Spin–Orbit Misalignments of Three Jovian Planets via Doppler Tomography

Spin–Orbit Misalignments of Three Jovian Planets via Doppler Tomography

Authors:

Johnson et al

Abstract:
We present measurements of the spin–orbit misalignments of the hot Jupiters HAT-P-41 b and WASP-79 b, and the aligned warm Jupiter Kepler-448 b. We obtain these measurements with Doppler tomography, where we spectroscopically resolve the line profile perturbation during the transit due to the Rossiter–McLaughlin effect. We analyze time series spectra obtained during portions of five transits of HAT-P-41 b, and find a value of the spin–orbit misalignment of $\lambda =-{22.1}_{-6.0}^{{+0.8}^{^\circ }}$. We reanalyze the radial velocity Rossiter–McLaughlin data on WASP-79 b obtained by Addison et al. using Doppler tomographic methodology. We measure $\lambda =-{99.1}_{-3.9}^{{+4.1}^{^\circ }}$, consistent with but more precise than the value found by Addison et al. For Kepler-448 b we perform a joint fit to the Kepler light curve, Doppler tomographic data, and a radial velocity data set from Lillo-Box et al. We find an approximately aligned orbit ($\lambda =-{7.1}_{-2.8}^{{+4.2}^{^\circ }}$), in agreement with the value found by Bourrier et al. Through analysis of the Kepler light curve we measure a stellar rotation period of ${P}_{\mathrm{rot}}=1.27\pm 0.11$ days, and use this to argue that the full three-dimensional spin–orbit misalignment is small, $\psi \sim 0^\circ $.

Rossiter-McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems

Rossiter-McLaughlin models and their effect on estimates of stellar rotation, illustrated using six WASP systems

Authors:

brown et al

Abstract:

We present new measurements of the projected spin–orbit angle λ for six WASP hot Jupiters, four of which are new to the literature (WASP-61, -62, -76, and -78), and two of which are new analyses of previously measured systems using new data (WASP-71, and -79). We use three different models based on two different techniques: radial velocity measurements of the Rossiter-McLaughlin effect, and Doppler tomography. Our comparison of the different models reveals that they produce projected stellar rotation velocities (vsin Is) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boué model for the Rossiter-McLaughlin effect consistently underestimates the value of vsin Is compared to the Hirano model. Although vsin Is differed, the effect on λ was small for our sample, with all three methods producing values in agreement with each other. Using Doppler tomography, we find that WASP-61 b (λ=4.0∘+17.1−18.4), WASP-71 b (λ=−1.9∘+7.1−7.5), and WASP-78 b (λ = −6.4° ± 5.9) are aligned. WASP-62 b (λ=19.4∘+5.1−4.9) is found to be slightly misaligned, while WASP-79 b (λ=−95.2∘+0.9−1.0) is confirmed to be strongly misaligned and has a retrograde orbit. We explore a range of possibilities for the orbit of WASP-76 b, finding that the orbit is likely to be strongly misaligned in the positive λ direction.

Using WASP-79b to Explain Hot-jupiter Spin-Orbit Misalignment

Planets in Spin-Orbit Misalignment and the Search for Stellar Companions

Authors:

Addison et al

Abstract:

The discovery of giant planets orbiting close to their host stars was one of the most unexpected results of early exoplanetary science. Astronomers have since found that a significant fraction of these 'Hot Jupiters' move on orbits substantially misaligned with the rotation axis of their host star. We recently reported the measurement of the spin-orbit misalignment for WASP-79b by using data from the 3.9 m Anglo-Australian Telescope. Contemporary models of planetary formation produce planets on nearly coplanar orbits with respect to their host star's equator. We discuss the mechanisms which could drive planets into spin-orbit misalignment. The most commonly proposed being the Kozai mechanism, which requires the presence of a distant, massive companion to the star-planet system. We therefore describe a volume-limited direct-imaging survey of Hot Jupiter systems with measured spin-orbit angles, to search for the presence of stellar companions and test the Kozai hypothesis.