On the possibilities of classical nova identifications among historical Far Eastern guest star observations

Abstract

More than 100 guest star observations have been obtained by Chinese, Korean, Japanese and Vietnamese astronomers between ~600 BCE and ~1690 CE. Comparing the coordinates from the information given in old texts for eight supernova recoveries with modern supernova remnant positions, we estimate a typical positional accuracy of the order of 0.3 to 7 deg for these supernovae. These values turn out to be also a start for the expected deviation angle between a classical nova observed as a guest star and its modern counterpart among known cataclysmic variables (CVs). However, there are considerable disagreements among modern authors in the interpretation of ancient Far Eastern texts, emphasizing the need to consult again the original historic sources, in order to improve the positioning reliability. We also discuss the typical amplitudes of well observed classical novae and find that modern counterparts of nova guest stars should be V = 18 mag and thus easily observable. In this context we also consider the "hibernation scenario" and conclude that it is impossible to decide from currently-available observations whether hibernation is common. In addition to the limiting magnitude around 2 mag for ancient guest star detections mentioned in the literature, we consider the possibility that also fainter guest stars (4-5 mag) could have been detected by ancient observers and give arguments in favor of this possibility. For these limits we compare the expected nova detection rate of ancient naked-eye observers with that during modern times, and conclude that they coincide in order of magnitude, which implies that, indeed, a considerable number of classical nova remnants should be hidden among the Far Eastern guest star reports. Finally, we present a statistical analysis of the probability of casual misidentifications based on frequency and galactic distribution of CVs in the AAVSO-VSX catalogue.

arXiv comment9 pages, 2 figures, accepted for Astronomische Nachrichten

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