arXiv subjects

C. Lovis

Publications and source records attributed to C. Lovis.

At least 19 recordsLinked to original sources

arXiv2026

Resolving protoplanetary H-alpha emission with the high-resolution spectrograph RISTRETTO

Thousands of exoplanets have been discovered to date, but only a handful of them are young planets in the latter stages of their formation. H-alpha emission is a strong tracer of this process, but it is difficult to isolate the planetary H-alpha signal from the stellar signal due to the small angular separation. RISTRETTO is a high-resolution (R~140,000) integral-field unit spectrograph with an attached coronagraph and extreme adaptive system that is currently under construction. Used in tandem with the VLT, its resolving power and seven-spaxel layout is designed to characterise the atmospheres of exoplanets in reflected light. It can also be leveraged to obtain spatially and spectrally resolved observations of planetary H-alpha emission lines. Using a combination of synthetic and real observations, we determined the detection limits for theoretical observations of protoplanets with on-sky separations of 37-600 mas (the equivalent of 4-70 AU at 113 pc). We used theoretical BT-Settl photospheric spectra, observed HARPS spectra of PDS70, and a model for the line emission at the planetary accretion shock to estimate the planetary H-alpha signal. Models with the PyEchelle simulator show that the H-alpha emission from theoretical objects similar to the four known protoplanet candidates (PDS70b, PDS70c, WISPIT2b, and 2MJ1612b) can be spectrally resolved with VLT/RISTRETTO down to a line flux between $F\sim(1.4-2.7)\times10^{-16} erg \;s^{-1} cm^{-2}$ with a 1 hour exposure. We show that the planetary H-alpha line can be spatially resolved from that of its stellar host and that the shape of the line can be used to constrain the pre-shock density (n0) and velocity (v0), thereby enabling new constraints on the accretion rate and flow geometry. This study and the instrument act as a pathfinder for the next generation of high-resolution spectrographs such as ELT/PCS and ELT/ANDES.

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arXiv2026

The small transiting planet population revealed by ESPRESSO with extreme precision radial velocities

Small planets are extremely common in the Galaxy, including planets with masses and radii between those of Earth and Neptune. Characterizing these planets' masses requires ultra-precise radial velocities. The ESPRESSO spectrograph was designed and built for this purpose. We present an overview of the ESPRESSO Guaranteed Time Observations transit follow-up sub-program, aimed at confirming and characterizing small transiting planet candidates from the K2 and TESS space missions. We analyse the global stellar and planetary properties of the sample of 65 planets in 30 systems characterized by this sub-program. This includes six systems presented in this paper, for which we either obtain only upper mass limits, or provide updates to previously published parameters. We also place this sample in the context of the overall population of precisely characterized small planets. Separating the population into insolation regimes, we find a tentative mass threshold at $\simeq6\,M_\oplus}$ for the rocky to volatile-rich composition transition in the medium-insolation regime, and a population of likely stripped massive rocky planets in the high-insolation regime. We likewise find a correlation between planet mass and stellar metallicity, with more massive planets being hosted by more metal-rich stars. We also explore the radius valley, finding that planets below the gap have a tighter mass distribution. We compare planet masses with typical protoplanetary disk masses and draw tentative conclusions about likely formation conditions. Finally, we discuss the impact of our observing strategy on our results. The ESPRESSO transit follow-up sub-program has been highly productive, characterizing a diverse population of small planets that allows us to identify population-level features. Likewise, the lessons learned from this sub-program will be valuable for PLATO follow-up planning.

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arXiv2025

A Decade of Solar High-Fidelity Spectroscopy and Precise Radial Velocities from HARPS-N

