SIMBAD references

High S/N (∼200), high spectral resolution (∼25km/s) optical time series spectroscopy of the extreme O8 supergiant HD151804 is presented. These data were collected over ∼5 nights in 1992 July in a coordinated campaign between Australia (Mount Stromlo Observatory) and Chile (Cerro Tololo Inter-American Observatory). Variability in the strong wind of HD151804 is principally monitored via the HeI λ5876 P Cygni and the Hα emission profiles, both of which are sensitive diagnostics of density structures in the wind close to the star. Systematic changes are present in the HeI profiles, which take the form of: (i) blueward migrating optical depth enhancements, which travel from ∼0.14 of the terminal velocity (v_∞) to ∼0.5v_∞ in about 24 hours; and (ii) blueward and redward motion of up to 50km/s of the low-velocity emission portion of the HeI profile. Fluctuations are also evident in the blue emission wing of Hα between -200km/s and -750km/s, which are in sympathy with the systematic changes in HeI absorption. These results indicate that the inner stellar wind of HD151804, i.e., between 1.0 and 2.0 stellar radii, is unstable and affected by coherent, evolving structures. Constraints on global mass-flux variations and localised column density enhancements based on steady-state stellar atmosphere modelling are presented.