EDP Sciences
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Volume 399, Number 1, February III 2003
Page(s) 315 - 327
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20021789

A&A 399, 315-327 (2003)
DOI: 10.1051/0004-6361:20021789

Doppler imaging of stellar surface structure

XIX. The solar-type components of the close binary $\sigma\mathsf{^{2}}$ Coronae Borealis
K. G. Strassmeier1 and J. B. Rice2

1  Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: KStrassmeier@aip.de
2  Department of Physics, Brandon University, Brandon, Manitoba R7A 6A9, Canada
    e-mail: rice@BrandonU.ca

(Received 18 October 2002 / Accepted 29 November 2002 )

We present the first Doppler image for both stellar components of the F9+G0 ZAMS binary $\sigma^2$ CrB and found evidence for the coexistence of cool and warm spots on both stars. Cool spots appear mainly at polar or high latitudes while a confined equatorial warm belt appears on the trailing hemisphere of each of the two stars with respect to the orbital motion. We also present an update of the TempMap imaging code that allows us to solve the stellar surface temperature distribution on both binary components simultaneously, including photometric input. Several test reconstructions are performed to demonstrate its reliability and robustness. Our new orbital solution results in very precise masses for both components - good to 0.4% - and confirms the spectral classifications of F9 and G0 for the primary and secondary, respectively. The visual component, $\sigma^1$ CrB, seems to be G4 rather than G0. All three components are on or very close to the ZAMS which is also confirmed by the relatively high lithium abundance of about twenty times the solar abundance. Photometric light variations are detected with a period of $1.157\pm 0.002$ days that we interpret to be the rotation period of both binary components. A 0 $\fm$04 dimming in y together with a reddening of 0 $\fm$01 in b-y during the year 2000 suggests a long-term spot variability compatible with a period of at least 260 days.

Key words: stars: activity -- stars: starspots -- stars: imaging -- stars: individual: $\sigma^2$ CrB -- stars: late-type

Offprint request: K. G. Strassmeier, KStrassmeier@aip.de

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