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1. Millisecond exoplanet imaging: I. method and simulation results

   https://doi.org/10.1364/JOSAA.426046  

   Rodack, Alexander T. ; Frazin, Richard A. ; Males, Jared R. ; Guyon, Olivier ( September 2021 , Journal of the Optical Society of America A)

   One of the top priorities in observational astronomy is the direct imaging and characterization of extrasolar planets (exoplanets) and planetary systems. Direct images of rocky exoplanets are of particular interest in the search for life beyond the Earth, but they tend to be rather challenging targets since they are orders-of-magnitude dimmer than their host stars and are separated by small angular distances that are comparable to the classical$\mathrm{\lambda <\#comment/>}/D$diffraction limit, even for the coming generation of 30 m class telescopes. Current and planned efforts for ground-based direct imaging of exoplanets combine high-order adaptive optics (AO) with a stellar coronagraph observing at wavelengths ranging from the visible to the mid-IR. The primary barrier to achieving high contrast with current direct imaging methods is quasi-static speckles, caused largely by non-common path aberrations (NCPAs) in the coronagraph optical train. Recent work has demonstrated that millisecond imaging, which effectively “freezes” the atmosphere’s turbulent phase screens, should allow the wavefront sensor (WFS) telemetry to be used as a probe of the optical system to measure NCPAs. Starting with a realistic model of a telescope with an AO system and a stellar coronagraph, this paper provides simulations of several closely related regression models that take advantage of millisecond telemetry from the WFS and coronagraph’s science camera. The simplest regression model, called the naïve estimator, does not treat the noise and other sources of information loss in the WFS. Despite its flaws, in one of the simulations presented herein, the naïve estimator provides a useful estimate of an NCPA of$\sim <\#comment/>0.5$radian RMS ($\approx <\#comment/>\mathrm{\lambda <\#comment/>}/13$), with an accuracy of$\sim <\#comment/>0.06$radian RMS in 1 min of simulated sky time on a magnitude 8 star. Thebias-corrected estimatorgeneralizes the regression model to account for the noise and information loss in the WFS. A simulation of the bias-corrected estimator with 4 min of sky time included an NCPA of$\sim <\#comment/>0.05$radian RMS ($\approx <\#comment/>\mathrm{\lambda <\#comment/>}/130$) and an extended exoplanet scene. The joint regression of the bias-corrected estimator simultaneously achieved an NCPA estimate with an accuracy of$\sim <\#comment/>5\times <\#comment/>{10}^{-<\#comment/>3}$radian RMS and an estimate of the exoplanet scene that was free of the self-subtraction artifacts typically associated with differential imaging. The$5\mathrm{\sigma <\#comment/>}$contrast achieved by imaging of the exoplanet scene was$\sim <\#comment/>1.7\times <\#comment/>{10}^{-<\#comment/>4}$at a distance of$3\mathrm{\lambda <\#comment/>}/D$from the star and$\sim <\#comment/>2.1\times <\#comment/>{10}^{-<\#comment/>5}$at$10\mathrm{\lambda <\#comment/>}/D$. These contrast values are comparable to the very best on-sky results obtained from multi-wavelength observations that employ both angular differential imaging (ADI) and spectral differential imaging (SDI). This comparable performance is despite the fact that our simulations are quasi-monochromatic, which makes SDI impossible, nor do they have diurnal field rotation, which makes ADI impossible. The error covariance matrix of the joint regression shows substantial correlations in the exoplanet and NCPA estimation errors, indicating that exoplanet intensity and NCPA need to be estimated self-consistently to achieve high contrast.

    

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2. Exoplanet detection with photonic lanterns for focal-plane wavefront sensing and control

   https://doi.org/10.1117/12.2630692  

   Lin, Jonathan ; Xin, Yinzi ; Norris, Barnaby R. ; Kim, Yoo Jung ; Sallum, Steph ; Betters, Christopher ; Leon-Saval, Sergio ; Lozi, Julien ; Vievard, Sebastian ; Guyon, Olivier ; et al ( August 2022 , Adaptive Optics Systems VIII)

   Schmidt, Dirk ; Schreiber, Laura ; Vernet, Elise (Ed.)

   Inner working angle is a key parameter for enabling scientific discovery in direct exoplanet imaging and characterization. Approaches to improving the inner working angle to reach the diffraction limit center on the sensing and control of wavefront errors, starlight suppression via coronagraphy, and differential techniques applied in post-processing. These approaches are ultimately limited by the shot noise of the residual starlight, placing a premium on the ability of the adaptive optics system to sense and control wavefront errors so that the coronagraph can effectively suppress starlight reaching the science focal plane. Photonic lanterns are attractive for use in the science focal plane because of their ability to spatially filter light using a finite basis of accepted modes and effectively couple the results to diffraction-limited spectrometers, providing a compact and cost-effective means to implement post-processing based on spectral diversity. We aim to characterize the ability of photonic lanterns to serve as focal-plane wavefront sensors, allowing the adaptive optics system to control aberrations affecting the science focal plane and reject additional stellar photon noise. By serving as focal-plane wavefront sensors, photonic lanterns can improve sensitivity to exoplanets through both direct and coronagraphic observations. We have studied the sensing capabilities of photonic lanterns in the linear and quadratic regimes with analytical and numerical treatments for different lantern geometries (including non-mode-selective, mode-selective, and hybrid geometries) as a function of port number. In this presentation we report on the sensitivity of such lanterns and comment on the relative suitability and sensitivity impacts of different lantern geometries for focal-plane wavefront sensing. 

