The Solar Neighborhood. XXVI. AP Col: The Closest (8.4 pc) Pre-Main-Sequence Star

TL;DR

This study identifies AP Col as the nearest pre-main-sequence star at 8.4 parsecs, using multi-technique observations to determine its properties and likely membership in a young stellar association.

Contribution

It provides the first detailed characterization of AP Col as the closest known pre-main-sequence star within 10 parsecs, including its astrometry, spectroscopy, and age estimation.

Findings

AP Col is the nearest pre-main-sequence star at 8.4 pc.

AP Col is likely a member of the ~40 Myr old Argus/IC 2391 association.

AP Col is one of only two known systems within 10 pc younger than 100 Myr.

Abstract

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.