arXiv subjects

Justin R. Crepp

Publications and source records attributed to Justin R. Crepp.

At least 19 recordsLinked to original sources

arXiv2026

Performance Comparison of the Nonlinear Curvature and Shack-Hartmann Wavefront Sensors in Strong Turbulence

Strong turbulence induces spatial variations in beam intensity that hinder the reconstruction process of many commonly deployed adaptive optics (AO) systems that use gradient-based wavefront sensors (WFS), such as the Shack-Hartmann wavefront sensor (SHWFS) and pyramid wavefront sensor. The nonlinear curvature WFS (nlCWFS) uses Fresnel diffraction to extract wavefront phase and amplitude information, suggesting that it may be able to operate under challenging turbulence conditions. In this work, we investigate nlCWFS reconstruction accuracy as a function of turbulence strength and relative flux by modeling high spherical-wave Rytov number ($R_{sw}$) environments where scintillation and branch points impact sensing performance. We present open-loop as well as static and dynamic closed-loop results benchmarked against a comparable Shack-Hartmann WFS (SHWFS). In static and weak-to-moderate scintillation regimes, the nlCWFS consistently outperforms the SHWFS by leveraging amplitude-phase coupling inaccessible to gradient-based sensors. However, dynamic closed-loop simulations reveal a crossover behavior at higher scintillation strengths, where deep intensity nulls and proliferating branch points degrade the performance of Gerchberg-Saxton-based nlCWFS reconstruction, while the SHWFS degrades more gradually due to its insensitivity to such topological phase structure. These results highlight the regime-dependent advantages of the nlCWFS and emphasize the need for branch-point-tolerant reconstruction algorithms to fully realize its potential in strong-turbulence, low-flux conditions.

astro-ph.IM↗

arXiv2026

A New Sirius-like System at Only 21 Parsecs: An Elusive White Dwarf Companion to the Nearby K-dwarf HD 38230

White dwarfs are among the rarest and faintest stars found in the solar neighbourhood and are therefore persistently challenging to detect. Whereas the \textit{Gaia} mission has vastly expanded our knowledge of isolated white dwarfs, limited contrast sensitivity means that white dwarfs companions to much brighter solar-type stars are easily missed, leaving a subset of white dwarfs in "Sirius-like systems" that can only be discovered via high-contrast imaging. Here we report the discovery of a white dwarf companion to the nearby K0V star HD 38230 (HIP 27207). The companion, HD 38230 B, was originally detected with Keck/NIRC2 observations taken as part of the TRENDS high-contrast imaging survey, was detected by \textit{Gaia} without an astrometric solution, and was independently observed using Lick/ShaneAO and Palomar/PHARO in the literature. Combining these multiple imaging detections spanning 6 years, we demonstrate that HD 38230 B is a gravitationally bound companion and has photometry consistent only with a white dwarf. Our analysis of the binary orbit, combining relative astrometry with over 25 years of precise radial velocity observations and \textit{Hipparcos-Gaia} astrometry, results in strong constraints on the $P$ = $1390^{+310}_{-200}$ year orbit despite the short observational span, and provides a precise dynamical mass of $M_B$ = $0.71^{+0.06}_{-0.05}$ $M_\odot$ for the white dwarf. At 21 pc, this is the 11th-nearest Sirius-like system known to date, highlighting residual incompleteness in the local white dwarf census.

astro-ph.SR↗

arXiv2026

The Calibration System of the iLocater Spectrograph

iLocater is a new near-infrared, extreme precision radial velocity (EPRV) instrument delivered to the Large Binocular Telescope in the summer of 2026. The instrument utilizes single-mode fibers (SMFs) for light transmission, including its calibration systems. We present an overview of the iLocater calibration system, detailing the specific sources and the hardware required to inject calibration light into the SMFs. Furthermore, we discuss the hardware that efficiently switches between these sources and distributes the light to all necessary instrument locations, entirely eliminating the need for free-space propagation.

astro-ph.IM↗

arXiv2026

Commissioning and on-sky performance verification of iLocater

iLocater is a high-resolution near-infrared extreme precision radial velocity (EPRV) spectrograph that was deployed to the Large Binocular Telescope (LBT) in June 2026. iLocater operates over $\lambda=966-1312$ nm with a median resolving power of $R=205,000$ as measured in the laboratory. We present the commissioning and initial on-sky verification program using solar and night-time observations at the LBT. First light was achieved on 27 June 2026, and nearly 150 on-sky spectra have now been recorded. Observations include single stars ranging in spectral type from B5 to M6. iLocater uses the LBT AO system, and we have demonstrated its ability to obtain spatially resolved spectra of close ($\theta < 1''$) binary stars.

