Nuclear ashes and outflow in the eruptive star Nova Vul 1670

TL;DR

CK Vul 1670, previously considered a nova, is shown to be a stellar merger remnant based on unique chemical and mass characteristics of its surrounding gas and dust, challenging its traditional classification.

Contribution

The paper provides new evidence that CK Vul is a stellar merger remnant, not a nova, based on molecular composition and mass analysis of its circumstellar material.

Findings

Chemically rich molecular gas with peculiar isotopic ratios

Mass of surrounding gas too high for a nova

Dust and gas composition inconsistent with known explosions

Abstract

CK Vulpeculae was observed in outburst in 1670-16721, but no counterpart was seen until 1982, when a bipolar nebula was found at its location. Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but a similarity to 'red transients', which are more luminous than classical nova and thought to be the result of stellar collisions, has re-opened the question of CK Vul's status. Red transients cool to resemble late M-type stars, surrounded by circumstellar material rich in molecules and dust. No stellar source has been seen in CK Vul, though a radio continuum source was identified at the expansion centre of the nebula. Here we report CK Vul is surrounded by chemically rich molecular gas with peculiar isotopic ratios, as well as dust. The chemical composition cannot be reconciled with a nova or indeed any other known explosion. In addition, the mass of the surrounding gas is too high for a nova, though the conversion from observations of CO to a total mass is uncertain. We conclude that CK Vul is best explained as the remnant of a merger of two stars.