#### Presentation Title

Modeling the Frequency Spectrum of AM CVn Systems by Solving the Radiative Transfer Equation

#### Faculty Mentor

Omer Blaes

#### Start Date

18-11-2017 2:15 PM

#### End Date

18-11-2017 3:15 PM

#### Location

BSC-Ursa Minor 8

#### Session

Poster 3

#### Type of Presentation

Poster

#### Subject Area

physical_mathematical_sciences

#### Abstract

AM Canum Venaticorum (AM CVn) systems are binary systems composed of a white dwarf accreting from a helium donor star. The system is formed after the binary systems becomes so compact that the helium star starts depositing matter around the white dwarf, creating an accretion disk. AM CVn systems are of great interest since they have the smallest spatial dynamic range of all other binary systems, making them perfect for global simulations of the accretion disk around the white dwarf star. Similarly, they are a prominent source of gravitational waves because of their compactness. We attempt to reproduce the frequency spectrum of AM CVn systems by calculating line spectra and including scattering effects in the accretion disk. To obtain the frequency spectrum we use Python scripts to solve the time independent radiative transfer equation using the method of short characteristics. We hope to better understand turbulent dynamics and thermodynamics of accretion disks in binary systems in general, not just AM CVn systems. So far, we have successfully reproduced absorption line spectra for hydrogen accretion disks using local shearing box simulations. We then make the transition to local and global simulations of AM CVn systems (helium systems) and including scattering effects. By calculating the frequency spectrum and comparing it to the observational data, we aim to understand how well our simulations of turbulence in accretion disks can explain observations. We will then analyze this information to further our understanding of other accretion disk systems, such as black hole and hydrogen accretion disks.

#### Summary of research results to be presented

In order to reproduce the frequency spectrum of AM CVn systems, we utilize numerical methods to solve the radiative transfer equation. After analyzing and reproducing the intensity of one-dimensional simulation data using two numerical methods: Short Characteristics and Feautrier's Method, we have concluded that the Method of Short Characteristics is better suited for our purposes. The Method of Short Characteristics is optimal because of its straight forward manner of solving the radiative transfer equation, while Feautrier's Method induces error from its usage of finite differences.

Similarly, we have successfully calculated the corresponding absorption coefficients for the bound-bound and free-free transitions. We have a working script to include bound-bound transitions (absorption lines) in the visible region of the electromagnetic spectrum. The absorption lines are, however very narrow and further research is needed to obtain broader transitions. This might imply that the line profile function is not only dependent on Doppler broadening, taking into account the velocity field of matter orbiting the disk.

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Modeling the Frequency Spectrum of AM CVn Systems by Solving the Radiative Transfer Equation

BSC-Ursa Minor 8

AM Canum Venaticorum (AM CVn) systems are binary systems composed of a white dwarf accreting from a helium donor star. The system is formed after the binary systems becomes so compact that the helium star starts depositing matter around the white dwarf, creating an accretion disk. AM CVn systems are of great interest since they have the smallest spatial dynamic range of all other binary systems, making them perfect for global simulations of the accretion disk around the white dwarf star. Similarly, they are a prominent source of gravitational waves because of their compactness. We attempt to reproduce the frequency spectrum of AM CVn systems by calculating line spectra and including scattering effects in the accretion disk. To obtain the frequency spectrum we use Python scripts to solve the time independent radiative transfer equation using the method of short characteristics. We hope to better understand turbulent dynamics and thermodynamics of accretion disks in binary systems in general, not just AM CVn systems. So far, we have successfully reproduced absorption line spectra for hydrogen accretion disks using local shearing box simulations. We then make the transition to local and global simulations of AM CVn systems (helium systems) and including scattering effects. By calculating the frequency spectrum and comparing it to the observational data, we aim to understand how well our simulations of turbulence in accretion disks can explain observations. We will then analyze this information to further our understanding of other accretion disk systems, such as black hole and hydrogen accretion disks.