One class of protoplanetary disc models, the X-wind model, predicts strongly subkeplerian orbital gas velocities, a configuration that can be sustained by magnetic tension. We investigate disc-planet interactions in these subkeplerian discs, focusing on orbital migration for low-mass planets and gap formation for high-mass planets. We use linear calculations and nonlinear hydrodynamical simulations to measure the torque and look at gap formation. In both cases, the subkeplerian nature of the disc is treated as a fixed external constraint. We show that, depending on the degree to which the disc is subkeplerian, the torque on low-mass planets varies between the usual Type I torque and the one-sided outer Lindblad torque, which is also negative but an order of magnitude stronger. In strongly subkeplerian discs, corotation effects can be ignored, making migration fast and inward. Gap formation near the planet's orbit is more difficult in such discs, since there are no resonances close to the planet accommodating angular momentum transport. In stead, the location of the gap is shifted inwards with respect to the planet, leaving the planet on the outside of a surface density depression. Depending on the degree to which a protoplanetary disc is subkeplerian, disc-planet interactions can be very different from the usual Keplerian picture, making these discs in general more hazardous for young planets.
Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet-disc interactions and their observability in CO rotational emission lines. We perform three-dimensional hydrodynamical simulations of single giant planets, and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes and vortices bear strong kinematic counterparts. The iso-velocity contours in the CO(2-1) line centroids $v_\circ$ reveal large-scale perturba…
In the past years, high angular resolution observations have revealed that circumstellar discs appear in a variety of shapes with diverse substructures being ubiquitous. This has given rise to the question of whether these substructures are triggered by planet-disc interactions. Besides direct imaging, one of the most promising methods to distinguish between different disc shaping mechanisms is to study the kinematics of the gas disc. In particular, the deviations of the rotation profile from Keplerian velocity can be used to probe perturbations in the gas pressure profile that may be caused b…
When, in the course of searching for exoplanets, sparse sampling and noisy data make it necessary to disentangle possible solutions to the observations, one must consider the possibility that what appears to be a single eccentric Keplerian signal may in reality be attributed to two planets in near-circular orbits. There is precedent in the literature for such outcomes, whereby further data or new analysis techniques reveal hitherto occulted signals. Here, we perform suites of simulations to explore the range of possible two-planet configurations that can result in such confusion. We find that …
Radial velocity searches for exoplanets have detected many multi-planet systems around nearby bright stars. An advantage of this technique is that it generally samples the orbit outside of inferior/superior conjunction, potentially allowing the Keplerian elements of eccentricity and argument of periastron to be well characterized. The orbital architectures for some of these systems show signs of close planetary encounters that may render the systems unstable as described. We provide an in-depth analysis of two such systems: HD 5319 and HD 7924, for which the scenario of coplanar orbits results…
Protoplanetary disks are gaseous systems in Keplerian rotation around young stars, known to be turbulent. They include a small fraction of dust from which planets form. In the incremental scenario for planet growth, the formation of kilometer-size objects (planetesimals) from pebbles is a major open question. Clustering of particles is necessary for solids to undergo a local gravitational collapse. To address this question, the dynamic of inertial particles in turbulent flows with Keplerian rotation and shear is studied. Two-dimensional direct numerical simulations are performed to explore sys…
While Keplerian orbits account for the majority of the astrometric motion of directly-imaged planets, perturbations due to N-body interactions allow us to directly constrain exoplanet masses in multiplanet systems. This has the potential to improve our understanding of massive directly-imaged planets, which nearly all currently have only model-dependent masses. The VLTI-GRAVITY instrument has demonstrated that interferometry can achieve 100x better astrometric precision (Gravity Collaboration et al. 2019) than existing methods, a level of precision that makes detection of planet-planet interac…
Transition disks are protoplanetary disks with inner cavities possibly cleared by massive companions, which makes them prime targets to observe at high resolution to map their velocity structure. We present ALMA Band 6 dust and gas observations of the transition disk around RXJ1604.3-2130 A, known to feature nearly symmetric shadows in scattered light. We studied the $^{12}$CO line channel maps and moment maps of the line of sight velocity and peak intensity. We fitted a Keplerian model of the channel-by-channel emission to study line profile differences and produced deprojected radial profile…