We recently released 10 years of HARPS-N solar telescope and the goal of this manuscript is to present the different optimisations made to the data reduction, to describe data curation, and to perform some analyses that demonstrate the extreme RV precision of those data. By analysing all the HARPS-N wavelength solutions over 13 years, we bring to light instrumental systematics at the 1 m/s level. After correction, we demonstrate a peak-to-peak precision on the HARPS-N wavelength solution better than 0.75 m/s over 13 years. We then carefully curate the decade of HARPS-N re-reduced solar observations by rejecting 30% of the data affected either by clouds, bad atmospheric conditions or well-understood instrumental systematics. Finally, we correct the curated data for spurious sub-m/s RV effects caused by erroneous instrumental drift measurements and by changes in the spectral blaze function over time. After curation and correction, a total of 109,466 HARPS-N solar spectra and respective RVs over a decade are available. The median photon-noise precision of the RV data is 0.28 m/s and, on daily timescales, the median RV rms is 0.49 m/s, similar to the level imposed by stellar granulation signals. On 10-year timescales, the large RV rms of 2.95 m/s results from the RV signature of the Sun's magnetic cycle. When modelling this long-term effect using the Magnesium II activity index, we demonstrate a long-term RV precision of 0.41 m/s. We also analysed contemporaneous HARPS-N and NEID solar RVs and found the data from both instruments to be of similar quality and precision, with an overall RV differece rms of 0.79 m/s. This decade of high-cadence HARPS-N solar observations with short- and long-term precision below 1 m/s represents a crucial dataset to further understand stellar activity signals in solar-type stars , and to advance other science cases requiring such an extreme precision.

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arXiv2025

TOI-283 b: A transiting mini-Neptune in a 17.6-day orbit discovered with TESS and ESPRESSO

Super-Earths and mini-Neptunes are missing from our Solar System, yet they appear to be the most abundant planetary types in our Galaxy. A detailed characterization of key planets within this population is important for understanding the formation mechanisms of rocky and gas giant planets and the diversity of planetary interior structures. In 2019, NASA's TESS satellite found a transiting planet candidate in a 17.6-day orbit around the star TOI-283. We started radial velocity (RV) follow-up observations with ESPRESSO to obtain a mass measurement. Mass and radius are measurements critical for planetary classification and internal composition modeling. We used ESPRESSO spectra to derive the stellar parameters of the planet candidate host star TOI-283. We then performed a joint analysis of the photometric and RV data of this star, using Gaussian processes to model the systematic noise present in both datasets. We find that the host is a bright K-type star ($d = 82.4$ pc, $\mathrm{T}_\mathrm{eff} = 5213 \pm 70$ K, $V = 10.4$ mag) with a mass and radius of $\mathrm{M}_\star = 0.80 \pm 0.01\; \mathrm{M}_\odot$ and $\mathrm{R}_\star = 0.85 \pm 0.03\; \mathrm{R}_\odot$. The planet has an orbital period of $P = 17.617$ days, a size of $\mathrm{R}_\mathrm{p} = 2.34 \pm 0.09\; \mathrm{R}_\oplus$, and a mass of $\mathrm{M}_\mathrm{p} = 6.54 \pm 2.04\; \mathrm{M}_\oplus$. With an equilibrium temperature of $\sim$600 K and a bulk density of $\rho_\mathrm{p} = 2.81 \pm 0.93$ g cm$^{-3}$, this planet is positioned in the mass-radius diagram where planetary models predict H$_2$O- and H/He-rich envelopes. The ESPRESSO RV data also reveal a long-term trend that is probably related to the star's activity cycle. Further RV observations are required to confirm whether this signal originates from stellar activity or another planetary body in the system.

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arXiv2025

Architecture of planetary systems with and without outer giant planets I. Inner planet detections around HD 23079, HD 196067, and HD 86226

Understanding the link between outer giant planets (OGPs) and inner light planets (ILPs) is key to understanding planetary system formation and architecture. The correlation between these two populations of planets is debated both theoretically -- different formation models predict either a correlation or an anticorrelation -- and observationally. Several recent attempts to constrain this correlation have yielded contradictory results, due to small-number statistics and heterogeneous samples. We present an ongoing long-term observational effort with CORALIE, HARPS, and ESPRESSO to probe the ILP occurrence in systems with and without OGP. In this first article of a series, we discuss how, from the design to the observations, we ensured the homogeneity of the samples, both in terms of stellar properties and observing strategy. We also present the first three detections of ILPs in our OGP host sample. We find a 8.3 mE planet at 5.75 d around HD 23079, a 10.4 mE planet at 4.6 d around HD 196067, and we confirm the 7.5 mE planet at 3.98 d around HD 86226. While a rigorous statistical analysis of our samples will be performed in subsequent studies, the relatively low number of detections in our sample seems to contradict previous studies that found a strong OGP-ILP correlation.

