The A-X infrared bands of Aluminum Oxide in stars: search and new detections

TL;DR

This study investigates the presence of AlO A-X infrared bands in stellar spectra, revealing their prevalence in cool, oxygen-rich stars and exploring their implications for dust formation and radioactive isotope detection.

Contribution

It provides the first extensive survey of AlO A-X bands in 13 stars, highlighting their occurrence in AGB stars and discussing their potential applications in astrophysics.

Findings

AlO A-X bands detected in 13 out of 17 stars surveyed

Bands are common in low-temperature, O-rich stellar environments

Variation in band strength observed in IRAS 18530+0817

Abstract

We describe a search for the A-X infrared bands of AlO with a view to better understand the characteristics of this radical. These bands are infrequently encountered in astronomical sources but surprisingly were very prominent in the spectra of two well-known, nova-like variables (V838 Mon and V4332 Sgr) thereby motivating us to explore the physical conditions necessary for their excitation. In this study, we present the detection of A-X bands in the spectra of 13 out of 17 stars, selected on the basis of their J-K colors as potential candidates for detection of these bands. The majority of the AlO detections are in AGB stars viz. 9 OH/IR stars, 2 Mira variables and 2 bright infrared sources. Our study shows that the A-X bands are fairly prevalent in sources with low temperature and O-rich environments. Interesting variation in strength of the AlO bands in one of the sources (IRAS 18530+0817) is reported and the cause for this is examined. Possible applications of the present study are discussed in terms of the role of AlO in alumina dust formation, the scope for estimating the radioactive $^{26}$Al content in AGB stars from the A-X bands, and providing possible targets for further mm/radio studies of AlO which has recently been discovered at millimeter wavelengths.