• DOI:10.1086/499344
• Corpus ID: 9291848

A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs

@article{Burgasser2005AMF,
  title={A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs},
  author={Adam J. Burgasser and Adam Burrows and J. Davy Kirkpatrick},
  journal={The Astrophysical Journal},
  year={2005},
  volume={639},
  pages={1095-1113}
}

• A. Burgasser, A. Burrows, J. Kirkpatrick
• Published 25 October 2005
• Physics, Geology
• The Astrophysical Journal

We present a method for measuring the physical parameters of the coldest T-type brown dwarfs using lowresolution
near-infrared spectra. By comparing H_(2)O and H_2-sensitive spectral ratios between empirical data and theoretical atmosphere models, and calibrating these ratios to measurements for the well-characterized 2–5 Gyr
companion brown dwarf Gliese 570D, we derive estimates of the effective temperatures and surface gravities for
13 mid- and late-type field T dwarfs. We also deduce the first quantitative estimate of subsolar metallicity for the
peculiar T dwarf 2MASS 0937+2931. Derived temperatures are consistent with prior estimates based on parallax and
bolometric luminosity measurements, and examination of possible systematic effects indicate that the results are
robust. Two recently discovered late-type T dwarfs, 2MASS 09392448 and 2MASS 11142618, both appear to be ≳50 K cooler than the latest type T dwarf, 2MASS 04150935, and are potentially the coldest and least luminous brown dwarfs currently known. We find that, in general, higher surface gravity T dwarfs have lower effective temperatures and luminosities for a given spectral type, explaining previously observed scatter in the T_(eff) /spectral type relation for these objects. Masses, radii, and ages are estimated for the T dwarfs in our sample using the
evolutionary models of Burrows et al.; we also determine masses and radii independently for eight T dwarfs with
measured luminosities. These two determinations are largely consistent, lending support to the validity of evolutionary
models at late ages. Our method is well suited to large samples of faint brown dwarfs and can ultimately be
used to directly measure the substellar mass function and formation history in the Galaxy.