Gliese 86 / HR 637 AB

As a relatively bright star in Earth's night sky, Gliese 86 is catalogued as Harvard Revised (HR) 637, a numbering system derived from the 1908 Revised Harvard Photometry catalogue of stars visible to many Humans with the naked eye. The HR system has been preserved through its successor, the Yale Bright Star Catalogue -- updated and expanded through the hard work of E. Dorrit Hoffleit and others. HR 637 is also listed as HD 13445 in the Henry Draper (1837-82) Catalogue with extension (HDE), a massive photographic stellar spectrum survey carried out by Annie Jump Cannon (1863-1941) and Edward Charles Pickering (1846-1919) from 1911 to 1915 under the sponsorship of a memorial fund created by Henry's wife, Anna Mary Palmer. (More discussion on star names and catalogue numbers is available from Alan MacRobert at Sky and Telescope and from Professor James B. Kaler's Star Names.)

On November 24, 1998, astronomers announced the discovery of a substellar companion to this star (see ESO press release, initial summary data, and exoplanets.org, with more details below). In 2001, astronomers announced that that they had imaged a brown dwarf in an outer orbit (more below). Beginning in 2005, some astronomers with additional data began arguing that the outer companion is more likely to be a white dwarf depending on the age of the star (more below). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

Gliese 86

Gliese 86 is an orange-red main-sequence dwarf star of spectral and luminosity type K0-1 V. The star may have 77 percent of Sol's mass (Desidera and Barbieri, 2007, pp. 10, 11, and 16; and Observatoire de Genève), 86 percent of its diameter (Johnson and Wright, 1983, page 649), and 40 percent of its theoretical bolometric luminosity (NASA Stars and Exoplanet Database; and Kenneth R. Lang, 1980). The star appears to be around 63 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Desidera and Barbieri, 2007, pp. 10, 11, and 16; and Observatoire de Genève; and Morell et al, 1994). It may be around 10 billion years old (Saffe et al, 2005). Gliese 86 A has a very close substellar companion "b" orbiting the star at around 0.11 AUs brown dwarf "c" around 20 AUs away. Useful catalogue numbers and designations for the star include: HR 637, Gl 86, Hip 10138, HD 13445, CD-51 532, CP(D)-51 282, SAO 232658, LHS 13, LTT 1130, LFT 186, and LPM 103.

The orbit of an Earth-like planet with surface water would be centered within 0.63 AU -- between the orbital distances of Venus and Earth in the Solar System -- and take around 209 days (more than half a year) to complete. However, the inner orbit of a giant planetary companion "b" recently discovered around Gliese 86 would probably disturb the orbit of such an Earth-type planet. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods.

Substellar Companion "b"

© John Whatmough -- larger image
(Artwork from Extrasolar Visions, used with permission)

Gliese 86 "b" is an inner orbit superplanet or brown dwarf,
similar to 55 Cancri "A1" as imagined by Whatmough.

On November 24, 1998, a team of astronomers (including Michel Mayor, Didier Queloz, and Stephane Udry) announced the discovery of a substellar companion "b," whose latest minimum mass estimate has been calculated as 4.02 times that of Jupiter (exoplanets.org; Butler et al, 2002; initial summary data, and ESO press release) with a similar diameter. This object moves around Gliese 86 A at an average separation of 0.11 AUs, which would be well within the orbital distance of Mercury in the Solar System. Its highly circular orbit (e= 0.04) takes less than 15.8 days to complete (exoplanets.org; and Queloz et al, 2000; in ps). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

Astrometric analysis suggests that the object may actually have 15 times the mass of Jupiter with an inclination of 164.0° from Earth's line of sight (Han et al, 2001, in pdf). Thus, the object could be an extremely dim brown dwarf, substellar companion of Gliese 86 A. The authors consider their analysis to be preliminary, needing confirmation with additional astrometric as well as other observations.

White(?) Dwarf Companion "B"