Search for additional bodies with the transit timing method

Unter den derzeit bekannten extrasolaren Planeten gibt es eine Anzahl von Systemen, deren Umlaufebenen so ausgerichtet sind, dass sie die Sichtlinie auf den Stern durchkreuzen. Passiert dies, so wird für den Beobachter ist eine kurzzeitige Verdunkelung des Sterns messbar. Das Studium dieser planetaren Transits bietet uns die Möglichkeit, fundamentale Parameter des Planeten, nämlich Masse, Radius und Bahninklination, festzulegen. Auch eröffnen uns Transits die Möglichkeit, die Periode des Planeten mit großer Genauigkeit zu messen und dadurch kleine Variationen in dieser festzustellen, Variationen die durch den gravitativen Einfluss weiterer Körper im Planetensystem insbesondere weiterer eventuell erdähnlicher Planeten) entstehen können. In dieser Arbeit untersuche ich das System OGLE2-TR-L9 nach derartigen Variationen und bestimme die Parameter des Planeten an Hand der neuen Daten neu.In the study of transiting exoplanets the re-observation of known extrasolar planets has a number of benefits, since it allows to constrain the system parameters, as well as gather a set of central transit times which can be used to reveal the presence of so called transit-timing-variations. These variations in the central transit time and consequently in the planetary period which can be attributed to additional bodies, such as moons, Trojans and additional planets. In this work, I probe the system OGLE2-TR-L9 for such variations and use the data collected to redetermine the system parameters

High Precision Photometry from EulerCam and TRAPPIST: The Case of WASP-42, WASP-49 and WASP-50

Transiting extrasolar planets provide unmatched insights into the structure and composition of close-in planets. When a planet transits its host star, its radius is known, which together with radial velocity measurements, allows accessing the planetary density. We present results obtained using the Euler and TRAPPIST telescopes that aim at reaching very high accuracy on the parameters derived from transit lightcurves. Here, we show the case of the recently discovered WASP-42b and WASP-49b and new observations of WASP-50

The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats

Since the Archean, N2 has been a major atmospheric constituent in Earth's atmosphere. Nitrogen is an essential element in the building blocks of life, therefore the geobiological nitrogen cycle is a fundamental factor in the long term evolution of both Earth and Earth-like exoplanets. We discuss the development of the Earth's N2 atmosphere since the planet's formation and its relation with the geobiological cycle. Then we suggest atmospheric evolution scenarios and their possible interaction with life forms: firstly, for a stagnant-lid anoxic world, secondly for a tectonically active anoxic world, and thirdly for an oxidized tectonically active world. Furthermore, we discuss a possible demise of present Earth's biosphere and its effects on the atmosphere. Since life forms are the most efficient means for recycling deposited nitrogen back into the atmosphere nowadays, they sustain its surface partial pressure at high levels. Also, the simultaneous presence of significant N2 and O2 is chemically incompatible in an atmosphere over geological timescales. Thus, we argue that an N2-dominated atmosphere in combination with O2 on Earth-like planets within circumstellar habitable zones can be considered as a geo-biosignature. Terrestrial planets with such atmospheres will have an operating tectonic regime connected with an aerobe biosphere, whereas other scenarios in most cases end up with a CO2-dominated atmosphere. We conclude with implications for the search for life on Earth-like exoplanets inside the habitable zones of M to K-stars

The Peculiar Atmospheric Chemistry of KELT-9b

The atmospheric temperatures of the ultra-hot Jupiter KELT-9b straddle the transition between gas giants and stars, and therefore between two traditionally distinct regimes of atmospheric chemistry. Previous theoretical studies assume the atmosphere of KELT-9b to be in chemical equilibrium. Despite the high ultraviolet flux from KELT-9, we show using photochemical kinetics calculations that the observable atmosphere of KELT-9b is predicted to be close to chemical equilibrium, which greatly simplifies any theoretical interpretation of its spectra. It also makes the atmosphere of KELT-9b, which is expected to be cloudfree, a tightly constrained chemical system that lends itself to a clean set of theoretical predictions. Due to the lower pressures probed in transmission (compared to emission) spectroscopy, we predict the abundance of water to vary by several orders of magnitude across the atmospheric limb depending on temperature, which makes water a sensitive thermometer. Carbon monoxide is predicted to be the dominant molecule under a wide range of scenarios, rendering it a robust diagnostic of the metallicity when analyzed in tandem with water. All of the other usual suspects (acetylene, ammonia, carbon dioxide, hydrogen cyanide, methane) are predicted to be subdominant at solar metallicity, while atomic oxygen, iron and magnesium are predicted to have relative abundances as high as 1 part in 10,000. Neutral atomic iron is predicted to be seen through a forest of optical and near-infrared lines, which makes KELT-9b suitable for high-resolution ground-based spectroscopy with HARPS-N or CARMENES. We summarize future observational prospects of characterizing the atmosphere of KELT-9b.Comment: Accepted by ApJ. 9 pages, 6 figures. Corrected minor errors in Figures 1a and 1b (some line styles were switched by accident), text and conclusions unchanged, these minor changes will be updated in final ApJ proo

