Adaptive Optics Imaging Research Articles

Correlation Between Photoreceptor and Vascular Parameters in Diabetic Retinopathy Using Adaptive Optics.

This study aimed to investigate correlations between photoreceptor and vascular parameters in varying stages of diabetic retinopathy (DR) using adaptive optics (AO) imaging. In this single-center, prospective cohort study, 29 participants (46 eyes) were classified into control/mild non-proliferative DR (NPDR), moderate/severe NPDR, and proliferative DR. AO images of photoreceptors and retinal vasculature were analyzed, and Spearman's correlation (ρ) was used to assess relationships between photoreceptor density and vascular parameters. Higher cone density was inversely associated with total vessel (ρ = 0.22, P = 0.03) and lumen diameters (ρ = -0.24, P = 0.01), while higher dispersion was associated with total vessel (ρ = 0.19, P = 0.06) and lumen diameters (ρ = 0.21, P = 0.04). These associations were primarily significant in mild NPDR. No significant correlations were found in advanced DR stages. This study underscores intricate neurovascular correlations in early-stage DR, suggesting these parameters may aid in early disease detection. Further research is needed to understand whether similar correlations exist in advanced DR. [Ophthalmic Surg Lasers Imaging Retina 2024;55:XX-XX.].

The possibilities of using adaptive optics in modern ophthalmology

Until recently, the assessment of individual retinal cells was possible only with the help of histological examination, since such retinal imaging methods as scanning laser ophthalmoscopy and optical coherence tomography had low resolution to obtain images of structures at the cellular level, which was mainly due to aberrations caused by the optics of the eye. Adaptive optics technology has improved the performance of optical systems by correcting optical wavefront aberrations. Adaptive optics allows noninvasively visualizing the retina at the microscopic level in vivo, providing the opportunity to analyze individual structures such as photoreceptors, blood vessels, nerve fibers, ganglion cells and a lattice plate. Adaptive optics imaging in patients with diabetic retinopathy makes it possible to accurately determine the spatial distribution of cones, a decrease in which is associated with the presence of diabetic retinopathy and an increase in the severity of the disease. The detection of differences in cone distribution density between the control group and patients with diabetes mellitus without clinical signs of diabetic retinopathy may contribute to its early diagnosis, as well as a deeper understanding of the consequences of changes in the photoreceptor apparatus. Adaptive optics imaging methods are able to identify disorders of photoreceptor cells and assess the degree of progression of age-related macular degeneration, which definitely expands diagnostic capabilities at the early stages of its detection. Assessment of the condition of nerve fiber bundles through the use of Adaptive optics helps to identify changes associated with glaucoma, and also provides the ability to visualize details that cannot be evaluated using optical coherence tomography. Adaptive optics imaging allows you to directly measure the wall of retinal vessels and the diameter of their lumen. The ratio of wall thickness to vessel lumen and the cross-sectional area of the vessel wall directly reflect the remodeling process and can be used for the purpose of early diagnosis and monitoring of hypertension.

Comparison of the Photoreceptor Mosaic Before and After Macular Hole Surgery with High Resolution Adaptive Optics Imaging

