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Observation and Analysis of Transits of TRAPPIST-1 Systems

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Observation and Analysis of Transits of TRAPPIST-1 Systems http://lib.uliege.be https://matheo.uliege.be Observation and analysis of transits of TRAPPIST-1 systems Auteur : Thimmarayappa, Darshini Promoteur(s) : Gillon, Michaël Faculté : Faculté des Sciences Diplôme : Master en sciences spatiales, à finalité approfondie Année académique : 2017-2018 URI/URL : http://hdl.handle.net/2268.2/5544 Avertissement à l'attention des usagers : Tous les documents placés en accès ouvert sur le site le site MatheO sont protégés par le droit d'auteur. Conformément aux principes énoncés par la "Budapest Open Access Initiative"(BOAI, 2002), l'utilisateur du site peut lire, télécharger, copier, transmettre, imprimer, chercher ou faire un lien vers le texte intégral de ces documents, les disséquer pour les indexer, s'en servir de données pour un logiciel, ou s'en servir à toute autre fin légale (ou prévue par la réglementation relative au droit d'auteur). 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University of Liège Faculty of Sciences Exoplanets in Transit: Identification and Characterization (ExoTIC) Observation and analysis of transits of TRAPPIST-1 systems Master Thesis in Space Sciences Research Focus Author: Supervisor: Darshini Thimmarayappa Dr. Michaël Gillon Academic year 2017-2018 ii Acknowledgements I owe my deepest gratitude to Dr. Michaël Gillon, for always inspiring me, motivating me and teaching me at every step of my thesis. He always believed in me from the day I walked into his door asking to be a part of this up to now. I also thank him for his constant availability to clear all my doubts and for always keeping his door open for me. His advises and numerous readings of my drafts helped produce a better thesis. I think he’s the best mentor that I could have asked for. I am also deeply grateful to Mr Artem Burdanov, Miss Elsa Ducrot for helping me out whenever I had doubts about my work and for fruitful discussions of the results. I would like to thank them for their patience and for clearing my doubts in spite of their busy schedule. I would also like to thank Miss Sandrine Sohy who helped solve all my queries related to programming. I would like to thank Mr Amaury Triaud for giving me this opportunity to use the data for my reduction and also for many of his suggestions and remarks on the results obtained in my thesis. I thank all the staff members of the space science department and my friends for helping me throughout the course and for this wonderful experience. Last but not the least, I would like to thank my parents Mr. Thimmarayapaa T and Mrs. Pushpavathi for showing constant support from India and for encouraging me throughout. I owe them my deepest gratitude as it would not have been possible for me to come to Belgium from India and pursue my masters. iii iv Abstract My chosen topic for this thesis is the newly discovered TRAPPIST-1 planetary system with its seven planets revolving around the nearby ultracool dwarf star. The main need to focus on the TRAPPIST-1 system is to refine the masses of the seven planets, to constrain their composition and also their dynamics. In order to do that we use the measured tran- sit timing variations (TTVs) to constrain their masses, orbits and hence refine the transit parameters through analysis. Measured TTVs are used to detect a change in the orbital period of each planet caused by gravitational pull of the planets in a resonant chain, this causes the planets to accelerate and decelerate along its orbit in a packed planetary system and therefore change the orbital period. We also reduce the photometric data obtained from the Liverpool telescope over the time span of 2017/05/31 to 2017/10/28. The photometric data obtained consists of 19 light curves and each of these light curves were analyzed individually and then a global analysis was performed on all the transits pertaining to a single planet. The individual and global analysis was performed with the most recent version of the adaptive Markov Chain Monte-Carlo (MCMC) code developed by M. Gillon. For the reduction of the data, we first performed differential photometry to measure the flux of our target star with respect to a standard star in the field of view and eventually from this we obtain the dip in the value of the measured flux of a star during a