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High-precision space-based photometry obtained by the \emph{Kepler} and\emph{TESS} missions has revealed evidence of rotational modulation associatedwith main sequence (MS) A and late-B type stars. Generally, such variability inthese objects is attributed to inhomogeneous surface structures (e.g. chemicalspots), which are typically linked to strong magnetic fields($B\gtrsim100\,{\rm G}$) 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 surprisingconsidering that $\lesssim10$~per~cent of all MS A-type stars are known to bestrongly magnetic (i.e. they are Ap/Bp stars). We present a spectroscopicmonitoring survey of 44 A and late-B type stars reported to exhibit rotationalmodulation in their \emph{Kepler} light curves. The primary goal of this surveyis to test the hypothesis that the variability is rotational modulation bycomparing each star's rotational broadening ($v\sin{i}$) with the equatorialvelocities ($v_{\rm eq}$) inferred from the photometric periods. We searchedfor chemical peculiarities and binary companions in order to provide insightinto the origin of the apparent rotational modulation. We find that 14 stars inour sample have $v\sin{i}>v_{\rm eq}$ and/or have low-mass companions that maycontribute to or be responsible for the observed variability. Our resultssuggest that more than $10$~per~cent of all MS A and late-B type stars mayexhibit inhomogeneous surface structures; however, the incidence rate is likely$\lesssim30$~per~cent.

A spectroscopic test of the rotational modulation origin of periodic \emph{Kepler} photometric variability of A-type stars