Journal
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
Volume 228, Issue 2, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/1538-4365/228/2/18
Keywords
brown dwarfs; methods: data analysis; open clusters and associations: individual (TW Hya); stars: kinematics and dynamics; stars: low mass; stars: luminosity function, mass function
Categories
Funding
- Natural Science and Engineering Research Council of Canada
- National Science Foundation (NSF) [AST-1313029]
- NASA NExSS program
- NSF [AST09-08419]
- CNTAC program [CN2013A-135]
- ESO Progam [179.A-2010]
- Gemini Observatory [GN-2013A-Q-106, GN2014A-Q-94, GS-2012B-Q-70, GS-2013A-Q-66, GS-2014A-Q55, GS-2015A-Q-85, GS-2015A-Q-60]
- IRTF [2015B091]
- AURA [AST 0132798]
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A determination of the initial mass function (IMF) of the current, incomplete census of the 10 Myr-old TW. Hya association (TWA) is presented. This census is built from a literature compilation supplemented with new spectra and 17 new radial velocities from ongoing membership surveys, as well as a reanalysis of Hipparcos data that confirmed HR. 4334 (A2 Vn) as a member. Although the dominant uncertainty in the IMF remains census incompleteness, a detailed statistical treatment is carried out to make the IMF determination independent of binning while accounting for small number statistics. The currently known high-likelihood members are fitted by a log-normal distribution with a central mass of 0.21(-0.06) M-+0.11(circle dot) Me and a characteristic width of 0.8(-0.1)(+0.2) dex in the 12M(Jup)-2M(circle dot) range, whereas a Salpeter power law with alpha= 2.2(-0.5)(+1.1) best describes the IMF slope in the 0.1-2M(circle dot) range. This characteristic width is higher than other young associations, which may be due to incompleteness in the current census of low-mass TWA stars. A tentative overpopulation of isolated planetary-mass members similar to 2MASS. J11472421-2040204 and 2MASS. J11193254-1137466 is identified: this indicates that there might be as many as 10(-5)(+13) similar members of TWA with hot-start model-dependent masses estimated at similar to 5-7M(Jup), most of which would be too faint to be detected in 2MASS. Our new radial velocity measurements corroborate the membership of 2MASS. J11472421-2040204, and secure TWA. 28 (M8.5 gamma), TWA. 29 (M9.5 gamma), and TWA. 33 (M4.5 e) as members. The discovery of 2MASS. J09553336-0208403, a young L7-type interloper unrelated to TWA, is also presented.
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