arXiv subjects

Muskan Shinde

Publications and source records attributed to Muskan Shinde.

5 recordsLinked to original sources

arXiv2026

The infrared unmodulated pyramid wavefront sensor: simulations, lab and on sky

Direct imaging of Earth-like exoplanets requires strong suppression of stellar light at small angular separations, achievable with extreme adaptive optics (XAO). The pyramid wavefront sensor (PWFS) is widely used for its sensitivity but suffers from nonlinearities and limited dynamic range. Modulation extends the range but reduces sensitivity and limits loop speed. We investigate an unmodulated infrared PWFS (IR-umPWFS), where the dynamic range scales with wavelength, removing the need for modulation and enabling faster operation. We adopt a 3-sided PWFS, which eliminates the roof defect of the classical 4-sided design. We assess its feasibility and performance through end-to-end simulations, lab tests, and on-sky observations on the PAPYRUS bench at the Observatoire de Haute-Provence (OHP), and compare it with a visible modulated PWFS (VIS-mPWFS). Simulations show reliable operation, reaching Strehl ratios up to ~60% at 1400 nm for seeing up to 4''. Infrared operation improves linearity, reduces optical-gain variations and modal cross-talk. Laboratory results validate the simulations and confirm the pyramid quality. On sky, stable closed-loop operation was achieved over three nights. Compared with the VIS-mPWFS at 500 Hz, the IR-umPWFS at 1000 Hz showed gains of ~1.63 in Strehl ratio and ~1.26 in encircled energy, and a ~2.03-fold reduction in residual wavefront error. The IR-umPWFS remained robust to tip-tilt offsets up to 3 lambda/D at 1400 nm. It is a strong candidate for future XAO systems: operating in the infrared extends the linear range sufficiently to remove the need for modulation, enabling higher loop speeds no longer limited by the modulation mirror, which contributed to the improved on-sky performance. The OHP turbulence (D/r0 ~ 17 at 1400 nm) is comparable to typical VLT conditions (D/r0 ~ 20), supporting the relevance of these results for VLT/RISTRETTO.

astro-ph.IM↗

arXiv2025

The changing transit shape of TOI-3884 b

TOI-3884 b is a sub-Saturn transiting a fully convective M-dwarf. Observations indicate that the transit shape is chromatic and asymmetric as a result of persistent starspot crossings. This, along with the lack of photometric variability of the host star, indicates that the rotational axis of the star is tilted along our line of sight and the planet-occulted starspot is located close to the stellar pole. We acquired photometric transits over a period of three years with the Swiss 1.2-meter Euler telescope to track changes in the starspot configuration and detect any signs of decay or growth. The shape of the transit changes over time, and so far no two observations match perfectly. We conclude that the observed variability is likely not caused by changes in the temperature and size of the spot, but due to a slight (5.64 $\pm$ 0.64$^{\circ}$) misalignment between the spot center and the stellar pole, i.e., a small spin-spot angle ($Θ$). In addition, we were able to obtain precise measurements of the sky-projected spin-orbit angle ($λ$) of 37.3 $\pm$ 1.5\degree, and the true spin-orbit angle ($ψ$) of 54.3 $\pm$ 1.4\degree. The precise alignment measurements along with future atmospheric characterisation with the James Webb Space Telescope will be vital for understanding the formation and evolution of close-in, massive planets around fully convective stars.

astro-ph.EP↗

arXiv2024

RISTRETTO: a comparative performance analysis of the unmodulated Pyramid wavefront sensor and the Zernike wavefront sensor

The RISTRETTO instrument, a proposed visible high-contrast, high-resolution spectrograph for the VLT, has the primary science goal of detecting reflected light from nearby exoplanets and characterizing their atmospheres. Specifically, it aims to atmospherically characterize Proxima b, our closest temperate rocky exoplanet, located $37 mas$ from its host star, corresponding to $2λ/D$ at $λ=750 nm$. To achieve this goal, a raw contrast of less than $10^{-4}$ at $2λ/D$ and a Strehl ratio greater than 70% are required, necessitating an extreme adaptive optics system (XAO) for the spectrograph. To meet the performance requirements for RISTRETTO, high sensitivity to low-order wavefront aberrations and petal modes is essential. Therefore, unmodulated Pyramid wavefront sensors (PWFS) and Zernike wavefront sensors (ZWFS) are under consideration. However, these sensors exhibit non-linearities and have a limited dynamic range, requiring different strategies to optimize their performance. The dynamic range of the sensors increases at longer wavelengths. Thus, in this study, we compare the performance of the 3-sided unmodulated PWFS, the 4-sided unmodulated PWFS, and the Zerniike WFS at different wavelengths in the visible and near-infrared regime.

astro-ph.IM↗

arXiv2024

Characterizing the performance of two C-RED ONE cameras for implementation in RISTRETTO and SAXO+ projects

In the near-infrared wavelength regime, atmospheric turbulence fluctuates at a scale of a few milliseconds, and its precise control requires the use of extreme adaptive optics (XAO) systems equipped with fast and sensitive detectors operating at kHz speeds. The C-RED One cameras developed by First Light Imaging (FLI), based on SAPHIRA detectors made of HgCdTe e-APD array sensitive to 0.8-2.5 $μ$m light, featuring a 320x256 pixels with 24 $μ$m pitch, offering sub-electron readout noise and the ability to read subarrays, at frame-rates of up to few 10-kHz, are state-of-the-art for XAO wavefront sensing. The Observatory of Geneva purchased two C-RED One cameras identified as necessary for RISTRETTO (a proposed high-contrast high-resolution spectrograph for the VLT) and SAXO+ (an upgrade of the VLT/SPHERE XAO system) projects. We present a comprehensive characterization and comparative analysis of both the cameras. We present test results examining key noise contributors, including readout noise, detector bias, etc. And we also study their temporal variability. Additionally, we assess the conversion gain and the avalanche gain calibration of the detector. We also study the evolution some of these parameters over time.

astro-ph.IM↗

arXiv2024

RISTRETTO: reflected-light exoplanet spectroscopy at the diffraction limit of the VLT

RISTRETTO is a visible high-resolution spectrograph fed by an extreme adaptive optics (AO) system, to be proposed as a visitor instrument on ESO VLT. The main science goal of RISTRETTO is to pioneer the detection and atmospheric characterisation of exoplanets in reflected light, in particular the temperate rocky planet Proxima b. RISTRETTO will be able to measure albedos and detect atmospheric features in a number of exoplanets orbiting nearby stars for the first time. It will do so by combining a high-contrast AO system working at the diffraction limit of the telescope to a high-resolution spectrograph, via a 7-spaxel integral-field unit (IFU) feeding single-mode fibers. Further science cases for RISTRETTO include the study of accreting protoplanets such as PDS70b/c through spectrally-resolved H-alpha emission, and spatially-resolved studies of Solar System objects such as icy moons and the ice giants Uranus and Neptune. The project is in the manufacturing phase for the spectrograph sub-system, and the preliminary design phase for the AO front-end. Specific developments for RISTRETTO include a novel coronagraphic IFU combining a phase-induced amplitude apodizer (PIAA) to a 3D-printed microlens array feeding a bundle of single-mode fibers. It also features an XAO system with a dual wavefront sensor aiming at high robustness and sensitivity, including to pupil fragmentation. RISTRETTO is a pathfinder instrument in view of similar developments at the ELT, in particular the SCAO-IFU mode of ELT-ANDES and the future ELT-PCS instrument.

astro-ph.EP↗