On the formation of multiple concentric rings and gaps in protoplanetary disks

On the formation of multiple concentric rings and gaps in protoplanetary disks

Authors:

Bae et al

Abstract:

As spiral waves driven by a planet in a gaseous disk steepen into a shock, they deposit angular momentum, opening a gap in the disk. This has been well studied using both linear theory and numerical simulations, but so far, only for the primary spiral arm -- the one directly attached to the planet. Using two-dimensional hydrodynamic simulations, we show that the secondary and tertiary arms driven by a planet can also open gaps as they steepen into shocks. The depths of the secondary/tertiary gaps in surface density grow with time in a low viscosity disk (α=5×10−5), so even low-mass planets (e.g., super-Earth or mini-Neptune) embedded in the disk can open multiple observable gaps, provided that sufficient time has passed. Applying our results to the HL Tau disk, we show that a single 30 Earth-mass planet embedded in the ring at 68.8 au (B5) can reasonably well reproduce the positions of the two major gaps at 13.2 and 32.3 au (D1 and D2), and roughly reproduce two other major gaps at 64.2 and 74.7 au (D5 and D6) seen in the mm continuum. The positions of secondary/tertiary gaps are found to be sensitive to the planetary mass and the disk temperature profile, so with accurate observational measurements on the temperature structure we can use the positions of multiple gaps to constrain the mass of the planet. We also comment on the gaps seen in the TW Hya and HD 163296 disk.

Constraints on the size and dynamics of brown dwarf J1407b ring system

Constraints on the size and dynamics of the J1407b ring system

Authors:

Rieder et al

Abstract:

Context.

J1407 (1SWASP J140747.93-394542.6 in full) is a young star in the Scorpius-Centaurus OB association that underwent a series of complex eclipses over 56 days in 2007. To explain these, it was hypothesised that a secondary substellar companion, J1407b, has a giant ring system filling a large fraction of the Hill sphere, causing the eclipses. Observations have not successfully detected J1407b, but do rule out circular orbits for the companion around the primary star.

Aims.

We test to what degree the ring model of J1407b could survive in an eccentric orbit required to fit the observations.

Methods.

We run N-body simulations under the AMUSE framework to test the stability of Hill radius-filling systems where the companion is on an eccentric orbit.

Results.

We strongly rule out prograde ring systems and find that a secondary of 60 to 100 MJup with an 11 yr orbital period and retrograde orbiting material can survive for at least 104 orbits and produce eclipses with similar durations as the observed one.

Does Brown Dwarf G196-3B Have Saturn-like Rings?

Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G196-3B

Authors:

Zakhozhay et al

Abstract:

The origin of the very red optical and infrared colours of intermediate-age (∼10 - 500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of dust may account for the observed reddish nature. We explored an alternative scenario by simulating protoplanetary and debris discs around G196-3B, which is an L3 young brown dwarf with a mass of ∼15 MJup and an age in the interval 20 - 300 Myr. The best-fit solution to G196-3B's photometric spectral energy distribution from optical wavelengths through 24 μm corresponds to the combination of an unreddened L3 atmosphere (Teff≈1870~K) and a warm (≈ 1280 K), narrow (≈ 0.07 - 0.11 R⊙) debris disc located at very close distances (≈ 0.12 - 0.20 R⊙) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass ≥7×10−10 M⊕ comprised of sub-micron/micron characteristic dusty particles with temperatures close to the sublimation threshold of silicates. Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G196-3B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height (≈6×103 km). Our inferred debris disc model is able to reproduce G196-3B's spectral energy distribution to a satisfactory level of achievement.

Gas GIant Exoplanet J1407b's Rings Intrigue

Back in 2007, astronomers observed a series of unusual eclipses coming from a star 420 light years from Earth. In 2012, a team from Japan and the Netherlands reasoned that this phenomena was due to the presence of a large exoplanet – designated J1407b – with a massive ring system orbiting the star. Since then, several surprising finds have been made.

For example, in 2015, the same team concluded that the ring system is one-hundred times larger and heavier than Saturn’s (and may be similarly sculpted by exomoons). And in their most recent study, they have shown that these giant rings may last for over 100,000 years, assuming they have a rare and unusual orbit around their planet.

In their previous work, Rieder and Kenworth determined that the ring system around J1407b consisted about 37 rings that extend to a distance of 0.6 AU (90 million km) from the planet. They also estimated that these rings are 100 times as massive as our Moon – 7342 trillion trillion metric tons. What’s more, while J1407b’s existence is yet to be confirmed, they were able to rule out the possibility of it having a circular orbit around the star.

link.

