Polarimetry is about to become a powerful tool for determining the atmospheric properties of exoplanets. To provide the basis for the interpretation of observational results and for predictive studies to guide future observations, sophisticated analysis tools are required. Our goal is to develop a radiative transfer tool that contains all the relevant continuum polarization mechanisms for the comprehensive analysis of the polarized flux resulting from the scattering in the atmosphere of, on the surface of, and in the local planetary environment (e.g., planetary rings, exomoons) of extra-solar planets. Furthermore, our goal is to avoid common simplifications such as locally plane-parallel planetary atmospheres, the missing cross-talk between latitudinal and longitudinal regions, or the assumption of either a point-like star or plane-parallel illumination. As a platform for the newly developed numerical algorithms, we use the 3D Monte Carlo radiative transfer code POLARIS. The code is extended and optimized for the radiative transfer in exoplanetary atmospheres. We investigate the reflected flux and its degree of polarization for different phase angles for a homogeneous cloud-free atmosphere and an inhomogeneous cloudy atmosphere. To take advantage of the 3D radiative transfer and to demonstrate the potential of the code, the impact of an additional circumplanetary ring on the reflected polarized flux is studied. The presence of a circumplanetary ring consisting of small water-ice particles has a noticeable impact on the reflected polarized radiation. In particular, the reflected flux strongly increases at larger phase angles if the planetary orbit is seen edge-on because the considered particles tend to scatter forwards. In contrast, the degree of polarization decreases at these phase angles.
The study of exoplanetary atmospheres is one of the most exciting and dynamic frontiers in astronomy. Over the past two decades ongoing surveys have revealed an astonishing diversity in the planetary masses, radii, temperatures, orbital parameters, and host stellar properties of exoplanetary systems. We are now moving into an era where we can begin to address fundamental questions concerning the diversity of exoplanetary compositions, atmospheric and interior processes, and formation histories, just as have been pursued for solar system planets over the past century. Exoplanetary atmospheres p…
Exoplanetary science is on the verge of an unprecedented revolution. The thousands of exoplanets discovered over the past decade have most recently been supplemented by discoveries of potentially habitable planets around nearby low-mass stars. Currently, the field is rapidly progressing towards detailed spectroscopic observations to characterise the atmospheres of these planets. While various surveys from space and ground are expected to detect numerous more exoplanets orbiting nearby stars, the imminent launch of JWST along with large ground-based facilities are expected to revolutionise exop…
We review several aspects of the calculation of exoplanet model atmospheres in the current era, with a focus on understanding the temperature-pressure profiles of atmospheres and their emitted spectra. Most of the focus is on gas giant planets, both under strong stellar irradiation and in isolation. The roles of stellar irradiation, metallicity, surface gravity, C/O ratio, interior fluxes, and cloud opacity are discussed. Connections are made to the well-studied atmospheres of brown dwarfs as well as sub-Neptunes and terrestrial planets, where appropriate. Illustrative examples of model atmosp…
Until recently, infrared observations of exoplanetary atmospheres have typically been interpreted using models that assumed solar elemental abundances. With the chemical composition fixed, attempts have been made to classify hot Jupiter atmospheres on the basis of stellar irradiation. However, recent observations have revealed deviations from predictions based on such classification schemes, and chemical compositions retrieved from some datasets have also indicated non-solar abundances. In hot hydrogen-dominated atmospheres, the C/O ratio critically influences the relative concentrations of se…
Characterizing the atmospheres of extrasolar planets is the new frontier in exoplanetary science. The last two decades of exoplanet discoveries have revealed that exoplanets are very common and extremely diverse in their orbital and bulk properties. We now enter a new era as we begin to investigate the chemical diversity of exoplanets, their atmospheric and interior processes, and their formation conditions. Recent developments in the field have led to unprecedented advancements in our understanding of atmospheric chemistry of exoplanets and the implications for their formation conditions. We …
