Latitude distributions and lifetimes of starspots on G dwarfs in the Alpha Persei cluster

J.R. Barnes, A. Collier Cameron, Y.C. Unruh, J.-F.Donati, G.A.J. Hussain

MNRAS 299, 904-920 (1998)

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We present a set of maximum entropy reconstructions of the starspot distributions on two rapidly rotating G dwarfs in the Alpha Persei Cluster, from spectra taken at the William Herschel Telescope on three nights in 1996 October and November. Since these stars are too faint for conventional Doppler imaging, which makes use of only one or a few lines, we take the large number of photospheric metal lines available in an echelle spectrum, and deconvolve them into a single, high S:N profile. We show that this technique results in a typical multiplex gain of 22.5 in S:N for a given spectrum, the equivalent of using a single line obtained on a 63 m telescope. The image reconstructions demonstrate that both these stars have cool high latitude regions or polar crowns, and low latitude features, in contradiction to the suggestion that only high latitude spots should be present.
Cross-correlation between image reconstructions of He 699, 31 days apart, reveals a lack of correlation between detail ed small scale structures. This places an upper limit for the lifetime of the observed features at less than one month. The H-alpha profiles are also found to exhibit absorption features indicating the presence of prominence clouds, at or below the co-rotation radius.