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A&A Supplement series, Vol. 128, February II 1998, 29-33

Received February 3; accepted June 16, 1997

X-ray/optical observations of stars with shallow convection zones tex2html_wrap_inline1067gif

A.J.M. Piterstex2html_wrap1083 - J. van Paradijstex2html_wrap1085 - J.H.M.M. Schmitttex2html_wrap1087

Send offprint request: J. van Paradijs

tex2html_wrap1089  Astronomical Institute "Anton Pannekoek" / CHEAF, Kruislaan 403, NL-1098 SJ Amsterdam, The Netherlands
tex2html_wrap1091  Physics Department UAH, Huntsville, AL 35899, U.S.A.
tex2html_wrap1093  Max Planck Institut für Extraterrestrische Physik, Giessenbachstraße 1, 8046 Garching bei München, Germany


We present Walraven photometry and ROSAT All-Sky Survey data for a sample of 173 bright main-sequence stars with spectral types between A8V and G2V. These observations are part of a study of the onset of magnetic surface activity along the main sequence. Values for the effective temperature, surface gravity and interstellar reddening have been obtained from a comparison of the observed Walraven colours with theoretical values. These parameters have been used to derive accurate X-ray surface flux densities.

keywords: stars: activity; fundamental parameters -- X-rays: stars

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