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

We present new measurements of the projected spin-orbit angle lambda 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 (v sin I-s) measurements often in disagreement with each other and with estimates obtained from spectral line broadening. The Boue model for the Rossiter-McLaughlin effect consistently underestimates the value of v sin I-s compared to the Hirano model. Although v sin Is differed, the effect on lambda 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 (lambda = 4 degrees.0(-18.4)(+17.1)), WASP-71 b (lambda = -1 degrees.9(-7.5)(+7.1)), and WASP-78 b (lambda = -6 degrees.4 +/- 5.9) are aligned. WASP-62 b (lambda = 19 degrees.4(-4.9)(+5.1)) is found to be slightly misaligned, whileWASP-79 b (lambda= -95 degrees.2(-1.0)(+0.9)) 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 lambda direction.