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E. F. Guinan (Villanova University), I. Ribas (University of Barcelona), G. M. Harper (CASA)
We present FUSE observations of solar analogs of different ages which serve as proxies for the Sun during most of its main-sequence lifetime. We are carrying out an in-depth study of the evolution of the transition region and low corona of the Sun from its active youth through its distant terminal main-sequence future. The FUSE program is part of a comprehensive study of the Sun in Time across the electromagnetic spectrum. We have defined a homogeneous sample of single G0-5 V stars with well known rotation periods that are proxies for the Sun at different ages. We are studying the dynamics and energetics of the lower layers of the atmospheres of these solar like stars, and investigating the variations of magnetic related properties with age and rotation period. The FUSE spectral region (920-1180 Å), although narrow, includes a number of important diagnostic lines such as C III \lambda\lambda976,1175, O VI \lambda\lambda1032,1038, and Fe XVIII \lambda975 that cover a broad temperature range (30\,000 K < T < 20 MK). Emission measure and temperature analysis allow us to obtain a complete 3-D atmospheric model of active regions that we is linked to the previously obtained coronal X-ray and EUV data. Transition region electron densities are inferred through the well-established density sensitive ratio of the C III 1176 & 977 Å\ lines. This FUSE investigation is central to the understanding of the evolution of magneto-dynamic atmospheric phenomena, and the associated high energy emissions of the Sun and of solar type stars. It also bears on the crucial question of the influence of the young Sun's strong FUV emissions on the developing planetary system -- in particular on the photochemical and photoionization evolution (and possible erosion) of early planetary atmospheres and ionospheres. To this end, we are constructing spectral irradiance tables (from 10 to 7500 Å) for the Sun at different ages. The results of these studies will be discussed.
This research is supported from NASA FUSE Grants NAG 5-8985 and NAG 5-10387 which we gratefully acknowledge.
The author(s) of this abstract have provided an email address for comments about the abstract: edward.guinan@villanova.edu