Confirmation of the Luminous Blue Variable Status of MWC 930

A S Miroshnichenko,E A Laag,N Manset,J Zsargó,D E Reichart,H Levato,J H Groh,A P Lacluyze,J A Juárez Jiménez,M C Nysewander,J B Haislip,K M Ivarsen,R J Rudy,S V Zharikov,M Grosso,R C Puetter,K B Crawford

doi:10.1155/2014/130378

Abstract

We present spectroscopic and photometric observations of the emission-line star MWC 930 (V446 Sct) during its long-term optical brightening in 2006–2013. Based on our earlier data we suggested that the object has features found in Luminous Blue Variables (LBV), such as a high luminosity (~3 105 L⊙), a low wind terminal velocity (~140 km s−1), and a tendency to show strong brightness variations (~1 mag over 20 years). For the last~7 years it has been exhibiting a continuous optical and near-IR brightening along with a change of the emission-line spectrum appearance and cooling of the star’s photosphere. We present the object’sV-band light curve, analyze the spectral variations, and compare the observed properties with those of other recognized Galactic LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide Galactic LBV that is currently in the middle of an S Dor cycle.

Highlights

Luminous Blue Variables are evolved massive stars that undergo an evolutionary phase associated with a very strong mass loss
Based on our earlier data we suggested that the object has features found in Luminous Blue Variables (LBV), such as a high luminosity (∼3 105 L⊙), a low wind terminal velocity (∼140 km s−1), and a tendency to show strong brightness variations (∼1 mag over 20 years)
In our previous paper [3] we suggested that the emissionline star MWC 930 = V446 Sct is an LBV candidate

Summary

Introduction

Luminous Blue Variables are evolved massive stars that undergo an evolutionary phase associated with a very strong mass loss. Unlike fast winds of most supergiants with terminal velocities of thousands km s−1, winds of LBVs are typically slow and dense These properties in some cases are responsible for formation of circumstellar (CS) dust around LBVs. Other features of LBVs include eruptions on time scales of years when an optical brightening is accompanied by a photospheric cooling and corresponding changes in the ionization state of the CS gas. Other features of LBVs include eruptions on time scales of years when an optical brightening is accompanied by a photospheric cooling and corresponding changes in the ionization state of the CS gas These variations, which are called S Dor cycles, along with the wind signatures (narrow spectral lines and rich emission-line spectra) and B-A spectral types allow identifying LBVs almost unambiguously. They are known to undergo giant eruptions (e.g., P Cyg near 1600 and η Car in 1830’s), but these events are rare and much harder to catch

Results

Discussion

Conclusion