Exposing the Sun's Exuberant Youth: A Multi-wavelength Study of the Young ZAMS Solar Analog HD 49855

Over the last several years we have been carrying out a study of stellar magnetic activity and dynamos, atmospheric physics, and X-UV spectral irradiances from a sample of G0-5 V stars with different ages (see Guinan et al. 2003, ApJ, 594, 561). One of the major goals of this program is to study the change in rotation with time for solar-type stars, measuring the spin down of G-type stars as they age through the main sequence. Of particular interest in this study is the physical parameters and magnetic activity of zero age main sequence (ZAMS) solar twins, because it allows a rare look into our own Sun's distant past shortly after planet formation. The young ZAMS Sun was spinning rapidly and consequently possessed a vigorous magnetic dynamo that resulted in intense corona X-ray and chromospheric UV emissions.

The focus of this study is on the 8^th mag G5 V star HD49855. As a member of the Tuc/HorA association, HD49855 is only ∼30 Myr, providing a near perfect ZAMS analog for the Sun. Photometric, spectroscopic, and parallax measures yield: L/L_⊙ ≈ 0.7, R/R_⊙ ≈ 0.9 and T_eff ≈ 5650K -- very close to what are expected for the properties of 1M_⊙ ZAMS age Sun. Utilizing available All-Sky Automated Survey (ASAS) photometry, and FUSE FUV spectra on HD49855, we were able to determine the rotation period (3.83 ± 0.02 days), and investigate the magnetic activity of this young star (starspot coverage, X-ray/FUV emissions). This young star is an important analog for investigating planet formation and remnant debris disk properties for young solar stars and the young Sun.

This research is supported by grants from NASA/FUSE, NSF/RUI, and from the Villanova University Research for Undergraduates Award Program, which we gratefully acknowledge.