PERIODIC BEHAVIOUR OF STARS IN THE GEOS RR LYRAE DATABASE PAPER 3: EF CANCRI AND BD DRACONIS

摘要

The GEOS values for the times of maximum light have been investigated for the RR Lyrae stars EF Cancri and BD Draconis. Both are shown to have longer periods in addition to their pulsation periods. The data for EF Cnc are insufficient to determine which of three possible periods is the definitive one, but a period of near to II days is currently the most likely. The O – C values folded with this period show a continuous sine-like curve with a total range of about o.o25 days. BD Dra has changed its pulsation period at least three times over the last IIO years. Additionally it has a very definite period of near to 24 days, clearly visible in the more-recent observations. The data folded with this period show a continuous variation with a broad maximum and a short and deep minimum. The total range of this variation is about o.o8 days. The shape of this variation is what one might expect to be due to light-travel times from a star in an eccentric binary orbit, but the combination of a 24-day period with a total amplitude of o.o8 days is not compatible with a simple binary model. In both cases the phase diagrams have very different characteristics to those of the stars RR Lyr and AR Her discussed earlier in this series of papers. If the variations in both RR Lyr and AR Her are Blazhko-effect-type variations then the question arises as to what is the source of the variations in EF Cnc and BD Dra. If they are Blazhko-type variations then some explanation has to be found for the very different shapes of the variations. If they are not Blazhko-type variations then their source needs to be discovered.