D. Schertl, K.-H. Hofmann, W. Seggewiss, und G. Weigelt
Speckle masking observations of R 64, the dense stellar core of the OB association LH9 in the Large Magellanic Cloud*
Astronomy and Astrophysics, 302, 327-334 (1995)
We present speckle masking observations of R 64 (=HD 32228; O9.5II: + WC5), the central object of the OB association LH9 in the Large Magellanic Cloud. Two sets of speckle interferograms were taken to select the Johnson V spectral band and the strong Wolf-Rayet emission lines between 450 and 490nm. In the 6.4"x6.4" field of view 25 stellar components were detected in R 64 with V magnitudes in the range 12.5 to 17.1 and down to a resolution of 0.12". The brightest star in the visual component B is the only Wolf-Rayet star in R 64. The colour-magnitude diagram of LH9, completed with the components of R 64, serves for the discussion of the evolutionary state of the association. There is evidence that the outer regions of LH9 are its youngest parts with an upper age of about 5Myr, in accordance with estimates by Walborn & Parker (1992). The WC5 star in the centre is most likely the product of mass exchange in a massive close binary system with an age in excess of 5Myr. The mass density in R 64 is about 250M☉ pc-3 for stars more massive than 5M☉.