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Astronomical precision spectroscopy underpins searches for life beyond Earth, direct observation of the expanding Universe and constraining the potential variability of physical constants on cosmological scales. Laser frequency combs can provide the required accurate and precise calibration to the astronomical spectrographs. For cosmological studies, extending the calibration with such astrocombs to the ultraviolet spectral range is desirable, however, strong material dispersion and large spectral separation from the established infrared laser oscillators have made this challenging. Here, we demonstrate astronomical spectrograph calibration with an astrocomb in the ultraviolet spectral range below 400 nm. This is accomplished via chip-integrated highly nonlinear photonics in periodically-poled, nano-fabricated lithium niobate waveguides in conjunction with a robust infrared electro-optic comb generator, as well as a chip-integrated microresonator comb. These results demonstrate a viable route towards astronomical precision spectroscopy in the ultraviolet and could contribute to unlock the full potential of next-generation ground-based and future space-based instruments. Here the authors demonstrate ultraviolet astronomical frequency combs, derived from the near-infrared domain via efficient harmonic generation in nanophotonic waveguides, to provide precision calibration to astronomical spectrographs for exoplanet science and precision cosmology.

A microphotonic astrocomb is demonstrated via temporal dissipative Kerr solitons in photonic-chip-based silicon nitride microresonators with a precision of 25 cm s–1 (radial velocity equivalent), useful for Earth-like planet detection and cosmological research.

The characterization of exoplanet atmospheres is one of the key topics in modern astrophysics. To date, transmission spectroscopy has been the primary method used, but upcoming instruments will lay the foundation for advancing reflected-light spectroscopy. The main challenge in this area of research is the high contrast ratio between the planet and its star. RISTRETTO, a high-resolution integral-field spectrograph designed for ESO's VLT, aims to address these limitations through a combination of extreme AO, coronagraphy, and high-resolution spectroscopy. The goal of this paper is to demonstrate the detectability of the temperate rocky planet Proxima b with RISTRETTO, using realistic end-to-end simulations and a specifically developed data analysis methodology. We created high-resolution star and planet spectra, selecting realistic observational epochs and incorporating the predicted performance of the AO and coronagraphic systems. We implemented noise and spectrograph effects through the Pyechelle spectrograph simulator. We then applied a new methodology to isolate the signal of the planet from the stellar one and proceeded to fit several planetary models in order of increasing complexity. We also introduced a method to determine the sky orientation of the stellar spin axis, which constrains the orientation of the planetary orbit for aligned systems. Assuming an Earth-like atmosphere, our results show that RISTRETTO can detect Proxima b in reflected light in about 55 hours of observing time, offering the ability to characterize the planet orbital inclination, true mass, and broadband albedo. In addition, molecular absorption by O\\(_2\\) and H\\(_2\\)O can be detected in about 85 hours of observations. These findings highlight the potential of RISTRETTO to significantly advance the field of exoplanetary science by enabling reflected-light spectroscopy of a sample of nearby exoplanets.

The Next Generation Transit Survey (NGTS) is a new ground-based survey for transiting exoplanets. Our primary goal is to find the first statistically-significant sample of Neptunes and super-Earths that are bright enough for radial velocity confirmation. By measuring precise masses and radii we will constrain the bulk composition and internal structure of planets that span the transition between the gas giants and terrestrial planets. Our brightest exoplanets will also be suitable for atmospheric characterisation with large facilities such as the VLT, JWST and the E-ELT. NGTS construction began in June 2013, and the survey is due to commence in 2014.

The RISTRETTO project is aiming to build an instrument that will detect the reflected light from close-by exoplanet. It is a two stage instrument: An extreme AO system in the visible, followed by a seven spaxel single mode High resolution Spectrograph. In this paper we present the design of this spectrograph: a classical echelle spectrograph fed with single mode fibers. Standard single mode fibers have been chosen and are forming a long tilted slit in order to have the right order spacing on the detector. The instrument will be under vacuum and thermally controlled in order to make it stable.

This paper provides a comprehensive overview of the subsystems of the NIGHT instrument. NIGHT (the Near Infrared Gatherer of Helium Transits) is a narrowband, high-resolution spectrograph, marking the first dedicated survey instrument for exoplanetary atmosphere observations. Developed through a collaboration between the Observatory of Geneva and the Universite de Montreal, NIGHT aims to conduct an extensive statistical survey of helium atmospheres around 100+ exoplanets over several years. The instrument will report new detections of helium in exoplanet atmospheres and perform temporal monitoring of a subset of these. NIGHT measures absorption from the metastable helium state during exoplanet transits, observable in a triplet of lines around 1083nm. The instrument comprises a vacuum enclosure housing the spectrograph, a front end unit for fiber injection at the telescope's focal plane, and a calibration and control rack containing calibration light sources and control hardware. The spectrograph is optimized for efficiency, achieving a uniform throughput of approximately 71%. The primary disperser employs a VPH grating in a unique double-pass configuration, enabling a spectral resolution of 75,000 while maintaining high throughput. The detector is a HAWAII-1 infrared array, cooled to 85K, with the spectrograph operating at room temperature. Thanks to its relatively high throughput, NIGHT on a 2m class telescope is predicted to be as sensitive as existing instruments on 4m class telescopes. The front end unit injects starlight and sky background into two separate fibers leading to the spectrograph. It also performs near-infrared guiding and includes a mechanism for injecting calibration light. The assembly and optical alignment of NIGHT's spectrograph and front end unit are scheduled for July to September 2024, with the first light anticipated before early 2025.

