Cross-dispersed echelle spectrographs (CDESs) are a fundamental tool for modern astronomy. The spectral resolution achieved by these instruments is directly related to the size of the echelle grating and the focal length of the collimator. However, when they are used in ground-based observatories, they are typically seeing-limited, meaning that the achievable spectral resolving power is limited by the coherent fraction of the telescope aperture. As a result, achieving high-spectral resolution requires large echelle apertures and long collimator focal lengths, leading to instruments with significant dimensions. These dimensions are often also necessary to ensure the thermal and mechanical stability required by demanding science cases. With the advent of large-aperture telescopes and the unrelenting demand for high resolution, the prevailing trajectory of these instruments leans toward escalating in both size and complexity. However, it is important to explore miniaturization strategies for CDESs, which are particularly valuable, for example, for space-based instruments where size, weight, and power are crucial. In addition, space-based observatories are not affected by atmospheric seeing and can therefore operate in a diffraction-limited regime, allowing the full grating-limited spectral resolution to be exploited. In this work, we demonstrate the working principle of a parametric model that describes two configurations of CDES: the Three-fold (3F) and the Cassegrain (CA) design. The Three-fold CDES is a white-pupil design that is currently used at major observatories, and it is based on a single parabolic mirror for collimation and folding of the optical path. The Cassegrain CDES, a white-pupil design with a novel approach to the collimator, uses an inverted Cassegrain telescope design as a telephoto collimator. This allows for the design to achieve the same collimator focal length as with a single parabolic mirror but in a smaller footprint, paving the way for a possible miniaturization strategy for the 3F design. The presented model evaluates both configurations using two merit figures: the spectral resolving power and the design dimensions without the need to use conventional graphical ray-tracing software. This is used to systematically explore the design space of both configurations. Using Zemax simulations, we validate the model outputs in terms of spectral resolving power and instrument dimensions.

Atmospheric seeing arises from stochastic fluctuations in the refractive index of the Earth's atmosphere, producing random variations in the apparent direction of incoming light from astronomical sources. Scintillation refers to the associated intensity fluctuations induced by these refractive index inhomogeneities. A quantitative relationship between seeing and scintillation was established in 1993, enabling daytime seeing measurements by exploiting the Sun as an extended, bright source and using non-telescopic instrumentation. PoET, the Paranal solar ESPRESSO Telescope, will feed the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, ESPRESSO, at the European Southern Observatory Very Large Telescope. By using the Sun as a proxy for solar-type stars, PoET will facilitate detailed investigations of the physical processes that drive stellar noise in ultra-high-precision radial-velocity measurements for exoplanet studies. The instrument is capable of targeting any region on the solar disc and acquiring spatially resolved spectra over areas ranging from 1 to 55 arcsec. Accurate characterization of daytime atmospheric seeing is therefore essential for selecting the optimal observing aperture and ensuring the scientific performance of PoET. To support this requirement, we have developed and implemented a dedicated solar seeing monitor for daytime deployment at Paranal, Chile, where PoET will operate. In this work, we describe the instrument design and present the results from commissioning and initial on-sky validation.

BlueMUSE is a blue-optimised, medium spectral resolution, panoramic integral field spectrograph under development for the ESO's Very Large Telescope (VLT). The project is now entering preliminary design phase. With an optimised transmission down to 350 nm, spectral resolution of R ∼ 3500 on average across the wavelength range, and a large FoV (1 arcmin2), BlueMUSE will open up a new range of galactic and extragalactic science cases facilitated by its specific capabilities. BlueMUSE consists of several subsystems arranged along the light path. A calibration unit reproduces the VLT's optical conditions, while the fore optics reshape the telescope's focal image. The splitting and relay optics divide the field of view into 16 channels, each feeding an integral field unit that contains an image slicer, a spectrograph, and a detector vessel. The image slicer converts the 2D sub-field into a 1D pseudo-slit, which the spectrograph disperses into spectra recorded by a 4k x 4k CCD in each detector vessel. A vacuum and cryogenic system cools the detectors, and the data reduction software processes the raw data into data cubes which are subsequently processed by a data analysis software system. All subsystems are supported by the instrument main structure and enclosed in a thermal housing for stability. The whole instrument is managed by an integrated control system combining electronics and software. This paper summarizes the baseline architecture, interfaces, and functional descriptions of the BlueMUSE instrument at the start of Design Phase. This architecture is derived from the top-level requirements and the experience acquired from MUSE. It presents the global concepts along with their preliminary performance estimates.

