A novel method for estimating the far-ultraviolet flux, and a catalogue for disc-hosting stars in nearby star-forming regions

Abstract

When protoplanetary discs are externally irradiated by far-ultraviolet (FUV) photons from OBA-type stars, they lose material through photoevaporative winds. This reduces the amount of material that is available to form planets. Understanding the link between the environmental irradiation and the observed disc properties requires accurately evaluating the FUV flux at disc-hosting stars, which can be challenging because of the uncertainty in stellar parallax. We addressed this issue by proposing a novel approach: using the local density distribution of a star-forming region (i.e. 2D pairwise star separation distribution) and assuming isotropy, we inferred the 3D separation between disc-hosting stars and massive stars. We tested this approach on synthetic clusters and showed that it significantly improves accuracy compared to previous methods. We computed the FUV fluxes for numerous star-bearing discs in seven regions within ~200 pc, six regions in Orion and in Serpens sub-regions. We provided a publicly accessible catalogue. We found that discs in regions hosting late-type B and early-type A stars can reach non-negligible FUV radiation levels for the disc evolution (10–100 G₀). We investigated dust disc masses relative to FUV fluxes and detected indications of a negative correlation when we restricted the investigation to average region ages. However, we emphasize the need for more stellar and disc measurements at >10² G₀ to probe the dependence of disc properties on environmental irradiation. The method presented in this work is a powerful tool that can be expanded to additional regions.