Spica, or Alpha Virginis, is another example in the constellation Virgo. Its type is B1 III-IV, so it is intermediate between a giant and sub-giant star. It is about 11 times the mass of the sun, 7.8 times the diameter, and about 260 light-years away. It is a "Beta Cephei variable" which means that the variation in its brightness is due to pulsations of its surface over a period of about 0.17 days. It is a double star, with the two stars very close together, and makes them appear to be a single star. Their proximity is such that they distort each other leading to another source of variability coinciding with their mutual orbit period of about 4 days. The companion, a type B main sequence star, is about 7 times the mass of the sun, and 4 times as large.
A well known example is Rigel, or Beta Orionis, a blue intermediate luminous supergiant of type B8Iab. Strictly speaking, it is Rigel A; Rigel B is its fainter companion that is itself a binary comprising two class B stars of 2.5 and 1.9 solar masses. Rigel A is the lower right star in Orion. It is around 78 times the size of the sun, 17 times the mass, and approximately 800 light-years away. It is a slightly variable star varying by up to 0.3 magnitudes over a period of 22 to 25 days. In the photograph, you can see Rigel lighting up the Witch Head Nebula, which is behind Rigel as viewed from the Earth.
Alnilam, or Epsilon Orionis, is another intermediate luminous supergiant, type B0Iab, and is the middle star in Orion's belt. It is around 26 times the size of the sun, 40 times the mass, and about 1,300 light-years away. It is about four million years old. The image to the left shows Epsilon Orionis lighting up the nebula NGC 1990.
Type B Stars
VV Cephei B is a type B0 main sequence star that orbits the red hypergiant VV Cephei A once every 20.4 years at a separation of between 2.5 and 5 billion km (1.6 to 3.2 billion miles) on a very eccentric orbit. VV Cephei B is about 20 times the mass and 10 times the diameter of the Sun. They are estimated at about 20,000 light years away, but this distance is highly uncertain. VV Cephei B is drawing material from the surface of its bloated companion, giving it a tear-drop shape. VV Cephei A dominates in the image to the left.
Achernar, or Alpha Eridani, a type B3Vpe star, weighs around six to eight solar masses. It is a bright blue star with over 3,000 times the total luminosity of the Sun, and is approximately 144 light-years away. It is interesting in that it is the most oblate star known, with its equatorial diameter around 11.6 times that of the Sun, and its polar diameter about 7.5 times as large as the Sun, as it spins on its axis so rapidly. It has a slight, highly regular Lambda Eridani type variability, and also has a disk of material around it formed from matter it has ejected. It is quite a young star at a few hundred million years old.
Astronomy & Cosmology
Stars - Stellar Classes
Type B stars are similar to, but cooler and less massive than type O stars.
Beta Orionis (Rigel)
Epsilon Orionis (Alnilam)
Alpha Eridani (Achernar)
Alpha Virginis (Spica)
VV Cephei B