V4332 Sagittarii: A circumstellar disc obscuring the main object

TL;DR

V4332 Sagittarii's 2009 spectrum reveals a circumstellar disc obscuring its M6 giant core, with emission features caused by radiative pumping and an infrared excess indicating a complex, dusty environment.

Contribution

This study provides detailed spectral analysis and SED modeling of V4332 Sgr, confirming the presence of an edge-on circumstellar disc obscuring the main star.

Findings

Main object is an M6 giant obscured by a circumstellar disc.

Emission features are likely produced by radiative pumping.

Infrared excess indicates a dusty environment with two blackbody components.

Abstract

V4332 Sgr experienced an outburst in 1994 whose observational characteristics in many respects resemble those of the eruption of V838 Mon in 2002. It has been proposed that these objects erupted because of a stellar-merger event. Our aim is to derive, from observational data, information on the present (10-15 yrs after the outburst) nature and structure of the object. We present and analyse a high-resolution (R = 21 000) spectrum of V4332 Sgr obtained with the Subaru Telescope in June 2009. Various components (stellar-like continuum, atomic emission lines, molecular bands in emission) in the spectrum are analysed and discussed. We also investigate a global spectral energy distribution (SED) of the object mostly derived from broadband optical and infrared photometry. The observed continuum resembles that of an M6 giant. The emission features (atomic and molecular) are most probably produced by radiative pumping. The observed strengths of the emission features strongly suggest that we only observe a small part of the radiation of the main object responsible for pumping the emission features. An infrared component seen in the observed SED, which can be roughly approximated by two blackbodies of 950 and 200 K, is 50 times brighter than the M6 stellar component seen in the optical. This further supports the idea that the main object is mostly obscured for us. The main object in V4332 Sgr, an M6 (super)giant, is surrounded by a circumstellar disc, which is seen almost edge-on so the central star is obscured. The observed M6 spectrum probably results from scattering the central star spectrum on dust grains at the outer edge of the disc.