A subgiant is a class of star that is brighter than most normal dwarf main sequence stars but not bright enough to be classed as a giant.
A subgiant star is bigger than a neutron star. Neutron stars are incredibly dense and compact, with a radius of about 10-15 kilometers, while subgiant stars have a larger radius of several million kilometers.
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Both. A subgiant can be a young star (1,000 years old) to an old star (10 billion years old). See related question.
Dubhe is not a red giant but rather a subgiant star. It is the brightest star in the Big Dipper asterism and is classified as an evolved F-type subgiant star.
A binary star. The main component is a Be-type subgiant.
A subgiant star is larger than a neutron star. Neutron stars are incredibly dense and compact remnants of massive stars, while subgiant stars are in a transitional phase between main sequence and red giant stages, typically larger and more diffuse than neutron stars.
If you are referring to the Yerkes spectral classification, a Class IV star is known as a subgiant.
Sarin is not a type of star; it is a highly toxic chemical compound known as a nerve agent.
Alnath is classified as a B7IV blue-white subgiant star, so it appears white to the human eye but may have a slight blue tinge due to its spectral characteristics.
Rastaban is a binary star system in the constellation of Draco. The primary star is a yellow-white subgiant, while the secondary star is most likely a red dwarf.
Zeta Phe is a blue-white main sequence star that is approximately 610 light-years away from Earth. It is a subgiant star with a spectral type of B7 IV.
Apparent magnitude: +2.9Absolute magnitude: -0.7See related question.