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

Tennessee State Univ. telescopes at Fairborn Observatory

Lou Boyd, input

Greg Henry, output

Lowell 21 inch

Lowell 42-inch

Fairborn Obs. 30-32 inch

Mt. Wilson 100-inch

Conceptual breakthrough 1978

Olin C. Wilson, 1978

1969 1977

Stellar magnetic cycles are

discovered In Ca II H & K

The whole-disk Sun

behaves similarly

O. R. White et al., 1998

1969 1977 1973

What we measure

Location of

Strömgren b & y passbands

b y

The expanded survey: 290 stars The sample centers on solar values

warmer cooler

more active

less active

warmer cooler

more active

less active

warmer cooler

more active

less active

18 Sco minus comparison star A

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 ~0.15%

Range ~0.08%

Range ~0.13%

Pairwise differential photometry A target star and its three comparison stars

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 y

ACRIM data degraded to 18 Sco

window and precision

Variability of 244 stars

0.1%

1%

0.01%

Solar variability from SORCE

Ratio of brightness & activity variations

SORCE 2008-2015 is most consistent with stars