Extremely Large Telescopes Research Articles

Probing Na in giant exoplanets with ESPRESSO and 3D NLTE stellar spectra

Neutral sodium was the first atom that was detected in an exoplanetary atmosphere using the transmission spectroscopy technique. To date, it remains the most successfully detected species due to its strong doublet in the optical at 5890\ A and 5896\ A . However, the center-to-limb variation (CLV) of these lines in the host star can bias the Na I detection. When combined with the Rossiter-McLaughlin (RM) effect, the CLV can mimic or obscure a planetary absorption feature if it is not properly accounted for. This work aims to investigate the impact of three-dimensional (3D) radiation hydrodynamic stellar atmospheres and non-local thermodynamic equilibrium (NLTE) radiative transfer on the modeling of the CLV+RM effect in single-line transmission spectroscopy to improve the detection and characterization of exoplanet atmospheres. We produced a grid of 3D NLTE synthetic spectra for Na I for FGK-type dwarfs within the following parameter space: $T_ eff =4500-6500$\,K, $ g =4.0-5.0$, and Fe/H . This grid was then interpolated to match the stellar parameters of four stars hosting well-known giant exoplanets, generating stellar spectra to correct for the CLV+RM effect in their transmission spectra. We used archival observations taken with the high-resolution ESPRESSO spectrograph. Our work confirms the Na I detections in three systems, namely WASP-52b, WASP-76b, and WASP-127b, also improving the accuracy of the measured absorption depth. Furthermore, we find that 3D NLTE stellar models can explain the spectral features in the transmission spectra of HD 209458b without the need for any planetary absorption. In the grid of stellar synthetic spectra, we observe that the CLV effect is stronger for stars with low $T_ eff $ and high $ g$. However, the combined effect of CLV and RM is highly dependent on the orbital geometry of the planet-star system. With the continuous improvement of instrumentation, it is crucial to use the most accurate stellar models available to correct for the CLV+RM effect in high-resolution transmission spectra to achieve the best possible characterization of exoplanet atmospheres. This will be fundamental in preparation for instruments such as ANDES at the Extremely Large Telescope to fully exploit its capabilities in the near future. We make our grid of 3D NLTE synthetic spectra for Na I publicly available.

Large Fiber Array Spectroscopic Telescope: Optical Design for a Scalable Unit Telescope

The Large Fiber Array Spectroscopic Telescope (LFAST) concept involves the utilization of 2640 individual, 0.76 m “unit telescopes” to collect light from a target object. Through optical fibers, the lights from all telescope foci are directed to a high-resolution spectrograph, with fibers subtending a 1.47 arcsec diameter on the sky. The total light-collecting area of all telescopes combined is 1200 m2. Given the telescope’s application for spectroscopy of seeing-limited images, the need for coherence is eliminated. The primary goal of the LFAST prototype is to demonstrate a telescope design that can be rapidly and cost-effectively replicated to achieve a 1200 m2 collecting area and match the capabilities of extremely large telescopes (ELTs) presently under construction. Engineering, manufacturing, and design challenges unique to LFAST differ significantly from those encountered in traditional ELTs. Considering that the unit telescope is to be replicated thousands of times, reducing the manufacturing cost per telescope is essential. The aim of the described design is to achieve this goal, with strong considerations for manufacturability, alignment, few moving parts, and high yield. Experience from the first prototype unit telescope built in 2022 will be leveraged to build the first 20-unit tracking module in 2024, with a collecting area of a 3.4-m-diameter mirror. The design is minimalistic and features commercial tolerances, thereby ensuring cost-effectiveness in manufacturing, assembly, and alignment processes. Moreover, the telescope is designed to operate at angles as low as 70° from the zenith by laterally translating a single lens to correct for atmospheric dispersion. We present a combined average of over 80% encircled energy across 2640 Monte Carlo trials. Simulations were conducted using commercially specified tolerances and capabilities to model the overall performance of the array.

