Inferring giant planets from ALMA mm continuum and line observations in (transition) disks

Inferring giant planets from ALMA mm continuum and line observations in (transition) disks 

Authors:

Facchini et al

Abstract:
Potential signatures of proto-planets embedded in their natal protoplanetary disk are radial gaps or cavities in the continuum emission in the IR-mm wavelength range. ALMA observations are now probing spatially resolved rotational line emission of CO and other chemical species. These observations can provide complementary information on the mechanism carving the gaps in dust and additional constraints on the purported planet mass. We post-process 2D hydrodynamical simulations of planet-disk models, where the dust densities and grain size distributions are computed with a dust evolution code. The simulations explore different planet masses (1MJ≤Mp≤15MJ) and turbulent parameters. The outputs are post-processed with the thermo-chemical code DALI, accounting for the radially and vertically varying dust properties as in Facchini et al. (2017). We obtain the gas and dust temperature structures, chemical abundances, and synthetic emission maps of both thermal continuum and CO rotational lines. This is the first study combining hydro simulations, dust evolution and chemistry to predict gas emission of disks hosting massive planets. All radial intensity profiles of the CO main isotopologues show a gap at the planet location. The ratio between the location of the gap as seen in CO and the peak in the mm continuum at the pressure maximum outside the orbit of the planet shows a clear dependence on planet mass. Due to the low dust density in the gaps, the dust and gas components can become thermally decoupled, with the gas being colder than the dust. The gaps seen in CO are due to a combination of gas temperature dropping at the location of the planet, and of the underlying surface density profile. In none of the models is a CO cavity observed, only CO gaps, indicating that one single massive planet is not able to explain the CO cavities observed in transition disks.

Multiple rings in the transition disk and companion candidates around RX J1615.3-3255

Multiple rings in the transition disk and companion candidates around RX J1615.3-3255

High contrast imaging with VLT/SPHERE

Authors:

de Boer et al

Abstract:

Context.

The effects of a planet sculpting the disk from which it formed are most likely to be found in disks that are in transition between being classical protoplanetary and debris disks. Recent direct imaging of transition disks has revealed structures such as dust rings, gaps, and spiral arms, but an unambiguous link between these structures and sculpting planets is yet to be found.

Aims.

We aim to find signs of ongoing planet-disk interaction and study the distribution of small grains at the surface of the transition disk around RX J1615.3-3255 (RX J1615).

Methods.

We observed RX J1615 with VLT/SPHERE. From these observations, we obtained polarimetric imaging with ZIMPOL (R′-band) and IRDIS (J), and IRDIS (H2H3) dual-band imaging with simultaneous spatially resolved spectra with the IFS (YJ).

Results.

We image the disk for the first time in scattered light and detect two arcs, two rings, a gap and an inner disk with marginal evidence for an inner cavity. The shapes of the arcs suggest that they are probably segments of full rings. Ellipse fitting for the two rings and inner disk yield a disk inclination i = 47 ± 2° and find semi-major axes of 1.50 ± 0.01′′ (278 au), 1.06 ± 0.01′′ (196 au) and 0.30 ± 0.01′′ (56 au), respectively. We determine the scattering surface height above the midplane, based on the projected ring center offsets. Nine point sources are detected between 2.1′′ and 8.0′′ separation and considered as companion candidates. With NACO data we recover four of the nine point sources, which we determine to be not co-moving, and therefore unbound to the system.

Conclusions.

We present the first detection of the transition disk of RX J1615 in scattered light. The height of the rings indicate limited flaring of the disk surface, which enables partial self-shadowing in the disk. The outermost arc either traces the bottom of the disk or it is another ring with semi-major axis ≳ 2.35′′ (435 au). We explore both scenarios, extrapolating the complete shape of the feature, which will allow us to distinguish between the two in future observations. The most attractive scenario, where the arc traces the bottom of the outer ring, requires the disk to be truncated at r ≈ 360 au. If the closest companion candidate is indeed orbiting the disk at 540 au, then it would be the most likely cause for such truncation. This companion candidate, as well as the remaining four, all require follow up observations to determine if they are bound to the system.

Shadows cast on the transition disk of HD 135344B

Shadows cast on the transition disk of HD 135344B
Multiwavelength VLT/SPHERE polarimetric differential imaging
Author:

Stolker et al

Abstract:

Context.

The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal (sub-)millimeter emission which are possibly related to planet formation processes.