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arXiv2025

ATREIDES I. Embarking on a trek across the exo-Neptunian landscape with the TOI-421 system

The distribution of close-in exoplanets is shaped by the interplay between atmospheric and dynamical processes. The Neptunian Desert, Ridge, and Savanna illustrate the sensitivity of these worlds to such processes, making them ideal to disentangle their roles. Determining how many Neptunes were brought close-in by early disk-driven migration (DDM; maintaining primordial spin-orbit alignment) or late high-eccentricity migration (HEM; generating large misalignments) is essential to understand how much atmosphere they lost. We propose a unified view of the Neptunian landscape to guide its exploration, speculating that the Ridge is a hot spot for evolutionary processes. Low-density Neptunes would mainly undergo DDM, getting fully eroded at shorter periods than the Ridge, while denser Neptunes would be brought to the Ridge and Desert by HEM. We embark on this exploration via ATREIDES, which relies on spectroscopy and photometry of 60 close-in Neptunes, their reduction with robust pipelines, and their interpretation through internal structure, atmospheric, and evolutionary models. We carried out a systematic RM census with VLT/ESPRESSO to measure the distribution of 3D spin-orbit angles, correlate its shape with system properties and thus relate the fraction of aligned-misaligned systems to DDM, HEM, and atmospheric erosion. Our first target, TOI-421c, lies in the Savanna with a neighboring sub-Neptune TOI-421b. We measured their 3D spin-orbit angles (Psib = 57+11-15 deg; Psic = 44.9+4.4-4.1 deg). Together with the eccentricity and possibly large mutual inclination of their orbits, this hints at a chaotic dynamical origin that could result from DDM followed by HEM. ATREIDES will provide the community with a wealth of constraints for formation and evolution models. We welcome collaborations that will contribute to pushing our understanding of the Neptunian landscape forward.

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arXiv2025

TOI-2322: two transiting rocky planets close to the stellar rotation period and its first harmonic

Context. Active regions on the stellar surface can induce quasi-periodic radial velocity (RV) variations that can mimic planets and mask true planetary signals. These spurious signals can be problematic for RV surveys such as those carried out by the ESPRESSO consortium. Aims. Using ESPRESSO and HARPS RVs and activity indicators, we aim to confirm and characterize two candidate transiting planets from TESS orbiting a K4 star with strong activity signals. Methods. From the ESPRESSO FWHM, TESS photometry, and ASAS-SN photometry, we measure a stellar rotation period of 21.28 $\pm$ 0.08 d. We jointly model the TESS photometry, ESPRESSO and HARPS RVs, and activity indicators, applying a multivariate Gaussian Process (GP) framework to the spectroscopic data. Results. We are able to disentangle the planetary and activity components, finding that TOI-2322 b has a $11.307170^{+0.000085}_{-0.000079}$ d period, close to the first harmonic of the rotation period, a $\leq 2.03 M_\oplus$ mass upper limit and a $0.994^{+0.057}_{-0.059}$ $\mathrm{R_\oplus}$ radius. TOI-2322 c orbits close to the stellar rotation period, with a $20.225528^{+0.000039}_{-0.000044}$ d period; it has a $18.10^{+4.34}_{-5.36}$ $\mathrm{M_\oplus}$ mass and a $1.874^{+0.066}_{-0.057}$ $\mathrm{R_\oplus}$ radius. Conclusions. The multivariate GP framework is crucial to separating the stellar and planetary signals, significantly outperforming a one-dimensional GP. Likewise, the transit data is fundamental to constraining the periods and epochs, enabling the retrieval of the planetary signals in the RVs. The internal structure of TOI-2322 c is very similar to that of Earth, making it one of the most massive planets with an Earth-like composition known.

