459 research outputs found
Radial Stellar Pulsation and 3D Convection. I. Numerical Methods and Adiabatic Test Cases
We are developing a 3D radiation hydrodynamics code to simulate the
interaction of convection and pulsation in classical variable stars. One key
goal is the ability to carry these simulations to full amplitude in order to
compare them with observed light and velocity curves. Previous 2D calculations
were prevented from doing this because of drift in the radial coordinate
system, due to the algorithm defining radial movement of the coordinate system
during the pulsation cycle. We remove this difficulty by defining our
coordinate system flow algorithm to require that the mass in a spherical shell
remain constant throughout the pulsation cycle. We perform adiabatic test
calculations to show that large amplitude solutions repeat over more than 150
pulsation periods. We also verify that the computational method conserves the
peak kinetic energy per period, as must be true for adiabatic pulsation models
Radial and Nonradial Oscillation Modes in Rapidly Rotating Stars
Radial and nonradial oscillations offer the opportunity to investigate the
interior properties of stars. We use 2D stellar models and a 2D finite
difference integration of the linearized pulsation equations to calculate
non-radial oscillations. This approach allows us to directly calculate the
pulsation modes for a distorted rotating star without treating the rotation as
a perturbation. We are also able to express the finite difference solution in
the horizontal direction as a sum of multiple spherical harmonics for any given
mode. Using these methods, we have investigated the effects of increasing
rotation and the number of spherical harmonics on the calculated
eigenfrequencies and eigenfunctions and compared the results to perturbation
theory. In slowly rotating stars, current methods work well, and we show that
the eigenfunction can be accurately modelled using 2nd order perturbation
theory and a single spherical harmonic. We use 10 Msun models with velocities
ranging from 0 to 420 km/s (0.89 Omega_c) and examine low order p modes. We
find that one spherical harmonic remains reasonable up to a rotation rate
around 300km s^{-1} (0.69 Omega_c) for the radial fundamental mode, but can
fail at rotation rates as low as 90 km/s (0.23 Omega_c) for the 2H mode or l =
2 p_2 mode, based on the eigenfrequencies alone. Depending on the mode in
question, a single spherical harmonic may fail at lower rotation rates if the
shape of the eigenfunction is taken into consideration. Perturbation theory, in
contrast, remains valid up to relatively high rotation rates for most modes. We
find the lowest failure surface equatorial velocity is 120 km/s (0.30 Omega_c)
for the l = 2 p_2 mode, but failure velocities between 240 and 300 km/s
(0.58-0.69 Omega_c)are more typical.Comment: accepted for publication in Ap
Nobody
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Bary Add
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Next to the denominational schools
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The Women of Sparta
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