The recurrent nova V3890~Sgr: a near-infrared and optical study of the red giant component and its environment

TL;DR

This study analyzes the red giant component of the recurrent nova V3890 Sgr, revealing its temperature, chemical abundances, dust environment, and interactions with nova ejecta through near-infrared and optical observations.

Contribution

It provides detailed chemical and environmental characterization of the red giant in V3890 Sgr, including new insights into its composition, dust, and interaction with nova ejecta, expanding understanding of recurrent nova systems.

Findings

Red giant temperature estimated at 3050 K with modest variations.

Overabundance of carbon and sodium relative to solar values.

Evidence of ejecta interaction with the red giant environment.

Abstract

We present an analysis of the red giant component of the recurrent nova V3890 Sgr, using data obtained before and after its 2019 eruption. Its effective temperature is $T_{\rm eff}=3050\pm$200 K for $\log{g}=0.7$, although there are modest changes in $T_{\rm eff}$. There is an overabundance of both carbon ($0.20\pm0.05$~dex) and sodium ($1.0\pm0.3$~dex) relative to their solar values, possibly the result of ejecta from the 1990 nova eruption being entrained into the red giant photosphere. We find $^{12}$C/$^{13}$C $=25\pm2$, a value similar to that found in red giants in other recurrent novae. The interpretation of the quiescent spectrum in the 5--38$\,mu$m region requires the presence of photospheric SiO absorption and cool ($\sim400$~K) dust in the red giant environment. The spectrum in the region of the Na{\sc i} D lines is complex, and includes at least six interstellar components, together with likely evidence for interaction between ejecta from the 2019 eruption and material accumulated in the plane of the binary. Three recurrent novae with giant secondaries have been shown to have environments with different dust content, but photospheres with similar $^{12}$C/$^{13}$C ratios. The SiO fundamental bands most likely have a photospheric origin in the all three stars.