Multi-Epoch precise photometry from the ground: MUDEHaR, magnetic stars and everything around

MUDEHaR is an on-going multi-epoch photometric survey with two narrow filters in H$\alpha$ and the calcium triplet window that uses the T80Cam wide-field imager at the JAST/T80 telescope at Spanish Javalambre astronomical observatory. It is obtaining 100 epochs/year per field for 20 fields in the Galactic disk, each of 2\,deg$^2$, for a total of 40\,deg$^2$. Focused on stellar clusters and HII regions including bright stars, its main objective is to detect tens of thousands OB stars that present emission variability in H$\alpha$ on days-months-years scale. The observed targets include magnetic massive stars, pulsating stars, and all kinds of variable stars. Among our driving scientific objectives of MUDEHaR observations is to identify potential magnetic candidates in massive stars. Only 10--20\,\% of OB stars display a measurable magnetic field, and its origin is still in debate. We outline here the multi-step process involved in identifying OB magnetic stars, highlighting the significance of MUDEHaR observations in this process.