Extended Transiting Disks and Rings Around Planets and Brown Dwarfs

Extended Transiting Disks and Rings Around Planets and Brown Dwarfs: Theoretical Constraints

Authors:

Zanazzi et al

Abstract:

Newly formed planets (or brown dwarfs) may possess disks or rings that occupy an appreciable fraction of the planet's Hill sphere and extend beyond the Laplace radius, where the tidal torque from the host star dominates over the torque from the oblate planet. Such a disk/ring can exhibit unique, detectable transit signatures, provided that the disk/ring is significantly misaligned with the orbital plane of the planet. There exists tentative evidence for an extended ring system around the young K5 star 1 SWASP J140747-354542. We present a general theoretical study of the inclination (warp) profile of circumplanetary disks under the combined influences of the tidal torque from the central star, the torque from the oblate planet and the self-gravity of the disk. We calculate the steady-state warp profile ("generalized Laplace Surface") and investigate the condition for coherent precession of the disk. We find that to maintain non-negligible misalignment between the extended outer disk and the planet's orbital plane, and to ensure coherent disk precession, the disk surface density must be sufficiently large so that the self-gravity torque overcomes the tidal torque from the central star. Our analysis and quantitative results can be used to constrain the parameters of transiting circumplanetary disks that may be detected in the future.

Gaps, rings, and non-axisymmetric structures in protoplanetary disks

Gaps, rings, and non-axisymmetric structures in protoplanetary disks - Emission from large grains

Authors:

Ruge et al

Abstract:

Dust grains with sizes around (sub)mm are expected to couple only weakly to the gas motion in regions beyond 10 au of circumstellar disks. In this work, we investigate the influence of the spatial distribution of such grains on the (sub)mm appearance of magnetized protoplanetary disks. We perform non-ideal global 3D magneto-hydrodynamic stratified disk simulations including particles of different sizes (50 micron to 1 cm), using a Lagrangian particle solver. We calculate the spatial dust temperature distribution, including the dynamically coupled submicron-sized dust grains, and derive ideal continuum re-emission maps of the disk through radiative transfer simulations. Finally, we investigate the feasibility to observe specific structures in the thermal re-emission maps with the Atacama Large Millimeter/submillimeter Array (ALMA). The pressure bump close to the outer edge of the dead-zone leads to particle trapping in ring structures. More specifically, vortices in the disk concentrate the dust and create an inhomogeneous distribution of the solid material in the azimuthal direction. The large-scale disk perturbations are preserved in the (sub)mm re-emission maps. The observable structures are very similar to those expected to result from planet-disk interaction. The larger dust particles increase the brightness contrast between gap and ring structures. We find that rings, gaps and the dust accumulation in the vortex could be traced with ALMA down to a scale of a few astronomical units in circumstellar disks located in nearby star-forming regions. Finally, we present a brief comparison of these structures with those recently found with ALMA in the young circumstellar disks of HL Tau and Oph IRS 48.

A Gap and Ring in TW Hydrae's Protoplanetary Disk

ALMA Observations of a Gap and a Ring in the Protoplanetary Disk around TW Hya

Authors:

Nomura et al

Abstract:

We report the first detection of a gap and a ring in dust continuum emission from the protoplanetary disk around TW Hya, using the Atacama Large Millimeter/Submillimeter Array. The gap and ring are located at 25 and 41 AU from the central star, respectively, and are associated with the CO snowline at ~ 30AU. The gap width and depth are 15AU at the maximum and 23% at the minimum, respectively, regarding that the observations are limited to an angular resolution of ~ 15AU. In addition, we detect a decrement in CO line emission down to ~ 10AU, indicating freeze-out of gas-phase CO onto grain surfaces and possible subsequent surface reactions to form larger molecules. According to theoretical studies, the gap could be caused by gravitational interaction between the disk gas and a planet with a mass less than super-Neptune (2 Neptune mass), or result from destruction of large dust aggregates due to the sintering of CO ice.

How to map an Exoplanets Rings

In “Astronomers Make a Map of a Super Saturn's Rings,” from the January issue of Scientific American, the Leiden University astronomer Matthew Kenworthy tells the story of discovering a ring system some 200 times larger than Saturn’s around the distant star J1407. Despite its rather large size, across interstellar distances this ring system would normally be totally invisible to us—and in fact Kenworthy and his peers have yet to glimpse J1407b, the giant planet that must be its host. The only reason we know the ring system exists at all is that, by chance, Kenworthy and other researchers happened to see its shadow after it “transited” across the face of its star in 2007.

link.

