We present the results of a long-term monitoring campaign of the H \alpha line in a sample of bright OB-supergiants ( O7.5–B9 ) that aims at detecting rotationally modulated changes potentially related to the existence of large-scale wind structures .
A total of 22 objects were monitored during 36 nights spread over 6 months in 2001–2002 .
Coordinated broad-band photometric observations were also obtained for some targets .
Conspicuous evidence for variability in H \alpha is found for the stars displaying a feature contaminated by wind emission .
Most changes take place on a daily time-scale , although hourly variations are also occasionally detected .
Convincing evidence for a cyclical pattern of variability in H \alpha has been found in 2 stars : HD 14134 and HD 42087 ( periodic signals are also detected in other stars , but independent confirmation is required ) .
Rotational modulation is suggested from the similarity between the observed recurrence time-scales ( in the range 13–25 days ) and estimated periods of stellar rotation .
We call attention to the atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the photometric and in the spectroscopic data sets .
This places this object among a handful of early-type stars where one may observe a clear link between extended wind structures and photospheric disturbances .
Further modelling may test the hypothesis that azimuthally-extended wind streams are responsible for the patterns of spectral variability in our target stars .