Context : Red giant branch ( RGB ) stars are very bright objects in galaxies and are often used as standard candles .
Interferometry is the ideal tool to characterize the dynamics and morphology of their atmospheres .

Aims : We aim at precisely characterising the surface dynamics of a sample of RGB stars .

Methods : We obtained interferometric observations for three RGB stars with the MIRC instrument mounted at the CHARA interferometer .
We looked for asymmetries on the stellar surfaces using limb-darkening models .

Results : We measured the apparent diameters of HD197989 ( \epsilon Cyg ) = 4.61 \pm 0.02 mas , HD189276 ( HR7633 ) = 2.95 \pm 0.01 mas , and HD161096 ( \beta Oph ) = 4.43 \pm 0.01 mas .
We detected departures from the centrosymmetric case for all three stars with the tendency of a greater effect for lower log g of the sample .
We explored the causes of this signal and conclude that a possible explanation to the interferometric signal is the convection-related and/or the magnetic-related surface activity .
However , it is necessary to monitor these stars with new observations , possibly coupled with spectroscopy , in order to firmly establish the cause .

Conclusions :