Ultra-short-period (USP) planets reside inside the expected truncation radius for typical T Tauri disks. As a result, their current orbital locations require an explanation beyond standard disk migration or in situ formation. Modern theories of planet-disk interactions indicate that once a planet migrates close to the disk's inner truncation radius, Type I torques vanish or switch direction, depending on the stellar and disk conditions, so that the planet is expected to stop its orbital decay and become trapped. In this work, we show that that magnetically-driven sub-Keplerian gas flow in the …
A couple of dozen Earth-like planets orbiting M dwarfs have been discovered so far. Some of them have attracted interest because of their potential long-term habitability; such a possibility is currently vigorously debated in the literature. I show that post-Keplerian (pK) orbit precessions may impact the habitability of a fictitious telluric planet orbiting an oblate late-type M dwarf of spectral class M9V with $M_\star=0.08\,M_\odot$ at $a=0.02\,\mathrm{au}$, corresponding to an orbital period $P_\mathrm{b}\simeq 4\,\mathrm{d}$, inducing long-term variations of the planetary obliquity $\vare…
The detection and characterisation of Earth-like planets with Doppler signals of the order of 1 m/s currently represent one of the greatest challenge for extrasolar-planet hunters. As results for such findings are often controversial, it is desirable to provide independent confirmations of the discoveries. Testing different models for the suppression of non-Keplerian stellar signals usually plaguing radial velocity data is essential to ensuring findings are robust and reproducible. Using an alternative treatment of the stellar noise to that discussed in the discovery paper, we re-analyse the r…
The origin of the spins of giant planets is an open question in astrophysics. As planets and stars accrete from discs, if the specific angular momentum accreted corresponds to that of a Keplerian orbit at the surface of the object, it is possible for planets and stars to be spun up to near-breakup speeds. However, accretion cannot proceed onto planets and stars in the same way that accretion proceeds through the disk. For example, the magneto-rotational instability cannot operate in the region between the nearly-Keplerian disk and more slowly-rotating surface because of the sign of the angular…
Axisymmetric disks of high eccentricity, low mass bodies on near-Keplerian orbits are unstable to an out-of-plane buckling. This "inclination instability" exponentially grows the orbital inclinations, raises perihelia distances and clusters in argument of perihelion. Here we examine the instability in a massive primordial scattered disk including the orbit-averaged gravitational influence of the giant planets. We show that differential apsidal precession induced by the giant planets will suppress the inclination instability unless the primordial mass is $\gtrsim 20$ Earth masses. We also show …
By controlling instrumental errors to below 10 cm/s, the EXtreme PREcision Spectrograph (EXPRES) allows for a more insightful study of photospheric velocities that can mask weak Keplerian signals. Gaussian Processes (GP) have become a standard tool for modeling correlated noise in radial velocity datasets. While GPs are constrained and motivated by physical properties of the star, in some cases they are still flexible enough to absorb unresolved Keplerian signals. We apply GP regression to EXPRES radial velocity measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD 101501.…
Within the general framework of core-nucleated accretion theory of giant planet formation, the conglomeration of massive gaseous envelopes is facilitated by a transient period of rapid accumulation of nebular material. While the concurrent buildup of angular momentum is expected to leave newly formed planets spinning at near-breakup velocities, Jupiter and Saturn, as well as super-Jovian long-period extrasolar planets, are observed to rotate well below criticality. In this work, we demonstrate that the large luminosity of a young giant planet simultaneously leads to the generation of a strong …
In recent years, high-angular-resolution observations of the dust and gas in circumstellar discs have revealed a variety of morphologies, naturally triggering the question of whether these substructures are driven by forming planets. While it remains difficult to directly image embedded planets, a promising method to distinguish disc-shaping mechanisms is to study the gas kinematics as characterising deviations from Keplerian rotation can be used to probe underlying perturbations such as planets. Creating spiral structures, the latter can also be traced in the brightness temperature. Here we a…
Kinematic Evidence of an Embedded Protoplanet in HD 142666 Identified by Machine Learning
The University of Georgia（佐治亚大学）；University of California, San Francisco（加州大学旧金山分校）；Cardiovascular Research Institute（心血管研究所）；The University of Alabama（阿拉巴马大学）
Three new exoplanet systems from the Dispersed Matter Planet Project
The Open University（开放大学）；European Space Agency (ESA)（欧洲空间局）；University of Birmingham（伯明翰大学）；Austrian Academy of Sciences（奥地利科学院）；Universidad Diego Portales（迭戈·波特莱斯大学）；Centro de Astrofísica y Tecnologías Afines (CATA)（天体物理学及相关技术中心）；Universidad de Chile（智利大学）
