The year-long flux variations in Boyajian's star are asymmetric or aperiodic

We combine and calibrate publicly available data for Boyajian's star including photometry from ASAS (SN, V, I), Kepler, Gaia, SuperWASP, and citizen scientist observations (AAVSO, HAO and Burke-Gaffney). Precise (mmag) photometry covers the years 2006-2017. We show that the year-long flux variations with an amplitude of ~4% can not be explained with cyclical symmetric or asymmetric models with periods shorter than ten years. If the dips are transits, their period must exceed ten years, or their structure must evolve significantly during each 4-year long cycle.