Radiative and Magnetic Properties of Plages on Solar-Type Dwarfs
Abstract
Our objective is to determine the functional and spatial relationship between magnetic and radiative fluxes on the surfaces of solar-like stars. While these relationships are known for the Sun and are consistent with a very limited set, of observations of one star, xi Boo A, we believe that a major accomplishment of IUE in its remaining years would be to establish these functional relationships definitively for solar-like stars. We will obtain a sequence of spectra for three active solar-type dwarfs: 59 Vir (GO V), Xi Boo A (G8 V), and HD 131511 (K1 V), because they are among the brightest solartype dwarfs that show large rotational modulation, have rotational periods of 5-10 days, do not rotate too fast for magnetic field observations, and he dose enough together in the sky. Crude surface brightness maps in the CII, CIV and Mg II will be compared with simultaneous ground-based observations of the magnetic field strength, the magnetic filling factor, and the net, transverse magnetic field (as measured by broadband linear polarization). These maps will provide estimates of plage areas and surface brightnesses. Our IUE data will serve as a basis for realistic two-component models (quiet+plage) for the chromospheres and transition-regions of active solar-like dwarfs. The new observations of Xi Boo A can be compared with those made in June 1986 to study the evolution of magnetic features on magnetic cycle timescales. We propose this ambitious observing program while IUE is still operating. One of IUE's great, strengths is that it can monitor stars daily to study variations in their ultraviolet spectra. No other satellite, existing or under construction, can accomplish this important task. The observations are deliberately planned to extend over 2 rotational periods in order to separate secular flux variations from the rotational modulation of an inhomogeneous spatial distribution of brightness across the stellar surface, which is our indicator of the presence and sizes of plages.
- Publication:
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IUE Proposal
- Pub Date:
- 1993
- Bibcode:
- 1993iue..prop.4549L