Gl 777 / HR 7670 / BD+29 3872 ABab
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Gl 777 A is located about 51.8 light-years from Sol, while NASA's NStar Database suggests that Star B may lie as far as 56 ly away. It lies at the southern edge of (20:3:37.4+29:53:48.5, ICRS 2000.0) of Constellation Cygnus, the Swan -- northeast of Albireo (Beta1 Cygni); and south of Sadr (Gamma Cygni), the Crescent Nebula (NGC 6888), and the open star cluster NGC 6871; west of Zeta Cygni and the Network Nebula and the Veil Nebula; and north of the Lacework Nebula. On June 17, 2000, astronomers announced the discovery of a Jupiter-class planet around this Sun-like star (press release and initial data -- details below). In January 2005, another team of astronomers reported finding a Neptune-sized planet in a inner "torch" orbit (Vogt et al, 2005, in pdf -- 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.) As Gl 777 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.
Many astronomers now refer to this star by its designation in the famous Gliese Catalogue of Nearby Stars (CNS, now ARICNS database) of Wilhelm Gliese (1915-93), who was a longtime astronomer at the Astronomiches Rechen-Institut at Heidelberg (even when it was at Berlin). The star was included in the third version of the catalogue that was updated with Hartmut Jahreiss (also at (ARI) as "CNS3" in 1991. As a relatively bright star in Earth's night sky, however, Star A is also catalogued as Harvard Revised (HR) 7670, 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.
Gl 777, however, may have been first designated as BD+29 3872, in a catalogue by Friedrich Wilhelm August Argelander (1799-1875) 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, made with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896), which became famous as the Bonner Durchmusterung ("Bonn Survey") abbreviated as BD. The BD and the later Cordoba Durchmusterung (CD) that was surveyed from Argentina were greatly expanded and extended into the modern age of photographic surveys with the subsequent creation of the Cape Photographic Durchmusterung from South Africa. (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.)
Gl 777 A is a yellow-orange dwarf star of spectral and luminosity type G6-8 V-IV+. The star has about 96 percent of Sol's mass (Santos et al, 2003), around 1.3 to 1.74 times its diameter (Johnson and Wright, 1983, page 695), and 1.13 times of its visual luminosity Geneva data). The star may be 1.78 times as enriched than Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (initial data; Santos et al, 2003; and J.B. Hearnshaw, 1974). With a high velocity and relatively high age (J.B. Hearnshaw, 1974), Gl 777 A appears to be unusually bright and large for its spectral type and may be evolving off the main sequence as a subgiant star. It may have a binary companion (Olin Jeuck Eggen, 1956, pp. 409 and 427), actually a pair of dim binary companions (Stars Bab) located over 2,800 AUs away; however, NASA's NStar Database suggests that the binary pair Star Bab may lie as far as four light-years away (and the pair would not be gravitationally bound to Star A). Useful catalogue numbers and designations for the star include: HR 7670, Gl 777 A, HIP 98767, BD+29 3872, HD 190360, SAO 88133, LHS 3510, LTT 15867, LFT 1515, and Wo or GJ 9683.
On June 13, 2000, a team of astronomers (Dominique Naef, Francisco Pepe, Michel Mayor, Nuno C. Santos, Didier Queloz, and Stephane Udry) announced the discovery of a Jupiter-class planet around Gl 777 A using highly sensitive radial-velocity methods (press release and initial data). According to the latest radial velocity data, planet "b" (or "A1") has 1.50 +/- 0.13 times Jupiter's mass. It moves around Gl 777 A at an average distance that has been revised to 3.9 +/- 0.2 AUs (a semi-major axis around the outer margins of the Main Asteroid Belt in the Solar System) but with an highly eccentric orbit (e=0.36 +/- 0.03) that takes around 7.9 years (2,891 days +/- 85 days) to complete (Vogt et al, 2005; and Extrasolar Planets Encyclopaedia).
In January 2005, another team of astronomers reported possibly detecting second planet of Neptune size in a highly circular, inner "torch" orbit that is completed in only 17.1 days (e=0.01 +/- 0.1). Planet "c" has around 18.1 +/- 4.8 Earth-masses and orbits Star A at an average distance of only 0.128 +/- 0.002 AUs. While it is possible that this "detection" results from the passage of surface "features across the visible hemispere of the rotating star" which can be verified with new photometry, the discovery team believed that an inner planet with the announced characteristics remained the best explanation for the reduction in residuals of the radial velocity variations detected (Vogt et al, 2005, in pdf; and Extrasolar Planets Encyclopaedia).
The orbit of an Earth-like planet (with liquid water) around GJ 777 A may be centered around 1.1 AU -- between the orbital distances of Earth and Mars in the Solar System -- with an orbital period around 430 days (1.2 years). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.) 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 Gl 777 A. 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.
NASA -- larger image
Gl 777 Ba and Bb are dim red dwarf stars, like
Gliese 623 A (M2.5 V) and B (M5.8Ve) at lower right.
Gl 777 Ba is a very dim red dwarf star of spectral and luminosity type M4.5-6 V. The star has about percent of Sol's mass, 19 percent of its diameter (Johnson and Wright, 1983, page 695), and 4/10,000th of its visual luminosity. According to the ARICNS entry for Star B, it appears to have a faint companion star Bb that is separated by about 69.9 AUs (4.4" at a distance of 51.8 ly, 114d (1971.2), m = 15.5) (Wulff Dietz Heintz, 1996; AJ96, 1072-88). Useful catalogue numbers and designations for the star include: Gl 777 B, BD+29 3872 B, LHS 3509, LTT 15865, LFT 1514, G 125-055, and G 186-9.
Gl 777 Bb may be a very dim red dwarf star of spectral and luminosity type M4.5-6 V. The star is less massive than Sol and smaller than its diameter, as well as much dimmer.
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 Gl 777 A.
|Star System||Spectra &|
|L 1501-39||M3 V||5.5|
|BD+22 3908||K1 V||6.0|
|Gl 794||DA3 /VII||8.1|
|HR 7368||G8-K0 V||8.3|
|Ross 164||M3.5 V||8.6|
|BD+31 3767 AB||M0.5 V |
|Ross 188||M4 V||9.2|
|G 185-32||DA5 /VII||9.4|
|* plus bright stars *||. . .|
|HR 7683 AB||G5 IV |
|HR 7162 AB||F9-G0 V |
|BD+22 3887||G5 V||13|
|15 Sagittae||G1 V||14|
|17 Cygni 3?||F5-7 V-IV |
|BD+21 3822||G5 V||18|
|31 Aquilae 3?||G8 IV |
|BD+15 4026||G7-8 V||18|
The late John Whatmough created illustrated web pages on this system in Extrasolar Visions.
Up-to-date technical summaries on these stars can be found at: Jean Schneiders's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's ARICNS entries for Star A and Star B, and the Nearby Stars Database. Additional information may be available at Roger Wilcox's Internet Stellar Database.
The Swan lies between Constellations Pegasus and Draco and is often shown with outstretched wings flying parallel with the Milky Way. Deneb, the tail star, along with Vega in Constellation Lyra and Altair in Constellation Aquila form the Summer Triangle. While the mythology of Constellation Cygnus is not known with certainty, the Greek myth of Leda and the Swan involves Zeus, the King of the Gods, who fell in love with Leda and ravaged her disguised as a swan. Subsequently, Leda laid an egg which bore Helen, the most beautiful woman in the world, and Castor and Pollux, the Gemini twins. For more information about the stars and objects in this constellation and an illustration, go to Christine Kronberg's Cygnus. For another illustration, see David Haworth's Cygnus.
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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