A starsStars of spectral type A. They are blue-white or white and have a surface temperature (T eff) of about 7500 to 9900 kelvin for main-sequence stars, and up to 12 000 K for supergiants. Balmer absorption lines of hydrogen dominate the spectrum, reaching maximum strength for A0 to A3 stars; lines of ionized and neutral metals slowly strengthen with the H and K lines of ionized calcium appearing in later subdivisions. A few A stars (Am and Ap stars) have anomalously high abundances of metals and rare earth elements. Color indices for A0 stars are zero. Vega, Sirius, Deneb, and Altair are A stars.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006