PurposeTo assess the photoreceptor mosaic in patients with idiopathic full thickness macular hole (MH) before and after pars plana vitrectomy (PPV) with adaptive optics enhanced retinal imaging (AO). DesignProspective case series. MethodsProspective cohort study of patients who presented at the Kensington Eye Institute, Toronto, Canada with a diagnosis of macular hole treated with PPV. Exclusion criteria: secondary MH, high myopia (axial length >26.5 mm), media opacity precluding OCT or AO imaging, previous intraocular surgery except for cataract extraction. Imaging using an AO fundus camera (Imagine Eyes, RTX1) was performed preoperatively and 3-months following successful MH repair in both eyes. Cone density (CD), regularity, dispersion, regularity, dispersion, and spacing were measured at 2° and 4° of eccentricity in 4 quadrants (superior, inferior, nasal, and temporal) with pre- and postoperative values compared. ResultsWe included 18 eyes of 9 patients. At 2° there was significant reduction in CD and increase in spacing and dispersion and a non-significant change in regularity post-operatively. Comparison between preoperative and postoperative measurements at 2° mean (Standard Error= SE) were: CD: 14612 ± 3003 and 12280 ± 4632 photoreceptors/mm2 [95%CIs= -2413 to -702] p=0.0004, regularity: 88 ± 7% and 84 ± 12% [95%CIs= -4.67 to 0.04] p=0.054, dispersion: 19 ± 6% and 23 ± 10% [95%CIs= 0.5 to 4.24] p=0.013, spacing: 9 ± 1 microns and 10 ± 2microns [95%CIs= 0.40 to 1.27] p=0.0002; at 4° was: CD: 13377 ± 4339 and 12770 ± 4391 photoreceptors/mm2 [95%CIs= -1368 to 252] p=0.176, regularity:87 ± 9% and 86 ± 12% [95%CIs= -4.65 to 0.08] p=0.74, dispersion: 20 ± 8% and 20 ±9 % [95%CIs= -2.11 to 1.5] p=0.74, spacing:10 ± 2 microns and 10 ± 3 microns [95%CIs= -0.23 to 0.58] p=0.39. ConclusionAdaptive optics imaging allows quantitative assessment of the photoreceptor mosaic pre- and post-PPV in patients with MH. There was a significant change to the photoreceptor mosaic related to the MH at 2° pre- and post-operatively. AO imaging enables high-resolution investigation of the photoreceptor remodeling process following surgery, which may allow for a more thorough assessment of surgical outcomes.

Photoreceptor Characteristics in Diabetic Retinopathy vs Controls Using Adaptive Optics Imaging: Systematic Review.

Purpose: To assess the differences in morphological photoreceptor outcomes measured using adaptive optics (AO)-assisted imaging between individuals with diabetes or prediabetes and healthy controls. Methods: A systematic search was conducted across MEDLINE, Embase, and Cochrane databases from January 2000 to June 2023. Studies that used AO-assisted imaging modalities to quantitatively compare photoreceptor outcomes in patients with diabetes or prediabetes with healthy controls were included. Results: Eleven studies consisting of 551 eyes were included. Most studies reported significant differences in photoreceptor outcomes between diabetic and healthy populations, particularly as diabetic retinopathy (DR) severity increased. Cone regularity was the most sensitive parameter for detecting significant differences between groups. AO imaging was less reliable in distinguishing individuals with diabetes without DR or with mild DR severity from controls. Conclusions: AO imaging showed promise in detecting significant differences associated with diabetes and DR, in particular with increasing disease severity. Further research is warranted to assess AO's utility as a diabetes and DR screening tool. Standardizing imaging protocols in future studies is recommended to allow for more direct quantitative comparisons. These findings highlight the current evidence on photoreceptor changes in patients with diabetes and the potential of AO in advancing diabetic eye care.

The radius distribution of M dwarf-hosted planets and its evolution

Abstract M dwarf stars are the most promising hosts for detection and characterization of small and potentially habitable planets, and provide leverage relative to solar-type stars to test models of planet formation and evolution. Using Gaia astrometry, adaptive optics imaging, and calibrated gyrochronologic relations to estimate stellar properties and filter binaries we refined the radii of 117 Kepler Objects of Interest (confirmed or candidate planets) transiting 74 single late K- and early M-type stars, and assigned stellar rotation-based ages to 113 of these. We constructed the radius distribution of 115 small (<4R⊕) planets and assessed its evolution. As for solar-type stars, the inferred distribution contains distinct populations of ‘super-Earths’ (at ∼1.3R⊕) and ‘sub-Neptunes’ (at ∼2.2 R⊕) separated by a gap or ‘valley’ at ≈1.7R⊕that has a period dependence that is significantly weaker (power law index of -0.03$^{+0.01}_{-0.03}$) than for solar-type stars. Sub-Neptunes are largely absent at short periods (<2 days) and high irradiance, a feature analogous to the ‘Neptune desert’ observed around solar-type stars. The relative number of sub-Neptunes to super-Earths declines between the younger and older halves of the sample (median age 3.86 Gyr), although the formal significance is low (p = 0.08) because of the small sample size. The decline in sub-Neptunes appears to be more pronounced on wider orbits and low stellar irradiance. This is not due to detection bias and suggests a role for H2O as steam in inflating the radii of sub-Neptunes and/or regulating the escape of H/He from them.

