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M.S. Giampapa (NSO/NOAO), R.R. Radick (AFGL), J.C. Hall (Lowell Obs.), S.L. Baliunas (SAO)
We present an update on a long-term study of the solar-type stars in the solar-age and solar-metallicity open cluster, M67. The primary objective of this program is to gain insight on the possible range of solar chromospheric activity and the associated, potential long-term variability of the Sun through the observation of stellar analogs of the Sun. Spectra in the Ca II H & K line region of over 100 stars in M67, including 76 `solar-type' stars (with unreddened colors in the range +0.60 \leq~B-V~\leq +0.76) and 21 `solar-twins' (+0.63 \leq~B-V~\leq +0.67), were obtained with the 3.5-m WIYN telescope on Kitt Peak in conjunction with the Hydra multi-fiber positioner to perform multi-object spectroscopy over a 1 degree field. We find that the distribution of chromospheric H&K line strengths in the solar-type stars is broader than the distribution of H&K line emission recorded in modern observations of the Sun, suggesting that the potential excursion in the amplitude of the solar cycle is greater than what we have seen so far in the contemporary record. Approximately 30% of the solar-type stars in M67 exhibit levels of activity that are outside the present envelope of solar activity. We interpret this to mean that the Sun can be in a state of magnetic activity---either exceptional quiescence similar to the Maunder-minimum episode or enhanced activity---about 30% of the time.
The authors gratefully acknowledge both the NOAO Telescope Allocation Committee and the WIYN Queue Program for their support of this investigation. The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the NOAO. The NSO and NOAO are operated by AURA, Inc., under cooperative agreement with the National Science Foundation.
The author(s) of this abstract have provided an email address for comments about the abstract: giampapa@noao.edu