Extra-galactic distances with massive stars: the role of stellar
  variability in the case of M33
  In modern cosmology, determining the Hubble constant (H0) using distance
ladder to percent level and comparing with the results from Planck satellite
can shed light on the nature of the dark energy, the physics of neutrino, and
the curvature of the universe. Thanks to the endeavor of the SH0ES team, the
uncertainty of the H0 has be dramatically reduced from 10% to 2.4%, with the
promise to reach even 1% in the near future. In this regard, it is
fundamentally important to beat and investigate the systematics. This is best
be done with other independent good distance indicators. One of the promising
method is the flux-weighted gravity luminosity relation (FGLR) of the blue
supergiants. As the blue supergiants are the brightest objects in the galaxies,
they can probe distance up to 10 Mpc, with negligible blending effects. While
the FGLR method delivered distance in good agreement with other distance
indicators, it has been shown that this method delivers larger distance in the
case of M33 and NGC 55. Here we investigate whether the M33 distance estimate
of FGLR suffers systematics from stellar variability. Using CFHT M33 monitoring
data, we found 9 out of 22 BSGs showed variability during the course of 500
days, however with amplitudes as small as 0.05 magnitudes. This suggests that
stellar variability plays negligible role in the FGLR distance determination.
