Comet-like activity in the circumstellar debris disk surrounding the 1.4 Gyr-old F2V star HD 109085

Here, we present high signal-to-noise, medium-resolution spectral observations of the CaII K-line absorption (R≈60,000) recorded towards the 1.4 Gyr-old F2V star HD 109085( h Crv) on two sets of nights in 2017 and 2018. Variability of the circumstellar CaII K-line has been widely observed in the gas disks surrounding many fast rotating A-type stars with ages <100Myr (Welsh & Montgomery 2018). This variability is attributed to the presence of evaporating gaseous material associated with comet /asteroid-like bodies as they fall towards the central star due to the gravitational perturbation of their orbits by exoplanets. Our present observations show that the circumstellar absorption of CaII K-line HD 109085 similarly varies over time-scales as short as 48 hours. To our knowledge, this is the first example of an (old) F-star with a known associated cold and dusty debris disk that also possesses warm (ionized) gas associated with evaporating `exocomet' material. Organic material and water are thought to have been brought to the Earth via the bombardment by asteroids / comets. A similar process may still be operating after 1.4 Gyrs in the HD 109085 stellar system, which is thought to possess several exoplanets (Marino et al 2017).