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Title: Near-infrared spectroscopy of the Y0 WISEP J173835.52+273258.9 and the Y1 WISE J035000.32–565830.2: The importance of non-equilibrium chemistry

Here, we present new near-infrared spectra, obtained at Gemini Observatory, for two Y dwarfs: WISE J035000.32–565830.2 (W0350) and WISEP J173835.52+273258.9 (W1738). A FLAMINGOS-2 R = 540 spectrum was obtained for W0350, covering $$1.0\lt \lambda \;\mu {\rm{m}}$$ $$\lt \;1.7$$, and a cross-dispersed Gemini near-infrared spectrograph R = 2800 spectrum was obtained for W1738, covering 0.993–1.087 μm, 1.191–1.305 μm, 1.589–1.631 μm, and 1.985–2.175 μm, in four orders. We also present revised YJH photometry for W1738, using new NIRI Y and J imaging, and a re-analysis of the previously published NIRI H-band images. We compare these data, together with previously published data for late-T and Y dwarfs, to cloud-free models of solar metallicity, calculated both in chemical equilibrium and with disequilibrium driven by vertical transport. We find that for the Y dwarfs, the non-equilibrium models reproduce the near-infrared data better than the equilibrium models. The remaining discrepancies suggest that fine-tuning the CH 4/CO and NH 3/N 2 balance is needed. Improved trigonometric parallaxes would improve the analysis. Despite the uncertainties and discrepancies, the models reproduce the observed near-infrared spectra well. We find that for the Y0, W1738, $${T}_{{\rm{eff}}}=425\pm 25\;{\rm{K}}$$, and log $$g=4.0\pm 0.25$$, and for the Y1, W0350, $${T}_{{\rm{eff}}}=350\pm 25\;{\rm{K}}$$, and log $$g=4.0\pm 0.25$$. W1738 may be metal-rich. Based on evolutionary models, these temperatures and gravities correspond to a mass range for both Y dwarfs of 3–9 Jupiter masses, with W0350 being a cooler, slightly older, version of W1738; the age of W0350 is 0.3–3 Gyr, and the age of W1738 is 0.15–1 Gyr.
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [7]
  1. Gemini Observatory, Hilo, HI (United States)
  2. Maison de la Simulation, CEA-CNRS-INRIA-UPS-UVSQ, USR, Gif-Sur-Yvette (France); Univ. of Exeter, Exeter (United Kingdom)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. NASA Ames Research Center, Moffett Field, CA (United States)
  5. Univ. of California, Santa Cruz, CA (United States)
  6. Univ. of Exeter, Exeter (United Kingdom)
  7. Univ. of Exeter, Exeter (United Kingdom); Ecole Normale Superieure de Lyon, CRAL, UMR, CNRS, Lyon Cedex (France)
Publication Date:
OSTI Identifier:
Report Number(s):
LA-UR-16-21256; LA-UR-15-27260
Journal ID: ISSN 1538-4357
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 824; Journal Issue: 1; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
National Aeronautic and Space Administration (NASA); USDOE; National Aeronautics and Space Administration (NASA)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; molecular processes; stars: brown dwarfs; stars: atmospheres; stars: individual (WISE J035000.32-565830.2, WISEP J173835.52+273258.9); 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; brown dwarfs; stars: individual; (WISE J035000.32–565830.2, WISEP J173835.52+273258.9); stars:individual