HCN and HNC in the Disk of an Outbursting Young Star, V883 Ori

TL;DR

This study investigates the distribution of HCN and HNC molecules in the protoplanetary disk of the outbursting young star V883 Ori, revealing how temperature-driven chemical reactions influence their abundance ratios during stellar outbursts.

Contribution

The paper presents a chemical model that explains the observed HCN/HNC distribution in V883 Ori's disk, linking it to ongoing stellar outburst activity and temperature-dependent chemistry.

Findings

HCN and HNC form ring structures in the disk.

HNC is depleted in the warmer inner regions.

Chemical modeling matches observed abundance ratios.

Abstract

Hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) are isomers with similar chemical properties. However, HNC can be converted into other molecules by reactions with atomic hydrogen (H) and atomic oxygen (O), resulting in a variation of the HCN/HNC abundance ratio. These reaction rates are sensitive to gas temperature, resulting in different abundance ratios in different temperature environments. The emission of HCN and HNC was found to distribute along ring structures in the protoplanetary disk of V883 Ori. HCN exhibits a multi-ring structure consisting of inner and outer rings. The outer ring represents a genuine chemical structure, whereas the inner ring appears to display such characteristics due to the high dust continuum optical depth at the center. However, HNC is entirely depleted in the warmer inner ring, while its line intensity is similar to that of HCN in the colder outer ring. In this study, we present a chemical calculation that reproduces the observed HCN/HNC abundance ratio in the inner and outer rings. This calculation suggests that the distinct emission distribution between HCN and HNC results from a currently ongoing outburst in V883 Ori. The sublimation of HCN and HNC from grain surfaces and the conversion of HNC to HCN determine their chemical distribution in the heated, warm inner disk.