GAMMA TRI (Gamma Trianguli). Its Greek letter name properly fitting the third brightest star in Triangulum (the Triangle), fourth magnitude (4.01) Gamma Trianguli anchors the eastern apex of one of the two celestial Triangles (the other Triangulum Australe in the deep southern hemisphere). Together with fainter Delta Trianguli and Flamsteed's 7 Trianguli, this white class A (A1) hydrogen-fusing dwarf at first appears as part of an attractive naked-eye triple star (Delta and Gamma respectively Flamsteed 8 and 9). However, the small gathering is simply a line of sight coincidence, as Gamma is 118 light years away, while Delta (a fifth magnitude class G double dwarf) lies much closer at only 35 light years, and 7 Tri (a class A dwarf similar to Gamma) is much farther, 293 light years away, quite dramatically showing the importance of factoring in the third dimension. The star at first appears as just one more of its class A kind, much like Sirius, though farther away and one with no companion to keep it company. With an estimated temperature of 9200 Kelvin, the star shines with the luminosity of 28 Suns, its radius 2.1 times solar. The temperature and luminosity coupled with the theory of stellar evolution point to a 2.3 solar mass star with a fairly youthful age of 200 million years. Not until we look at the spectrum -- the rainbow of starlight spread from red to violet -- do we see that Gamma Trianguli is, for its class, a champion spinner much in the mold of Altair, though hotter. The spin washes out the "spectrum lines," the narrow absorptions produced by the different kinds of atoms in the stellar gases. Analysis of these features reveals that at the equator, the star rotates with a speed of at least 208 kilometers per second, 104 times that of the Sun. Since we do not know the axial tilt, Gamma Tri might well be rotating even faster (if the axis were pointing at us, for example, as nearly is Vega's, we would note no rotation at all). Like Altair, the star is almost certainly oblate instead of spherical. Factoring in the stellar radius, Gamma Trianguli has a rotation period of only 12 hours, and quite possibly less (as opposed to the solar period of 25 days).
Written by Jim Kaler. Return to STARS.