The Transit Ingress and the Tilted Orbit of the Extraordinarily Eccentric Exoplanet HD 80606b

TL;DR

This study reports the first detection of the ingress of exoplanet HD 80606b, revealing its highly eccentric and tilted orbit, with evidence of spin-orbit misalignment, supporting theories of complex planetary migration.

Contribution

First detection of transit ingress for HD 80606b, providing precise system parameters and evidence of a significant spin-orbit misalignment in an eccentric exoplanet.

Findings

Transit duration is 11.64 hours with precise measurement.

Projected spin-orbit angle is between 14-87 degrees.

The planet's orbit is highly eccentric and tilted from the star's equatorial plane.

Abstract

We present the results of a transcontinental campaign to observe the 2009 June 5 transit of the exoplanet HD 80606b. We report the first detection of the transit ingress, revealing the transit duration to be 11.64 +/- 0.25 hr and allowing more robust determinations of the system parameters. Keck spectra obtained at midtransit exhibit an anomalous blueshift, giving definitive evidence that the stellar spin axis and planetary orbital axis are misaligned. The Keck data show that the projected spin-orbit angle is between 32-87 deg with 68.3% confidence and between 14-142 deg with 99.73% confidence. Thus the orbit of this planet is not only highly eccentric (e=0.93), but is also tilted away from the equatorial plane of its parent star. A large tilt had been predicted, based on the idea that the planet's eccentric orbit was caused by the Kozai mechanism. Independently of the theory, it is noteworthy that all 3 exoplanetary systems with known spin-orbit misalignments have massive planets on eccentric orbits, suggesting that those systems migrate differently than lower-mass planets on circular orbits.