We apply the picket fence treatment to model the effects brought about by spectral lines on the thermal structure of irradiated atmospheres. The lines may be due to purely absorption processes, purely coherent scattering processes or some combination of absorption and scattering. If the lines arise as a pure absorption process, the surface layers of the atmosphere are cooler whereas this surface cooling is completely absent if the lines are due to pure coherent isotropic scattering. The lines also lead to a warming of the deeper atmosphere. The warming of the deeper layers is, however, indepen…
Transmission spectrum surveys have suggested the ubiquity of high-altitude clouds in exoplanetary atmospheres. Theoretical studies have investigated the formation processes of the high-altitude clouds; however, cloud particles have been commonly approximated as compact spheres, which is not always true for solid mineral particles that likely constitute exoplanetary clouds. Here, we investigate how the porosity of cloud particles evolve in exoplanetary atmospheres and influence the cloud vertical profiles. We first construct a porosity evolution model that takes into account the fractal aggrega…
Hot giant exoplanets are very exotic objects with no equivalent in the Solar System that allow us to study the behavior of atmospheres under extreme conditions. Their thermal and chemical day--night dichotomies associated with extreme wind dynamics make them intrinsically 3D objects. Thus, the common 1D assumption, relevant to study colder atmospheres, reaches its limits in order to be able to explain hot and ultra-hot atmospheres and their evolution in a consistent way. In this review, we highlight the importance of these 3D considerations and how they impact transit, eclipse and phase curve …
Spectroscopy of exoplanetary atmospheres has become a well established method for the characterisation of extrasolar planets. We here present a novel inverse retrieval code for exoplanetary atmospheres. TauRex (Tau Retrieval for Exoplanets) is a line-by-line radiative transfer fully Bayesian retrieval framework. TauRex includes the following features: 1) the optimised use of molecular line-lists from the Exomol project; 2) an unbiased atmospheric composition prior selection, through custom built pattern recognition software; 3) the use of two independent algorithms to fully sample the Bayesian…
Chemical compositions of exoplanets can provide key insights into their physical processes, and formation and evolutionary histories. Atmospheric spectroscopy provides a direct avenue to probe exoplanetary compositions. However, whether obtained in transit or thermal emission, spectroscopic observations probe limited pressure windows of planetary atmospheres and are directly sensitive to only a limited set of spectroscopically active species. It is therefore critical to have chemical models that can relate retrieved atmospheric compositions to an atmosphere's bulk physical and chemical state. …
The polarization state of starlight reflected by a planetary atmosphere uniquely reveals coverage, particle size, and composition of aerosols as well as changing cloud patterns. It is not possible to obtain a comparable level of detailed from flux-only observations. Furthermore, polarization observations can probe the atmosphere of planets independently of the orbital geometry (i.e., transiting and non-transiting planets). We show that a high-resolution spectropolarimeter with a broad wavelength coverage, particularly if attached to a large space telescope, would enable simultaneous study of t…
We investigated the impact of selected cloud condensates in exoplanetary atmospheres on the polarization of scattered stellar radiation. We considered a selection of 25 cloud condensates that are expected to be present in extrasolar planetary atmospheres. Using the three-dimensional Monte Carlo radiative transfer code POLARIS and assuming Mie scattering theory, we calculated and studied the net polarization of scattered radiation as a function of planetary phase angle at optical to near-infrared wavelengths. In addition to the well-known characteristics in the state of polarization, such as th…
Spectroscopic observations of exoplanets are leading to unprecedented constraints on their atmospheric compositions. However, molecular abundances derived from spectra are degenerate with the absorption cross sections which form critical input data in atmospheric models. Therefore, it is important to quantify the uncertainties in molecular cross sections to reliably estimate the uncertainties in derived molecular abundances. However, converting line lists into cross sections via line broadening involves a series of prescriptions for which the uncertainties are not well understood. We investiga…
