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

TL;DR

This paper investigates the central binary system of planetary nebula LoTr 5, confirming its long orbital period, suggesting a possible third component, and analyzing spectral features to understand the system's dynamics and structure.

Contribution

It provides new radial velocity data confirming the binary period and explores the potential existence of a third component in the system.

Findings

Confirmed the orbital period of ~2700 days for the binary system.

Suggested the possible presence of a third component at ~129 days.

Analyzed spectral features indicating no correlation with rotation period.

Abstract

LoTr 5 is a planetary nebula with an unusual long-period binary central star. As far as we know, the pair consists of a rapidly rotating G-type star and a hot star, which is responsible for the ionization of the nebula. The rotation period of the G-type star is 5.95 days and the orbital period of the binary is now known to be $\sim$2700 days, one of the longest in central star of planetary nebulae. The spectrum of the G central star shows a complex H$\alpha$ double-peaked profile which varies with very short time scales, also reported in other central stars of planetary nebulae and whose origin is still unknown. We present new radial velocity observations of the central star which allow us to confirm the orbital period for 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 temperature of $T_{\rm eff}$ = 5410$\pm$250 K and surface gravity of $\log g$ = 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 period and that the presence of an accretion disk via Roche lobe overflow is unlikely.