scholarly journals Spiral structure generated by major planets in protoplanetary disks

2020 ◽  
Vol 641 ◽  
pp. A169
Author(s):  
R. H. Sanders
Keyword(s):  
Pitch Angle ◽  
Kinematic Viscosity ◽  
Spiral Structure ◽  
Orbital Motion ◽  
Protoplanetary Disks ◽  
Simple Algorithm ◽  
Solar Mass ◽  
Families Of Periodic Orbits ◽  
Physical Effects ◽  
Orbital Periods

In this paper I describe numerical calculations of the motion of particles in a disk about a solar-mass object perturbed by a planet on a circular orbit with mass greater than 0.001 of the stellar mass. A simple algorithm for simulating bulk viscosity is added to the ensemble of particles, and the response of the disk is followed for several planet orbital periods. A two-arm spiral structure forms near the inner resonance (2–1) and extends to the planetary orbit radius (corotation). In the same way for gaseous disks on a galactic scale perturbed by a weak rotating bar-like distortion, this is shown to be related to the appearance of two perpendicular families of periodic orbits near the resonance combined with dissipation which inhibits the crossing of streamlines. Spiral density enhancements result from the crowding of streamlines due to the gradual shift between families. The results, such as the dependence of pitch-angle on radius and the asymmetry of the spiral features, resemble those of sophisticated calculations that include more physical effects. The morphology of structure generated in this way clearly resembles that observed in objects with well-defined two-arm spirals, such as SAO 206462. This illustrates that the process of spiral formation via interaction with planets in such disks can be due to orbital motion in a perturbed Keplerian field combined with kinematic viscosity.

scholarly journals VLT/SPHERE astrometric confirmation and orbital analysis of the brown dwarf companion HR 2562 B

2018 ◽  
Vol 615 ◽  
pp. A177 ◽  
Author(s):  
A.-L. Maire ◽  
L. Rodet ◽  
C. Lazzoni ◽  
A. Boccaletti ◽  
W. Brandner ◽  
...  
Keyword(s):  
Orbital Motion ◽  
Orbital Plane ◽  
Real Data ◽  
Far Infrared ◽  
Brown Dwarf ◽  
Orbital Parameters ◽  
System A ◽  
Low Mass ◽  
Debris Disk ◽  
Orbital Periods

Context. A low-mass brown dwarf has recently been imaged around HR 2562 (HD 50571), a star hosting a debris disk resolved in the far infrared. Interestingly, the companion location is compatible with an orbit coplanar with the disk and interior to the debris belt. This feature makes the system a valuable laboratory to analyze the formation of substellar companions in a circumstellar disk and potential disk-companion dynamical interactions. Aims. We aim to further characterize the orbital motion of HR 2562 B and its interactions with the host star debris disk. Methods. We performed a monitoring of the system over ~10 months in 2016 and 2017 with the VLT/SPHERE exoplanet imager. Results. We confirm that the companion is comoving with the star and detect for the first time an orbital motion at high significance, with a current orbital motion projected in the plane of the sky of 25 mas (~0.85 au) per year. No orbital curvature is seen in the measurements. An orbital fit of the SPHERE and literature astrometry of the companion without priors on the orbital plane clearly indicates that its orbit is (quasi-)coplanar with the disk. To further constrain the other orbital parameters, we used empirical laws for a companion chaotic zone validated by N-body simulations to test the orbital solutions that are compatible with the estimated disk cavity size. Non-zero eccentricities (>0.15) are allowed for orbital periods shorter than 100 yr, while only moderate eccentricities up to ~0.3 for orbital periods longer than 200 yr are compatible with the disk observations. A comparison of synthetic Herschel images to the real data does not allow us to constrain the upper eccentricity of the companion.

scholarly journals Spiral structure of the Galaxy Derived from the Hat Creek survey of neutral hydrogen

1970 ◽  
Vol 38 ◽  
pp. 126-139 ◽  
Author(s):  
H. Weaver
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Neutral Hydrogen ◽  
The Sun ◽  
General Picture ◽  
Contour Maps ◽  
The Galaxy ◽  
External Galaxies ◽  
Perseus Arm ◽  
Spiral Arm

