Remarkable changes in the near-infrared spectrum of the nova-like variable V4332 Sgr

TL;DR

This study presents near-infrared observations of V4332 Sgr, revealing unique molecular features and dust formation, suggesting it belongs to a new class of eruptive variables called 'quasi-novae' with distinct post-outburst evolution.

Contribution

It reports the first detection of AlO molecular bands in V4332 Sgr and identifies spectral similarities with V838 Mon, proposing a new classification for these objects.

Findings

Detection of AlO molecular bands in V4332 Sgr's spectra.

Identification of a new dust shell with ~900K temperature.

Evidence of a second mass-loss episode post-outburst.

Abstract

We report on recent near-IR observations of V4332 Sgr - the nova-like variable that erupted in 1994. Its rapid, post-outburst evolution to a cool M type giant/supergiant, soon after its outburst, had showed that it was an unusual object differing from other eruptive variables like classical/symbiotic novae or born-again AGB stars. The present study of V4332 Sgr was motivated by the keen interest in the recent eruption of V838 Mon - which along with V4332 Sgr - is believed to belong to a new class of objects (we propose they may be called "quasi-novae"). Our observations show new developments in the evolution of V4332 Sgr. The most striking feature is the detection of several molecular bands of AlO - a rarely seen molecule in astronomical spectra - in the JHK spectra. Many of these bands are being detected for the first time. The only other detection of some of these AlO bands are in V838 Mon, thereby showing further spectral similarities between the two objects. JHK photometry shows the development of a new dust shell around V4332 Sgr with a temperature of ~ 900K. This dust shell does not appear to be associated with ejecta of the 1994 outburst but is due to a second mass-loss episode which is not expected in a classical nova outburst. The cold molecular environment, suggested by the AlO emission, is also not expected in novae ejecta. We model the AlO bands and also discuss the possible formation mechanism of the AlO.