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Page de résumé pour ULgetd-12112011-113623

Auteur : Mahy, Laurent
E-mail de l'auteur : mahy@astro.ulg.ac.be
URN : ULgetd-12112011-113623
Langue : Anglais/English
Titre : Astrophysical parameters and multiplicity of massive stars: a mathematical approach
Intitulé du diplôme : Doctorat en sciences
Département : FS - Département d'astrophysique, géophysique et océanographie
Jury :
Nom : Titre :
Cuypers, J. Membre du jury/Committee Member
Dupret, Marc-Antoine Membre du jury/Committee Member
Pavlovski, K. Membre du jury/Committee Member
Rauw, Grégor Membre du jury/Committee Member
Surdej, Jean Président du jury/Committee Chair
Gosset, Eric Promoteur/Director
Nazé, Yaël Promoteur/Director
Mots-clés :
  • mathematical tools/outils mathématiques
  • stellar parameters/paramètres stellaires
  • massive stars/étoiles massives
Date de soutenance : 2011-12-12
Type d'accès : Public/Internet
Résumé :

Often quoted for their crucial role in the ecology of galaxies, massive stars remain mysterious.

The exact process leading to their formation, their stability or their stellar winds are so

many questions which are still unanswered. Since the lifetime of these objects is too short to allow

them to move far away from their birth places, the large majority of massive stars are located in

young open clusters or in OB associations. The observations of massive stars in these locations

thus provide with promising information on their formation mechanisms. One of the most interesting

properties, in this context, is their multiplicity. Indeed, the proportion of multiple systems,

the values of orbital periods, of eccentricities, or of mass ratios are parameters directly linked to

the formation mechanism and to the dynamical interactions occuring during the earliest stages of

their existence. Moreover, constraining this multiplicity with a sufficient accuracy allows to obtain

a better determination of the nature and physical parameters of massive stars.

The present work is devoted to the study of the O star populations located in the young open cluster

NGC2244 and in the surrounding Mon OB2 association as well as in several OB associations of

the Cygnus complex. We establish not only the multiplicity of about thirty stars but also their

fundamental parameters such as their masses or their N content. However, the complexity of

observed spectra of multiple systems makes these objects difficult to investigate. Their analysis

thus requires the development and the utilization of mathematical tools such as the "disentangling"

which allows to separate the spectra of the components from the observed ones or such as the

Doppler tomography which aims at mapping the wind interactions seen in some binary systems.

The first part of this dissertation is dedicated to the development and to the characterization of

these mathematical methods whilst the second part focuses on the study of populations of massive

stars. We refine the orbital and physical parameters of systems already known as multiple. In this

context, the analysis of the two components of LZ Cep system reveals modified abundances for

the secondary star, confirming a mass transfer from the secondary towards to primary. We also

detect for the first time a third star in the HD150136 system. This object, composed of an O3, an

O5.5 and an O6.5, constitutes a new test to apply these mathematical methods and thus to better

constrain the physical properties of the system as well as those of each component. Moreover, we

find, in the population of NGC2244, of Mon OB2 and of the Cygnus OB associations, six new

binary systems and derive the orbital solutions for five of them. These results show that NGC2244

hosts only one long-period binary and none with a short period whilst four short-period and no

long-period systems are detected in the Cygnus complex. This obvious lack of short-period system

in NGC2244 contrasts with the O star populations in other young open clusters such as NGC6231

or IC 2944. Besides the multiplicity, the fundamental parameters such as the N content also allows

us to, notably, adapt the so-called Hunter-diagram to galactic O stars. Moreover, we have obtained

photometric data for six O-type stars in NGC2244 and Mon OB2 with the CoRoT satellite. These

data of unprecedented quality allow us to detect the presence, in the O star light curves, of red noise

which is supposed to originate from either the sub-surface convection zone, the granulation or an

onset of clumping in the winds of the stars. We also highlight the existence of non-radial pulsations

in the light curve of Plaskett’s Star as well as a hot spot located between the two components of

that system. In addition, numerous frequencies, extracted from the CoRoT light curves, reveal, for

some of the observed stars, solar-like oscillations or beta Cephei-like pulsations. This analysis thus

gives a first observational constraint on the bright end of the massive star instability strip.

Autre version : http://hdl.handle.net/2268/105084
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