astro-ph.IM↗

arXiv2026

Laboratory characterization of iLocater

iLocater is a diffraction-limited, fiber-fed spectrograph designed for the Large Binocular Telescope (LBT), which targets high-precision radial velocity measurements in the near-infrared. Prior to deployment, comprehensive laboratory characterization was essential to validate instrument performance and inform alignment strategies. This paper presents results from four key areas of lab characterization: (1) adjustment and optimization of detector orientation to optimize spectrum alignment with the detector pixel grid across the focal plane; (2) the design and installation of a LED illumination source to enable high-fidelity flat-fields; (3) a model-based focusing methodology using OpticStudio image simulations to optimize the optical alignment of the spectrograph; and (4) assessment of instrument mechanical and optical stability under laboratory conditions. Together, these efforts established baseline performance metrics and demonstrated instrument readiness for delivery and on-sky commissioning.

astro-ph.IM↗

arXiv2026

Phase Retrieval using Nonlinear Curvature Sensing within Convergent Beams

Path-length diversity methods may be used for adaptive optics (AO) systems to retrieve phase and amplitude information by measuring intensity across multiple planes. Observations that rely on free-space propagation, such as the nonlinear curvature wavefront sensor (WFS), have been shown to offer excellent sensitivity and robustness to scintillation. However, the default design results in a large opto-mechanical footprint due to unavoidable geometric-optics and wave-optics effects. Measurements recorded in a convergent beam would improve instrument compactness, while concentrating light into smaller detector regions of interest, improving signal-to-noise ratio and possibly wavefront reconstruction speed. In this paper, we study path-length diversity wavefront sensing using four planes of contemporaneous intensity measurements made in a convergent beam. We develop a physical optics propagation model and validate the model by performing wavefront reconstructions in both simulations and lab experiments. The manuscripts core contribution is a practical, intensity-domain, Fourier-transform-based recipe to use a conventional multi-plane Gerchberg-Saxton (or comparable) reconstruction pipeline with convergent-beam measurements, enabling a compact optical layout. We find that this approach offers practical benefits over an equivalent free-space wavefront sensor, in particular reducing size, weight, complexity and cost.

physics.optics↗

arXiv2025

Comparison of Phase-Unwrapping Methods for Adaptive Optics Wavefront Sensing

Advanced wavefront sensors (WFS) are essential for enabling new science cases for telescopes that utilize adaptive optics (AO) systems. While complex field WFS -- those that estimate the electric field phase and amplitude through interference or diffraction effects -- can achieve extraordinary sensitivity compared to existing devices, they typically reconstruct the wrapped phase of the measured wavefront, which must then be unwrapped for correction by continuous-surface deformable mirrors (DM). Another requirement is that the phase function must be unwrapped within 1 millisecond or faster for real-time AO operations. Using simulations of atmospheric turbulence that follow a Kolmogorov spectrum, we study four prevalent and mature phase unwrapping methods: Fast2D, Zernike Gradient (Zernike), Discrete Fourier Transform (DFT), and Least Squares Principle Value (LSPV). In this paper, we examine the strengths and limitations of each method. In particular, we consider performance with and without a binary circular aperture boundary that defines the edge of monolithic telescopes.

astro-ph.IM↗

arXiv2025

Jitter Sensing and Control for Multi-Plane Phase Retrieval

The family of multi-plane phase retrieval sensors, such as the curvature and nonlinear curvature wavefront sensors (WFS), contain tip/tilt information embedded in their signals. We have built a nonlinear curvature WFS to study different wavefront reconstruction methods and test the ability to extract tip/tilt information. Using reliable and fast centroiding algorithms, combined with knowledge of the measured $z$-distance to each measurement plane, we demonstrate that image jitter may be sensed and compensated for using a fast steering mirror and the WFS in closed loop. This approach obviates the need for peripheral components such as quad-cells or access to a separate scientific imaging channel. Our laboratory experiments validate tip/tilt estimation and correction using nlCWFS data, achieving tip/tilt accuracy of +/-0.1, lambda/D for an unaberrated beam and better than ~+/-0.5, lambda/D in the presence of aberrations, consistent with prior numerical simulations. We further demonstrate a closed-loop tip/tilt control implementation and show a qualitative improvement in the stability and overall quality of multi-plane phase retrieval reconstructions.

