Imaging the photoevaporating disk and radio jet of GM Aur

TL;DR

This study uses multi-frequency radio observations to image and analyze the components of the GM Aur transitional disk, revealing the roles of photoevaporation, jets, and EUV radiation in disk dispersal.

Contribution

First spatially resolved imaging of the dust disk, ionized jet, and photoevaporative wind in GM Aur at multiple radio wavelengths, linking EUV radiation to wind ionization.

Findings

Radio jet mass loss rate aligns with ejection-accretion ratios in young objects.

EUV radiation is the main ionizing mechanism of the photoevaporative wind.

EUV alone cannot account for the observed disk dispersal timescale.

Abstract

Photoevaporation is probably the main agent for gas dispersal during the last stages of protoplanetary disk evolution. However, the overall mass loss rate in the photoevaporative wind and its driving mechanism are still not well understood. Here we report multi-configuration Very Large Array observations at 0.7, 3, and 5 cm towards the transitional disk of GM Aur. Our radio continuum observations allow us to image and spatially resolve, for the first time, the three main components at work in this stage of the disk evolution: the disk of dust, the ionized radio jet perpendicular to it, and the photoevaporative wind arising from the disk. The mass loss rate inferred from the flux density of the radio jet is consistent with the ratio between ejection and accretion rates found in younger objects, suggesting that transitional disks can power collimated ejections of material apparently following the same physical mechanisms as much younger protostars. Our results indicate that extreme-UV (EUV) radiation is the main ionizing mechanism of the photoevaporative wind traced by the free-free emission. The required low EUV photon luminosity of $\sim6\times10^{40}$ s$^{-1}$ would produce a photoevaporation rate of only $\dot{M}_{\rm w,EUV}\simeq1.3\times10^{-10}~M_{\odot}$ yr$^{-1}$. Therefore, other mechanisms are required to disperse the disk in the timescale imposed by observations.