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arXiv2025

A comprehensive study on radial velocity signals using ESPRESSO: Pushing precision to the 10 cm/s level

We analyse ESPRESSO data for the stars HD10700, HD20794, HD102365, and HD304636 acquired via its Guaranteed Time Observations (GTO) programme. We characterise the stars' radial velocity (RV) signals down to a precision of 10 cm/s on timescales ranging from minutes to planetary periods falling within the host's habitable zone (HZ). We study the RV signature of pulsation, granulation, and stellar activity, inferring the potential presence of planets around these stars. Thus, we outline the population of planets that while undetectable remain compatible with the available data. A simple model of stellar pulsations successfully reproduced the intra-night RV scatter of HD10700 down to a few cm/s. For HD102365 and HD20794, an additional source of scatter at the level of several 10 cm/s remains necessary to explain the data. A kima analysis was used to evaluate the number of planets supported by the nightly averaged time series of each of HD10700, HD102365, and HD304636, under the assumption that a quasi-periodic Gaussian process (GP) regression is able to model the activity signal. While a frequency analysis of HD10700 RVs is able to identify a periodic signal at 20d, when it is modelled along with the activity signal the signal is formally non-significant. ESPRESSO data on their own do not provide conclusive evidence for the existence of planets around these three stars. ESPRESSO is shown to reach an on-sky RV precision of better than 10 cm/s on short timescales (<1h) and of 40 cm/s over 3.5 yr. A subdivision of the datasets showcases a precision reaching 20-30 cm/s over one year. These results impose stringent constraints on the impact of granulation mechanisms on RV. In spite of no detections, our analysis of HD10700 RVs demonstrates a sensitivity to planets with a mass of 1.7M$_{\oplus}$ for periods of up to 100 d, and a mass of 2-5M$_{\oplus}$ for the star's HZ. (abridged)

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arXiv2025

The ESPRESSO transmission spectrum of HD$\,$189733$\,$b : Extracting the planetary sodium and lithium signatures amid stellar contamination

While transmission spectroscopy has allowed us to detect many atomic and molecular species in exoplanet atmospheres, the improvement in resolution and signal-to-noise ratio enabled us to become sensitive to planet-occulted line distortions (POLDs) in the spectrum that are induced by center-to-limb variations and the Rossiter-McLaughlin effect. POLDs can bias the interpretation of the transmission spectrum, and it is difficult to correct for them with stellar models. We analyzed two ESPRESSO transits (R $\sim$ 140$\,$000) of the archetypal hot Jupiter HD$\,$189733$\,$b. The transmission spectrum of this aligned system is heavily affected by POLDs, stellar activity, and instrumental effects. It is therefore a challenging study case of how to account for these effects when the planetary signal is retrieved from chemical species through transmission spectroscopy. We confirm the previous detections of the sodium doublet signature in the upper atmosphere of HD$\,$189733$\,$b. When we accounted for POLDs and isolated the planetary signal from uncorrected stellar residuals, we found a shallower (0.432 $\pm$ 0.027 %) and more strongly blueshifted (-7.97 $\pm$ 0.28 km/s) signal. We attempted to reinterpret the other high-resolution sodium studies of this system in light of our results. We suggest that the POLDs and stellar activity are insufficiently corrected for in all analyses, including ours. We also detected a planetary lithium signature of 0.102 $\pm$ 0.016 % (6.4$\sigma$) at a blueshift of -2.4 $\pm$ 1.8 km/s.

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arXiv2025

CORALIE radial-velocity search for companions around evolved stars (CASCADES) IV: New planetary systems around HD 87816, HD 94890, and HD 102888 and an update on HD 121056

With around 200 detections of exoplanets around giant stars to date, our knowledge of the population of exoplanets orbiting evolved hosts more massive than the Sun remains limited. The CORALIE radial-velocity search for companions around evolved stars (CASCADES) was launched in 2006 with the aim of improving our understanding of the demographics of exoplanets around intermediate-mass stars, by studying them once they have evolved off the main sequence. We intend to refine the current sample of known exoplanets orbiting intermediate-mass (1.5 - 5 M$_\odot$) giant stars of spectral types G and early K. We searched for exoplanets orbiting the four stars HD 87816, HD 94890, HD 102888, and HD 121056. We used data obtained with the CORALIE spectrograph, mounted on the Leonhard Euler Swiss telescope located at La Silla Observatory in Chile. We gathered high-precision radial-velocity measurements over more than ten years for each of the aforementioned targets. We started by performing a search for periodic signals in the radial-velocity time series of the four targets by using periodograms. Following this, we fit for a Keplerian model using the significant peak with the highest power of the periodogram as the starting guess for the period. We then subtracted this model and repeated the procedure iteratively on the residuals until no significant peaks were found. Finally, to explore the posterior distribution of our models, the final solution was determined using a Markov chain Monte Carlo approach. We report the discovery of five new massive planets around HD 87816, HD 94890, and HD 102888 as well as the presence of a distant, potentially substellar, companion around HD 102888. We confirm the presence of a previously announced exoplanet orbiting the HD 121056 multi-object system with a period of 89 days and propose an update to the period of the outer companion.

