A new look inside planetary nebula LoTr 5: a long-period binary with hints of a possible third component

LoTr 5 is a planetary nebulawith an unusual long-period binary central star. As far as we know, the pair consists of a rapidly rotating G-type starand a hot star, which is responsible for the ionization of the nebula. The rotation periodof the G-type staris 5.95 days and the orbital periodof the binary is now known to be $\sim$2700 days, one of the longest in central starof planetary nebulae. The spectrum of the G central starshows a complex H$\ alpha$ double-peaked profile which varies with very short time scales, also reported in other central starsof planetary nebulaeand whose origin is still unknown. We present new radial velocity observations of the central starwhich allow us to confirm the orbital periodfor the long-period binary and discuss the possibility of a third component in the system at $\sim$129 days to the G star. This is complemented with the analysis of archival light curves from SuperWASP, ASAS and OMC. From the spectral fitting of the G-type star, we obtain a effective temperatureof $T_{\rm eff}$ = 5410$\pm$250 K and surface gravityof $\log g$ = 2.7$\pm$0.5, consistent with both giant and subgiant stars. We also present a detailed analysis of the H$\ alpha$ double-peaked profile and conclude that it does not present correlation with the rotation periodand that the presence of an accretion disk via Roche lobeoverflow is unlikely.