Critical comments on publications by S. Hoffmann and N. Vogt on historical novae/supernovae and their candidates

Abstract

We critically discuss recent articles by S. Hoffmann and N. Vogt on historical novae and supernovae (SNe) as well as their list of `24 most promising events' `with rather high probability to be a nova' (Hoffmann et al. 2020). Their alleged positional accuracy of previously suggested historical nova/SN records is based on inhomogeneous datasets (Vogt et al. 2019), but then used for the nova search in Hoffmann et al. (2020). Their claim that previously only `point coordinates' for nova/SN candidates were published, is fabricated. Their estimate of expected nova detection rates is off by a factor of 10 due to miscalculation. They accept counterparts down to 4 to 7 mag at peak, which is against the consensus for the typical limit of naked-eye discovery. When they discuss previously suggested identifications of historical novae, which they all doubt, they do not present new facts (Hoffmann 2019). Their catalog of `24 most promising events' for novae (Hoffmann et al. 2020) neglects important recent literature (e.g. Pankenier et al. 2008 and Stephenson and Green 2009), the claimed methods are not followed, etc. At least half of their short-list candidates were and are to be considered comets. For many of the others, duration of more than one night and/or a precise position is missing and/or the sources were treated mistakenly. Two highlights, a fabricated SN AD 667/668 and a presumable recurrent nova in AD 891, are already rejected in detail in Neuhaeuser et al. (2021); in both cases, all evidence speaks in favor of comets. There remains only one reliable case, where close to one (possible) historically reported position, a nova shell was already found (AD 1437, Shara et al. 2017). Follow-up observations cannot be recommended.