We present the first on-sky demonstration of dual-field interferometry at the Center for High Angular Resolution Astronomy (CHARA) Array and the first direct resolution of the inner Ba-Bb subsystem in the bright hierarchical triple alpha Piscium. Using H-band fringe tracking on component A with MIRC-X to stabilize K-band science fringes on component B with MYSTIC, we detected a companion at a projected separation of 7 mas, confirming a long-suspected but previously unresolved short-period subsystem within the B component. The nearly equal H/K-band flux ratio indicates that Ba and Bb are near-twin F-type stars, consistent with the two narrow-lined components seen in optical spectra of B. By combining CHARA interferometry with archival VLTI/GRAVITY astrometry and radial velocities from archival and new spectroscopy (NARVAL and ARCES), we derive a well-constrained orbit with a period of P = 25 days, eccentricity e similar or equal to 0.6, and inclination i similar or equal to 65 degrees, yielding precise dynamical masses of 1.668 +/- 0.033 M circle dot and 1.646 +/- 0.029 M circle dot. No additional companion is detected down to Delta H approximate to 5 at separations of 0.2-2 au. We also obtained dual-field differential astrometry of the wide A-B pair with a precision of similar to 0.234 mas at a separation of 1 .'' 85, with an error budget dominated by internal delay-line actuators, fringe-tracking performance, and chromatic dispersion. While the long-period outer orbit is not refined by these measurements, their agreement with the published astrometric orbit provides an on-sky validation of the CHARA dual-field mode. These results establish alpha Psc as a well-characterized hierarchical system suitable for future benchmark studies and demonstrate CHARA's new capability for off-axis interferometry and submilliarcsecond astrometry on arcsecond-scale binaries.

Dual-field interferometry uses a bright reference star for real-time fringe tracking, allowing a second beam combiner to record long coherent integrations on a fainter off-axis science target. At the Center for High Angular Resolution Astronomy (CHARA) Array, we implement this mode using the six-telescope MIRC-X and MYSTIC beam combiners in the H and K bands, respectively. We first demonstrated this capability in summer 2025 on the hierarchical triple α Piscium. MIRC-X tracked component A in the H band, while MYSTIC observed component B in the K band, resolving the 7 mas Ba–Bb subsystem and measuring the relative astrometry of the 1.85 arcsec A–B pair with an uncertainty of 234 μas. Here, we describe subsequent phase-tracking testing, preliminary sensitivity simulations, and planned instrumental upgrades aimed at extending this mode to faint off-axis science targets.

Long baseline optical and infrared interferometric arrays achieve high angular resolution and enable detailed astrophysical measurements. Interferometers have enabled observations of stars at various stages of evolution, as well as studies of binary stars, circumstellar disks, and active galactic nuclei. The Center for High Angular Resolution Astronomy (CHARA) Array is a long-baseline interferometric array at the Mount Wilson Observatory, United States. At the core of CHARA operations are the delay lines, which equalize the optical path length for all telescopes as the Earth rotates and compensate for optical path variations induced by atmospheric turbulence. We report recent upgrades and performance of the CHARA Array optical delay lines for high-precision interferometric observations. The legacy system had been operational for over two decades, and it was increasingly difficult to acquire replacement parts. Beginning in mid-2021, the control system underwent a major upgrade, replacing the aging Versa Module Eurocard-based architecture with a modern hybrid field-programmable gate array and Linux-based system; this modernization continued through the end of 2024. We describe hardware/software changes, the servo architecture, and lab/on-sky performance. The upgraded system achieves residual delay line cart tracking errors of similar to 12 nm, the same level as the legacy system, and a control bandwidth of 100 to 130 Hz, allowing fringe tracking across the R-, H-, and K-bands. Initial commissioning revealed key issues such as metrology time-tick jitter and vibration-induced visibility loss, which were diagnosed and resolved. We note ongoing and future efforts to extend baselines up to 1 km and support advanced observing modes such as dual-field interferometry and nulling. This is a reference for current and future use of the CHARA Array and for next-generation instrument design.

Since its inception, speckle interferometry has revolutionized high-resolution astronomical imaging, overcoming atmospheric challenges to achieve the diffraction limits of telescopes. Almost a decade ago, in 2018, a pair of speckle cameras – ‘Alopeke and Zorro–were installed at two of the largest apertures in the world, the twin 8.1-m Gemini North and South telescopes in Hawai’i and Chile. Equipped with dual blue and red channels, ’Alopeke and Zorro deliver high-resolution imaging across the optical bandpass from 350 to 1,000 nm, which has led to crucial discoveries in both stellar multiplicity and exoplanetary science. Furthermore, the broad and nonrestrictive access to these instruments, given by each Gemini Observatory partner and via the US NOIRLab open skies policy, has allowed the community to expand the applications of the instruments, supporting a wide range of scientific investigations from Solar System bodies, to morphological studies of stellar remnants and quasars, to evolved stars, to transient phenomena. This paper reviews the instrument technology and observational capabilities, and highlights key scientific contributions and discoveries of ‘Alopeke and Zorro, emphasizing the enduring importance of speckle interferometry in advancing modern observational astronomy and expanding the frontiers of astronomical research.

