The ISO Long Wavelength Spectrometer line spectrum of VY Canis Majoris and other oxygen-rich evolved stars

TL;DR

This study analyzes far-infrared spectra of oxygen-rich stars, especially VY CMa, using ISO LWS data to identify molecular lines, develop a fitting method for blended water lines, and compare results across multiple stars.

Contribution

It introduces a new fitting approach for blended water lines in infrared spectra and provides detailed line flux measurements for VY CMa and other stars.

Findings

Identified multiple water, CO, OH, NH3, and H3O+ lines in spectra.

Developed a method to disentangle blended water lines.

Compared molecular line fluxes across different stars.

Abstract

The far-infrared spectra of circumstellar envelopes around various oxygen-rich stars were observed using the ISO Long Wavelength Spectrometer (LWS). We have examined high signal-to-noise ISO LWS observations of the luminous supergiant star, VY CMa, with the aim of identifying all of the spectral lines. By paying particular attention to water lines, we aim to separate the lines due to other species, in particular, to prepare for forthcoming observations that will cover the same spectral range using Herschel PACS and at higher spectral resolution using Herschel HIFI and SOFIA. We have developed a fitting method to account for blended water lines using a simple weighting scheme to distribute the flux. We have applied this approach to several other stars which we compare with VY CMa. We present line fluxes for the unblended H2O and CO lines, and present detections of several possible nu_2=1 vibrationally excited water lines. We also identify blended lines of OH, one unblended and several blended lines of NH3, and one possible detection of H3O+.