2,369 research outputs found
Simulations of core convection in rotating A-type stars: Differential rotation and overshooting
We present the results of 3--D simulations of core convection within A-type
stars of 2 solar masses, at a range of rotation rates. We consider the inner
30% by radius of such stars, thereby encompassing the convective core and some
of the surrounding radiative envelope. We utilize our anelastic spherical
harmonic (ASH) code, which solves the compressible Navier-Stokes equations in
the anelastic approximation, to examine highly nonlinear flows that can span
multiple scale heights. The cores of these stars are found to rotate
differentially, with central cylindrical regions of strikingly slow rotation
achieved in our simulations of stars whose convective Rossby number (R_{oc}) is
less than unity. Such differential rotation results from the redistribution of
angular momentum by the nonlinear convection that strongly senses the overall
rotation of the star. Penetrative convective motions extend into the overlying
radiative zone, yielding a prolate shape (aligned with the rotation axis) to
the central region in which nearly adiabatic stratification is achieved. This
is further surrounded by a region of overshooting motions, the extent of which
is greater at the equator than at the poles, yielding an overall spherical
shape to the domain experiencing at least some convective mixing. We assess the
overshooting achieved as the stability of the radiative exterior is varied, and
the weak circulations that result in that exterior. The convective plumes serve
to excite gravity waves in the radiative envelope, ranging from localized
ripples of many scales to some remarkable global resonances.Comment: 48 pages, 16 figures, some color. Accepted to Astrophys. J. Color
figures compressed with appreciable loss of quality; a PDF of the paper with
better figures is available at
http://lcd-www.colorado.edu/~brownim/core_convectsep24.pd
Workshop proceedings: Information Systems for Space Astrophysics in the 21st Century, volume 1
The Astrophysical Information Systems Workshop was one of the three Integrated Technology Planning workshops. Its objectives were to develop an understanding of future mission requirements for information systems, the potential role of technology in meeting these requirements, and the areas in which NASA investment might have the greatest impact. Workshop participants were briefed on the astrophysical mission set with an emphasis on those missions that drive information systems technology, the existing NASA space-science operations infrastructure, and the ongoing and planned NASA information systems technology programs. Program plans and recommendations were prepared in five technical areas: Mission Planning and Operations; Space-Borne Data Processing; Space-to-Earth Communications; Science Data Systems; and Data Analysis, Integration, and Visualization
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