arXiv subjects

Ignas Snellen

Publications and source records attributed to Ignas Snellen.

At least 19 recordsLinked to original sources

arXiv2026

The Isotopic and Elemental Abundances of Planet-Host Star TRAPPIST-1

Elemental and isotopic abundances are key tracers of planet formation, stellar evolution, and Galactic chemical evolution. Very low-mass stars are particularly interesting in this regard, because unlike more massive or evolved stars their photospheric abundances retain the star's natal composition. Cool dwarf spectra have historically been challenging to use for measurements of chemical abundances because of the blending of molecular and atomic features. However, recent advances in molecular line lists, atmospheric models, fitting techniques and IR spectrographs have enabled the successful measurement of elemental and isotopic ratios in a few dozen very low-mass stars. Here, we present near-infrared high-resolution spectroscopy of TRAPPIST-1 covering the fundamental and overtone bands of carbon monoxide and its prominent isotopologues. From the joint analysis of the $K$-band (CFHT/SPIRou) and $M$-band (Keck/NIRSPEC) spectra, we derive the first stellar C/O ratio and the first carbon and oxygen isotope ratios for this star. We obtain a metallicity of $[\mathrm{M/H}] = 0.00 \pm 0.06$, a C/O ratio of $0.60 \pm 0.02$, $^{12}\mathrm{C}/^{13}\mathrm{C} = 154{}^{+17}_{-16}$, and $^{16}\mathrm{O}/^{18}\mathrm{O} = 490{}^{+78}_{-64}$. TRAPPIST-1 has generally solar-like elemental abundances, with a $^{12}\mathrm{C}/^{13}\mathrm{C}$ ratio that is higher than the solar value and may be modestly elevated relative to some nearby cool dwarfs at similar metallicity. While C/O is most tightly constrained by the $K$-band, the isotopic detections are driven by the $M$-band data.

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arXiv2026

Strong and variable stratospheric CO emission from lava-planet 55 Cnc e observed with NIRCam/JWST

Some rocky planets orbit so close to their host stars that stellar heating melts their surfaces. They offer a rare glimpse of planets in a magma-ocean state, providing an observable analogue to processes that likely shaped the early Earth and other terrestrial planets during their infancy. Recent JWST observations of five eclipses of the prototypical lava planet 55 Cnc e have confirmed earlier hints that it exhibits highly variable thermal emission, with low-resolution spectroscopy pointing to a possible volatile-rich atmosphere likely rich in CO and CO2. Here we report on an analysis of the same JWST datasets but at their native spectral resolution, utilizing cross-correlation techniques. An unambiguously strong ~8 sigma signal from CO in emission is recovered during one out of five epochs, with potential ~3 sigma detections during two others. The strongest observed cross-correlation signal is difficult to reconcile with a hydrostatic atmosphere, requiring a steep and strong thermal inversion at the right pressure level (~1-10 mbar) and a relative abundance of CO2 that is at least 3 orders of magnitude lower which would otherwise mask the CO signal. Self-consistent atmospheric modelling indicates that this is most readily achieved in a hydrogen-rich atmosphere, which produces the steepest inversions and highest CO/CO2 ratios. The pronounced epoch-to-epoch variability suggests that the CO signal does not trace a static atmosphere alone, but may reveal a transient, dynamically active component, potentially linked to variable atmospheric outflow.

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arXiv2026

JWST high-contrast spectroscopy with speckle modelling: Atmospheric retrievals of the T dwarf companion HD 19467 B

