# The Evolution of Luminous Red Nova AT 2017jfs in NGC 4470

## TL;DR

This paper reports detailed photometric and spectroscopic observations of the luminous red nova AT 2017jfs, revealing its double-peaked light curve, spectral evolution, and suggesting it resulted from a binary merger event.

## Contribution

It provides a comprehensive analysis of AT 2017jfs's light curves and spectra, proposing it as a common-envelope transient from a binary merger, which is a novel interpretation for this object.

## Key findings

- Double-peaked light curve typical of LRNe
- Spectral evolution from blue continuum to M-type features
- Evidence of dust formation or IR echo at late times

## Abstract

We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of Mg=-15.46+-0.15 mag and a bolometric luminosity of 5.5x10^41 erg/s. Its light curve has the double-peak shape typical of Luminous Red Novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappeared in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.