Aims.

We aim to study the morphology and surface brightness of the disk in scattered light to gain insight into the innermost disk regions, the formation of protoplanets, planet-disk interactions traced in the surface and midplane layers, and the dust grain properties of the disk surface.

Methods.

We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in the R and I-bands and with IRDIS in the Y and J-bands. The scattered light images and surface brightness profiles are used to study in detail structures in the disk surface and brightness variations. We have constructed a 3D radiative transfer model to support the interpretation of several detected shadow features.

Results.

The scattered light images reveal with unprecedented angular resolution and sensitivity the spiral arms as well as the 25 au cavity of the disk. Multiple shadow features are discovered on the outer disk with one shadow only being present during the second observation epoch. A positive surface brightness gradient is observed in the stellar irradiation corrected (r²-scaled) images in southwest direction possibly due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The disk integrated polarized flux, normalized to the stellar flux, shows a positive trend towards longer wavelengths which we attribute to large (2πa ≳ λ) aggregate dust grains in the disk surface. Part of the non-azimuthal polarization signal in the U_φ image of the J-band observation can be attributed to multiple scattering in the disk.

Conclusions.

The detected shadow features and their possible variability have the potential to provide insight into the structure of and processes occurring in the innermost disk regions. Possible explanations for the presence of the shadows include a 22° misaligned inner disk, a warped disk region that connects the inner disk with the outer disk, and variable or transient phenomena such as a perturbation of the inner disk or an asymmetric accretion flow. The spiral arms are best explained by one or multiple protoplanets in the exterior of the disk although no gap is detected beyond the spiral arms up to 1.′′0.

Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

Radial decoupling of small and large dust grains in the transitional disk RX J1615.3-3255

Authors:

Kooistra et al

Abstract:

We present H-band (1.6 {\mu}m) scattered light observations of the transitional disk RX J1615.3-3255, located in the ~1 Myr old Lupus association. From a polarized intensity image, taken with the HiCIAO instrument of the Subaru Telescope, we deduce the position angle and the inclination angle of the disk. The disk is found to extend out to 68 ± 12 AU in scattered light and no clear structure is observed. Our inner working angle of 24 AU does not allow us to detect a central decrease in intensity similar to that seen at 30 AU in the 880 {\mu}m continuum observations. We compare the observations with multiple disk models based on the Spectral Energy Distribution (SED) and submm interferometry and find that an inner rim of the outer disk at 30 AU containing small silicate grains produces a polarized intensity signal which is an order of magnitude larger than observed. We show that a model in which the small dust grains extend smoothly into the cavity found for large grains is closer to the actual H-band observations. A comparison of models with different dust size distributions suggests that the dust in the disk might have undergone significant processing compared to the interstellar medium.

Can dead zones create transition disk like structures?

Can dead zones create transition disk like structures?

Authors:

Pinilla et al

Abstract:

Regions of low ionisation where the activity of the magneto-rotational instability is suppressed, the so called dead zones, have been suggested to explain gaps and asymmetries of transition disks. We investigate the gas and dust evolution simultaneously assuming simplified prescriptions for a dead zone and a magnetohydrodynamic (MHD) wind acting on the disk. We explore whether or not the resulting gas and dust distribution can create signatures similar to the ones observed in transition disks. For the dust evolution, we include the transport, growth, and fragmentation of dust particles. To compare with observations, we produce synthetic images in scattered optical light and in thermal emission at mm wavelengths. In all models with a dead zone, a bump in the gas surface density is produced, which is able to efficiently trap large particles (≳1 mm) at the outer edge of the dead zone. The gas bump reaches an amplitude of a factor of ∼5, which can be enhanced by the presence of a MHD wind that removes mass from the inner disk. While our 1D simulations suggest that such a structure can be present only for ∼1 Myr, the structure may be maintained for a longer time when a more realistic 2D/3D simulations are performed. In the synthetic images, gap-like low emission regions are seen at scattered light and in thermal emission at mm wavelengths, as previously predicted in the case of planet-disk interaction. As a conclusion, main signatures of transition disks can be reproduced by assuming a dead zone in the disk, including gap-like structure in scattered light and millimetre continuum emission, and a lower gas surface density within the dead zone. Previous studies showed that the Rossby wave instability can also develop at the edge of such dead zones, forming vortices and creating also asymmetries.

