Challenging historical novae: AT Cnc (1645), Te-11 (483), and M22 (BC 48) revisited

TL;DR

The paper critically reevaluates three historical-nova links (M22/BC48, Te-11/AD 483, AT Cnc/1645) by marrying precise translations and contextual analysis of East Asian records with detailed three-phase shell-expansion modelling and Gaia-based distances. It concludes that the BC 48 event was likely a comet rather than a nova, Te-11's feature is more consistent with a planetary nebula than a nova shell, and the 1645 Korean record does not credibly link to AT Cnc; in each case, robust dating requires consistent position, object type, and photometric evolution. The study introduces a rigorous, interdisciplinary procedure for testing historical-nova identifications and highlights that only well-constrained positional, temporal, and brightness/color evolution data can yield credible connections to long-term nova shell evolution. These findings bear on nova rates, CV evolution, and the interpretation of ancient records in informing modern astrophysical models. The methodology and results underscore the importance of integrating archival text criticism with physically grounded shell-expansion analyses to extract reliable astrophysical insights from historical observations.

Abstract

Connections between novae with shells and historical observations are crucial for astrophysical understanding of long-term evolution of shells and cataclysmic variables. Three of five previously considered links are revisited here: extended features in M22 in BC48, Te-11 in 483, and AT Cnc in 1645. We aim to develop a procedure to check whether these links are credible. Literal translations of the Chinese texts, historically based arguments, and close readings are combined with astrophysics, (peak brightness, decay time estimate, shell age expansion model calculation, etc.). (a) Nandou's second star, near which the BC48 `guest star' was reported, is identified as tau Sgr, not lambda Sgr, far from the M22 location. A nova in M22 would peak at only m=6.4 \pm 1.4 mag, and thus a description as a `blue-white' `melon' does not fit; it was likely a comet. (b) The imprecise position (`Shen['s] east') of the `guest star' in 483, its extended (dipper-like) radiance, and the context speak for a bolide. Considering the new (larger) Gaia distance and small extinction towards Te-11 (outside a cloud), its bi-polar morphology and current expansion velocity point to a planetary nebula; as a nova, the shell expansion age is 1100-2000 yr from detailed supersonic expansion calculations. (c) Most certainly, Mars was meant when the source for 1645 reported `a large star entered Yugui'; the verb implies motion. AT Cnc lies neither in Yugui's asterism box nor in the eponymous lunar mansion range. The fluid drag expansion age of AT Cancri's ejecta is 128-631 yr. All three exact ages are unsubstantiated. True novae or nova shells can be connected to historical records only if the position and object type are plausible. Duration, brightness (light curve), and color (evolution) should fit and could provide more astrophysical insight ...

Figures (7)

• Figure 1: Expansion of the AT Cnc ejecta blobs was calculated following the fluid drag equation (Williams 2013). For input parameters and details, see Sects. 4 and 5 and Appendix D. The solution ranges are shown for initial expansion velocities of 3000 (grey), 670 (red), and 1200 km s$^{-1}$ (blue), the latter to differentiate between fast and slow novae. (We show 670 km s$^{-1}$, the minimum initial expansion velocity for Sedov-Taylor solutions, for better comparison with Fig. 2.) Left: Evolution of shell radius. Right: Evolution of expansion velocity. The current radius and velocity (in 2016) of the AT Cnc ejecta (horizontal lines) are reached simultaneously for an age range of ca. 128-631 yr (dash-dotted green lines).
• Figure 2: Expansion of AT Cnc's nova shell through free expansion and Sedov-Taylor phase with supersonic model calculations: For input parameters and details, see Sect. 4 and 5 and Appendix D. We use the same initial velocities as in Fig. 1. Left: Evolution of the shell radius. Right: Evolution of the expansion velocity. Both the current radius and the current expansion velocity (horizontal lines) are reached simultaneously only for an age range of ca. 111-285 yr (dash-dotted green lines).
• Figure 3: The Chinese lunar mansion asterism Nandou (Sgr); star sizes correspond to brightness; stars are numbered both according to the new reconstruction found here (red, historical counting, Table A.1) and the previous assumption (black, modern counting). The new search area for the BC 48 'guest star' east of Nandou's second star is shown with uncertainty. Previously suggested nova counterparts (NGC 6578, V363 Sgr, M22) and also the CV GSC 06883-00545 (GSC) are outside this field, see text -- and do not reflect the record of BC 48, which pertains most certainly to a comet sighting. For the two-star asterism Guo, the three suggested stars are shown.
• Figure 4: The Chinese lunar mansion asterisms Shen and Zuixi in Orion in red and black, respectively, plus Te-11 in black; the western borders of the lunar mansion RA ranges (LM) Zuixi, Shen, and Dongjing in blue; Te-11 is in the eastern part of the asterism Shen.
• Figure 5: The lunar mansion asterism Yugui with the M44 cluster in Cnc in red; the western border of lunar mansion RA range (LM) Yugui in blue; AT Cnc is in lunar mansion RA range LM) Dongjing.