摘要：Six billion years from now, while evolving on the asymptotic giant branch (AGB), the Sun
will metamorphose from a red giant into a beautiful planetary nebula. This spectacular
evolution will impact the solar system planets, but observational confirmations of the
predictions of evolution models are still elusive as no planet orbiting an AGB star has
yet been discovered. The nearby AGB red giant L2 Puppis (d = 64 pc) is surrounded by an almost edge-on
circumstellar dust disk. We report new observations with ALMA at very high angular
resolution (18 × 15 mas) in
band 7 (ν ≈
350 GHz) that allow us to resolve the velocity profile of the molecular
disk. We establish that the gas velocity profile is Keplerian within the central cavity of
the dust disk, allowing us to derive the mass of the central star L2 Pup A, mA = 0.659 ± 0.011 ± 0.041
M⊙ (± 6.6%). From evolutionary models, we
determine that L2 Pup A had a near-solar main-sequence mass, and is therefore
a close analog of the future Sun in 5 to 6 Gyr. The continuum map reveals a secondary
source (B) at a radius of 2 AU contributing fB/fA = 1.3
± 0.1% of the flux of the AGB star. L2 Pup B is also detected in CO
emission lines at a radial velocity of vB = 12.2 ± 1.0 km s-1. The close coincidence of the
center of rotation of the gaseous disk with the position of the continuum emission from
the AGB star allows us to constrain the mass of the companion to mB = 12 ± 16
MJup. L2 Pup B is most likely a planet
or low-mass brown dwarf with an orbital period of about five years. Its continuum
brightness and molecular emission suggest that it may be surrounded by an extended
molecular atmosphere or an accretion disk. L2 Pup therefore emerges as a promising vantage point on
the distant future of our solar system.
关键词：stars: individual: HD 56096;stars: AGB and post-AGB;circumstellar matter;techniques: high angular resolution;planetary systems;planets and satellites: detection