Photonic components play an important role in the development of astronomical instruments, both to increase the capabilities of instruments at existing telescope facilities and for the next generation of extremely large (30-m class) telescopes. These chip- and fiber-based astrophotonic components [1] can reduce the footprint of instruments as well as their sensitivity to undesired environmental changes. Stellar interferometry has particularly benefited from photonic developments. Here, information about the astronomical source can be extracted from interferometric signals obtained by overlapping light from different telescopes. Photonic beam combiners can overlap multiple beams within a em-scale device, drastically reducing the required space compared to using bulk optics. In addition, the single-mode waveguides provide spatial filtering, which increases measurement precision. Photolithography-based photonic beam combiners have been successfully used in instruments (e.g. GRAVITY at VLTI), but developments in ultrafast laser inscription (ULI)-based beam combiners are still ongoing. These are currently at technology readiness level (TRL) 3. Due to low photon flux, these photonic components are required to have high throughput, uniform wavelength response, polarisation insensitivity, with operation over a broad wavelength range (several 100 nm). Performance has to be tested in the laboratory, followed by validation on the telescope (TRL 5).

Studying binary systems with faint close companions requires high-resolution and high-contrast imaging. The 'Alopeke speckle instrument, located at Gemini North, detects such binary systems. We optimize the spatial resolution in our speckle data using the multi-frame blind deconvolution (MFBD) technique. However, as the instrumental optical aberrations are static, their contribution to the blurring of the image remains in the digitally restored object estimate, in effect limiting the achievable resolution. This residual image blur can fortunately be removed by an additional single-frame blind deconvolution. The estimated aberrations from this second step show excellent agreement with the expectations for the aberrations of the 'Alopeke instrument and pave the way to improving the optical alignment. Furthermore this technique can be used for any speckle imaging system.

The Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new worlds, with TESS planet candidates now outnumbering the total number of confirmed planets from Kepler. Owing to differences in survey design, TESS continues to provide planets that are better suited for subsequent follow-up studies, including mass measurement through radial velocity (RV) observations, compared to Kepler targets. In this work, we present the TESS-Keck Survey’s (TKS) Mass Catalog: a uniform analysis of all TKS RV survey data that has resulted in mass constraints for 126 planets and candidate signals. This includes 58 mass measurements that have reached ≥5 σ precision. We confirm or validate 32 new planets from the TESS mission either by significant mass measurement (15) or statistical validation (17), and we find no evidence of likely false positives among our entire sample. This work also serves as a data release for all previously unpublished TKS survey data, including 9,204 RV measurements and associated activity indicators over our three-year survey. We took the opportunity to assess the performance of our survey and found that we achieved many of our goals, including measuring the mass of 38 small (<4 R ⊕ ) planets, nearly achieving the TESS mission’s basic science requirement. In addition, we evaluated the performance of the Automated Planet Finder as survey support and observed meaningful constraints on system parameters, due to its more uniform phase coverage. Finally, we compared our measured masses to those predicted by commonly used mass–radius relations and investigated evidence of systematic bias.

A fiber-connectorized K-band integrated-optics two-telescope beam combiner was developed for long-baseline interferometry at the CHARA telescope array utilizing the ultrafast laser inscription (ULI) technique. Single-mode waveguide insertion losses were measured to be ∼1.1dB over the 2–2.3 µm window. The development of asymmetric directional couplers enabled the construction of a beam combiner that includes a 50:50 coupler for interferometric combination and two ∼75:25 couplers for photometric calibration. The visibility of the bare beam combiner was measured at 87% and then at 82% after fiber-connectorization by optimizing the input polarization. These results indicate that ULI technique can fabricate efficient fiber-connectorized K-band beam combiners for astronomical purposes.

The CHARA Array has added a 7th telescope to extend the existing 6 telescope array. The CHARA Michelson Array Pathfinder (CMAP) includes a 1m Planewave RC Telescope mounted in a custom designed mobile trailer and pier system. The telescope and trailer can be placed at multiple locations around the Mount Wilson Observatory site; each site consisting of a flat concrete pad with a novel pier design. Optical fibers will connect each site to the CHARA optical delay and combiner lab. This enables new short baselines of similar to 17m for imaging the surfaces of large stars and new long baselines on the order of similar to 600m for resolving small stars. There are two sites developed at the array for this telescope. In the future, there are plans to expand the array to greater than 1 km maximum baselines. These baselines will be used in conjunction with the existing 15 baselines that range from 34 to 331m. Moving such a telescope around the observatory presents some unique challenges. The telescope can make use of the same optical delay lines and beam combiners as the other CHARA Array telescopes.

