Exocomets of beta Pictoris HARPS spectra

We find a general absence of exocometary sodium line absorption, with only two instances of clear ~2% deep exocometary sodium out of 198 nights of observation, as well as a weaker ~1% feature that persists over 13 nights in 2004. We find that these events occur during times of exceptionally deep CaII absorption, at the same red-shift, implying that strongly CaII-evaporating exocomets also exhibit detectable levels of Na I, in spite of the vast majority of NaI being rapidly photo-ionised in close proximity to the star.

We find long-lived CaII absorption in 2017 and 2018 that persists on a timescale of a year, which may be difficult to explain with the classical exocomet model. Finally, we investigate two strongly accelerating, blue-shifted exocomet features observed in 2019 that show strong and sudden departures from Keplerian motion, suggesting rapid changes to the dynamics of the exocomet cloud. We hypothesize that this is caused by the destruction of the comet nuclei shortly after their periastron passages.