Constraints on the Atmospheric Circulation and Variability of the Eccentric Hot Jupiter XO-3b

TL;DR

This study uses twelve years of Spitzer data to analyze the atmospheric circulation, variability, and orbital dynamics of the eccentric hot Jupiter XO-3b, providing new constraints on its precession and brightness changes.

Contribution

It presents the most precise measurements of XO-3b's secondary eclipses, constrains its orbital precession rate, and assesses brightness variability over multiple years.

Findings

Secondary eclipse depth of 0.1580% with high precision.

Upper limit on brightness variability of 0.05%.

Tightest constraints on orbital precession rate for a hot Jupiter.

Abstract

We report secondary eclipse photometry of the hot Jupiter XO-3b in the 4.5~$\mu$m band taken with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We measure individual eclipse depths and center of eclipse times for a total of twelve secondary eclipses. We fit these data simultaneously with two transits observed in the same band in order to obtain a global best-fit secondary eclipse depth of $0.1580\pm 0.0036\%$ and a center of eclipse phase of $0.67004\pm 0.00013 $. We assess the relative magnitude of variations in the dayside brightness of the planet by measuring the size of the residuals during ingress and egress from fitting the combined eclipse light curve with a uniform disk model and place an upper limit of 0.05$\%$. The new secondary eclipse observations extend the total baseline from one and a half years to nearly three years, allowing us to place an upper limit on the periastron precession rate of $2.9\times 10^{-3}$ degrees/day the tightest constraint to date on the periastron precession rate of a hot Jupiter. We use the new transit observations to calculate improved estimates for the system properties, including an updated orbital ephemeris. We also use the large number of secondary eclipses to obtain the most stringent limits to date on the orbit-to-orbit variability of an eccentric hot Jupiter and demonstrate the consistency of multiple-epoch Spitzer observations.