Warm HCN in the planet formation zone of GV Tau N

TL;DR

This study uses interferometric observations to analyze the distribution and chemistry of HCN and HCO+ in the disks of the binary star GV Tau, revealing high HCN abundance in the warm inner disk of GV Tau N due to photo-chemical processes.

Contribution

First spatially resolved detection of HCN in the inner disk of GV Tau N, highlighting chemical differences in binary star disks.

Findings

HCN 3->2 line detected only in GV Tau N's disk.

HCN/HCO+ ratio >300 in GV Tau N's inner disk.

High HCN abundance explained by warm, dense, photo-chemical processes.

Abstract

The Plateau de Bure Interferometer has been used to map the continuum emission at 3.4 mm and 1.1 mm together with the J=1->0 and J=3->2 lines of HCN and HCO+ towards the binary star GV Tau. The 3.4 mm observations did not resolve the binary components and the HCN J=1->0 and HCO+ J=1->0 line emissions trace the circumbinary disk and the flattened envelope. However, the 1.1 mm observations resolved the individual disks of GV Tau N and GV Tau S and allowed us to study their chemistry. We detected the HCN 3->2 line only towards the individual disk of GV Tau N, and the emission of the HCO+ 3->2 line towards GV Tau S. Simple calculations indicate that the 3->2 line of HCN is formed in the inner R<12 AU of the disk around GV Tau N where the HCN/HCO+ abundance ratio is >300. On the contrary, this ratio is <1.6 in the disk around GV Tau S. The high HCN abundance measured in GV Tau N is well explained by photo-chemical processes in the warm (>400K) and dense disk surface.