The Debris Disk of Vega: A Steady-State Collisional Cascade, Naturally

TL;DR

This study models Vega's debris disk as a steady-state collisional cascade, successfully matching observations and constraining disk parameters, thus resolving previous contradictions with standard disk evolution theories.

Contribution

It provides a comprehensive physical model of Vega's debris disk that aligns with observations and incorporates new factors like stellar luminosity variations and cratering collisions.

Findings

Vega's debris disk can be explained by a steady-state collisional cascade.

Estimated total mass of disk solids is about 10 Earth masses.

Including stellar luminosity variations and cratering is essential for accurate modeling.

Abstract

It has been argued that the photometric data and images of the archetypical debris disk around Vega may be in contradiction with the standard, steady-state collisional scenario of the disk evolution. Here we perform physical modeling of the Vega disk "from the sources". We assume that dust is maintained by a "Kuiper belt" of parent planetesimals at ~ 100 AU and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-infrared to millimeter, as well as the mid-IR and sub-millimeter radial brightness profiles of the Vega disk. Thus our results suggest that the Vega disk observations are compatible with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in < 100 km-sized bodies is estimated to be ~ 10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of ~ 350 Myr, the disk must have lost a few Earth masses of solids during that time. We also demonstrate that using an intermediate luminosity of the star between the pole and the equator, as derived from its fast rotation, is required to reproduce the debris disk observations. Finally, we show that including cratering collisions into the model is mandatory.