We report the selection and spectroscopic confirmation of 129 new late-type ( SpT = K3–M6 ) members of the Tucana-Horologium moving group , a nearby ( d \sim 40 pc ) , young ( \tau \sim 40 Myr ) population of comoving stars .
We also report observations for 13 of the 17 known Tuc-Hor members in this spectral type range , and that 62 additional candidates are likely to be unassociated field stars ; the confirmation frequency for new candidates is therefore 129 / 191 = 67 \% .
We have used radial velocities , H \alpha emission , and Li _ { 6708 } absorption to distinguish between contaminants and bona fide members .
Our expanded census of Tuc-Hor increases the known population by a factor of \sim 3 in total and by a factor of \sim 8 for members with SpT \geq K3 , but even so , the K-M dwarf population of Tuc-Hor is still markedly incomplete .
Our expanded census allows for a much more detailed study of Tuc-Hor than was previously feasible .
The spatial distribution of members appears to trace a two-dimensional sheet , with a broad distribution in X and Y , but a very narrow distribution ( \pm 5 pc ) in Z .
The corresponding velocity distribution is very small , with a scatter of \pm 1.1 km/s about the mean UVW velocity for stars spanning the entire 50 pc extent of Tuc-Hor .
We also show that the isochronal age ( \tau \sim 20 –30 Myr ) and the lithium depletion boundary age ( \tau \sim 40 Myr ) disagree , following the trend in other pre-main sequence populations for isochrones to yield systematically younger ages .
The H \alpha emission line strength follows a trend of increasing equivalent width with later spectral type , as is seen for young clusters .
We find that moving group members have been depleted of measurable lithium for spectral types of K7.0–M4.5 .
None of our targets have significant infrared excesses in the WISE W3 band , yielding an upper limit on warm debris disks of F < 0.7 \% .
Finally , our purely kinematic and color-magnitude selection procedure allows us to test the efficiency and completeness for activity-based selection of young stars .
We find that 60 % of K-M dwarfs in Tuc-Hor do not have ROSAT counterparts and would have been omitted in X-ray selected samples .
In contrast , GALEX UV-selected samples using a previously suggested criterion for youth achieve completeness of 77 % and purity of 78 % , and we suggest new SpT-dependent selection criteria that will yield > 95 % completeness for \tau \sim 40 Myr populations with GALEX data available .