A Search for Light Hydrides in the Envelopes of Evolved Stars

TL;DR

This study searched for specific light hydrides in the envelopes of evolved stars using SOFIA but found none, providing upper limits on their abundances and insights into circumstellar chemistry.

Contribution

First observational constraints on SiH, PH, and FeH in evolved star envelopes, informing models of hydride formation and destruction in dense circumstellar environments.

Findings

No detections of targeted hydrides in the observed spectra.

Upper limits established for the abundances of SiH, PH, and FeH.

Non-detections suggest formation barriers and reactive environments limit hydride presence.

Abstract

We report a search for the diatomic hydrides SiH, PH, and FeH along the line of sight toward the chemically rich circumstellar envelopes of IRC+10216 and VY Canis Majoris. These molecules are thought to form in high temperature regions near the photospheres of these stars, and may then further react via gas-phase and dust-grain interactions leading to more complex species, but have yet to be constrained by observation. We used the GREAT spectrometer on SOFIA to search for rotational emission lines of these molecules in four spectral windows ranging from 600 GHz to 1500 GHz. Though none of the targeted species were detected in our search, we report their upper limit abundances in each source and discuss how they influence the current understanding of hydride chemistry in dense circumstellar media. We attribute the non-detections of these hydrides to their compact source sizes, high barriers of formation, and proclivity to react with other molecules in the winds.