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J.W. Drescher, E.F. Guinan, L.E. DeWarf, G.P. McCook, R.T. Hamilton (Villanova University), I. Ribas (U. de Barcelona)
As part of the ``Sun in Time'' Program, we have been carrying out multi-wavelength (X-ray to near-IR) observations of solar-type (G0 V-G5 V) stars with different ages. These stars serve as proxies for the Sun (and other solar type stars) and cover ages that include most of the Sun's main sequence life time. This program addresses a variety of topics that include: the study of short and long term magnetic dynamo evolution; the physics and energy transfer mechanisms of the chromosphere, transition region, and corona; and the evolution of the XUV spectral irradiance of the Sun and of the high energy radiation effects on paleo-planetary environments and atmospheres. As part of this program, excellent correlations were found among age, rotation period, and magnetically generated coronal X-ray and EUV emissions, transition region and chromospheric FUV-NUV emissions. For example, for this narrow spectral range of solar type stars, the coronal X-ray emission of young main sequence early G stars are ~100-1000 times stronger than stars near the Sun's age of 4.6 Gyr.
We have expanded this program to include samples of nearby dG, dK, and dM stars. The stars selected for study have well determined parallaxes, colors, spectral types and also have observations of age-sensitive measures (= rotation) such as LX, O VI, Ca II HK, Mg II hk emission fluxes. As was done in the ``Sun in Time'' program, most younger stars selected are members of clusters or moving groups. The ages of the some of the older, less active stars are estimated using isochronal fits. The ages of some of the dM stars were estimated from kinematic considerations or associations with nearby hotter stars of known age.
We discuss the initial results of this program and show relations between magnetic activity indicators (such LX or Ca II) and age (rotation). We find relations for the late dG and dK stars as long as the physical properties of these stars (colors, Teff, and spectral types) are kept very narrow. We discuss the implications of this program for identifying late type stars that might be suitable for life.
This research is supported by NSF/RUI Grant AST-00 71260, NASA Grant NAG5 08985, and the Delaware Space Grant College Consortium through the Undergraduate Summer Research Assistance program.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.