Alpha Piscium - Alrischa

Alpha Piscium is the third brightest star in the constellation Pisces, the Fishes, at magnitude 3.94. It has the traditional name Alrischa or Alrescha (Arabic for "the rope"). Alrescha has a central place, at the southeastern intersection of two lines of stars that represent the ribbon which connects the two celestial fish.

Components

Alpha Piscium is a very close pair of bluish-white stars that are rather difficult to split. The components are of magnitudes +4.33 and 5.23, with a current angular separation of 1.8". At 200x, they appear as two disks in contact. Though both stars are white, subtle contrast effects can make the stars seem colored, one observer even reporting pale green and blue. They average about 120 AU apart, varying from 50 to 190 AU over their 720-year period, and will make their closest approach around 2060. One or both of the stars may be a spectroscopic binary as well.

Properties

The distance to α Psc is about 139 light years. The brighter star is of spectral type A0p V, while its companion belongs to spectral class A3 Vm. Both are ordinary hydrogen-fusing main-sequence stars. They contain 2.3 and 1.8 solar masses, respectively, and shine with total luminosities of 31 and 12 suns.

Neither star rotates especially quickly, about 70 km/sec at the equator. As a result, each is chemically peculiar. α Psc A has a magnetic field a thousand times that of Earth, which wobbles as a result of the star's rotation over a 1.5 day period. The star shows enhancements of silicon, strontium, and chromium, produced by the action of magnetism in the relatively quiet stellar atmosphere. Concentration of elements into magnetic regions, coupled with rotation, makes the star's spectrum variable. α Psc B is a metallic-line star, having enhancements of copper, zinc, strontium, zirconium, and barium.

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