Stellar systems

R.C. Peterson et al. Mid-Ultraviolet Spectral Templates for Old Stellar Systems . In Space Telescope Science Newsletter 4, 1 (2004)... 

Abstract. We present preliminary results of an extensive low and high-resolution ESO-VLT spectroscopic survey of Subgiant stars in the stellar system uj Centauri. Basing on infrared Ca II triplet lines we derived metallicities and radial velocities for more than 110 stars belonging to different stellar populations of the system. The most metal rich component, the SGB-a, appears to have metallicity [Fe/H] -0.5. Moreover, SGB-a stars have been found to stray from the dynamical behaviour of the bulk population. Such evidence adds new puzzling questions on the formation and the chemical enrichment history of this stellar system. 

R.Pallavicini, S. Randich, P. Sestito Lithium abundances in intermediate age and old clusters . In 13th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, ed. by F. Favata et al. (ESA, Special Publication), in press (2004)... 

Study of the relative importances of assembly of stellar systems and in situ star formation remains extremely active, and will presumably soon converge as the large area CCD photometric surveys cover the whole sky, and accurate spectroscopic surveys begin to acquire large samples. 

Lynden-Bell, D. 1973, in G. Contopulos, M. Henon D. Lynden-Bell, Dynamical Structure and Evolution of Stellar Systems, Geneva Geneva Observatory, p. 132. Lynden-Bell, D. 1975, Vistas in Astr., 19, 299. 

In these considerations, it must be kept in mind that there is a stellar spike around the black hole at the Galactic Center. The steepness of this stellar spike is however not very well know. With large uncertainties, Genzel et al.(2003) estimate the slope of the stellar spike to be 7stars 1.3-1.4. This means that the current stellar spike is probably shallow. We may think that the stellar spike is our best proxy for the dark matter spike. If so, also the dark matter spike would also be shallow, and thus inconsequential for neutralino signals. However, the dark matter and stellar spikes follow very different evolution histories, because contrary to the dark matter, binary collisions of stars and coalescence of two stars into one at collisions effectively relax the stellar system to a shallower spike. 

Our Galaxy is one of billions of similar stellar systems which together make up the observable universe. The total mass of our galaxy is 1.8 x 1011 M . About 10% of that mass is in the form of interstellar matter whose principal constituents are gas and fine dust particles. The dust and gas appear to be... 

Fig. 3. Distribution of stars and interstellar matter in the Galaxy. The lower part of the diagram is a cross section perpendicular to the galactic plane. Globular clusters are the oldest stellar systems and must therefore have been formed in the early evolutionary stages of the Galaxy. The mass of the stars, however, forms a flat layer with a nuclear bulge in the center. The interstellar matter forms an even flatter layer which widens up towards the edges of the Galaxy.

One recent development in astrophysical stochastic processes has been the widespread use of coagulation calculations for both nucleation phenomena and dust formation and processes that relate to the distribution function for masses and mass ratios in forming stellar systems. The use of the coagulation equation for the study of star and stellar system formation in particular has been quite recent and warrants a review. 

For the spectroscopic analyses, I identify three kinds of environments stellar atmospheres, stellar ejecta and interstellar gas, and stellar systems. 

The dEs are deceptively simple stellar systems, with no young stars and apparently kinematically-relaxed stellar populations. Recent high-precision ground-based and HST CCD photometry have demonstrated that this is far from the truth. The dEs display a variety of complex multi-episode star formation histories. For example, Carina shows evidence for several distinct star formation events spread over several Gyr (Smecker-Hane et al. 1994) Sculptor and Fornax appear morphologically similar, but Sculptor appears to formed the bulk of its stars at an earlier time than Fornax (Tolstoy et al. 2001). Only... 

Accretion of extant stellar systems which eventually settle in the center of the Galaxy. 

Merging of early formed stellar systems in a wide redshift range and preferentially at late epochs (Kauffmann et al. 1993). A burst of star formation can occur during the major merging where 30% of the stars can be formed (Kauffmann 1996). 

To study the chemical evolution of galaxies and stellar systems, it is essential to have an estimate of what elements are produced (or destroyed) by stars of different mass ranges. Stellar yields provide this information, by quantifying the amount (in mass) of species i that is expelled into the interstellar medium over the course of a star s life. The definition of the yield that we use is given by the following expression... 

The Newtonian gravitational force is the dominant force in the N-Body systems in the universe, as for example in a planetary system, a planet with its satellites, or a multiple stellar system. The long term evolution of the system depends on the topology of its phase space and on the existence of ordered or chaotic regions. The topology of the phase space is determined by the position and the stability character of the periodic orbits of the system (the fixed points of the Poincare map on a surface of section). Islands of stable motion exist around the stable periodic orbits, chaotic motion appears at unstable periodic orbits. This makes clear the importance of the periodic orbits in the study of the dynamics of such systems. 

The general three-body problem Three bodies with finite masses moving under their gravitational attraction. This is a model for a triple stellar system. In many astronomical applications one of the three bodies has a large mass and the other two bodies have small, but not negligible masses. This is a model for an extrasolar planetary system, or a system of two satellites moving around a major planet. In the latter two cases the two small bodies move in perturbed Keplerian orbits. 

A large majority of known triple stellar systems have the Hill-type stability, and so is the Sun-Jupiter-Saturn system (99.99% of the mass of the Solar System). The close binary is then the Sun and Jupiter, while Saturn is the third body. 

Solar system Jupiter and satellites Saturn and satellites Uranus and satellites Multi stellar systems The Galaxy 1.16 1.25 1.043 1.2 from 1.15 to 7.2 about 1.2... 

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