@conferencepres{Melbourne_2024,
author = {Esseldeurs, Mats},
title = {Tidal Dissipation in Cool Evolved Stars},
publisher = {ACES: Advances in Cool Evolved Stars},
year = {2024},
recording = {https://www.youtube.com/watch?v=5Ix0R9k42rk}
}
As the observed occurrence of companions orbiting cool evolved stars is increasing, so does the importance of understanding and evaluating the strength of their interactions. This is important for both the further evolution of each component in the system, but also the evolution of the system itself. One of the fundamental mechanisms to understand this interaction is the tidal dissipation in these stars, as it is one of the engines of orbital/rotational evolution of star-planet/star-star systems. As current population-synthesis models don’t agree with the observed period and eccentricity distribution of post-AGB stars, the need arises to revise the tidal dissipation mechanisms used in these studies. In this presentation I will present the first ab-initio calculations of tidal dissipation strengths during the entire evolution of low and intermediate mass stars, of both the equilibrium tide (currently equations are used calibrated on the MS), and the dynamical tide (currently not accounted for), showing their importance in different regions of the parameter space. These parameters are key in predicting the future evolution of these binary stars, offering a way forward to a renewed understanding of orbital evolution during the evolved phases.
@conferencepres{Heidelberg_2024,
author = {Esseldeurs, Mats},
title = {Ray Tracing in Fluid Simulations: Enhancing AGB Outflow Simulations},
publisher = {RT24 workshop},
year = {2024}
}
In computational astrophysics, pursuing computational efficiency is a constant challenge. Ray tracing, renowned for its capacity to generate visually captivating astronomical representations, has experienced a continuous evolution in recent years. Simultaneously, Smoothed Particle Hydrodynamics (SPH), utilized in astrophysical fluid simulations, has established itself as a strong computational instrument for modeling intricate cosmic phenomena. In the pursuit of performing coupled radiation-hydrodynamic calculations, this presentation introduces a recently developed ray-tracing algorithm that fuses the capabilities of ray tracing with the inherent strengths of SPH. This allows for efficient radiative transfer calculations in an on-the-fly manner while performing computationally demanding hydrodynamical calculations.
@conferencepres{Phantom_2024,
author = {Esseldeurs, Mats},
title = {Enhancing AGB Outflow Simulations: Implementing a Ray-Tracing Algorithm in PHANTOM for Efficient Radiation Field Computation},
publisher = {5th Phantom and MCFOST Users Workshop 2024},
year = {2024}
}
Asymptotic Giant Branch (AGB) stars play a crucial role in our understanding of stellar evolution and galactic enrichment processes. The simulation of outflows from these stars, however, faces significant computational challenges, primarily due to the complex interplay of involved physical processes. We utilize the 3D Smoothed Particle Hydrodynamics code PHANTOM to simulate AGB outflows, incorporating a novel ray-tracing algorithm designed to create a more efficient and accurate proxy for the radiation field in these simulations. Our method addresses the computational intensity of traditional ray-tracing techniques by customizing the algorithm for SPH environments and exploiting symmetries in the physical setup. This strategic optimization notably reduces computational intensity while maintaining high accuracy. The algorithm rapidly computes the local radiative equilibrium temperature and radiation force on each particle, facilitating more realistic simulations of AGB outflows and providing deeper insights into their morphology and dynamics, previously limited by computational constraints. Continuing efforts are focused on enhancing cooling prescriptions within our physical model and merging these ray-tracing computations with existing dust formation modules in PHANTOM. The ultimate goal is to synchronize our PHANTOM simulations with high-resolution observations. We aim to post-process our hydrodynamic models using the radiative transfer code MAGRITTE to produce synthetic observations that mirror actual ALMA data. This approach aims to shed light on the complex wind structures of evolved stars and provides essential data for determining fundamental stellar and wind parameters. These parameters are key in forecasting the future evolution of these stars, offering a renewed understanding in the study of AGB outflows.
@conferencepres{Namur_2023,
author = {Esseldeurs, Mats},
title = {Towards a complete picture of the evolution of planetary systems around evolved stars},
publisher = {Complex Planetary Systems II – Kavli-IAU Symposium 382},
year = {2023},
proceedings = {Esseldeurs+2023b.pdf}
}
About 95% of all stars in the galaxy have an initial mass lower than 8 solar masses. When these stars evolve off the Main Sequence, they will go through the Asymptotic Giant Branch (AGB) phase, just before turning into a White Dwarf (WD). This evolutionary phase is characterized by significant mass loss, large stellar radii, strong pulsations, and extreme luminosities. It must be studied to get a complete picture of the evolution of planetary systems from the birth to the end of their host stars. Indeed, population synthesis studies indicate that the majority of these stars have at least one (sub)stellar companion, where the abrupt changes in stellar characteristics may completely transform a planetary/binary system. In order to establish whether the planetary/(sub)stellar companion survives this evolutionary phase, and explain the presence of planets orbiting around WDs, one must study their orbital evolution for which both the stellar mass loss rate and mass accretion efficiency onto the companion and tidal interactions between the star and its companion play an important role. In current literature this is only addressed taking into account the simplest equilibrium tide, with mass-loss rate prescriptions and mass accretion efficiencies now considered outdated. For this reason, the treatment of these processes needs to be improved. First, we now study the dynamical tide, which can exceed the dissipation of the equilibrium tide by 3 orders of magnitude, which needs to be studied all along the evolution of stars. Second, we compute complex 3D hydrodynamic simulations that take into account all the complex components of the wind launching mechanism, as well as the gravitational perturbation of the companion. This makes it possible to account for the companion in simulating the mass loss rates, model for wind Roche Lobe overflow determining the mass accretion efficiency on the companion, as well as simulate the morphological structure of the AGB surroundings created by the companion. This allows us to build step by step coherent models of planetary systems orbiting evolved AGB stars.
