# Radio Monitoring of Protoplanetary Discs

## TL;DR

This study uses multi-year radio monitoring of T Tauri stars to identify variability and multiple emission mechanisms, revealing that single-epoch radio observations are insufficient to understand the physical processes in protoplanetary discs.

## Contribution

It provides the first long-term radio variability data for T Tauri stars, highlighting the complexity of emission mechanisms and the presence of grain growth to centimeter-sized pebbles.

## Key findings

- Most sources show variability at 7 mm, indicating non-thermal emission processes.
- Evidence of grain growth to cm-sized pebbles in some sources.
- Multiple emission mechanisms are common, complicating single-epoch interpretations.

## Abstract

Protoplanetary disc systems observed at radio wavelengths often show excess emission above that expected from a simple extrapolation of thermal dust emission observed at short millimetre wavelengths. Monitoring the emission at radio wavelengths can be used to help disentangle the physical mechanisms responsible for this excess, including free-free emission from a wind or jet, and chromospheric emission associated with stellar activity. We present new results from a radio monitoring survey conducted with Australia Telescope Compact Array over the course of several years with observation intervals spanning days, months and years, where the flux variability of 11 T Tauri stars in the Chamaeleon and Lupus star forming regions was measured at 7 and 15 mm and 3 and 6 cm. Results show that for most sources are variable to some degree at 7 mm, indicating the presence of emission mechanisms other than thermal dust in some sources. Additionally, evidence of grain growth to cm-sized pebbles was found for some sources that also have signs of variable flux at 7 mm. We conclude that multiple processes contributing to the emission are common in T Tauri stars at 7 mm and beyond, and that a detection at a single epoch at radio wavelengths should not be used to determine all processes contributing to the emission.