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Recent developments in asteroseismology -- thanks to space-based missionssuch as {\it CoRoT} and {\it Kepler} -- provide handles on those properties ofstars that were either completely inaccessible in the past or only poorlymeasured. Among several such properties is the surface helium abundance of Fand G stars. We used the oscillatory signature introduced by the ionization ofhelium in the observed oscillation frequencies to constrain the amount ofhelium settling in F stars. For this purpose, we identified three promising Fstars for which the standard models of atomic diffusion predict large settling(or complete depletion) of surface helium. Assuming turbulence at the base ofenvelope convection zone slows down settling of the helium and heavy elements,we found an envelope mixed mass of approximately $5 \times 10^{-4}$M$_\odot$necessary to reproduce the observed amplitude of helium signature for all thethree stars. This is much larger than the mixed mass of the order of$10^{-6}$M$_\odot$ found in the previous studies performed using themeasurements of the heavy element abundances. This demonstrates the potentialof using the helium signature together with measurements of the heavy elementabundances to identify the most important physical processes competing againstatomic diffusion, allowing eventually to correctly interpret the observedsurface abundances of hot stars, consistent use of atomic diffusion inmodelling both hot and cool stars, and shed some light on the long-standingcosmological lithium problem.

Helium settling in F stars: constraining turbulent mixing using observed helium glitch signature