also yield information about source symmetry

Combine the phases measured in a closed triangle of three telescopes in a way that cancels out the atmospheric turbulence.

Monnier 2007, NAR 51, 604

symmetry

Spectrally dispersed fringes produce differential visibilities and differential phases

• visibility and phase of emission lines relative to the stellar continuum.
• measure the size and velocity structure of rotating circumstellar disks, outflows, and winds around stars.

Differential Vis and Differential Phases

Star + disk.

• drop in the visibility across the emission lines indicate that the disk is more resolved than the stellar continuum.  
• double-peaked profile corresponds rotating disk.
• S-shaped profile shows a shift in the photo-center across the wavelength channels.

Meilland et al. 2012, A&A, 538, 110

Exoplanet Systems

Gardner+2026 searched for the NIR signal of the hot Jupiter planet orbiting ups Andromeda

• 1.7MJup mass ~ 4 mas separation, flux should be detectable with CHARA
• 2021 MIRC-X → hints at the expected separation
• 2023 MIRC-X and MYSTIC → no evidence of a planetary flux signal

→ may indicate that the NIR flux is lower than predicted.

Ashley Elliott developed the RADPy code

→ reliable angular diameters of stars from CHARA observations

51 Eridani system

• resolved massive planet in 32 yr orbit

PARSEC evolutionary models

​→ stellar mass and age, & a planetary mass of 4MJup

github.com/spaceashley/radpy

Elliott+2024

Stellar Pulsations

Evans+2024 investigated the mass of Polaris

CHARA observations made around periastron of a faint companion (2016 - 2021)

• 1300x fainter Polaris in H

radial velocity + angular position measurement → 29.4 yr orbit + Gaia distance → Cepheid mass of 5.13 ± 0.28M⊙

• luminosity > predicted
• additional structure beyond a simple limb darkened disk
• SURFING code image reconstruction revealed a surface with several bright spots
  • magnetic spots or convective supergranules?

similar analysis of the Cepheid AW Per

• triple system: 6.8 ± 0.9M⊙ Cepheid and a close binary companion of two similar mass stars → total mass 8.8 ± 0.5M⊙

Relative orbit of Polaris companion from multiple observations

False color image of Polaris in H

Chowhan+2026 PAVO observations of the “secondary red clump” star κ Cyg that exhibits solar-like oscillations

• angular size + Gaia distance → 8.65±0.10R⊙
• oscillation frequencies predicted are poor match to NASA TESS observations

→ mismatch - incomplete treatment of convective boundary mixing in the interior models

Gallenne+2025 triple system Cepheid SU Cyg

• derived mass of the Cepheid is 4.859 ± 0.058M⊙
• orbits a close pair with masses of 3.595 ± 0.033M⊙ and 1.546 ± 0.009M⊙
• component velocities + angular orbit → independent distance estimate of 926.3 ± 5.0 pc
  • most accurate distance ever measured for a Cepheid variable
  • evolutionary models fail to account for the apparent over-luminosity of the Cepheid for its derived mass

→ revisions to the model tracks are needed.

Stellar Pulsations II

Bras 2026 Cepheid η Aql

• angular size variation & limb darkening variation over pulsation period
• variation in limb darkening coefficient ~2x predicted by current stellar atmospheres model for Cepheids,

→ physical model of the center-to-limb intensity variations may be incomplete

Circumstellar Environments

Setterholm+2025 evolution of inner disk of Herbig Ae star HD 163296 - MIRC-X and VLTI PIONIER

• unresolved central star, uniform background, & structured disk
• bright spot migrates clockwise over 44d

> Keplerian motion at that separation

→ might be related to a tidal wake from wider proto-planet

Rivinius+2025 spectroscopic survey of Be stars in the post-mass transfer stage before the donor star shrinks to subdwarf

• 6 binaries, including HD 698 (V742 Cas) 
• 58.4d, 0.663 mas orbit

→ the smallest orbit yet resolved with the CHARA Array.

Circumstellar Environments II

hypergiant star RW Per during and after the Great Dimming

Anugu+2024 RW Per, R = 5 AU in the bright state

→ one of the largest diameter stars

hypergiant star ρ Cas20, R = 3 AU.

