Measuring Organic Molecular Emission in Disks with Low Resolution Spitzer Spectroscopy

TL;DR

This study assesses the effectiveness of low resolution Spitzer IRS spectra in quantitatively analyzing organic molecular emissions, particularly HCN, from protoplanetary disks around young stars, enabling broader statistical studies.

Contribution

It demonstrates that low resolution spectra can reliably measure molecular emission trends and reveals correlations with stellar properties, expanding the utility of archival data.

Findings

Low resolution spectra can recover trends seen in high resolution data.

HCN emission correlates with stellar accretion rate.

HCN emission correlates with X-ray luminosity.

Abstract

We explore the extent to which Spitzer IRS spectra taken at low spectral resolution can be used in quantitative studies of organic molecular emission from disks surrounding low mass young stars. We use Spitzer IRS spectra taken in both the high and low resolution modules for the same sources to investigate whether it is possible to define line indices that can measure trends in the strength of the molecular features in low resolution data. We find that trends in HCN emission strength seen in the high resolution data can be recovered in low resolution data. In examining the factors that influence the HCN emission strength, we find that the low resolution HCN flux is modestly correlated with stellar accretion rate and X-ray luminosity. Correlations of this kind are perhaps expected based on recent observational and theoretical studies of inner disk atmospheres. Our results demonstrate the potential of using the large number of low resolution disk spectra that reside in the Spitzer archive to study the factors that influence the strength of molecular emission from disks. Such studies would complement results for the much smaller number of circumstellar disks that have been observed at high resolution with IRS.