The continued optical to mid-IR evolution of V838 Monocerotis

TL;DR

This study presents multi-wavelength observations of V838 Monocerotis from 2008 to 2012, revising its spectral type to L3 supergiant, and analyzes its evolving properties, including a surrounding ejecta shell and potential stellar interaction.

Contribution

The paper provides the first optical data for an L supergiant, proposes V838 Mon as a prototype for such stars, and models its ejecta and interaction phenomena in detail.

Findings

V838 Mon is an L3 supergiant with Teff~2000-2200 K.

A shell of ejecta surrounds V838 Mon at ~263 AU with T~285 K.

Evidence of binary interaction or stellar collision activity.

Abstract

The eruptive variable V838 Monocerotis gained notoriety in 2002 when it brightened nine magnitudes in a series of three outbursts and then rapidly evolved into an extremely cool supergiant. We present optical, near-IR, and mid-IR spectroscopic and photometric observations of V838 Monocerotis obtained between 2008 and 2012 at the Apache Point Observatory 3.5m, NASA IRTF 3m, and Gemini South 8m telescopes. We contemporaneously analyze the optical & IR spectroscopic properties of V838 Monocerotis to arrive at a revised spectral type L3 supergiant and effective temperature Teff~2000--2200 K. Because there are no existing optical observational data for L supergiants in the optical, we speculate that V838 Monocerotis may represent the prototype for L supergiants in this wavelength regime. We find a low level of Halpha emission present in the system, consistent with interaction between V838 Monocerotis and its B3V binary; however, we cannot rule out a stellar collision as the genesis event, which could result in the observed Halpha activity. Based upon a two-component blackbody fit to all wavelengths of our data, we conclude that, as of 2009, a shell of ejecta surrounded V838 Monocerotis at a radius of R=263+/-10 AU with a temperature of T=285+/-2 K. This result is consistent with IR interferometric observations from the same era and predictions from the Lynch et al. model of the expanding system, which provides a simple framework for understanding this complicated system.