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Groombridge 1830 is located about 29.9 light-years (ly) from our Sun, Sol. It lies in the southern part (11:52:58.77+37:43:07.24, ICRS 2000.0) of Constellation Ursa Major, the Great Bear, which also encompasses the Big Dipper -- northeast of Alula Borealis (Nu Ursae Majoris) and Alula Australis (Xi or Ksi Ursae Majoris). This star was listed by Stephen Groombridge (1755-1834), whose "A Catalog of Circumpolar Stars, Reduced to January 1, 1810" [see page 54] was published posthumously in 1838. In 1842, Friedrich Wilhelm August Argelander (1799-1875) noted its exceptionally large proper motion -- now the third highest after Barnard's and Kapteyn's stars (Wulff Dieter Heintz, 1984). Argelander published a catalog in 1863 on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896), which became famous as the Bonner Durchmusterung ("Bonn Survey") abbreviated as BD and was greatly expanded and extended into the 20th Century with the Cordoba then the Cape Photographic Durchmusterung from South Africa.
Unusually faint for its spectral type, Groombridge 1830 is a yellow-orange halo subdwarf star of spectral and luminosity type sdG8p /VI. The star may have about sixth tenths of Sol's mass (Smith et al, 1992), 64 percent of its diameter, but only 19 percent of its luminosity. It may only be about three to 10 percent as enriched as Sol in elements heavier than hydrogen (Cayrel de Strobel et al, 1991, page 20; and J. Tomkin, 1972). As a G8, it is sufficiently cool not to have evolved appreciably despite a high probable age. The star is at least 5.4 billion years old based on chromospheric anaysis alone (Don C. Barry, 1998, page 3), but its halo subdwarf status would suggest that the star is at least 10 billion years old, having formed during a period of rapid collapse that lasted perhaps a billion years in the early history of the Milky Way galaxy prior the development of the galactic disk. It has the New Suspected Variable designation NSV 5374. Some useful catalogue numbers for this star are: HR 4550, Gl 451 A, Hip 57939, HD 103095, BD+38 2285, SAO 62738, FK5 1307, G 122-51, G 148-18, LHS 44, LTT 13276, LFT 855, and Gmb 1830.
In 1968, Peter van de Kamp (1901-1995) at Sproul Observatory detected a flare from what was presumed to be a dim companion that was two magnitudes fainter than the primary. Although there were later observations of flares, the faint companion did not appear on many other photographic plates, and it was presumed to be a rapid variable such as a flare star and given the variable star designation CF Ursae Majoris sometime after 1980. However, no changes in radial velocity were detected between 1974 and 1984 to confirm possible variations found around 1920 (R. F. Griffin, 1984; and Beardsley et al, 1974). Moreover, subsequent astrometric measurements were negative (Heintz, 1984), as were infrared speckle interferometric observations (ARICNS note). New observations announced in 1998 suggest that sightings of the "companion" were actually observations of a new gargantuan class of stellar mass ejection associated recently with Sol-type stars of spectral class F8 to G8 called a "superflare" from the primary star itself (Schaefer et al, 2000).
Hunt for Substellar Companions
Given the regular eruption of superflares, it is unlikely that Earth-type life could survive for long on any inner rocky planet. The distance from either Groombridge 1830 where an Earth-type planet would be comfortable with liquid water is only about 0.44 AU (around the orbit of Mercury), but at that distance, such a planet would be very difficult to detect using present methods. Given the low abundance of elements heavier than hydrogen, moreover, it is possible that the star is more likely to have gas giants in cold outer orbits.
According to one recent hypothesis, unusually intense stellar flares from a sun-like ("Sol-type") star could be caused by the interaction of the magnetic field of a giant planet in tight orbit with that star's own magnetic field (Rubenstein and Schaefer, 2000). Some Sol-type stars of spectral class F8 to G8 have been found have been observed to undergo enormous magnetic outbursts to produce "superflares" (coronal mass ejections) that release between 100 and 10 million times more energy than the largest flares ever observed on the sun, making them brighten briefly by up to 20 times. These superflares last from one hour to one week and increase the normal luminosity of a star as much as one thousand times. If our sun were to produce a large superflare, Earth's ozone layer would be destroyed, and ice on the daylight side of moons as far out as those of Jupiter or even Saturn would be melted, producing vast floodplains that refreeze after the flare subsides. No traces of past superflares have been detected in our Solar System.
