Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of epsilon Eridani

Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun's early angular momentum evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe XII 1349 angstrom and Fe XXI 1354 angstrom emission from epsilon Eridani (epsilon Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope's Cosmic Origins Spectrograph. Following a flare in 2015 February, epsilon Eri' s Fe XXI emission declined by 81 +/- 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe XXI decline was the decay of an earlier, unseen flare Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe MI-emitting (1 MK) plasma to less than a few x 10(15) g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on epsilon Eri. On the Sun, 10(15) g CMEs occur once every few days. For epsilon Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 (M) over dot(circle dot), well below the star's estimated 30 (M) over dot(circle dot) mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.