Detection and characteization of young exoplanets and circumplanetary disks

A faint companion around CrA-9: protoplanet or obscured binary?

Valentin Christiaens (Monash University)

Giant planet formation is poorly understood. Observational input from directly imaged planets caught while forming is crucial to constrain planet formation models. We used VLT/NACO and VLT/SPHERE to search for companions in the transition disc of CrA-9, an accreting M0.75 dwarf at the edge of the R CrA dark cloud with an estimated age of 1--2 Myr. We found a faint point source at ~ 0.7'' separation from the star (~108 AU projected separation). Our 3-epoch astrometry suggests it is co-moving at a 5sigma level. Our analysis of the 1.0--3.8micrometer spectrum extracted for the companion suggests a young age based on the 1.13 Na gravity-sensitive index. Both the near-IR absolute magnitudes of the object and the best-fit photometric radius (R~0.54 R_J) point towards a planetary-mass companion. However, the 1.0--3.8 micrometer spectrum is best reproduced with a high effective temperature (~3200 K) BT-SETTL or BT-DUSTY model. We discuss possible explanations to reconcile our measurements, including an M-dwarf companion obscured by a circum-secondary disc or an accreting nascent giant planet. Follow-up observations are required to provide a final answer and disentangle between these scenarios. Our work highlights the caution required in the interpretation of faint point-source companions in star-forming regions as possible protoplanets.

SCExAO/CHARIS Direct Imaging of Candidate Embedded Protoplanets and Planet-Forming Disks 

Thayne Currie(Subaru Telescope)

We present first results of efforts to directly image young, still-forming exoplanets embedded in planet-forming disks using the Subaru Coronagraphic Extreme Adaptive Optics system and the CHARIS integral field spectrograph.   We focus primarily on systems with previously claimed protoplanet detections -- LkCa 15,  HD 163296, and MWC 758 -- and other ALMA-imaged targets showing indirect evidence for planet formation. Our results thus far highlight the challenge of separating bona fide planets from disk signals, especially those obtained with conventional AO data or with sparse aperture masking, but do suggest the detection of at least one new protoplanet whose discovery may challenge models for jovian planet formation.

Occurrence rate of young hot Jupiters: the cautionary tale about V830 Tau

Mario Damasso (INAF-Astrophysical Observatory of Torino (Italy))

Detecting very young exoplanets (~20 Myr or less) on close-in orbits is crucial to put strong constraints on models of planet formation and evolution at the earliest stages. One of the most recent and intriguing results is the apparent high frequency of young hot Jupiters, which suggests in particular that migration driven by planet-disc interactions may play a significant role in the genesis of such planets, and can occur over short timescales. However, the typically very high levels of activity of the host stars hamper detections, in particular, for blind searches using the radial velocity method, and make really challenging measuring masses even for transiting planets. Here we present the exemplary case of the hot Jupiter V830 Tau b, detected in 2016 with the radial velocity method, and then followed-up with the HARPS-N spectrograph within the GAPS program. Our 2.5 yr long campaign could not confirm the existence of the planet, therefore cooling down the prospect for a high planetary occurrence rate around young T Tauri stars.

Direct Detection of CO in the Planet Around CI Tau: Planet Formation Constraints from a Young Hot Jupiter

Laura Flagg (Rice University) 

Using high-resolution IR spectroscopy from IGRINS, we confirm the existence of hot Jupiter CI Tau b based on a detection of CO in its atmosphere. Its magnitude implies it formed via a hot start formation mechanism. We also measured its mass.  It is the first planet around a T Tauri star with a model-independent, dynamical mass.

Are companions creating the gaps and rings in protoplanetary disks observed by ALMA?

