A Stellar Census Of The Tucana-Horologium Moving Group

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dc.contributor.utaustinauthorKraus, Adam L.en_US
dc.creatorKraus, Adam L.en_US
dc.creatorShkolnik, Evgenya L.en_US
dc.creatorAllers, Katelyn N.en_US
dc.creatorLiu, Michael C.en_US
dc.date.accessioned2016-04-22T19:44:18Z
dc.date.available2016-04-22T19:44:18Z
dc.date.issued2014-06en
dc.description.abstractWe report the selection and spectroscopic confirmation of 129 new late-type (SpT = K3-M6) members of the Tucana-Horologium moving group, a nearby (d similar to 40 pc), young (tau similar to 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, Ha 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 similar to 3 in total and by a factor of similar to 8 for members with SpT >= 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 (+/- 5 pc) in Z. The corresponding velocity distribution is very small, with a scatter of +/- 1.1 km s(-1) about the mean UVW velocity for stars spanning the entire 50 pc extent of Tuc-Hor. We also show that the isochronal age (tau similar to 20-30 Myr) and the lithium depletion boundary age (tau similar to 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 similar to 40 Myr populations with GALEX data available.en_US
dc.description.departmentAstronomyen_US
dc.description.sponsorshipClay Fellowshipen_US
dc.identifierdoi:10.15781/T2RN5B
dc.identifier.citationKraus, Adam L., Evgenya L. Shkolnik, Katelyn N. Allers, and Michael C. Liu. >A Stellar Census of the Tucana-Horologium Moving Group.> The Astronomical Journal, Vol. 147, No. 6 (Jun., 2014): 146.en_US
dc.identifier.doi10.1088/0004-6256/147/6/146en_US
dc.identifier.issn0004-6256en_US
dc.identifier.urihttp://hdl.handle.net/2152/34333
dc.language.isoEnglishen_US
dc.relation.ispartofserialAstronomical Journalen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.subjectbinaries: spectroscopicen_US
dc.subjectopen clusters and associations: individualen_US
dc.subject(tucana-horologium)en_US
dc.subjectstars: activityen_US
dc.subjectstars: kinematics and dynamicsen_US
dc.subjectstars: low-massen_US
dc.subjectstars: pre-main sequenceen_US
dc.subjectlow-mass starsen_US
dc.subjectlithium depletion boundaryen_US
dc.subjecttw-hydrae associationen_US
dc.subjectdigital sky surveyen_US
dc.subjecteta-chamaeleontis clusteren_US
dc.subjectgalaxy-evolution-exploreren_US
dc.subjectbrown dwarf candidatesen_US
dc.subjectmain-sequence starsen_US
dc.subjectnearby young starsen_US
dc.subjectbeta-pictorisen_US
dc.subjectastronomy & astrophysicsen_US
dc.titleA Stellar Census Of The Tucana-Horologium Moving Groupen_US
dc.typeArticleen_US

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