The nearby ( d = 7.7 pc ) A3V star Fomalhaut is orbited by a resolved dusty debris disk and a controversial candidate extrasolar planet .
The commonly cited age for the system ( 200 \pm 100 Myr ) from Barrado y Navascues et al .
( 4 ) relied on a combination of isochronal age plus youth indicators for the K4V common proper motion system TW PsA .
TW PsA is 1 ^ { \circ } .96 away from Fomalhaut , and was first proposed as a companion by Luyten ( 1938 ) , but the physicality of the binarity is worth testing with modern data .
I demonstrate that TW PsA is unequivocally a physical stellar companion to Fomalhaut , with true separation 0.280 ^ { +0.019 } _ { -0.012 } pc ( 57.4 ^ { +3.9 } _ { -2.5 } kAU ) and sharing velocities within 0.1 \pm 0.5 km s ^ { -1 } – consistent with being a bound system .
Hence , TW PsA should be considered “ Fomalhaut B ” .
Combining modern HR diagram constraints with four sets of evolutionary tracks , and assuming the star was born with protosolar composition , I estimate a new isochronal age for Fomalhaut of 450 \pm 40 Myr and mass of 1.92 \pm 0.02 M _ { \odot } .
Various stellar youth diagnostics are re-examined for TW PsA .
The star ’ s rotation , X-ray emission , and Li abundances are consistent with approximate ages of 410 , 380 , and 360 Myr , respectively , yielding a weighted mean age of 400 \pm 70 Myr .
Combining the independent ages , I estimate a mean age for the Fomalhaut-TW PsA binary of 440 \pm 40 Myr .
The older age implies that substellar companions of a given mass are approximately one magnitude fainter at IR wavelengths than previously assumed .