Research Highlight

Clues to alumina dust formation in space

doi:10.1038/nindia.2012.112 Published online 29 July 2012

Using an Earth-bound telescope, researchers have uncovered new clues on how alumina dust forms in asymptotic giant branch (AGB) stars, which burn hydrogen fuel vehemently and with great luminosity.

The clues came by studying the infrared bands of AlO radicals released from such stars. Detecting AlO radicals could lead to subsequent searches for radioactive aluminium in such stars.

Oxides of titanium and vanadium are often encountered in the spectra of cool, oxygen-rich stars. AlO, in contrast, is rarely detected and therefore poorly studied. The researchers decided to look for AlO by looking at AGB stars using the 3.8-m UK Infrared Telescope (UKIRT) located on the summit of Hawaii's Mauna Kea. They began by looking at 487 sources, and then narrowed the search to 17 stars.

The researchers detected AlO in the spectra of 13 stars. Of these 13, two were Mira variables, a type of fast-pulsating star, nine were hydroxyl or infrared (HO/IR) stars, and two were classified as infrared sources.

The bulk of positive AlO detections were in HO/IR stars and Mira variables, which are essentially AGB stars. HO/IR stars are much-evolved stars that are on the verge of becoming planetary nebulae and therefore belong to the tip of the AGB branch.

The researchers detected near-IR bands of AlO in the 1.0–1.35 μm region, which shows that the infrared bands are fairly prevalent in sources with low-temperature and oxygen-rich environments. They say that the AlO radical plays a pivotal role in the formation of silicate and alumina dust.

The authors of this work are from: Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad, Gujarat, India, Joint Astronomy Centre, Aohoku Place, University Park, Hilo, Hawaii,USA and KTH-AlbaNova, Applied Physics, Roslagstullsbacken, Stockholm, Sweden.


  1. Banerjee, D. P. K. et al. The A-X infrared bands of aluminum oxide in stars: Search and new detections. Astrophys. J. Lett. 753, L20 (2012)  | Article |