High-resolution Transmission Spectroscopy of Warm Jupiters: An ESPRESSO Sample with Predictions for ANDES

Abstract Warm Jupiters are ideal laboratories for testing the limitations of current tools for atmospheric studies. The cross-correlation technique is a commonly used method to investigate the atmospheres of close-in planets, leveraging their large orbital velocities to separate the spectrum of the planet from that of the star. Warm Jupiter atmospheres predominantly consist of molecular species, notably water, methane, and carbon monoxide, often accompanied by clouds and hazes muting their atmospheric features. In this study, we investigate the atmospheres of six warm Jupiters, K2-139 b, K2-329 b, TOI-3362 b, WASP-130 b, WASP-106 b, and TOI-677 b, to search for water absorption using the ESPRESSO spectrograph, reporting nondetections for all targets. These nondetections are partially attributed to planets having in-transit radial velocity changes that are typically too small (≲15 km s−1) to distinguish between the different components (star, planet, Rossiter-McLaughlin effect, and telluric contamination), as well as the relatively weak planetary absorption lines as compared to the signal-to-noise ratio of the spectra. We simulate observations for the upcoming high-resolution spectrograph ANDES at the Extremely Large Telescope for the two favourable planets on eccentric orbits, TOI-3362 b and TOI-677 b, searching for water, carbon monoxide, and methane. We predict a significant detection of water and CO, if ANDES indeed covers the K-band, in the atmospheres of TOI-677 b and a tentative detection of water in the atmosphere of TOI-3362 b. This suggests that planets on highly eccentric orbits with favourable orbital configurations present a unique opportunity to access cooler atmospheres.

Using synthetic disk-integrated reflectance spectra to constrain direct imaging sensitivity requirements for a Mars-like exoplanet

The 2020 Decadal Survey on Astronomy and Astrophysics 11https://doi.org/10.17226/26141. recommended the prioritization of a space-based telescope capable of directly characterizing Earth-like exoplanets in reflected light. The planned suite of instruments onboard such a mission are expected to provide disk-integrated spectra with moderate spectral resolution and signal-to-noise (SNR). Although the detection and characterization of Earth-like exoplanets remains the primary focus of such a mission, land planets with limited available water, such as Mars, may be much more common. Mars-like exoplanets, therefore, are an equally significant set of targets when investigating the diverse climatologies and potential habitability of other worlds, especially if our own Solar System is any indication of planetary diversity. In this study, we constrain the direct imaging sensitivity requirements for observing and characterizing Mars-like exoplanets with the goal of informing future telescope design and mission planning. Employing an instrument noise model simulating a coronagraph-equipped, space-based telescope, spatially- and spectrally-resolved synthetic observations of Mars are produced. We evaluate the direct imaging sensitivity requirements across a range of wavelengths, from the ultraviolet (UV) to near-infrared (near-IR), to enable the spectral characterization of key atmospheric and surface features from disk-integrated reflectance spectra. Detectability at a given SNR is assessed through optical wavelength integration times for a range of phase angles, host star spectral types, and levels of atmospheric dustiness. Our results indicate that a Decadal-recommended space telescope featuring an aperture of 6-m is likely only proficient in detecting Mars-like exoplanets around K-type stars located within a 10 parsec (pc) radius from Earth. Furthermore, we demonstrate that when integrating over visible and near-IR wavelengths, required exposure times to detect such a planet are reasonable, especially near full phase angles. In the context of upcoming and proposed observatories, such as the Habitable Exoplanet Observatory (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR), our findings provide valuable insights into the direct imaging capabilities and optimal observational strategies needed for detecting and studying Mars-like exoplanets.

Ingot-like class of wavefront sensors for laser guide stars

Context. Full sky coverage adaptive optics (AO) on extremely large telescopes requires the adoption of several laser guide stars as references. With such large apertures, the apparent elongation of the beacons is absolutely significant. With a few exceptions, wavefront sensors (WFSs) designed for natural guide stars can be adapted and used in suboptimal mode in this context. Aims. We analyse and describe the geometrical properties of a class of WFSs that are specifically designed to deal with laser guide stars propagated from a location in the immediate vicinity of the telescope aperture. Methods. We describe, in three dimensions, the loci where the light of the laser guide stars would focus in the focal volume located behind the focal plane where astronomical objects are reimaged. We also describe the properties of several types of optomechanical devices that act as perturbers for this new class of pupil plane sensors, through refraction and reflections. We refer to these as ingot WFSs. Results. We provide the recipes both for the most reasonably complex version of these WFSs, with six pupils and, for the simplest one, only three pupils. Both of them are referred to on the basis of the European Extremely Large Telescope (ELT) case. We outlined elements that are meant to give a qualitative idea of how the sensitivity of this new class of sensors compares to conventional ones. Conclusions. We present a new class of WFSs, based on an extension to the case of elongated sources at a finite distance of the pyramid WFS. We point out which advantages of the pyramid can be retained and how it may be adopted to optimize the sensing procedure.

