scholarly journals Dust Rings in the Circumstellar Gas Disks

2004 ◽  
Vol 202 ◽  
pp. 375-377
Author(s):  
Taku Takeuchi ◽  
Pawel Artymowicz
Keyword(s):  
Drag Force ◽  
Radiation Pressure ◽  
Brown Dwarfs ◽  
Central Star ◽  
Outer Edge ◽  
Dust Grains ◽  
Stellar Radiation ◽  
Circumstellar Gas ◽  
Gas Drag ◽  
Dust Ring

In optically thin gas disks around young Vega-type stars, dust grains are exposed to the stellar radiation pressure and gas drag force. The combination of these forces pushes the grains away from the central star. Typically, 10–100 μm grains migrate outward to become concentrated at the outer edge of the gas disk. A dust ring naturally forms without the help of clearing bodies, such as planets or brown dwarfs.

scholarly journals Dust Rings as a Footprint of Planet Formation in a Protoplanetary Disk

2021 ◽  
Vol 921 (2) ◽  
pp. 169
Author(s):  
Kazuhiro D. Kanagawa ◽  
Takayuki Muto ◽  
Hidekazu Tanaka
Keyword(s):  
Ring Structure ◽  
Protoplanetary Disk ◽  
Outer Edge ◽  
Planetary Orbit ◽  
Dust Grains ◽  
Asymmetric Structures ◽  
Low Viscosity ◽  
Initial Location ◽  
Gas Ratio ◽  
Dust Ring

Abstract Relatively large dust grains (referred to as pebbles) accumulate at the outer edge of the gap induced by a planet in a protoplanetary disk, and a ring structure with a high dust-to-gas ratio can be formed. Such a ring has been thought to be located immediately outside the planetary orbit. We examined the evolution of the dust ring formed by a migrating planet, by performing two-fluid (gas and dust) hydrodynamic simulations. We found that the initial dust ring does not follow the migrating planet and remains at the initial location of the planet in cases with a low viscosity of α ∼ 10−4. The initial ring is gradually deformed by viscous diffusion, and a new ring is formed in the vicinity of the migrating planet, which develops from the trapping of the dust grains leaking from the initial ring. During this phase, two rings coexist outside the planetary orbit. This phase can continue over ∼1 Myr for a planet migrating from 100 au. After the initial ring disappears, only the later ring remains. This change in the ring morphology can provide clues as to when and where the planet was formed, and is the footprint of the planet. We also carried out simulations with a planet growing in mass. These simulations show more complex asymmetric structures in the dust rings. The observed asymmetric structures in the protoplanetary disks may be related to a migrating and growing planet.

scholarly journals Formation of massive stars under protostellar radiation feedback: very metal-poor stars

2020 ◽  
Vol 497 (1) ◽  
pp. 829-845 ◽  
Author(s):  
Hajime Fukushima ◽  
Takashi Hosokawa ◽  
Gen Chiaki ◽  
Kazuyuki Omukai ◽  
Naoki Yoshida ◽  
...  
Keyword(s):  
Radiation Pressure ◽  
Central Star ◽  
Feedback Effect ◽  
Radiative Feedback ◽  
Star Forming ◽  
Circumstellar Gas ◽  
Low Metallicity ◽  
H Ii Region ◽  
Low Mass ◽  
Gas Accretion

ABSTRACT We study the formation of very metal-poor stars under protostellar radiative feedback effect. We use cosmological simulations to identify low-mass dark matter haloes and star-forming gas clouds within them. We then follow protostar formation and the subsequent long-term mass accretion phase of over one million years using two-dimensional radiation-hydrodynamics simulations. We show that the critical physical process that sets the final mass is the formation and expansion of a bipolar H ii region. The process is similar to the formation of massive primordial stars, but radiation pressure exerted on dust grains also contributes to halting the accretion flow in the low-metallicity case. We find that the net feedback effect in the case with metallicity Z = 10−2 Z⊙ is stronger than in the case with Z ∼ 1 Z⊙. With decreasing metallicity, the radiation-pressure effect becomes weaker, but photoionization heating of the circumstellar gas is more efficient owing to the reduced dust attenuation. In the case with Z = 10−2 Z⊙, the central star grows as massive as 200 solar masses, similarly to the case of primordial star formation. We conclude that metal-poor stars with a few hundred solar masses can be formed by gas accretion despite the strong radiative feedback.

