arXiv subjects

R. Landman

Publications and source records attributed to R. Landman.

16 recordsLinked to original sources

arXiv2026

Vector Apodizing Phase Plates for the ELT: From prototype to final optics for METIS and MICADO

The first generation of instruments for the upcoming Extremely Large Telescope (ELT) will allow for the direct imaging of exoplanets that were previously below the sensitivity or resolution limits of existing facilities through various different High Contrast Imaging capabilities. Both METIS and MICADO will feature one or more Vector Apodizing Phase Plates (vAPP), a type of pupil-plane coronagraph based on liquid crystal technology that allows for broadband phase modification to create zones of high contrast around an observed point source. The METIS vAPPs will operate at L- and M-band wavelengths between 3.1 and 5.1 $\mu$m, while the MICADO vAPP is optimized for shorter wavelengths in the J, H and Ks bands between 1.15 and 2.32 $\mu$m. In this work, we will provide a brief introduction to this type of coronagraph, followed by a discussion of the commonalities and differences between the METIS and MICADO vAPP designs. In the last year, the final optics have been in production. During preparations for the manufacturing and also during the production phase,various challenges were encountered related to coating inclusions, uniformity of the optically active layers and adhesion between the substrates. Through simulations and empirical findings, we argue that the effects of these imperfections on the on the final optical performance are limited. We will present the expected contrast curves, discuss the current status and reflect on the implications for on-sky observations with METIS and MICADO.

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arXiv2026

The ESO SupJup Survey XI. Atmospheric properties of six isolated M- and L-type dwarfs with CRIRES+

The distinct formation pathways of brown dwarfs and giant exoplanets may be encoded in their atmospheric composition. We present atmospheric retrievals for six isolated brown dwarfs of spectral types M7-L2.5 from the ESO SupJup Survey, aiming to constrain their thermal structures, chemical compositions, and isotope ratios. We analyse CRIRES+ K-band spectra, coupling the radiative transfer code petitRADTRANS with the nested sampling algorithm PyMultiNest under both free and equilibrium chemistry frameworks. The L0 dwarf 2MASS J09532126-1014205 emerges as one of the fastest-rotating ultracool dwarfs known, with $v\sin i = 85.9\pm0.5$ km s$^{-1}$. H$_2$O is strongly detected in all six targets and $^{12}$CO in five, with a marginal $^{12}$CO detection in the ultra-fast L0 rotator consistent with severe rotational broadening. $^{13}$CO is significantly detected in DENIS J060852.8-275358 and tentatively in three further targets. Retrieved compositions are consistent with isolated brown dwarfs: near-solar C/O ratios ($0.51$-$0.63$), predominantly near-solar metallicities, and $^{12}$C/$^{13}$C ratios of ~91-155, at or above the local ISM value, with constraints for the two fastest rotators resting on the spectral fit but not corroborated by a $^{13}$CO cross-correlation peak. The M7 dwarf 2MASS J04341527+2250309 shows discrepant gravity and metallicity values between chemistry frameworks. Apparent H$_2^{18}$O constraints for two targets are found to be spurious, and their H$_2^{(16)}$O/H$_2^{18}$O ratios are presented as lower limits, demonstrating the importance of cross-correlation validation for minor species detections. The near-solar C/O ratios and metallicities, with $^{12}$C/$^{13}$C ratios at or above the ISM value, support a molecular cloud fragmentation origin for the sample. The agreement of $^{12}$C/$^{13}$C between chemistry frameworks supports the robustness of these ratios.

