A. Aller, J. Lillo-Box, M. Vučković, H. Van Winckel, D. Jones, B. Montesinos, M. Zorotovic, L. F. Miranda. 2018. A new look inside planetary nebula LoTr 5: a long-period binary with hints of a possible third component. Monthly Notices of the Royal Astronomical Society, 476, 1, 1140-1150, DOI: 10.1093/mnras/sty174
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 d and the orbital period of the binary is now known to be similar to 2700 d, one of the longest in central star of planetary nebulae. The spectrum of the G central star shows a complex Ha 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 similar to 129 d to the G star. This is complemented with the analysis of archival light curves from Super Wide Angle Search for Planets, All Sky Automated Survey, and Optical Monitoring Camera. From the spectral fitting of the G-type star, we obtain an effective temperature of T-eff = 5410 +/- 250 K and surface gravity of log g = 2.7 +/- 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 disc via Roche lobe overflow is unlikely.