52 CYG (52 Cygni). Because of their general brightness and long- term stability, orange class K giants seem to populate the sky all out of proportion to their actual numbers. Remove them and the constellation patterns would be severely altered. While not part of the formal outline of Cygnus (the Swan, upside down the Northern Cross), Flamsteed's 52 Cygni falls into their lot as a classic K0 giant, though one of interest for its duplicity and especially for its location, which draws the eye to the famed Cygnus Loop (see below). Of fourth magnitude (4.22), about 3 degrees south of Epsilon Cygni (on a line from Lambda Cyg through Epsilon), the star lies 203 light years away, with an uncertainty of only about 3. Allowance for infrared radiation from a 4770 Kelvin surface and for a bit of interstellar dimming (0.16 magnitudes in the visible) leads to a luminosity 106 times that of the Sun. Luminosity combined with temperature then yields a radius of 15.1 times solar. Interferometric observations of angular diameter combined with distance gets a remarkably close value of 15.3 solar radii, showing the stellar parameters to be closely accurate. A projected equatorial rotation velocity similar to that of the Sun gives a rotation period that could be as long as a year. Theory suggests a mass of 2.5 to 3 times that of the Sun. So far, there is nothing unusual about the star. But at a separation of 6 seconds of arc, which has remained constant over the past two centuries, lies a ninth magnitude (8.7) companion ("A neat double star" say Smythe and Chambers") that bears close similarity to the Sun, its luminosity perhaps only 20 percent greater. 52 Cyg B, at least 370 Astronomical Units from 52 Cyg A (nearly 10 times the distance of Pluto from the Sun), must take at least 3500 years to make its orbital journey. From the solar-type star, the view would be grand, the giant shining 250 times brighter than the full Moon.

52 Cygni, however, is far better known as the gateway to the western arc (the star smack in the middle) of the Cygnus Loop. The whole structure is also known as the Cirrus Nebula, the Veil Nebula, and the Filamentary Nebula, specific parts given a variety of other names. Discovered by William Herschel in 1784, the Loop is made of two prominent arcs whose extended curves enclose and highlight additional ragged nebulosity. Again from 19th century Smythe and Chambers: "Having completed the micrometric observations (of 52 Cygni), the illumination was removed; and after considerable attention a peculiar glow indicated the presence in the field of the extraordinary branched nebulosity 15 H." The result of a supernova that shattered the sky 5000 or more years ago, the Loop is not the actual debris of the long-gone massive star, but the heated blast wave of the explosion, a shocked bubble that is expanding through the local interstellar gases. At a distance of around 1400 light years, it's now three degrees, or about 80 light years, across. Though it looks like 52 Cyg lights up the western arc, the much closer star clearly has nothing to do with the Loop other than being in the same line of sight, though the alignment is especially attractive, the star acting as a guide that allows one to see (with a wide- angle telescope) the results of violent stellar death in action. Disturbing and heating the interstellar medium, the Loop radiates across the spectrum, from X-rays to radio, and is but one of a large number of "supernova remnants" that are delivering energy, fresh elements, and compression for new star formation, to interstellar space, our Earth in large part a product of the exploding stars that came before us.
Written by Jim Kaler 8/31/12. Return to STARS.