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arXiv2026

The carbon isotope ratio of \beta\ Pic b with high-resolution spectroscopy

Isotopic ratios trace the formation and evolution of planets and link their atmospheres to the chemistry of their natal protoplanetary discs. We measure $^{12}\mathrm{C}/^{13}\mathrm{C} = 58^{+18}_{-15}$ in the atmosphere of the young super-Jupiter $\beta$ Pic b from 11 nights of CRIRES+ K-band spectroscopy ($\mathcal{R} \approx 100{,}000$) at the Very Large Telescope (VLT). We detect both $^{12}\mathrm{CO}$ and $^{13}\mathrm{CO}$ and constrain $^{12}\mathrm{C}/^{13}\mathrm{C}$ with a Bayesian retrieval jointly fitted with near-infrared photometry. The inferred $^{12}\mathrm{C}/^{13}\mathrm{C}$ is consistent with the present-day interstellar medium (ISM), is below the solar value, and is comparable to measurements in other young super-Jupiters. We also retrieve $T_{\rm eff} = 1629^{+30}_{-28}\,\mathrm{K}$, near-solar to mildly super-solar metallicity ([M/H]$ = 0.20^{+0.16}_{-0.12}$), a solar-like carbon-to-oxygen ratio (C/O$ = 0.52 \pm 0.03$), and tentative evidence for thick clouds. We analyse each night independently and combine the results of the six epochs with the highest signal-to-noise ratio (S/N), propagating night-to-night scatter into the final uncertainties. This provides an isotopic benchmark for a directly imaged planet interior to the CO snow line.

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arXiv2026

Upper limits on exosatellites around $\beta$ Pictoris b

$\beta$ Pictoris b is one of the closest known directly-imaged gas giant exoplanets with an orbit that is almost edge-on to our line of sight, making it an ideal target for radial velocity monitoring to search for massive exomoons. We measure the radial velocity of $\beta$ Pictoris b over several epochs between October 2024 and March 2025 by using the cross-correlation of a template spectrum with absorption lines in the planet's atmosphere, giving a mean precision of 160 m s$^{-1}$. The resultant set of radial velocities is analysed with a periodogram to search for candidate RV signals indicating a massive exomoon. Although we do not detect an exomoon signal in our data, our detection limits for a single moon are 80 Earth masses at P=1 day and 1 Jupiter at P=200 days, comparable to RV exomoon searches around other substellar companions. The RV limit is comparable with the astrometric exomoon limit at a period of 7 days and a mass of 150 Earth masses, where for longer periods the astrometric searches have lower mass limits. With an additional observing season, CRIRES+ can detect a planet/moon mass ratio of $10^{-3}$ (4 Earth masses) with a period of up to one day, and can detect a Neptune-mass moon at hundreds of Jupiter radii.

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arXiv2026

The ESO SupJup Survey. X. A carbon isotope contrast in the young ROXs 12 system

Emerging research suggests that elemental and isotopic ratios of exoplanet and brown dwarf atmospheres may serve as potential tracers of their formation pathways. The ESO SupJup Survey aims to shed light on this hypothesis, with a focus on the $^{12}$CO/$^{13}$CO ratio, by investigating the atmospheric composition of substellar companions and isolated brown dwarfs. In this work, we aim to characterize the atmospheres and determine the ratios of $^{12}$CO/$^{13}$CO of the Rho Ophiuchus X-ray source (ROXs) 12 system ($\sim$6Myrs), consisting of an M0 host with an L0 companion, as part of the ESO SupJup survey. Using high-resolution CRIRES+ K band spectra of these objects, we perform atmospheric retrieval analyses to derive their atmospheric properties, including the $^{12}$CO/$^{13}$CO ratio. Our retrieval framework is built on the radiative transfer code petitRADTRANS, with which we generate model spectra based on equilibrium chemistry tables computed with FastChem, coupled with the nested sampling algorithm PyMultiNest. We report the presence of H$_2$O, $^{12}$CO, $^{13}$CO, and HF in both the star and companion, with a tentative detection of H$_2^{18}$O in ROXs 12B. The $^{12}$CO/$^{13}$CO ratios of the two objects show a measurable, though not strongly significant, difference, namely $77\substack{+10 \\ -7}$ and $55\substack{+10 \\ -7}$ for ROXs 12A and B. We measure a C/O ratio of 0.54$\pm$0.01, while the C/O ratio of the star is not reliably constrained due to the absence of atomic oxygen lines in the K band. Furthermore, we retrieve moderate veiling in the host star of $r_k$=$0.17\substack{+0.02 \\ -0.03}$. Systems such as ROXs 12, in which both star and planet can be chemically and isotopically characterized, are crucial for constraining potential formation mechanisms of massive, wide-orbit super-Jupiters.

