M stars are ideal targets to search for Earth-like planets .
However , they usually have high levels of magnetic activity , which could affect their habitability and make difficult the detection of exoplanets orbiting around them .
Unfortunately , long-term variability of dM stars has not been extensively studied , due to their low intrinsic brightness .
For this reason , in 1999 we started the HK \alpha project , which systematically observes the spectra of a large number of stars , in particular dM stars , at the Complejo Astronómico El Leoncito ( CASLEO ) .
In this work , we study the long-term activity of the young active dM1 star AU Microscopii .
We analyze the Mount Wilson index S derived from CASLEO spectra obtained between 2004 and 2016 , which we complement with the S -index derived from HARPS , FEROS and UVES public spectra .
We also analyze the simultaneous photometric counterpart provided by the ASAS public database for this star between 2000 and 2009 , and our own photometry .
In both totally independent time series , we detect a possible activity cycle of period \sim 5 years .
We also derived a precise rotation period for this star P _ { rot } = 4.85 days , consistent with the literature .
This activity cycle reflects that an \alpha \Omega dynamo could be operating in this star .