GAMMA SER (Gamma Serpentis). Part of the "X" structure that makes the head of Serpens (the Serpent), at the top of the western portion of constellation (Serpens Caput), lies otherwise unnamed Gamma Serpentis. At mid-fourth magnitude (3.85), it hardly qualifies as the third brightest star in the constellation, exceeded in brightness not just by Alpha (Unukalhai) and Beta (as expected) but also by those with Greek letters Delta, Epsilon, and even Mu (though not by much). What makes the star special is its proximity and its sunlike properties. Only 36 light years away, this class F (F6) dwarf sports a temperature of 6280 Kelvin, just 500 Kelvin more than that of the Sun, and shines with a luminosity of just 2.9 times solar. From these parameters and the theory of stellar structure, we obtain a mass only 25 percent greater than our home star. Even that little bit, however, cuts Gamma Ser's potential lifetime in half. At an age of about 3 billion years (as compared with the Sun's 4.5 billion year age), it has another 2 billion years left to it before its core hydrogen fuel runs out and it begins to die. (The star has been called a subgiant, as if it were near the end of its days, but its temperature and luminosity clearly define it as a dwarf.) Like many stars hotter than solar, Gamma Ser rotates more quickly than the Sun, its rotation speed of at least 8 kilometers per second, coupled with a radius 1.4 times solar, giving it a rotation period of less than 9 days. (Only limits are known, since the tilt of the rotation axis cannot be determined). The star ought to display some magnetic activity, but none has been found; nor has a dusty disk that might indicate a planetary system. Hotter, slowly rotating stars (such as Alioth and Acubens) present abundance anomalies caused by the separation of chemical elements. Gamma Ser, with otherwise rather normal abundances (a metal content about 2/3 solar), seems on the fringe of such peculiar stars with a weirdly low aluminum abundance and some heavy element anomalies as well. The star has a reputation of being somewhat variable. If so, from its temperature and luminosity it may be an example of a "Gamma Doradus" star. Gamma Ser is often listed with two 11th magnitude companions ("B" and "C," located about 3 minutes of arc away. Alas, they are merely line of sight coincidences, which leaves Gamma Ser all alone, rather like the Sun itself. Thanks to Jose Rodriguez, who suggested this star.
Written by Jim Kaler. Return to STARS.