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Register a new userA wavelet analysis of photometric variability in Kepler white dwarf stars
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Suzierly De Lira Roque
Publication date
2019
fields
Physics
and research's language is
English
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This work brings a wavelet analysis for 14 Kepler white dwarf stars, in order to confirm their photometric variability behavior and to search for periodicities in these targets. From the observed Kepler light curves we obtained the wavelet local and global power spectra. Through this procedure, one can perform an analysis in time-frequency domain rich in details, and so to obtain a new perspective on the time evolution of the periodicities present in these stars. We identified a photometric variability behavior in ten white dwarfs, corresponding to period variations of ~ 2 h to 18 days: among these stars, three are new candidates and seven, earlier identified from other studies, are confirmed.
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High-precision space-based photometry obtained by the emph{Kepler} and emph{TESS} missions has revealed evidence of rotational modulation associated with main sequence (MS) A and late-B type stars. Generally, such variability in these objects is attributed to inhomogeneous surface structures (e.g. chemical spots), which are typically linked to strong magnetic fields ($Bgtrsim100,{rm G}$) visible at the surface. It has been reported that $approx44$~per~cent of all A-type stars observed during the emph{Kepler} mission exhibit rotationally modulated light curves. This is surprising considering that $lesssim10$~per~cent of all MS A-type stars are known to be strongly magnetic (i.e. they are Ap/Bp stars). We present a spectroscopic monitoring survey of 44 A and late-B type stars reported to exhibit rotational modulation in their emph{Kepler} light curves. The primary goal of this survey is to test the hypothesis that the variability is rotational modulation by comparing each stars rotational broadening ($vsin{i}$) with the equatorial velocities ($v_{rm eq}$) inferred from the photometric periods. We searched for chemical peculiarities and binary companions in order to provide insight into the origin of the apparent rotational modulation. We find that 14 stars in our sample have $vsin{i}>v_{rm eq}$ and/or have low-mass companions that may contribute to or be responsible for the observed variability. Our results suggest that more than $10$~per~cent of all MS A and late-B type stars may exhibit inhomogeneous surface structures; however, the incidence rate is likely $lesssim30$~per~cent.
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