# Ross 128 -- GL 447A possible activity cycle for a slow-rotating fully-convective star

## TL;DR

This study investigates the magnetic activity cycle of Ross 128, a slow-rotating fully convective star, revealing a potential 5-year cycle through analysis of spectral activity indicators over 14 years.

## Contribution

First detection of a possible 5-year activity cycle in a slow-rotating fully convective star, providing insights into stellar dynamo processes.

## Key findings

- Identified a potential 5-year activity cycle in Ross 128.
- Demonstrated long-term magnetic activity analysis using multiple spectral indices.
- Provided observational evidence for dynamo theories in low-mass stars.

## Abstract

Context. Long-term chromospheric activity in slow-rotating fully-convective stars has been scarcely explored. Ross 128 (Gl 447) is a slow-rotator and inactive dM4 star which has been extensively observed. It hosts the fourth closest extrasolar planet. Aims. Ross 128 is an ideal target to test dynamo theories in slow-rotating low-mass star. Methods. To characterize the magnetic activity of Ross 128 we study the SK indexes derived from CASLEO, HARPS, FEROS, UVES and XSHOOTER spectra. Using the Generalized Lomb-Scargle and CLEAN periodograms, we analyze the whole SK time-series obtained between 2004 and 2018. We perform a similar analysis for the Na I index and we analyze its relation with the SK-index. Results. From both indexes, we obtain a possible activity cycle with a 5-year period, which is one of a small handful of activity cycles reported for a slow-rotating fully convective star.