Stars with initial masses larger than 8 M ⊙ undergo substantial mass loss through mechanisms that remain elusive. Unraveling the origins of this mass loss is important for comprehending the evolutionary path of these stars, the type of supernova explosion, and whether they become neutron stars or black hole remnants. In 2022 December, RW Cep experienced the Great Dimming in its visible brightness, presenting a unique opportunity to understand mass-loss mechanisms. Our previous observations of RW Cep from the CHARA Array, taken during the dimming phase, show a compelling asymmetry in the star images, with a darker zone on the west side of the star indicating the presence of dust in front of the star in our line of sight. Here, we present multiepoch observations from CHARA while the star rebrightened in 2023. We created images using three image reconstruction methods and an analytical model fit. Comparisons of images acquired during the dimming and rebrightening phases reveal remarkable differences. Specifically, the west side of RW Cep, initially obscured during the dimming phase, reappeared during the subsequent rebrightening phase, and the measured angular diameter became larger by 8%. We also observed image changes from epoch to epoch while the star is brightening, indicating the time evolution of dust in front of the star. We suggest that the dimming of RW Cep was a result of a recent surface mass ejection event, generating a dust cloud that partially obstructed the stellar photosphere.

ABSTRACT We present the confirmation of a hot super-Neptune with an exterior Neptune companion orbiting a bright (V = 10.1 mag) F-dwarf identified by the Transiting Exoplanet Survey Satellite (TESS). The two planets, observed in sectors 45, 46, and 48 of the TESS extended mission, are $4.74_{-0.14}^{+0.16}$ and $3.86_{-0.16}^{+0.17}$ R⊕ with $5.4588385_{-0.0000072}^{+0.0000070}$ and $17.8999_{-0.0013}^{+0.0018}$ d orbital periods, respectively. We also obtained precise space-based photometric follow-up of the system with ESA’s CHaracterising ExOplanets Satellite to constrain the radius and ephemeris of TOI-5126 b. TOI-5126 b is located in the ‘hot Neptune Desert’ and is an ideal candidate for follow-up transmission spectroscopy due to its high-predicted equilibrium temperature (Teq = ${1442}_{-40}^{+46}$ K) implying a cloud-free atmosphere. TOI-5126 c is a warm Neptune (Teq = $971_{-27}^{+31}$ K) also suitable for follow-up. Tentative transit timing variations have also been identified in analysis, suggesting the presence of at least one additional planet, however this signal may be caused by spot-crossing events, necessitating further precise photometric follow-up to confirm these signals.

The goal of the CHara ARray Integrated Optics Testbench (CHARIOT) is to establish a fully characterized (nulling) interferometry setup for on-sky tests of novel astrophotonic 2D or 3D beam combiners for the interferometry community worldwide. CHARIOT is planned for four telescope beams covering the J-, H-, and K-bands with plug-and-play fiber interfaces. Verifying novel astrophotonics on-sky with CHARIOT will enable the development of components and advances in instruments in many fields, including nulling and spectro-interferometry.

We report the discovery of the transiting planet GJ 238 b, with a radius of 0.566 +/- 0.014 R-circle plus (1.064 +/- 0.026 times the radius of Mars) and an orbital period of 1.74 days. The transit signal was detected by the TESS mission and designated TOI-486.01. The star's position close to the southern ecliptic pole allows for almost continuous observations by TESS when it is observing the southern sky. The host star is an M2.5 dwarf with V = 11.57 +/- 0.02 mag, K = 7.030 +/- 0.023 mag, a distance of 15.2156 +/- 0.0030 pc, a mass of 0.4193(-0.0098)(+0.0095) M-circle dot, a radius of 0.4314(-0.0071)(+0.0075) R-circle dot, and an effective temperature of 3485 +/- 140 K. We validate the planet candidate by ruling out or rendering highly unlikely each of the false positive scenarios, based on archival data and ground-based follow-up observations. Validation was facilitated by the host star's small size and high proper motion of 892.633 +/- 0.025 mas yr(-1).