High-contrast, medium-resolution spectroscopy with JWST can resolve molecular and isotopic features in cool substellar atmospheres, but for close-in companions the extracted spectra can be biased by wavelength-dependent residual stellar contamination. We assess the impact of residual speckles on atmospheric inference for the T dwarf companion HD 19467 B and compare the results to the field T dwarf 2MASS J0415-0935. We analyse JWST/NIRSpec G395H spectra ($2.87$--$5.2$$\mu$m; $R\sim2700$) and perform Bayesian atmospheric retrievals with petitRADTRANS coupled to nested sampling using ultranest. We use a flexible, parameterised pressure-temperature profile with free, constant-with-altitude molecular abundances. For HD 19467 B we fit the PSF-subtracted spectrum with a linear model that includes the atmospheric model and a set of speckle spectra from the integral field unit. We detect H$_2$O, CH$_4$, CO, CO$_2$, and NH$_3$ in both atmospheres and measure carbon isotopic ratios from CO isotopologues, finding $^{12}$C/$^{13}$C$=154^{+19}_{-17}$ for HD 19467 B and $^{12}$C/$^{13}$C$=85\pm5$ for 2MASS J0415-0935. Speckle contamination primarily affects the low-frequency spectral shape at $3.0$--$3.7$$\mu$m and can affect retrieved abundances if not accounted for. We obtain seemingly constrained posteriors for some additional species (e.g.\ SiO and H$_2$S) in some cases, but treat these as tentative because cross-correlation does not yield significant detections; PH$_3$ is not detected in either target. Joint fitting of the atmospheric spectrum and the speckle contamination enables native-resolution retrievals of the high-contrast companion HD 19467 B with JWST/NIRSpec without continuum subtraction. Over $2.87$--$5.2$$\mu$m, medium-resolution spectroscopy constrains elemental and isotopic composition; both objects exhibit near-solar metallicity and subsolar C/O ratios.

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arXiv2026

Chemistry and Isotope Ratios of Substellar Atmospheres in the $\beta$ Pictoris Young Moving Group and Vicinity

Measuring the chemical and isotopic compositions of gas giants and brown dwarfs provides insights into their formation pathways and birth environments. 2MASS J0249-0557 c is an L2-type planetary mass companion ($\sim 12 M_{\mathrm{Jup}}$) orbiting a pair of brown dwarfs in the $\beta$ Pic young moving group and vicinity. Its mass places it at the intersection of planets and brown dwarfs, making it an interesting target for constraining formation pathways at the planet-brown-dwarf boundary. Using high-resolution spectroscopic data of the planet acquired with CRIRES+ mounted on VLT, we conduct atmospheric retrieval with the radiative transfer code \texttt{petitRADTRANS} and the nested sampling tool PyMultiNest. We retrieve a C/O ratio of $0.57\pm0.01$, a metallicity of [M/H] = $0.18\pm0.05$, and a $^{12}$CO/$^{13}$CO ratio of $95^{+23}_{-17}$. We also retrieve atmospheric compositions for two benchmark brown dwarfs in the $\beta$ Pic YMG, 2MASSI J0443+0002 and SIPS J2000-7523, using CRIRES+ data and find consistent compositions. Together with 2MASS J0249-0557 c's wide separation from its host, its compositional consistency with benchmark brown dwarfs supports gravitational collapse in a star-like manner as its most likely formation mechanism. These results deliver a homogeneous comparison of three substellar members in the $\beta$ Pic YMG and vicinity. Their solar-like abundances provide a baseline for exoplanet members in the same moving group, such as $\beta$ Pic b, 51 Eri b, and AF Lep b, whose host stellar compositions are difficult to measure. Future comparisons of atmospheric compositions among this moving group offer the potential to distinguish between formation mechanisms for its planetary members.

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arXiv2026

The Third Option: Color Phase Curves to Characterize the Atmospheres of Temperate Rocky Exoplanets

Detecting and characterizing the atmospheres of rocky exoplanets has proven to be challenging for JWST. Transit spectroscopy of the TRAPPIST-1 planets has been impacted by the effects of spots and faculae on the host star. Secondary eclipses have detected hot rocks, but evidence for atmospheres has been difficult to obtain. However, there is a third option that we call color phase curves. This method will apply to synchronously rotating non-transiting planets as well as transiting planets. A color phase curve uses photometry at a long-IR wavelength where the planetary thermal emission is strong (e.g., 21 microns) divided by photometry at a shorter wavelength where the star dominates (e.g., 12 microns). We avoid wavelengths having potentially strong molecular absorption (e.g., 15 microns) to minimize degeneracies in the color phase curve, and we aim to detect and characterize the planetary atmosphere via its longitudinal heat transfer. The ratio of two wavelengths observed nearly simultaneously is designed to isolate thermal emission from the planet, discriminate against the star, and largely cancel instrumental systematic effects. Moreover, we show that invoking mass-radius relations, and using self-consistent physical models, will permit the longitudinal heat transfer to be measured independent of the orbital inclination. Radial velocity surveys are detecting many new exoplanets, including temperate rocky worlds with Earth-like masses. Most of those planets will not transit, but color phase curves have the potential to detect and characterize their atmospheres.

