The HK Project is the longest-running program to monitor stellar activity cycles similar to the 11-year sunspot cycle. Almost 100 stars have been observed continuously since 1966; at present the project is monitoring long-term changes in chromospheric activity for approximately 400 dwarf and giant stars. Here is a sample of the long-term behavior for several stars with measured activity cycles: |
HD 136202 (F8IV-V) 23 yrs |
The Sun (G2V) 10.0 yrs |
HD 103095 (G8VI) 7.3 yrs |
HD 81809 (K0V?) 8.2 yrs |
HD 3651 (K2V) 13.8 yrs |
HD 10476 (K1V) 9.6 yrs |
HD 166620 (K2V) 15.8 yrs |
HD 160346 (K3V) 7.0 yrs |
HD 16160 (K3V) 13.2 yrs |
HD 4628 (K4V) 8.4 yrs |
HD 201091 (K5V) 7.3 yrs |
HD 32147 (K5V) 11.1 yrs |
The data for the Sun were taken from observations of reflected sunlight from the Moon by Olin Wilson on the 100-inch telescope (green), and two long-term programs which measure the disk-integrated K-line flux at Sacramento Peak Observatory (red) and Kitt Peak National Observatory (blue). Some stars show two simultaneous cycle periods. Other stars either have variable activity, or long trends in activity - longer than our 30-year baseline, or appear to be very inactive: |
HD 190406 (G1V) 2.6 + 16.9 yrs |
HD 149661 (K0V) 17.4 + 4.0 yrs |
HD 114378 (F5V) Long |
HD 39587 (G0V) Var |
HD 101501 (G8V) Var |
HD 9562 (G2V) Flat |
The Sun is the only star that can be spatially resolved. The size and extent of chromospheric active regions varies dramatically over the course of the activity cycle. |
Driving Map & Directions |
News from Mount Wilson: 1/6/2012 - U.S. Forest Service undertakes a fire fuels reduction program on Mount Wilson - More here. 12/1/2011 - The Observatory's Cosmic Cafe is closed for the winter. We will reopen the Cafe and resume our 1 pm guided tours on April 1, 2012.
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Mount Wilson Observatory is operated by the Mount Wilson Institute under an agreement with the Carnegie Institution of Washington. The Observatory occupies lands belonging to the USDA Forest Service set aside under a long-term leasehold agreement between CIW and the USDA Forest Service. The Observatory subscribes to the USDA non-discrimination policy as expressed here. |