On the origin of horseshoes in transitional discs

On the origin of horseshoes in transitional discs

Authors:

Ragusa et al

Abstract:

We investigate whether the rings, lopsided features and horseshoes observed at millimetre wavelengths in transitional discs can be explained by the dynamics of gas and dust at the edge of the cavity in circumbinary discs. We use 3D dusty smoothed particle hydrodynamics calculations to show that binaries with mass ratio q≳0.04 drive eccentricity in the central cavity, naturally leading to a crescent-like feature in the gas density, which is accentuated in the mm dust grain population with intensity contrasts in mm-continuum emission of 10 or higher. We perform mock observations to demonstrate that these features closely match those observed by ALMA, suggesting that the origin of rings, dust horseshoes and other non-axisymmetric structures in transition discs can be explained by the presence of massive companions.

Hunting for Pebbles in Protoplanetary Disks

3.3 cm JVLA observations of transitional disks: searching for centimeter pebbles

Authors:

Zapata et al

Abstract:

We present sensitive (rms-noises ∼ 4 -- 25 μJy) and high angular resolution (∼1--2") 8.9 GHz (3.3 cm) Karl G. Jansky Very Large Array (JVLA) radio continuum observations of 10 presumed transitional disks associated with young low-mass stars. We report the detection of radio continuum emission in 5 out of the 10 objects (RXJ1615, UX Tau A, LkCa15, RXJ1633, and SR24s). In the case of LkCa15, the centimeter emission is extended, and has a similar morphology to that of the transitional disk observed at mm wavelengths with an inner depression. For these five detections, we construct the Spectral Energy Distributions (SEDs) from the centimeter to submillimeter wavelengths, and find that they can be well fitted with a single (RXJ 1633 and UX Tau A) or a two component power-law (LkCa 15, RXJ 1615, and SR24s). For the cases where a single power-law fits well the data, the centimeter emission is likely produced by optically thin dust with large grains i.e. centimeter-size pebbles) present in the transitional disks. For the cases where a double power-law fits the data, the centimeter emission might be produced by the combination of photoevaporation and/or a free-free jet. We conclude that RXJ1633 and UX Tau A are excellent examples of transitional disks where the structure of the emission from centimeter/millimeter pebbles can be studied. In the other cases, some other physical emitting mechanisms are also important in the centimeter regime.

Protoplanetary and Transitional Disks in the Open Stellar Cluster IC 2395

Protoplanetary and Transitional Disks in the Open Stellar Cluster IC 2395

Authors:

Balog et al

Abstract:

We present new deep UBVRI images and high-resolution multi-object optical spectroscopy of the young (~ 6 - 10 Myr old), relatively nearby (800 pc) open cluster IC 2395. We identify nearly 300 cluster members and use the photometry to estimate their spectral types, which extend from early B to middle M. We also present an infrared imaging survey of the central region using the IRAC and MIPS instruments on board the Spitzer Space Telescope, covering the wavelength range from 3.6 to 24 microns. Our infrared observations allow us to detect dust in circumstellar disks originating over a typical range of radii ~ 0.1 to ~ 10AU from the central star. We identify 18 Class II, 8 transitional disk, and 23 debris disk candidates, respectively 6.5%, 2.9%, and 8.3% of the cluster members with appropriate data. We apply the same criteria for transitional disk identification to 19 other stellar clusters and associations spanning ages from ~ 1 to ~ 18 Myr. We find that the number of disks in the transitional phase as a fraction of the total with strong 24 micron excesses ([8] - [24] > 1.5) increases from 8.4 +\- 1.3% at ~ 3 Myr to 46 +\- 5% at ~ 10 Myr. Alternative definitions of transitional disks will yield different percentages but should show the same trend.

Imaging Protoplanets in Transition Disks

Imaging protoplanets: observing transition disks with non-redundant masking

Authors:

Sallum et al

Abstract:

Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.