Sebastián Jorquera (Departamento de Astronomía, Universidad de Chile) 

Observations of the ALMA Large Program DSHARP (Disks substructures at High Angular Resolution Project) have revealed a variety of substructures in a sample of 20 protoplanetary disks; in particular, the presence of dark gaps and bright rings, which trace zones where solid particles have been depleted and concentrated, respectively. Numerous mechanisms may explain these substructures, but if planetary- or stellar-mass companions are preferentially found inside the gaps of disks with ring morphology, then dynamical clearing from embedded companions become the favored mechanism for their creation. In this talk, I will briefly introduce the DSHARP sample an the motivation to search for possible companions into the observed gaps, as well as the methods for their detection. Next, I will present the results from our attempt of observing these objects, applying different algorithms used to detect planetary companions via Direct Imaging to observations carried by the NaCo/VLT instrument, as well as some constraints derived for the observable mass and magnitudes of companions into the disks.

Planet formation with NIR interferometry

Jens Kammerer (ESO/Australian National University) 

The recent detection of HR 8799 e with GRAVITY marks the beginning of a new era of exoplanet observations with near-infrared long-baseline interferometry. In this talk, I will present recent science highlights of the ExoGRAVITY team. We were able to measure the C/O abundance ratio of beta Pic b and infer a formation via core accretion for this young gas giant. Moreover, we managed to directly detect beta Pic c, another gas giant in the same system inferred from radial velocity data, demonstrating that NIR interferometry can bridge the gap between companions detected via direct and indirect methods. Thanks to the high angular resolution of GRAVITY, we could further place an upper limit on the dynamical mass and the size of the circumplanetary disk (CPD) of PDS 70 b. Currently, we are peering into the cloud composition of the reddest known sub-stellar companion HD 206893 B, whose extreme color is challenging available atmospheric models. Finally, I will illustrate the capabilities of future interferometers such as GRAVITY+ and Hi-5 for planet formation science and highlight the need for high-angular resolution."

The theory of kinks - An analytical model of velocity perturbations induced by planets in discs

Giuseppe Lodato (Universita' degli Studi di Milano) 

Protoplanets can be detected through the characteristic kinematics of the surrounding gas, perturbed by the gravitational interaction with the planet itself, resulting in peculiar `kinks' in the channel maps of different gas species. In this talk, I will present a theory of such kinks in terms of a semi-analytic model for the velocity perturbation induced by a planet. In doing so, I will i) confirm that the observed kinks are caused by the planet-induced wake ii) I will show how to quantify the planet mass from the kink amplitude and iii) I will demonstrate that the localised nature of the observed kinks implies some additional dissipation of the wake besides shocks.

Constraining Protoplanetary Disk Accretion and Young Planets Using ALMA Kinematic Observations

Ian Rabago (University of Nevada, Las Vegas)

Recent ALMA molecular line observations have revealed 3-D gas velocity structure in protoplanetary disks, which has shed light on mechanisms of disk accretion and ring/gap formation. 1) By carrying out viscous simulations with different vertical stress profiles that are motivated by different disk turbulence simulations, we confirm that the disk's velocity structure differs dramatically with different stress profiles. Thus, kinematic observations tracing flows at different disk heights can potentially distinguish different accretion mechanisms. On the other hand, the disk surface density evolution is only determined by the vertically integrated stress. Thus, the sharp disk outer edge constrained by recent kinematic observations can be explained by the vertically integrated alpha decreasing with radii, without invoking photoevaporation or external perturbers. 2) We also study the kinematic signatures of a young planet by carrying out 3-D planet-disk simulations. The relationship between the planet mass and the "kink" velocity is derived, showing little dependence on the disk viscosity. The deviation of azimuthal velocity from the Keplerian velocity at the gap edge is constant within 3 disk scale heights, and the relationship between the deviation and the planet mass is consistent with those derived in 2-D simulations. Finally, by removing the planet from the gap, we find that most of the velocity deviation is unchanged and thus is due to the presence of the gap itself and not directly related to the planet. The axisymmetric kinematic observations probe the gaseous rings and gaps, but may not be sufficient to confirm the presence of the planet.

Constraining Planet Formation Models with Current and Future Instruments 

Alexander Wallace (Australian National University) 

Planet formation is best observed through direct imaging however, with the exception of PDS 70, there has been little success detecting planets in the process of formation.  Applying models of planet formation and brightness evolution, I discuss how likely we are to detect accreting exoplanets with future instruments at ESO and whether we can constrain the formation conditions of directly imaged planets.