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 86687 HIP 8669 HIP 86706 HIP 86712 HIP 86717 HIP 86723 HIP 86724 HIP 8675 HIP 86772 HIP 86777 HIP 8678 HIP 86785 HIP 86787 HIP 86789 HIP 8679 HIP 86802 HIP 86806 HIP 86809 HIP 86812 HIP 86813 HIP 86820 HIP 86822 HIP 86835 HIP 86839 HIP 86843 HIP 86847 HIP 8685 HIP 86862 HIP 86863 HIP 86864 HIP 86865 HIP 86867 HIP 86890 HIP 86908 HIP 86917 HIP 86924 HIP 86925 HIP 86930 HIP 86935 HIP 86936 HIP 86941 HIP 86942 HIP 86949 HIP 86955 HIP 86979 HIP 86982 HIP 86983 HIP 86988

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