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arXiv2025

The next frontier in exoplanet science: Imaging our neighbouring planetary systems

Transmission and eclipse spectroscopy have been invaluable tools for the characterisation of extrasolar planet atmospheres. While they will continue to provide many new insights and discoveries in the decade(s) to come, these methods are running up against sources of stellar noise from stellar surface inhomogeneities and variability. In this white paper we discuss how the next steps in the characterisation of small, temperate rocky planets requires high-contrast imaging, making the planetary systems around our closest neighbouring stars the new frontier in exoplanet science. The Extremely Large Telescopes (ELTs) will be at the forefront of this quest. The Planetary Camera and Spectrograph (PCS) on ESO's ELT and GmagAO-X on the GMT are planned to become operational in the 2035-2040 time-frame, allowing the characterisation of up to dozen(s) of rocky planets around nearby red dwarf stars. We discuss what role there will be still to play for ground-based exoplanet characterisation in the era of the space-borne Habitable Worlds Observatory and LIFE missions.

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arXiv2025

WIde Separation Planets In Time (WISPIT): A Gap-clearing Planet in a Multi-ringed Disk around the Young Solar-type Star WISPIT 2

In the past decades several thousand exoplanet systems have been discovered around evolved, main-sequence stars, revealing a wide diversity in their architectures. To understand how the planet formation process can lead to vastly different outcomes in system architecture we have to study the starting conditions of planet formation within the disks around young stars. In this study we are presenting high resolution direct imaging observations with VLT/SPHERE of the young ($\sim$5 Myr), nearby ($\sim$133 pc), solar-analog designated as WISPIT 2($=$ TYC~5709-354-1). These observations were taken as part of our survey program that explores the formation and orbital evolution of wide-separation gas giants. WISPIT 2 was observed in four independent epochs using polarized light and total intensity observations. They reveal for the first time an extended (380 au) disk in scattered light with a multi-ringed sub-structure. We directly detect a young proto-planet WISPIT 2b, embedded in a disk gap and show that it is co-moving with its host star. Multiple SPHERE epochs demonstrate that it shows orbital motion consistent with Keplerian motion in the observed disk gap. Our $H$ and $K_s$-band photometric data are consistent with thermal emission from a young planet. By comparison with planet evolutionary models, we find a mass of the planet of $4.9^{+0.9}_{-0.6}$ Jupiter masses. This mass is also consistent with the width of the observed disk gap, retrieved from hydrodynamic models. WISPIT 2b is the first unambiguous planet detection in a multi-ringed disk, making the WISPIT 2 system the ideal laboratory to study planet-disk interaction and subsequent evolution.

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arXiv2025

Chemical evolution imprints in the rare isotopes of nearby M dwarfs

Elements heavier than hydrogen and helium, collectively termed metals, were created inside stars and dispersed through space at the final stages of stellar evolution. The relative amounts of different isotopes (variants of the same element with different masses) in stellar atmospheres provide clues about how our galaxy evolved chemically over billions of years. M dwarfs are small, cool, long-lived stars that comprise three-quarters of all stars in our galaxy. Their spectra exhibit rich fingerprints of their composition, making them potential tracers of chemical evolution. We measure rare carbon and oxygen isotopes in 32 nearby M dwarfs spanning a range of metallicities using high-resolution infrared spectroscopy. We find that stars with higher metal content have lower 12C/13C ratios, indicating they formed from material progressively enriched in 13C over time. This pattern is consistent with models where novae eruptions contributed significant amounts of 13C to the interstellar medium over the past few billion years. Our measurements of 16O/18O ratio match theoretical predictions and suggest that metal-rich stars reach 16O/18O ratios significantly lower than the Sun. These results establish M dwarfs as tracers of chemical enrichment throughout cosmic history.