@conferencepres{Krakow_AGB_2023,
author = {Esseldeurs, Mats},
title = {Impact of different radiative transfer prescriptions on the morphological structures of AGB outflows},
publisher = {EAS Annual Meeting},
year = {2023}
}
About 95% of all stars in the galaxy have an initial mass lower than 8 solar masses. When these stars evolve off the Main Sequence, they will go through the Asymptotic Giant Branch (AGB) phase, just before turning into a White Dwarf (WD). This evolutionary phase is characterized by their significant mass loss caused by the so-called dust-driven winds. In this wind, the radiation force acts on newly formed dust grains, accelerating the material outwards. High-resolution observation of AGB outflows have revealed complex structures, most probably caused by interaction with a binary companion. To investigate this hypothesis, 3D hydrodynamic studies need to be performed, including the gravitational force of the companion. In recent years, more and more physical processes have been added to such 3D simulations, although the treatment of radiative transfer remains poorly implemented. Using the smoothed particle hydrodynamic (SPH) code Phantom, as well as a newly implemented ray-tracer optimised for the SPH formalism, I will present an investigation into different radiative acceleration prescriptions. I will discuss how each of these prescriptions has its own influence on the velocity profiles and morphological structures around the AGB stars, and which prescription to favour. This investigation is a step forward on the route towards complete 3D radiation-hydro-chemical simulations of companion-perturbed AGB outflows.
@conferencepres{Krakow_planet_2023,
author = {Esseldeurs, Mats},
title = {The Orbital Evolution of (Sub)Stellar Companions to Asymptotic Giant Branch Stars},
publisher = {EAS Annual Meeting},
year = {2023}
}
About 95% of all stars in the galaxy have an initial mass lower than 8 solar masses. When these stars evolve off the Main Sequence, they will go through the Asymptotic Giant Branch (AGB) phase, just before turning into a White Dwarf (WD). This evolutionary phase is characterized by significant mass loss, large stellar radii, strong pulsations, and extreme luminosities. It must be studied to get a complete picture of the evolution of planetary systems from the birth to the end of their host stars. Indeed, population synthesis studies indicate that the majority of these stars have at least one (sub)stellar companion, where the abrupt changes in stellar characteristics may completely transform a planetary/binary system. In order to establish whether the planetary/(sub)stellar companion survives this evolutionary phase, and explain the presence of planets orbiting around WDs, one must study their orbital evolution for which both the stellar mass loss rate and mass accretion efficiency onto the companion and tidal interactions between the star and its companion play an important role. In current literature this is only addressed taking into account the simplest equilibrium tide, with mass-loss rate prescriptions and mass accretion efficiencies now considered outdated. For this reason, the treatment of these processes needs to be improved. First, we now study the dynamical tide, which can exceed the dissipation of the equilibrium tide by 3 orders of magnitude, which needs to be studied all along the evolution of stars. Second, we compute complex 3D hydrodynamic simulations that take into account all the complex components of the wind launching mechanism, as well as the gravitational perturbation of the companion. This makes it possible to account for the companion in simulating the mass loss rates, model for wind Roche Lobe overflow determining the mass accretion efficiency on the companion, as well as simulate the morphological structure of the AGB surroundings created by the companion. This allows us to build step by step coherent models of planetary systems orbiting evolved AGB stars.
@conferencepres{ATOMIUM_2023,
author = {Esseldeurs, Mats},
title = {Impact of different radiative transfer prescriptions on the morphological structures of AGB outlows},
publisher = {ATOMIUM 2023 winter meeting},
year = {2023}
}
@conferencepres{NAC_2022,
author = {Esseldeurs, Mats},
title = {Radiation pressure in 3D hydrodynamical simulations of companion-perturbed AGB outflows},
publisher = {77th Dutch Astronomers' Conference},
year = {2022}
}
The cool and dusty circumstellar envelopes of asymptotic giant branch (AGB) have for a long time been modelled assuming a spherical symmetry. High spatial resolution observations of these stars have shown that their surroundings exhibit a variety of complex structures. Most of these structures are believed to originate from the interaction of the AGB wind with an obfuscated, nearby, orbiting stellar or planetary companion. Due to the inherent three-dimensional nature of these structures, a detailed understanding of these objects and the dominant wind-shaping mechanisms can therefore only be obtained from advanced three-dimensional treatments. Hydrodynamics simulations (with both particle- and grid-based codes) in the literature show that some of the observed morphologies can indeed be reproduced. However, due to the large computational cost a lot of critical physics has been strongly simplified, or even omitted. It is in this context that we present our work on upgrading the way in which attenuation of the stellar radiation field affects the effective radiation pressure on the dust by abandoning the widely adopted optically thin limit in calculating the dust acceleration. In this talk I will present my master thesis project where I coupled a ray-tracer with the smoothed-particle-hydrodynamics code Phantom to calculate the dust acceleration everywhere in the wind, and how to make it feasible for on-the-fly calculations. I will present the implications of this new treatment on the dynamics and morphology of the AGB outflows by means of three-dimensional AGB binary simulations.