Cyclic activity in dM Stars

MAUAS, P.; BUCCINO, A.; PETRUCCI, R.; VIEYTES, M; JOFRÉ, E.

Madrid

Workshop; 17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun; 2012

Due to their low masses, dM stars are primary targets to search for terrestrial planets. However, they tend to be more active than earlier type stars, a fact which can hinder the detection of orbiting planets. Furthermore, the levels of UV radiation, which are strongly related to stellar activity, can also limit the habitability. These facts make the analysis of activity in M stars relevant. The usually accepted model to describe the generation and intensification of magnetic fields in late F- to early M-type stars is the alfaω-dynamo, first invoked to explain solar activity. In this model the large-scale magnetic field generation results from the interaction of differential rotation in the tachocline and the convective turbulence. Since stars with spectral type later than M3 are believed to be fully convective, they should not be able to sustain a solar-like dynamo. To date, activity cycles have been detected in several late-type stars. However, these works are mainly concentrated on F to K stars, since due to the long exposure times needed to observe them, the red and faint M dwarfs are usually not the target of long-term observational studies of stellar activity. As a contribution to this subject, we have developed an observing program dedicated to periodically obtain medium resolution echelle spectra of southern late-type stars, including those stars which are fully-convective. In this work, we summarized our main results on cyclic activity of dM stars.