A Pilot Study from A Course-Based Undergraduate Research Experience for Online Degree-Seeking Astronomy Students

Research-based active learning approaches are critical for the teaching and learning of undergraduate STEM majors. Course-based undergraduate research experiences (CUREs) are becoming more commonplace in traditional, in-person academic environments, but have only just started to be utilized in online education. Online education has been shown to create accessible pathways to knowledge for individuals from nontraditional student backgrounds, and increasing the diversity of STEM fields has been identified as a priority for future generations of scientists and engineers. We developed and instructed a rigorous, six-week curriculum on the topic of observational astronomy, dedicated to educating second year online astronomy students in practices and techniques for astronomical research. Throughout the course, the students learned about telescopes, the atmosphere, filter systems, adaptive optics systems, astronomical catalogs, and image viewing/processing tools. We developed a survey informed by previous research validated assessments aimed to evaluate course feedback, course impact, student self-efficacy, student science identity and community values, and student sense of belonging. The survey was administered at the conclusion of the course to all eleven students yielding eight total responses. Although preliminary, the results of our analysis indicate that students’ confidence in utilizing the tools and skills taught in the course was significant. Students also felt a great sense of belonging to the astronomy community and increased confidence in conducting astronomical research in the future.

Applications of Adaptive Optics Imaging for Studying Conditions Affecting the Fovea.

The fovea is a highly specialized region of the central retina, defined by an absence of inner retinal layers and the accompanying vasculature, an increased density of cone photoreceptors, a near absence of rod photoreceptors, and unique private-line photoreceptor to midget ganglion cell circuitry. These anatomical specializations support high-acuity vision in humans. While direct study of foveal shape and size is routinely performed using optical coherence tomography, examination of the other anatomical specializations of the fovea has only recently become possible using an array of adaptive optics (AO)-based imaging tools. These devices correct for the eye's monochromatic aberrations and permit cellular-resolution imaging of the living retina. In this article, we review the application of AO-based imaging techniques to conditions affecting the fovea, with an emphasis on how imaging has advanced our understanding of pathophysiology.

The Environments of Fast Radio Bursts Viewed Using Adaptive Optics

We present observations from the Gemini Multi-Conjugate Adaptive Optics System/Gemini South Adaptive Optics Imager at Gemini South of five fast radio burst (FRB) host galaxies of FRBs with subarcsecond localizations. We examine and quantify the spatial distributions and locations of the FRBs with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 half-light radii (r e ) and the trend that these FRBs occur in fainter regions of their host galaxies. When combined with the FRB host galaxy sample from Mannings et al., we find that FRBs are statistically distinct from Ca-rich transients in terms of light at the source location and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, along with the finding that the FRB locations trace the distribution of stellar mass, points toward a possible similarity of the environments of CCSNe and FRBs. We also find that four out of five FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to their host’s spiral structure, with a median distance of 0.53 ± 0.27 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes. Such insights may only require us to double the number of FRBs with subarcsecond localizations.

The progenitor star of SN 2023ixf: a massive red supergiant with enhanced, episodic pre-supernova mass loss

