TY - THES A1 - Alexoudi, Xanthippi T1 - Clarifying the discrepant results in the characterization of exoplanetary atmospheres T1 - Klärung der widersprüchlichen Ergebnisse bei der Charakterisierung von exoplaneten Atmosphären N2 - Planets outside our solar system, so-called "exoplanets", can be detected with different methods, and currently more than 5000 exoplanets have been confirmed, according to NASA Exoplanet Archive. One major highlight of the studies on exoplanets in the past twenty years is the characterization of their atmospheres usingtransmission spectroscopy as the exoplanet transits. However, this characterization is a challenging process and sometimes there are reported discrepancies in the literature regarding the atmosphere of the same exoplanet. One potential reason for the observed atmospheric inconsistencies is called impact parameter degeneracy, and it is highly driven by the limb darkening effect of the host star. A brief introductionto those topics in presented in chapter 1, while the motivation and objectives of thiswork are described in chapter 2.The first goal is to clarify the origin of the transmission spectrum, which is anindicator of an exoplanet’s atmosphere; whether it is real or influenced by the impactparameter degeneracy. A second goal is to determine whether photometry from space using the Transiting Exoplanet Survey Satellite (TESS), could improve on the major parameters, which are responsible for the aforementioned degeneracy, of known exoplanetary systems. Three individual projects were conducted in order toaddress those goals. The three manuscripts are presented, in short, in the manuscriptoverview in chapter 3.More specifically, in chapter 4, the first manuscript is presented, which is an ex-tended investigation on the impact parameter degeneracy and its application onsynthetic transmission spectra. Evidently, the limb darkening of the host star isan important driver for this effect. It keeps the degeneracy persisting through different groups of exoplanets, based on the uncertainty of their impact parameter and on the type of their host star. The second goal, was addressed in the second and third manuscripts (chapter 5 and chapter 6 respectively). Using observationsfrom the TESS mission, two samples of exoplanets were studied; 10 transiting inflated hot-Jupiters and 43 transiting grazing systems. Potentially, the refinement or confirmation of their major system parameters’ measurements can assist in solving current or future discrepancies regarding their atmospheric characterization.In chapter 7 the conclusions of this work are discussed, while in chapter 8 itis proposed how TESS’s measurements can be able to discern between erroneousinterpretations of transmission spectra, especially on systems where the impact parameter degeneracy is likely not applicable. N2 - Planeten außerhalb unseres Sonnensystems, sogenannte Exoplaneten", lassen sichmit verschiedenen Methoden aufspüren, und nach Angaben des NASA ExoplanetArchive wurden bisher mehr als 5000 Exoplaneten bestätigt. Ein großer Höhepunktder Studien über Exoplaneten in den letzten zwanzig Jahren ist die Charakterisierung ihrer Atmosphäre mit Hilfe der Methode der Transmissionsspektroskopie. Diese Charakterisierung ist jedoch ein schwieriger Prozess, und manchmal wird in derLiteratur für den gleichen Planeten unterschiedliche Resultate bezüglich seiner Systemparameter gezeigt. Ein möglicher Grund für die beobachteten atmosphärischen Unstimmigkeiten könnte durch die Entartung des Impaktparameters herrühren, diein hohem Maße durch den Verdunkelungseffekt des Muttersterns beeinflusst wird.Eine kurze Einführung in diese Themen wird in Kapitel 1 gegeben, während die Motivation und die Ziele dieser Arbeit in Kapitel 2 beschrieben werden.Das erste Ziel dieser Arbeit ist die Klärung der Herkunft von Merkmalen im Transmissionsspektrum, die Indikatoren für die Atmosphäre eines Exoplaneten sind; obsie real sind oder durch die Entartung des Impaktparameters beeinflusst werden. Einzweites Ziel ist es, festzustellen, ob die Photometrie aus dem Weltraum mit Hilfe desTransiting Exoplanet Survey Satellite (TESS) die atmosphärischen Systemparameter bekannter Exoplanetensysteme verbessern könnte. Drei Einzelprojekte wurdendurchgeführt, um diese Ziele zu erreichen. Die drei Manuskripte werden in der Manuskriptübersicht in Kapitel 3 kurz vorgestellt.Genauer gesagt, wird in Kapitel 4 das erste Manuskript