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Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey

Martin, Emily C. and Mace, Gregory N. and McLean, Ian S. and Logsdon, Sarah E. and Rice, Emily L. and Kirkpatrick, J. Davy and Burgasser, Adam J. and McGovern, Mark R. and Prato, Lisa (2017) Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey. Astrophysical Journal, 838 (1). Art. No. 73. ISSN 1538-4357.

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We combine 131 new medium-resolution (R ~ 2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5–T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6–L7 objects in our sample by measuring the equivalent widths (EW) of the K I lines at 1.1692, 1.1778, and 1.2529 μm, and the 1.2 μm FeH_J absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak—at ~L5 and T5—in K I EW as a function of spectral type. We analyze the K I EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6–L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Martin, Emily C.0000-0002-0618-5128
Mace, Gregory N.0000-0001-7875-6391
Logsdon, Sarah E.0000-0002-9632-9382
Rice, Emily L.0000-0002-3252-5886
Kirkpatrick, J. Davy0000-0003-4269-260X
Burgasser, Adam J.0000-0002-6523-9536
Additional Information:© 2017 The American Astronomical Society. Received 2016 August 12; revised 2017 February 22; accepted 2017 February 23; published 2017 March 27. The 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. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This research has benefitted from the M, L, T, and Y dwarf compendium housed at This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. We thank the anonymous referee for their insightful comments which improved the paper. Facility: Keck:II(NIRSPEC) - KECK II Telescope.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:brown dwarfs – infrared: stars – stars: atmospheres – stars: low-mass – surveys
Issue or Number:1
Record Number:CaltechAUTHORS:20170327-103657029
Persistent URL:
Official Citation:Emily C. Martin et al 2017 ApJ 838 73
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75412
Deposited By: Tony Diaz
Deposited On:27 Mar 2017 19:09
Last Modified:09 Mar 2020 13:19

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