astro-ph.IM↗

arXiv2025

Planet Masses, Radii, and Orbits from NASA's K2 Mission

We report the masses, sizes, and orbital properties of 86 planets orbiting 55 stars observed by NASA's K2 Mission with follow-up Doppler measurements by the HIRES spectrometer at the W. M. Keck Observatory and the Automated Planet Finder at Lick Observatory. Eighty-one of the planets were discovered from their transits in the K2 photometry, while five were found based on subsequent Doppler measurements of transiting planet host stars. The sizes of the transiting planets range from Earth-size to larger than Jupiter (1-3 REarth is typical), while the orbital periods range from less than a day to a few months. For 32 of the planets, the Doppler signal was detected with significance greater than 5-sigma (51 were detected with >3-sigma significance). An important characteristic of this catalog is the use of uniform analysis procedures to determine stellar and planetary properties. This includes the transit search and fitting procedures applied to the K2 photometry, the Doppler fitting techniques applied to the radial velocities, and the spectral modeling to determine bulk stellar parameters. Such a uniform treatment will make the catalog useful for statistical studies of the masses, densities, and system architectures of exoplanetary systems. This work also serves as a data release for all previously unpublished RVs and associated stellar activity indicators obtained by our team for these systems, along with derived stellar and planet parameters.

astro-ph.EP↗

arXiv2024

Little iLocater: paving the way for iLocater

Diffraction-limited radial velocity instruments offer a pathway towards improved precision and stability, and the exploration of new parameter spaces at high spatial and spectral resolution. However, achieving the necessary performance requires careful instrument design and considerable on-sky testing. We describe the design and construction of ``Little iLocater'' (Lili), a compact spectrograph that has been used to validate the performance of the front-end fibre-injection system of the iLocater spectrograph. We present the design, assembly, and performance using on-sky data obtained at the Large Binocular Telescope (LBT), including extraction of spectra from standard stars, testing of the atmospheric dispersion corrector to elevations of 40 degrees, and spatially resolved spectra from close companion systems. These results show the front-end fibre-injection system is performing as expected and is indicative of iLocater's capabilities once installed at the LBT.

astro-ph.IM↗

arXiv2024

Resolving the Young 2 Cygni Run-away Star into a Binary using iLocater

Precision radial velocity (RV) spectrographs that use adaptive optics (AO) show promise to advance telescope observing capabilities beyond those of seeing-limited designs. We are building a spectrograph for the Large Binocular Telescope (LBT) named iLocater that uses AO to inject starlight directly into single mode fibers (SMF). iLocater's first acquisition camera system (the `SX' camera), which receives light from one of the 8.4m diameter primary mirrors of the LBT, was initially installed in summer 2019 and has since been used for several commissioning runs. We present results from first-light observations that include on-sky measurements as part of commissioning activities. Imaging measurements of the bright B3IV star 2 Cygni ($V=4.98$) resulted in the direct detection of a candidate companion star at an angular separation of only $\theta = 70$ mas. Follow-up AO measurements using Keck/NIRC2 recover the candidate companion in multiple filters. An $R\approx1500$ miniature spectrograph recently installed at the LBT named ``Lili'' provides spatially resolved spectra of each binary component, indicating similar spectral types and strengthening the case for companionship. Studying the multiplicity of young runaway star systems like 2 Cygni ($36.6 \pm 0.5$ Myr) can help to understand formation mechanisms for stars that exhibit anomalous velocities through the galaxy. This on-sky demonstration illustrates the spatial resolution of the iLocater SX acquisition camera working in tandem with the LBT AO system; it further derisks a number of technical hurdles involved in combining AO with Doppler spectroscopy.

