On Activity and Planets of Low-Mass Stars

Over the past 30 years, thousands of planetary systems have been discovered, mainly around lowmass stars (Mstar <1.2 MSun). The two primary methods used for this purpose are the transit and radial
velocity (RV) technique. The former is sensitive to the planet's size, while the latter is sensitive to the
planet’s mass, and together they enable the estimation of the planet’s density and, in some cases, even
its atmospheric composition. However, stellar activity remains the primary factor limiting the detection
and characterization of many more planets around nearby stars. The CARMENES instrument and
survey were designed to address this challenge. It has been ten years since CARMENES opened its
two spectroscopic eyes at the Calar-Alto observatory, and I will review its achievements.
In the last 6 years, my research group at Ariel University has been developing tools to discriminate
activity from planets in high-resolution spectroscopic timeseries. Fortunately, activity-related variability
differs from orbital Doppler shifts: it is usually incoherent, wavelength-dependent, and accompanied by
variations in spectral shape. These differences can help us distinguish between activity-related and
planetary signals, allowing us to model both phenomena simultaneously. We developed diagnostic
tools, such as activity-index measurements and Gaussian Process (GP) periodogram analysis, and
performed complementary photometric measurements. Additional tools are being developed to
characterize transiting planets in terms of their internal structure and atmospheric composition. I will
briefly review these efforts.