* Astronomy

Title: The Sun-like activity of the solar twin 18 Scorpii
Authors: Jeffrey C. Hall, Gregory W. Henry, G. Wesley Lockwood

We present the results of 10 yr of complementary spectroscopic and photometric observations of the solar twin 18 Scorpii. We show that over the course of its ~7 year chromospheric activity cycle, 18 Scorpii's brightness varies in the same manner as the Sun's and with a likely brightness variation of 0.09%, similar to the 0.1% decadal variation in the total solar irradiance.


The photometric and spectroscopic behaviour of 18 Scorpii, 1997-2006. In panel A, the variation of the Ca II H&K magnetic flux about its mean is shown by blue diamonds. Our thirteen years of observations of the solar HK variation (purple squares) are shown for comparison, scaled the same way. In panel B, we present the photometric light curves. Brightness increases upward. Orange and yellow diamonds show the individual variations relative to two different comparison stars. The red series is the weighted mean of the first two, and is offset by 0.2% for clarity.

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18 Scorpii (HD 146233, HR 6060) is a star located some 45.7 light years from earth at the northern edge of the Scorpius constellation.

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