The effect of lightning on the atmospheric chemistry of exoplanets and potential biosignatures

Context. Lightning has been suggested to play a role in triggering the occurrence of bio-ready chemical species. Future missions such as PLATO, ARIEL, HWO, and LIFE, as well as ground-based extremely large telescopes (ELTs), will carry out investigations of the atmospheres of potentially habitable exoplanets. Aims. We aim to study the effect of lightning on the atmospheric chemistry. We also consider how it affects false-positive and false-negative biosignatures and whether these effects would be observable on exo-Earth and TRAPPIST-1 planets. Methods. We utilised a combination of laboratory experiments and photochemical and radiative transfer modelling. We conducted spark discharge experiments in N2−CO2−H2 gas mixtures, representing a range of possible rocky-planet atmospheres. We investigated the production of potential lightning signatures (CO and NO), possible biosignature gases (N2O, NH3, and CH4), and important prebiotic precursors (HCN and urea). Using the measured CO and NO production rates, we conducted photochemical simulations for oxygen-rich and anoxic atmospheres for rocky planets orbiting in the habitable zones of the Sun and TRAPPIST-1 for a range of lightning flash rates. Synthetic spectra were calculated using SMART to study the atmosphere’s reflectance, along with the emission and transmission spectra. Results. Lightning enhances the spectral features of NO, NO2, and (in some cases) CO through direct production; whereas CH4 and C2H6 may be enhanced indirectly. Lightning at a flash rate slightly higher than on modern-day Earth is able to mask the ozone features of an oxygen-rich, biotic atmosphere, making it harder to detect the biosphere of such a planet. Similarly, lightning at a flash rate at least ten times higher than on modern-day Earth is also able to mask the presence of ozone in the anoxic, abiotic atmosphere of a planet orbiting a late M dwarf, reducing the potential for a false-positive life detection. Conclusions. The threshold lightning flash rates to eliminate oxygen (>0.1%) and ozone false positive biosignatures on planets orbiting ultra-cool dwarfs is up to ten times higher than the modern flash rate. This result indicates that lightning cannot always prevent these false-positive scenarios.

Making the diamond vortex phase masks for the METIS instrument

Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.

Differential optical transfer function (dOTF) broad-spectrum wavefront sensing using integral field unit spectroscopy

Context. Detecting and characterizing Earth-like exoplanets is a critical scientific goal for the next generation of telescopes. However, current direct imaging instruments are hindered by evolving noncommon path aberrations (NCPAs), which lead to persistent speckles in the images. The differential optical transfer function (dOTF) is an image-based, noniterative, and model-independent wavefront sensor that combines differential images to estimate the complex field of the pupil. Aims. Given the objective of spectrally characterizing exoplanets to discern their composition and potentially detect biosignatures, we aim to explore the integration of the dOTF sensing method with an integral field unit (IFU) spectrograph. An IFU spectrograph generates a spectral data cube that contains diverse spectral information within a single dataset. Combining these two concepts is expected to improve the efficiency with which NCPAs can be spectrally measured and characterized. Methods. This Letter presents an implementation strategy for integrating dOTF and IFU spectroscopy data, enabling estimations of the electric field at various wavelengths simultaneously. Results. This method is specifically optimized to provide the most effective combination with minimal hardware requirements. It involves the use of multiple simultaneous deformable mirror actuator displacements in conjunction with an adapted Lyot stop employing a circular variable filter. Conclusions. The dOTF wavefront sensor coupled with an IFU spectrograph promises to be rapid and efficient, capable of measuring NCPAs across the entire spectrum provided by the spectrograph. Because the combination of dOTF and IFU spectroscopy is immediately applicable, it is of potential interest for various present-day on-sky instruments, as well as future IFU-based instruments coupled to the next generation of extremely large telescopes (ELTs).

