Many post-AGB star binaries are observed to have relatively high orbital
eccentricities (up to 0.6). Recently, AC Her was observed to have a
polar-aligned circumbinary disk. We perform hydrodynamic simulations to explore
the impact of a polar-aligned disk on the eccentricity of a binary. For a
binary system with central masses of 0.73 M_sun and 1.4 M_sun, we find that a
disk with a total mass of 0.1 M_sun can enhance the binary eccentricity from
0.2 to 0.7 within 5000 years, or from 0.01 to 0.65 within 15000 years. Even if
the disk mass is as low as 0.01 M_sun, the binary eccentricity grows within our
simulation time while the system remains stable. These eccentricity variations
are associated with the variations of the inclination between the disk and the
binary orbit due to von Zeipel-Kozai-Lidov oscillations. The oscillations
eventually damp and leave the binary eccentricity at a high value. The
numerical results are in good agreement with analytical estimates. In addition,
we examine the AC-Her system and find that the disk mass should be on the order
of 10^(-3)M_sun for the disk to remain polar.

Este artículo explora los viajes en el tiempo y sus implicaciones.

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