arXiv subjects

Tiziano Zingales

Publications and source records attributed to Tiziano Zingales.

18 recordsLinked to original sources

arXiv2026

Performance of AutoRegressive Planet Search methodology on simulated PLATO lightcurves

AIM. This study examines the PLATO mission sensitivity to small transiting planets (radii between 0.5 and 2.0 R$_\oplus$) using Autoregressive Planet Search (ARPS) methodology based on simulated lightcurves. Methods. Several thousand simulations of PLATO-like lightcurves from magnetically active stars expected from the PLATO Long Observation Phase South 2 (LOPS2) field with injected transiting planets smaller than 2.0 R$_\oplus$ radius are examined. The lightcurves are analyzed with ARPS that uses autoregressive modeling for filtering of nonplanetary signals and the Transit Comb Filter periodogram for planetary transit detection. False alarms of nonexistent periodic signals are reduced by thresholds on two ARPS parameters, peak periodogram power, and transit duration. Results. When applied to PLATO's simulated first three months observations of bright stars (P1 and P2 samples), at least 50% of Earth-size planets are recovered for periods shorter than 40 d. In two years of LOPS2 observation, 25% are recovered for periods less than 240 d. Methodological implications on detrending, periodograms, False Alarms, vetting, and catalog evaluation are discussed. The utility of a positive predicted value heat map after detection and vetting is demonstrated. Conclusions: While the ARPS planet detection procedure is not entirely well-suited for PLATO analysis, this study provides methodological insight into the sensitivity and reliability of small transiting planet detection.

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arXiv2026

An Ultra-Short Period Super-Earth and a Sub-Neptune Orbiting the K dwarf TOI-4311

We report the discovery and characterisation of the multi-planetary system around TOI-4311, a K dwarf kinematically between the Galactic thick disk and Hercules stream. TOI-4311 hosts an ultra-short-period super-Earth (P$\sim$0.99 d, $1.376\substack{+0.077\\-0.080}$ R$_\oplus$) and a longer period sub-Neptune (P$\sim$15 d, $2.47\substack{+0.12\\-0.11}$ R$_\oplus$) that was first detected in the TESS photometry. Using follow-up observations with CHEOPS and HARPS, we refine the planetary radius of both planets, derive the mass of planet b ($4.5\substack{+1.5\\-1.4}$ M$_\oplus$) and confirm the planetary nature of planet c. Intriguingly, a third periodic signal is clearly detected in our HARPS RVs that we cannot link to stellar activity. This signal could be attributed to a third planet (P$\sim$38 d, Msin(i)=$26.4\substack{+6.3\\-6.8}$ M$_\oplus$) in the system, however with the current photometric dataset we do not find a transit. Our dynamical analysis highlights that this potential outer planet would remain stable. Using the precise radius and mass for TOI-4311 b we model its interior structure and find that it is very dense given the host star's galactic kinematics and chemistry. Hence this system could challenge current formation theories and provide insights into planet formation across the galaxy.

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arXiv2026

Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903

Small exoplanet radii show two populations, referred to as super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This may be produced by the removal of atmospheres due to stellar or internal heating, or lack of an initial envelope. We us transit photometry and radial velocity measurements to detect and characterize four planets orbiting LHS 1903, a red dwarf (M-dwarf) star in the Milky Way's thick disk. The planets have orbital periods between 2.2 and 29.3 days, and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, while LHS 1903 c and LHS 1903 d have extended atmospheres. Although the most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating it formed from gas-depleted material.

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arXiv2025

Data availability and requirements relevant for the Ariel space mission and other exoplanet atmosphere applications

The goal of this white paper is to provide a snapshot of the data availability and data needs primarily for the Ariel space mission, but also for related atmospheric studies of exoplanets and brown dwarfs. It covers the following data-related topics: molecular and atomic line lists, line profiles, computed cross-sections and opacities, collision-induced absorption and other continuum data, optical properties of aerosols and surfaces, atmospheric chemistry, UV photodissociation and photoabsorption cross-sections, and standards in the description and format of such data. These data aspects are discussed by addressing the following questions for each topic, based on the experience of the "data-provider" and "data-user" communities: (1) what are the types and sources of currently available data, (2) what work is currently in progress, and (3) what are the current and anticipated data needs. We present a GitHub platform for Ariel-related data, with the goal to provide a go-to place for both data-users and data-providers, for the users to make requests for their data needs and for the data-providers to link to their available data. Our aim throughout the paper is to provide practical information on existing sources of data whether in databases, theoretical, or literature sources.