We present 20 years of radial velocity (RV) measurements of the M1 dwarf Gl15A, combining 5 years of intensive RV monitoring with the HARPS-N spectrograph with 15 years of archival HIRES/Keck RV data. We carry out an MCMC-based analysis of the RV time series, inclusive of Gaussian Process (GP) approach to the description of stellar activity induced RV variations. Our analysis confirms the Keplerian nature and refines the orbital solution for the 11.44-day period super Earth, Gl15A\,b, reducing its amplitude to $1.68^{+0.17}_{-0.18}$ m s$^{-1}$ ($M \sin i = 3.03^{+0.46}_{-0.44}$ M$_\oplus$), an…
Early Planet Formation in Embedded Disks (eDisk). VII. Keplerian Disk, Disk Substructure, and Accretion Streamers in the Class 0 Protostar IRAS 16544-1604 in CB 68
基于 ALMA eDisk 项目对 CB 68 中 0 类原恒星 IRAS 16544-1604 的观测，研究揭示了其具有耀展和非轴对称结构的 ~30 au 开普勒旋转盘，并发现了连接盘面的 ~1500 au 吸积流及伴随的吸积激波与外流。
[Abridged] The study of disc kinematics has recently opened up as a promising method to detect unseen planets. However, a systematic, statistically meaningful analysis of such an approach remains missing. The aim of this work is to devise an automated, statistically robust technique to identify kinematical perturbations induced by the presence of planets in a gas disc, and to accurately infer their location. For this purpose, we produce hydro simulations of planet-disc interactions with different planet masses, 0.3, 1.0 and 3.0 $M_{Jup}$, at a radius of $R=100$ au in the disc, and perform radi…
Dynamical mass estimates down to the planet-mass regime can help to understand planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of FW Tau C, a proposed ~10 $M_{\rm Jup}$ planet-mass companion at ~330 au from the host binary FW Tau AB. We spatially and spectrally resolve the accretion disk of FW Tau C in ${}^{12}$CO (2-1). By modeling the Keplerian rotation of gas, we derive a dynamical mass of ~0.1 $M_\odot$. Therefore, FW Tau C is unlikely a planet, but rather a low-mass star with a highly inclined disk. This also suggests that FW Tau is a t…
We present the re-detection of a compact source in the face-on protoplanetary disc surrounding HD 169142, using VLT/SPHERE data in YJH bands. The source is found at a separation of 0.''319 ($\sim$37 au) from the star. Three lines of evidence argue in favour of the signal tracing a protoplanet: (i) it is found in the annular gap separating the two bright rings of the disc, as predicted by theory; (ii) it is moving at the expected Keplerian velocity for an object at $\sim$37 au in the 2015, 2017 and 2019 datasets; (iii) we also detect a spiral-shaped signal whose morphology is consistent with th…
We demonstrate the utility of CI as a tracer of photoevaporative winds that are being driven from discs by their ambient UV environment. Commonly observed CO lines only trace these winds in relatively weak UV environments and are otherwise dissociated in the wind at the intermediate to high UV fields that most young stars experience. However, CI traces unsubtle kinematic signatures of a wind in intermediate UV environments ($\sim1000$G$_0$) and can be used to place constraints on the kinematics and temperature of the wind. In CI position-velocity diagrams external photoevaporation results in v…
AB Aur, a Rosetta stone for studies of planet formation (IV): C/O estimates from CS and SO interferometric observations
Observatorio Astronómico Nacional (OAN,IGN)（国家天文台）；Centro de Astrobiología (CAB), INTA-CSIC（天体生物学中心）；Institut de Radioastronomie Millimétrique（毫米波射电天文学研究所）；Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes, CNRS（格勒诺布尔行星学与天体物理学研究所）；Max-Planck-Institut für Astronomie (MPIA)（马克斯·普朗克天文学研究所）；Ludwig-Maximilians-Universität（路德维希-马克西米利安大学）；Massachusetts Institute of Technology（麻省理工学院）
Early Planet Formation in Embedded Disks (eDisk) XVII: A Compact but Structured Keplerian Disk and Large-scale Streamers Revealed in the Class I Protostellar System IRAS 04169+2702
针对 Class I 原恒星 IRAS 04169+2702 的高分辨率观测揭示了半径约 21 天文单位的开普勒盘、毫米/厘米级尘埃颗粒，以及延伸至 1400 天文单位的吸积流丝，并发现与螺旋臂吸积相关的激波证据。
We test the hypothesis that an embedded giant planet in the IM Lupi protostellar disc can produce velocity kinks seen in CO line observations as well as the spiral arms seen in scattered light and continuum emission. We inject planets into 3D hydrodynamics simulations of IM Lupi, generating synthetic observations using Monte Carlo radiative transfer. We find that an embedded planet of 2-3 times the mass of Jupiter can reproduce non-Keplerian velocity perturbations, or `kinks', in the 12CO J=2-1 channel maps. Such a planet can also explain the spiral arms seen in 1.25mm dust continuum emission …
Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets. II. A giant planet in a close-in orbit around the RGB star HIP63242
Discs of gas and dust surrounding young stars are the birthplace of planets. However, direct detection of protoplanets forming within discs has proved elusive to date. We present the detection of a large, localized deviation from Keplerian velocity in the protoplanetary disc surrounding the young star HD163296. The observed velocity pattern is consistent with the dynamical effect of a two Jupiter-mass planet orbiting at a radius $\approx$ 260au from the star.
Exoplanets display incredible diversity, from planetary system architectures around Sun-like stars that are very different to our Solar System, to planets orbiting post-main sequence stars or stellar remnants. Recently the B-star Exoplanet Abundance STudy (BEAST) reported the discovery of at least two super-Jovian planets orbiting massive stars in the Sco Cen OB association. Whilst such massive stars do have Keplerian discs, it is hard to envisage gas giant planets being able to form in such hostile environments. We use N-body simulations of star-forming regions to show that these systems can …