Cosmic Pathways to Life: From Interstellar Molecules to the First Traces of Life

2018 ◽  
Vol 14 (S345) ◽  
pp. 1-14
Author(s):  
Manuel Güdel ◽  
Bruce G. Elmegreen ◽  
L. Viktor Tóth
Keyword(s):  
Central Star ◽  
Life Forms ◽  
Disk Accretion ◽  
Nearby Star ◽  
Long Period ◽  
Cosmic Evolution ◽  
Stellar Radiation ◽  
Solid Bodies ◽  
Gaseous Envelope ◽  
Central Stars

AbstractThe present-day Earth with its innumerable life forms is a product of cosmic evolution starting with the formation of our galaxy and the dense gas clouds within it, and proceeding through the contraction of one of those clouds about 4.6 Gyr ago, first into filaments and then one or more protostellar disks, planets, and central stars, one of which was our Sun. Radioactive debris from a massive nearby star was included. The planets themselves formed through coagulation, accretion, and fragmentation of solid bodies. Habitability depends on a delicate balance between disk accretion by gravity and dispersal by the central star, which determine the size of the planet and its gaseous envelope, combined with a long period of stellar radiation, which has to disperse this envelope but leave a hospitable secondary atmosphere. The final step toward life involves even more complexity as self-replicating bio-molecules form with ever increasing stability.

scholarly journals Testing viscous disc theory using the balance between stellar accretion and external photoevaporation of protoplanetary discs

2020 ◽  
Vol 497 (1) ◽  
pp. L40-L45
Author(s):  
Andrew J Winter ◽  
Megan Ansdell ◽  
Thomas J Haworth ◽  
J M Diederik Kruijssen
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Central Star ◽  
Outer Edge ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Accretion Rates ◽  
Novel Method ◽  
Viscous Models ◽  
Protoplanetary Discs

ABSTRACT The nature and rate of (viscous) angular momentum transport in protoplanetary discs (PPDs) have important consequences for the formation process of planetary systems. While accretion rates on to 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 irradiation from a neighbouring OB star. We demonstrate that this external photoevaporation can explain the observed depletion of discs in the 3–5 Myr old σ Orionis region, and use our model to make predictions motivating future empirical investigations of disc winds. For populations of intermediate-age PPDs, in viscous models we show that the mass flux outwards due to angular momentum redistribution is balanced by the mass-loss in the photoevaporative wind. A comparison between wind mass-loss and stellar accretion rates therefore offers an independent constraint on viscous models in the outer regions of PPDs.

scholarly journals Planetesimal formation in turbulent circumstellar disks

2010 ◽  
Vol 6 (S276) ◽  
pp. 434-435
Author(s):  
David Kirsh ◽  
Ralph Pudritz
Keyword(s):  
Solar System ◽  
Gravitational Collapse ◽  
Planet Formation ◽  
Circumstellar Disks ◽  
Circumstellar Gas ◽  
Embedded Particles ◽  
Gas Drag

AbstractPlanetesimal formation occurs early in the evolution of a solar system, embedded in the circumstellar gas disk, and it is the crucial first step in planet formation. Their growth is difficult beyond boulder size, and likely proceeds via the accumulation of many rocks in turbulence followed by gravitational collapse - a process we are only beginning to understand. We have performed global simulations of the gas disk with embedded particles in the FLASH code. Particles and gas feel drag based on differential velocities and densities. Grains and boulders of various sizes have been investigated, from micron to km, with the goal of understanding where in the disk large planetesimals will tend to form, what sizes will result, and what size ranges of grains will be preferentially incorporated. We have so far simulated particles vertical settling and radial drift under the influence of gas drag, and their accumulations in turbulent clumps.

scholarly journals The search for disks or planetary objects around directly imaged companions: a candidate around DH Tauri B

2020 ◽  
Vol 641 ◽  
pp. A131
Author(s):  
C. Lazzoni ◽  
A. Zurlo ◽  
S. Desidera ◽  
D. Mesa ◽  
C. Fontanive ◽  
...  
Keyword(s):  
Ad Hoc ◽  
Direct Methods ◽  
Brown Dwarfs ◽  
Central Star ◽  
Formation Mechanisms ◽  
Sources Of Information ◽  
Substellar Objects ◽  
Extended Sources ◽  
Substellar Companions ◽  
Differential Imaging