ABSTRACT We identify the progenitor star of SN 2023ixf in Messier 101 using Keck/NIRC2 adaptive optics imaging and pre-explosion Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) images. The supernova, localized with diffraction spikes and high-precision astrometry, unambiguously coincides with a progenitor candidate of $m_\text{F814W}=24.87\pm 0.05$ (AB). Given its reported infrared excess and semiregular variability, we fit a time-dependent spectral energy distribution (SED) model of a dusty red supergiant (RSG) to a combined data set of HST optical, ground-based near-infrared, and Spitzer Infrared Array Camera (IRAC) [3.6], [4.5] photometry. The progenitor resembles an RSG of $T_\text{eff}=3488\pm 39$ K and $\log (L/\mathrm{L}_\odot)=5.15\pm 0.02$, with a $0.13\pm 0.01$ dex ($31.1\pm 1.7$ per cent) luminosity variation at a period of $P=1144.7\pm 4.8$ d, obscured by a dusty envelope of $\tau =2.92\pm 0.02$ at $1\, \mu \text{m}$ in optical depth (or $A_\text{V}=8.43\pm 0.11$ mag). The signatures match a post-main-sequence star of $18.2_{-0.6}^{+1.3}\, \mathrm{M}_\odot$ in zero-age main-sequence mass, among the most massive SN II progenitor, with a pulsation-enhanced mass-loss rate of $\dot{M}=(4.32\pm 0.26)\times 10^{-4} \, \mathrm{M}_\odot \, \text{yr}^{-1}$. The dense and confined circumstellar material is ejected during the last episode of radial pulsation before the explosion. Notably, we find strong evidence for variations of $\tau$ or $T_\text{eff}$ along with luminosity, a necessary assumption to reproduce the wavelength-dependent variability, which implies periodic dust sublimation and condensation. Given the observed SED, partial dust obscuration remains possible, but any unobstructed binary companion over $5.6\, \mathrm{ M}_\odot$ can be ruled out.

Measurement of retinal blood flow precision in the human eye with multimodal adaptive optics imaging.

Impaired retinal blood flow (RBF) autoregulation plays a key role in the development and progression of several ocular diseases, including glaucoma and diabetic retinopathy. Clinically, reproducible RBF quantitation could significantly improve early diagnosis and disease management. Several non-invasive techniques have been developed but are limited for retinal microvasculature flow measurements due to their low signal-to-noise ratio and poor lateral resolution. In this study, we demonstrate reproducible vessel caliber and retinal blood flow velocity measurements in healthy human volunteers using a high-resolution (spatial and temporal) multimodal adaptive optics system with scanning laser ophthalmoscopy and optical coherence tomography.

Multimodal phenotyping of foveal hypoplasia in albinism and albino-like conditions: a pediatric case series with adaptive optics insights

Aim of the present study is to evaluate the relationship between genetic and phenotypic data in a series of patients affected by grade I and II of foveal hypoplasia with stable fixation and good visual acuity using multimodal imaging techniques. All patients underwent complete clinical and instrumental assessment including structural Optical Coherence Tomography (OCT), OCT Angiography and Adaptive Optics (AO) imaging. Central macular thickness (CMT), inner nuclear layer (INL), vessel density in superficial capillary plexus were the main variables evaluated with OCT technology. Cone density, cone spacing, cone regularity, cone dispersion and angular density were the parameters evaluated with AO. Genetic evaluation and trio exome sequencing were performed in all affected individuals. Eight patients (3 males and 5 females) with a mean age of 12.62 years (range 8–18) were enrolled. The mean best corrected visual acuity (BCVA) was 0.18 ± 0.13 logMAR, mean CMT was 291.9 ± 16.6 µm and INL was 26.2 ± 4.6 µm. The absence of a foveal avascular zone (FAZ) was documented by examination of OCT-A in seven patients in the superficial capillary plexus. However, there was a partial FAZ in the deep plexus in patients P5 and P8. Of note, all the patients presented with major retinal vessels clearly crossing the foveal center. All individuals exhibited a grade I or II of foveal hypoplasia. In 5 patients molecular analyses showed an extremely mild form of albinism caused by compound heterozygosity of a TYR pathogenic variant and the hypomorphic p.[Ser192Tyr;Arg402Gln] haplotype. One patient had Waardenburg syndrome type 2A caused by a de novo variant in MITF. Two patients had inconclusive molecular analyses. All the patients displayed abnormalities on OCT-A. Photoreceptor count did not differ from normal subjects according to the current literature, but qualitative analysis of AO imaging showed distinctive features likely related to an abnormal pigment distribution in this subset of individuals. In patients with foveal hypoplasia, genetic and multimodal imaging data, including AO findings, can help understand the physiopathology of the foveal hypoplasia phenotype. This study confirms that cone density and visual function can both be preserved despite the absence of a pit.

