Free-free Emission and Radio Recombination Lines from Photoevaporating Disks

TL;DR

This paper predicts that photoevaporative winds from protoplanetary disks produce detectable free-free radio emission and recombination lines, which can be used to study disk dispersal and wind properties.

Contribution

It demonstrates that radio observations can detect and analyze photoevaporative winds from disks, providing new methods to measure wind parameters and disk dispersal processes.

Findings

VLA observations may have already detected free-free emission from TWHya.

Radio recombination lines can be used to confirm the emission origin.

Radio data can constrain wind temperature and electron density.

Abstract

Recent infrared observations have demonstrated that photoevaporation driven by high-energy photons from the central star contributes to the dispersal of protoplanetary disks. Here, we show that photoevaporative winds should produce a detectable free-free continuum emission given the range of stellar ionizing photons and X-ray luminosities inferred for young sun-like stars. We point out that VLA observations of the nearby disk around TWHya might have already detected this emission at centimeter wavelengths and calculate the wind electron density and mass flow rate. We also estimate the intensities of H radio recombination lines tracing the wind and discuss which ones could be detected with current instrumentation. The detection and profiles of these recombination lines would unambiguously prove our inference of free-free emission from photoevaporating disks like TWHya. In addition, radio/millimeter data can help constraining wind parameters such as temperature and electron density that are fundamental in measuring mass flow rates.