Invited Speaker 1 : Ignasi Ribas
Affiliation: Institute of Space Sciences (ICE, CSIC) & Institut d’Estudis Espacials de Catalunya (IEEC)
Talk Title: The Star Is the Signal: Taming Stellar Activity to Reveal Sun–Earth Analogues
Abstract: Extreme-precision radial velocity (RV) instruments, such as ESPRESSO, have now achieved long-term stability at the 10 cm s⁻¹ level. In principle, this level of precision enables the detection and characterisation of small rocky planets, including true Sun–Earth analogues. In practice, however, intrinsic stellar variability often exceeds instrumental noise and becomes the dominant source of uncertainty, even for relatively quiet stars like the Sun. In this talk, I will examine the impact of stellar activity on RV planet detection and describe ongoing efforts to mitigate its effects. I will highlight recent advances, emerging physical insights, and the key challenges that remain. The overarching goal is clear: to reach the level of performance required to robustly detect and confirm true exo-Earths.
Invited Speaker 2 : Dainis Dravins
Affiliation: Lund Observatory, Lund University, Sweden
Talk Title: Radial-velocity microvariability of the Sun and solar-type stars
Abstract: Detections of exoEarths around solar-type stars remain elusive because of physical variability in the host star which overwhelms the tiny signal from any small exoplanet. Different absorption lines have disparate responses to stellar activity, which should permit to disentangle wavelength shifts induced by exoplanets from those originating in stellar atmospheres. 3-D hydrodynamic modeling of magnetic and non-magnetic solar surface convection, followed by computations of high-resolution spectra during successive simulation timesteps, yields time-resolved movies of synthetic spectral atlases. Non-magnetic granulation produces asymmetric spectral lines and convective blueshifts whose radial velocities jitter by about +-2 m/s for the full solar disk. Different lines jitter in phase, but amplitudes differ by about one tenth of their values: greater for stronger and ionized lines, decreasing at longer wavelengths. Lines in magnetic granulation reflect dampened velocities, smaller asymmetries, and even display redshifts, since hot and bright elements are created through adiabatic compression when rising gas turns over into magnetically channelled downflows. New instruments for the study of the Sun-as-a-star, such as PoET at the ESPRESSO spectrometer at ESO in Chile, should enable new tests of magnetohydrodynamic models. What is currently least understood, and in need of modeling, are the causes and effects of supergranulation, whose extended timescales may overlap those of expected exoplanet modulation.