The Distant Future of Solar Activity: A Case Study of beta Hydri. III. Transition Region, Corona, and Stellar Wind
Linsky, J. L.; Simon, T.; Ayres, T. R.; Linde, P.; Dravins, D.; Monsignori-Fossi, B.; Wallinder, F.
Sweden, United States, Italy
Abstract
The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind.