The identification and classification of variability in stellar sources observed with SuperWasp

Payne, Stanley George (2013). The identification and classification of variability in stellar sources observed with SuperWasp. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000d62d

Abstract

The purpose of this thesis was to create an automated classifier for periodic stellar objects in the Wide- Angle Search for Planets Survey (SuperW ASP) and to use the classified stars to investigate three phenomena: differentiation of Beta Lyrae and W UMa eclipsing binary stars using eclipse-depth ratio; identification of RR Lyrae stars exhibiting the Blazhko effect; and, the presence of the Oosterhoff dichotomy in the Milky Way.

During this work, period/amplitude ranges and distribution maps were created for the classified stars in stellar classes Algol, Beta Lyrae, W UMa, Delta Scuti and RR Lyrae (RRAB) and comparison made with published equivalents. SuperW ASP objects known in the General Catalogue of Variable Stars (GCVS) were also assessed to identify differences.

The automated system contained three neural networks (NNs) that processed parameters defining the' shape of the phase-folded light-curve and they were trained with representative sets of eclipsing binary, pulsating and sinusoidal-like stars. The system, installed at Leicester University processed 4.3 million object/periods from the SuperWASP database, of which 1.1 million were given prospective classifications. From these, approximately 64 thousand objects consisting of eclipsing binary and pulsating stars were assessed manually to confirm the given period/classifications and roughly half were classified correctly. The reasons for the misclassifications were identified and recommendations made on improving the results.

The manually confirmed objects consisted of 12,882 Algols, 5,226 Beta Lyrae, 2,875 W UMa, 1,979 Delta Scutis and 8,322 RR Lyraes (RRAB), where significant numbers of each were unknowrr in SIMBAD or the GCVS. Many objects had periods and/or amplitudes outside published ranges with the surprising result that the majority of Beta Lyraes had periods shorter than published.

A separation range for eclipse-depth ratio was identified but a cross-over point existed where differentiation was not possible. A number of new RRAB Blazhko stars were identified and the amplitude range between peaks calculated. The presence of the Oosterhoff dichotomy in the Milky Way galaxy was supported, but the causative factors could not be confirmed.

Comparison of the SuperW ASP periods with the GCVS resulted in 649 variable stars being added to the GCVS catalogue where the period was unknown in the GCVS and also revision of the variability period of 194 GCVS variable stars was suggested. For comparison of classification, sub-classes were suggested for 333 unconfirmed objects in the GCVS (e.g. CEP:, EA:, RR etc.) and re-classification was suggested for 197 GCVS objects with suspected incorrect classes.