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Numerical Adventures in Exoplanet Formation, Detection and Characterization

  • Author(s): Meschiari, Stefano
  • Advisor(s): Laughlin, Gregory
  • et al.

In this thesis I investigate the use of numerical modeling

techniques applied to the study of extrasolar planets. In the first

part (Chapters 2-4) I discuss the algorithms and applications of

the systemic code in the detection and characterization of

exoplanets through radial velocity (RV) and transit timing

observations. The second part (Chapters 5-6) deals with

hydrodynamic and N-body simulations applied to the study of

planet formation. For each chapter, I provide a detailed review of

the numerical techniques involved in the respective introductions.

Chapter 2 discusses several aspects related to the dynamical

fitting of RV observations. I introduce the systemic package I

developed, and describe several applications of the numerical

algorithms developed for the code. As a case study, I investigate

the dynamical fitting of HD128311 and the characterization of the

2:1 mean motion resonance (MMR) through radial velocities and a

small number of central transit times. I present an updated Keck RV

dataset and show that the addition of three years of new RV

coverage yields only a modest improvement in the characterization

of the system.

In Chapter 3, I study planet detection through transit timing

variations (TTV), deviations from linear transit ephemeris that can

be caused by additional planets exerting gravitational

perturbations on a transiting planet. I created synthetic RV and

TTV datasets for several planetary configurations, with the intent

of modeling timing observations from the Kepler mission. I use

the algorithms described in Chapter 2 to solve the so-called

"inverse problem", the task of characterizing additional,

non-transiting planets through their signatures in the RV and TTV

datasets of transiting. I show that the space of the best-fitting

solutions may be remarkably degenerate if the perturbing planet is

not observed directly (e.g. as in the case of Kepler 19-c), and

that more extensive RV coverage can be used to break the


In Chapter 4, I present the discovery of four new exoplanet

candidates characterized with Keck/HIRES RV observations. The new

exoplanets discovered around the host stars HD31253, HD218566,

HD177830 and HD99492 comprise masses between Msini ~

27 M_earth to Msini ~ 8 M_jupiter. Of particular

interest for the scope of this thesis, HD177830 is currently the

only multiple-planet system orbiting a binary with a_B < 100 AU.

This separation is slightly below the limit at which the binarity

of the system influences planet formation. Finally, we strengthen

the case for the non-detection of HD74156d, the detection of which

was claimed to be in accordance to the "Packed Planetary System"


Chapter 5 explores a class of self-gravitating instabilities

driven by features in the surface density of protoplanetary disks

("groove modes"). The emergence of these instabilities is

studied via a generalized eigenvalue code and full two-dimensional

hydrodynamical simulations. I find that gaps in the surface

density, such as those naturally carved in response to the

formation of a giant planet, can excite a global two-armed mode at

comparatively lower disk masses than in absence of such gaps.

Chapter 6 describes a new code, SPHIGA, used to explore the

issue of forming planets in circumstellar (CS) or circumbinary (CB)

orbits during the planetesimal accretion phase and its feasibility

within the core accretion framework. I investigate the balance

between accreting and erosive impacts for the circumbinary planet

Kepler 16-b and the feasibility of planet formation in situ

as opposed to migration of an embryo formed at or outside the ice


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