Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth orbiting $pi$ Men. (arXiv:2007.01871v1 [astro-ph.EP])

Evidence for a high mutual inclination between the cold Jupiter and transiting super Earth orbiting $pi$ Men. (arXiv:2007.01871v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Xuan_J/0/1/0/all/0/1">Jerry W. Xuan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wyatt_M/0/1/0/all/0/1">Mark C. Wyatt</a>

$pi$ Men hosts a transiting super Earth ($Papprox6.27$ d, $mapprox4.82$
$M_{oplus}$, $Rapprox2.04$ $R_{oplus}$) discovered by TESS and a cold
Jupiter ($Papprox2093$ d, $m sin Iapprox10.02$ $M_{rm{Jup}}$,
$eapprox0.64$) discovered from radial velocity. We use Gaia DR2 and Hipparcos
astrometry to derive the star’s velocity caused by the orbiting planets and
constrain the cold Jupiter’s sky-projected inclination ($I_b=41-65^{circ}$).
From this we derive the mutual inclination ($Delta I$) between the two
planets, and find that $49^{circ}< Delta I < 131^{circ}$ (1$sigma$), and
$28^{circ} < Delta I < 152^{circ}$ (2$sigma$). We examine the dynamics of
the system using $N$-body simulations, and find that potentially large
oscillations in the super Earth’s eccentricity and inclination are suppressed
by General Relativistic precession. However, nodal precession of the inner
orbit around the invariable plane causes the super Earth to only transit
between 7-22 per cent of the time, and to usually be observed as misaligned
with the stellar spin axis. We repeat our analysis for HAT-P-11, finding a
large $Delta I$ between its close-in Neptune and cold Jupiter and similar
dynamics. $pi$ Men and HAT-P-11 are prime examples of systems where
dynamically hot outer planets excite their inner planets, with the effects of
increasing planet eccentricities, planet-star misalignments, and potentially
reducing the transit multiplicity. Formation of such systems likely involves
scattering between multiple giant planets or misaligned protoplanetary discs.
Future imaging of the faint debris disc in $pi$ Men and precise constraints on
the stellar spin orientation would provide strong tests for these formation
scenarios.

$pi$ Men hosts a transiting super Earth ($Papprox6.27$ d, $mapprox4.82$
$M_{oplus}$, $Rapprox2.04$ $R_{oplus}$) discovered by TESS and a cold
Jupiter ($Papprox2093$ d, $m sin Iapprox10.02$ $M_{rm{Jup}}$,
$eapprox0.64$) discovered from radial velocity. We use Gaia DR2 and Hipparcos
astrometry to derive the star’s velocity caused by the orbiting planets and
constrain the cold Jupiter’s sky-projected inclination ($I_b=41-65^{circ}$).
From this we derive the mutual inclination ($Delta I$) between the two
planets, and find that $49^{circ}< Delta I < 131^{circ}$ (1$sigma$), and
$28^{circ} < Delta I < 152^{circ}$ (2$sigma$). We examine the dynamics of
the system using $N$-body simulations, and find that potentially large
oscillations in the super Earth’s eccentricity and inclination are suppressed
by General Relativistic precession. However, nodal precession of the inner
orbit around the invariable plane causes the super Earth to only transit
between 7-22 per cent of the time, and to usually be observed as misaligned
with the stellar spin axis. We repeat our analysis for HAT-P-11, finding a
large $Delta I$ between its close-in Neptune and cold Jupiter and similar
dynamics. $pi$ Men and HAT-P-11 are prime examples of systems where
dynamically hot outer planets excite their inner planets, with the effects of
increasing planet eccentricities, planet-star misalignments, and potentially
reducing the transit multiplicity. Formation of such systems likely involves
scattering between multiple giant planets or misaligned protoplanetary discs.
Future imaging of the faint debris disc in $pi$ Men and precise constraints on
the stellar spin orientation would provide strong tests for these formation
scenarios.

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