A window on exoplanet dynamical histories: Rossiter–McLaughlin observations of WASP-13b and WASP-32b

• Published in: Monthly notices of the Royal Astronomical Society Vol. 440; no. 4; pp. 3392 - 3401
• Main Authors: Brothwell, R. D., Watson, C. A., Hébrard, G., Triaud, A. H. M. J., Cegla, H. M., Santerne, A., Hébrard, E., Anderson, D. R., Pollacco, D., Simpson, E. K., Bouchy, F., Brown, D. J. A., Chew, Y. Gómez Maqueo, Cameron, A. Collier, Armstrong, D. J., Barros, S. C. C., Bento, J., Bochinski, J., Burwitz, V., Busuttil, R., Delrez, L., Doyle, A. P., Faedi, F., Fumel, A., Gillon, M., Haswell, C. A., Hellier, C., Jehin, E., Kolb, U., Lendl, M., Liebig, C., Maxted, P. F. L., McCormac, J., Miller, G. R. M., Norton, A. J., Pepe, F., Queloz, D., Rodríguez, J., Ségransan, D., Skillen, I., Smalley, B., Stassun, K. G., Udry, S., West, R. G., Wheatley, P. J.
• Format: Journal Article Web Resource
• Language: English
• Published: London Oxford University Press 01.06.2014; Oxford University Press (OUP): Policy P - Oxford Open Option A; Blackwell Publishing
• Subjects: Astrophysics; Aérospatiale, astronomie & astrophysique; Energy dissipation; Extrasolar planets; Orbits; Physical, chemical, mathematical & earth Sciences; Physique, chimie, mathématiques & sciences de la terre; Sciences of the Universe; Solar system; Space science, astronomy & astrophysics; Stars & galaxies; planetary systems; stars: individual: WASP-13; techniques: radial velocities; techniques: photometric; stars: individual: WASP-32
• ISSN: 0035-8711; 1365-2966; 1365-2966
• DOI: 10.1093/mnras/stu520

We present Rossiter–McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis (λ). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of $\lambda =8{^{\circ }}^{+13}_{-12}$ and $\lambda =-2{^{\circ }}^{+17}_{-19}$, respectively. Both WASP-13 and WASP-32 have T eff < 6250 K, and therefore, these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb–Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9 per cent confidence) was identified for the WASP-32 system with P rot = 11.6 ± 1.0 days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, R *, and vsin i if a stellar inclination of i * = 90° is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, ψ, was found to be ψ = 11° ± 14°. We conclude with a discussion on the alignment of systems around cool host stars with T eff < 6150 K by calculating the tidal dissipation time-scale. We find that systems with short tidal dissipation time-scales are preferentially aligned and systems with long tidal dissipation time-scales have a broad range of obliquities.