On Magnesium Sulfide as the Carrier of the 30micron Emission Feature in Evolved Stars

TL;DR

This paper investigates the origin of the 30 micron emission feature in evolved stars and argues that magnesium sulfide (MgS) is unlikely to be its carrier due to mass constraints.

Contribution

The study challenges the prevailing hypothesis that MgS causes the 30 micron feature, providing evidence against it based on mass availability in observed sources.

Findings

MgS mass required exceeds available in HD 56126

MgS unlikely to be the carrier of the 30 micron feature

Alternative carriers need to be considered

Abstract

A large number of carbon-rich evolved objects (asymptotic giant branch stars, protoplanetary nebulae, and planetary nebulae) in both the Milky Way galaxy and the Magellanic Clouds exhibit an enigmatic broad emission feature at 30 micron. This feature, extending from 24 micron to 45 micron, is very strong and accounts for up to 30% of the total infrared luminosity of the object. In literature it is tentatively attributed to magnesium sulfide (MgS) dust. Using the prototypical protoplanetary nebula around HD 56126 for illustrative purpose, however, in this work we show that in order for MgS to be responsible for the 30 micron feature, one would require an amount of MgS mass substantially exceeding what would be available in this source. We therefore argue that MgS is unlikely the carrier of the 30 micron feature seen in this source and in other sources as well.