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arXiv2025

WIde Separation Planets In Time (WISPIT): Two directly imaged exoplanets around the Sun-like stellar binary WISPIT 1

Wide separation gas giant planets present a challenge to current planet formation theories, and the detection and characterisation of these systems enables us to constrain their formation pathways. The WIde Separation Planets In Time (WISPIT) survey aims to detect and characterise wide separation planetary-mass companions over a range of ages from <5 to 20 Myr around solar-type host stars at distances of 75-500 (median: 140) parsecs. The WISPIT survey carries out two 5 minute H-band exposures with the VLT/SPHERE instrument and IRDIS camera, separated by at least six months to identify co-moving companions via proper motion analysis. These two H-band observations in combination with a follow-up Ks-band observation were used to determine the colour-magnitude of the co-moving companions and to derive their masses by comparing to AMES-COND and AMES-DUSTY evolutionary tracks. We report the discovery of WISPIT 1b and WISPIT 1c, two gas giant exoplanets that are co-moving with the stellar binary WISPIT 1, which itself consists of a K4 star and M5.5 star in a multi-decadal orbit. The planets are at projected separations of 338 au and 840 au and have masses of 10 Mj and 4 Mj respectively. We identified two common proper motion planetary companions to a (previously unknown) stellar binary with a Sun-like primary. These targets are ideal for follow up characterisation with both ground and space-based telescopes. Monitoring of the orbit with the GRAVITY interferometer will place constraints on their eccentricity, and spectroscopic characterisation will identify the composition and metallicity, providing information on their formation pathways.

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arXiv2025

Exoplanet atmospheres at high spectral resolution

High-resolution spectroscopy (HRS) has grown into one of the main techniques to characterise the atmospheres of extrasolar planets. High spectral resolving power allows for the efficient removal of telluric and host-star contamination. Combined with the large collecting area of ground-based telescopes it enables detailed studies of atmospheric species, temperature structure, atmospheric loss, and global winds and circulation patterns. In this review, the wide range of HRS observation and data-analysis techniques are described and literature results discussed. Key findings include: * The highest irradiated planets show a rich spectrum of atomic and ionic species, just like stars. * Retrieval analyses of Hot Jupiters and directly imaged Super- Jupiters point to Solar metallicities and chemistry, but observed samples are still heterogeneous and incomplete. * There appears to be a clear dichotomy between Hot Jupiters with and without atmospheric inversions, depending on their equilibrium temperature. * Some highly irradiated planets exhibit enormous leading and/or trailing tails of helium gas, providing unique insights into planet evolution and atmospheric escape processes. * Minor isotopes of carbon and oxygen are now being detected in gas giant planets and brown dwarfs with the interesting potential to shed light on formation pathways. A list of potential pitfalls is provided for those new to the field, and synergies with JWST are discussed. HRS has a great future ahead with the advent of the extremely large telescopes, promising to bring temperate rocky exoplanets into view with their increase in HRS detection speed of up to three orders of magnitude.

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arXiv2025

The ESO SupJup Survey V: Exploring Atmospheric Variability and Orbit of the Super-Jupiter AB Pictoris b with CRIRES+

A growing number of directly-imaged companions have been recently characterised, with robust constraints on carbon-to-oxygen ratios and even isotopic ratios. Many companions and isolated targets have also shown spectral variability. In this work we observed the super-Jupiter AB~Pictoris~b across four consecutive nights using VLT/CRIRES+ as part of the ESO SupJup survey, exploring how the constraints on chemical composition and temperature profile change over time using spectral line shape variations between nights. We performed atmospheric retrievals of the high-resolution observations and found broadly consistent results across all four nights, but there were differences for some parameters. We clearly detect H$_2$O, $^{12}$CO and $^{13}$CO in each night, but abundances varied by $\sim2\sigma$, which was correlated to the deep atmosphere temperature profiles. We also found differences in the $^{12}$C$/^{13}$C ratios in each night by up to $\sim3\sigma$, which seemed to be correlated with the cloud deck pressure. Our combined retrieval simultaneously analysing all nights together constrained broadly the average of each night individually, with the C/O$=0.59\pm0.01$, consistent with solar composition, and $^{12}$C$/^{13}$C~$ = 102\pm8$, slightly higher than the ISM and Solar System values. We also find a low projected rotational velocity, suggesting that AB~Pictoris~b is either intrinsically a slow rotator due to its young age or that the spin axis is observed pole-on with a $\sim90^\circ$ misalignment with its orbit inclination. Future observations will be able to further explore the variability and orbit of AB~Pictoris~b as well as for other companions.

