Spin-orbit misalignments, planet candidate validation, and nodal precession via Doppler tomography




Johnson, Marshall Caleb

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Transiting planets around intermediate-mass stars (1.5 MSun < M* < 2.5MSun , or 6500 K < Teff < 10000 K on the main sequence) occupy a largely unexplored part of parameter space; these stars tend to rotate rapidly, and thus are unsuitable for the precise radial velocity observations that are typically used to follow up and confirm transiting planet candidates. In this dissertation I demonstrate the use of Doppler tomography, where I spectroscopically resolve the perturbation to the rotationally broadened stellar line profile during the transit due to the Rossiter-McLaughlin effect, to confirm transiting planet candidates around rapidly-rotating stars and to measure the (mis)alignment of the planetary orbit with respect to the stellar rotation. The demographics of planets around intermediate-mass stars are important for constraining models of planet formation as a function of stellar mass, while the distribution of spin-orbit misalignments of transiting planets is a powerful statistical tracer of planet migration processes. Using Doppler tomography, I show that the hot Jupiter Kepler-13 Ab has a misaligned but prograde orbit; I improve upon the precision of the misalignment measurement for the hot Jupiter WASP-79 b, which has a nearly polar orbit; and I measure an aligned orbit for the warm Jupiter Kepler-448 b, and two degenerate solutions (both prograde) for the hot Jupiter HAT-P-41 b. I also analyze observations of several Kepler planet candidates–KOI-366.01, KOI-368.01, and KOI-972.01–in an attempt to validate them as bona fide planets. Unfortunately, due to small planetary radii and/or limited amounts of data, I am able to achieve only a ∼ 2σ detection of KOI-368.01, and am unable to detect KOI-366.01 or KOI-972.01. I also analyze two epochs of Doppler tomographic observations of the highly inclined hot Jupiter WASP-33 b taken six years apart, and show that the path of the transit across the stellar disk has changed between the two epochs due to nodal precession of the planetary orbit. This allows me to measure the precession rate, and constrain the stellar gravitational quadrupole moment J2. Overall, I show that Doppler tomography is an effective tool for confirming and characterizing transiting planets around rapidly-rotating stars, where typical methods have difficulty.



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