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arXiv2026

The ESO SupJup Survey IX: Isotopic evidence of a recent formation for Luhman 16AB

The distinct formation pathways of directly-imaged exoplanets and isolated brown dwarfs might leave imprints in the inherited elemental and isotopic abundances, but such measurements require careful characterisation of the atmospheres. In particular, L-T transition objects exhibit signs of dynamics that drive their atmospheres out of chemical equilibrium. In this work, we studied the nearest L-T brown dwarfs, Luhman 16A and B, to assess the chemical dis-equilibrium in their atmospheres and to investigate their elemental and isotopic composition. As part of the ESO SupJup Survey, we obtained high-resolution CRIRES$^+$ K-band spectra of the binary, which were analysed using an atmospheric retrieval framework. We detect and retrieve the abundances of $^{12}$CO, H$_2$O, CH$_4$, NH$_3$, H$_2$S, HF, and the $^{13}$CO isotopologue. Both atmospheres are in chemical dis-equilibrium with somewhat stronger vertical mixing in Luhman 16A compared to B ($K_\mathrm{zz,A}\sim10^{8.7}$, $K_\mathrm{zz,B}\sim10^{8.2}\ \mathrm{cm^2\ s^{-1}}$). The tested chemical models, free- and dis-equilibrium chemistry, yield consistent mixing ratios and agree with earlier work at shorter wavelengths. The gaseous C/O ratios show evidence of oxygen trapping in silicate-oxide clouds. While the C/O ratios are consistent with solar, the metallicities are modestly enhanced with $\mathrm{[C/H]}\sim0.15$. The carbon isotope ratios are measured at $\mathrm{^{12}C/^{13}C_A}=74^{+2}_{-2}$ and $\mathrm{^{12}C/^{13}C_B}=74^{+3}_{-3}$. The coincident constraints of metallicities and isotopes across the binary reinforce their likely shared formation. The $\mathrm{^{12}C/^{13}C}$ ratios are aligned with the present-day interstellar medium, but lower than the solar-system value. This suggests a recent inheritance and corroborates the relatively young age ($\sim500$ Myr) of Luhman 16AB as members of the Oceanus moving group.

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arXiv2025

Multi-modal atmospheric characterization of $\beta$ Pictoris b: Adding high-resolution continuum spectra from GRAVITY

We present the first VLTI/GRAVITY observations at R$_\lambda \sim 4000$ of $\beta$ Pic b. These four high S/N ($\sim$20) K-band spectra conserve both the pseudo-continuum and molecular absorption patterns. We analyze them with four self-consistent forward model grids (Exo-REM, ATMO, BT-Settl, Sonora) exploring $T_{\mathrm{eff}}$, log(g), metallicity, C/O, and $^{12}$CO/$^{13}$CO ratio. We also upgrade our forward modeling code ForMoSA to account for the data multi-modality and combine the GRAVITY epochs with published 1-5 $\mu$m photometry, low- to medium-resolution spectra (0.9-7 $\mu$m), and high-resolution echelle spectra (2.1-5.2 $\mu$m). Sonora and Exo-REM are statistically preferred. Exo-REM yields $T_{\mathrm{eff}}$ $=1607.45^{+4.85}_{-6.20}$ K and log(g) $=4.46^{+0.02}_{-0.04}$ dex from GRAVITY alone, and $T_{\mathrm{eff}}$ $=1502.74^{+2.32}_{-2.14}$ K and log(g) $=4.00\pm0.01$ dex when including all datasets. Archival data significantly affect the retrieved parameters. C/O remains solar ($0.552^{+0.003}_{-0.002}$) while [M/H] reaches super-solar values (0.50$\pm$0.01). We report the first tentative constraint on log($^{12}$CO/$^{13}$CO) $\sim$1.12, though this remains inconclusive due to telluric residuals. Additionally, we estimate the luminosity to be log(L/L$_\odot$) $=-4.01^{+0.04}_{-0.05}$, implying a heavy-element content of up to $\sim$5% (20-80 M$_\oplus$) given the system age and dynamical mass measurements. Access to both continuum and molecular lines at K-band significantly impacts the metallicity, possibly owing to collision-induced absorption shaping the continuum. Echelle spectra do not dominate the final fit with respect to lower resolution data. Future multi-modal frameworks should include weighting schemes reflecting bandwidth and central wavelength coverage.