Knowing the bulk elemental abundances of an exoplanetary atmosphere is not an easy task, but it is crucial to understand the formation history of planets. The purpose of this work is to show that the observability of TiO features at optical wavelengths in the transmission spectra of hot Jupiter atmospheres is sensitive to the bulk chemical properties of the atmosphere. For that, we run a grid of chemical models which include TiO formation and destruction, for the ultra-hot Jupiter WASP-19b and an ultra-hot version of HD~209458b. We take into account non-equilibrium chemistry and changes in the…
An important source of opacity in exoplanet atmospheres at short visible and near-UV wavelengths is Rayleigh scattering of light on molecules. It is accompanied by a related, albeit weaker process -- Raman scattering. We analyze the signatures of Raman scattering imprinted in the reflected light and the geometric albedo of exoplanets, which could provide information about atmospheric properties. Raman scattering affects the geometric albedo spectra of planets in following ways. Firstly, it causes filling-in of strong absorption lines in the incident radiation, thus producing sharp peaks in the…
We describe the recent updates to the ExoMol database regarding the molecular spectral line shapes. ExoMol provides comprehensive molecular line lists with a special emphasis on the applications involving characterization of atmospheres of exoplanets and cool stars. Among important requirements of such applications are (i) the broadening parameters for hydrogen and helium dominating atmospheres and (ii) very broad ranges of temperature and pressures. The current status of the available line shape data in the literature, demands from the exoplanetary community and their specific needs are discu…
We provide a new framework to model the day side and night side atmospheres of irradiated exoplanets using 1-D radiative transfer by incorporating a self-consistent heat flux carried by circulation currents (winds) between the two sides. The advantages of our model are its physical motivation and computational efficiency, which allows for an exploration of a wide range of atmospheric parameters. We use this forward model to explore the day and night side atmosphere of WASP-76~b, an ultra-hot Jupiter which shows evidence for a thermal inversion and Fe condensation, and WASP-43~b, comparing our …
We are entering the era of high-precision and high-resolution spectroscopy of exoplanets. Such observations herald the need for robust self-consistent spectral models of exoplanetary atmospheres to investigate intricate atmospheric processes and to make observable predictions. Spectral models of plane-parallel exoplanetary atmospheres exist, mostly adapted from other astrophysical applications, with different levels of sophistication and accuracy. There is a growing need for a new generation of models custom-built for exoplanets and incorporating state-of-the-art numerical methods and opacitie…
Context. Collecting a large variety of exoplanetary atmosphere measurements is crucial to improve our understanding of exoplanets. In this context, it is likely that the field would benefit from broad species surveys, particularly using transit spectroscopy, which is the most successful technique of exoplanetary atmosphere characterization so far. Aims: Our goal is to develop a model-unbiased technique using transit spectroscopy to analyze every qualified atomic spectral line in exoplanetary transit data, and search for relative absorption, that is, a decrease in the flux of the line when the …
Transmission spectroscopy can be used to constrain the properties of exoplanetary atmospheres. During a transit, the light blocked from the atmosphere of the planet leaves an imprint in the light coming from the star. This has been shown for many exoplanets with different techniques, with both photometry and spectroscopy. We aim at testing chromatic line-profile tomography as a new tool to investigate exoplanetary atmospheres. The signal imprinted on the cross-correlation function (CCF) by a planet transiting its star is dependent on the planet-to-star radius ratio. We want to verify if the pr…
