Variability of White Dwarf Debris Disks
(2024) FYSK04 20241Department of Physics
Astrophysics
- Abstract
- Disks around single white dwarfs have been observed as infrared excesses since 1987. Over time, these excesses have shown variability, leading to the conclusion that these debris disks undergo changes. However, the infrared excess should not be the only detectable signature from these disks. They are also expected to reflect visible light, a phenomenon yet to be studied for white dwarf debris disks. This project aims to first find disk parameters that approximately reproduce the observed changes in infrared excess. These parameters will then be used to predict the amount of visible reflected light and asses its detectability. In doing so, I rederive the flat disk model originally proposed by Jura and add one parameter for the albedo and... (More)
- Disks around single white dwarfs have been observed as infrared excesses since 1987. Over time, these excesses have shown variability, leading to the conclusion that these debris disks undergo changes. However, the infrared excess should not be the only detectable signature from these disks. They are also expected to reflect visible light, a phenomenon yet to be studied for white dwarf debris disks. This project aims to first find disk parameters that approximately reproduce the observed changes in infrared excess. These parameters will then be used to predict the amount of visible reflected light and asses its detectability. In doing so, I rederive the flat disk model originally proposed by Jura and add one parameter for the albedo and one for the packing fraction of the disk. Next, I derive two models for the reflected light: one assuming a Lambertian surface and one using the Henyey–Greenstein phase function. I find that the flat disk model can match the observed variability when allowing changes in packing fraction. Such changes can for example correspond to mass loss due to collisional grinding within the disk. The reflected light coming from the disk makes up about 0.03% of the stellar light, which could be detectable using relative photometry over months and years using a precise telescope such as CHEOPS, TESS, or PLATO. (Less)
- Popular Abstract
- Despite the misleading name white dwarfs have nothing to do with Snow White and the Seven Dwarfs from Grimm’s fairytales. Instead, these types of stars unfold the final chapter of the fascinating life cycle of a star. When a star runs out of fuel a series of events takes place leading to drastic changes. Planets close to the star are either engulfed by the dying star or destroyed by collisions with other objects. The core of the star, known as a white dwarf, is the only remainder of this destructive event. For many years this was thought to be true until dust was found to orbit a white dwarf by Zuckerman and Becklin in 1987. Since then, more and more white dwarfs have been found to host rings of dust. These so-called debris disks give rise... (More)
- Despite the misleading name white dwarfs have nothing to do with Snow White and the Seven Dwarfs from Grimm’s fairytales. Instead, these types of stars unfold the final chapter of the fascinating life cycle of a star. When a star runs out of fuel a series of events takes place leading to drastic changes. Planets close to the star are either engulfed by the dying star or destroyed by collisions with other objects. The core of the star, known as a white dwarf, is the only remainder of this destructive event. For many years this was thought to be true until dust was found to orbit a white dwarf by Zuckerman and Becklin in 1987. Since then, more and more white dwarfs have been found to host rings of dust. These so-called debris disks give rise to many questions: How do these rocks survive the violent death of the star? What do these disks look like and what are they made of?
Answering these questions is challenging since one cannot quickly send a spacecraft to a white dwarf and take a picture. Instead, one must measure the incoming light from the star and create theoretical models that can explain the observations. As if this was not difficult enough, these disks seem to change with time, as recent observations show. This variability is yet unexplained, but with the help of more advanced mathematical models, astrophysicists are on the hunt for answers.
The easiest way to imagine the debris around white dwarfs is by viewing them as a similar system to Saturn and its rings: a so-called flat debris disk. Rocks of many different sizes and forms lie in the same plane and orbit around the star. If this disk then becomes smaller or larger in radius, the light measured from the white dwarf is going to look different. Depending on how many rocks there are in the disk, or in other words, how packed the disk is, the observed spectrum changes as well.
In my project, I derive two models for debris disks: one that simulates the light coming from the disk heating up, also called the infrared excess and one that simulates the reflected light from the disk. Each model has parameters that describe different properties of the disks. By changing them, I can see how different disks correspond to different spectra. This knowledge is helpful to for example see what parameters of the infrared excess model I have to change to match the observed variability of the disk. Using these parameters, I can then show what the reflected light is expected to look like in theory. This endeavour is particularly valuable given that reflected light from a white dwarf debris disk has not been observed yet.
White dwarfs are the remains after a star dies, yet their story is still unfolding. A fascinating part of this story are debris disks, which describe the rock formations orbiting these stars. To understand the stories behind white dwarfs and their debris disks one has to look at observed data and establish theoretical models that can recreate the data observed. My models simulate the heat and the reflected light coming from a debris disk and by changing parameters I can see what disk properties correspond to observed spectra. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9160749
- author
- Bormann, Amelie LU
- supervisor
- organization
- course
- FYSK04 20241
- year
- 2024
- type
- M2 - Bachelor Degree
- subject
- keywords
- white dwarfs, circumstellar matter, stars: WD 0145+234, stars: G 29-38, reflected light
- report number
- 2024–EXA226
- language
- English
- id
- 9160749
- date added to LUP
- 2024-06-11 13:45:42
- date last changed
- 2024-06-11 13:45:42
@misc{9160749,
abstract = {{Disks around single white dwarfs have been observed as infrared excesses since 1987. Over time, these excesses have shown variability, leading to the conclusion that these debris disks undergo changes. However, the infrared excess should not be the only detectable signature from these disks. They are also expected to reflect visible light, a phenomenon yet to be studied for white dwarf debris disks. This project aims to first find disk parameters that approximately reproduce the observed changes in infrared excess. These parameters will then be used to predict the amount of visible reflected light and asses its detectability. In doing so, I rederive the flat disk model originally proposed by Jura and add one parameter for the albedo and one for the packing fraction of the disk. Next, I derive two models for the reflected light: one assuming a Lambertian surface and one using the Henyey–Greenstein phase function. I find that the flat disk model can match the observed variability when allowing changes in packing fraction. Such changes can for example correspond to mass loss due to collisional grinding within the disk. The reflected light coming from the disk makes up about 0.03% of the stellar light, which could be detectable using relative photometry over months and years using a precise telescope such as CHEOPS, TESS, or PLATO.}},
author = {{Bormann, Amelie}},
language = {{eng}},
note = {{Student Paper}},
title = {{Variability of White Dwarf Debris Disks}},
year = {{2024}},
}