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arXiv2024

The $\beta$ Pictoris b Hill sphere transit campaign. Paper II: Searching for the signatures of the $\beta$ Pictoris exoplanets through time delay analysis of the $\delta$ Scuti pulsations

The $\beta$ Pictoris system is the closest known stellar system with directly detected gas giant planets, an edge-on circumstellar disc, and evidence of falling sublimating bodies and transiting exocomets. The inner planet, $\beta$ Pictoris c, has also been indirectly detected with radial velocity (RV) measurements. The star is a known $\delta$ Scuti pulsator, and the long-term stability of these pulsations opens up the possibility of indirectly detecting the gas giant planets through time delays of the pulsations due to a varying light travel time. We search for phase shifts in the $\delta$ Scuti pulsations consistent with the known planets $\beta$ Pictoris b and c and carry out an analysis of the stellar pulsations of $\beta$ Pictoris over a multi-year timescale. We used photometric data collected by the BRITE-Constellation, bRing, ASTEP, and TESS to derive a list of the strongest and most significant $\delta$ Scuti pulsations. We carried out an analysis with the open-source python package maelstrom to study the stability of the pulsation modes of $\beta$ Pictoris in order to determine the long-term trends in the observed pulsations. We did not detect the expected signal for $\beta$ Pictoris b or $\beta$ Pictoris c. The expected time delay is 6 seconds for $\beta$ Pictoris c and 24 seconds for $\beta$ Pictoris b. With simulations, we determined that the photometric noise in all the combined data sets cannot reach the sensitivity needed to detect the expected timing drifts. An analysis of the pulsational modes of $\beta$ Pictoris using maelstrom showed that the modes themselves drift on the timescale of a year, fundamentally limiting our ability to detect exoplanets around $\beta$ Pictoris via pulsation timing.

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arXiv2024

Revealing H$_2$O dissociation in WASP-76~b through combined high- and low-resolution transmission spectroscopy

Numerous chemical constraints have been possible for exoplanetary atmospheres thanks to high-resolution spectroscopy (HRS) from ground-based facilities as well as low-resolution spectroscopy (LRS) from space. These two techniques have complementary strengths, and hence combined HRS and LRS analyses have the potential for more accurate abundance constraints and increased sensitivity to trace species. In this work we retrieve the atmosphere of the ultra-hot Jupiter WASP-76~b, using high-resolution CARMENES/CAHA and low-resolution HST WFC3 and Spitzer observations of the primary eclipse. As such hot planets are expected to have a substantial fraction of H$_2$O dissociated, we conduct retrievals including both H$_2$O and OH. We explore two retrieval models, one with self-consistent treatment of H$_2$O dissociation and another where H$_2$O and OH are vertically-homogeneous. Both models constrain H$_2$O and OH, with H$_2$O primarily detected by LRS and OH through HRS, highlighting the strengths of each technique and demonstrating the need for combined retrievals to fully constrain chemical compositions. We see only a slight preference for the H$_2$O-dissociation model given that the photospheric constraints for both are very similar, indicating $\log(\mathrm{OH/H_2O}) = 0.7^{+0.3}_{-0.3}$ at 1.5~mbar, showing that the majority of the H$_2$O in the photosphere is dissociated. However, the bulk O/H and C/O ratios inferred from the models differs significantly, and highlights the challenge of constraining bulk compositions from photospheric abundances with strong vertical chemical gradients. Further observations with JWST and ground-based facilities may help shed more light on these processes.