HIGH-RESOLUTION IMAGING OF THE OUTER RETINA IN TYPE 2 ACUTE MACULAR NEURORETINOPATHY.

The purpose of this study was to investigate the outer retinal changes in a patient with type 2 acute macular neuroretinopathy (AMN). A 35-year-old White woman complaining of a unilateral blind spot was imaged using various retinal imaging modalities including clinical optical coherence tomography (OCT), OCT-angiography, fundus fluorescein angiography, and adaptive optics (AO). Fundus examination revealed multiple paracentral reddish brown petaloid lesions in the symptomatic left eye, while the other eye was unremarkable. Clinical OCT showed areas of hyperreflectance at the outer plexiform layer/outer nuclear layer complex with a disrupted inner/outer segment junction, which are characteristic features of type 2 AMN. AO imaging further revealed either shortening or absence of cone outer segments within the AMN lesions attributing to the darker features observed in the en face images from fundus photography and scanning laser ophthalmoscopy. The AO findings indicate that the petaloid lesions in type 2 AMN are caused by a combination of the shortening and absence of the outer segment in individual cone photoreceptors.

Reference optical turbulence characteristics at the Large Solar Vacuum Telescope site

Abstract Large ground-based solar telescopes are equipped with adaptive optics systems to correct wavefront distortions induced in the turbulent atmosphere. The design of the adaptive optics system strongly depends on the vertical profiles of the optical turbulence. In particular, the characteristics of the optical turbulence determine the design of tomographic adaptive optics systems, which provide image correction within a wide field of view. In the article, a new method to estimate reference optical turbulence characteristics from Era-5 reanalysis assimilated data is presented. This method is based on the dependence of the air refractive index structure constant $C_n^2$ on the vertical shears of wind speed as well as the outer scale of turbulence L0. The L0 parameter is estimated by minimization of the dispersion between the modeled and measured values of the refractive index structure constant $C_n^2$ within the surface layer. For the first time, parametrization coefficients and reference profiles of optical turbulence averaged for the period 1940–2022 are calculated for the Large Solar Vacuum Telescope (LSVT) site. The calculated optical turbulence profiles are representative; these profiles correspond to typical changes of the measured values of the Fried parameter, the isoplanatic angle, and the outer scale of turbulence at the LSVT site. The model turbulence profiles are verified taking into account the Shack–Hartmann wavefront sensor measurements at the LSVT. The higher accuracy of estimation of the optical turbulence characteristics makes it possible to refine parameters relevant to the LSVT adaptive optics system. The obtained results can be used in order to develop high-resolution solar adaptive optics technologies as applied to ground-based telescopes including those using the principles of atmospheric tomography.

DESCRIBING THE LOCATION AND MORPHOLOGY OF THE DOTS IN WHITE DOT FOVEA USING ADAPTIVE OPTICS.

To characterize the white dots in white dot fovea, an entity chiefly described in Japan, using adaptive optics imaging and propose a hypothesis regarding their origin. The patient underwent comprehensive ophthalmic examination, including color and green monochromatic fundus photography, fluorescein angiography, spectral-domain optical coherence tomography, and adaptive optics imaging. An asymptomatic 66-year-old Korean woman presented with bilateral white, glistening deposits in a ring pattern around the fovea of both eyes. The dots were highly reflective on green monochromatic images, were not visible on fluorescein angiography, and appeared hyperreflective in the inner retina using spectral-domain optical coherence tomography. Adaptive optics showed polygonal granules ranging from 1 to 10 μ m in size. The patient denied any systemic disorder or the use of any medications related to crystalline retinopathy. The patient had lived in Japan for 35 years before just moving to the United States. The location, small size, and polygonal shape of the dots in white dot fovea are suggestive of intraretinal deposition of crystals, and not cells on the surface of the fovea as has been previously proposed. Carotenoid deposition related to dietary habits is a plausible cause because of the similarity to other retinopathies associated to these compounds.