Fires in the deep: The luminosity distribution of early-time gamma-ray-burst afterglows in light of the Gamow Explorer sensitivity requirements

Gamma-ray bursts (GRBs) are ideal probes of the Universe at high redshift ($z$), pinpointing the locations of the earliest star-forming galaxies and providing bright backlights with simple featureless power-law spectra that can be used to spectrally fingerprint the intergalactic medium and host galaxy during the period of reionization. Future missions such as Gamow Explorer (hereafter )\ are being proposed to unlock this potential by increasing the rate of identification of high-$z$ ($z>5$) GRBs in order to rapidly trigger observations from $6-10$ m ground telescopes, the James Webb Space Telescope (JWST), and the upcoming Extremely Large Telescopes (ELTs). was proposed to the NASA 2021 Medium-Class Explorer (MIDEX) program as a fast-slewing satellite featuring a wide-field lobster-eye X-ray telescope (LEXT) to detect and localize GRBs with arcminute accuracy, and a narrow-field multi-channel photo-$z$ infrared telescope (PIRT) to measure their photometric redshifts for $>80<!PCT!>$ of the LEXT detections using the Lyman-alpha dropout technique. We use a large sample of observed GRB afterglows to derive the PIRT sensitivity requirement. We compiled a complete sample of GRB optical--near-infrared (optical--NIR) afterglows from 2008 to 2021, adding a total of 66 new afterglows to our earlier sample, including all known high-$z$ GRB afterglows. This sample is expanded with over 2837 unpublished data points for 40 of these GRBs. We performed full light-curve and spectral-energy-distribution analyses of these afterglows to derive their true luminosity at very early times. We compared the high-$z$ sample to the comparison sample at lower redshifts. For all the light curves, where possible, we determined the brightness at the time of the initial finding chart of at different high redshifts and in different NIR bands. This was validated using a theoretical approach to predicting the afterglow brightness. We then followed the evolution of the luminosity to predict requirements for ground- and space-based follow-up. Finally, we discuss the potential biases between known GRB afterglow samples and those to be detected by We find that the luminosity distribution of high-$z$ GRB afterglows is comparable to those at lower redshift, and we therefore are able to use the afterglows of lower-$z$ GRBs as proxies for those at high $z$. We find that a PIRT sensitivity of $15\ (21 mag AB) in a 500 s exposure simultaneously in five NIR bands within 1000s of the GRB trigger will meet the mission requirements. Depending on the $z$ and NIR band, we find that between 75<!PCT!> and 85<!PCT!> of all afterglows at $z>5$ will be recovered by at $5 detection significance, allowing the determination of a robust photo-$z$. As a check for possible observational biases and selection effects, we compared the results with those obtained through population-synthesis models, and find them to be consistent. and other high-$z$ GRB missions will be capable of using a relatively modest 0.3m onboard NIR photo-$z$ telescope to rapidly identify and report high-$z$ GRBs for further follow-up by larger facilities, opening a new window onto the era of reionization and the high-redshift Universe.

Into nonlinearity and beyond for Zernike-like wavefront sensors

Context. Telescopes like the Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT) will be used together with extreme adaptive optics (AO) instruments to directly image Earth-like planets. The AO systems will need to perform at the fundamental limit in order to image Earth twins. A crucial component is the wavefront sensor. Interferometric wavefront sensors, such as the Zernike wavefront sensor (ZWFS), have been shown to perform close to the fundamental sensitivity limit. However, sensitivity comes at the cost of linearity; the ZWFS has strong nonlinear behavior. Aims. The aim of this work is to increase the dynamic range of Zernike-like wavefront sensors by using nonlinear reconstruction algorithms combined with phase sorting interferometry (PSI) and multi-wavelength measurements. Methods. The response of the ZWFS is explored analytically and numerically. Results. The proposed iterative (non)linear reconstructors reach the machine precision for small aberrations (<0.25 rad rms). Coupling the nonlinear reconstruction algorithm with PSI increases the dynamic range of the ZWFS by a factor of three to about 0.75 rad rms. Adding multiple wavebands doubles the dynamic range again, to 1.4 radians rms. Conclusions. The ZWFS is one of the most sensitive wavefront sensors, but has a limited dynamic range. The ZWFS will be an ideal second-stage wavefront sensor if it is combined with the proposed nonlinear reconstruction algorithm.