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arXiv2025

The ESO SupJup Survey VIII. Chemical fingerprints of young L dwarf twins

The potentially distinct formation pathways of exoplanets and brown dwarfs may be imprinted in their elemental and isotopic ratios. This work is part of the ESO SupJup Survey, which aims to disentangle the formation pathways of super-Jupiters and brown dwarfs through the analysis of their chemical and isotopic ratios. In this study, we characterize the atmospheres of two young L4 dwarfs, 2MASS J03552337+1133437 (2M0355) and 2MASS J14252798-3650229 (2M1425), in the AB Doradus Moving Group. This involved constraining their chemical composition, $^{12}$CO/$^{13}$CO ratio, pressure-temperature profile, surface gravity, and rotational velocity. We have obtained high-resolution CRIRES+ K-band spectra of these brown dwarfs, which we analyzed with an atmospheric retrieval pipeline. Atmospheric models were generated with the radiative transfer code petitRADTRANS, for which we employed a free and equilibrium chemistry approach, which we coupled with the PyMultiNest sampling algorithm to determine the best fit. We report robust detections of $^{13}$CO (13.4 & 8.0 $\sigma$) and HF (11.6 & 15.8 $\sigma$) in 2M0355 and 2M1425, respectively. The objects have similar overall atmospheric properties, including $^{12}$CO/$^{13}$CO isotope ratios of $95.5\substack{+6.8 \\ -6.4}$ for 2M0355 and $109.6\substack{+10.6 \\ -9.6}$ for 2M1425. In both brown dwarfs, we find only tentative hints of H$_2^{18}$O (1.1 & 3.0 $\sigma$), with lower limits of H$_2^{16}$O/H$_2^{18}$O $\sim$ 1000. Both objects appear to be close to chemical equilibrium, considering the main spectral contributors. Future studies will put them into the context of other objects observed as part of the ESO SupJup Survey.

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arXiv2025

The ESO SupJup Survey VII: Clouds and line asymmetries in CRIRES$^+$ J-band spectra of the Luhman 16 binary

Brown dwarfs at the L-T transition likely experience an inhomogeneous clearing of the clouds in their atmospheres. The resulting surface of thin and thick cloudy patches has been put forward to explain the observed variability, J-band brightening, and re-emergence of FeH absorption. We study the closest brown dwarf binary, Luhman 16A and B, in an effort to constrain their chemical and cloud compositions. As this binary consists of an L7.5 and T0.5 component, we gain insight into the atmospheric properties at the L-T transition. As part of the ESO SupJup Survey, we observed Luhman 16AB at high spectral resolution in the J-band ($1.1-1.4\ \mathrm{\mu m}$) using CRIRES$^+$. To analyse the spectra, we employ an atmospheric retrieval framework, coupling the radiative transfer code petitRADTRANS with the MultiNest sampling algorithm. For both objects, we report detections of H$_2$O, K, Na, FeH, and, for the first time in the J-band, hydrogen-fluoride (HF). The K doublet at $1250\ \mathrm{nm}$ shows asymmetric absorption in the blue line wings, which are reproduced via pressure- and temperature-dependent shifts of the line cores. We find evidence for clouds in both spectra and we place constraints on an FeH-depletion in the Luhman 16A photosphere. The inferred over-abundance of FeH for Luhman 16B opposes its predicted rainout into iron clouds. A two-column model, which emulates the patchy surface expected at the L-T transition, is weakly preferred ($\sim 1.8\sigma$) for component B but disfavoured for A ($\sim 5.5\sigma$). The results suggest a uniform surface on Luhman 16A, which is in good agreement with the reduced variability observed for this L-type component. While the presented evidence is not sufficient to draw conclusions about any inhomogeneity on Luhman 16B, future observations covering a broader wavelength range could help to test the cloud-clearing hypothesis.

