Herschel observations of extra-ordinary sources: Detection of Hydrogen Fluoride in absorption towards Orion~KL

TL;DR

This paper reports the first detection of hydrogen fluoride in absorption towards Orion KL using Herschel, revealing its abundance in the molecular outflow and providing insights into fluorine chemistry in star-forming regions.

Contribution

First detection of HF in absorption towards Orion KL with Herschel, analyzing its abundance and outflow characteristics in a high-mass star-forming region.

Findings

HF absorption shows a P-Cygni profile indicating outflow dynamics.

HF abundance relative to hydrogen is about 0.6% of solar fluorine abundance.

HF column density estimated at 2.9 x 10^13 cm^-2.

Abstract

We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal of contaminating features associated with common molecules ("weeds"), the HF spectrum shows a P-Cygni profile, with weak redshifted emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity molecular outflow, we obtain a lower limit of ~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding to 0.6% of the solar abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2, but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4.