Reloaded Rossiter-McLaughlin (RRM) Technique

• Reloaded Rossiter-McLaughlin (RRM) is a method that measures the spatially resolved stellar spectrum by scaling and subtracting in-transit and out-of-transit spectra based on the transit light curve.
• It directly extracts local stellar cross-correlation functions, enabling analysis of line shape changes and incorporating differential rotation and centre-to-limb convective blueshift.
• Applications to systems like HD 189733 and WASP-8 demonstrate its potential for probing 3D spin-orbit geometry and revealing biases in traditional RM methods.

The Reloaded Rossiter-McLaughlin (RRM) technique is a Rossiter-McLaughlin (RM) modelling method in which the spatially resolved stellar spectrum behind a transiting planet is measured directly by scaling the continuum flux of the spectra by the transit light curve and subtracting the in-transit spectra from the out-of-transit spectra to isolate the starlight behind the planet (Cegla et al., 2016). In contrast to traditional velocimetric RM analyses, which fit the radial-velocity anomaly of disk-integrated line profiles and generally assume rigid rotation and homogeneous local line shapes, RRM directly extracts local stellar cross-correlation functions (CCFs), permits the analysis of their shape, and can incorporate differential stellar rotation and centre-to-limb variations in the convective blueshift (Cegla et al., 2016). Applications to HD 189733 and WASP-8 established RRM as a method for probing the 3D spin-orbit geometry, differential stellar rotation, and spatially resolved stellar spectra, while also demonstrating that traditional RM analyses can be significantly biased when local CCF contrast or FWHM vary along the transit chord (Cegla et al., 2016, Bourrier et al., 2016).

1. Conceptual basis

The classical RM effect is the apparent radial-velocity anomaly produced when a transiting planet occults different parts of a rotating stellar surface. Since the line-of-sight velocities depend on stellar rotation, the RM waveform is sensitive to the star-planet alignment and has been widely used to estimate the sky-projected spin-orbit angle, $\