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Register a new userMeridional flows in the disk around a young star
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Protoplanetary disks are known to posses a stunning variety of substructure in the distribution of their mm~sized grains, predominantly seen as rings and gaps (Andrews et al. 2018), which are frequently interpreted as due to the shepherding of large grains by either hidden, still-forming planets within the disk (Zhang et al. 2018) or (magneto-)hydrodynamic instabilities (Flock et al. 2015). The velocity structure of the gas offers a unique probe of both the underlying mechanisms driving the evolution of the disk, the presence of embedded planets and characterising the transportation of material within the disk, such as following planet-building material from volatile-rich regions to the chemically-inert midplane, or detailing the required removal of angular momentum. Here we present the radial profiles of the three velocity components of gas in upper disk layers in the disk of HD 163296 as traced by 12CO molecular emission. These velocities reveal significant flows from the disk surface towards the midplane of disk at the radial locations of gaps argued to be opened by embedded planets (Isella et al. 2016, 2018, Teague et al. 2018, Pinte et al. 2018), bearing striking resemblance to meridional flows, long predicted to occur during the early stages of planet formation (Szulagyi et al. 2014, Morbidelli et al. 2014, Fung & Chiang 2016, Dong et al. 2019). In addition, a persistent radial outflow is seen at the outer edge of the disk, potentially the base of a wind associated with previously detected extended emission (Klaassen et al. 2013).
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Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such fallback is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsars X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of order 10 Earth masses, and its lifetime (at least a million years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.
We observed the embedded, young 8--10 Msun star AFGL 490 at subarcsecond resolution with the Plateau de Bure Interferometer in the C17O (2--1) transition and found convincing evidence that AFGL 490 is surrounded by a rotating disk. Using two-dimensional modeling of the physical and chemical disk structure coupled to line radiative transfer, we constrain its basic parameters. We obtain a relatively high disk mass of 1 Msun and a radius of ~ 1500 AU. A plausible explanation for the apparent asymmetry of the disk morphology is given.
We present the confirmation of the eccentric warm giant planet TOI-201 b, first identified as a candidate in textit{TESS} photometry (Sectors 1-8, 10-13, and 27-28) and confirmed using ground-based photometry from NGTS and radial velocities from FEROS, HARPS, CORALIE, and textsc{Minerva}-Australis. TOI-201 b orbits a young ($mathrm{0.87^{+0.46}_{-0.49} , Gyr}$) and bright(V=9.07 mag) F-type star with a $mathrm{52.9781 , d}$ period. The planet has a mass of $mathrm{0.42^{+0.05}_{-0.03}, M_J}$, a radius of $mathrm{1.008^{+0.012}_{-0.015}, R_J}$, and an orbital eccentricity of $0.28^{+0.06}_{-0.09}$; it appears to still be undergoing fairly rapid cooling, as expected given the youth of the host star. The star also shows long-term variability in both the radial velocities and several activity indicators, which we attribute to stellar activity. The discovery and characterization of warm giant planets such as TOI-201 b is important for constraining formation and evolution theories for giant planets.
Observations of protoplanetary disks around very low-mass stars and brown dwarfs remain challenging and little is known about their properties. The disk around CIDA1 ($sim$0.1-0.2$M_odot$) is one of the very few known disks that host a large cavity (20au radius in size) around a very low-mass star. We present new ALMA observations at Band7 (0.9mm) and Band4 (2.1mm) of CIDA1 with a resolution of $sim 0.05times 0.034$. These new ALMA observations reveal a very bright and unresolved inner disk, a shallow spectral index of the dust emission ($sim2$), and a complex morphology of a ring located at 20au. We also present X-Shooter (VLT) observations that confirm the high accretion rate of CIDA1 of $dot{M}_{rm acc}$=1.4 $times~10^{-8}M_odot$/yr. This high value of $dot{M}_{rm acc}$, the observed inner disk, and the large cavity of 20au exclude models of photo-evaporation to explain the observed cavity. When comparing these observations with models that combine planet-disk interaction, dust evolution, and radiative transfer, we exclude planets more massive than 0.5$M_{rm{Jup}}$ as the potential origin of the large cavity because with these it is difficult to maintain a long-lived and bright inner disk. Even in this planet mass regime, an additional physical process may be needed to stop the particles from migrating inwards and to maintain a bright inner disk on timescales of millions of years. Such mechanisms include a trap formed by a very close-in extra planet or the inner edge of a dead zone. The low spectral index of the disk around CIDA1 is difficult to explain and challenges our current dust evolution models, in particular processes like fragmentation, growth, and diffusion of particles inside pressure bumps.
We have obtained Hubble Space Telescope (HST) coronagraphic observations of the circumstellar disk around M star TWA 7 using the STIS instrument in visible light. Together with archival observations including HST/NICMOS using the F160W filter and Very Large Telescope/SPHERE at $H$-band in polarized light, we investigate the system in scattered light. By studying this nearly face-on system using geometric disk models and Henyey--Greenstein phase functions, we report new discovery of a tertiary ring and a clump. We identify a layered architecture: three rings, a spiral, and an ${approx}150$ au$^2$ elliptical clump. The most extended ring peaks at $28$ au, and the other components are on its outskirts. Our point source detection limit calculations demonstrate the necessity of disk modeling in imaging fainter planets. Morphologically, we witness a clockwise spiral motion, and the motion pattern is consistent with both solid body and local Keplerian; we also observe underdensity regions for the secondary ring that might result from mean motion resonance or moving shadows: both call for re-observations to determine their nature. Comparing multi-instrument observations, we obtain blue STIS-NICMOS color, STIS-SPHERE radial distribution peak difference for the tertiary ring, and high SPHERE-NICMOS polarization fraction; these aspects indicate that TWA 7 could retain small dust particles. By viewing the debris disk around M star TWA 7 at a nearly face-on vantage point, our study allows for the understanding of such disks in scattered light in both system architecture and dust property.
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