Strain-insensitive viscoelastic perovskite film for intrinsically stretchable neuromorphic vision-adaptive transistors

Stretchable neuromorphic optoelectronics present tantalizing opportunities for intelligent vision applications that necessitate high spatial resolution and multimodal interaction. Existing neuromorphic devices are either stretchable but not reconcilable with multifunctionality, or discrete but with low-end neurological function and limited flexibility. Herein, we propose a defect-tunable viscoelastic perovskite film that is assembled into strain-insensitive quasi-continuous microsphere morphologies for intrinsically stretchable neuromorphic vision-adaptive transistors. The resulting device achieves trichromatic photoadaptation and a rapid adaptive speed (<150 s) beyond human eyes (3 ~ 30 min) even under 100% mechanical strain. When acted as an artificial synapse, the device can operate at an ultra-low energy consumption (15 aJ) (far below the human brain of 1 ~ 10 fJ) with a high paired-pulse facilitation index of 270% (one of the best figures of merit in stretchable synaptic phototransistors). Furthermore, adaptive optical imaging is achieved by the strain-insensitive perovskite films, accelerating the implementation of next-generation neuromorphic vision systems.

Pushing the limits of near-infrared photometry with the Gemini Multi-Conjugate Adaptive Optics System: study of crowded fields in the globular cluster M5

ABSTRACT We present the deepest J −Ks near-infrared photometry of the globular cluster M5 (NGC 5904) from observations taken with the Gemini South Adaptive Optics Imager in tandem with the Gemini Multi-conjugate adaptive optics System (GeMS) on the 8.1-m Gemini South telescope. Point spread function (PSF) photometry was carried out using a spatially variable PSF, zero-point calibrations based on correlations to a standard photometric catalogue, colour corrections, and crowding corrections. The latter corrections provided a new challenge given the field variations of the adaptive optics corrections in the central crowded regions of this cluster. The final photometric precision in our J− Ks colour–magnitude diagram exposes a dispersion among the lower main-sequence stars of M5 for the first time. This dispersion occurs below a main-sequence knee due to variations in the helium and CNO (carbon, nitrogen, and oxygen) abundances from multiple stellar populations, consistent with results from the bright evolved stars in this cluster from ultraviolet to near-infrared Hubble Space Telescope photometry and ground-based spectroscopy. This paper completes our original GeMS quality analysis programme, providing insights into adaptive optics analyses in crowded fields.

Fundamental Limits on Earth-like Exoplanet Imaging with Large Telescopes Employing Laser Tomographic Adaptive Optics Systems: A Comparative Analysis of LGS AO and LTAO Systems

Exoplanet imaging with high-contrast imaging adaptive optics systems, though challenging, is a promising path toward the characterization of terrestrial planets. We analyzed the fundamental limitations associated with the direct imaging of terrestrial exoplanets around low-mass stars with Extremely Large Telescopes using laser tomographic adaptive optics (LTAO) and derived the post-coronagraph image shape in the focal plane from LTAO systems. Additionally, the fundamental limitation of direct imaging was found to come from unseen spatial frequencies during tomographic reconstruction. Through the provision of optimization strategies for laser guide star (LGS) asterisms, based on the post-coronagraph image contrast, we aimed to assist in the design of LTAO systems for Extremely Large Telescopes, resulting in a six-fold improvement in the LTAO post-coronagraph image plane at 0.1 arcseconds.

FOVEAL PHENOTYPES IN CHOROIDEREMIA ON ADAPTIVE OPTICS SCANNING LIGHT OPHTHALMOSCOPY.