The Frequency Of Binary Star Interlopers Amongst Transitional Disks

The Frequency Of Binary Star Interlopers Amongst Transitional Discs

Authors:

Ruíz-Rodríguez et al

Abstract:

Using Non-Redundant Mask interferometry (NRM), we searched for binary companions to objects previously classified as Transitional Disks (TD). These objects are thought to be an evolutionary stage between an optically thick disk and optically thin disk. We investigate the presence of a stellar companion as a possible mechanism of material depletion in the inner region of these disks, which would rule out an ongoing planetary formation process in distances comparable to the binary separation. For our detection limits, we implement a new method of completeness correction using a combination of randomly sampled binary orbits and Bayesian inference. The selected sample of 24 TDs belong to the nearby and young star forming regions: Ophiuchus (∼ 130 pc), Taurus-Auriga (∼ 140 pc) and IC348 ( ∼ 220 pc). These regions are suitable to resolve faint stellar companions with moderate to high confidence levels at distances as low as 2 au from the central star. With a total of 31 objects, including 11 known TDs and circumbinary disks from the literature, we have found that a fraction of 0.38 ± 0.09 of the SEDs of these objects are likely due to the tidal interaction between a close binary and its disk, while the remaining SEDs are likely the result of other internal processes such as photoevaporation, grain growth, planet disk interactions. In addition, we detected four companions orbiting outside the area of the truncation radii and we propose that the IR excesses of these systems are due to a disk orbiting a secondary companion

The Disk of GM Aur

Panchromatic Imaging of a Transitional Disk: The Disk of GM Aur in Optical and FUV Scattered Light

Authors:

Hornbeck et al

Abstract:

We have imaged GM Aur with HST, detected its disk in scattered light at 1400A and 1650A, and compared these with observations at 3300A, 5550A, 1.1 microns, and 1.6 microns. The scattered light increases at shorter wavelengths. The radial surface brightness profile at 3300A shows no evidence of the 24AU radius cavity that has been previously observed in sub-mm observations. Comparison with dust grain opacity models indicates the surface of the entire disk is populated with sub-micron grains. We have compiled an SED from 0.1 microns to 1 mm, and used it to constrain a model of the star+disk system that includes the sub-mm cavity using the Monte Carlo Radiative Transfer code by Barbara Whitney. The best-fit model image indicates that the cavity should be detectable in the F330W bandpass if the cavity has been cleared of both large and small dust grains, but we do not detect it. The lack of an observed cavity can be explained by the presence of sub-microns grains interior to the sub-mm cavity wall. We suggest one explanation for this which could be due to a planet of mass

Dipper disks not inclined towards edge-on orbits

Dipper disks not inclined towards edge-on orbits

Authors:

Ansdell et al

Abstract:

The so-called "dipper" stars host circumstellar disks and have optical and infrared light curves that exhibit quasi-periodic or aperiodic dimming events consistent with extinction by transiting dusty structures orbiting in the inner disk. Most of the proposed mechanisms explaining the dips---i.e., occulting disk warps, vortices, and forming planetesimals---assume nearly edge-on viewing geometries. However, our analysis of the three known dippers with publicly available resolved sub-mm data reveals disks with a range of inclinations, most notably the face-on transition disk J1604-2130 (EPIC 204638512). This suggests that nearly edge-on viewing geometries are not a defining characteristic of the dippers and that additional models should be explored. If confirmed by further observations of more dippers, this would point to inner disk processes that regularly produce dusty structures far above the outer disk midplane in regions relevant to planet formation.

STABILITY AND OCCURRENCE RATE CONSTRAINTS ON THE PLANETARY SCULPTING HYPOTHESIS FOR "TRANSITIONAL" DISKS

STABILITY AND OCCURRENCE RATE CONSTRAINTS ON THE PLANETARY SCULPTING HYPOTHESIS FOR "TRANSITIONAL" DISKS

Authors:

Dong et al

Abstract:

Transitional disks, protoplanetary disks with deep and wide central gaps, may be the result of planetary sculpting. By comparing numerical planet-opening-gap models with observed gaps, we find systems of 3–6 giant planets are needed in order to open gaps with the observed depths and widths. We explore the dynamical stability of such multi-planet systems using N-body simulations that incorporate prescriptions for gas effects. We find they can be stable over a typical disk lifetime, with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances. However, in order to account for the occurrence rate of transitional disks, the planet sculpting scenario demands gap-opening-friendly disk conditions, in particular, a disk viscosity α lesssim 0.001. In addition, the demography of giant planets at ~3–30 au separations, poorly constrained by current data, has to largely follow occurrence rates extrapolated outward from radial velocity surveys, not the lower occurrence rates extrapolated inward from direct imaging surveys. Even with the most optimistic occurrence rates, transitional disks cannot be a common phase that most gas disks experience at the end of their life, as popularly assumed, simply because there are not enough planets to open these gaps. Finally, as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting, the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime.

