SOFIA/FORCAST Observations of the Luminous Blue Variable Candidates MN 90 and HD 168625

TL;DR

This study uses SOFIA/FORCAST infrared imaging to analyze dust shells around LBV candidates MN 90 and HD 168625, estimating dust properties, mass-loss rates, and evolutionary states of these massive stars.

Contribution

It provides new detailed infrared observations and radiative transfer modeling of dust shells around LBV candidates, enhancing understanding of their mass-loss processes and evolutionary stages.

Findings

MN 90 has a spherical dust shell with a temperature of 59 K.

HD 168625 exhibits a limb-brightened torus with dust at 170 K.

Mass-loss rates are estimated at ~7.3x10^-7 and ~3.2x10^-7 M_sun/yr for MN 90 and HD 168625, respectively.

Abstract

We present SOFIA/FORCAST imaging of the circumstellar dust shells surrounding the luminous blue variable (LBV) candidates MN 90 and HD 168625 to quantify the mineral abundances of the dust and to constrain the evolutionary state of these objects. Our image at 37.1 micron of MN 90 shows a limb-brightened, spherical dust shell. A least-squares fit to the spectral energy distribution of MN 90 yields a dust temperature of 59 \pm 10 K, with the peak of the emission at 42.7 micron. Using 2-Dust radiative transfer code, we estimate for MN 90 that mass-loss occurred at a rate of (7.3 \pm 0.4)x10^-7 M_sun/yr x (v_exp/50 km/s) to create a dust shell with a dust mass of (3.2 \pm 0.1)x10^-2 M_sun. Our images between 7.7 - 37.1 micron of HD 168625 complement previously obtained mid-IR imaging of its bipolar nebulae. The SOFIA/FORCAST imaging of HD 168625 shows evidence for the limb-brightened peaks of an equatorial torus. We estimate a dust temperature of 170 \pm 40 K for the equatorial dust surrounding HD 168625, with the peak of the emission at 18.3 micron. Our 2-Dust model for HD 168625 estimates that mass-loss occurred at a rate of (3.2 \pm 0.2)x10^-7 M_sun/yr to create a dust torus/shell with a dust mass of (2.5 \pm 0.1)x10^-3 M_sun.