The extensive Hat Creek survey of neutral hydrogen combined with southern observations provides the basis for a new discussion of the spiral structure of the galaxy. The purpose of this investigation is to provide a general picture of the galaxy. It is found that the pitch of the spiral arms is approximately 12°.5 and that there are many spurs and interarm features as we observe in external galaxies.The sun is not located in a major spiral arm, but rather in a spur or offshoot originating near or at the Sagittarius arm, which is a major structure in the galaxy. The young stars in the general vicinity of the sun delineate this spur, not a major arm structure. The stars and the gas are in agreement in indicating a large pitch angle (20°–25°) for this local structure, which differs from the smaller pitch angle for the arms which form the system as a whole.In the presentation a computer-produced movie of the galaxy based on Hat Creek hydrogen contour maps similar to those in Figure 1 was shown. It was used to illustrate generally the complexity of the gas structure and, in particular, to show (i) observational aspects of the spur in which the sun is located and (ii) the point of origin of the so-called Perseus arm.

scholarly journals The White Dwarf Mass and Orbital Period Distributions in Zero-Age Cataclysmic Variables

1990 ◽  
Vol 122 ◽  
pp. 392-393
Author(s):  
M. Politano ◽  
R.F. Webbink
Keyword(s):  
Mass Distribution ◽  
White Dwarf ◽  
White Dwarfs ◽  
Stellar Population ◽  
Cataclysmic Variables ◽  
Cataclysmic Variable ◽  
Solar Mass ◽  
Orbital Periods ◽  
Rapid Mass ◽  
Made In

A zero-age cataclysmic variable (ZACV) we define as a binary system at the onset of interaction as a cataclysmic variable. We present here the results of calculations of the distributions of white dwarf masses and of orbital periods in ZACVs, due to binaries present in a stellar population which has undergone continuous, constant star formation for 1010 years. These results differ from previous work (Politano and Webbink 1988) in that an improved criterion for stability against rapid mass transfer by the secondary to the white dwarf has been used. A brief outline of the method and key assumptions made in this calculation is given in Politano and Webbink (1988).The white dwarf mass distribution of ZACVs (shown in Figure 1) contains two components: systems with helium white dwarfs and systems with C-0 white dwarfs. Systems with helium white dwarfs comprise slightly greater than 50% of all ZACVs. The helium white dwarfs have masses which range from 0.27 to 0.46 solar mass. The C-0 white dwarfs have masses which range from 0.54 solar mass up to the Chandrasekhar mass. (Note: systems with O-Ne-Mg white dwarfs are not distinguished from systems with C-0 white dwarfs in this calculation. Presumably, these O-Ne-Mg systems comprise the upper end of the white dwarf mass distribution.)

The role of stellar cosmic rays in protoplanetary disk evolution

2020 ◽  
Author(s):  
Donna Rodgers-Lee ◽  
Andrew Taylor ◽  
Turlough Downes ◽  
Tom Ray
Keyword(s):  
Cosmic Rays ◽  
Organic Molecules ◽  
Protoplanetary Disks ◽  
Protoplanetary Disk ◽  
X Rays ◽  
Solar Mass ◽  
Density Profiles ◽  
Disk Mass ◽  
Solar Type