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 ± 0.47 M⊕, which, combined with our derived radius of 2.18 ± 0.06 R⊕, yields a density of 2.40−0.30+0.33 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 ± 1.3 M⊕, 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 intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. In this work we present the simultaneous detections of H2O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned Near InfraRed Planet Searcher (NIRPS). We retrieved a photospheric abundance ratio of log(10)(OH/H2O) = -0.15 +/- 0.20, indicating that there is about as much OH as H2O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compared the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of 4.79(-0.97)(+0.93) km s(-1) in the H2O signal, which is not reproduced by current global circulation models. Finally, in addition to H2O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we inferred a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, thus paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.

We obtained 420 high-resolution spectra of Proxima, over 159 nights, using the Near Infra Red Planet Searcher (NIRPS). We derived 149 nightly binned radial velocity measurements with a standard deviation of 1.69 ms −1 and a median uncertainty of 55 cms −1 , and performed a joint analysis combining radial velocities, spectroscopic activity indicators, and ground-based photometry, to model the planetary and stellar signals present in the data, applying multi-dimensional Gaussian process regression to model the activity signals. We detect the radial velocity signal of Proxima b in the NIRPS data. All planetary characteristics are consistent with those previously derived using visible light spectrographs. In addition, we find evidence of the presence of the sub-Earth Proxima d in the NIRPS data. When combining the data with the HARPS observations taken simultaneous to NIRPS, we obtain a tentative detection of Proxima d and parameters consistent with those measured with ESPRESSO. By combining the NIRPS data with simultaneously obtained HARPS observations and archival data, we confirm the existence of Proxima d, and demonstrate that its parameters are stable over time and against change of instrument. We refine the planetary parameters of Proxima b and d, and find inconclusive evidence of the signal attributed to Proxima c (P = 1900 d) being present in the data. We measure Proxima b and d to have minimum masses of 1.055 ± 0.055 M ⊕ , and 0.260 ± 0.038 M ⊕ , respectively. Our results show that, in the case of Proxima, NIRPS provides more precise radial velocity data than HARPS, and a more significant detection of the planetary signals. The standard deviation of the residuals of NIRPS after the fit is ~80 cm s −1 , showcasing the potential of NIRPS to measure precise radial velocities in the near-infrared.

Context . Near-infrared high-resolution échelle spectrographs unlock access to fundamental properties of exoplanets, from their atmospheric escape and composition to their orbital architecture, which can all be studied simultaneously from transit observations. Aims . We present the first results of the newly commissioned ESO near-infrared spectrograph, Near-InfraRed Planet Searcher (NIRPS), from three transits of the well-studied warm Saturn WASP-69b. Our goals are to measure the orbital architecture of the planet through the Rossiter-McLaughlin (RM) effect and its atmospheric escape through the 1083 nm helium triplet. Methods . We used the RM Revolutions technique to better constrain the orbital architecture of the system. We extracted the high-resolution helium absorption profile to study its spectral shape and temporal variations. Then, we made 3D simulations from the EVE code to fit the helium absorption time series. Results . We measure a slightly misaligned orbit for WASP-69 b (3D spin-orbit angle of 28.7 −5.3 +6.1 ∘ ). We confirm the detection of helium with an average excess absorption of 3.17±0.05% (maximum of 4.02%). The helium absorption is spectrally and temporally resolved, extends to high altitudes and has a strong velocity shift up to −29.5±2.5 km s −1 50 minutes after egress. The signature cannot be explained by a thermosphere alone and thus requires 3D modeling of the thermosphere and exosphere. EVE simulations put constraints on the mass loss of 2.25 · 10 11 g s −1 and hint at reactive chemistry within the cometary-like tail and interaction with the stellar winds that allow the metastable helium to survive longer than expected. Conclusions . Our results suggest that WASP-69 b is going through a transformative phase of its history by losing mass while evolving on a misaligned orbit, similar to a growing number of Neptunian worlds. This work shows how combining multiple observational tracers such as orbital architecture, atmospheric escape, and composition is critical to understand exoplanet demographics and their formation and evolution. We demonstrate that NIRPS in the near-infrared can reach precisions similar to HARPS in the optical for RM studies, and the high data quality of NIRPS leads to unprecedented atmospheric characterization. Therefore, the addition of NIRPS to HARPS on the ESO 3.6 m makes it the driving force of such new studies. The high stability of NIRPS combined with the large Guaranteed Time Observation (GTO) available for its consortium enables in-depth studies of exoplanets as well as large population surveys.

