HR 7162 / HD 176051 AB
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Apparently sometimes referenced as "Inrakluk" by at least one astronomer as a reference to his name in reverse, the HR 7162, close-binary system is located around 48.9 light-years from Sol. It lies in the southwestern part (18:57:1.6+32:54:4.6, ICRS 2000.0) of Constellation Lyra, the Lyre -- south of Vega (Alpha Lyrae), southwest of Sheliak (Beta Lyrae) and Sulafat (Gamma Lyrae), west of Globular Cluster M56, northwest of Albireo (Beta1 Cygni), east-northeast of Iota, Xi, and Mu Herculis, and southeast of Theta Herculis. On October 21, 2010, astronomers submitted a paper which revealed the presence of a Jupiter-class planet around one of the stars of this close-binary system using precision astrometry, by tracking periodic variations in the position of stars over time (TSU press release; TSU's Automated Astronomy Group press release with links to related papers and articles; Ian O'Neill, MSNBC News, October 22, 2010; and Muterspaugh et al, 2010). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)
Larger image from the surface of a
a hypothetical terrestrial planet
orbiting close-binary stars.
A Jupiter-class planet has been
discovered in orbit around one of
the stars in the HR 7162 AB,
close-binary star system (more).
Today, some astronomers prefer to refer to Star A as HD 176051, 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) 7162, 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 (1907-2007) and others.
Star A also has an older designation as BD+32 3267 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 Sch÷nfeld (1828-1891) and Aldalbert KrŘger (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).
The duplicity of this star may have been first noted by Sherburne Wesley Burnham (1838-1921), who numbered it as the 648th record in his double star catalogue (BU) called "A General Catalogue of Double Stars Within 121░ of the North Pole," which was published in two parts by the Carnegie Institution of Washington in 1906 and is now known as the Burnham Double Star Catalogue (BDS). Star A has a dimmer spectroscopic companion, which is less massive and more orange, and so their combined visual luminosity is nearly 1.6 that of Sol's. Their orbits around each other take just about 61.4 years to complete, with a semi-major axis of 19.1 AUs, an eccentricity of 0.2667, and an inclination of 114.2 degrees from Earth's line of sight (Muterspaugh et al, 2010, Table 1 and Table 4, pages 1659 and 1661; and Pourbaix et al, 2004; and Duquennoy and Mayor, 1991).
|AB Mass Center||0.0||...||...||...||...||...||...||...||...|
|HR 7162 A||7.6||61.4||0.2667||114.2||353,000||~120||...||...||0.78|
|Inner H.Z. A||1.0||0.97||0||115.8||...||...||...||...||...|
|Outer H.Z. A||1.9||2.57||0||115.8||...||...||...||...||...|
|HR 7162 B||11.5||61.4||0.2667||114.2||234,000||~88||...||...||0.78|
|Center H.Z. B||0.57||0.49||0||115.8||...||...||...||...||...|
|Outer H.Z. B||1.1||1.4||0||115.8||...||...||...||...||...|
This is a yellowish main sequence dwarf star of spectral and luminosity type F9-G0 V, with 1.07 to nearly 1.2 times Sol's mass (Muterspaugh et al, 2010, Table 1, page 1659); NASA Star and Exoplanet Database; and David F. Gray, 1992), close to 1.1 times of its diameter (Pasinetti-Fracassini et al, 2001; Johnson and Wright, 1983; and S. Leone, 1973), and nearly 1.4 times its bolometric luminosity (Muterspaugh et al, 2010, Table 1, page 1659); NASA Star and Exoplanet Database; David F. Gray, 1992; and Kenneth R. Lang, 1980). The star appears to be less enriched in elements heavier than hydrogen and helium ("metals") because it has only 78 percent of Sol's abundance of iron (Luck and Heiter, 2006, Table 3, page 3076). Based on chromospheric analysis, it appears to be around 3.8 billion years old (Don C. Barry, 1978), but an estimate derived from gyrochronology suggests around 2.4 billion years (Sydney A. Barnes, 2007, Table 6, page 32), while another study used theoretical, stellar evolutionary tracks and isochrones to estimate an age of 8.1 billion years (Holmberg et al, 2006). Useful catalogue numbers and designations for the star include: Inrakluk, HR 7162, Gl 728, Hip 93017, HD 176051, BD+32 3267, SAO 67612, LTT 15567, BU 648 A, and ADS 11871 A.
