The PDS 70 system has been subject to many studies in the past year following the discovery of two accreting planets in the gap of its circumstellar disk. Nevertheless, the mass accretion rate onto the star is still not well known. Here we determined the stellar mass accretion rate and its variability based on TESS and HARPS observations. The stellar light curve shows a strong signal with a $3.03\pm0.06$ days period, which we attribute to stellar rotation. Our analysis of the HARPS spectra shows a rotational velocity of $v\sin\,i=16.0\pm0.5\,{\rm km\,s^{-1}}$, indicating that the inclination of the rotation axis is $50\pm8$ degrees. This implies that the rotation axes of the star and its circumstellar disk are parallel within the measurement error. We apply magnetospheric accretion models to fit the profiles of the H$α$ line and derive mass accretion rates onto the star in the range of $0.6-2.2\times10^{-10}\,{\rm M_{\odot}yr^{-1}}$, varying over the rotation phase. The measured accretion rates are in agreement with those estimated from NUV fluxes using accretion shock models. The derived accretion rates are higher than expected from the disk mass and planets properties for the low values of the viscous parameter $α$ suggested by recent studies, potentially pointing to an additional mass reservoir in the inner disk to feed the accretion, such as a dead zone. We find that the He I $λ$10830 line shows a blueshifted absorption feature, indicative of a wind. The mass-loss rate estimated from the line depth is consistent with an accretion-driven inner disk MHD wind.
Direct observations of young stellar objects are important to test established theories of planet formation. PDS 70 is one of the few cases where robust evidence favours the presence of two planetary mass companions inside the gap of the transition disk. Those planets are believed to be going through the last stages of accretion from the protoplanetary disk, a process likely mediated by a circumplanetary disk (CPD). We aim to develop a three dimensional radiative transfer model for the dust component of the PDS 70 system which reproduces the system's global features observed at two different w…
We present $L$'-band imaging of the PDS 70 planetary system with Keck/NIRC2 using the new infrared pyramid wavefront sensor. We detected both PDS 70 b and c in our images, as well as the front rim of the circumstellar disk. After subtracting off a model of the disk, we measured the astrometry and photometry of both planets. Placing priors based on the dynamics of the system, we estimated PDS 70 b to have a semi-major axis of $20^{+3}_{-4}$~au and PDS 70 c to have a semi-major axis of $34^{+12}_{-6}$~au (95\% credible interval). We fit the spectral energy distribution (SED) of both planets. For…
Scattered light imaging has revealed nearly a dozen circumstellar disks around young Herbig Ae/Be stars$-$enabling studies of structures in the upper disk layers as potential signs of on-going planet formation. We present the first images of the disk around the variable Herbig Ae star PDS 201 (V* V351 Ori), and an analysis of the images and spectral energy distribution through 3D Monte-Carlo radiative transfer simulations and forward modelling. The disk is detected in three datasets with LBTI/LMIRCam at the LBT, including direct observations in the $Ks$ and $L'$ filters, and an $L'$ observatio…
We present K-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained K-band spectra and 100 $μ$as precision astrometry of both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of $0.17 \pm 0.06$, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of…
We present the discovery of a spatially unresolved source of sub-millimeter continuum emission ($λ=855$ $μ$m) associated with a young planet, PDS 70 c, recently detected in H$α$ emission around the 5 Myr old T Tauri star PDS 70. We interpret the emission as originating from a dusty circumplanetary disk with a dust mass between $2\times10^{-3}$ and $4.2 \times 10^{-3}$ Earth masses. Assuming a standard gas-to-dust ratio of 100, the ratio between the total mass of the circumplanetary disk and the mass of the central planet would be between $10^{-4}-10^{-5}$. Furthermore, we report the discovery …
We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is ~70 AU. Our data show that the geometric center of the disk shifts by ~6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a resu…
The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-$μ$m size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations c…
Through detailed radiative transfer modeling, we present a disk+cavity model to simultaneously explain both the SED and Subaru H-band polarized light imaging for the pre-transitional protoplanetary disk PDS 70. Particularly, we are able to match not only the radial dependence, but also the absolute scale, of the surface brightness of the scattered light. Our disk model has a cavity 65 AU in radius, which is heavily depleted of sub-micron-sized dust grains, and a small residual inner disk which produces a weak but still optically thick NIR excess in the SED. To explain the contrast of the cavit…
PDS 70b is a recently discovered and directly imaged exoplanet within the wide ($\gtrsim$40 au) cavity around PDS 70 (Keppler et al. 2018, Müller et al. 2018). Ongoing accretion onto the central star suggests that accretion onto PDS 70b may also be ongoing. We present the first high contrast images at H$α$ (656 nm) and nearby continuum (643 nm) of PDS 70 utilizing the MagAO system. The combination of these filters allows for the accretion rate of the young planet to be inferred, as hot infalling hydrogen gas will emit strongly at H$α$ over the optical continuum. We detected a source in H$α$ at…