Context. The Near-InfraRed Planet Searcher (NIRPS) is a high-resolution, high-stability near-infrared (NIR) spectrograph equipped with an adaptive optics (AO) system. Installed on the ESO 3.6-m telescope at La Silla Observatory, Chile, it was developed to enable radial velocity (RV) measurements of low-mass exoplanets around M dwarfs and to characterise exoplanet atmospheres in the NIR. Aims. This paper provides a comprehensive design overview and characterisation of the NIRPS instrument, reporting on its on-sky performance, advising on how to carry out observations, and presenting its guaranteed time observation (GTO) programme. Methods. Intensive on-sky testing phases were conducted between November 2019 and March 2023. The instrument started its operations on 1 April 2023. Results. The spectral range continuously covers the Y, J, and H bands from 972.4 to 1919.6 nm. The thermal control system maintains 1mK stability over several months, thereby minimising drift. The NIRPS's AO-assisted fibre link improves coupling efficiency and offers a unique high-angular resolution capability with a fibre acceptance of only 0.4 ''. A high spectral resolving power of R similar to 90 000 and R similar to 75 000 is provided in high-accuracy (HA) and high-efficiency (HE) modes, respectively. The overall throughput from the top of the atmosphere to the detector peaks at 13%. The RV precision, measured on the bright star Proxima with a known exoplanetary system, is 77 cm s(-1). NIRPS and HARPS can be used simultaneously, offering unprecedented spectral coverage for spectroscopic characterisation and stellar activity mitigation. Modal noise can be aptly mitigated by the implementation of fibre stretchers and AO scanning mode. Conclusions. Initial results confirm that NIRPS opens new possibilities for RV measurements, stellar characterisation, and exoplanet atmosphere studies with high precision and high spectral fidelity. NIRPS demonstrated stable RV precision at the level of 1 m s(-1) over several weeks. The instrument's high throughput, particularly in the H band, offers a notable improvement over previous spectrographs, enhancing our ability to detect small exoplanets.

Context. Stellar activity variability is one of the main obstacles to the detection of Earth-like planets using the radial velocity (RV) method. Aims. The aim of this work is to measure the effect of activity in the spectra of M dwarfs and detect activity-sensitive lines in the near-infrared (NIR) to help improve exoplanet detection and characterisation and contribute to further stellar activity analysis in the NIR. Methods. We took advantage of the simultaneous observations of HARPS and the newly commissioned NIRPS spectrograph to carry out a blind search of the most activity-sensitive spectral lines in the NIR using NIRPS spectra and known activity indicators in the optical from HARPS as a reference. We analysed the spectra of Proxima (M5.5V) and Gl 581 (M3V), two M dwarfs with different activity levels and internal structures. Spectral lines were identified for both stars and their profiles were fitted using different models. Results. We found hundreds of lines sensitive to activity for both stars; the Proxima spectra were more affected. For Proxima, around 32% of the identified lines can be used to measure the rotation period of the star, while for Gl 581 the numbers drops to 1%. The fraction of lines sensitive to activity increases with increasing line depth for both stars. A list of 17 lines with rotation period detection for both stars is provided. Conclusions. Stellar activity is able to affect a significant number of spectral lines in the NIR, and methods should be developed to mitigate those effects at the spectral level. The line distortions detected here are expected to come mainly from the flux effect due to temperature contrasts between active regions and the quiet photosphere; however, we cannot rule out the possibility that core-emission from chromospheric activity or Zeeman splitting are also affecting some lines. The new line lists presented here can be used to improve the RV extraction and the detection of RV variability due to stellar activity signals, and to help false positive detection and the modelling of activity variability, thereby enhancing exoplanet detection in the NIR.

