NATURE VERSUS NURTURE: LUMINOUS BLUE VARIABLE NEBULAE IN AND NEAR MASSIVE STELLAR CLUSTERS AT THE GALACTIC CENTER

Abstract

Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet Cluster at the Galactic Center: the Pistol star, G0.120-0.048, and qF362. We present imaging at 19, 25, 31, and 37 {\mu}m of the region containing these three LBVs, obtained with SOFIA using FORCAST. We argue that the Pistol and G0.120-0.048 are identical ``twins" that exhibit contrasting nebulae due to the external influence of their different environments. Our images reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding G0.120-0.048. Dust and gas composing the Pistol nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars. The northern region of the Pistol nebula is decelerated due to the interaction with the high-velocity (2000 km/s) winds from adjacent Wolf-Rayet Carbon (WC) stars. With the DustEM code we determine that the Pistol nebula is composed of a distribution of very small, transiently-heated grains (10-~35 {\AA}) and that it exhibits a gradient of decreasing grain size from the south to the north due to differential sputtering by the winds from the WC stars. Dust in the G0.120-0.048 nebula is primarily heated by the central star; however, the nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol nebula, the G0.120-0.048 nebula is freely expanding into the surrounding medium. Given independent dust and gas mass estimates we find that the Pistol and G0.120-0.048 nebulae exhibit similar gas-to-dust mass ratios of ~310 and ~290, respectively. Both nebulae share identical size scales (~ 0.7 pc) which suggests that they have similar dynamical timescales of ~10^5 yrs, assuming a shell expansion velocity of v_exp 60 km/s.