• DOI:10.1086/420707
• Corpus ID: 119436129

Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity

@article{Knapp2004NearInfraredPA,
  title={Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity},
  author={Gillian R. Knapp and Sandy K. Leggett and X. L. Fan and Mark. S. Marley and Thomas R. Geballe and David A. Golimowski and Douglas P. Finkbeiner and James E. Gunn and Joseph F. Hennawi and Željko Ivezi{\'c} and Robert H. Lupton and David J. Schlegel and Michael A. Strauss and Zlatan I. Tsvetanov and Kuenley Chiu and Erik Andrew Hoversten and Karl Glazebrook and Wei Zheng and M. Hendrickson and C. C. Williams and Alan K. Uomoto and Frederick John Vrba and Arne Anthon Henden and Christian B. Luginbuhl and Harry H. Guetter and Jeffrey A. Munn and Blaise Canzian and Donald P. Schneider and Jonathan Brinkmann},
  journal={The Astronomical Journal},
  year={2004},
  volume={127},
  pages={3553 - 3578}
}

• G. Knapp, S. Leggett, +26 authors J. Brinkmann
• Published 19 February 2004
• Physics, Geology
• The Astronomical Journal

We present new JHK photometry on the MKO-NIR system and JHK spectroscopy for a large sample of L and T dwarfs. Photometry has been obtained for 71 dwarfs, and spectroscopy for 56. The sample comprises newly identified very red objects from the Sloan Digital Sky Survey (SDSS) and known dwarfs from the SDSS and the Two Micron All Sky Survey (2MASS). Spectral classification has been carried out using four previously defined indices from Geballe et al. that measure the strengths of the near infrared water and methane bands. We identify nine new L8–9.5 dwarfs and 14 new T dwarfs from SDSS, including the latest yet found by SDSS, the T7 dwarf SDSS J175805.46+463311.9. We classify 2MASS J04151954-0935066 as T9, the latest and coolest dwarf found to date. We combine the new results with our previously published data to produce a sample of 59 L dwarfs and 42 T dwarfs with imaging data on a single photometric system and with uniform spectroscopic classification. We compare the near-infrared colors and absolute magnitudes of brown dwarfs near the L–T transition with predictions made by models of the distribution and evolution of photospheric condensates. There is some scatter in the Geballe et al. spectral indices for L dwarfs, suggesting that these indices are probing different levels of the atmosphere and are affected by the location of the condensate cloud layer. The near-infrared colors of the L dwarfs also show scatter within a given spectral type, which is likely due to variations in the altitudes, spatial distributions, and thicknesses of the clouds. We have identified a small group of late-L dwarfs that are relatively blue for their spectral type and that have enhanced FeH, H2O, and K I absorption, possibly due to an unusually small amount of condensates. The scatter seen in the H-K color for late-T dwarfs can be reproduced by models with a range in surface gravity. The variation is probably due to the effect on the K-band flux of pressure-induced H2 opacity. The correlation of H-K color with gravity is supported by the observed strengths of the J-band K I doublet. Gravity is closely related to mass for field T dwarfs with ages greater than108 yr and the gravities implied by the H-K colors indicate that the T dwarfs in our sample have masses in the range 15–75MJupiter. One of the SDSS dwarfs, SDSS J111010.01+011613.1, is possibly a very low mass object, with log g ∼ 4.2–4.5 and mass ∼ 10–15MJupiter.