  Adsorbates can drastically alter physical properties of graphene.
Particularly important are adatoms and admolecules that induce resonances at
the Dirac point. Such resonances limit electron mobilities and spin relaxation
times. We present a systematic tight-binding as well as analytical modeling to
investigate the properties of resonant states in the presence of a quantizing
magnetic field. Landau levels are strongly influenced by the resonances,
especially close to the Dirac point. Here the cyclotron motion of electrons
around a defect leads to the formation of circulating local currents which are
manifested by the appearance of side peaks around the zero-energy Landau level.
Our study is based on realistic parameters for H, F, and Cu adatoms, each
exhibiting distinct spectral features in the magnetic field. We also show that
by observing a local density of states around an adatom in the presence of
Landau levels useful microscopic model parameters can be extracted.