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arXiv2025

Exoplanetary atmospheres retrieval via a quantum extreme learning machine

The study of exoplanetary atmospheres traditionally relies on forward models to analytically compute the spectrum of an exoplanet by fine-tuning numerous chemical and physical parameters. However, the high-dimensionality of parameter space often results in a significant computational overhead. In this work, we introduce a novel approach to atmospheric retrieval leveraging on quantum extreme learning machines (QELMs). QELMs are quantum machine learning techniques that employ quantum systems as a black box for processing input data. In this work, we propose a framework for extracting exoplanetary atmospheric features using QELMs, employing an intrinsically fault-tolerant strategy suitable for near-term quantum devices, and we demonstrate such fault tolerance with a direct implementation on IBM Fez. The QELM architecture we present shows the potential of quantum computing in the analysis of astrophysical datasets and may, in the near-term future, unlock new computational tools to implement fast, efficient, and more accurate models in the study of exoplanetary atmospheres.

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arXiv2024

Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815

We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K-M binary system. Analysis of the spectra and rotation period reveal it to be a young star with an age of $200^{+400}_{-200}$Myr. TOI-815b has a 11.2-day period and a radius of 2.94$\pm$0.05$\it{R_{\rm\mathrm{\oplus}}}$ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62$\pm$0.10$\it{R_{\rm\mathrm{\oplus}}}$, based on observations of three non-consecutive transits with TESS, while targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6$\pm$1.5 $\it{M_{\rm \mathrm{\oplus}}}$ ($ρ_\mathrm{P}$=1.64$^{+0.33}_{-0.31}$gcm$^{-3}$) and 23.5$\pm$2.4$\it{M_{\rm\mathrm{\oplus}}}$ ($ρ_\mathrm{P}$=7.2$^{+1.1}_{-1.0}$gcm$^{-3}$) respectively. Thus, the planets have very different masses, unlike the usual similarity of masses in compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those suffering strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere constituting a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3$σ$ level.

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arXiv2022

Toward a multidimensional analysis of transmission spectroscopy. Part III: Modelling 2D effects in retrievals with TauREx

New-generation spectrographs dedicated to the study of exoplanetary atmospheres require a high accuracy in the atmospheric models to better interpret the input spectra. Thanks to space missions, the observed spectra will cover a large wavelength range from visible to mid-infrared with an higher precision compared to the old-generation instrumentation, revealing complex features coming from different regions of the atmosphere. For hot and ultra hot Jupiters (HJs and UHJs), the main source of complexity in the spectra comes from thermal and chemical differences between the day and the night sides. In this context, one-dimensional plane parallel retrieval models of atmospheres may not be suitable to extract the complexity of such spectra. In addition, Bayesian frameworks are computationally intensive and prevent us from using complete three-dimensional self-consistent models to retrieve exoplanetary atmospheres. We propose the TauREx 2D retrieval code, which uses two-dimensional atmospheric models as a good compromise between computational cost and model accuracy to better infer exoplanetary atmospheric characteristics for the hottest planets. TauREx 2D uses a 2D parametrization across the limb which computes the transmission spectrum from an exoplanetary atmosphere assuming azimuthal symmetry. It also includes a thermal dissociation model of various species. We demonstrate that, given an input observation, TauREx 2D mitigates the biases between the retrieved atmospheric parameters and the real atmospheric parameters. We also show that having a prior knowledge on the link between local temperature and composition is instrumental in inferring the temperature structure of the atmosphere. Finally, we apply such a model on a synthetic spectrum computed from a GCM simulation of WASP-121b and show how parameter biases can be removed when using two-dimensional forward models across the limb.

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arXiv2021

Toward a multidimensional analysis of transmission spectroscopy. Part I: Computation of transmission spectra using a 1D, 2D, or 3D atmosphere structure

