摘要：I report on close encounters of stars to the Sun found in the firstGaiadata release (GDR1). CombiningGaiaastrometry with radial velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which pass within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a similar study based on Hipparcosdata, even though the present study has many more candidates. This is partly because I reject stars with large radial velocity uncertainties (>10 km s-1), and partly because of missing stars in GDR1 (especially at the bright end). The closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. TheGaiaastrometry predict a much closer passage than pre-Gaiaestimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together with an approximation of the observational selection function, I model the incompleteness of thisGaia-based search as a function of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be545 ± 59 Myr-1. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds to87 ± 9 Myr-1within 2 pc. A more accurate analysis and assessment will be possible with futureGaiadata releases.
关键词：enOort cloudsolar neighborhoodstars: kinematics and dynamicssurveysmethods: statisticalmethods: analytical