vorgestellt, welches eineerweiterte Untersuchung der Entartung des Impaktparameters und seine Anwendungauf synthetische Transmissionsspektren darstellt. Offensichtlich ist die Randverdunkelung des Muttersterns ein wichtiger Treiber für diesen Effekt. Sie sorgt dafür, dass die Entartung über verschiedene Gruppen von Exoplaneten, die auf der Unsicherheitihrer Impaktparameters und dem Typ ihres Muttersterns beruhen, auftaucht. Daszweite Ziel wurde im zweiten und dritten Manuskript behandelt (Kapitel 5 und Kapitel 6, jeweils). Anhand von Beobachtungen der TESS-Mission wurden zwei Populationen von Exoplaneten untersucht: zehn transitierende, aufgeblähte heiße-Jupiter Planeten und 43 nicht-zentral transitierende. Möglicherweise kann die Verbesserungoder Bestätigung der Messungen der wichtigsten Systemparameter dazu beitragen,aktuelle oder zukünftige Diskrepanzen bei der Charakterisierung ihrer Atmosphärezu lösen.In Kapitel 7 werden die Schlussfolgerungen dieser Arbeit erörtert, während inKapitel 8 diskutiert wird, wie die Messungen von TESS in der Lage sein können,zwischen fehlerhaften Interpretationen von Transmissionsspektren zu unterscheiden,insbesondere bei Systemen, bei denen die Entartung des Impaktparameters wahrscheinlich nicht zutrifft. KW - Exoplaneten KW - exoplanets KW - atmosphere KW - Atmosphäre KW - photometry KW - Photometrie KW - transmission spectroscopy KW - Transmissionsspektroskopie KW - observations with TESS KW - Beobachtungen mit TESS Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-605659 ER - TY - JOUR A1 - Alexoudi, Xanthippi T1 - On the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations JF - Astronomische Nachrichten = Astronomical notes N2 - We revisited 10 known exoplanetary systems using publicly available data provided by the transiting exoplanet survey satellite (TESS). The sample presented in this work consists of short period transiting exoplanets, with inflated radii and large reported uncertainty on their planetary radii. The precise determination of these values is crucial in order to develop accurate evolutionary models and understand the inflation mechanisms of these systems. Aiming to evaluate the planetary radius measurement, we made use of the planet-to-star radii ratio, a quantity that can be measured during a transit event. We fit the obtained transit light curves of each target with a detrending model and a transit model. Furthermore, we used emcee, which is based on a Markov chain Monte Carlo approach, to assess the best fit posterior distributions of each system parameter of interest. We refined the planetary radius of WASP-140 b by approximately 12%, and we derived a better precision on its reported asymmetric radius uncertainty by approximately 86 and 67%. We also refined the orbital parameters of WASP-120 b by 2 sigma. Moreover, using the high-cadence TESS datasets, we were able to solve a discrepancy in the literature, regarding the planetary radius of the exoplanet WASP-93 b. For all the other exoplanets in our sample, even though there is a tentative trend that planetary radii of (near-) grazing systems have been slightly overestimated in the literature, the planetary radius estimation and the orbital parameters were confirmed with independent observations from space, showing that TESS and ground-based observations are overall in good agreement. KW - planetary systems KW - techniques KW - photometric KW - stars KW - WASP-140 KW - HAT-P-16 KW - WASP-108 KW - WASP-113 KW - WASP-120 KW - WASP-123 KW - WASP-136 KW - WASP-20 KW - WASP-76 KW - WASP-93 Y1 - 2022 U6 - https://doi.org/10.1002/asna.20224012 SN - 0004-6337 SN - 1521-3994 VL - 343 IS - 3 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Keles, Engin A1 - Kitzmann, Daniel A1 - Mallonn, Matthias A1 - Alexoudi, Xanthippi A1 - Fossati, Luca A1 - Pino, Lorenzo A1 - Seidel, Julia Victoria A1 - Caroll, Thorsten A. A1 - Steffen, M. A1 - Ilyin, Ilya A1 - Poppenhäger, Katja A1 - Strassmeier, Klaus G. A1 - von Essen, Carolina A1 - Nascimbeni, Valerio A1 - Turner, Jake D. T1 - Probing the atmosphere of HD189733b with the Na i and K i lines JF - Monthly Notices of the Royal Astronomical Society N2 - High spectral resolution transmission spectroscopy is a powerful tool to characterize exoplanet atmospheres. Especially for hot Jupiters, this technique is highly relevant, due to their high-altitude absorption, e.g. from resonant sodium (Na i) and potassium (K i) lines. We resolve