Decadal variations of 290
Sun-like stars
Wes Lockwood, Lowell Observatory
Greg Henry, Tennessee State University
with thanks to….
Jeffrey Hall, Lowell Observatory
Richard Radick, NSO
Gauging the stars 1953-2015
Lowell 21 inch
Lowell 42-inch
Fairborn Obs. 30-32 inch
Mt. Wilson 100-inch
Lou Boyd, input
Greg Henry, output
Tennessee State Univ. telescopes at Fairborn Observatory
Conceptual breakthrough 1978
Stellar magnetic cycles are
discovered In Ca II H & K
1969
1973
1977
Olin C. Wilson, 1978
The whole-disk Sun
behaves similarly
1969
O. R. White et al., 1998
1977
What we measure
Location of
Strömgren b & y passbands
b y
The expanded survey: 290 stars
The sample centers on solar values
more
more
more
active
active
active
less
less
active
active
warmer
warmer
warmer
cooler
cooler
cooler
Pairwise differential photometry
Range ~0.15%
A target star and its three comparison
stars
18 Sco minus comparison star A
Range ~0.13%
18 Sco minus comparison star B
18 Sco minus rejected comp. star C
rejected star C minus star A
rejected star C minus star B
comp. star B – comp. star A
Range ~0.08%
A real solar twin: 18 Sco
Ca II S index
(b+y)/2
brightness
b + y irradiance is positively correlated with
the chromospheric emission index, S
Could we detect the Sun’s variability?
Yes, but only for about 30% of the comparison star pairs
Cumulative distribution of
comp. star rms
measurement noise
b
ACRIM data degraded to 18 Sco
window and precision
y
Variability of 244 stars
1%
0.1%
0.01%
Solar variability from SORCE
Ratio of brightness & activity variations
SORCE 2008-2015 is most consistent with stars