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Register a new userAtmospheric Characterization and Further Orbital Modeling of $kappa$ And b
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We present $kappa$ Andromeda bs photometry and astrometry taken with Subaru/SCExAO+HiCIAO and Keck/NIRC2, combined with recently published SCExAO/CHARIS low-resolution spectroscopy and published thermal infrared photometry to further constrain the companions atmospheric properties and orbit. $kappa$ And bs Y/Y-K colors are redder than field dwarfs, consistent with its youth and lower gravity. Empirical comparisons of its Y-band photometry and CHARIS spectrum to a large spectral library of isolated field dwarfs reaffirm the conclusion from Currie et al. (2018) that it likely has a low gravity but admit a wider range of most plausible spectral types (L0-L2). Our gravitational classification also suggests that the best-fit objects for $kappa$ And b may have lower gravity than those previously reported. Atmospheric models lacking dust/clouds fail to reproduce its entire 1--4.7 $mu m$ spectral energy distribution, cloudy atmosphere models with temperatures of $sim$ 1700--2000 $K$ better match $kappa$ And b data. Most well-fitting model comparisons favor 1700--1900 $K$, a surface gravity of log(g) $sim$ 4--4.5, and a radius of 1.3--1.6,$R_{rm Jup}$; the best-fit model (DRIFT-Phoenix) yields the coolest and lowest-gravity values: $T_{rm eff}$=1700 K and $log g$=4.0. An update to $kappa$ And bs orbit with ExoSOFT using new astrometry spanning seven years reaffirms its high eccentricity ($0.77pm0.08$). We consider a scenario where unseen companions are responsible for scattering $kappa$ And b to a wide separation and high eccentricity. If three planets, including $kappa$ And b, were born with coplanar orbits and one of them was ejected by gravitational scattering, a potential inner companion with mass $gtrsim10M_{rm Jup}$ could be located at $lesssim$ 25 au.
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We previously reported the direct detection of a low mass companion at a projected separation of 55+-2 AU around the B9 type star {kappa} Andromedae. The properties of the system (mass ratio, separation) make it a benchmark for the understanding of the formation and evolution of gas giant planets and brown dwarfs on wide-orbits. We present new angular differential imaging (ADI) images of the Kappa Andromedae system at 2.146 (Ks), 3.776 (L), 4.052 (NB 4.05) and 4.78 {mu}m (M) obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more accurate near-infrared photometry of the star with the MIMIR instrument. We derive a more accurate J = 15.86 +- 0.21, H = 14.95 +- 0.13, Ks = 14.32 +- 0.09 mag for {kappa} And b. We redetect the companion in all our high contrast observations. We confirm previous contrasts obtained at Ks and L band. We derive NB 4.05 = 13.0 +- 0.2 and M = 13.3 +- 0.3 mag and estimate Log10(L/Lsun) = -3.76 +- 0.06. We build the 1-5 microns spectral energy distribution of the companion and compare it to seven PHOENIX-based atmospheric models in order to derive Teff = 1900+100-200 K. Models do not set constrains on the surface gravity. ``Hot-start evolutionary models predict masses of 14+25-2 MJup based on the luminosity and temperature estimates, and considering a conservative age range for the system (30+120-10 Myr). ``warm-start evolutionary tracks constrain the mass to M >= 11 MJup. Therefore, the mass of {kappa} Andromedae b mostly falls in the brown-dwarf regime, due to remaining uncertainties in age and mass-luminosity models. According to the formation models, disk instability in a primordial disk could account for the position and a wide range of plausible masses of {kappa} And b.
