44 BOO (44 Bootis). Just when you think that star systems can get no odder, along comes something like 44 Bootis, known best by its Flamsteed number and less romantically as HR 5618 in the Bright Star Catalogue, qualifying at fifth magnitude (4.81). Nothing about the star is very secure. At first look, a magnitude 5.2 solar type class G2 dwarf (but given as warm as F7) is in mutual orbit with a magnitude 6.10 K2 (G? K4?) dwarf with a period of 209.8 years, the two never more than a few tenths of a second of arc apart, making them quite difficult to separate. Yet they have been split since William Herschel first did it in 1781, referring to the binary as "a miniature of Castor." In the nineteenth century, Smythe and Chambers saw the two as "pale white" and "lucid grey," and called it "a remarkable and highly interesting star." They should only have known! Given a distance of 41 light years (give or take just one), the two orbit at an average separation of 46 Astronomical Units, a substantial eccentricity taking them as far apart as 69 AU and as close as 22. Kepler's laws give a total mass to the system of 2.2 Suns.

44 Boo The components of 44 Bootis, 44 Boo A and B, go around each other every 209.8 years averaging 46 Astronomical Units apart, a fairly high orbital eccentricity taking them between 22 and 69 AU away from each other. Though each orbits a common center of mass that lies between them, they are presented here as if 44 B, which is itself an eclipsing contact binary (making the system triple), goes about 44 A, which lies at the cross. Note the small angular separation, as seen on the axes. The orbital semi-major axis (dot-dash line) and focus (the cross) are offset from the apparent orbital ellipse because of the orbital tilt and orientation against the plane of the sky. (W. I. Hartkopf and B. D. Mason, Sixth Catalog of Orbits of Visual Binary Stars, US Naval Observatory Double Star Catalog, 2006.)

With a temperature of 5670 Kelvin, 44 Boo A shines with the total light of just 1.13 times that of the Sun, which leads to a radius of 1.1 solar radii, all consistent with a solar mass star of a bit more age than our own. 44 Boo B should then have a mass roughly equal to that of 44 A. But here comes the surprise, as 44 B is not only itself double, but is an eclipsing binary with an orbital period of a mere 6.43 hours, the little system varying continuously between magnitudes 5.8 and 6.4. The two stars, seemingly each lesser than the Sun, must be so close as to be in contact with each other, or at least nearly so, the little system shaped something like a peanut, which explains the continuous variation as the two whirl around presenting different faces to us. Mass is probably being transferred from one star to the other, indeed one star may be consuming the other. 44 Boo B is the nearest "W Ursae Majoris" star (named after the eighth magnitude "contact binary" prototype in Ursa Major), falling near the lower mass limit for the type. The members of 44 Boo must also be in some kind of synchronous rotation, the mad spin making them magnetically active. An active corona, similar to the one that surrounds the Sun, seems to envelop both stars, since its X-ray brightness does not respond to the eclipses. 44 Boo A and 44 B (the eclipser) were physically closest together early in 2012. But because of the tilt of the orbit against the plane of the sky, they will appear to be angularly closest around 2020. The metal content of 44 A is low (about half solar). No planets have been detected. Too bad, because residents would have quite a show watching 44 B act out its double life. For that matter, 44 B may well have prevented any planets from forming around 44 A. Most likely, 44 B was once a more or less well-behaved higher-mass double that has suffered the ravages of stellar evolution and mass loss. (Thanks to the April 2014 issue of "Sky and Telescope" and to P. Gondoin in "Astronomy and Astrophysics," vol. 426, 1025, 2004.)

Written byJim Kaler 8/01/14. Return to STARS.