Massive evolved stars such as red supergiants and hypergiants are potential progenitors of Type II supernovae, and they are known for ejecting substantial amounts of matter, up to half their initial mass, during their final evolutionary phases. The rate and mechanism of this mass loss play a crucial role in determining their ultimate fate and the likelihood of their progression to supernovae. However, the exact mechanisms driving this mass ejection have long been a subject of research. Recent observations, such as the Great Dimming of Betelgeuse, have suggested that the activity of large convective cells, combined with pulsation, could be a plausible explanation for such mass-loss events. In this context, we conducted interferometric observations of the famous yellow hypergiant, rho Cassiopeiae using the CHARA Array in H- and K-band wavelengths. rho Cas is well known for its recurrent eruptions, characterized by periods of visual dimming (similar to 1.5-2 mag) followed by recovery. From our observations, we derived the diameter of the limb-darkened disk and found that this star has a radius of 1.04 +/- 0.01 mas, or 564-700 R (circle dot). We performed image reconstructions with three different image reconstruction software packages, and they unveiled the presence of giant hot and cold spots on the stellar surface. We interpret these prominent hot spots as giant convection cells, suggesting a possible connection to mass ejections from the star's envelope. Furthermore, we detected spectral CO emission lines in the K band (lambda = 2.31-2.38 mu m), and the image reconstructions in these spectral lines revealed an extended circumstellar envelope with a radius of 1.45 +/- 0.10 mas.

In the framework of the ALOHA (Astronomical Light Optical Hybrid Analysis) project, we have implemented a fibre-linked interferometer connecting two telescopes of the CHARA (Center for High Angular Resolution Astronomy) array to the recombination beam facility using servo controlled hectometric outdoor fibres (240 m). During two consecutive nights, on-sky fringes at 810 nm were recorded on the star Vega (mag 0), with servo control of the fibre lengths. The optical path difference was set close to zero using internal fringes found before the on-sky observations. The repeatability of the delay line position offset between internal and on-sky fringes was less than 0.2 mm. The efficiency of the servo control systems has been demonstrated, leading to an enhancement of the signal-to-noise ratio from 68.9 with the servo off to 91.6 with the servo on. This result is a cornerstone for the ALOHA project goal of interferometry at 3.5 mu m and a seminal step for the future kilometric infrared fibre-linked interferometer at CHARA.

We validate the presence of a two-planet system orbiting the 0.15–1.4 Gyr K4 dwarf TOI 560 (HD 73583). The system consists of an inner moderately eccentric transiting mini-Neptune (TOI 560 b, P=6.3980661−0.0000097+0.0000095 days, e=0.294−0.062+0.13 , M=0.94−0.23+0.31MNep ) initially discovered in the Sector 8 Transiting Exoplanet Survey Satellite (TESS) mission observations, and a transiting mini-Neptune (TOI 560 c, P=18.8805−0.0011+0.0024 days, M=1.32−0.32+0.29MNep ) discovered in the Sector 34 observations, in a rare near-1:3 orbital resonance. We utilize photometric data from TESS Spitzer, and ground-based follow-up observations to confirm the ephemerides and period of the transiting planets, vet false-positive scenarios, and detect the photoeccentric effect for TOI 560 b. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with the iSHELL spectrograph at the NASA Infrared Telescope Facility and the HIRES Spectrograph at Keck Observatory to validate the planetary nature of these signals, which we combine with published Planet Finder Spectrograph RVs from the Magellan Observatory. We detect the masses of both planets at >3σ significance. We apply a Gaussian process (GP) model to the TESS light curves to place priors on a chromatic RV GP model to constrain the stellar activity of the TOI 560 host star, and confirm a strong wavelength dependence for the stellar activity demonstrating the ability of near-IR RVs to mitigate stellar activity for young K dwarfs. TOI 560 is a nearby moderately young multiplanet system with two planets suitable for atmospheric characterization with the James Webb Space Telescope and other upcoming missions. In particular, it will undergo six transit pairs separated by <6 hr before 2027 June.

NASA’s Transiting Exoplanet Survey Satellite (TESS) mission promises to improve our understanding of hot Jupiters by providing an all-sky, magnitude-limited sample of transiting hot Jupiters suitable for population studies. Assembling such a sample requires confirming hundreds of planet candidates with additional follow-up observations. Here we present 20 hot Jupiters that were detected using TESS data and confirmed to be planets through photometric, spectroscopic, and imaging observations coordinated by the TESS Follow-up Observing Program. These 20 planets have orbital periods shorter than 7 days and orbit relatively bright FGK stars (10.9 < G < 13.0). Most of the planets are comparable in mass to Jupiter, although there are four planets with masses less than that of Saturn. TOI-3976b, the longest-period planet in our sample ( P = 6.6 days), may be on a moderately eccentric orbit ( e = 0.18 ± 0.06), while observations of the other targets are consistent with them being on circular orbits. We measured the projected stellar obliquity of TOI-1937A b, a hot Jupiter on a 22.4 hr orbit with the Rossiter–McLaughlin effect, finding the planet’s orbit to be well aligned with the stellar spin axis (∣ λ ∣ = 4.°0 ± 3.°5). We also investigated the possibility that TOI-1937 is a member of the NGC 2516 open cluster but ultimately found the evidence for cluster membership to be ambiguous. These objects are part of a larger effort to build a complete sample of hot Jupiters to be used for future demographic and detailed characterization work.