FRIED v2. A new grid of mass loss rates for externally irradiated protoplanetary discs

TL;DR

This paper introduces an updated FRIED grid of mass loss rates for externally irradiated protoplanetary discs, incorporating new physics such as PAH abundance and grain growth, to better model disc evolution and lifetime.

Contribution

The paper presents a new, expanded FRIED grid that includes variable PAH abundance and grain growth effects, improving modeling of external photoevaporation in protoplanetary discs.

Findings

Metallicity variations have minimal impact on mass loss rates.

Lower PAH-to-dust ratios reduce mass loss rates significantly.

Grain growth influences disc evolution and lifetime.

Abstract

We present a new FRIED grid of mass loss rates for externally far-ultraviolet (FUV) irradiated protoplanetary discs. As a precursor to the new grid, we also explore the microphysics of external photoevaporation, determining the impact of polycyclic aromatic hydrocarbon (PAH) abundance, metallicity, coolant depletion (via freeze out and radial drift) and grain growth (depletion of small dust in the outer disc) on disc mass loss rates. We find that metallicity variations typically have a small effect on the mass loss rate, since the impact of changes in heating, cooling and optical depth to the disc approximately cancel out. The new FRIED grid therefore focuses on i) expanding the basic physical parameter space (disc mass, radius, UV field, stellar mass) ii) on enabling variation of the the PAH abundance and iii) including an option for grain growth to have occurred or not in the disc. What we suggest is the fiducial model is comparable to the original FRIED grid. When the PAH-to-dust ratio is lower, or the dust in the wind more abundant, the mass loss rate can be substantially lower. We demonstrate with a small set of illustrative disc evolutionary calculations that this in turn can have a significant impact on the disc mass/radius/ evolution and lifetime.