Advanced

Common Envelope Evolution

Wissing, Robert LU (2016) In Lund Obsrvatory Examensarbeten ASTK02 20152
Lund Observatory
Abstract
We present simulations done on the onset of common envelope evolution with giant donors by taking into account the mass loss through the outer Lagrange point and the forming of the common envelope. In addition we apply proper stellar models and evolve our simulations using an Runge-Kutta integrator with adaptive step-size. We show that each of these processes are significant in the onset of common envelope evolution. The mass loss through the outer Lagrange point has significant effect, if the atmospheric scale height is high(as is the case for red giants $H_p=0.01 R_*$). In addition to this we find that subgiants with a scale height of about $H_p=0.1 R_*$ can have a stable mass transfer period during its evolution and can as a result... (More)
We present simulations done on the onset of common envelope evolution with giant donors by taking into account the mass loss through the outer Lagrange point and the forming of the common envelope. In addition we apply proper stellar models and evolve our simulations using an Runge-Kutta integrator with adaptive step-size. We show that each of these processes are significant in the onset of common envelope evolution. The mass loss through the outer Lagrange point has significant effect, if the atmospheric scale height is high(as is the case for red giants $H_p=0.01 R_*$). In addition to this we find that subgiants with a scale height of about $H_p=0.1 R_*$ can have a stable mass transfer period during its evolution and can as a result exhaust its envelope before starting Roche lobe overflow. The nature of the mass transfer is found to be heavily dependent on the atmospheric scale height of the star. As different scale heights lead to very different evolutionary paths for the mass transfer. We also make comparisons with the conservative case and show that simple stability analysis of unstable mass transfer do not concur with the non-conservative case. We discuss the standard application of the alpha formalism and show that there are severe flaws in using it at the start of Roche lobe overflow, as opposed to at the start of common envelope evolution for giant donor stars. (Less)
Popular Abstract
A binary star system contains two stars which orbits each other around their common center of gravity. In the past it was thought that binaries were quite rare; but as our instruments of observation got better and better we found that the universe is teeming with them. The stars in a binary usually evolve independently and follow simple and similar physics as that of our own solar system. However a big difference arises if the separation between the two stars are sufficiently small that the individual evolution of each star leads to the initiation of mass transfer. As a consequence to mass transfer, a binary system can evolve through several evolutionary paths and result in some of the most exotic astronomical objects seen in the night... (More)
A binary star system contains two stars which orbits each other around their common center of gravity. In the past it was thought that binaries were quite rare; but as our instruments of observation got better and better we found that the universe is teeming with them. The stars in a binary usually evolve independently and follow simple and similar physics as that of our own solar system. However a big difference arises if the separation between the two stars are sufficiently small that the individual evolution of each star leads to the initiation of mass transfer. As a consequence to mass transfer, a binary system can evolve through several evolutionary paths and result in some of the most exotic astronomical objects seen in the night sky.

The mass transfer that unfolds can either be stable or unstable. A stable mass transfer will slowly transfer mass from one star to the other. But an unstable mass transfer will quickly go out of control and pour its material on to the other star. However a star can only accept a finite amount of material at once and this results in the buildup of an envelope that can eventually engulf both stars. The system has now become a common envelope system. Due to frictional processes the stars spiral together and the final product will either be a tighter binary or a merger between the two stars.

An interesting product of common envelope evolution is a cataclysmic variable star, which are the predecessors to Type 1a supernova explosions. These are very important in astronomy as they are “standard candles” that have a specific brightness associated with them. They are used to calculate the distance to very distant objects. So as we can see it becomes quite essential to understand and investigate the physics of common envelope evolution.

This bachelor thesis will focus on the onset of common envelope evolution. We will investigate under what conditions it occurs and how likely they are to happen. Simulations are done on the onset of common envelope evolution and we discover what processes play a major role in it. Finally we will apply a method for evolving the system through its common envelope evolution and discover the final state of the binary. (Less)
Please use this url to cite or link to this publication:
author
Wissing, Robert LU
supervisor
organization
course
ASTK02 20152
year
type
M2 - Bachelor Degree
subject
publication/series
Lund Obsrvatory Examensarbeten
report number
2016-EXA100
language
English
id
8776803
date added to LUP
2016-03-01 14:29:40
date last changed
2016-03-01 14:29:40
@misc{8776803,
  abstract     = {We present simulations done on the onset of common envelope evolution with giant donors by taking into account the mass loss through the outer Lagrange point and the forming of the common envelope. In addition we apply proper stellar models and evolve our simulations using an Runge-Kutta integrator with adaptive step-size. We show that each of these processes are significant in the onset of common envelope evolution. The mass loss through the outer Lagrange point has significant effect, if the atmospheric scale height is high(as is the case for red giants $H_p=0.01 R_*$). In addition to this we find that subgiants with a scale height of about $H_p=0.1 R_*$ can have a stable mass transfer period during its evolution and can as a result exhaust its envelope before starting Roche lobe overflow. The nature of the mass transfer is found to be heavily dependent on the atmospheric scale height of the star. As different scale heights lead to very different evolutionary paths for the mass transfer. We also make comparisons with the conservative case and show that simple stability analysis of unstable mass transfer do not concur with the non-conservative case. We discuss the standard application of the alpha formalism and show that there are severe flaws in using it at the start of Roche lobe overflow, as opposed to at the start of common envelope evolution for giant donor stars.},
  author       = {Wissing, Robert},
  language     = {eng},
  note         = {Student Paper},
  series       = {Lund Obsrvatory Examensarbeten},
  title        = {Common Envelope Evolution},
  year         = {2016},
}