Periodic variations in the O-C diagrams of five pulsation frequencies of the DB white dwarf EC 20058-5234

摘要

Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarfEC 20058−5234 individually imitate the effects of reflex motion induced by a planet or companion but areinconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle andundergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude ofthe periodic and secular variations increases with the period of the pulsations, possibly hinting that the correspondingphysical mechanism is located near the surface of the star. The phase of the periodic variations appears coupledto the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companionsaround pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated.The physical mechanism responsible for this surprising result may involve a redistribution of angular momentumor a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sumof the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmationof theoretical predictions.