the atmospheric K i absorption on HD189733b with the aim to compare the resolved K i line and previously obtained high-resolution Na i-D line observations with synthetic transmission spectra. The line profiles suggest atmospheric processes leading to a line broadening of the order of ∼10 km/s for the Na i-D lines and only a few km/s for the K i line. The investigation hints that either the atmosphere of HD189733b lacks a significant amount of K i or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences we see in the resolved absorption lines. Y1 - 2020 U6 - https://doi.org/10.1093/mnras/staa2435 VL - 498 IS - 1 SP - 1033 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Alexoudi, Xanthippi A1 - Mallonn, Matthias A1 - Keles, Engin A1 - Poppenhäger, Katja A1 - von Essen, Carolina A1 - Strassmeier, Klaus T1 - Role of the impact parameter in exoplanet transmission spectroscopy JF - Astronomy and astrophysics : an international weekly journal N2 - Context Transmission spectroscopy is a promising tool for the atmospheric characterization of transiting exoplanets. Because the planetary signal is faint, discrepancies have been reported regarding individual targets. Aims We investigate the dependence of the estimated transmission spectrum on deviations of the orbital parameters of the star-planet system that are due to the limb-darkening effects of the host star. We describe how the uncertainty on the orbital parameters translates into an uncertainty on the planetary spectral slope. Methods We created synthetic transit light curves in seven different wavelength bands, from the near-ultraviolet to the near-infrared, and fit them with transit models parameterized by fixed deviating values of the impact parameter b. First, we performed a qualitative study to illustrate the effect by presenting the changes in the transmission spectrum slope with different deviations of b. Then, we quantified these variations by creating an error envelope (for centrally transiting, off-center, and grazing systems) based on a derived typical uncertainty on b from the literature. Finally, we compared the variations in the transmission spectra for different spectral types of host stars. Results Our simulations show a wavelength-dependent offset that is more pronounced at the blue wavelengths where the limb-darkening effect is stronger. This offset introduces a slope in the planetary transmission spectrum that becomes steeper with increasing b values. Variations of b by positive or negative values within its uncertainty interval introduce positive or negative slopes, thus the formation of an error envelope. The amplitude from blue optical to near-infrared wavelength for a typical uncertainty on b corresponds to one atmospheric pressure scale height and more. This impact parameter degeneracy is confirmed for different host types; K stars present prominently steeper slopes, while M stars indicate features at the blue wavelengths. Conclusions We demonstrate that transmission spectra can be hard to interpret, basically because of the limitations in defining a precise impact parameter value for a transiting exoplanet. This consequently limits a characterization of its atmosphere. KW - planets and satellites: atmospheres KW - planets and satellites: gaseous KW - planets Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-605378 SN - 0004-6361 SN - 1432-0746 VL - 640 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Keles, Engin A1 - Mallom, Matthias A1 - von Essen, Carolina A1 - Caroll, Thorsten A. A1 - Alexoudi, Xanthippi A1 - Pino, Lorenzo A1 - Ilyin, Ilya A1 - Poppenhäger, Katja A1 - Kitzmann, Daniel A1 - Nascimbeni, Valerino A1 - Turner, Jake D. A1 - Strassmeier, Klaus G. T1 - The potassium absorption on HD189733b and HD209458b JF - Monthly Notices of the Royal Astronomical Society: Letters N2 - In this work, we investigate the potassium excess absorption around 7699 Å of the exoplanets HD189733b and HD209458b. For this purpose, we used high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 Å, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though we do not detect a K-excess absorption. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b. This comparison confirms previous claims that the atmospheres of these two planets must have fundamentally different properties. Y1 - 2021 U6 - https://doi.org/10.1093/mnrasl/slz123 VL - 489 IS - 1 SP - L37 EP - L41 PB - Oxford Univ. Press CY - Oxford ER -