Spectral Ratio Analysis: probing of a new suite of stellar activity indicators as a tool for astrophysical noise mitigation

Stellar activity is the main barrier to detecting and/or confirming low-mass/long-period (and Earth-analogue) planets using radial-velocity (RV) measurements. Searching forreliable indicatorsthat bettertrace magnetic activity may be key for both distinguishing more clearly between stellar and planetary signals, and for probing the underlying physics occurring on the stellar surface. In this work we have compared observations taken for magnetically active and inactive stellar phases over multiple time-scales to study the spectral imprint due to varying stellar activity. This serves as a proof-of-concept demonstration of a technique (named Spectral Ratio Analysis, SRA) that can be used to isolate activity-driven changes directly in the stellar photospheric absorption lines where RVs are measured. Using 14 relatively quiet and well sampled G- and K-type starsthatshow stellar activity cycles, we identified hundreds of activity-sensitive spectral features. Reducing this variability information into two global metrics – amplitude and velocity shift – uncovers potential evidence of a decoupling of the photospheric and chromospheric responsesto stellar activity in earlier-type stars. Additionally, potential signatures of the variations in the magnitude of the suppression of the convective blueshift throughout the activity cycle were observed via SRA. Finally, we show that these SRA indicators better capture RV variability than classical activity proxies, such as the chromospheric log R HK index and other cross-correlation function-based parameters such as bisector span and full width at half-maximum, by up to a factor of two. The direct link between photospheric line behaviour and stellar-induced RV variability offers a promising path for improving astrophysical noise mitigation. In these files you will find for each star a .fits file in which the seasonal and nightly difference spectra and its associated SDATemplate are given per order. Their respective errors have been added as well. Finally, the wavelength for each order, as well as the seasonal and nightly bjd of each observation and its measured logRHK are availbale in these files.Additionally, a .txt file have been added for each star showing the atlas of all the SDA detected features. The wavelength of each feature, its amplitude, its width and its potentially associated lines obtained from VALD are given in these files.