Molecular abundances in the atmosphere of the T dwarf G1 229B

D. Saumon, T. R. Geballe, S. K. Leggett, M. S. Marley, R. S. Freedman, K. Lodders, B. Fegley, S. K. Sengupta

Research output: Contribution to journalArticlepeer-review

119 Scopus citations

Abstract

We present new high-resolution infrared spectra of the T dwarf Gliese 229B in the J, H, and K band-passes. We analyze each of these as well as previously published spectra to determine its metallicity and the abundances of NH3 and CO in terms of the surface gravity of G1 229B, which remains poorly constrained. The metallicity increases with increasing gravity and is below the solar value unless G1 229B is a high-gravity brown dwarf with log g (cgs) ≈ 5.5. The NH3 abundance is determined from both the H-and the K-band spectra, which probe two different levels in the atmosphere. We find that the abundance from the K-band data is well below that expected from chemical equilibrium, which we interpret as strong evidence for dynamical transport of NH3 in the atmosphere. This is consistent with the previous detection of CO and provides additional constraints on the dynamics of the atmosphere of this T dwarf.

Original languageEnglish (US)
Pages (from-to)374-389
Number of pages16
JournalAstrophysical Journal
Volume541
Issue number1 PART 1
DOIs
StatePublished - Sep 20 2000
Externally publishedYes

Keywords

  • Stars: abundances
  • Stars: atmospheres
  • Stars: individual (G1 229B)
  • Stars: low-mass, brown dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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