Luminosity class in the context of Diffraction grating

A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star.

A G-type main-sequence star is a main-sequence star of spectral type G. The spectral luminosity class is typically V. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about 5,300 and 6,000 K (5,000 and 5,700 °C; 9,100 and 10,000 °F). Like other main-sequence stars, a G-type main-sequence star converts the element hydrogen to helium in its core by means of nuclear fusion.

The Sun is an example of a G-type main-sequence star. Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, and 51 Pegasi.

A B-type main-sequence star is a main-sequence (core hydrogen-burning) star of spectral type B. The spectral luminosity class is typically V. These stars have from 2 to 18 times the mass of the Sun and surface temperatures between about 10,000 and 30,000 K.

B-type stars are luminous and blue-white. Their spectra have strong neutral helium absorption lines, which are most prominent at the B2 subclass, and moderately strong hydrogen lines. Examples include Regulus, Algol A and Acrux.

Mu Serpentis, Latinized from μ Serpentis, is a binary star in the Serpens Caput (head) section of the equatorial constellation Serpens. It is visible to the naked eye with an apparent visual magnitude of 3.543. Based upon an annual parallax shift of 19.23 mas as seen from Earth, it is located around 170 light years from the Sun.

This is an astrometric binary for which coarse orbital elements have been determined based on interferometric observations. The pair orbit each other with a period of around 36 years and an eccentricity of roughly 0.4. The primary member, component A, is a white-hued A-type main sequence star with a stellar classification of A0 V. The nature of the secondary, component B, is less certain – it may be a class A or F type star of unknown luminosity class.

A K-type main-sequence star is a main-sequence (core hydrogen-burning) star of spectral type K. The luminosity class is typically V. These stars are intermediate in size between red dwarfs and yellow dwarfs, hence the term orange dwarfs often applied to this type.

An A-type main-sequence star is a main-sequence (core hydrogen burning) star of spectral type A. The spectral luminosity class is typically V. These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1.7 and 2.1 solar masses (M_☉), have surface temperatures between 7,600 and 10,000 K, and live for about a quarter of the lifetime of the Sun. Bright and nearby examples are Altair (A7), Sirius A (A1), and Vega (A0). A-type stars do not have convective zones and thus are not expected to harbor magnetic dynamos. As a consequence, because they do not have strong stellar winds; they lack a means to generate X-ray emission.