High Resolution Mid-Infrared Spectroscopy of NGC 7538 IRS 1: Probing Chemistry in a Massive Young Stellar Object

TL;DR

This study uses high-resolution mid-infrared spectroscopy to analyze the chemical composition and physical conditions of a massive young stellar object, revealing high molecular column densities and supporting a disk-based model.

Contribution

It provides detailed molecular absorption data and supports a disk model for the environment of a massive young star, with new measurements for CH3 and HNCO.

Findings

High molecular column densities (~10^16 cm^2) observed for all molecules.

Two velocity components identified between -54 and -63 km/s.

Support for a nearly edge-on disk model around the star.

Abstract

We present high resolution (R = 75,000-100,000) mid-infrared spectra of the high-mass embedded young star IRS 1 in the NGC 7538 star-forming region. Absorption lines from many rotational states of C2H2, 13C12CH2, CH3, CH4, NH3, HCN, HNCO, and CS are seen. The gas temperature, column density, covering factor, line width, and Doppler shift for each molecule are derived. All molecules were fit with two velocity components between -54 and -63 km/s. We find high column densities (~ 10e16 cm^2) for all the observed molecules compared to values previously reported and present new results for CH3 and HNCO. Several physical and chemical models are considered. The favored model involves a nearly edge-on disk around a massive star. Radiation from dust in the inner disk passes through the disk atmosphere, where large molecular column densities can produce the observed absorption line spectrum.