scholarly journals OUTWARD MOTION OF POROUS DUST AGGREGATES BY STELLAR RADIATION PRESSURE IN PROTOPLANETARY DISKS

2015 ◽  
Vol 799 (2) ◽  
pp. 119 ◽  
Author(s):  
Ryo Tazaki ◽  
Hideko Nomura
Keyword(s):  
Radiation Pressure ◽  
Protoplanetary Disks ◽  
Stellar Radiation ◽  
Outward Motion

scholarly journals Detection of nitrogen gas in the β Pictoris circumstellar disc

2019 ◽  
Vol 621 ◽  
pp. A121 ◽  
Author(s):  
P. A. Wilson ◽  
R. Kerr ◽  
A. Lecavelier des Etangs ◽  
V. Bourrier ◽  
A. Vidal-Madjar ◽  
...  
Keyword(s):  
Radiation Pressure ◽  
Column Density ◽  
Gas Composition ◽  
Nitrogen Gas ◽  
Current State ◽  
Stellar Radiation ◽  
Solar Abundances ◽  
Nitrogen Abundance ◽  
First Time ◽  
Good Agreement

Context. The gas composition of the debris disc surrounding β Pictoris is rich in carbon and oxygen relative to solar abundances. Two possible scenarios have been proposed to explain this enrichment. The preferential production scenario suggests that the produced gas may be naturally rich in carbon and oxygen, while the alternative preferential depletion scenario states that the enrichment has evolved to the current state from a gas with solar-like abundances. In the latter case, the radiation pressure from the star expels the gas outwards, leaving behind species that are less sensitive to stellar radiation such as C and O. Nitrogen is not sensitive to radiation pressure either as a result of its low oscillator strength, which would make it also overabundant under the preferential depletion scenario. The abundance of nitrogen in the disc may therefore provide clues to why C and O are overabundant. Aims. We aim to measure the nitrogen column density in the direction of β Pictoris (including contributions by the interstellar medium and circumstellar disc), and use this information to distinguish these different scenarios to explain the C and O overabundance. Methods. Using far-UV spectroscopic data collected by the Hubble Space Telescope’s Cosmic Origins Spectrograph (COS) instrument, we analysed the spectrum and characterised the NI triplet by modelling the absorption lines. Results. We measure the nitrogen column density in the direction of β Pictoris for the first time, and find it to be log(NNI/1 cm2) = 14.9 ± 0.7. The nitrogen gas is found to be consistent with solar abundances and Halley dust. We also measure an upper limit for the column density of MnII in the disc at log(NMnII/1 cm2)CS = 12.7+0.1 and calculate the column density of SIII** in the disc to be log(NSIII★★/1 cm2)CSX = 14.2 ± 0.1. Both results are in good agreement with previous studies. Conclusions. The solar nitrogen abundance supports the preferential production hypothesis, in which the composition of gas in β Pictoris is the result of photodesorption from icy grains that are rich in C and O or collisional vaporisation of C- and O-rich dust in the disc. It does not support the hypothesis that C and O are overabundant because C and O are insensitive to radiation pressure, which would cause them to accumulate in the disc.

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 Characterization of mid-infrared polarization due to scattering in protoplanetary disks

2020 ◽  
Vol 634 ◽  
pp. A129 ◽  
Author(s):  
S. Heese ◽  
S. Wolf ◽  
R. Brauer
Keyword(s):  
Magnetic Fields ◽  
Linear Polarization ◽  
Radial Distance ◽  
Protoplanetary Disks ◽  
Field Studies ◽  
Central Star ◽  
Polarization Degree ◽  
Mid Infrared ◽  
Stellar Radiation ◽  
Linearly Polarized

Context. It is generally assumed that magnetic fields play an important role in the formation and evolution of protoplanetary disks. One way of observationally constraining magnetic fields is to measure polarized emission and absorption produced by magnetically aligned elongated dust grains. The fact that radiation also becomes linearly polarized by light scattering at optical to millimeter wavelengths complicates magnetic field studies. Aims. We characterize the linear polarization of mid-infrared radiation due to scattering of the stellar radiation and dust thermal re-emission radiation (self-scattering). Methods. We computed the radial polarization profiles at wavelengths across the N and Q bands for a broad range of circumstellar disk configurations. These simulations served as a basis to analyze the correlations between selected disk parameters and the resulting linear polarization. Results. We find that the thermal re-emission radiation is stronger than the scattered stellar radiation for disks with inner holes smaller than ~10 au within the considered parameter range. The mid-infrared polarization due to scattering shows several clear trends: for scattered stellar radiation only, the linear polarization degree decreases slightly with increasing radial distance, while it increases with radial distance for thermal re-emission radiation only and for a combination of scattered stellar radiation and thermal re-emission radiation. The linear polarization degree decreases with increasing disk flaring and luminosity of the central star. An increasing inner radius shifts the increase of the linear polarization degree further outside, while a larger scale height increases the linear polarization degree for small radial distances and decreases this degree further outside. For longer wavelengths, i.e., toward the Q band in our study, the linear polarization degree converges more slowly. Conclusions. We found several clear trends for polarization due to scattering. These trends are the basis to distinguish polarization due to scattering from polarization due to dichroic emission and absorption.

