38 LYN (38 Lyncis). Double stars, sprinkled all over the sky, fascinate. Though coming in a great many varieties, the ones we best know love are those that can be seen directly by eye through the telescope. Among the many favorites are Mizar, Albireo, Almach (Gamma Andromedae), and Algieba (Gamma Leonis). Of their many charms is a visual effect that strongly enhances slight differences in the colors of stars that lie next to each other. Nineteenth century astronomers were eloquent in ascribing double-star colors, even thinking that binaries were really colored differently from single stars. We need not stick to classical constellations to find such gems. Between Auriga and Ursa Major sprawls a long string of stars that represents Lynx, the (no surprise here) Lynx. The luminary, Alpha Lyncis, lies almost due south of the most western of the three pairs of stars that represents the Great Bear's paws (the Arab's three "leaps of the gazelle"), made of Iota and Kappa Ursae Majoris. Immediately to the north of Alpha Lyn find fourth magnitude (3.8) 38 Lyncis. Even a modest telescope splits it into a close pair of stars 2.6 seconds of arc apart that consists of a brighter fourth magnitude (3.92) class A3 hydrogen- fusing dwarf coupled to a somewhat mysterious, lesser, cooler sixth magnitude (6.09) secondary. Though both are really white (38 Lyn B somewhat less so), the proximity effect led to early colors given as "silvery white and lilac." With a temperature of 8400 Kelvin, 39 Lyncis A radiates at a rate 31 times that of the Sun, which in turn leads to a radius of 2.4 times solar and a mass 2.2 times solar, the star about midway through its 900 million year hydrogen-fusing lifetime. A very rapid equatorial rotation of at least 190 kilometers per second gives the star a rotation period of under 15 hours! Now the small mystery. 38 Lyn B is classed as an A4 or A6 dwarf. But such a star would be expected to be more than a magnitude brighter than it is. Either the pair is a line-of-sight coincidence, or the class is way off, as 38-B shines more like an F4 star. Given that the stars have been tracking each other since the discovery of duplicity by William Herschel in the 1700s, they almost have to be gravitationally bound, leading to an error of classification that perhaps might be linked to a peculiar chemical abundance (38 A oddly sometimes called a Lambda Bootis star, one deficient in metals). If really cooler than expected, then 38 B is a 1.4 solar mass star glowing with the light of 4 Suns from a 6800 Kelvin surface. Now the mystery deepens. Interferometry shows 30 Lyn B also to be double with a close separation of (at last look) 0.23 seconds of arc, which corresponds to 7.5 Astronomical Units; 38 A might be similarly duplicitous with the two at less than half that separation. So the star might really be quadruple. With 11th magnitude "companions" at separations of about one and three minutes of arc, how about sextuple? No: their motions show that these are clearly just lying along the line of sight, leaving the inner system to itself. (Thanks to Bill Hartkopf for discussion.)
Written by Jim Kaler 12/26/08. Return to STARS.