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+/-0.5 mas yr^-1, a trigonometric parallax of 119.21+/-0.98 mas
(8.39+/-0.07 pc), and photometry and photometric variability at optical
wavelengths. We also provide spectroscopic data, including radial velocity
(22.4+/-0.3 km s^-1), lithium Equivalent Width (EW) (0.28+/-0.02 A), H-alpha EW
(-6.0 to -35 A), {\it vsini} (11+/-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 ~40 Myr old Argus/IC 2391 association.Comment: 31 pages, 11 figure
