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

Abstract

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 μ m, and the 1.2 μ m FeH{sub 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 datamore » sets cannot be used to provide a precise age estimate.« less

Authors:
; ; ;  [1];  [2];  [3];  [4];  [5];  [6]
  1. Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States)
  2. Department of Engineering Science and Physics, College of Staten Island, 2800 Victory Boulevard, Staten Island, NY 10301 (United States)
  3. Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)
  4. Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States)
  5. Math and Sciences Division, Antelope Valley College, 3041 West Avenue K, Lancaster, CA 93536 (United States)
  6. Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)
Publication Date:
OSTI Identifier:
22661225
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 838; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; CLASSIFICATION; DWARF STARS; GRAVITATION; MASS; RESOLUTION; SPECTRA; STARS; SURFACES

Citation Formats

Martin, Emily C., Mace, Gregory N., McLean, Ian S., Logsdon, Sarah E., Rice, Emily L., Kirkpatrick, J. Davy, Burgasser, Adam J., McGovern, Mark R., and Prato, Lisa, E-mail: emartin@astro.ucla.edu. Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA6338.
Martin, Emily C., Mace, Gregory N., McLean, Ian S., Logsdon, Sarah E., Rice, Emily L., Kirkpatrick, J. Davy, Burgasser, Adam J., McGovern, Mark R., & Prato, Lisa, E-mail: emartin@astro.ucla.edu. Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey. United States. doi:10.3847/1538-4357/AA6338.
Martin, Emily C., Mace, Gregory N., McLean, Ian S., Logsdon, Sarah E., Rice, Emily L., Kirkpatrick, J. Davy, Burgasser, Adam J., McGovern, Mark R., and Prato, Lisa, E-mail: emartin@astro.ucla.edu. Mon . "Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey". United States. doi:10.3847/1538-4357/AA6338.
@article{osti_22661225,
title = {Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey},
author = {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, E-mail: emartin@astro.ucla.edu},
abstractNote = {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 μ m, and the 1.2 μ m FeH{sub 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.},
doi = {10.3847/1538-4357/AA6338},
journal = {Astrophysical Journal},
number = 1,
volume = 838,
place = {United States},
year = {Mon Mar 20 00:00:00 EDT 2017},
month = {Mon Mar 20 00:00:00 EDT 2017}
}
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