# Luminosity outburst chemistry in protoplanetary discs: going beyond standard tracers

## TL;DR

This study investigates how luminosity outbursts in protoplanetary discs affect chemical compositions, revealing different response types and highlighting the importance of dust size distribution and burst duration on chemical signatures.

## Contribution

It extends understanding of outburst-induced chemistry by categorizing species responses and emphasizing the role of dust size and burst timing in chemical evolution.

## Key findings

- Icy mantle evaporation occurs during outbursts, with quick recovery except for benzene ice.
- Organic molecules can retain altered abundances for centuries after outbursts.
- CO and CO₂ trace past outbursts mainly in outer disc regions.

## Abstract

The chemical influence of luminosity outbursts on the environments of young solar-type stars is explored. Species are categorised into several types according to their response to the outburst. The first and second types imply chemical changes only during the outburst (with slightly different behaviours). These response types are mostly observed close to the star and are caused by icy mantle evaporation. However, mantles recover after the outburst almost immediately. A notable exception is benzene ice, which is accumulated on dust surfaces during and after the outburst, so that its abundance exceeds the pre-outburst level by orders of magnitude. The third type of response is mostly seen at the disc periphery and implies alteration of abundances during the outburst and preservation of these `abnormal' abundances for centuries. This behaviour is typical of organic compounds, like HCOOCH$_3$, CH$_3$CN, CH$_2$CO. Their presence in the dark disc regions can be a manifestation of the past outburst. CO and CO$_2$ only trace past outbursts at the remote disc regions. The outburst changes the C/O ratio, but it quickly returns to the pre-outburst value almost everywhere in the disc. An important factor determining the sensitivity of molecular composition to the outburst is the dust size distribution. The duration of the pre-outburst stage and of the outburst itself influence the chemical effects, if the burst duration is shorter than 50 yr and the duration of the quiescent phase between the bursts is shorter than 100 kyr.