We present the results of a multi-technique investigation of the M4.5Ve flare star AP Col , which we discover to be the nearest pre-main-sequence star .
These include astrometric data from the CTIO 0.9m , from which we derive a proper motion of 342.0 \pm 0.5 mas yr ^ { -1 } , a trigonometric parallax of 119.21 \pm 0.98 mas ( 8.39 \pm 0.07 pc ) , and photometry and photometric variability at optical wavelengths .
We also provide spectroscopic data , including radial velocity ( 22.4 \pm 0.3 km s ^ { -1 } ) , lithium Equivalent Width ( EW ) ( 0.28 \pm 0.02Å ) , H \alpha EW ( - 6.0 to - 35Å ) , vsini ( 11 \pm 1 km s ^ { -1 } ) , and gravity indicators from the Siding Spring 2.3-m WiFeS , Lick 3-m Hamilton echelle , and Keck-I HIRES echelle spectrographs .
The combined observations demonstrate that AP Col is the closer of only two known systems within 10 pc of the Sun younger than 100 Myr .
Given its space motion and apparent age of 12-50 Myr , AP Col is likely a member of the recently proposed \sim 40 Myr old Argus/IC 2391 association .