The shape of Achernar

Profile of the rapidly rotating star Achernar, as deduced from observations with the VLT Interferometer (VLTI). The size is indicated in units of 0.001 arcsec (milli-arcsec). Individual angular diameter measurements are indicated by pairs of small points with associated error bars on opposite sides of the centre. The fully drawn curve represents the best fitting ellipse. The ratio of the axes is 1.56 ± 0.05. The major axis of this ellipse is a measure of the "real" size of the star. Because of the projection effect, the minor axis shows the largest possible extension in the perpendicular direction. The axes ratio is therefore a minimal value; the star may be even more flattened than suggested by this ellipse.