Studying the Atmospheres of the Most Intriguing WASP Hot Jupiters

Among the over 300 transiting planets confirmed to date, approximately 130 have been found by groundbased wide angle transit surveys such asWASP. While these surveys are not sensitive enough to detect lowmass planets, they excel at picking out rare hot- Jupiters orbiting reasonably bright stars (V mag = 9 - 11) across the sky. These planets occupy a favorable region in parameter space, as they show frequent and deep transits. Due to the proximity to their host stars these gas giants possess hot extended atmospheres making them ideal targets for the study of their atmospheres via transmission and occultation spectrophotometry. During occultation, the flux emerging from the planetary dayside is eliminated. By comparing the flux in- and out-of occultation, the planet-to-star brightness ratio can be measured. Observations in different passbands yield a measure of the planetary spectral energy distribution and thereby allow to determine the atmospheric temperature structure, heat redistribution efficiency, albedo, and to place constraints on the atmospheric composition. From the spectro-photometric observation of transits, we can measure wavelength dependencies in the effective planetary radius that are sensitive to signatures of chemical elements in the planetary atmosphere. We present results of ongoing observing campaigns employing these methods to study the atmospheres of hot Jupiters discovered by the WASP survey. In particular we show results for the very short-period planet WASP-19b based on data from the 1m-class Euler-Swiss and TRAPPIST telescopes, as well as a transmission spectrum of the low-density hot Saturn WASP-49b obtained from FORS2 at the VLT/UT1

SAGE: A tool to constrain impacts of stellar activity on transmission spectroscopy

Transmission spectroscopy is a proven technique to study a transiting exoplanet's atmosphere. However, stellar surface inhomogeneities, spots and faculae, alter the observed transmission spectra: the stellar contamination effect. The variable nature of the stellar activity also makes it difficult to stitch together multi-epoch observations and evaluate any potential variability in the exoplanet's atmosphere. This paper introduces SAGE, a tool to correct for the time-dependent impact of stellar activity on transmission spectra. It uses a pixelation approach to model the stellar surface with spots and faculae, while fully accounting for limb-darkening and rotational line-broadening. The current version is designed for low to medium-resolution spectra. We used SAGE to evaluate stellar contamination for F to M-type hosts, testing various spot sizes and locations, and quantify the impact of limb-darkening. We find that limb-darkening enhances the importance of the spot location on the stellar disk, with spots close to the disk center impacting the transmission spectra more strongly than spots near the limb. Moreover, due to the chromaticity of limb darkening, the shape of the contamination spectrum is also altered. Additionally, SAGE can be used to retrieve the properties and distribution of active regions on the stellar surface from photometric monitoring. We demonstrate this for WASP-69 using TESS data, finding that two spots at mid-latitudes and a combined coverage fraction of $\sim$1% are favoured. SAGE allows us to connect the photometric variability to the stellar contamination of transmission spectra, enhancing our ability to jointly interpret transmission spectra obtained at different epochs.Comment: Accepted for publication in A&

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 its spectra and rotation period reveal the star to be young, with an age of 200−200+400 Myr. TOI-8l5b has a 11.2-day period and a radius of 2.94 ± 0.05 R⊕ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-8l5c, has a radius of 2.62 ± 0.10 R⊕, based on observations of three nonconsecutive transits with TESS; 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 ± 1.5 M⊕ (ρP = 1.64−0.31+0.33 g cm−3) and 23.5 ± 2.4 M⊕ (ρP = 7.2−1.0+1.1 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for 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 undergoing 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 that constitutes 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 3σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history