Considering the relatively high precision that will be reached by future observatories, it has recently become clear that one dimensional (1D) atmospheric models, in which the atmospheric temperature and composition of a planet are considered to vary only in the vertical, will be unable to represent exoplanetary transmission spectra with a sufficient accuracy. This is particularly true for warm to (ultra-) hot exoplanets because the atmosphere is unable to redistribute all the energy deposited on the dayside, creating a strong thermal and often compositional dichotomy on the planet. This situation is exacerbated by transmission spectroscopy, which probes the terminator region. This is the most heterogeneous region of the atmosphere. However, if being able to compute transmission spectra from 3D atmospheric structures (from a global climate model, e.g.) is necessary to predict realistic observables, it is too computationally expensive to be used in a data inversion framework. For this reason, there is a need for a medium-complexity 2D approach that captures the most salient features of the 3D model in a sufficiently fast implementation. With this in mind, we present a new open-source documented version of Pytmosph3R that handles the computation of transmission spectra for atmospheres with up to three spatial dimensions and can account for time variability. Taking the example of an ultra hot Jupiter, we illustrate how the changing orientation of the planet during the transit can allow us to probe the horizontal variations in the atmosphere. We further implement our algorithm in TauREx to allow the community to perform 2D retrievals. We describe our extensive cross-validation benchmarks and discuss the accuracy and numerical performance of each model.

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arXiv2021

Towards multi-dimensional analysis of transmission spectroscopy. Part II: Day-night induced biases in retrievals from hot to ultra-hot Jupiters

Hot Jupiters are very good targets for transmission spectroscopy analysis. Their atmospheres have a large scale height implying a high signal to noise ratio. As these planets orbit close to their stars, they often present strong thermal and chemical hetereogeneities between the day and the night side of their atmosphere. For the hottest ones, the thermal dissociation of several species occurs in their atmospheres which leads to a stronger chemical dichotomy between the two hemispheres. It has already been shown that the current retrieval algorithms, which are using 1D forward models, find biased molecular abundances in ultra hot Jupiters. Here, we quantify the effective temperature domain over which these biases are present. We use a set of 12 simulations of typical Hot Jupiters from Teq = 1000 K to Teq = 2100 K performed with the Substellar and Planetary Atmospheric Radiation and Circulation global climate model and generate transmission spectra that fully account for the 3D structure of the atmosphere with Pytmosph3R. These spectra are then analyzed using the 1D TauREx retrieval code. We find that for JWST-like data, accounting for non-isothermal vertical temperature profiles is required over the whole temperature range. We further find that 1D retrieval codes start to estimate wrong parameter values for planets with equilibrium temperatures greater than 1400 K if there are absorbers in the visible able to create a hot stratosphere. The high temperatures at low pressures indeed entail a thermal dissociation of species which creates a strong chemical day-night dichotomy. As a by-product, we demonstrate that when using synthetic observations to assess the detectability of a given feature or process using a Bayesian framework, it is valid to use non-randomized input data, as long as the anticipated observational uncertainties are correctly taken into account.

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arXiv2021

ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b

We present a study on the spatially scanned spectroscopic observations of the transit of GJ 1132 b, a warm ($\sim$500 K) Super-Earth (1.13 R$_\oplus$) that was obtained with the G141 grism (1.125 - 1.650 $μ$m) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We used the publicly available Iraclis pipeline to extract the planetary transmission spectra from the five visits and produce a precise transmission spectrum. We analysed the spectrum using the TauREx3 atmospheric retrieval code with which we show that the measurements do not contain molecular signatures in the investigated wavelength range and are best-fit with a flat-line model. Our results suggest that the planet does not have a clear primordial, hydrogen-dominated atmosphere. Instead, GJ 1132 b could have a cloudy hydrogen-dominated envelope, a very enriched secondary atmosphere, be airless, or have a tenuous atmosphere that has not been detected. Due to the narrow wavelength coverage of WFC3, these scenarios cannot be distinguished yet but the James Webb Space Telescope may be capable of detecting atmospheric features, although several observations may be required to provide useful constraints.

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arXiv2020

ARES I: WASP-76 b, A Tale of Two HST Spectra

We analyse the transmission and emission spectra of the ultra-hot Jupiter WASP-76b, observed with the G141 grism of the Hubble Space Telescope's Wide Field Camera 3 (WFC3). We reduce and fit the raw data for each observation using the open-source software Iraclis before performing a fully Bayesian retrieval using the publicly available analysis suite TauRex 3. Previous studies of the WFC3 transmission spectra of WASP-76 b found hints of titanium oxide (TiO) and vanadium oxide (VO) or non-grey clouds. Accounting for a fainter stellar companion to WASP-76, we reanalyse this data and show that removing the effects of this background star changes the slope of the spectrum, resulting in these visible absorbers no longer being detected, eliminating the need for a non-grey cloud model to adequately fit the data but maintaining the strong water feature previously seen. However, our analysis of the emission spectrum suggests the presence of TiO and an atmospheric thermal inversion, along with a significant amount of water. Given the brightness of the host star and the size of the atmospheric features, WASP-76 b is an excellent target for further characterisation with HST, or with future facilities, to better understand the nature of its atmosphere, to confirm the presence of TiO and to search for other optical absorbers.