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arXiv2025

Two neighbours of the ultra-short-period Earth-sized planet K2-157 b in the warm Neptunian savanna

The formation and evolution of ultra-short-period (USP) planets is poorly understood. However, it is widely thought that these planets migrated inwards through interactions with outer neighbours. We aim to confirm and characterise the USP Earth-sized planet K2-157 b ($P_{\rm orb}$ = 8.8 h). To do so, we measured 49 radial velocities (RVs) with the ESPRESSO spectrograph and derived the properties of the system through an RV and transit model. We detect two additional super-Neptune-mass planets within the warm Neptunian savanna, K2-157 c ($P_{\rm orb, c}$ = $25.942^{+0.045}_{-0.044}$ d, $M_{\rm p, c} \, \textrm{sin} \, i$ = $30.8 \pm 1.9$ $\rm M_{\oplus}$), and K2-157 d ($P_{\rm orb, d}$ = $66.50^{+0.71}_{-0.59}$ d, $M_{\rm p,d} \, \textrm{sin}\,i$ = $23.3 \pm 2.5$ $\rm M_{\oplus}$). The mass of K2-157 b, $M_{\rm p,b}$ = $1.14^{+0.41}_{-0.42}$ $\rm M_{\oplus}$ ($<$ 2.4 $\rm M_{\oplus}$ at 3$\sigma$), together with its radius, $R_{\rm p}$ = 0.935 $\pm$ 0.090 $\rm R_{\oplus}$, make the planet compatible with a rocky composition. K2 data discard non-grazing transit configurations for K2-157 c ($i_{\rm c}$ $<$ 88.4$^{\circ}$ at 3$\sigma$), and ESPRESSO data constrain the eccentricities of K2-157 c and K2-157 d to $e_{\rm c}$ $<$ 0.2 and $e_{\rm d}$ $<$ 0.5 at 3$\sigma$. At a population level, we find that the trend that the closest USP planets tend to orbit late-type stars does not hold when scaling the orbital separation to the Roche limit, which suggests that the orbital distribution of the closest planets across spectral types is determined by tidal disruption. The orbital architecture of K2-157 is unusual, with only one similar case reported to date: 55 Cnc. The USP planets of these systems, being accompanied by massive, long-period, relatively spaced, and possibly misaligned neighbours, could have migrated inwards through eccentricity-based mechanisms triggered by secular interactions.

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arXiv2025

The Phase Induced Amplitude Apodizer and Nuller -- High transmission, high dispersion coronagraphy at 2{\lambda}/D

Context. Proxima Cen b is the prime target for the search of life around a nearby exoplanet by characterizing its atmosphere in reflected light. Due to the very high star/companion contrast (<1E-6), High Dispersion Coronagraphy is the most promising technique to perform such a characterization. Aims. With a maximum separation of 37 mas, Proxima b can be observed with a VLT in the visible. It requires a coronagraph providing high contrast (< 1E-4 ) very close from the star (< 2 {\lambda}/D ) over a broad spectral range (~30%), with a high transmission of the companion (> 50%). We look for an optimal solution that takes benefit of the properties of single-mode fibers. Methods. We introduce the Phase Induced Amplitude Apodizer and Nuller (PIAAN), a coronagraphic integral field unit, designed to feed a diffraction limited spectrograph. It uses a pupil remapping optics with moderate apodization, combined to a single mode fiber integral field unit. It exploits the properties of single mode fibers to null the star light without reducing the companion coupling. The study focuses on a proper tolerance analysis and proposes a wavefront optimization strategy. A prototype is built to demonstrate its performance. Results. We show that the PIAAN can theoretically provide contrasts of 7E-7 and a transmission of 72% at 2 {\lambda}/D over a bandwidth of 30%. A prototype is built and characterized and the proposed wavefront control strategy is also demonstrated in the lab. We reach contrast levels of 3E-5 over the full bandwidth, as expected from the tolerance analysis. Conclusions. We demonstrated the potential of the new PIAAN coronagraph, from simulations to prototype. Its performance will eventually be limited by the XAO capabilities. It is the main coronagraph candidate for the RISTRETTO instrument to observe Proxima Cen b on the VLT and its first technology milestone.