Directly imaged planets and substellar companions are key targets for the characterization of self-luminous atmospheres. Their photometric appearance at 4-5 $mu$m is sensitive to the chemical composition and cloud content of their atmosphere. We aim at systematically characterizing the atmospheres of directly imaged low-mass companions at 4-5 $mu$m. We want to homogeneously process the data and compile a photometric library at thermal wavelengths of these mostly young, low-gravity objects. In this way, we want to find trends related to their spectral type and surface gravity by comparing with isolated brown dwarfs and predictions from atmospheric models. We have used the high-resolution, high-contrast capabilities of NACO at the VLT to directly image the companions of HIP 65426, PZ Tel, and HD 206893 in the NB4.05 and/or $M$ filters. For the same targets, and additionally $beta$ Pic, we have also analyzed six archival VLT/NACO datasets which were taken with the NB3.74, $L$, NB4.05, and $M$ filters. The $L$-NB4.05 and $L$-$M$ colors of the studied sample are all red while the NB4.05-$M$ color is blue for $beta$ Pic b, gray for PZ Tel B, and red for HIP 65426 b and HD 206893 B (although typically with low significance). The absolute NB4.05 and $M$ fluxes of our sample are all larger than those of field dwarfs with similar spectral types. Finally, the surface gravity of $beta$ Pic b has been constrained to $log{g} = 4.17_{-0.13}^{+0.10}$ dex from its photometry and dynamical mass. A red color at 3-4 $mu$m and a blue color at 4-5 $mu$m might be (partially) caused by H$_2$O and CO absorption, respectively. The red characteristics of $beta$ Pic b, HIP 65426 b, and HD 206893 B at 3-5$mu$m, as well as their higher fluxes in NB4.05 and $M$ compared to field dwarfs, indicate that cloud densities are enhanced close to the photosphere as a result of their low surface gravity.
51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, recently discovered by direct imaging. Being only 0.5 away from its host star it is well suited for spectroscopic analysis using integral field spectrographs. We aim to refine the atmospheric properties of this and to further constrain the architecture of the system by searching for additional companions. Using the SPHERE instrument at the VLT we extend the spectral coverage of the planet to the complete Y- to H-band range and provide photometry in the K12-bands (2.11, 2.25 micron). The object is compared to other cool and peculiar dwarfs. Furthermore, the posterior probability distributions of cloudy and clear atmospheric models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. For probing the innermost region for additional companions, archival VLT-NACO (L) SAM data is used. We present the first spectrophotometric measurements in the Y- and K-bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity and cloud sedimentation parameter f_sed. We find that the atmosphere is highly super-solar (Fe/H~1.0) with an extended, thick cloud cover of small particles. The model radius and surface gravity suggest planetary masses of about 9 M_jup. The evolutionary model only provides a lower mass limit of >2 M_jup (for pure hot-start). The cold-start model cannot explain the planets luminosity. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at Solar System scales and exclude brown-dwarf companions more massive than 20 M_jup beyond separations of ~2.5 au and giant planets more massive than 2 M_jup beyond 9 au.
Kappa Andromedae is a B9IVn star at 52 pc for which a faint substellar companion separated by 55 AU was recently announced. In this work, we present the first spectrum of the companion, kappa And B, using the Project 1640 high-contrast imaging platform. Comparison of our low-resolution YJH-band spectra to empirical brown dwarf spectra suggests an early-L spectral type. Fitting synthetic spectra from PHOENIX model atmospheres to our observed spectrum allows us to constrain the effective temperature to ~2000K, as well as place constraints on the companion surface gravity. Further, we use previously reported log(g) and effective temperature measurements of the host star to argue that the kappa And system has an isochronal age of 220 +/- 100 Myr, older than the 30 Myr age reported previously. This interpretation of an older age is corroborated by the photometric properties of kappa And B, which appear to be marginally inconsistent with other 10-100 Myr low-gravity L-dwarfs for the spectral type range we derive. In addition, we use Keck aperture masking interferometry combined with published radial velocity measurements to rule out the existence of any tight stellar companions to kappa And A that might be responsible for the systems overluminosity. Further, we show that luminosity enhancements due to a nearly pole-on viewing angle coupled with extremely rapid rotation is unlikely. Kappa And A is thus consistent with its slightly evolved luminosity class (IV) and we propose here that kappa And, with a revised age of 220 +/- 100 Myr, is an interloper to the 30 Myr Columba association with which it was previously associated. The photometric and spectroscopic evidence for kappa And B combined with our re-assesment of the system age implies a substellar companion mass of 50^{+16}_{-13} Jupiter Masses, consistent with a brown dwarf rather than a planetary mass companion.
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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