astro-ph.IM↗

arXiv2024

JWST/NIRCam 4-5 $μ$m Imaging of the Giant Planet AF Lep b

With a dynamical mass of $3 \, M_\mathrm{Jup}$, the recently discovered giant planet AF Lep b is the lowest-mass imaged planet with a direct mass measurement. Its youth and spectral type near the L/T transition make it a promising target to study the impact of clouds and atmospheric chemistry at low surface gravities. In this work, we present JWST/NIRCam imaging of AF Lep b. Across two epochs, we detect AF Lep b in F444W ($4.4 \, \mathrm{μm}$) with S/N ratios of $9.6$ and $8.7$, respectively. At the planet's separation of $320 \, \mathrm{mas}$ during the observations, the coronagraphic throughput is ${\approx}7\%$, demonstrating that NIRCam's excellent sensitivity persists down to small separations. The F444W photometry of AF Lep b affirms the presence of disequilibrium carbon chemistry and enhanced atmospheric metallicity. These observations also place deep limits on wider-separation planets in the system, ruling out $1.1 \, M_\mathrm{Jup}$ planets beyond $15.6 \, \mathrm{au}$ ($0.58$ arcsec), $1.1 \, M_\mathrm{Sat}$ planets beyond $27 \, \mathrm{au}$ ($1$ arcsec), and $2.8 \, M_\mathrm{Nep}$ planets beyond $67 \, \mathrm{au}$ ($2.5$ arcsec). We also present new Keck/NIRC2 $L'$ imaging of AF Lep b; combining this with the two epochs of F444W photometry and previous Keck $L'$ photometry provides limits on the long-term $3{-}5 \, \mathrm{μm}$ variability of AF Lep b on months-to-years timescales. AF Lep b is the closest-separation planet imaged with JWST to date, demonstrating that planets can be recovered well inside the nominal (50\% throughput) NIRCam coronagraph inner working angle.

astro-ph.EP↗

arXiv2024

Performance of the Nonlinear Curvature Wavefront Sensor as a Function of Scintillation Strength

Local amplitude aberrations caused by scintillation can impact the reconstruction process of a wavefront sensor (WFS) by inducing a spatially non-uniform intensity at the pupil plane. This effect is especially relevant for the commonly-used Shack-Hartmann WFS (SHWFS), which can lose slope information for portions of the beam where the signal is faint, leading to reduced reconstruction performance and eventually total failure as the level of scintillation increases. An alternative WFS is needed for such conditions. The nonlinear curvature wavefront sensor (nlCWFS) has been shown to achieve better sensitivity compared to the SHWFS under low light levels. Additionally, the nlCWFS has demonstrated the ability to maintain its sensitivity in the presence of scintillation, using amplitude aberrations to help inform the reconstruction process, rather than hinder. Experiments to date have thus far only shown reconstruction results for a single scintillation value. Building upon previous simulations and laboratory experiments, we have built a testbed to quantify the effects of varying scintillation strength on the wavefront reconstruction performance of the nlCWFS compared to an equivalent SHWFS. In this paper, we present results showing the difference in performance between the nlCWFS and SHWFS as a function of relative flux and scintillation strength.

astro-ph.IM↗

arXiv2024

Centroiding and Extraction of Tip/Tilt Information from Nonlinear Curvature Wavefront Sensor Measurements

The nonlinear curvature wavefront sensor (nlCWFS) uses multiple (typically four) out-of-focus images to reconstruct the phase and amplitude of a propagating light beam. Because these images are located between the pupil and focal planes, they contain tip/tilt information. Rather than using a separate sensor to measure image locations, it would be beneficial to extract tip/tilt information directly and routinely as part of the reconstruction process. In the presence of atmospheric turbulence, recovering precise centroid offsets for each out-of-focus image becomes a dynamic process as image structure is altered by changing aberrations. We examine several tip/tilt extraction methods and compare their precision and accuracy using numerical simulations. We find that the nlCWFS outer measurement planes confer more accurate and reliable tip/tilt information than the inner measurement planes, due to their larger geometric lever arm. However, in practice, finite field of view (detector region of interest) effects bias tip/tilt retrieval when using the outer planes due to diffraction. Using knowledge of the $z$-distance to each plane, we find that applying a best-fit linear model to multiple image centroid locations can offer fast and accurate tip/tilt mode retrieval. For the most demanding applications, a non-linear tip/tilt extraction method that self-consistently uses the speckle field may need to be developed.

astro-ph.IM↗

arXiv2024

The instrumentation program at the Large Binocular Telescope Observatory in 2024

The Large Binocular Telescope, with its expansive collecting area, angular resolving power, and advanced optical design, provides a robust platform for development and operation of advanced instrumentation for astronomical research. The LBT currently hosts a mature suite of instruments for spectroscopy and imaging at optical through mid-infrared wavelengths, supported by sophisticated adaptive optics systems. This contribution summarizes the current state of instrumentation, including upgrades to existing instruments and commissioning of second generation instruments now in progress. The LBT is soliciting proposals for next generation instrument concepts, with participation open to consortium members and others interested in participation in the Observatory.

astro-ph.IM↗

arXiv2023

Assessing Phase Reconstruction Accuracy for Different Nonlinear Curvature Wavefront Sensor Configurations

