Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas

TL;DR

This study analyzes two luminous WN stars in the Galactic center, revealing for the first time dust presence near WN stars and detecting molecular hydrogen lines, providing insights into their circumstellar environments.

Contribution

The paper introduces the first detection of dust close to WN stars and identifies molecular hydrogen lines in a massive-star nebula, expanding understanding of their circumstellar material.

Findings

WR102ka and WR102c are among the most luminous stars in the Milky Way.

Dust emission dominates the mid-IR spectra of both stars.

A resolved nebula around WR102ka is linked to its evolutionary history.

Abstract

We study relatively isolated massive WN-type stars in the Galactic center. The K-band spectra of WR102ka and WR102c are exploited to infer the stellar parameters and to compute synthetic stellar spectra using the Potsdam Wolf-Rayet (PoWR) model atmosphere code. These models are combined with dust-shell models for analyzing the Spitzer IRS spectra of these objects. Archival IR images complement the interpretation. We report that WR102ka and WR102c are among the most luminous stars in the Milky Way. The mid-IR continua for both objects are dominated by dust emission. For the first time we report the presence of dust in the close vicinity of WN stars. Also for the first time, we have detected lines of pure-rotational transitions of molecular hydrogen in a massive-star nebula. A peony-shaped nebula around 102ka is resolved by the Spitzer MIPS camera. We attribute the formation of this nebula to the recent evolutionary history of WR102ka.