Khaled Al Moulla
IA

Abstract
The radial velocity (RV) technique for detecting exoplanets has in recent years been limited in its applicability to search for Earth-mass planets due to their small semi-amplitudes relative to the intrinsic variability of their host stars. In this talk, I will present the signatures of stellar activity in high-resolution optical and near-infrared (NIR) spectral time series of the Sun, observed with HELIOS—the solar telescope connected to the HARPS and NIRPS spectrographs—and the HARPS-N solar telescope. In the search for optimal tracers of stellar variability, crucial for the identification of planet-mimicking signals, I investigate the chromatic impact of magnetic activity on the RV. Specifically, I extract a proxy for the unsigned magnetic flux (UMF), previously shown to be an excellent activity indicator at optical wavelengths. The advantage of the UMF is that it relies on the Zeeman effect of magnetically sensitive lines, making it applicable to any spectral type and wavelength range with sufficient spectral information. This potentially universal activity indicator could be of great importance for the NIR, where there are currently few established indicators, and for the upcoming PoET solar telescope which will provide disk-resolved observations of, e.g., magnetically active surface regions whose contribution to the disk-integrated RV is an essential piece of information toward achieving extreme velocimetric precision.

2025 May 09, 13:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto