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A star


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A star of spectral type A, whose spectrum is dominated by absorption lines of hydrogen (the Balmer series); in fact, their hydrogen absorption lines are the strongest of any normal stars. They appear blue-white in colour. A-type stars on the main sequence have temperatures in the range 7200–9500 K, are 7–50 times more luminous than the Sun, and are of 1.5–3 solar masses. Sirius, the brightest star in the sky, is of spectral type A1, and Vega is type A0. A-type supergiants, such as Deneb, are more massive stars (up to 16 solar masses) evolving off the main sequence, with temperatures up to 9700 K, and luminosities over 35 000 times the Sun's. There are a number of peculiar groups among stars of this spectral type, particularly the Ae stars, Am stars, and Ap stars. Also, two of the principal types of pulsating variable (RR Lyrae stars and Delta Scuti stars) are evolved stars whose surface temperatures are in the A-star range.

Subjects: Astronomy and Astrophysics.


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