ASAS J174406+2446.8 is identified as a marginal-contact binary with a possible cool third body

Abstract

ASAS J174406+2446.8 was originally found as a δ Scuti-type pulsating star with the period P = 0.189068 d by ASAS survey. However, the LAMOST stellar parameters reveal that it is far beyond the red edge of pulsational instability strip on the log g − T diagram of δ Scuti pulsating stars. To understand the physical properties of the variable star, we observed it by the 1.0-m Cassegrain reflecting telescope at Yunnan Observatories. Multi-color light curves in B, V, Rc and Ic bands were obtained and are analyzed by using the W-D program. It is found that this variable star is a shallow-contact binary with an EB-type light curve and an orbital period of 0.3781 d rather than a δ Scuti star. It is a W-subtype contact binary with a mass ratio of 1.135(± 0.019) and a fill-out factor of 10.4%(± 5.6)%. The situation of ASAS J174406+2446.8 resembles those of other EB-type marginal-contact binaries such as UU Lyn, II Per and GW Tau. All of them are at a key evolutionary phase from a semi-detached configuration to a contact system predicted by the thermal relaxation oscillation theory. The linear ephemeris was corrected by using 303 new determined times of light minimum. It is detected that the O – C curve shows a sinusoidal variation that could be explained by the light-travel-time effect via the presence of a cool red dwarf. The present investigation reveals that some of the δ Scuti-type stars beyond the red edge of pulsating instability strip on the log g – T diagram are misclassified eclipsing binaries. To understand their structures and evolutionary states, more studies are required in the future.