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Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function

Kirkpatrick, J. Davy and Gelino, Christopher R. and Cushing, Michael C. and Mace, Gregory N. and Griffith, Roger L. and Skrutskie, Michael F. and Marsh, Kenneth A. and Wright, Edward L. and Eisenhardt, Peter R. and McLean, Ian S. and Mainzer, Amanda K. and Burgasser, Adam J. and Tinney, C. G. and Parker, Stephen and Salter, Graeme (2012) Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function. Astrophysical Journal, 753 (2). Art. No. 156. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20120521-074552875

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Abstract

We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al., we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J-H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6 µm) and W2 (4.6 µm) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the Solar Neighborhood. We present a table that updates the entire stellar and substellar constituency within 8 parsecs of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope -0.5 < α < 0.0; however, a power-law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/1205.2122arXivDiscussion Paper
http://dx.doi.org/10.1088/0004-637X/753/2/156 DOIArticle
http://iopscience.iop.org/0004-637X/753/2/156/PublisherArticle
ORCID:
AuthorORCID
Wright, Edward L.0000-0001-5058-1593
Burgasser, Adam J.0000-0002-6523-9536
Additional Information:© 2012 The American Astronomical Society. Received 2012 April 1; accepted 2012 May 9; published 2012 June 25. We thank the referee, Sandy Leggett, for constructive comments that helped to improve the paper. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication also makes use of data products from 2MASS, SDSS, and DSS. 2MASS is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. SDSS is funded by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The DSS were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Support for this work was provided by NASA through an award issued to program 70062 and 80109 by JPL/Caltech. This work is also based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #12044 and #12330. Support for these programs was provided by NASA through a grant from the Space Telescope Science Institute. Some of the spectroscopic data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. In acknowledgement of our observing time at Keck and the IRTF, we further wish to recognize the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawai’ian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Our research has benefitted from the M, L, and T dwarf compendium housed at Dwarf Archives. org, whose server was funded by a NASA Small Research Grant, administered by the American Astronomical Society. This research has made use of the NASA/IPAC Infrared Science Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We are also indebted to the SIMBAD database, operated at CDS, Strasbourg, France.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NSFUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Participating InstitutionsUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Japanese MonbukagakushoUNSPECIFIED
Max Planck SocietyUNSPECIFIED
Higher Education Funding Council for EnglandUNSPECIFIED
NASA/JPL/Caltech70062
NASA/JPL/Caltech80109
NASANAS 5-26555
Space Telescope Science InstituteUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:brown dwarfs – solar neighborhood – stars: low-mass – stars: luminosity function, mass function – surveys – techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20120521-074552875
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20120521-074552875
Official Citation:Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function J. Davy Kirkpatrick et al. 2012 ApJ 753 156
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31552
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:02 Aug 2012 21:15
Last Modified:03 Oct 2019 03:52

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