We have identified a sample of 33 Sun-like stars observed by the International Ultraviolet Explorer ( IUE ) with the short wavelength ( SW ) spectrographs that have ground-based detections of chromospheric Ca II H+K activity .
Our objective is to determine if these observations can provide an estimate of the decrease in ultraviolet ( UV ) surface flux associated with a transition from a normal stellar cycle to a grand minimum state .
The activity detections , corrected to solar metallicity , span the range - 5.16 < log R ^ { \prime } _ { HK } < - 4.26 , and eight stars have log R ^ { \prime } _ { HK } < - 5.00 .
The IUE -observed flux spectra are integrated over the wavelength range 1250 - 1910 Å , transformed to surface fluxes , and then normalized to solar B - V. These normalized surface fluxes show a strong linear relationship with activity R ^ { \prime } _ { HK } ( R ^ { 2 } = 0.857 after three outliers are omitted ) .
From this linear regression we estimate a range in UV flux of 9.3 % over solar cycle 22 , and a reduction of 6.9 % below solar cycle minimum under a grand minimum .
The 95 % confidence interval in this grand minimum estimate is 5.5 % - 8.4 % .
An alternative estimate is provided by the IUE observations of \tau Cet ( HD 10700 ) , a star having strong evidence of being in a grand-minimum state , and this star ’ s normalized surface flux is 23.0 \pm 5.7 % lower than solar cycle minimum .