ALRESCHA (Alpha Piscium). While only third brightest in the ancient and sprawling zodiacal constellation of Pisces, the Fishes, Alrescha has a central place, at the southeastern point of two lines of stars that represent the ribbon that connects the two celestial fish, and thus was chosen by Bayer to be the Alpha star. At mid-fourth magnitude (3.94), it is not third by much, and is exceeded only by brighter fourth magnitude Eta and Gamma. One of the few named stars in the constellation, "Alrescha" (which appropriately comes from the Arabic word for "the cord") may refer to the original fishy Babylonian constellation. Alternatively, it may refer an Arabic constellation and to a string of stars that runs through both Pisces and Andromeda that have more to do with a rope that raises pail from a well. Whatever the name's origin, the star (a delight in a small telescope) is a close double, and consists of pair of class A stars that take 720 years to orbit each other. Though both stars are white, subtle contrast effects can make the stars seem colored, one observer even reporting pale green and blue. Now separated by 1.3 seconds of arc (a bit of a challenge to separate), they will make their closest approach about 2060. The brighter eastern component, Alrescha-A (by itself magnitude 4.3 and class A0), is the hotter, its temperature about 9500 Kelvin. The fifth magnitude companion, Alrescha-B (5.23, class A3), is some 900 Kelvin degrees cooler. Both are ordinary hydrogen-fusing dwarfs. From their distance of 139 light years, we find respective luminosities of 31 and 12 times that of the Sun, implying masses of 2.3 and 1.8 solar (the orbit is not well-enough determined to provide accurate masses). The two stars average about 120 astronomical units (three times the distance between Pluto and the Sun) apart, the distance varying from 50 to 190 AU over the 720-year period. Each star has been reported as a spectroscopic double, rather like those that make Mizar. Alrescha-B's orbital period may be about a week, though nothing else is known of the system. These results may be spurious, however, and almost certainly are for Alrescha-A. Neither star rotates especially quickly (about 70 kilometers per second at the equator), and as a result each is chemically peculiar (again like Mizar). Alrescha-A is an "Ap" (class A peculiar) star with a magnetic field a thousand or so times that of Earth that is wobbling with a 1.5 day period as a result of the star's rotation. Alrescha-A shows enhancements of silicon, strontium, and chromium produced by separation of atoms in the relatively quiet atmosphere coupled with the action of stellar magnetism. Concentration of elements into magnetic regions coupled with rotation then make the star's spectrum variable. Alrescha-B, not to be outdone, is a metallic-line star, such stars typically having enhancements of copper, zinc, strontium, zirconium, and barium.
Written by Jim Kaler. Return to STARS.