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Titolo:
Dynamics of circumstellar disks
Autore:
Nelson, AF; Benz, W; Adams, FC; Arnett, D;
Indirizzi:
Univ Arizona, Dept Phys, Tucson, AZ 85721 USA Univ Arizona Tucson AZ USA 85721 Arizona, Dept Phys, Tucson, AZ 85721 USA Univ Arizona, Steward Observ, Tucson, AZ 85721 USA Univ Arizona Tucson AZUSA 85721 na, Steward Observ, Tucson, AZ 85721 USA Univ Bern, Inst Phys, CH-3012 Bern, Switzerland Univ Bern Bern Switzerland CH-3012 Inst Phys, CH-3012 Bern, Switzerland Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA Univ Michigan Ann ArborMI USA 48109 , Dept Phys, Ann Arbor, MI 48109 USA
Titolo Testata:
ASTROPHYSICAL JOURNAL
fascicolo: 1, volume: 502, anno: 1998,
parte:, 1
pagine: 342 - 371
SICI:
0004-637X(19980720)502:1<342:DOCD>2.0.ZU;2-H
Fonte:
ISI
Lingua:
ENG
Soggetto:
ECCENTRIC GRAVITATIONAL INSTABILITIES; SMOOTHED PARTICLE HYDRODYNAMICS; PIECEWISE-PARABOLIC METHOD; STAR-FORMING REGIONS; PROTOSTELLAR DISKS; DENSITY WAVES; IMAGING SURVEY; GASEOUS DISKS; EVOLUTION; FRAGMENTATION;
Keywords:
accretion, accretion disks; circumstellar matter; hydrodynamics; methods : numerical; stars : formation; stars : pre-main-sequence;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
55
Recensione:
Indirizzi per estratti:
Indirizzo: Nelson, AF Univ Arizona, Dept Phys, Tucson, AZ 85721 USA Univ Arizona Tucson AZ USA 85721 pt Phys, Tucson, AZ 85721 USA
Citazione:
A.F. Nelson et al., "Dynamics of circumstellar disks", ASTROPHYS J, 502(1), 1998, pp. 342-371

Abstract

We present a series of two-dimensional hydrodynamic simulations of massivedisks around protostars. We simulate the same physical problem using both a Piecewise Parabolic Method (PPM) code and a Smoothed Particle Hydrodynamic (SPH) code and analyze their differences. The disks studied here range inmass from 0.05M* to 1.0M* and in initial minimum Toomre Q value from 1.1 to 3.0. We adopt simple power laws for the initial density and temperature in the disk with an isothermal (gamma = 1) equation of state. The disks are locally isothermal. We allow the central star to move freely in response togrowing perturbations. The simulations using each code are compared to discover differences due to error in the methods used. For this problem, the strengths of the codes overlap only in a limited fashion, but similarities exist in their predictions, including spiral arm pattern speeds and morphological features. Our results represent limiting cases (i.e., systems evolvedisothermally) rather than true physical systems. Disks become active from the inner regions outward. From the earliest times, their evolution is a strongly dynamic process rather than a smooth progression toward eventual nonlinear behavior. Processes that occur in both the extreme inner and outer radial regions affect the growth of instabilities over the entire disk. Effects important for the global morphology of the system can originate at quite small distances from the star. We calculate approximate growth rates for the spiral patterns; the one-armed (m = 1) spiral arm is not the fastest growing pattern of most disks. Nonetheless, it plays a significant role because of factors that can excite it more quickly than other patterns. A markedchange in the character of spiral structure occurs with varying disk mass. Low-mass disks form filamentary spiral structures with many arms while high-mass disks form grand design spiral structures with few arms. In our SPH simulations, disks with initial minimum Q = 1.5 or lower break up into protobinary or protoplanetary clumps. However, these simulations cannot follow the physics important for the flow and must be terminated before the systemhas completely evolved. At their termination, PPM simulations with similarinitial conditions show uneven mass distributions within spiral arms: suggesting that clumping behavior might result if they were carried further. Simulations of tori, for which SPH and PPM are directly comparable, do show clumping in both codes. Concerns that the pointlike nature of SPH exaggerates clumping, that our representation of the gravitational potential in PPM is too coarse, and that our physics assumptions are too simple suggest caution in interpretation of the clumping in both the disk and torus simulations.

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Documento generato il 26/11/20 alle ore 09:03:45