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Description
We present moderate-resolution (R~4000) K-band spectra of the "super- Jupiter," {kappa}-Andromedae-b. The data were taken with the OSIRIS integral field spectrograph at Keck Observatory. The spectra reveal resolved molecular lines from H2O and CO, and are compared to a custom PHOENIX atmosphere model grid appropriate for young planetary-mass objects. We fit the data using a Markov chain Monte Carlo forward-modeling method. Using a combination of our moderate-resolution spectrum and low-resolution, broadband data from the literature, we derive an effective temperature of Teff=1950-2150K, a surface gravity of logg=3.5--4.5, and a metallicity of [M/H]=-0.2--0.0. These values are consistent with previous estimates from atmospheric modeling and the currently favored young age of the system (<50Myr). We derive a C/O ratio of 0.70_-0.24_^+0.09^ for the source, broadly consistent with the solar C/O ratio. This, coupled with the slightly subsolar metallicity, implies a composition consistent with that of the host star, and is suggestive of formation by a rapid process. The subsolar metallicity of {kappa}-Andromedae-b is also consistent with predictions of formation via gravitational instability. Further constraints on formation of the companion will require measurement of the C/O ratio of {kappa}-Andromedae-A. We also measure the radial velocity of {kappa}-Andromedae-b for the first time, with a value of -1.4{+/-}0.9km/s relative to the host star. We find that the derived radial velocity is consistent with the estimated high eccentricity of {kappa}-Andromedae-b.
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