Amplitude modulation and energy conservation of pulsation modes in delta Scuti stars
type: CreativeWork
description: The pulsations in δ Sct stars are excited by a heat engine driving mechanism caused by in-creased opacity in their surface layers, and have pulsation periods of order a few hours. Space based observations in the last decade have revealed a diverse range of pulsational be-haviour in these stars, which is investigated using an ensemble of 983 δ Sct stars observed continuously for 4 yr by the Kepler Space Tele-scope. A statistical search for amplitude modu-lation of pulsation modes is carried out and it is shown that 61.3 per cent of the 983 δ Sct stars exhibit significant amplitude modulation in at least a single pulsation mode, and that this is uncorrelated with effective temperature and surface gravity. Hence, the majority of δ Sct stars exhibit amplitude modulation, with time-scales of years and longer demonstrated to be significant in these stars both observationally and theoretically. An archetypal example of amplitude modulation in a δ Sct star is KIC 7106205, which contains only a single pulsation mode that varies signifi-cantly in amplitude whilst all other pulsation modes stay constant in amplitude and phase throughout the 4-yr Kepler data set. Therefore, the visible pulsational energy budget in this star, and many others, is not conserved over 4 yr. Models of beating of close-frequency pulsation modes are used to identify δ Sct stars with fre-quencies that lie closer than 0.001 d−1, which are barely resolved using 4 yr of Kepler observa-tions, and maintain their independent identi-ties over 4 yr. Mode coupling models are used to quantify the strength of coupling and distin-guish between non-linearity in the form of combination frequencies and non-linearity in the form of resonant mode coupling for families of pulsation modes in several stars. The changes in stellar structure caused by stel-lar evolution are investigated for two high am-plitude δ Sct (HADS) stars in the Kepler data set, revealing a positive quadratic change in phase for the fundamental and fi…
abstract: The pulsations in δ Sct stars are excited by a heat engine driving mechanism caused by in-creased opacity in their surface layers, and have pulsation periods of order a few hours. Space based observations in the last decade have revealed a diverse range of pulsational be-haviour in these stars, which is investigated using an ensemble of 983 δ Sct stars observed continuously for 4 yr by the Kepler Space Tele-scope. A statistical search for amplitude modu-lation of pulsation modes is carried out and it is shown that 61.3 per cent of the 983 δ Sct stars exhibit significant amplitude modulation in at least a single pulsation mode, and that this is uncorrelated with effective temperature and surface gravity. Hence, the majority of δ Sct stars exhibit amplitude modulation, with time-scales of years and longer demonstrated to be significant in these stars both observationally and theoretically. An archetypal example of amplitude modulation in a δ Sct star is KIC 7106205, which contains only a single pulsation mode that varies signifi-cantly in amplitude whilst all other pulsation modes stay constant in amplitude and phase throughout the 4-yr Kepler data set. Therefore, the visible pulsational energy budget in this star, and many others, is not conserved over 4 yr. Models of beating of close-frequency pulsation modes are used to identify δ Sct stars with fre-quencies that lie closer than 0.001 d−1, which are barely resolved using 4 yr of Kepler observa-tions, and maintain their independent identi-ties over 4 yr. Mode coupling models are used to quantify the strength of coupling and distin-guish between non-linearity in the form of combination frequencies and non-linearity in the form of resonant mode coupling for families of pulsation modes in several stars. The changes in stellar structure caused by stel-lar evolution are investigated for two high am-plitude δ Sct (HADS) stars in the Kepler data set, revealing a positive quadratic change in phase for the fundamental and fi…
author: Bowman, Dominic Matthew
language: en
keywords: F500 - Astronomy
date published: 2016-10
date modified: 2026-07-24T01:35:56Z
provider: University of Central Lancashire
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Central Lancashire