We describe how the accurate characterization of exoplanetary atmospheres in the ELT and JWST era will inevitably require taking into consideration the stellar inhomogeneities caused by convection and magnetic fields. The existing evidence that demonstrates the mixture of stellar and planetary signatures in observed transiting spectra is presented. Finally, we discuss how to disentangle these two components through a multipronged approach that includes new solar reference spectra, improved MHD modeling, and synergistic collaborations between the communities involved, from solar to stellar and …
This work presents theoretical studies which combine aspects of combustion and explosion theory with exoplanetary atmospheric science. Super Earths could possess a large amount of molecular hydrogen depending on disk, planetary and stellar properties. Super Earths orbiting pre-main sequence-M-dwarf stars have been suggested to possess large amounts of O2 produced abiotically via water photolysis followed by hydrogen escape . If these two constituents were present simultaneously, such large amounts of H2 and O2 can react via photochemistry to form up to about 10 Earth oceans. In cases where pho…
Polarized scattering in planetary atmospheres is computed in the context of exoplanets. The problem of polarized radiative transfer is solved for a general case of absorption and scattering, while Rayleigh and Mie polarized scattering are considered as most relevant examples. We show that (1) relative contributions of single and multiple scattering depend on the stellar irradiation and opacities in the planetary atmosphere; (2) cloud (particle) physical parameters can be deduced from the wavelength-dependent measurements of the continuum polarization and from a differential analysis of molecul…
Sophisticated atmospheric retrieval algorithms, such as Nested Sampling, explore large parameter spaces by iterating over millions of radiative transfer (RT) calculations. Probability distribution functions for retrieved parameters are highly sensitive to assumptions made within the RT forward model. One key difference between RT models is the computation of the gaseous absorption throughout the atmosphere. We compare two methods of calculating gaseous absorption, cross-sections and correlated-$k$, by examining their resulting spectra of a number of typical \ce{H2}-He dominated exoplanetary an…
To understand the role that planet formation history has on the observable atmospheric carbon-to-oxygen ratio (C/O) we have produced a population of astrochemically evolving protoplanetary disks. Based on the parameters used in a pre-computed population of growing planets their combination allows us to trace the molecular abundances of the gas that is being collected into planetary atmospheres. We include atmospheric pollution of incoming (icy) planetesimals as well as the effect of refractory carbon erosion noted to exist in our own solar system. We find that the carbon and oxygen content of …
Transmission spectroscopy is an important technique to probe the atmospheres of exoplanets. With the advent of TESS and, in the future, of PLATO, more and more transiting planets around bright stars will be found and the observing time at large telescopes currently used to apply these techniques will not suffice. We demonstrate here that 2-m class telescopes equipped with spectrographs with high resolving power may be used for a certain number of potential targets. We obtained a time series of high-resolution FEROS spectra at the 2.2-m telescope at La Silla of the very hot Jupiter hosting plan…
We present an open-source and validated chemical kinetics code for studying hot exoplanetary atmospheres, which we name VULCAN. It is constructed for gaseous chemistry from 500 to 2500 K using a reduced C-H-O chemical network with about 300 reactions. It uses eddy diffusion to mimic atmospheric dynamics and excludes photochemistry. We have provided a full description of the rate coefficients and thermodynamic data used. We validate VULCAN by reproducing chemical equilibrium and by comparing its output versus the disequilibrium-chemistry calculations of Moses et al. and Rimmer & Helling. It rep…
The prevalence of clouds in currently observable exoplanetary atmospheres motivates the compilation and calculation of their optical properties. First, we present a new open-source Mie scattering code known as LX-MIE, which is able to consider large size parameters ($\sim 10^7$) using a single computational treatment. We validate LX-MIE against the classical MIEV0 code as well as previous studies. Second, we embark on an expanded survey of the published literature for both the real and imaginary components of the refractive indices of 32 condensate species. As much as possible, we rely on expe…
Radiatively Controlled Thermal Stability of High-Altitude Clouds in Exoplanetary Atmospheres
