
TL;DR
This study uses Hubble observations to analyze a massive FUV flare on EK Draconis, revealing persistent high-density, flaring activity and downflows that suggest the star's corona is continuously active in a scale-free manner.
Contribution
It provides detailed spectroscopic evidence of continuous flaring and high-density plasma in EK Draconis's corona, supporting the concept of a persistent 'flare-ona' in hyperactive stars.
Findings
Record large FUV flare observed on EK Draconis.
Persistent high-density plasma indicative of continuous flaring.
Detected downflows consistent with coronal rain phenomena.
Abstract
EK Draconis (HD 129333: G1.5 V) is a well-known young (50 Myr) solar analog. In 2012, Hubble Space Telescope returned to EK Dra to follow up a far-ultraviolet (FUV) SNAPshot visit by Cosmic Origins Spectrograph (COS) two years earlier. The brief SNAP pointing had found surprisingly redshifted, impulsively variable subcoronal "hot-line" emission of Si IV 140 nm (T~ 80,000 K). Serendipitously, the 2012 follow-on program witnessed one of the largest FUV flares ever recorded on a sunlike star, which again displayed strong redshifts (downflows) of 30-40 km/s, even after compensating for small systematics in the COS velocity scales, uncovered through a cross-calibration by Space Telescope Imaging Spectrograph (STIS). The (now reduced, but still substantial) ~10 km/s hot-line redshifts outside the flaring interval did not vary with rotational phase, so cannot be caused by "Doppler Imaging"…
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