NASA (Krist, et al, 1999)
Until the discovery of superflares by stars like
Groombridge 1830, enormous coronal mass ejections
releasing energy from 100 to 10 million times
greater than a typical Solar flare by stars of spectral
classes F8 to G8 were thought to be limited to very
young stars -- like this magnetically-driven outburst
by the million-year-old binary pair of pre-main-sequence
stars, XZ Tauri AB.
In 1998, nine Sol-type stars (naked-eye objects Omicron Aquilae, Kappa Ceti, and Pi1 Ursae Majoris, as well as MQ/5 Serpentis, UU Coronae Borealis, S Fornacis, MT Tauri, BD+10 2783, and Groombridge 1830) were observed to have produced superflares, on average, about once per century. None of these yellowish stars rotate particularly fast, have close binary companions, or are very young (Schaefer et al, 2000). Previously, such large flares had not been observed in Sol-type main sequence stars, although they are common in a group of dim main-sequence, reddish M dwarfs known as flare stars.
Subdwarfs and Halo Stars
Subdwarfs, such as nearby Kapteyn's Star (M0VI or M0sd) as well as Groombridge 1830, are dimmer more bluish than younger main-sequence dwarf stars (Wing et al, 1976). They have a lower "metals" content of elements heavier than helium. This low metallicity is thought to be due to their birth in an earlier age (or region) of the galaxy when relatively few supernovae had as yet spewed their metals into surrounding dust clouds (John E. Gizis, 1997).
Most of the stars in the central bulge and in the globular clusters of the galactic halo are old, low metals stars, and halo stars account for only 0.1 to 0.2 percent of the stars near Sol. Halo stars are distributed somewhat spherically around the galactic core but most members of the halo lie far above or far below the galactic plane. Including the stars of the distant globular clusters, halo stars are among the galaxy's oldest, thought to be mostly 10 billion years and older. While halo stars are only very weakly concentrated towards the galactic plane, they exhibit a strong concentration towards and including the galactic nucleus but with highly eccentric orbits. As a group, these stars as a group show little if any net rotation around the galaxy, and so a halo member has a very negative V velocity ("retrograde direction"), since the Sun's motion around the galactic center is in the positive V direction. Like Groombridge 1830, they tend to have a high space velocity (R. F. Griffin, 1984) and a highly eccentric galactic orbit.
These stars contain a very low metals abundance relative to the sun (with a mean around two percent of Sol's). While halo stars may only total as few as 0.1 percent of the stars in the solar neighborhood, they include Kapteyn's Star. Also called Population II stars because of their later discovery, this group also includes RR Lyrae variables with periods greater than 12 hours, subdwarfs and other extremely metal-poor stars, and some red giants.
The following star systems are located within 10 ly of Groombridge 1830.
|Star System||Spectra &|
|BD+36 2219 AB||M1 Ve |
|61 Ursae Majoris||G8 Ve||2.6|
|Alula Australis 4?||F8.5-G0 Ve |
|G 122-49||M V||6.2|
|Ross 1003||M3.5-5 V||6.9|
|Gl 436 / AC+27 28217||M2.2-3.5 V||7.1|
|GJ 1138||M V||7.4|
|GJ 1134||M V||9.1|
|Beta Comae Berenices||F9.5-G0 V||10.0|
Up-to-date technical summaries on this star can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS). Additional information may be available at Roger Wilcox's Internet Stellar Database.
Constellation Ursa Major is only visible from the northern hemisphere. The seven stars of the Big Dipper in this constellation are famous as the traveller's guide to the Polaris, the North Star. For more information and an illustration of the constellation and an illustration, go to Christine Kronberg's Ursa Major. For another illustration, see David Haworth's Ursa Major.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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