61 Cygni

1916

1951

61 Cygni was christened the "Flying Star" in 1792 by Giuseppe Piazzi (1746-1826) for its unusually large proper motion. Its apparent position would shift by an amount equal to the width of the full moon in only 150 years.

This visual binary system is located about 11.4 light-years (ly) away from our Sun, Sol, in the south central part (21:08:52.1+38:56:51:D~, ICRS 2000.0) of Constellation Cygnus, the Swan -- southeast of Sadr (Gamma Cygni) and east of the open star clusters M 29 and NGC 6871, and the Crescent Nebula (NGC 6888). It is the title member of the 61 Cygni group.(Solstation)

In 1830, Friedrich Georg Wilhelm von Struve (1793-1864) made the first measurements of the star as a binary system. It is now known that 61 Cygni A and B orbit each other at an "average" distance (semi-major axis) of 86.4 times the Earth-Sun distance, or about 86 astronomical units (AUs) -- which is more than twice Pluto's orbital distance in the Solar System. 61 Cygni was the first star system (other than the Sun) to have its distance to Earth successfully calculated by Friedrich Wilhelm Bessel (1784-1846) using trigonometric parallax and the diameter of the Earth's orbit around the Sun in 1838. Smaller and dimmer than the Sun, the stars are barely visible with the naked eye.(Solstation)

61 Cygni-A is an orange-red main-sequence dwarf star of spectral type K3.5-5.0Ve. It has about 70 percent of a solar mass, 72 percent of its diameter and about 8.5 percent of its luminosity. It appears to have about 79 percent of the Sun's metallicity. It appears to be a variable star. It orbits 61 Cygni-B with a highly elliptical orbit (e=0.40) that gives distance extremes 51.7 and 121.0 AUs in an orbit of period about 722 years. 61 Cygni B is and orange-red main sequence dwarf of spectral type K4.7-7.0 Ve. It has about 63 percent of of a solar mass, 67 percent of its diameter, and 3.9 percent of its luminosity.

Sources:

• http://www.solstation.com/stars/61cygni2.htm

Sigma 2398

This binary system is designated Struve 2398 and are probably dim red dwarf stars similar to Gliese 623A and B shown in the NASA HST image at left.

This system is located about 11.4 light-years (ly) away from our Sun, Sol. It lies in the northeastern part (18:42:46.69+59:37:49.42, ICRS 2000.0) in Constellation Draco, the Dragon -- northeast of Grumium (Xi Draconis) and southwest of Altais or Nodus Secundus (Delta Draconis). Struve 2398 is too dim to be seen with the naked eye.

There are two stars, Struve 2398 A and B, that orbit each other at an "average" distance of about 56 times the Earth-Sun distance -- 42 astronomical unit (AUs) of an orbital semi-major axis -- which is roughly Pluto's orbital distance in the Solar System. The separation of the two components was first measured in 1832 by Friedrich Georg Wilhelm von Struve (1793-1864), who became director of Russia's Dorpat Observatory in 1817 and founded and directed the Pulkovo Observatory in 1837, surveyed 120,000 stars from 1819 to 1827, published an extensive monograph of Halley's Comet based on observations in 1835 and his findings on 2,640 double stars in 1837, and measured the parallax of Vega from 1835 to 1838. While now often named in his honor, Struve's stars were originally numbered after the Greek letter "Sigma," so that this binary pair was designated as Sigma 2398.(Solstation)

Sources:

• http://www.solstation.com/stars/st2398ab.htm
• http://adsabs.harvard.edu/abs/1972ApJ...174L..87D