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

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.

To appear in Astrophysical Journal (Letters), 14 pages, 2 figures

References in corpus (4)

• The Photometric and Spectral Evolution of the 2008 Luminous Optical Transient in NGC 300
• Reaction rate uncertainties and 26Al in AGB silicon carbide stardust
• Spitzer observations of V4332 Sagittarii: Detection of Alumina Dust
• Spitzer Observations of V838 Monocerotis: Detection of a Rare Infrared Light Echo

Cited by in corpus (12)

• ExoMol molecular line lists: IX The spectrum of AlO
• Tracing the phase transition of Al-bearing species from molecules to dust in AGB winds. Constraining the presence of gas-phase (Al2O3)n clusters
• An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species
• The ASAS-SN Catalog of Variable Stars IX: The Spectroscopic Properties of Galactic Variable Stars
• Radiative lifetimes and cooling functions for astrophysically important molecules
• Post-outburst spectra of a stellar-merger remnant of V1309 Scorpii: from a twin of V838 Monocerotis to a clone of V4332 Sagittarii
• A high-resolution line list for AlO
• Search for aluminium monoxide in the winds of oxygen-rich AGB stars
• The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars
• The continued optical to mid-IR evolution of V838 Monocerotis
• Evolution of the dust in V4332 Sagittarii
• VVV-WIT-13: an eruptive young star with cool molecular features