ON THE AGE OF GLIESE 86

Abstract

Gliese 86 is a nearby planet hosting a visual binary consisting of a K-type primary, Gl 86 A, and a white dwarf secondary, Gl 86 B. In this work, we present a model atmosphere analysis of the MA = 0.83 M☉ primary, whose chemistry unambiguously identifies it as a 10 Gyr old disk star. For the secondary, this gives rise to a progenitor mass Mprog = 1.11 ± 0.05 M☉, and—by inference with its local sibling o2 Eri—a white dwarf mass MB = 0.49 ± 0.02 M☉. The discrepancy with the 2–3 Gyr chromospheric age of Gl 86 A, as first noted by Rocha-Pinto, Castilho & Maciel, is thus most plausibly the result of a former accretion of mass and angular momentum from the distant degenerate. In consequence, this also implies that with respect to shorter-period systems, like Sirius or Procyon, one must expect significant wind accretion when they evolve through the planetary nebula phase, such that the system ages cannot be reliably determined from their currently bright primaries.