planetary transit. Individual analysis is performed for each light curve to obtain the astrophysical and instrumental effects observed at the photometric variation level and finally we perform global analysis for a set of light curves obtained for the same planet. Both individual and global analysis is done in a preliminary chain of 10,000 steps and a secondary chain of 100,000 steps. In the global analysis, we improve the accuracy of the system parameters, de-trended light curves along with photometric representations which are also included in the report. The global analysis result for TRAPPIST-1b gave us a transit duration of 0.025 ±0.00050 days with its 1 σ limit of the posterior PDF, similarly we have a value of 0.029±0.00076 days for TRAPPIST-1c and a value of 0.0388±0.00075 days for TRAPPIST-1e. These values are in good agreement with the values obtained from the Spitzer analysis. These timings will be useful to constrain further the dynamics of the TRAPPIST-1 system and the masses and compositions of its planets. We also compare the results with the already reduced Spritzer results, to check the accuracy of the results obtained from the Liverpool telescope. Some of our results are presented in the paper "The 0.6-4.55m broadband transmission spectra of TRAPPIST-1 planets" (Ducrot et al. 2018, under review). v vi Contents Introduction 1 Habitability of planets and the habitable zone . .3 Classification of exoplanets . .4 1 Transiting planets: treasures in the sky 7 1.1 Transit method . .8 1.2 Physical parameters . 10 1.3 Limb darkening . 11 1.4 Transmission and emission spectroscopy . 13 1.5 Transiting planets with the James Webb space telescope (JWST) . 15 2 Ultracool dwarfs and their planets 17 2.1 Description of ultracool dwarfs . 17 2.2 Ultracool dwarfs and planets . 18 2.3 The SPECULOOS project . 18 2.4 Prototype survey for SPECULOOS on TRAPPIST . 20 3 The TRAPPIST-1 system 23 3.1 The host star TRAPPIST-1 . 23 3.2 The TRAPPIST-1 planetary system . 24 3.3 Characterization of TRAPPIST-1 planets: present and future . 25 3.4 On the scientific importance of TRAPPIST-1 . 26 4 Concept and goal of this thesis 29 5 Reduction method 1- Observations 31 5.1 Liverpool telescope . 31 5.1.1 IO:O . 31 5.2 Reduction methods . 32 vii viii CONTENTS 5.2.1 Observations . 32 5.2.2 Data reduction . 33 5.2.3 Differential photometry . 34 6 Reduction method 2- Data analysis 37 6.1 Introduction to Markov-chain Monte Carlo (MCMC) method . 37 6.1.1 Individual analysis . 41 6.1.2 Global analysis . 42 7 Results 43 7.1 Differential photometry . 43 7.1.1 Differential light curves obtained for TRAPPIST-1 system with IO:O camera . 45 7.2 Individual analysis . 64 7.2.1 Parameters obtained from Individual analysis for TRAPPIST-1b . 65 7.2.2 Parameters obtained from Individual analysis for TRAPPIST-1c . 67 7.2.3 Parameters obtained from individual analysis for TRAPPIST-1d . 69 7.2.4 Parameters obtained from individual analysis for TRAPPIST-1e . 70 7.2.5 Parameters obtained from individual analysis for TRAPPIST-1g . 71 7.2.6 Parameters obtained from individual analysis for TRAPPIST-1h . 72 7.3 Global analysis . 73 7.3.1 Parameters obtained from global analysis for TRAPPIST-1b . 73 7.3.2 Parameters obtained from global analysis for TRAPPIST-1c . 75 7.3.3 Parameters obtained from global analysis for TRAPPIST-1e . 76 7.3.4 Transit depth variations . 77 8 Discussion and conclusion 79 Introduction There are 400B stars in Milky way galaxy,but could the Sun be the only one with an inhabited planet ? May be ! May be the origin of life and intelligence is exceedingly improbable or may be civilizations arise all the time and wipe themselves out as soon as they are able. Or here and there , peppered across space, may be there are worlds, something like our own, on which other beings gaze upon us and wonder like we do about who else lives in the dark. Life is a comparative rarity, you can survey dozens of world and only find only in on one of them there is life.....But we continue to search for inhabited, life looks for life. - Carl Sagan (Carl Sagan series - http://saganseries.com/) We humans, with our curious minds have always wondered about the two questions that connect us to our existence. "Where do we come from? " and "Are we alone? ". As the quote by Carl Sagan clearly summarizes, we want to find out if our existence or life is limited only to the Earth and if our Earth is a special and a unique place.
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