  We present a study of the bar fraction in the Coma cluster galaxies based on
a sample of $\sim 190$ galaxies selected from the Sloan Digital Sky Survey Data
Release 6 (SDSS-DR6) and observed with the Hubble Space Telescope (HST)
Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS
images allow us to explore the presence of bars, detected by visual
classification, throughout a luminosity range of 9 magnitudes ($-23 \lesssim$
M$_{r} \lesssim -14$), permitting us to study the poor known region of dwarf
galaxies. We find that bars are hosted by galaxies in a tight range of both
luminosities ($-22 \lesssim$ M$_{r} \lesssim -17$) and masses ($10^{9} \lesssim
{\cal M_{*}}/{\cal M}_{\sun} \lesssim 10^{11}$). This result holds when
comparing with a sample of bright/massive field galaxies. In addition, we find
that the bar fraction does not vary significantly when going from the center to
the cluster outskirts, implying that cluster environment plays a second order
role in bar formation/evolution. The shape of the bar fraction distribution
with respect to both luminosity and mass is well matched by the luminosity
distribution of disk galaxies in Coma, indicating that bars are good tracers of
cold stellar disks. We discuss the implications of our results for the
formation and evolution scenarios of bars and disks.
