Other
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21915218d&link_type=abstract
American Astronomical Society, AAS Meeting #219, #152.18
Other
Scientific paper
We have been involved in a comprehensive study of the evolution of coronal (X-ray; Einstein/ROSAT/ASCA/XMM/Chandra), transition-region (FUV
IUE/FUSE/HST), and chromospheric (FUV-UV; IUE/HST) emissions of solar-type stars with a wide range of ages. This project uses a sample of solar analogs, narrowly confined between spectral types G0-5 V that vary only by their (reasonably) well determined ages and rotation periods, and hence magnetic activity. An important component of this "Sun in Time" project focuses on the identification of stars whose properties are most like the Sun (solar twins). Additionally, this study provides an important check on the magnetic behavior of our present Sun and solar-like stars. For example, is our Sun "normal" for its age and mass?
Studies of cosmogenic isotopes have been employed to trace the Sun's activity back over the last 12,000 years. Curiously, this study reveals that the solar magnetic activity (defined by solar winds and sunspots) appears to have been exceptionally high over the last 70 years, but is perhaps declining now. This may help to explain the apparently low (relative to the present Sun) coronal soft X-ray luminosities observed for the solar analog alpha Cen A. Three other well-studied solar-type stars (18 Sco, 16 Cyg A and B) also appear to have X-ray emissions considerably lower than current solar values. 18 Sco is the best known match to the Sun with regard to age, rotation, and physical properties, and has an observed X-ray luminosity (logL=26.9 cgs at the maximum of its 7-11 year activity cycle) that is comparable to the maximum value for the older alpha Cen A (logL=27), but less than one half of the present solar max values (logL=27.9).
This research is supported by grants from NASA/Chandra (GO101Q035X), NASA/HST (GO-12303), and NSF/RUI (1009903).
DePasquale Joseph M.
DeWarf Laurence E.
Engle Scott G.
Guinan Edward F.
Robertson John A.
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