<p>The role of magnetic fields in the evolution and dispersal of protoplanetary disks remains unclear to date partially due to the uncertainty regarding the sources of ionisation present in protoplanetary disks. Magnetic fields can only influence protoplanetary disk dynamics if the disks are sufficiently ionised. Ionisation due to X-rays, FUV photons and radioactivity is well-studied and generally only leads to high levels of ionisation close to the young star and in the surface layers of protoplanetary disks due to high disk column densities. Here I will instead focus on the importance of stellar cosmic rays which may provide a source of ionisation for the outer regions, and closer to the midplane, of protoplanetary disks.</p> <p>Young solar-type stars are very magnetically active and drive stronger stellar winds in comparison to the present day Sun. The increased magnetic activity of young solar-type stars suggests that they are efficient ~GeV particle accelerators producing so-called stellar cosmic rays. Thus, protoplanetary disks are likely to be bombarded by stellar cosmic rays, influencing their chemical and dynamic evolution. These incident particles are believed to trigger the formation of complex organic molecules. Thus, they are essential to advance our understanding of how organic molecules, the building blocks of life in the Universe, form.</p> <p>Recent ALMA observations have provided a number of tantalising clues as to the possible importance of stellar cosmic rays in protoplanetary disks. On the one hand, chemical modelling of observations of TW Hya’s protoplanetary disk suggest that the overall ionisation rate is remarkably low. While on the other hand, ALMA observations have been used to infer the presence of significant turbulent motion in DM Tau’s protoplanetary disk. This turbulent motion is likely driven by the magneto-rotational instability which would require a much higher level of ionisation than was inferred in TW Hya’s disk for instance. I will discuss the potential influence of stellar cosmic rays in these disks. </p> <p>More generally, I will present recent results which investigated the propagation, and ionising effect, of stellar cosmic rays in protoplanetary disks around young solar-mass stars. Unlike X-rays and FUV photons, stellar cosmic rays may effectively avoid being attenuated by the high column densities in the inner regions of protoplanetary disks due to their diffusive transport. To construct our disk density profiles, we use observationally inferred values from nearby star-forming regions for the total disk mass and the radial density profile. By varying the disk mass within the observed scatter for a solar-mass star, we find for a large range of disk masses and density profiles that protoplanetary disks are “optically thin” to low energy stellar cosmic rays. I will describe how our results indicate, for a wide range of disk masses, that low energy stellar cosmic rays provide an important source of ionisation at the disk midplane at large radii (∼70 au). Finally, I will discuss the type of systems where we expect that stellar cosmic rays are likely to be most influential. </p>

scholarly journals Zooming in on the Formation of Protoplanetary Disks

2013 ◽  
Vol 8 (S299) ◽  
pp. 131-135 ◽  
Author(s):  
Åke Nordlund ◽  
Troels Haugbølle ◽  
Michael Küffmeier ◽  
Paolo Padoan ◽  
Aris Vasileiades
Keyword(s):  
Magnetic Field ◽  
Energy Efficient ◽  
Adaptive Mesh Refinement ◽  
Accretion Rate ◽  
Magnetic Energy ◽  
Protoplanetary Disks ◽  
Adaptive Mesh ◽  
Gravitational Energy ◽  
Solar Mass ◽  
The Magnetic Field

AbstractWe use the adaptive mesh refinement code RAMSES to model the formation of protoplanetary disks in realistic star formation environments. The resolution scales over up to 29 powers of two (~ 9 orders of magnitude) covering a range from outer scales of 40 pc to inner scales of 0.015 AU. The accretion rate from a 1.5 solar mass envelope peaks near 10−4 M⊙ about 6 kyr after sink particle formation and then decays approximately exponentially, reaching 10−6 M⊙ in 100 kyr. The models suggest universal scalings of physical properties with radius during the main accretion phase, with kinetic and / or magnetic energy in approximate balance with gravitational energy. Efficient accretion is made possible by the braking action of the magnetic field, which nevertheless allows a near-Keplerian disk to grow to a 100 AU size. The magnetic field strength ranges from more than 10 G at 0.1 AU to less than 1 mG at 100 AU, and drives a time dependent bipolar outflow, with a collimated jet and a broader disk wind.

scholarly journals A multiwavelength study of spiral structure in galaxies. I. General characteristics in the optical

2020 ◽  
Vol 493 (1) ◽  
pp. 390-409
Author(s):  
Sergey Savchenko ◽  
Alexander Marchuk ◽  
Aleksandr Mosenkov ◽  
Konstantin Grishunin
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Wavelength Dependence ◽  
Sloan Digital Sky Survey ◽  
Galactocentric Distance ◽  
Distinctive Features ◽  
Sky Survey ◽  
Grand Design ◽  
Generation Mechanisms ◽  
Spiral Arm

ABSTRACT Different spiral generation mechanisms are expected to produce different morphological and kinematic features. In this first paper in a series, we carefully study the parameters of spiral structure in 155 face-on spiral galaxies, selected from the Sloan Digital Sky Survey, in the three gri bands. We use a method for deriving a set of parameters of spiral structure, such as the width of the spiral arms, their fraction to the total galaxy luminosity, and their colour, which have not been properly studied before. Our method is based on an analysis of a set of photometric cuts perpendicular to the direction of a spiral arm. Based on the results of our study, we compare the main three classes of spirals: grand design, multi-armed, and flocculent. We conclude that: (i) for the vast majority of galaxies (86 per cent), we observe an increase of their arm width with Galactocentric distance; (ii) more luminous spirals in grand design galaxies exhibit smaller variations of the pitch angle with radius than those in less luminous grand design spirals; (iii) grand design galaxies show less difference between the pitch angles of individual arms than multi-armed galaxies. Apart from these distinctive features, all three spiral classes do not differ significantly by their pitch angle, arm width, width asymmetry, and environment. Wavelength dependence is found only for the arm fraction. Therefore, observationally we find no strong difference (except for the view and number of arms) between grand design, multi-armed, and flocculent spirals in the sample galaxies.