The nonlinear curvature wavefront sensor (nlCWFS) offers improved sensitivity for adaptive optics (AO) systems compared to existing wavefront sensors, such as the Shack-Hartmann. The nominal nlCWFS design uses a series of imaging planes offset from the pupil along the optical propagation axis as inputs to a numerically-iterative reconstruction algorithm. Research into the nlCWFS has assumed that the device uses four measurement planes configured symmetrically around the optical system pupil. This assumption is not strictly required. In this paper, we perform the first systematic exploration of the location, number, and spatial sampling of measurement planes for the nlCWFS. Our numerical simulations show that the original, symmetric four-plane configuration produces the most consistently accurate results in the shortest time over a broad range of seeing conditions. We find that the inner measurement planes should be situated past the Talbot distance corresponding to a spatial period of $r_0$. The outer planes should be large enough to fully capture field intensity and be situated beyond a distance corresponding to a Fresnel-number-scaled equivalent of $Z\approx50$ km for a $D=0.5$ m pupil with $λ=532$ nm. The minimum spatial sampling required for diffraction-limited performance is 4-5 pixels per $r_0$ as defined in the pupil plane. We find that neither three-plane nor five-plane configurations offer significant improvements compared to the original design. These results can impact future implementations of the nlCWFS by informing sensor design.

astro-ph.IM↗

arXiv2023

Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged Inside the Debris Disk of the Young Star AF Lep

We present the direct imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2 $M_{\odot}$ member of the 24 $\pm$ 3 Myr $β$ Pic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in $L'$ with the Vector Vortex Coronagraph reveal a point source, AF Lep b, at ${\approx}340$ mas which exhibits orbital motion at the 6-$σ$ level over the course of 13 months. A joint orbit fit yields precise constraints on the planet's dynamical mass of 3.2$^{+0.7}_{-0.6}$ $M_\mathrm{Jup}$, semi-major axis of $8.4^{+1.1}_{-1.3}$ au, and eccentricity of $0.24^{+0.27}_{-0.15}$. AF Lep hosts a debris disk located at $\sim$50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination ($i_* = 54^{+11}_{-9} {}^\circ$) and orbital inclination ($i_o = 50^{+9}_{-12} {}^\circ$) are in good agreement, which is consistent with the system having spin-orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.

astro-ph.EP↗

arXiv2022

Astrometric Accelerations as Dynamical Beacons: Discovery and Characterization of HIP 21152 B, the First T-Dwarf Companion in the Hyades

Benchmark brown dwarf companions with well-determined ages and model-independent masses are powerful tools to test substellar evolutionary models and probe the formation of giant planets and brown dwarfs. Here, we report the independent discovery of HIP~21152~B, the first imaged brown dwarf companion in the Hyades, and conduct a comprehensive orbital and atmospheric characterization of the system. HIP~21152 was targeted in an ongoing high-contrast imaging campaign of stars exhibiting proper motion changes between Hipparcos and Gaia, and was also recently identified by Bonavita et al. (2022) and Kuzuhara et al. (2022). Our Keck/NIRC2 and SCExAO/CHARIS imaging of HIP~21152 revealed a comoving companion at a separation of $0.37^{\prime\prime}$ (16 au). We perform a joint orbit fit of all available relative astrometry and radial velocities together with the Hipparcos-Gaia proper motions, yielding a dynamical mass of $24^{+6}_{-4}\,\mathrm{M_{Jup}}$, which is $1{-}2σ$ lower than evolutionary model predictions. Hybrid grids that include the evolution of cloud properties best reproduce the dynamical mass. We also identify a comoving wide-separation ($1837^{\prime\prime}$ or $7.9 \times 10^4 \, \mathrm{au}$) early-L dwarf with an inferred mass near the hydrogen-burning limit. Finally, we analyze the spectra and photometry of HIP~21152~B using the Saumon & Marley (2008) atmospheric models and a suite of retrievals. The best-fit grid-based models have $f_{\mathrm{sed}}=2$, indicating the presence of clouds, $T_{\mathrm{eff}}=1400 \, \mathrm{K}$, and $\log{g}=4.5 \, \mathrm{dex}$. These results are consistent with the object's spectral type of $\mathrm{T0\pm1}$. As the first benchmark brown dwarf companion in the Hyades, HIP~21152~B joins the small but growing number of substellar companions with well-determined ages and dynamical masses.

astro-ph.SR↗