ALMA 873 $μ$m Polarization Observations of the PDS~70 Disk
National Sun Yat-Sen University（国立中山大学）；National Taiwan Normal University（台湾师范大学）；Graduate University for Advanced Studies (SOKENDAI)（综合研究大学院大学）；National Astronomical Observatory of Japan（日本国立天文台）；Universidad de Chile（智利大学）；Peking University（北京大学）；Academia Sinica（中央研究院）；Universidad de Santiago de Chile（圣地亚哥德智利大学）
Advances in high-resolution imaging have revealed H$α$ emission separated from the host star. It is generally believed that the emission is associated with forming planets in protoplanetary disks. However, the nature of this emission is still not fully understood. Here we report a modeling effort of H$α$ emission from the planets around the young star PDS 70. Using standard magnetospheric accretion models previously applied to accreting young stars, we find that the observed line fluxes can be reproduced using a range of parameters relevant to PDS 70b and c, with the mean mass accretion rate o…
We report a new evaluation of the accretion properties of PDS~70b obtained with VLT/MUSE. The main difference from previous studies in Haffert et al. (2019) and Aoyama & Ikoma (2019) is in the mass accretion rate. Simultaneous multiple line observations, such as H$α$ and H$β$, can better constrain the physical properties of an accreting planet. While we clearly detected H$α$ emissions from PDS~70b, no H$β$ emissions were detected. We estimate the line flux of H$β$ with a 3-$σ$ upper limit to be 2.3~$\times$~10$^{-16}$~erg~s$^{-1}$~cm$^{-2}$. The flux ratio $F_{\rm Hβ}$/$F_{\rm Hα}$ for PDS~70b…
We investigate gas accretion onto a protoplanet, by considering the thermal effect of gas in three-dimensional hydrodynamical simulations, in which the wide region from a protoplanetary gas disk to a Jovian radius planet is resolved using the nested-grid method. We estimate the mass accretion rate and growth timescale of gas giant planets. The mass accretion rate increases with protoplanet mass for M_p < M_cri, while it becomes saturated or decreases for M_p > M_cri, where M_cri = 0.036 M_Jup (a_p/1AU)^0.75, and M_Jup and a_p are the Jovian mass and the orbital radius, respectively. The growth…
We present a massive accreting gap (MAG) planet model that ensures large gaps in transitional disks are kept dust free by the scattering action of three co-planar quasi-circular planets in a 1:2:4 Mean Motion Resonance (MMR). This model uses the constraint of the observed gap size, and the dust-free nature of the gap, to determine within ~10% the possible orbits for 3 massive planets in an MMR. Calculated orbits are consistent with the observed orbits and H-alpha emission (the brightest line to observe these planets) for LkCa 15 b and PDS 70 b and PDS 70 c within observational errors. Moreover…
Recent observations suggest late accretion, which is generally nonaxisymmetric, onto protoplanetary disks. We investigated nonaxisymmetric late accretion considering the effects of magnetic fields. Our model assumes a cloudlet encounter event at a few hundred au scale, where a magnetized gas clump (cloudlet) encounters a protoplanetary disk. We studied how the cloudlet size and the magnetic field strength affect the rotational velocity profile in the disk after the cloudlet encounter. The results show that a magnetic field can either decelerate or accelerate the rotational motion of the cloudl…
Aims: We present mid-infrared observations and photometry of the circumstellar disks around PDS 66 and CRBR 2422.8-3423, obtained with VISIR/VLT in the N band and for the latter also in the Q band. Our aim is to resolve the inner regions of these protoplanetary disks, which carry potential signatures of intermediate or later stages of disk evolution and ongoing planet formation. Methods: We determined the radial brightness profiles of our target objects and the corresponding PSF reference that were observed before and after our target objects. Background standard deviations, the standard error…
A relation between the mass accretion rate onto the central young star and the mass of the surrounding protoplanetary disk has long been theoretically predicted and observationally sought. For the first time, we have accurately and homogeneously determined the photospheric parameters, mass accretion rate, and disk mass for an essentially complete sample of young stars with disks in the Lupus clouds. Our work combines the results of surveys conducted with VLT/X-Shooter and ALMA. With this dataset we are able to test a basic prediction of viscous accretion theory, the existence of a linear relat…
Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind-accretion leads to long-lived stable disks over the lifetime of the AG…
Gaps imaged in protoplanetary discs are suspected to be opened by planets. We compute the present-day mass accretion rates $\dot{M}_{\rm p}$ of seven hypothesized gap-embedded planets, plus the two confirmed planets in the PDS 70 disc. The accretion rates are based on disc gas surface densities $Σ_{\rm gas}$ from C$^{18}$O observations, and planet masses $M_{\rm p}$ from simulations fitted to observed gaps. Assuming accretion is Bondi-like, we find in eight out of nine cases that $\dot{M}_{\rm p}$ is consistent with the time-averaged value given by the current planet mass and system age, $M_{\…
