Keck/HIRES spectroscopy of V838 Monocerotis in October 2005

TL;DR

This study presents high-resolution spectroscopy of V838 Monocerotis in 2005, revealing molecular and atomic features, a B-type companion, and insights into the post-outburst stellar environment, supporting the stellar merger scenario.

Contribution

First detailed high-resolution spectrum of V838 Mon in 2005 with molecular/atomic feature atlas and modeling, confirming the B3V companion and post-outburst atmospheric conditions.

Findings

Molecular absorption dominates at ~2400 K and colder outer layers (~500 K).

Resonance lines of neutral alkali metals show P-Cyg profiles.

The B-type companion is consistent with B3V spectral type.

Abstract

V838 Mon erupted at the beginning of 2002 becoming an extremely luminous star. Among various scenarios proposed to explain the nature of the outburst the most promising is a stellar merger event. In this paper we investigate the observational properties of the star and its surroundings in the post outburst phase. We have obtained a high resolution optical spectrum of V838 Mon in October 2005 using the Keck I telescope.We have identified numerous atomic features and molecular bands present in the spectrum and provided an atlas of those features. In order to improve the spectrum interpretation we have performed simple modeling of the molecular bands. Our analysis indicates that the spectrum is dominated by molecular absorption features arising in photospheric regions with temperatures of ~2400 K and in colder outer layers, where the temperature decreases down to ~500 K. A number of resonance lines of neutral alkali metals are observed to show P-Cyg profiles. Particularly interesting are numerous prominent emission lines of [FeII]. All of them show practically the same profile, which can be well described by a Lorentzian profile. In the blue part of the spectrum photospheric signatures of the B-type companion are easily seen. We have fitted the observed spectrum with a synthetic one and the obtained parameters are consistent with the B3V type. We have also estimated radial and rotational velocities of the companion.