A strategy for sensing the petal mode in the presence of AO residual turbulence with the pyramid wavefront sensor

Context. With the Extremely Large Telescope (ELT) generation of telescopes come new challenges. The complexity of these telescopes’ pupils creates new problems for adaptive optics (AO) that prevent the telescopes from reaching the theoretical resolutions that their size allows. In particular, the large spiders necessary to support the massive optics of these telescopes create discontinuities in the wavefront measurement. These discontinuities appear as a new phase error dubbed the “petal mode.” This error is described as a differential piston between the fragment of the pupil separated by the spiders and is responsible for a strong degradation in the imaging quality, reducing the European ELT’s resolution to that of a 15m telescope. Aims. The aim of this paper is to study the measurement of the petal mode by AO sensors. In particular, we want to understand why the pyramid wavefront sensor (PyWFS), the first-light wavefront sensor of any ELT-generation telescope, cannot measure this petal mode under normal conditions, and how to enable this measurement by adapting the AO control scheme and the PyWFS. Methods. To facilitate our study, we considered a simplified version of the petal mode, featuring a simpler pupil than the ELT. This allowed us to quickly simulate the properties of the petal mode and its measurement by the PyWFS. We studied specifically how a system that separates the atmospheric turbulence from the petal measurement would behave. Studying the petal mode’s power spectral density, we proposed using a spatial filter to reduce the contribution of AO residuals to the benefit of petal mode contribution, eventually enabling it to be measured. Finally, we demonstrated our proposed system with end-to-end simulations. Results. A solution proposed to measure the petal mode is to use an unmodulated PyWFS (uPyWFS), but the uPyWFS does not make accurate measurements in the presence of atmospheric residuals. A spatial filtering step, consisting of a pinhole around the pyramid tip, reduces the first path residuals seen by the uPyWFS and restores its accuracy. This system was able to measure and control the petal mode during the end-to-end simulation. Conclusions. To address the petal problem, a two-path AO with a sensor dedicated to the measurement of the petal mode seems necessary. The question remains as to what could be used as the second path petalometer. Through this paper, we demonstrate that an uPyWFS can confuse the petal mode with the residuals from the first path. However, adding a spatial filter on top of said uPyWFS makes it a good petalometer candidate. This spatial filtering step makes the uPyWFS less sensitive to the first path residuals while retaining its ability to measure the petal mode.

The Bi–O edge wavefront sensor

Context. Direct detection of exoplanets around nearby stars requires advanced adaptive optics (AO) systems. High-order systems are needed to reach a high Strehl ratio (SR) in near-infrared and optical wavelengths on future giant segmented-mirror telescopes (GSMTs). Direct detection of faint exoplanets with the European Southern Observatory (ESO) Extremely Large Telescope (ELT) will require some tens of thousands of correction modes. The resolution and sensitivity of the wavefront sensor (WFS) are key requirements for this science case. We present a new class of WFSs, the bi-orthogonal Foucault knife-edge sensors (or Bi–O edge), that is directly inspired by the Foucault knife-edge test. The idea consists of using a beam-splitter producing two foci, each of which is sensed by an edge with a direction orthogonal to the other focus. Aims. We describe two implementation concepts: The Bi–O edge sensor can be realised with a sharp edge and a tip-tilt modulation device (sharp Bi–O edge) or with a smooth gradual transmission over a grey edge (grey Bi–O edge). A comparison of the Bi–O edge concepts and the four-sided classical pyramid wavefront sensor (PWS) gives some important insights into the nature of the measurements. Methods. We analytically computed the photon noise error propagation, and we compared the results to end-to-end simulations of a closed-loop AO system. Results. Our analysis shows that the sensitivity gain of the Bi–O edge with respect to the PWS depends on the system configuration. The gain is a function of the number of control modes and the modulation angle. We found that for the sharp Bi–O edge, the gain in reduction of propagated photon noise variance approaches a theoretical factor of 2 for a large number of control modes and small modulation angle, meaning that the sharp Bi–O edge only needs half of the photons of the PWS to reach similar measurement accuracy. In contrast, the PWS is twice more sensitive than the Bi–O edge in the case of very low order correction and/or large modulation angles. Preliminary end-to-end simulations illustrate some of the results. The grey version of the Bi–O edge opens the door to advanced amplitude filtering, which replaces the need for a tip-tilt modulator while keeping the same dynamic range. We show that an additional factor of 2 in reduction of propagated photon noise variance can be obtained for high orders, such that the theoretical maximum gain of a factor of 4 in photon efficiency can be obtained. A diffractive Fourier model that accurately includes the effect of modulation and control modes shows that for the extreme AO (XAO) system configuration of the ELT, the overall gain will well exceed one magnitude in guide-star brightness when compared to the modulated PWS. Conclusions. We conclude that the Bi–O edge is an excellent candidate sensor for future very high order Adaptive Optics systems, in particular on GSMTs.

