  Line-driven wind instability is expected to cause small-scale wind
inhomogeneities, X-ray emission, and wind line profile variability. The
instability can already develop around the sonic point if it is initiated close
to the photosphere due to stochastic turbulent motions. In such cases, it may
leave its imprint on the light curve as a result of wind blanketing. We study
the photometric signatures of the line-driven wind instability. We used
line-driven wind instability simulations to determine the wind variability
close to the star. We applied two types of boundary perturbations: a sinusoidal
one that enables us to study in detail the development of the instability and a
stochastic one given by a Langevin process that provides a more realistic
boundary perturbation. We estimated the photometric variability from the
resulting mass-flux variations. The variability was simulated assuming that the
wind consists of a large number of independent conical wind sectors. We
compared the simulated light curves with TESS light curves of OB stars that
show stochastic variability. We find two typical signatures of line-driven wind
instability in photometric data: a knee in the power spectrum of magnitude
fluctuations, which appears due to engulfment of small-scale structure by
larger structures, and a negative skewness of the distribution of fluctuations,
which is the result of spatial dominance of rarefied regions. These features
endure even when combining the light curves from independent wind sectors. The
stochastic photometric variability of OB stars bears certain signatures of the
line-driven wind instability. The distribution function of observed photometric
data shows negative skewness and the power spectra of a fraction of light
curves exhibit a knee. This can be explained as a result of the line-driven
wind instability triggered by stochastic base perturbations.
