1999A&A...347..225S

The active K0 giant HD 12545 is the star with the largest starspots ever observed. We report a record light-curve amplitude of 0.63mag in V and 0.17mag in V-I in January 1998. At the same time, HD 12545 was at its brightest magnitude since the discovery of its light variability in 1985. We present the first Doppler image of HD 12545 from observations during this state of high-amplitude light variability and find that the star exhibits one cool high-latitude spot of gigantic dimensions (≃12x20solar radii, i.e. 60 times the extension of the largest sunspot group or 10,000 times larger areal coverage). Furthermore, our map shows one smaller cool spot and one equatorial warm (bright) spot. The warm spot is situated approximately 180° from the large cool spot in the opposite hemisphere and is the cause of the exceptionally large light-curve amplitude and the stellar brightening. Within our model, no light-curve nor a reasonable line-profile solution with only cool spots was possible. Surprisingly, the fact that HD 12545 is brighter at a time of high spot activity is in agreement with solar analogy. Our data also allow to refine the orbital elements of HD 12545 and we use the Hipparcos parallax to determine absolute astrophysical quantities for this rapidly rotating K giant.