IOTA PSC (Iota Piscium). Among the classic and best-loved celestial asterisms -- informal constellations -- is the Circlet of Pisces, the body of the western fish. And where would the Circlet be without Iota? Though at mid-fourth magnitude (4.13) not very bright (much like the rest of the huge constellation), it not only helps complete the ragged circle, but sits at the juncture between the Circlet and the line of stars that begins the fish's tail and continues with the ribbon that joins it to the eastern fish. (The Circlet provides something of a guide to the Vernal Equinox, which lies a few degrees to the southeast of it.) More importantly, Iota Psc intrigues as one of "us," as a star rather similar in properties to the Sun, one of those we look at and wonder if it too has planets. A yellow-white class F (F7) hydrogen-fusing dwarf with a temperature only a bit warmer than the Sun (6300 Kelvin), Iota Psc shines with a luminosity 3.3 times solar, from which we derive a radius 1.5 times that of our own star. Place our Earth at a distance of 1.8 Astronomical Units from it and we would feel very much at home. Stellar structure theory tells of a star that carries 1.25 times the mass of the Sun, one that, with an age of 3.7 billion years, is closing in on the end of its projected 4.3 billion year hydrogen-fusing lifetime (higher mass stars living shorter lives). Among the bigger differences is the shorter rotation period of under 13 days (about half that of the Sun), which certainly stirs up some significant magnetic activity (yet to be explored). Though listed as "variable," there is precious little evidence of it. Indeed, the star is used a spectroscopic standard for velocity measures. But are there planets? None has as yet been detected. Neither has any circumstellar debris that might suggest something of an asteroid belt. Perhaps unsurprisingly. Planet-holding stars tend to be metal-rich as compared with the Sun, while Iota goes in the other direction, being slightly metal-poor, its iron content relative to hydrogen 70 percent of solar. While once thought to have one or two dim stellar companions at separations of 70 and 280 seconds of arc, both are simply line-of-sight coincidences, the star at the juncture of the Circlet seeming very much alone.
Written by Jim Kaler. Return to STARS.