On the Age and Binarity of Fomalhaut

摘要: The nearby (d = 7.7 pc) A3V star Fomalhaut is orbited by a resolved dusty debris disk and controversial candidate extrasolar planet. commonly cited age for the system (200 ± 100 Myr) from Barrado y Navascues et al. relied on combination of isochronal plus youth indicators K4V common proper-motion TW PsA. PsA 196 away was first proposed as companion Luyten, but physicality binarity worth testing with modern data. I demonstrate that unequivocally physical stellar to Fomalhaut, true separation 0.280+0.019 – 0.012 pc (57.4+3.9 2.5 kAU) sharing velocities within 0.1 0.5 km s–1—consistent being bound system. Hence, should be considered "Fomalhaut B." Combining H-R diagram constraints four sets evolutionary tracks, assuming born protosolar composition, estimate new 450 40 Myr mass 1.92 0.02 M ☉. Various diagnostics are re-examined star's rotation, X-ray emission, Li abundances consistent approximate ages 410, 380, 360 Myr, respectively, yielding weighted mean 400 70 Myr. independent ages, Fomalhaut-TW binary 440 older implies substellar companions given approximately 1 mag fainter at IR wavelengths than previously assumed.