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arXiv2025

TOI-512: Super-Earth transiting a K-type star discovered by TESS and ESPRESSO

One of the goals of the ESPRESSO guaranteed time observations (GTOs) at the ESO 8.2m telescope is to follow up on candidate planets from transit surveys such as the TESS mission. High-precision radial velocities are required to characterize small exoplanets. Aims. We intend to confirm the existence of a transiting super-Earth around the bright (V=9.74) K0-type star TOI-512 (TIC 119292328) and provide a characterization. Combining photometric data from TESS and 37 high-resolution spectroscopic observations from ESPRESSO in a joint Markov chain Monte Carlo analysis, we determined the planetary parameters of TOI-512b and characterized its internal structure. We find that TOI-512b is a super-Earth, with a radius of $1.54 \pm 0.10$ R$_\oplus$ and mass of $3.57_{-0.55}^{+0.53}$~M$_\oplus$, on a $7.19_{-6.1\cdot 10^{-5}}^{+7\cdot 10^{-5}}$ day orbit. This corresponds to a bulk density of $5.62_{-1.28}^{+1.59}$ g cm$^{-3}$. Our interior structure analysis presents a small inner core representing $0.13^{+0.13}_{-0.11}$ of the solid mass fraction for the planet, surrounded by a mantle with a mass fraction of $0.69^{+0.20}_{-0.22}$, and an upper limit of the water layer of $0.16$. The gas mass below $10^{-8.93}$ indicates a very small amount of gas on the planet. We find no evidence of the second candidate found by the TESS pipeline, TOI-512.02, neither in TESS photometry, nor in the ESPRESSO radial velocities. The low stellar activity makes it an interesting transmission spectroscopy candidate for future-generation instruments.

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arXiv2025

Radial velocity homogeneous analysis of M dwarfs observed with HARPS I. Exoplanet detection and candidates

The census of planets around M dwarfs in the solar neighbourhood meets two challenges: detecting the best targets for the future characterisation of planets with ELTs, and studying the statistics of planet occurrence that are crucial to formation scenarios. The radial velocity (RV) method remains the most appropriate for such a census as it is sensitive to the widest ranges of masses and periods. HARPS, mounted on the 3.6 m telescope at La Silla Observatory (ESO, Chile), has been obtaining velocity measurements since 2003, and can therefore be used to analyse a very large and homogeneous dataset. We performed a homogeneous analysis of the RV time series of 200 M dwarfs observed with HARPS from 2003 to 2019 (gathering more than 15000 spectra), with the aim of understanding detectable signals such as stellar and planetary companions and activity signals. The RVs were computed with a template matching method before carrying out the time series analysis. First, we focused on the systematic analysis of the presence of a dominant long-term pattern in the RV time series (linear or quadratic trend and sine function). Then, we analysed higher-frequency perdiodic signals using periodograms of the residual time series and Keplerian function fitting. We found long-term variability in 57 RV time series (28.5%). This led to the revision of the parameters of the massive planet (GJ9482 b), as well as the detection of four substellar and stellar companions (around GJ3307, GJ4001, GJ4254, andGJ9588), for which we characterised inclinations and masses by combining RV and astrometry. The periodic analysis allowed us to recover 97% of the planetary systems already published in this sample, but also to propose three new planetary candidates orbiting GJ300 (7.3Me), GJ654(5Me), and GJ739 (39Me), which require additional measurements before they can be confirmed.