Bayesian calibration of quasi-static field distortions in HARMONI

ABSTRACT The high angular resolution monolithic optical and near-infrared Integral field spectrograph is the first light visible and near-infrared integral field spectrograph for the Extremely Large Telescope. To reach the diffraction limit of the telescope (≈ 10 mas) and maintain an optimal image quality over long exposures, an accurate measurement of geometrical distortions in the instrument’s guide star field is needed. Geometrical distortions affecting the guide stars map directly to pointing errors of the science field. The systematic contribution to the pointing error can be calibrated and removed by a corrective model. In this work, we propose a formulation of the corrective model that aims to calibrate the geometrical field distortions down to a given target residual, as well as reducing the time spent in calibrations. We also propose a calibration procedure that accounts for the uncertainties of the measurement process. We developed a tool named harmoni-pm to simulate the expected pointing error caused by geometrical distortions and validate the effectiveness of the proposed corrective model. We also relied on pseudo Zernike polynomials to formulate the model, and the Bayesian theoretical framework to study the propagation of uncertainties along the calibration process. Compared with the classical calibration algorithm, the Bayesian calibration algorithm was able to reduce the number of calibration points required to reach the same model residual. Additionally, we were able to optimize the hardware of the Geometrical Calibration Unit and reduce the time required to achieve the calibration goal.

Detecting Biosignatures in Nearby Rocky Exoplanets Using High-contrast Imaging and Medium-resolution Spectroscopy with the Extremely Large Telescope

In the upcoming decades, one of the primary objectives in exoplanet science is to search for habitable planets and signs of extraterrestrial life in the Universe. Signs of life can be indicated by thermal-dynamical imbalance in terrestrial planet atmospheres. O2 and CH4 in the modern Earth’s atmosphere are such signs, commonly termed biosignatures. These biosignatures in exoplanetary atmospheres can potentially be detectable through high-contrast imaging instruments on future extremely large telescopes. To quantify the signal-to-noise ratio (S/N) with extremely large telescopes, we select up to 10 nearby rocky planets and simulate medium-resolution (R ∼ 1000) direct imaging of these planets using the Mid-infrared ELT Imager and Spectrograph (ELT/METIS, 3–5.6 μm) and the High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (ELT/HARMONI, 0.5–2.45 μm). We calculate the S/N for the detection of biosignatures including CH4, O2, H2O, and CO2. Our results show that GJ 887 b has the highest detection of S/N for biosignatures, and Proxima Cen b exhibits the only detectable CO2 among the targets for ELT/METIS direct imaging. We also investigate the TRAPPIST-1 system, the archetype of nearby transiting rocky planet systems, and compare the biosignature detection of transit spectroscopy with JWST versus direct spectroscopy with ELT/HARMONI. Our findings indicate JWST is more suitable for detecting and characterizing the atmospheres of transiting planet systems such as TRAPPIST-1 that are relatively further away and have smaller angular separations than more nearby nontransiting planets.

