Class A — A-type (White)

A-type stars are white or blue-white stars with surface temperatures of 7,500 to 10,000 K. They comprise about 0.6% of main-sequence stars and are known for having the strongest hydrogen absorption lines in their spectra. Many of the best-known stars are A-type, including Sirius (A1V), the brightest star in the night sky, and Vega (A0V), which was historically the reference star for the magnitude system. A-type stars live for roughly 1-2 billion years.

A-type stars are white to blue-white stars with surface temperatures between 7,500 and 10,000 K. They represent about 0.6% of main-sequence stars and include many of the most culturally important stars in the sky. A-type stars are particularly significant in astronomical history: Vega, the prototypical A0V star, served as the original definition of apparent magnitude 0.0 and was the first star (other than the Sun) to be photographed (1850) and to have its spectrum recorded (1872).

Characteristics

A-type spectra are dominated by the hydrogen Balmer series, which reaches maximum strength at A0. These stars are massive enough (1.4-2.1 solar masses) to have radiative envelopes rather than convective ones, which allows chemical peculiarities to develop. The Am (metallic-line) and Ap (peculiar) stars show unusual abundances of certain elements concentrated by diffusion in their stable atmospheres. A-type main-sequence stars live for roughly 1-3 billion years. The debris disks detected around many A stars (notably Vega and Fomalhaut) hint at planetary systems in formation.

Notable Examples

Sirius (Alpha Canis Majoris, A1V) is the brightest star in the night sky at magnitude -1.46, largely due to its proximity at 8.6 light-years. Its white dwarf companion Sirius B was the first white dwarf discovered. Vega (Alpha Lyrae, A0V) and Altair (Alpha Aquilae, A7V) join Deneb to form the Summer Triangle. Fomalhaut (Alpha Piscis Austrini, A3V) hosts a dramatic debris ring and was the first star with a directly imaged exoplanet candidate. Castor (Alpha Geminorum) is a spectacular sextuple star system dominated by A-type components.

HIP 95030 HIP 95009 HIP 37817 HIP 37818 HIP 37824 HIP 37829 HIP 37833 HIP 37836 HIP 37837 HIP 37839 HIP 37840 HIP 37849 HIP 95078 HIP 95079 HIP 95086 HIP 95240 HIP 95243 HIP 95257 HIP 95236 HIP 40342 HIP 95246 HIP 95248 HIP 95269 HIP 95272 HIP 95284 HIP 95259 HIP 95273 HIP 95295 HIP 95300 HIP 95301 HIP 95303 HIP 95304 HIP 9561 HIP 3791 HIP 37913 HIP 37920 HIP 9563 HIP 9571 HIP 95330 HIP 95339 HIP 95343 HIP 95353 HIP 95367 HIP 95368 HIP 95371 HIP 95376 HIP 95379 HIP 95355

Frequently Asked Questions

What is a class A star?

Class A (A-type (White)) stars are white stars. A-type stars are white or blue-white stars with surface temperatures of 7,500 to 10,000 K. They comprise about 0.6% of main-sequence stars and are known for having the strongest hydrogen absorption li

How hot are class A stars?

Class A stars have surface temperatures between 7,500 K and 10,000 K.

What color are class A stars?

Class A stars appear white.

How many class A stars are in the StarFYI database?

StarFYI currently catalogs 18,693 class A stars.

How luminous are class A stars?

Luminous, 5-25 solar luminosities