PACS and SPIRE Spectroscopy of the Red Supergiant VY CMa

TL;DR

This study presents comprehensive Herschel PACS and SPIRE spectroscopy of the red supergiant VY CMa, revealing over 900 spectral lines and detailed molecular composition, providing insights into its circumstellar chemistry and mass-loss processes.

Contribution

First full spectral survey of VY CMa from 55 to 672 microns, identifying over 900 lines and 13 molecules, highlighting complex circumstellar chemistry.

Findings

Detection of over 900 spectral lines, including 13 molecules.

Water is highly abundant with a low ortho-to-para ratio.

Chemical non-equilibrium influences molecular abundances.

Abstract

With a luminosity > 10^5 Lsun and a mass-loss rate of about 2.10-4 Msun/yr, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VYCMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55 to 672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as 1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.