Watching the Universe’s acceleration era with the SKAO

ABSTRACT The possibility of watching the Universe expand in real time and in a model-independent way, first envisaged by Allan Sandage more than 60 yr ago and known as the redshift drift, is within reach of forthcoming astrophysical facilities, particularly the Extremely Large Telescope (ELT) and the Square Kilometre Array Observatory (SKAO). The latter, probing lower redshifts, enables us to watch the Universe’s acceleration era in real time, while the former does the same for the matter era. We use Fisher matrix analysis techniques, which we show to give comparable results to those of a Markov Chain Monte Carlo approach, to discuss forecasts for SKAO measurements of the redshift drift and their cosmological impact. We consider specific fiducial cosmological models but mainly rely on a more agnostic cosmographic series (which includes the deceleration and jerk parameters), and we also discuss prospects for measurements of the drift of the drift. Overall, our analysis shows that SKAO measurements, with a reasonable amount of observing time, can provide a competitive probe of the low-redshift accelerating Universe.

Optique adaptative : correction des effets de la turbulence atmosphérique sur les images astronomiques

Today, adaptive optics (AO) is installed on all very large astronomical telescopes. It allows to overcome the limitation in angular resolution imposed on large ground-based telescopes by the atmospheric turbulence perturbations. This review paper presents the state of the art of the field for astronomical applications. It gives the principles of AO and describes its main components which are the deformable mirrors, the wavefront sensors and the control algorithms. The paper also presents the main recent achievements and ongoing projects. First, for the direct imaging of extra-solar planets by extreme AO and coronography, taking as example the SPHERE instrument. Then to solve the problem of the very limited sky coverage by using laser guide star and to extend the AO correction beyond the isoplanatic patch. Thus, the various laser-assisted tomographic AO concepts are presented with examples of each realization as for the laser tomography AO, the multi-conjugate AO and the multi-object AO. Finally, the challenges of the new generation of giant telescopes are discussed at the end of the paper with a particular focus on the European Extremely Large Telescope (ELT) project.

Discerning Parallax Amplitude in Astrometric Microlensing

Gravitational microlensing is a powerful method for discovering isolated stellar-mass black holes (ISMBHs). These objects make long-duration microlensing events. To characterize these lensing objects by fully resolving the microlensing degeneracy, measurements of parallax and astrometric deflections are necessary. Microlensing events due to ISMBHs have considerable astrometric deflections but small parallax amplitudes, , where M l is the lens mass. We numerically investigate the possibility of inferring parallax amplitude from astrometric deflection in microlensing events due to ISMBHs. The parallax amplitude in astrometric deflections is proportional to the relative parallax π rel, which means that it (i) does not strongly depend on M l and (ii) increases in microlensing observations toward the Magellanic Clouds. We assume that these events will be potentially detected in upcoming microlensing surveys such as (1) the Roman observations of the Galactic bulge (GB) and (2) the LSST observations of the Large Magellanic Cloud (LMC) and that the Extremely Large Telescope (ELT) will follow up on them with one data point every 10 days. We evaluate the probability of inferring parallax amplitude from these observations by calculating the Fisher and covariance matrices. For the GB, the efficiencies for discerning parallax amplitudes with a relative error of <4% through astrometric and photometric observations are 3.8% and 29.1%, respectively. For observations toward the LMC, these efficiencies are 41.1% and 23.0%, respectively. Measuring parallax amplitude through astrometric deflections is plausible in GB events with a lens distance of ≲2.7 kpc and in LMC halo lensing. By monitoring long-duration microlensing events, the ELT can detect astrometric deflections and their parallax-induced deviations.

