Obliquity Constraints on an Extrasolar Planetary-Mass Companion. (arXiv:2002.11131v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bryan_M/0/1/0/all/0/1">Marta L. Bryan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chiang_E/0/1/0/all/0/1">Eugene Chiang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bowler_B/0/1/0/all/0/1">Brendan P. Bowler</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Morley_C/0/1/0/all/0/1">Caroline V. Morley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Millholland_S/0/1/0/all/0/1">Sarah Millholland</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blunt_S/0/1/0/all/0/1">Sarah Blunt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ashok_K/0/1/0/all/0/1">Katelyn B. Ashok</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nielsen_E/0/1/0/all/0/1">Eric Nielsen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ngo_H/0/1/0/all/0/1">Henry Ngo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mawet_D/0/1/0/all/0/1">Dimitri Mawet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knutson_H/0/1/0/all/0/1">Heather A. Knutson</a>
We place the first constraints on the obliquity of a planetary-mass companion
(PMC) outside of the Solar System. Our target is the directly imaged system
2MASS J01225093-2439505 (2M0122), which consists of a 120 Myr 0.4 M_sun star
hosting a 12-27 M_J companion at 50 AU. We constrain all three of the system’s
angular momentum vectors: how the companion spin axis, the stellar spin axis,
and the orbit normal are inclined relative to our line of sight. To accomplish
this, we measure projected rotation rates (vsini) for both the star and the
companion using new near-infrared high-resolution spectra with NIRSPEC at Keck
Observatory. We combine these with a new stellar photometric rotation period
from TESS and a published companion rotation period from HST to obtain spin
axis inclinations for both objects. We also fitted multiple epochs of
astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b’s
orbital inclination. The three line-of-sight inclinations place limits on the
true de-projected companion obliquity and stellar obliquity. We find that while
the stellar obliquity marginally prefers alignment, the companion obliquity
tentatively favors misalignment. We evaluate possible origin scenarios. While
collisions, secular spin-orbit resonances, and Kozai-Lidov oscillations are
unlikely, formation by gravitational instability in a gravito-turbulent disk –
the scenario favored for brown dwarf companions to stars – appears promising.
We place the first constraints on the obliquity of a planetary-mass companion
(PMC) outside of the Solar System. Our target is the directly imaged system
2MASS J01225093-2439505 (2M0122), which consists of a 120 Myr 0.4 M_sun star
hosting a 12-27 M_J companion at 50 AU. We constrain all three of the system’s
angular momentum vectors: how the companion spin axis, the stellar spin axis,
and the orbit normal are inclined relative to our line of sight. To accomplish
this, we measure projected rotation rates (vsini) for both the star and the
companion using new near-infrared high-resolution spectra with NIRSPEC at Keck
Observatory. We combine these with a new stellar photometric rotation period
from TESS and a published companion rotation period from HST to obtain spin
axis inclinations for both objects. We also fitted multiple epochs of
astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b’s
orbital inclination. The three line-of-sight inclinations place limits on the
true de-projected companion obliquity and stellar obliquity. We find that while
the stellar obliquity marginally prefers alignment, the companion obliquity
tentatively favors misalignment. We evaluate possible origin scenarios. While
collisions, secular spin-orbit resonances, and Kozai-Lidov oscillations are
unlikely, formation by gravitational instability in a gravito-turbulent disk –
the scenario favored for brown dwarf companions to stars – appears promising.
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