• photospheric, limb-darkened angdia = 2.09 ± 0.2 in 2.0-2.3 μm
• 2.91 ± 0.19 mas in 2.3-2.4 μm

→ latter range contains many CO lines, add to the overall opacity and shifts line forming region to higher in the atmosphere

Codron+2025 disk structure around T Tauri HD 143006

• inner and outer disks are misaligned by ~39°
• dark shadow regions in the outer disk cast by the misaligned inner disk

→ no inner binary companion is detected, so the origin of the misalignment remains a mystery

Circumstellar Environments III

2002: luminous red nova V838 Mon erupts:

high mass star + low mass companion merger → dust outflow enshrouding 

Aydi et al. 2025 ToO observations with MIRC-X of 2 novae explosions in 2021

interferometric imaging + contemporary spectroscopy + high E γ-ray measurements Fermi fast nova V1674 Her

• 2 and 3 days after the eruption

→ thermonuclear explosion on WD → fast bipolar outflow + slow equatorial expansion  

slow nova V1405 Cas

• 53, 55, and 67 days after explosion
• ellipsoidal structure that is smaller in the final observation

→ outflow concentrated in the orbital plane and that appears smaller as the net optical depth decreases with expansion and the inner regions are revealed.

Mobeen+2024

→ merger led to jet formation → bipolar structure of the dust emission

Imaging Luminous Stars

The cool hypergiant star RW Cep experienced a Great Dimming event in 2022:

• imaged near photometric minimum
• H & K-band images show an asymmetric intensity distribution and a distorted shape
• NIR spectroscopy found fading increased towards shorter wavelengths
• implicates dust formation from stellar ejecta as the explanation for the fading and unusual appearance.  

Anugu et al. 2023

Patchy appearance results from dust created by a huge ejection from the star

Illustration credit: NASA, ESA, and E. Wheatley (STScI)

Anugu and colleagues are continuing to monitor the star with CHARA to explore how the surface appearance changes as the star brightens again.  

Binary and Multiple Stars

Torres+2025 binary star Atlas, in the Pleiades cluster, age = 104 Myr

• 291d angular orbit + radial velocity measurements → mass 5.04 ± 0.17M⊙ and 3.64 ± 0.12M⊙.
• brighter star is rapid rotator
• rotationally distorted shape + spectroscopic projected rotation velocity → equatorial rotational velocity of 233 ± 45 km s−1 (77% of the critical)​

→ Rotational distortion of evolved primary

Mass - abs mag for Hyades cluster members

inset - shows how the PARSEC code tends to overestimate the V fluxes

Relative orbit of companion to Atlas

Torres+2024 interferometry + spectroscopy of 6 solar-mass binaries in the Hyades cluster

• CHARA + Palomar Testbed Interferometer (PTI) + a large set of RV measurements to derive masses with sub-1% accuracies 
• good agreement with the predicted mass – luminosity relation
• but PARSEC models slightly overestimate the V-band fluxes of such stars

→ perhaps due to some missing component of opacity code calculation

"A gain of a single magnitude doubles the available sample of AGN."

7T Imaging improvements

The RECONS 25 Parsec Database

animation: Adric Riedel

https://www.youtube.com/embed/up_MqNBv0FE

• Taurus star forming region (d=140 pc)
• Measure contraction of young stars to the main sequence.
• Need  < 0.2 mas to achieve this.

Angular Diameter of Pre-MS stars

• Verify diameter measurements between eclipsing binaries and singles
• 8% of M dwarfs are photometrically variable by 2% in V, R, I. 92% are stable
• Study flares, spots
• Magnetically active M dwarfs have very large spots that could be imaged

20pc sample → 600 M dwarfs

• volume complete sample to 20pc
• How many could chara resolve/image?

Diameters and resolved surfaces of M dwarfs

http://recons.org/published.annrev.pdf
https://aasnova.org/2018/07/11/3796/

Image an exoplanet during transit

• There are some 250 known exoplanets with host stars accessible to CHARA.
• The new baselines will enable resolution of solar-like stars out to about 70pc in H-band.
• Numerical simulations of the transiting hot-Jupiter in HD189773 indicate that the silhouette of the planet can be measured in long baseline observations made during transits.

1100m

600m

~17m

S3

S4

W5

Max spatial resolution

• 0.06 mas at R (650 nm)

• 0.16 mas at H (1.67 μm)

• 0.20 mas at K (2.13 μm)

20 to 1100m

• 36 possible baselines: array + CMAP [6+3]  (15 simultaneous)

The full Michelson Array would offer 12 total positions, creating 66 possible baselines.

• installed 2025 by the SPICA team
• 10-cm telescope on fixed Polar mount
• automatically captures an image of Polaris every minute
• real time analysis
• seeing parameters broadcast on the CHARA network
• 10min mean values smooth individual data and reveal nightly trends

PSAUM → r0, t0, isoplanetism, and isopistonic angle, and index of scintillation

PSAUM (Polar inStrument for Atmospheric tUrbulence Monitoring)