According to one type of model used in calculations for the NASA Star and Exoplanet Database, the habitable zone orbits of an Earth-like planet (with liquid water) around HR 7162 A may range between 1.0 to 1.9 AUs -- between the orbital distances of Earth and the Main Asteroid Belt in the Solar System. Assuming that the mass of Star A is 1.07 Solar-masses, then such orbital periods could range from around 353 days (0.967 year) to 937 days (2.57 years). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)
A orange-red main sequence dwarf star of spectral and luminosity type K1 V, Star B has around 0.71 percent of Sol's mass (Muterspaugh et al, 2010, Table 1, page 1659), 81 percent of Sol's diameter (Pasinetti-Fracassini et al, 2001; and Johnson and Wright, 1983), and than than Solar luminosity. Useful catalogue numbers and designations for the star include: HR 7162 B, Gl 728 B, HD 176051 B, BD+32 3267 B, BU 648 B, and ADS 11871 B.
Using Omicron Eridani A as a proxy for Star B, the habitable zone orbits of an Earth-like planet (with liquid water) around HR 7162 B can range between 0.6 to 1.1 AUs -- between the orbital distances of Venus and Mars in the Solar System. Assuming that the mass of Star B is 0.71 Solar-masses, then such orbital periods could range from around 180 days, or 0.49 year, to 502 days, or 1.4 years. (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)
On October 21, 2010, astronomers submitted a paper which revealed the presence of a Jupiter-class planet around one of the stars of this close-binary system using precision astrometry, by tracking periodic variations in the position of stars over time (TSU press release; TSU's Automated Astronomy Group press release with links to related papers and articles; Ian O'Neill, MSNBC News, October 22, 2010; and Muterspaugh et al, 2010). In theory, astrometry is particularly useful for detecting planets around binary stars that between 10 and 50 AUs apart, such as Errai 2 (Gamma Cephei), HD 126614, and HD 188753 (Muterspaugh et al, 2010, page 1658). The planet appears to have 1.5 +/- 0.3 Jupiter-masses if it is orbiting Star B, but it would be more massive (at around 2.26 Jupiter-masses) if orbiting Star A (Ibid., page 1661). It has an orbital period of 1,016 +/- 40 days or 2.78 years, an inclination around 115.8 degrees from Earth's line of sight, and a semi-major axis of around 2.02 AUs from Star A, but of 1.76 AUs around Star B (partially derived from Muterspaugh et al, 2010, pages 1660-1661 and Table 4). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)
Core accretion models of planetary formation indicate that that binary stars can create a turbulent environment in a star's circumstellar debris disk that can be unfavorable for planetary formation. In close orbiting binary systems, disk instability models of giant planet formation suggest that some regions of the star's disk of gas and dust could become "overdense," so that large masses of dust gravitationally grouped together until the mutual gravity of such a cloud causes it to rapidly collapse. In the case of HR 7162, the presence of its Jupiter-class planet (if confirmed) would suggest that it may have taken only a few thousand years to form, before the host star's debris disk was ejected from the system by gravitationally interactions with its binary stellar companion.
The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of HR 7162 AB.
|Star System||Spectra &|
|HR 7368||G8-K0 V||5.0|
|Ross 164||M3.5 V||6.2|
|G 205-35||M V||6.9|
|LP 229-30||M V||7.4|
|G 207-22||M V||8.0|
|Ross 708||M3 V||8.3|
|L 1499-34||M V||8.8|
|G 207-18||M V||9.5|
|BD+31 3767 A||M0.5 V||9.9|
|99 Herculis 3||F7 V |
|* plus bright stars *||. . .|
|HR 7670 AB||G6-8 V-IV |
|72 Herculis A?||G0 V||17|
|110 Herculis A?||F6 V||18|
|31 Aquilae 3?||G8 IV |
|HR 7683 AB||G5 IV |
Up-to-date technical summaries on these stars can be found at: Jean Schneider's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's ARICNS for Star A and Star B, the NASA Star and Exoplanet Database, and the SIMBAD astronomical database for Star A and Star B. Additional information may be available at Roger Wilcox's Internet Stellar Database.
Although Constellation Lyra (the Lyre) is thought to represent the harp given by Apollo to Orpheus, it represented the Vulture for the Ancient Egyptians and Greeks, who regarded the Vulture as one of three birds hunted by Hercules -- together with Cygnus (the Swan and Aquila (the Eagle). In another myth, however, Mercury was said to have invented the lyre by placing strings across the back of a tortoise shell, and so sometimes this constellation was drawn as a tortoise. For more information about the stars and objects in this constellation, go to Christine Kronberg's Lyra. For an illustration, see David Haworth's Lyra.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
Note: Thanks to Andrew Tribick for the clue to the joke behind the name "Inrakluk."
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