Meikei Gakuen High School（明海学园高等学校）；Division of Science, National Astronomical Observatory of Japan（日本国立天文台科学部）；Graduate Institute for Advanced Studies, SOKENDAI（SOKENDAI高等研究院）
The lowest-mass stars, brown dwarfs and extrasolar planets present challenges and opportunities for understanding dynamics and cloud formation processes in low-temperature atmospheres. For brown dwarfs, the formation, variation and rapid depletion of photospheric clouds in L- and T-type dwarfs, and spectroscopic evidence for non-equilibrium chemistry associated with vertical mixing, all point to a fundamental role for dynamics in vertical abundance distributions and cloud/grain formation cycles. For exoplanets, azimuthal heat variations and the detection of stratospheric and exospheric layers …
Supersonic flows are expected to exist in the atmospheres of irradiated exoplanets, but the question of whether shocks develop lingers. Specifically, it reduces to whether continuous flow in a closed loop may become supersonic and if some portions of the supersonic flow steepen into shocks. We first demonstrate that continuous, supersonic flow may exist in two flavors: isentropic and non-isentropic, with shocks being included in the latter class of solutions. Supersonic flow is a necessary but insufficient condition for shocks to develop. The development of a shock requires the characteristics…
This invited review for young researchers presents key ideas on cloud formation as key part for virtual laboratories for exoplanet atmospheres. The basic concepts are presented, followed by utilising a time-scale analysis to disentangle process hierarchies. The kinetic approach to cloud formation modelling is described in some detail to allow the discussion of cloud structures as prerequisite for future extrasolar weather forecasts.
A major motivation of spectroscopic observations of giant exoplanets is to unveil planet formation processes from atmospheric compositions. Several recent studies suggested that atmospheric nitrogen, like carbon and oxygen, can provide important constrains on planetary formation environments. Since nitrogen chemistry can be far from thermochemical equilibrium in warm atmospheres, we extensively investigate under what conditions, and with what assumptions, the observable NH3 abundances can diagnose an atmosphere's bulk nitrogen abundance. In the first paper of this series, we investigate atmosp…
Transiting exoplanets provide detailed access to their atmospheres, as the planet's signal can be effectively separated from that of its host star. For transiting exoplanets three fundamental atmospheric measurements are possible: transmission spectra - where atmospheric absorption features are detected across an exoplanets limb during transit, emission spectra - where the day-side average emission of the planet is detected during secondary eclipse events, and phase curves - where the spectral emission of the planet is mapped globally following the planet around its orbit. All of these techniq…
This dissertation as a whole aims to provide means to better understand hot-Jupiter planets through observing, performing thermochemical calculations, and modeling their atmospheres. We used Spitzer multi-wavelength secondary-eclipse observations and targets with high signal-to-noise ratios, as their deep eclipses allow us to detect signatures of spectral features and assess planetary atmospheric structure and composition with greater certainty. Chapter 1 gives a short introduction. Chapter 2 presents the Spitzer secondary-eclipse analysis and atmospheric characterization of WASP-14b. WASP-14b…
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 wid…
Planets can emit polarized thermal radiation, just like brown dwarfs. We present calculated thermal polarization signals from hot exoplanets, using an advanced radiative transfer code that fully includes all orders of scattering by gaseous molecules and cloud particles. The code spatially resolves the disk of the planet, allowing simulations for horizontally inhomogeneous planets. Our results show that the degree of linear polarization, P, of an exoplanet's thermal radiation is expected to be highest near the planet's limb and that this P depends on the temperature and its gradient, the scatte…
One of the desired outcomes of studying exoplanetary atmospheres is to set decisive constraints on exoplanet formation theories. Astronomers often speak of the "metallicity" in broad terms. When modeling the bulk metallicity, workers refer to the elemental iron abundance (Fe/H). By contrast, when exo-atmospheric astronomers speak of the "metallicity" derived from analysing low-resolution Hubble and Spitzer spectrophotometry, they are referring to the elemental abundances of oxygen (O/H), carbon (C/H) and nitrogen (N/H): in decreasing order of importance, since spectra from the Hubble Wide Fiel…