Stability and Occurrence Rate Constraints on the Planetary Sculpting Hypothesis for "Transitional" Disks

Stability and Occurrence Rate Constraints on the Planetary Sculpting Hypothesis for "Transitional" Disks

Authors:

Dong et al

Abstract:

Transitional disks, protoplanetary disks with deep and wide central gaps, may be the result of planetary sculpting. By comparing numerical planet-opening-gap models with observed gaps, we find systems of 3-6 giant planets are needed in order to open gaps with the observed depths and widths. We explore the dynamical stability of such multi-planet systems using N-body simulations that incorporate prescriptions for gas effects. We find they can be stable over a typical disk lifetime, with the help of eccentricity damping from the residual gap gas that facilitates planets locking into mean motion resonances. However, in order to account for the occurrence rate of transitional disks, the planet sculpting scenario demands gap-opening-friendly disk conditions, in particular, a disk viscosity α≲0.001. In addition, the demography of giant planets at ∼3−30 AU separations, poorly constrained by current data, has to largely follow occurrence rates extrapolated outward from radial velocity surveys, not the lower occurrence rates extrapolated inward from direct imaging surveys. Even with the most optimistic occurrence rates, transitional disks cannot be a common phase that most gas disks experience at the end of their life, as popularly assumed, simply because there are not enough planets to open these gaps. Finally, as consequences of demanding almost all giant planets at large separations participate in transitional disk sculpting, the majority of such planets must form early and end up in a chain of mean motion resonances at the end of disk lifetime.

HD 135344B's Protoplanetary Disk Shows Evidence of at Least one Gas Giant Protoplanet

Shadows cast on the transition disk of HD 135344B

Authors:

Stolker et al

Abstract:

The protoplanetary disk of the F-type star HD 135344B (SAO 206462) is in a transition stage and shows many intriguing structures both in scattered light and thermal millimeter emission which are possibly related to planet formation processes and planet-disk interactions. We have carried out high-contrast polarimetric differential imaging (PDI) observations with VLT/SPHERE and obtained the first optical polarized scattered light images with the sub-instrument ZIMPOL in R- and I-band. Additionally, near-infrared polarimetric observations were done with IRDIS in Y- and J-band. We will use the scattered light images, surface brightness profiles and color to study in detail disk structures and brightness variations. The scattered light images reveal with unprecedented sensitivity and angular resolution the spiral arm structure of the disk as well as the inner disk cavity of 25 au in all filters. Multiple shadow features are discovered on the outer disk and the observations of the two epochs show indications of variability of one shadow. A positive surface brightness gradient is observed in the r^2-scaled images in south-west direction due to an azimuthally asymmetric perturbation of the temperature and/or surface density by the passing spiral arms. The scattering efficiency in polarized light shows a positive linear trend towards longer wavelengths presumably because of large/aggregate dust grains (2pi a greater than or equal lambda) in the disk surface. The shadows on the outer disk of HD 135344B could be cast by an inner dust belt which is 22 degrees inclined with respect to the outer disk, a warped disk region which connects the inner disk with the cavity and an accretion funnel flow from the inner disk onto the star. The wide open spiral arms indicate the presence of one or multiple massive protoplanets, a local disk instability beyond the dust cavity or a combination of the two.

Hunting for Binaries in Transition Disks

Searching for spectroscopic binaries within transition disk objects

Authors:

Kohn et al

Abstract:

Transition disks (TDs) are intermediate stage circumstellar disks characterized by an inner gap within the disk structure. To test whether these gaps may have been formed by closely orbiting, previously undetected stellar companions, we collected high-resolution optical spectra of 31 TD objects to search for spectroscopic binaries (SBs). Twenty-four of these objects are in Ophiuchus and seven are within the Coronet, Corona Australis, and Chameleon I star-forming regions. We measured radial velocities for multiple epochs, obtaining a median precision of 400 ms−1. We identified double-lined SB SSTc2d J163154.7-250324 in Ophiuchus, which we determined to be composed of a K7(±0.5) and a K9(±0.5) star, with orbital limits of a less than 0.6 AU and P less than 150 days. This results in an SB fraction of 0.04+0.12−0.03 in Ophiuchus, which is consistent with other spectroscopic surveys of non-TD objects in the region. This similarity suggests that TDs are not preferentially sculpted by the presence of close binaries and that planet formation around close binaries may take place over similar timescales to that around single stars.

