V5856 Sagittarii/2016: Broad Multi-Epoch Spectral Coverage of a Sustained High Luminosity Nova

TL;DR

This study presents extensive multi-epoch spectral observations of Nova V5856 Sagittarii, revealing a sustained high luminosity over six years and identifying a persistent common envelope as the emission source.

Contribution

The paper provides the first detailed multi-epoch spectral analysis of this long-lasting nova, highlighting the role of a post-outburst common envelope in its prolonged brightness.

Findings

Spectral data show distinct emission regions with different characteristics.

Permitted lines exhibit P Cygni profiles indicating high optical depth.

Spectral evidence suggests a common envelope, not ongoing wind, sustains the nova's luminosity.

Abstract

Nova V5856 Sagittarii is unique for having remained more than nine magnitudes above its pre-outburst brightness for more than six years. Extensive visible and IR spectra from the time of outburst to the present epoch reveal separate emitting regions with distinct spectral characteristics. Permitted emission lines have both broad and narrow components, whereas the forbidden line profiles are almost entirely broad. The permitted line components frequently display P Cygni profiles indicating high optical depth, whereas the broad components do not show detectable absorption. The densities and velocities deduced from the spectra, including differences in the O I 7773 and 8446 lines, are not consistent with an on-going wind. Instead, the prolonged high luminosity and spectral characteristics are indicative of a post-outburst common envelope that enshrouds the binary, and is likely the primary source of the visible and IR emission.