Atmospheric retrievals of exoplanetary transmission spectra provide important constraints on various properties such as chemical abundances, cloud/haze properties, and characteristic temperatures, at the day-night atmospheric terminator. To date, most spectra have been observed for giant exoplanets due to which retrievals typically assume H-rich atmospheres. However, recent observations of mini-Neptunes/super-Earths, and the promise of upcoming facilities including JWST, call for a new generation of retrievals that can address a wide range of atmospheric compositions and related complexities. …
We obtained over 90 hours of spectroscopic observations of four exoplanetary systems with the Hobby-Eberly Telescope (HET). Observations were taken in transit and out of transit, and we analyzed the differenced spectra---i.e., the transmission spectra---to inspect it for absorption at the wavelengths of the neutral sodium (\ion{Na}{1}) doublet at $λ\lambda5889, 5895$ and neutral potassium (\ion{K}{1}) at $\lambda7698$. We used the transmission spectrum at \ion{Ca}{1} $\lambda6122$---which shows strong stellar absorption but is not an alkali metal resonance line that we expect to show significa…
The large number of new planets expected from wide-area transit surveys means that follow-up transmission spectroscopy studies of their atmospheres will be limited by the availability of telescope assets. We argue that telescopes covering a broad range of apertures will be required, with even 1m-class instruments providing a potentially important contribution. Survey strategies that employ automated target selection will enable robust population studies. As part of such a strategy, we propose a decision metric to pair the best target to the most suitable telescope, and demonstrate its effectiv…
Exoplanetary atmospheres retrieval via a quantum extreme learning machine
Università degli Studi di Palermo, Dipartimento di Fisica e Chimica - Emilio Segrè（意大利帕尔马大学物理与化学系）；Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova（意大利帕多瓦大学伽利略·伽利莱物理与天文学系）；INAF Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）
Over the last twenty years, the search for extrasolar planets revealed us the rich diversity of the outcomes of the formation and evolution of planetary systems. In order to fully understand how these extrasolar planets came to be, however, the orbital and physical data we possess are not enough, and they need to be complemented with information on the composition of the exoplanets. Ground-based and space-based observations provided the first data on the atmospheric composition of a few extrasolar planets, but a larger and more detailed sample is required before we can fully take advantage of …
Thermal emission spectra of exoplanets provide constraints on the chemical compositions, pressure-temperature (P-T) profiles, and energy transport in exoplanetary atmospheres. Accurate inferences of these properties rely on the robustness of the atmospheric retrieval methods employed. While extant retrieval codes have provided significant constraints on molecular abundances and temperature profiles in several exoplanetary atmospheres, the constraints on their deviations from thermal and chemical equilibria have yet to be fully explored. Our present work is a step in this direction. We report H…
We present new methodological features and physical ingredients included in the 1D radiative transfer code HELIOS, improving the hemispheric two-stream formalism. We conduct a thorough intercomparison survey with several established forward models, including COOLTLUSTY, PHOENIX, and find satisfactory consistency with their results. Then, we explore the impact of (i) different groups of opacity sources, (ii) a stellar path length adjustment, and (iii) a scattering correction on self-consistently calculated atmospheric temperatures and planetary emission spectra. First, we observe that temperatu…
We present novel, analytical, equilibrium-chemistry formulae for the abundances of molecules in hot exoplanetary atmospheres that include the carbon, oxygen and nitrogen networks. Our hydrogen-dominated solutions involve acetylene (C$_2$H$_2$), ammonia (NH$_3$), carbon dioxide (CO$_2$), carbon monoxide (CO), ethylene (C$_2$H$_4$), hydrogen cyanide (HCN), methane (CH$_4$), molecular nitrogen (N$_2$) and water (H$_2$O). By considering only the gas phase, we prove that the mixing ratio of carbon monoxide is governed by a decic equation (polynomial equation of degree 10). We validate our solutions…
