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Testing the Models: NIR Imaging and Spectroscopy of the Benchmark T-Dwarf Binary Eps Indi B
The relative roles of metallicity and surface gravity on thenear-infrared spectra of late-T brown dwarfs are not yet fullyunderstood, and evolutionary models still need to be calibrated in orderto provide accurate estimates of brown dwarf physical parameters frommeasured spectra. The T-type brown dwarfs Eps Indi Ba and Bb forming thetightly bound binary Eps Indi B, which orbits the K4V star Eps Indi A,are nowadays the only such benchmark T dwarfs for which all importantphysical parameters such as metallicity, age, and mass are (or soon willbe) known. We present spatially resolved VLT/NACO images andlow-resolution spectra of Eps Indi B in the J, H, and K near-infraredbands. The spectral types of Eps Indi Ba and Bb are determined by directcomparison of the flux-calibrated JHK spectra with T dwarf standardtemplate spectra and also by near-infrared spectral indices. Eps Indi Bbis confirmed as a T6 while the spectral type of Eps Indi Ba is T1.5,somewhat later than the previously reported T1. Constrained values forsurface gravity and effective temperature are derived by comparison withmodel spectra. The evolutionary models predict masses around ~ 53 M J for Eps Indi Ba and ~ 34 M J for Eps IndiBb, slightly higher than previously reported values. The suppressed Jband and enhanced K band flux of Eps Indi Ba indicates that a noticeablecloud layer is still present in a T1.5 dwarf, while no clouds are neededto model the spectrum of Eps Indi Bb.Based on observations collected at the European Southern Observatory,Chile, through proposal 381.C-0860(A).
| Gemini-South+FLAMINGOS Demonstration Science: Near-Infrared Spectroscopy of the z = 5.77 Quasar SDSS J083643.85+005453.3
We report an infrared 1-1.8 μm (J+H-band), low-resolution (R=450)spectrogram of the highest redshift radio-loud quasar currently known,SDSS J083643.85+005453.3, obtained during the spectroscopiccommissioning run of the FLAMINGOS multiobject, near-IR spectrograph atthe 8 m Gemini-South Observatory. These data show broad emission fromboth C IV λ1549 and C III] λ1909, with strengthscomparable to lower redshift quasar composite spectra. The implicationis that there is substantial enrichment of the quasar environment, evenat times less than a billion years after the big bang. The redshiftderived from these features is z=5.774+/-0.003, more accurate andslightly lower than the z=5.82 reported in the discovery paper based onthe partially absorbed Lyα emission line. The infrared continuumis significantly redder than lower redshift quasar composites. Fittingthe spectrum from 1.0 to 1.7 μm with a power lawfν~ν-α, the derived power-law index isα=1.55 compared to the average continuum spectral index<α>=0.44 derived from the first Sloan Digital Sky Surveycomposite quasar. Assuming an SMC-like extinction curve, we infer acolor excess of E(B-V)=0.09+/-0.01. Only ~6% of quasars in the opticallyselected Sloan Digital Sky Survey show comparable levels of dustreddening.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc., under a cooperative agreement with the NSF on behalf of the Geminipartnership: the National Science Foundation (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).
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