Magnetic braking in low-mass stars
type: CreativeWork
description: Low-mass stars with masses below about 1.3 solar masses exhibit intriguing trends in the evolution of their spins. These stars also exist in tidally locked binaries with a white dwarf (WD) companion, the cataclysmic variables (CVs). Their orbital evolution is driven by angular momentum loss due to magnetic braking (MB). Although the same fundamental mechanism likely drives MB in all these systems, a holistic study of such a mechanism has not been carried out before. Here I aim to investigate whether observations of CV evolution and the spins of single stars can be explained by the same fundamental mechanism driving MB in all low-mass stars. In Chapter 1, I illustrate the salient features of the evolution of low-mass stars with convective exteriors and radiative cores (if any), describe the physics of MB and provide a background on CVs and their evolution. I also touch upon the working of the Cambridge stellar evolution code with which I evolve and model these stellar systems. In Chapter 2, I model the secular evolution of CVs with a double dynamo model wherein there is an interplay between two α-Ω dynamos, one in the convective envelope and the other at the boundary of the radiative core and the convective envelope. I confirm that this model provides a physical formalism for the interrupted magnetic braking paradigm. I construct the relative probability distribution of orbital periods from the mass distribution of white dwarfs in CVs and find that this model reproduces the period gap and the observed period minimum spike in CV distribution. In Chapter 3, I explore the implications of the hypothesis that MB, which may be an angular momentum loss mechanism working in addition to gravitational wave radiation for CVs below the period gap, weakens around their period minimum. This explains the strong disagreement between theory and observations of the relative fraction of period bouncer CVs. I find that, with such a mechanism, the CV virtually stalls around the period mi…
abstract: Low-mass stars with masses below about 1.3 solar masses exhibit intriguing trends in the evolution of their spins. These stars also exist in tidally locked binaries with a white dwarf (WD) companion, the cataclysmic variables (CVs). Their orbital evolution is driven by angular momentum loss due to magnetic braking (MB). Although the same fundamental mechanism likely drives MB in all these systems, a holistic study of such a mechanism has not been carried out before. Here I aim to investigate whether observations of CV evolution and the spins of single stars can be explained by the same fundamental mechanism driving MB in all low-mass stars. In Chapter 1, I illustrate the salient features of the evolution of low-mass stars with convective exteriors and radiative cores (if any), describe the physics of MB and provide a background on CVs and their evolution. I also touch upon the working of the Cambridge stellar evolution code with which I evolve and model these stellar systems. In Chapter 2, I model the secular evolution of CVs with a double dynamo model wherein there is an interplay between two α-Ω dynamos, one in the convective envelope and the other at the boundary of the radiative core and the convective envelope. I confirm that this model provides a physical formalism for the interrupted magnetic braking paradigm. I construct the relative probability distribution of orbital periods from the mass distribution of white dwarfs in CVs and find that this model reproduces the period gap and the observed period minimum spike in CV distribution. In Chapter 3, I explore the implications of the hypothesis that MB, which may be an angular momentum loss mechanism working in addition to gravitational wave radiation for CVs below the period gap, weakens around their period minimum. This explains the strong disagreement between theory and observations of the relative fraction of period bouncer CVs. I find that, with such a mechanism, the CV virtually stalls around the period mi…
author: Sarkar, Arnab
language: eng
keywords: low-mass stars, magnetic braking, stellar evolution
license: https://www.repository.cam.ac.uk/bitstreams/d2727978-cb7a-4e6e-9073-34f5eacbcada/download
license: http://purl.org/NET/rdflicense/allrightsreserved
date published: 2025-03-27
date modified: 2026-07-22T22:24:03Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.122617