Gloucester Area Astronomy Club

Izar (ε Bootis)
by Glenn Chaple

Most of us are familiar with the novel Moby Dick, whose protagonist Captain Ahab relentlessly hunts a great white whale. I can sympathize with the obsessive Captain. For several years back in the late 1970s, I pursued an astronomical white whale- the double star epsilon (ε) Bootis. Instead of the Pequod, my vessel of pursuit was a 3-inch f/10 reflector.

Trying to capture Izar with a 3-inch reflector is like attempting to harpoon a whale from a rowboat. The difficulty lies in the magnitude difference between the components (2.6 and 4.8) and their closeness (2.9 arc-seconds). On numerous evenings I tried to resolve Izar’s component stars without success. Notching this stellar duo became an overpowering obsession. On the evening when I at last split Izar, skies were remarkably steady and I used the highest practical magnification (120X) my little reflector could handle. Even then, the companion played hide-and-seek in the diffraction ring of the primary.

A larger telescope and magnifying power of 200X will readily split Izar and reveal a striking color contrast between the golden yellow primary and its bluish companion. The Russian astronomer Wilhelm Struve, who conducted a double star survey in the late 1820s and early 1830s (Izar became Σ1877 in his double star catalog), nick-named it “Pulcherrima” (The Most Beautiful).

But Izar is more than just a close pair of stellar specks. The main component is a K0 spectral class giant 30 times as large as the sun. Its A2-type companion is twice the sun’s size – a virtual twin to Sirius. Separated by 180 Astronomical Units, the two undergo a slow gravitational dance, their orbital cycle encompassing perhaps a thousand years.

Imagine that Izar were moved from its current location 250 light-years away to a distance equal to that separating us from Sirius. The star would be a dazzling sight, rivaling Venus in brilliance. Viewed with even the smallest telescopes, the magnitude -3.6 and -1.4 components, separated by 85 arc-seconds, would be an absolutely magnificent sight.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com

M40 – the “Unknown” Messier Object
by Glenn Chaple

What is the most most-observed deep-sky object in the Messier Catalog? Some might suggest the Orion Nebula (M43) or Andromeda Galaxy (M31), both cosmic showpieces. More likely, it’s the Pleiades (M45), a striking and easily observed naked eye cluster.

What about the other end of the spectrum – those Messier objects that receive scant attention? The least-observed might well be Messier 40. Arguably the oddest member of the Catalog, M40 isn’t a cluster, nebula, or galaxy. It’s a double star! We might well label M40 “Messier’s Mistake.”

Messier stumbled upon this stellar duo while searching for a nebulous object reported to be in the area. For some reason, perhaps because it might appear nebulous at low power or in an inferior instrument, he added it to his Catalog. A century later, another comet hunter, Friedrich Auguste Theodor Winnecke, rediscovered the object. He correctly catalogued it as a double star, and it bears the alternate identity Winnecke 4.

Finding M40 isn’t a problem. Start at delta (δ) Ursae Majoris, then move about a degree northeast to 70 UMa. In the same low-power field a quarter degree further northeastward is M40. As double stars go, M40 isn’t a very inspirational sight. Its magnitude 9.7 and 10.1 component stars are separated by over 52 arc-seconds. Quite likely, it’s an optical pair. It may not be one of the night sky’s spectacles, but the path to observing all of the Messier objects goes through M40.

Your comments on this column are welcome. E-mail me at gchaple@hotmail.com