Caltech/IPAC Lunch Seminar

Carbon-rich Wolf-Rayet (WC) binaries can evolve to a dust formation phase in less than a few million years, suggesting that their contribution to the dust and polycyclic aromatic hydrocarbons (PAH) budget of the early universe may have been long overlooked. Recent JWST observations have revealed that the carbonaceous material produced by these stars survives for hundreds of years and therefore likely enriches the ISM with dust and aromatic molecules. The textbook example of such a dust producer is WR140. In this work, we investigate the bulk dust properties to explore the carbonaceous nanodust associated with the PAH emission features detected by MRS. By calculating the dust color-temperature using MIRI Images, we find direct evidence of dust grains that are not in thermal equilibrium with the stellar radiation field. This confirms that there is a population of nano-sized dust grains that are heated by the intense stellar radiation, resulting in high, stochastic, temperature spikes. The dust surrounding WR140 remains in this transiently heated regime out to over 50,000 au from the central binary. This implies that the PAH-like molecules created by WR140 are robust; They survive the intense stellar environment and high velocities. Additionally, we modeled the dust emission with DustEM, employing a Hydrogen-poor amorphous-carbon grain model. Our models show that the dust mass ratio of very small grains (a≈0.002μm) to larger grains (a≈0.15μm) remains relatively constant as a function of distance from the stars. These results confirm that the dust pushed toward the ISM by WR140 is composed, in part, of H-poor nanodust. It is evident that WR140 is a unique laboratory for studying the survivability of aromatic nanodust in an environment that may represent a major source for such molecules in the early universe.