An investigation of cross-harmonics as the cause of long secondary periods in long period variable stars

Sherren, Galina (2024) An investigation of cross-harmonics as the cause of long secondary periods in long period variable stars. Memorial University of Newfoundland. (Unpublished)

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (3MB)

Abstract

Long period variables (LPVs) are stars that have ceased burning Hydrogen in their cores and have moved to the asymptotic giant branch [1]. During this phase of evolution LPVs have periods of over 100 days [2]. LPVs can pulsate in the fundamental of overtone modes, and can display multiple pulsation frequencies at once. While the exact driving mechanism of this pulsation is unknown, it is likely that the large convection zone in the star plays into this oscillation period [2]. Some LPVs display a phenomenon called long secondary periods (LSPs) that are 5-10 times the length of the main pulsation period. During the summer of 2023, preliminary analysis to this project involved analyzing the brightness data of a sample of six LPV stars. One of the stars, V CVn, displayed an extra-long secondary period over 30 times the length of the main period of the star. Other stars analyzed also displayed traditional LSPs of 5-10 times the main period. One proposed explanation of V CVn's extra-long LSP was cross-harmonics: the interplay of two simultaneously occuring periods in an LPV. This thesis serves as an investigation of the possibility of LSPs and V CVn's extralong LSP being caused by cross-harmonics. In order to do this, a stellar evolution models of 0:85 M⊙, 0:9 M⊙, 1 M⊙, 1:2 M⊙, and 1:3 M⊙ stars were made using Modules for Experiments in Stellar Astrophysics (MESA). These evolution models were then analyzed using GYRE for their pulsation periods during the LPV phase, and the cross-harmonics calculated using python. As a result of this analysis, we do not �nd evidence of LSPs in the cross-harmonic calculations of the models used for this study. However, periods consistent with LSPs were observed in the pulsation period calculation.

Actions (login required)

View Item