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arXiv2025

Making the unmodulated pyramid wavefront sensor smart II. First on-sky demonstration of extreme adaptive optics with deep learning

Pyramid wavefront sensors (PWFSs) are the preferred choice for current and future extreme adaptive optics (XAO) systems. Almost all instruments use the PWFS in its modulated form to mitigate its limited linearity range. However, this modulation comes at the cost of a reduction in sensitivity, a blindness to petal-piston modes, and a limit to the sensor's ability to operate at high speeds. Therefore, there is strong interest to use the PWFS without modulation, which can be enabled with nonlinear reconstructors. Here, we present the first on-sky demonstration of XAO with an unmodulated PWFS using a nonlinear reconstructor based on convolutional neural networks. We discuss the real-time implementation on the Magellan Adaptive Optics eXtreme (MagAO-X) instrument using the optimized TensorRT framework and show that inference is fast enough to run the control loop at >2 kHz frequencies. Our on-sky results demonstrate a successful closed-loop operation using a model calibrated with internal source data that delivers stable and robust correction under varying conditions. Performance analysis reveals that our smart PWFS achieves nearly the same Strehl ratio as the highly optimized modulated PWFS under favorable conditions on bright stars. Notably, we observe an improvement in performance on a fainter star under the influence of strong winds. These findings confirm the feasibility of using the PWFS in its unmodulated form and highlight its potential for next-generation instruments. Future efforts will focus on achieving even higher control loop frequencies (>3 kHz), optimizing the calibration procedures, and testing its performance on fainter stars, where more gain is expected for the unmodulated PWFS compared to its modulated counterpart.

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arXiv2025

The ESO SupJup Survey IV. Unveiling the carbon isotope ratio of GQ Lup B and its host star

The carbon isotope ratio ($^{12}\mathrm{C}/^{13}\mathrm{C}$) is a potential tracer of giant planet and brown dwarf formation. The GQ Lup system, hosting the K7 T Tauri star GQ Lup A and its substellar companion GQ Lup B, offers a unique opportunity to investigate this ratio in a young system. We aim to characterise the atmosphere of GQ Lup B, determining its temperature, chemical composition, spin, surface gravity, and $^{12}\mathrm{C}/^{13}\mathrm{C}$, while also measuring the same ratio for its host star, GQ Lup A. High-resolution K-band spectra of GQ Lup were obtained using CRIRES+ at the VLT. We modelled the starlight contribution from GQ Lup A and fitted GQ Lup B\'s spectrum with atmospheric models from petitRADTRANS. The $^{12}\mathrm{C}/^{13}\mathrm{C}$ ratio for GQ Lup A was derived using isotope-sensitive PHOENIX models. Atmospheric analysis of GQ Lup B revealed abundances of H$_2$O, $^{12}$CO, $^{13}$CO, HF, Na, Ca, and Ti, along with a C/O ratio of $0.50 \pm 0.01$, consistent with the solar value. The carbon isotope ratio was measured as $^{12}\mathrm{C}/^{13}\mathrm{C} = 53^{+7}_{-6}$ for GQ Lup B and $^{12}\mathrm{C}/^{13}\mathrm{C} = 51^{+10}_{-8}$ for GQ Lup A. Strong veiling of the photospheric lines of GQ Lup A was identified and accounted for. The similar $^{12}\mathrm{C}/^{13}\mathrm{C}$ values in GQ Lup A and B suggest a common origin from a shared material reservoir, supporting formation via disc fragmentation or gravitational collapse.

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arXiv2024

Four HD 209458 b transits through CRIRES+: Detection of H$_2$O and non-detections of C$_2$H$_2$, CH$_4$, and HCN

