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Rossiter-McLaughlin Observations of WASP-13b, WASP-32b and WASP-37b
R. D. Brothwell1, C. A. Watson1 et al.
1Astrophysic

s Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast, BT7 1NN

Introduction & Background
The Rossiter-McLaughlin (RM) effect can be used to measure the projected spin-orbit alignment () of a planetary system. Hot-Jupiters are known to arrive at their short-period orbits either via dynamically gentle planet-disc interactions1 or more dynamically violent gravitational interactions2. Measuring for an ensemble of hotJupiters is thought to provide clues on the dynamical history of hot-Jupiters. A Lomb-Scargle periodogram analysis of WASP-32 SuperWASP data revealed a stellar rotation period of Prot=11.6Б1.0 days. Combined with the measured , and planetary inclination, the 3D alignment angle, , was measured, where =11АБ14А. WASP-37b Due to weather constraints only a halftransit was observed, meaning a weak constraint on the misalignment angle was found. The modeled . Further observations are required to constrain .
Host Star: Teff=5800K and vsini=2.4Б1.6 km s-1

Results
High resolution spectroscopy for all targets was obtained using SOPHIE at the Observatoire Haute Provence (OHP), France. The RM effect was modeled using the OTS model3 and the orbit was fitted simultaneously assuming a Keplerian orbit. Photometric parameters derived from transits were used as priors in the fits and an MCMC analysis was used to derive system parameters. WASP-13b WASP-13b orbits a G1V type star and is a slow rotator. The modeled RM effect indicates WASP-13b is aligned with and orbits in a prograde sense.

Plotting against convective alignment timescale, ce, for `cool' host stars5 (Teff<6150K) indicates tides likely play a role in damping the obliquities of hot-Jupiters6,7. Aligned systems preferentially have a shorter tidal dissipation timescale relative to the misaligned hotJupiter population. The equivalent distribution is not observed around hot host stars dominated by a radiative envelope.



Host Star: Teff=5989K and vsini=5.7Б0.4 km s-1

WASP-32b

Host Star: Teff=6100K and vsini=3.9Б0.5 km s-1

WASP-32b has previously been modeled4 and our measurement provides an independent verification of using new transit RV data. The modeled supporting spin-orbit alignment. WASP-32b is a massive exoplanet (Mp>3MJ) indicating it is possible for massive planets to realign around relatively hot host stars.

(Plot of || against a quantity proportional to the sixth root of the tidal dissipation timescale (chosen for plotting convenience). The convective mass for each system was derived using the EZ-Web stellar evolution code8. Systems with measured ages are shown as purple triangle symbols and those with an assumed age of 4 Gyrs are shown as green square symbols. WASP-13b and WASP-32b are shown as starred symbols on the plot.)



Conclusions
З WASP-13b is an aligned, prograde planetary system З WASP-32b alignment supported and measured 3D alignment angle indicates WASP-32b is unambiguously aligned З Planet-star tidal interactions perhaps important in aligning planets orbiting cool host stars.
Contact: Email:

References:
[1] Goldreich P., Tremaine S., 1980, ApJ, 241, 425 [2] Kozai Y., 1962, ApJ, 67, 591 [3] Ohta Y., Taruya A., Suto Y., 2005, ApJ, 622, 1118 [4] Brown D. J. A. et al., 2012, ApJ, 760, 139 [5] Brothwell R. D. et al., 2014, MNRAS accepted

[6] Albrecht S., Winn J. N., Marcy G. W., Howard A. W., Isaacson H., Johnson J. A., 2013, ApJ, 771, 11 [7] Winn J. N. et al., 2010, ApJ, 718, L145 [8] R. Townsend's EZ-Web stellar evolution code: http://www.astro.wisc.edu/ townsend/static.php?ref=ez-web

Ryan Brothwell Astrophysics Research Centre School of Mathematics & Physics Queen's University Belfast Belfast BT7 1NN

rbrothwell01@qub.ac.uk