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Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime

Kirkpatrick, J. Davy and Martin, Emily C. and Smart, Richard L. and Cayago, Alfred J. and Beichman, Charles A. and Marocco, Federico and Gelino, Christopher R. and Faherty, Jacqueline K. and Cushing, Michael C. and Schneider, Adam C. and Mace, Gregory N. and Tinney, Christopher G. and Wright, Edward L. and Lowrance, Patrick J. and Ingalls, James G. and Vrba, Frederick J. and Munn, Jeffrey A. and Dahm, Scott E. and McLean, Ian S. (2019) Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime. Astrophysical Journal Supplement Series, 240 (2). Art. No. 19. ISSN 1538-4365.

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We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United Kingdom Infrared Telescope (9). To complete the 20 pc census of ⩾T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150 K wide T_(eff) bins covering the range 300–1050 K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20 pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in T_(eff). The best fit of these predictions to our L, T, and Y observations is a simple power-law model with α ≈ 0.6 (where dN/dM ∝ M^(-α)), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350 K. We also find that the low-mass cutoff to formation, if one exists, is lower than ~5 M_(Jup), which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Kirkpatrick, J. Davy0000-0003-4269-260X
Martin, Emily C.0000-0002-0618-5128
Smart, Richard L.0000-0002-4424-4766
Faherty, Jacqueline K.0000-0001-6251-0573
Cushing, Michael C.0000-0001-7780-3352
Schneider, Adam C.0000-0002-6294-5937
Mace, Gregory N.0000-0001-7875-6391
Wright, Edward L.0000-0001-5058-1593
Lowrance, Patrick J.0000-0001-8014-0270
Ingalls, James G.0000-0003-4714-1364
Munn, Jeffrey A.0000-0002-4603-4834
Dahm, Scott E.0000-0002-2968-2418
Additional Information:© 2019 The American Astronomical Society. Received 2018 October 11; revised 2018 November 29; accepted 2018 December 3; published 2019 January 24. J.D.K. thanks the staff of the Spitzer Science Center for their assistance in making this project possible; Frank Masci, Lee Rottler, and Steve Schurr for programming advice; Yossi Shvartzvald and Sergio Fajardo-Acosta for lucrative discussions; and the anonymous referee and the U.S. Naval Observatory Editorial Board for comments that improved the paper. We also thank Trudy M. Tilleman and Justice E. Bruursema for their contributions to the USNO observing effort. We further thank David Ciardi for acquiring Keck/NIRC2 H-band imaging for WISE 0226−0211AB. Research by R.L.S. was supported by the 2015 Henri Chrétien International Research Grant administered by the American Astronomical Society. E.C.M. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1801978. A.J.C. gratefully acknowledges financial support through the Fellowships and Internships in Extremely Large Data Sets (FIELDS) Program, a National Aeronautics and Space Administration (NASA) science/technology/engineering/math (STEM) grant administered by the University of California, Riverside. F.M. is supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory (JPL), administered by Universities Space Research Association under contract with NASA. Work in this paper is based on observations made with the Spitzer Space Telescope, which is operated by JPL, California Institute of Technology (Caltech), under a contract with NASA. Support for this work was provided by NASA through Cycle 9 and Cycle 13 awards issued by JPL/Caltech. This publication makes use of data products from WISE, which is a joint project of the University of California, Los Angeles, and JPL/Caltech, funded by NASA. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of IRSA, which is operated by JPL/Caltech, under contract with NASA, and KOA, which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with NASA. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France. Facilities: Spitzer(IRAC) - Spitzer Space Telescope satellite, USNO:61in(ASTROCAM) - , NTT (SOFI) - , UKIRT(WFCAM) - , WISE - , Gaia - , IRSA. - Software: IDL (, MOPEX/APEX (, R (, STILTS Taylor (2006), mpfit Markwardt (2009).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
American Astronomical SocietyUNSPECIFIED
NSF Astronomy and Astrophysics FellowshipAST-1801978
University of California, RiversideUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Subject Keywords:brown dwarfs – parallaxes – solar neighborhood – stars: distances – stars: luminosity function, mass function
Record Number:CaltechAUTHORS:20190123-150939357
Persistent URL:
Official Citation:J. Davy Kirkpatrick et al 2019 ApJS 240 19
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92435
Deposited By: Tony Diaz
Deposited On:24 Jan 2019 00:34
Last Modified:24 Jan 2019 20:12

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