HR 483 / HD 10307 AB

In late September 2003, astrobiologist Maggie Turnbull identified HR 483 A as one of the best candidates for hosting Earth-type life. The star was chosen from a shortlist of 30 stars (screened from the 5,000 or so stars that are estimated to be located within 100 ly of Earth) that were presented to a group of scientists from NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories (Astrobiology Magazine). The stars examined were selected from a larger list of 17,129 (of which 75 percent are located within around 450 ly, or 140 parsecs, of Sol) that were assembled into a Catalog of Nearby Habitable Stellar Systems (HabCat) by Turnbull and Jill Tarter of the SETI Institute (see: Margaret C. Turnbull, 2002, in pdf). Selection criteria for the 30-star shortlist included: X-ray luminosity, rotation, spectral types or color, kinematics, metallicity, and Strömgren photometry (Margaret C. Turnbull, 2004). On February 19, 2006, Turnbull named HR 483 A as a Sun-like star that is old enough to qualify as a top-five candidate for those listening for radio signals from intelligent civilizations, such as the SETI Institute.

Medialab, NASA
© ESA 2001



Larger image.



To find life around nearby stars,
the ESA's Darwin mission will look
for traces of water, oxygen, and
carbon dioxide in the atmospheres
of Earth-type planets found in
stellar habitable zones (more).

Today, some astronomers prefer to refer to Star A as HD 10307, as it is listed 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. As a relatively bright star in Earth's night sky, however, Star A is also catalogued as Harvard Revised (HR) 483, 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 -- revised and expanded through the hard work of E. Dorrit Hoffleit and others.

Star A also has an older designation as BD+41 328 from a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) 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). The catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

HR 483 A

HR 483 A is a yellow-orange main sequence dwarf star of spectral and luminosity type G1.5 V. A little bigger and brighter than Sol, the star may have 97 +/- 23 percent of Sol's mass (Henry et al, 1992), the same diameter (Johnson and Wright, 1983, page 649), and close to 1.4 times its luminosity. It may be 96 percent as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Ibukiyama and Arimoto, 2002). Based on isochrone fitting, the star may be older than Sol at around 5.9 billion years of age (Margaret C. Turnbull, 2004; and Ibukiyama and Arimoto, 2002). Useful catalogue numbers and designations for the star include: HR 483, Gl 67, Hip 7918, HD 10307, BD+41 328, SAO 37434, LHS 1284, LTT 10590, LFT 150, and PGC 372.

According to the Sixth Catalog of Orbits of Visual Binaries, Stars A and B move around each other at an average distance of 7.33 AUs (semi-major axis a= 0.58") in a very eccentric (e= 0.43) orbit that takes 19.5 years to complete. The two stars would get as close as 4.2 AUs and as far away from each other as 10.5 AUs. Their orbits around each other is inclined by 103° with respect to an observer on Earth (Staffan Söderhjelm, 1999; Henry et al, 1992; Lippincott et al, 1983; and Lippincott and Manning, 1976). (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.)

An Earth-type planet could have liquid water in a stable orbit centered around 1.18 AU from Star A -- between the orbital distances of Earth and Mars in the Solar System. Such a planet would have an orbital period of around 1.3 Earth years. Unfortunately, current estimates of the masses and orbits of Stars A and B -- whose large margins of errors result in significant uncertainty -- suggest that the orbit of a planet in the habitable zone of Star A could be disrupted. Such a planet would be difficult to detect using present astronomical methods and equipment.

NASA -- larger image

HR 483 B is a dim red dwarf star, like
Gliese 623 A (M2.5 V) and B (M5.8Ve) at lower right.

HR 483 B

HR 483 B is an "intermediate mass," red main sequence dwarf star of spectral and luminosity type M V (Henry et al, 1992). Much smaller and dimmer than Sol, the star may have 29 +/- 7 percent of Sol's mass (Henry et al, 1992), a smaller diameter, and only 0.13 percent of its luminosity. An Earth-type planet could have liquid water in a stable orbit centered around 0.036 AU from Star B -- well within the orbital distance of Mercury in the Solar System. Such a planet would have an orbital period of less than five days and would be tidally locked with respect to Star B. Such a planet would be difficult to detect using present astronomical methods and equipment.