In the last decade, white-light illuminated Fabry-Pérot interferometers wave been established as a widely used, relatively simple, reliable, and cost-effective way to precisely calibrate high-resolution echelle spectrographs. However, Terrien et al. (2021) recently reported a chromatic drift of the Fabry-Pérot interferometer installed at the Habitable-zone Planet Finder spectrograph. In particular, they found that the variation of the etalon effective gap size is not achromatic as usually assumed but in fact depends on wavelength. Here, we present a similar study of the Espresso Fabry-Pérot interferometer. Using daily calibrations spanning a period of over 2.5 years, we also find clear evidence for a chromatic drift with an amplitude of a few cm/s per day that has a characteristic, quasi-oscillatory dependence on wavelength. We conclude that this effect is probably caused by an aging of the dielectric mirror coatings and expect that similar chromatic drifts might affect all Fabry-Pérot interferometers used for calibration of astronomical spectrographs. However, we also demonstrate that the chromatic drift can be measured and in principle corrected using only standard calibrations based on hollow cathode lamp spectra.

We present an updated characterization of the planetary system orbiting the nearby M2 dwarf GJ 3090 (TOI-177; \\(d = 22\\) pc), based on new high-precision radial velocity (RV) observations from NIRPS and HARPS. With an orbital period of 2.85 d, the transiting sub-Neptune GJ 3090 b has a mass we refine to \\(4.52 \\pm 0.47 M_{\\oplus}\\), which, combined with our derived radius of \\(2.18 \\pm 0.06 R_{\\oplus}\\), yields a density of \\(2.40^{+0.33}_{-0.30}\\) g cm\\(^{-3}\\). The combined interior structure and atmospheric constraints indicate that GJ 3090 b is a compelling water-world candidate, with a volatile-rich envelope in which water likely represents a significant fraction. We also confirm the presence of a second planet, GJ 3090 c, a sub-Neptune with a 15.9 d orbit and a minimum mass of \\(10.0 \\pm 1.3 M_{\\oplus}\\), which does not transit. Despite its proximity to the star's 18 d rotation period, our joint analysis using a multidimensional Gaussian process (GP) model that incorporates TESS photometry and differential stellar temperature measurements distinguishes this planetary signal from activity-induced variability. In addition, we place new constraints on a non-transiting planet candidate with a period of 12.7 d, suggested in earlier RV analyses. This candidate remains a compelling target for future monitoring. These results highlight the crucial role of multidimensional GP modelling in disentangling planetary signals from stellar activity, enabling the detection of a planet near the stellar rotation period that could have remained undetected with traditional approaches.

The Near InfraRed Planet Searcher (NIRPS) joined HARPS on the 3.6-m ESO telescope at La Silla Observatory in April 2023, dedicating part of its Guaranteed Time Observations (GTO) program to the radial velocity follow-up of TESS planet candidates to confirm and characterize transiting planets around M dwarfs. We report the first results of this program with the characterization of the TOI-756 system, which consists of TOI-756 b, a transiting sub-Neptune candidate detected by TESS, as well as TOI-756 c, an additional non-transiting planet discovered by NIRPS and HARPS. TOI-756 b is a 1.24-day period sub-Neptune with a radius of 2.81 \\(\\pm\\) 0.10 \\(R_\\oplus\\) and a mass of 9.8\\(^{+1.8}_{-1.6}\\) \\(M_\\oplus\\). TOI-756 c is a cold eccentric (e\\(_c\\) = 0.45 \\(\\pm\\) 0.01) giant planet orbiting with a period of 149.6 days around its star with a minimum mass of 4.05 \\(\\pm\\) 0.11 \\(M_\\mathrm{jup}\\). Additionally, a linear trend of 146\\(~\\mathrm{m\\,s}^{-1}\\,\\mathrm{yr}^{-1}\\) is visible in the radial velocities, hinting at a third component, possibly in the planetary or brown dwarf regime. This system is unique in the exoplanet landscape, standing as the first confirmed example of such a planetary architecture around an M dwarf. With a density of 2.42 \\(\\pm\\) 0.49 g cm\\(^{-3}\\), the inner planet, TOI-756 b, is a volatile-rich sub-Neptune. Assuming a pure H/He envelope, we inferred an atmospheric mass fraction of 0.023 and a core mass fraction of 0.27, which is well constrained by stellar refractory abundances derived from NIRPS spectra. It falls within the still poorly explored radius cliff and at the lower boundary of the Neptune desert, making it a prime target for a future atmospheric characterization with JWST to improve our understanding of this population.

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.