Photoevaporation of Protoplanetary Disks by UV Photons from Nearby Massive Stars : Observations of Proplyds and Modeling Jason Champion

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Photoevaporation of Protoplanetary Disks by UV Photons from Nearby Massive Stars : Observations of Proplyds and Modeling Jason Champion Photoevaporation of protoplanetary disks by UV photons from nearby massive stars : observations of proplyds and modeling Jason Champion To cite this version: Jason Champion. Photoevaporation of protoplanetary disks by UV photons from nearby massive stars : observations of proplyds and modeling. Solar and Stellar Astrophysics [astro-ph.SR]. Université Paul Sabatier - Toulouse III, 2017. English. NNT : 2017TOU30392. tel-02307075 HAL Id: tel-02307075 https://tel.archives-ouvertes.fr/tel-02307075 Submitted on 7 Oct 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Pr´esent´ee et soutenue le 25/09/2017 par : Jason CHAMPION Photoevaporation des disques protoplanétaires par les photons UV d’étoiles massives proches : observation de proplyds et modélisation JURY Maryvonne GERIN Directeur de Recherche Pr´esident du Jury Yann ALIBERT Maître de Conférence Rapporteur Emilie HABART Charg´ede Recherche Examinateur Karine DEMYK Directeur de Recherche Examinateur Emmanuel CAUX Directeur de Recherche Examinateur Olivier BERNE Charg´ede Recherche Directeur de Thèse Ecole´ doctorale et sp´ecialit´e : SDU2E : Astrophysique, Sciences de l’Espace, Plan´etologie Unit´e de Recherche : Institut de Recherche en Astrophysique et Plan´etologie (UMR 5277) Directeur de Th`ese : Olivier BERNE Rapporteurs : Maryvonne GERIN et Yann ALIBERT ii Remerciements Enfin, nous pouvons commencer. Je vous propose de débuter votre lecture à travers mes derniers mots car, vous ne le savez probablement pas, ces remerciements ont été rédigés bien après la sou- tenance de ma thèse. En retard, oui, très en retard! Ce n’est pas qu’une question de relâchement d’après thèse (il y en a...), car il s’agit aussi, et surtout, d’un passage des plus importants et des plus difficiles à écrire. Difficile, en effet, de mentionner toutes les personnes qui mériteraient de l’être. Difficile, d’ordonner ce bazar social des êtres qui nous entourent. Difficile, de ne plus s’accrocher à ce mémoire et de le libérer, enfin, pour que le reste du monde puisse s’y intéresser. Ainsi, je vous passe le témoin. Ici s’achève ma rédaction, et la suite vous appartient désormais. Voici donc, un bref aperçu des personnes qui me sont chères et qui ont été présentes, avec moi, durant cette aventure. Continuons sur notre désordre temporel en commençant par ce qu’il y a de plus frais, la fin! Je voudrais remercier toutes les personnes venues, me voir ou me soutenir, le 25 septembre 2017 à ma soutenance. Je pense notamment à tous les membres de mon jury, pour avoir accepté d’en faire parti et pour vos commentaires bienveillants avant ou après ma soutenance. Que vous étiez présents ou non, je remercie également mes collaborateurs, notamment Franck, Clément, Silvia, Inga et Christine, pour l’aide que vous m’avez apporté. Bien plus que des collègues, je tiens à remercier infiniment l’ensemble des membres de l’équipe MICMAC de l’IRAP. Je n’ai pas besoin de lister les meilleurs, puisque vous êtes tous formidable! Je ne compte d’ailleurs pas que les membres de mon équipe mais aussi, plus largement, toutes les personnes se trouvant à proximité ou dans l’aile de notre couloir. Non, je ne vous oublie pas Mathieu, Bernard, Antoine et les autres voisins de bureau. Un grand merci pour l’ambiance, la sympathie et l’amitié que j’ai pu avoir avec vous tous. Dans une thèse, l’histoire le dit, le choix du directeur est toujours critique. Dans mon cas, je considère que celui-ci à été très bon! Je te remercie, Olivier, pour m’avoir dirigé comme tu l’as fait, avec beaucoup de sympathie et de liberté à mon égard. Merci de m’avoir permis d’aller où je le souhaitais, autant pour nos projets scientifiques que pour mes projets parallèles. Merci pour tes mots à la fin de ma soutenance qui m’ont beaucoup touché. Chaque génération de doctorants crée de nouvelles amitiés. Ce fut évidemment le cas pour moi, bien trop pour que je vous cite tous, mais je me dois d’en nommer au moins une, celle avec Gabriel, mon frérot de thèse avec qui j’ai partagé un temps un bureau, partagé mes pauses, et partagé quelques unes de mes activités extra-recherche. Merci à toi d’avoir été là. Merci à tous les autres, anciens ou nouveaux doctorants, avec une pensée particulière envers ceux avec qui j’ai vécu de nombreuses aventures via l’association UniverSCiel. Il était si amusant de faire partager la science aux jeunes avec vous! Merci à mes amis du M2 Planétologie qui forment un groupe exceptionnel, je voudrais citer en particulier Anne, Lucile