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arXiv2020

ARES II: Characterising the Hot Jupiters WASP-127 b, WASP-79 b and WASP-62 b with HST

This paper presents the atmospheric characterisation of three large, gaseous planets: WASP-127b, WASP-79b and WASP-62b. We analysed spectroscopic data obtained with the G141 grism (1.088 - 1.68 $μ$m) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) using the Iraclis pipeline and the TauREx3 retrieval code, both of which are publicly available. For WASP-127 b, which is the least dense planet discovered so far and is located in the short-period Neptune desert, our retrieval results found strong water absorption corresponding to an abundance of log(H$_2$O) = -2.71$^{+0.78}_{-1.05}$, and absorption compatible with an iron hydride abundance of log(FeH)=$-5.25^{+0.88}_{-1.10}$, with an extended cloudy atmosphere. We also detected water vapour in the atmospheres of WASP-79 b and WASP-62 b, with best-fit models indicating the presence of iron hydride, too. We used the Atmospheric Detectability Index (ADI) as well as Bayesian log evidence to quantify the strength of the detection and compared our results to the hot Jupiter population study by Tsiaras et al. 2018. While all the planets studied here are suitable targets for characterisation with upcoming facilities such as the James Webb Space Telescope (JWST) and Ariel, WASP-127 b is of particular interest due to its low density, and a thorough atmospheric study would develop our understanding of planet formation and migration.

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arXiv2020

ARES III: Unveiling the Two Faces of KELT-7 b with HST WFC3

We present the analysis of the hot-Jupiter KELT-7b using transmission and emission spectroscopy from the Hubble Space Telescope (HST), both taken with the Wide Field Camera 3 (WFC3). Our study uncovers a rich transmission spectrum which is consistent with a cloud-free atmosphere and suggests the presence of H2O and H-. In contrast, the extracted emission spectrum does not contain strong absorption features and, although it is not consistent with a simple blackbody, it can be explained by a varying temperature-pressure profile, collision induced absorption (CIA) and H-. KELT-7 b had also been studied with other space-based instruments and we explore the effects of introducing these additional datasets. Further observations with Hubble, or the next generation of space-based telescopes, are needed to allow for the optical opacity source in transmission to be confirmed and for molecular features to be disentangled in emission.

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arXiv2020

Strong biases in retrieved atmospheric composition caused by strong day-night chemical heterogeneities

Most planets currently amenable to transit spectroscopy are close enough to their host star to exhibit a relatively strong day to night temperature gradient. For hot planets, this leads to cause a chemical composition dichotomy between the two hemispheres. In the extreme case of ultra hot jupiters, some species, such as molecular hydrogen and water, are strongly dissociated on the day-side while others, such as carbon monoxide, are not. However, most current retrieval algorithm rely on 1D forward models that are unable to model this effect. We thus investigate how the 3D structure of the atmosphere biases the abundances retrieved using commonly used algorithms. We study the case of Wasp-121b as a prototypical ultra hot Jupiter. We use the simulations of this planet performed with the SPARC/MIT global climate model (GCM) and generate transmission spectra that fully account for the 3D structure of the atmosphere with Pytmopsh3R. These spectra are then analyzed using the \taurex retrieval code. We find that such ultra hot jupiter's transmission spectra exhibit muted H$_2$O features that originate in the night-side where the temperature, hence the scale-height, is smaller than on the day-side. However, the spectral features of molecules present on the day-side are boosted by both its high temperature and low mean molecular weight. As a result, the retrieved parameters are strongly biased compared to the ground truth. In particular the [CO]/[H$_2$O] is overestimated by one to three orders of magnitude. This must be kept in mind when using such retrieval analysis to infer the C/O ratio of a planet's atmosphere. We also discuss whether indicators can allow us to infer the 3D structure of an observed atmosphere. Finally we show that HST/WFC3 transmission data of Wasp-121b are compatible with the day-night thermal and compositional dichotomy predicted by models.