Characterization of extrasolar giant planets with machine learning

ABSTRACT More than 5000 extrasolar planets have already been detected. JWST and near-term ground-based telescopes like the Extremely Large Telescope (ELT), Giant Magellan Telescope (GMT), Thirty Meter Telescope (TMT), and upcoming telescopes such as the Nancy Grace Roman Space Telescope, Xuntian, and Ariel are designed to characterize the atmosphere of directly imaged Jovian planets. Here, we used five diverse machine learning algorithms to investigate how well broad-band filter photometric fluxes could initially characterize giant exoplanets. We use an established grid of 8813 reflected light model spectra of different metallicities, planet–star distances, and cloud properties to assess the performance of several machine learning algorithms on both noiseless and noisy data to provide classification and regression results as a function of signal to noise of the data. In all cases, the algorithms were tested on noisy validation data. The results show that the use of machine learning to characterize giant planets from reflected broad-band filter photometry provides a promising tool for initial characterization, with over 65 per cent accuracy in characterizing metallicity for signal-to-noise ratios (S/N) ≳ 30, over 80 per cent for cloud coverage for S/N ≳ 30. This approach will allow initial characterization for large surveys of giant exoplanets and prioritization for spectroscopy observations of a subset of these worlds.

CROCODILE

Context. The investigation of the atmospheres of closely separated, directly imaged gas giant exoplanets is challenging due to the presence of stellar speckles that pollute their spectrum. To remedy this, the analysis of medium- to high-resolution spectroscopic data via cross-correlation with spectral templates (cross-correlation spectroscopy) is emerging as a leading technique. Aims. We aim to define a robust Bayesian framework combining, for the first time, three widespread direct-imaging techniques, namely photometry, low-resolution spectroscopy, and medium-resolution cross-correlation spectroscopy in order to derive the atmospheric properties of close-in directly imaged exoplanets. Current atmospheric characterisation frameworks are indeed either not compatible with all three observing techniques or they lack the commitment to efficient sampling strategies that allow high-dimensional forward models. Methods. Our framework CROCODILE (cross-correlation retrievals of directly imaged self-luminous exoplanets) naturally combines the three techniques by adopting adequate likelihood functions. To validate our routine, we simulated observations of gas giants similar to the well-studied β Pictoris b planet and we explored the parameter space of their atmospheres to search for potential biases. Results. We obtain more accurate measurements of atmospheric properties when combining photometry, low- and medium-resolution spectroscopy into atmospheric retrievals than when using the techniques separately as is usually done in the literature. Indeed, the combined fit is, on average, 20% more accurate than fitting only medium-resolution cross-correlation spectroscopy. We find that medium-resolution (R ≈ 4000) K-band cross-correlation spectroscopy alone is not suitable to constrain the atmospheric properties of our synthetic datasets; however, this problem disappears when simultaneously fitting photometry throughout the Y and M bands and low-resolution (R ≈ 60) spectroscopy between the Y and H bands. Our thorough testing demonstrates that free chemistry is a suitable forward model to retrieve the atmospheric thermal and chemical properties of cloudless gas giants at chemical equilibrium. Conclusions. CROCODILE provides a robust statistical framework to interpret medium-resolution spectroscopic data of close-in directly imaged exoplanets, where speckles originating from stellar stray light render the extraction of the continuum difficult. Our framework allows the atmospheric characterisation of directly imaged exoplanets using the high-quality spectral data that will be provided by the new generation of instruments such as the Enhanced Resolution Imager and Spectrograph (ERIS) at the Very Large Telescope, the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope, and in the future the Mid-infrared ELT Imager and Spectrograph (METIS) at the Extremely Large Telescope.

Teledyne imaging sensors' recent contributions to astronomy, earth science, and planetary science

AbstractTeledyne Imaging Sensors (TIS) is the leading supplier of infrared focal plane arrays (FPAs) to astronomy and TIS plays a strong role in providing image sensors for Earth and Planetary Science. This article starts with a brief introduction to TIS' technologies and image sensor products. We then present some of TIS' deliveries to space missions and ground‐based telescopes. The space missions include ESA's Euclid Dark Universe mission and several NASA missions (James Webb Space Telescope, Roman Space Telescope, SPHEREx, EMIT). TIS continues to serve ground‐based astronomy by providing the H2RG and the world's largest high‐performance infrared astronomy FPA, the H4RG‐15, to several ground‐based observatories. Active programs will be described. Ongoing work includes NASA's NEO Surveyor asteroid surveillance mission, ESA's Ariel exo‐planet spectroscopy mission, and deliveries to the European Southern Observatory's Extremely Large Telescope.