Exoplanets and Stellar Physics

Abstract:

We report the first results of an extensive new study of the Galactic center stellar cluster. The central parsec is powered by a cluster of about two dozen luminous and helium-rich blue supergiants/Wolf-Rayet stars (Teff i 20,000-30,000 K) with ZAMS masses up to -100 MQ. The most likely scenario for the formation of the massive stars is a small star formation burst between 3 X 106 and 7 X 106 years ago. In this scenario the Galactic center is presently in a short-lived, post-main-sequence “wind phase.” In addition, there is evidence for another star formation event about 108 years ago, as well as for recently formed massive stars that may have been transported into the central core along with orbiting gas streamers. The radial velocity dispersion of 35 early- and late-type stars with distances of 1"-12" from Sgr A* is 154 ± 19 km s-1. Our new results strongly favor the existence of a central dark mass of -3 X 106 M⊙ (density > 108.5 M⊙ pc-3, M/L > 10 M⊙/L⊙) within 0.14 pc of the dynamic center. © 1995 The American Astronomical Society.

Abstract:

The study of baroclinic instability has its origins in attempts to explain the genesis of midlatitude synoptic storm systems. The authors provide an account of the fundamental material and unfamiliar aspects of the linear theory. Essential observational background is provided in section 2, and the mathematical basics are laid out in section 3. The review for the most part focuses on quasigeostrophic dynamics, considering only dry dynamics. Discussion is slanted towards the terrestrial atmosphere. Stability criteria are treated in section 4, and normal modes are discussed in section 5. Aspects of the linear initial value problem are taken up in section 6. Section 7 considers briefly the difficult subject of nonlinear equilibration. Finally, section 8, takes stock of where the subject stands and where it is going. (from Authors)