83 Leonis AB

The system is also known as Struve 1540 AB due to its observation and measurement as binary stars by Friedrich Georg Wilhelm von Struve (1793-1864). Struve 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 originally designated as Sigma 1540 AB.

83 Leonis A

Star A is a yellow-orange to orange-red subgiant of spectral and luminosity type G6/8-K0 IV. The star may has a mass near or somewhat smaller than Sol's, as much as 1.9 times its diameter (Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983), and about 66 percent of its visual luminosity. The star appears to be around 1.2 to 2.3 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 292; and Extrasolar Planets Encyclopaedia). Other useful star catalogue designations for 83 Leonis A include: 83 Leo A, HR 4414, Gl 429 A, Hip 55846, HD 99491, BD+03 2502, SAO 118864, FK5 1296, LHS 2407, LTT 13109, LFT 805, Wolf 393, STF 1540 A, and ADS 8162 A.

According to the Sixth Catalog of Visual Orbits of Binary Stars, stars A and B are separated on average by 720 AUs (40.76" of a semi-major axis at 57.64 ly) in an eccentric orbit (e= 0.46) that takes around 32,000 years to complete -- with a catalog note that the "Hopmann orbit [was] rejected from Fourth Catalog ('period over 4000 years')." The orbit is inclined by 126.6° to Earth's line of sight (Josef Hopmann, 1960a). (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.)

83 Leonis B

© Torben Krogh & Mogens Winther,


(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)


83 Leonis B is a orange-red
star that is similar in color to
Epsilon Eridani at left center
of meteor. (See a Digitized
Sky Survey image of 83 Leonis B
from NASA's NStars Database.)

Star B is a orange-red main sequence dwarf to subgiant star of spectral and luminosity type K2 V-IV. The star has 88 percent of Sol's mass (exoplanets.org), around 81 percent of its diameter (Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983), and about 24 percent of its visual luminosity. Other useful star catalogue designations for 83 Leonis B include: 83 Leo B, Gl 429 B, Hip 55848, HD 99492, BD+03 2503, SAO 118865, LHS 2408, LTT 13110, LFT 806, Wolf 394, STF 1540 B, and ADS 8162 B.

HD 94492 b (83 Leonis Bb)

JPL, NASA



Larger image.



It is unknown whether planetary
candidate "b" is rocky or gaseous
like Neptune, but it appears to have
more than twice Neptune's mass.

On January 2005, a team of astronomers (Geoffrey W. Marcy, R. Paul Butler, Steven S. Vogt, Debra Fischer, Gregory W. Henry, Greg Laughlin, Jason T. Wright, and John A. Johnson) announced the discovery of a planet around Star B (exoplanets.org; and Marcy et al, 2005). Designated "HD 99492 b," the planet has at least 36 times the mass of Earth (more than twice the mass of Neptune and Uranus, and 11.2 percent of Jupiter's mass). It moves around 83 Leonis B at an average distance of only 0.119 AUs in a highly circular orbit (e= 0.05 +/- 0.12) that takes only 17.038 +/- 0.00536 days to complete (Extrasolar Planets Encyclopaedia). (See an animation of the the orbits of the potentially habitable zone and planetary companion around Star B, with a table of basic orbital and physical characteristics.)

The distance from 83 Leonis A where an Earth-type planet would be "comfortable" with liquid water may be centered around 0.81 AU -- between the orbital distances of Venus and Earth in the Solar System. At that distance from the star, such a planet would have an orbital period of around three fourths of an Earth year assuming that Star A has a mass near Sol's. For Star B, the water-zone orbital distance may be centered around 0.49 AU (between the orbit distances of Mercury and Venus) with a period of about 133 days -- 36.6 percent of an Earth year. However, the present of a large planet with at least 36 Earth-masses at 0.12 AUs would probably disrupt the orbit of such a Earth-type planet. Astronomers would find it very difficult to detect such planets using present methods.