WS1: one more new Galactic bona fide luminous blue variable

TL;DR

This paper confirms WS1 as a genuine Galactic luminous blue variable through spectroscopic and photometric monitoring, showing significant brightness and spectral changes that demonstrate its LBV nature and update the known count of such stars.

Contribution

It provides the first detailed observational confirmation of WS1 as a bona fide LBV, adding to the Galactic LBV census and illustrating characteristic variability.

Findings

WS1 brightened by over 1 mag in multiple bands

Spectral changes indicate the star became cooler

Brightness peaked in December 2013 and then declined

Abstract

In this Letter, we report the results of spectroscopic and photometric monitoring of the candidate luminous blue variable (LBV) WS1, which was discovered in 2011 through the detection of a mid-infrared circular shell and follow-up optical spectroscopy of its central star. Our monitoring showed that WS1 brightened in the B, V and I bands by more than 1 mag during the last three years, while its spectrum revealed dramatic changes during the same time period, indicating that the star became much cooler. The light curve of WS1 demonstrates that the brightness of this star has reached maximum in 2013 December and then starts to decline. These findings unambiguously proved the LBV nature of WS1 and added one more member to the class of Galactic bona fide LBVs, bringing their number to sixteen (an updated census of these objects is provided).