Signatures of Obliquity in Thermal Phase Curves of Hot Jupiters. (arXiv:1906.07615v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Adams_A/0/1/0/all/0/1">Arthur D. Adams</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:+Laughlin_G/0/1/0/all/0/1">Gregory P. Laughlin</a>
Recent work suggests that many short-period extrasolar planets may have spin
obliquities that are significantly tilted with respect to their orbital planes.
These large obliquities are a natural outcome of “secular spin-orbit
resonance”, a configuration in which the planetary spin precession frequency
matches the frequency of orbit nodal regression, or a Fourier component
thereof. While exoplanet spin obliquities have not yet been measured directly,
they may be detectable indirectly through their signatures in various
observations, such as photometric measurements across the full phase of a
planet’s orbit. In this work, we employ a thermal radiative model to explore
how large polar tilts affect full-phase light curves, and we discuss the range
of unique signatures that are expected to result. We show that the well-studied
short-period planets HD 149026 b, WASP-12 b, and CoRoT-2 b all exhibit phase
curve features that may arise from being in high-obliquity states. We also
constrain the parameters and assess the detectability of hypothetical
perturbing planets that could maintain the planets in these states. Among the
three planets considered, CoRoT-2 b has the tightest constraints on its
proposed obliquity ($45.8^{circ} pm 1.4^{circ}$) and axial orientation. For
HD 149026 b, we find no significant evidence for a non-zero obliquity, and the
phase curve of WASP-12 b is too complicated by strong tidal distortions for a
conclusive assessment.
Recent work suggests that many short-period extrasolar planets may have spin
obliquities that are significantly tilted with respect to their orbital planes.
These large obliquities are a natural outcome of “secular spin-orbit
resonance”, a configuration in which the planetary spin precession frequency
matches the frequency of orbit nodal regression, or a Fourier component
thereof. While exoplanet spin obliquities have not yet been measured directly,
they may be detectable indirectly through their signatures in various
observations, such as photometric measurements across the full phase of a
planet’s orbit. In this work, we employ a thermal radiative model to explore
how large polar tilts affect full-phase light curves, and we discuss the range
of unique signatures that are expected to result. We show that the well-studied
short-period planets HD 149026 b, WASP-12 b, and CoRoT-2 b all exhibit phase
curve features that may arise from being in high-obliquity states. We also
constrain the parameters and assess the detectability of hypothetical
perturbing planets that could maintain the planets in these states. Among the
three planets considered, CoRoT-2 b has the tightest constraints on its
proposed obliquity ($45.8^{circ} pm 1.4^{circ}$) and axial orientation. For
HD 149026 b, we find no significant evidence for a non-zero obliquity, and the
phase curve of WASP-12 b is too complicated by strong tidal distortions for a
conclusive assessment.
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