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

Citation:
Lubin, D, Melis C, Tytler D.  2018.  Ultraviolet flux decrease under a grand minimum from IUE short-wavelength observation of solar analogs. Astrophysical Journal Letters. 852

Date Published:

2018/01

Keywords:

ca-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

Abstract:

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.

Notes:

n/a

Website

DOI:

10.3847/2041-8213/aaa124

Scripps Publication ID:

L4