Atmospheric haze is the leading candidate for the flattening of expolanetary spectra, as it's also an important source of opacity in the atmospheres of solar system planets, satellites, and comets. Exoplanetary transmission spectra, which carry information about how the planetary atmospheres become opaque to stellar light in transit, show broad featureless absorption in the region of wavelengths corresponding to spectral lines of sodium, potassium and water. We develop a detailed atomistic model, describing interactions of atomic or molecular radiators with dust and atmospheric haze particulat…
Within the context of exoplanetary atmospheres, we present a comprehensive linear analysis of forced, damped, magnetized shallow water systems, exploring the effects of dimensionality, geometry (Cartesian, pseudo-spherical and spherical), rotation, magnetic tension and hydrodynamic and magnetic sources of friction. Across a broad range of conditions, we find that the key governing equation for atmospheres and quantum harmonic oscillators are identical, even when forcing (stellar irradiation), sources of friction (molecular viscosity, Rayleigh drag and magnetic drag) and magnetic tension are in…
We present the first exoplanet atmosphere detection made as part of the SPIRou Legacy Survey, a Large Observing Program of 300 nights exploiting the capabilities of SPIRou, the new near-infrared high-resolution (R ~ 70 000) spectro-polarimeter installed on the Canada-France-Hawaii Telescope (CFHT; 3.6-m). We observed two transits of HD 189733, an extensively studied hot Jupiter that is known to show prominent water vapor absorption in its transmission spectrum. When combining the two transits, we successfully detect the planet's water vapor absorption at 5.9 sigma using a cross-correlation t-t…
Optical phase curves have become one of the common probes of exoplanetary atmospheres, but the information they encode has not been fully elucidated. Building on a diverse body of work, we upgrade the Flexible Modeling System (FMS) to include scattering in the two-stream, dual-band approximation and generate plausible, three-dimensional structures of irradiated atmospheres to study the radiative effects of aerosols or condensates. In the optical, we treat the scattering of starlight using a generalisation of Beer's law that allows for a finite Bond albedo to be prescribed. In the infrared, we …
The past twenty years have revealed the diversity of planets that exist in the Universe. It turned out that most of exoplanets are different from the planets of our Solar System and thus, everything about them needs to be explored. Thanks to current observational technologies, we are able to determine some information about the atmospheric composition, the thermal structure and the dynamics of these exoplanets, but many questions remain still unanswered. To improve our knowledge about exoplanetary systems, more accurate observations are needed and that is why the Exoplanet Characterisation Obs…
It has been shown that spectroscopy of transiting extrasolar planets can potentially provide a wealth of information about their atmospheres. Herein, we set up the inverse problem in spectroscopic retrieval. We use non-linear optimal estimation to retrieve the atmospheric state (pioneered for Earth sounding by Rodgers 1976, 2000). The formulation quantifies the the degrees-of-freedom and information content of the spectrum with respect to geophysical parameters; herein, we focus specifically on temperature and composition. First, we apply the technique to synthetic near infrared spectra, and e…
Basic atmospheric properties such as albedo and heat redistribution between day and nightside have been inferred for a number of planets using observations of secondary eclipses and thermal phase curves. Optical phase curves have not yet been used to constrain these atmospheric properties consistently. We re-model previously published phase curves of CoRoT-1b, TrES-2b and HAT-P-7b and infer albedos and recirculation efficiencies. These are then compared to previous estimates based on secondary eclipse data. We use a physically consistent model to construct optical phase curves. This model take…
We report on a search for H-alpha absorption in four exoplanets. Strong features at H-alpha are observed in the transmission spectra of both HD 189733b and HD 209458b. We attempt to characterize and remove the effects of stellar variability in HD 189733b, and along with an empirical Monte Carlo test the results imply a statistically significant transit-dependent feature of (-8.72+/-1.48)x10^-4 integrated over a 16 Angstrom band relative to the adjacent continuum. We interpret this as the first detection of this line in an exoplanetary atmosphere. A previous detection of Ly-alpha in HD 189733b'…
