scholarly journals Assessing the role of oxygen on ring current formation and evolution through numerical experiments

2015 ◽  
Vol 120 (6) ◽  
pp. 4656-4668 ◽  
Author(s):  
R. Ilie ◽  
M. W. Liemohn ◽  
G. Toth ◽  
N. Yu Ganushkina ◽  
L. K. S. Daldorff
Keyword(s):  
Numerical Experiments ◽  
Ring Current ◽  
Formation And Evolution

scholarly journals The Role of Radio Loud Phase of Nuclear Activity in Galaxy Formation and Evolution

2013 ◽  
Vol 9 (S304) ◽  
pp. 419-420
Author(s):  
Gabriel A. Ohanian
Keyword(s):  
Galaxy Formation ◽  
Subsequent Development ◽  
Nuclear Activity ◽  
Evolution Of Galaxies ◽  
Galaxy Formation And Evolution ◽  
Formation And Evolution ◽  
Key Questions

AbstractKey questions, which arise when one tries to clear up a problem of formation and evolution of galaxies, is the question of energy: what is the energetic budget of AGN owing to form galaxies and provide its subsequent development? Hence, for understanding the formation and evolution of galaxies, it is important to estimate the energetic budget of AGN which we try to do involving radio loud phase of nuclear activity.

scholarly journals Stochastic Flips on Dimer Tilings

2010 ◽  
Vol DMTCS Proceedings vol. AM,... (Proceedings) ◽  
Author(s):  
Thomas Fernique ◽  
Damien Regnault
Keyword(s):  
Fixed Point ◽  
Markov Process ◽  
Upper Bound ◽  
Numerical Experiments ◽  
Triangular Grid ◽  
Expected Number ◽  
Worst Case ◽  
Average Case ◽  
International Audience

International audience This paper introduces a Markov process inspired by the problem of quasicrystal growth. It acts over dimer tilings of the triangular grid by randomly performing local transformations, called $\textit{flips}$, which do not increase the number of identical adjacent tiles (this number can be thought as the tiling energy). Fixed-points of such a process play the role of quasicrystals. We are here interested in the worst-case expected number of flips to converge towards a fixed-point. Numerical experiments suggest a $\Theta (n^2)$ bound, where $n$ is the number of tiles of the tiling. We prove a $O(n^{2.5})$ upper bound and discuss the gap between this bound and the previous one. We also briefly discuss the average-case.

scholarly journals Rapid destruction of planetary debris around white dwarfs through aeolian erosion

2021 ◽  
Vol 502 (4) ◽  
pp. 5176-5184
Author(s):  
Mor Rozner ◽  
Dimitri Veras ◽  
Hagai B Perets
Keyword(s):  
White Dwarfs ◽  
Extensive Study ◽  
Destructive Process ◽  
Rapid Destruction ◽  
Aeolian Erosion ◽  
Formation And Evolution ◽  
Destructive Processes ◽  
Solid Bodies ◽  
Erosive Effect

ABSTRACT The discovery of numerous debris discs around white dwarfs (WDs) gave rise to extensive study of such discs and their role in polluting WDs, but the formation and evolution of these discs is not yet well understood. Here, we study the role of aeolian (wind) erosion in the evolution of solids in WD debris discs. Aeolian erosion is a destructive process that plays a key role in shaping the properties and size distribution of planetesimals, boulders, and pebbles in gaseous protoplanetary discs. Our analysis of aeolian erosion in WD debris discs shows that it can also play an important role in these environments. We study the effects of aeolian erosion under different conditions of the disc and its erosive effect on planetesimals and boulders of different sizes. We find that solid bodies smaller than $\sim \! 5 \, \rm {km}$ will be eroded within the short disc lifetime. We compare the role of aeolian erosion in respect to other destructive processes such as collisional fragmentation and thermal ablation. We find that aeolian erosion is the dominant destructive process for objects with radius $\lesssim \! 10^3 \, \rm {cm}$ and at distances $\lesssim \! 0.6 \, \mathrm{R}_\odot$ from the WD. Thereby, aeolian erosion constitutes the main destructive pathway linking fragmentational collisions operating on large objects with sublimation of the smallest objects and Poynting–Robertson drag, which leads to the accretion of the smallest particles on to the photosphere of WDs, and the production of polluted WDs.