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3. Wavefront profiling via correlation of GLAO open loop telemetry

   https://doi.org/10.1117/12.2629613  

   McEwen, Eden ; Dungee, Ryan ; Chun, Mark R. ; Lu, Jessica ; Lai, Olivier ; Baranec, Christoph ( August 2022 , Proc. SPIE 12185, Adaptive Optics Systems VIII)

   Schmidt, Dirk ; Schreiber, Laura ; Vernet, Elise (Ed.)

   Adaptive Optics (AO) used in ground based observatories can be strengthened in both design and algorithms by a more detailed understanding of the atmosphere they seek to correct. Nowhere is this more true than on Maunakea, where a clearer profile of the atmosphere informs AO system development from the small separations of Extreme AO (ExAO) to the wide field Ground Layer AO (GLAO). Employing telemetry obtained from the ımaka GLAO demonstrator on the University of Hawaii 2.2-meter telescope, we apply a wind profiling method that identifies turbulent layer velocities through spatial-temporal cross correlations of multiple wavefront sensors (WFSs). We compare the derived layer velocities with nearby wind anemometer data and meteorological model predictions of the upper wind speeds and discuss similarities and differences. The strengths and limitations of this profiling method are evaluated through successful recovery of injected, simulated layers into real telemetry. We detail the profilers’ results, including the percentage of data with viable estimates, on four characteristic ımaka observing runs on open loop telemetry throughout both winter and summer targets. We report on how similar layers are to external measures, the confidence of these results, and the potential for future use of this technique on other multi conjugate AO systems. 

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4. Residual wavefront control of segmented mirror telescopes

   https://doi.org/10.1117/12.2630269  

   Ragland, Sam ; Wizinowich, Peter L. ; van Kooten, Maaike A. ; Bottom, Michael ; Calvin, Ben ; Fitzgerald, Michael P. ; Hinz, Philip M. ; Jensen-Clem, Rebecca M. ; Mawet, Dimitri ; Peretz, Eliad ( January 2022 , Adaptive Optics Systems VIII, SPIE, 2022.)

   Schmidt, Dirk ; Schreiber, Laura ; Vernet, Elise (Ed.)

   Uncorrected residual wavefront errors limit the ultimate performance of adaptive optics (AO) systems. We present different contributing factors and techniques to estimate and compensate these wavefront errors in the Keck natural guide star (NGS) AO systems. The error terms include low order static and semi-static aberrations from multiple sources, periodic and random segment piston errors, single-segment low order aberrations, wavefront sensor aliasing, vibrations, calibration drifts, and AO-to-telescope offload related errors. We present the design of a new AO subsystem, a residual wavefront controller (rWFC) to monitor the performance of the AO control loops and the image quality of the AO science instruments and apply the necessary changes to the telescope and AO parameters to minimize the residual wavefront errors. The distributed system consists of components at the telescope, AO bench and the science instruments. A few components of this system are already tested as on-demand standalone tools and will be integrated into a high-level graphical user interface (GUI) to operate the system. The software tool will periodically collect AO telemetry data, perform control loop parameter optimization and update AO parameters such as loop gains, centroid gain, etc. In addition, the system will analyze the science data at the end of each exposure and estimate telescope/AO performance when a bright point source is available in the science field. The benefits of reducing or eliminating the residual wavefront errors have broad implications for optical astronomy. Testing these techniques on a segmented telescope will be extremely useful to the teams developing high contrast AO systems for all extremely large telescopes and future segmented space telescopes. 

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5. Detecting Exomoons from Radial Velocity Measurements of Self-luminous Planets: Application to Observations of HR 7672 B and Future Prospects

   https://doi.org/10.3847/1538-3881/acb34a  

   Ruffio, Jean-Baptiste ; Horstman, Katelyn ; Mawet, Dimitri ; Rosenthal, Lee J. ; Batygin, Konstantin ; Wang 王, Jason J. 劲飞 ; Millar-Blanchaer, Maxwell ; Wang 王, Ji 吉. ; Fulton, Benjamin J. ; Konopacky, Quinn M. ; et al ( February 2023 , The Astronomical Journal)

   The detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory. In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous, directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging. First, we demonstrate a sensitivity to satellites with a mass ratio of 1%–4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B;K_mag= 13; 0.″7 separation) with the Keck Planet Imager and Characterizer (R∼ 35,000 in theKband) at the W. M. Keck Observatory. Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as the Multi-Object Diffraction-limited High-resolution Infrared Spectrograph, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ∼10⁻⁴. Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system. Looking for the Rossiter–McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars.

    

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