TY  - JOUR
A1  - Krtička, Jiří
A1  - Feldmeier, Achim
T1  - Stochastic light variations in hot stars from wind instability
T2  - Astronomy and astrophysics : an international weekly journal / European Southern Observatory (ESO)
N2  - Context
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.

Aims
We study the photometric signatures of the line-driven wind instability.

Methods
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.

Results
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.

Conclusions
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.
KW  - stars: winds
KW  - outflows
KW  - stars: mass-loss
KW  - stars: early-type
KW  - hydrodynamics
KW  - instabilities
KW  - stars: variables: general
Y1  - 2021
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/60087
SN  - 1432-0746
VL  - 648
PB  - EDP Sciences
CY  - Les Ulis
ER  -