Found 33 talks width keyword exoplanets

Tuesday June 30, 2020
Luis Welbanks
Institute of Astronomy (University of Cambridge)


Atmospheric compositions can provide powerful diagnostics of formation and migration histories of planetary systems. In this talk, I will present the results of our latest survey of atmospheric compositions focused on atmospheric abundances of H2O, Na, and K. We employ a sample of 19 exoplanets spanning from cool mini-Neptunes to hot Jupiters, with equilibrium temperatures between ~300 and 2700 K. We employ the latest transmission spectra, new H2 broadened opacities of Na and K, and homogeneous Bayesian retrievals. We confirm detections of H2O in 14 planets and detections of Na and K in 6 planets each. Among our sample, we find a mass-metallicity trend of increasing H2O abundances with decreasing mass, spanning generally substellar values for gas giants and stellar/superstellar for Neptunes and mini-Neptunes. However, the overall trend in H2O abundances, is significantly lower than the mass-metallicity relation for carbon in the solar system giant planets and similar predictions for exoplanets. On the other hand, the Na and K abundances for the gas giants are stellar or superstellar, consistent with each other, and generally consistent with the solar system metallicity trend. The H2O abundances in hot gas giants are likely due to low oxygen abundances relative to other elements rather than low overall metallicities, and provide new constraints on their formation mechanisms. Our results show that the differing trends in the abundances of species argue against the use of chemical equilibrium models with metallicity as one free parameter in atmospheric retrievals, as different elements can be differently enhanced.

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Monday October 28, 2019
Dr. James Benford
Microwave Sciences


Breakthrough Starshot is an initiative by the Breakthrough Foundation to prove ultra-fast ultra-light nanospacecraft can be launched by laser radiation pressure to nearby stars, and will lay the foundations for a first launch to Alpha Centauri within the next generation. Designs for a 0.2c Alpha Centauri mission minimize beam director capital cost by accelerating a ~4 m, several gram diameter sailcraft for ~10 min. A number of hard engineering challenges remain to be solved before these missions can become a reality: Large coherent laser arrays are required. No consensus has been reached on the most suitable sail geometry for stable flight, “beam-riding”. The sail itself requires major advances in materials science and photonic design to produce materials with the required absorptance, emittance, reflectance, areal density and operating temperature. Along the way, the project will enable increasingly fast outer solar system and interstellar precursor missions. Breakthrough Starshot will pave the way for multi-lightyear pipelines of sailcraft that fly past each target star every few weeks. Beams such as Starshot will produce an extremely observable transient feature of Earth and therefore could be an observable of extraterrestrial advanced civilizations.

Tuesday September 12, 2017
Dr. Monika Lendl
Austrian Academy of Sciences, Space Research Institute


Planetary transits have proven to be one of the most efficient means of finding planets outside the Solar system, counting over 2500 exoplanet discoveries. These transiting planets are paramount for the study of exoplanet atmospheres as the stellar light is filtered through the planetary atmosphere during transit and planetary absorption signatures become imprinted on the stellar spectrum. Observations of hot-Jupiter transmission spectra have become increasingly numerous and reliable throughout recent years, allowing detailed constrains on the planet's physical and chemical atmospheric properties, interactions between planet and host star, and planet formation history. While early work relied largely on space-based facilities, ground-based techniques have seen major advances recently and have become instrumental in performing an extensive and comparative study of exoplanet atmospheres. I will review the current state of knowledge, summarize recent results and discuss future prospects of exoplanet characterization, with a focus on the potential of ground-based facilities. In particular, I will present recent and new results by our team on the transmission spectra of hot Jupiters.

Thursday July 9, 2015
Mr. Néstor Espinoza
Pontificia Universidad Católica de Chile


One of the most exciting possibilities enabled by transiting exoplanets is to measure their atmospheric properties through the technique of transmission spectroscopy: the variation of the transit depth as a function of wavelength due to starlight interacting with the atmosphere of the exoplanet. Motivated by the need of optical transmission spectra of exoplanets, we recently launched the Arizona-CfA-Católica Exoplanet Spectroscopy Survey (ACCESS), which aims at studying the atmospheres of ~20 exoplanets ranging from super-Earths to hot-Jupiters in the entire optical atmospheric window using ground-based facilities. In this talk, I will present the survey, the astrostatistical challenges it poses and first results.

Thursday June 11, 2015
Dr. Federico Marocco
University of Hertforshire


 A comprehensive understanding of sub-stellar objects (brown dwarfs and extrasolar giant planets) and their population characteristics (e.g. IMF, formation history) is only possible through the robust interpretation of ultra-cool objects spectroscopy. However, the physics of ultra-cool atmospheres is complicated by a variety of challenging ingredients (dust properties, non-equilibrium chemistry, molecular opacities). Moreover, while hydrogen-burning stars stabilize on the stellar main-sequence, sub-stellar objects continuously cool down (since they lack an internal source of energy) and evolve towards later spectral types. Their atmospheric parameters are a strong function of age. In this talk I will present the spectroscopic analysis of a large sample of L and T dwarfs, complementing the spectroscopic data with astrometry from the PARSEC program, in order to constrain the sub-stellar initial mass function and formation history. I will then describe our new effort to identify and characterize a large sample of benchmark systems, combining Gaia capabilities with large area near-infrared surveys such as UKIDSS, SDSS, and VVV, in order to calibrate effectively the theoretical models.

