1997A&A...323..183V

The blue super-giant P Cygni has been observed with the Grand Interferometre a 2 Telescopes (GI2T). Using high spatial resolution data at low spectral resolution (R=3860) of Hα and HeI6678 emission lines we clearly resolve the extended enveloppe of this Luminous Blue Variable on August 1994. The angular diameter of the equivalent uniform disk taken over the total extent of these lines corresponds to {PHI}_Hα=5.52±0.47 and {PHI}_He=2.48±2.16mas respectively. We also analysed spectrally-resolved fringes in both lines for 3.4Å width narrow channels across the emission profiles. Based on robust calibrations from two reference stars γ Lyr and α Cep we detect subtle spatial structures throughout P Cyg's wind. First: we find that the maximum extension of P Cyg occurs at -130km/s. This value agrees well with a picture of P Cyg where matter is radially blown outward according to the classical theory of P Cyg line profiles. Secondly: we detect a significant local phase-shift of the fringe signal at -208km/s which corresponds to an angular separation of 0.8mas from the continuum source. This is interpreted as a localized blob of moving gas with enhanced brightness whose position is about 4 photospheric radii to the south of P Cyg's underlying star.