HD 209458 b is one of the most studied exoplanets to date. Despite this, atmospheric characterisation studies yielded inconsistent species detections and abundances. Values reported for the C/O ratio range from 0.1 to 1.0. Of particular interest is the simultaneous detection of H2O and HCN reported by some studies using high-resolution ground-based observations, which would require the atmospheric C/O ratio to be fine-tuned to a narrow interval around 1. HCN has however not been detected from recent space-based observations. We aim to provide an independent study of HD 209458 b's atmosphere with high-resolution observations, in order to infer the presence of several species, including H2O and HCN. We observed four primary transits of HD 209458 b at a high resolution (R=92000) with CRIRES+ in the near infrared (band H, 1.4--1.8 um). After reducing the data with pycrires, we prepared the data using the SysRem algorithm and performed a cross-correlation (CCF) analysis of the transmission spectra. We also compared the results with those obtained from simulated datasets constructed by combining the Exo-REM self-consistent model with the petitRADTRANS package. Combining the four transits, we detect H2O with a signal-to-noise CCF metric of 8.7. This corresponds to a signal emitted at $K_p=151.3^{+31.1}_{-23.4}$ km/s and blueshifted by $-6^{+1}_{-2}$ km/s, consistent with what is expected for HD 209458 b. We do not detect any other species among C2H2, CH4, CO, CO2, H2S, HCN, and NH3. Comparing this with our simulated datasets, this result is consistent with a C/O ratio of 0.1 and an opaque cloud top pressure of 50 Pa, at a 3 times solar metallicity. This would also be consistent with recent JWST observations. However, none of the simulated results obtained with a bulk C/O ratio of 0.8, a value suggested by previous studies using GIANO-B and CRIRES, are consistent with our observations.

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arXiv2024

The ESO SupJup Survey II: The 12C/13C ratios of three young brown dwarfs with CRIRES$^+$

Young brown dwarfs exhibit atmospheric characteristics similar to those of super-Jupiters, providing a unique opportunity to study planetary atmospheres. The ESO SupJup Survey, utilizing CRIRES$^+$ on the Very Large Telescope, aims to assess the role of $^{12}$C/$^{13}$C as a formation tracer. We present observations of three young brown dwarfs: 2MASS J12003792-7845082, TWA 28, and 2MASS J08561384-1342242, with the goal of constraining their chemical compositions, thermal profiles, surface gravities, spin rotations, and $^{12}$C/$^{13}$C. Atmospheric retrievals of CRIRES$^+$ K-band spectra were conducted using the radiative transfer code petitRADTRANS coupled with the Bayesian inference algorithm MultiNest, resulting in a detailed characterization of the atmospheres of these objects. We report the volume mixing ratios of main molecular and atomic species, including the novel detection of hydrogen fluoride (HF) in a brown dwarf's atmosphere, and determine $^{12}$C/$^{13}$C values of $81^{+28}_{-19}$ and $79^{+20}_{-14}$ in the atmospheres of TWA 28 and J0856, respectively, with strong significance ($>3\sigma$). Tentative evidence ($\sim 2\sigma$) of $^{13}$C in J1200 was found, with $^{12}$C/$^{13}$C = $114^{+69}_{-33}$, along with $^{18}$O detected at moderate significance in J0856 (3.3$\sigma$) and TWA 28 (2.1$\sigma$). The retrieved thermal profiles indicate hot atmospheres (2300-2600 K) with low surface gravities and slow spins, consistent with young objects. The consistent carbon isotope ratios among the three objects, showing no significant deviation from the local ISM, suggest a fragmentation-based formation mechanism similar to star formation. The tentative detection of $^{18}$O in two objects highlights the potential of high-resolution spectroscopy to probe additional isotope ratios, such as $^{16}$O/$^{18}$O, in the atmospheres of brown dwarfs and super-Jupiters.

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arXiv2024

The ESO SupJup Survey I: Chemical and isotopic characterisation of the late L-dwarf DENIS J0255-4700 with CRIRES$^+$