There's a video on the other end.

Searching for Rings Around Exoplanets

A Search for Ringed Exoplanets using Kepler Photometry

Authors:

Heising et al

Abstract:

Models are developed to simulate lightcurves of stars dimmed by transiting exoplanets with and without rings. These models are then applied to Kepler photometry to search for planetary rings in a sample of 21 exoplanets, mostly hot Jupiters, chosen to offer the best observational opportunity for discovering potential rings. We also examine what kinds of rings might be expected for these planets, in terms of both size and orientation, based on arguments involving the host planet's equilibrium temperature, its likely obliquities, and the formation and stability of possible ring systems. Finding no evidence for rings, for each of the 21 studied planets it is determined on an observational basis which potential rings can be rejected out of a representative set of fiducial rings, varying in both size and orientation. For 12 of the 21 planets, we determined that Saturn-like rings could be ruled out for at least certain orientations. Additionally, the detectability of rings is studied, and it is found that ringed planets with small obliquities (roughly 5∘−10∘) can yield large signals, which is encouraging for future work, since such small obliquities are expected for hot Jupiters.

The Effects of Wakes on Dense Planetary Rings

Dynamics of Self-Gravity Wakes in Dense Planetary Rings I. Pitch Angle

Authors:

Michikoshi et al

Abstract:

We investigate the dynamics of self-gravity wakes in dense planetary rings. In particular, we examine how the pitch angle of self-gravity wakes depend on ring parameters using N-body simulations. We calculate the pitch angles using the two-dimensional autocorrelation function of the ring surface density. We obtain the pitch angles for the inner and outer parts of the autocorrelation function separately. We confirm that the pitch angles are 15 to 30 degrees for reasonable ring parameters, which are consistent with previous studies. We find that the inner pitch angle increases with the Saturnicentric distance, while it barely depends on the optical depth and the restitution coefficient of ring particles. The increase of the inner pitch angle with the Saturnicentric distance is consistent with the observations of the A ring. The outer pitch angle does not have the clear dependence on any ring parameters and is about 10 - 15 degrees. This value is consistent with the pitch angle of spiral arms in collisionless systems.

Hot Jupiter 51 Pegasi b Does NOT have a Ring System

Detecting ring systems around exoplanets using high resolution spectroscopy: the case of 51Pegb

Authors:

Santos et al

Abstract:

In this paper we explore the possibility that the recently detected reflected light signal of 51\,Peg\,b could be caused by a ring system around the planet. We use a simple model to compare the observed signal with the expected signal from a short-period giant planet with rings. We also use simple dynamical arguments to understand the possible geometry of such a system. We provide evidence that, to a good approximation, the observations are compatible with the signal expected from a ringed planet, assuming that the rings are non-coplanar with the orbital plane. However, based on dynamical arguments, we also show that this configuration is unlikely. In the case of coplanar rings we then demonstrate that the incident flux on the ring surface is about 2\% the value received by the planet, a value that renders the ring explanation unlikely. The results suggest that the signal observed cannot in principle be explained by a planet+ring system. We discuss, however, the possibility of using reflected light spectra to detect and characterize the presence of rings around short-period planets. Finally, we show that ring systems could have already been detected by photometric transit campaigns, but their signal could have been easily misinterpreted by the expected light curve of an eclipsing binary.

How Dust Collects into Rings in Protoplanetary Disks

Toroidal vortices and the conglomeration of dust into rings in protoplanetary discs

Authors:

Loren-Aguilar et al

Abstract:

We identify a new hydrodynamical instability in protoplanetary discs that may arise due to variations in the dust-to-gas ratio and may lead to concentration of dust grains within a disc. The instability can arise due to dust settling, which produces a vertical compositional entropy gradient. The entropy gradient drives a baroclinic instability that is capable of creating toroidal gas vortices that gather dust into rings. Such dust rings are potentially observable via continuum emission of the dust or scattered light. Indeed, this instability may offer an explanation for the rings recently observed in the discs around the young stars HL Tau and TW Hya that does not rely on clearing by protoplanets. The instability may also have wider ramifications, potentially aiding dust agglomeration, altering the radial migration of larger planetesimals, and modifying angular momentum transport within a disc.

