The Sun in Time Updated: Magnetic Activity of the Sun Over Time and Changes in X-ray, Coronal, and Chromospheric UV Emissions and Their Effects on Hosted Planets

Since its birth nearly 4.6 Gyr ago, our Sun has been undergoing drastic changes in magnetic activity, resulting in changes in its coronal X-ray and chromospheric UV emissions, as well as in its star spot activity. We report on the magnetic evolution of the Sun and related solar-type stars by utilizing solar-proxies with spectral types from G0-5V and ages ~50 Myr to 8 Gyr. This program builds on the Villanova Sun in Time program started over 25 years ago and utilizes X-ray data from ROSAT, XMM-Newton, Chandra and FUV-UV data from the IUE and the HST. Additional stellar rotation-age determinations from Kepler and K2 Mission are also used to better define the loss of angular momentum with time from magnetic braking effects and to calibrate rotation vs. age. For the first time, we added new data for the strong FUV emission fluxes from HI Lyman α (1216 Å). The Lyα emission line dominants the EUVE-FUV flux, contributing ~80-90% of the stellar or solar flux from ~400 -1500Å. It is a major source for photo-dissociation of important molecules including H2O, CH4, and CO2 in planetary atmospheres, including the Earth. The Lyα flux measures were obtained from Linsky et al. 2013 (ApJ. 766, 69) while we determined the corresponding stellar ages. We have also added measures of the strong chromospheric Mg II HK 2800Å emission line fluxes. We developed relations between Mg II HK flux vs. Age, as well as vs. Lyα flux. We present the updated results as improved relations among rotation period, age, and X-ray as well as (FUV) Lyα and Mg II HK 2800Å fluxes and irradiances at a standardized distance of 1AU from the host stars. This research is sponsored by NASA grants HST GO-13861 & GO-13020 and Chandra GO5-16002X that we gratefully acknowledge.