Tuesday March 17, 2015
Mr. Bartek Gauza


Direct imaging of wide planetary mass companions provide a unique opportunity to fully characterize their spectroscopic and photometric properties. They share similar physical properties to gas giant exoplanets found by radial velocity and transit techniques, with overlapping temperatures in the range of ~1000–1500K and masses from a few to a dozen Jupiter masses. We have recently identified a young L-type companion at ~100 AU of a previously unrecognized M dwarf. We determined the parallactic distance of the system of 12.7 ± 1.0 pc. By comparison with evolutionary models we derived a mass of 73 (+20, -15) MJup for the primary, at around the substellar mass limit and 11.2 (+9.7, -1.8) MJup for the secondary, near the deuterium burning mass limit. In this talk I will present the properties of the two components of this new pair and discuss the possibilities for future thorough characterization.

Tuesday February 10, 2015
Dr. Hannu Parviainen
University of Oxford


Detection and characterisation of weak periodic signals from noisy time series is a common problem in many different fields of astrophysics. Here I detail one approach for testing whether a signal with roughly known characteristics exists in the data, using a search of secondary eclipses from Kepler-observed photometric time series as an example. The method is based on Bayesian model selection and uses Gaussian processes to model the stochastic variability in the data in non-parametric fashion.

Thursday January 29, 2015
Dr. France Allard
Centre de Recherche Astronomique de Lyon


Understanding the atmospheric and evolutive properties of very low mass stars, brown dwarfs, and gas giant exoplanets have been important challenges for modelers around the world since the discovery of the first brown dwarfs in the Pleiades cluster (Rebolo et al. 1995) and in the field (Nakajima et al. 1995). The early studies of brown dwarfs have provided rich insights into atmospheric physics, with discoveries ranging from cloud formation (Tsuji et al. 1996), methane bands (Oppenheimer et al. 1995) and ammonia bands (Delorme et al. 2008), to the formation of wasi-molecular KI-H2 absorption (Allard et al. 2007), and to disequilibrium chemistry (Yelle & Griffith 2001). New classical 1D models yield spectral energy distribution (SED) that match relatively well despite these complexities. These models have for instance explained the spectral transition from M to L, T and now Y brown dwarf spectral types (Allard et al. 2013). However, in presence of surface inhomogeneities revealed recently for a nearby (2 pc) brown dwarf (Crossfield et al. 2014), the SED may well fit even exactly, but the model parameters could be far from exact, e.g. with the effective temperature by several hundred kelvins too cool in the case of dusty brown dwarfs and young gas giant exoplanets! I will review the progress achieved in reproducing the spectral properties of very low mass stars, brown dwarfs and gas giant exoplanets, and review progress in modeling more accurately their atmospheres using Radiation HydroDynamical (RHD) simulations.

Tuesday December 2, 2014
Prof. Tsevi Mazeh
Tel Aviv University


The angle between the stellar spin axis and the orbital planetary angular momentum of a planet, also referred to as the obliquity of the system, is a matter of intense study in recent years, for the transiting planets of the Kepler mission in particular. Some evidence was found for two populations of hot Jupiters - one around cool stars with orbits well-aligned with the stellar rotational axes, and the other one around hot stars with isotropic distribution of obliquities, including planets with retrograde motion. It was suggested that the primordial planetary obliquity is isotropic, and cool stars have reached their zero-obliquity state by tidal re-alignment.

The talk will summarize the observational techniques for measuring planetary obliquities, and the different theoretical approaches to interpret this new, unexpected feature of exo-planet population. Finally, I will present a surprising statistical new result that emerges from the study of Kepler light curves of stellar rotation, suggesting the alignment of cool stars is probably not the result of tidal interaction.

Thursday October 23, 2014
Prof. Sara Seager


The discovery and characterization of exoplanets have the potential to offer the world one of the most impactful findings ever in the history of astronomy?the identification of life beyond Earth. Life can be inferred by the presence of atmospheric biosignature gases? Gases produced by life that can accumulate to detectable levels in an exoplanet atmosphere. Detection will be made by remote sensing by sophisticated space telescopes. The conviction that biosignature gases will actually be detected in the future is moderated by lessons learned from the dozens of exoplanet atmospheres studied in last decade, namely the difficulty in robustly identifying molecules, the possible interference of clouds, and the permanent limitations from a spectrum of spatially unresolved and globally mixed gases without direct surface observations. The vision for the path to assess the presence of life beyond Earth is being established.

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