| Maintainer | https://mastodon.social/@hannorein |
| REBOUND code | https://github.com/hannorein/rebound |
| Bot source code | https://github.com/hannorein/reboundcitationbot |
The TOI-178 system hosts six planets with five of them locked in a 2:4:6:9:12 Laplace resonance chain. We perform N-body simulations to investigate the dynamics of test particles in this system. We observe that co-orbital regions around each planet are approximately 30% wider than predicted by classical theory for planets in the resonance chain, while TOI-178b, which lies outside the chain, shows a 52% enhancement. The region between TOI-178e and TOI-178f reveals Kirkwood gap-like structures created by mean-motion resonances with TOI-178f (4:3, 5:4, 6:5) and TOI-178g (5:3), where particle clearing occurs on 500-year timescales. An extended integration of the innermost region (0.015─0.025 au) shows periodic inclination oscillations with period 196 years, coincident with TOI-178b's own oscillation period, with maximum amplitude occurring near the 3:2 resonance location. These structures are consistent with the system's resonant architecture and provide a baseline characterization that enables future comparative studies of similar phenomena in other multi-planet systems with resonant configurations.
Binaries in the cores of globular clusters are known to prevent the gravitational collapse of the cluster, and simulations predict that the core of NGC 6397 contains a high number of white dwarfs (WDs), of which many are expected to be part of a binary system. In this work, we report the discovery of a compact binary system consisting of two WDs in the centre of the Galactic globular cluster NGC 6397. The system, known in the literature as NF1, was observed as part of a MUSE radial-velocity survey aiming at characterizing the binary population in the centre of NGC 6397. The spectral analysis of NF1 provides an effective temperature of 16 000 K and a surface gravity (log g) of 5.72 (cgs), which is consistent with the characteristics of an extremely low-mass He-core WD. This is further supported by the mass of 0.23 ± 0.03 M<SUB>⊙</SUB> obtained from fitting the star's spectral energy distribution using its HST magnitude in various filters. The system has a circular orbit with a period of 0.54 days. The radial velocities show a large semi-amplitude of 200 km/s, implying a minimum mass of 0.78 M<SUB>⊙</SUB> for the invisible companion, which is likely another WD, or a neutron star if the inclination of the system is smaller than about 50°. Some significant residuals in radial velocity remain with our best orbital solution, and we tested whether a model with a third body can explain these deviations. While this possibility seems promising, additional measurements are needed to confirm whether the star is actually part of a triple system.