Kavli Affiliate: Bruce Macintosh
| First 5 Authors: Kielan K. Wilcomb, Quinn M. Konopacky, Travis S. Barman, Christopher A. Theissen, Jean-Baptiste Ruffio
| Summary:
We present moderate-resolution ($Rsim4000$) $K$ 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 H$_{2}$O and CO. The spectra 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
$T_mathrm{eff}$ = 1950 – 2150 K, a surface gravity of $log g=3.5 – 4.5$, 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 ($<$50 Myr). We derive a C/O ratio of 0.70$_{-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
$-1.4pm0.9,mathrm{km},mathrm{s}^{-1}$ 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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