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Register a new userPhotometric and spectroscopic evidence for a dense ring system around Centaur Chariklo
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In this work we aim to study if the variability in the absolute magnitude of Chariklo and the temporal variation of the spectral ice feature, even its disappearance in 2007, can be explained by an icy ring system whose aspect angle changes with time. We modeled the light reflected by a system as the one described above to explain the variations on the absolute magnitude of Chariklo and its rings. Using X-Shooter at VLT we obtained a new reflectance spectra, here we compared this new set of data with the ones available in the literature. We showed how the water ice feature is visible in 2013 in accordance with the ring configuration, which had an opening angle of nearly 34$^o$ in 2013. Finally we also used models of the scattering of light to fit the visible and near-infrared spectra showing different characteristic to obtain information on the composition of Chariklo and its rings. {We showed that past absolute photometry of Chariklo from the literature and new photometric data that we obtained in 2013 can be explained by a ring of particles whose opening angle changes as a function of time. We used the two possible pole solutions for the ring system and found that only one of them, $alpha$=151.30$pm0.5$, $delta=41.48pm0.2$ $^o$ ($lambda=137.9pm0.5$, $beta=27.7pm0.2$ $^o$) provides the right variation of the aspect angle with time to explain the photometry, whereas the other possible pole solution fails to explain the photometry. From spectral modeling, using the result on the pole solution, we derived the composition of Chariklo surface and of that of the rings. Chariklo surface is composed by nearly 60% of amorphous carbon, 30% of silicates and 10% of organics, no water ice was found on the surface. Whereas the ring contains 20% of water ice, 40-70% of silicates and 10-30% of tholins and small quantities of amorphous carbon.
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Until now, rings have been detected in the Solar System exclusively around the four giant planets. Here we report the discovery of the first minor-body ring system around the Centaur object (10199) Chariklo, a body with equivalent radius 124$pm$9 km. A multi-chord stellar occultation revealed the presence of two dense rings around Chariklo, with widths of about 7 km and 3 km, optical depths 0.4 and 0.06, and orbital radii 391 and 405 km, respectively. The present orientation of the ring is consistent with an edge-on geometry in 2008, thus providing a simple explanation for the dimming of Chariklos system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partially composed of water ice. These rings may be the remnants of a debris disk, which were possibly confined by embedded kilometre-sized satellites.
Dense and narrow rings have been discovered recently around the small Centaur object Chariklo and the dwarf planet Haumea, while being suspected around the Centaur Chiron. They are the first rings observed in the Solar System elsewhere than around giant planets. Contrarily to the latters, gravitational fields of small bodies may exhibit large non-axisymmetric terms that create strong resonances between the spin of the object and the mean motion of rings particles. Here we show that modest topographic features or elongations of Chariklo and Haumea explain why their rings are relatively far away from the central body, when scaled to those of the giant planets. Lindblad-type resonances actually clear on decadal time-scales an initial collisional disk that straddles the corotation resonance (where the particles mean motion matches the spin rate of the body). The disk material inside the corotation radius migrates onto the body, while the material outside the corotation radius is pushed outside the 1/2 resonance, where the particles complete one revolution while the body completes two rotations. Consequently, the existence of rings around non-axisymmetric bodies requires that the 1/2 resonance resides inside the Roche limit of the body, favoring fast rotators for being surrounded by rings.
We set out a simulation to explore the follow-up of exoplanet candidates. We look at comparing photometric (transit method) and spectroscopic (Doppler shift method) techniques using three instruments: NGTS, HARPS and CORALIE. We take into account precision of follow-up and required observing time in attempt to rank each method for a given set of planetary system parameters. The methods are assessed on two criteria, SNR of the detection and follow-up time before characterisation. We find that different follow-up techniques are preferred for different regions of parameter space. For SNR we find that the ratio of spectroscopic to photometric SNR for a given system goes like $R_p/P^{frac{1}{3}}$. For follow-up time we find that photometry is favoured for the shortest period systems ($<10$ d) as well as systems with small planet radii. Spectroscopy is then preferred for systems with larger radius, and thus more massive, planets (given our assumed mass-radius relationship). Finally, we attempt to account for availability of telescopes and weight the two methods accordingly.
We consider the formation of satellites around the Pluto-Charon binary. An early collision between the two partners likely produced the binary and a narrow ring of debris, out of which arose the moons Styx, Nix, Kerberos and Hydra. How the satellites emerged from the compact ring is uncertain. Here we show that a particle ring spreads from physical collisions and collective gravitational scattering, similar to migration. Around a binary, these processes take place in the reference frames of most circular orbits, akin to circular ones in a Keplerian potential. Ring particles damp to these orbits and avoid destructive collisions. Damping and diffusion also help particles survive dynamical instabilities driven by resonances with the binary. In some situations, particles become trapped near resonances that sweep outward with the tidal evolution of the Pluto-Charon binary. With simple models and numerical experiments, we show how the Pluto-Charon impact ring may have expanded into a broad disk, out of which grew the circumbinary moons. In some scenarios, the ring can spread well beyond the orbit of Hydra, the most distant moon, to form a handful of smaller satellites. If these small moons exist, New Horizons will find them.
We present the first observational evidence for a circumplanetary disk around the protoplanet PDS~70~b, based on a new spectrum in the $K$ band acquired with VLT/SINFONI. We tested three hypotheses to explain the spectrum: Atmospheric emission from the planet with either (1) a single value of extinction or (2) variable extinction, and (3) a combined atmospheric and circumplanetary disk model. Goodness-of-fit indicators favour the third option, suggesting circumplanetary material contributing excess thermal emission --- most prominent at $lambda gtrsim 2.3 mu$m. Inferred accretion rates ($sim 10^{-7.8}$--$10^{-7.3} M_J$ yr$^{-1}$) are compatible with observational constraints based on the H$alpha$ and Br$gamma$ lines. For the planet, we derive an effective temperature of 1500--1600 K, surface gravity $log(g)sim 4.0$, radius $sim 1.6 R_J$, mass $sim 10 M_J$, and possible thick clouds. Models with variable extinction lead to slightly worse fits. However, the amplitude ($Delta A_V gtrsim 3$mag) and timescale of variation ($lesssim$~years) required for the extinction would also suggest circumplanetary material.
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