The role of ions in the formation and evolution of particles in aircraft plumes

1997 ◽  
Vol 24 (15) ◽  
pp. 1927-1930 ◽  
Author(s):  
Fangqun Yu ◽  
Richard P. Turco
Keyword(s):  
Formation And Evolution

scholarly journals Flare Stars Database

1994 ◽  
Vol 161 ◽  
pp. 380-382
Author(s):  
M. Tsvetkov ◽  
M. Chukova ◽  
K. Tsvetkova
Keyword(s):  
Wide Field ◽  
Flare Activity ◽  
The Galaxy ◽  
Statistical Regularities ◽  
Ceti Type ◽  
Formation And Evolution ◽  
Flare Stars ◽  
Machine Readable

The important role of flare stars (UV Ceti type variables) in astrophysics is due to the fact that the flare activity is not only typical for red stars with small masses but is a necessary stage during their evolution. The flare star search in stellar aggregates has led to the accumulation of rich observational material allowing us to look for statistical regularities in star formation and evolution. At present, there are more than 1500 known flare stars in the Galaxy; these were discovered mainly during the last 30 years. Most results of the long term monitoring with wide-field telescopes are listed in existing catalogues of flare stars in stellar aggregates and in the solar neighbourhood. These catalogues and their machine-readable versions were the basis for the present database of flare stars in the Galaxy.

scholarly journals Paired and Interacting Galaxies: Conference Summary

1990 ◽  
Vol 124 ◽  
pp. 765-770 ◽  
Author(s):  
Colin A. Norman
Keyword(s):  
Initial Conditions ◽  
Galactic Nuclei ◽  
Interacting Galaxies ◽  
Compact Groups ◽  
Data Sets ◽  
University Of Alabama ◽  
Conference Summary ◽  
Formation And Evolution ◽  
The University

This has been an excellent conference with a very international component and a rich and wide ranging diversity of views on the topical subject of paired and interacting galaxies. The southern hospitality shown to us by our hosts Jack Sulentic and Bill Keel has been most gracious and the general growth of the astronomy group at the University of Alabama is most impressive.The conference began with the presentation of the basic data sets on pairs, groups, and interacting galaxies with the latter being further discussed with respect to both global properties and properties of the galactic nuclei. Then followed the theory, modelling and interpretation using analytic techniques, simulations and general modelling for spirals and ellipticals, starbursts and active galactic nuclei. Before the conference I had written down the three questions concerning pairs, groups and interacting galaxies that I hoped would be answered at the meeting: (1) How do they form? including the role of initial conditions, the importance of subclustering, the evolution of groups to compact groups, and the fate of compact groups; (2) How do they evolve? including issues such as relevant timescales, the role of halos and the problem of overmerging, the triggering and enhancement of star formation and activity in the galactic nuclei, and the relative importance of dwarf versus giant encounters; and (3) Are they important? including the frequency of pairs and interactions, whether merging and interactions are very important aspects of the life of a normal galaxy at formation, during its evolution, in forming bars, shells, rings, bulges etc., and in the formation and evolution of active galaxies. In what follows I shall summarize the meeting and where possible focus on these three central issues. Since this is a conference summary my references are all to papers presented at this meeting.

scholarly journals A high binary fraction for the most massive close-in giant planets and brown dwarf desert members

2019 ◽  
Vol 485 (4) ◽  
pp. 4967-4996 ◽  
Author(s):  
C Fontanive ◽  
K Rice ◽  
M Bonavita ◽  
E Lopez ◽  
K Mužić ◽  
...  
Keyword(s):  
Giant Planets ◽  
Close Binaries ◽  
Brown Dwarf ◽  
Multiple Systems ◽  
Binary Separation ◽  
Short Period ◽  
Formation And Evolution ◽  
Gaia Dr2 ◽  
Independent Confirmation

ABSTRACT Stellar multiplicity is believed to influence planetary formation and evolution, although the precise nature and extent of this role remain ambiguous. We present a study aimed at testing the role of stellar multiplicity in the formation and/or evolution of the most massive, close-in planetary and substellar companions. Using past and new direct imaging observations, as well as the Gaia DR2 catalogue, we searched for wide binary companions to 38 stars hosting massive giant planets or brown dwarfs (M > 7 MJup) on orbits shorter than ∼1 au. We report the discovery of a new component in the WASP-14 system, and present an independent confirmation of a comoving companion to WASP-18. From a robust Bayesian statistical analysis, we derived a binary fraction of $79.0^{+13.2}_{-14.7}$ per cent between 20 and 10 000 au for our sample, twice as high as for field stars with a 3σ significance. This binary frequency was found to be larger than for lower-mass planets on similar orbits, and we observed a marginally higher binary rate for inner companions with periods shorter than 10 d. These results demonstrate that stellar companions greatly influence the formation and/or evolution of these systems, suggesting that the role played by binary companions becomes more important for higher-mass planets, and that this trend may be enhanced for systems with tighter orbits. Our analysis also revealed a peak in binary separation at 250 au, highlighting a shortfall of close binaries among our sample. This indicates that the mechanisms affecting planet and brown dwarf formation or evolution in binaries must operate from wide separations, although we found that the Kozai–Lidov mechanism is unlikely to be the dominant underlying process. We conclude that binarity plays a crucial role in the existence of very massive short-period giant planets and brown dwarf desert inhabitants, which are almost exclusively observed in multiple systems.

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