scholarly journals A comparison of the Andromeda and Milky Way galaxies

1985 ◽  
Vol 106 ◽  
pp. 423-430
Author(s):  
Paul Hodge
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Structure ◽  
Type A ◽  
Detailed Comparison ◽  
Basic Properties ◽  
Density Enhancement ◽  
The Galaxy ◽  
Optical Tracers

A comparison of some of the basic properties of M31 and the Milky Way indicates that in almost every respect M31 is larger than the Galaxy. It is more luminous, redder, more massive, and of earlier Hubble type. A detailed comparison of the spiral structure, based on optical tracers, for comparable areas in the outer parts of each galaxy shows differences in the arm spacings, in density enhancement, and in pitch angle.

scholarly journals A new interpretation of the galactic structure from H II regions

1970 ◽  
Vol 38 ◽  
pp. 209-212 ◽  
Author(s):  
Y.P. G. Courtès ◽  
Y.M. Georgelin ◽  
G. Monnet
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Galactic Structure ◽  
Radial Velocities ◽  
H Ii Regions ◽  
B Stars ◽  
New Interpretation

From 6000 optical radial velocities of H II regions a new spiral structure (4 arms of pitch angle 20°) is found. The radial velocities of the observed H II regions are the same with the velocities of the H I regions. The kinematics of H II regions is similar to that of Cepheids and B stars.

scholarly journals How the bar properties affect the induced spiral structure

2021 ◽  
Vol 502 (4) ◽  
pp. 4708-4722
Author(s):  
L Garma-Oehmichen ◽  
L Martinez-Medina ◽  
H Hernández-Toledo ◽  
I Puerari
Keyword(s):  
Pitch Angle ◽  
Spiral Structure ◽  
Physical Nature ◽  
Axial Ratio ◽  
Rotation Curves ◽  
Local Universe ◽  
Grand Design ◽  
Radial Anisotropy ◽  
Pattern Speed ◽  
Disc Galaxies

ABSTRACT Stellar bars and spiral arms coexist and co-evolve in most disc galaxies in the local Universe. However, the physical nature of this interaction remains a matter of debate. In this work, we present a set of numerical simulations based on isolated galactic models aimed to explore how the bar properties affect the induced spiral structure. We cover a large combination of bar properties, including the bar length, axial ratio, mass, and rotation rate. We use three galactic models describing galaxies with rising, flat, and declining rotation curves. We found that the pitch angle best correlates with the bar pattern speed and the spiral amplitude with the bar quadrupole moment. Our results suggest that galaxies with declining rotation curves are the most efficient forming grand design spiral structure, evidenced by spirals with larger amplitude and pitch angle. We also test the effects of the velocity ellipsoid in a subset of simulations. We found that as we increase the radial anisotropy, spirals increase their pitch angle but become less coherent with smaller amplitude.

On the Dissipative Propagation in Oppositely Charged Dusty Fluids

2019 ◽  
Vol 74 (3) ◽  
pp. 227-234
Author(s):  
Sultan Z. Alamri
Keyword(s):  
Acoustic Wave ◽  
Kinematic Viscosity ◽  
Burgers Equation ◽  
Charged Dust ◽  
Trapped Ion ◽  
Viscosity Coefficients ◽  
Nonlinear Shock ◽  
Physical Effects ◽  
Oppositely Charged ◽  
Positively Charged

AbstractThe dissipative propagation due to the dust viscosity of dust nonlinear shock acoustic wave in a collisionless, unmagnetised, oppositely charged viscous dusty plasma with trapped ion has been examined using parameters related to mesosphere and magnetosphere of Jupiter. The modified dissipative Korteweg de Vries–Burgers equation describes the model and solves according to different physical dissipation conditions. The physical effects of two dusty kinematic viscosity coefficients and positively charged dust grains on the shock properties are investigated.

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