Modeling Massive Rings

Gravito-electromagnetic Effects of Massive Rings

Author:

Ruggiero et al

Abstract:

The Einstein field equations in linear post-Newtonian approximation can be written in analogy with electromagnetism, in the so-called gravito-electromagnetic formalism. We use this analogy to study the gravitational field of a massive ring: in particular, we consider a continuous mass distribution on Keplerian orbit around a central body, and we work out the gravitational field generated by this mass distribution in the intermediate zone between the central body and the ring, focusing on the gravito-magnetic component that originates from the rotation of the ring. In doing so, we generalize and complement some previous results that focused on the purely Newtonian effects of the ring (thus neglecting its rotation) or that were applied to the case of rotating spherical shells. Eventually, we study in some simple cases the effect of the the rotation of the ring, and suggest that, in principle, this approach could be used to infer information about the angular momentum of the ring.

Exomoons, Asteroids & Rings: Extracting Periodic Transit Signals from Noisy Light Curves

Extracting Periodic Transit Signals from Noisy Light Curves using Fourier Series

Authors:

Samsing et al

Abstract:

We present a simple and powerful method for extracting a transit signal from noisy light curves. Assuming the signal is periodic, we illustrate that systematic noise can be removed in Fourier space at all frequencies, by only using data from inside a time window which is matched to the main planet transits. This results in a reconstruction of the signal which on average is unbiased, despite that no prior knowledge of either the noise or the transit signal itself is used in the analysis. The method has therefore clear advantages over standard phase folding, which normally requires external input such as nearby stars or noise models for removing systematic components. In addition, we extract the full 360 degree transit signal simultaneously, and Kepler like data can be analyzed in just a few seconds. We illustrate the performance of our method by applying it to a dataset composed of light curves from Kepler with a fake injected signal emulating a planet with rings. For extracting periodic transit signals, our presented method is in general the optimal and least biased estimator and could therefore lead the way towards the first detections of, e.g., planet rings and exo-trojan asteroids.

A new way to Identify Exoplanetary Rings

A novel method for identifying exoplanetary rings

Authors:

Zuluaga et al

Abstract:

The discovery of rings around extrasolar planets ("exorings") is one of the next breakthroughs in exoplanetary research. Previous studies have explored the feasibility of detecting exorings with present and future photometric sensitivities by seeking anomalous deviations in the residuals of a standard transit light curve fit, at the level of ~100 ppm for Kronian rings. In this work, we explore two much larger observational consequences of exorings: (1) the significant increase in transit depth that may lead to misclassification of ringed planetary candidates as false-positives and/or the underestimation of planetary density; and (2) the so-called "photo-ring" effect, a new asterodensity profiling effect, revealed by a comparison of the light curve derived stellar density to that measured with independent methods (e.g. asteroseismology). Whilst these methods do not provide an unambiguous discovery of exorings, we show that the large amplitude of these effects combined with their relatively simple analytic description, makes them highly suited to large scale surveys to identify candidate ringed planets worthy of more detailed investigation. Moreover, these methods lend themselves to ensemble analyses seeking to uncover evidence for a population of ringed planets. We describe the method in detail, develop the basic underlying formalism and test it in the parameter space of rings and transit configuration. We discuss the prospects of using the method for the first systematic search of exoplanetary rings in the Kepler database and provide basic computational code for implementing it.

Massive Rings of J1407b Dwarf Saturn's, Sculpted by Giant ExoMoon?

Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?

Authors:

Kenworthy et al

Abstract:

The light curve of 1SWASP J140747.93-394542.6, a ∼16 Myr old star in the Sco-Cen OB association, underwent a complex series of deep eclipses that lasted 56 days, centered on April 2007. This light curve is interpreted as the transit of a giant ring system that is filling up a fraction of the Hill sphere of an unseen secondary companion, J1407b. We fit the light curve with a model of an azimuthally symmetric ring system, including spatial scales down to the temporal limit set by the star's diameter and relative velocity. The best ring model has 37 rings and extends out to a radius of 0.6 AU (90 million km), and the rings have an estimated total mass on the order of 100MMoon. The ring system has one clearly defined gap at 0.4 AU (61 million km), which we hypothesize is being cleared out by a less than 0.8M⊕ exosatellite orbiting around J1407b. This eclipse and model implies that we are seeing a circumplanetary disk undergoing a dynamic transition to an exosatellite-sculpted ring structure and is one of the first seen outside our Solar system.