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In recent years, the scientific community has made significant progress in researching exoplanets, with a particular focus on characterizing their atmospheres. One promising method for achieving this is through the use of the chromatic Rossiter-McLaughlin (CRM) effect. This technique relies on the fact that a planetary atmosphere has different scale-heights depending on its composition and the wavelength of light it is observed in. By measuring the Rossiter-McLaughlin effect, which is highly dependent on the ratio between the planet and stellar radius, we can obtain the broadband transmission spectra of the exoplanets.
However, there are challenges associated with using the CRM effect, including the need for a precise understanding of the system architecture and velocity map of the stellar surface. With current state-of-the-art spectrometers achieving a precision of less than 1 m/s, it is essential to consider phenomena previously referred to as "second-order" , such as differential rotation and center-to-limb variations, which are caused by the granular structure of the stellar surface.
To address these challenges, the Spot Oscillation And Planet code (SOAP) is being improved to model the stellar surface in both the radial velocity and spectral domains while accounting for these effects. These developments aim to improve the accuracy of the CRM effect and reduce biases in broadband transmission spectra measurements.
Preliminary testing of the improved SOAP model in the RV domain using ESPRESSO data of HD 189733 has yielded promising results. With further refinements to the SOAP code and the commissioning of dedicated solar telescopes such as PoET, we can continue to improve our understanding of exoplanet atmospheres and their composition as well as their host stars.
Paulo Brás, Paulo Silva, Jaime Silva