Co-supervised PhD thesis: Multiplicity signatures in accretion discs
Student: Simone Ceppi (U. Milano, Italy)
Duration: 3 years, November 2020 - onwards
Advisors: Giuseppe Lodato (U. Milano) & Nicolás Cuello (IPAG)
Keywords: protoplanetary discs, accretion, multiple systems
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Multiplicity is ubiquitous in the process of star formation and multiples are also very common in stellar populations. Thus, it is reasonable to think that multiplicity is an important ingredient in the formation of stars and planetary systems. Since the advent of the ALMA observatory we started to detect young triple systems with their discs, and many candidates are waiting to be discovered. Moreover, some currently studied young protoplanetary discs could be orbiting around a not yet acknowledged system of higher multiplicity, as recently found in the GG Tau A system and recent studies has shown how important it can be the shaping of a protoplanetary disc by specific triple configurations.
However, as of today there are no general studies about the impact of triplicity on accretion systems. In this framework it is crucial to tackle unresolved questions such as: what can the disc morphology tell us about the multiplicity of its central object? How is the evolution of a multiple accretion system with respect to one of lower multiplicity? How does multiplicity affect planet and stellar formation? The mutual interaction between a multiple system and its accretion discs has consequences on both the stellar system, whose orbital parameters are expected to vary overtime, and on the accretion discs, that are shaped by the angular momentum exchange with the stars. We aim to identify observable signatures of multiplicity on accretion discs and relate these features to the parameters and configuration of the central stellar system.
Internship #3: Disc dynamics in triple stellar systems
Student: Antoine Alaguero (M1, UGA, Grenoble, France)
Duration: 2 months, June & July 2021
Advisor: Nicolás Cuello (IPAG)
Keywords: disc dynamics, celestial mechanics, hydrodynamical simulations
The recent discovery of young stellar systems with three or more stars with protoplanetary discs – such as GW Ori and GG Tau – opened new perspectives in the field of planet formation. These discs are expected to form planets, as the notorious case of the disc around PDS70 where a young planet has been recently imaged while accreting. Disc dynamics around single stars is reasonably well understood. However, it remains unclear how discs evolve in binary and triple stellar systems.
The aim of this internship will be to explore protoplanetary disc evolution in multiple stellar systems through hydrodynamical simulations. To this end we will use the 3D Lagrangian SPH code called Phantom (Price et al. 2018). The work will focus on characterizing the disc morphology and evolution by analyzing simulation outputs, already available or produced during the internship. This will allow to establish a categorization of discs within hierarchical triple stellar systems and identify the regions where planets could form.
Internship #2: Planetary systems in triple stellar systems
Student: Damien Latafi (M2, UGA, Grenoble, France)
Duration: 2 months, April & May 2021
Advisor: Nicolás Cuello (IPAG)
Keywords: planetary systems, celestial mechanics, N-body integrations
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The recent discovery of young stellar systems with three or more stars with protoplanetary discs – such as GW Ori and GG Tau – opened new perspectives in the field of planet formation. These discs are expected to form planets and therefore planetary systems should form in multiple stellar systems. As a matter of fact a few dozens of exoplanets have been detected in binary stellar systems, which strongly suggests that planetary systems form and survive within multiple stellar systems. The stability of planetary systems is reasonably well understood around single stars. However, it remains unclear how planetary systems evolve in binary and triple stellar systems.
The aim of this internship will be to explore planetary system dynamics and stability in triple stellar systems through N-body calculations. To this end we will use state-of-the-art N-body integrators (e.g. rebound and hnbody codes). The final choice of the method will depend on the type of problem considered. The work will focus on identifying the regions of stability and chaos for planets within triple stellar systems. Eventually, these results will serve as a proxy to identify where planets could form, evolve, and survive around young triple stellar systems recently observed.
Internship #1: Mutual interaction of hierarchical triple systems with accretion discs
Student: Simone Ceppi (M2, U. degli studi di Milano, Italy)
Duration: 7 months, March-September 2020
Advisors: G. Lodato (U. Milano), C. Toci (U. Milano), Nicolás Cuello (IPAG)
Keywords: triple stellar systems, disc dynamics, accretion, simulations
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We aim to investigate the different behaviours among binary systems and hierarchical triple systems systems in accretion. To perform numerical simulations of HT systems in accretion, that are the topic of this thesis, we needed to implement a dedicated setup in an Smoothed Particle Hydrodynamics code developed for hydrodynamical astrophysical applications, PHANTOM (Price et al. [2018]).
On one hand it is interesting to check if hierarchical systems in accretion shape the accretion discs in peculiar ways with respect to binary systems. This will allow to both better understand signatures in accretion discs around triple systems, and in the future to recognise a hierarchical triple systems in accretion from the signatures of its disc. On the other hand, the back-reaction on multiple stellar systems due to the tidal torques surely affects the orbital parameters of young stellar populations, and in particular their multiplicity.