The detection of a wide range of substructures such as rings, cavities and spirals has become a common outcome of high spatial resolution imaging of protoplanetary disks, both in the near-infrared scattered light and in the thermal millimetre continuum emission. The most frequent interpretation of their origin is the presence of planetary-mass companions perturbing the gas and dust distribution in the disk (perturbers), but so far the only bona-fide detection has been the two giant planets around PDS 70. Here, we collect a sample of 15 protoplanetary disks showing substructures in SPHERE scatt…
Observations indicate that stars generally lose their protoplanetary discs on a timescale of about 5 Myr. Which mechanisms are responsible for the disc dissipation is still debated. Here we investigate the movement through an ambient medium as a possible cause of disc dispersal. The ram pressure exerted by the flow can truncate the disc and the accretion of material with no azimuthal angular momentum leads to further disc contraction. We derive a theoretical model from accretion disc theory that describes the evolution of the disc radius, mass, and surface density profile as a function of the …
In this article, we proceed to study convection as a possible factor of episodic accretion in protoplanetary disks. Within the model presented in Article~I, the accretion history is analyzed at different rates and areas of matter inflow from the envelope onto the disk. It is shown that the burst-like regime occurs in a wide range of parameters. The long-term evolution of the disk is also modeled, including the decreasing-with-time matter inflow from the envelope. It is demonstrated that the disk becomes convectively unstable and maintains burst-like accretion onto the star for several million …
Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary disk; the potential importance of this `tail-end' accretion for planet formation was recently highlighted by Throop & Bally (2008). While accretion onto a point mass is successfully modeled by the classical Bondi-Hoyle-Lyttleton solutions, the more complicated c…
We investigate the formation process of self-gravitating protoplanetary disks in unmagnetized molecular clouds. The angular momentum is redistributed by the action of gravitational torques in the massive disk during its early formation. We develop a simplified one-dimensional accretion disk model that takes into account the infall of gas from the envelope onto the disk and the transfer of angular momentum in the disk with an effective viscosity. First we evaluate the gas accretion rate from the cloud core onto the disk by approximately estimating the effects of gas pressure and gravity acting …
A Quiet Host in an Active Planet-Forming Disk: Optical Spectroscopy of WISPIT 2
Indian Institute of Astrophysics（印度天体物理研究所）；European Southern Observatory（欧洲南方天文台）；Indian Institute of Technology (Indian School of Mines) Dhanbad（印度理工学院（印度矿业学院）丹巴德分校）；Physical Research Laboratory（物理研究实验室）；Tata Institute of Fundamental Research（塔塔基础研究所）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）
Young solar-type stars grow through the accretion of material from the circumstellar disk during pre-main sequence (PMS) evolution. The ultraviolet radiation generated in this process plays a key role in the chemistry and evolution of young planetary disks. In particular, the hydrogen Lyman-alpha line (Lya) etches the disk surface by driving photoevaporative flows that control disk evolution. Using the Hubble Space Telescope, we have monitored the PMS binary star AK Sco during the periastron passage and have detected a drop of the H2 flux by up to 10% lasting 5.9 hours. We show that the decrea…
Companions embedded in the cavities of transitional circumstellar disks have been observed to exhibit excess luminosity at H$α$, an indication that they are actively accreting. We report 5 years (2013-2018) of monitoring of the position and H$α$ excess luminosity of the embedded, accreting low-mass stellar companion HD 142527 B from the MagAO/VisAO instrument. We use pyklip, a python implementation of the Karhounen-Loeve Image Processing algorithm, to detect the companion. Using pyklip forward modeling, we constrain the relative astrometry to $1-2 \mathrm{mas}$ precision and achieve sufficient…
Globular clusters (GCs) are known to harbor multiple stellar populations. To explain these observations Bastian et al. suggested a scenario in which a second population is formed by the accretion of enriched material onto the low-mass stars in the initial GC population. The idea is that the low-mass, pre-main sequence stars sweep up gas expelled by the massive stars of the same generation into their protoplanetary disc as they move through the GC core. We perform simulations with 2 different smoothed particle hydrodynamics codes to investigate if a low-mass star surrounded by a protoplanetary …
Spiral formation caused by late infall onto protoplanetary disks
Institut für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心理论天体物理研究所）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）
Accreting protoplanets enable the direct characterization of planet formation. As part of a high-contrast imaging search for accreting planets with the Hubble Space Telescope (HST) Wide Field Camera 3, we present H$α$ images of AB Aurigae (AB Aur), a Herbig Ae/Be star harboring a transition disk. The data were collected in two epochs of direct-imaging observations using the F656N narrow-band filter. After subtracting the point spread function of the primary star, we identify a point-like source located at a P.A. of $182.5^{\circ}\pm1.4^{\circ}$ and a separation of $600\pm22$~mas relative to th…
Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence that protoplanetary disks are engaged in accretion, the process(es) responsible remain unclear. Here we present evidence for redshifted molecular absorption in the spectrum of a Class I source that indicates rapid inflow at the disk surface. High resolution mid-infrared spectroscopy of GV Tau N reveals a rich absorption spectrum of individual lines of C2H2, HCN, NH3, and water. From the propertie…
In the core accretion model for the formation of gas giant planets, runaway gas accretion onto a core is the primary requisite, triggered when the core mass reaches a critical value. The recently revealed wide diversity of the extrasolar giant planets suggests the necessity to further the understanding of the conditions resulting in the critical core mass that initiates runaway accretion. We study the internal structure of protoplanets under hydrostatic and thermal equilibria represented in terms of a polytropic equation of state to investigate what factors determine and affect the critical co…
While it is generally accepted that the magnetic field and its non-ideal effects play important roles during the stellar formation, simple models of pure hydrodynamics and angular momentum conservation are still widely employed in the studies of disk assemblage in the framework of the so-called "alpha-disk" model due to their simplicity. There has only been a few efforts trying to bridge the gap between a collapsing prestellar core and a developed disk. The goal of the present work is to revisit the assemblage of the protoplanetary disk (PPD), by performing 3D MHD simulations with ambipolar di…
We describe an analytic model for an evolving protoplanetary disk driven by viscosity and a disk wind. The disk is heated by stellar irradiation and energy generated by viscosity. The evolution is controlled by 3 parameters: (i) the inflow velocity towards the central star at a reference distance and temperature, (ii) the fraction of this inflow caused by the disk wind, and (iii) the mass loss rate via the wind relative to the inward flux in the disk. The model gives the disk midplane temperature and surface density as a function of time and distance from the star. It is intended to provide an…
The C/O ratio is a defining feature of both gas giant atmospheric and protoplanetary disk chemistry. In disks, the C/O ratio is regulated by the presence of snowlines of major volatiles at different distances from the central star. We explore the effect of radial drift of solids and viscous gas accretion onto the central star on the snowline locations of the main C and O carriers in a protoplanetary disk, H2O, CO2 and CO, and their consequences for the C/O ratio in gas and dust throughout the disk. We determine the snowline locations for a range of fixed initial particle sizes and disk types. …
Flattened, rotating disks of cool dust and gas extending for tens to hundreds of AU are found around almost all low mass stars shortly after their birth. These disks generally persist for several Myr, during which time some material accretes onto the star, some is lost through outflows and photoevaporation, and some condenses into centimeter- and larger-sized bodies or planetesimals. Through observations mainly at infrared through millimeter wavelengths, we can determine how common disks are at different ages, measure basic properties including mass, size, structure, and composition, and follo…
We report FUV, optical, and NIR observations of three T Tauri stars in the Orion OB1b subassociation with H$α$ equivalent widths consistent with low or absent accretion and various degrees of excess flux in the mid-infrared. We aim to search for evidence of gas in the inner disk in HST ACS/SBC spectra, and to probe the accretion flows onto the star using H$α$ and He I $λ$10830 in spectra obtained at the Magellan and SOAR telescopes. At the critical age of 5 Myr, the targets are at different stages of disk evolution. One of our targets is clearly accreting, as shown by redshifted absorption at …
The nature and rate of (viscous) angular momentum transport in protoplanetary discs (PPDs) has important consequences for the formation process of planetary systems. While accretion rates onto the central star yield constraints on such transport in the inner regions of a PPD, empirical constraints on viscous spreading in the outer regions remain challenging to obtain. Here we demonstrate a novel method to probe the angular momentum transport at the outer edge of the disc. This method applies to PPDs that have lost a significant fraction of their mass due to thermal winds driven by UV irradiati…
Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields), white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron stars and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.
Stellar masses are fundamental but often difficult to measure. Thanks to the Atacama Large Millimeter Array (ALMA) and $Gaia$, dynamical masses of pre-main sequence stars can be precisely measured using the Keplerian rotation of protoplanetary disks. We used ALMA CO(2-1) and CO(3-2) observations of CT Cha and DS Tau to determine their masses by modeling the geometry, kinematics, and physical properties of their disks with a Bayesian-based radiative transfer modeling code $pdspy$. We found that the posterior distributions of the masses from the two transitions are inconsistent at the 2-4 $σ$ le…