Resolved observations of transition disks

Resolved observations of transition disks

Author:

Cassuset al

Abstract:

Resolved observations are bringing new constraints on the origin of radial gaps in protoplanetary disks. The kinematics, sampled in detail in one case-study, are indicative of non-Keplerian flows, corresponding to warped structures and accretion which may both play a role in the development of cavities. Disk asymmetries seen in the radio continuum are being interpreted in the context of dust segregation via aerodynamic trapping. We summarise recent observational progress, and also describe prospects for improvements in the near term.

Constraining the properties of transitional disks in Chamaeleon I with Herschel

Constraining the properties of transitional disks in Chamaeleon I with Herschel

Authors:

Ribas et al

Abstract:

Transitional disks are protoplanetary disks with opacity gaps/cavities in their dust distribution, a feature that may be linked to planet formation. We perform Bayesian modeling of the three transitional disks SZ Cha, CS Cha and T25 including photometry from the Herschel Space Observatory to quantify the improvements added by these new data. We find disk dust masses between 2x10^-5 and 4x10^-4 Msun, and gap radii in the range of 7-18 AU, with uncertainties of ~ one order of magnitude and ~ 4 AU, respectively. Our results show that adding Herschel data can significantly improve these estimates with respect to mid-infrared data alone, which have roughly twice as large uncertainties on both disk mass and gap radius. We also find weak evidence for different density profiles with respect to full disks. These results open exciting new possibilities to study the distribution of disk masses for large samples of disks.

the first SO image in a transitional disk

High spatial resolution imaging of SO and H2CO in AB Auriga: the first SO image in a transitional disk

Authors:

Pacheco-Vázquez et al

Abstract:

Transitional disks are structures of dust and gas around young stars with large inner cavities in which planet formation may occur. Lopsided dust distributions are observed in the dust continuum emission at millimeter wavelengths. These asymmetrical structures can be explained as the result of an enhanced gas density vortex where the dust is trapped potentially promoting the rapid growth to the planetesimal scale. AB Aur hosts a transitional disk with a clear horseshoe morphology which strongly suggests the presence of a dust trap. Our goal is to investigate its formation and the possible effects on the gas chemistry. We used the NOEMA interferometer to image the 1mm continuum dust emission and the 13CO J=2 →1, C18O J=2 →1, SO J=56 →45 and H2CO J=303 →202 rotational lines. Line integrated intensity ratio images are built to investigate the chemical changes within the disk. We have used a single point (n,T) chemical model to investigate the lifetime of gaseous CO, H2CO and SO in the dust trap. Our model shows that for densities greater than 107~cm−3, the SO molecules are depleted (directly frozen or converted into SO2 and then frozen out) in less than 0.1~Myr. The lower SO abundance towards the dust trap could indicate that a larger fraction of the gas is in a high density environment. Gas dynamics, grain growth and gas chemistry are coupled in the planet formation process. Because of the strong dependence of SO abundance on the gas density, the sulfur chemistry can be used as a chemical diagnostic to detect the birthsites of future planets. However, the large uncertainties inherent to chemical models and the limited knowledge of the disk physical structure and initial conditions are important drawbacks.

Spiral Waves Triggered by Shadows in Transition Disks

Spiral waves triggered by shadows in transition disks

Authors:

Montesinos et al

Abstract:

Circumstellar asymmetries such as central warps have recently been shown to cast shadows on outer disks. We investigate the hydrodynamical consequences of such variable illumination on the outer regions of a transition disk, and the development of spiral arms. Using 2D simulations, we follow the evolution of a gaseous disk passively heated by the central star, under the periodic forcing of shadows with an opening angle of ∼28∘. With a lower pressure under the shadows, each crossing results in a variable azimuthal acceleration, which in time develops into spiral density waves. Their pitch angles evolves from Π∼15∘−22∘ at onset, to ∼11∘-14∘, over ∼65~AU to 150~AU. Self-gravity enhances the density contrast of the spiral waves, as also reported previously for spirals launched by planets. Our control simulations with unshadowed irradiation do not develop structures, except a different form of spiral waves seen at later times only in the gravitationally unstable control case. Scattered light predictions in H band show that such illumination spirals should be observable. We suggest that spiral arms in the case-study transition disk HD~142527 could be explained as a result of shadowing from the tilted inner disk.