The detection and characterisation of other "Earths", orbiting other suns, is a bold objective of present-day astrophysics. However, this quest is severely challenged by astrophysical "noise" from the host stars, whose signatures distort the observed spectra. Motivated by this problem, we are building a dedicated facility, the Paranal solar ESPRESSO Telescope (PoET). PoET will collect solar light and channel it into the ESPRESSO spectrograph, allowing us to use the Sun as a proxy to unambiguously identify and understand the sources of relevant variability in solar-type stars.

We obtained 420 high-resolution spectra of Proxima, over 159 nights, using the Near Infra Red Planet Searcher (NIRPS). We derived 149 nightly binned radial velocity measurements with a standard deviation of 1.69 ms(-1) and a median uncertainty of 55 cms(-1), and performed a joint analysis combining radial velocities, spectroscopic activity indicators, and ground-based photometry, to model the planetary and stellar signals present in the data, applying multi-dimensional Gaussian process regression to model the activity signals. We detect the radial velocity signal of Proxima b in the NIRPS data. All planetary characteristics are consistent with those previously derived using visible light spectrographs. In addition, we find evidence of the presence of the sub-Earth Proxima d in the NIRPS data. When combining the data with the HARPS observations taken simultaneous to NIRPS, we obtain a tentative detection of Proxima d and parameters consistent with those measured with ESPRESSO. By combining the NIRPS data with simultaneously obtained HARPS observations and archival data, we confirm the existence of Proxima d, and demonstrate that its parameters are stable over time and against change of instrument. We refine the planetary parameters of Proxima b and d, and find inconclusive evidence of the signal attributed to Proxima c (P = 1900 d) being present in the data. We measure Proxima b and d to have minimum masses of 1.055 +/- 0.055 M-circle plus, and 0.260 +/- 0.038 M circle plus, respectively. Our results show that, in the case of Proxima, NIRPS provides more precise radial velocity data than HARPS, and a more significant detection of the planetary signals. The standard deviation of the residuals of NIRPS after the fit is similar to 80 cm s(-1), showcasing the potential of NIRPS to measure precise radial velocities in the near-infrared.

Context. 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. Aims. We present the "Sub-Neptunes" subprogram of the NIRPS-GTO, aimed at investigating the composition and formation of sub-Neptunes orbiting 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. Methods. We analyzed TESS and ground-based photometry, high-resolution imaging, and high-precision radial velocities (RVs) from NIRPS and HARPS to characterize the two newly discovered planets orbiting TOI-756, as well as to derive the fundamental properties of the host star. A dedicated approach was employed for the NIRPS RV extraction to mitigate telluric contamination, particularly when the star's systemic velocity was shown to overlap with the barycentric Earth radial velocity. Results. TOI-756 is a M1V-type star with an effective temperature of T-eff similar to 3657 K and a super-solar metallicity ([Fe/H]) of 0.20 +/- 0.03 dex. TOI-756 b is a 1.24-day period sub-Neptune with a radius of 2.81 +/- 0.10 R-circle plus and a mass of 9.8(-1.6)(+1.8) M-circle plus. TOI-756 c is a cold eccentric (e(c) = 0.45 +/- 0.01) giant planet orbiting with a period of 149.6 days around its star with a minimum mass of 4.05 +/- 0.11 M-Jup. Additionally, a linear trend of 146 m s(-1) yr(-1) is visible in the radial velocities, hinting at a third component, possibly in the planetary or brown dwarf regime. Conclusions. We present the discovery and characterization of the transiting sub-Neptune TOI-756 b and the non-transiting eccentric cold giant TOI-756 c. 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 +/- 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.

