Ultraviolet flux decrease under a grand minimum from IUE short-wavelength observation of solar analogs

TitleUltraviolet flux decrease under a grand minimum from IUE short-wavelength observation of solar analogs
Publication TypeJournal Article
Year of Publication2018
AuthorsLubin D., Melis C., Tytler D.
JournalAstrophysical Journal Letters
Date Published2018/01
Type of ArticleArticle
ISBN Number2041-8205
Accession NumberWOS:000418932600001
Keywordsca-ii h; calibration; chromospheric emission; hubble-space-telescope; main-sequence; maunder minimum; planet-search; spectroscopy; stars; stars: activity; stars: solar-type; stellar-activity indicators; Sun: activity; Sun: UV radiation; ultraviolet: stars; variability

We have identified a sample of 33 Sun-like stars observed by the International Ultraviolet Explorer (IUE) with the short-wavelength 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'(HK) < -4.26, and eight stars have log R'(HK) < -5.00. The IUE-observed flux spectra are integrated over the wavelength range 1250-1910 A, transformed to surface fluxes, and then normalized to solar B - V. These normalized surface fluxes show a strong linear relationship with activity R'(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 +/- 5.7% lower than solar cycle minimum.

Short TitleAstrophys. J. Lett.
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