1,116 research outputs found
Compact planetary systems perturbed by an inclined companion: II. Stellar spin-orbit evolution
The stellar spin orientation relative to the orbital planes of multiplanet
systems are becoming accessible to observations. Here, we analyze and classify
different types of spin-orbit evolution in compact multiplanet systems
perturbed by an inclined outer companion. Our study is based on classical
secular theory, using a vectorial approach developed in a separate paper. When
planet-planet perturbations are truncated at the second order in eccentricity
and mutual inclination, and the planet-companion perturbations are developed at
the quadrupole order, the problem becomes integrable. The motion is composed of
a uniform precession of the whole system around the total angular momentum, and
in the rotating frame, the evolution is periodic. Here, we focus on the
relative motion associated to the oscillations of the inclination between the
planet system and the outer orbit, and of the obliquities of the star with
respect to the two orbital planes. The solution is obtained using a powerful
geometric method. With this technique, we identify four different regimes
characterized by the nutation amplitude of the stellar spin-axis relative to
the orbital plane of the planets. In particular, the obliquity of the star
reaches its maximum when the system is in the Cassini regime where planets have
more angular momentum than the star, and where the precession rate of the star
is similar to that of the planets induced by the companion. In that case,
spin-orbit oscillations exceed twice the inclination between the planets and
the companion. Even if mutual inclination is only ~ 20 deg, this resonant case
can cause the spin-orbit angle to oscillate between perfectly aligned and
retrograde values.Comment: 29 pages, 15 figures, accepted for publication in Ap
Mergers and Obliquities in Stellar Triples
Many close stellar binaries are accompanied by a far-away star. The
"eccentric Kozai-Lidov" (EKL) mechanism can cause dramatic inclination and
eccentricity fluctuations, resulting in tidal tightening of inner binaries of
triple stars. We run a large set of Monte-Carlo simulations including the
secular evolution of the orbits, general relativistic precession and tides, and
we determine the semimajor axis, eccentricity, inclination and spin-orbit angle
distributions of the final configurations. We find that the efficiency of
forming tight binaries (<~16 d) when taking the EKL mechanism into account is ~
21%, and about 4% of all simulated systems ended up in a merger event. These
merger events can lead to the formation of blue-stragglers. Furthermore, we
find that the spin-orbit angle distribution of the inner binaries carries a
signature of the initial setup of the system, thus observations can be used to
disentangle close binaries' birth configuration. The resulting inner and outer
final orbits' period distributions, and their estimated fraction, suggests
secular dynamics may be a significant channel for the formation of close
binaries in triples and even blue stragglers.Comment: Accepted to ApJ, 10 figure
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