IOTA ARI (Iota Arietis). The sky is filled with cool (3800-4800 Kelvin) class K orange, helium-fusing giants, in part the result of their being generally so bright, their apparent population all out of proportion to their real number. Remove them from the sky and our constellation patterns would be profoundly altered. In contrast, the naked-eye class K hydrogen- fusing dwarfs are faint enough that they make little impact on the nightly sky. The best known are probably fifth magnitude 61 Cygni (a double that contained the first star to have had a distance measure through direct parallax), the dimmer component of Alpha Centauri, and 40 Eridani (which has both red dwarf and white dwarf companions). It's exciting then to seem to come on to another one, fifth magnitude (5.10) Iota Arietis, which can be found just under two degrees southeast of Gamma Arietis, the southernmost of the trio that forms the flat triangle that makes most of classical Aries, the zodiacal Ram. Listed as a "peculiar" class K1 dwarf, it certainly is, as measure of its distance of 520 light years, and subsequent calculation of its absolute brightness, clearly reveal a case of mistaken identity. Using a poorly-defined temperature of 4630 Kelvin (to estimate the amount of infrared radiation), the luminosity comes in at 294 times that of the Sun, the radius at 27 solar, clearly making the star a true giant (even though the color is still more that of a dwarf). A slow projected equatorial rotation speed of 3.3 kilometers per second gives a rotation period as long as 400 days. Theory then also shows the star to carry a mass of 3.5 to 4 Suns, depending on the exact state of evolution. But the misclassification, or at best the oddness, carries along through the literature, and even gets more bizarre, one source making the star out to be a class G supergiant, which it is not. The star does have going for it that it is a spectroscopic double with a period of 1567.7 days, 4.29 years. Another source gives a one magnitude difference between the stars. If so, Iota Ari A's luminosity goes down to 210 Suns, the mass to 3 solar), and the companion is a class A dwarf with a luminosity of 113 Suns and a mass of 2.8 solar. The magnitude difference is probably much more however, voiding the interpretation. Given a minimum mass for the companion, it is at least 4.8 AU from Iota-A. Little else is known except that Iota Ari proper has only about half the metals found in the Sun (iron used as a general proxy), but that conclusion might be voided by the poorly-known temperature. The star begs to be re- observed, if only to understand the reason for the mis- identifications, which might prove interesting.
Written by Jim Kaler 9/30/11. Return to STARS.