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arXiv2025

Radial velocity homogeneous analysis of M dwarfs observed with HARPS. II. Detection limits and planetary occurrence statistics

We re-determine planetary occurrences around M dwarfs using 20 years of observations from HARPS on 197 targets. The first aim of this study is to propose more precise occurrence rates using the large volume of the sample but also variations to previous calculations, particularly by considering multiplicity, which is now an integral part of planetary occurrence calculations. The second aim is to exploit the extreme longevity of HARPS to determine occurrence rates in the unexplored domain of very long periods. This work relies entirely on the 197 radial velocity time series obtained and analysed in our previous study. By considering they are cleaned of any detectable signal, we convert them into detection limits. We use these 197 limits to produce a detectability map and combine it with confirmed planet detections to establish our occurrence rates. Finally, we also convert the detection limits from orbital period to insolation in order to construct an occurrence statistics for the temperate zone. We find a strong prevalence of low-mass planets around M dwarfs, with an occurrence rate of 120% for planets with a mass between 0.75 and 3 Me. In addition, we compute an occurrence rate of 45.3% +20-16% for temperate zone planets around M dwarfs. We obtain an occurrence rate of a few percent for giant planets with wide separations. In our sample these giant planets with wide separations are only detected around the most massive M dwarfs.

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arXiv2025

Revisiting the multi-planetary system of the nearby star HD 20794: Confirmation of a low-mass planet in the habitable zone of a nearby G-dwarf

Close-by Earth analogs and super-Earths are of primary importance because they will be preferential targets for the next generation of direct imaging instruments. Bright and close-by G-to-M type stars are preferential targets in radial velocity surveys to find Earth analogs. We present an analysis of the RV data of the star HD 20794, a target whose planetary system has been extensively debated in the literature. The broad time span of the observations makes it possible to find planets with signal semi-amplitudes below 1 m/s in the habitable zone. We monitored the system with ESPRESSO. We joined ESPRESSO data with the HARPS data, including archival data and new measurements from a recent program. We applied the post-processing pipeline YARARA to HARPS data to correct systematics, improve the quality of RV measurements, and mitigate the impact of stellar activity. Results. We confirm the presence of three planets, with periods of 18.3142 +/- 0.0022 d, 89.68 +/- 0.10 d, and 647.6 +/- 2.6 d, along with masses of 2.15 +/- 0.17 MEarth, 2.98 +/- 0.29 MEarth, and 5.82 +/- 0.57 MEarth respectively. For the outer planet, we find an eccentricity of 0.45 +/- 0.10, whereas the inner planets are compatible with circular orbits. The latter is likely to be a rocky planet in the habitable zone of HD 20794. From the analysis of activity indicators, we find evidence of a magnetic cycle with a period around 3000 d, along with evidence pointing to a rotation period around 39 d. We have determined the presence of a system of three planets orbiting the solar-type star HD 20794. This star is bright (V=4.34 mag) and close (d = 6.04 pc), and HD 20794 d resides in the stellar habitable zone, making this system a high-priority target for future atmospheric characterization with direct imaging facilities.

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arXiv2024

The RISTRETTO simulator: Exoplanet reflected spectra

The upcoming Ristretto spectrograph is dedicated to the detection and analysis of exoplanetary atmospheres, with a primary focus on the temperate rocky world Proxima b. This scientific endeavor relies on the interplay of a high-contrast adaptive optics (AO) system and a high-resolution echelle spectrograph. In this work, I present a comprehensive simulation of Ristretto's output spectra, employing the Python package Pyechelle. Starting from realistic spectra of both exoplanets and their host stars, I generate synthetic 2D spectra to closely resemble those that will be produced by Ristretto itself. These synthetic spectra are subsequently treated as authentic data and therefore analyzed. These simulations facilitate not only the investigation of potential exoplanetary atmospheres but also an in-depth assessment of the inherent capabilities and limitations of the Ristretto spectrograph.

astro-ph.IM↗

arXiv2024

RISTRETTO: the PIAA Nuller in the prototyping phase

The objective of the coronagraphic IFU of RISTRETTO is to enable High Dispersion Coronagraphy of planets at a distance of 2$\lambda$/D from their star, without compromising on transmission. The new idea of a PIAA Nuller (PIAAN) allows contrast down to 10$^{-5}$ over large bandwidth $\ge$ 25%, with high transmission $\ge$ 70% at the distance of 2$\lambda$/D. While RISTRETTO will be installed on a VLT, this development is of tremendous importance for fully exploiting future ELTs XAO. We will discuss our PIAAN prototyping activities. This covers 1) the characterisation of our 2nd set of IFU bundles, with 3D-printed MLAs; 2) the characterisation of our first PIAA optics; 3) the integration of a high contrast bench, planned for prototyping of Front-End control strategies; 4) the characterisation of the PIAAN system on the bench.

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