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arXiv2018

Exoplanet Spectroscopy and Photometry with the Twinkle Space Telescope

The Twinkle space telescope has been designed for the characterisation of exoplanets and Solar System objects. Operating in a low Earth, Sun-synchronous orbit, Twinkle is equipped with a 45 cm telescope and visible (0.4 - 1um) and infrared (1.3 - 4.5um) spectrometers which can be operated simultaneously. Twinkle is a general observatory which will provide on-demand observations of a wide variety of targets within wavelength ranges that are currently not accessible using other space telescopes or accessible only to oversubscribed observatories in the short-term future. Here we explore the ability of Twinkle's spectrometers to characterise the currently-known exoplanets. We study the spectral resolution achievable by combining multiple observations for various planetary and stellar types. We also simulate spectral retrievals for some well-known planets (HD 209458 b, GJ 3470 b and 55 Cnc e). From the exoplanets known today, we find that with a single transit or eclipse, Twinkle could probe 89 planets at low spectral resolution (R < 20) as well as 12 planets at higher resolution (R > 20) in channel 1 (1.3 - 4.5um). With 10 observations, the atmospheres of 144 planets could be characterised with R < 20 and 81 at higher resolutions. Upcoming surveys will reveal thousands of new exoplanets, many of which will be located within Twinkle's field of regard. TESS in particular is predicted to discover many targets around bright stars which will be suitable for follow-up observations. We include these anticipated planets and find that the number of planets Twinkle could observe in the near infrared in a single transit or eclipse increases to 558 for R > 20 and 41 at lower resolutions. By stacking 10 transits or eclipses, there are 1185 potential targets for study at R < 20 as well as 388 planets at higher resolutions.

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arXiv2018

ExoGAN: Retrieving Exoplanetary Atmospheres Using Deep Convolutional Generative Adversarial Networks

Atmospheric retrievals on exoplanets usually involve computationally intensive Bayesian sampling methods. Large parameter spaces and increasingly complex atmospheric models create a computational bottleneck forcing a trade-off between statistical sampling accuracy and model complexity. It is especially true for upcoming JWST and ARIEL observations. We introduce ExoGAN, the Exoplanet Generative Adversarial Network, a new deep learning algorithm able to recognise molecular features, atmospheric trace-gas abundances and planetary parameters using unsupervised learning. Once trained, ExoGAN is widely applicable to a large number of instruments and planetary types. The ExoGAN retrievals constitute a significant speed improvement over traditional retrievals and can be used either as a final atmospheric analysis or provide prior constraints to subsequent retrieval.

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arXiv2018

A better characterization of the chemical composition of exoplanets atmospheres with ARIEL

Since the discovery of the first extrasolar planet more than twenty years ago, we have discovered nearly four thousand planets orbiting stars other than the Sun. Current observational instruments (on board the Hubble Space Telescope, Spitzer, and on ground-based facilities) have allowed the scientific community to obtain important information on the physical and chemical properties of these planets. However, for a more in-depth characterisation of these worlds, more powerful telescopes are needed. Thanks to the high sensitivity of their instruments, the next generation of space observatories (e.g. JWST, ARIEL) will provide observations of unprecedented quality, allowing us to extract far more information than what was previously possible. Such high quality observations will provide constraints on theoretical models of exoplanet atmospheres and lead to a greater understanding of their physics and chemistry. Important modelling efforts have been carried out during the past few years, showing that numerous parameters and processes (such as the elemental abundances, temperature, mixing, etc.) are likely to affect the atmospheric composition of exoplanets and subsequently the observable spectra. In this manuscript, we review the different parameters that can influence the molecular composition of exoplanet atmospheres. We show that the high-precision of ARIEL observations will improve our view and characterisation of exoplanet atmospheres. We also consider future developments that are necessary to improve atmospheric models, driven by the need to interpret the available observations.

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arXiv2018

The ARIEL Mission Reference Sample

The ARIEL (Atmospheric Remote-sensing Exoplanet Large-survey) mission concept is one of the three M4 mission candidates selected by the European Space Agency (ESA) for a Phase A study, competing for a launch in 2026. ARIEL has been designed to study the physical and chemical properties of a large and diverse sample of exoplanets, and through those understand how planets form and evolve in our galaxy. Here we describe the assumptions made to estimate an optimal sample of exoplanets - including both the already known exoplanets and the "expected" ones yet to be discovered - observable by ARIEL and define a realistic mission scenario. To achieve the mission objectives, the sample should include gaseous and rocky planets with a range of temperatures around stars of different spectral type and metallicity. The current ARIEL design enables the observation of ~1000 planets, covering a broad range of planetary and stellar parameters, during its four year mission lifetime. This nominal list of planets is expected to evolve over the years depending on the new exoplanet discoveries.

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