The European Space Agency has selected PLATO (PLAnetary Transits and Oscillations of stars) for its M3 launch which is scheduled for 2026. With its extremely large field of view, PLATO is designed to obtain photometric measurements over an extended period for bright stars in order to detect and characterise (primarily) rocky planets in the habitable zones of solar type stars. The PLATO measurements will have sufficient sensitivity to determine the mass, radius and age of the host stars with unprecedented accuracy. The PLATO planet database will provide the first large-scale catalogue of accurately and homogeneously characterised small planets at intermediate orbital periods, which will can be used to severely constraint planet formation theories. This would facilitate large scale comparative exo-planetology. In addition the bright PLATO host stars will be ideal targets for atmospheric study with next generation facilities such as the ELT. The PLATO sensitivity will be sufficient to detect pulsations from stars across the HR diagram allowing a deep understanding of stellar structure and evolution to be developed using parameters determined from asteroseismology.

ANDES (ArmazoNes high Dispersion Echelle Spectrograph) is a fibre-fed echelle spectrograph for the ELT with three spectral arms, spanning 0.4-1.8 mu m (goal 0.35-2.4 mu m) at similar to 100,000 resolution. It enables sensitive observations of astronomical objects, such as exoplanets, fundamental physics and other frontier science cases. We describe the instrument's design and architecture, emphasizing its unique features. The design is driven by requirements on resolving power, slit area, spectral coverage and stability. The instrument can operate in seeing-limited or SCAO modes, with options for sky and/or calibration measurements. In SCAO mode, it can use a small Integral Field Unit (IFU) with different spaxel scales. The light from the telescope reaches the Front-End on the Nasmyth platform, which has four insertable modules: two seeing-limited arms, one SCAO arm and one IFU arm. They are connected by fibres or fibre bundles to the Spectrographs in different locations: the Nasmyth Platform and the Coude room. The wavelength splitting depends on the fibre transparency. The subsystems are placed at different distances from the telescope. In Phase-B-one, we performed analyses to define the best trade-off for the budgets and architecture. We extended the spectrographs toward the goal ranges as much as possible. ANDES is complex, but its sophisticated and modular design will enable next-generation astronomy research.

Cross-dispersed echelle spectrographs (CDESs) are a fundamental tool for modern astronomy. Their spectral power relies on the echelle pupil size and collimator focal length. Due to this, seeing-limited ground-based observatories often require large instrument sizes to achieve high spectral resolutions. With the advent of large-aperture telescopes and the unrelenting demand for high resolution, the prevailing trajectory of these instruments leans toward escalating in both size and complexity. However, it is important to explore miniaturization strategies for CDESs, which are particularly valuable for space-based instruments where size, weight, and power are crucial. Miniaturization also offers benefits for ground-based instruments, enabling the use of compact, high-resolution CDES systems in lab setups for academic use and as cost-effective solutions for small to medium telescopes in professional observatories. Although there exist miniaturization strategies and designs such as the double pass with a three-mirror anastigmat, they can be challenging to implement due to their sensitivity to alignment. We present a first approach design of a CDES using a Cassegrain collimator. This approach effectively has a reduction in instrument footprint while achieving high spectral power, when compared with the three-fold design. We also performed a sensitivity analysis for the alignment of this design and showed that at a smaller scale, the design does not offer added complexity when compared with the three-fold design.

BlueMUSE is a blue-optimised, medium spectral resolution, panoramic integral field spectrograph under development for the Very Large Telescope (VLT). With an optimised transmission down to 350 nm, spectral resolution of R similar to 3500 on average across the wavelength range, and a large FoV (1 arcmin(2)), BlueMUSE will open up a new range of galactic and extragalactic science cases facilitated by its specific capabilities. The BlueMUSE consortium includes 9 institutes located in 7 countries and is led by the Centre de Recherche Astrophysique de Lyon (CRAL). The BlueMUSE project development is currently in Phase A, with an expected first light at the VLT in 2031. We introduce here the Top Level Requirements (TLRs) derived from the main science cases, and then present an overview of the BlueMUSE system and its subsystems fulfilling these TLRs. We specifically emphasize the tradeoffs that are made and the key distinctions compared to the MUSE instrument, upon which the system architecture is built.