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Full-Text Articles in Physical Sciences and Mathematics
Adiabatic Invariants In Stellar Dynamics .2. Gravitational Shocking, Md Weinberg
Adiabatic Invariants In Stellar Dynamics .2. Gravitational Shocking, Md Weinberg
Astronomy Department Faculty Publication Series
A new theory of gravitational shocking based on time-dependent perturbation theory shows that the changes in energy and angular momentum due to a slowly varying disturbance are not exponentially small for stellar dynamical systems in general. It predicts significant shock heating by slowly varying perturbations previously thought to be negligible according to the adiabatic criterion. The theory extends the scenarios traditionally computed only with the impulse approximation and is applicable to a wide class of disturbances. The approach is applied specifically to the problem of the disk shocking of star clusters.
Adiabatic Invariants In Stellar Dynamics .3. Application To Globular-Cluster Evolution, Md Weinberg
Adiabatic Invariants In Stellar Dynamics .3. Application To Globular-Cluster Evolution, Md Weinberg
Astronomy Department Faculty Publication Series
The previous two companion papers demonstrate that slowly varying perturbations do not result in adiabatic cutoffs and provide a formalism for computing the long term effects of time dependent perturbations on stellar systems. Here, the theory is implemented in Fokker Planck code and a suite of runs illustrating the effects of shock heating on globular cluster evolution are described. Shock heating alone results in a considerable mass loss for clusters with Rg < S kpc: a concentration c = 1.5 cluster with Rg = 8kpc loses up to 95% of the initial mass in 15 Gyr. Only those with concentration c < 1.3 survive disk shock inside of this radius. Other effects, such as mass loss by stellar evolution, will increase this survival bound. Loss of the initial halo together with mass segregation leads to mass spectral induces, x, which may be considerably large than their initial values.
Kinematic Signature Of A Rotating Bar Near A Resonance, Md Weinberg
Kinematic Signature Of A Rotating Bar Near A Resonance, Md Weinberg
Astronomy Department Faculty Publication Series
There have been several recent suggestions that the Milky Way has rotating bar-like features based on HI and star count data. In this paper, I show that such features cause distinctive stellar kinematic signatures near OLR and ILR. The effects of these resonances may be observable far from the peak density of the pattern and relatively nearby the solar position. The details of the kinematic signatures depend on the evolutionary history of the ‘bar’ and therefore velocity data, both systemic and velocity dispersion, may be used to probe the evolutionary history as well as the present state of the Galaxy. …
Adiabatic Invariants In Stellar Dynamics .1. Basic Concepts, Md Weinberg
Adiabatic Invariants In Stellar Dynamics .1. Basic Concepts, Md Weinberg
Astronomy Department Faculty Publication Series
The adiabatic criterion, widely used in astronomical dynamics, is based on the harmonic oscillator. It asserts that the change in action under a slow varying perturbation is exponentially small. Recent mathematical results precisely define the conditions for invariance show that this model does not apply in general. In particular, a slowly varying perturbation may cause significant evolution stellar dynamical systems even if its time scale is longer than any internal orbital time scale. This additional 'heating' may have serious implications for the evolution of star clusters and dwarf galaxies which are subject to long-term environmental forces. the mathematical developments leading …
Weakly Damped Modes In Star-Clusters And Galaxies, Md Weinberg
Weakly Damped Modes In Star-Clusters And Galaxies, Md Weinberg
Astronomy Department Faculty Publication Series
A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing momentum and energy deposited by the perturber. This paper demonstrates that this assumption is false; weakly damped modes exist and may persist long enough to have observable consequences. To do this, a method for investigating the dispersion relation for spherical stellar systems and for locating weakly damped modes in particular is developed and applied to King models of varying concentration. …
(Co)-C-12 (3-2) And (1-0) Emission-Line Observations Of Nearby Starburst Starburst Galaxy Nuclei, Nicholas Devereux, Yoshiaki Taniguchi, D. B. Sanders, N. Nakai, J. S. Young
(Co)-C-12 (3-2) And (1-0) Emission-Line Observations Of Nearby Starburst Starburst Galaxy Nuclei, Nicholas Devereux, Yoshiaki Taniguchi, D. B. Sanders, N. Nakai, J. S. Young
Astronomy Department Faculty Publication Series
New measurements of the ^12^CO (1-0) and ^12^CO (3-2) line emission are presented for the nuclei of seven nearby starburst galaxies selected from a complete sample of 21 nearby starburst galaxies for which the nuclear star formation rates are measured to be comparable to the archetype starburst galaxies M82 and NGC 253. The new observations capitalize on the coincidence between the beam size of the 45 m Nobeyama telescope at 115 GHz and that of the 15 m James Clerk Maxwell Telescope at 345 GHz to measure the value of the ^12^CO (3-2)/(1-0) emission line ratio in a 15" ( …