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 $ 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 Boué model for the Rossiter-McLaughlin effect consistently underestimates the value of v sin I$_s$ compared to the Hirano model. Although v sin I$_s$ differed, the effect on $ 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 ($ =4.0deg$$+17.1$$$$-18.4$$), WASP-71 b ($ =-1.9deg$$+7.1$$$$-7.5$$), and WASP-78 b ($ = -6.4deg plusmn 5.9) are aligned. WASP-62 b ($ =19.4deg$$+5.1$$$$ -4.9$$) is found to be slightly misaligned, while WASP-79 b ($ =-95.2deg$$+0.9$$$$ -1.0$$) 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 $ direction.