Delta Corvi - Algorab

Delta Corvi, or Algorab, is the third brightest star in the constellation Corvus, the Crow. Algorab, of apparent magnitude +3.1, lies at the upper left corner of the constellation, and with Gienah Ghurab (γ Corvi) points eastward to Spica in Virgo.

The name Algorab used to belong to γ Crv; both names come from an Arabic phrase that means "the raven's wing" (Gienah from the word for "wing", and Algorab from the word for "raven"). δ Corvi is known as the Third Star of the Chariot in Chinese. It was also the namesake of the USS Algorab (AKA-8), an Arcturus-class attack cargo ship that served from 1941 - 1945.

Properties

Gienah is 165 light years away, whereas Algorab only 88, so the two really have nothing to do with each other. Algorab is a beautiful and easy-to-see double star with a separation of 24.3". It consists of a white magnitude 2.95 class A0 V star, and an orange magnitude 8.51 class K star. The contrast gives them interesting colors, described ages ago as "yellowish and pale lilac," or "pale yellow and purple".

The brighter component, δ Crv A, is a very normal 2.5 solar mass hydrogen-fusing main-sequence star, with a temperature of almost exactly 10,000 K. It shines with a luminosity of 48 suns, and its radius is about double solar. The orange companion, δ Crv B, with a mass three-fourths solar, has a surface temperature of about 5000 K, and radiates much more dimly, producing only one third the Sun's luminosity.

At a minimum distance of 650 AU from δ Crv A, little B takes at least 9400 years to orbit A. From δ Crv B, A would shine with the light of 500 full Moons.

Evolution

The more interesting component is actually Algorab-B. Stars are formed by the collapse of cold, dark, dusty interstellar clouds. A high level of infrared radiation shows that the δ Crv system contains a great deal of dust left over from its formation. It appears to be less than 110 million years old, and has yet to clear the dust out of the system.

Algorab-B is a "post-T Tauri star" which is now settling down to the stable main-sequence phase, fusing its core hydrogen into helium. "T Tauri stars" are very youthful stars that have just formed, and are surrounded by disks of dust from which planets may be formed.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]