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arXiv2023

$\beta$ Pictoris b through the eyes of the upgraded CRIRES+

Context: High-resolution spectrographs fed by adaptive optics (AO) provide a unique opportunity to characterize directly imaged exoplanets. Observations with such instruments allow us to probe the atmospheric composition, spin rotation, and radial velocity of the planet, thereby helping to reveal information on its formation and migration history. The recent upgrade of the Cryogenic High-Resolution Infrared Echelle Spectrograph (CRIRES+) at the VLT makes it a highly suitable instrument for characterizing directly imaged exoplanets. Aims: In this work, we report on observations of $\beta$ Pictoris b with CRIRES+ and use them to constrain the planets atmospheric properties and update the estimation of its spin rotation. Methods: The data were reduced using the open-source \textit{pycrires} package. We subsequently forward-modeled the stellar, planetary, and systematic contribution to the data to detect molecules in the planet's atmosphere. We also used atmospheric retrievals to provide new constraints on its atmosphere. Results: We confidently detected water and carbon monoxide in the atmosphere of $\beta$ Pictoris b and retrieved a slightly sub-solar carbon-to-oxygen ratio, which is in agreement with previous results. The interpretation is hampered by our limited knowledge of the C/O ratio of the host star. We also obtained a much improved constraint on its spin rotation of $19.9 \pm 1.0$ km/s, which gives a rotation period of $8.7 \pm 0.8$ hours, assuming no obliquity. We find that there is a degeneracy between the metallicity and clouds, but this has minimal impact on the retrieved C/O, $v\sin{i}$, and radial velocity. Our results show that CRIRES+ is performing well and stands as a highly useful instrument for characterizing directly imaged planets.

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arXiv2023

JWST measurements of $^{13}$C, $^{18}$O and $^{17}$O in the atmosphere of super-Jupiter VHS 1256 b

Isotope ratios have recently been measured in the atmospheres of directly-imaged and transiting exoplanets from ground-based observations. The arrival of JWST allows us to characterise exoplanetary atmospheres in further detail and opens up wavelengths inaccessible from the ground. In this work we constrain the carbon and oxygen isotopes $^{13}$C, $^{18}$O and $^{17}$O from CO in the atmosphere of the directly-imaged companion VHS 1256 b through retrievals of the $\sim$4.1-5.3 $\mu$m NIRSpec G395H/F290LP observations from the early release science programme (ERS 1386). We detect and constrain $^{13}$C$^{16}$O, $^{12}$C$^{18}$O and $^{12}$C$^{17}$O at 32, 16 and 10$\sigma$ confidence respectively, thanks to the very high signal-to-noise observations. We find the ratio of abundances are more precisely constrained than their absolute values, with $\mathrm{^{12}C/^{13}C=62^{+2}_{-2}}$, in between previous measurements for companions ($\sim$30) and isolated brown dwarfs ($\sim$100). The oxygen isotope ratios are $\mathrm{^{16}O/^{18}O =425^{+33}_{-28}}$ and $\mathrm{^{16}O/^{17}O=1010^{+120}_{-100}}$. All of the ratios are lower than the local inter-stellar medium and Solar System, suggesting that abundances of the more minor isotopes are enhanced compared to the primary. This could be driven by isotope fractionation in protoplanetary disks, which can potentially alter the carbon and oxygen ratios through isotope selective photodissociation, gas/ice partitioning and isotopic exchange reactions. In addition to CO, we constrain $^{1}$H$_2$$^{16}$O and $^{12}$C$^{16}$O$_2$ (the primary isotopologues of both species), but find only upper limits on $^{12}$C$^1$H$_4$ and $^{14}$N$^{1}$H$_3$. This work highlights the power of JWST to constrain isotopes in exoplanet atmospheres, with great promise in determining formation histories in the future.

