WARM CORONAL RAIN ON YOUNG SOLAR ANALOG EK DRACONIS?

Abstract

We report a moderate-resolution, 1290–1430 Å spectrum of young solar analog EK Draconis (HD 129333: G1.5 V), obtained by Cosmic Origins Spectrograph on Hubble Space Telescope. The 20 minute observation, remarkably, captured two distinct "flares" in the Si iv 1400 Å doublet (T ∼ 6 × 104 K); very broad profiles of Si iv and the C ii 1335 Å multiplet (T ∼ 3 × 104 K); and prominent Fe xxi λ1354 coronal forbidden line emission (T ∼ 10 MK). The bright Si iv features are significantly redshifted compared to the milder, although still redshifted, equivalent components of solar-twin α1 Cen (HD 128620: G2 V). The broad, shifted, flaring hot-line profiles of EK Dra indicate not only that the subcoronal plasma of the young sun is highly dynamic, but also that the Si iv-bearing gas must be continually accreting onto the lower atmosphere, perhaps the stellar equivalent of warm "coronal rain."