Holdsworth, Daniel L. (2015) A survey for pulsations in A-type stars using SuperWASP. Doctoral thesis, Keele University.
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A survey of A-type stars is conducted with the SuperWASP archive in the search for pulsationally variable stars. Over 1.5 million stars are selected based on their (J − H) colour. Periodograms are calculated for light curves which have been extracted from the archive and cleaned of spurious points. Peaks which have amplitudes greater than 0.5 millimagnitude are identiﬁed in the periodograms. In total, 202 656 stars are identiﬁed to show variability in the range 5 − 300 d−1.
Spectroscopic follow-up was obtained for 38 stars which showed high-frequency pulsations between 60 and 235 d−1, and a further object with variability at 636 d−1. In this sample, 13 were identiﬁed to be normal A-type δ Sct stars, 14 to be pulsating metallic-lined Am stars, 11 to be rapidly oscillating Ap (roAp) stars, and one to be a subdwarf B variable star. The spectra were used not only to classify the stars, but to determine an eﬀective temperature through Balmer line ﬁtting.
Hybrid stars have been identiﬁed in this study, which show pulsations in both the high- and low-overtone domains; an observation not predicted by theory. These stars are prime targets to perform follow-up observations, as a conﬁrmed detection of this phenomenon will have signiﬁcant impact on the theory of pulsations in A-type stars.
The detected number of roAp stars has expanded the known number of this pulsator class by 22 per cent. Within these results both the hottest and coolest roAp star have been identiﬁed. Further to this, one object, KIC 7582608, was observed by the Kepler telescope for 4 yr, enabling a detailed frequency analysis. This analysis has identiﬁed signiﬁcant frequency variations in this star, leading to the hypothesis that this is the ﬁrst close binary star of its type.
The observational results presented in this thesis are able to present new challenges to the theory of pulsations in A-type stars, with potentially having the eﬀect of further delaying the full understanding of ‘so simple a thing as a star’.
|Item Type:||Thesis (Doctoral)|
|Subjects:||Q Science > QB Astronomy|
|Divisions:||Faculty of Natural Sciences > School of Physical and Geographical Sciences|
|Depositing User:||Michael Debenham|
|Date Deposited:||10 Mar 2016 16:43|
|Last Modified:||10 Mar 2016 16:43|
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