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arXiv2023

Trade-offs in high-contrast integral field spectroscopy for exoplanet detection and characterisation: Young gas giants in emission

Context: Combining high-contrast imaging with medium- or high-resolution integral field spectroscopy has the potential to boost the detection rate of exoplanets, especially at small angular separations. Furthermore, it immediately provides a spectrum of the planet that can be used to characterise its atmosphere. The achievable spectral resolution, wavelength coverage, and FOV of such an instrument are limited by the number of available detector pixels. Methods: The trade-offs are studied through end-to-end simulations of a typical high-contrast imaging instrument, analytical considerations, and atmospheric retrievals. The results are then validated with archival VLT/SINFONI data of the planet beta Pictoris b. Results: We show that molecular absorption spectra generally have decreasing power towards higher spectral resolution and that molecule mapping is already powerful for moderate resolutions (R>300). When choosing between wavelength coverage and spectral resolution for a given number of spectral bins, it is best to first increase the spectral resolution until R~2,000 and then maximise the bandwidth within an observing band. We find that T-type companions are most easily detected in the J/H band through methane and water features, while L-type companions are best observed in the H/K band through water and CO features. Such an instrument does not need to have a large FOV, as most of the gain in contrast is obtained in the speckle-limited regime close to the star. We show that the same conclusions are valid for the constraints on atmospheric parameters such as the C/O ratio, metallicity, surface gravity, and temperature, while higher spectral resolution (R~10,000) is required to constrain the radial velocity and spin of the planet.

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arXiv2023

Retrieval survey of metals in six ultra-hot Jupiters: Trends in chemistry, rain-out, ionisation and atmospheric dynamics

Ground-based high-resolution spectroscopy (HRS) has detected numerous chemical species and atmospheric dynamics in exoplanets, most notably ultra-hot Jupiters (UHJs). However, quantitative estimates on abundances have been challenging but are essential for accurate comparative characterisation and to determine formation scenarios. In this work we retrieve the atmospheres of six UHJs (WASP-76~b, MASCARA-4~b, MASCARA-2~b, WASP-121~b, HAT-P-70~b and WASP-189~b) with ESPRESSO and HARPS-N/HARPS observations, exploring trends in eleven neutral species and dynamics. While Fe abundances agree well with stellar values, Mg, Ni, Cr, Mn and V show more variation, highlighting the difficulty in using a single species as a proxy for metallicity. We find that Ca, Na, Ti and TiO are under-abundant, potentially due to ionisation and/or night-side rain-out. Our retrievals also show that relative abundances between species are more robust, consistent with previous works. We perform spatially- and phase-resolved retrievals for WASP-76~b and WASP-121~b given their high signal-to-noise observations, and find the chemical abundances in each of the terminator regions are broadly consistent. We additionally constrain dynamics for our sample through Doppler shifts and broadening of the planetary signals during the primary eclipse, with median blue shifts between $\sim$0.9-9.0~km/s due to day-night winds. Furthermore, we constrain spectroscopic masses for MASCARA-2~b and HAT-P-70~b consistent with their known upper limits, but we note that these may be biased due to degeneracies. This work highlights the importance of future HRS studies to further probe differences and trends between exoplanets.

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arXiv2023

The beta Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR

[abridged] We analyzed mid-infrared high-contrast coronagraphic images of the beta Pictoris system, taking advantage of the NEAR experiment using the VLT/VISIR instrument. The goal of our analysis is to investigate both the detection of the planet beta Pictoris b and of the disk features at mid-IR wavelengths. In addition, by combining several epochs of observation, we expect to constrain the position of the known clumps and improve our knowledge on the dynamics of the disk. To evaluate the planet b flux contribution, we extracted the photometry and compared it to the flux published in the literature. In addition, we used previous data from T-ReCS and VISIR, to study the evolution of the position of the southwest clump that was initially observed in the planetary disk back in 2003. While we did not detect the planet b, we were able to put constraints on the presence of circumplanetary material, ruling out the equivalent of a Saturn-like planetary ring around the planet. The disk presents several noticeable structures, including the known southwest clump. Using a 16-year baseline, sampled with five epochs of observations, we were able to examine the evolution of the clump: the clump orbits in a Keplerian motion with an sma of 56.1+-0.4 au. In addition to the known clump, the images clearly show the presence of a second clump on the northeast side of the disk and fainter and closer structures that are yet to be confirmed. We found correlations between the CO clumps detected with ALMA and the mid-IR images. If the circumplanetary material were located at the Roche radius, the maximum amount of dust determined from the flux upper limit around beta Pictoris b would correspond to the mass of an asteroid of 5 km in diameter. Finally, the Keplerian motion of the southwestern clump is possibly indicative of a yet-to-be-detected planet or signals the presence of a vortex.

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