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 8742 HIP 8754 HIP 8756 HIP 8760 HIP 8763 HIP 8771 HIP 8772 HIP 8783 HIP 8784 HIP 8791 HIP 8797 HIP 8809 HIP 8847 HIP 8866 HIP 8871 HIP 8877 HIP 8896 HIP 8898 HIP 8907 HIP 8937 HIP 8939 HIP 8941 HIP 8949 HIP 8950 HIP 8962 HIP 8965 HIP 8966 HIP 8971 HIP 8985 HIP 8986 HIP 9002 HIP 9008 HIP 9038 HIP 9054 HIP 9055 HIP 9075 HIP 9097 HIP 9101 HIP 9112 HIP 9116 HIP 9117 HIP 9128 HIP 9129 HIP 9154 HIP 9155 HIP 9160 HIP 9165 HIP 9166

الأسئلة الشائعة

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