Convection and Thermal Bifurcation in the A-Type Stars

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Session 98 -- Activity and Abundances Near the Main Sequence
Oral presentation, Wednesday, 11, 1995, 2:00pm - 3:30pm

[98.03] Convection and Thermal Bifurcation in the A-Type Stars

Theodore Simon (U. Hawaii), Wayne B. Landsman (Hughes STX)

Others have suggested that there are two distinct branches of main sequence A stars in the color-magnitude diagram: a high temperature branch populated by convective stars, and a low temperature branch comprised of purely radiative stars. We re-examine this issue, making use of a large collection of Str\"{o}mgren photometry, broadband UV photometry from TD-1, and UV spectroscopy from IUE. We find no evidence to support any claim for the existence of a temperature bifurcation among the A-type stars. However, we do observe a large (0.5 mags) spread in the UV colors of normal A stars. The scatter does not appear to be related to differences in surface gravity, metallicity or other peculiarity in chemical composition, rotation speed, binarity, or known pulsation properties of individual stars. We discuss several possible explanations for this finding.

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