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@ARTICLE{Breslau:862168,
      author       = {Breslau, Andreas and Pfalzner, Susanne},
      title        = {{C}reating retrogradely orbiting planets by prograde
                      stellar fly-bys},
      journal      = {Astronomy and astrophysics},
      volume       = {621},
      issn         = {1432-0746},
      address      = {Les Ulis},
      publisher    = {EDP Sciences},
      reportid     = {FZJ-2019-02522},
      pages        = {A101 -},
      year         = {2019},
      abstract     = {Several planets have been found that orbit their host star
                      on retrograde orbits (spin–orbit angle φ > 90°).
                      Currently, the largest measured projected angle between the
                      orbital angular momentum axis of a planet and the rotation
                      axis of its host star has been found for HAT-P-14b to be ≈
                      171°. One possible mechanism for the formation of such
                      misalignments is through long-term interactions between the
                      planet and other planetary or stellar companions. However,
                      with this process, it has been found to be difficult to
                      achieve retrogradely orbiting planets, especially planets
                      that almost exactly counter-orbit their host star (φ ≈
                      180°) such as HAT-P-14b. By contrast, orbital misalignment
                      can be produced efficiently by perturbations of planetary
                      systems that are passed by stars. Here we demonstrate that
                      not only retrograde fly-bys, but surprisingly, even prograde
                      fly-bys can induce retrograde orbits. Our simulations show
                      that depending on the mass ratio of the involved stars,
                      there are significant ranges of planetary pre-encounter
                      parameters for which counter-orbiting planets are the
                      natural consequence. We find that the highest probability to
                      produce counter-orbiting planets $(≈20\%)$ is achieved
                      with close prograde, coplanar fly-bys of an equal-mass
                      perturber with a pericentre distance of one-third of the
                      initial orbital radius of the planet. For fly-bys where the
                      pericentre distance equals the initial orbital radius of the
                      planet, we still find a probability to produce retrograde
                      planets of $≈10\%$ for high-mass perturbers on inclined
                      (60° < i < 120°) orbits. As usually more distant fly-bys
                      are more common in star clusters, this means that inclined
                      fly-bys probably lead to more retrograde planets than those
                      with inclinations <60°. Such close fly-bys are in general
                      relatively rare in most types of stellar clusters, and only
                      in very dense clusters will this mechanism play a
                      significant role. The total production rate of retrograde
                      planets depends then on the cluster environment. Finally, we
                      briefly discuss the application of our results to the
                      retrograde minor bodies in the solar system and to the
                      formation of retrograde moons during the planet–planet
                      scattering phase.},
      cin          = {JSC},
      ddc          = {520},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {511 - Computational Science and Mathematical Methods
                      (POF3-511)},
      pid          = {G:(DE-HGF)POF3-511},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000455572100001},
      doi          = {10.1051/0004-6361/201833729},
      url          = {https://juser.fz-juelich.de/record/862168},
}