Choroideremia is an X-linked inherited retinal degeneration involving the choriocapillaris, retinal pigment epithelium, and photoreceptors. Adaptive optics scanning light ophthalmoscopy allows visualization of retinal structure at the level of individual cells and is well poised to provide insight into the pathophysiologic mechanisms underpinning the retinal degeneration in choroideremia. Foveal adaptive optics scanning light ophthalmoscopy images of 102 eyes of 54 individuals with choroideremia were analyzed. Measures were compared with those from standard clinical imaging. Visual acuity was also measured and compared with quantitative foveal metrics. The 3 distinct phenotypes observed were: relatively normal (5 eyes, 4 individuals), spiderweb (9 eyes, 7 individuals), and salt and pepper (87 eyes, 47 individuals). Peak cone density (86 eyes of 51 individuals) was significantly lower in choroideremia than in healthy retinas (P < 0.0001, range: 29,382-157,717 cones/mm2). Peak cone density was significantly related to extent of retained ellipsoid zone on en face optical coherence tomography (r2 = 0.47, P = 0.0009) and inversely related to visual acuity (r2 = 0.20, P = 0.001). Distinct phenotypes can be observed on adaptive optics scanning light ophthalmoscopy imaging in choroideremia that cannot always be discerned on standard clinical imaging. Quantitative measures on adaptive optics imaging are related to the structural and functional severity of disease.

An Estimate of the Binary Star Fraction among Young Stars at the Galactic Center: Possible Evidence of a Radial Dependence

We present the first estimate of the intrinsic binary fraction of young stars across the central ≈0.4 pc surrounding the supermassive black hole (SMBH) at the Milky Way Galactic center (GC). This experiment searched for photometric variability in 102 spectroscopically confirmed young stars, using 119 nights of 10″ wide adaptive optics imaging observations taken at W. M. Keck Observatory over 16 yr in the K′ -[2.1 μm] and H-[1.6 μm] bands. We photometrically detected three binary stars, all of which are situated more than 1″ (0.04 pc) from the SMBH and one of which, S2-36, is newly reported here with spectroscopic confirmation. All are contact binaries or have photometric variability originating from stellar irradiation. To convert the observed binary fraction into an estimate of the underlying binary fraction, we determined the experimental sensitivity through detailed light-curve simulations, incorporating photometric effects of eclipses, irradiation, and tidal distortion in binaries. The simulations assumed a population of young binaries, with stellar ages (4 Myr) and masses matched to the most probable values measured for the GC young star population, and underlying binary system parameters (periods, mass ratios, and eccentricities) similar to those of local massive stars. As might be expected, our experimental sensitivity decreases for eclipses narrower in phase. The detections and simulations imply that the young, massive stars in the GC have a stellar binary fraction ≥71% (68% confidence), or ≥42% (95% confidence). This inferred GC young star binary fraction is consistent with that typically seen in young stellar populations in the solar neighborhood. Furthermore, our measured binary fraction is significantly higher than that recently reported by Chu et al. based on radial velocity measurements for stars ≲1″ of the SMBH. Constrained with these two studies, the probability that the same underlying young star binary fraction extends across the entire region is <1.4%. This tension provides support for a radial dependence of the binary star fraction, and therefore, for the dynamical predictions of binary merger and evaporation events close to the SMBH.

Defining reference values of arterioles in healthy individuals for studies with adaptive optics imaging.

To investigate age-dependent wall to lumen ratio (WLR) reference values for healthy individuals in adaptive optics imaging (AO). WLR serves as an objective, dimensionless parameter for the evaluation of structural changes in vessels caused by conditions like arterial hypertension, diabetes or vascular stenosis. 50 right eyes of healthy individuals were examined by adaptive optics imaging. The central big arterioles and smaller arterial branches at least one disc diameter away from the optic disc, approximately above or below the macula were measured by the manufacturer's software. The wall-lumen-ratio (WLR), the wall cross-sectional area (WCSA) and lumen diameter (LD) were assessed. Subsequent data analysis was performed with a focus on variables including age, gender and blood pressure. Normative values for WLR, WCSA and LD in 5 different age groups could be established. However, no significant differences between the age groups were found. Intra-subject comparisons revealed significantly higher WLRs on peripheral branches when compared to central arterioles. WLR showed in this normotensive cohort no relevant correlation with the systolic, diastolic and mean blood pressure. Gender and intraocular pressure had no influence on the vascular parameters. AO is capable of examining vascular alterations in arterioles at an almost microscopic level. Age did not seem to alter WLR, normotensive blood pressure parameters showed also no significant impact. AO-based vessel analysis may provide clinically useful biomarkers for cardiovascular health and should be tested in future studies.