61 Ursae Majoris
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61 Ursae Majoris is located about 31.1 light-years from Sol. It lies in the southeastern corner (11:41:03.02+34:12:05.89, ICRS 2000.0) of Constellation Ursa Major, the Great Bear, which also encompasses the Big Dipper or Plow (Plough) -- east of Alula Borealis (Nu Ursae Majoris) and northeast of Alula Australis (Xi or Ksi Ursae Majoris). As 61 Ursae Majoris has become one of the top 100 target stars for NASA's planned Terrestrial Planet Finder (TPF), images of this star and its position relative to the Milky Way in Earth's night sky are now available from the TPF-C team.
61 Ursae Majoris is a yellow-orange main sequence dwarf star of spectral and luminosity type G8 Ve, with about 81 percent of Sol's mass, 84 to 89 percent of its diameter (Morossi and Malagnini, 1985, page 369; and Johnson and Wright, 1983, page 673), and around 57 percent of its luminosity. The star may be only 40 to 105 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 292). It is a New Suspected Variable star designated as NSV 5291. While chromospheric activity measurements suggest that the star may be as young as 500 million years (see HD 101501 in Table 2 from Don Barry, 1988), the lack of an easily observable dust disk -- as is found at Epsilon Eridani -- suggests that the stars could be well over a billion years old. Useful star catalogue numbers for the star include: 61 UMa, HR 4496, Gl 434, Hip 56997, HD 101501, BD+35 2270, SAO 62655, FK5 1300, and LTT 13200.
Hunt for Substellar Companions
The failure, thus far, to find large substellar objects like brown dwarfs or a Jupiter- or Saturn-class planet in a "torch" orbit (closer than the Mercury to Sun distance) around 61 Ursae Majoris -- with even the highly sensitive radial-velocity methods of Geoffrey W. Marcy and R. Paul Butler -- bodes well for the possibility of Earth-type terrestrial planets around this star (Cumming et al, 1999). The orbit of an Earth-like planet (with liquid water) around this star would be centered around 0.77 AU -- somewhat farther than the orbital distance of Venus in the Solar System -- with an orbital period under 273 days or more than two thirds of an Earth year. However, if this star is as young as chromospheric activity alone would suggest, then it is likely that only primitive organisms like bacteria that can survive heavy meteorite or cometary bombardment would be likely to survive on any Earth-type planet that has cooled sufficiently to allow carbon-based lifeforms to develop.
Astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around 61 Ursae Majoris. As currently planned, the TPF will include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning in 2015.
The following star systems are located within 10 light-years of 61 Ursae Majoris.
|Star System||Spectra &|
|Groombridge 1830||G8 VIp||2.6|
|BD+36 2219 AB||M1 Ve |
|Alula Australis 4?||F8.5-G0 Ve |
|AC+27 28217||M3.5 V||4.8|
|GJ 1138||M V||6.2|
|Ross 1003||M3.5-5 V||6.2|
|GJ 1134||M V||7.9|
|G 122-49||M V||8.5|
|WD 1126+185||DC8 /VII||8.7|
|BD+31 2240 A |
|K8 V |
|G 119-62||M4 V||9.5|
Up-to-date technical summaries on these stars 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 Polaris, the North Star. For more information about the stars and objects in this 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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