et Kelly, qui ont été très souvent là. Ces quelques années passées à Toulouse mon aussi permis de rencontrer de nombreuses per- sonnes au sein du club de montagne de l’Université Paul Sabatier. Merci aux encadrants, Romain et Olivier, de m’avoir formé et de m’avoir donné l’opportunité de profiter à fond des Pyrénées. iii Merci à l’équipe de jeunes moniteurs qui ont également suivi la formation et avec qui j’ai partagé de nombreuses aventures. Enfin, ceux qui ont toujours été là, ma famille. Mes parents évidemment, à qui je dois tous, ma tante Muriel et mon oncle Jacky qui sont venus me voir à la soutenance et mes grand-parents qui auraient souhaité le faire. Puis, tous les autres, pour le bonheur que vous m’apportez depuis toujours. Merci! Je remercie également la plus récente membre de ma famille, ma Lélette ¡3, qui est présente à mes côtés depuis la dernière année de thèse et qui l’a rendue, elle aussi, beaucoup plus belle. Bref, ces trois années ont été merveilleuses grâce à vous tous, je vous aime, merci! iv Résumé Les disques protoplanétaires entourant les jeunes étoiles sont les embryons des systèmes plané- taires. A différentes phases de leur évolution, ils peuvent subir d’importantes pertes de masse par photoévaporation : des photons énergétiques, issus de l’étoile centrale ou d’une étoile voisine, chauffe le disque qui perd en masse sous l’échappement des particules. Cependant, ce mécanisme et la physique sous-jacente n’ont que peu été contraints par les observations. Les objectifs de cette thèse sont d’étudier la photoévaporation dans le cas particulier où elle est due à des pho- tons FUV, d’identifier les principaux paramètres physiques (densité, température) et processus (chauffage et refroidissement) impliqués, et d’estimer son impact sur l’évolution dynamique des disques. L’étude repose sur le couplage observations – modélisations des disques photoévaporés par les photons UV en provenance d’étoiles massives proches. Ces objets, appelés ”proplyds”, ont leur disque entouré d’une large enveloppe nourrie des flots de photoévaporation. A l’aide d’un modèle 1D d’une région de photodissociation, j’ai développé un modèle pour l’émission dans l’infrarouge lointain des proplyds. Ce modèle a été utilisé pour interpréter les observations, issues principalement de Herschel, pour quatre proplyds. Il apparait que les con- 6 3 ditions physiques en surface de leur disque sont similaires: une densité de l’ordre de 10 cm− et une température d’environ 1000 K. Cette température est maintenue par un équilibre dynamique : si la surface se refroidit, la perte de masse diminue et l’enveloppe se réduit. L’atténuation UV produite par l’enveloppe diminue alors et le disque, recevant plus de photons UV, chauffe. La majorité du disque peut s’échapper sous forme de flots de photoévaporation avec des taux de 7 1 perte de masse de quelques 10− M yr− ou plus, en accord avec les observations précédentes des traceurs du gaz ionisé. ⊙ A la suite de ce travail, j’ai développé un modèle hydrodynamique 1D pour étudier l’évolution dynamique d’un disque en photoévaporation par un champ de rayonnement externe. Le code inclut l’évolution visqueuse due à la turbulence et des prescriptions pour différents types de photoévaporation, incluant la prescription dans le cas défini par les observations et modèles décrits précédemment. Dans ce cas, deux régions du disque évoluent différemment. L’évolution dynamique du disque externe, où les flots de photoévaporation se développent, est dominée par la photoévaporation. Le disque externe se dissipe dans un temps de 105 ans, laissant un disque tronqué. Le disque interne, où la gravitation retient les flots, est aussi impacté en raison d’un transfert de masse vers le disque externe en photoévaporation, mais l’accroissement de la perte de masse est faible. Le disque interne, dont l’évolution est dominée par la viscosité, peut survivre quelques 106 ans. Finalement, j’ai effectué une étude statistique en utilisant ce modèle et montré qu’il était capable de reproduire des observations d’un grand échantillon de disques dans Orion où la photoévaporation externe est supposée modifier la fonction de masse des disques. D’après mes résultats, la photoévaporation externe est très efficace dans le disque externe. A moins que des planètes puissent se former en moins de 105 ans, leur formation semble difficile ici. Le disque interne est un environnement beaucoup plus favorable. Les modèles de synthèse de populations planétaires, étudiant les impacts à l’échelle d’une grande population, sont une v perspective prometteuse de ce travail car ils peuvent offrir la possibilité d’étudier l’évolution de systèmes planétaires en formation et irradiés par les étoiles massives voisines.
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