scholarly journals Hubble PanCET: an extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470b

2018 ◽  
Vol 620 ◽  
pp. A147 ◽  
Author(s):  
V. Bourrier ◽  
A. Lecavelier des Etangs ◽  
D. Ehrenreich ◽  
J. Sanz-Forcada ◽  
R. Allart ◽  
...  
Keyword(s):  
Radiation Pressure ◽  
Neutral Hydrogen ◽  
Upper Atmosphere ◽  
Hydrogen Atoms ◽  
Stellar Radiation ◽  
Blue Wing ◽  
Current Mass ◽  
Low Mass ◽  
M Dwarf ◽  
Host Stars

GJ 3470b is a warm Neptune transiting an M-dwarf star at the edge of the evaporation desert. It offers the possibility of investigating how low-mass, close-in exoplanets evolve under the irradiation from their host stars. We observed three transits of GJ 3470b in the Lyman-α line with the Hubble Space Telescope (HST) as part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program. Absorption signatures are detected with similar properties in all three independent epochs, with absorption depths of 35 ± 7% in the blue wing of the line, and 23 ± 5% in the red wing. The repeatability of these signatures, their phasing with the planet transit, and the radial velocity of the absorbing gas allow us to conclude that there is an extended upper atmosphere of neutral hydrogen around GJ 3470b. We determine from our observations the stellar radiation pressure and XUV irradiation from GJ 3470 and use them to perform numerical simulations of the upper atmosphere of GJ 3470b with the EVaporating Exoplanets (EVE) code. The unusual redshifted signature can be explained by the damping wings of dense layers of neutral hydrogen that extend beyond the Roche lobe and are elongated in the direction of the planet motion. This structure could correspond to a shocked layer of planetary material formed by the collision of the expanding thermosphere with the wind of the star. The blueshifted signature is well explained by neutral hydrogen atoms escaping at rates of about 1010 g s−1 that are blown away from the star by its strong radiation pressure and are quickly photoionized, resulting in a smaller exosphere than that of the warm Neptune GJ 436b. The stronger escape from GJ 3470b, however, may have led to the loss of about 4–35% of its current mass over its ~2 Gyr lifetime.

scholarly journals The birth and death of organic molecules in protoplanetary disks

2008 ◽  
Vol 4 (S251) ◽  
pp. 89-98 ◽  
Author(s):  
Thomas Henning ◽  
Dmitry Semenov
Keyword(s):  
Organic Molecules ◽  
Protoplanetary Disks ◽  
High Energy ◽  
Physical Structure ◽  
Low Mass Stars ◽  
Stellar Radiation ◽  
Theoretical Predictions ◽  
Low Mass ◽  
Dust Grain ◽  
Observational Knowledge

AbstractThe most intriguing question related to the chemical evolution of protoplanetary disks is the genesis of pre-biotic organic molecules in the planet-forming zone. In this contribution we briefly review current observational knowledge of physical structure and chemical composition of disks and discuss whether organic molecules can be present in large amounts at the verge of planet formation. We predict that some molecules, including CO-bearing species such as H2CO, can be underabundant in inner regions of accreting protoplanetary disks around low-mass stars due to the high-energy stellar radiation and chemical processing on dust grain surfaces. These theoretical predictions are further compared with high-resolution observational data and the limitations of current models are discussed.

scholarly journals Planet signatures and Size Segregation in Debris Discs

2013 ◽  
Vol 8 (S299) ◽  
pp. 358-359
Author(s):  
Philippe Thébault
Keyword(s):  
Particle Size ◽  
Steady State ◽  
Radiation Pressure ◽  
Surface Density ◽  
Size Segregation ◽  
Complex Interplay ◽  
Gravitational Effects ◽  
Stellar Radiation ◽  
Free Parameters ◽  
Narrow Ring

The response of a debris disc to a planetary perturber is the result of the complex interplay between gravitational effects, grain collisions and stellar radiation pressure (Stark & Kuchner (2009). We investigate to what extent this response can depart from the pure gravitational case when including grain collisional production and radiation pressure. We use the DyCoSS code (Thébault (2012), designed to study the coupled effect of collisions and dynamics for systems at steady state with one perturbing body. We focus on two outcomes: the 2D surface density profile of the disc+planet system, and the way the Particle Size Distribution (PSD) is spatially segregated within the disc. We consider two set-ups: 1) a narrow ring with an exterior “shepherding” planet, and 2) an extended disc in which a planet is embedded. For each case, the planet mass and orbit are explored as free parameters, and an unperturbed “no-planet” case is also considered. Another parameter is the disc's collisional activity, as parameterized by its optical depth τ.

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