Discovery of a Second Nova Eruption of V2487 Ophiuchi

TL;DR

This paper reports the discovery of a second eruption of V2487 Ophiuchi in 1900, confirming it as a recurrent nova with an estimated recurrence interval of about 18 years, based on archival plate analysis.

Contribution

It identifies a previously unknown eruption of V2487 Ophiuchi, establishing it as a recurrent nova and estimating its recurrence period from archival data.

Findings

Discovered a 1900 eruption of V2487 Oph in archival plates.

Confirmed V2487 Oph as a recurrent nova based on spectral features.

Estimated recurrence interval of approximately 18 years.

Abstract

A directed search for previously-undiscovered nova eruptions was conducted in the astronomical plate archives at Harvard College Observatory and Sonneberg Observatory. We found that an eruption of V2487 Oph (Nova Oph 1998) occurred on 1900 June 20. V2487 Oph was previously classified as a classical nova, which we identified as a probable recurrent nova based on its large expansion velocities and the presence of high excitation lines in the outburst spectrum. The event was recorded on Harvard plate AM 505, at a B magnitude of 10.27 +/- 0.11, which is near peak. The outburst can only be seen on one plate, but the image has a characteristic dumbbell shape (caused by a double exposure) that is identical to the other star images on the plate, and thus is not a plate defect. We conclude that this is in fact a previously-undiscovered nova outburst of V2487 Oph, confirming our prediction that it is a recurrent nova. We also examine the discovery efficiency for eruptions of the system and conclude that a randomly-timed outburst has, on average, a 30% chance of being discovered in the past century. Using this, we deduce a recurrence time for V2487 Oph of approximately 18 years, which implies that the next eruption is expected around 2016.