TY - JOUR

T1 - Tidally Distorted Exoplanets: Density Corrections for Short-period Hot-Jupiters Based Solely on Observable Parameters

AU - Burton, J. R.

AU - Watson, Christopher

AU - Fitzsimmons, A.

AU - Pollacco, D.

AU - Moulds, V.

AU - Littlefair, S. P.

AU - Wheatley, P. J.

PY - 2014/7/10

Y1 - 2014/7/10

N2 - The close proximity of short-period hot-Jupiters to their parent star
means they are subject to extreme tidal forces. This has a profound
effect on their structure and, as a result, density measurements that
assume that the planet is spherical can be incorrect. We have simulated
the tidally distorted surface for 34 known short-period hot-Jupiters,
assuming surfaces of constant gravitational equipotential for the
planet, and the resulting densities have been calculated based only on
observed parameters of the exoplanet systems. Comparing these results to
the density values, assuming the planets are spherical, shows that there
is an appreciable change in the measured density for planets with very
short periods (typically less than two days). For one of the
shortest-period systems, WASP-19b, we determine a decrease in bulk
density of 12% from the spherical case and, for the majority of systems
in this study, this value is in the range of 1%-5%. On the other hand,
we also find cases where the distortion is negligible (relative to the
measurement errors on the planetary parameters) even in the cases of
some very short period systems, depending on the mass ratio and
planetary radius. For high-density gas planets requiring apparently
anomalously large core masses, density corrections due to tidal
deformation could become important for the shortest-period systems.

AB - The close proximity of short-period hot-Jupiters to their parent star
means they are subject to extreme tidal forces. This has a profound
effect on their structure and, as a result, density measurements that
assume that the planet is spherical can be incorrect. We have simulated
the tidally distorted surface for 34 known short-period hot-Jupiters,
assuming surfaces of constant gravitational equipotential for the
planet, and the resulting densities have been calculated based only on
observed parameters of the exoplanet systems. Comparing these results to
the density values, assuming the planets are spherical, shows that there
is an appreciable change in the measured density for planets with very
short periods (typically less than two days). For one of the
shortest-period systems, WASP-19b, we determine a decrease in bulk
density of 12% from the spherical case and, for the majority of systems
in this study, this value is in the range of 1%-5%. On the other hand,
we also find cases where the distortion is negligible (relative to the
measurement errors on the planetary parameters) even in the cases of
some very short period systems, depending on the mass ratio and
planetary radius. For high-density gas planets requiring apparently
anomalously large core masses, density corrections due to tidal
deformation could become important for the shortest-period systems.

KW - planets and satellites: atmospheres

KW - planets and satellites: fundamental parameters

U2 - 10.1088/0004-637X/789/2/113

DO - 10.1088/0004-637X/789/2/113

M3 - Article

VL - 789

SP - 113

JO - The Astrophysical Journal

JF - The Astrophysical Journal

SN - 0004-637X

IS - 2

ER -