It has been proposed that the distinct formation and evolution of exoplanets and brown dwarfs may affect the chemical and isotopic content of their atmospheres. Recent work has indeed shown differences in the $^{12}$C/$^{13}$C isotope ratio, provisionally attributed to the top-down formation of brown dwarfs and the core accretion pathway of super-Jupiters. The ESO SupJup Survey aims to disentangle the formation pathways of isolated brown dwarfs and planetary-mass companions using chemical and isotopic tracers. The survey uses high-resolution spectroscopy with the recently upgraded VLT/CRIRES$^+$ spectrograph, covering a total of 49 targets. Here, we present the first results: an atmospheric characterisation of DENIS J0255-4700, an isolated brown dwarf near the L-T transition. We analyse its K-band spectrum using a retrieval framework where the radiative transfer code petitRADTRANS is coupled to PyMultiNest. Gaussian Processes are employed to model inter-pixel correlations and we adopt an updated parameterisation of the PT-profile. Abundances of CO, H$_2$O, CH$_4$, and NH$_3$ are retrieved for this fast-rotating L-dwarf. The ExoMol H$_2$O line list provides a significantly better fit than that of HITEMP. A free-chemistry retrieval is strongly favoured over equilibrium chemistry, caused by an under-abundance of CH$_4$. The free-chemistry retrieval constrains a super-solar C/O-ratio of $\sim0.68$ and a solar metallicity. We find tentative evidence ($\sim3\sigma$) for the presence of $^{13}$CO, with a constraint on the isotope ratio of $\mathrm{^{12}C/^{13}C}=184^{+61}_{-40}$ and a lower limit of $\gtrsim97$, suggesting a depletion of $^{13}$C compared to the interstellar medium ($\sim68$). High-resolution, high signal-to-noise K-band spectra provide an excellent means to constrain the chemistry and isotopic content of sub-stellar objects, as is the main objective of the ESO SupJup Survey.

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arXiv2022

Upgrading the high contrast imaging facility SPHERE: science drivers and instrument choices

SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT, which is intended to boost the current performances of detection and characterization for exoplanets and disks. SPHERE+ will also serve as a demonstrator for the future planet finder (PCS) of the European ELT. The main science drivers for SPHERE+ are 1/ to access the bulk of the young giant planet population down to the snow line ($3-10$ au), to bridge the gap with complementary techniques (radial velocity, astrometry); 2/ to observe fainter and redder targets in the youngest ($1-10$\,Myr) associations compared to those observed with SPHERE to directly study the formation of giant planets in their birth environment; 3/ to improve the level of characterization of exoplanetary atmospheres by increasing the spectral resolution in order to break degeneracies in giant planet atmosphere models. Achieving these objectives requires to increase the bandwidth of the xAO system (from $\sim$1 to 3\,kHz) as well as the sensitivity in the infrared (2 to 3\,mag). These features will be brought by a second stage AO system optimized in the infrared with a pyramid wavefront sensor. As a new science instrument, a medium resolution integral field spectrograph will provide a spectral resolution from 1000 to 5000 in the J and H bands. This paper gives an overview of the science drivers, requirements and key instrumental trade-off that were done for SPHERE+ to reach the final selected baseline concept.

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arXiv2022

Searching for the origin of the Ehrenreich effect in ultra-hot Jupiters: Evidence for strong C/O gradients in the atmosphere of WASP-76b?

Extreme temperature contrasts between the day and nightside of ultra-hot Jupiters result in significantly asymmetric atmospheres, with a large expansion occurring over a small range of longitude around the terminator. Over the course of a transit, WASP-76b rotates by about 30 degree, changing the observable part of the atmosphere and invoking variations in the appearance of its constituents. As recently reported, this results in time-variable effects in the neutral iron signal, which are amplified by its possible condensation on the nightside. Here, we study the presence of molecular signals during a transit of WASP-76b observed with the CARMENES spectrograph and compare the contributions from this planet's morning and evening terminators. The results are somewhat puzzling, with formal detections of water vapor (5.5$\sigma$) and hydrogen cyanide (5.2$\sigma$) but at significantly different positions in the K$_p$-V$_{sys}$ diagram, with a blueshift of -14.3 $\pm$ 2.6 km/s and a redshift of $+$20.8 $^{+7.8}_{-3.9}$ km/s respectively, and a higher K$_p$ than expected. The H$_2$O signal also appears stronger later on in the transit, in contrast to that of HCN, which seems stronger early on. We tentatively explain this by silicate clouds forming and raining out on the nightside, partially removing oxygen from the upper atmosphere. For C/O values between 0.7 and 1, this leads to the formation of HCN at the morning limb. At the evening terminator, with the sequestered oxygen being returned to the gas phase due to evaporation, these C/O values lead to formation of H$_2$O instead of HCN. If confirmed, these results indicate that individual molecules trace different parts of the atmosphere, as well as nightside condensation, allowing spatial characterization. As these results are based on a single transit, we advocate that more data are needed to confirm them and further explore these scenarios.

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