Determining Exoplanetary Oblateness Using Transit Depth Variations

Abstract

The measurement of an exoplanet's oblateness and obliquity provides insights into the planet's internal structure and formation history. Previous work using small differences in the shape of the transit light curve has been moderately successful, but was hampered by the small signal and extreme photometric precision required. The measurement of changes in transit depth, caused by the spin precession of an oblate planet, was proposed as an alternative method. Here, we present the first attempt to measure these changes. Using Kepler photometry, we examined the brown dwarf Kepler-39b and the warm Saturn Kepler-427b. We could not reliably constrain the oblateness of Kepler-39b. We find transit depth variations for Kepler-427b at $90.1\%$ significance ($1.65\sigma$) consistent with a precession period of $P_{\mathrm{prec}}=5.45_{-0.37}^{+0.46}\mathrm{years}$ and an oblateness, $f=0.19_{-0.16}^{+0.32}$. This oblateness is comparable to Solar System gas giants, and would raise questions about the dynamics and tidal synchronization of Kepler-427b.

20 pages, 14 figures, accepted for publication in AJ

References in corpus (8)

• The Transiting Exoplanet Survey Satellite
• The K2 Mission: Characterization and Early results
• Rotation periods and ages of solar analogs and solar twins revealed by the Kepler Mission
• Constraining the Oblateness of Kepler Planets
• Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star
• Improved parameters of seven Kepler giant companions characterized with SOPHIE and HARPS-N
• The Ratio of Retrograde to Prograde Orbits: A Test for Kuiper Belt Binary Formation Theories
• Characterization of the four new transiting planets KOI-188b, KOI-195b, KOI-192b, and KOI-830b