Context. In recent decades, thousands of substellar companions have been discovered with both indirect and direct methods of detection. While the majority of the sample is populated by objects discovered using radial velocity and transit techniques, an increasing number have been directly imaged. These planets and brown dwarfs are extraordinary sources of information that help in rounding out our understanding of planetary systems. Aims. In this paper, we focus our attention on substellar companions detected with the latter technique, with the primary goal of investigating their close surroundings and looking for additional companions and satellites, as well as disks and rings. Any such discovery would shed light on many unresolved questions, particularly with regard to their possible formation mechanisms. Methods. To reveal bound features of directly imaged companions, whether for point-like or extended sources, we need to suppress the contribution from the source itself. Therefore, we developed a method based on the negative fake companion technique that first estimates the position in the field of view (FoV) and the flux of the imaged companion with high precision, then subtracts a rescaled model point spread function (PSF) from the imaged companion, using either an image of the central star or another PSF in the FoV. Next it performs techniques, such as angular differential imaging, to further remove quasi-static patterns of the star (i.e., speckle contaminants) that affect the residuals of close-in companions. Results. After testing our tools on simulated companions and disks and on systems that were chosen ad hoc, we applied the method to the sample of substellar objects observed with SPHERE during the SHINE GTO survey. Among the 27 planets and brown dwarfs we analyzed, most objects did not show remarkable features, which was as expected, with the possible exception of a point source close to DH Tau B. This candidate companion was detected in four different SPHERE observations, with an estimated mass of ~1MJup, and a mass ratio with respect to the brown dwarf of 1∕10. This binary system, if confirmed, would be the first of its kind, opening up interesting questions for the formation mechanism, evolution, and frequency of such pairs. In order to address the latter, the residuals and contrasts reached for 25 companions in the sample of substellar objects observed with SPHERE were derived. If the DH Tau Bb companion is real, the binary fraction obtained is ~7%, which is in good agreement with the results obtained for field brown dwarfs. Conclusions. While there may currently be many limitations affecting the exploration of bound features to directly imaged exoplanets and brown dwarfs, next-generation instruments from the ground and space (i.e., JWST, ELT, and LUVOIR) will be able to image fainter objects and, thus, drive the application of this technique in upcoming searches for exo-moons and circumplanetary disks.

scholarly journals On the Solar Dust Ring(s)

1985 ◽  
Vol 85 ◽  
pp. 59-62
Author(s):  
T. Mukai
Keyword(s):  
Physical Properties ◽  
Preliminary Analysis ◽  
Dust Grains ◽  
Ring Particle ◽  
Dust Ring ◽  
Infrared Data

AbstractBased on a mechanism to form the solar dust ring, it is proved that the observed peak in infrared F-corona cannot be explained by silicate type grain alone. Preliminary analysis on the recent infrared data of F-corona by Maihara et al.(1984) has suggested that the ring particle has different physical properties compared with the dust grains, which produce the background F-corona.

scholarly journals A Mechanism for Variability of Cometary Nebulae

1987 ◽  
Vol 115 ◽  
pp. 398-400
Author(s):  
G. M. Rudnitskij
Keyword(s):  
Tilt Angle ◽  
Stellar Wind ◽  
Large Scale ◽  
Central Star ◽  
Similar Model ◽  
Conical Cavity ◽  
Bipolar Outflow ◽  
Circumstellar Gas ◽  
Small Disc ◽  
Optical Structure

A model is suggested to explain the variability of the optical structure and the integral brightness of cometary nebulae (CN) occurring at timescales of several years and tens of years (Gyulbudaghian et al. 1977, Cohen et al. 1977, 1981, Magakyan 1981, Gyulbudaghian 1982). A CN is assumed to be a reflection nebula; it is a wall of a conical cavity in the circumstellar gas-and-dust torus illuminated by the central star (Cohen 1974). I explain the CN's variability by the presence of small tilted circumstellar disc of gas-and-dust, located inside the internal channel of the large circumstellar torus (see Figure 1). A similar model was put forward by Ward-Thompson et al. (1985) to account for a tilt angle of about 30° between the direction of short optical jets (stellar wind, channelled by the small disc) and the large-scale bipolar outflow (focused by the large torus) in the CN NGC 6729 associated with the star R CrA. Tilt angles of about 30° between optical and radio structures exist in CN NGC 2261 (Cantó et al. 1981) and GM 1-29 (Levreault 1984).

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