HD 164615: a probable spotted single F type star

This star shows light variations by 0.05 mag in a period of about 0.815 deg, but there are substantial differences from cycle to cycle. Various possible explanations for the variations were explored. First, the star is not an Ap variable because its spectrum is normal (F2 IV) and it does not have the color variations that are typical of an Ap star. It is not an ellipsoidal primary because the radial velocity does not change; a lack of change in line widths excludes the possibility of its being a double-lined binary with unresolved lines. It is probably not a pulsating star because of the lack of color and velocity changes. However, the hypothesis of a single rotating spotted star fits because the rotational period (1.7 deg sin i) is compatible with the light period (0.815 deg) and it offers a natural explanation for changes from cycle to cycle in terms of changes in spot activity. It has not been possible to determine whether the spots are bright or dark ones in this rapid rotator.